Optimal Design Of Hybrid Modular DC Solid State Transformer

As the key equipment of flexible dc distribution network,the control performance and conversion efficiency of DC solid-state transformers(DCSST)are significant for improving system practicability and economic efficiency.Unlike the existing DCSST,this paper presents a hybrid modular solid-state transformer(HMDCSST),which combines the phase shift dual active-bridge(PS-DAB)and the series resonant DAB(SR-DAB)in the way that the inputs are in series and the outputs are paralleled.The PS-DAB has the advantage of flexible voltage control while the SR-DAB features high efficiency,both of which can be inherited by the HMDCSST.Thus comparing with the original DCSST,the HMDCSST can improve power efficiency and reduce system design complexity,without sacrificing the flexible controllability.Firstly,Working principle of the HMDCSST is analyzed,and the average mathematical model and power loss model are derived.Then detailed analysis of the input/output characteristics and power transmission efficiency under constant output voltage control mode are carried out.The experimental platform was set up to verify the operating efficiency characteristics and input-output characteristics of the proposed hybrid model.Secondly,at the device parameter level of the basic module,this thesis studies the parameter optimization design of HMDSST;First,the system performance requirements are determined,and based on the sensitivity analysis of the influence of system parameters on performance indicators,the optimization parameter subspace is divided,and a multi-level optimization strategy is adopted to improve the optimization efficiency.In addition,a simulation model is built to verify the obtained optimization results.Finally,at the cascaded modular topology level,with the specific number of unit modules as the target parameter,this paper studies the configuration of redundant modules in HMDCSST to improve its performance in terms of reliability,operating efficiency and economy;Based on analyses of the topology and working principle,the detailed reliability model of HMDCSST is established,by comprehensively considering the main parts including sub-module,main control and valve cooling systems.Then based on the reliability model,the impacts of running time and redundancy configuration on system reliability are analyzed quantitatively,An optimal configuration method of redundant modules is proposed,and corresponding simulation examples are verified.