The Research On Three Phase Photovoltaic Grid-connected Inverter Control Strategy

As the world energy crisis and environmental pollution intensifies, the use of renewableresources which is attracting lots of attention. At present, there are two kinds of forms of solarenergy: heat utilization and photovoltaic power generation. Among them, photovoltaic grid isthe development trend of the solar energy utilization, it will be mainly used for load powerstation and roof photovoltaic system. Solar photovoltaic power generation is an importantform of utilization of solar energy and it is a power generation that using solar cell convertslight energy into electrical energy. Solar photovoltaic power generation from energy resources,raw materials and the application of environmental restrictions, and as technology continuesto progress, with broad prospects for development, it is one of the States to focus on thedevelopment of renewable energy technologies. Photovoltaic grid-connected inverter is thecore of energy conversion and control of photovoltaic grid system, its performance is not onlyto influence and decide the entire photovoltaic grid system to be stable, safe, reliable, andefficient to run, also affect the entire life of the system. In the photovoltaic grid system,system efficiency and the quality of output power are related to tracking control of powersystem,which is the core of the system and the key technology. As technology advances,inverter is more and more tend to small volume, high efficiency, low loss, integrated,intelligent.A variety of photovoltaic grid-connected inverter composition, with or withouttransformer classification of photovoltaic grid-connected inverter, its typical topology analysis,in accordance with the characteristics of the topology, the paper selected three-phase powerfrequency isolated photovoltaic grid-connected inverter as the research object and put forwardtwo commonly used control mode: grid voltage oriented vector control and directional gridvoltage direct power control.Grid voltage oriented vector control is essentially a current vector control, the currentcontroller is one of the key technologies for the control mode. This paper put forwaed twocurrent controller: PI controller and quasi-resonant controller. Power grid voltageorientation of direct power control is essentially respectively on instantaneous active powerp and reactive power q control, to achieve fast power response. This paper simulates the twocontrol modes with Matlab, and puts forward the simulation results of theoretical analysis,the analysis results show that the quasi-resonant controller is able to accurately track the sine wave current to the quantitative, and can effectively inhibit the grid harmonic currentcomponents in the current and improve grid power quality.The performance of phase-locked loop is a direct impact on the stability of the controlsystem, this paper proposes a three-phase software PLL which based on (d, q) coordinatesystem, its Matlab simulation, and the simulation results of theoretical analysis, the analysisshowed that the software PLL which based on (d, q) coordinate system be able to accuratelytrack the phase of the grid voltage, and to achieve rapid phase angle response.Based on the above control method designed in this paper a software control system,and the design of the control circuit and main circuit parameter design, equipped with athree-phase power frequency isolation-type photovoltaic grid-connected inverterexperimental device, through the analysis of the experimental results verify the correctnessof the simulation results.