Research On High Step-up/step-down Nonisolated Bidirectional DC/DC Conversion

Bidirectional DC/DC converters are key devices to reach bidirectional energy transmission between low voltage energy storage devices like battery or super-capacitor and dc-grid bus.Generally,the voltage of battery is low and varies in a wide range,thus the bidirectional DC/DC converters are required to achieve high voltage gain and wide voltage range regulation.Meanwhile,with the increase capacity in energy storage system,more parallel converters are needed to expand system capacity.How to realize high-efficiency power transmission among full opetating range while considering the SOC balance of multi battery modules is a great challenge in energy storage system.Firstly,the topology structure of high voltage gain nonisolated bidirectional DC-DC converter based on integration of nonisolated bidirectional Buck/Boost converter and DC transformer is studies.Through sharing switch bridge arm between bidirectional Buck/Boost converter and DC transformer and superimposing the output voltage of them,high voltage gain and fewer devices can be realized.The bidirectional full-bridge DC/DC converter with high conversion ratio is taken as an example to analyze its operational principles,control strategy and characteristics.With PWM plus phase-shifting control(PPS),voltage regulation and control in bidirectional power transmission can be realized while ZVS of all switches in wide operating range can be achieved.A 1000 W prototype is built to verify the feasibility of the analysis.Furthermore,the three-port operating control of high voltage gain nonisolated bidirectional DC-DC converter is studied.By utilizing the middle port of high voltage gain bidirectional converter as external power interface,bidirectional power transmission among three ports can be realized.Detailed analysis and experimental verification are carried out with a high conversion ratio half-bridge bidirectional converter.What’s more,based on the above analysis,bidirectional three-port parallel structure is built to realize independent charge or discharge regulation of multi battery modules and efficiency optimization in energy storage system at the same time.By utilizing the middle port as energy transmission link among every module,the efficiency optimization of the parallel system at light load can be achieved.Two 1000 W prototypes are built to verify the feasibility and effectiveness of the analyzed method.