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Transformerless photovoltaic (PV) inverters are going to be more widely adopted in order to achieve high efficiency, as the penetration level of PV systems is continuously booming. However, problems may arise in highly PV-integrated distribution systems. For example, a sudden stoppage of all PV systems due to anti-islanding protection may contribute to grid disturbances. Thus, standards featuring with ancillary services for the next-generation PV systems are under a revision in some countries. The future PV systems have to provide a full range of services as what the conventional power plants do, e.g., low-voltage ride-through (LVRT) under grid faults and grid support service. In order to map future challenges, the LVRT capability of three mainstream single-phase transformerless PV inverters under grid faults is explored in this paper. Control strategies with reactive power injection are also discussed. The selected inverters are the full-bridge (FB) inverter with bipolar modulation, the FB inverter with dc bypass, and the Highly Efficient and Reliable Inverter Concept (HERIC). A 1-kW single-phase grid-connected PV system is analyzed to verify the discussions. The tests confirmed that, although the HERIC inverter is the best candidate in terms of efficiency, it is not very particularly feasible in case of a voltage sag. The other two topologies are capable of providing reactive current during LVRT. A benchmarking of those inverters is also provided in this paper, which offers the possibility to select appropriate devices and to further optimize the transformerless system.
Yang et al. (Fri,) studied this question.
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