Studies On Input-Parallel Output-Parallel DC-DC Converter And Its Control Strategies

With rapid development of science and technology, high-capacity power supply, such as high-power communication power supply, large high-speed computer CPU power supply, the secondary power supply of aerospace vehicle, UPS of banking data switching center, get more and more widely used, which requires increasingly high capacity and large power density. Multiphase DC-DC converter studied in this paper consists of multiphase dual active bridge (DAB) converters, input-paralleled and output-paralleled, thus possessing the merits of DAB converters, such as higher power density with its relatively small size, transferring power in both directions and less power loss due to its ability of zero voltage switching, and enlarging the capacity of DC-DC converter without changing component ratings. So the researches on multiphase DAB IPOP DC-DC converter have great significance.Firstly, the background of this research is introduced, including four different kinds of multiphase DC-DC converters and their characteristics, applications, merits and their current-sharing or voltage-sharing strategy.Secondly, the operating principle of the basic module of multiphase DC-DC converter, namely DAB converter, is analyzed. The operating modes in a single switching cycle with the single-phase-shift (SPS) control are given and accordingly the characteristics of transmission power and input and output current, as well as realization condition of ZVS of DAB converter are deduced. In order to reduce impact current, a new soft start strategy of DAB converter is developed.On the basis of former analysis, novel current-sharing strategies for two-phase and multiphase DAB IPOP DC-DC converter are proposed. For two-phase DAB IPOP DC-DC converter, the working principle and realization process of proposed strategy are given in detail, including common shift phase duty cycle stage, common shift phase duty cycle with perturbation stage, phase parameter ratio calculation stage and current sharing stage. For multiphase DAB IPOP DC-DC converter, the working principle and realization process of proposed strategy are given in detail as well.Next, the experimental prototypes of two-phase and multiphase DAB IPOP DC-DC converter are designed from the aspect of hardware and software. The hardware circuits consist of main circuit, control system, detection circuit, protection circuit and drive circuit, and the software includes DSP program and FPGA program. According to the design requirements, the experiment platforms are made and experiment program is written.Finally, the simulation modes of two-phase and three-phase DAB IPOP DC-DC converter are built in simulation software PSIM, and the simulation results verify the feasibility of the proposed current-sharing strategies. Experiments are conducted on the prototypes and the experimental results conform to the simulation results, therefore verifying the correctness and validness of the proposed current-sharing strategies.