The result is an increase of the L inverter output voltage during the boost operation. The increase in voltage VL causes increase of current IL and introduces an increase of amount of the energy transferred from the source of low voltage VL. The increase in the control frequency causes at some point that the tov interval disappears. When there are no tov interval at all, the voltage is not increased and the energy is not transmitted in direction from L to H. The process of energy transmission from the H source to the L source is different. Since increasing of the voltage is not required in that case, the H inverter can be controlled in a higher frequency region, and tov interval is not present. The corresponding diagram of the H inverter control pulses at its maximum switching frequency is shown in Fig. 3.