Application of non-ideal resonant controllers for DC link voltage ripple reduction in large wind turbine converters

Medium voltage power conversion is increasingly being preferred as the technology of choice for large offshore wind turbines. This is primarily due to the reduced current rating as the voltage rating is increased, allowing sizeable reductions in cable cost and weight. With the application of low speed permanent magnet machines in wind turbines the main cause of mechanical failure, the gear box may be eliminated. This paper reviews the Cascaded H-Bridge topology, in a back to back structure with a conventional three phase inverter. The key drawback of this topology is the requirement of a large DC link capacitor. A non-ideal resonant controller is applied to attenuate the DC-link voltage ripple, allowing for sizeable reductions in the capacitance requirements. The performance of the control strategy is verified through simulation and experimentation.