Session: 08-07-01: Energy Systems Components

Paper Number: 94653

94653 - Design Strategies for Flywheel Energy Storage Systems in EV Fast Charging 

Electric vehicles (EVs), including private, public transit, and fleet vehicles, have become an important part for meeting global greenhouse gas reduction and climate change mitigation goals. With rising numbers of EVs, alleviating strain on the electrical grid from EV charging, specifically fast-charging applications, has become a significant challenge, especially since adapting grid infrastructure for fast-charging applications is not only complex but costly. Energy storage systems (ESS) can be employed to support electric vehicle fast-charging and lessen peak loads on the grid. Requirements for ESS in this application include a long service life and a high-power charge and discharge capacity. In this context, interest in flywheel energy storage systems (FESS) has been growing in recent years due to favorable power characteristics and the absence of depth of discharge and cycle aging effects that FESS offer over actual electrochemical systems. Typically, FESS design and development has focused on small-scale transportation systems, large-scale grid frequency regulation applications, aerospace ESS, uninterruptible power supply systems, and vehicle regenerative braking such as in motorsports. Basic FESS components are the flywheel rotor for kinetic energy storage, an electrical machine and controller for converting kinetic to electrical energy and vice versa, and a safety enclosure that accommodates the rotor supports (bearings). Ensuring a high level of safety is imperative to abate the possibility of high energy dissipation should a flywheel failure occur. The enclosure typically also maintains a vacuum environment to minimize air friction losses on fast-rotating components. The present contribution investigates the use of FESS for EV charging support. A parametric study was performed considering 145 kW, 250 kW and 350 kW fast-charging capable cars having either 75 kWh or 212 kWh of battery capacity. For each fast-charge power requirement, different FESS units were dimensioned, including units featuring rotor designs resembling a thin ring or tube, a solid disk, and a Laval disk. Two different material types, i.e., steel and fiber reinforced polymer composite, were considered for the rotor. FESS units were designed with the goal of mitigating peak electricity demand on the grid during EV fast-charging. Air friction and bearing losses were estimated for comparison between the proposed design solutions. Lastly, an analysis for each fast-charge requirement was made, contrasting flywheel characteristics such as material type, angular velocity, energy and power capacity, cost for rotor and components, and electric machine requirements. Moreover, aspects concerning the housing and placement in EV fast charge stations are discussed. This study thus contributes to the development of design strategies for FESS in fast-charging applications, which signifies a promising and innovative approach for alleviating peak loads that EV fast-charging imposes on the electrical grid.

Presenting Author: Francisco Basaure University of Alberta

Presenting Author Biography: N/A

Authors:

Francisco Basaure University of Alberta
Pierre Mertiny University of Alberta