A frequency approach for current loop modeling with a PWM converter

A new method based on a frequency approach is used to obtain a transfer function model of a DC permanent magnet actuator driven by a pulse width modulated (PWM) amplifier for robot applications. The paper investigates two carrier waves used in industrial applications with analog or digital control. The accurate model presented takes into account supply amplifier-motor dynamics and includes the input control voltage sampling effect. Advantages and limitations of both carriers and control waves are discussed. As a result, information about harmonics angle, magnitude and distortion are provided. The PWM model is tested through simulations and experiments with initially an open loop system then with a closed loop system, which introduces ripple current effect in the feedback control path.