Basic Modulation Strategy and Sub-module Voltage Balancing Control for Half-Wave Inverter AC-AC Converter

Flexible low-frequency transmission technology has competitive advantages in offshore wind power transmission, and the converter is the key equipment of flexible low-frequency transmission technology. According to the requirements of high-voltage and large-capacity scenarios, the topology and working principle of a half-wave variable-frequency AC converter applied to flexible low-frequency transmission are introduced. The topology can realize four-quadrant operation, and the number of sub-modules at the same voltage level is less than that of a modular multi-level matrix converter (M3C). On this basis, the modulation strategy and the sub-module capacitor voltage control are studied, and a sub-module capacitor voltage balance throwing strategy based on the nearest level approximation is proposed. This method can quickly realize the output voltage modulation, effectively control the capacitor voltage unbalance, and reduce the switching loss. Finally, MATLAB/Simulink simulation is used to verify the effectiveness of the proposed throwing strategy in the half-wave low-frequency AC converter.