KR101434497B1 - An apparatus and a method for power conversion - Google Patents

Abstract

The present invention relates to a power conversion apparatus having a synchronous rectification function and simultaneously changing a frequency and a pulse width of a control signal according to an output characteristic so that switching loss is small and high efficiency operation is possible.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a power conversion apparatus,

The present invention relates to a power conversion apparatus having a synchronous rectification function and simultaneously changing a frequency and a pulse width of a control signal according to an output characteristic so that switching loss is small and high efficiency operation is possible.

First, the prior art related to the present invention is as follows.

- Korean Patent Publication No. 2012-0035911

- Korean Patent Publication No. 2012-0072800

The switching control method of the DC-DC converter includes pulse frequency modulation (PFM) for adjusting the frequency of the control signal and pulse width modulation (PWM) for adjusting the width of the control signal. Uses a diode rectification method and a synchronous rectification method using a switch.

In the isolated DC / DC converter, the pulse width modulation method is mainly used. However, the pulse frequency modulation method is widely used for the soft switching using the resonance characteristic in order to improve the efficiency.

Conventionally, in order to solve the problem of the pulse frequency modulation method, a method of switching the pulse frequency modulation and the pulse width modulation according to the conditions such as the load and the output voltage has been used.

In this connection, Korean Patent Laid-Open Publication No. 2002-0035911 discloses a method of changing the pulse frequency modulation (PFM) and the pulse width modulation (PWM) according to the load condition, and Korean Patent Publication No. 2012-0072800 Discloses a method of switching from pulse frequency modulation (PFM) to pulse width modulation (PWM) when a short circuit occurs.

However, the pulse frequency modulation method using the resonance characteristics has a limitation on the switching frequency that can be efficiently used for peripheral components and design reasons.

In pulse frequency modulation, the switching frequency is controlled to a high frequency band where the voltage gain is low to control the output voltage under light load or low. In the high frequency band, the voltage gain is not significantly lowered even if the switching frequency is greatly increased. There was a problem that limitations occurred.

In the pulse frequency modulation, the frequency is varied to change the power while the pulse width is fixed. At this time, the low-frequency ripple component carried on the DC link voltage is directly transmitted to the secondary coil side by the winding ratio of the transformer I have a problem. Conventionally, in order to solve such a problem, a capacitor capacity increase or an LC filter is additionally used. However, in this case, there is a problem that the volume increases and the circuit becomes complicated, and the cost increases and miniaturization becomes difficult.

On the other hand, in the secondary rectification part of the isolated DC-DC converter, a diode rectification method is generally used. However, in the diode rectification method, power loss due to forward voltage loss is very large, There was a problem. Accordingly, a synchronous rectification method has been used for the high efficiency of the power source. This is a method of rectifying the switching of the power by using a small-resistance power switching element instead of a diode having a large forward loss.

In this synchronous rectification method, the switching frequency and the pulse width of the primary switching unit and the secondary rectifying unit of the transformer of the isolated DC-DC converter are used equally. Particularly, when operating at a high frequency, There is a problem that the switching element is broken when a delay occurs. In the LLC resonant converter, if the switching frequency is lower than the resonant frequency, there is a problem that the switching element is damaged by the secondary reverse current due to the resonant current.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a power conversion apparatus capable of reliably outputting a desired target voltage and current over a wide output voltage variable range and a wide load range by solving the problems as described above.

In order to achieve the above object, the present invention adjusts a voltage gain by using pulse frequency modulation (PFM) and pulse width modulation (PWM) simultaneously. This makes it possible to actively control the desired target voltage under light load or low output voltage conditions.

Further, the present invention uses both pulse frequency modulation (PFM) and pulse width modulation (PWM) in the entire switching period. Thus, it is possible to solve the problem that the low frequency noise carried on the DC link voltage is directly transmitted to the secondary side of the transformer without using an additional capacitor capacity increase or an LC filter.

In the present invention, the secondary side synchronous rectification controls the pulse width of the secondary side to be equal to or smaller than the switching frequency of the primary side. Thus, breakage of parts can be prevented and reliability can be ensured.

A power conversion apparatus according to an embodiment of the present invention includes a switching unit connected to a primary side of a transformer and a rectifying unit connected to a secondary side of the transformer, The power conversion unit comprising: And a control unit for generating and outputting a control signal for controlling the switch of the switching unit and the switch of the rectifying unit and receiving the output voltage as feedback and sensing an output current, The pulse width can be changed at the same time.

