Optimal operation of a single phase converter by switching frequency changes

The control of the power flow from an AC grid to a DC load leads to reactive power increase and affects the efficiency. Especially when the converters operate by the power grid´s frequency, the switching power losses of the semiconductor elements get minimal value but the power factor becomes poor. This happens because of the high order harmonics injection and the change of the phase angle between the first order harmonic of the grid current and the grid voltage when DC voltage control is necessary. The under consideration converter topology in this paper operates in such a way that the basic current harmonic is in phase with the grid sinusoidal voltage. So, for higher switching frequency values the power factor becomes higher while the power losses increase and consequently the efficiency becomes lower. In this case the power factor depends only on the grid current high order harmonics. These high order harmonics can be removed from the power grid by the use of a passive L - C filter, and so the power factor becomes high. It is obvious that the L-C filter value depends on the switching frequency. In the present work both the optimization of the power factor and efficiency by switching frequency changes is investigated, also an appropriate L-C filter is chosen.