PWM modeling and application to disturbance observer-based precision motion control

In this paper, we address the problem relating to the precision motion control of PMLMs (permanent magnet linear motors) which are under the influence of significant disturbances. A mathematical model of a PMLM driven by a sinusoidal PWM (pulse width modulated) amplifier is first established. The PWM amplifier model used is obtained from a describing function analysis of the essentially nonlinear characteristics. The overall model (PWM+PMLM) inevitably inherits uncertainties in the face of load changes, system parameter perturbation, noise and inherent system nonlinearities etc., all constitute disturbances to the control system which will adversely affect the precision and accuracy achievable. A robust control scheme employing a disturbance observer is then proposed to address the sensitivity of the control performance to the disturbances. Real-time experimental results are provided to verify and confirm the practical effectiveness of the proposed approach