According to one embodiment, the switch of the switching section is controlled by the first control signal, and the switch of the rectifying section is controlled by the second control signal.

According to an embodiment, the first control signal and the second control signal may be the same in frequency and the pulse width may be different from each other, and in particular, the pulse width of the second control signal may be equal to or shorter than the pulse width of the first control signal have.

According to one embodiment, the control unit may be a digital controller, i.e., a DSP or a MICOM, and the power conversion unit may be a flyback, a forward, a push-pull, a half- Bridge, and Full-Bridge, and the rectification part may be a synchronous rectifier, and the switches in the power conversion part may be switches with little power loss.

A power conversion method according to an embodiment of the present invention includes the steps of converting an input power source to a predetermined output voltage and switching at a primary side of a transformer and rectifying at a secondary side of the transformer , The converting step; Generating and outputting a control signal for controlling switching of the switching step and switching of the rectifying step; And feedbacking the output voltage and sensing an output current to generate the control signal, wherein the frequency and the pulse width of the control signal can be changed at the same time.

According to one embodiment, the switching of the switching step is controlled by the first control signal, and the switching of the step of rectifying can be controlled by the second control signal.

According to an embodiment, the first control signal of the switching step and the second control signal of the rectifying step may be the same in frequency and different in pulse width, and in particular, the pulse width of the second control signal may be 1 pulse width of the control signal.

According to one embodiment, the control signal may be generated by a digital controller, i. E., A DSP or MICOM, and the step of converting may be a flyback, a forward, a push- A DC-DC converter of any one of a bridge, a half bridge and a full-bridge, and the step of rectifying may be a rectification by a synchronous rectification method, The switches may be switches with low power loss.

The technique disclosed in the present invention can have the following effects. It is to be understood, however, that the scope of the disclosed technology is not to be construed as limited thereby, as it is not meant to imply that a particular embodiment should include all of the following effects or only the following effects.

The present invention according to one embodiment can operate in a stable range regardless of the operating conditions of the output at full load, using pulse frequency modulation and pulse width modulation at the same time.

In addition, since the present invention employs a soft switching technique using a synchronous rectifier, it is possible to operate at a high efficiency with a small switching loss. By using pulse voltage modulation and pulse width modulation using both voltage and current information, Reliability can be improved.

And, the present invention can stably adjust a desired target voltage and current in a wide output voltage variable range and a wide load range. Further, by controlling the duty of the synchronous rectification section to be equal to or smaller than the primary pulse width, there is an effect that the risk of breakage or the like in operation can be eliminated and the stability of the product can be ensured.

1 shows voltage gain characteristics with respect to a frequency according to a load change in a resonant converter.
2 is a circuit diagram of an LLC resonant converter according to an embodiment of the present invention.

For the embodiments of the invention disclosed herein, specific structural and functional descriptions are set forth for the purpose of describing an embodiment of the invention only, and it is to be understood that the embodiments of the invention may be practiced in various forms, The present invention should not be construed as limited to the embodiments described in Figs.

The present invention is capable of various modifications and various forms, and specific embodiments are illustrated in the drawings and described in detail in the text. It is to be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but on the contrary, is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms may be used for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between. Other expressions that describe the relationship between components, such as "between" and "between" or "neighboring to" and "directly adjacent to" should be interpreted as well.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprise", "having", and the like are intended to specify the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, , Steps, operations, components, parts, or combinations thereof, as a matter of principle.

Each step may take place differently from the stated order unless explicitly stated in a specific order in the context. That is, each step may occur in the same order as described, may be performed substantially concurrently, or may be performed in reverse order.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be construed as meaning consistent with meaning in the context of the relevant art and are not to be construed as ideal or overly formal in meaning unless expressly defined in the present application .

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same reference numerals are used for the same constituent elements in the drawings and redundant explanations for the same constituent elements are omitted.

In general, the LLC resonant converter uses pulse frequency modulation (PFM) to control the output voltage. At this time, due to peripheral components and design reasons, there is a limitation of the usable switching frequency. This will be described below with reference to Fig.

1 shows voltage gain characteristics with respect to a frequency according to a load change in a resonant converter.

