A Discontinuous Pulse Width Modulation Method and Control Circuit for a Three-Phase Four-Level Inverter

Abstract

The present invention discloses a discontinuous pulse width modulation method and a control circuit for a three-phase four-level inverter, belonging to the technical field of power electronic converters. The control circuit includes a grid voltage sampling unit, an inductor current sampling unit, a MOSFET driving unit, and a DSP control unit. The discontinuous pulse width modulation method is used in the DSP control unit. Based on the vector diagram of the four-level inverter, small sector division of the discontinuous pulse width modulation method for the four-level inverter and corresponding switch state sequences in each small sector are designed, reducing the number of switching times. By adding a DC bus filter capacitor voltage balance constraint when calculating the action time of each basic vector, natural balance of the DC bus filter capacitor voltage and low switching losses are achieved simultaneously. The present invention can reduce the number of switching times while realizing natural balance of the DC bus filter capacitor voltage of the three-phase four-level inverter, reduce the switching losses of the inverter, has high converter efficiency, and is applicable to occasions such as photovoltaic power generation.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic converters, and particularly relates to a discontinuous pulse width modulation method and a control circuit for a three-phase four-level inverter. Background Art

[0002] Due to advantages such as low voltage stress of power devices and low total harmonic distortion, three-phase four-level inverters have received increasing attention in high-voltage and large-capacity applications. The voltage imbalance of the DC bus capacitors is an inherent problem of multi-level inverters. The voltage imbalance of the DC bus capacitors will cause output current disturbances and increased voltage stress on some switching devices.

[0003] Compared with three-level inverters, it is more difficult to balance the DC bus capacitor voltages of four-level inverters. In the prior art document 1, "J. Pou, R. Pindado, and D. Boroyevich, Voltage-balance limits in four-level diode-clamped converters with passive front ends, IEEE Trans. Ind. Electron. , vol. 52, no. 1, pp. 190-196, Feb 2005.", it is pointed out that when the three-phase four-level inverter uses the nearest three-vector pulse width modulation (NTV PWM) technology, it is impossible to achieve the balance of the DC bus filter capacitor voltages under full modulation ratios in the full power factor range, and there are theoretical limitations. Therefore, traditional modulation strategies cannot achieve the stable operation of three-phase four-level inverters, and additional voltage balance strategies need to be adopted.

[0004] In the prior art document 2, "S. Busquets-Monge, J. Bordonau, and J. Rocabert, AVirtual-Vector Pulsewidth Modulation for the Four-Level Diode-Clamped DC–ACConverter, IEEE Trans. Power Electron. , vol. 23, no. 4, pp. 1964-1972, July2008.", multiple switching states of the three-phase four-level inverter are combined with each other to generate virtual vectors that do not affect the balance of the DC bus capacitor voltages, and then the required reference vectors are synthesized using the virtual vectors, so as to ensure that the average current flowing through each DC bus filter capacitor in each switching period is zero, and the balance of the DC bus filter capacitor voltages within the switching period is achieved.

[0005] Prior art document 3, "K. Wang, Z. Zheng, and Y. Li, A Novel Carrier-Overlapped PWM Method for Four-Level Neutral-Point Clamped Converters, IEEE Trans. Power Electron. , vol. 34, no. 1, pp. 7-12, Jan. 2019." designs an overlapping carrier modulation strategy by overlapping carrier signals with different amplitudes, enabling a three-level voltage to be used in one phase leg within a switching period. Meanwhile, the duty cycles of each level are configured to eliminate the DC current component flowing through the intermediate capacitor, achieving the balance of the DC bus intermediate filter capacitor voltage within the switching period and the balance of the outer filter capacitor voltage within the power frequency period. The above voltage balance strategy achieves the balance of the DC bus capacitor voltage under full power factor and full modulation ratio conditions, but the switching times of the inverter increase significantly, resulting in high switching losses in high-frequency applications.

[0006] Prior art document 4, "J. Wang, X. Yuan, and B. Jin, Carrier-based Closed-loop DC-link Voltage Balancing Algorithm for Four Level NPC Converters Basedon Redundant Level Modulation, IEEE Trans. Ind. Electron. , vol. 68, no. 12,pp. 11707-11718, Dec 2021." combines the zero-sequence component injection-based and redundant-level-based capacitor voltage balancing methods. On the basis of injecting the zero-sequence component to balance the DC bus capacitor voltage, only one phase leg adopts the redundant level modulation algorithm, reducing the switching times while achieving the balance of the DC bus capacitor voltage. However, this scheme is still a continuous pulse width modulation scheme, and the phase with the largest output current still needs to switch at high frequency within the switching period, resulting in high switching losses.

[0007] In summary, it is necessary to study a low-switching-loss discontinuous pulse width modulation method and its circuit that are applicable to a three-phase four-level inverter and its control circuit and can naturally balance the DC bus capacitor voltage of the inverter. Summary of the Invention

[0008] To solve the above technical problems, the present invention proposes a low-switching-loss discontinuous pulse width modulation method for naturally balancing the DC bus capacitor voltage of a three-phase four-level inverter and its control circuit.

[0009] To achieve the above technical objectives, the present invention adopts the following technical solutions:

[0010] A discontinuous pulse width modulation method for a control circuit of a three-phase four-level inverter. The three-phase four-level inverter is connected to a three-phase power grid, and the three-phase power grid includes an A-phase AC power supply, a B-phase AC power supply, and a C-phase AC power supply. The three-phase four-level inverter includes a DC power supply, a first DC bus filter capacitor, a second DC bus filter capacitor, a third DC bus filter capacitor, an A-phase bridge arm, a B-phase bridge arm, a C-phase bridge arm, an A-phase filter inductor, a B-phase filter inductor, a C-phase filter inductor, an A-phase filter capacitor, a B-phase filter capacitor, and a C-phase filter capacitor; the positive electrode of the DC power supply and the positive electrode of the first DC bus filter capacitor are respectively connected to both ends of point 3 on the DC side; the negative electrode of the first DC bus filter capacitor and the positive electrode of the second DC bus filter capacitor are respectively connected to both ends of point 2 on the DC side; the negative electrode of the second DC bus filter capacitor and the positive electrode of the third DC bus filter capacitor are respectively connected to both ends of point 1 on the DC side; the negative electrode of the third DC bus filter capacitor and the negative electrode of the DC power supply are respectively connected to both ends of point 0 on the DC side; O is the virtual midpoint on the DC side ， The voltage between and point 0 on the DC side is one-half of the DC power supply voltage;

[0011] The discontinuous pulse width modulation method includes step S1 of collecting the DC bus voltage of the three-phase four-level inverter and establishing a four-level vector space in the complex plane according to the DC bus voltage. The four-level vector space is composed of 64 basic vectors, and the coordinates of each basic vector The calculation expression is:

[0012]

[0013] Wherein, S A , S B , S C are the A-phase switching function, B-phase switching function, and C-phase switching function respectively, and j is the imaginary unit; the switching function S X , X represents A, B, or C, and its calculation expression is:

[0014]

[0015] Wherein, the switching state 3 represents X The output point of the phase bridge arm X is connected to point 3 on the DC side through a power switch tube, X The output point of the phase bridge arm X and the virtual midpoint on the DC sideO The voltage between them is the DC power supply voltage U dc is one-half; Switch state 2 indicates X The output point of the phase bridge arm X is connected to point 2 on the DC side through a power switch tube, X The output point of the phase bridge arm X and the virtual midpoint of the DC side O The voltage between them is the DC power supply voltage U dc is one-sixth; Switch state 1 indicates X The output point of the phase bridge arm X is connected to point 1 on the DC side through a power switch tube, X The output point of the phase bridge arm X and the virtual midpoint of the DC side O The voltage between them is the DC power supply voltage U dc is the opposite of one-sixth; Switch state 0 indicates X The output point of the phase bridge arm X is connected to point 0 on the DC side through a power switch tube, X The output point of the phase bridge arm X and the virtual midpoint of the DC side O The voltage between them is the DC power supply voltage U dc is the opposite of one-half;

[0016] Step S2, divide the four-level vector space into 6 large sectors according to 64 basic vectors, and each large sector is further divided into 10 small sectors;

[0017] Step S3, the dq / αβ converter generates the d-axis control component by the active current PI regulator according to the input signal u d and the reactive current PI regulator generates the q-axis control component according to the input signal u q The control components in the αβ coordinate system obtained by transformation u α and u β Calculate the vector to be synthesized V ref The coordinates of are calculated, and the calculation formula is:

[0018]

[0019] where j is the imaginary unit;

[0020] Step S4, according to the vector to be synthesized V ref coordinates, obtain the vector to be synthesizedV ref For the large and small sectors located, five basic vectors that keep the switching state of one phase unchanged are selected in the four-level vector space to form a nine-segment basic vector action sequence.

[0021] Step S5: Determine the action time of each basic vector within the basic vector action sequence according to the DC bus filter capacitor voltage balance constraint and the volt-second balance principle.

[0022] In step S1 of the discontinuous pulse width modulation method for the control circuit of the above three-phase four-level inverter, the 64 basic vectors in the four-level vector space are respectively 333, 222, 111, 000, 322, 211, 100, 311, 200, 300, 321, 210, 310, 320, 332, 221, 110, 331, 220, 330, 231, 120, 230, 130, 232, 121, 010, 131, 020, 030, 132, 021, 031, 032, 233, 122, 011, 133, 022, 033, 123, 012, 023, 013, 223, 112, 001, 113, 002, 003, 213, 102, 103, 203, 323, 212, 101, 313, 202, 303, 312, 201, 302, 301, where 3 represents X The phase bridge arm is in switching state 3, 2 represents X The phase bridge arm is in switching state 2, 1 represents X The phase bridge arm is in switching state 1, 0 represents X The phase bridge arm is in switching state 0.

[0023] In step S2 of the discontinuous pulse width modulation method for the control circuit of the above three-phase four-level inverter, the division rule of the large sectors is as follows: The first large sector is the area enclosed by the basic vectors 333, 300, and 330; the second large sector is the area enclosed by the basic vectors 333, 330, and 030; the third large sector is the area enclosed by the basic vectors 333, 030, and 033; the fourth large sector is the area enclosed by the basic vectors 333, 033, and 003; the fifth large sector is the area enclosed by the basic vectors 333, 003, and 303; the sixth large sector is the area enclosed by the basic vectors 333, 303, and 300.

[0024] In step S2 of the discontinuous pulse width modulation method for the control circuit of the above three-phase four-level inverter, each large sector is divided into 10 small sectors according to the following rules: In the first large sector, the first small sector is the part below the line connecting 000 and the midpoint of the line connecting 300 and 330 in the area surrounded by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 110 and 220, and 000; the second small sector is the part above the line connecting 000 and the midpoint of the line connecting 300 and 330 in the area surrounded by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 110 and 220, and 000; the third small sector is the part below the line connecting 000 and the midpoint of the line connecting 300 and 330 and to the lower left of the line connecting 321 and 300 in the area surrounded by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 300 and 330; the fourth small sector is the part above the line connecting 000 and the midpoint of the line connecting 300 and 330 and to the lower left of the line connecting 321 and 330 in the area surrounded by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 300 and 330; the fifth small sector is the part below the line connecting 000 and the midpoint of the line connecting 300 and 330 and to the upper right of the line connecting 321 and 300 in the area surrounded by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 300 and 330; the sixth small sector is the part above the line connecting 000 and the midpoint of the line connecting 300 and 330 and to the upper right of the line connecting 321 and 330 in the area surrounded by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 300 and 330; the seventh small sector is the part to the lower left of the line connecting 321 and 300 in the area surrounded by the midpoint of the line connecting 322 and 311, 300, and the midpoint of the line connecting 300 and 330; the eighth small sector is the part to the left of the line connecting 321 and 330 in the area surrounded by the midpoint of the line connecting 110 and 220, 330, and the midpoint of the line connecting 300 and 330; the ninth small sector is the part to the upper right of the line connecting 321 and 300 in the area surrounded by the midpoint of the line connecting 322 and 311, 300, and the midpoint of the line connecting 300 and 330; the tenth small sector is the part to the right of the line connecting 321 and 330 in the area surrounded by the midpoint of the line connecting 110 and 220, 330, and the midpoint of the line connecting 300 and 330;

[0025] In the second largest sector, the first small sector is the part to the left of the line connecting 000 and the midpoint of the line connecting 030 and 330 within the area enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 110 and 220, and 000; the second small sector is the part to the right of the line connecting 000 and the midpoint of the line connecting 030 and 330 within the area enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 110 and 220, and 000; the third small sector is the part to the left of the line connecting 000 and the midpoint of the line connecting 030 and 330 and below the lower left of the line connecting 231 and 030 within the area enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 030 and 330; the fourth small sector is the part to the right of the line connecting 000 and the midpoint of the line connecting 030 and 330 and below the lower right of the line connecting 231 and 330 within the area enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 030 and 330; the fifth small sector is the part to the left of the line connecting 000 and the midpoint of the line connecting 030 and 330 and above the upper right of the line connecting 231 and 030 within the area enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 030 and 330; the sixth small sector is the part to the right of the line connecting 000 and the midpoint of the line connecting 030 and 330 and above the upper left of the line connecting 231 and 330 within the area enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 030 and 330; the seventh small sector is the part below the lower left of the line connecting 231 and 030 within the area enclosed by the midpoint of the line connecting 232 and 131, 030, and the midpoint of the line connecting 030 and 330; the eighth small sector is the part below the lower right of the line connecting 231 and 330 within the area enclosed by the midpoint of the line connecting 110 and 220, 330, and the midpoint of the line connecting 030 and 330; the ninth small sector is the part above the upper right of the line connecting 231 and 030 within the area enclosed by the midpoint of the line connecting 232 and 131, 030, and the midpoint of the line connecting 030 and 330; the tenth small sector is the part above the upper left of the line connecting 231 and 330 within the area enclosed by the midpoint of the line connecting 110 and 220, 330, and the midpoint of the line connecting 030 and 330;

