Minimum time speed control of the induction motor drive using discrete time sliding mode

The Induction Motor (IM) and Permanent Magnet Synchronous Motor (PMSM) are widely used in the electric and hybrid-electric vehicle. To obtain fast dynamics during acceleration/braking, they are controlled using field-orientation. Typically, inner controllers are used for dq current control; additionally, the PMSM needs an outer speed controller while the IM needs both a speed and a flux controller. PI controllers are easy to use because they can be tuned without exact knowledge of the plant. Tuning by trial and error yields reasonable transient performance and zero steady-state error. However, if the objective is to accelerate or decelerate as fast as possible, this is not the best approach. This paper presents a design for the speed controller that moves the speed of the drive from one value to another in minimum time. Observers for the load torque are also presented; it is shown that using them does not really improve the speed dynamics. The paper presents a speed controller design based on optimal control concepts and discrete time sliding mode control.