Current-sharing control technique for interleaving VRMs using intercell transformers

Parallel converter architecture using intercell transformers is one of the most adapted architecture for low-voltage, high-current and fast transient power conversion applications. Interleaved buck converter with intercell transformers main interest is the current ripple reduction in each converter arms which is not the case with non-coupled inductor architectures. As a consequence, current constraints on switches and inductors are less severe and lower Joule losses are obtained leading to a higher efficiency. This paper highlights a fundamental limitation for those interleaved converters using intercell transformers. A differential current error through transformer causes flux drift and can lead to magnetic core saturation. In case of temporary control failure, arm currents get back to proper balance with a very slow dynamic response. State-space study allows us to calculate arm current transfer function and deduce the differential current time constant. Finally, a stability study with standard filters is presented and a proper current-sharing loop regulator filter is proposed in order to speed up system return to equilibrium.