Loss and Rating Considerations of a Wind Energy Conversion System with Reactive Compensation by Magnetic Energy Recovery Switch (MERS)

Abstract

SummaryElectrical conversion system for permanent magnet wind generators is challenging due to the large rating of power semiconductor devices needed and the associated costs and losses. This motivates the search for new configurations improving these relationships. Additionally, due to the large inductance present in the generator (synchronous reactance), voltage drops results with resistive load and the generator output power is limited. Traditionally, a conventional active rectifier is used, with a 3-level type illustrated in Fig. 1a. The main challenges with this solution are the costs and also increased losses resulting from high speed switching and filter operation.A solution utilizing an active series compensation device combined with a diode bridge is investigated in this paper as shown in Fig. 1b. The series compensator supplies only reactive power with a resulting good generator utilization. This also means that the VA capability of the active semiconductor part can be reduced compared to an active rectifier since the active rectifier also needs to supply the full active power.The use of an active series compensator called Magnetic Energy Recovery Switch (MERS) is studied. MERS is a simple configuration with low switching losses and simple control acting as a variable capacitor. Due to the special characteristics of this configuration, a new IGBT with low on-state voltage has been developed. The performance of the configuration has been confirmed with experiments on a 50 kW multi-pole permanent magnet generator. Numerical investigations on large scale system indicate potential for loss reductions and power semiconductor rating reduction compared to using an active rectifier solution.