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.
Highlights
Cleaner production of energy is urgently needed in today’s world due to the concerns about global warming and growing population
The squirrel cage induction machine (SCIM)-Flywheel energy storage systems (FESS) is set to run for 20 min and dynamic analysis is performed during acceleration and deceleration states within a speed range of 10–20 krpm
The SCIM-FESS is designed to deliver 5 kWh of useable energy during which the DC-link voltage is set to 600 V and maintained by the gridconverter side converter (GSC) and machine side converter (MSC)
Summary
Cleaner production of energy is urgently needed in today’s world due to the concerns about global warming and growing population. This need has allowed widespread use of distributed generation (DG) and renewable energy sources (RES) integrated to electricity networks [1]. Flywheels are one of the early forms of mechanical storage systems in history and were first used in boats, steam engines and trains during the industrial revolution in the 18th century [42]. Successful research and advancement in magnetic materials, magnetic bearings and modern power electronics have made it possible for flywheel technology to compete with other energy storage systems and with electro chemical batteries and super capacitors [45]. A modern steel rotor flywheel with a weight of 1t can run at peripheral speed of 500 m/s compared to the flywheels used in stationary steam engines during the industrial age, which could barely exceed the peripheral speed of 20 m/s, modern flywheels can store up to 25 kWh of useable energy when compared to the industrial age flywheels that weighed
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