一种低漏电流七开关无变压器型光伏并网逆变器拓扑

A Low Leakage Current Seven-Switch Transformerless Photovoltaic Grid-Connected Inverter Topology

无变压器型光伏逆变系统中的漏电流高于300 m A时规定必须在0.3 s内从电网中切除。为解决系统中脉动共模电压引起的漏电流问题,提出新型七开关逆变拓扑(H7),该拓扑在直流输入端引入两个高频开关管,续流阶段确保直交两侧完全解耦,维持共模电压的恒定。在调制方法上,还可以实现倍频SPWM策略,降低电流纹波。在任意模态中开关管始终交错工作,有助于热应力均衡。最后,通过2 k W的样机平台验证了抑制后漏电流峰值仅为60 m A,相对于传统拓扑性能更优越,提高了系统的安全裕度。

The transformerless photovoltaic inverter systems should be disconnected from the grid within 0.3 s,in case,the leakage current is higher than 300 mA.In order to solve the leakage current caused by the common-mode voltage variation,a new seven-switches inverter topology(H7)is proposed.It uses two switches in the input DC side to ensure DC-AC decoupling during free wheeling period to keep the common-mode voltage in a constant status.Judging from the modulation mode,the inverter topology can also achieve double-frequency SPWM strategy to reduce current ripple wave.The heat balance is benefited with the switches working criss-crossed.Finally,a 2 kW prototype is built to verify peak value of leakage current suppressed is only 60 mA.Comparing with the traditional topology,capability of H7 is better.It provides an effective improvement in safe margin of systems.