CN107070234A - The control circuit and control method of series resonant converter - Google Patents

Abstract

The application provides a control circuit for a series resonant converter. The series resonant converter includes an inverter circuit. The inverter circuit includes a left bridge arm and a right bridge arm. The left bridge arm and the right bridge arm respectively include two switching devices. The control circuit Including: a driving circuit, which provides a driving signal for the switching device of the inverter circuit, and the driving signal is used to periodically modulate the switching device. The periodic modulation includes at least one switching cycle, and the switching device of the inverter circuit exists within one switching cycle. A hard shutdown. The control circuit of the present application can effectively reduce the turn-off loss of the switch device and improve the reliability of the inverter circuit. Meanwhile, the present application also proposes a control method of the series resonant converter.

Description

Control circuit and control method of series resonant converter

technical field

The present application mainly relates to an X-ray high-voltage generator, and in particular to a control circuit and a control method for a series resonant converter of the X-ray high-voltage generator.

Background technique

X-ray high-voltage generators are used in X-ray therapy equipment, X-ray diagnostic equipment, X-ray computed tomography (CT), positron emission computed tomography (PET-CT) and other equipment. In the inverter circuit of the high-power X-ray high-voltage generator, in order to meet the requirement of long-time work, an insulated gate bipolar switching device (Insulated Gate Bipolar Transistor, IGBT) is usually selected as the switching device. In practical applications, on the one hand, in order to ensure the reliable operation of the IGBT, its switching frequency cannot be selected too high; on the other hand, in order to reduce the volume of the high-voltage generator and rectification part and improve the power density of the converter, the switching frequency cannot be selected too low . At the same time, the X-ray tube is used as the load of the high-voltage generator, which has a wide range of voltage from 60kV to 140kV and a wide range of current from 10mA to 420mA. Further, in order to improve the compatibility of the high-voltage generator, it needs to adapt to a variety of different grid power ranges. Typical grid power ranges include 400VAC (-20% to +10%) and 480VAC (-15% to +15%) Wait.

Resonant (including series-parallel resonance) inverter circuits can use the leakage inductance of high-voltage transformers as series resonant inductors, and DC blocking capacitors as series resonant capacitors without output filter inductors. The circuit components are few and the structure is simple, which is suitable for X-ray high-voltage generation device. Usually, pulse width modulation (Pulse Width Modulation, PWM) is the main modulation mode of the resonant inverter circuit. For the resonant inverter circuit using PWM modulation, the high-voltage generator can be operated at a relatively high switching frequency by adjusting the duty cycle of the IGBT, while ensuring the volume of the high-voltage transformer and rectifier circuit, and meeting the wide voltage of the X-ray tube current range requirements.

However, a major problem in the PWM modulated LC series resonant inverter circuit is that the switching loss of the IGBT is relatively large, which leads to serious heating. For example, when the bipolar PWM modulation method is used, the diagonal tubes of the inverter circuit switch simultaneously, resulting in large disconnection loss, and the energy feedback ratio of the inverter circuit is relatively large, resulting in a large peak current. For the inverter circuit using phase-shift PWM modulation, the duty cycle of the left and right bridge arms in the inverter circuit is 50%, and the output voltage can be adjusted by changing the phase of the left and right bridge arms, and the disconnection loss is lower than that of bipolar PWM modulation. However, due to the large number of turns and large distributed capacitance on the high-voltage side of the high-voltage transformer, and the phase-shift PWM modulation inverter bridge has a zero-voltage vector, the distributed capacitance of the high-voltage transformer will resonate with the series resonant inductor during this period, making the voltage and current waveforms Distortion occurs, increasing the switching loss of the IGBT. For the inverter circuit using asymmetric bipolar PWM modulation, one bridge arm adopts bipolar modulation, and the other bridge arm can adopt fixed 50% duty cycle modulation, which can ensure that the switching loss is equivalent to that of phase-shift PWM modulation, and There is no zero-voltage vector, which can effectively suppress the oscillation caused by the distributed capacitance of the high-voltage transformer. However, the asymmetric bipolar PWM modulation still has the problem of serious switching loss, and the positive and negative half-cycle IGBTs of each switching cycle must be hard-disconnected with a large current.

Based on this, it is necessary to improve the modulation mode of the existing resonant inverter circuit to reduce the IGBT switching loss.

Contents of the invention

The technical problem to be solved in the present application is to provide a modulation method for a series resonant inverter circuit, which overcomes the problems of the existing modulation mode of the series resonant converter.

In order to solve the above technical problems, according to one aspect of the present application, a control circuit of a series resonant converter is provided, the series resonant converter includes an inverter circuit, and the inverter circuit includes a left bridge arm and a right bridge arm, so The left bridge arm and the right bridge arm respectively include two switching devices, and the control circuit includes:

A driving circuit, which provides a driving signal for the switching device of the inverter circuit, and the driving signal is used for periodically modulating the switching device, and the periodic modulation includes at least one switching period, and during the one switching period There is a hard shutdown of the switching device in the inverter circuit, wherein,

In a positive half cycle of a switching cycle, the driving circuit drives a switching device of the left bridge arm to perform PWM modulation, and drives two switching devices of the right bridge arm to work with a set duty ratio;

In the negative half period of a switching period, the driving circuit drives the switching devices of the left bridge arm and the right bridge arm, so that the series resonant converter works in a free oscillation mode.

Further, the left bridge arm includes a first switching device and a second switching device, the right bridge arm includes a third switching device and a fourth switching device, and the driving circuit provides a first driving signal to the first switch device, providing a second driving signal to the second switching device, providing a third driving signal to the third switching device, providing a fourth driving signal to the fourth switching device, and the equivalent of the inverter circuit Voltage transfer gain greater than 0.5:

In a positive half period of a switching period, the first driving signal drives the first switching device to perform PWM modulation, and the fourth driving signal drives the fourth switching device to work with a set duty ratio;

In the negative half cycle of a switching cycle, the second driving signal drives the second switching device to work at a set duty ratio, and the third driving signal drives the third switching device to work at a set duty cycle .

Further, the left bridge arm includes a first switching device and a second switching device, the right bridge arm includes a third switching device and a fourth switching device, and the driving circuit provides a first driving signal to the first switch device, providing a second driving signal to the second switching device, providing a third driving signal to the third switching device, providing a fourth driving signal to the fourth switching device, and the equivalent of the inverter circuit The voltage transmission gain is less than 0.5: the first driving signal drives the first switching device to be in an off state;

In a positive half period of a switching period, the fourth driving signal drives the fourth switching device to work with a set duty ratio;

In a negative half cycle of a switching cycle, the second driving signal drives the second switching device to perform PWM modulation, and the third driving signal drives the third switching device to work with a set duty cycle.

According to another aspect of the present application, a control circuit of a series resonant converter is proposed, the series resonant converter includes an inverter circuit, the inverter circuit includes a left bridge arm and a right bridge arm, the left bridge arm and the The right bridge arm includes two switching devices respectively, and the control circuit includes:

A driving circuit, which provides a driving signal for the switching device of the inverter circuit, and the driving signal is used for periodically modulating the switching device, and the periodic modulation includes at least one switching period, and during the one switching period There is a hard shutdown of the switching device in the inverter circuit, wherein,

In the positive half cycle of a switching cycle, the driving circuit drives the two switching devices of the left bridge arm to work with a set duty ratio, and drives a switching device of the right bridge arm to perform PWM modulation;

In the negative half period of a switching period, the driving circuit drives the switching devices of the left bridge arm and the right bridge arm, so that the series resonant converter works in a free oscillation mode.

