Design For400W Single-phase Photovoltaic Grid-connected Inverter Based On Z-source Network

As the depletion of traditional fossil energy sources and theincreasing environmental pollution, the problem of energy andenvironment has become an important issue of concern to all countries.Researching and developing the clean renewable energy is the inevitablesocial development needs in order to achieve the goal of sustainabledevelopment. Photovoltaic generation technology is taking an importantrole in new energy power generation technology and it is also on thelimelight which has aroused a wide concern. The inverter is a major part inPV grid-connected system. The topology of traditional voltage sourceconverter has barriers and limitations which have bad influence to itsworking effect. Z-source inverter is a new type of inverter structureemerged in recent years. The special Z-source network topology canovercome the defects such as poor reliability, the dead zone in controlsystem, low working efficiency of the traditional inverter. This dissertationfocuses on the design for the400W single-phase photovoltaicgrid-connected inverter based on Z-source network.Firstly, this dissertation introduced the development and trends ofBIPV technology which is the specific application background for myresearch. The research showed the defects of traditional invert byanalyzing the topology and application. I elaborated the basic workingprinciple and control method of the Z-source network, then made themathematical model using the state space averaging method and finished the small signal analysis. I also derived the calculation for the Z-sourcecapacitor, Z-source inductor, the grid-connected inductor and the LCLfilter network. These parameter values are the foundation for thesimulation analysis and experimental prototype validation.According to the special topology of the Z-source inverter and therequirement of the PV grid-connected system, the dissertation designed thewhole control strategy for the single-phase photovoltaic grid-connectedinverter based on the Z-source network. The entire control systemconsisted of three closed-loop structures: the MPPT vector loop, the outerbus voltage loop, the grid-connected AC current loop. The MPPT methodis proposed combined Constant Voltage (CV) method with the Perturb andObserve (PO) method. I designed a lead compensation controller for theZ-source network boost control to stable the capacitor’s voltage andimprove the stability of the inverter control system. The grid-connectedAC current control is proposed combined the quasi-PR controller with theZ-source capacitor voltage control for the grid current. The simulationmodel was built in Matlab/Simulink and such results verified the effect ofcontrol strategies.A400W experimental prototype of single-phase PV grid-connectedinverter based on Z-source network using DSP TMS320F2812controllerwas built after finishing above research. The experimental results showedthat when the prototype worked in the normal operating state, the outputpower is400W and the output current had the same frequency and phasewith the grid voltage. The prototype worked in the unity-power factor stateand its quality of output achieved the design goals. For the further study,the output waveforms of the prototype were in agreement with thewaveforms of the simulation model. The simulation and experimentalvalidation have played the supporting role for the earlier theoreticalresearch.The innovation of this paper is that:1) derive calculation formulas forthe Z-source capacitor, Z-source inductor of network, the grid-connected inductor and the filter. These parameter values are the foundation for thesimulation analysis and experimental prototype validation2) design thewhole three closed-loop control structures for the single-phase Z-sourcegrid-connected inverter. The MPPT method is proposed combinedConstant Voltage (CV) method with the Perturb and Observe (PO) method.Using a lead compensation controller for the Z-source network boostcontrol to stable the capacitor’s voltage and improve the stability of theinverter control system. The grid-connected AC current control is proposedcombined the quasi-PR controller with the Z-source capacitor voltagecontrol for the grid current.3) A400W experimental prototype ofsingle-phase PV grid-connected inverter based on Z-source network usingDSP TMS320F2812controller was built. The output current had the samefrequency and phase with the grid voltage. The prototype worked in theunity-power factor state and its quality of output achieved the design goals.The simulation and experimental validation have played the supportingrole for the earlier theoretical research.