Synergistic speed control strategy for PMDC motor

This paper presents the synthesis of a linear-quadratic-regulator (LQR) augmented with a nonlinear-integral controller to optimize the speed regulation of a permanent magnet DC (PMDC) motor. The LQR utilizes the full state-feedback and minimizes the quadratic performance index to deliver optimal speed control decisions. However, the LQR lacks the ability to eliminate the steady-state error and damp the oscillations occurring during transients. For this purpose, the LQR is combined with an integral controller. In order to synergize the controller combination, the integral gain is dynamically varied via smooth hyperbolic secant function of error-dynamics in motor speed; such that, the contribution rendered by the integral-action increases as the response converges towards the reference speed and vice-versa. The results of real-time experiments are presented and analyzed to validate the effectiveness of the proposed controller.