Multirate Cascaded Discrete-Time Sliding Mode Control With Dual-Loop Disturbance Estimation for Energy Storage Interfaces in DC Microgrids

Abstract

This paper presents a robust discrete-time sliding mode controller (DT–SMC) for a bidirectional DC/DC converter that is used as an energy storage interface in DC microgrids. The proposed controller is implemented in a hierarchical cascaded control structure comprising an inner current loop and an outer voltage loop, together with a current-reference limiter and duty-cycle saturation. Both loops adopt DT–SMC to achieve fast sampled-data tracking under nominal non-saturated operation. A multirate framework is implemented to balance dynamic performance, control accuracy, and computational complexity. To improve disturbance rejection, disturbance estimators (DEs) based on the sliding variable are incorporated in both loops and equipped with an anti-windup compensation to suppress error accumulation. The controller requires only the converter current and terminal voltages, facilitating practical digital implementation with fixed-frequency pulse-width modulation (PWM). Simulation results compare the proposed method with benchmark cascaded DT–PI and STA–SMC controllers, while experimental tests on a laboratory prototype confirm its practical feasibility. The presented results indicate chattering mitigation through reduced duty-cycle variation, accurate reference tracking, fast transient response, and disturbance rejection under the tested operating conditions.