Research On Power Quality And Interaction In High Permeability Photovoltaic Grid-connected System

Energy is the basis of human survival and development. Traditional non-renewable energy such as coal and oil is diminishing and it will be depleted someday. Moreover, serious environmental pollution will be caused by using traditional energy. Therefore,looking for renewable clean energy is important for human sustainable development. Solar energy has the advantages of abundant resources, without geographical restrictions and non-pollution, attracts more and more attention recently.Presently, photovoltaic energy transfer and conversion are based on power electronics technology. So, abundant power electronics converters will be introduced into power system by extensive PV microsources connecting to the grid, which will bring pollution to power system and cause serious power quality problem. In addition, island effect and microgrid circulation, which caused by photovoltaic connecting grid cosmically, also seriously endanger the safety and stability of the power system. Consequently, research of power quality problem and study on control strategy of PV grid-connected system with high permeability is of great significance for safety operation of the electric power system.The effect of the power quality in distributed network caused by PV connecting to the grid with high permeability is firstly researched in this paper. An indicator system and a comprehensive assessment method base on radar chart are proposed to insure integrated control of the high permeability system power quality such as voltage level, power level, harmonic distortion rate, three phase imbalance degree and so on.Then, the interaction between power quality control devices and photovoltaic generation equipment is researched. The study on control method and simulation analysis is done to the PV generation system configuring typical power quality devices SVC and DSTATCOM separately. Simulation result shows that power quality can be improved by the collaboration system consist of photovoltaic and power quality devices. The harmonics brought by the load and TCR can be suppressed by SVC and gird connected inverter with filter function, high quality power supply can be realized. Also,photovoltaic microsource can produce large capacity reactive power while provide power supply in the collaboration system with DSTATCOM, the cost of the power quality devices is reduced and the stability of the system is improved.The control method of suppressing micro-grid circulation and the control strategy of multi-inverters operation in parallel connection are also studied in the thesis. A solution to solve power coupling problem is proposed. Dummy V/f control strategy considering resistance and reactance based on rotating frame is adopted, and decoupling of active and reactive power is realized. Parallel operation control and load-sharing control among different microsources or between photovoltaic and the grid also can be realized.According to the condition and function demand of PV connecting to the grid, a 2kW single phase photovoltaic gird-connected inverter is developed by the project team independently. The detail software and hardware design of the controller, man-machine interface, development of inverter system are introduced in this paper. System modulation and experiment result indicate that the inverter can run steady and the control method can fulfill the demand of PV connecting to the gird.