The Design Of The Superconducting Flywheel Energy Storage System And Its Energy Feedback Technology

In the recent years, the continuous increscent power demand has brought on the augment of system capacity and the interconnection of electrical networks. However, the operation mode of the interconnection has many disadvantages, such as complicated structure and low security, and the utilization ratio of power and transmission equipments are also not high. Accordingly, power storage technology can be applied to solve these demerits. The application of storage technology in power system can help to decrease the peak-valley difference of load, suppress the concussion of system and improve the stability and supply quality of system. In addition, the combination of storage technology and new energy power generation can also enhance the utilization ratio of energy to certain extent.The test of superconducting maglev bearing, which is one of key technologies for flywheel storage system, is studied in this thesis firstly. The combination of superconducting maglev and mechanical bearings is chosen as the bearing system, and there are few researches on this combination system at present. The operation principle of superconducting maglev is introduced. Based on the test results, the relationship between the levitation force F and the distance of superconductors h is analyzed, and further the best distance, where storage device's loss is lowest, is acquired correspondingly. During the research of release energy link of superconducting maglev flywheel storage system prototype, the bulk superconductors are tested in the normal and superconducting state respectively. According to the release energy results, it is known that high superconducting maglev bearing can help to decrease the energy loss of flywheel storage system.Further, on the basis of the above results, the energy feedback link of flywheel storage system is analyzed and designed. As the continuous fall of flywheel speed during the process of release energy, the output voltage of permanent magnet brushless dc motor (used for generator) will decrease correspondingly. In order to ensure the stability of flywheel storage system's feedback voltage and satisfy the requirement of load, the DC-DC boost circuit is needed to make dc bus voltage remain at 360V and after the conversion of DC-AC, the ac voltage of 220V can be insured. As a result, the flexible seamless connection of flywheel storage system and electrical network can be realized.In this thesis, a novel design scheme about the low-voltage DC/AC converter (10-15Vdc/220V) is proposed. The push-pull type DC-DC boost converter is chosen for the DC-DC boost link. This type converter has low loss and high efficiency in the case of medium and low power. The single-phase half-bridge inverter circuit is adopted for the DC-AC conversion link. The operation principle of these two circuit structures are introduced in detail, and the design and selection of main circuit and control circuit are also studied.This thesis presents the design process of the energy feedback link of flywheel storage system, and then provides reference for subsequent design.