Thermal optimised modulation methods of three-level neutral-point-clamped inverter for 10 MW wind turbines under low-voltage ride through

The three-level neutral-point-clamped (3L-NPC) converter is a promising multilevel topology for use in the megawatts wind power generation system. However, the requirements for the grid side inverter under low-voltage ride through (LVRT) of power grid could impose extreme stress to the switching devices in this converter topology. The study investigates the loss and thermal performances of a 10 MW 3L-NPC wind power inverter undergoing LVRT condition. A new space vector modulation method is proposed to optimise the thermal distribution of this extreme situation. It is concluded that, with the proposed modulation method, the thermal distribution in the 3L-NPC wind power inverter under LVRT becomes more equal and the junction temperature of the most stressed power device can be significantly reduced, whereas the control ability of DC-bus neutral point potential is not compromised.