Development Of Three-phase Photovoltaic Inverter

With the development of society and economy, human demand for energy is increasing.The energy crisis and environmental pollution become more and more serious, promoting theresearch on renewable energy power generation. Solar energy is clean, pollution-free, widelydistributed and nearly inexhaustible, therefore photovoltaic (PV) technology has been aresearch hotspot in recent years. In this paper, the three-phase PV inverter is taken as theresearch object, and deep study has been made in the following aspects: the main circuitworking principle and parameter design, the grid-connected control method, and the hardwareand software design based on DSP controller. Based on the research above, a prototype of thethree-phase PV grid-connected inverter has been built.Firstly, this paper analyzes the main circuit topology of PV grid-connected invertersystem. By comparing the principle and performance of several common three-phasephotovoltaic inverter main circuit topology, the single-stage non-isolated topology has beenadopted. Then, parameters calculation of DC capacitor, inverter output filter inductor andother main circuit element are analyzed in detail.After determining the main circuit scheme, a double closed-loop control strategy of DCvoltage outer-loop and AC current inner-loop for three-phase photovoltaic grid-connectedinverter has been presented. This paper respectively establishes the PI control model and thedeadbeat control model for AC current inner-loop. By theoretical analysis and simulationverification, the deadbeat control has been adopted. Then, by comparing principle andperformance of several common maximum power point tracking (MPPT) algorithms, thispaper presents a variable step size disturbance observer algorithm and its performance isverified by simulation. Finally, considering local load, this paper adopts passive voltagefrequency test as islanding detection method for the PV grid-connected system, and designsits software flow in detail.It is a key point to design the hardware and software based on DSP controller. Firstly,this paper introduces the design methods of the hardware circuits and its parameters in detail,including peripheral sampling circuit, zero capture circuit, protection circuit, serialcommunication circuit and so on. Then, this paper designs the software flow of main program,interrupt program and serial communication program.Finally, a simulation model for three-phase PV grid-connected inverter is built withPSIM to verify the its output characteristics. According to the analysis and design above, a prototype of the three-phase photovoltaic grid-connected inverter has been built in thelaboratory and has been used for testing its grid-connected performance. The experimentalresults prove the availability of the circuit topology and the control methods designed in thepaper.The conclusions in the paper could offer reference to PV grid-connected inverters systemof different power levels.