Instabilities in transformer-coupled Cuk-converters and their solution at higher power levels

In many power control applications, a buck-boost chopper is necessary, in principle operating between two DC sources. When transformer isolation is a prerequisite, the Cuk-converter becomes a minimum component topology when considering certain conditions that do not normally manifest themselves at low power levels. The authors describe an application where it was necessary to achieve efficiencies in excess of 90%, placing a premium on low loss technology so that all the magnetic components for a 1.5 kVA converter of this type were carefully optimised for low losses, using existing CAD facilities. This resulted in a system that was inherently unstable, and had to be stabilised without appreciably sacrificing efficiency or increasing system complexity. The work outlined covers the approach adopted to arrive at a satisfactory practical solution