Further, the left bridge arm includes a first switching device and a second switching device, the right bridge arm includes a third switching device and a fourth switching device, and the driving circuit provides a first driving signal to the first switch device, providing a second driving signal to the second switching device, providing a third driving signal to the third switching device, providing a fourth driving signal to the fourth switching device, and the equivalent of the inverter circuit Voltage transfer gain greater than 0.5:

In a positive half cycle of a switching cycle, the first driving signal drives the first switching device to work at a set duty ratio, and the fourth driving signal drives the fourth switching device to perform PWM modulation;

In the negative half cycle of a switching cycle, the second driving signal drives the second switching device to work at a set duty ratio, and the third driving signal drives the third switching device to work at a set duty cycle .

Further, the left bridge arm includes a first switching device and a second switching device, the right bridge arm includes a third switching device and a fourth switching device, and the driving circuit provides a first driving signal to the first switch device, providing a second driving signal to the second switching device, providing a third driving signal to the third switching device, providing a fourth driving signal to the fourth switching device, and the equivalent of the inverter circuit The voltage transmission gain is less than 0.5: the fourth driving signal drives the fourth switching device to be in an off state;

In a positive half period of a switching period, the first driving signal drives the first switching device to work with a set duty ratio;

In a negative half cycle of a switching cycle, the second driving signal drives the second switching device to work at a set duty cycle, and the third driving signal drives the third switching device to perform PWM modulation.

According to yet another aspect of the present application, a control method for a series resonant converter is proposed, the series resonant converter includes an inverter circuit, the inverter circuit includes a left bridge arm and a right bridge arm, the left bridge arm and the right bridge arm The right bridge arm contains two switching devices respectively, and the control method includes:

A driving signal is provided for the switching device of the inverter circuit, the driving signal drives the switching device to be turned on or off periodically, and the periodic modulation includes at least a first switching period and a second switching period, wherein,

In the positive half period of the first switching period, the driving circuit drives one switching device of the left bridge arm to perform PWM modulation, and drives the two switching devices of the right bridge arm to work with a set duty ratio;

In the negative half period of the first switching period, the driving circuit drives the switching devices of the left bridge arm and the right bridge arm, so that the series resonant converter works in a free oscillation mode;

In the positive half period of the second switching period, the driving circuit drives the two switching devices of the left bridge arm to work at a set duty ratio, and drives one switching device of the right bridge arm to perform PWM modulation;

In the negative half period of the second switching period, the driving circuit drives the switching device to make the series resonant converter work in a free oscillation mode.

Further, the left bridge arm includes a first switching device and a second switching device, the right bridge arm includes a third switching device and a fourth switching device, and provides a first driving signal to the first switching device, providing The second driving signal is provided to the second switching device, the third driving signal is provided to the third switching device, and the fourth driving signal is provided to the fourth switching device, wherein,

In the positive half period of the first switching period, the first driving signal drives the first switching device to perform PWM modulation, and the fourth driving signal drives the fourth switching device to work with a set duty ratio;

In the negative half period of the first switching period, the second driving signal drives the second switching device to work with a set duty ratio, and the third driving signal drives the third switching device to work with a set duty ratio Work;

In the positive half period of the second switching period, the first driving signal drives the first switching device to work with a set duty ratio, and the fourth driving signal drives the fourth switching device to perform PWM modulation;

In the negative half period of the second switching period, the second driving signal drives the second switching device to work at a set duty ratio, and the third driving signal drives the third switching device to work at a set duty ratio Work.

Further, the left bridge arm includes a first switching device and a second switching device, the right bridge arm includes a third switching device and a fourth switching device, and provides a first driving signal to the first switching device, providing The second driving signal is provided to the second switching device, the third driving signal is provided to the third switching device, and the fourth driving signal is provided to the fourth switching device, wherein: the first driving signal drives the first switching device A switching device is in an off state;

In the positive half period of the first switching period, the fourth driving signal drives the fourth switching device to work with a set duty ratio;

In the negative half period of the first switching period, the second driving signal drives the second switching device to perform PWM modulation, and the third driving signal drives the third switching device to work with a set duty ratio;

In the positive half period of the second switching period, the fourth driving signal drives the fourth switching device to work with a set duty ratio;

In the negative half period of the second switching period, the second driving signal drives the second switching device to work at a set duty cycle, and the third driving signal drives the third switching device to perform PWM modulation.

Further, the set duty cycle is 50%.

Compared with the prior art, the control method of the series resonant converter of the present application only performs PWM modulation on the switching device through the driving signal in the positive half cycle or the negative half cycle of the switching cycle in one switching cycle; and in the other half cycle , the series resonant circuit controls the switching device to work in the free oscillation mode through the driving signal. Through the above method, the circuit of the resonant converter does not exist, and at the same time the disconnection loss is reduced by nearly half, so that the heat generation of the IGBT can be greatly reduced. Ensure that the inverter circuit works safely and reliably at a relatively high switching frequency.

Description of drawings

FIG. 1A is a circuit diagram of an X-ray high voltage generator based on a series resonant converter according to an embodiment of the present application;

FIG. 1B is a circuit diagram of an X-ray high voltage generator based on a series resonant converter according to another embodiment of the present application;

FIG. 2 is a modulation waveform diagram of the series resonant inverter according to Embodiment 1 of the present application;

FIG. 3 is a modulation waveform diagram of a series resonant inverter according to Embodiment 2 of the present application;

FIG. 4 is a modulation waveform diagram of a series resonant inverter according to Embodiment 3 of the present application;

FIG. 5 is a modulation waveform diagram of a series resonant inverter according to Embodiment 4 of the present application;

FIG. 6 is a modulation waveform diagram of the series resonant inverter according to Embodiment 5 of the present application;

FIG. 7 is a modulation waveform diagram of the series resonant inverter according to Embodiment 6 of the present application.

detailed description

In order to make the above objects, features and advantages of the present application more comprehensible, the specific implementation manners of the present application will be described in detail below in conjunction with the accompanying drawings.

Many specific details are set forth in the following description to facilitate a full understanding of the present application, but the present application can also be implemented in other ways than those described here, so the present application is not limited by the specific embodiments disclosed below.

Embodiments of the present application describe a series resonant inverter circuit for an X-ray high voltage generator. X-ray high-voltage generators can be used in equipment such as X-ray therapy equipment, X-ray diagnostic equipment, X-ray computed tomography equipment (CT), positron emission computed tomography (PET-CT) and other equipment, but not in This is the limit.

FIG. 1A is a circuit diagram of a series resonant inverter of an X-ray high voltage generator based on a series resonant converter according to an embodiment of the present application. As shown in Fig. 1a, the series resonant inverter of the X-ray high voltage generator of this embodiment includes an inverter circuit 11, a series resonant circuit 12, a transformer Tr and a voltage doubler rectifier circuit 13, and the inverter circuit can control the The current i _Ls of the voltage doubler rectifier circuit 13 and the output currents i _and i _cath can respectively provide currents for the anode and cathode of the high voltage generator, and the X-ray high voltage generator includes a control circuit for controlling the series resonant converter. Further, the transformers included in the transformer Tr and the voltage doubler rectifier circuit 13 adopt cathode and anode discrete structures.

