Interleaved Buck Converter with Variable Number of Active Phases and a Predictive Current Sharing Scheme

Abstract

The efficiency of an interleaved Buck converter is typically low at light load conditions because of the switching losses in each of the switching stages. Improvements in the converter efficiency can be achieved by dynamically changing the number of active phases depending on the load current. This paper addresses the issues related to the transient response of the converter when the number of active phases is changed by a digital control scheme. The problem arises because the current in the individual phases of the interleaved Buck converter will not be equal immediately after the controller has changed the number of active phases. This paper proposes a current equalisation scheme that adjusts the duty cycle of each phase in a manner that ensures equal average inductor current in all active phases in one or two PWM periods. The current equalisation scheme relies on the measurement of the output current and the knowledge of a few converter parameters and it does not require a measurement of the current in each phase. A digital PWM modulator has been designed that allows the current equalisation scheme to work. Simulations and measurements for a four phase interleaved Buck converter are presented and shows that the predictive current equalisation scheme can equalise the phase currents in a single PWM period.