The voltage-fed Z-source inverter/quasi-Z-source inverter (ZSI/qZSI) has been presented suitable for photovoltaic (PV) applications mainly because of its single-stage buck and boost capability and improved reliability. This paper further addresses detailed modeling and control issues of the quasi-Z-source inverter (QZSI) used for distributed generation (DG), such as PV or fuel cell power conditioning. The dynamical characteristics of the qZSI-network are firstly investigated by small-signal analysis. Based on the dynamic model, stand-alone and grid-connected operation with closed-loop control methods are carried out, which are the two necessary operation modes of DG in distributed power grids. Due to the mutual limitation between the modulation index and shoot-through duty ratio of qZSI, constant capacitor voltage control method is proposed in a two-stage control manner. Minimum switching stress on devices can be achieved by choosing a proper capacitor voltage reference. Experimental results are presented for validation of the theoretical analysis and controller design.Index Terms-Dc-ac converter, distributed generation, Quasi-Z-Source inverter, renewable energy source.

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In this paper the Quasi-Z-Source Inverter (QZSI) with Energy Storage for Photovoltaic Power Generation Systems is presented. The energy storage device was integrated to QZSI topology with no need for an extra charging circuit. This upgraded topology acquires the operating characteristics from the traditional QZSI, plus the capability of operating under very low PV power conditions. Its main operating points are classified into two modes, the low PV power mode, where the battery is discharged and the high power mode, where the battery is charge up. An extended input power operating range is achieved since the lack of Photovoltaic power can be compensated by the battery. Quasi-Z-Source inverters are very suitable for Photovoltaic power generation systems and this upgrade makes them even more suitable for this type of applications. To obtain the experimental data, a prototype was built and used to demonstrate that the Quasi-Z-Source inverter is capable of managing the State of Charge of a battery and the AC output voltage in each operating mode.

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