The research of flywheel energy storage device spans many disciplines, such as electronics, motor, mechanics, machinery, materials and so on. Its key technologies mainly include the following aspects.
(1) Rotor structure and manufacturing process
There are three ways to improve the ultimate energy storage density of flywheel: using alloys and composites with higher specific strength; Optimize the shape and structure of the rotor to obtain a higher shape coefficient of the flywheel structure; Optimize the stress distribution of each material and improve the utilization coefficient of the material.
(2) High speed bearing support technology
High speed bearing is the key factor that restricts the development of flywheel energy storage technology. Due to the relatively large mass and moment of inertia of the energy storage flywheel, which requires ultra-high speed, its gyroscopic effect is very obvious and there is an over critical problem. The system belongs to a typical frequency varying system. Therefore, high requirements are put forward for the support bearing. The influence of rotor support dynamics, gyroscopic effect and power consumption should be considered for superconducting magnetic bearings, active control electromagnetic bearings, mechanical gem bearings, etc.
(3) High speed rotor dynamics technology
The flywheel rotor rotating at high speed has a large moment of momentum, and its gyroscopic effect has a great impact. To achieve high-speed rotation, we should solve the problems of dynamic balance and stability.
When a flywheel is used in an automobile, due to the gyro effect caused by the change of the flywheel axis orientation when the automobile is driving, additional gyro torque is generated on the constraint during the flywheel rotation, causing excessive additional pressure on mechanical parts such as bearings, so that the parts are damaged. Moreover, the gyro effect may be the vibration source of the system vibration. Therefore, it should be considered in the design. The gyro moment can be expressed as
Where, I is the moment of inertia of the flywheel; ω Is the angular speed of flywheel rotation; Ω is the precession angular speed of the flywheel shaft.
From the above formula, it can be found that when the flywheel shaft is parallel to the ground, the system will force the flywheel shaft to precession and produce gyro torque due to the change of vehicle driving direction; When the flywheel axis is placed perpendicular to the ground, the system will produce gyro torque due to the forward and backward pitching of the car. It is impossible to completely eliminate the gyroscopic effect produced by the car during driving, and it can only be minimized. Therefore, trying to reduce the influence of gyro effect will be another difficult problem in automobile design.
(4) High speed motor / engine and energy conversion technology
The motor and its control system used in flywheel energy storage device must have the characteristics of high running speed, high energy conversion efficiency, high power conversion efficiency, low loss, fast charging and discharging speed, which puts forward high requirements for the motor and energy conversion system.
(5) Vacuum sealing technology
The high-speed flywheel must operate in the vacuum chamber, and the friction loss can be reduced as much as possible when the vacuum degree reaches 0.1~0.01pa. It is not difficult to achieve a high vacuum, but the difficulty lies in maintaining a high vacuum. Therefore, it is still a very difficult task to solve the problem of high sealing of the vacuum chamber and the deflation of indoor components, so as to maintain a high vacuum for a long time.
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