State Of Charge Balancing Research Articles

Dynamic SOC Balance Strategy for Modular Energy Storage System Based on Adaptive Droop Control

This paper proposes a dynamic state-of-charge (SOC) balance control strategy for the modular super capacitor energy storage system (ESS). The strategy takes SOC information as the droop variable and introduces the SOC of each module into its independent current closed loop by inverse droop control, so that the system can adjust the average operating current of each sub-module according to its SOC in the system dynamic charging and discharging process. Moreover, a concise unified current compensation method is proposed to minimize system current deviation caused by the balance algorithm. Compared with the traditional control strategies, the proposed strategy does not need to exchange SOC information between sub-modules, thus effectively reduces system communication data. In addition, the proposed strategy not only has favorable voltage control ability and stability, but also has a concise control structure. The proposed balance control strategy can further improve the modularity and reliability of the modular ESS, which is helpful to promote the application of the system in medium and high voltage applications.

An Improved Droop Control Method for Energy Storage Module of DC Microgrid

This paper proposes an improved droop control method with state of charge (SOC) balance function for energy storage module of DC microgrid. The average SOC of all energy storage modules is obtained by low bandwidth network. The SOC balance controller calculates the difference between each module’s SOC and average SOC and then adjust the droop coefficients according to the difference. As the coefficient changes, the output power of module is allocated according to its SOC and eventually achieve balance. Besides, secondary voltage controller is employed to compensate DC bus voltage drop. Also, the stability of the proposed method is studied by small-signal analysis. The effectiveness of the proposed method is finally verified by MATLAB/Simulink simulation.

A centralized coordinated control strategy for distributed generation when microgrid on grid

This paper presents a centralized and coordinated control strategy for microgrid, whose control strategy includes the coordinated control of renewable energy sources (RESs) and energy storage systems (ESSs). To solve the schedulability of distributed generation in a microgrid, when it operates in grid-connected, a multiple operation mode is adopted, through switching the operation mode, the charge/discharge and state of charge (SOC) of ESSs can be maintained, and the loads will be shared by RESs first when microgrid occurs power deficiency, it reduces loss of ESSs. In this paper, a secondary control strategy for the microgrid model by simulated in MATLAB/Simulink, it through switched three modes, improves schedulability of microgrid and realizes SOC balance smoothly. The results show centralized and coordinated control strategy is accurate and useful.

Research on integration simulation and balance control of a novel load isolated pure electric driving system

Battery safety and driving range hinder the development of electric vehicles (EVs). This paper proposes a novel dynamic driving system-load isolated pure electric driving (LIPED) system. Keep working in its most economical point/area as energy source, a generator set is integrated and completely isolated from driving load. Two battery packs can be intelligently switched to ensure stable and sufficient power/energy supplying within their optimal discharge depths. A LIPED-EV prototype model on the basis of a light truck is developed by matching various components parameters of the power system, and the feasibility and superiority of the LIPED system are verified through performance simulations on power and economy performance. The comprehensive fuel consumption saves 17.4% compared with the prototype car. Besides, a collaborative driving control strategy is developed based on nine state of charge (SOC) combinations and five driving conditions. Additionally, to realize rapid SOC balancing of battery modules and adaptively recover braking energy, a discrete-input series-output battery grouping system is proposed via adopting a flip-up four-quadrant topology. The SOC convergence effects in various situations such as congenital inconsistency and voltage surge after module exits are also verified through multiple sets of experiments under the new European driving cycle.

Voltage-SOC balancing control scheme for series-connected lithium-ion battery packs

Abstract The basis for determining whether the cell needs to be balanced is generally the voltage or SOC (state of charge), the voltage balancing control scheme is simple but performs poorly, the SOC balancing control scheme performs well but needs to estimate the SOC of all cells. Based on the analysis why existing naive approaches are not effective for voltage balancing control scheme, the voltage-SOC balancing control scheme is proposed, which has the advantages of simple of voltage balancing control scheme and well performance of SOC balancing control scheme. By utilizing the difference of voltage of cell and SOC of battery pack, the difference of SOC between two cells can be obtained indirectly, and the transition from voltage balancing control scheme to SOC balancing control scheme can be realized, while the advantages of voltage balancing control scheme and SOC balancing control scheme are retained. The 4 experiments designed show that the estimated errors of the difference between the SOCs of the two cells are 0.24%, 5.3%, -5%, and 0.8%, respectively, which proves the excellent performance of voltage-SOC balancing control scheme.

