Research On Topology And Control Of AC-DC Hybrid Multi-port Power Router

In recent years,the increasing shortage of traditional fossil fuels as conventional energy and negative environmental impact have prompted the global research to replace traditional fossil fuels with renewable energy.The penetration rate of renewable energy represented by wind energy and solar energy in power grid is higher and higher.Most of these renewable energy resources depend on environmental conditions and have strong randomness and volatility.The high penetration of this intermittent energy in the power system reduces the energy security of the power system.In addition,the structure of the power system is changing from the traditional grid with one-way power flow to the smart grid with distributed generation structure.In this context,the concept of energy Internet came into being.Electric energy router is an important part of energy Internet.It can not only be used as a traditional transformer to achieve voltage conversion and voltage isolation,but also provide AC and DC ports with different voltage levels to realize the access of different distributed generation devices.Therefore,this paper studies the core equipment of AC/DC hybrid multi-port electric energy router,and focuses on its topology and control strategy.Firstly,the topology and working principle of electric energy router are studied.By comparing the advantages and disadvantages of several topologies,the topology of three stage multi-port electric energy router with DC port is determined,including cascaded Hbridge rectifier stage,intermediate DAB isolation stage and low voltage AC/ DC output stage.The working principle of cascaded H-bridge rectifier circuit is studied,four working states of cascaded H-bridge rectifier circuit are analyzed,and the modulation mode of carrier phase shift is determined;By comparing and analyzing the half bridge and full bridge structures of the isolation stage,the DAB structure of the isolation stage is determined,and six working modes of the DAB under the single phase shift control are analyzed,and the relationship between the DAB transmission power and the duty cycle is analyzed;The topology of low voltage AC and DC port is given and its functional requirements are analyzed.Secondly,the key parameters of three stage electric energy router are designed.The parameter design of electric energy router is closely related to system efficiency and performance.After determining the connection mode of the rectifier stage,the number of cascaded H-bridges and the topology of each stage,the principle and characteristics of parameter design of electric energy router are discussed,and based on the principle of energy balance,the key parameters of three-stage electric energy router are designed.In the rectifier stage,the AC filter inductance and DC filter capacitor are analyzed and designed;The parameters of transformer leakage inductance and low voltage DC bus capacitance are designed in isolation stage;The design of output stage parameters is similar to the rectifier stage,and the filter inductance and capacitance of output stage are determined.Then,the control strategy of three stage electric energy router is studied.The mathematical model of cascaded H-bridge circuit is established,the small signal model is established by linearizing the average model,and the common duty cycle control strategy is adopted.On this basis,the traditional voltage balancing method is improved to solve the DC side voltage imbalance problem.The switch equivalent model and small signal model of DAB isolation stage are established,and a power balance method without current sensor is adopted based on single phase shift control,which saves the cost.Aiming at the problem of bus voltage instability at low voltage output port,this paper focuses on the electric spring control method,and a control strategy based on electric spring is proposed for low voltage AC and DC load ports,which effectively ensure the stability of port voltage and improves the reliability of electric energy router.Finally,the simulation model of AC/DC hybrid multi-port electric energy router is built.The electric energy router is simulated and analyzed in three working conditions: stable state,load switching state and AC/DC port connected to distributed photovoltaic,and the electric energy router is applied to improve the power quality,and the two situations of voltage swell and droop are simulated and analyzed.The simulation results show that the designed AC/DC hybrid multi-port electric energy router can realize the interconnection between different power forms and voltage levels,and provide a standardized interface for voltage stability of distributed generations and loads,which can achieve voltage isolation transformation and improve power quality at the same time.