By the term permanent magnet (PM) synchronous generators (SGs), we imply here radial or axial air gap PM brushless generators with distributed (q greater than 1) or concentrated (q ≤ 1) windings & rectangular or sinusoidal current control having surface PM or interior PM (IPM) rotors.
A PMSG’s output voltage amplitude & frequency both are proportional to speed. In case of constant speed prime mover applications, PMSGs might carry out voltage self-regulation by appropriate design; i.e., inset or interior PM pole rotors. Small speed variation (from ±10 to 15%) may be suitable for diode rectified loads with series capacitors & voltage self-regulation. However, the majority applications require operation at variable speed, and, in this case, constant output voltage vs. load, be it direct current (DC) or alternating current (AC), requires full static power conversion & close-loop control.
