Adaptive-Gain Second Order Sliding Mode Observer Design for Switching Power Converters

In this paper, a novel adaptive-gain, Second Order Sliding Mode (SOSM) observer for multi-cell converters is designed by considering it as a type of hybrid system. The objective is to reduce the number of voltage sensors by estimating the capacitor voltages from only measurements of the load current. The proposed observer is proven to be robust in the presence of perturbations with unknown boundaries. However, the states of the system are only partially observable based on the observability matrix rank condition. Because its observability depends upon the switching control signals, a recent concept known as Z(TN )-observability, which can be used to analyze the observability of hybrid systems, is used to address the switching behavior. Under certain conditions of the switching sequences, the voltage across each capacitor becomes observable. Simulation results and comparisons with a Luenberger switched observer demonstrate the effectiveness and the robustness of the proposed observer with respect to output measurement noise and system uncertainties (load variations).