Decoupled Control Strategy of a Back-To-Back Modular Multilevel Matrix Converter Operating in Low Frequency Ac Transmission Systems

Low Frequency Alternating Current (LFAC) transmission systems offer an efficient alternative to conventional high-voltage AC or DC transmission for connecting offshore wind parks to the onshore grid. The Modular Multilevel Matrix Converter (M3C) is an appropriate technology for this application as it performs direct conversion at high power and voltage levels. However, the need for bulky isolation transformers can increase size, weight, and volume while decreasing efficiency. Consequently, this paper proposes a novel M3C in back-to-back equipped with a medium-frequency transformer. A novel decoupled control strategy is proposed to regulate floating capacitor voltages, enable medium-frequency transformer regulation, and provide bidirectional power control. Further, a grid-forming and grid-following strategy is implemented at the converter ports to regulate the LFAC grid. Simulation results obtained with PLECS software demonstrate the effectiveness of the proposed decoupled control strategy providing regulation of the converter variables, medium-frequency and bidirectional power flow control. © 2024 IEEE