CN113489352B - A single-phase PWM rectifier power decoupling method with fault ride-through function - Google Patents

Abstract

The invention relates to a single-phase PWM rectifier power decoupling method with a fault ride-through function, and belongs to the technical field of single-phase PWM rectification. By designing the energy feedback loop of the miniature PWM rectification system with the fault ride-through function in the short-time power failure, the secondary pulse energy on the direct current side absorbed in the power decoupling process is utilized, so that under the condition that the short-time power failure is measured by the alternating current of the whole system, the voltage on the whole direct current side can be prevented from falling, the energy stored in the decoupling capacitor is reasonably utilized, and an idea for protecting equipment is provided for certain equipment which needs to operate without power failure.

Description

A single-phase PWM rectifier power decoupling method with fault ride-through function

technical field

The invention belongs to the technical field of single-phase PWM rectification, and in particular relates to a single-phase PWM rectifier with power decoupling function and a fault ride-through method.

Background technique

In a single-phase PWM rectification system, the AC instantaneous power includes the DC side component and the power oscillation of twice the fundamental frequency, which will cause significant current or voltage fluctuations on the DC side. Most of the traditional power electronic devices use traditional electrolytic capacitors with large volume, low efficiency and short life cycle to suppress the high-frequency interference on the DC bus to absorb the secondary power ripple on the DC side. However, electrolytic capacitors in the traditional sense have short life, large size and low reliability. Therefore, how to reduce the size of the converter, replace the use of electrolytic capacitors, and obtain higher power density and higher power efficiency has become the main problem of research. In order to solve the above problems, in recent years, active power decoupling (APD) technology is often used to replace the bulky capacitor bank to realize the decoupling function, that is, to replace the bulky capacitor bank with inductors or film capacitors with lower capacitance.

APD technology is usually implemented using an auxiliary circuit composed of power switches and energy storage devices (such as capacitors or inductors), which can better meet the needs of single-phase converters. As rectifiers are more and more used in various power electronic devices, their power decoupling has become a part that cannot be ignored. APD technology can not only ensure the inherent high efficiency of rectifiers, but also maintain the stability of output voltage. As the APD technology becomes more and more mature, different types of decoupling auxiliary circuits with different functions have been developed by researchers at home and abroad.

The use of APD technology can better solve the reliability problems caused by traditional electrolytic capacitors, but the accompanying problem is that due to the use of film capacitors, the DC side capacitance becomes smaller. If a short-term power failure occurs on the AC input side, a short-term failure will occur. When the DC side voltage drops, some types of DC side loads will stop working if the voltage drops, resulting in data loss and serious losses; or when the uninterruptible power supply system (UPS) fails to switch power supply Sometimes, there will be intermittent power outages in the middle, which will also make the voltage of the electrical equipment unstable. In order to solve this problem, it is necessary to study a power decoupling fault ride-through method, so that when the voltage or frequency exceeds the normal range allowed by the standard in the event of a fault on the AC input side, the Within the time interval, it is guaranteed that the entire system can run uninterrupted and can transition to normal operation smoothly. By realizing the scheduling control of energy, the support of the DC side voltage during the fault period can be realized, which can prevent the restart of the electrical equipment caused by the AC short circuit or power failure, and reduce unnecessary losses.

Contents of the invention

technical problem to be solved

During the operation of the entire PWM rectification system, if the input end is disconnected at a certain point in time, resulting in a reduction in output power, since the load on the output side will not change, the voltage on the output side will decrease when the power is cut off. For the load, when the voltage drops to a certain voltage value, it will stop working, causing the entire power-consuming side equipment to stop working, affecting the stability of the entire system. At this time, it is necessary to perform fault ride-through. That is, during the power-off time, provide enough energy to the electrical equipment by other means to maintain sufficient voltage and power during the power-off time so that it can operate stably.

Taking the power decoupling single-phase PWM rectifier as an example, the goal of fault ride-through is to design a suitable and correct energy flow circuit when the system is temporarily powered off, so as to ensure that the DC side is under the condition of short-term power failure on the AC side. The voltage will not drop to a certain amplitude, that is, when the AC side is powered off, if the power-off time is assumed to be 1ms, how to design that the DC side can continue to run until the end of the power-off time without detaching from the AC side within this 1ms. The main goal is to design the energy flow of the entire system within this 1ms, and the power transmission method to ensure the stable operation of the DC side.

