Three-Level Full-bridge Bi-directional DC-DC Converter Based On PWM Control

With the rapid development of the global economy, there is a increasing demand of the fossilresources, which results in a more serious energy crisis. Besides, the burning of fossil fuels has causedserious pollution to the natural environment. So it is one of the most effective ways to solve the aboveproblems using of green energy such as solar energy and wind energy instead of traditional fossilfuels.Based on the utilization of renewable energy, the issue focused on the management of energystorage devices in the new energy generating system. The research object of the issue is thebidirectional DC-DC converter which is responsible for the system energy balance, that is to realize abalanced energy relationship between the new energy power supply, grid, energy storage devices andload according to the demand of energy. Thus, the bidirectional converter is a necessary and vital partof the system, so our research on it has a theoretical and practical significance.After a detailed derivation, a three-level full bridge bidirectional DC-DC converter was proposedin this paper,among some control strategies which are better for the topology, the asymmetry PWMcontrol strategy was adopted. Based on the asymmetry PWM control strategy, the bidirectionaloperating mode of the converter as well as the realization of the ZVS in the forward operating modewas analyzed in details. Also, the computing formulas of the voltage and current of each operatingmode in the forward direction were listed. Besides, the application in the system and the realization ofthe flying capacitor voltage-sharing strategy used in the circuit were discussed, then the energymanagement strategy that energy can flow bilaterally was clarified and the effect of the clampingcircuit used in the circuit was explained. According to the design index, the parameters of the maincircuit and control circuit were designed, which included the selection of the main switch, theparameter of the main transformer, resonant and output inductors that belong to the main circuitparameters and the sampling circuit, external clock synchronous circuit, dead band circuit and thedriving transformer that belong to the control circuit parameters.A2kW prototype is built and tested in the lab.The experimental results are presented to verify thevalidity of the proposed thress-level full-bridge bidirectional DC/DC converter and effectiveness ofthe flying capacitor voltage-sharing control and the active clamp technique in the secondary lowvoltage side.