With the shortage of energy and environmental pollution caused by the consumption of traditional fossil fuels, renewable energy sources (RESs) such as solar energy, wind energy, etc. have been widely concerned because of their recycling ability, environmental protection and cleanliness. However, the intermittency and fluctuation of renewable energy will also affect the quality of power supply and bring challenges to the power system. Moreover, the traditional electrical equipment cannot meet the needs of multiple energy supply methods and multi-directional energy flow in the power system under the background of Energy Internet (EI). Energy router (ER) as the key equipment of EI provides a new approach to solve the above-mentioned problems. ER can provide a variety of energy interface, meet the plug-and-play of sources, storages, and loads, manage the multi-direction flow of energy through energy management strategy (EMS) to improve the utilization of renewable energy. Therefore, it has become a research hotspot in the field of EI.
Energy routers are widely used in distribution network, microgrid, house, etc. Current researches of ER in different application fields focus on hardware design based on solid state transformer, EMS, transient process simulation and energy routing mechanism of multi-ER. In most researches, the design of energy router with single DC bus is adopted. On the microgrid level, the ER structures and corresponding EMS are investigated in Refs. [1,2]. The low power house ER structures are presented in Refs. [3,4], the coordinated control strategies and energy management strategies are developed in Refs. [, , , , ]. A hybrid AC-DC system constructed by DC multi-port energy routers (MERs) and AC MERs with smart EMS for the power flow management is presented in Ref. .  proposes and describes the control strategies for ERs in smart community, which considers power interchange between the small-scale RES and the small-scale energy storage unit (ESU) to increase the controllability of the ER . proposes a coordinated energy management strategy of ER for data centers in EI, which reduces the uncertainty in the power supply by combining several energy sources . develops a coordinated control scheme to make full use of RESs and maintaining operational friendly, which consists of reference voltage and current compensation strategy and fuzzy logic control-based power management strategy. A hierarchical coordinated control strategy is proposed for ER used in urban rail transit in Ref.  to enable the multi-port ER operate in a coordinated fashion. The exchanged power of ESUs can be accurately controlled to ensure the service life of ESUs and stabilize the DC bus voltage.
In recent years, ER with multi-DC buses structure such as three-stage structure is applied in some researches, which has the characteristics of more flexible energy flow, higher extensibility, larger system capacity and more networking forms. A model of voltage source converter (VSC) based ERs in microgrids is developed in Ref. , then the power flows between AC and DC sides of ER is optimized and the flexible resources are scheduled strategically . presents an AC-DC hybrid MER as the interface between the power consumer and the distribution network. To prolong battery life and smooth fluctuations of renewable energy generation or load consumption, a corresponding coordinated control strategy with fuzzy logic controller considering unit-time electricity is proposed . provides an advanced EMS for DC MER, the battery state of charge, real-time electricity price and user-side electricity charge are considered to improve the utilization of batteries and the economic benefits. For DC microgrid cluster , presents a novel modular-based topology of ER, which has more advantages in capacity and voltage match than classical topology. A control strategy of solid-state transformer and ESU coordinated operation based on DC bus voltage is presented in Ref.  to realize the system operation of multiple distributed devices in ER. To improve the performance of ER in complex operation mode , proposes a free switching coordinated control strategy . construct a minimum loss model of energy buffer devices, then based on efficiency optimization, presents a rule-based energy buffer strategy for ER. However, due to the impact on DC buses caused by the fluctuation of renewable energy, no ESU or a single ESU configured on one of the DC buses cannot provide better support for both two DC bus voltage of the three-stage structure ER simultaneously, which will affect the reliable operation of ER in certain working conditions. On the other hand, the impact of internal and external shocks from ER on the power quality needs to be fully considered, and redundancy design for the reliable operation of ER is also significant.