[0026] In the third major sector, the first minor sector is the part of the area enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 011 and 022, and 000, which is to the upper right of the line connecting 000 and the midpoint of the line connecting 030 and 033; the second minor sector is the part of the area enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 011 and 022, and 000, which is to the lower left of the line connecting 000 and the midpoint of the line connecting 030 and 033; the third minor sector is the part of the area enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 030 and 033, which is to the upper right of the line connecting 000 and the midpoint of the line connecting 030 and 033 and to the right of the line connecting 132 and 030; the fourth minor sector is the part of the area enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 030 and 033, which is to the lower left of the line connecting 000 and the midpoint of the line connecting 030 and 033 and to the lower right of the line connecting 132 and 033; the fifth minor sector is the part of the area enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 030 and 033, which is to the upper right of the line connecting 000 and the midpoint of the line connecting 030 and 033 and to the left of the line connecting 132 and 030; the sixth minor sector is the part of the area enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 030 and 033, which is to the lower left of the line connecting 000 and the midpoint of the line connecting 030 and 033 and to the upper left of the line connecting 132 and 033; the seventh minor sector is the part of the area enclosed by the midpoint of the line connecting 232 and 131, 030, and the midpoint of the line connecting 030 and 033, which is to the right of the line connecting 132 and 030; the eighth minor sector is the part of the area enclosed by the midpoint of the line connecting 011 and 022, 033, and the midpoint of the line connecting 030 and 033, which is to the lower right of the line connecting 132 and 033; the ninth minor sector is the part of the area enclosed by the midpoint of the line connecting 232 and 131, 030, and the midpoint of the line connecting 030 and 033, which is to the left of the line connecting 132 and 030; the tenth minor sector is the part of the area enclosed by the midpoint of the line connecting 011 and 022, 033, and the midpoint of the line connecting 030 and 033, which is to the upper left of the line connecting 132 and 033;

[0027] In the fourth major sector, the first minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 011 and 022, and 000, which is to the lower right of the line connecting 000 and the midpoint of the line connecting 003 and 033; the second minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 011 and 022, and 000, which is to the upper left of the line connecting 000 and the midpoint of the line connecting 003 and 033; the third minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 003 and 033, which is to the lower right of the line connecting 000 and the midpoint of the line connecting 003 and 033 and to the right of the line connecting 123 and 003; the fourth minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 003 and 033, which is to the upper left of the line connecting 000 and the midpoint of the line connecting 003 and 033 and to the upper right of the line connecting 123 and 033; the fifth minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 003 and 033, which is to the lower right of the line connecting 000 and the midpoint of the line connecting 003 and 033 and to the left of the line connecting 123 and 003; the sixth minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 003 and 033, which is to the upper left of the line connecting 000 and the midpoint of the line connecting 003 and 033 and to the lower left of the line connecting 123 and 033; the seventh minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, 003, and the midpoint of the line connecting 003 and 033, which is to the right of the line connecting 123 and 003; the eighth minor sector is the part in the region enclosed by the midpoint of the line connecting 011 and 022, 033, and the midpoint of the line connecting 003 and 033, which is to the upper right of the line connecting 123 and 033; the ninth minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, 003, and the midpoint of the line connecting 003 and 033, which is to the left of the line connecting 123 and 003; the tenth minor sector is the part in the region enclosed by the midpoint of the line connecting 011 and 022, 033, and the midpoint of the line connecting 003 and 033, which is to the lower left of the line connecting 123 and 033;

[0028] In the fifth largest sector, the first small sector is the part on the left of the line connecting 000 and the midpoint of the line connecting 003 and 303 within the area enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 101 and 202, and 000; the second small sector is the part on the right of the line connecting 000 and the midpoint of the line connecting 003 and 303 within the area enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 101 and 202, and 000; the third small sector is the part on the left of the line connecting 000 and the midpoint of the line connecting 003 and 303 and above the upper left of the line connecting 213 and 003 within the area enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 003 and 303; the fourth small sector is the part on the right of the line connecting 000 and the midpoint of the line connecting 003 and 303 and above the upper right of the line connecting 123 and 303 within the area enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 003 and 303; the fifth small sector is the part on the left of the line connecting 000 and the midpoint of the line connecting 003 and 303 and below the lower right of the line connecting 213 and 003 within the area enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 003 and 303; the sixth small sector is the part on the right of the line connecting 000 and the midpoint of the line connecting 003 and 303 and below the lower left of the line connecting 123 and 303 within the area enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 003 and 303; the seventh small sector is the part above the upper left of the line connecting 213 and 003 within the area enclosed by the midpoint of the line connecting 223 and 113, 003, and the midpoint of the line connecting 003 and 303; the eighth small sector is the part above the upper right of the line connecting 213 and 303 within the area enclosed by the midpoint of the line connecting 101 and 202, 303, and the midpoint of the line connecting 003 and 303; the ninth small sector is the part below the lower right of the line connecting 213 and 003 within the area enclosed by the midpoint of the line connecting 223 and 113, 003, and the midpoint of the line connecting 003 and 303; the tenth small sector is the part below the lower left of the line connecting 213 and 303 within the area enclosed by the midpoint of the line connecting 101 and 202, 303, and the midpoint of the line connecting 003 and 303;

[0029] In the sixth major sector, the first minor sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 101 and 202, and 000 that is to the upper right of the line connecting 000 and the midpoint of the line connecting 300 and 303; the second minor sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 101 and 202, and 000 that is to the lower left of the line connecting 000 and the midpoint of the line connecting 300 and 303; the third minor sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 300 and 303 that is to the upper right of the line connecting 000 and the midpoint of the line connecting 300 and 303 and to the upper left of the line connecting 312 and 300; the fourth minor sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 300 and 303 that is to the lower left of the line connecting 000 and the midpoint of the line connecting 300 and 303 and to the left of the line connecting 312 and 303; the fifth minor sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 300 and 303 that is to the upper right of the line connecting 000 and the midpoint of the line connecting 300 and 303 and to the lower right of the line connecting 312 and 300; the sixth minor sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 300 and 303 that is to the lower left of the line connecting 000 and the midpoint of the line connecting 300 and 303 and to the right of the line connecting 312 and 303; the seventh minor sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, 300, and the midpoint of the line connecting 300 and 303 that is to the upper left of the line connecting 312 and 300; the eighth minor sector is the part of the region enclosed by the midpoint of the line connecting 101 and 202, 303, and the midpoint of the line connecting 300 and 303 that is to the left of the line connecting 312 and 303; the ninth minor sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, 300, and the midpoint of the line connecting 300 and 303 that is to the lower right of the line connecting 312 and 300; the tenth minor sector is the part of the region enclosed by the midpoint of the line connecting 101 and 202, 303, and the midpoint of the line connecting 300 and 303 that is to the right of the line connecting 312 and 303.

[0030] In step S4 of the discontinuous pulse width modulation method of the above three-phase four-level inverter control circuit, the basic vector action sequence is determined according to the following rules: If the vector to be synthesized V ref is located in the first minor sector of the first major sector, the basic vector action sequence is 311 - 321 - 322 - 332 - 333 - 332 - 322 - 321 - 311; if the vector to be synthesized V ref is located in the second minor sector of the first major sector, the basic vector action sequence is 000 - 100 - 110 - 210 - 220 - 210 - 110 - 100 - 000; if the vector to be synthesized Vref is located in the 3rd minor sector of the 1st major sector, the basic vector action sequence is 310 - 311 - 321 - 322 - 332 - 322 - 321 - 311 - 310; if the vector to be synthesized V ref is located in the 4th minor sector of the 1st major sector, the basic vector action sequence is 100 - 110 - 210 - 220 - 320 - 220 - 210 - 110 - 100; if the vector to be synthesized V ref is located in the 5th minor sector of the 1st major sector, the basic vector action sequence is 310 - 320 - 321 - 322 - 332 - 322 - 321 - 320 - 310; if the vector to be synthesized V ref is located in the 6th minor sector of the 1st major sector, the basic vector action sequence is 100 - 110 - 210 - 310 - 320 - 310 - 210 - 110 - 100; if the vector to be synthesized V ref is located in the 7th minor sector of the 1st major sector, the basic vector action sequence is 300 - 310 - 311 - 321 - 322 - 321 - 311 - 310 - 300; if the vector to be synthesized V ref is located in the 8th minor sector of the 1st major sector, the basic vector action sequence is 110 - 210 - 220 - 320 - 330 - 320 - 220 - 210 - 110; if the vector to be synthesized V ref is located in the 9th minor sector of the 1st major sector, the basic vector action sequence is 300 - 310 - 320 - 321 - 322 - 321 - 320 - 310 - 300; if the vector to be synthesized V ref is located in the 10th minor sector of the 1st major sector, the basic vector action sequence is 110 - 210 - 310 - 320 - 330 - 320 - 310 - 210 - 110;

[0031] If the vector to be synthesized V ref is located in the 1st minor sector of the 2nd major sector, the basic vector action sequence is 131 - 231 - 232 - 332 - 333 - 332 - 232 - 231 - 131; if the vector to be synthesized V ref is located in the 2nd minor sector of the 2nd major sector, the basic vector action sequence is 000 - 010 - 110 - 120 - 220 - 120 - 110 - 010 - 000; if the vector to be synthesized V refIf it is located in the 3rd minor sector of the 2nd major sector, the basic vector action sequence is 130 - 131 - 231 - 232 - 332 - 232 - 231 - 131 - 130; if the vector to be synthesized V ref If it is located in the 4th minor sector of the 2nd major sector, the basic vector action sequence is 010 - 110 - 120 - 220 - 230 - 220 - 120 - 110 - 010; if the vector to be synthesized V ref If it is located in the 5th minor sector of the 2nd major sector, the basic vector action sequence is 130 - 230 - 231 - 232 - 332 - 232 - 231 - 230 - 130; if the vector to be synthesized V ref If it is located in the 6th minor sector of the 2nd major sector, the basic vector action sequence is 010 - 110 - 120 - 130 - 230 - 130 - 120 - 110 - 010; if the vector to be synthesized V ref If it is located in the 7th minor sector of the 2nd major sector, the basic vector action sequence is 030 - 130 - 131 - 231 - 232 - 231 - 131 - 130 - 030; if the vector to be synthesized V ref If it is located in the 8th minor sector of the 2nd major sector, the basic vector action sequence is 110 - 120 - 220 - 230 - 330 - 230 - 220 - 120 - 110; if the vector to be synthesized V ref If it is located in the 9th minor sector of the 2nd major sector, the basic vector action sequence is 030 - 130 - 230 - 231 - 232 - 231 - 230 - 130 - 030; if the vector to be synthesized V ref If it is located in the 10th minor sector of the 2nd major sector, the basic vector action sequence is 110 - 120 - 130 - 230 - 330 - 230 - 130 - 120 - 110;

[0032] If the vector to be synthesized V ref If it is located in the 1st minor sector of the 3rd major sector, the basic vector action sequence is 131 - 132 - 232 - 233 - 333 - 233 - 232 - 132 - 131; if the vector to be synthesized V ref If it is located in the 2nd minor sector of the 3rd major sector, the basic vector action sequence is 000 - 010 - 011 - 021 - 022 - 021 - 011 - 010 - 000; if the vector to be synthesized V refLocated in the 3rd minor sector of the 3rd major sector, the basic vector action sequence is 031 - 131 - 132 - 232 - 233 - 232 - 132 - 131 - 031; If the vector to be synthesized V ref Located in the 4th minor sector of the 3rd major sector, the basic vector action sequence is 010 - 011 - 021 - 022 - 032 - 022 - 021 - 011 - 010; If the vector to be synthesized V ref Located in the 5th minor sector of the 3rd major sector, the basic vector action sequence is 031 - 032 - 132 - 232 - 233 - 232 - 132 - 032 - 031; If the vector to be synthesized V ref Located in the 6th minor sector of the 3rd major sector, the basic vector action sequence is 010 - 011 - 021 - 031 - 032 - 031 - 021 - 011 - 010; If the vector to be synthesized V ref Located in the 7th minor sector of the 3rd major sector, the basic vector action sequence is 030 - 031 - 131 - 132 - 232 - 132 - 131 - 031 - 030; If the vector to be synthesized V ref Located in the 8th minor sector of the 3rd major sector, the basic vector action sequence is 011 - 021 - 022 - 032 - 033 - 032 - 022 - 021 - 011; If the vector to be synthesized V ref Located in the 9th minor sector of the 3rd major sector, the basic vector action sequence is 030 - 031 - 032 - 132 - 232 - 132 - 032 - 031 - 030; If the vector to be synthesized V ref Located in the 10th minor sector of the 3rd major sector, the basic vector action sequence is 011 - 021 - 031 - 032 - 033 - 032 - 031 - 021 - 011;

[0033] If the vector to be synthesized V ref Located in the 1st minor sector of the 4th major sector, the basic vector action sequence is 113 - 123 - 223 - 233 - 333 - 233 - 223 - 123 - 113; If the vector to be synthesized V ref Located in the 2nd minor sector of the 4th major sector, the basic vector action sequence is 000 - 001 - 011 - 012 - 022 - 012 - 011 - 001 - 000; If the vector to be synthesized V refIf it is located in the 3rd minor sector of the 4th major sector, the basic vector action sequence is 013 - 113 - 123 - 223 - 233 - 223 - 123 - 113 - 013; if the vector to be synthesized V ref If it is located in the 4th minor sector of the 4th major sector, the basic vector action sequence is 001 - 011 - 012 - 022 - 032 - 022 - 012 - 011 - 001; if the vector to be synthesized V ref If it is located in the 5th minor sector of the 4th major sector, the basic vector action sequence is 013 - 023 - 123 - 223 - 233 - 223 - 123 - 023 - 013; if the vector to be synthesized V ref If it is located in the 6th minor sector of the 4th major sector, the basic vector action sequence is 001 - 011 - 012 - 013 - 023 - 013 - 012 - 011 - 001; if the vector to be synthesized V ref If it is located in the 7th minor sector of the 4th major sector, the basic vector action sequence is 003 - 013 - 113 - 123 - 223 - 123 - 113 - 013 - 003; if the vector to be synthesized V ref If it is located in the 8th minor sector of the 4th major sector, the basic vector action sequence is 011 - 012 - 022 - 023 - 033 - 023 - 022 - 012 - 011; if the vector to be synthesized V ref If it is located in the 9th minor sector of the 4th major sector, the basic vector action sequence is 003 - 013 - 023 - 123 - 223 - 123 - 023 - 013 - 003; if the vector to be synthesized V ref If it is located in the 10th minor sector of the 4th major sector, the basic vector action sequence is 011 - 012 - 013 - 023 - 033 - 023 - 013 - 012 - 011;

