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Flywheel Energy Storage Systems and Applications
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Flywheel Energy Storage Systems and Applications

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "D: Energy Storage and Application".

Deadline for manuscript submissions: closed (5 August 2021) | Viewed by 25478

Special Issue Editor

Prof. Dr. Keith Robert Pullen

E-Mail Website
Guest Editor
Department of Engineering, School of Mathematics, Computer Science and Engineering, City University of London, London, UK
Interests: flywheel energy storage; power systems; high-speed machines; hybrid power systems; energy recovery; small turbomachines
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear colleagues,

Flywheel energy storage has the potential to play a significant role in the transformation of electrical power systems to those with the highest sustainability yet lowest cost. The penetration of renewable energy generation has created new challenges, which ultimately can only be solved by means of fast response energy storage. For example, as synchronous generation is removed from electricity grids, the ability of the system to maintain a steady frequency is compromised. Here lies the opportunity for flywheel storage, whose characteristics typically place it between ultra-capacitors and electrochemical batteries. Although electrochemical batteries are currently dominating the market for fast response storage, flywheels offer a very high cycle and calendar life, and are fully sustainable in terms of raw materials’ ease of recycling. Flywheels may also be hybridized with batteries in order to benefit from the strengths of each technology. As well as stationary grid applications, flywheels may be deployed for energy recovery in transport, either on board the vehicles or at strategic locations, for instance, in railway stations.

Contributions are invited in the following areas:

  • Rotor research including safety and containment
  • Low loss bearing systems
  • Novel motor-generator technologies and drives
  • Integrated flywheel motor-generator systems
  • Vacuum systems
  • Rotor dynamics
  • Hybrid micro and mini grids—integration of renewables with flywheel storage
  • Hybrid storage system—integration of flywheel storage with batteries or other storage systems
  • Trackside storage in electrified rail transport
  • Vehicle kinetic energy recovery

Prof. Keith Robert Pullen
Guest Editor

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • flywheel energy storage
  • low friction bearings
  • vacuum systems
  • mini grids
  • kinetic energy recovery

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Published Papers (6 papers)

