Rule-based energy buffer strategy of energy router considering efficiency optimization

The next-generation electric power system, known as the smart grid, will incorporate a large number of renewable energy resources that fundamentally change the energy management paradigm. In order to manage efficiently the energy supply and demand in the power grid, energy routers are required which adjust dynamically the energy distribution in the grid, which is so called the Energy Internet. We discuss in this paper the functional expectations on the energy router design and present our preliminary research results on the energy router architectural construction and communication performance. This paper documents our work-in-progress on the design and implementation of energy router, a critical equipment to enable intelligent energy management in the smart grid.

Background: The energy router based on power electronic technology is the core equipment of energy internet. Energy router can control the voltage of the port and regulate the power injected into the network flexibly. It is of great significance to study how the capability of the energy router can be used to improve characteristics of the power system. Methods: Based on the analysis of energy router, we construct a unified AC-DC power flow model for energy router considering its different control modes. Then, we establish an optimal power flow formulation for the energy router incorporated AC-DC network and propose the multi-objective function to optimize the comprehensive performance of the network. Several cases are observed and analyzed on a modified IEEE-57 system. Results: The result verifies that the optimal power flow formulation can optimize the control values of ports of the energy router and improve the operating state of the power system. The optimal target presented in this paper can improve the characteristics of the grid better than a single optimal target. Conclusion: Energy router will play a vital role in the energy internet based on the power system. The characters of the power system can be improved and the operating costs can be reduced by utilizing the functionality of energy router in regulating power flow.

A hybrid energy storage system (HESS) consists of two or more types of energy storage components and the power electronics circuit to connect them. Therefore, the real-time capacity of this system highly depends on the state of the system and cannot be simply evaluated with traditional battery models. To tackle this challenge, an equivalent state of charge (ESOC) which reflects the remaining capacity of a HESS unit in a specific operation mode, is proposed in this paper. Furthermore, the proposed ESOC is applied to the control of the distributed HESS which contains several units with their own local targets. To optimally distribute the overall power target among these units, a sparse communication network-based hierarchical control framework is proposed. This framework considers the distributed control and optimal power distribution in the HESS from two aspects - the power output capability and the ESOC balance. Based on the primary droop control, the total power is allocated according to the maximum output capacity of each unit, and the secondary control is used to adjust the power from the perspective of ESOC balance. Therefore, each energy storage unit can be controlled to meet the local power demand of the microgrid. Simulation results based on MATLAB/Simulink verify the effectiveness of the application of the proposed equivalent SOC.

This paper takes the energy router with DC bus as the research object. Due to the needs of DC bus voltage stability regulation in the energy router, a voltage hierarchical coordinated control method using the droop control principle is proposed. The DC bus voltage of the system is divided into three layers. In different voltage control layers, grid connected unit, energy storage unit and photovoltaic unit are used as voltage sources to control bus voltage stability and power balance. This control method only needs each converter to control its own working state according to the local voltage signal, and does not need the communication line between the central controller and each converter, which can simplify the system structure. A simulation model is built in Matlab / Simulink to verify the proposed voltage hierarchical coordinated control strategy. The simulation results show that the control strategy can realize the stable operation of the energy router, and the operation modes of each converter can switch smoothly, which verifies the effectiveness of the control strategy.

The usage of batteries and supercapacitors in the field of electric vehicles is becoming increasingly prominent in both research and development. Due to the complementary advantages of the two systems, high energy density, and high power density, a combined battery/supercapacitor system offers potential. To effectively utilise the potential of such a hybrid energy storage system (HESS), one requires an intelligent energy management system (EMS). The EMS is responsible for controlling the electrical power between the battery and the supercapacitor in such a way that the required power can be optimally distributed at all times (currently and in the future). For this purpose, the energy management system utilises information on the driving route and, based on this information, shall calculate a global strategy for the continuous power distribution. The controlled power distribution should take place in real time and be robust against discrepancies so that unpredictable or unreliably predictable events do not significantly influence the functionality. For the implementation of the concept, a rule-based power distribution is implemented in combination with a predictive energy management. Here, the energy management is combined with a rule-based strategy calculation based on data on the route to be driven with a global optimization for the calculation of a route-specific strategy. Depending on the selected objective, the increase in energy efficiency, or lifetime, the operation of the power control is optimised. Due to the functional separation, the continuous power control can operate in real time, while more computational time can be spent on the calculations of the power management strategy, which accordingly does not need to be executed in real time. The results show that by using the presented EMS, especially in combination with a route-specific parameterisation, a significant effect on the energy efficiency and/or battery lifetime can be achieved. The average battery energy consumption can be reduced by up to 9.14% on urban routes. Regarding battery lifetime, the average battery usage can be reduced up to 13.35% and the battery energy losses even up to 62.72%.