[0034] If the vector to be synthesized V ref If it is located in the 1st minor sector of the 5th major sector, the basic vector action sequence is 113 - 213 - 223 - 323 - 333 - 323 - 223 - 213 - 113; if the vector to be synthesized V ref If it is located in the 2nd minor sector of the 5th major sector, the basic vector action sequence is 000 - 001 - 101 - 102 - 202 - 102 - 101 - 001 - 000; if the vector to be synthesized V refLocated in the 3rd minor sector of the 5th major sector, the basic vector action sequence is 103 - 113 - 213 - 223 - 323 - 223 - 213 - 113 - 103; if the vector to be synthesized V ref Located in the 4th minor sector of the 5th major sector, the basic vector action sequence is 001 - 101 - 102 - 202 - 302 - 202 - 102 - 101 - 001; if the vector to be synthesized V ref Located in the 5th minor sector of the 5th major sector, the basic vector action sequence is 103 - 203 - 213 - 223 - 323 - 223 - 210 - 203 - 103; if the vector to be synthesized V ref Located in the 6th minor sector of the 5th major sector, the basic vector action sequence is 001 - 101 - 102 - 103 - 203 - 103 - 102 - 101 - 001; if the vector to be synthesized V ref Located in the 7th minor sector of the 5th major sector, the basic vector action sequence is 003 - 103 - 113 - 213 - 223 - 213 - 113 - 103 - 003; if the vector to be synthesized V ref Located in the 8th minor sector of the 5th major sector, the basic vector action sequence is 101 - 102 - 202 - 203 - 303 - 203 - 202 - 102 - 101; if the vector to be synthesized V ref Located in the 9th minor sector of the 5th major sector, the basic vector action sequence is 003 - 103 - 203 - 213 - 223 - 213 - 203 - 103 - 003; if the vector to be synthesized V ref Located in the 10th minor sector of the 5th major sector, the basic vector action sequence is 101 - 102 - 103 - 203 - 303 - 203 - 103 - 102 - 101;

[0035] If the vector to be synthesized V ref Located in the 1st minor sector of the 6th major sector, the basic vector action sequence is 311 - 312 - 322 - 323 - 333 - 323 - 322 - 312 - 311; if the vector to be synthesized V ref Located in the 2nd minor sector of the 6th major sector, the basic vector action sequence is 000 - 100 - 101 - 201 - 202 - 201 - 101 - 100 - 000; if the vector to be synthesized V refLocated in the 3rd minor sector of the 6th major sector, the basic vector action sequence is 301 - 311 - 312 - 322 - 323 - 322 - 312 - 311 - 301; if the vector to be synthesized V ref Located in the 4th minor sector of the 6th major sector, the basic vector action sequence is 100 - 101 - 201 - 202 - 203 - 202 - 201 - 101 - 100; if the vector to be synthesized V ref Located in the 5th minor sector of the 6th major sector, the basic vector action sequence is 301 - 302 - 312 - 322 - 323 - 322 - 312 - 302 - 301; if the vector to be synthesized V ref Located in the 6th minor sector of the 6th major sector, the basic vector action sequence is 100 - 101 - 201 - 301 - 302 - 301 - 201 - 101 - 100; if the vector to be synthesized V ref Located in the 7th minor sector of the 6th major sector, the basic vector action sequence is 300 - 301 - 311 - 312 - 322 - 312 - 311 - 301 - 300; if the vector to be synthesized V ref Located in the 8th minor sector of the 6th major sector, the basic vector action sequence is 101 - 201 - 202 - 302 - 303 - 302 - 202 - 201 - 101; if the vector to be synthesized V ref Located in the 9th minor sector of the 6th major sector, the basic vector action sequence is 300 - 301 - 302 - 312 - 322 - 312 - 302 - 301 - 300; if the vector to be synthesized V ref Located in the 10th minor sector of the 6th major sector, the basic vector action sequence is 101 - 201 - 301 - 302 - 303 - 302 - 301 - 201 - 101.

[0036] In step S5 of the discontinuous pulse width modulation method for the above three - phase four - level inverter control circuit, the action time of each basic vector in the vector sequence is determined according to the following rules: The calculation expression for the action time of each basic vector is:

[0037]

[0038] Among them, V sn_α and V sn_β are the components of the basic vector V sn on the α and β axes, k sn andj sn is the correlation coefficient for the DC bus capacitor voltage balance constraint T s is the duration of one switching period T Vsn represents the action time of the basic vector V sn within one switching period

[0039] If the vector to be synthesized V ref is located in the first small sector of any large sector, its DC bus capacitor voltage balance constraint is

[0040]

[0041] If the vector to be synthesized V ref is located in the second small sector of any large sector, its DC bus capacitor voltage balance constraint is

[0042]

[0043] If the vector to be synthesized V ref is located in the third small sector of any large sector, its DC bus capacitor voltage balance constraint is

[0044]

[0045] If the vector to be synthesized V ref is located in the fourth small sector of any large sector, its DC bus capacitor voltage balance constraint is

[0046]

[0047] If the vector to be synthesized V ref is located in the fifth small sector of any large sector, its DC bus capacitor voltage balance constraint is

[0048]

[0049] If the vector to be synthesized V ref is located in the sixth small sector of any large sector, its DC bus capacitor voltage balance constraint is

[0050]

[0051] If the vector to be synthesized V refLocated in the 7th smallest sector of any large sector, the DC bus capacitor voltage balance constraint is:

[0052]

[0053] If the vector to be synthesized V ref Located in the 8th smallest sector of any large sector, the DC bus capacitor voltage balance constraint is:

[0054]

[0055] If the vector to be synthesized V ref Located in the 9th smallest sector of any large sector, the DC bus capacitor voltage balance constraint is:

[0056]

[0057] If the vector to be synthesized V ref Located in the 10th smallest sector of any large sector, the DC bus capacitor voltage balance constraint is:

[0058] .

[0059] The present invention also relates to a control circuit of a three-phase four-level inverter, and the control circuit executes the above discontinuous pulse width modulation method.

[0060] In the control circuit of the above-mentioned three-phase four-level inverter, the control circuit includes a MOSFET driving unit, an inductor current sampling unit, a grid voltage sampling unit, and a DSP control unit; the DSP control unit includes a first abc / dq converter, a second abc / dq converter, a phase-locked loop, a first subtractor, a second subtractor, a reactive current PI regulator, an active current PI regulator, a dq / αβ converter, and a DPWM controller; the three input terminals of the grid voltage sampling unit are respectively connected to the connection between the A-phase filter capacitor and the A-phase AC power supply, the connection between the B-phase filter capacitor and the B-phase AC power supply, and the connection between the C-phase filter capacitor and the C-phase AC power supply; the output terminal of the grid voltage sampling unit is connected to the first input terminal of the first abc / dq converter; the three input terminals of the inductor current sampling unit are correspondingly connected to the connection between the A-phase filter inductor and the A-phase bridge arm output voltage point A, the connection between the B-phase filter inductor and the B-phase bridge arm output voltage point B, and the connection between the C-phase filter inductor and the C-phase bridge arm output voltage point C; the output terminal of the inductor current sampling unit is connected to the first input terminal of the second abc / dq converter; the two output terminals of the first abc / dq converter are respectively connected to the two input terminals of the phase-locked loop, and the output terminal of the phase-locked loop is connected to the second input terminal of the first abc / dq converter, the second input terminal of the second abc / dq converter, and the first input terminal of the dq / αβ converter; the first output terminal of the second abc / dq converter is connected to the first input terminal of the first subtractor, the second input terminal of the first subtractor inputs a given reference value 0, and the output terminal of the second subtractor is connected to the input terminal of the reactive current PI regulator; the second output terminal of the second abc / dq converter is connected to the first input terminal of the second subtractor, and the second input terminal of the second subtractor inputs a given reference value i d_ref , the output terminal of the second subtractor is connected to the input terminal of the active current PI regulator; the second input terminal and the third input terminal of the dq / αβ converter are respectively connected to the output terminal of the reactive current PI regulator and the output terminal of the active current PI regulator; the two output terminals of the dq / αβ converter are respectively connected to the two input terminals of the DPWM controller; the output terminal of the DPWM controller is connected to the input terminal of the MOSFET driving unit, and the respective output terminals of the MOSFET driving unit are respectively connected to the gates of the power switching tubes of the A-phase bridge arm, the B-phase bridge arm, and the C-phase bridge arm, and drive signals corresponding to the respective power switching tubes are output; the three-phase grid voltage sampled by the grid voltage sampling unit u sA 、 u sB 、 u sC After passing through the first abc / dq converter, the components in the dq coordinate system are obtained u dand u q and sent into a phase-locked loop, from which the phase information of the grid voltage is obtained θ , and the phase information θ is input into a first abc / dq converter, a second abc / dq converter, and a dq / αβ converter; the three-phase inductor currents sampled by the inductor current sampling unit i La , i Lb , i Lc , after being transformed by the second abc / dq converter, obtain the active components i La , i Lb , i Lc and reactive components i d of the three-phase inductor currents i q ; the active component i d is subtracted from a given reference value i d_ref by a second subtractor, and the difference is input into an active current PI regulator. The active current PI regulator generates a d-axis control component u d according to the input signal, and sends the d-axis control component u d to the dq / αβ converter; the reactive component i q is subtracted from 0 (the given reference value) by a first subtractor, and the difference is input into a reactive current PI regulator. The reactive current PI regulator generates a q-axis control component u q according to the input signal, and sends the q-axis control component u q to the dq / αβ converter; the dq / αβ converter transforms the d-axis control component u d and the q-axis control component u q into control components u α and u β in the αβ coordinate system, and inputs them into the DPWM controller.

[0061] Advantages brought by the above technical solutions: The present invention can achieve the natural balance of the DC bus capacitor voltage of the three-phase four-level inverter. Meanwhile, the switching state of one phase bridge arm is clamped, with fewer switching times, less switching loss, and high converter efficiency. Therefore, the modulation method and circuit involved in the present invention are applicable to occasions such as renewable power generation, and have broad application prospects in fields such as photovoltaic power generation.

[0062] To make the above features and advantages of the invention more obvious and understandable, specific embodiments are hereinafter given and described in detail in conjunction with the accompanying drawings as follows. Brief Description of the Drawings

[0063] Figure 1 It is a circuit schematic diagram of the three-phase four-level inverter and its control circuit of the present invention.

[0064] Figure 2 It is the space vector diagram of the three-phase four-level inverter in the present invention and the schematic diagram of the division of large sectors and small sectors.

[0065] Figure 3 It is the steady-state operation simulation waveform diagram of an example of the discontinuous pulse width modulation method of the control circuit of the three-phase four-level inverter adopting the present invention. Detailed Embodiments

[0066] To make the objectives and technical solutions of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0067] Figure 1 It is a circuit schematic diagram of the three-phase four-level inverter and its control circuit of the present invention.

[0068] As Figure 1 shown, the three-phase four-level inverter 40 is connected to the three-phase power grid 60. The three-phase power grid 60 includes a phase A AC power supply u sA , a phase B AC power supply u sB , and a phase C AC power supply u sC .

[0069] The three-phase four-level inverter 40 includes a DC power supply group 401, a DC bus filter capacitor group 402, a power switch group 403, a three-phase filter inductor group 404, and a three-phase filter capacitor group 405.

[0070] Among them, the DC power supply group 401 includes a DC power supplyU dc ; The DC bus filter capacitor bank 402 includes a first DC bus filter capacitor C d3 , a second DC bus filter capacitor C d2 , and a third DC bus filter capacitor C d1 ; The power switch bank 403 includes a first power switch transistor S 1, a second power switch transistor S 2, a third power switch transistor S 3, a fourth power switch transistor S 4, a fifth power switch transistor S 5, a sixth power switch transistor S 6, a seventh power switch transistor S 7, an eighth power switch transistor S 8, a ninth power switch transistor S 9, a tenth power switch transistor S 10 , an eleventh power switch transistor S 11 , a twelfth power switch transistor S 12 , a thirteenth power switch transistor S 13 , a fourteenth power switch transistor S 14 , a fifteenth power switch transistor S 15 , a sixteenth power switch transistor S 16 , a seventeenth power switch transistor S 17 , and an eighteenth power switch transistor S 18 ; The three-phase filter inductor bank 404 includes an A-phase filter inductor L fa , a B-phase filter inductor L fb , and a C-phase filter inductor L fc ; The three-phase filter capacitor bank 405 includes an A-phase filter capacitor C fa , a B-phase filter capacitor C fb , and a C-phase filter capacitor C fc .

[0071] The positive electrode of the DC power supply U dc and the first DC bus filter capacitor Cd1 The positive electrodes of the are respectively connected to both ends of point 3 on the DC side; the first DC bus filter capacitor C d1 The negative electrode of and the second DC bus filter capacitor C d2 The positive electrodes of are respectively connected to both ends of point 2 on the DC side; the second DC bus filter capacitor C d2 The negative electrode of and the third DC bus filter capacitor C d3 The positive electrodes of are respectively connected to both ends of point 1 on the DC side; the third DC bus filter capacitor C d3 The negative electrode of and the DC power supply U dc The negative electrodes of are respectively connected to both ends of point 0 on the DC side; O is the virtual midpoint of the DC side ， The voltage between and point 0 on the DC side is one-half of the DC power supply voltage.

[0072] In the power switch tube group 403, the first power switch tube S 1 to the sixth power switch tube S 6 are connected to form phase A bridge arm; the seventh power switch tube S 7 to the twelfth power switch tube S 12 are connected to form phase B bridge arm; the thirteenth power switch tube S 13 to the eighteenth power switch tube S 18 are connected to form phase C bridge arm. In the present invention, the first power switch tube S 1 to the eighteenth power switch tube S 18 Preferably, a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) is adopted.

[0073] In the phase A bridge arm, the drain of the first power switch tube S 1 is connected to the positive electrode of the DC power supply U dc and the positive electrode of the first DC bus filter capacitor C d1 The source of the first power switch tube S 1 is connected to the drain of the second power switch tube S 2; the source of the second power switch tube S 2 is connected to the first DC bus filter capacitorC d1 the negative electrode; the third power switch S The drain of 3 is connected to the third DC bus filter capacitor C d3 the positive electrode, the third power switch S The source of 3 is connected to the drain of the fourth power switch S 4; the fourth power switch S The source of 4 is connected to the DC power supply U dc the negative electrode and the third DC bus filter capacitor C d3 the negative electrode; the fifth power switch S The drain of 5 is connected to the source of the first power switch S 1, the fifth power switch S The source of 5 is connected to the drain of the sixth power switch S 6, the sixth power switch S The source of 6 is connected to the drain of the fourth power switch S 4; the fifth power switch S 5 and the sixth power switch S The connection point of 6 is the output point A of the A-phase bridge arm.

