Software controllers for permanent magnet synchronous motor drive

High performance brushless DC [BLDC] drives based on permanent magnet synchronous motor require fast acting current/torque controllers. The key to good torque control is the ability of the current control to track the current reference signals adequately. This paper describes approaches to achieve this objective using fully digital speed and current control structures in software. It will be shown that current regulated PWM (CRPWM) inverter using the asynchronous PWM/PI regulators has a phase lag problem. An improved controller which eliminates this problem using state feedback of the back EMFs in the current loop regulators is then demonstrated. Both these approaches do not regulate the d-axis dynamics when they are viewed in the synchronous reference frame. Better performance can be expected by performing the current regulation in the synchronous reference frame at the expense of more computation time. In this paper, the design and implementation issues of such a controller on a fully software platform are discussed. Experimental results of these implementations are also presented