Research On Current Source Grid-connected Inverter For Medium And Small Power Photovoltaic Systems

The current source inverter has some outstanding advantages over the voltage source inverter.First,the current source inverter does not require electrolytic capacitors;on the other hand,it has a single-stage boosting capability,and the current source inverters are compatible with medium and small power photovoltaics inverter requirements.However,the traditional current source inverter inverter is difficult to meet the requirements of small and medium power photovoltaic systems.On the one hand,the current source inverter needs a large DC-side inductance;on the other hand,the conventional current source inverter will be parasitic on the photovoltaic panel.A leakage current is generated in the capacitor.For the above problems of current source inverters,this paper first proposes a nonlinear modulation strategy,which effectively solves the problem of large value of inductors of current source inverters.Aiming at the leakage current problem of non-isolated current source inverters for photovoltaic systems,this paper proposes a novel current source inverter topology,which can effectively suppress leakage current.In this paper,the relationship between the DC side inductance value and the ripple current is obtained by analyzing the DC side inductor operating characteristics.under the condition of inductor current pulsation,based on the area equivalent principle,a nonlinear modulation strategy is proposed,which effectively solves the problem of excessive inductance of single-phase current inverter when used in small and medium power systems.Aiming at the leakage current problem of non-isolated current source inverters in photovoltaic systems,a novel CH5 inverter is proposed,which can effectively suppress leakage current.Based on the new topology,an optimized switching modulation method is proposed.Then the working mode and common mode voltage of the novel CH5 structure are analyzed,and the principle of leakage current suppression is revealed.Then the model of the inverter is established.Based on this,a closed-loop control system is designed and the closed-loop control system is simulated.The results show that the closed-loop system can resist the disturbance of load and grid voltage.Finally,an experimental prototype was built to verify the above theory,which proved the correctness of the theoretical analysis and the feasibility of the method.