DC Voltage and Torque Ripple Mitigation in Modular PMSG Drives for Off-Shore Multi-MW WECSs with Linear SPWM modulation

A multi-modular axial flux machine is used for wind energy conversion systems (WECSs) where each module is connected to its own two-level converter. All converters are connected in series at the DC side to allow HVDC transmission. In the paper, an in-depth reasoning for the control of each individual voltage. A phase shift between PWM carrier signals of the neighbouring converters is implemented. A mathematical analysis is carried out. A criterion for the best choice of the phase shift to minimize dc voltage and torque harmonics is proposed.