Performance and Loss Analysis of Squirrel Cage Induction Machine Based Flywheel Energy Storage System

Abstract

Flywheel energy storage systems (FESS) are one of the earliest forms of energy storage technologies with several benefits of long service time, high power density, low maintenance, and insensitivity to environmental conditions being important areas of research in recent years. This paper focusses on the electrical machine and power electronics, an important part of a flywheel system, the electrical machine rotating with the flywheel inertia in order to perform charge-discharge cycles. The type of machine used in the electrical drive plays an important role in the characteristics governing electrical losses as well as standby losses. Permanent magnet synchronous machine (PMSM) and induction machines (IM) are the two most common types of electric machines used in FESS applications where the latter has negligible standby losses due to its lower rotor magnetic field until energised by the stator. This paper describes research in which the operational and standby losses of a squirrel-cage induction machine-based flywheel storage system (SCIM-FESS) are modelled as a system developed in MATLAB/Simulink environment inclusive of the control system for the power electronics converters. Using the proposed control algorithm and in-depth analysis of the system losses, a detailed assessment of the dynamic performance of the SCIM-FESS is performed for different states of charging, discharging, and standby modes. The results of the analysis show that, in presence of system losses including aerodynamic and bearing friction losses, the SCIM-FESS has satisfactory characteristics in energy regulation and dynamic response during load torque variations. The compliance of FESS and its conversion between the generating and motoring mode within milliseconds show the responsiveness of the proposed control system. Appl. Sci. 2019, 9, 4537 2 of 26 there are various solutions proposed to ensure network stability and reliability with RES including demand management, interconnection with external grids, and ESS [5].There are ranges of systems involved in energy storage process, which can convert, store and deliver energy on demand. Performance of these systems depends on the amount of energy they can store, the storage time and delivery of energy with minimum losses [6]. Therefore, high power capability, high efficiency, low capital cost and environmentally friendly attributes improve the value of ESS [7].A FESS is an assembly of a rotating mass, electrical machine, power electronics converter, bearing system and containment. The design of the rotor used in FESS depends on the materials from which they are made. Solid disk or solid cylinder are made from isotropic materials like steel. Rim type or hollow cylinder flywheel rotors are constructed from non-isotropic material like composite carbon fiber. Solid disk or solid cylinder flywheel rotors have simple construction and are commonly used [8]. Solid rotor flywheels exhibit less displacement from axes due to centrifugal forces hence simplifying flywheel attachment to the shaft and with ele...

Energy Management and Control of a Flywheel Storage System for Peak Shaving Applications

“…In the proposed representation, term C S corresponds to ω 2 r according to (6); thus, the termŝ c d C S t andĉ c C S t represent the polynomial term c 1 ω 2 r . Note that c 1 ω 2 r is the dominant power losses term of the polynomial function c 1 ω 2 r + c 2 ω r , especially at high speeds and with reduced bearing friction losses (since low-friction magnetic bearings are typically used in flywheel applications) [19], [22]- [23]. In addition, the termsb d P S t andb d P S t consider the FESS power losses for the charging and discharging modes.…”

Optimal sizing of a high‐speed flywheel in an electric vehicle using the optimal control theory approach

“…The bearing loss is usually hard to estimate and it is calculated either empirically or analytically. This loss can be expressed in terms of the velocity and total torque running on the bearing, hence, it depends non-linearly on the angular velocity [29].…”

“…The converter losses consist of switching and conduction losses which F I G U R E 1 Schematic of the power split in the under-study system configuration depend on the angular velocity [32]. Although it is negligible since they do not exceed 2% of total losses [29]. The amount of these losses greatly depends on the operating point of the FESS.…”