[0074] In the B-phase bridge arm, the seventh power switch S The drain of 7 is connected to the DC power supply U dc the positive electrode and the first DC bus filter capacitor C d1 the positive electrode, the seventh power switch S The source of 7 is connected to the drain of the eighth power switch S 8; the eighth power switch S The source of 8 is connected to the first DC bus filter capacitor C d1 the negative electrode; the ninth power switch S The drain of 9 is connected to the third DC bus filter capacitor C d3 the positive electrode, the ninth power switch S The source of 9 is connected to the drain of the tenth power switch S 10 ; the tenth power switch S 10 The source of is connected to the DC power supply U dc the negative electrode and the third DC bus filter capacitor Cd3 The negative electrode of; the eleventh power switch S 11 The drain of is connected to the source of the seventh power switch S 7, the eleventh power switch S 11 The source of is connected to the drain of the twelfth power switch S 12 The drain of the twelfth power switch S 12 The source of is connected to the drain of the tenth power switch S 10 The eleventh power switch S 11 And the twelfth power switch S 12 The connection point of is the output point B of the B-phase bridge arm.

[0075] In the C-phase bridge arm, the thirteenth power switch S 13 The drain of is connected to the positive electrode of the DC power supply U dc And the positive electrode of the first DC bus filter capacitor C d1 The thirteenth power switch S 13 The source of is connected to the drain of the fourteenth power switch S 14 The fourteenth power switch S 14 The source of is connected to the negative electrode of the first DC bus filter capacitor C d1 The fifteenth power switch S 15 The drain of is connected to the positive electrode of the third DC bus filter capacitor C d3 The fifteenth power switch S 15 The source of is connected to the drain of the sixteenth power switch S 16 The sixteenth power switch S 16 The source of is connected to the negative electrode of the DC power supply U dc And the negative electrode of the third DC bus filter capacitor C d3 The seventeenth power switch S 17 The drain of is connected to the thirteenth power switchS 13 The source electrode of the seventeenth power switch transistor S 17 is connected to the source electrode of the eighteenth power switch transistor S 18 The drain electrode of the eighteenth power switch transistor S 18 is connected to the source electrode of the sixteenth power switch transistor S 16 The drain electrode of the seventeenth power switch transistor S 17 and the eighteenth power switch transistor S 18 The connection point is the output point C of the C-phase bridge arm.

[0076] One end of the A-phase filter inductor L fa is connected to the output point A of the A-phase bridge arm, and the other end is connected to the first end of the A-phase filter capacitor C fa and the first end of the A-phase AC power supply u sA One end of the B-phase filter inductor L fb is connected to the output point B of the B-phase bridge arm, and the other end is connected to the first end of the B-phase filter capacitor and the first end of the B-phase AC power supply u sB One end of the C-phase filter inductor L fc is connected to the output point C of the C-phase bridge arm, and the other end is connected to the first end of the C-phase filter capacitor C fc and the first end of the C-phase AC power supply u sC The second end of the A-phase filter capacitor C fa The second end of the B-phase filter capacitor C fb And the second end of the C-phase filter capacitor C fc Are connected together to form a star-connected three-phase filter capacitor; the second end of the A-phase AC power supply u sA The second end of the B-phase AC power supply u sB The second end of the C-phase AC power supply u sC Are connected together to form a star-connected three-phase power grid, and the connection point is n .

[0077] The three-phase four-level inverter 40 includes a control circuit 50, and the control circuit 50 includes a MOSFET driving unit 501, an inductor current sampling unit 502, a grid voltage sampling unit 503, and a DSP control unit 504.

[0078] The DSP control unit 504 includes a first abc / dq converter 5041, a second abc / dq converter 5042, a phase-locked loop 5043, a first subtractor 5044, a second subtractor 5045, a reactive current PI regulator 5046, an active current PI regulator 5047, a dq / αβ converter 5048, and a DPWM controller 5049.

[0079] The three input terminals of the grid voltage sampling unit 503 are respectively connected to the connection between the A-phase filter capacitor and the A-phase AC power supply, the connection between the B-phase filter capacitor and the B-phase AC power supply, and the connection between the C-phase filter capacitor and the C-phase AC power supply; the output terminal of the grid voltage sampling unit 503 is connected to the first input terminal of the first abc / dq converter 5041; the three input terminals of the inductor current sampling unit 502 are correspondingly connected to the connection between the A-phase filter inductor and the A-phase bridge arm output voltage point A, the connection between the B-phase filter inductor and the B-phase bridge arm output voltage point B, and the connection between the C-phase filter inductor and the C-phase bridge arm output voltage point C, and the output terminal of the inductor current sampling unit 502 is connected to the first input terminal of the second abc / dq converter 5042.

[0080] The two output terminals of the first abc / dq converter 5041 are respectively connected to the two input terminals of the phase-locked loop 5043, and the output terminal of the phase-locked loop 5043 is connected to the second input terminal of the first abc / dq converter 5041, the second input terminal of the second abc / dq converter 5042, and the first input terminal of the dq / αβ converter 5048; the first output terminal of the second abc / dq converter 5042 is connected to the first input terminal of the first subtractor 5044, the second input terminal of the first subtractor 5044 inputs a given reference value of 0, and the output terminal of the second subtractor 5045 is connected to the input terminal of the reactive current PI regulator 5046; the second output terminal of the second abc / dq converter 5042 is connected to the first input terminal of the second subtractor 5045, and the second input terminal of the second subtractor 5045 inputs a given reference value i d_ref, the output terminal of the second subtractor 5045 is connected to the input terminal of the active current PI regulator 5047; the second input terminal and the third input terminal of the dq / αβ converter 5048 are respectively connected to the output terminal of the reactive current PI regulator 5046 and the output terminal of the active current PI regulator 5047; the two output terminals of the dq / αβ converter 5048 are respectively connected to the two input terminals of the DPWM controller 5049; the output terminal of the DPWM controller 5049 is connected to the input terminal of the MOSFET driving unit 501, and each output terminal of the MOSFET driving unit 501 is respectively connected to the gates of the first to the eighteenth power switching transistors, for outputting driving signals corresponding to the respective power switching transistors.

[0081] The three-phase grid voltage sampled by the grid voltage sampling unit 503 u sA , u sB , u sC After passing through the first abc / dq converter 5041, the components in the dq coordinate system are obtained u d and u q and are sent to the phase-locked loop 5043, and the phase-locked loop 5043 obtains the phase information of the grid voltage accordingly θ , and the phase information θ is input into the first abc / dq converter 5041, the second abc / dq converter 5042 and the dq / αβ converter 5048; the three-phase inductor current sampled by the inductor current sampling unit 502 i La , i Lb , i Lc , after being transformed by the second abc / dq converter 5042, the active component i La , i Lb , i Lc and the reactive component i d of the three-phase inductor current are obtained; the active component i q is subtracted from the given reference value i d by the second subtractor 5045, and the difference is input into the active current PI regulator 5047. The active current PI regulator 5047 generates the d-axis control component i d_ref according to the input signal u d, and send the d-axis control component u d to the dq / αβ converter 5048; the reactive power component i q is subtracted from the given reference value 0 by the first subtractor 5044, and the difference is input to the reactive current PI regulator 5046. The reactive current PI regulator 5046 generates the q-axis control component u q , and send the q-axis control component u q to the dq / αβ converter 5048; the dq / αβ converter 5048 converts the d-axis control component u d and the q-axis control component u q into the control components u α and u β in the αβ coordinate system, and input them to the DPWM controller 5049.

[0082] The present invention proposes a discontinuous pulse width modulation method for the control circuit of a three-phase four-level inverter, which is used for the DPWM controller 5049 in the control circuit 50 of the above-mentioned three-phase four-level inverter, and specifically includes the following steps.

[0083] Step S1, establish a four-level vector space in the complex plane according to the DC bus voltage. The four-level vector space is composed of 64 basic vectors, and the coordinates of each basic vector are calculated by the following expression:

[0084]

[0085] where, S A , S B , S C are the switching functions of phase A, phase B, and phase C respectively, j is the imaginary unit, and the switching function S X , X represents A, B, or C, and the calculation expression is:

[0086]

[0087] where the switching state 3 represents X the output point of the X phase bridge arm is connected to the DC side 3 point through the power switch tube, X the output point of the X phase bridge arm is connected to the virtual midpoint of the DC side OThe voltage between them is the DC power supply voltage U dc is one half of, that is U dc / 2; Switch state 2 means X The output point of the phase bridge arm X is connected to point 2 of the DC side through a power switch tube, X The output point of the phase bridge arm X and the virtual midpoint of the DC side O The voltage between them is the DC power supply voltage U dc is one sixth of, that is U dc / 6; Switch state 1 means X The output point of the phase bridge arm X is connected to point 1 of the DC side through a power switch tube, X The output point of the phase bridge arm X and the virtual midpoint of the DC side O The voltage between them is the DC power supply voltage U dc is the opposite of one sixth of, that is - U dc / 6; Switch state 0 means X The output point of the phase bridge arm X is connected to point 0 of the DC side through a power switch tube, X The output point of the phase bridge arm X and the virtual midpoint of the DC side O The voltage between them is the DC power supply voltage U dc is the opposite of one half of, that is - U dc / 2;

[0088] Step S2, divide the four-level vector space into 6 large sectors according to 64 basic vectors, and each large sector is further divided into 10 small sectors;

[0089] Step S3, according to the control components in the αβ coordinate system u α and u β , calculate the coordinates of the vector to be synthesized V ref , and the calculation expression is:

[0090]

[0091] Among them, u α and u βThe dq / αβ converter respectively generates the d-axis control component by the active current PI regulator according to the input signal u d and the reactive current PI regulator generates the q-axis control component according to the input signal u q which is transformed into the control component in the αβ coordinate system, where j is the imaginary unit;

[0092] Step S4, determining the basic vector action sequence according to the coordinates of the vector to be synthesized V ref ;

[0093] Step S5, determining the action time of each basic vector in the vector action sequence according to the DC bus capacitor voltage balance constraint and the volt-second balance principle.

[0094] Figure 2 This is the space vector diagram of the three-phase four-level inverter and the schematic diagram of the division of large sectors and small sectors in the present invention. As Figure 2 shown, in the above step S1, the 64 basic vectors of the three-phase four-level inverter are respectively 333, 222, 111, 000, 322, 211, 100, 311, 200, 300, 321, 210, 310, 320, 332, 221, 110, 331, 220, 330, 231, 120, 230, 130, 232, 121, 010, 131, 020, 030, 132, 021, 031, 032, 233, 122, 011, 133, 022, 033, 123, 012, 023, 013, 223, 112, 001, 113, 002, 003, 213, 102, 103, 203, 323, 212, 101, 313, 202, 303, 312, 201, 302, 301, corresponding to Figure 2 each of the basic vectors marked in the figure, where 3 means that one phase leg is in the switching state 3, 2 means that one phase leg is in the switching state 2, 1 means that one phase leg is in the switching state 1, and 0 means that one phase leg is in the switching state 0.

[0095] In the above step S2, the large sectors are divided according to the following rules: The first large sector is the area surrounded by the basic vectors 333, 300, and 330; the second large sector is the area surrounded by the basic vectors 333, 330, and 030; the third large sector is the area surrounded by the basic vectors 333, 030, and 033; the fourth large sector is the area surrounded by the basic vectors 333, 033, and 003; the fifth large sector is the area surrounded by the basic vectors 333, 003, and 303; the sixth large sector is the area surrounded by the basic vectors 333, 303, and 300.

[0096] Among them, each large sector is divided into 10 small sectors. In the I-th large sector, the 1st small sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 110 and 220, and 000 that is below the line connecting 000 and the midpoint of the line connecting 300 and 330; the 2nd small sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 110 and 220, and 000 that is above the line connecting 000 and the midpoint of the line connecting 300 and 330; the 3rd small sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 300 and 330 that is below the line connecting 000 and the midpoint of the line connecting 300 and 330 and to the lower left of the line connecting 321 and 300; the 4th small sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 300 and 330 that is above the line connecting 000 and the midpoint of the line connecting 300 and 330 and to the lower left of the line connecting 321 and 330; the 5th small sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 300 and 330 that is below the line connecting 000 and the midpoint of the line connecting 300 and 330 and to the upper right of the line connecting 321 and 300; the 6th small sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 300 and 330 that is above the line connecting 000 and the midpoint of the line connecting 300 and 330 and to the upper right of the line connecting 321 and 330; the 7th small sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, 300, and the midpoint of the line connecting 300 and 330 that is to the lower left of the line connecting 321 and 300; the 8th small sector is the part of the region enclosed by the midpoint of the line connecting 110 and 220, 330, and the midpoint of the line connecting 300 and 330 that is to the left of the line connecting 321 and 330; the 9th small sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, 300, and the midpoint of the line connecting 300 and 330 that is to the upper right of the line connecting 321 and 300; the 10th small sector is the part of the region enclosed by the midpoint of the line connecting 110 and 220, 330, and the midpoint of the line connecting 300 and 330 that is to the right of the line connecting 321 and 330.