As it is shown in Figure 1, if you decrease the switching frequency (f _s) increases the voltage gain and increasing the switching frequency (f _s) a voltage gain is reduced. Also, if the load is small, the switching frequency increases and the voltage gain decreases. When the load is large, the switching frequency decreases and the voltage gain increases. In particular, when the load is controlled to a low or low output voltage, a high frequency band switching frequency having a low voltage gain is used.

However, as shown in Fig. 1, in the high frequency band, that is, when the switching frequency is large in Fig. 1, the slope of the voltage gain characteristic curve with respect to the frequency decreases. Therefore, when the load is controlled to a low or low output voltage, the voltage gain is not greatly reduced even if the switching frequency is greatly increased, because the width of the voltage gain decreases with the increase of the switching frequency. So that the voltage can not be controlled.

In order to solve such a problem, the resonance converter according to the embodiment of the present invention can control the voltage gain by using pulse frequency modulation (PFM) and pulse width modulation (PWM) simultaneously. As a result, the output of the desired target voltage can be actively controlled even under a low or low output voltage condition.

2 is a circuit diagram of an LLC resonant converter according to an embodiment of the present invention.

2, the switching unit 101 including the LLC resonant tanks L _m , L _R , and C _R is connected to the primary coil side of the transformer TX 1 and the switches Q 1 and Q 2 are connected to the primary coil side of the transformer TX 1. And is switched by a control signal. A synchronous rectification part 102 is connected to the secondary coil side of the transformer TX1.

The LLC resonant converter according to the embodiment of FIG. 2 uses switches Q1, Q2, Q3, and Q4 as switching elements for power conversion, and switches and regulates the gate signals of these switches.

2, a control signal for controlling the gate signals of the switches Q1, Q2, Q3 and Q4 used as switching elements for power conversion is generated and outputted by the control unit, and at the same time, the output voltage Vout is fed back to the control unit and the output current is sensed.

The present invention is not limited to the conventional method of switching the pulse frequency modulation (PFM) and the pulse width modulation (PWM) according to the output condition in the generation of the control signal for such a switching element, Pulse width modulation (PWM). Accordingly, the frequency and the pulse width of the control signal for the switching element are simultaneously changed.

However, in the case where the frequency and the pulse width of the control signal for the switching element are changed at the same time, it is difficult to set the frequency and the pulse width of the control signal due to the non-linearity. A method of changing only the frequency while keeping it as it is, or fixing the frequency of the control signal and changing only the pulse width was used.

However, in the embodiment of the present invention, the frequency and the pulse width of the control signal are set according to the slope of the voltage gain curve as shown in FIG. 1, and are simultaneously changed according to the load and the output condition .

On the other hand, the pulse frequency modulation (PFM) is a method of varying the frequency with the pulse width fixed, in which a low-frequency ripple component loaded on the DC link voltage of the input terminal is directly connected to the secondary voltage of the transformer according to the winding ratio of the transformer It has a problem to be delivered.

2, in the pulse frequency modulation (PFM) method, a low-frequency ripple component is included in the input voltage Vin, and the low-frequency ripple component of the low- There is a problem that the voltage is directly transmitted to the coil side voltage.

Conventionally, in order to solve such a problem, a capacitor capacity increase or an LC filter is additionally used. However, in an embodiment of the present invention, pulse frequency modulation (PFM) and pulse width modulation (PWM) at the same time. Thus, it is possible to solve the problem that such a low frequency ripple component is transmitted without increasing the capacitor capacity or adding the LC filter, which is conventionally used.

On the other hand, in the secondary rectification part of the isolated DC-DC converter, a synchronous rectification method with high efficiency is used instead of the conventional diode method as a rectification method. This uses a switch with low power loss with low resistance as a switching element, (Turn-on) / turn-off (turn-off) alternately.

In this synchronous rectification method, a soft switching technique is used. In the normal switching (hard switching), since the switching control signal is not an ideal rectangular wave but a collapsed ladder type, A part of the waveform of the control signal overlaps to generate a switching loss, whereas the soft switching prevents such switching control signals from overlapping.

In an embodiment according to the present invention, a synchronous rectification system for switching by using the switches Q3 and Q4 corresponding to the rectifying unit 102 in Fig. 2 is used.

In such a synchronous rectification method, the switching frequency and the pulse width of the primary switching unit and the secondary rectifying unit switches of the transformer of the isolated DC-DC converter are the same. Particularly, in case of operating at a high frequency, dead time There arises a problem that the switching element is broken when a shortage or a delay in control occurs. In the LLC resonant converter, if the switching frequency is lower than the resonant frequency, the switching element may be damaged due to the secondary reverse current due to the resonant current.

