Parallel Converter Fed High-Performance PMSM Drive with Reduced Circulating Current Meant for High-Speed Applications

Abstract

High-speed permanent magnet synchronous motor (PMSM) drives are preferred for high-speed electric vehicle applications due to their high power density and efficiency. This project aims to enhance drive performance by reducing peak-peak torque ripple and total harmonic distortion (THD) in motor line current over the entire range of frequency. In this project, two parallel converter-fed permanent magnet synchronous motor drives are proposed and it is compared with the single converter-based Stan dard PMSM drive. Standard PMSM drive consists of a voltage source inverter (VSI) feeding a permanent magnet synchronous motor operated in vector control mode. Such motor drives operate at a fundamental frequency of more than 750 Hz and power levels ranging up to a few tens of kW (≥ 50 kW). The rated speed for PMSM used in the standard PMSM drive is 5500 rpm. High-speed operations result into high switching frequency for the inverter which can lead to switching energy losses reducing the efficiency of the drive and deteriorating the thermal performance of the drive. To restrict switching energy losses, the switching frequency is restricted below 10 kHz for standard PMSM drive. Thus, the pulse number (i.e., the ratio of switch ing frequency and fundamental frequency) drops below 15 over moderate and high fundamental frequency operation. Consequently, drive performance deteriorates sig nificantly in terms of total harmonic distortion in line current and peak-peak torque ripple. This project proposes parallel converter-based PMSM drive-I to improve mo tor line current THD and peak to peak torque ripple through carrier interleaving. Through carrier interleaving, the optimum interleaving angle can be analyzed which can reduce torque ripple significantly. An optimized interleaving angle is identified to confine high frequency circulating current within ratings of power converter while maintaining nearly minimum THD in motor line current. Operation of converters in parallel produces high circulating current which can increase energy losses in the drive. Thus, the performance of the drive deteriorates when operated for longer durations. To achieve a reduction in circulating current flowing between converters without compromising on line current THD and torque ripple, this project further proposes coupled inductors based PMSM drive-II. Proposed PMSM drive-II also uses vector control for the drive operation. Value for the coupled inductor is chosen in such a way that both the proposed PMSM drives can be fairly compared in terms of circulating current while maintaining the same motor line current THD and peak to peak torque ripple as the proposed drive-I. The performance of proposed PMSM drives I and II are compared with the standard PMSM drive in terms of line current THD and peak to peak torque ripple. Simulation results pertaining to three-phase, 50 kW, and 916 Hz PMSM drive are presented in the report to validate the propositions. A Trial version of plecs software is used to generate the results.