An Automatic Load Current Sharing Scheme in Parallel Connected DC-DC converters and its Application in Spacecraft Power System

Abstract

A simple scheme has been proposed and implemented to achieve equal load current sharing between parallel connected non-isolated (Buck) DC-DC converters. The same scheme can be used for isolated DC-DC converters. The scheme is implemented using Average current mode control and has been tested for output voltage of 50V & high output power of up to 700W. Two nos. of 50V/7A Buck converters have been implemented in parallel so as to achieve 700W (50V/14A) output power. The scheme is simple and automatic, in the sense that no additional circuit is required to ensure equal load current sharing between them. The scheme utilizes the already existing components of control loop to achieve the objective. This design can easily be used for Auxillary Bus Regulators (ABRs) in Satellite Power system, to step down 70V bus to 40V. All the loads can be connected directly to the paralleled (n+1) DC/DC converters. In case of one DC/DC (Slave) failure other ‘n’ converters (including Master) can take over the sharing of load and thus provide redundancy in the system. As far as the loads are concerned, they will not see any change and will remain connected at the same point. Redundancy can be provided for Voltage Error Amplifier placed in ‘Master’ Converter. This design can also be upgraded to make high power Anode supply of 1.4KW (350V/4A) for HET thruster. A current sensing scheme has been implemented to sense ‘error free’ inductor current waveform during mass production of dc-dc converters.