Off-time control that reduces boost current imbalance for a bi-directional isolated parallel DC-DC converter

A DC-DC converter for electric vehicles requires higher efficiency, bi-directionality, and higher power. Therefore, a parallel DC-DC converter is sometimes used. The problem with this type of circuit is its current imbalance between each circuit. The current imbalance causes higher losses and higher costs. Therefore, technology that reduces the current imbalance is required in the parallel circuit. This paper presents an off-time control method that reduces the boost current imbalance for a bi-directional isolated parallel DC-DC converter. This method delays the off-time for the switching device at the high-voltage side. To accomplish this, clamp capacitor voltage is supplied at the resonant coil (Lr) and the current of resonant coil increases rapidly during off-time period. The results of a simulation were that the current imbalance ratio on the low-voltage side was reduced from 27% to 4% when the voltage of the high-voltage battery was 400 V and from 27% to 0.1% when the voltage of the high-voltage battery was 200 V when the inductance of the resonant coil differed from +30% to -30%.