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Research

28 pages, 9829 KiB  
Article
Design of a Low-Loss, Low-Cost Rolling Element Bearing System for a 5 kWh/100 kW Flywheel Energy Storage System
by Peter Haidl and Armin Buchroithner
Energies 2021, 14(21), 7195; https://doi.org/10.3390/en14217195 - 2 Nov 2021
Cited by 4 | Viewed by 2621
Abstract
The bearings of a flywheel energy storage system (FESS) are critical machine elements, as they determine several important properties such as self-discharge, service life, maintenance intervals and most importantly cost. This paper describes the design of a low-cost, low-loss bearing system for a [...] Read more.
The bearings of a flywheel energy storage system (FESS) are critical machine elements, as they determine several important properties such as self-discharge, service life, maintenance intervals and most importantly cost. This paper describes the design of a low-cost, low-loss bearing system for a 5 kWh/100 kW FESS based on analytical, numerical and experimental methods. The special operating conditions of the FESS rotor (e.g., high rotational speeds, high rotor mass, vacuum) do not allow isolated consideration of the bearings alone, but require a systematic approach, taking into account aspects of rotor dynamics, thermal management, bearing loads and lubrication. The proposed design incorporates measures to mitigate both axial and radial bearing loads, by deploying resilient bearing seats and a lifting magnet for rotor weight compensation. As a consequence of minimized external loading, bearing kinematics also need to be considered during the design process. A generally valid, well-structured guideline for the design of such low-loss rolling bearing systems is presented and applied to the 5 kWh/100 kW FESS use case. Full article
(This article belongs to the Special Issue Flywheel Energy Storage Systems and Applications)
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19 pages, 5138 KiB  
Article
Design Trade-Offs and Feasibility Assessment of a Novel One-Body, Laminated-Rotor Flywheel Switched Reluctance Machine
by Roberto Rocca, Savvas Papadopoulos, Mohamed Rashed, George Prassinos, Fabio Giulii Capponi and Michael Galea
Energies 2020, 13(22), 5857; https://doi.org/10.3390/en13225857 - 10 Nov 2020
Cited by 9 | Viewed by 2351
Abstract
In a bid to respond to the challenges being faced in the installation of flywheel-based electric energy storage systems (EESSs) in customer-side facilities, namely high safety, high energy/power densities and low cost, research work towards the development of a novel, one-body, laminated-rotor flywheel, [...] Read more.
In a bid to respond to the challenges being faced in the installation of flywheel-based electric energy storage systems (EESSs) in customer-side facilities, namely high safety, high energy/power densities and low cost, research work towards the development of a novel, one-body, laminated-rotor flywheel, based on a switched reluctance machine (OBOLAR-Fly SR machine) is presented, where the laminated rotor provides both the energy storage and motor/generator functions. The one-body architecture improves compactness and robustness. Besides, the rotor’s laminated body ensures inherently high safety. From the design perspective, the rotor’s dual purpose causes the traditional electrical machines design aspects, such as power development, cooling, losses, torque ripple, etc., to clash with the typical requirements of a flywheel, namely in-vacuum operation and moment of inertia. This results in six main trade-offs to be addressed during the design process: rotor material, speed ratio, number of drive phases, split ratio, optimal vacuum level, and controller hysteresis band. A 60 kW, 2.2 kWh OBOLAR-Fly SR system is developed with a twofold objective: (1) provide an in-depth description of the six bespoke design trade-offs and give some useful guidelines to tackle them; (2) prove the OBOLAR-Fly concept and compare the prototype’s performance with the current state of the art flywheels. Preliminary experimental results prove the viability of the OBOLAR idea and show its competitiveness in terms of efficiency and power density. On the other hand, a gap in energy density to be filled in future research works is highlighted. Full article
(This article belongs to the Special Issue Flywheel Energy Storage Systems and Applications)
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22 pages, 5602 KiB  
Article
Analysis of Standby Losses and Charging Cycles in Flywheel Energy Storage Systems
by Mustafa E. Amiryar and Keith R. Pullen
Energies 2020, 13(17), 4441; https://doi.org/10.3390/en13174441 - 27 Aug 2020
Cited by 20 | Viewed by 5686
Abstract
Aerodynamic drag and bearing friction are the main sources of standby losses in the flywheel rotor part of a flywheel energy storage system (FESS). Although these losses are typically small in a well-designed system, the energy losses can become significant due to the [...] Read more.
Aerodynamic drag and bearing friction are the main sources of standby losses in the flywheel rotor part of a flywheel energy storage system (FESS). Although these losses are typically small in a well-designed system, the energy losses can become significant due to the continuous operation of the flywheel over time. For aerodynamic drag, commonly known as windage, there is scarcity of information available for loss estimation since most of the publications do not cover the partial vacuum conditions as required in the design of low loss energy storage flywheels. These conditions cause the flow regime to fall between continuum and molecular flow. Bearings may be of mechanical or magnetic type and in this paper the former is considered, typically hybridized with a passive magnetic thrust bearing. Mechanical bearing loss calculations have been extensively addressed in the open literature, including technical information from manufacturers but this has not previously been presented clearly and simply with reference to this application. The purpose of this paper is therefore to provide a loss assessment methodology for flywheel windage losses and bearing friction losses using the latest available information. An assessment of windage losses based on various flow regimes is presented with two different methods for calculation of windage losses in FESS under rarefied vacuum conditions discussed and compared. The findings of the research show that both methods closely correlate with each other for vacuum conditions typically required for flywheels. The effect of the air gap between the flywheel rotor and containment is also considered and justified for both calculation methods. Estimation of the bearing losses and considerations for selection of a low maintenance, soft mounted, bearing system is also discussed and analysed for a flywheel of realistic dimensions. The effect of the number of charging cycles on the relative importance of flywheel standby losses has also been investigated and the system total losses and efficiency have been calculated accordingly. Full article
