Abstract
Efficiency and leakage current are two major issues for transformerless grid-connected inverters (TLI). Soft-switching technologies can reduce switching losses and be applied in TLIs. Herein, a zero-voltage-transition H5 type (ZVT-H5) inverter with soft turn-on and turn-off transitions of high-frequency main switches is derived from basic resonant tanks. Compared with the hard-switching H5 (HS-H5) inverter, the conversion efficiency of ZVT-H5 is significantly improved. Moreover, the reverse recovery problem of freewheeling diodes is alleviated under the operation of the auxiliary resonant network. Meanwhile, a diode clamping branch is employed to achieve constant common-mode characteristic for the ZVT-H5. The construction process of the proposed topology is described, and the operation principle of the auxiliary resonant network is analyzed. Moreover, the resonant parameter design of ZVT-H5 and its circuit performance are discussed in detail. Finally, the experimental results of a 3-kW prototype at 100 kHz switching frequency are provided to verify the effectiveness of the ZVT-H5.
Highlights
The distributed photovoltaic generation system has been applied in many areas
In conventional transformerless PV grid-connected inverters, their switching frequency is still chosen at a lower level for maintaining the converter efficiency, which limits the miniaturization of passive components
The resonant action of the passive components could worsen the PV inverters’ differentialmode voltage (DMV) and common-mode voltage (CMV) performance, which closely relates to the implement of high efficiency and low leakage current in transformerless grid-connected inverters (TLI), respectively
Summary
The distributed photovoltaic generation system has been applied in many areas. The auxiliary resonant commutated pole concept, the resonant dc link concept and resonant ac link concept were brought into PV inverters in literature [11], [12] and [13], respectively These soft-switching technologies are effective to reduce switching losses. The resonant action of the passive components could worsen the PV inverters’ differentialmode voltage (DMV) and common-mode voltage (CMV) performance, which closely relates to the implement of high efficiency and low leakage current in TLIs, respectively. Leakage current suppression performance compared with other typical TLI topologies [15] Both of them can be further improved with the added ZVT resonant network and freewheeling clamping branch, respectively. CIRCUIT STRUCTURE OF THE IMPROVED ZVT-H5 the HS-H5 topology involves an extra fifth switch S5 compared with the classical full bridge inverter in order to decouple PV array from the grid during freewheeling period. The potential of its freewheeling path may deviate from the midpoint voltage, which results in a high-frequency commonmode voltage and poor leakage current suppression performance
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