Study Of Grid-Connected Photovoltaic System Based On Z-Source Inverter

In order to make use of the renewable energy source, in the whole world, the technique of photovoltaic(PV) grid-connected is growing fleetly. The grid-connected inverter is the key element for the PV system. For making the whole PV generating system more flexible, reliable and improve the quality of electricity, a new Z-Source inverter topology may be adopted in the system. Base on the analysis of Z-Source, the whole PV grid-connected generating system is researched. The main contents of this paper are:1. The analysis of Z-Source topology and operation principle. For different bus output speciality, there are two modes : Voltage Mode Z-Source Inverter-VMZSI and Current Mode Z-Source Inverter-CMZSI. The operation principles of the two modes are analyzed. Lastly, by the compare with the traditional inverter, the advantages and disadvantages of Z-Source inverter are summarized.2. The analysis of VMZSI using State-Space averaging method. Putting the non-linearity and time change equation to linearity equation and getting the transfer functions.3. Analyzing the control strategies of PV grid-connected system based on VMZSI. Three loop configuration for whole control system is built: the grid current loop, Z-Source capacitance voltage loop and PV array output voltage loop. By the analysis of principles, the control adjustors have been designed through the root locus method.4. Designing the main circuit parameters for VMZSI. The grid inductance is chosen by satisfying the speediness of current tracking and restraining the harmonic;the Z-Source capacitance is chosen by restraining the ripple;the Z-Source inductance is chosen by satisfying not resonance and restraining the ripple;the PV array out filter capacitance is chosen by restraining the ripple.5. Analyzing and Summarizing the maximum power point tracking(MPPT) control method and non-islanding protection. The perturb & observe algorithms and Incremental Conductance Algorithm are mainly introduced for MPPT. The Sandia frequency shift method are main introduced for non-islanding protection, and realizing the reliable and operation stability.6. In order to validate the analysis conclude, a 3Kw PV grid-connected system based on VMZSI is built. The experiment results explain the validity.