Time-optimal control of DC-DC buck converter using single-input fuzzy augmented fractional-order PI controller

This paper presents a robust and optimal output-voltage tracking controller for a DC-DC buck converter. A fractional-order proportional-integral (FPI) controller is primarily used to eliminate the steady-state error and damp the oscillations. In order to improve the error convergence rate of the response, the FPI controller is augmented with a single-input fuzzy-logic based precompensator stage. The fuzzy precompensator aggregates the information regarding the error and error derivative using the signed-distance method. The derived aggregated signal is used to infer logical control decisions based on a predefined one-dimensional rule base. The simplification yields shorter computation time and a piecewise linear control surface that improves the system's immunity against exogenous disturbances and unprecedented nonlinearities. The error derivative is indirectly computed by measuring the capacitor current in real time. This modification further enhances the computational efficiency, offers minimum-time transient recovery, and compensates the hysteresis effect rendered by parasitic impedances. The controller gains are optimally selected using the particle swarm optimization algorithm. Credible hardware-in-the-loop experiments are conducted to validate the time optimality and robustness of the proposed controller. The experimental results clearly demonstrate the significant improvement rendered by the proposed controller in the system's reference tracking performance, disturbance-rejection capability, and transient recovery time.