| In recent years,new energy,such as hydro power,photovoltaic,have been developed and utilized on a large scale,and when new energy system is connected with the grid,there are problems with large fluctuations and energy unstable transmission.Meanwhile,the distribution-grid of the economic zone in tourist areas generally has obvious seasonal overload problems during the peak tourist season.In order to realize the flexible access of new energy system,it is necessary to study an efficient multi-port energy router with multi-source access,and study how to realize the dynamic and flexible access of new energy system.In this paper,a set of multi-port energy router scheme and its control methods is studied,which realizes the nearby access and consumption of new energy systems and provides new ideas for the realization of clean and low-carbon power supply.This paper is supported by the National Power Conversion and Control Engineering Technology Research Center with the project "Key Technologies of Multi-port Energy Routers Adapted to New Energy Access",Hunan Provincial Innovation Foundation for Postgraduate-Key technology research on “Multi-port power router and control method adapted to new energy access” [CX20190298],National Natural Science Foundation of China,"Multi-port Power Regulator and Its Cooperative Control for High-speed Railway Adapted to New Energy Access" [51977067],and also supported by the Program for Guangdong Introducing Innovative and Enterpreneurial Teams [2017ZT07G237].This paper mainly focuses on the problems of wide-range voltage access of DC new energy systems,bus voltage fluctuations caused by port power disturbance,the energy management probl em with uncertain parameters of multi-port system,and coupling oscillation and the attraction domain estimation of energy router.This paper is studied and discussed with several aspects,that is,the topological structure design and selection of the energy router port,the wide-range voltage smooth transition strategy of the DC port converter,the smooth output control based on the natural switching surface of the AC port converter,the energy management strategy based on the adaptive dynamic p rogramming control,and stability analysis of energy router.The main work and innovations are embodied in the following five aspects:(1)As to the wide-range voltage access of new energy system,a smooth transition control method of a three-level cascaded noninverting Buck-Boost converter(TL-CNIBB)topology for wide-range voltage input are proposed.The modes of the three-level cascaded noninverting Buck-Boost converter are classified and its working principle is analyzed.It is pointed out that the converter has several problems: the optimal mode and the optimal switching sequence are difficult to determine under different voltage gain ratio,and the dead zone/jump problem,voltage balance problem,multi-mode "chattering" problem.As to select the optimal mode and the optimal switching sequence under different voltage gain ratios,the concept of the "nearest two-point criterion" and "nearest triangle criterion" are proposed.Through a hybrid modulation method and the smooth transition technique,the optimal switching modal is selected and the optimal switching sequence is determined.In addition,to comprehensively solve dead zone,voltage balance and multi-mode "chattering" problems,a smoothing control method is proposed for the wide-range voltage input.Finally,the converter is modeled in different modes,and the controllers are designed to ensure the stable operation of the system.Simulation and experiment verified the effectiveness of the method.(2)As to the problem of the DC-side voltage fluctuations of AC ports,a smooth output control method based on Natural Switching Surface(NSS)is proposed.T-type neutral point clamped(T-type-NPC)topology is selected as the AC port of the multi-port energy router.The working mode and working principle are analyzed and it is pointed out that the mathematical model in the dq rotating coordinate system can be simplified to a second-order switching system model.Through the switching system models of different modes,the phase trajectory relationship between the d-axis component of the inductor current and the DC output voltage is derived.When the converter is in the situations ‘start-up’,the DC-side voltage can be quickly followed to the bus voltage reference by the natural switching surface control method;when the power disturbance is injected,T-type-NPC converter can quickly switch to the fastest power tracking mode according to the phase trajectory relationship.Thus,the voltage smooth output control is completed.At the same time,in order to suppress transient current spikes,a natural switching surface control method with the current limit is proposed,which realizes the overall smooth output control of voltage and current and it effectively suppresses voltage fluctuations caused by power mutation and disturbance.Simulations and experiments have verified the effectiveness of the method.(3)As to the multi-port interconnection operation of energy routers,an adaptive dynamic programming(ADP)control based energy management strategy are proposed.ADP is studied to optimize the design of controller parameter to improve the control performance and achieve fast tracking control.Furthermore,the power quality is optimized.In addition,in order to realize the energy optimization management of the system,a multi-modal collaborative optimization control strategy of the energy router is proposed.The system is divided into multiple operating modes according to the system state.In different operating modes,each port of the energy router adopts suitable control strategies and control commands to realize the energy optimal control and the integrated management of system.Here,the energy management strategy based on ADP control realizes the integration and unification of the parame ter optimization of the controllers and the operating mode selection of the system.(4)Aiming to the source-source oscillation and large signal disturbance of energy routers,static stability analysis based on impedance modeling an d domain of attraction estimation based on TS fuzzy modeling are proposed.The impedance model of the multi-port energy router is established and it is obtained that each port converter has different impedance characteristics under different control modes.When the capacitive source,inductive source and negative resistance source are interconnected,the system is prone to impedance coupling and caused the source-source oscillation phenomenon.At the same time,a domain of attraction estimation model of a multi-port energy router is established by TS fuzzy modeling.Based on the Lyapunov energy function and Linear Matrix Inequation(LMI),the region of attraction of the energy router is estimated under different control modes.Here,the calculation method of the stability boundary is given and a theoretical basis is provided for the selection and evaluation of the control mode of the energy router,which avoids the failure and instability problem,caused by the intermittent access to the energy router from multiple sources.In all,it provides the theoretical support for the safe and stable operation of the system.(5)This paper has developed a set of four-port energy router deviceand its energy management system for new energy(h ydropower,photovoltaic)access.It is realized that the efficient utilization of new energy and the reliable power supply of the distribution network around Erhai Lake. |
