| Abstract |
This paper presents a new structure for the speed control of surface mounted permanent magnet synchronous motors (PMSM) based on the inverse drive model (IDM). Compared to the classical cascade control structure, the IDM doesn’t require any current sensor because the current is not controlled. The inverter voltages are directly computed from the desired torque. Thus, contrary to the cascade structure, there is no limitation of the dynamic performance due to the delay of the inverter. The inverter voltage limits are considered in the IDM in order to avoid deviations of the estimated torque from its actual value. This can be achieved by a feedback of the DC-link voltage, which limits the derivative of the quadrature current. Above the base speed range the IDM operates even without supplementary non linear block or voltage controller for field weakening. It can be shown that, compared to the cascade control, the IDM has a higher dynamic over the whole speed range. In addition to its stability and the insensitivity to position error, the IDM operates at better efficiency than the cascade control when the motor is controlled above the base speed range. This is due to the fact that no voltage reserve is required at steady state. The amplitude of the voltage space vector is set to its maximum and torque changes are performed by phase shifts. It can be also proven that the proposed structure guaranties safety against accidental demagnetising of the magnets in the rotor. |
