A Three-phase And Three-level PV’s Grid Inverter Research And Design

With the rapid increase of energy requirement for economic globalization, thenon-renewable energy such as petroleum, coal, chemical industry and sources increasinglybecomes scarce; what’ more, the environmental pollution becomes increasingly serious; thedevelopment of new renewable energy has become an important strategic. Because solarenergy has lots of characteristics, for example, a wide range, convenient, unlimited storage,clean etc; it is called "the world’s most desirable green resources." This paper regardsthree-phase three-level photovoltaic grid-connected inverter system as the research object andstudies two important issues of photovoltaic grid-connected inverter, which are an in-depthstudy of the problem of MPPT and inverter control.Firstly, the MPPT control of photovoltaic cell is studied. Through studying the principleand equivalent model of photovoltaic cells, getting the output characteristic curves ofphotovoltaic cells. Then this paper focuses on the implementation process of incrementalconductance method. In addition, to meet the tracking precision and speed of system, variablestep incremental conductance method is put forward. When the external environment hasmutation, the method remains strong adaptability. In addition, the method has lots ofadvantages, such as simple controlling model, convenient calculation and high universality.Secondly, this paper emphasizes on the three-level inverter control method. It makes useof voltage space vector as phase three-level inverter control and research principles andmethods of SVPWM steps, which can reduce the switching frequency, weaken t he waveformdistortion of line current on the AC side and improve the power factor on the AC side. Thengrid control adopts the dual closed-loop control strategy and research on the structure of thecontrol system on the basis of dq coordinates. This paper design the double closed-loopcontrol system which regard voltage as the outer ring and regard current as inner ring, so thatPI controller parameters are obtained. At last, the system performance is analyzed. TheSimulink simulation shows that the control system can well follow voltage and currentwaveforms.Finally, according to the technical specifications of photovoltaic power generationsystem, this paper designs the hardware and software of system. The hardware part consists ofthe main circuit, control circuit, driver circuit, detection and conditioning circuit of voltageand current signals, fault detection and grid synchronization signal detection ect. The softwarepart is made up of the main program loop, interrupt routines and subroutines SVPWMgeneration.