A strategy for balancing switching losses of FB-PS-ZVS DC-DC converters in pulse and sinusoidal ripple current charging applications

A control scheme that balances the switching losses in the full bridge phase shift zero voltage switching DC-DC converter topology is presented. Typically, this type of converter is employed for battery chargers in electric vehicles because of advantages including high power capability, zero voltage switching, and galvanic isolation. Unfortunately, this topology has different switching and conduction losses between leading and lagging legs of the full bridge stage. If this converter is operated in full rated load condition, it is not necessary to consider the unbalanced losses because losses are almost the same. However, there are a variety of batteries charging schemes including sinusoidal ripple current charging, pulse charging and the optimized current charging, which might be operated in light or half load conditions. In low load condition, the disparity of unbalanced losses is increased. The degradation between leading and lagging leg devices grows over long term operation and affects the reliability of the converter. In order to balance the losses of the legs equally, the switching pattern needs to be considered. This approach is quite applicable for pulse and sinusoidal ripple current charging, because these charging methods require a rest period. This paper proposes an optimal switching pattern control scheme that incorporates thermal balance control and a discontinuous conduction mode detector. As a result, uncompensated thermal losses between the legs are balanced. Heat dissipation of the leading leg was reduced by approximately 16% compared to that of the conventional switching pattern. The proposed scheme was validated in PSIM.