The coordinated neutral point voltage balance control for back-to-back NPC converters used in the wind power system

The neutral point voltage balance control for back-to-back NPC converter used in the wind power application is researched in this paper. The two main operation modes are focused to analyze the possible problems of voltage balance control, based on which a coordinated control method for the neutral point voltage regulation is proposed to suppress its drift. According to the operation conditions of the wind power generation, only the grid side converter (GSC) has the voltage balance control function when it´s at standby mode or under light load conditions such as during the soft cut-in process, while the GSC predominates the voltage balance control when both GSC and rotor side converter (RSC) have the abilities to control neutral point (NP) voltage, but RSC only control the remaining NP voltage drift which GSC can´t control. Detailed simulation have proved that the coordinated control method can improve the neutral point voltage balance control ability.