Resarch On Photovoltaic Grid-connected/energy Storage Combined Control Based On Quasi-Z Source Inverter

As an important aspect in the field of new energy development,photovoltaic power generation has received extensive attention from many scholars at home and abroad.As the bridge connecting the solar cell array and the public power grid,the photovoltaic grid-connected inverter is the key to realize the safe,efficient and stable operation of the photovoltaic power generation system.Due to the influence of climate change and other uncertain factors,the output power of the photovoltaic power generation system has typical intermittent and fluctuating characteristics.Through storage devices such as storage batteries and their control,the randomness and intermittency of the power supply output of the photovoltaic power generation system can be suppressed.Energy storage technology has an important position and role in the new energy power generation system.(1)This article first analyzes a new type of power converter,a Quasi-Z source inverter(QZSI),which is applied to photovoltaic power generation systems,which can not only meet the needs of converter boost,but also reduce the circuit switching device.The unique Quasi-Z source impedance network is added to QZSI,which allows the through state to appear in the circuit.Because there is no dead time,the output current waveform is improved,and the reliability of the system is enhanced.The existing direct-pass segmented space vector modulation strategies of quasi-z-source inverters are compared and analyzed to obtain the direct-pass segmented space vectors that minimize the inductor current ripple,capacitor voltage stress,and zero vector utilization in the impedance source network modulation.(2)Analyze the relationship between the through duty cycle and the modulation ratio,and the relationship between the grid-connected current amplitude and the grid-side filter inductance respectively,and find that there is mutual coupling between the through duty cycle and the modulation ratio;and The increase of the side filter inductance and the magnitude of the grid-connected current will increase the modulation ratio,which in turn leads to insufficient pass-through duty cycle margins,resulting in the entire system not working properly.Aiming at the above problems,corresponding solutions are proposed.(3)Combined with the direct segmented space vector modulation,the photovoltaic cell output power feed forward and quasi-proportional resonance control are introduced in the two-phase static coordinate system,and the control strategy of the L-filter quasi-Z source photovoltaic grid-connected inverter is designed,including PV cell maximum power tracking control,DC link bus voltage control and grid-connected current control.Simulation experiments show that the quasi-proportional resonance control strategy using power feed forward can make the system transition to another steady state faster and can realize the tracking of the given value without static error and has strong ability to resist grid frequency offset.(4)Analyze and study the characteristics of Quasi-Z source photovoltaic grid-connected inverter with energy storage device,on this basis,put forward the photovoltaic grid-connected/energy storage combined control strategy based on Quasi-Z source inverter,this strategy According to the different states of the battery,applying different control schemes to the system can not only achieve the maximum utilization of photovoltaic cell energy efficiency,enhance the stability of grid-connected power,but also improve the battery’s use environment.In the Quasi-Z source photovoltaic grid-connected inverter system with energy storage device,due to the particularity of its circuit topology,changes in the external environment will cause changes in the peak value of the DC link voltage,which will affect the quality of the grid-connected current.Finally,based on MATLAB/Simulink simulation,the simulation of the control strategy studied in this paper is completed,and a Quasi-Z source three-phase inverter platform with energy storage device is further built.Based on this platform,the control strategy of this paper is carried out Experimental verification.Simulations and experiments show that the control strategy studied in this paper can not only ensure the maximum utilization of photovoltaic energy,but also protect the battery to the maximum extent.