Performance analysis of a magnetic-geared linear permanent magnet generator for wave energy conversion

Ocean wave energy is a renewable energy source with a large potential that may contribute to increasing demand for power. Traditional conversion system uses hydraulic or air turbine to drive rotary electrical machines. The low efficiency and high cost in the transmission system become significant issues. Using direct-drive structure, linear permanent magnet(PM) machine eliminates intermediate transmission mechanism, and improves the efficiency of the overall system. Hence, linear PM machines have been receiving increasing attention in wave energy conversion. However, since the speed of reciprocating wave motion is low (typically 0.5m/s), the linear PM generator suffers from running at a low speed, thus significantly degrading its power density[1]. This paper proposes a magnetic-geared linear PM generator, which artfully integrates a linear magnetic gear(LMG) and a linear PM generator, for wave power generation. The low reciprocating wave motion is directly captured by the low-speed mover of the LMG. By the speed transformation of magnetic gear, the high-speed mover of the gear to actuate the linear PM generator, hence producing higher power density.