| High efficiency and operating life grid feeding solar photovoltaic(PV)inverters are demanded.Due to reduced dc-link capacitor requirement,current source inverter(CSI)offer higher reliability than the voltage source based solar inverter.The current source inverter has the capability of boost,and with a large DC inductance in its DC side,it also have a function of short circuit protection.With a long lifetime,the current source inverter is well suited as a photovoltaic inverter.However,conventional three-phase pulse width modulated(PWM)current source based solar inverter injects high earth leakage current into the grid.In order to suppress this current,an isolation transformer can be used.Use of this transformer increases the cost and size,and decreases overall efficiency.In order to suppress the leakage current,a modified CSI is proposed in this paper,it is three-phase current source Buck-boost inverter.Without an isolation transformer,the leakage current can be suppressed effectively by this topology.Frist,the basic working principle of this inverter is analyzed,and the expression of the common-mode voltage of the inverter at any working time is deduced in this paper.Through the expression of common-mode voltage,it can be seen: common-mode voltage is constant,therefore,the leakage current has been suppressed effectively.Secondly,the mathematical model of the three-phase Buck-boost inverter is established,its buck-boosting ability is analyzed,and the mathematical model of the modulation ratio between the DC input voltage and the AC output phase voltage is deduced.On this basis,a double current loop structure with direct current control is designed,and the simulation is carried out.On the basis of theoretical analysis and simulation research,the experimental platform of three-phase current source Buck-boost inverter is built in this paper.The correctness of the theoretical analysis and the feasibility of the control scheme are verified by experiments. |
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