Optimization of the winding arrangement to increase the leakage inductance of a synchronous machine with multi-functional converter drive

An automotive electric power steering synchronous machine has been optimized for operation with a multi-functional converter. The multi-functional converter system integrates an inverter to drive the motor and a front-end boost converter to increase the dc-link voltage. The integration leads to new requirements for the machine due to dc currents and increased high-frequency ripple currents in the motor windings. In this paper the high-frequency ripple currents of a synchronous machine with multi-functional converter are investigated and three winding arrangements are analyzed and compared to increase the leakage inductances and therefore to reduce the high-frequency ripple currents. The paper contains analyses of the high-frequency ripple currents with and without low frequency ac modulation and hence, when operated at high and low rotational speed. An interleaved switching scheme is implemented to reduce the high-frequency ripple currents and evaluated for the given application. Experimental results are in good correlation with theoretical predictions and demonstrate the reduction of the high-frequency phase and star-point ripple currents with the optimized winding arrangement.