Auxiliary power supplies for high voltage converter systems

Almost all power electronic conversion systems require an auxiliary power supply to energize their control electronics. Two alternatives are commonplace-either a low frequency AC transformer/rectifier/regulator combination supplied separately to the main converter system, or a high frequency switched mode power supply (SMPS) supplied from the DC bus of the main converter. The SMPS approach has the benefits of reduced size, increased efficiency and can often be integrated onto the main converter control board. Hence it is usually the preferred solution. However, it is quite challenging to design a SMPS based converter to operate at the higher DC voltage levels that are typically used with multilevel conversion systems. This paper presents two alternatives for low power regulated supplies, derived from multilevel topologies and which address many of the challenges associated with their implementation in a HV system. Derivation and experimental results are presented for an NPC derived SMPS operating from a 1500 V DC rail, while simulation results are presented for a flying capacitor derived step down auxiliary supply.