A method for testing the feasibility of a three-level rectifier circuit

Abstract

The present invention relates to a method for testing the feasibility of a three-level rectifier circuit. The method can independently test the feasibility of each switch. The method includes applying a test voltage between the input side and the neutral point of each phase, and simultaneously applying a PWM wave to the bidirectional switch of that phase to test the feasibility of the bidirectional switch. Phases B and C of the three-level rectifier circuit have the same operating principle as phase A, so the three-level voltage rectifier can be decomposed into three groups of bidirectional boost circuits. The method of the present invention tests the feasibility of six switches in a manufactured three-level rectifier circuit, independently testing the feasibility of each switch. Testing a complete machine or device using the three-level rectifier circuit allows for timely locating and troubleshooting of faults, improving product yield, and accelerating maintenance and repair.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic and electrical equipment and electrical engineering, and in particular to a method for testing the feasibility of a three-level rectifier circuit. Background Art

[0002] Traditional uncontrolled rectifiers (diode rectifiers) or phase-controlled rectifiers (thyristor rectifiers) are widely used in the power electronics industry. However, they suffer from numerous issues, such as low grid-side power when phase-controlled, and the injection of high current harmonics into the grid, which can cause serious grid pollution. With stricter limits on current harmonics in electrical equipment and the need for converters to operate over a wide input voltage range, VIENNA rectifiers are gaining widespread application.

[0003] The VIENNA rectifier is a two-quadrant, midpoint-clamped, three-level PWM rectifier topology. In applications where bidirectional energy flow is not required, the VIENNA rectifier offers numerous advantages. On the one hand, compared to traditional two-level structures, the increased number of levels reduces current harmonic distortion (THD) and voltage stress on power switching devices. On the other hand, compared to two-level rectifiers, Figure 1 As shown, the number of required power switching devices is reduced from 12 to 6, reducing switching losses, costs and control complexity. In addition, when the power switching device is turned on, the diode connected to the DC bus can block the through-current, and there is no problem of output voltage bridge arm through-current. There is no need to set the drive dead time, which further improves the reliability of the rectifier. However, a test method is required to independently test the feasibility of each switch tube to ensure the operation of the overall device or circuit. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a method for testing the feasibility of a three-level rectifier circuit. This method can independently test the feasibility of each switch tube. A test voltage is applied between the input side and the neutral point of each phase, and a PWM wave is applied to the bidirectional switch of that phase to test the feasibility of the bidirectional switch. At the same time, phases B and C in the three-level rectifier circuit have the same operating principle as phase A. Therefore, the three-level voltage rectifier can be decomposed into three groups of bidirectional boost circuits. The method includes the following steps:

[0005] Step S1: Add two diodes on the DC side of the three-level rectifier circuit to prevent reverse charging of the electrolytic capacitor; then disconnect the three-phase voltage input on the AC side and apply a test voltage Ut between point a of one phase and the neutral point M;

[0006] Step S2: The pulse generator generates a pulse signal of 10 kHz and 50% duty cycle. If the bidirectional conduction switch works normally, then phase a can be equivalent to an open-loop boost circuit, and the Uc2 voltage waveform is equal to 0.

[0007] Step S3: Reverse the test voltage Ut and repeat the above method until Uc1 in the DC side voltage waveform is equal to 0;

[0008] Step S4: If the voltage waveforms in steps S2 and S3 are not obtained, it means that there is a problem with the feasibility of MOSFET tubes M1 and M2, and MOSFET tube M1 fails. When the test voltage Ut = +10V, the phase a circuit is equivalent to an LCR circuit, in which the Uc2 voltage waveform is equal to 0, and Uc1 and Udc also tend to 0 after oscillation;

[0009] Step S5: If the MOSFET tube M2 fails, when the test voltage Ut = -10V, the voltage waveform of Uc1 in the DC side voltage is equal to 0, and Uc2 and Udc also tend to 0 after oscillation;

[0010] Step S6: Repeat the test of phase b and phase c in the same way.

[0011] In one embodiment of the present invention, if the DC voltage side of the three-level rectifier circuit can obtain a boosted voltage, the bidirectional switch works normally; if the DC side voltage is not boosted, it indicates that there is a problem with the feasibility of the bidirectional switch.

[0012] In one embodiment of the present invention, the test voltage Ut in step S1 is set to 10V, and the bidirectional conducting switches in step S2 are MOSFET tubes M1 and M2, and the input and output voltage relationship in normal operation is:

[0013]

[0014] From the above formula, we can get U O =20V.

