DC Current and torque ripple mitigation in modular PMSG drives for Multi-MW WECSs with linear PWM inverter modulation

The paper analyzes a torque and DC-current ripple mitigation strategy in a modular axial-flux permanent magnet synchronous generator for multi-MW Wind Energy Conversion Systems (WECSs). The machine modules are aligned with one another and driven by the same shaft. Each module is connected to its own two-level converter and the converters are paralleled at the DC side. In order to reduce the DC-side current harmonics and the ripple in the resultant torque, a phase shift between the converters' PWM carrier signals is implemented. The converters are operated within the linear PWM modulation range. A mathematical analysis is carried out. A criterion for the best choice of the phase shift in two- and three-module configurations is developed. Theoretical results are compared with those from simulations in Matlab/Simulink, verifying the soundness of the method.