Vaclav Knap

Sizing of an Energy Storage System for Grid Inertial Response and Primary Frequency Reserve

Large-scale integration of renewable energy sources in power system leads to the replacement of conventional power plants (CPPs) and consequently challenges in power system reliability and security are introduced. This study is focused on improving the grid frequency response after a contingency event in the power system with a high penetration of wind power. An energy storage system (ESS) might be a viable solution for providing inertial response and primary frequency regulation. A methodology has been presented here for the sizing of the ESS in terms of required power and energy. It describes the contribution of the ESS to the grid, in terms of inertial constant and droop. The methodology is applied to a 12-bus grid model with high wind power penetration. The estimated ESS size for inertial response and primary frequency regulation services are validated through real-time simulations. Moreover, it is demonstrated that the ESS can provide the response similar to that provided by the CPPs.

Operation of a Grid-Connected Lithium-Ion Battery Energy Storage System for Primary Frequency Regulation: A Battery Lifetime Perspective

Because of their characteristics, which have been continuously improved during the last years, Lithium-ion batteries have been proposed as an alternative viable solution to present fast-reacting conventional generating units to deliver the primary frequency regulation service. However, even though there are worldwide demonstration projects, where energy storage systems based on Lithium-ion batteries are evaluated for such applications, the field experience is still very limited. In consequence, at present, there are no very clear requirements on how the Lithium-ion battery energy storage systems should be operated, while providing frequency regulation service and how the system has to reestablish its state of charge (SOC) once the frequency event has passed. Therefore, this paper aims to investigate the effect on the lifetime of the Lithium-ion batteries energy storage system of various strategies for reestablishing the batteries’ SOC after the primary frequency regulation is successfully delivered.

Grid inertial response with Lithium-ion battery energy storage systems

The increased grid-penetration levels of energy produced by renewable sources, which have almost no inertia, might have a negative impact on the reliable and stable operation of the power system. Various solutions for mitigating the aforementioned problem were proposed in the literature. The aim of this paper is to evaluate the technical viability of utilizing energy storage systems based on Lithium-ion batteries for providing inertial response in grids with high penetration levels of wind power. In order to perform this evaluation, the 12-bus system grid model was used; the inertia of the grid was varied by decreasing the number of conventional power plants in the studied grid model while in the same time increasing the load and the wind power penetration levels. Moreover, in order to perform a realistic investigation, a dynamic model of the Lithium-ion battery was considered and parameterized. All the studies were performed in real time on a laboratory setup composed of RTDS and dSPACE platforms.

Evaluation of different methods for measuring the impedance of Lithium-ion batteries during ageing

The impedance represents one of the most important performance parameters of the Lithium-ion batteries since it used for power capability calculations, battery pack and system design, cooling system design and also for state-of-health estimation. In the literature, different approaches are presented for measuring the impedance of Lithium-ion batteries and electrochemical impedance spectroscopy and dc current pulses are the most used ones; each of these approaches has its own advantages and drawbacks. The goal of this paper is to investigate which of the most encountered impedance measurement approaches is the most suitable for measuring the impedance of Lithium-ion batteries during ageing.

Comparison of parametrization techniques for an electrical circuit model of Lithium-Sulfur batteries

Lithium-Sulfur (Li-S) batteries are an emerging energy storage technology, which draw interest due to its high theoretical specific capacity (approx. 1675 Ah/kg) and theoretical energy density of almost 2600 Wh/kg. In order to analyse their dynamic behaviour and to determine their suitability for various commercial applications, battery performance models are needed. The development of such models represents a challenging task especially for Li-S batteries because this technology during their operation undergo several different chemical reactions, known as polysulfide shuttle. This paper focuses on the comparison of different parametrization methods of electrical circuit models (ECMs) for Li-S batteries. These methods are used to parametrize an ECM based on laboratory measurements performed on a Li-S pouch cell. Simulation results of ECMs are presented and compared against measurement values and the accuracy of parametrization methods are evaluated and compared.

Comparison of lithium-ion battery performance at beginning-of-life and end-of-life

Abstract In this paper, a comparison between the performance of a Lithium-ion battery at beginning-of-life (BOL) and at two increased degradation levels is presented. The capacity, internal resistance, and open circuit voltage of a 13 Ah high-power Lithium-ion battery had been measured at BOL for different temperatures, C-rates, and state-of-charge (SOC) levels. Then, two battery cells were aged at two different cycle aging conditions until they lost 40% and 60% of their initial capacity, respectively. At that moment, the two battery cells were removed from the aging processes and were subjected to characterization measurements similar to the ones performed at BOL. The obtained results shown that besides the expected capacity fade and internal resistance increase, there is a dramatic change in the variation of the battery performance parameters with the temperature, C-rate, and/or SOC, between a fresh cell and the two heavily degraded cells.

Electric circuit modeling of lithium-sulfur batteries during discharging state

Lithium-ion batteries are characterized by having very good performance in terms of efficiency, lifetime, and self-discharge, which allowed them to become the major player in the electric vehicle applications. However, they were not able to totally overcome the EV range anxiety. Thus, research is carried out nowadays to develop batteries with even higher gravimetric energy density, which should allow a substantial range increase. One of the technologies, which should be able to meet the range requirements is the Lithium-Sulfur (Li-S) battery. Thanks to the extensive research and development efforts, these cells are close to enter the market, being evaluate in various projects. In this paper, we have proposed an electrical circuit model for a Li-S pouch cell, which was parameterized based on extensive electrochemical impedance spectroscopy measurements. The developed model was verified using static and pulse discharge profiles, showing a good accuracy in predicting the voltage of the tested Li-S battery cell.

Characterization, Modelling and State Estimation of Lithium-Sulfur Batteries

Lithium-Sulfur (Li-S) batteries represent an appealing battery technology, which might become an alternative for the currently wide spread Lithium-ion batteries. However, the current limitations concerning the cell performance and lifetime are the major factors, which slow down their commercialization. Vast research efforts are carried out to improve the cell design and composition; nevertheless, only a minimum of work has been focused on characterizing their behavior and developing tools for a prospective use in practical applications. Thus, this thesis has tried to fill in the aforementioned gap and it studied several aspects for understanding the Li-S batteries behavior for prospective practical applications. Therefore, the equivalent electrical circuit model for discharging of the Li-S batteries has been developed. The proposed model is able to simulate the dynamic voltage response of the studied Li-S battery cell during the discharge and is also suitable to be used for extended Kalman filter based state-of-charge (SOC) estimation. Moreover, an equivalent electrical circuit approach was also used for the analysis of the electrochemical impedance spectroscopy performed at the Li-S cell under various temperature and state-of-charge levels. An extensive experimental laboratory testing procedure was used to characterize the Li-S cell and to develop its models. The short-term self-discharge was experimentally investigated in detail and a simple, but effective model was proposed for it. Based on this self-discharge model, the self-balancing feature of the Li-S batteries was identified, which enhances their balancing and might even lead to avoid an additional electronic circuitry usually implemented for this purpose. Furthermore, the charge recovery effect and thermal attributes were investigated. Because of the specific behavior of Li-S batteries, a specially tailored testing methodology to evaluate the battery’s performance parameters change during the ageing was proposed. The testing methodology covers the characteristic behavior such as the cumulative history, rapid self-discharge and it also includes the measurements of the unique polysulfide shuttle current. The work was also focused on state estimation, which is an important