1396 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 39, NO. 5, SEPTEMBER/OCTOBER 2003 Comparative Investigation of PWM Techniques for a New Drive for Electric Vehicles Andrzej M. Trzynadlowski, Fellow, IEEE, Zhiqiang Wang, James M. Nagashima, Member, IEEE, Costin Stancu, Member, IEEE, and Marcin H. Zelechowski, Student Member, IEEE Abstract—Results of a comparative investigation of determin- istic and random pulsewidth modulation (PWM) techniques to be employed in a new ac drive for electric vehicles are presented. The study, employing the advanced simulation package SABER from Avant! Corporation, was focused on the reduction of electro- magnetic interference (EMI) when a deterministic PWM strategy is replaced with an RPWM method. To assess the impact of the PWM technique on the drive performance, the drive efficiency, torque ripple, and dynamic response of the current control system were also investigated. Two RPWM techniques characterized by random variations of switching frequency of the inverter were considered: one with the sampling frequency of the modulator varying in step with the switching frequency, and one with a fixed sampling frequency equal to the average switching frequency. The study has demonstrated good EMI-mitigating potentials of RPWM techniques, whose use results in EMI reduction by 10 dB and more, while the drive performance is barely affected. Index Terms—AC drives, electric cars, electromagnetic inter- ference (EMI), inverter control, random pulsewidth modulation (RPWM). I. INTRODUCTION V ARIOUS means for size reduction have been considered for the ac drive for electric and hybrid vehicles, currently under development at a major automaker. One of them is the use of a random pulsewidth modulation (RPWM) technique in the inverter that supplies the motor driving the vehicle. Originally, RPWM has been developed to mitigate the acoustic noise emitted from inverter-fed ac drives, and numerous exper- imental studies have confirmed its usefulness in that respect, e.g., [1]–[3]. With respect to electric cars, the issue of acoustic noise is not important, thanks to the high switching frequencies employed and the efficient sound insulation in modern cars. Here, potentials of RPWM for reduction of electromagnetic interference (EMI), which have already been indicated in [4] and [5], are explored. It is expected that the EMI filter can be Paper IPCSD 03–077, presented at the 2002 Industry Applications Society Annual Meeting, Pittsburgh, PA, October 13–18, and approved for publication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by the Industrial Power Converter Committee of the IEEE Industry Applications Society. Manuscript submitted for review August 1, 2002 and released for publication June 23, 2003. A. M. Trzynadlowski and Z. Wang are with the Department of Electrical Engineering, University of Nevada, Reno, NV 89557-0153 USA (e-mail: chin@eng.unr.edu; richard_zq_wang@yahoo.com). J. M. Nagashima and C. Stancu are with the General Motors Advanced Tech- nology Center, Torrance, CA 90505 USA (e-mail: james.nagashima@gm.com; constantin.stancu@gm.com). M. H. Zelechowski is with the Institute of Control and Industrial Elec- tronics, Warsaw University of Technology, 00-662 Warsaw, Poland (e-mail: zelechom@ee.pw.edu.pl). Digital Object Identifier 10.1109/TIA.2003.816555 Fig. 1. Example frequency spectrum of inverter output voltage with DPWM. significantly downsized in comparison with that needed for an inverter controlled using deterministic PWM (DPWM). In order to evaluate this possibility, and to assess the impact of RPWM on the drive performance, a massive simulation study was commissioned. The software package SABER from Avant! Corp. was employed. Results of the study are presented in this paper. II. SCOPE OF THE STUDY The drive constitutes the classic cascade of a battery, a dc link, an inverter, and an ac motor. Contemporary automobiles are equipped with sensitive communication and control systems, making the issue of EMI radiated from the dc-supply cables very important. Modeling of the radiated EMI is difficult and inaccurate. Therefore, for the purpose of comparative analysis of the PWM techniques, the study was focused on frequency spectra of the battery current. The ac component of this current, subsequently referred to as current noise, is the main source of radiated EMI. To reduce the current noise, an EMI filter, a lumped or dis- tributed inductive–capacitive circuit, must be employed. The size of the filter is related to the desired degree of attenua- tion of harmonics of the current noise. Thus, flattening the fre- quency spectrum of the noise by replacing deterministic PWM (DPWM) with RPWM is expected to lead to reduction of the bulk and weight of the filter, which passes the whole supply 0093-9994/03$17.00 © 2003 IEEE