Utilization of third harmonic-induced-voltages in PM generators

In permanent magnet (PM) generators used with rectifiers to produce a DC output, a trapezoidal generated voltage is often suggested advantageous. To help quantify and optimize assertion, the improvement in performance resulting from utilization of the third harmonic voltage is the topic of this paper. Two different topologies are studied; series rectification (SRS) and polyphase rectification. It is shown that, for a constant value of peak flux density, a maximum power gain of 15.5%, with respect to the pure sinusoidal case, can be obtained and that this gain is primarily a result of an increase in fundamental volts. The presence of a third harmonic in the flux density distribution yields higher core losses. For a constant peak flux density the hysteresis loss remains constant and the eddy current loss increases. However, the net increase in output power offsets the increment in core losses and a higher efficiency is achieved. The analytical predictions are compared to simulation results and experimental measurements for the three phase case. For the experimental set-up, having a third harmonic voltage of 20%, the overall efficiency is estimated to have increased by nearly 1% when compared to the pure sinusoidal case.