Disturbance observer-based sliding mode control for dynamic performance enhancement and current-sensorless of buck/boost converter

Bidirectional DC-DC converters are widely used in electric vehicle charger, where excellent steady-state and dynamic performances are crucial. However, those two performances are easily affected by external disturbances and parameter uncertainties. To solve this problem, this paper proposes a disturbance observer-based second-order sliding mode control (SOSMC) for the buck/boost converter. With the super-twisting algorithm (STA) second-order sliding mode control method, satisfactory steady-state and dynamic performance is achieved. In addition, to further improve the dynamic performance and reduce the control burden, a high-order sliding mode disturbance observer (HOSMDO) is employed to estimate the lumped disturbances. Thus, the mismatched disturbances caused by input voltage fluctuation, load variation, output voltage regulation, power flow change, and model uncertainties can be effectively suppressed. Moreover, the state variable containing inductor current is also observed, which removes one current sensor, reducing system cost. The design methods of the second-order sliding mode control and the high-order sliding mode disturbance observer are presented as well as the stability analysed through the Lyapunov theory. Simulation and experimental results verify the effectiveness of the proposed control strategy.