Referring to FIG. 2, in an embodiment according to the present invention, switching of switching control signals for the switches Q1 and Q2 of the primary switching unit of the transformer and the switches Q3 and Q4 of the secondary rectifying unit, The frequencies are the same, but their pulse widths are different.

Particularly, the switching control signals for the switches Q1 and Q2 of the primary switching unit of the transformer and the switching control signals for the switches Q3 and Q4 of the secondary rectifying unit are made equal to the switching frequency of the switches Q3 and Q4 of the secondary rectifying unit The pulse width of the switching control signal for the first switching unit is made smaller or equal to the pulse width of the switching control signal for the switches Q1 and Q2 of the primary switching unit. That is, the duty of the switching signal of the secondary rectification part is made smaller than or equal to the duty of the switching signal of the primary switching part. This solves the problem that the switching element is broken when the dead time is short or the control delay occurs when operating at a high frequency and when the switching frequency is smaller than the resonance frequency, It is possible to prevent breakage of the switching element which may be caused by reverse current.

As described above, when the switching frequency of the switching element used in the synchronous rectification in the LLC resonant converter according to the embodiment of the present invention is smaller than the resonant frequency, pulse frequency modulation (PFM) and pulse width modulation (PWM) By making the pulse width of the switches used for the synchronous rectification smaller or equal, it is possible to prevent the parts from being damaged and ensure the reliability.

Meanwhile, the LLC resonant converter according to an embodiment of the present invention is an isolated DC-DC converter using a transformer. Specifically, the LLC resonant converter is an isolated DC-DC converter such as a flyback, a forward, Push-Pull, Half-Bridge, and Full-Bridge.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the following claims. It will be understood.

100: power converter
101:
102: rectification part
103:

Claims (14)

1. A power conversion apparatus comprising:
A power conversion unit for converting input power to a predetermined output voltage, the power conversion unit including a switching unit connected to a primary side of a transformer and a rectifying unit connected to a secondary side of the transformer; And
And a control unit for generating and outputting a control signal for controlling the switch of the switching unit and the switch of the rectifying unit and receiving the output voltage as feedback and sensing an output current,
Wherein the controller uses a pulse frequency modulation (PFM) and a pulse width modulation (PWM) simultaneously,
The frequency and the pulse width of the control signal are simultaneously changed,
Wherein the switch of the switching unit is controlled by a first control signal,
The switch of the rectifying section is controlled by a second control signal,
Wherein the power converter is a DC-DC converter,
Wherein the DC-DC converter is an LLC resonant converter. delete The method according to claim 1,
Wherein the first control signal and the second control signal are the same in frequency and different in pulse width from each other. The method of claim 3,
Wherein a pulse width of the second control signal is equal to or less than a pulse width of the first control signal. The method according to claim 1,
Wherein the control unit is a digital controller. The method according to claim 1,
Wherein the power conversion unit is an LLC resonant converter of any one of a half-bridge and a full-bridge. The method according to claim 1,
Wherein the rectifying unit is a synchronous rectifier. A power conversion method comprising:
Converting the input power to a predetermined output voltage, comprising the steps of: switching at the primary side of the transformer and rectifying at the secondary side of the transformer;
Generating and outputting a control signal for controlling switching of the switching step and switching of the rectifying step; And
Feedbacking the output voltage and sensing an output current to generate the control signal,
The switching is controlled by using both Pulse Frequency Modulation (PFM) and Pulse Width Modulation (PWM)
The frequency and the pulse width of the control signal are simultaneously changed,
Wherein the switching of the switching step is controlled by a first control signal,
The switching of the rectifying step is controlled by a second control signal,
Wherein the converting step is performed by a DC-DC converter,
Wherein the DC-DC converter is an LLC resonant converter. delete 9. The method of claim 8,
Wherein the first control signal and the second control signal have the same frequency and different pulse widths from each other. 11. The method of claim 10,
Wherein a pulse width of the second control signal is equal to or less than a pulse width of the first control signal. 9. The method of claim 8,
Wherein the control signal is generated by a digital controller. 9. The method of claim 8,
Wherein the converting is performed by an LLC resonant converter of any one of a half-bridge and a full-bridge. 9. The method of claim 8,
Wherein the step of rectifying is rectified in a synchronous rectification manner.

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