Research On Solar Inverter Control Strategy With Active Power Filter

With the continuous depletion of traditional fossil energy sources and the increasingly serious environmental problems,the photovoltaic industry is facing greater development opportunities and bright prospects.However,due to climate change and day-night alternation,photovoltaic power generation exists intermittently,the spread and application of PV have great limitations,and a large number of nonlinear power electronic devices into the power grid,to the system to inject harmonics,so that the power quality continues to decline.Therefore,this thesis studies the photovoltaic grid-connected and harmonic suppression cooperative control strategy,combined with the control principle of both,without changing the main circuit topology,the dual function of the photovoltaic grid-connected system with active filter function is realized,and the utilization ratio of the system equipment is effectively increased.Based on the similarity of structure,function and control strategy between the single-stage solar inverter and the parallel Active Power Filter(APF),this thesis Active Filter that,using a set of solar inverter to achieve both grid-connected PV and active filtering.First of all,in harmonic detection,becausei_p-i_q detection method is less susceptible to grid voltage distortion than p-q detection method,the detection results are more accurate,so choosei_p-i_q detection method to study.In order to improve the response speed of the system,the average current module is used instead of the low-pass filter low-pass filter to obtain the fundamental component.The simulation results of the i_p-i_q detection method based on the average current value show that the method can obtain the harmonic current accurately and quickly.Secondly,on current tracking Control strategy,this thesis adopts Model Predictive Control(MPC)to realize current tracking of cooperative system.Based on the solar inverter topology,the state equations of MPC in two-phase stationary coordinates are derived,in view of the disadvantages of single vector MPC,such as large current fluctuation,fixed direction of voltage vector,less searching times and poor accuracy,a two-step three-vector MPC prediction method is proposed in this thesis,in a control period,two non-zero vectors and one zero vector are used to control the voltage solar inverter.By calculating the action time of the three voltage vectors,the optimal voltage vector is selected,two-step prediction is used to realize delay compensation and accurate current tracking control.Compared with single-vector MPC,two-step prediction of three-vector MPC is more effective in the aspects of grid-connected current waveform,FFT harmonic analysis,steady-state and dynamic response speed,etc.Finally,the simulation model of grid-connected PV and APF is built on MATLAB/Simulink platform,the system runs in three modes:Full PV grid-connected,full active filter and PV grid-connected and active filter co-control.The simulation results show that the proposed co-control strategy is effective,at the same time,the harmonic distortion rate of grid-connected current is less 5%,and the utilization ratio of grid-connected photovoltaic energy is increased.