Electrical machines for power generation in oscillating wave energy conversion system ? A comparative study

In this paper, system level design of an oscillating wave energy conversion system (WECS) using doubly-fed induction generator (DFIG) is compared with systems using squirrel-cage induction generator (SCIG) and permanent magnet synchronous generator (PMSG). The comparative study is carried out considering major hardware components and their rating requirements for each system. Although, SCIG and PMSG based systems are more simple and reliable, DFIG can enable compact and cost effective systems especially for high power WECS design. DFIG can generate power above its nominal rating at super-synchronous rotor speed and hence can offer an attractive solution for the oscillating power pattern of WECS. Moreover, rotor side control of the DFIG enables one to work with lower voltage and power level which effectively reduces the ratings of the power converters and other passive elements in the system. The system design comparison is performed with a wave energy converter (WEC) modeled for maximum power output around 500 kW. System operation with singly-fed generator (SCIG) and doubly-fed generator (DFIG) have been studied through simulation in real time simulator (OPAL-RT). The results of the comparison are shown with details of the major component rating of each system.