Novel Complex Fractional Order Speed Controller for IM Drive Under Varying Operating Conditions With Enhanced Robustness

This article presents a novel complex fractional order (CFO) speed controller design and its implementation on an induction motor (IM) drive. This controller with multiple dimensions of control parameters as compared with existing industrial controllers provides more robust performance under variable operating conditions. Mostly, detuning of the existing controllers under varying operating parameters has limited bandwidth tolerance in low speed operation and temperature dependent circuit parameters, which is enhanced by the CFO controllers. A frequency domain design methodology for the CFO speed controller is incorporated with the fractional order (FO) nature of voltage source inverter fed IM. The realistic FO-IM transfer function model identification is provided with the chirp signal injection method. Within the designed bandwidth of a CFO speed controller, the surface curve fitting-based approximation technique provides ease in its implementation. The stator resistance variation up to 150% of nominal value and the rotor inertia variation up to eight times of the no-load value is tested to verify the performance under dynamic operating conditions. Under the same stability boundary limits, the results show the superiority of the CFO controller performance over FO proportional integral and integer order proportional integral controllers. On the hardware-in-loop system, the experimental validation of these controllers is performed.