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In order to meet the energy storage requirements, a battery unit is required for the voltage-fed quasi Z-source inverter (qZSI) system in renewable energy applications. However, the order of the system will be increased accordingly, which make the control of the high order nonlinear systems more complicated. This paper presents a sliding mode current control based on fixed frequency operating with fast response and improved stability. Unlikely the conventional sliding mode control (SMC), the proposed controller engaged a fixed-frequency SMC based on the equivalent control theory to cooperate the modulation index and shoot through duty ratio. By establishing the large-signal dynamic model, the system will obtain a wide operating range to adapt to the renewable energy system. Using linear approximation, the small-signal model near steady-state operating point will be obtained to analysis the stable working conditions of the control system. Compared to the conventional current mode controller, the proposed controller can achieve a faster response, lower current ripple and better stability for qZSI when the supply and load variation is large. Experimental results are presented to validate the theoretical design and the effectiveness of the proposed controller.