Due to the different characteristics of energy storages (ESs), proper dynamic power allocation to ESs in a hybrid energy storage system (HESS) is of high significance. To this end, integral droop (ID) controllers have been applied to a class of ESs (denoted as ES $_H$ s) with high ramp rates but low energy density. Conventional V-P droops have been adopted to regulate a class of ESs (referred to as ES $_L$ s) with high energy density but limited response speeds. Based on the cooperation of IDs and V-P droops, high/low frequency components of the load change can be autonomously responded to by ES $_H$ s/ES $_L$ s, thus possibly prolonging the HESS lifetime. However, existing works only focus on the small signal stabilization of HESSs, whose validity may only hold under certain equilibria. To address this issue, an original self-disciplined large signal stabilizing scheme is presented in this paper. Under this scheme, a compound stabilizer comprising disturbance observers and a backstepping controller is delicately designed for an ES-interfaced converter. The observers estimate the possible disturbances induced in the converter. Those estimations would be further neutralized by the backstepping controller, which simultaneously guarantees converter system stability in the large signal sense and drives the converter terminal voltage tracking the reference given by either the ID or V-P droop. Because of the proposed stabilizer, no communication happens in HESS, and the large signal stability of overall system can be spontaneously realized with rigorous mathematical proofs by Lyapunov techniques. This stabilizing scheme for HESS application is arguably reported for the first time in this article. A detailed parameter selection guideline is also provided. The effectiveness and feasibility of the compound stabilizer are verified by both simulations and hardware experiments.

Public transportation based on electric vehicles has attracted significant attention in recent years due to the lower overall emissions it generates. However, there are some barriers to further development and commercialization. Fewer charging facilities in comparison to gas stations, limited battery lifetime, and extra costs associated with its replacement present some barriers to achieve better acceptance. A practical solution to improve the battery lifetime and driving range is to eliminate the large-magnitude pulse current flow from and to the battery during acceleration and deceleration. Hybrid energy storage systems which combine high-power (HP) and high-energy (HE) storage units can be used for this purpose. Lithium-ion capacitors (LiC) can be used as a HP storage unit, which is similar to a supercapacitor cell but with a higher rate capability, a higher energy density, and better cyclability. In this design, the LiC can provide the excess power required while the battery fails to do so. Moreover, hybridization enables a downsizing of the overall energy storage system and decreases the total cost as a consequence of lifetime, performance, and efficiency improvement. The aim of this paper is to investigate the effectiveness of the hybrid energy storage system in protecting the battery from damage due to the high-power rates during charging and discharging. The procedure followed and presented in this paper demonstrates the good performance of the evaluated hybrid storage system to reduce the negative consequences of the power peaks associated with urban driving cycles and its ability to improve the lifespan by 16%.

In the context of energy management during digital transformation, traditional energy storage devices face challenges in multi-source coordination and efficient management. The key issue for system optimization is how to stabilize the management of multiple energy storage units. To address this, the study innovatively proposes a Hybrid Energy Storage System integrating a Multi-Port Transformer and Direct Current Bus. By constructing multi-port control factors, the system achieves coordinated optimization of the energy storage units, through dynamic adjustment of multi-port control factors and energy conversion matrices, the system can flexibly allocate power output from various energy storage units according to load demands, ensuring stable system operation. Experimental results in a microgrid system show that the integrated control system has a response time of 2.3 ms under 80% load, significantly outperforming the Proportional Integral Control (8.7 ms) and during the energy storage unit switching process, the voltage fluctuation rate is only 0.8% with a switching time of just 1.8 ms, and system stability reaching 98.5%. Under high-load conditions, the energy conversion efficiency is 96.8%, and the power distribution error is only 1.2%. Compared to traditional energy storage devices, the initial investment cost of this device is reduced by 7.4%, and the annual maintenance cost is reduced by 21.7%. These results indicate that the improved hybrid energy storage device not only possesses excellent energy management capabilities but also significantly reduces operational costs and environmental impact. The study provides an efficient technical solution for managing complex energy systems, which is of great significance for promoting smart grid construction and achieving green, low-carbon goals.

A Hybrid Energy Storage System (HESS), consists of two or more types of energy storage technologies, mostly includingbatteries, flywheels, super-capacitors, and fuel cells. The complementary features of HESS make it outperform any single energy storage device depending on the application energy requirements in different scenarios/conditions. To overcome the opposing limitations of battery and supercapacitor, the battery has relatively high energy density but low power density as compared to the supercapacitor, an active battery/supercapacitor hybrid energy storage system (HESS) with dc/dc converter is proposed. However, the main issue with an active battery/supercapacitor HESS is current flow control to accomplish two goals: minimizing the magnitude fluctuation of current flowing in/out of the battery and minimizing energy loss experienced by the supercapacitor/s. The purpose of this article is to perform optimization of an active battery/supercapacitor HESS for a Hybrid Electric Vehicle (HEV). The HESS topology used for the optimization consists of a parallel connected battery and supercapacitor/s to drive the load through the respective dc/dc converters. In this article, an efficient multiplicative-increase-additive-decrease concept-based algorithm is used to ensure an optimal solution. MATLAB simulations are used to demonstrate that the proposed scheme can optimally minimize the magnitude fluctuation of the battery current and the SC energy loss.