In order to solve this problem, the present invention proposes a fault ride-through method of power decoupling, so that in the case of a fault on the AC input side (when the voltage or frequency exceeds the normal range allowed by the standard), within a certain voltage or frequency range and its Within the continuous time interval, it is guaranteed that the entire system can run uninterrupted and can smoothly transition to the normal operation state. By realizing the scheduling control of energy, the support of the DC side voltage during the fault period can be realized, which can prevent the restart of the electrical equipment caused by the AC short circuit or power failure, and reduce unnecessary losses.

Technical solutions

A single-phase PWM rectifier power decoupling method with fault ride-through function, characterized in that the steps are as follows:

Step 1: The harmonic output on the DC side of the single-phase PWM rectifier is the second harmonic, and the fundamental wave of the output voltage is filtered out using a high-pass filter to obtain the target second pulsating voltage that needs to be decoupled;

Step 2: Suppress the secondary pulsation voltage, set the secondary pulsation reference voltage to 0, so that the secondary pulsation can be completely suppressed in the end;

Step 3: Suppress the secondary pulsation and the quaternary pulsation existing in the harmonics through the PR controller to obtain the reference current of the decoupling current;

Step 4: Adjust the reference value of the decoupling current to a 100Hz sinusoidal curve to compensate the ripple power, and then add a proportional controller to make the decoupling current track the reference value;

Step 5: Set a fixed DC offset voltage for the decoupling capacitor to ensure that the DC output of the single-phase rectifier is less than the voltage on the decoupling capacitor under any required load conditions, and the SPWM modulation wave is obtained by sampling through the zero-order keeper , modulate the SPWM modulation wave with the PWM carrier to obtain the signal to control the decoupling topology switch tube, so as to realize the purpose of power decoupling;

Step 6: By detecting the voltage at the DC output terminal of the rectifier, it is determined that a fault has occurred when it is lower than the set minimum voltage standard; at this time, energy needs to be fed back from the decoupling capacitor to the load side of the rectifier to maintain the voltage at the DC side not lower than the minimum voltage Standard; at the moment when the short-term fault is detected, the obtained signal lower than the minimum voltage standard is maintained, and the voltage at the end of the energy storage capacitor is pulled down, so that the stored energy is fed back to the DC side.

The second harmonic in step 1 is 100Hz.

The four pulses in step 3 are 200Hz.

In step 5, since the topology of the decoupling loop is the Boost topology, in order to keep the whole system running normally during the decoupling process, it is necessary to ensure that the DC side voltage is always higher than the AC side input voltage on the single-phase rectifier side. In the Boost decoupling loop Always keep the DC output of the single-phase rectifier smaller than the voltage on the decoupling capacitor, and considering the complexity and cost of system control, it is decided to set a fixed DC offset voltage for the decoupling capacitor.

The minimum voltage standard in step 6 is set according to the application circuit of the fault decoupling technology, which can be set by observing the voltage change when the load is switched; when the voltage of the DC output terminal is lower than this standard, it is judged as a fault state, and the fault ride-through function Enable; the edge trigger is used to maintain the detected fault signal so that it can be maintained, and the SR flip-flop is selected as the edge trigger.

Beneficial effect

A single-phase PWM rectifier power decoupling method with fault ride-through function proposed by the present invention, by designing the energy feedback loop of the miniature PWM rectifier system with fault ride-through function during short-term power failure, the energy absorbed during power decoupling is utilized The secondary ripple energy of the DC side makes it possible to prevent the voltage of the entire DC side from falling in the event of a short-term power failure in the AC measurement of the entire system, and reasonably utilize the energy stored in the decoupling capacitor to provide constant Equipment that runs without power provides a way to protect equipment.

1. By using power decoupling, the present invention can replace the electrolytic capacitor used in the original circuit with a thin film capacitor with a smaller volume and longer life, which reduces the size of the circuit, improves the expected life of the system, and reduces the cost of the circuit. maintenance costs.

