A Coordinated Control Method of Cascaded Multilevel Converter Based on Improved Time Series

Abstract

Cascaded multilevel converter is a new type of converter suitable for light DC transmission system. Its control performance has a direct impact on the operation stability of transmission system. In order to effectively control the output waveform of cascaded multilevel converter, the coordinated control method of cascaded multilevel converter based on improved time series is studied. According to the structure form of module unit, the cascaded multilevel converter is divided into the same unit and different units. The time series method is used to predict the AC side and DC side voltages of various cascaded multilevel converters. Considering that the AC side and DC side voltages of cascaded multilevel converters belong to non-stationary process, the difference method is used to improve the time series. The non-stationary process of voltage value is transformed into an approximately stationary random process. On this basis, the idea of phase-shifting carrier modulation strategy is adopted to equalize the capacitance of cascaded multilevel converter by reassigning the trigger pulse sequence of module. The experimental results show that this method can accurately predict the AC side and DC side voltage of the converter, and make more modules in series, and the output waveform will be very close to the sine wave, so as to realize the capacitor voltage equalization control of the module.