Although steam is widely used in industrial production, there is often an imbalance between steam supply and demand, which ultimately results in steam waste. To solve this problem, steam accumulators (SAs) can be used as thermal energy storage and buffer units. However, it is difficult to promote the application of SAs due to high investment costs, which directly depend on the usage volume. Thus, the operation of SAs should be optimized to reduce initial investment through volume minimization. In this work, steam sources (SSs) are classified into two types: controllable steam sources (CSSs) and uncontrollable steam sources (UCSSs). A basic oxygen furnace (BOF) was selected as an example of a UCSS to study the optimal operation of an SA with a single BOF and sets of parallel-operating BOFs. In another case, a new method whereby CSSs cooperate with SAs is reported, and the mathematical model of the minimum necessary thermal energy storage capacity (NTESC) is established. A solving program for this mathematical model is also designed. The results show that for UCSSs, applying an SA in two parallel-operating SSs requires less capacity than that required between a single SS and its consumer. For CSSs, the proposed minimum NTESC method can effectively find the optimal operation and the minimum volume of an SA. The optimized volume of an SA is smaller than that used in practice, which results in a better steam storage effect.

Hybrid Energy Storage Systems (HESSs) are based on different storage elements such as batteries or ultra capacitors (UC), aiming to implement a system with high energy and power density. These HESSs using multi-modular power converters to incorporate in each power electronics module a different storage element and then, these modules are interconnected to create the total system. On the other hand, the Modular Multilevel Series Parallel Converter (MMSPC) not only allows dynamic interconnection among the modules in series connection but also in parallel connection. This extra switching state among the modules allows new features and operation modes. In this paper, a HESS based on MMSPC topology is presented. The novel HESS-MMSPC topology is simulated with UC and batteries as storage units, and this proposed system is interconnected to an electrical grid. The control strategy and evaluation of the operation of the proposed system are presented.

Multi-agent deep reinforcement learning based distributed control architecture for interconnected multi-energy microgrid energy management and optimization

In general, one of the most important goals of smart grids; the establishment of networks that allow for more distributed generation and energy storage at the end-user side. Energy storage technology; It has great potential to improve electric power systems, increase renewable electricity generation and offer alternatives to petroleum-derived fuels in the transportation sector. This study sheds light on the advantages offered by energy storage technologies, which play an active role in solving the problems encountered during the grid integration of renewable energy sources in smart grid applications. In addition, different solutions offered by different energy storage technologies such as Vanadium are also evaluated in this study. In this study, an energy storage unit with high energy and high power density was designed with the Hybrid Energy Storage System (V-HEES) consisting of vanadium and ultra-capacitor. In addition, the results of the hybrid energy storage system consisting of vanadium and ultra-capacitors and the application areas of these technologies in smart grids are also included.

Supercapacitors, often referred to as Ultracapacitors, are electrochemical energy storage devices with high power density and moderate energy storage which serves as a bridge between the conventional capacitors and batteries. While conventional capacitors offer extreme power but negligible energy and batteries provide high energy density for long-term storage, Supercapacitors fill the gap between these technologies. By combining the rapid charge-discharge characteristics of conventional capacitors with comparatively enhanced energy storage capability associated with electrochemical systems, supercapacitors become highly suitable for applications that require substantial power delivery over short time interval. These distinct abilities of supercapacitors offer exceptional cycle stability, operational reliability and long service durability. The review focuses on the use of supercapacitors in power density and long cycle life applications, such as quick acceleration and regenerative braking in HEVs, power management in HESS, and battery-less electric vehicle technology based on supercapacitors with ultra-fast charging capabilities. In this paper, a comprehensive review of supercapacitor technology is presented, including the working principle, classification, materials, characteristics, and latest developments in supercapacitor technology. Moreover, the review critically discusses the applications of supercapacitors, such as RBS and HESS, along with the current challenges, limitations, and future research avenues for the betterment of supercapacitor technology. Keywords— Supercapacitors; High Power Density; Hybrid Energy Storage System (HESS); Regenerative Braking System (RBS); Electric Vehicles; Energy Management

Batteries and supercapacitors (SC) complement one another; a battery has a relatively high energy density but a low power density, whereas an SC has a relatively high power density but a low energy density. In order to offset their opposing limitations, an active battery/SC hybrid energy storage system (HESS) using a dc/dc converter has been proposed. The major problem concerning an active HESS is in how to control the current flow in order to achieve two objectives: the minimization of the magnitude/fluctuation of the current flowing in and out of the battery and the energy loss seen by the SCs. This problem has not been analytically investigated for an optimal solution regarding these two goals. In this paper, we present an optimal energy management scheme for active HESS. In order to obtain the optimal solution, we formulate the problem as an optimization problem concerning these two objectives. Observing that the feasibility and optimality of the solution critically depends on the boundary parameters of the problem, we present an algorithm that effectively adjusts the parameter values. The proposed algorithm is based on the multiplicative-increase- additive-decrease principle, which guarantees a feasible optimal solution. Through MATLAB simulations, we demonstrate that the proposed scheme can optimally minimize the magnitude/fluctuation of the battery current and the SC energy loss.