It should be noted that the equivalent voltage transfer gain of the series resonant inverter circuit can be characterized by the duty cycle of the driving signal, and can also be determined by the ratio of the input and output voltages of the series resonant inverter circuit. In one embodiment, when the voltage duty cycle of a bridge arm in the inverter circuit is less than 50%, the equivalent voltage transfer gain of the inverter circuit M<0.5; when the voltage duty cycle of a bridge arm in the inverter circuit is greater than 50%, the inverter circuit equivalent voltage transmission gain M>0.5. In another embodiment, when the ratio of the output voltage to the input voltage of the series resonant inverter circuit is less than 0.5, the equivalent voltage transmission gain of the inverter circuit M<0.5; when the ratio of the output voltage to the input voltage of the series resonant inverter circuit is greater than 0.5, the inverter circuit equivalent voltage transmission gain M>0.5.

FIG. 1B is a circuit diagram of a series resonant inverter of an X-ray high voltage generator based on a series resonant converter according to another embodiment of the present application. The difference from the circuit diagram of the series resonant inverter of the X-ray high voltage generator based on the series resonant converter above is that the transformer Tr and the transformer in the voltage doubler rectifier circuit 13 adopt an integrated cathode and anode structure.

The control circuit includes a driving circuit 14, and the inverter circuit includes one or more switching devices, and the driving circuit 14 provides a driving signal for the switching device of the inverter circuit 11, and the driving signal is used to drive the switching device to be turned on or off periodically .

When the switching device is in the conduction state, the switching device can withstand high forward current, which tends to infinity; the forward conduction voltage drop is low enough, tending to zero; the on-resistance is low enough, tending to zero, and the conduction loss is also tends to zero. When the switching device is in the off state, the switching device can withstand high forward and reverse voltages, tending to infinity; the off-state (off) leakage current is low enough, tending to zero; the off resistance is high enough, tending to infinity, off breaking loss tends to zero.

In this embodiment, the inverter circuit 11 includes a first switching device Q ₁ , a second switching device Q ₂ , a third switching device Q ₃ and a fourth switching device Q ₄ . The _first switching device Q1 and the second switching device _Q2 form the left bridge arm (leading bridge arm), and the midpoint A of the bridge arm of the left bridge arm serves as the first output terminal of the inverter circuit 11 . The third switching device _Q3 and the fourth switching device _Q4 form the right bridge arm (lag bridge arm), and the midpoint B of the bridge arm of the right bridge arm is used as the second output terminal of the inverter circuit 11 .

The first switch device Q ₁ to the fourth switch device Q ₄ may be an insulated gate bipolar transistor (Insulated Gate Bipolar Transistor, IGBT), a bipolar transistor (Bipolar Junction Transistor, BJT) or an insulated gate field effect transistor (Insulated Gate Field Effect Transistor, IGFET), etc. In this embodiment, the switching device selects an IGBT. The collector of the _first switching device Q1 is connected to the positive terminal of the power supply _Vin , and the emitter is connected to the midpoint A of the bridge arm. The collector of the second switching device _Q2 is connected to the midpoint A of the bridge arm, and the emitter is connected to the negative terminal of the power supply _Vin . The collector of the third switching device Q ₃ is connected to the positive terminal of the power supply _Vin , and the emitter is connected to the midpoint B of the bridge arm. The collector of the fourth switching device _Q4 is connected to the midpoint A of the bridge arm, and the emitter is connected to the negative terminal of the power supply _Vin . Each switching device Q ₁ -Q ₄ has parasitic diodes D ₁ -D ₄ , respectively.

The series resonant circuit 12 includes a resonant cavity and is connected to the first output terminal A of the inverter circuit 11 . Optionally, the series resonant circuit 12 may include an inductor Ls and a capacitor Cs.

The transformer Tr is connected to the series resonant circuit 12 and the second output terminal B of the inverter circuit 11 . The transformer Tr has a parasitic inductance L _lk and a parasitic capacitance C _w .

The driving circuit 14 provides a first driving signal S ₁ to the first switching device Q ₁ , a second driving signal S ₂ to the second switching device Q ₂ , a third driving signal S ₃ to the third switching device Q ₃ , and a second driving signal S 2 to the third switching device Q 3 . The four drive signals Q ₄ are given to the fourth switching device Q ₄ , so that the inverter circuit only performs one PWM operation in the positive half cycle or the negative half cycle in one switching cycle, while the series resonant circuit works in the free oscillation mode in the other half cycle. In one embodiment, the drive circuit provides a drive signal to drive the inverter circuit to perform PWM modulation in a positive half cycle of a switching cycle; while in a negative half cycle, the drive signal drives the inverter circuit to work in a free oscillation mode. In another embodiment, the driving circuit provides a driving signal to drive the inverter circuit to work in the free oscillation mode in the positive half cycle of a switching cycle; while in the negative half cycle, the driving signal drives the inverter circuit to perform PWM modulation. Optionally, the above modulation mode may be performed periodically or the modulation modes involved in the two embodiments may be performed alternately.

Example 1

In this embodiment, the driving signal is used to drive the switching device to perform periodic modulation (drive the switching device to be turned on or off periodically), and the periodic modulation includes at least one switching period, and the inverter circuit There is only one hard turn-off for one switching device. In the positive half cycle of a switching cycle, the driving circuit 14 drives a switching device of the left bridge arm to perform PWM modulation, and drives two switching devices of the right bridge arm to work with a set duty ratio; in the negative half cycle of a switching cycle, The driving circuit 14 drives the switching device, so that the series resonant converter works in a free oscillation mode. It should be noted that in this application, the "positive half cycle" may also be referred to as the "first half cycle", and the "negative half cycle" may also be referred to as the "second half cycle". It should be noted that when the driving signal is at a high level, the switching device is turned on, and when the driving signal is at a low level, the switching device is turned off, that is, the driving signal is consistent with the action of the switching organ. Therefore, in the present application, the switching period may refer to the period of the driving signal, and may also refer to the periodic turn-on or turn-off of the switching device.

When the equivalent voltage transmission gain of the series resonant inverter circuit is M>0.5, the first switching device Q ₁ that can control the left bridge arm works in PWM mode, and a PWM operation is only performed once in the positive half cycle of a switching cycle, controlling the left bridge arm The second switching device Q ₂ works with a fixed duty cycle of 50% in the negative half cycle of a switching cycle; the third switching device and the fourth switching device belonging to the right bridge arm work complementary with a 50% duty cycle, and only Certain dead time to avoid shoot-through. Fig. 2 is the modulation waveform diagram of the series resonant inverter of the embodiment 1 of the present application, the circuit corresponding to the series resonant inverter may correspond to the accompanying drawing 1, wherein: the horizontal axis represents time (unit is s); the vertical axis is from top to bottom Below are the voltage waveforms of driving signals S ₁ , S ₂ , S ₃ and S ₄ , the voltage difference V _AB between A and B, and the current i _Ls flowing through the resonant cavity. It should be noted that, in this embodiment, the duty cycle of the left bridge arm in the inverter circuit is greater than 50%, corresponding to the equivalent voltage transmission gain of the series resonant inverter circuit M>0.5.

