A high-efficiency DC-to-AC inverter for stand-alone and direct AC mains connection is described. This structure uses only off-line switches to generate the AC voltage. Due to safety reasons, the input voltage (e.g., the voltage of solar cells or batteries) is limited. Therefore, high currents on the primary side are necessary to obtain the required output power. The overall efficiency of the inverter depends to a high degree on the number of switching elements in the current path. The structure described here has only one active switch in the main path. This can be obtained by applying a diode with controlled turn-off capability (like a thyristor or other derivatives). High duty cycles (d near one) of the main switch at high currents lead to low duty cycles (1-d near zero) of the switchable diode. For that reason, a series connection of two active switches in the main path has to be avoided. The new inverter leads to improved efficiency and is therefore well suited for solar and renewable energy as well as for aerospace applications. The improvement of the efficiency is due to the new topology and not due to overdimensioning of the semiconductors. Hence, an additional potential of efficiency improvement is still available.
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