Power conditioning of the output from a linear vernier hybrid permanent magnet generator for use in direct drive wave energy converters

A linear electrical generator may be used to convert the energy in sea waves directly into electrical energy. The reciprocating movement of the generator caused by the waves results in an electrical output that is variable in voltage and frequency, with a low-frequency amplitude oscillation of the same frequency as the reciprocating vertical movement of the waves. Power conditioning is required to extract the energy from the linear generator, and invert it into a mains supply of constant voltage and frequency. A type of power conditioner based on an AC/AC converter is illustrated. Inversion into the mains must take place at constant power by the power conditioner, which must therefore buffer the energy fluctuations produced by the wave energy device. The energy storage requirement for the power conditioner is derived as a function of the generated power, the reciprocating frequency of the wave energy device, the average AC/AC converter DC voltage and the capacitor voltage ripple. Results are presented for the operation of a prototype linear generator and power conditioner inverting into the three-phase supply.