Control requirements of direct drive wave energy converters

In a direct drive wave energy converter the electrical generator is directly coupled to the reciprocating motion of the waves, resulting in a variable frequency, variable voltage output with zero power dips within each wave cycle. Variable reluctance permanent magnet machines are capable of reacting the large forces required in a direct drive wave energy converter, but they suffer from low power factor. A power control strategy is presented for optimizing the electrical power from VRPM machines and for satisfying the grid requirements of constant voltage, frequency and power. Frequency tuning, control of wave energy devices using the electrical system is demonstrated by simulation of a test rig designed to emulate a wave energy converter.