As shown with reference to FIG. 2, in the positive half cycle of a switching cycle, the _first driving signal S1 drives the _first switching device Q1 to perform PWM modulation, and the _fourth driving signal S4 drives the fourth switching device _Q4 to set the duty cycle. Duty work:

During a period of time in the positive half cycle: the driving signal drives the switching devices Q ₁ and Q ₄ to be turned on at the same time, the switching devices Q ₂ and Q ₃ are in the off state, the input voltage V _in , the switching device Q ₁ , the resonant cavity, and the switching device Q ₄ are connected in series to form a loop, the voltage V _AB of A and B is high level (same direction as the set voltage), and the inverter current output by the inverter circuit 51 or the current i _Ls flowing through the resonant cavity gradually increases Large (the current direction in the resonant cavity is the same as the predetermined current direction);

Afterwards, only Q ₄ is turned on, and Q ₁ , Q ₂ , and Q ₃ are in the off state at the same time. The resonant cavity, the switching device Q ₄ , and the second diode D ₂ are connected in series to form a loop, and the voltage V _AB at points A and B is zero level, and the series inductance _of the resonant cavity discharges, the current i _Ls flowing through the resonant cavity gradually decreases until it decreases to zero. turn off;

After that, only Q ₄ is turned on, Q ₁ , Q ₂ , and Q ₃ are in the off state at the same time, Q ₁ , Q ₂ , Q ₃ , and Q ₄ are in the off state at the same time, and the voltage across the capacitor Cs in the resonant cavity is zero. The voltage V _AB of the two points A and B is zero level, at this time no current flows through the resonant cavity, the turn-off loss when Q ₄ is turned off is zero, and there is no hard turn-off of the switching device.

In the negative half cycle of a switching cycle, the second driving signal drives the second switching device to work with a set duty ratio, and the third drive signal drives the third switching device to work with a set duty cycle:

During a period of time in the negative half cycle, the driving signal drives the switching devices Q ₂ and Q ₃ to be turned on at the same time, the switching devices Q ₁ and Q ₄ are in the off state, the input voltage V _in , the switching device Q ₃ , the resonant cavity, and the switching device Q ₂ is connected in series to form a loop, the voltage V _AB of A and B is high level (but opposite to the specified direction), and the resonant cavity works in the free oscillation mode. In this embodiment, the free oscillation mode means that the inverter current output by the inverter or the current flowing through the resonant cavity first gradually increases to the peak position (the direction of the current in the resonant cavity is opposite to the predetermined current direction), and then the inverse The inverter current output by the transformer or the current flowing through the resonant cavity gradually decreases from the peak value.

Afterwards, when the inverter current output by the inverter or the current flowing through the resonant cavity decreases to zero, the switching devices Q ₂ and Q ₃ are in the off state at the same time (in the second half cycle, there is no hard turn-off of the switching devices ), while the switching devices Q1 and _Q4 are turned _on at the same time, and the modulation of the inverter circuit enters the next cycle. In this embodiment, the working state of each switching device in the next period is consistent with the above description.

It should be noted that when the negative half-cycle series resonant circuit of the same switching cycle works in the free resonance mode under the excitation of the input source, in order to ensure the switching action when the resonant cavity current is at zero, the switching frequency f _s should be equal to the series resonant frequency f _r , the switching loss is also small at this time. In addition, during the entire switching period, there is only one hard turn-off of the switching device, which effectively reduces the switching loss of the IGBT.

Example 2

According to this embodiment, the driving signal is used to drive the switching device to be turned on or off periodically, and the periodic turning on or off of the switching device includes at least one switching cycle, and only one switching device has a hard drive in the switching cycle. off. In the positive half cycle of a switching cycle, the driving circuit 14 drives a switching device of the left bridge arm to perform PWM modulation, and drives two switching devices of the right bridge arm to work with a set duty ratio; in the negative half cycle of a switching cycle, The driving circuit 14 drives the switching device, so that the series resonant converter works in a free oscillation mode.

When the equivalent voltage transmission gain of the inverter circuit M<0.5, the first switching device Q ₁ that can control the left bridge arm is always in the off state, and the second switching device Q ₂ that controls the left bridge arm works in PWM mode, and a The switching cycle only performs one PWM operation in the negative half cycle; the third switching device _Q3 and the _fourth switching device Q4 controlling the right bridge arm are still working complementary with 50% duty cycle, and only a certain dead zone is reserved to avoid shoot-through. Fig. 3 is a modulation waveform diagram of the series resonant inverter according to Embodiment 2 of the present application, wherein: the horizontal axis represents time (unit is s); the vertical axis represents driving signals S ₁ , S ₂ , S ₃ and The voltage waveform of S ₄ , the voltage difference V _AB between A and B, the current i _Ls flowing through the resonant cavity, and the circuit corresponding to the series resonant inverter can correspond to Fig. 1 . It should be noted that, in this embodiment, the duty cycle of the left bridge arm in the inverter circuit is less than 50%, corresponding to the equivalent voltage transmission gain M<0.5 of the series resonant inverter circuit.

As shown in FIG. 3 , the first driving signal S ₁ drives the first switching device Q ₁ to be in an off state, and in the positive half cycle of a switching cycle, the fourth driving signal S ₄ drives the fourth switching device Q ₄ to set Duty cycle works, set the duty cycle to 50% in this example:

At the initial moment of the positive half cycle, the fourth driving signal S ₄ drives the fourth switching device Q ₄ to be turned on, the switching devices Q ₂ and Q ₃ are turned off, and the switching device Q1 is always in an off state. At the moment when Q ₂ and Q ₃ are disconnected, the inductance element contained in the resonant cavity will generate a large induced electromotive force due to the sudden change of current in the circuit, so at the initial moment of the positive half cycle, there will be a sudden change in voltage at both ends of A and B, and A The voltage V _AB of two points, B, is high level. At this time, the resonant cavity, D ₁ , V _in and Q ₄ can form a series loop; at the same time, the electromotive force generated by the inductance element in the resonant cavity can be offset by Vin, so that the current i _Ls of the resonant cavity is rapidly reduced to zero. In the following period of time, the series resonant converter works in the free oscillation mode, and the current i _Ls of the resonant cavity changes in a sinusoidal waveform. It should be noted that in the positive half cycle, there is only a hard turn-off of _Q2 at a higher current.

_At the initial moment of the negative half cycle, S4 drives _Q4 to turn off, and S3 drives _Q3 to turn _on . At this time, there is still some current in the resonant cavity, and the inductance element contained in the resonant cavity will generate a large induced electromotive force (to prevent the decrease of the forward current) due to the sudden change of the current in the circuit, and the voltage V _AB of the two points A and B It is also high level, but in the opposite direction from the regulation. At this time, the resonant cavity, D ₁ , _Vin and D ₄ can form a series loop; at the same time, the electromotive force generated by the inductance element in the resonant cavity can be connected in series with Vin, so that the current i _Ls of the resonant cavity decreases slowly to zero. In the following period of time, only Q ₃ is turned on, and the current i _Ls of the resonant cavity remains in a zero state.

