Analysis and control of three phase AC-DC PWM boost-buck and buck-boost bidirectional power converters.

摘要

Three phase ac-dc Pulse Width Modulated (PWM) boost-buck and buck-boost bidirectional power converters have been investigated from the vantage of active rectifier front-end. The power converters under focus are capable of (I) both voltage step-up and step-down, (II) bidirectional power processing, and (III) almost unity power factor operation with nearly sinusoidal ac current.; Four realizations with these capabilities (Ćuk-Ćuk, sepic-zeta, buck-boost/buck-boost and zeta-sepic converters) have been obtained from a systematic power stage topology derivation. Their operating principles and suitable modulation schemes have been studied. In particular, it has been clarified that the derived power converter topologies have similarities to the conventional Voltage Stiff Converter (VSC) or Current Stiff Converter (CSC) from ac current control viewpoint and that they have accentuating differences from VSC or CSC in terms of the zero voltage or zero current space vectors. It has also been made clear the key role of the seventh active switch on the do link side for inverter operation.; Analytical steady-state and dynamic models of four converters for controller design have been derived. These models have been validated with detailed circuit simulations.; A hardware prototype of a Ćuk-Ćuk converter has been built and its feasibility has been experimentally demonstrated.; A modified PWM scheme has been proposed which can be utilized for low order harmonic reduction and intermediate energy storage component reduction.; Component ratings and efficiency have been estimated not only for the derived four power converter topologies but also two existing cascaded topologies having the similar function (VSC plus dc-dc and CSC plus dc-dc converters) for comparative evaluation purpose.; A common mode voltage issue has also been discussed with taking the Ćuk-Ćuk converter and the VSC plus dc-dc converter topologies as representative examples. It has been shown that the boost-buck converter specific PWM scheme with the phase leg-short zero voltage space vector can eliminate the main source of the common mode voltage which would be generated in the conventional VSC.; Through the investigation carried out in this project, not only the feasibility of the derived converter topologies has been verified but also their advantages, disadvantages and operating limitation have been made clear.