Voltage ripple elimination in inductor-less AC-to-AC converters for multi-pole permanent magnet synchronous generators

This paper discusses reduction of the output voltage ripples in an inductor-less three-phase to single-phase converter for a multi-pole three-phase permanent-magnet synchronous generator having open-end stator windings. The converter consists of only two three-phase bridge converters, and no output filter inductor is installed. The analysis in this paper is conducted to reveal the output voltage ripples based on the equivalent circuit of the generator. Thus, the output voltage ripples are caused by the stability problems in the current feedback control due to a low zero-sequence impedance and the distorted EMF. To solve these problems, this paper proposes a new current control method based on αβ0 transformation and feed forward harmonic compensation. The proposed new control method has been examined in a 2-kW prototype of the inductor-less converter. As a result, the high-frequency ringings and 1.25 kHz harmonic voltage are suppressed, and the voltage THD has been also reduced from 8.4% to 3.7%.