Design And Control Of The Three-Port Bidirectional DC/DC Converter

With the rapid development of society and economic, the demand of energy is increasing. At the same time, the energy and environment problems become more and more severer. The development and utilization of renewable energy can alleviate the energy crisis and improve the environment effectively, which leads to the rapid development of renewable energy technology in recent years. Different from the traditional power plants, power fluctuation is a critical issue of renewable energy technology due to its intermittent nature. Energy storage devices can be used to address this issue, in which multiple dc converters with power generation unit and energy storage unit as well as DC-links are required. The isolated three-port bidirectional DC/DC converter consists of a three-winding transformer linking up multiple dc sources. The structure is compact and the power density is high. Without additional circuits, the leakage inductances of transformer and parasitic capacitors of switching devices can realize soft-switching operation by their own and therefore reduce the power losses. The main objective of this thesis is to systematically study the isolated three-port bidirectional DC/DC converter.Firstly, based on the dual active bridge isolated DC/DC converter, the equivalent circuit, power equation, and soft-switching range of the isolated three-port bidirectional DC/DC converter are analyzed in detail, and 18 kinds of work modes are given in this thesis. The design of hardware platform and software program of the isolated three-port bidirectional DC/DC converter is introduced. Experimental results of steady-state verify the correctness of the software/hardware design and the phase shifting control strategy. Meanwhile, the experimental results of transient state show that the system has a good dynamic performance.Secondly, the continuous and discrete chaotic modulation strategies and phase shift control technology are combined and applied to the isolated three-port bidirectional DC/DC converter to reduce the conducted electromagnetic interference and improve the electromagnetic compatibility of the converter. Based on the small signal model, decoupled network is designed to decouple the interactions between the input and output variables and improve system performance. Both the simulations and experiments verify the validity of chaotic modulation strategies and decoupled control.Finally, the designed dc converter is connected to a three-phase voltage source inverter with three-phase resistance and inductance loads to emulate the distributed generation system. The results of simulation and experiment show that the dc converter and three-phase inverter can be operated in good conditions and well meet the control requirements. The soft-switching condition of the converter is analyzed with duty cycle and phase-shifting control based on volt-second product equal. The result shows that when the voltages of three ports are mismatch, soft-switching conditions of all switching devices are met as long as three ports volt-second products are equal. The effectiveness of the duty cycle and phase-shifting control strategy are validated by both the simulation and experimental results.