Optimization of flexibility indices for large-scale renewable energy integration by varying control strategies on hybrid energy storage systems

The Project Objective is to design innovative energy storage architecture and associated controls for high wind penetration to increase reliability and market acceptance of wind power. The project goals are to facilitate wind energy integration at different levels by design and control of suitable energy storage systems. The three levels of wind power system are: Balancing Control Center level, Wind Power Plant level, and Wind Power Generator level. Our scopes are to smooth the wind power fluctuation and also ensure adequate battery life. In the new hybrid energy storage system (HESS) design for wind power generation application, the boundary levels of the state of charge of the battery and that of the supercapacitor are used in the control strategy. In the controller, some logic gates are also used to control the operating time durations of the battery. The sizing method is based on the average fluctuation of wind profiles of a specific wind station. The calculated battery size is dependent on the size of the supercapacitor, state of charge of the supercapacitor and battery wear. To accommodate the wind power fluctuation, a hybrid energy storage system (HESS) consisting of battery energy system (BESS) and super-capacitor is adopted in this project.more » A probability-based power capacity specification approach for the BESS and super-capacitors is proposed. Through this method the capacities of BESS and super-capacitor are properly designed to combine the characteristics of high energy density of BESS and the characteristics of high power density of super-capacitor. It turns out that the super-capacitor within HESS deals with the high power fluctuations, which contributes to the extension of BESS lifetime, and the super-capacitor can handle the peaks in wind power fluctuations without the severe penalty of round trip losses associated with a BESS. The proposed approach has been verified based on the real wind data from an existing wind power plant in Iowa. An intelligent controller that increases battery life within hybrid energy storage systems for wind application was developed. Comprehensive studies have been conducted and simulation results are analyzed. A permanent magnet synchronous generator, coupled with a variable speed wind turbine, is connected to a power grid (14-bus system). A rectifier, a DC-DC converter and an inverter are used to provide a complete model of the wind system. An Energy Storage System (ESS) is connected to a DC-link through a DC-DC converter. An intelligent controller is applied to the DC-DC converter to help the Voltage Source Inverter (VSI) to regulate output power and also to control the operation of the battery and supercapacitor. This ensures a longer life time for the batteries. The detailed model is simulated in PSCAD/EMTP. Additionally, economic analysis has been done for different methods that can reduce the wind power output fluctuation. These methods are, wind power curtailment, dumping loads, battery energy storage system and hybrid energy storage system. From the results, application of single advanced HESS can save more money for wind turbines owners. Generally the income would be the same for most of methods because the wind does not change and maximum power point tracking can be applied to most systems. On the other hand, the cost is the key point. For short term and small wind turbine, the BESS is the cheapest and applicable method while for large scale wind turbines and wind farms the application of advanced HESS would be the best method to reduce the power fluctuation. The key outcomes of this project include a new intelligent controller that can reduce energy exchanged between the battery and DC-link, reduce charging/discharging cycles, reduce depth of discharge and increase time interval between charge/discharge, and lower battery temperature. This improves the overall lifetime of battery energy storages. Additionally, a new design method based on probability help optimize the power capacity specification for BESS and super-capacitors. Recommendations include experimental implementation of the controller and energy storage systems in laboratory environment for further testing and verification, which will help commercialization of the proposed system design and controller.« less

Study on adaptive VSG parameters and SOC control strategy for PV-HESS primary frequency regulation

This study examines the issue of wind power smoothing in renewable-energy-grid integration scenarios. Under the “dual-carbon” policy initiative, large-scale renewable energy integration (particularly wind power) has become a global focus. However, the intermittency and uncertainty of wind power output exacerbate grid power fluctuations, posing challenges to power system stability. Consequently, smoothing strategies for wind power energy storage systems are desperately needed to improve operational economics and grid stability. According to current research, single energy storage technologies are unable to satisfy both the system-level economic operating requirements and high-frequency power fluctuation compensation at the same time, resulting in a trade-off between economic efficiency and precision of frequency regulation. Therefore, hybrid energy storage technologies have emerged as a key research focus in wind power energy storage. This study employs the SE-SGMD method, utilizing the distinct characteristics of lithium batteries and supercapacitors to decompose frequency regulation commands into low- and high-frequency components via frequency separation strategies, thereby controlling the output of supercapacitors and lithium batteries, respectively. Additionally, the GA-GWO algorithm is applied to optimize energy-storage-system configuration, with experimental validation conducted. The theoretical contributions of this study include the following: (1) introducing the SE-SGMD frequency separation strategy into hybrid energy storage systems, overcoming the performance limitations of single energy storage devices, and (2) developing a power allocation mechanism on the basis of the inherent properties of energy storage devices. In terms of methodological innovation, the designed hybrid GA-GWO algorithm achieves a balance between optimization accuracy and efficiency. Compared to PSO-DE and GWO-PSO, the GA-GWO energy storage system demonstrates improvements of 21.10% and 17.47% in revenue, along with reductions of 6.26% and 12.57% in costs, respectively.

