Current Sharing Analysis for Novel Paralleled CLLLC Converters

Abstract

In the field of high-capacity bidirectional converters, paralleled LLC converters are usually used to increase the output power and system power density. However, because of the production tolerances the parameters of the resonant components for each paralleled unit may not be completely identical. The gain characteristic of the LLC resonant converter is sensitive to the parameters of the resonant components. For the paralleled converters, because voltage gains can be slightly different from each other for a same input, system output current may be poorly shared among the parallel units. In this paper, novel paralleled CLLLC converters are proposed. For the proposed converters, the load current sharing performance is not sensitive to component parameter differences or derivations. Equal load sharing can be realized easily. And no additional components or controllers are needed. The gain characteristics are analyzed and they are similar with that of a single CLLLC resonant converter. The mathematical model of the paralleled converters is deduced based on fundamental harmonic approximation (FHA) method. And the load current sharing errors for the conventional and proposed paralleled CLLLC converters are compared or analyzed by introducing variables such as the load current sharing coefficient. It is shown that for the same set of component parameters, when the conventional paralleled converters are used most of the load may be supported by a single converter while the output power of another one is small. On the other hand, for the cases of parameter derivations, the current sharing performance of the novel proposed paralleled converters is obviously much better. And finally the effectiveness of current sharing for the proposed paralleled CLLLC converters is verified by simulations and experiments.

Keywords

• Current sharing
• paralleled CLLLC converters
• component parameter derivation
• equivalent circuit