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Title: Magnetic suspension systems, motor/generators and power electronics for flywheel energy storage
Author: Wright, Derek Thomas.
Awarding Body: University of Sussex
Current Institution: University of Sussex
Date of Award: 2001
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A flywheel energy store comprises a motor/generator driving a flywheel where the noload losses are reduced so that half of the stored energy remains available after six hours of coasting. Analysis of the permitted level of losses is followed by discussion of how the losses can be minimised. The merits of induction and permanent magnet machines are compared in terms of their coasting losses. There is discussion of zero-power magnetic bearing systems developed to suspend vertical-axis energy-storage flywheels. With permanent magnet material in the magnetic circuit, an electronic control system can hold the airgap at the otherwise unstable point of equilibrium, where the attractive force due to the magnetic flux exactly balances the weight of the flywheel. Under steady state conditions the power dissipated in the control coil is virtually zero. The torque generation characteristic of an induction machine is explained from first principles. This is followed by an equivalent circuit analysis that is specific to operation at a constant flux level with a variable supply frequency and voltage. The supply voltage for constant flux operation is specified as a function of the rotational speed and the absolute slip frequency. An all-digital, three-phase inverter developed for use with an induction motor gives four-quadrant control of the torque applied to a load. A low cost incremental shaft encoder and straightforward digital logic allows precise and instantaneous generation of absolute slip frequency. A modified PWM switching topology minimises switching losses and maximises the utilisation of the DC link voltage. The inherent speed of the all-hardware design and its precise control of slip frequency, make it ideal for highspeed motors or for drives requiring frequent and rapid reversal. A new design for an ironless stator winding for a permanent magnet motor/generator minimises electromagnetic drag when coasting. The winding meets the predicted reduction in drag torque and provides an extremely pure sine wave output with very low source impedance.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available