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The grid inverters play an important role in renewable energy systems, transferring the dc power to the ac grid. Galvanic isolation is usually needed between the dc source and the grid due to safety reasons and grounding leakage current mitigation. In this article, a soft-switching isolated grid inverter is proposed based on the current-fed matrix-type configuration. The topology of this converter is composed of a current-fed H-bridge on the side of dc source and a direct matrix converter on the grid side, which are linked by a high-frequency transformer. The current-fed H-bridge on the primary-side can smooth the dc-source current and control the dc-source current directly. The avoidance of dc-link energy-storage element in the single-stage matrix converter can prolong the system's life. A space-vector-modulation-based soft-switching scheme is proposed for the matrix converter on the grid side and a model-based commutation method is adopted in the current-fed H-bridge on the dc side. With the proposed modulation methods, the soft switching can be realized for all devices in the converter. Finally, a laboratory prototype of the proposed converter has been built to verify the effectiveness of the proposed method experimentally. [ABSTRACT FROM AUTHOR]

Soft-switching techniques of transformerless photovoltaic grid-connected inverters (TLIs) can significantly reduce switching losses, as well as soften switching processes. Conventional dc–ac soft-switching configurations proposed by Dr. Deepakraj M. Divan are invalid in TLIs because of the leakage current problem. In order to develop soft-switching techniques in TLIs, this paper proposes a new soft-switching configuration and a procedure to guide the invention of soft-switching TLIs. First, this paper proposes two basic resonance tanks related to dc bus polarities, and then, uses these basic tanks to elevate four popular full-bridge-type TLIs according to the proposed guideline. As a result, four soft-switching TLIs are gained. Second, this paper picks obtained soft-switching highly efficient and reliable inverter concept (HERIC) as example to analyze its soft-switching operation principle and performance. As a consequence, all active switches of the gained soft-switching HERIC circuit are switched under both of zero-current turn-on and turn-off conditions; the reverse recovery problem of freewheeling diodes is alleviated owing to the zero-current turn-off of diodes; meanwhile, the common-mode voltage at the switching frequency scale is still constant. Finally, some experimental results from a 3-kW universal prototype at 50-kHz switching frequency are provided to verify the effectiveness of the main contributions of this paper. [ABSTRACT FROM AUTHOR]