Power-down rapid protection method for single-phase PWM (Pulse-Width Modulation) rectifier

Abstract

The invention discloses a power failure rapid protection method for a single-phase PWM rectifier. The single-phase PWM rectifier comprises a full-bridge circuit formed by connecting four switching tubes. In the positive half cycle of the alternating current signal, the S2 tube is the main control tube of the bridgeless PFC circuit, and in the negative half cycle of the alternating current signal, the S4 tube is the main control tube of the bridgeless PFC circuit; and in five power frequency periods after power failure, the switch tube is controlled to discharge the inductance current at the alternating current side. When the power supply is just turned off, the current at the inductor is not zero, in order not to cause oscillation, the inductor current continues to flow along the original direction, sudden change of the current direction is avoided until the consumption is zero, and overlarge oscillation caused by backflow is avoided. Oscillation of the alternating current side after power failure can be effectively suppressed, stability of output voltage of the direct current side can be achieved, and output stability of the rectifier is guaranteed.

Description

Technical Field

[0001] The invention relates to a single-phase PWM rectifier, and in particular to a power-off fast protection method for the single-phase PWM rectifier. Background Art

[0002] Single-phase PWM rectifier has the advantages of controllable input power factor, low input current harmonic pollution, and bidirectional energy flow, so it is widely used in power electronic conversion devices and other fields.

[0003] For a single-phase PWM rectifier, the main control objectives are:

[0004] Improve the power factor on the AC side, reduce the harmonic content of the grid-side current, output a stable DC voltage and reduce switching losses. However, when the PWM single-phase rectifier is powered off, a reverse current will appear and oscillate with the EMI filter on the AC side. To address the problem of oscillation of the power-off current of the single-phase PWM rectifier, the PWM signal is controlled to output a 5-cycle pulse after power failure, consuming the current on the AC side inductor and reducing the oscillation.

[0005] Existing technology and defects:

[0006] The methods commonly used in existing literature to suppress inductive current are mostly to control the circuit through the protection module in the DSP code on the control panel, but the switch tube is not turned off immediately when the rectifier loses power. Therefore, at the moment of power failure, the AC side power supply potential drops to 0, but the DC side potential does not decrease immediately. At this time, the rectifier circuit will be transformed into an inverter, the DC side voltage is greater than the AC side voltage, and the current flows from right to left. At this time, the switch tube is not turned off immediately, so the current will flow from the high-potential left side through the switch tube to the right side, and oscillate with the capacitor and inductor of the AC incoming EMI filter, causing the AC side waveform to oscillate. Failure to control the switch tube after power failure will cause the circuit output to be out of control, such as Figure 1 shown.

[0007] If all switches are turned off immediately after power failure detection, the current flowing through the inductor will no longer be able to enter the H-bridge, the current flow will be blocked, and the energy transmission loop will be affected. If the direction of the inductor current changes suddenly, the sudden change in potential will increase the instability of the system at this time. Therefore, it is necessary to consider the direction of the inductor current after power failure, and try to keep the direction of the inductor current unchanged so that the energy on the AC side is gradually consumed in the circuit.

[0008] In view of this, the present invention is proposed. Summary of the invention

[0009] The purpose of the present invention is to provide a power-off fast protection method for a single-phase PWM rectifier to solve the above technical problems existing in the prior art.

[0010] The objective of the present invention is achieved through the following technical solutions:

[0011] The single-phase PWM rectifier power-off fast protection method of the present invention comprises a full-bridge circuit formed by connecting four switch tubes, wherein the S1 tube is coupled between the output voltage of the bridgeless PFC circuit and the inductance of the bridgeless PFC circuit, the S2 tube is coupled between the S1 tube and the ground terminal, the S3 tube is coupled between the input AC power supply of the bridgeless PFC circuit and the ground terminal, and the S4 tube is coupled between the S3 tube and the ground terminal;

[0012] In the positive half cycle of the AC signal, the S2 tube is the main control tube of the bridgeless PFC circuit, and in the negative half cycle of the AC signal, the S4 tube is the main control tube of the bridgeless PFC circuit;

[0013] After power failure, the AC side inductor current is discharged through the switch tube.

[0014] Compared with the prior art, the power-off fast protection method for a single-phase PWM rectifier provided by the present invention can effectively suppress the oscillation on the AC side after power-off, achieve the stability of the DC side output voltage, and ensure the output stability of the rectifier. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The output waveform of the power circuit that oscillates after power failure in the prior art;

[0016] Figure 2 It is a PWM rectifier topology with EMI filter;

[0017] Figure 3 This is the PWM control signal waveform with EMI filter;

[0018] Figure 4 This is the PWM control signal waveform before adding power-off protection;

[0019] Figure 5 The PWM control signal waveform after adding power-off protection in the embodiment of the present invention;

[0020] Figure 6 The control signal waveform of the actual circuit in the power-off protection; in the figure: (a) the control signal waveform before and after the power-off; (b) the control signal waveform in the power-off protection;

[0021] Figure 7 The actual circuit output waveform of the embodiment of the present invention with power-off protection added. DETAILED DESCRIPTION

[0022] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, not all of the embodiments, which does not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0023] The contents not described in detail in the examples of the present invention belong to the prior art known to professionals in the field. If no specific conditions are specified in the examples of the present invention, the conditions are carried out according to the conventional conditions in the field or the conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used in the examples of the present invention, they are all conventional products that can be purchased commercially.

