Modularized multi-level converter optimization control method actively using second harmonic generation loop current

Abstract

The invention relates to a modularized multi-level converter optimization control method actively using a second harmonic generation loop current, and belongs to the technical field of high-voltage high-capacity power electronic converter control. The method comprises the following steps: dynamically calculating alternating-current and direct-current reference voltages of a modularized multi-level converter according to a command sent by an upper-level controller; calculating an initial second harmonic generation loop current according to each parameter of an alternating current obtained according to real-time measurement; using reversion of the initial second harmonic generation loop current as a control target, and dynamically calculating the second harmonic generation loop current target value of the modularized multi-level converter; then overlaying a second harmonic generation reference voltage needing to be injected obtained according to dq decoupling control calculation to obtained alternating-current and direct-current reference voltages so as to obtain a bridge-arm reference voltage, carrying out pulse modulation and direct-current capacitor voltage balance control, and generating a pulse signal to carry out optimization control. According to the method, the direct-current capacitor voltage fluctuation can be greatly reduced, the optimization for the cost and volume of the modularized multi-level converter is effectively realized, and the method is particularly applicable to high-voltage large-capacity application occasions.

Description

technical field [0001] The invention belongs to the technical field of high-voltage and large-capacity power electronic converter control, and in particular relates to an optimal control method for a modular multilevel converter that actively utilizes double frequency circulating current. Background technique [0002] Modular multilevel converter is a voltage source power electronic converter, based on fully controlled power electronic devices such as insulated gate bipolar transistors and pulse width modulation technology, it can stably control active power and reactive power in AC and DC transfer between systems. The circuit principle of the modular multilevel converter is as follows: figure 1 shown. The modular multilevel converter includes three phase units a, b, and c, and each phase unit includes two bridge arms, that is, an upper bridge arm and a lower bridge arm, for a total of six bridge arms. The three phase units are connected in parallel between the DC positiv...

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Problems solved by technology

The conventional double-frequency circulating current control method aims to suppress the double-frequency circulating current to zero. Although it can reduce the converter loss to a certain extent, the effect of reducing the DC capacitor voltage fluctuation is not obvious.

Another double-frequency circulating current control method takes the minimum fluctuation of the DC capacitor voltage as the control target. Although it can minimize the fluctuation of the DC capacitor voltage, excessive reduction of the DC capacitor voltage fluctuation often requires a very large double-frequency circulating current. Not only will the loss of the converter increase significantly, but also because the current stress that the IGBT in the sub-module needs to bear rises sharply, it will make it difficult to select the IGBT, especially in high-voltage and large-capacity applications. It may not even be possible to select a suitable IGBT

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