Research On Multiple Ports DC-DC Converters

The development of electric vehicles has been becoming the important solution for the energy crisis and environmental pollution that result from the rapid development of the transport industry. Unlike traditional car, the power system of electric vehicles integrate several new energy sources and traditional energy sources to power the load, along with the batteries and super capacitors, which will improve the stability and flexibility of the power system and achieve optimal utilization of the sources. In such system, a multiple ports dc/dc converter (MPC) can be introduced into the system instead of several conventional single-input converters, which leads to a simpler configuration and lower cost. In this dissertation, the topologies and control strategies of MPCs are proposed, and the therorectical analysis is validated by the experimental results.According to the energy flow between the ports of the MPC, available MPC are classified into different types, and the characteristics of each type are illustrated. In order to obtain the simple isolated MPC topology of Type I, this thesis proposes the concept of alternative pulsating source cell (APSC), and the combination rules of APSCs, therefore some isolated MPCs of Type I are derived and further simplified. Taking the double-input converter incorporating a half-bridge three-level cell and a full-bridge cell as the example, the operation principles and characteristics of the converter are presented and the power management strategy is introduced. Finally, the theoretical analysis is verified by the experimental results from a 1000 W prototype.To derive the new MPC topologies of Type II and Type III, the bidirectional unipolar pulsating source cells (BUPSC) are extracted from the conventional bidirectional converters, and the approach to construct MPC by BUPSC and buffer cells is proposed, along with the corresponding rules for combination and cascade of BUPSCs and buffer cells. Finally, five synthesizing rules for MPC are generalized and a series of MPC topologies are derived.In order to verify the effectiveness of the control strategy for MPC, the three-port buck&boost converter is taken as the example in this thesis. Then the six operation modes and characteristics of the converter are presented. According to the equivalent circuit of each mode, the corresponding control strategy is proposed. The parameter design of the converter is discussed, and then a 1000 W prototype is built in the laboratory. The experimental results are shown in detail to verify the operating principle of the converter and the effectiveness of the power management strategy.