Distributed State-of-Charge Balance Control With Event-Triggered Signal Transmissions for Multiple Energy Storage Systems in Smart Grid

Modern power grid is increasingly integrated with battery energy storage systems (BESSs). This paper deals with the problem of state-of-charge (SoC) balance control for multiple distributed BESSs in smart grid. The BESSs are expected to work cooperatively to not only fulfil the overall power requirement but also meet the constraints of the same relative SoC variation rate. To achieve this objective, a distributed SoC balance control approach is presented with event-triggered signal transmissions. It is designed with the dynamic average consensus (DAC) mechanism for parameter estimations. The DAC enables distributed control of each BESS through communicating with its neighboring BESSs. Different from traditional periodic signal transmission, the event-triggered signal transmission embedded in our approach allows each BESS to transmit signal to its neighboring BESSs only when needed, thus reducing the communication traffic. Theoretical lower bounds are established for consecutive interevent intervals such that the Zeno behavior is excluded. Case studies are conducted to demonstrate the effectiveness of the presented approach.

Decentralised primary and secondary control strategies for islanded microgrids considering energy storage systems characteristics

One of the main subjects of Microgrid (MG) islanded operation is its stability. Using the Energy Storage Systems (ESSs) in MGs, the stability can be improved. To ensure the proper operation of the ESSs, their State of Charge (SoC) should be monitored and controlled. In this paper, a new decentralized control method based on the conventional droop method is proposed which considers different types of ESSs used in islanded MG, i.e. ESSs with high power density and high energy density. In the proposed method, the ESS units are divided into two main categories. The master ESS is the main primary frequency control unit and the other ESSs respond to active and reactive power variations of the load and participate in the secondary control of frequency. For each of these categories, a new control method is proposed. The proposed method, including the primary and secondary control, is decentralized, and based on local measurements. Moreover, in the proposed method, a SoC equalization of ESSs is considered. To assess the stability of the MG, a small signal stability model is developed. Three scenarios are simulated to verify the effectiveness of the proposed method in MG frequency control and ESSs SoC balancing.

Distributed Control System With Aperiodic Sampled Time-Delayed Data for Batteries and Renewable Energy Sources in Microgrid

This paper proposes an aperiodic sampled and time delayed data based distributed control system for frequency restoration, state of charge balancing and voltage restoration in a microgrid with distributed batteries and PV systems. Lyapunov–Krasovskii functionals and linear matrix inequalities are used to calculate the control system parameters and ensure its stability. The proposed control method is scalable since the stability depends only on the largest and smallest/second smallest eigenvalues of the communication graph Laplacian matrices. Real-time digital simulator is used to verify the proposed control method on an IEEE 13 node test feeder with variable loads.

A Cooperative Adaptive Droop Based Energy Management and Optimal Voltage Regulation Scheme for DC Microgrids

This paper presents an adaptive droop based cooperative energy management scheme for a photovoltaic (PV) battery based autonomous dc microgrid. To overcome the basic challenges in managing multiple batteries in a distributed dc network, a cooperative cyber network is employed to formulate an enhanced adaptive droop control philosophy. With PV panels operating as a constant power source at maximum power point tracking (MPPT), battery energy storage systems cooperate among themselves to balance state-of-charge (SoC) between them and undergo constant voltage (CV) charging mode when the condition arises, which is handled using the proposed adaptive droop concept. Further emphasis is given on optimal voltage regulation to induce robustness against time-delay as compared to the conventional voltage observers, which cause high observing error. Moreover, the design criteria of the proposed strategy is provided to ensure system stability under normal and time-delayed conditions. The proposed control strategy is simulated in MATLAB/SIMULINK environment to demonstrate SoC balancing, CV charging albeit various communication issues such as delay and multiple link failure. The proposed strategy is further tested on an field-programmable gate array (FPGA)-based experimental prototype to validate the effectiveness of the proposed strategy.

Active SOC Balancing Control Strategy for Modular Multilevel Super Capacitor Energy Storage System

This paper presents an active state-of-charge (SOC) balancing control strategy for modular super capacitor energy storage system (ESS). The strategy has a master–slave structure, including a common dc bus voltage loop and individual slave current loop for each submodule. The common voltage loop ensures the ability of the system to stabilize dc bus voltage cannot be affected by SOC balancing control, and provides a same original current reference for all submodules. SOC information is introduced into current loops to achieve SOC balancing control. The highest SOC is taken as a reference for low SOC modules, thus, the low SOC modules can regulate the submodule average operation current according to the SOC reference and their own SOC. In order to minimize system current deviation caused by the introduction of SOC, a current correction method is proposed to improve system current regulate performance. The proposed strategy can achieve SOC balancing control during ESS charging and discharging process dynamically, in addition, the modularity of the system is improved and the proposed strategy has favorable stability. A modular ESS prototype consisting of three half-bridge submodules is tested in the laboratory, and the experimental results verify the effectiveness of the proposed control strategy.