[0097] In the second major sector, the first minor sector is the part of the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 110 and 220, and 000 that is to the left of the line connecting 000 and the midpoint of the line connecting 030 and 330; the second minor sector is the part of the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 110 and 220, and 000 that is to the right of the line connecting 000 and the midpoint of the line connecting 030 and 330; the third minor sector is the part of the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 030 and 330 that is to the left of the line connecting 000 and the midpoint of the line connecting 030 and 330 and is below and to the left of the line connecting 231 and 030; the fourth minor sector is the part of the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 030 and 330 that is to the right of the line connecting 000 and the midpoint of the line connecting 030 and 330 and is below and to the right of the line connecting 231 and 330; the fifth minor sector is the part of the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 030 and 330 that is to the left of the line connecting 000 and the midpoint of the line connecting 030 and 330 and is above and to the right of the line connecting 231 and 030; the sixth minor sector is the part of the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 030 and 330 that is to the right of the line connecting 000 and the midpoint of the line connecting 030 and 330 and is above and to the left of the line connecting 231 and 330; the seventh minor sector is the part of the region enclosed by the midpoint of the line connecting 232 and 131, 030, and the midpoint of the line connecting 030 and 330 that is below and to the left of the line connecting 231 and 030; the eighth minor sector is the part of the region enclosed by the midpoint of the line connecting 110 and 220, 330, and the midpoint of the line connecting 030 and 330 that is below and to the right of the line connecting 231 and 330; the ninth minor sector is the part of the region enclosed by the midpoint of the line connecting 232 and 131, 030, and the midpoint of the line connecting 030 and 330 that is above and to the right of the line connecting 231 and 030; the tenth minor sector is the part of the region enclosed by the midpoint of the line connecting 110 and 220, 330, and the midpoint of the line connecting 030 and 330 that is above and to the left of the line connecting 231 and 330.

[0098] In the third major sector, the first minor sector is the part of the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 011 and 022, and 000, which is to the upper right of the line connecting 000 and the midpoint of the line connecting 030 and 033; the second minor sector is the part of the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 011 and 022, and 000, which is to the lower left of the line connecting 000 and the midpoint of the line connecting 030 and 033; the third minor sector is the part of the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 030 and 033, which is to the upper right of the line connecting 000 and the midpoint of the line connecting 030 and 033 and to the right of the line connecting 132 and 030; the fourth minor sector is the part of the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 030 and 033, which is to the lower left of the line connecting 000 and the midpoint of the line connecting 030 and 033 and to the lower right of the line connecting 132 and 033; the fifth minor sector is the part of the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 030 and 033, which is to the upper right of the line connecting 000 and the midpoint of the line connecting 030 and 033 and to the left of the line connecting 132 and 030; the sixth minor sector is the part of the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 030 and 033, which is to the lower left of the line connecting 000 and the midpoint of the line connecting 030 and 033 and to the upper left of the line connecting 132 and 033; the seventh minor sector is the part of the region enclosed by the midpoint of the line connecting 232 and 131, 030, and the midpoint of the line connecting 030 and 033, which is to the right of the line connecting 132 and 030; the eighth minor sector is the part of the region enclosed by the midpoint of the line connecting 011 and 022, 033, and the midpoint of the line connecting 030 and 033, which is to the lower right of the line connecting 132 and 033; the ninth minor sector is the part of the region enclosed by the midpoint of the line connecting 232 and 131, 030, and the midpoint of the line connecting 030 and 033, which is to the left of the line connecting 132 and 030; the tenth minor sector is the part of the region enclosed by the midpoint of the line connecting 011 and 022, 033, and the midpoint of the line connecting 030 and 033, which is to the upper left of the line connecting 132 and 033.

[0099] In the fourth major sector, the first minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 011 and 022, and 000, which is to the lower right of the line connecting 000 and the midpoint of the line connecting 003 and 033; the second minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 011 and 022, and 000, which is to the upper left of the line connecting 000 and the midpoint of the line connecting 003 and 033; the third minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 003 and 033, which is to the lower right of the line connecting 000 and the midpoint of the line connecting 003 and 033 and to the right of the line connecting 123 and 003; the fourth minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 003 and 033, which is to the upper left of the line connecting 000 and the midpoint of the line connecting 003 and 033 and to the upper right of the line connecting 123 and 033; the fifth minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 003 and 033, which is to the lower right of the line connecting 000 and the midpoint of the line connecting 003 and 033 and to the left of the line connecting 123 and 003; the sixth minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 003 and 033, which is to the upper left of the line connecting 000 and the midpoint of the line connecting 003 and 033 and to the lower left of the line connecting 123 and 033; the seventh minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, 003, and the midpoint of the line connecting 003 and 033, which is to the right of the line connecting 123 and 003; the eighth minor sector is the part in the region enclosed by the midpoint of the line connecting 011 and 022, 033, and the midpoint of the line connecting 003 and 033, which is to the upper right of the line connecting 123 and 033; the ninth minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, 003, and the midpoint of the line connecting 003 and 033, which is to the left of the line connecting 123 and 003; the tenth minor sector is the part in the region enclosed by the midpoint of the line connecting 011 and 022, 033, and the midpoint of the line connecting 003 and 033, which is to the lower left of the line connecting 123 and 033.

[0100] In the fifth largest sector, the first small sector is the part on the left of the line connecting 000 and the midpoint of the line connecting 003 and 303 within the area enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 101 and 202, and 000; the second small sector is the part on the right of the line connecting 000 and the midpoint of the line connecting 003 and 303 within the area enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 101 and 202, and 000; the third small sector is the part on the left of the line connecting 000 and the midpoint of the line connecting 003 and 303 and above and to the left of the line connecting 213 and 003 within the area enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 003 and 303; the fourth small sector is the part on the right of the line connecting 000 and the midpoint of the line connecting 003 and 303 and above and to the right of the line connecting 123 and 303 within the area enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 003 and 303; the fifth small sector is the part on the left of the line connecting 000 and the midpoint of the line connecting 003 and 303 and below and to the right of the line connecting 213 and 003 within the area enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 003 and 303; the sixth small sector is the part on the right of the line connecting 000 and the midpoint of the line connecting 003 and 303 and below and to the left of the line connecting 123 and 303 within the area enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 003 and 303; the seventh small sector is the part above and to the left of the line connecting 213 and 003 within the area enclosed by the midpoint of the line connecting 223 and 113, 003, and the midpoint of the line connecting 003 and 303; the eighth small sector is the part above and to the right of the line connecting 213 and 303 within the area enclosed by the midpoint of the line connecting 101 and 202, 303, and the midpoint of the line connecting 003 and 303; the ninth small sector is the part below and to the right of the line connecting 213 and 003 within the area enclosed by the midpoint of the line connecting 223 and 113, 003, and the midpoint of the line connecting 003 and 303; the tenth small sector is the part below and to the left of the line connecting 213 and 303 within the area enclosed by the midpoint of the line connecting 101 and 202, 303, and the midpoint of the line connecting 003 and 303.

[0101] In the sixth major sector, the first minor sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 101 and 202, and 000, which is to the upper right of the line connecting 000 and the midpoint of the line connecting 300 and 303; the second minor sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 101 and 202, and 000, which is to the lower left of the line connecting 000 and the midpoint of the line connecting 300 and 303; the third minor sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 300 and 303, which is to the upper right of the line connecting 000 and the midpoint of the line connecting 300 and 303 and to the upper left of the line connecting 312 and 300; the fourth minor sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 300 and 303, which is to the lower left of the line connecting 000 and the midpoint of the line connecting 300 and 303 and to the left of the line connecting 312 and 303; the fifth minor sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 300 and 303, which is to the upper right of the line connecting 000 and the midpoint of the line connecting 300 and 303 and to the lower right of the line connecting 312 and 300; the sixth minor sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 300 and 303, which is to the lower left of the line connecting 000 and the midpoint of the line connecting 300 and 303 and to the right of the line connecting 312 and 303; the seventh minor sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, 300, and the midpoint of the line connecting 300 and 303, which is to the upper left of the line connecting 312 and 300; the eighth minor sector is the part of the region enclosed by the midpoint of the line connecting 101 and 202, 303, and the midpoint of the line connecting 300 and 303, which is to the left of the line connecting 312 and 303; the ninth minor sector is the part of the region enclosed by the midpoint of the line connecting 322 and 311, 300, and the midpoint of the line connecting 300 and 303, which is to the lower right of the line connecting 312 and 300; the tenth minor sector is the part of the region enclosed by the midpoint of the line connecting 101 and 202, 303, and the midpoint of the line connecting 300 and 303, which is to the right of the line connecting 312 and 303.

[0102] In the above step S4, the method for determining the basic vector action sequence is as follows:

[0103] If the vector to be synthesized V ref is located in the first minor sector of the first major sector, the basic vector action sequence is 311 - 321 - 322 - 332 - 333 - 332 - 322 - 321 - 311; if the vector to be synthesized V ref is located in the second minor sector of the first major sector, the basic vector action sequence is 000 - 100 - 110 - 210 - 220 - 210 - 110 - 100 - 000; if the vector to be synthesized Vref is located in the 3rd minor sector of the 1st major sector, the basic vector action sequence is 310 - 311 - 321 - 322 - 332 - 322 - 321 - 311 - 310; if the vector to be synthesized V ref is located in the 4th minor sector of the 1st major sector, the basic vector action sequence is 100 - 110 - 210 - 220 - 320 - 220 - 210 - 110 - 100; if the vector to be synthesized V ref is located in the 5th minor sector of the 1st major sector, the basic vector action sequence is 310 - 320 - 321 - 322 - 332 - 322 - 321 - 320 - 310; if the vector to be synthesized V ref is located in the 6th minor sector of the 1st major sector, the basic vector action sequence is 100 - 110 - 210 - 310 - 320 - 310 - 210 - 110 - 100; if the vector to be synthesized V ref is located in the 7th minor sector of the 1st major sector, the basic vector action sequence is 300 - 310 - 311 - 321 - 322 - 321 - 311 - 310 - 300; if the vector to be synthesized V ref is located in the 8th minor sector of the 1st major sector, the basic vector action sequence is 110 - 210 - 220 - 320 - 330 - 320 - 220 - 210 - 110; if the vector to be synthesized V ref is located in the 9th minor sector of the 1st major sector, the basic vector action sequence is 300 - 310 - 320 - 321 - 322 - 321 - 320 - 310 - 300; if the vector to be synthesized V ref is located in the 10th minor sector of the 1st major sector, the basic vector action sequence is 110 - 210 - 310 - 320 - 330 - 320 - 310 - 210 - 110.

[0104] If the vector to be synthesized V ref is located in the 1st minor sector of the 2nd major sector, the basic vector action sequence is 131 - 231 - 232 - 332 - 333 - 332 - 232 - 231 - 131; if the vector to be synthesized V ref is located in the 2nd minor sector of the 2nd major sector, the basic vector action sequence is 000 - 010 - 110 - 120 - 220 - 120 - 110 - 010 - 000; if the vector to be synthesized V refIf it is located in the 3rd minor sector of the 2nd major sector, the basic vector action sequence is 130 - 131 - 231 - 232 - 332 - 232 - 231 - 131 - 130; if the vector to be synthesized V ref If it is located in the 4th minor sector of the 2nd major sector, the basic vector action sequence is 010 - 110 - 120 - 220 - 230 - 220 - 120 - 110 - 010; if the vector to be synthesized V ref If it is located in the 5th minor sector of the 2nd major sector, the basic vector action sequence is 130 - 230 - 231 - 232 - 332 - 232 - 231 - 230 - 130; if the vector to be synthesized V ref If it is located in the 6th minor sector of the 2nd major sector, the basic vector action sequence is 010 - 110 - 120 - 130 - 230 - 130 - 120 - 110 - 010; if the vector to be synthesized V ref If it is located in the 7th minor sector of the 2nd major sector, the basic vector action sequence is 030 - 130 - 131 - 231 - 232 - 231 - 131 - 130 - 030; if the vector to be synthesized V ref If it is located in the 8th minor sector of the 2nd major sector, the basic vector action sequence is 110 - 120 - 220 - 230 - 330 - 230 - 220 - 120 - 110; if the vector to be synthesized V ref If it is located in the 9th minor sector of the 2nd major sector, the basic vector action sequence is 030 - 130 - 230 - 231 - 232 - 231 - 230 - 130 - 030; if the vector to be synthesized V ref If it is located in the 10th minor sector of the 2nd major sector, the basic vector action sequence is 110 - 120 - 130 - 230 - 330 - 230 - 130 - 120 - 110.

[0105] If the vector to be synthesized V ref If it is located in the 1st minor sector of the 3rd major sector, the basic vector action sequence is 131 - 132 - 232 - 233 - 333 - 233 - 232 - 132 - 131; if the vector to be synthesized V ref If it is located in the 2nd minor sector of the 3rd major sector, the basic vector action sequence is 000 - 010 - 011 - 021 - 022 - 021 - 011 - 010 - 000; if the vector to be synthesized V refLocated in the 3rd minor sector of the IIIrd major sector, the basic vector action sequence is 031 - 131 - 132 - 232 - 233 - 232 - 132 - 131 - 031; if the vector to be synthesized V ref Located in the 4th minor sector of the IIIrd major sector, the basic vector action sequence is 010 - 011 - 021 - 022 - 032 - 022 - 021 - 011 - 010; if the vector to be synthesized V ref Located in the 5th minor sector of the IIIrd major sector, the basic vector action sequence is 031 - 032 - 132 - 232 - 233 - 232 - 132 - 032 - 031; if the vector to be synthesized V ref Located in the 6th minor sector of the IIIrd major sector, the basic vector action sequence is 010 - 011 - 021 - 031 - 032 - 031 - 021 - 011 - 010; if the vector to be synthesized V ref Located in the 7th minor sector of the IIIrd major sector, the basic vector action sequence is 030 - 031 - 131 - 132 - 232 - 132 - 131 - 031 - 030; if the vector to be synthesized V ref Located in the 8th minor sector of the IIIrd major sector, the basic vector action sequence is 011 - 021 - 022 - 032 - 033 - 032 - 022 - 021 - 011; if the vector to be synthesized V ref Located in the 9th minor sector of the IIIrd major sector, the basic vector action sequence is 030 - 031 - 032 - 132 - 232 - 132 - 032 - 031 - 030; if the vector to be synthesized V ref Located in the 10th minor sector of the IIIrd major sector, the basic vector action sequence is 011 - 021 - 031 - 032 - 033 - 032 - 031 - 021 - 011.

