Development of a flywheel energy storage system : uninterrupted power supply (FLY-UPS)
Janse van Rensburg, Jan Jacobus
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The School of Electrical, Electronic and Computer Engineering is in the process of establishing an active magnetic bearing (AMB) and high speed permanent magnet synchronous machine (PMSM) laboratory. This is done to gain knowledge on AMB, flywheel and high speed PMSM technologies. Some of the advantages of using AMBs are: no mechanical wear or friction, no need for lubrication, active vibration control and unbalance compensation. This project’s purpose is the development of an AMB suspended flywheel energy storage system. This system should be able to store energy for a certain period with minimal losses. Energy stored should then be readily available for use by a load such as a personal computer. This system will be similar to a conventional uninterrupted power supply (UPS). Instead of using a lead-acid cell to store the energy, a flywheel is used. The acronym for the system is FLY-UPS (FLYwheel Uninterrupted Power Supply). Charging the system should not take longer than 5 minutes using 2000 W of power. One of the system’s main function is to protect sensitive equipment from mains power spikes and short power interruptions. This system should be able to supply 2000Wfor at least 3 minutes, allowing enough time to switch sensitive equipment off in a controlled manner. Two heteropolar radial AMBs, one axial AMB, a high speed permanent magnet synchronous machine (PMSM) for propulsion and generating purposes, and a disc that will serve as the flywheel is the main components of this system. This system should be operated at a rotational speed of 30000 rpm. Development of this system facilitates testing of control algorithms and establishes knowledge on AMBs and flywheels. An important outcome of this project is delivering a working FLY-UPS system. Future research on advanced control techniques, low loss AMB’s and flywheel design optimising is made possible with the development of the FLY-UPS system. An in depth investigation into rotor-dynamics and flywheels has been conducted. Research into flywheels is relevant because recently there has been a growing focus on renewable energy. A modular approach was used in the design of the FLY-UPS system. A rotor-dynamic analysis has been done on the rotor/flywheel assembly, resulting in predicted displacements and the critical frequencies of the rotor/flywheel assembly. Analytical and computer aided strength analysis has been done on the rotor/flywheel assembly. Both the analytical and computer aided strength analysis concludes that the rotor/flywheel achieves the minimum factor of safety of 1.5. Measured critical frequencies correlate to the predicted critical frequencies. Predicted displacement does not correlate to the measured displacement. This is attributed to insufficient balancing of the rotor/flywheel. Rotational speed of the rotor/flywheel is currently limited to 7000 rpm, in stead of the required 30000 rpm, due to the greater displacements. Further investigation into the reasons for the greater displacement is still required. A possible solution to this problem is re-balancing the rotor/flywheel assembly. Further research is required on the dynamic stiffness of the AMBs. A delevitation system needs to be developed. Research has to be done on the accurate prediction of the behaviour of a rotor during delevitation. An investigation into the development of a carbon-fibre composite flywheel needs to be conducted. Measured against the outcomes, the project has been a success.
- Engineering