State-of-charge balancing control for battery energy storage system based on event-triggered scheme

In this paper, an event-triggered control strategy is proposed to achieve state of charge (SoC) balancing control for distributed battery energy storage system (BESS) with different capacities’ battery units under an undirected topology. The energy-dispatching tasks of the (BEES) consist of the supply–demand balance and the (SoC) balance. Multi-agent consensus theory is utilized to achieve SoC balance. The introduction of event-triggered mechanism can reduce the consumption of communication. A sufficient condition is derived to achieve the consensus of the BESS’s SoC and power. Simulations are presented to illustrate the validity of the theoretical result.

Distributed Reactive Power Control and SOC Sharing Method for Battery Energy Storage System in Microgrids

Battery energy storage system (BESS) is a pivotal component to increase the penetration of renewable generation and to strengthen the stability and reliability of the power system. In this paper, for the purpose of the state of charge (SOC) balancing and reactive power sharing, a multiagent system (MAS)-based distributed control model, which contains a top layer communication network built by agents and a bottom-layer microgrid composed of BESSs, distributed generators (DGs), and Loads, is provided. Next, a systematic method is designed to build the control laws for agents from any given network, where each agent on the top communication network collects the states of BESSs, DGs it connects and exchanges information with its neighboring agents. Moreover, two theorems, which provide guidelines to design distributed control laws for SOC balancing and reactive power sharing between BESSs, are proposed to show the convergent property of the proposed control laws. Furthermore, several simulation cases are employed to validate the effectiveness of the proposed control model when environmental conditions and time-varying load demands are considered. Finally, the simulation results verify the effectiveness of the proposed control model, i.e., the SOC balancing and proportional reactive power sharing are achieved as expected. Furthermore, our approach has the fast convergent speed of SOC balancing of BESSs, compared to the existed method.

State-of-Charge Balancing Control for ON/OFF-Line Internal Cells Using Hybrid Modular Multi-Level Converter and Parallel Modular Dual L-Bridge in a Grid-Scale Battery Energy Storage System

Cell state-of-charge (SoC) balancing within a battery energy-storage system (BESS) is the key to optimizing capacity utilization of a BESS. Many cell SoC balancing strategies have been proposed; however, control complexity and slow SoC convergence remain as key issues. This paper presents two strategies to achieve SoC balancing among cells: main balancing strategy (MBS) using a cascaded hybrid modular multi-level converter (CHMMC) and a supplementary balancing strategy (SBS) using a cascaded parallel modular dual L-bridge (CPMDLB). The control and monitoring of individual cells with a reduction in the component count and the losses of BESS are achieved by integrating each individual cell into an L-bridge instead of an H-bridge. The simulation results demonstrate a satisfactory performance of the proposed SoC balancing strategy. In this result, SoC balancing convergence point for the cells/modules is achieved at 1000 min when cell-prioritized MBS-CHMMC works without SBS-CPMDLB and at 216.7 min when CPMBS-CHMMC works together with SBS-CPMDLB and when the duration required reduces by 78.33 %. Similarly, a substantial improvement in SoC balancing convergence point for the cells/modules is achieved when module-prioritized MBS-CHMMC works together with SBS-CPMDLB; the duration needed to reach the SoC balancing convergence point for the cells/modules is achieved after 333.3 and 183.3 min.

A Distributed State-of-Charge Balancing Control Scheme for Three-Port Output-Series Converters in DC Hybrid Energy Storage Systems

In this study, a distributed state-of-charge (SoC) balancing control strategy is proposed for output-series, hybrid energy storage, three-port converters (TPCs), to address the problem of SoC and voltage imbalance as well as the power distribution in the series converters. The topology of a single hybrid energy storage TPC is described first. On this basis, a brief analysis on the key operating waveforms with the phase shift plus duty cycle modulation is also presented. The principle of the proposed SoC balancing control strategy for the TPC-based output-series system is then analyzed in detail, including the analysis of battery SoC balancing and supercapacitor SoC self-recovery. By performing generalized averaging modelling, both the output-series converter system model and the control model are established, and the influences of the balancing coefficient on the dynamic behavior and stability of the system are then analyzed. Finally, the simulation validation of the output-series converter system with its SoC balancing control strategy is performed in PLECS, and an experimental prototype of the output-series, hybrid energy storage TPC, is constructed to verify the proposed control strategy in various experimental scenarios.

A Hierarchical Control Structure for Distributed Energy Storage System in DC Micro-Grid

To adapt to the rapid development of the renewable generations, DC micro-grid has been becoming an attractive technical route. Energy storages are widely employed in DC micro-grid to balance the power generation and usage. Therefore, the coordination and energy control among these distributed energy storage systems are critical technical issues to guarantee the overall efficiency and security. In this paper, the concept and characteristic of the distributed energy storage system in DC micro-grid are first analyzed. A hierarchical control system for power sharing is proposed to achieve the state-of-charge (SOC) balancing among energy storage units (ESU). In the lower layer of the control system, the DC droop control is applied to allocate the output power of each ESU based on its maximum output power. In the upper layer, consensus algorithm is utilized to adjust the output power reference of each ESU to reduce the SOC difference. Finally, a Matlab/Simulink model is built to verify the proposed approaches. The simulation results indicate that the proposed method can achieve the SOC balancing robust operation in distributed energy storage system.

