Research On Dual-Active-Bridge-Based Grid-Tied Bidirectional AC/DC Converter

In recent years, some standards of the DC power supply system in data center were published at home and abroad. And it turns out that up to 400V(260~400V) DC power feed system is the development trend in DC power supply system. Compared to the narrow DC bus scheme, the bus voltage range of the wide DC bus scheme is directly decided by the output voltage of the battery group. Therefore the system structure becomes simplified and the cost is relatively lower.But the latter stage converter will have more requirements about the wide range voltage.As the interface between the DC power supply system and the grid, the bidirectional AC/DC converter is of great importance to the DC power supply system. Such converter bearing the task of controlling the continuous energy flow into and out of the grid, should not only apply to the wide range of DC bus, but also control the grid side current to achieve better power factor.According to the requirements above, this paper gives a solution of the dual-active-bridge-based bidirectional grid-tied AC/DC converter. The converter is a two-stage topology, the former is the dual-active-bridge-based bidirectional DC/DC converter(DAB), the latter is a single-phase-fullbridge bidirectional AC/DC converter. The former is responsible for the stability of DC bus voltages, the latter is responsible for the stability of the middle dc capacitance voltage and controlling the grid current.In this paper, a detailed analysis about the working principle of the two-stage converter is given. The traditional phase-shift modulation of DAB has many problems, reflux phenomenon at light load power is serious, and the soft switching range is narrow. In view of the problems, this paper gives an improved phase-shift modulation,which is the dual-phase-shift modulation. The grid-tied control target of the bidirectional AC/DC converter is achieved through the V-I curve of the interface between the dc power supply system and the grid. The control strategy and the design process of the converter are put forward.By the theory analysis, a 3k W prototype based on TMS320F28335 DSP was designed. The paper gives detailed hardware and software design. The working principle of the two-stage converter and the proposed control strategy described previously have been implemented using the prototype. According to an experimental result, the DAB converter can work in a wide voltage range. The static performance and the dynamic performance of the double-loop control scheme also satisfy the control requirements. The grid-tied bidirectional AC/DC converter proposed in this paper can be run in rectifier mode, and has good grid current quality, providing a pretty good reference for the construction of the DC power supply system.