Current harmonic compensation in symmetrical multiphase machines by resonant controllers in synchronous reference frames—Part 1: Extension to any phase number

Abstract

Low-order odd harmonics arise in practical multiphase drives because of the machine and converter nonlinear behavior (e.g., deadtime and saturation). If the windings are distributed, some of the harmonics cause torque ripple, while others cause losses. The latter is aggravated by the small impedance in the no-torque subspaces. The harmonics can be compensated without steady-state error by proportional-integral controllers in multiple synchronous reference frames (SRFs); however, a heavy computational load is required. In three-phase systems, the computational burden of this multiple SRF (MRF) scheme is often avoided by implementing instead resonant controllers (RCs) tuned at the harmonics that are multiples of six in an SRF rotating with the fundamental frequency. A similar structure has been proved to be satisfactory for deadtime compensation in an asymmetrical six-phase machine. Part 1 of this paper extends that harmonic current control strategy to symmetrical machines of any phase number. The optimum frequencies for the SRFs and for the RCs in each plane, so that the total number of RCs is minimized, are assessed. Part 2 studies the computational load and compares it with that of the MRF scheme.