In the following period of time in the negative half cycle, S ₃ continues to drive Q ₃ to maintain the on state, S ₂ drives Q ₂ to conduct, Q ₄ and Q ₁ continue to maintain the off state, at this time _Vin , Q ₃ , resonant cavity , Q ₂ form a series circuit, at this time, the voltage V _AB of A and B is also high level, but opposite to the prescribed direction. The series resonant converter works in the series oscillation mode, and the current i _Ls of the resonant cavity changes in a sinusoidal waveform. In this embodiment, the working state of each switching device in the next period is consistent with the above description.

In this embodiment, Q ₁ of the left bridge arm is always in the off state, and Q ₂ works in PWM mode, and a PWM operation is only performed once in the negative half cycle of a switching cycle; The % duty cycle works complementary, leaving only a certain deadband to avoid shoot-through. In this way, the positive half-cycle series resonant circuit in the same switching period works in the free resonance mode, and the negative half-cycle works in the series resonant mode under the excitation of the input source. By making the switching frequency f _s of the switching device slightly greater than the series resonant inverter circuit The resonant frequency f _r can ensure a small switching loss.

Example 3

In this embodiment, the driving signal is used to drive the switching device to be turned on or off periodically, and the periodic turning on or off of the switching device includes at least one switching cycle, and only one switching device has one switching cycle in this switching cycle. Hard shutdown. In the positive half cycle of a switching cycle, the driving circuit 14 drives the two switching devices of the left bridge arm to work with a set duty ratio, and drives a switching device of the right bridge arm to perform PWM modulation; in the negative half cycle of a switching cycle, The driving circuit 14 drives the switching device, so that the series resonant converter works in a free oscillation mode. It should be noted that in this application, the "positive half cycle" may also be referred to as the "first half cycle", and the "negative half cycle" may also be referred to as the "second half cycle".

When the equivalent voltage transmission gain of the inverter circuit M>0.5, the fourth switching device Q ₄ of the right bridge arm can be controlled to work in PWM mode, and a PWM action is only performed once in the positive half cycle of a switching cycle, and the fourth switching device Q 4 of the right bridge arm is controlled. The three switching devices Q ₃ work with a fixed duty cycle of 50% in the negative half cycle of a switching cycle; the first switching device Q ₁ and the second switching device Q ₂ belonging to the left bridge arm work complementary with a 50% duty cycle, Only a certain dead zone is reserved to avoid shoot-through. FIG. 4 is a modulation waveform diagram of the series resonant inverter according to Embodiment 3 of the present application, and the circuit corresponding to the series resonant inverter may correspond to FIG. 1 . It should be noted that, in this embodiment, the duty ratio of the right bridge arm in the inverter circuit is greater than 50%, corresponding to the equivalent voltage transmission gain of the series resonant inverter circuit M>0.5.

As shown with reference to FIG. 4, in the positive half cycle of a switching cycle, the _first driving signal S1 drives the _first switching device Q1 to work with a set duty cycle, and in this embodiment the set duty cycle selects 50% Duty ratio, the _fourth driving signal S4 drives the fourth switching device _Q4 to perform PWM modulation:

During a period of time in the positive half cycle: the driving signal drives the switching devices Q ₁ and Q ₄ to be turned on at the same time, the switching devices Q ₂ and Q ₃ are in the off state, the input voltage V _in , the switching device Q ₁ , the resonant cavity, and the switching device Q ₄ is connected in series to form a loop, the voltage V _AB of A and B points is high level (same direction as the set voltage), and the inverter current output by the inverter circuit or the current i _Ls flowing through the resonant cavity gradually increases (the current direction in the resonant cavity is the same as the predetermined current direction);

Afterwards, only Q ₁ is turned on, and Q ₂ , Q ₃ and Q ₄ are in the off state at the same time, the resonant cavity, switching device Q ₁ , and the third diode D ₃ are connected in series to form a loop, and the voltage V _AB at points A and B is zero level, and the series inductor of the resonant cavity discharges, the current i _Ls flowing through the resonant cavity gradually decreases until it decreases to zero. During this process, there is a turn-off loss in the circuit, that is, the hard turn off;

Afterwards, Q ₁ continues to be turned on, and Q ₁ , Q ₂ , and Q ₃ are kept in the off state at the same time. When Q ₁ , Q ₂ , Q ₃ , and Q ₄ are in the off state at the same time, the voltage across the capacitor Cs in the resonant cavity is zero, the voltage V _AB of A and B is zero level, no current flows through the resonant cavity at this time, the turn-off loss when Q ₁ is turned off is zero, and there is no hard turn-off of the switching device.

In the negative half cycle of a switching cycle, the _second drive signal S2 drives the second switching device _Q2 to work with a set duty cycle, and the _third drive signal S3 drives the third switch device _Q3 to work with a set duty cycle :

During a period of time in the negative half cycle, the driving signal drives the switching devices Q ₂ and Q ₃ to be turned on at the same time, the switching devices Q ₁ and Q ₄ are in the off state, the input voltage V _in , the switching device Q ₃ , the resonant cavity, and the switching device Q ₂ is connected in series to form a loop, the voltage V _AB of A and B is high level (but opposite to the specified direction), and the resonant cavity works in the free oscillation mode. In this embodiment, the free oscillation mode means that the inverter current output by the inverter or the current flowing through the resonant cavity first gradually increases to the peak position (the direction of the current in the resonant cavity is opposite to the predetermined current direction), and then the inverse The inverter current output by the transformer or the current flowing through the resonant cavity gradually decreases from the peak value.

Afterwards, when the inverter current output by the inverter or the current flowing through the resonant cavity decreases to zero, the switching devices Q ₂ and Q ₃ are in the off state at the same time (in the second half cycle, there is no hard turn-off of the switching devices ), while the switching devices Q1 and _Q4 are turned _on at the same time, and the modulation of the inverter circuit enters the next cycle. In this embodiment, the working state of each switching device in the next period is consistent with the above description.

It should be noted that when the negative half-cycle series resonant circuit of the same switching cycle works in the free resonance mode under the excitation of the input source, in order to ensure the switching action when the resonant cavity current is at zero, the switching frequency f _s should be equal to the series resonant frequency f _r , the switching loss is also small at this time. In addition, during the entire switching period, there is only one hard turn-off of the switching device, which effectively reduces the switching loss of the IGBT.

Example 4

According to this embodiment, the driving signal is used to drive the switching device to be turned on or off periodically, and the periodic turning on or off of the switching device includes at least one switching cycle, and only one switching device has a hard drive in this switching cycle. off. In the positive half cycle of a switching cycle, the driving circuit 14 drives the two switching devices of the left bridge arm to work with a set duty ratio, and drives a switching device of the right bridge arm to perform PWM modulation; in the negative half cycle of a switching cycle, The driving circuit 14 drives the switching device, so that the series resonant converter works in a free oscillation mode. It should be noted that in this application, the "positive half cycle" may also be referred to as the "first half cycle", and the "negative half cycle" may also be referred to as the "second half cycle".

