Mitigation of Reflected Overvoltage in Wind Turbine Generator-Converter Systems with a Smart Coil Concept

In wind-turbine power generation systems, generators are typically located in the nacelles, and medium-voltage power converters are mostly placed at the bottom of the tower for maintenance convenience, resulting in long cables (e.g., 50–150 meters) interconnected between generators and power converters. Consequently, the high dv/dt caused by fast-switching high-voltage semiconductor devices such as silicon carbide (SiC) MOSFETs coupled with the long cables induces high-frequency reflected overvoltage across the generator stator windings. Due to uneven voltage distributions across various coils in each phase, significantly higher voltage spikes will be induced in the first few coils close to the converter side, leading to insulation degradation and winding short-circuit failures. To mitigate such reflected overvoltage across the generator windings and improve the wind-turbine system reliability, a high-efficiency, ultra-compact and low-cost mitigation solution targeting the first few coils will be developed and presented in this paper.