Torque and Current Ripple Reduction in PM Generator Based Multi Modular - Multi MW WECSs with Extended PWM Inverter Modulation

The paper presents a method to reduce both the torque ripple and the dc current ripple in the machine side converter, in a multi megawatt Wind Energy Conversion System, based on a PM Synchronous Generator which has a multi modular structure. Each converter module consists of a three-phase, two level inverter, operating as a rectifier, with PWM sinusoidal modulation. The first aim of the method is exploiting not only the linear PWM region but also over modulation region, in order to allow a higher AC voltage, with the same dc link voltage. The ripple mitigation is gained by means of a suited shifting among the carrier signals and the control signals in the several modules. The paper describes the method, and discusses the criteria that can be adopted to choose the suited shifting angles. Some simulation results are reported.