When the equivalent voltage transmission gain of the inverter circuit M<0.5, the fourth switching device Q ₄ that can control the right bridge arm is always in the off state, and the third switching device Q ₃ that controls the right bridge arm works in PWM mode, and a The switching cycle only performs one PWM action in the negative half cycle; the first switching device Q ₁ and the second switching device Q ₂ controlling the left bridge arm are still working complementary with 50% duty cycle, and only a certain dead zone is reserved to avoid shoot-through. Fig. 5 is a modulation waveform diagram of the series resonant inverter according to Embodiment 4 of the present application, wherein: the horizontal axis represents the time (unit is s); the vertical axis represents the drive signals S ₁ , S ₂ , S ₃ and The voltage waveform of S ₄ , the voltage difference V _AB between A and B, the current i _Ls flowing through the resonant cavity, and the circuit corresponding to the series resonant inverter can correspond to Fig. 1 . It should be noted that, in this embodiment, the duty cycle of the right bridge arm in the inverter circuit is less than 50%, corresponding to the equivalent voltage transmission gain M<0.5 of the series resonant inverter circuit.

As shown in FIG. 5, the fourth driving signal S4 drives the _fourth switching device Q4 to be in an off state, and in the positive half cycle of _a switching cycle, the _first driving signal S1 drives the _fourth switching device Q1 to set Duty cycle works, set the duty cycle to 50% in this example:

At the initial moment of the positive half cycle, the first driving signal S ₁ drives the first switching device Q ₁ to be turned on, the switching devices Q ₂ and Q ₃ are turned off, and the switching device Q ₄ is always in an off state. At the moment when Q ₂ and Q ₃ are disconnected, the inductance element contained in the resonant cavity will generate a large induced electromotive force due to the sudden change of current in the circuit, so at the initial moment of the positive half cycle, there will be a sudden change in voltage at both ends of A and B, and A The voltage V _AB of two points, B, is high level. At this time, the resonant cavity, Q ₁ , V _in and D ₄ can form a series loop; at the same time, the electromotive force generated by the inductance element in the resonant cavity can be offset by V _in , so that the current i _Ls of the resonant cavity is rapidly reduced to zero. In the following period of time, the series resonant converter works in the free oscillation mode, and the current i _Ls of the resonant cavity changes in a sinusoidal waveform.

At the initial moment of the negative half cycle, S ₁ drives Q ₁ to turn off, and S ₂ drives Q ₂ to turn on. At this time, there is still some current in the resonant cavity, and the inductance element contained in the resonant cavity will generate a large induced electromotive force (to prevent the decrease of the forward current) due to the sudden change of the current in the circuit, and the voltage V _AB of the two points A and B It is also high level, but in the opposite direction from the regulation. At this time, the resonant cavity, D ₁ , _Vin and D ₄ can form a series loop; at the same time, the electromotive force generated by the inductance element in the resonant cavity can be connected in series with Vin, so that the current i _Ls of the resonant cavity decreases slowly to zero. In the following period of time, only Q ₂ is turned on, and the current i _Ls of the resonant cavity remains in a zero state.

In the following period of time in the negative half cycle, S ₂ continues to drive Q ₂ to maintain the on state, S ₃ drives Q ₃ to conduct, and Q ₄ and Q ₁ continue to maintain the off state. At this time, V _in , Q ₃ , and the resonant cavity , Q ₂ form a series circuit, at this time, the voltage V _AB of A and B is also high level, but opposite to the prescribed direction. The series resonant converter works in the series oscillation mode, and the current i _Ls of the resonant cavity changes in a sinusoidal waveform. In this embodiment, the working state of each switching device in the next period is consistent with the above description.

In this embodiment, Q ₄ of the right bridge arm is always in the off state, and Q ₃ works in PWM mode, and a PWM operation is only performed once in the negative half cycle of a switching cycle; The % duty cycle works complementary, leaving only a certain deadband to avoid shoot-through. In this way, the positive half-cycle series resonant circuit in the same switching period works in the free resonance mode, and the negative half-cycle works in the series resonant mode under the excitation of the input source. By making the switching frequency f _s of the switching device slightly greater than the series resonant inverter circuit Resonant frequency f _r , Q ₃ is hard turned off at a higher current only in the positive half cycle, which can ensure a small switching loss.

Example 5

In this embodiment, the driving signal is used to drive the switching device to be turned on or off periodically, and the periodic turning on or off of the switching device includes at least two switching periods, and there is only one switch in each switching period hard shutdown of the device. The driving circuit 14 can provide a driving signal to drive the inverter circuit 11 to perform periodic modulation, the equivalent voltage transmission gain of the series resonant inverter circuit is M>0.5, and the periodic modulation can include a first switching period and a second switching period, wherein;

In the positive half period of the first switching period, the driving circuit 14 drives a switching device of the left bridge arm to perform PWM modulation, and drives two switching devices of the right bridge arm to work with a set duty ratio; in the negative half period of the first switching period period, the driving circuit 14 drives the switching device/inverting circuit 11 to make the series resonant converter work in a free oscillation mode.

In the positive half period of the second switching period, the drive circuit 14 drives the two switching devices of the left bridge arm to work with a set duty ratio, and drives a switching device of the right bridge arm to perform PWM modulation; in the negative half period of the second switching period Period, the driving circuit 14 drives the switching device, so that the series resonant converter works in the free oscillation mode.

In this embodiment, as shown in FIG. 1 , the left bridge arm of the inverter circuit 11 includes a first switching device Q ₁ and a second switching device Q ₂ , and the right bridge arm includes a third switching device Q ₃ and a fourth switching device Q ₄ , and provide the first driving signal S ₁ to the first switching device Q ₁ , provide the second driving signal S ₂ to the second switching device Q ₂ , provide the third driving signal S ₃ to the third switching device Q ₃ , and provide The fourth driving signal S ₄ is given to the fourth switching device Q ₄ , and the above-mentioned multiple driving signals drive the switching devices in the inverter circuit 11 to be turned on or off periodically. Fig. 6 is a modulation waveform diagram of the series resonant inverter in Embodiment 5 of the present application, and the driving process is as follows:

In the positive half period of the first switching period, the _first driving signal S1 drives the _first switching device Q1 to perform PWM modulation, and the _fourth driving signal S4 drives the fourth switching device _Q4 to operate with a set duty cycle. The working state of each electronic component is: within a period of time in the positive half cycle, the driving signal drives the switching devices Q ₁ and Q ₄ to be turned on at the same time, the switching devices Q ₂ and Q ₃ are in the off state, the input voltage V _in , the switching devices Q ₁ , resonant cavity, and switching device Q ₄ are connected in series to form a loop. The voltage V _AB at points A and B is at a high level (in the same direction as the set voltage), and the inverter current output by the inverter circuit or flows through the resonance The current i _Ls of the cavity gradually increases (the current direction in the resonant cavity is the same as the predetermined current direction); after that, only Q ₄ is turned on, and Q ₁ , Q ₂ , and Q ₃ are in the off state at the same time, and the resonant cavity and switching device Q _4. The second diode D ₂ is connected in series to form a loop, the voltage V _AB at points A and B is zero level, and the series inductor of the resonant cavity is discharged, the current i _Ls flowing through the resonant cavity gradually decreases until it decreases to Zero, there is a turn-off loss in the circuit during this process, that is, the hard turn _- off of Q1 at high current;

After that, Q ₄ changes from on to off/off state, Q ₁ , Q ₂ , Q ₃ , and Q ₄ are in the off state at the same time, the voltage across the capacitor Cs in the resonant cavity is zero, and the voltage at points A and B V _AB is zero level, there is no current flowing through the resonant cavity at this time, the turn-off loss when Q ₄ is turned off is zero, and there is no hard turn-off of the switching device.

