Research On The Three-Port DC Energy Router And Its Control In Microgrid

Microgrid and the energy internet technologies can achieve the local consumption and regulation of distributed energy and the optimization of integrated energy,which are also considered to be an effective way to fulfill the function of different renewable energy and load interfacing with the increasing demand for energy and the increasingly scarce fossil energy.With the access of AC/DC distributed energy and the demand of multi-voltage level power supply for low-voltage DC load,some important areas of the DC distribution network may form multiple low-voltage DC microgrids.The traditional dual-port power converter can not meet the energy scheduling and power coordinated control of interconnection operation between multiple DC microgrids,and the concept of microgrid energry router emerges as the times require.In view of the key technical issues of energy router in the application scenario of DC microgrid,this paper mainly carries out the following research work:Firstly,the domestic and international research statuses of DC microgrid and energy router are introduced.The three-port DC energy router topology based on triple active bridge(TAB)converter is presented and its basic working mechanism is analyzed.The power flow between the ports is analyzed by the Y-type equivalent circuit of the three-winding transformer.The power control equation is derived and the mathematical model of the three-port DC energy router is also established based on the classical linear control theory.Furthermore,to prevent defecs of conventional phase-shift modulation such as large rms current and system losses in three-port DC energy router,an optimal modulation scheme of triangular current mode modulation(TCM)is proposed from the perspective of reducing TAB reactive power and RMS current.The TCM operation mechanism is analyzed.The characteristics of voltage,current and transmission power of each component are deduced.The method eliminating circulating current or non-active current component by making the inductor current discontinue to reduce conduction losses is discussed.In addition,the characteristics of load power fluctuations or power flow switch are analyzed.Appropriate voltage stability control strategy is designed.The validity and effectiveness of the proposed TCM strategy applied to three-port DC energy router are verified with simulation and experiment.Moreover,for the port power coordinated control of three-port DC energy router in DC microgrid,the operating state of the three-port dc microgrids and the working mode of each port of the energy router are analyzed.On this basis,the problems and limitations of conventional droop control of single-bus DC microgrids are revealed.And the power coordinated control strategy based on the normalized droop phase-shifted control is proposed for three-port DC energy router.Comparing to the conventional single droop control method,this power coordinated control method can realize effectively rational allocation energy among multiple DC microgrids and reduce the bus voltage deviation in each DC microgrid.The required exchange power between the dc sub-grids of different voltage levels can be obtained by standardizing the voltage-active power droop characteristic of the single-bus DC microgris.In addition,there is no need to switch port working mode of the three-port dc energy router to ensure the power support of each DC sub-microgrid under normal,abnormal and power failure conditions.The correctness and feasibility of the proposed droop phase shift coordinated control method applied to the three-port DC energy router are verified by the simulation results.