Abstract
Hybrid pulse width modulation schemes are widely used in high-power traction converters with a limited switching frequency. During the transition between modulation modes, sudden changes in the voltage harmonics cause the induction motor to enter a transient process, and ultimately lead to torque impacts, current shocks and other adverse effects. To improve the existing solution for such effects, theoretical support is provided in this paper by using an equivalent circuit model and a dynamic model of an induction motor, and a specific implementation scheme for a smooth transition is given considering the third-harmonic frequency component that appears in the phase voltage during the transition. The feasibility and correctness of the scheme are proven by a simulation and an experiment.
Highlights
The rail transit industry has always been aiming toward higher speed, higher stability and higher efficiency, and for this reason the insulated gate bipolar transistor (IGBT)-based induction motor (IM) propulsion system still dominates [1]
This paper considers a common hybrid pulse width modulation (PWM) scheme as an example and proposes a basic principle for a smooth transition between different modulation modes
HARMONIC CHARACTERISTICS To achieve a smooth transition among the PWM modes in the full speed range, first, it is necessary to identify the law governing the variation in the voltage harmonics when transitioning between two different kinds of PWM algorithms
Summary
The rail transit industry has always been aiming toward higher speed, higher stability and higher efficiency, and for this reason the insulated gate bipolar transistor (IGBT)-based induction motor (IM) propulsion system still dominates [1]. With the improvement of microprocessor chips, optimal synchronous modulation schemes, such as selected harmonic elimination PWM (SHEPWM) and current harmonic minimum PWM (CHMPWM), can deliver an acceptable performance with a low switching frequency and are widely used in traction propulsion systems [18]–[22]. Unlike the optimization results of CHMPWM, SHEPWM is designed to eliminate selected harmonics precisely [22], which will lead to sudden changes in the voltage harmonic components when transitioning between different PWM modes in the hybrid PWM scheme. More specific solutions in practical engineering scenarios were given in [23]–[25] but lacked theoretical support To solve this problem, this paper considers a common hybrid PWM scheme (asynchronous SPWM + synchronous SPWM + optimized synchronous modulation SHEPWM + square wave modulation) as an example and proposes a basic principle for a smooth transition between different modulation modes.
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