CN-121984364-A - Neutral point balance control method of three-level inverter and three-level inverter

CN121984364ACN 121984364 ACN121984364 ACN 121984364ACN-121984364-A

Abstract

The application provides a neutral point balance control method of a three-level inverter and the three-level inverter, and belongs to the technical field of inverters. The method comprises the steps of generating a first discontinuous pulse width modulation wave and a second discontinuous pulse width modulation wave based on three-phase reference voltages input from the outside, respectively determining weighting coefficients corresponding to the two discontinuous pulse width modulation waves according to the current midpoint potential offset state of a three-level inverter and space vector sector information of the three-phase reference voltages, carrying out weighted fusion on the two discontinuous pulse width modulation waves according to the weighting coefficients to obtain a target three-phase modulation wave, generating a target driving signal based on a comparison result of a preset reference three-phase carrier wave and the target three-phase modulation wave, and sending the target driving signal to a switching tube circuit in the three-level inverter so as to balance midpoint potential of the three-level inverter. The application can reduce the switching loss and improve the neutral point potential balance capacity at the same time, thereby improving the system stability and the electric energy quality.

Inventors

FENG HONGYU
HUANG XIAOFENG
YU JIAN
WANG XIAORONG
BAI YONGGANG

Assignees

宁夏宝丰昱能科技有限公司

Dates

Publication Date: 20260505
Application Date: 20260206

Claims (10)

1. A method for controlling midpoint balance of a three-level inverter, the method being applied to a control module in the three-level inverter, the method comprising: Generating a first discontinuous pulse width modulation wave and a second discontinuous pulse width modulation wave based on an externally input three-phase reference voltage; according to the current midpoint potential offset state of the three-level inverter and space vector sector information of the current three-phase reference voltage, respectively determining a first weighting coefficient corresponding to the first discontinuous pulse width modulation wave and a second weighting coefficient corresponding to the second discontinuous pulse width modulation wave; According to the first weighting coefficient and the second weighting coefficient, carrying out weighted fusion on the first discontinuous pulse width modulation wave and the second discontinuous pulse width modulation wave to obtain a target three-phase modulation wave; And generating a target driving signal based on a comparison result of a preset reference three-phase carrier wave and the target three-phase modulation wave, and sending the target driving signal to a switching tube circuit in the three-level inverter so as to balance the midpoint potential of the three-level inverter.
2. The method of claim 1, wherein generating the first discontinuous pulse width modulation wave and the second discontinuous pulse width modulation wave based on the externally input three-phase reference voltage comprises: Injecting a first zero sequence voltage into an externally input three-phase reference voltage to generate the first discontinuous pulse width modulation wave; And injecting a second zero sequence voltage into the externally input three-phase reference voltage to generate the second discontinuous pulse width modulation wave.
3. The method according to claim 2, wherein before generating the first discontinuous pulse width modulation wave and the second discontinuous pulse width modulation wave based on the externally input three-phase reference voltage, comprising: Determining carrier upper boundary difference values and carrier lower boundary difference values corresponding to the three-phase reference voltages according to the three-phase reference voltages and preset reference three-phase carrier waves; Determining a minimum zero sequence voltage component and a maximum zero sequence voltage component corresponding to each phase reference voltage according to the carrier upper boundary difference value and the carrier lower boundary difference value corresponding to each phase reference voltage; determining the first zero sequence voltage according to the minimum zero sequence voltage component corresponding to each phase reference voltage; and determining the second zero sequence voltage according to the maximum zero sequence voltage component corresponding to each phase reference voltage.
4. The method for controlling the neutral point balance of the three-level inverter according to claim 1, wherein the current neutral point potential offset state includes a current neutral point potential offset and an absolute value of the current neutral point potential offset, and before determining the first weighting coefficient corresponding to the first discontinuous pulse width modulation wave and the second weighting coefficient corresponding to the second discontinuous pulse width modulation wave according to the current neutral point potential offset state of the three-level inverter and space vector sector information where the three-phase reference voltage is currently located, respectively, the method further includes: Acquiring positive bus voltage and negative bus voltage of the three-level inverter at the current moment, and acquiring externally input three-phase reference voltage; determining the current midpoint potential offset and the absolute value of the current midpoint potential offset of the three-level inverter according to the positive bus voltage and the negative bus voltage; and determining space vector sector information of the current three-phase reference voltage according to the space vector phase angle synthesized by the three-phase reference voltage.
5. The method of claim 4, wherein determining the first weighting coefficient corresponding to the first discontinuous pulse width modulation wave and the second weighting coefficient corresponding to the second discontinuous pulse width modulation wave according to the current neutral-point potential offset state of the three-level inverter and space vector sector information where the three-phase reference voltage is currently located, respectively, comprises: obtaining direct-current voltage of the three-level inverter, and determining a potential offset limit value according to the direct-current voltage and a preset voltage coefficient; and determining the first weighting coefficient and the second weighting coefficient according to the absolute value of the current midpoint potential offset, the potential offset limit value, the current midpoint potential offset and the space vector sector information.
6. The method according to claim 5, wherein determining the first weighting factor and the second weighting factor based on the absolute value of the current midpoint potential offset, the potential offset limit, the current midpoint potential offset, and the space vector sector information comprises: Judging whether the absolute value of the current midpoint potential offset is greater than or equal to the potential offset limit value; If yes, respectively determining the first weighting coefficient and the second weighting coefficient according to the current midpoint potential offset, the space vector sector information and the potential offset limit value, wherein the sum of the first weighting coefficient and the second weighting coefficient is 1; If not, determining that the first weighting coefficient is 1 and the second weighting coefficient is 0.
7. The method according to claim 6, wherein determining the first weighting factor and the second weighting factor based on the current midpoint potential offset, the space vector sector information, and the potential offset limit value, respectively, comprises: judging whether the current midpoint potential offset is greater than or equal to a preset potential offset limit value; If yes, respectively determining the first weighting coefficient and the second weighting coefficient according to the space vector sector information; If not, determining that the first weighting coefficient is 1 and the second weighting coefficient is 0.
8. The method of claim 7, wherein determining the first weighting factor and the second weighting factor according to the space vector sector information, respectively, comprises: Judging whether the space vector sector information is in an effective sector or not; if yes, determining the second weighting coefficient as a preset adjusting factor, and determining the first weighting coefficient according to the second weighting coefficient; If not, determining that the first weighting coefficient is 1 and the second weighting coefficient is 0.
9. The three-level inverter is characterized by comprising a filter, a switching tube circuit, a control module and two direct current supporting capacitors connected in series between a positive bus and a negative bus; One end of the filter is connected with an external alternating current power grid, the other end of the filter is connected with one end of the switching tube circuit, and the other end of the switching tube circuit is respectively connected with the positive bus, the negative bus and a common connection point of the two direct current supporting capacitors; The control module is configured to perform the steps of the midpoint balance control method of the three-level inverter of any one of claims 1-8, such that a midpoint potential of the three-level inverter is balanced.
10. An energy storage system comprising the three-level inverter of claim 9.