[0106] If the vector to be synthesized V ref Located in the 1st minor sector of the IVth major sector, the basic vector action sequence is 113 - 123 - 223 - 233 - 333 - 233 - 223 - 123 - 113; if the vector to be synthesized V ref Located in the 2nd minor sector of the IVth major sector, the basic vector action sequence is 000 - 001 - 011 - 012 - 022 - 012 - 011 - 001 - 000; if the vector to be synthesized V refIf it is located in the 3rd minor sector of the 4th major sector, the basic vector action sequence is 013 - 113 - 123 - 223 - 233 - 223 - 123 - 113 - 013; if the vector to be synthesized V ref If it is located in the 4th minor sector of the 4th major sector, the basic vector action sequence is 001 - 011 - 012 - 022 - 032 - 022 - 012 - 011 - 001; if the vector to be synthesized V ref If it is located in the 5th minor sector of the 4th major sector, the basic vector action sequence is 013 - 023 - 123 - 223 - 233 - 223 - 123 - 023 - 013; if the vector to be synthesized V ref If it is located in the 6th minor sector of the 4th major sector, the basic vector action sequence is 001 - 011 - 012 - 013 - 023 - 013 - 012 - 011 - 001; if the vector to be synthesized V ref If it is located in the 7th minor sector of the 4th major sector, the basic vector action sequence is 003 - 013 - 113 - 123 - 223 - 123 - 113 - 013 - 003; if the vector to be synthesized V ref If it is located in the 8th minor sector of the 4th major sector, the basic vector action sequence is 011 - 012 - 022 - 023 - 033 - 023 - 022 - 012 - 011; if the vector to be synthesized V ref If it is located in the 9th minor sector of the 4th major sector, the basic vector action sequence is 003 - 013 - 023 - 123 - 223 - 123 - 023 - 013 - 003; if the vector to be synthesized V ref If it is located in the 10th minor sector of the 4th major sector, the basic vector action sequence is 011 - 012 - 013 - 023 - 033 - 023 - 013 - 012 - 011.

[0107] If the vector to be synthesized V ref If it is located in the 1st minor sector of the 5th major sector, the basic vector action sequence is 113 - 213 - 223 - 323 - 333 - 323 - 223 - 213 - 113; if the vector to be synthesized V ref If it is located in the 2nd minor sector of the 5th major sector, the basic vector action sequence is 000 - 001 - 101 - 102 - 202 - 102 - 101 - 001 - 000; if the vector to be synthesized V refLocated in the 3rd minor sector of the 5th major sector, the basic vector action sequence is 103 - 113 - 213 - 223 - 323 - 223 - 213 - 113 - 103; if the vector to be synthesized V ref Located in the 4th minor sector of the 5th major sector, the basic vector action sequence is 001 - 101 - 102 - 202 - 302 - 202 - 102 - 101 - 001; if the vector to be synthesized V ref Located in the 5th minor sector of the 5th major sector, the basic vector action sequence is 103 - 203 - 213 - 223 - 323 - 223 - 210 - 203 - 103; if the vector to be synthesized V ref Located in the 6th minor sector of the 5th major sector, the basic vector action sequence is 001 - 101 - 102 - 103 - 203 - 103 - 102 - 101 - 001; if the vector to be synthesized V ref Located in the 7th minor sector of the 5th major sector, the basic vector action sequence is 003 - 103 - 113 - 213 - 223 - 213 - 113 - 103 - 003; if the vector to be synthesized V ref Located in the 8th minor sector of the 5th major sector, the basic vector action sequence is 101 - 102 - 202 - 203 - 303 - 203 - 202 - 102 - 101; if the vector to be synthesized V ref Located in the 9th minor sector of the 5th major sector, the basic vector action sequence is 003 - 103 - 203 - 213 - 223 - 213 - 203 - 103 - 003; if the vector to be synthesized V ref Located in the 10th minor sector of the 5th major sector, the basic vector action sequence is 101 - 102 - 103 - 203 - 303 - 203 - 103 - 102 - 101.

[0108] If the vector to be synthesized V ref Located in the 1st minor sector of the 6th major sector, the basic vector action sequence is 311 - 312 - 322 - 323 - 333 - 323 - 322 - 312 - 311; if the vector to be synthesized V ref Located in the 2nd minor sector of the 6th major sector, the basic vector action sequence is 000 - 100 - 101 - 201 - 202 - 201 - 101 - 100 - 000; if the vector to be synthesized V refLocated in the 3rd minor sector of the 6th major sector, the basic vector action sequence is 301 - 311 - 312 - 322 - 323 - 322 - 312 - 311 - 301; if the vector to be synthesized V ref Located in the 4th minor sector of the 6th major sector, the basic vector action sequence is 100 - 101 - 201 - 202 - 203 - 202 - 201 - 101 - 100; if the vector to be synthesized V ref Located in the 5th minor sector of the 6th major sector, the basic vector action sequence is 301 - 302 - 312 - 322 - 323 - 322 - 312 - 302 - 301; if the vector to be synthesized V ref Located in the 6th minor sector of the 6th major sector, the basic vector action sequence is 100 - 101 - 201 - 301 - 302 - 301 - 201 - 101 - 100; if the vector to be synthesized V ref Located in the 7th minor sector of the 6th major sector, the basic vector action sequence is 300 - 301 - 311 - 312 - 322 - 312 - 311 - 301 - 300; if the vector to be synthesized V ref Located in the 8th minor sector of the 6th major sector, the basic vector action sequence is 101 - 201 - 202 - 302 - 303 - 302 - 202 - 201 - 101; if the vector to be synthesized V ref Located in the 9th minor sector of the 6th major sector, the basic vector action sequence is 300 - 301 - 302 - 312 - 322 - 312 - 302 - 301 - 300; if the vector to be synthesized V ref Located in the 10th minor sector of the 6th major sector, the basic vector action sequence is 101 - 201 - 301 - 302 - 303 - 302 - 301 - 201 - 101.

[0109] In the above step S5, the method for determining the action time of each basic vector in the vector sequence is as follows.

[0110] The calculation expression for the action time of each basic vector is:

[0111]

[0112] Among them, V sn_α and V sn_β are the components of the basic vector V sn on the α and β axes, k sn andj sn is the correlation coefficient for the DC bus capacitor voltage balance constraint, T s is the duration of one switching period, T Vsn represents the action time of the basic vector V sn within one switching period.

[0113] If the vector to be synthesized V ref is located in the first small sector of any large sector, its DC bus capacitor voltage balance constraint is:

[0114]

[0115] If the vector to be synthesized V ref is located in the second small sector of any large sector, its DC bus capacitor voltage balance constraint is:

[0116]

[0117] If the vector to be synthesized V ref is located in the third small sector of any large sector, its DC bus capacitor voltage balance constraint is:

[0118]

[0119] If the vector to be synthesized V ref is located in the fourth small sector of any large sector, its DC bus capacitor voltage balance constraint is:

[0120]

[0121] If the vector to be synthesized V ref is located in the fifth small sector of any large sector, its DC bus capacitor voltage balance constraint is:

[0122]

[0123] If the vector to be synthesized V ref is located in the sixth small sector of any large sector, its DC bus capacitor voltage balance constraint is:

[0124]

[0125] If the vector to be synthesized V refLocated in the 7th smallest sector of any large sector, the DC bus capacitor voltage balance constraint is:

[0126]

[0127] If the vector to be synthesized V ref Located in the 8th smallest sector of any large sector, the DC bus capacitor voltage balance constraint is:

[0128]

[0129] If the vector to be synthesized V ref Located in the 9th smallest sector of any large sector, the DC bus capacitor voltage balance constraint is:

[0130]

[0131] If the vector to be synthesized V ref Located in the 10th smallest sector of any large sector, the DC bus capacitor voltage balance constraint is:

[0132]

[0133] Next, taking a specific example to verify the discontinuous pulse width modulation method of the three-phase four-level inverter control circuit of the present invention. The AC voltage standard of the three-phase four-level inverter is 220V / 50Hz, the DC side input voltage is 900V, the power is 6kVA, and the switching frequency is 60kHz. Figure 3 It is the steady-state operation simulation waveform diagram of an example adopting the discontinuous pulse width modulation method of the control circuit of the three-phase four-level inverter of the present invention. Figure 3 In u cd1 is the voltage of the first DC bus filter capacitor. u cd2 is the voltage of the second DC bus filter capacitor. u cd3 is the voltage of the third DC bus filter capacitor. N sub is the vector to be synthesized. V ref is the small sector where it is located. u AO is the voltage of the A-phase bridge arm. i a is the output current of the A-phase inverter. φ is the power factor angle by which the grid voltage leads the output current of the inverter.

[0134] It can be seen that at Figure 3Under the three different power factor angles shown in (a), (b), and (c), the voltage of the second DC bus filter capacitor u cd2 remains balanced within the switching period and is always maintained at U dc / 3. The voltage of the first DC bus filter capacitor u cd1 and the voltage of the third DC bus filter capacitor u cd3 maintain dynamic balance around U dc / 3 within the power frequency period, achieving the natural balance of the DC bus capacitor voltage.

[0135] In addition, when the present invention is adopted, the voltage of each phase bridge arm is clamped in a specific area, indicating that the present invention has fewer switching times and can reduce the switching loss.

[0136] In summary, when the present invention is adopted, the DC bus capacitor voltage of the three-phase four-level inverter achieves natural balance. At the same time, the switching state of one phase bridge arm is clamped, the number of switching times is small, the switching loss is small, and the converter efficiency is high.

[0137] The embodiments are only used to illustrate the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A discontinuous pulse width modulation method for the control circuit of a three-phase four-level inverter. The three-phase four-level inverter is connected to a three-phase power grid, which includes an A-phase AC power supply, a B-phase AC power supply, and a C-phase AC power supply. The three-phase four-level inverter includes a DC power supply, a first DC bus filter capacitor, a second DC bus filter capacitor, a third DC bus filter capacitor, an A-phase bridge arm, a B-phase bridge arm, a C-phase bridge arm, an A-phase filter inductor, a B-phase filter inductor, a C-phase filter inductor, an A-phase filter capacitor, a B-phase filter capacitor, and a C-phase filter capacitor; The positive electrode of the DC power supply and the positive electrode of the first DC bus filter capacitor are respectively connected to both ends of point 3 on the DC side; the negative electrode of the first DC bus filter capacitor and the positive electrode of the second DC bus filter capacitor are respectively connected to both ends of point 2 on the DC side; the negative electrode of the second DC bus filter capacitor and the positive electrode of the third DC bus filter capacitor are respectively connected to both ends of point 1 on the DC side; the negative electrode of the third DC bus filter capacitor and the negative electrode of the DC power supply are respectively connected to both ends of point 0 on the DC side; O is the virtual midpoint of the DC side ， The voltage between it and point 0 on the DC side is half of the DC power supply voltage; It is characterized in that The discontinuous pulse width modulation method includes: Step S1, collect the DC bus voltage of the three-phase four-level inverter, and establish a four-level vector space in the complex plane according to the DC bus voltage. The four-level vector space is composed of 64 basic vectors, and the coordinates of each basic vector are calculated by the following expression: Among them, S A , S B , S C are the switching functions of phase A, phase B, and phase C respectively, and j is the imaginary unit; Switch function S X , X represents A, B, or C, and its calculation expression is: Among them, switch state 3 means X the output point of the phase bridge arm X is connected to point 3 of the DC side through a power switch tube, X the output point of the phase bridge arm X and the voltage between it and the virtual midpoint of the DC side O is half of the DC power supply voltage U dc ; switch state 2 means X the output point of the phase bridge arm X is connected to point 2 of the DC side through a power switch tube, X the output point of the phase bridge arm X and the voltage between it and the virtual midpoint of the DC side O is one-sixth of the DC power supply voltage U dc ; switch state 1 means X the output point of the phase bridge arm X is connected to point 1 of the DC side through a power switch tube, X the output point of the phase bridge arm X and the voltage between it and the virtual midpoint of the DC side O is one-sixth of the DC power supply voltage with the opposite sign; U dc switch state 0 means X the output point of the phase bridge arm X is connected to point 0 of the DC side through a power switch tube, X the output point of the phase bridge arm X and the voltage between it and the virtual midpoint of the DC side O is half of the DC power supply voltage with the opposite sign; U dc ​ Step S2: Divide the four-level vector space into 6 large sectors according to 64 basic vectors, and each large sector is further divided into 10 small sectors; Step S3: The active current PI regulator generates a d-axis control component according to the input signal through a dq / αβ converter u d and the reactive current PI regulator generates a q-axis control component according to the input signal u q to obtain the control components in the αβ coordinate system after transformation u α and u β calculate the coordinates of the vector to be synthesized V ref The calculation expression is: where j is the imaginary unit; Step S4, according to the coordinates of the vector to be synthesized V ref , obtain the large sector and small sector where the vector to be synthesized V ref is located. Select five basic vectors that do not act on the switching state of one phase in the four-level vector space to form a nine-segment basic vector action sequence; Step S5: Determine the action time of each basic vector in the basic vector action sequence according to the DC bus filter capacitor voltage balance constraint and the volt-second balance principle.

2. The discontinuous pulse width modulation method for the control circuit of a three-phase four-level inverter according to claim 1, characterized in that In step S1, the 64 basic vectors of the four-level vector space are respectively 333, 222, 111, 000, 322, 211, 100, 311, 200, 300, 321, 210, 310, 320, 332, 221, 110, 331, 220, 330, 231, 120, 230, 130, 232, 121, 010, 131, 020, 030, 132, 021, 031, 032, 233, 122, 011, 133, 022, 033, 123, 012, 023, 013, 223, 112, 001, 113, 002, 003, 213, 102, 103, 203, 323, 212, 101, 313, 202, 303, 312, 201, 302, 301, where 3 represents X the phase bridge arm is in switching state 3, 2 represents X the phase bridge arm is in switching state 2, 1 represents X the phase bridge arm is in switching state 1, 0 represents X the phase bridge arm is in switching state 0.

3. The discontinuous pulse width modulation method of the control circuit of a three-phase four-level inverter according to claim 2, characterized in that, In Step S2, the division rule of the large sectors is as follows: The first large sector is the area surrounded by the basic vectors 333, 300, and 330; the second large sector is the area surrounded by the basic vectors 333, 330, and 030; the third large sector is the area surrounded by the basic vectors 333, 030, and 033; the fourth large sector is the area surrounded by the basic vectors 333, 033, and 003; the fifth large sector is the area surrounded by the basic vectors 333, 003, and 303; the sixth large sector is the area surrounded by the basic vectors 333, 303, and 300.

