Manipulation of rotor flux for time-optimal single-step velocity response of field-oriented induction machines

A single-step time-optimal velocity response control of an induction motor by manipulation of rotor flux is proposed as a control strategy that maintains fast velocity response, even if the flux level is reduced, to attain high efficiency of low acoustic noise drives. This control scheme includes minimization of startup time from standstill and recovery time against impact load. However, the final value of rotor flux is unconstrained, and the proposed control scheme could not be implemented with a field-oriented controller, which accommodates the dynamically changing rotor flux. Introduction of the variable-flux concept causes the induction motor to be nonlinear. Therefore most of the optimal control problems are discussed only numerically. Saturation of the flux has also been treated and the analytical results show that the optimal solution is uniquely defined, being independent of the mechanical load conditions