In recent years, the energy storage sector has been booming, with new energy storage technologies such as lithium-ion batteries, sodium-ion batteries, flywheel energy storage, and compressed air energy storage being updated and iterated at an unprecedented speed.
Flywheel energy storage is a type of mechanical energy storage with advantages such as long lifespan and environmental friendliness, and has become increasingly popular in the market in recent years.
The working principle of flywheel energy storage is that the flywheel is driven to rotate by energy such as electricity, and converts electrical energy into mechanical energy for storage. When needed, the mechanical energy stored by the rotation of the flywheel is converted back into electrical energy and released.
In terms of structure, flywheel energy storage systems generally consist of five main parts, including the energy storage wheel body, motor, shell, power electronics system, and servo system.
The energy storage wheel determines the amount of energy that a flywheel can store; there are two common types.
First, there are low-speed wheels made of alloy steel, with a speed generally less than 10,000 r/min. The advantages are low cost and simple manufacturing, while the disadvantages are large weight and high requirements for installation location.
Secondly, there are high-speed wheels made of carbon fiber, which generally have a rotational speed of more than 10,000 r/min. The advantage is that they are lightweight, but the disadvantages are that they are more expensive and more difficult to manufacture.
The electric motor is key to flywheel energy storage's conversion of electrical energy into mechanical energy. Electric motors suitable for flywheel energy storage need to possess four characteristics.
First, the motor must be able to operate under both motor and generator conditions, enabling bidirectional conversion between electrical and mechanical energy;
Secondly, to ensure the long-term operation and energy conversion efficiency of the flywheel energy storage system, the no-load loss rate and conversion efficiency of the motor also have high requirements;
Third, when the flywheel energy storage system is working normally, the speed range is large, and the motor needs to meet the requirements of a wide speed range and a simple and reliable speed regulation method;
Fourth, the energy density of the motor must reach a certain level to ensure a large output torque and power.
Currently, the industry believes that permanent magnet motors have great potential with the development of permanent magnet materials.
The flywheel housing typically includes a vacuum chamber, bearing system, and heat dissipation system, and its main function is to ensure the safe operation of the flywheel.
The vacuum chamber ensures that the electric flywheel rotates without being affected by wind resistance at high speeds; the heat dissipation system generally uses air cooling and air conditioning to prevent the permanent magnets from demagnetizing and to ensure system stability; the bearing system includes two types: passive magnetic bearings and active magnetic bearings.
The power electronic system is responsible for regulating the rotation, charging, and discharging of the motor, and is the "brain" of flywheel energy storage.
The servo system consists of a lubrication system, a monitoring system, a vacuum system, etc. It is responsible for monitoring various parameters during flywheel operation and will issue an early warning if any parameter becomes abnormal.