2. Through the fault ride-through technology, the present invention provides enough energy to the load on the rectifier side in other ways during the power-off time to maintain its stable operation during the power-off time, which is reliable for the circuit when the load on the output side changes. Operation is guaranteed.

3. Through the fault ride-through technology, the present invention provides an idea for providing sufficient energy supply for the circuit when the main power supply is switched to the backup power supply in the UPS system, ensuring that there is enough energy to maintain the normal operation of the system at the moment of switching.

Description of drawings

The drawings are for the purpose of illustrating specific embodiments only and are not to be considered as limitations of the invention, and like reference numerals refer to like parts throughout the drawings.

Figure 1 shows a PWM rectifier with power decoupling.

Fig. 2 is when the load changes from 1600Ω to 100Ω, the voltage waveform diagram under different power-down time.

Figure 3 is a voltage waveform diagram of different power-down times when the load is changed from 1600Ω to 50Ω.

Fig. 4 is when the load changes from 1600Ω to 10Ω, the voltage waveform diagram under different power-down time.

FIG. 5 is a diagram of a fault ride-through control method.

Figure 6 is a fault ride-through effect diagram.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

The present invention proposes a micro-rectification system with power decoupling function, and designs a control loop in the case of a short-term power failure in AC measurement, and supplies energy to the DC side by controlling the energy storage capacitor at the decoupling end to maintain its voltage It does not continue to fall, and completes the fault ride-through when the AC side is powered off for a short time.

The single-phase PWM rectifier fault ride-through method of this embodiment includes the following steps:

Step 1. The harmonic output on the DC side of the single-phase PWM rectifier is the second harmonic. Use a high-pass filter to filter the fundamental wave of the output voltage, and then you will get the second pulsating voltage, which needs to be decoupled. The goal.

Step 2, in order to suppress the secondary pulsating voltage, set the reference pulsating voltage to 0, so that the secondary pulsating voltage can be completely suppressed in the end.

In step 3, the second pulsation and a little fourth pulsation are suppressed by the PR controller, so as to obtain the reference current of the decoupling current.

Step 4, adjust the reference value of the decoupling current to a 100Hz sinusoidal curve to compensate the ripple power, and then make the decoupling current track the reference value by adding a proportional controller.

Step 5, set a fixed DC offset voltage for the decoupling capacitor to ensure that the DC output of the single-phase rectifier is less than the voltage on the decoupling capacitor under any load conditions required, by sampling this signal through the zero-order keeper The SPWM modulation wave can obtain the signal to control the decoupling topology switch tube, and then realize the purpose of power decoupling. It can be seen from Figure 1 that the topology of the decoupling loop used is Boost topology. In order to keep the whole system running normally during the decoupling process, it is necessary to ensure that the DC side voltage is always higher than the AC side input voltage on the single-phase rectifier side. In the coupling circuit, the DC output of the single-phase rectifier is always kept smaller than the voltage on the decoupling capacitor, and considering the complexity and cost of system control, it is decided to set a fixed DC offset voltage for the decoupling capacitor.

Step 6, in order to understand the specific fault situation, design a simulation situation when the single-phase PWM rectifier has a power-off fault at the input end, so that it can be judged as a fault when the voltage on the DC side drops to what value, in the simulation environment A single-phase PWM rectifier model with power decoupling function is built in the paper, and the influence of different load changes and power-off time on the voltage is obtained through simulation.

Step 7, from Figure 2 to Figure 4, it can be known that when the load is suddenly switched from no load to rated load, the voltage will first drop to about 350V, and then when the load switching is completed and the system adapts to the new load, the entire system will recover Run to 400V; when a power failure occurs, the voltage will suddenly drop at the moment of power failure, and as the power failure time increases, the voltage will drop even lower, and after the short-term power failure ends, the voltage will return to steady state. Through three simulation experiments, it can be known that in this system, when the voltage on the DC side drops below 350V, it can be judged as a fault state.

