| As the photovoltaic power generation system contains more high-order harmonics,there is still a small amount of harmonics getting into the large power grid when the PV getting into the large power,which can influence the power supply quality and stability of large power despite of the filter device.And due to a large number of applications to promote the construction of photovoltaic and advocat self-use at present,the large power grid only supply the power to user when the PV can not afford the load demand.However,the national standard provides that there can be no electricity to the power grid.Therefore,the main content of this research is how to control the current flow to the grid is 0,that is zero-flow control of photovoltaic grid-connected.Firstly,in this paper,the background and significance of the research are introduced,and several traditional control methods and inverse power detection methods of PV grid-connected inverter are listed.The advantages and disadvantages are analyzed,which lay the foundation of the zero counter current control strategy.Then,the mathematic model of the PV system is established,and the mathematical model under different coordinate systems is analyzed.The appropriate mathematical model is selected and the circuit topology of the PV grid-connected inverter is determined.Then,the realization method of PV grid-connected zero-flow control strategy is described specificly.Firstly,the occurrence of reverse power should be predicted.Then the principle of coordinate transformation and its transformation and the generation of SVPWM pulse modulation are introduced.Finally,a vector control based on grid voltage orientation is selected on the basis of a series of previous analyzes as a zero counter current control strategy.The inverter can closely track the changes in load power,lock the phase of the large power grid,quickly and accurately adjust the the output of the inverter to meet the needs of the load.Finally,the hardware and software parts of the control system are designed in detail,including the design of the main circuit,the design of the phase-locked loop and the flow chart of the system programming,and builds the simulation model of the grid-connected inverter in the Matlab simulation platform.The simulation model of the control strategy is verified by a series of simulation experiments to verify the effectiveness of the zero-flow control strategy.Through the comparison between the simulation waveforms and the analysis of the simulation results,it can be seen that PV grid-connected zero-flow control strategy designed in this paper can track the change of load power and can quickly lock the grid phase and provide the SVPWM pulse phase reference value,but also allows the inverter to adjust the output in time,so that it can meet the needs of the load and not produce countercurrent. |