Ship propulsion systems experience large power and torque fluctuations on their drive shaft due to hydrodynamic interactions and wave excitation. For electric propulsions, a hybrid energy storage system (HESS) could be an effective solution to address the negative impact of these fluctuations. However, the HESS, when introduced into the existing shipboard electrical propulsion system, will interact with the power generation control systems. In this paper, a model-based analysis is performed to evaluate the interactions of the multiple power sources when a hybrid energy storage system is incorporated. The study has revealed undesirable interactions when the controls are not coordinated properly, and leads to the conclusion that a system-level energy management strategy (EMS) will be needed. To evaluate the benefits of the system-level EMS, a comparative study is performed, and results show that the system-level EMS has advantages over other strategies in terms of many of the performance metrics.

Energy storage systems are particularly suitable for renewable energy sources, such as wind power, because these renewable energy sources are volatile. The hybrid energy storage system (HESS) considers the advantages of multiple energy storage systems and is considered very promising; therefore, the energy configuration strategy of an excellent HESS that considers both cost and performance is crucial. This article based on HESS consists of battery and supercapacitor (SC), additional consideration of user load; thus, by adjusting user translatable load and reducible load, the pressure of wind power and HESS can be alleviated to take into account the cost and performance of HESS. Further, a simple and easy-to-implement energy configuration strategy for HESS is proposed, which takes into account that the energy stored in the battery is almost the energy stored in the HESS and calculates the battery energy and then the SC energy through the gap between the load and the wind power. We used three sets of cases: without HESS, with HESS but without load control, and with HESS and load control. The results show that, compared with HESS without load control, HESS with load control can achieve lower HESS cost, wind abandonment rate, and load power shortage rate, which is impossible to combine with traditional strategies.

Storage systems are needed to boost the reliability of intermittent solar and wind resources in power networks. Rather than focus on one storage system or one hybrid energy storage system (HESS), this work models the operation of six HESS configurations in a Renewable Energy (RE) based grid-tied network. The objective is to minimise the daily operational costs of the microgrid while prolonging the storage lifetime by considering storage degradation costs. The influence of fixed tariffs and time-of-use (TOU) tariffs on the optimal operational of the HESS configurations have also been investigated; as well as deferrable demand satisfaction, charge-discharge pattern of different HESS and availability of the power-dense storage system within the microgrid. Results show that the lead-acid battery and hydrogen fuel cell (HFC) HESS incurs the highest operational costs, while the supercapacitor-lead-acid battery HESS incurs the lowest operational costs. The supercapacitor-lead acid battery and the supercapacitor-HFC HESS incur the highest annual storage degradation costs. The grid expenses were seen to be the same for all HESS under each tariff scheme. Lastly, decreasing the minimum storage level further by 10% from the 30% in the base case, led to an increase in the number of hours of availability of the power-dense storage system of five of the six HESS. These results have given a deeper understanding to the operation of HESS systems and can inform better decision making of the suitable HESS to be deployed in different operating scenarios.

An assessment of hybrid-energy storage systems in the renewable environments

This paper introduces an improved decentralized control strategy for a photovoltaic (PV) hybrid energy storage (HES) system (HESS) in a DC microgrid. The power sharing method of the HES system is discussed in depth. The basic principle of virtual resistance and capacitance droop (VRCD) control, which consists of virtual resistance droop (VRD) and virtual capacitance droop (VCD) control, is analyzed in detail to achieve the decoupling of the HES system for high- and low-frequency load power distribution. For the virtual capacitance control loop, the voltage compensator is added to achieve terminal voltage restoration of the supercapacitor (SC). For the virtual resistance control loop, in order to solve the problems of the unbalanced state of charge (SOC) of battery storage, a virtual resistance droop control based on a novel adaptive function is introduced. Finally, a model of the HESS in a DC microgrid is built in a real-time emulator to verify the effectiveness of the proposed control strategy.

The global transition to renewable energy sources (RESs) is accelerating to combat the rapid depletion of fossil fuels and mitigate their devastating environmental impact. However, the increasing integration of large-scale intermittent RESs, such as solar photovoltaics (PVs) and wind power systems, introduces significant technical challenges related to power supply stability, reliability, and quality. This paper provides a comprehensive review of these challenges, with a focus on the critical role of energy storage systems (ESSs) in overcoming them by evaluating their technical, economic, and environmental performance. Various types of energy storage systems, including mechanical, electrochemical, electrical, thermal, and chemical systems, are analyzed to identify their distinct strengths and limitations. This study further examines the current state and potential applications of ESSs, identifying strategies to enhance grid flexibility and the increased adoption of RESs. The findings reveal that while each ESS type has specific advantages, no single technology can tackle all grid challenges. Consequently, hybrid energy storage systems (HESSs), which combine multiple technologies, are emphasized for their ability to improve efficiency and adaptability, making them especially suitable for modern power grids.

