Optimized Transformer Winding Configurations for Bipolar Modular Ac-Ac Converter in Low-Frequency Transmission

Conventional AC-AC converters face challenges such as complex structures and limited control flexibility. A novel bipolar modular AC-AC converter (BMAC) addresses these challenges through a unique triple-winding transformer design. However, the triple-winding transformer in BMAC employs a Y0/Y0/Y6 winding configuration, which introduces third-order harmonic in output voltage and current. This paper focuses on optimizing the transformer winding configurations of the BMAC to address this problem. Twelve transformer winding connection configurations are proposed and differences in their mathematical models and control strategies are analyzed. The Y0/D5/D11 configuration is identified as the optimal choice, which reduces the 60 Hz third-order harmonic and the 150 Hz third-order harmonic. The transformer achieves a reduction in the total harmonic distortion. Simulation of a 300 MW BMAC system is conducted, and the results confirm the effectiveness of the Y0/D5/D11 configuration.