Energy Sharing of Zero-Energy Buildings: A Consensus-Based Approach

Energy sharing is critical for zero-energy buildings on the community level. However, most existing works studied the energy sharing problems without considering the physical energy sharing circuit. In this paper, we provide a new perspective to explore the energy sharing among building with a specific energy sharing circuit, and then, the modeling, control, and verification of the energy sharing system are presented. The energy sharing system is modeled as a cyber-physical system, where the physical layer characterizes the physical energy sharing circuit, and the cyber layer represents the communication topology among buildings. In the control layer, an average state-of-charge (SoC) estimator is designed for energy storage systems (ESSs) of each building using the dynamic consensus protocol, and a cooperative SoC tracking law is designed to achieve the SoC balancing of ESSs. The closed-loop model of the energy sharing system is developed using the block diagram. A laboratory prototype is built to verify the effectiveness of the proposed energy sharing method. The experimental results verify that the proposed energy sharing system can achieve energy sharing among ESSs effectively and efficiently.

Modified State-of-Charge Balancing Control of Modular Multilevel Converter with Integrated Battery Energy Storage System

Modular multilevel converter with integrated battery energy storage system (MMC-BESS) has been proposed for energy storage requirements in high-voltage applications. The state-of-charge (SOC) equilibrium of batteries is essential for BESS to guarantee the capacity utilization. However, submodule voltage regulation can lead to over-modulation of individual submodules, which will limit the efficiency of SOC balancing control. Focusing on this problem, a modified SOC balancing control method with high efficiency is proposed in this paper. The tolerance for battery power unbalance is defined to quantize the convergence of SOC balancing control. Both the DC component and AC component are considered while regulating submodule voltage. The linear programming method is introduced to realize the maximum tolerance for battery power unbalance in different operation modes. Based on the analysis, by choosing appropriate submodule voltage regulation method, the efficiency of SOC balancing control is improved greatly. In addition, the SOC controller is also optimally designed to avoid over-modulation of submodules. Finally, the detailed simulation and experiment results verify the effectiveness of the analysis and proposed control strategy.

SoC Balancing Strategy for Multiple Energy Storage Units With Different Capacities in Islanded Microgrids Based on Droop Control

Due to the differences of line impedance, initial state-of-charge (SoC), and capacities among distributed energy storage units (DESUs), the SoC of the DESUs with different capacities in an ac islanded microgrid will be unbalanced when using the conventional droop control. A droop control based on the SoC balancing scheme is introduced in this paper to eliminate the influence of capacity on SoC balancing and maintain a good power quality. The proposed control strategy does not require communications or central controller, and the scalability of system is greatly improved. The effectiveness of the proposed approach has been validated by simulation and experimental results.

Power conditioning system control strategy for cascaded H‐bridge converter battery energy storage system

Large capability for a cascaded H-bridge converter battery energy storage system is one of the effective tools to solve the grid-connection problem of renewable energy resource such as large-scale wind farm. The power conditioning system (PCS) control strategy is used proportional-resonant regulator to implement the control with decoupled current control for instantaneous power. The balancing control of the state of charge (SOC) is divided into individual balancing control between bridges is implemented by means of the proportional controller and cluster control between three phases is based on the zero-sequence-voltage injection. The system designed in high-power medium voltage 6.6 kV combining 30 LiFePO 4 (lithium iron phosphate) battery units with cascaded H-bridge multilevel inverter. The simulation results of SOC balancing control was carried out. As a result, a steady-state error of PCS can be smaller and three-phase output power balancing has been achieved, thus, a system simulation model has verified the effectiveness of control strategy. The waveforms of PCS in quadrant operation show voltage and current at active power 1 MW.

Design Enhancement of a Power Supply System for a BLDC Motor-Driven Circuit With State-of-Charge Equalization and Capacity Expansion

This paper presents a design enhancement of a power supply system for brushless dc (BLDC) motor-driven circuits with state-of-charge (SOC) equalization and capacity expansion. The proposed design incorporates different types of battery as the input power, in which SOC equalization and battery modularization are both concerned. Through the proposed control strategy, it achieves the SOC balance among batteries, avoiding damages caused by overdischarging. Meanwhile, considering that BLDC motors require multiple input sources, this study develops an integrated dual-output converter that exhibits the features of both forward converter and flyback converter. To validate the feasibility of this proposed method, different test scenarios have been evaluated via the prototype completed in the laboratory. Experimental results reveal that this approach is capable of providing consistent outputs under different load conditions along with the achievement of SOC equalization among batteries, thereby serving as beneficial references for BLDC circuit applications.