[0015] In one embodiment of the present invention, the a-phase circuit in step S4 is equivalent to an LCR circuit, and the transfer function is:

[0016]

[0017] From the above formula, we can see

[0018] The above-mentioned technical solution of the present invention has the following advantages over the existing technology: the method for testing the feasibility of a three-level rectifier circuit described in the present invention tests the effectiveness of six switching tubes on an already manufactured three-level rectifier circuit, and can independently test the feasibility of each switching tube. The whole machine or equipment using the three-level rectifier circuit is tested, and the fault point can be located and the fault can be eliminated in time, thereby improving the product yield and speeding up maintenance and repair. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings.

[0020] Figure 1 Schematic diagram of a three-level rectifier in the present invention;

[0021] Figure 2 It is the circuit topology of different switching states of phase a of the present invention;

[0022] Figure 3 It is a Simulink simulation diagram of the three-level rectifier circuit of the present invention;

[0023] Figure 4 It is the three-level rectifier circuit test circuit of the present invention;

[0024] Figure 5 is a schematic diagram of the DC side voltage I of the present invention;

[0025] Figure 6 is a schematic diagram of the DC side voltage II of the present invention;

[0026] Figure 7 This is a failure simulation diagram of the MOSFET tube M1 in the three-level rectifier circuit of the present invention;

[0027] Figure 8 is a schematic diagram of the DC side voltage III of the present invention;

[0028] Figure 9 This is a failure simulation diagram of the MOSFET tube M2 in the three-level rectifier circuit of the present invention;

[0029] Figure 10 Schematic diagram of the DC side voltage IV of the present invention. DETAILED DESCRIPTION

[0030] This embodiment provides a method for testing the feasibility of a three-level rectifier circuit. The method can independently test the feasibility of each switch. A test voltage is applied between the input side and the neutral point of each phase, and a PWM wave is applied to the bidirectional switch of that phase to test the feasibility of the bidirectional switch. Phases B and C in the three-level rectifier circuit have the same operating principle as phase A. Therefore, the three-level voltage rectifier can be decomposed into three groups of bidirectional boost circuits. The method includes the following steps:

[0031] Step S1: Figure 3 Add two diodes on the DC side to prevent the electrolytic capacitor from reverse charging (such as Figure 4 Then disconnect the three-phase voltage input on the AC side and add a test voltage Ut (the voltage is set to 10V) between point a of one phase (such as phase a) and the neutral point M.

[0032] Step S2: The pulse generator generates a pulse signal with a frequency of 10 kHz and a duty cycle of 50%. If the bidirectional conduction switches (MOSFETs M1 and M2) operate normally, then phase a can be equivalent to an open-loop boost circuit. The relationship between the input and output voltages is:

[0033]

[0034] From the above formula, we can get U O =20V. The simulation waveform is as follows Figure 5 shown.

[0035] Step S3: Reverse the test voltage Ut and repeat the above method. The DC side voltage is as follows: Figure 6 As shown, Uc1 in the DC side voltage waveform is equal to 0;

[0036] The test voltage can be applied in both positive and negative directions between point a and point M to obtain a boost effect, which can verify that the MOSFET tubes M1 and M2 are working normally.

[0037] Step S4: If step 1 does not yield Figure 5 、 Figure 6 Voltage waveform, it means that there is a problem with the feasibility of MOSFET tubes M1 and M2. Next, test the failure of MOSFET tubes M1 and M2 - MOSFET tube M1 fails (such as Figure 7 As shown, M1g side is disconnected), the test voltage Ut=+10V, the phase a circuit is equivalent to the LCR circuit, and the transfer function is:

[0038]

[0039] From the above formula, we can see The DC side simulation voltage waveform is as follows Figure 8 shown.

[0040] Step S5: If the MOSFET tube M2 fails (such as Figure 9 As shown, M2g side is disconnected), when the test voltage Ut=-10V, the DC side voltage is as follows Figure 10 shown.

[0041] The above method can be used to independently test the failure conditions of the a-phase MOSFET tubes M1 and M2.

[0042] Step S6: Repeat the test of phase b and phase c in the same way.

