Output power capability of surface PM generators with switched-mode rectifiers

Surface permanent magnet (SPM) machines operate with maximum output power for a given current when the induced voltage and the current are in phase. For an SPM generator this is obtained with a leading power-factor load. The inverter topology can achieve a leading input power-factor but this generally requires rotor position information. A lower-cost approach is to use a switched-mode rectifier (SMR) however with conventional modulation control its unity power factor operation results in a lower output power capability, particularly at low speeds. This paper examines performance of phase advance modulation methods to improve the low-speed output power capability of SPM generators when operated with a SMR. A simplified phase advance modulation called zero-epsilon is proposed. Analytical and simulation approaches are used to understand the fundamental limitations, and the results are then confirmed experimentally.