A Novel Current Source Converter-Based Ultra-High-Power Wind Energy Conversion System

In medium voltage (MV) ultra-high-power (over 10 MW) offshore wind energy conversion systems (WECS), current source converter (CSC)-based series-connected configurations are a good candidate. However, existing CSC-based WECS use a bulky low-frequency transformer (LFT), have a high rotor torque ripple or require an active rectifier with higher cost and lower reliability than a diode rectifier. To address these issues, the paper proposes a novel CSC-based series-connected MV WECS, combining the six-phase generator connected to two diode rectifiers with two medium frequency transformers (MFTs)-based modular converters on the generator side and using the conventional current source inverter (CSI) on the grid side. This configuration effectively mitigates rotor torque ripple caused by diode rectifiers. Additionally, the proposed modular converter has voltage and current imbalance issues, so a corresponding control scheme is proposed. Simulated verification is provided.