Research On Photovoltaic Grid-connected Control Based On Switching Inductive Quasi-Z Source Inverter

The massive use of fossil energy has caused serious environmental pollution,and countries have increased their attention and research on new energy sources.Among them,solar power generation,wind power generation,etc.are called hot spots of green power generation because of their advantages of no pollution,inexhaustible use and inexhaustible use.However,the electrical energy directly obtained from the photovoltaic cells is DC electrical energy and cannot be directly connected to the grid.Therefore,the power generated by the photovoltaic cells needs to be boosted and boosted.The selection of these converters will directly determine the power quality of the grid-connected power,so the selection is particularly important.The traditional inverter device is a three-phase voltage type inverter,and the voltage level obtained after the inverter is not up to the grid connection requirement,and an additional boost circuit is usually required.Such a two-stage structure will degrade the stability and real-time performance of the system,and will be more complicated in control,and a dead zone is added to the switching signal to prevent the switching device on the same bridge from being turned on at the same time to cause the loss of device.In this way,it is inevitable that the waveform output from the inverter is added to a large number of harmonics.The proposed Z source overcomes the above problems,but it still has some shortcomings.In this paper,the topology of a switched-inductive quasi-Z source inverter is proposed to improve the performance of the inverter.Double closed loop control for effective grid connection.The research content of this thesis includes the following aspects.First,the photovoltaic cell is modeled and analyzed and its corresponding change law is obtained.The disturbance observation method commonly used in photovoltaic maximum power point tracking technology is analyzed to improve the misjudgment that may be caused.Finally,the improved disturbance observation method is compared with the traditional method in MATLAB,which proves that the new method has some improvement compared with the traditional disturbance observation method.Secondly,the Z-source simple analysis is carried out on the traditional,and the topology of the switched-inductive quasi-Z-source inverter is proposed for their deficiency.That is,one of the inductors is switched to two series-connected switches based on the traditional quasi-Z source impedance network,which greatly enhances the boosting capability of the system.And compare the common modulation strategy sinusoidal pulse width modulation and space vector modulation analysis,choose the appropriate modulation strategy.Finally,the small-signal model of the switched-inductive quasi-Z source inverter proposed in this paper is established under the state space averaging method.According to the established mathematical model,the double closed loop control strategy is determined,that is,the current inner loop on the AC user side ensures the real-time rapidity of the system,and the capacitor voltage outer loop on the DC input side ensures the stability of the DC bus chain voltage.Based on this,the simulation analysis of the switch-inductive quasi-Z source inverter grid-connected system is carried out in MATLAB,and the representative common Z-source inverters are simulated and compared under the same conditions.It is verified that the boosting capability of the switched-inductive quasi-Z source inverter proposed in this thesis is more prominent,and more Z-source inverters have certain advantages.