4. The discontinuous pulse width modulation method for the control circuit of a three-phase four-level inverter according to claim 3, characterized in that, In Step S2, each large sector is divided into 10 small sectors according to the following rules: In the first major sector, the first minor sector is the part of the region enclosed by the midpoints of the lines connecting 322 and 311, the midpoints of the lines connecting 110 and 220, and 000 that is below the line connecting 000 and the midpoint of the line connecting 300 and 330; the second minor sector is the part of the region enclosed by the midpoints of the lines connecting 322 and 311, the midpoints of the lines connecting 110 and 220, and 000 that is above the line connecting 000 and the midpoint of the line connecting 300 and 330; the third minor sector is the part of the region enclosed by the midpoints of the lines connecting 322 and 311, the midpoints of the lines connecting 110 and 220, and the midpoints of the lines connecting 300 and 330 that is below the line connecting 000 and the midpoint of the line connecting 300 and 330 and to the lower left of the line connecting 321 and 300; the fourth minor sector is the part of the region enclosed by the midpoints of the lines connecting 322 and 311, the midpoints of the lines connecting 110 and 220, and the midpoints of the lines connecting 300 and 330 that is above the line connecting 000 and the midpoint of the line connecting 300 and 330 and to the lower left of the line connecting 321 and 330; the fifth minor sector is the part of the region enclosed by the midpoints of the lines connecting 322 and 311, the midpoints of the lines connecting 110 and 220, and the midpoints of the lines connecting 300 and 330 that is below the line connecting 000 and the midpoint of the line connecting 300 and 330 and to the upper right of the line connecting 321 and 300; the sixth minor sector is the part of the region enclosed by the midpoints of the lines connecting 322 and 311, the midpoints of the lines connecting 110 and 220, and the midpoints of the lines connecting 300 and 330 that is above the line connecting 000 and the midpoint of the line connecting 300 and 330 and to the upper right of the line connecting 321 and 330; the seventh minor sector is the part of the region enclosed by the midpoints of the lines connecting 322 and 311, 300, and the midpoints of the lines connecting 300 and 330 that is to the lower left of the line connecting 321 and 300; the eighth minor sector is the part of the region enclosed by the midpoints of the lines connecting 110 and 220, 330, and the midpoints of the lines connecting 300 and 330 that is to the left of the line connecting 321 and 330; the ninth minor sector is the part of the region enclosed by the midpoints of the lines connecting 322 and 311, 300, and the midpoints of the lines connecting 300 and 330 that is to the upper right of the line connecting 321 and 300; the tenth minor sector is the part of the region enclosed by the midpoints of the lines connecting 110 and 220, 330, and the midpoints of the lines connecting 300 and 330 that is to the right of the line connecting 321 and 330; In the second major sector, the first minor sector is the part on the left of the line connecting 000 and the midpoint of the line connecting 030 and 330 within the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 110 and 220, and 000; the second minor sector is the part on the right of the line connecting 000 and the midpoint of the line connecting 030 and 330 within the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 110 and 220, and 000; the third minor sector is the part on the left of the line connecting 000 and the midpoint of the line connecting 030 and 330, and below and to the left of the line connecting 231 and 030 within the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 030 and 330; the fourth minor sector is the part on the right of the line connecting 000 and the midpoint of the line connecting 030 and 330, and below and to the right of the line connecting 231 and 330 within the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 030 and 330; the fifth minor sector is the part on the left of the line connecting 000 and the midpoint of the line connecting 030 and 330, and above and to the right of the line connecting 231 and 030 within the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 030 and 330; the sixth minor sector is the part on the right of the line connecting 000 and the midpoint of the line connecting 030 and 330, and above and to the left of the line connecting 231 and 330 within the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 110 and 220, and the midpoint of the line connecting 030 and 330; the seventh minor sector is the part below and to the left of the line connecting 231 and 030 within the region enclosed by the midpoint of the line connecting 232 and 131, 030, and the midpoint of the line connecting 030 and 330; the eighth minor sector is the part below and to the right of the line connecting 231 and 330 within the region enclosed by the midpoint of the line connecting 110 and 220, 330, and the midpoint of the line connecting 030 and 330; the ninth minor sector is the part above and to the right of the line connecting 231 and 030 within the region enclosed by the midpoint of the line connecting 232 and 131, 030, and the midpoint of the line connecting 030 and 330; the tenth minor sector is the part above and to the left of the line connecting 231 and 330 within the region enclosed by the midpoint of the line connecting 110 and 220, 330, and the midpoint of the line connecting 030 and 330; In the third major sector, the first minor sector is the part in the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 011 and 022, and 000, which is to the upper right of the line connecting 000 and the midpoint of the line connecting 030 and 033; the second minor sector is the part in the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 011 and 022, and 000, which is to the lower left of the line connecting 000 and the midpoint of the line connecting 030 and 033; the third minor sector is the part in the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 030 and 033, which is to the upper right of the line connecting 000 and the midpoint of the line connecting 030 and 033 and to the right of the line connecting 132 and 030; the fourth minor sector is the part in the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 030 and 033, which is to the lower left of the line connecting 000 and the midpoint of the line connecting 030 and 033 and to the lower right of the line connecting 132 and 033; the fifth minor sector is the part in the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 030 and 033, which is to the upper right of the line connecting 000 and the midpoint of the line connecting 030 and 033 and to the left of the line connecting 132 and 030; the sixth minor sector is the part in the region enclosed by the midpoint of the line connecting 232 and 131, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 030 and 033, which is to the lower left of the line connecting 000 and the midpoint of the line connecting 030 and 033 and to the upper left of the line connecting 132 and 033; the seventh minor sector is the part in the region enclosed by the midpoint of the line connecting 232 and 131, 030, and the midpoint of the line connecting 030 and 033, which is to the right of the line connecting 132 and 030; the eighth minor sector is the part in the region enclosed by the midpoint of the line connecting 011 and 022, 033, and the midpoint of the line connecting 030 and 033, which is to the lower right of the line connecting 132 and 033; the ninth minor sector is the part in the region enclosed by the midpoint of the line connecting 232 and 131, 030, and the midpoint of the line connecting 030 and 033, which is to the left of the line connecting 132 and 030; the tenth minor sector is the part in the region enclosed by the midpoint of the line connecting 011 and 022, 033, and the midpoint of the line connecting 030 and 033, which is to the upper left of the line connecting 132 and 033; In the fourth major sector, the first minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 011 and 022, and 000, which is to the lower right of the line connecting 000 and the midpoint of the line connecting 003 and 033; the second minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 011 and 022, and 000, which is to the upper left of the line connecting 000 and the midpoint of the line connecting 003 and 033; the third minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 003 and 033, which is to the lower right of the line connecting 000 and the midpoint of the line connecting 003 and 033 and to the right of the line connecting 123 and 003; the fourth minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 003 and 033, which is to the upper left of the line connecting 000 and the midpoint of the line connecting 003 and 033 and to the upper right of the line connecting 123 and 033; the fifth minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 003 and 033, which is to the lower right of the line connecting 000 and the midpoint of the line connecting 003 and 033 and to the left of the line connecting 123 and 003; the sixth minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 011 and 022, and the midpoint of the line connecting 003 and 033, which is to the upper left of the line connecting 000 and the midpoint of the line connecting 003 and 033 and to the lower left of the line connecting 123 and 033; the seventh minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, 003, and the midpoint of the line connecting 003 and 033, which is to the right of the line connecting 123 and 003; the eighth minor sector is the part in the region enclosed by the midpoint of the line connecting 011 and 022, 033, and the midpoint of the line connecting 003 and 033, which is to the upper right of the line connecting 123 and 033; the ninth minor sector is the part in the region enclosed by the midpoint of the line connecting 223 and 113, 003, and the midpoint of the line connecting 003 and 033, which is to the left of the line connecting 123 and 003; the tenth minor sector is the part in the region enclosed by the midpoint of the line connecting 011 and 022, 033, and the midpoint of the line connecting 003 and 033, which is to the lower left of the line connecting 123 and 033; In the Vth major sector, the 1st minor sector is the part on the left of the line connecting 000 and the midpoint of the line connecting 003 and 303 within the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 101 and 202, and 000; the 2nd minor sector is the part on the right of the line connecting 000 and the midpoint of the line connecting 003 and 303 within the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 101 and 202, and 000; the 3rd minor sector is the part on the left of the line connecting 000 and the midpoint of the line connecting 003 and 303, and above and to the left of the line connecting 213 and 003 within the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 003 and 303; the 4th minor sector is the part on the right of the line connecting 000 and the midpoint of the line connecting 003 and 303, and above and to the right of the line connecting 123 and 303 within the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 003 and 303; the 5th minor sector is the part on the left of the line connecting 000 and the midpoint of the line connecting 003 and 303, and below and to the right of the line connecting 213 and 003 within the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 003 and 303; the 6th minor sector is the part on the right of the line connecting 000 and the midpoint of the line connecting 003 and 303, and below and to the left of the line connecting 123 and 303 within the region enclosed by the midpoint of the line connecting 223 and 113, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 003 and 303; the 7th minor sector is the part above and to the left of the line connecting 213 and 003 within the region enclosed by the midpoint of the line connecting 223 and 113, 003, and the midpoint of the line connecting 003 and 303; the 8th minor sector is the part above and to the right of the line connecting 213 and 303 within the region enclosed by the midpoint of the line connecting 101 and 202, 303, and the midpoint of the line connecting 003 and 303; the 9th minor sector is the part below and to the right of the line connecting 213 and 003 within the region enclosed by the midpoint of the line connecting 223 and 113, 003, and the midpoint of the line connecting 003 and 303; the 10th minor sector is the part below and to the left of the line connecting 213 and 303 within the region enclosed by the midpoint of the line connecting 101 and 202, 303, and the midpoint of the line connecting 003 and 303; In the sixth major sector, the first minor sector is the part of the area enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 101 and 202, and 000 that is to the upper right of the line connecting 000 and the midpoint of the line connecting 300 and 303; the second minor sector is the part of the area enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 101 and 202, and 000 that is to the lower left of the line connecting 000 and the midpoint of the line connecting 300 and 303; the third minor sector is the part of the area enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 300 and 303 that is to the upper right of the line connecting 000 and the midpoint of the line connecting 300 and 303 and to the upper left of the line connecting 312 and 300; the fourth minor sector is the part of the area enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 300 and 303 that is to the lower left of the line connecting 000 and the midpoint of the line connecting 300 and 303 and to the left of the line connecting 312 and 303; the fifth minor sector is the part of the area enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 300 and 303 that is to the upper right of the line connecting 000 and the midpoint of the line connecting 300 and 303 and to the lower right of the line connecting 312 and 300; the sixth minor sector is the part of the area enclosed by the midpoint of the line connecting 322 and 311, the midpoint of the line connecting 101 and 202, and the midpoint of the line connecting 300 and 303 that is to the lower left of the line connecting 000 and the midpoint of the line connecting 300 and 303 and to the right of the line connecting 312 and 303; the seventh minor sector is the part of the area enclosed by the midpoint of the line connecting 322 and 311, 300, and the midpoint of the line connecting 300 and 303 that is to the upper left of the line connecting 312 and 300; the eighth minor sector is the part of the area enclosed by the midpoint of the line connecting 101 and 202, 303, and the midpoint of the line connecting 300 and 303 that is to the left of the line connecting 312 and 303; the ninth minor sector is the part of the area enclosed by the midpoint of the line connecting 322 and 311, 300, and the midpoint of the line connecting 300 and 303 that is to the lower right of the line connecting 312 and 300; the tenth minor sector is the part of the area enclosed by the midpoint of the line connecting 101 and 202, 303, and the midpoint of the line connecting 300 and 303 that is to the right of the line connecting 312 and 303.

