Research On A PV Grid-connected Inverter Module Based On The Time Domain Analysis Method

Energy development and utilization is becoming the bottleneck of thedevelopment of human society, So it is imperative to develop the green energy sourcefor human’s sustainable development. Solar energy because of its uniquecharacteristics has become one of the most promising green energy, so thatPhotovoltaic generation system has become an important direction of scholars, andthe grid connected inverter system is the key point of photovoltaic generation system.Because of the massive use of inductive load and non-linear loads, the reactive andharmonic current increase, the power line and the electrical equipment hazards tovarious degree. The Photovoltaic(PV) grid-connected inverter can compensate thereactive current and harmonic current while injecting active current to the grid. Thereare three key points when the inverter compensate the load current. First, the accuratedetection algorithm of harmonic current reactive current and active current. Second,an appropriate derivation of current commands so that the compensation of reactiveand harmonic current can be realized and the utilization rate of the inverter moduleincrease. Third, the suitable inverter topology and control algorithm, which makesthe control system has a rapid response and little steady state error.In this paper, the development of PV power generation and application prospect,the main technology of grid connected inverter system are reviewed. Then theinverter output mode, the PWM modulation, the mathematical model of single phasegrid-connected inverter and the compensation principle of active current and reactivecurrent are analysed.Then a module grid-connected PV inverter system is proposed which is basedon the time domain analysis. By calculating the average conductance and averagesusceptance, the load active current, reactive current and harmonic current areobtained. From the power quality control on the spot point of view, a strategy forsynthesizing the inverter command output current is proposed. The control target ofthe module inverter system is to compensate the harmonic current, reactive current,active current of the load and inject active current to the grid which is realized by means of PI close-loop control of the output current and the feed-forward control ofthe grid voltage.The inverter system is simulated by Matlab/Simulink. At the same time, thesystem hardware design and software design are introduced. The hardware design isconsist of the inverter main circuit, the snubber circuit, the driver circuit and signaldetection circuit. The software design mainly include the digital low-passfilter(DLPF), the all pass phase shift compensation network, sliding windowintegration and PI controller. The STM32F103micro-controller is used, theflowchart of its peripheral and the application program is presented.Finally, a test setup base on STM32F103is implemented, the experiment resultindicate that the PV grid-connected inverter module which is base on the timedomain analysis method has a good effect on compensating harmonic current,reactive current and active current of the load and injecting active current to the grid.Consequently the feasibility and correctness of the proposed method are verified.