Current sensorless sliding mode control for direct current-alternating current inverter with load variations via a USDO approach

Abstract

In this study, a current sensorless sliding mode control (SMC) approach is proposed for a direct current-alternating current inverter system. The SMC scheme shows advantages in dealing with matched disturbances and model uncertainties. However, it fails to remove the effects of mismatched disturbances. In distributed generation systems, wide range of load variations and effects of non-linear loads result in performance degradation. Load disturbances, as the mismatched disturbances, entry the system via a channel different from the control input. Load variations are coupled with the output voltage, resulting in periodic disturbances. Meanwhile, the cost increases significantly due to the requirement of wideband current sensors. In the existing current sensorless approaches, observers are designed to reconstruct current without considering disturbances. Addressing it, a novel universal state and disturbance observer (USDO) is developed to reconstruct the inductor current and load disturbances. By integrating the estimations into the design of sliding surface, a current sensorless sliding mode controller is proposed. Rigorous stability analysis for the closed-loop system is presented. Furthermore, considering higher-order harmonics, the baseline USDO is extended to reject these harmonics. Experimental results are illustrated to verify the effectiveness of the proposed scheme.