Low-frequency operation integrated control system and method of modularization multi-level converters

Abstract

The invention discloses a low-frequency operation integrated control system and method of modularization multi-level converters. The system comprises M phase modularization multi-level converters. Each phase modularization multi-level converter is connected with an integrated control device thereof. The integrated control devices are connected with a PWM signal generator. The integrated control devices comprise low-pass filtering units, average value computing units C, upper bridge arm controllers, head controllers and lower bridge arm controllers. The modularization multi-level converters are connected with the low-pass filtering units respectively. The low-pass filtering units are connected with the upper bridge arm controllers, the lower bridge arm controllers and the average value computing units C respectively. The average value computing units C carry out output to the upper bridge arm controllers, the lower bridge arm controllers and the head controllers which are connected with the upper bridge arm controllers, the lower bridge arm controllers and the PWM signal generators. Sub-module capacitor voltage balance, low-frequency ripple wave restraining, ring current constrained control and bridge arm current control are achieved.

Description

technical field [0001] The invention relates to a low-frequency operation comprehensive control system and method of a modular multilevel converter, which belongs to the control field of multilevel power electronic power converters. Background technique [0002] Modular multilevel converters have lower harmonics and dU / dt in input / output voltages, do not require a large number of clamping diodes and flying capacitors, are easy to modularize, can operate in four quadrants, and do not require phase-shifting transformers, etc. It has become a research hotspot in the field of new energy at home and abroad. Modular multilevel converters have broad development prospects in high-voltage and large-capacity applications such as light DC transmission, reactive power compensation, and medium-high voltage AC speed regulation. The converter topology is as figure 1 As shown, each bridge arm is cascaded with N sub-modules, each sub-module is a half-bridge structure, and the same capacito...

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Problems solved by technology

[0006] The Chinese invention patent with the publication number CN103337977A "A Low-Frequency Mode Operation Control Method for Modular Multilevel Converters" also superimposes high-frequency zero-sequence voltage and high-frequency circulating current to suppress voltage fluctuations of sub-module capacitors, but only through the front Feedback superimposed circulating current, which limits the degree of suppression of low-frequency ripple, also does not involve circulating current constraint control; this method also uses bridge arm common-mode current feedback, which will lose current information of opposite polarity in the upper and lower bridge arm currents, and is prone to The internal circulation affects the balance control performance of the capacitor voltage in low-frequency conditions; the voltage outer loop adopts PI control, and there is a steady-state error in low-frequency ripple control

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