A High Voltage Converter for Auxiliary Supply Applications using a Reduced Flying Capacitor Topology

Most power electronic conversion systems use low voltage control and supervisory circuitry to manage the switching processes and other ancillary functions. This circuitry is typically supplied from a separate low power auxiliary supply, commonly derived from the main power stage supply. Usually it must be energized prior to the main power stage to ensure safe operation of the converter. Auxiliary supplies can be realized using either a low frequency AC transformer/diode rectifier, or a switched mode power supply (SMPS) supplied directly from the power converter´s main DC bus. While transformer/diode based rectifiers are simple to design and build, SMPS´s have the advantages of improved efficiency, reduced size and weight, regulation and the ability to operate directly from the main converter´s DC bus. However, SMPS based auxiliary power supplies for higher voltage converter systems are more challenging to design, partly due to a more limited range of high voltage, low power, active components, and partially due to the increased level of second order and parasitic effects that become significant when switching higher voltages. This paper presents a design methodology and performance results for a fully regulated, non-isolated, DC-DC auxiliary SMPS derived from the flying capacitor family of multilevel converters. The topology achieves reduced device voltage switching stresses and a tightly regulated voltage output. The design methodology has been confirmed by constructing a 200 W converter operating from a 1500 Vdc supply. A topological extension is also presented to incorporate galvanic isolation, at the expense of poorer output voltage regulation