A hybrid energy storage system (HESS) that combines batteries and ultracapacitors (UCs) presents unique electric energy storage capability over traditional Energy Storage Systems (ESS) made of pure batteries or UCs. As a critical powertrain component of an electrified vehicle (EV), the performance and life of the ESS dominate the performance and life-cycle cost of the pure electric vehicle (PEV) and plug-in hybrid electric vehicle (PHEV) due to the large size of their ESS. Different from traditional power density and energy density considerations, the use of battery and UC HESS today is more geared toward the use of UCs to take over the high frequency, dynamic charge and discharge to ensure quick system response and to extend battery life by reducing its frequent charge and discharge. In this paper, the recent advance of HESS and relevant technologies have been reviewed. The state-of-the-art of battery ESS and modeling method, considering its performance degradation under different use patterns are first presented. Methods for modeling the UC and DC/DC converter in the HESS, along with various HESS architectures, are also overviewed. Energy management methods of HESS are then reviewed according to recent literature to derive appropriate energy split strategies between the batteries and UCs. Finally, various HESS-based applications from public transportation to construction machinery are discussed to illustrate the benefits of HESS.

Hybrid energy storage systems and control strategies for stand-alone renewable energy power systems

This study proposes a novel control strategy for a hybrid energy storage system (HESS), as a part of the grid-independent hybrid renewable energy system (HRES) which comprises diverse renewable energy resources and HESS - combination of battery energy storage system (BESS) and supercapacitor energy storage system (SCESS). The proposed control strategy is implemented into two parts: in the first part, HESS controller is designed and implemented to maintain the active power balance among different constituents of HRES and regulate DC-link voltage ( V DC ) under surplus power mode and deficit power mode. The low-frequency components of imbalance power are diverted to BESS while the high-frequency components are diverted to SCESS while maintaining the state of charge (SoC) constraints of HESS thereby reducing stress on BESS. In the second part, inverter controller is designed and implemented to maintain AC voltage and frequency within limits in the events of perturbation. The proposed HESS along with its novel control strategy, as implemented in the HRES, is a new proposition in this study. The detailed model of HRES is simulated in MATLAB/Simulink and the results prove the efficacy of the control strategy. Further, hardware-in-loop real-time simulation studies using OPAL-RT real-time simulator demonstrate the feasibility of hardware implementation of HRES with the proposed control strategy.

To improve the performance and economy of the hybrid energy storage system (HESS) coordinating thermal generators to participate in automatic generation control (AGC), a HESS bi-layer capacity configuration model that considers the control strategy and net benefits of HESS is proposed. In addition, an improved mode-pursuing sampling (MPS) optimization algorithm based on meta-model is presented to improve the accuracy of model solving. In the lower layer, to improve the performance of HESS participating in AGC, a model predictive control (MPC) strategy is presented to distribute HESS power reasonably. Based on this, the upper layer develops a life-cycle net benefit model of HESS participating in AGC to improve its economy. The bi-layer model realizes iterative optimization of HESS capacity and operation through parameter transmission. Furthermore, to improve the solution accuracy of the bi-layer model, the convergence speed of the MPS algorithm is improved, so that the global search and local convergence speed can be taken into account. The case study results show that the bi-layer model can comprehensively consider the interaction between the economy and operating strategy of HESS. The proposed MPC strategy has better frequency regulation performance and the improved MPS algorithm has better solution performance.

Multi-objective optimization of HESS control for optimal frequency regulation in a power system with RE penetration

Energy storage systems have a wide spectrum of functions. They must provide power quality, shaving of load change, matching in distributed power systems, bulk energy storage, and end-user reliability, e.g., uninterrupted power supply. Storage devices based on high-capacity batteries have a number of advantages: i) modular design and relatively compact size; ii) functional flexibility; iii) easy control and maintenance; iv) simple integration into Smart Grids. It is also well known that batteries have a number of unsolved problems, e.g.: i) high specific cost of stored energy; ii) insufficient cycle life (500 – 3 000 charge/discharge cycles); iii) significant decrease of cycle life at high charge/discharge current; iv) problem of depth discharge.To solve the above mentioned problems, we propose the Hybrid Energy Storage system (HESS) incorporating supercapacitors in addition to batteries. Cost analysis of electrochemical storage systems based on batteries of different types, supercapacitors and their combination has also been carried out.To verify the main principles of the proposal, we have designed and developed a HESS prototype. The main functional characteristics of the developed HESS were studied experimentally.The prototype bases on Li-ion batteries and supercapacitors. Such energy storage system includes three main components: Li-ion batteries, supercapacitors, and grid interconnection consisting of two invertors and control and monitoring system. Energy storage capacity of developed HESS prototype is 100 kWh, nominal power—100 kW, peak power—200 kW. HESS was created and tested within the experimental facility including 1.5 MW gas turbine power plant, 200 kW controllable active and reactive loads, and a control and measurement system.Experimental results showed that HESS successfully provides the following functions: (i) suppression of voltage, current, and frequency disturbances in the grid; (ii) compensation of reactive power in the circuit; (iii) uninterrupted power supply. In comparison with battery storage system without supercapacitors, HESS shows lower cost, and higher peak power. In hybrid energy storage system the presence of supercapacitors allows to shave peaks of power at the charge and discharge mode of the battery. We believe that this feature of HESS will prolong the life time of batteries and thus increase the life time and reliability of the entire system.