Optimization of the Winding Arrangement to Increase the Zero-Sequence Inductance of a Synchronous Machine With Multifunctional Converter Drive

An automotive electric-power-steering synchronous machine driven from a multifunctional converter has the advantage of increased system voltage. The integration of the boost converter in the inverter and the electrical machine leads to new requirements for the machine design due to dc currents and increased high-frequency ripple currents in the motor windings. In this paper, the ripple currents of a synchronous machine with a multifunctional converter are investigated. Three winding arrangements are analyzed and compared to reduce the ripple currents together with interleaved pulsewidth modulation. This paper contains finite-element simulations of the zero-sequence flux and analyses of the ripple currents with and without low-frequency ac modulation and, hence, when operated at high and low rotational speed. The magnitude of the ripple current depends on the zero-sequence inductance. By rearranging the coils in the stator slots, the zero-sequence inductance is significantly increased. Experimental results are correlating well with theoretical predictions and demonstrate that the phase and star-point ripple currents are almost halved.