In step 8, the system state can be judged by detecting the DC voltage. When the voltage on the DC side is lower than the minimum voltage standard, it can be judged that it is a fault state, and the fault ride-through function needs to be activated to maintain a fixed voltage on the DC side. When a fault is detected, it is necessary to immediately maintain the obtained voltage signal lower than 350V to control the bias voltage of the DC side and pull down the voltage of the energy storage capacitor so that the stored energy is fed back to the DC side. In this control, an edge trigger is used to maintain the detected fault signal so that it can be maintained. This edge trigger uses the SR flip-flop whose truth table is shown in Table 1. The control diagram is shown in Figure 5. . The fault signal can be held by the edge trigger, and a step control signal is generated to control the DC side bias voltage from the value of power decoupling to the value set during fault ride-through, so that the voltage across the decoupling capacitor can be changed Make it release energy to support the voltage on the DC side above 350V to complete short-term fault ride-through. The effect diagram of fault ride-through is shown in Figure 6. It can be seen that after fault ride-through is enabled, the DC side voltage can be kept above the set minimum voltage when a fault occurs, and the target function is successfully realized.

Table 1 SR flip-flop truth table

S R Q /Q 0 0 no change no change 0 1 0 1 1 0 1 0 1 1 Restricted(0) Restricted(0)

The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person familiar with the technical field can easily think of various equivalents within the technical scope disclosed by the present invention. Modifications or replacements shall all fall within the protection scope of the present invention.

Claims (5)

1. A single-phase PWM rectifier power decoupling method with a fault ride-through function is characterized by comprising the following steps:

step 1: harmonic waves output by the direct current side of the single-phase PWM rectifier are second harmonic waves, and the fundamental waves of the output voltage are filtered by using a high-pass filter to obtain target second pulsating voltage needing decoupling;

step 2: suppressing the secondary pulse voltage, and setting the secondary pulse reference voltage to be 0, so that the secondary pulse is completely suppressed;

and step 3: the PR controller is used for restraining the secondary pulsation and the quartic pulsation in the harmonic wave to obtain a reference current of the decoupling current;

and 4, step 4: adjusting the reference value of the decoupling current to be a 100Hz sine curve to compensate the ripple power, and adding a proportional controller to enable the decoupling current to track the reference value;

and 5: setting a fixed direct current offset voltage for the decoupling capacitor to ensure that the direct current output of the single-phase rectifier is smaller than the voltage on the decoupling capacitor under any required load condition, sampling through a zero-order retainer to obtain an SPWM (sinusoidal pulse width modulation) wave, modulating the SPWM wave and a PWM (pulse width modulation) carrier wave to obtain a signal for controlling a decoupling topology switch tube, and achieving the purpose of power decoupling;

and 6: the voltage of the direct current output end of the rectifier is detected, and when the voltage is lower than a set lowest voltage standard, the fault is determined to occur; at the moment, energy needs to be fed back from the decoupling capacitor to the load side of the rectifier to maintain the voltage of the direct current side not lower than the minimum voltage standard; at the moment of detecting the short-time fault, the obtained signal lower than the minimum voltage standard is kept, and the voltage of the energy storage capacitor end is pulled down, so that the stored energy is fed back to the direct current side.

2. The method for power decoupling of a single-phase PWM rectifier with fault-ride-through capability of claim 1, wherein the second harmonic in step 1 is 100Hz.

3. The method for power decoupling of a single-phase PWM rectifier with fault-ride-through capability of claim 1, wherein the four pulses in step 3 are 200Hz.

4. The method for decoupling power of a single-phase PWM rectifier with a fault ride-through function according to claim 1, wherein in step 5, since the topology of the decoupling loop is a Boost topology, in order to keep the whole system to operate normally in the decoupling process, it is necessary to always ensure that the voltage of the DC side is higher than the voltage of the input end of the AC side on the side of the single-phase rectifier, and always keep the DC output of the single-phase rectifier smaller than the voltage of the decoupling capacitor in the Boost decoupling loop, and a fixed DC offset voltage is determined to be set for the decoupling capacitor in consideration of the complexity and cost of system control.

5. The power decoupling method for the single-phase PWM rectifier with fault ride-through function according to claim 1, wherein the lowest voltage standard in step 6 is set according to the application circuit of the fault decoupling technology, and the standard is set by observing the voltage change when the load is switched; when the voltage of the direct current output end is lower than the standard, the fault state is judged, and the fault ride-through function is enabled; edge flip-flops are employed to hold the detected fault signal so that it is maintained, with SR flip-flops being selected for use as edge flip-flops.

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