| Solar photovoltaic(PV)power generation has broad application prospects,among which the non-isolated PV inverter has the advantages of small size,light weight and high efficiency because it does not contain a transformer structure,and has gradually attracted the attention of the PV industry.However,due to the lack of electrical isolation,leakage current will occur in the inverter system.Leakage current will affect the output power quality and threaten personal safety,so how to solve the leakage current problem of non-isolated PV inverter has become a research hotspot.In response to this problem,this paper first analyzes and summarizes the existing leakage current suppression technologies of non-isolated three-phase inverters,and adds a clamping circuit on the basis of the H8 PV inverter topology to construct a clamped H10 PV inverter topology.The clamping circuit mainly consists of three equal-value voltage-divider capacitors and two clamping switches,the voltage-divider capacitors divide the DC input voltage(U_d)into three equal parts,forming four potential points:0,U_d/3,2U_d/3 and U_d.One clamping switch is connected between the U_d/3 potential point and the common drain point of the upper-arm switches,and the other is connected between the2U_d/3 potential point and the common source point of the lower-arm switches,so that when the inverter is in the freewheeling mode,the common-mode voltage can be clamped to U_d/3 or 2U_d/3 as required.Then a voltage closed-loop SPWM control strategy based on zero vector judgment is proposed,the control strategy includes three parts:voltage closed-loop,SPWM control and Boolean logic operation based on zero vector judgment.The voltage closed-loop ensures the stability of the output voltage;SPWM control can generate two working modes of zero vector and non-zero vector;finally,through the judgment of zero vector or non-zero vector and combined with the characteristics of H10 PV inverter topology,the required working states are constructed by Boolean logic operation.In the non-zero vector working mode,the clamping circuit does not work,and the inverter is in normal working state.In the zero vector working mode,the two clamping switches are selectively turned on,so that the common-mode voltage is clamped to U_d/3 or 2U_d/3.Therefore,during the entire working cycle of the inverter,not only the range of common-mode voltage’s amplitude is reduced,but also the common-mode voltage’s frequency is three times the switching frequency,and the common-mode loop impedance is significantly increased,effectively suppressing the system leakage current.In addition,the problem of voltage imbalance of DC side voltage-divider capacitors is studied,and the analysis shows that the dead time of the circuit is the main factor causing the unbalance voltage of the capacitors.Then the influence law of the dead time of each switch on the voltage value of the voltage-divider capacitor is summarized,which creates a way to further realize the voltage equalization of the capacitors.Then,the power circuit and control circuit’s parameters of the inverter are designed,and the stability of the closed-loop system is judged by using the Routh stability criterion.Finally,a simulation platform and an experimental platform are built,the results show that the H10 PV inverter has better leakage current suppression effect than H8 PV inverter,which is consistent with the theoretical analysis and verifies the correctness of the proposed method. |
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