Therefore, an ER based on multi-hybrid energy storage system (MHESS) is proposed in this paper. Hybrid energy storage system (HESS) is composed of energy-type ESU and power-type ESU, which can inhibit the power fluctuation and improve the dynamic responsiveness of ER. The power-type ESU can quickly respond to the power fluctuation, while the energy-type ESU can respond to the power demand persistently. Multiple sets of HESSs are configured to both two DC buses provided by the ER, and to avoid the extra energy exchange of HESSs on different buses, the tailored energy coordinated management strategy composed of power allocation strategy for MHESS and mode coping strategy is proposed. HESSs are ensured to be as available as possible by power allocation strategy for MHESS. The island operation mode of ER is divided into 4 scenarios by mode coping strategy based on the principle of maximizing the utilization of renewable energy. The simulation results show that compared with the ER with single HESS, the proposed ER can maintain the stability of the DC bus voltage under different working conditions of the four scenarios, and quickly smooth the power fluctuations on different DC buses during scenarios switching, which verifies the feasibility and effectiveness of the proposed ER. The features of above-mentioned researches and the proposed ER are compared in Table 1.
The contributions of this paper are as follows:
The ER based on MHESS is proposed to support both two DC buses of three-stage structure simultaneously and improve the dynamic performance and redundancy;
The charging/discharging reference power of HESSs are optimized, the minimum discharging timespan is extended to improve the operation robustness of ER and the maximum charging timespan is shortened to improve the availability of ESUs.
The corresponding energy coordinated management strategy is proposed to maximize the utilization of renewable energy and improve power flow of HESSs on different DC buses.
The rest of this paper is organized as follows. Section 2 introduces the topology of ER based on MHESS. The energy coordinated management strategy is proposed in Section 3. Simulation verifications are implemented on MATLAB R2020a/Simulink platform and results are analyzed in Section 4. The paper is summarized in Section 5.
The topology of ER based on MHESS
The traditional three-stages structure of ER includes input stage AC/DC converter, isolated stage DC/DC converter and output stage DC/DC converter. It contains high voltage DC (HVDC) bus and low voltage DC (LVDC) bus, and can provide three-phase high voltage AC (HVAC) bus and single-phase low voltage AC (HVAC) bus to access loads of different voltage levels.
Based on the traditional three-stages structure, the ER based on the MHESS proposed in this paper access photovoltaic (PV) and NL sets of
Power allocation strategy for MHESS
The proposed energy coordinated management strategy consists of power allocation strategy for MHESS and mode coping strategy. Power allocation strategy for MHESS includes three parts: allocation of MHESS total reference power to each HESS, DC bus voltage regulation and allocation of a certain HESS reference power to its battery and SC, as shown in Fig. 7.
Configuration of multiple sets of HESS is benefit to improve the redundancy and control flexibility of ER. In order to extend the lifetime of
Simulation verification and results analysis
In order to verify the effectiveness of ER topology and the proposed energy coordinated management strategy in this paper, the simulation verifications are carried out on MATLAB R2020a/Simulink. The mode coping strategy in the proposed energy coordinated management strategy will be executed at intervals of 0.1 s. In the simulation, 4 sets of HESS are connected to DC buses. HESSs on the LVDC bus are numbered #1 and #2, HESSs on the HVDC bus are numbered #3 and #4. The key parameters of
In order to improve the ability of suppressing power shocks both inside and outside the ER, this paper proposes an ER topology based on MHESS. Compared with existing researches, HESSs are configured on both HVDC bus and LVDC bus to quickly respond the internal and external power demands. Due to the configuration of multiple sets of HESS, the redundancy and control flexibility of ER is improved. Based on the principle of maximizing the utilization of renewable energy, comprehensively considering
CRediT authorship contribution statement
Jingchuan Deng: Investigation, Methodology, Software, Visualization, Writing – original draft. Xinsheng Wang: Conceptualization, Investigation, Writing – review & editing, Supervision. Tao Chen: Data curation, Software, Methodology, Validation. Fangang Meng: Funding acquisition, Supervision, Writing – review & editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
This work was supported in part by the National Natural Foundation of China under Grant 51777042 and in part by the Natural Foundation of Shandong Province under Grant ZR2020ME199.
© 2023 Published by Elsevier Ltd.