Research On Novel Boost Circuit And Its Maximum Power Point Tracking Technology In PV Grid-connected System

With oil and natural gas and other fossil resources are gradually depleted, the continuous development of social economy and the increasing population, new energy technologies has become important issues of the international community and the academic world. The new kind of renewable energy---solar energy, which is safe and reliable and non-polluting, has great economic value. Countries in the world are increasing their attention and support of solar energy research.The development and utilization of solar energy has become an important way for humans to deal with environmental and energy crises.PV panels can convert solar energy into electrical energy to tens of volts of direct current. If people want to make use of it, it need to be converted to AC and then put into grid of with a load directly. In China power grid, the voltage generally requires 220VAC or 380VAC.Most common grid connected inverter of Voltage source type requires its DC input voltage higher than AC voltage peak, so PV panel output voltage need to be increased through voltage increase circuit first, then converted by the inverter.This paper reviews the development process of boost circuit in power electronic conversion technology, and analyzes the advantages and disadvantages of several existing major boost circuit topology. Analysis and comparison of existing major boost circuit topology show that multi-phase converter transformer can improve the power level, reduce voltage and current stress of the converter switches and transformers and other components, can also increase the margin in converter design, improve the performance of the converter. This paper takes a kind of boost circuit topology based on a high gain three-phase inverter. Through the adopting of series arrangement to transformer secondary side rectifier, the voltage gain of the converter improved. This paper also gives a alternately three-phase inverter control strategy, achieves the average sharing of the three-phase inductor current on the primary input side. The work mode of the half-bridge boost circuit in one switching cycle and the soft-switching condition of the transformer primary side switch is given in this paper and all switches achieve zero voltage turn. A three-phase inverter circuit is designed which its secondary structure in series based on boost half-bridge circuit, the circuit achieves the soft-switching of all switches, and the inverter needs no additional starting circuit, average current sharing can be achieved between the three-phase inductors. Secondary side rectifier circuit can acquire good equalizing. A control strategy implementations is proposed based on staggered TMS320F28335 controller, as well as the selection and design methods of the converter main circuit devices. This paper studies the PV grid system maximum power tracking problem, proposes improvement program of variable step disturbance observer method that combined with the boost DC circuit, also gives the maximum tracking strategy flow chart of PV systems which the after stage of DC circuit has voltage-boost characteristics.Partly, the project could solve the contradiction between state precision and dynamic performance, which exists in Maximum Power Point Tracking. This paper do a lot of PSIM simulation for the novel boost circuit and the maximum power tracking program in PV grid-connected system. The simulation results initially demonstrate the effectiveness and feasibility of the method proposed in this paper.