Description

Neutral point balance control method of three-level inverter and three-level inverter Technical Field The application relates to the technical field of inverters, in particular to a midpoint balance control method of a three-level inverter and the three-level inverter. Background With the rapid development of new energy power generation, energy storage systems and smart grids, the bidirectional inverter is used as a core device for realizing efficient and flexible energy conversion between direct current and alternating current, and is widely applied to the scenes of photovoltaic grid connection, battery energy storage, electric automobile charging and discharging and the like. Compared with the traditional two-level topology, the three-level bidirectional inverter can provide higher output voltage and better performance. The existing three-level bidirectional inverter generally adopts space vector pulse width modulation (Space Vector Pulse Width Modulation, SVPWM for short) to generate a modulated wave signal, but the control strategy has the problem of higher switching on and off frequency of a switch, so that the switching loss can be increased, and the service life of a switching tube is further shortened. Currently, to reduce switching losses, discontinuous pulse width modulation (Discontinuous PWM, abbreviated as DPWM) is introduced into three-level bi-directional inverters to reduce the number of switching actions and thus the switching losses. However, when the three-level bi-directional inverter adopts the DPWM technology to optimize the switching loss, a problem of midpoint voltage offset occurs, which makes two dc-side capacitors in the three-level bi-directional inverter not voltage-equalizing, wherein one capacitor can bear too high voltage stress, and the risk of device failure is increased. Meanwhile, the mode also introduces additional low-order harmonic components, so that the quality of output current is deteriorated, and the stability and the quality of electric energy of the system are affected. Disclosure of Invention The application aims to provide a midpoint balance control method of a three-level inverter and the three-level inverter, which can reduce switching loss and improve midpoint potential balance capacity at the same time, thereby improving the system stability and the electric energy quality. Embodiments of the present application are implemented as follows: In a first aspect of the embodiments of the present application, a midpoint balance control method of a three-level inverter is provided, where the method is applied to a control module in the three-level inverter, and the method includes: Generating a first discontinuous pulse width modulation wave and a second discontinuous pulse width modulation wave based on an externally input three-phase reference voltage; According to the current midpoint potential offset state of the three-level inverter and space vector sector information of the current three-phase reference voltage, respectively determining a first weighting coefficient corresponding to the first discontinuous pulse width modulation wave and a second weighting coefficient corresponding to the second discontinuous pulse width modulation wave; According to the first weighting coefficient and the second weighting coefficient, carrying out weighted fusion on the first discontinuous pulse width modulation wave and the second discontinuous pulse width modulation wave to obtain a target three-phase modulation wave; And generating a target driving signal based on a comparison result of the preset reference three-phase carrier wave and the target three-phase modulation wave, and sending the target driving signal to a switching tube circuit in the three-level inverter so as to balance the midpoint potential of the three-level inverter. As one possible implementation, generating the first discontinuous pulse width modulated wave and the second discontinuous pulse width modulated wave based on the externally input three-phase reference voltage includes: injecting a first zero sequence voltage into an externally input three-phase reference voltage to generate a first discontinuous pulse width modulation wave; and injecting a second zero sequence voltage into the externally input three-phase reference voltage to generate a second discontinuous pulse width modulation wave. As one possible implementation, before generating the first discontinuous pulse width modulation wave and the second discontinuous pulse width modulation wave based on the externally input three-phase reference voltage, the method includes: Determining carrier upper boundary difference values and carrier lower boundary difference values corresponding to the three-phase reference voltages according to the phase reference voltages contained in the three-phase reference voltages and a preset reference three-phase carrier; Determining a minimum zero sequence voltage component and a maximum zero sequence voltage