5. The discontinuous pulse width modulation method for the control circuit of a three-phase four-level inverter according to claim 4, characterized in that In step S4, the basic vector action sequence is determined according to the following rules: If the vector to be synthesized V ref is located in the 1st small sector of the Ith large sector, the basic vector action sequence is 311 - 321 - 322 - 332 - 333 - 332 - 322 - 321 - 311; if the vector to be synthesized V ref is located in the 2nd small sector of the Ith large sector, the basic vector action sequence is 000 - 100 - 110 - 210 - 220 - 210 - 110 - 100 - 000; if the vector to be synthesized V ref is located in the 3rd small sector of the Ith large sector, the basic vector action sequence is 310 - 311 - 321 - 322 - 332 - 322 - 321 - 311 - 310; if the vector to be synthesized V ref is located in the 4th small sector of the Ith large sector, the basic vector action sequence is 100 - 110 - 210 - 220 - 320 - 220 - 210 - 110 - 100; if the vector to be synthesized V ref is located in the 5th small sector of the Ith large sector, the basic vector action sequence is 310 - 320 - 321 - 322 - 332 - 322 - 321 - 320 - 310; if the vector to be synthesized V ref is located in the 6th small sector of the Ith large sector, the basic vector action sequence is 100 - 110 - 210 - 310 - 320 - 310 - 210 - 110 - 100; if the vector to be synthesized V ref is located in the 7th small sector of the Ith large sector, the basic vector action sequence is 300 - 310 - 311 - 321 - 322 - 321 - 311 - 310 - 300; if the vector to be synthesized V ref is located in the 8th small sector of the Ith large sector, the basic vector action sequence is 110 - 210 - 220 - 320 - 330 - 320 - 220 - 210 - 110; if the vector to be synthesized V ref is located in the 9th small sector of the Ith large sector, the basic vector action sequence is 300 - 310 - 320 - 321 - 322 - 321 - 320 - 310 - 300; if the vector to be synthesized V ref is located in the 10th small sector of the Ith large sector, the basic vector action sequence is 110 - 210 - 310 - 320 - 330 - 320 - 310 - 210 - 110; If the vector to be synthesized V ref is located in the 1st small sector of the 2nd large sector, the basic vector action sequence is 131 - 231 - 232 - 332 - 333 - 332 - 232 - 231 - 131; if the vector to be synthesized V ref is located in the 2nd small sector of the 2nd large sector, the basic vector action sequence is 000 - 010 - 110 - 120 - 220 - 120 - 110 - 010 - 000; if the vector to be synthesized V ref is located in the 3rd small sector of the 2nd large sector, the basic vector action sequence is 130 - 131 - 231 - 232 - 332 - 232 - 231 - 131 - 130; if the vector to be synthesized V ref is located in the 4th small sector of the 2nd large sector, the basic vector action sequence is 010 - 110 - 120 - 220 - 230 - 220 - 120 - 110 - 010; if the vector to be synthesized V ref is located in the 5th small sector of the 2nd large sector, the basic vector action sequence is 130 - 230 - 231 - 232 - 332 - 232 - 231 - 230 - 130; if the vector to be synthesized V ref is located in the 6th small sector of the 2nd large sector, the basic vector action sequence is 010 - 110 - 120 - 130 - 230 - 130 - 120 - 110 - 010; if the vector to be synthesized V ref is located in the 7th small sector of the 2nd large sector, the basic vector action sequence is 030 - 130 - 131 - 231 - 232 - 231 - 131 - 130 - 030; if the vector to be synthesized V ref is located in the 8th small sector of the 2nd large sector, the basic vector action sequence is 110 - 120 - 220 - 230 - 330 - 230 - 220 - 120 - 110; if the vector to be synthesized V ref is located in the 9th small sector of the 2nd large sector, the basic vector action sequence is 030 - 130 - 230 - 231 - 232 - 231 - 230 - 130 - 030; if the vector to be synthesized V ref is located in the 10th small sector of the 2nd large sector, the basic vector action sequence is 110 - 120 - 130 - 230 - 330 - 230 - 130 - 120 - 110; If the vector to be synthesized V ref is located in the 1st small sector of the 3rd large sector, the basic vector action sequence is 131 - 132 - 232 - 233 - 333 - 233 - 232 - 132 - 131; if the vector to be synthesized V ref is located in the 2nd small sector of the 3rd large sector, the basic vector action sequence is 000 - 010 - 011 - 021 - 022 - 021 - 011 - 010 - 000; if the vector to be synthesized V ref is located in the 3rd small sector of the 3rd large sector, the basic vector action sequence is 031 - 131 - 132 - 232 - 233 - 232 - 132 - 131 - 031; if the vector to be synthesized V ref is located in the 4th small sector of the 3rd large sector, the basic vector action sequence is 010 - 011 - 021 - 022 - 032 - 022 - 021 - 011 - 010; if the vector to be synthesized V ref is located in the 5th small sector of the 3rd large sector, the basic vector action sequence is 031 - 032 - 132 - 232 - 233 - 232 - 132 - 032 - 031; if the vector to be synthesized V ref is located in the 6th small sector of the 3rd large sector, the basic vector action sequence is 010 - 011 - 021 - 031 - 032 - 031 - 021 - 011 - 010; if the vector to be synthesized V ref is located in the 7th small sector of the 3rd large sector, the basic vector action sequence is 030 - 031 - 131 - 132 - 232 - 132 - 131 - 031 - 030; if the vector to be synthesized V ref is located in the 8th small sector of the 3rd large sector, the basic vector action sequence is 011 - 021 - 022 - 032 - 033 - 032 - 022 - 021 - 011; if the vector to be synthesized V ref is located in the 9th small sector of the 3rd large sector, the basic vector action sequence is 030 - 031 - 032 - 132 - 232 - 132 - 032 - 031 - 030; if the vector to be synthesized V ref is located in the 10th small sector of the 3rd large sector, the basic vector action sequence is 011 - 021 - 031 - 032 - 033 - 032 - 031 - 021 - 011; If the vector to be synthesized V ref is located in the 1st small sector of the 4th large sector, the basic vector action sequence is 113 - 123 - 223 - 233 - 333 - 233 - 223 - 123 - 113; if the vector to be synthesized V ref is located in the 2nd small sector of the 4th large sector, the basic vector action sequence is 000 - 001 - 011 - 012 - 022 - 012 - 011 - 001 - 000; if the vector to be synthesized V ref is located in the 3rd small sector of the 4th large sector, the basic vector action sequence is 013 - 113 - 123 - 223 - 233 - 223 - 123 - 113 - 013; if the vector to be synthesized V ref is located in the 4th small sector of the 4th large sector, the basic vector action sequence is 001 - 011 - 012 - 022 - 032 - 022 - 012 - 011 - 001; if the vector to be synthesized V ref is located in the 5th small sector of the 4th large sector, the basic vector action sequence is 013 - 023 - 123 - 223 - 233 - 223 - 123 - 023 - 013; if the vector to be synthesized V ref is located in the 6th small sector of the 4th large sector, the basic vector action sequence is 001 - 011 - 012 - 013 - 023 - 013 - 012 - 011 - 001; if the vector to be synthesized V ref is located in the 7th small sector of the 4th large sector, the basic vector action sequence is 003 - 013 - 113 - 123 - 223 - 123 - 113 - 013 - 003; if the vector to be synthesized V ref is located in the 8th small sector of the 4th large sector, the basic vector action sequence is 011 - 012 - 022 - 023 - 033 - 023 - 022 - 012 - 011; if the vector to be synthesized V ref is located in the 9th small sector of the 4th large sector, the basic vector action sequence is 003 - 013 - 023 - 123 - 223 - 123 - 023 - 013 - 003; if the vector to be synthesized V ref is located in the 10th small sector of the 4th large sector, the basic vector action sequence is 011 - 012 - 013 - 023 - 033 - 023 - 013 - 012 - 011; If the vector to be synthesized V ref is located in the 1st minor sector of the Vth major sector, the basic vector action sequence is 113 - 213 - 223 - 323 - 333 - 323 - 223 - 213 - 113; if the vector to be synthesized V ref is located in the 2nd minor sector of the Vth major sector, the basic vector action sequence is 000 - 001 - 101 - 102 - 202 - 102 - 101 - 001 - 000; if the vector to be synthesized V ref is located in the 3rd minor sector of the Vth major sector, the basic vector action sequence is 103 - 113 - 213 - 223 - 323 - 223 - 213 - 113 - 103; if the vector to be synthesized V ref is located in the 4th minor sector of the Vth major sector, the basic vector action sequence is 001 - 101 - 102 - 202 - 302 - 202 - 102 - 101 - 001; if the vector to be synthesized V ref is located in the 5th minor sector of the Vth major sector, the basic vector action sequence is 103 - 203 - 213 - 223 - 323 - 223 - 210 - 203 - 103; if the vector to be synthesized V ref is located in the 6th minor sector of the Vth major sector, the basic vector action sequence is 001 - 101 - 102 - 103 - 203 - 103 - 102 - 101 - 001; if the vector to be synthesized V ref is located in the 7th minor sector of the Vth major sector, the basic vector action sequence is 003 - 103 - 113 - 213 - 223 - 213 - 113 - 103 - 003; if the vector to be synthesized V ref is located in the 8th minor sector of the Vth major sector, the basic vector action sequence is 101 - 102 - 202 - 203 - 303 - 203 - 202 - 102 - 101; if the vector to be synthesized V ref is located in the 9th minor sector of the Vth major sector, the basic vector action sequence is 003 - 103 - 203 - 213 - 223 - 213 - 203 - 103 - 003; if the vector to be synthesized V ref is located in the 10th minor sector of the Vth major sector, the basic vector action sequence is 101 - 102 - 103 - 203 - 303 - 203 - 103 - 102 - 101; If the vector to be synthesized V ref is located in the 1st minor sector of the 6th major sector, the basic vector action sequence is 311 - 312 - 322 - 323 - 333 - 323 - 322 - 312 - 311; if the vector to be synthesized V ref is located in the 2nd minor sector of the 6th major sector, the basic vector action sequence is 000 - 100 - 101 - 201 - 202 - 201 - 101 - 100 - 000; if the vector to be synthesized V ref is located in the 3rd minor sector of the 6th major sector, the basic vector action sequence is 301 - 311 - 312 - 322 - 323 - 322 - 312 - 311 - 301; if the vector to be synthesized V ref is located in the 4th minor sector of the 6th major sector, the basic vector action sequence is 100 - 101 - 201 - 202 - 203 - 202 - 201 - 101 - 100; if the vector to be synthesized V ref is located in the 5th minor sector of the 6th major sector, the basic vector action sequence is 301 - 302 - 312 - 322 - 323 - 322 - 312 - 302 - 301; if the vector to be synthesized V ref is located in the 6th minor sector of the 6th major sector, the basic vector action sequence is 100 - 101 - 201 - 301 - 302 - 301 - 201 - 101 - 100; if the vector to be synthesized V ref is located in the 7th minor sector of the 6th major sector, the basic vector action sequence is 300 - 301 - 311 - 312 - 322 - 312 - 311 - 301 - 300; if the vector to be synthesized V ref is located in the 8th minor sector of the 6th major sector, the basic vector action sequence is 101 - 201 - 202 - 302 - 303 - 302 - 202 - 201 - 101; if the vector to be synthesized V ref is located in the 9th minor sector of the 6th major sector, the basic vector action sequence is 300 - 301 - 302 - 312 - 322 - 312 - 302 - 301 - 300; if the vector to be synthesized V ref is located in the 10th minor sector of the 6th major sector, the basic vector action sequence is 101 - 201 - 301 - 302 - 303 - 302 - 301 - 201 - 101.

6. The discontinuous pulse width modulation method of the control circuit of a three-phase four-level inverter according to claim 5, characterized in that, In step S5, the action time of each basic vector in the vector sequence is determined according to the following rules: The calculation expression for the action time of each basic vector is: Among them, V sn_α and V sn_β are the components of the basic vectors on the α and β axes, V sn and k sn and j sn are the correlation coefficients of the DC bus capacitor voltage balance constraint, T s is the duration of a switching period, T Vsn represents the action time of the basic vector V sn within a switching period; If the vector to be synthesized V ref is located in the first small sector of any large sector, the DC bus capacitor voltage balance constraint is as follows: If the vector to be synthesized V ref is located in the second smallest sector of any large sector, the DC bus capacitor voltage balance constraint is as follows: If the vector to be synthesized V ref is located in the third smallest sector of any large sector, the DC bus capacitor voltage balance constraint is as follows: If the vector to be synthesized V ref is located in the 4th smallest sector of any large sector, the DC bus capacitor voltage balance constraint is as follows: If the vector to be synthesized V ref is located in the fifth smallest sector of an arbitrarily large sector, the DC bus capacitor voltage balance constraint is as follows: If the vector to be synthesized V ref is located in the 6th smallest sector of an arbitrarily large sector, the DC bus capacitor voltage balance constraint is as follows: If the vector to be synthesized V ref is located in the seventh smallest sector of any large sector, the DC bus capacitor voltage balance constraint is as follows: If the vector to be synthesized V ref is located in the 8th small sector of any large sector, the DC bus capacitor voltage balance constraint is as follows: If the vector to be synthesized V ref is located in the 9th smallest sector of any large sector, the DC bus capacitor voltage balance constraint is as follows: If the vector to be synthesized V ref is located in the 10th smallest sector of any large sector, the DC bus capacitor voltage balance constraint is as follows: 。 7. A control circuit for a three-phase four-level inverter, characterized in that, The control circuit executes the discontinuous pulse width modulation method according to any one of claims 1-6.

8. The control circuit of a three-phase four-level inverter according to claim 7, characterized in that, The control circuit includes a MOSFET driving unit, an inductor current sampling unit, a grid voltage sampling unit, and a DSP control unit; The DSP control unit includes a first abc / dq converter, a second abc / dq converter, a phase-locked loop, a first subtractor, a second subtractor, a reactive current PI regulator, an active current PI regulator, a dq / αβ converter, and a DPWM controller; The three input terminals of the grid voltage sampling unit are respectively connected to the connection points of the A-phase filter capacitor and the A-phase AC power supply, the connection points of the B-phase filter capacitor and the B-phase AC power supply, and the connection points of the C-phase filter capacitor and the C-phase AC power supply; the output terminal of the grid voltage sampling unit is connected to the first input terminal of the first abc / dq converter; the three input terminals of the inductor current sampling unit are correspondingly connected to the connection points of the A-phase filter inductor and the A-phase bridge arm output voltage point A, the connection points of the B-phase filter inductor and the B-phase bridge arm output voltage point B, and the connection points of the C-phase filter inductor and the C-phase bridge arm output voltage point C; The output terminal of the inductor current sampling unit is connected to the first input terminal of the second abc / dq converter; The two output terminals of the first abc / dq converter are respectively connected to the two input terminals of the phase-locked loop. The output terminal of the phase-locked loop is connected to the second input terminal of the first abc / dq converter, the second input terminal of the second abc / dq converter, and the first input terminal of the dq / αβ converter. The first output terminal of the second abc / dq converter is connected to the first input terminal of the first subtractor. The given reference value 0 is input to the second input terminal of the first subtractor. The output terminal of the second subtractor is connected to the input terminal of the reactive current PI regulator. The second output terminal of the second abc / dq converter is connected to the first input terminal of the second subtractor. The given reference value i d_ref is input to the second input terminal of the second subtractor. The output terminal of the second subtractor is connected to the input terminal of the active current PI regulator. The second input terminal and the third input terminal of the dq / αβ converter are respectively connected to the output terminal of the reactive current PI regulator and the output terminal of the active current PI regulator. The two output terminals of the dq / αβ converter are respectively connected to the two input terminals of the DPWM controller. The output terminal of the DPWM controller is connected to the input terminal of the MOSFET driving unit. Each output terminal of the MOSFET driving unit is respectively connected to the gates of the power switching tubes of the A-phase bridge arm, the B-phase bridge arm, and the C-phase bridge arm, and drives signals corresponding to each power switching tube are output. The three-phase grid voltages sampled by the grid voltage sampling unit u sA 、 u sB 、 u sC After passing through the first abc / dq converter, the components in the dq coordinate system are obtained u d and u q and are sent to the phase-locked loop. Based on this, the phase-locked loop obtains the phase information of the grid voltage θ and the phase information θ is input into the first abc / dq converter, the second abc / dq converter, and the dq / αβ converter; The three-phase inductor currents sampled by the inductor current sampling unit i La 、 i Lb 、 i Lc After passing through the second abc / dq converter, the active components of the three-phase inductor currents are obtained i La 、 i Lb 、 i Lc and the reactive components i d and i q ; The active component i d is subtracted from the given reference value i d_ref by the second subtractor, and the difference is input into the active current PI regulator. The active current PI regulator generates the d-axis control component u d according to the input signal, and the d-axis control component u d is sent to the dq / αβ converter; The reactive component i q is subtracted from the given reference value 0 by the first subtractor, and the difference is input into the reactive current PI regulator. The reactive current PI regulator generates the q-axis control component u q according to the input signal, and the q-axis control component u q is sent to the dq / αβ converter; The dq / αβ converter converts the d-axis control component u d and the q-axis control component u q into the control components in the αβ coordinate system u α and u β , and input it into the DPWM controller.

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