Research On Topology And Control Strategy Of DC Solid State Transformer Based On Dual Active Bridge Integrated Boost Unit

The excessive development and utilization of traditional fossil energy has caused a serious energy crisis and environmental pollution,which makes the use of renewable energy an inevitable trend.With the support of fast-developing power electronics technology,the DC Energy Internet centered on DC energy router has demonstrated many advantages such as strong distributed energy capabilities,high power supply reliability,and low operating costs.As a key link in the DC energy router,the DC solid-state transformer composed of multiple DC-DC converters through a combination of input side series and output side parallel(ISOP)has become a research hot spot in academic circles in recent years.At present,there are many kinds of DC-DC converters that can be used for the DC solid state transformer and they all have three characteristics: voltage conversion,bidirectional power transmission,and electrical isolation.The most typical and most applied converter is the dual active bridge(DAB)DC-DC converter.However,the ISOP type DC solid state transformer based on DAB converter has the problems that the voltage on the primary and secondary sides of the transformer of the sub-modules cannot always be matched,and the failure to isolate the fault caused by the series-side concentrated capacitors.Based on the above researches,this paper proposes a dual active bridge integrated boost converter(DABIB)that can be used in DC solid state transformer by multiplexing the switches of the boost converter and the dual active bridge converter.The thesis first gives the topology of the dual active bridge integrated boost converter,and analyzes its working principle in the PWM and phase shift modulation.Based on the fundamental analysis method,the power transmission characteristics of the converter are deduced and the soft-switching conditions of the converter are analyzed,and the control strategy of the converter is obtained.The topology of the DC solid-state transformer with dual active bridge integrated boost converter as its sub-module and its operation under the joint control strategy composed of output voltage loop,input voltage stabilization loop and input voltage equalization loop are analyzed.The failure types and causes of the DC solid state transformer is analyzed,and the system's treatment method and system redundant operation scheme in the case of external faults and sub-module faults are given.Finally,the parameter selection and the design of the magnetic components were carried out.A 2-module experimental prototype with STM32 and FPGA as the core controller was built to verify the correctness of the topology and the feasibility of the control strategy.