Three-phase modulation multi-level converter energy balance control method

Abstract

The invention provides a three-phase modulation multi-level converter energy balance control method which comprises the steps that 1, calculating each phase bridge arm loop current order values; 2, calculating average values of capacitance and voltage of each phase upper bridge arm sub module and average values of capacitance and voltage of each phase lower bridge arm sub module; 3, calculating each actual bridge arm loop current and modulation voltage for tracing bridge arm loop current order values; 4, calculating order values of each phase upper bridge arm voltage and order values of each lower bridge arm voltage; 5, calculating order values of each phase upper bridge arm input module number and order values of each phase lower bridge arm input module number; and 6, control sub modules of each phase upper bridge arm and each phase lower bridge arm to be input or cut off, according to order values of the upper bridge arm input module number, order values of the lower bridge arm input module number and bridge arm current direction obtained in the step 5. The three-phase modulation multi-level converter energy balance control method can guarantee internal energy balance control and simultaneously guarantees alternating current output characteristics.

Description

Technical field [0001] The invention belongs to the technical field of power system flexible direct current transmission, and specifically relates to a three-phase modular multilevel converter energy balance control method. Background technique [0002] Modular Multilevel Converter (MMC) adopts a new type of multilevel topology that is currently popular in the world. Its modular design and good scalability have broad application prospects in high-voltage direct current transmission and other fields. It is composed of multiple submodules (Submodule, SM) stacked, such as figure 1 As shown, by controlling the input and withdrawal of the sub-modules, the AC side output voltage can be controlled, thereby realizing AC and DC power exchange. At the same time, the output AC voltage waveform contains a lot of voltage steps to approximate the sine wave to the maximum, thereby reducing or even eliminating the need to configure a filter device. The core unit of the modular multilevel conve...

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Problems solved by technology

The above control method to a certain extent eliminates the impact of the double frequency fluctuation of the total sub-module capacitor voltage on the output voltage of the DC side, but the balance control of the internal energy of the converter during the AC grid asymmetry has not been discussed in detail

[0007] The above-mentioned two sub-module capacitor voltage balance control methods have common shortcomings: first, the two control methods are not designed to balance the capacitor voltage of the upper and lower bridge arms, and the total capacitor voltage balance; The goal of the bridge arm circulation control of the modular multilevel converter under working conditions is clarified

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