In the negative half period of the first switching period, the second driving signal drives the second switching device to work at a set duty ratio, and the third driving signal drives the third switching device to work at a set duty ratio. The working state of each electronic component is: within a period of time in the negative half cycle, the driving signal drives the switching devices Q ₂ and Q ₃ to be turned on at the same time, the switching devices Q ₁ and Q ₄ are in the off state, the input voltage V _in , the switching devices Q ₃ , resonant cavity, and switching device Q ₂ are connected in series to form a loop. The voltages V _{A and B} at points A and B are at high level (but opposite to the specified direction), and the resonant cavity works in the free oscillation mode. The inverter current output by the inverter or the current flowing through the resonant cavity first gradually increases to the peak position (the direction of the current in the resonant cavity is opposite to the predetermined current direction), and then the inverter current output by the inverter or flows through The current of the resonant cavity gradually decreases from the peak value; later, when the inverter current output by the inverter or the current flowing through the resonant cavity decreases to zero, the switching devices Q ₂ and Q ₃ are in the off state at the same time, and there is no hard turn-off of the switching device.

In the positive half period of the second switching period, the first driving signal drives the first switching device to operate at a set duty ratio, and the fourth driving signal drives the fourth switching device to perform PWM modulation. The working state of each electronic component is: within a period of time in the positive half cycle, the driving signal drives the switching devices Q ₁ and Q ₄ to be turned on at the same time, the switching devices Q ₂ and Q ₃ are in the off state, the input voltage V _in , the switching devices Q ₁ , resonant cavity, and switching device Q ₄ are connected in series to form a loop, the voltage V _AB at points A and B is at a high level, and the inverter current output by the inverter circuit 51 or the current i _Ls flowing through the resonant cavity gradually increases ; Afterwards, only Q ₁ is turned on, Q ₂ , Q ₃ and Q ₄ are in the off state at the same time, the resonant cavity, switching device Q ₁ , and the third diode D ₃ are connected in series to form a loop, and the voltage V at points A and B _AB is zero level, and the series inductor of the resonant cavity discharges, the current i _Ls flowing through the resonant cavity gradually decreases until it decreases to zero, and there is a turn-off loss in the circuit during this process, that is, Q ₄ hard shutdown of

Afterwards, when Q ₁ turns from the on state to the off state, Q ₁ , Q ₂ , Q ₃ , and Q ₄ are in the off state at the same time, the voltage across the capacitor Cs in the resonant cavity is zero, and the voltage at the two points A and B V _AB is zero level, there is no current flowing through the resonant cavity at this time, the turn-off loss when Q ₁ is turned off is zero, and there is no hard turn-off of the switching device.

In the negative half period of the second switching cycle, the _second driving signal S2 drives the second switching device _Q2 to work with a set duty cycle, and the _third drive signal S3 drives the third switching device _Q3 to set a duty cycle Work. The working state of each electronic component is: within a period of time in the negative half cycle, the driving signal drives the switching devices Q ₂ and Q ₃ to be turned on at the same time, the switching devices Q ₁ and Q ₄ are in the off state, the input voltage V _in , the switching devices Q ₃ , resonant cavity, and switching device Q ₂ are connected in series to form a loop. The voltage V _AB at points A and B is at a high level, and the resonant cavity works in the free oscillation mode. In the free oscillation mode, the inverter current output by the inverter or The current flowing through the resonant cavity first gradually increases to the peak position, and then the inverter current output by the inverter or the current flowing through the resonant cavity gradually decreases from the peak value; after that, when the inverter output output by the inverter or When the current flowing through the resonant cavity decreases to zero, the switching devices Q ₂ and Q ₃ are turned off at the same time.

Of course, the periodic modulation of the driving signal driving the inverter circuit may also include multiple odd-numbered switching periods such as the third switching period, the fifth switching period, ..., the (2n-1)th switching period, and the fourth switching period, the sixth A plurality of even-numbered switching periods such as switching period, ..., (2n)th switching period, n is a positive integer. In one embodiment, in all odd-numbered switching periods, the action of each electronic component is the same as that of the first switching period of Embodiment 5; cycle or the second switching cycle acts the same. In another embodiment, in all odd-numbered switching periods, the action of each electronic component is the same as that of the first switching period or the second switching period of this embodiment; in all even-numbered switching periods, the action of each electronic component is the same as The operation of the second switching cycle in this embodiment is the same. It should be noted that, in this embodiment, the turn-off loss is evenly distributed between the left and right bridge arms, and the temperature rise of the switching device can be significantly reduced for the occasion where the half-bridge module is used as the switching device.

Example 6

In this embodiment, the driving circuit 14 can provide a driving signal to drive the inverter circuit 11 to perform periodic modulation, the equivalent voltage transmission gain of the series resonant inverter circuit is M<0.5, and the periodic modulation can include the first switching cycle and the second The switching period, and there is a hard turn-off of a switching device in the first switching period and the second switching period, the first driving signal S1 drives the first switching device to be in an off state, and:

In the positive half period of the first switching period, the _fourth driving signal S4 drives the fourth switching device _Q4 to work with a set duty cycle; in the negative half period of the first switching period, the _second driving signal S2 drives the second The switching device _Q2 performs PWM modulation, and the _third driving signal S3 drives the third switching device _Q3 to work with a set duty ratio.

In the positive half period of the second switching period, the _fourth driving signal S4 drives the fourth switching device _Q4 to work with a set duty cycle; in the negative half period of the second switching period, the _second driving signal S2 drives the second The switching device _Q2 works with a set duty ratio, and the third driving signal S3 drives the third switching device Q3 to perform PWM modulation.

It should be noted that, in the above-mentioned periodical modulation process, in the first period of modulation, only the switching device _Q3 has a turn-off loss at a higher current; in the second period of modulation, only the switching device _Q2 is at a higher current. There are turn-off losses. Of course, the periodic modulation of the drive signal driving the inverter circuit may also include other modulation cycles, and the other modulation cycles are the same as the first or second cycle above, and the turn-off loss is evenly distributed between the left and right bridge arms. For half-bridge modules In the case of a switching device, the temperature rise of the switching device can be significantly reduced.

Although the present application has been described with reference to the current specific embodiments, those of ordinary skill in the art should recognize that the above embodiments are only used to illustrate the present application, and can also be made without departing from the spirit of the present application. Various equivalent changes or substitutions, therefore, as long as the changes and modifications to the above-mentioned embodiments are within the spirit of the present application, they will all fall within the scope of the claims of the present application.

Claims (10)

1. a kind of control circuit of series resonant converter, the series resonant converter includes inverter circuit, the inversion electricity Road includes left side bridge arm and the right bridge arm, and the left side bridge arm and the right bridge arm are described respectively comprising two switching devices Control circuit includes：

Drive circuit, provides drive signal, the drive signal is used for the switch for the switching device of the inverter circuit Device carries out periodic modulation, and the periodic modulation at least includes a switch periods, and in one switch periods There is once hard shut-off in the switching device of the inverter circuit, wherein,

In the positive half period of a switch periods, the drive circuit drives a switching device of the left side bridge arm to carry out PWM, drives two switching devices of the right bridge arm to set duty cycle；

In the negative half-cycle of a switch periods, the drive circuit drives the derailing switch of the left side bridge arm and the right bridge arm Part, makes the series resonant converter be operated in free-run mode.

