Variable Topology Flexible Converter Based On Phase-shifted/PWM Dual-bridge Topology

Beam supply in the PPU(Power Processing Unit)of ion propulsion system is featured with extremely wide voltage gain range,in which case a traditional dc-dc converter is hard to apply.The technology of Variable Topology Flexible Converter(VTFC)is proposed to meet wide voltage gain demands in some special applications like this.In the concept of VTFC,there could be several equivalent topologies or operation modes with different gain ranges correspondingly in a single converter hardware.As voltage gain varies,VTFC can switch between these equivalent topologies or operation modes smoothly and seamlessly.In this paper,the application background of spacecraft propulsion system and the research status of beam supply and VTFC are introduced firstly.A basic idea of VTFC is proposed preliminarily.Secondly,the operation principle of a novel phase-shifted/pulsewidth modulated dual full-bridge topology is studied,and its operation modes and operation statuses that constitute the operation modes are classified by their power transfer characteristics.Based on these operation modes or statuses,some VTFCs are constructed with the dual-bridge topology.Thirdly,both digital and analog control strategies of VTFC are studied.Two digital control strategies,Unified Compensation and Independent Compensation,along with two analog control strategies,Direct Modulation and Indirect Modulation,are proposed.The specific implementation methods of each control strategy are introduced accordingly,which are based on an AVR MCU or some common power controllers like UCC3895 and SG3525.These methods are also applied to VTFCs constructed above.Finally,based on one type of VTFC and one kind of control strategy which are constructed or proposed above,small signal models of the main circuit and control circuit are derived,and proper close-loop compensation parameters are designed under average current mode control.A 1.2k W beam supply prototype is designed and fabricated.The main circuit parameters,magnetic component design and control scheme are analyzed and discussed.Experimental results of the prototype show the high efficiency and feasibility of VTFC with a peak efficiency of 96%.