Harmonic in Asymmetric Multiphase Converters

Symmetric multiphase dc-dc converters are widely used in power electronics, as they enable the processing of high power through splitting the overall load-current into multiple phases. Distributing the processed power symmetrically between the phases and performing ripple minimization through interleaving is well understood. However, in recent applications such as maximum powerpoint (MPP) tracking for solar photovoltaic (PV), converters are forced to operate under asymmetric conditions, due to differences in the sources or loads of each converter. This work presents a control technique, based on harmonic elimination, that allows for ripple minimization under asymmetric conditions.

The mathematical derivations are outlined and simulations are used to evaluate the performance of the proposed technique. Measurements taken from an experimental prototype, consisting of three dc-dc buck converters, demonstrate significant improvements in ripple reduction over conventional interleaving techniques. When the multi-phase converter is operated at the optimum asymmetric phase-shift found through the techniques presented here, a more than 3x reduction in net current ripple is observed under realistic operating conditions. Additionally, the undesirable first harmonic ripple component is reduced by 14.8 dB with the proposed technique.