[0024] The single-phase PWM rectifier power-off fast protection method of the present invention comprises a full-bridge circuit formed by connecting four switch tubes, wherein the S1 tube is coupled between the output voltage of the bridgeless PFC circuit and the inductance of the bridgeless PFC circuit, the S2 tube is coupled between the S1 tube and the ground terminal, the S3 tube is coupled between the input AC power supply of the bridgeless PFC circuit and the ground terminal, and the S4 tube is coupled between the S3 tube and the ground terminal;

[0025] In the positive half cycle of the AC signal, the S2 tube is the main control tube of the bridgeless PFC circuit, and in the negative half cycle of the AC signal, the S4 tube is the main control tube of the bridgeless PFC circuit;

[0026] After power failure, the AC side inductor current is discharged through the switch tube.

[0027] Within 5 power frequency cycles after power failure, the switch tube is controlled to discharge the AC side inductor current.

[0028] When the power-off protection is activated, S1 and S2 tubes perform high-frequency switching for 5 power frequency cycles, S3 tube is normally closed within five cycles, S4 is normally open, and all switch tubes are disconnected after the end.

[0029] When the power is just turned off, the current in the inductor is not zero. In order to avoid oscillation, the inductor current continues to flow in the original direction to avoid sudden changes in the current direction until the consumption is zero, and to avoid excessive oscillation caused by backflow.

[0030] In summary, the power-off fast protection method for a single-phase PWM rectifier according to an embodiment of the present invention can effectively suppress the oscillation of the AC side after power-off, achieve the stability of the DC side output voltage, and ensure the output stability of the rectifier.

[0031] In order to more clearly demonstrate the technical solution and technical effects provided by the present invention, the embodiments of the present invention are described in detail with specific embodiments below.

[0032] Example 1

[0033] 1. Description of the principle of the invention:

[0034] The PWM single-phase rectifier structure used in the present invention is as follows: Figure 2 As shown, the S1 tube is coupled between the output voltage of the bridgeless PFC circuit and the inductor of the bridgeless PFC circuit, the S2 tube is coupled between the S1 tube and the ground terminal, the S3 tube is coupled between the input AC power supply of the bridgeless PFC circuit and the ground terminal, and the S4 tube is coupled between the S3 tube and the ground terminal. In addition, in the positive half cycle of the AC signal, the S2 tube is the main control tube of the bridgeless PFC circuit, and in the negative half cycle of the AC signal, the S4 tube is the main control tube of the bridgeless PFC circuit.

[0035] The present invention provides a control scheme for discharging the inductive current on the AC side through a switch tube after power failure: within 5 power frequency cycles after power failure, the switch MOSFET tube is controlled to discharge the inductive current on the AC side.

[0036] When the power-off protection is activated, S1 and S2 tubes perform high-frequency switching for 5 power frequency cycles, S3 tube is normally closed within five cycles, S4 is normally open, and all switch tubes are disconnected after the end. The specific waveform is as follows Figure 3 shown.

[0037] When the power is just turned off, the current in the inductor is not zero. In order to avoid oscillation, the inductor current should continue to flow in the original direction to avoid sudden changes in the current direction until the current consumption is zero. This solution can keep the inductor current flowing in the original direction to avoid excessive oscillation caused by backflow.

[0038] 2. Testing and experimental verification:

[0039] The solution proposed in the present invention is simulated. First, in the simulation environment, the AC power supply is turned off at a certain moment to simulate the power failure scenario. The waveform without power failure protection is as follows: Figure 4 If at this moment, the S4 tube is kept turned on, the S3 tube is turned off, and the S1 and S2 tubes continue to conduct current, the specific waveform is as follows Figure 5 shown.

[0040] It can be seen that the proposed power-off control scheme can effectively suppress oscillation and quickly discharge the energy on the AC side, which can verify the effectiveness of the control scheme.

[0041] Figure 6 The control signal waveform of the power-off protection in the actual circuit; (a) the control signal waveform before and after power-off; (b) the control signal waveform within the power-off protection

[0042] Figure 7 This is the output waveform of the actual circuit with power-off protection added.

[0043] The experimental results of the actual circuit show that the control scheme can effectively suppress the oscillation on the AC side after power failure, achieve the stability of the output voltage on the DC side, and ensure the output stability of the rectifier.

[0044] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims. The information disclosed in the background technology section of this article is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. A power-off fast protection method for a single-phase PWM rectifier, the single-phase PWM rectifier comprising a full-bridge circuit connected by four switch tubes, wherein the S1 tube is coupled between the output voltage of the bridgeless PFC circuit and the inductor of the bridgeless PFC circuit, the S2 tube is coupled between the S1 tube and the ground terminal, the S3 tube is coupled between the input AC power supply of the bridgeless PFC circuit and the ground terminal, and the S4 tube is coupled between the S3 tube and the ground terminal; It is characterized in that In the positive half cycle of the AC signal, the S2 tube is the main control tube of the bridgeless PFC circuit, and in the negative half cycle of the AC signal, the S4 tube is the main control tube of the bridgeless PFC circuit; After power failure, the AC side inductor current is discharged through the switch tube.

2. The power-off fast protection method for a single-phase PWM rectifier according to claim 1, characterized in that: Within 5 power frequency cycles after power failure, the switch tube is controlled to discharge the AC side inductor current.

3. The power-off fast protection method for a single-phase PWM rectifier according to claim 2, characterized in that: When the power-off protection is activated, S1 and S2 tubes perform high-frequency switching for 5 power frequency cycles, S3 tube is normally closed within five cycles, S4 is normally open, and all switch tubes are disconnected after the end.

4. The power-off fast protection method for a single-phase PWM rectifier according to claim 3, characterized in that: When the power is just turned off, the current in the inductor is not zero. In order to avoid oscillation, the inductor current continues to flow in the original direction to avoid sudden changes in the current direction until the consumption is zero, and to avoid excessive oscillation caused by backflow.

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