Modulation Methods for Neutral-Point-Clamped Wind Power Converter Achieving Loss and Thermal Redistribution Under Low-Voltage Ride-Through

The three-level neutral-point (NP)-clamped (3L-NPC) converter is a promising multilevel topology in the application of megawatt wind power generation systems. However, the growing requirements by grid codes may impose high stress and even give reliability problem to this converter topology. This paper investigates the loss and thermal performances of a 10-MW 3L-NPC wind power inverter undergoing low-voltage ride-through (LVRT) operation. A series of new space vector modulation methods is then proposed to relocate the thermal loading among the power switching devices. It is concluded that, with the proposed modulation methods, the thermal distribution in the 3L-NPC wind power inverter undergoing LVRT becomes more equal, and the junction temperature of the most stressed devices can be also relieved. Also, the control ability of the dc-bus NP potential, which is one of the crucial considerations for the 3L-NPC converter, is even more improved by the proposed modulation methods.