(This article belongs to the Special Issue Flywheel Energy Storage Systems and Applications)
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17 pages, 8116 KiB  
Article
An Accurate Discrete Current Controller for High-Speed PMSMs/Gs in Flywheel Applications
by Xiang Zhang, Yunlong Chen, Yves Mollet, Jiaqiang Yang and Johan Gyselinck
Energies 2020, 13(6), 1458; https://doi.org/10.3390/en13061458 - 20 Mar 2020
Cited by 4 | Viewed by 2106
Abstract
High-speed Permanent-Magnet Synchronous Motors/Generators (PMSMs/Gs) in a Flywheel Energy Storage System (FESS) are faced with high cross-coupling voltages and low switching-to-fundamental frequency ratios. High cross-coupling voltages between d-q axis current loops lead to transient current errors, which is more serious at lower switching-to-fundamental-frequency [...] Read more.
High-speed Permanent-Magnet Synchronous Motors/Generators (PMSMs/Gs) in a Flywheel Energy Storage System (FESS) are faced with high cross-coupling voltages and low switching-to-fundamental frequency ratios. High cross-coupling voltages between d-q axis current loops lead to transient current errors, which is more serious at lower switching-to-fundamental-frequency ratios. If the delays are not properly considered during the current controller design in a digital control system, the low switching-to-fundamental-frequency ratios may result in oscillatory or unstable responses. In this study, an accurate discrete current controller for high-speed PMSMs/Gs is proposed based on an accurate discrete model that takes the phase and magnitude errors generated during the sampling period into consideration, and an Extended State Observer (ESO) is applied to estimate and compensate the back EMF error. The cross-coupling problem is well settled, and the current loop dynamic at lower switching-to-fundamental frequency ratios is improved. Finally, the proposed discrete controller is validated on a 12,000 rpm PMSM/G prototype. Full article
(This article belongs to the Special Issue Flywheel Energy Storage Systems and Applications)
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22 pages, 8036 KiB  
Article
Design and Modeling of an Integrated Flywheel Magnetic Suspension for Kinetic Energy Storage Systems
by Mauro Andriollo, Roberto Benato and Andrea Tortella
Energies 2020, 13(4), 847; https://doi.org/10.3390/en13040847 - 14 Feb 2020
Cited by 12 | Viewed by 3840
Abstract
The paper presents a novel configuration of an axial hybrid magnetic bearing (AHMB) for the suspension of steel flywheels applied in power-intensive energy storage systems. The combination of a permanent magnet (PM) with excited coil enables one to reduce the power consumption, to [...] Read more.
The paper presents a novel configuration of an axial hybrid magnetic bearing (AHMB) for the suspension of steel flywheels applied in power-intensive energy storage systems. The combination of a permanent magnet (PM) with excited coil enables one to reduce the power consumption, to limit the system volume, and to apply an effective control in the presence of several types of disturbances. The electromagnetic design of the AHMB parts is carried out by parametric finite element analyses with the purpose to optimize the force performances as well as the winding inductance affecting the electrical supply rating and control capability. Such investigation considers both the temperature dependence of the PM properties and the magnetic saturation effects. The electrical parameters and the force characteristics are then implemented in a control scheme, reproducing the electromechanical behavior of the AHMB-flywheel system. The parameter tuning of the controllers is executed by a Matlab/Simulink code, examining the instantaneous profiles of both the air-gap length and the winding ampere-turns. The results of different dynamic tests are presented, evidencing the smooth air-gap changes and the optimized coil utilization, which are desirable features for a safe and efficient flywheel energy storage. Full article
(This article belongs to the Special Issue Flywheel Energy Storage Systems and Applications)
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25 pages, 9865 KiB  
Article
A Novel Energy Recovery System Integrating Flywheel and Flow Regeneration for a Hydraulic Excavator Boom System
by Jiansong Li, Jiyun Zhao and Xiaochun Zhang
Energies 2020, 13(2), 315; https://doi.org/10.3390/en13020315 - 9 Jan 2020
Cited by 26 | Viewed by 6918
Abstract
Implementing an energy recovery system (ERS) is an effective solution to improve energy efficiency for hydraulic excavators (HEs). A flywheel energy recovery system (FERS) is proposed based on this concept. A hydraulic pump motor (PM) is employed as the energy conversion component and [...] Read more.
Implementing an energy recovery system (ERS) is an effective solution to improve energy efficiency for hydraulic excavators (HEs). A flywheel energy recovery system (FERS) is proposed based on this concept. A hydraulic pump motor (PM) is employed as the energy conversion component and a flywheel is used as the energy storage component. Since the pressure is low because the bucket is usually empty as the boom lowers, a relatively large PM should be used in the FERS. To overcome this drawback, a novel compound energy recovery system integrating flywheel and flow regeneration (FFERS) is proposed in this paper. The working principle of the system is analyzed in detail. The introduction of flow regeneration has two benefits; one is downsizing the displacement of PM and the other one is an extra improvement of energy efficiency. The primary parameters of both are matched based on a 4 t excavator. Compared with the PM used in the FERS, the PM displacement in the FFERS is reduced by 71%. For comparison, a general model that can operate in either the FERS mode or the FFERS mode is developed in AMESim. The modeling results show that the FFERS with a downsized PM contributes a 13% increase in energy recovery and reutilization efficiency (62%) as compared with the FERS. Full article
(This article belongs to the Special Issue Flywheel Energy Storage Systems and Applications)
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