[0043] Furthermore, the working principle of the three-level rectifier is as follows: the three-level rectifier circuit is a three-phase Boost half-bridge rectifier structure, the inductor plays the role of boosting the voltage and increasing the circuit damping; the DC side capacitor plays the role of stabilizing the output voltage; the bidirectional switch connects the power bridge arm of the three-phase rectifier and the neutral point of the DC side, and the total harmonic distortion rate of the grid-side current is zero (THD=0) through the controller PWM wave control.

[0044] Three-level rectifier circuit topology: Define the three-phase switching variables as (Sa, Sb, Sc), where Sk (k = a, b, c) is "1" when the bidirectional switch of phase k is on, and Sk is "0" when the bidirectional switch is off. Analyze the relationship between the voltage Ua from the power bridge leg A of phase a to the DC neutral point M in the VIENNA rectifier topology and the bidirectional switching variable Sa.

[0045] When the bidirectional switch is turned on (Sa=1), point A and point M are connected, Ua=0, as Figure 2 Shown on the left.

[0046] When the bidirectional switch is turned off (Sa=0), the voltage Ua from point A to point M is constrained by the direction of the current in phase a at this time, as shown in the following example: Figure 2 As shown on the right, the expression of Ua is:

[0047]

[0048] To explain the above formula, when the bidirectional switch is disconnected, the rectifier bridge arm A to the DC side neutral point M is equivalent to an uncontrolled rectifier structure. When the a-phase current flows in the positive direction (from the grid side power supply to the rectifier), the current ia charges the upward capacitor C1, and Ua=+V C1 When the current in phase a flows in the negative direction (from the rectifier to the grid), the lower capacitor C2 discharges to obtain the current ia, Ua = -V C2 Therefore, Ua has three values, which is the principle of the three-level structure of the VIENNA rectifier.

[0049] Phases b and c have the same working principle as phase a, so the three-level voltage rectifier can be decomposed into three groups of bidirectional boost circuits. Figure 3 shown.

[0050] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for testing the feasibility of a three-level rectifier circuit, capable of independently testing the feasibility of each switch. A test voltage is applied between the input side and the neutral point of each phase, and a PWM wave is applied to the bidirectional switch of that phase to test the feasibility of the bidirectional switch. Phases b and c in the three-level rectifier circuit have the same operating principle as phase a, so the three-level voltage rectifier can be decomposed into three groups of bidirectional boost circuits. The method is characterized by: The steps include: Step S1: Add two diodes on the DC side of the three-level rectifier circuit to prevent reverse charging of the electrolytic capacitor; then disconnect the three-phase voltage input on the AC side and apply a test voltage Ut between point a of one phase and the neutral point M; Step S2: The pulse generator generates a pulse signal of 10 kHz and 50% duty cycle. If the bidirectional conduction switch works normally, then phase a can be equivalent to an open-loop boost circuit, and the Uc2 voltage waveform is equal to 0. Step S3: Reverse the test voltage Ut and repeat the above method until Uc1 in the DC side voltage waveform is equal to 0; Step S4: If the voltage waveforms in steps S2 and S3 are not obtained, it means that there is a problem with the feasibility of MOSFET tubes M1 and M2, and MOSFET tube M1 fails. When the test voltage Ut = +10V, the phase a circuit is equivalent to an LCR circuit, in which the Uc2 voltage waveform is equal to 0, and Uc1 and Udc also tend to 0 after oscillation; Step S5: If the MOSFET tube M2 fails, when the test voltage Ut = -10V, the voltage waveform of Uc1 in the DC side voltage is equal to 0, and Uc2 and Udc also tend to 0 after oscillation; Step S6: Repeat the test of phase b and phase c in the same way.

2. The method for testing the feasibility of a three-level rectifier circuit according to claim 1, wherein: In the three-level rectifier circuit, if the DC voltage side can obtain a boosted voltage, the bidirectional switch works normally; if the DC side voltage is not boosted, it means that there is a problem with the feasibility of the bidirectional switch.

3. The method for testing the feasibility of a three-level rectifier circuit according to claim 1, wherein: The test voltage Ut in step S1 is set to 10V, and the bidirectional conducting switches in step S2 are MOSFET tubes M1 and M2. The relationship between the input and output voltages in normal operation is: From the above formula, we can get U O =20V.

4. The method for testing the feasibility of a three-level rectifier circuit according to claim 1, wherein: The a-phase circuit in step S4 is equivalent to an LCR circuit, and its transfer function is: From the above formula, we can see

Images