A robust control of permanent magnet synchronous motor using load torque estimation

Field-oriented control has made permanent magnet synchronous motor drives possible for the high performance applications. With a high-performance field oriented control system, the torque and flux producing components of the stator current are decoupled so that the independent torque and flux controls are possible as in DC motors. Thus, a high quality control of the stator current vector is essential for the successful implementation of the field-oriented control since the current controller has a direct influence on the drive performance. The current control schemes for a voltage source inverter-fed PMSM drive can be classified as hysteresis control, ramp comparison control, synchronous frame proportional-integral (PI) control, and predictive control. Among them, the predictive control is known to give a superior performance. However, this control scheme requires the information on the machine parameters and operation conditions with the sufficient accuracy, and cannot give a satisfactory response under parameter mismatch. To overcome such a limitation, the robust speed control of a PMSM using sliding mode control with load torque estimation is presented. The load disturbance is detected by the observer of an unknown and inaccessible input, and is compensated by the feedforward current. The proposed control schemes are applied to PMSM driven by a three-phase voltage-fed PWM inverter and the effectiveness is verified through the comparative simulations