An Efficient DSP–FPGA-Based Implementation of Hybrid PWM for Electric Rail Traction Induction Motor Control

• Published in: IEEE transactions on power electronics Vol. 33; no. 4; pp. 3276 - 3288
• Main Authors: Diao, Lijun, Tang, Jing, Loh, Poh Chiang, Yin, Shaobo, Wang, Lei, Liu, Zhigang
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-04-2018; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Computer simulation; Digital signal processing; Digital signal processor (DSP); Digital signal processors; Field programmable gate arrays; field programmable gate arrays (FPGA); Frequency modulation; Harmonic analysis; Harmonic distortion; hybrid pulse width modulation (PWM); Induction motors; low switching frequency; Microprocessors; Pulse duration modulation; Pulse width modulation; Rails; smooth transition; Switching; System reliability; Traction; traction motor
• ISSN: 0885-8993; 1941-0107
• DOI: 10.1109/TPEL.2017.2707639

Low switching frequency is always used in an electric rail traction induction motor control system, in order to reduce switching losses and increase system reliability. But under low switching frequency, the conventional single pulse width modulation (PWM) technique for the whole speed region will produce a large number of harmonic components, which in turn cause motor heating, torque ripple, and other adverse effects. In this paper, a hybrid PWM technique formed by merging carrier-based asynchronous and synchronous modulation and optimal synchronous modulation is proposed to achieve low losses and total harmonics based on very low switching frequency. A simple low-cost and low-power digital signal processor (DSP) and field programmable gate array (FPGA) hybrid hardware structure is then adopted for implementing the technique, which fully utilizes advantages and resources of each processor. Total harmonic distortion of the system can hence be reduced by operating with the high-precision hybrid PWM, while not compromising the multirate and multitask processing requirements of traction control. Detailed implementations in both DSP and FPGA with high accuracy, low usage of resources, and computational burden are then described, focusing particularly at the smooth transitions among different PWM schemes. Simulations and experiments are eventually performed with results captured for validating the presented hybrid PWM technique.