Power conversion and control of a pole-modulated permanent magnet synchronous generator for wave energy generation

This paper presents test results of the control of a pole-modulated permanent magnet synchronous generator (PM-PMSG) using a dedicated power conversion system to deliver power from an oscillating, low speed wave energy converter (WEC). Due to the low speed of the WEC, the size of the generator is increased and the machine is designed with large number of poles and concentrated winding. The electromotive force (emf) induced in the concentrated and not sufficiently distributed stator winding contains harmonic components which generate harmonic active power. Since the harmonic active power flows through the dc bus capacitor of the power converter, the frequency of the harmonic power can be the deciding factor for selecting the size of the capacitor. Lower frequency of the harmonic power can lead to large dc link capacitor. Since the concentrated winding is more economical with the simpler design and faster manufacturing, increasing the emf frequency is a better option to reduce the size of the capacitor. The fundamental frequency of the generator is increased by pole modulation. In this work, the control system for power conversion by the PM-PMSG is developed and the harmonic content in the power is analyzed. The generator is driven by a dc motor which emulates the characteristics of an oscillating WEC. An energy storage system is integrated at the dc link to smooth the output power. All corresponding experimental results are provided.