New bi-directional DC-AC converters with high frequency isolation

For applications such as UPSs (uninterruptible power supplies) and new energy systems, e.g photovoltaic or fuel cell systems connected to the grid, it is essential to isolate the load or the photovoltaic cells from the grid for the following reasons: a) to prevent a DC current from flowing to the AC side; b) to prevent high fault currents from flowing through the converter; c) to protect the user against electrical shocks or leakage currents as presented in M. Matsui and M. Yamagami (1998); and d) the need to adapt voltage level between battery and grid or battery and load. For these applications, the use of a converter that has high frequency isolation and also provides sinusoidal voltage would be very advantageous, since it would eliminate the low frequency transformer with an iron alloy core which is voluminous and heavy besides frequently producing audible noise.