2. the control circuit of series resonant converter according to claim 1, it is characterised in that the left side bridge arm includes First switch device and second switch device, the right bridge arm include the 3rd switching device and the 4th switching device, the drive Dynamic circuit provide the first drive signal to the first switch device there is provided the second drive signal to the second switch device, There is provided the 3rd drive signal to the 3rd switching device there is provided fourth drive signal to the 4th switching device, it is and described The equivalent voltage transmission gain of inverter circuit is more than 0.5：

In the positive half period of a switch periods, first drive signal drives the first switch device to carry out PWM, The fourth drive signal drives the 4th switching device to set duty cycle；

In the negative half-cycle of a switch periods, second drive signal drives the second switch device to set dutycycle Work, the 3rd drive signal drives the 3rd switching device to set duty cycle.

3. the control circuit of series resonant converter according to claim 1, it is characterised in that the left side bridge arm includes First switch device and second switch device, the right bridge arm include the 3rd switching device and the 4th switching device, the drive Dynamic circuit provide the first drive signal to the first switch device there is provided the second drive signal to the second switch device, There is provided the 3rd drive signal to the 3rd switching device there is provided fourth drive signal to the 4th switching device, it is and described The equivalent voltage transmission gain of inverter circuit is less than 0.5：It is disconnected that first drive signal drives the first switch device to be in Open state；

In the positive half period of a switch periods, the fourth drive signal drives the 4th switching device to set dutycycle Work；

In the negative half-cycle of a switch periods, second drive signal drives the second switch device to carry out PWM, 3rd drive signal drives the 3rd switching device to set duty cycle.

4. a kind of control circuit of series resonant converter, the series resonant converter includes inverter circuit, the inversion electricity Road includes left side bridge arm and the right bridge arm, and the left side bridge arm and the right bridge arm are described respectively comprising two switching devices Control circuit includes：

Drive circuit, provides drive signal, the drive signal is used for the switch for the switching device of the inverter circuit Device carries out periodic modulation, and the periodic modulation at least includes a switch periods, and in one switch periods There is once hard shut-off in the switching device of the inverter circuit, wherein,

In the positive half period of a switch periods, the drive circuit drives two switching devices of the left side bridge arm to set Duty cycle, drives a switching device of the right bridge arm to carry out PWM；

In the negative half-cycle of a switch periods, the drive circuit drives the derailing switch of the left side bridge arm and the right bridge arm Part, makes the series resonant converter be operated in free-run mode.

5. the control circuit of series resonant converter according to claim 4, it is characterised in that the left side bridge arm includes First switch device and second switch device, the right bridge arm include the 3rd switching device and the 4th switching device, the drive Dynamic circuit provide the first drive signal to the first switch device there is provided the second drive signal to the second switch device, There is provided the 3rd drive signal to the 3rd switching device there is provided fourth drive signal to the 4th switching device, it is and described The equivalent voltage transmission gain of inverter circuit is more than 0.5：

In the positive half period of a switch periods, first drive signal drives the first switch device to set dutycycle Work, the fourth drive signal drives the 4th switching device to carry out PWM；

In the negative half-cycle of a switch periods, second drive signal drives the second switch device to set dutycycle Work, the 3rd drive signal drives the 3rd switching device to set duty cycle.

6. the control circuit of series resonant converter according to claim 4, it is characterised in that the left side bridge arm includes First switch device and second switch device, the right bridge arm include the 3rd switching device and the 4th switching device, the drive Dynamic circuit provide the first drive signal to the first switch device there is provided the second drive signal to the second switch device, There is provided the 3rd drive signal to the 3rd switching device there is provided fourth drive signal to the 4th switching device, it is and described The equivalent voltage transmission gain of inverter circuit is less than 0.5：It is disconnected that the fourth drive signal drives the 4th switching device to be in Open state；

In the positive half period of a switch periods, first drive signal drives the first switch device to set dutycycle Work；

In the negative half-cycle of a switch periods, second drive signal drives the second switch device to set dutycycle Work, the 3rd drive signal drives the 3rd switching device to carry out PWM.

7. a kind of control method of series resonant converter, the series resonant converter includes inverter circuit, the inversion electricity Road includes left side bridge arm and the right bridge arm, and the left side bridge arm and the right bridge arm are respectively comprising two switching devices, the control Method includes：

Drive signal is provided for the switching device of the inverter circuit, the drive signal driving switch device periodically lead On-off is opened, and the periodic modulation at least includes first switch cycle and second switch cycle, wherein, in the first switch cycle Positive half period, the drive circuit drives a switching device of the left side bridge arm to carry out PWM, drives described the right Two switching devices of bridge arm are to set duty cycle；

In the negative half-cycle in first switch cycle, the drive circuit drives the derailing switch of the left side bridge arm and the right bridge arm Part, makes the series resonant converter be operated in free-run mode；

In the positive half period in second switch cycle, the drive circuit drives two switching devices of the left side bridge arm to set Duty cycle, drives a switching device of the right bridge arm to carry out PWM；

In the negative half-cycle in second switch cycle, the drive circuit driving switch device makes the series resonant converter work Make in free-run mode.

8. the control method of series resonant converter according to claim 7, it is characterised in that the left side bridge arm includes First switch device and second switch device, the right bridge arm include the 3rd switching device and the 4th switching device, and provide There is provided the second drive signal, to the second switch device, there is provided the 3rd drive to the first switch device for first drive signal Dynamic signal gives the 4th switching device to the 3rd switching device there is provided fourth drive signal, wherein,

In the positive half period in first switch cycle, first drive signal drives the first switch device to carry out PWM, The fourth drive signal drives the 4th switching device to set duty cycle；

In the negative half-cycle in first switch cycle, second drive signal drives the second switch device to set dutycycle Work, the 3rd drive signal drives the 3rd switching device to set duty cycle；

In the positive half period in second switch cycle, first drive signal drives the first switch device to set dutycycle Work, the fourth drive signal drives the 4th switching device to carry out PWM；

In the negative half-cycle in second switch cycle, second drive signal drives the second switch device to set dutycycle Work, the 3rd drive signal drives the 3rd switching device to set duty cycle.

9. the control method of series resonant converter according to claim 7, it is characterised in that the left side bridge arm includes First switch device and second switch device, the right bridge arm include the 3rd switching device and the 4th switching device, and provide There is provided the second drive signal, to the second switch device, there is provided the 3rd drive to the first switch device for first drive signal Dynamic signal gives the 4th switching device to the 3rd switching device there is provided fourth drive signal, wherein：First driving Signal drives the first switch device to be off；

In the positive half period in first switch cycle, the fourth drive signal drives the 4th switching device to set dutycycle Work；

In the negative half-cycle in first switch cycle, second drive signal drives the second switch device to carry out PWM, 3rd drive signal drives the 3rd switching device to set duty cycle；

In the positive half period in second switch cycle, the fourth drive signal drives the 4th switching device to set dutycycle Work；

In the negative half-cycle in second switch cycle, second drive signal drives the second switch device to set dutycycle Work, the 3rd drive signal drives the 3rd switching device to carry out PWM.

10. the control method of the series resonant converter according to claim any one of 7-9, it is characterised in that described to set It is 50% to determine dutycycle.