Method for controlling balance of direct current side of cascaded grid-connected inverter based on zero sequence and negative sequence voltage injection

Abstract

The invention discloses a method for controlling the balance of a direct current side of a cascaded grid-connected inverter based on zero sequence and negative sequence voltage injection. The method is based on the combination of zero sequence voltage and negative sequence voltage injection; and the method comprises the following steps of (1) integrally controlling the direct current voltage by using a control method of positive sequence current decoupling, and correcting the unbalance of the system on the basis of positive sequence decoupling, and decomposing network voltage and the positive and negative sequence of the current by using a second harmonic filtering method; and (2) controlling the phase balance of the direct current side, respectively calculating the zero sequence voltage component and the negative sequence voltage component needing injecting, starting the zero sequence voltage injection method under a normal condition, and using the negative sequence voltage injection method when the power difference of each phase is large according to switching conditions. Furthermore, when the zero sequence voltage injection is used, the condition that the maximum output phase voltage does not exceed the maximum value provided by the inverter needs to be satisfied. Through the method, three phases can be comprehensively combined; the voltage of different phase sequences can be injected under different conditions, the output performance and interphase power adjustment ability of the device are both considered; and for the application of three-phase cascaded grid-connected inverter matched renewable energy sources large-scale synchronization and large-scale energy storage, the method has an important value.

Description

technical field [0001] The invention relates to the technical field of application of high-voltage and high-power power electronic technology in electric power systems, in particular to a method for controlling interphase DC side balance of cascaded grid-connected inverters. Background technique [0002] In recent years, with the development of new energy, H-bridge cascade structure has become a research hotspot in the fields of grid-connected inverter, energy storage, power electronic transformer, etc. It is of great significance to enhance the stability of power system. [0003] This type of grid-connected inverter can be connected to the high-voltage power grid without a transformer. It is easy to realize modularization in structure, and has low switching loss and harmonic output. However, there are parallel connections on the DC sides of the independent H-bridges There are factors such as the difference of type loss and mixed type loss and the difference of pulse delay,...

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Problems solved by technology

[0003] This type of grid-connected inverter can be connected to the high-voltage power grid without a transformer. It is easy to realize modularization in structure, and has low switching loss and harmonic output. However, there are parallel connections on the DC sides of the independent H-bridges Type loss and mixed loss difference and pulse delay difference, there are factors such as voltage imbalance in the connected power grid, which causes the problem of voltage imbalance on the DC side

Compared with the cascaded static synchronous compensator (STATCOM), which is more mature in engineering applications, the cascaded grid-connected inverter itself may cause a greater The unbalanced difference will have a great impact on the output performance and reliability of the device

[0004] Chinese invention patent CN1514525 uses devices such as a voltage measuring instrument, a minimum capacitor voltage obtainer, a pulse width regulator, and a pulse amplifier to exchange active power between cascaded H-bridges, thereby realizing the balance control of the capacitor voltage. This method needs to be increased Additional devices increase the cost; Chinese invention patent CN102291030 calculates the voltage difference and obtains the offset through proportional integration, and then superimposes the offset on the basis of the original modulation wave to realize the voltage balance on the DC side without adding additional hardware device, but this method is based on a static coordinate system, the calculation is more complicated, and the proportional integral method requires a certain delay; the Chinese invention patent CN1913321 and the US invention patent US6075350 are also DC side voltage balance control methods based on control strategies, and their essence is the same as The Chinese invention patent CN102291030 is the same, and the offset value is obtained according to the power or voltage deviation of each H-bridge, and then superimposed on the modulation wave for adjustment and control

All the above are aimed at the intra-phase DC side balance control method of the cascaded inverter, and no research has been conducted on the balance control between the three phases.

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