Optimization of the light-load efficiency enhancement technique in a transformerless inverter aimed at DC microgrid

There is currently an ongoing effort to promote the installation of low power, residential and commercial, DC microgrids, which allow the incorporation of renewable energy sources (RES) into local generation systems. Since it is intended that RES generate as much energy as possible, and often this energy is not consumed locally, a common practice is to inject the surplus energy into the grid to ensure the DC bus stability. In this context, the inverter in charge of linking the microgrid with the mains becomes an essential element. The efficiency of today's inverters is relatively high, and allows large amounts of energy to be injected efficiently. However, in low power systems the inverters are required to work in light load regime for long periods of time, for which they often do not guarantee high efficiency. This paper presents a light load efficiency enhancement technique optimization in a transformerless inverter with hybrid switches. Based on the internal hybrid switch current distribution, a multi-objective optimization method was applied to improve the efficiency curve, ensure lower losses in light loads, and provide a wide high efficiency range. A noticeable improvement can be achieved by turning off a switch at the right time, when the converter is changing from operating regimes. The advantages of the aforementioned approach were verified in a 2 kW experimental prototype.