Full digital controller of permanent magnet AC servo motor for industrial robot and CNC machine tool

A method which fully controls current and speed of the permanent magnet AC servomotor in the discrete time domain with high dynamic performance and wide bandwidth is discussed. The current controller, which controls motor current in the stationary d-q coordinates, consists of a nonlinear feedback controller compensating back EMF, a phase lead compensator, and a PI controller with gains varying according to motor speed. The final output of the current control algorithm is pulsewidth modulated through comparison with a digital triangular carrier signal to produce a PWM waveform. To obtain accurate estimation of motor speed, a speed observer is utilized in the speed control loop. Furthermore, a repetitive controller is applied in order to compensate errors in the position transducer. To investigate the control performance, the full digital servo control algorithm is applied to a SCARA robot with four degrees of freedom through execution on the control system based on the one-chip microprocessor