Thermal analysis of multilevel grid side converters for 10 MW wind turbines under Low Voltage Ride Through

As the power level of a single wind turbine is continuously pushed up even to 7 MW, the wind power generation system are required to be more reliable, and able to withstand extreme grid disturbances. Moreover, it is becoming a need that the wind power generation system should be more active, and able to contribute to the grid recovery by injecting reactive current during grid faults. Consequently, the full-scale power converter solutions are becoming more and more popular to fulfill the growing challenges in the wind power application. Nevertheless, the loading of the power devices in full-scale power converters, especially during grid faults may compromise the reliability performance and further increase the cost of the system. In this paper, three promising grid side multilevel converter topologies for the next generation 10 MW wind turbines are proposed and basically designed as case study. The operation status, as well as loss and thermal distributions of power devices are investigated, simulated and compared aimed at various Low Voltage Ride Through (LVRT) conditions. It is found that the all of the proposed converter topologies will suffer from higher junction temperature in some heavy loaded power devices especially the diodes under LVRT, and both of the three-level and five-level H-bridge topologies show more potential to reduce the device stress than the well-known threelevel Neutral Point Clamped topology.