Robust digital pole-placer for electric drives based on uncertain diophantine equation and interval mathematics

In this paper, a novel robust digital controller design is proposed and implemented for induction motor speed control. The objective is to design a robust output feedback controller that places the closed-loop poles in a specified region in order to achieve the desired dynamic performance for a system with variable load. The design is carried out in the frequency domain by solving the uncertain Diophantine equation using interval mathematics and non-linear optimization method. In order to capture the load variations, the characteristic equation is relaxed and enlarged from a fixed-point to an interval set. A simple model-based design methodology is adopted in this work and implemented experimentally using a Hardware-in-the-Loop environment. The proposed design is simulated and then validated using real induction drive system. The proposed controller is compared with two other controllers: the auto tuned PID and a least-square-based robust controller. Experimental results show that the designed robust controller provides a better dynamic response than conventional controllers used in the industry when the motor's load is varied. These results validate the proposed design as the plant's output follows the reference signal with minimal overshoot and settling time.