Research On Single-Phase Non-Lsolated Z-Source Photovoltaic Grid-Connected Inverter

With the rapid development of the world economy,energy is closely related to social development.Due to the environmental pollution problems caused by the use of traditional fossil energy,clean energy power generation systems such as fuel cell,wind energy,photovoltaic power generation have gradually become the research focus of various countries.Among them,photovoltaic power generation develops most rapidly,and grid connected inverter is one of the core components of photovoltaic power generation system,which plays an important role in the process of energy conversion.Grid connected inverter can be divided into isolated inverter and non isolated inverter according to the presence or absence of isolation transformer.The power frequency isolation transformer has high cost and large volume,while the high frequency isolation transformer needs to introduce power conversion circuit,which increases the control difficulty.In contrast,non isolated inverter has the advantages of low cost,high efficiency and small size,which meets the development requirements of grid connected inverter for high power density,high reliability and high efficiency.Since the traditional inverter can only achieve the function of up / down,and Z-source inverter overcomes the defects of traditional inverter,and improves the performance of photovoltaic system,this paper studies the single-phase non isolated Z-source inverter.Since there is no isolation transformer in the non isolated Z-source inverter,there is an electrical connection between the photovoltaic array and the grid,thus forming a common mode resonant circuit composed of filter elements,parasitic capacitance and grid impedance.When the inverter is working,the common mode voltage at both ends of the parasitic capacitance will stimulate the common mode resonant circuit to generate common mode current.Aiming at the common mode current problem of single-phase non isolated Z-source photovoltaic grid connected inverter,a common ground method is studied to connect the grid neutral line with the negative end of photovoltaic array,which improves the inverter topology of traditional Z-source inverter.Capacitor is used as virtual DC bus instead of DC power supply to supply power to the grid side,and the grid neutral line of inverter is directly connected with the negative end of photovoltaic array The common mode current can be eliminated completely by bypassing the common mode current loop composed of photovoltaic stray capacitors.The working mode of single-phase Z-source photovoltaic grid connected inverter is analyzed,and a new PWM control strategy is designed.The switching stress of the proposed inverter is compared with the traditional Z-source inverter.The Z-source capacitor voltage control loop,grid current control loop and photovoltaic array output voltage control loop are designed.Through theoretical analysis,the Z-source capacitance and inductance parameters are calculated.Finally,the feasibility of suppressing common mode current is verified by simulation.