Input-output feedback linearization based control for quasi-Z-source inverter in photovoltaic application

Abstract

The quasi-Z-source inverter (QZSI) has been presented suitable for solar photovoltaic applications mainly because of its one stage buck/boost capability and improved reliability. Carefully designed closed-loop control strategy is usually demanded by QZSI in photovoltaic applications for voltage boost, grid-connection and the maximum power point tracking (MPPT). Cascaded QZSI as to further step up voltage has even put on higher controlling requirements because of the interactive influence of one cascaded module on another. However, commonly used small signal analysis is a local linearization approach which is limited to represent the model of QZSI near its equilibrium point. Moreover, the high order state equation of the quasi-Z-source network usually provides hurdle for high performance controller with stable or fast response. This paper presents an input-output feedback linearization based control strategy for QZSI in two purposes: 1) to build a global linearized QZSI model with a wide operating range; and 2) to help design a controller with improved stable and dynamic performance. An average model for QZSI using state space averaging method is firstly developed. According to the analytic relation of system state variables, i.e. capacitor voltage and inductor current of the QZSI network, the fourth-order mathematical model is reduced to the second-order. Input-output feedback theory is applied to the state space averaging model, where inductor current is selected deliberately as the output of the controller's inner loop. A dc-link feedback loop is developed to validate the input-output feedback linearized model. Evidences are provided by simulation and experiment to show the effectiveness of the proposed controller, where the effect of unstable zero-dynamic on dc-link voltage is reduced, and consequently the transferring of disturbance from dc side to the ac side of the QZSI is mitigated effectively.