Speed control for field-weakened induction motor drive

The speed control of a field-weakened (FW) indirect field-oriented (IFO) induction motor drive with compensations for system dead-time and parameter variations is presented. Firstly, the DSP-based motor drive with a field-weakening mechanism is designed. To handle the command tracking and load rejection speed controls simultaneously, the proposed control scheme consists of a feedback controller and a command feedforward controller (FC) to possess two degrees of freedom (2DOF). The feedback controller is designed according to the given load rejection control requirements, and the command FC is set as the inverse plant model to let the tracking response follow the one defined by a reference model. Then, to reduce the effects of system dead-time and parameter variations on the speed control performance, a dead-time and disturbance compensator (DTDC) is proposed with its parameters being adapted by a variable-structure system (VSS). In addition to dead-time compensation, an estimated signal containing plant uncertainties and disturbances is generated and used for cancelling their effects on dead-time compensation control. Moreover, the tracking response is further enhanced by adaptively adjusting the parameters set in the FC and the DTDC according to the estimated mechanical inertia change. The practical considerations for simultaneously providing a good load rejection control response are also presented. Finally, the closed-loop regulation control is provided by adding a linear model following control (LMFC) scheme.