Improved fractional order speed controller with non-linear VSI-IM model to enhance the load disturbance capability

The conventional PI-based speed controllers are susceptible to speed tracking error and limited load rejection capability. This paper presents the high-performance fractional-order PI speed controller (FOPI) for field oriented control of induction motor (FOC-IM) drives with enhanced disturbance rejection capability. The design of FOPI involves third-order voltage source inverter fed induction motor (VSI-IM) model identification, fitting it into the required phase margin and gain margin constraints and Oustaloups fractional element approximation. The identification algorithm using the hardware-in-loop system is provided. The non-linear integer order VSI-IM model improves the tracking and dynamic performance of the drive. The designed FOPI speed controller performance is compared with the literature’s existing FOPI controller design methods. The experimental analysis found that, in terms of speed tracking, parameter variations, inertia variations, and disturbance rejection capabilities, the suggested controller is more effective and resilient than existing tuning approaches. •A novel identification method based on a chirp signal is proposed to obtain an accurate integer order plant model for VSI-fed IM. Compared to existing identification techniques, the proposed method is more practical and yields comparable accuracy.•A robust FOPI controller is developed to address various operating conditions such as load disturbances, inertia changes, and parameter variations. The proposed controller’s speed control performance is evaluated in realistic field situations and found to be more robust than existng PI [ZN-method], FOPI (John etal, 2020), and FOPI (Sudheer and Aware, 2022) controllers.•The classical Oustaloup’s approximation method suitable for practical hardware implementation. A design procedure is presented to implement the FOPI controller for the identified nonlinear VSI-fed IM IO plant model. This makes the proposed controller more feasible for real-world induction motor applications.•A comparative study has been carried out on the Hardware-In-Loop (HIL) system with existing tuning rules of the FOPI controller and Ziegler and Nicholas (ZN) PI controller tuning method to evaluate the proposed design method advantages. The proposed controller’s error and control signals performance analysis, load disturbance rejection analysis, robustness against parameter and inertia variations are also demonstrated on the laboratory HIL prototype.