What is flywheel energy storage system ?
2024-11-21
The flywheel energy storage system is an energy storage device for electromechanical energy conversion.
The system uses physical methods to store energy, and realizes the mutual conversion and storage between electrical energy and the mechanical kinetic energy of the high-speed flying wheel through an electric/generating reciprocal bidirectional motor.
The flywheel energy storage system is a mechanical energy storage system with broad application prospects. It has the advantages of high energy storage density, strong adaptability, wide application range, high efficiency, long life, no pollution and low maintenance costs.
Flywheel energy storage systems have been used in aerospace, UPS power supply, transportation, wind power generation, nuclear industry and other fields. With the continuous advancement of composite material technology, magnetic support technology, dynamic-generator integrated machine technology and multidisciplinary optimization design technology, more and more attention has been paid to flywheel energy storage technology, and related new technologies have continued to emerge.
Working principle of flywheel energy storage system
When storing energy, external electrical energy is converted by the power converter to drive the motor to run, and the motor drives the flywheel rotor to accelerate until it reaches a certain set speed. During the process of accelerating the flywheel, the flywheel stores energy in the form of kinetic energy, completing the energy storage process of converting electrical energy to mechanical kinetic energy, and the energy is stored in the high-speed rotating flywheel body. After that, the flywheel rotates at the set speed until it receives a control signal for energy release. When releasing energy, the motor is used as a generator, and the high-speed rotating flywheel drags the motor to generate electricity. The power converter outputs current and voltage suitable for the load, completing the energy release process of converting mechanical kinetic energy to electrical energy. During the energy release process, the speed of the flywheel continues to decrease. The entire flywheel energy storage system realizes the input, storage and output of electrical energy.
Structure of flywheel energy storage system
A typical flywheel energy storage system consists of five main components: flywheel body, bearing, motor/generator, power converter and vacuum chamber.
In practical applications, there are many structures of flywheel energy storage systems. Figure 1 shows a schematic diagram of the structure of a flywheel energy storage system in which a flywheel and a motor are integrated into one. The flywheel body is the core component of the flywheel energy storage system.
Its function is to increase the limit angular velocity of the rotor, reduce the weight of the rotor, and maximize the energy storage capacity of the flywheel energy storage system. It is mostly made of carbon fiber material.
The performance of the bearing directly affects the reliability, efficiency and life of the flywheel energy storage system.
The flywheel energy storage system used mostly adopts a magnetic suspension system to reduce the friction when the motor rotor rotates, reduce mechanical losses, and improve energy storage efficiency.
The conversion between mechanical kinetic energy and electrical energy of the flywheel energy storage system is realized with the motor/generator and its control as the core.
The motor/generator integrates a component. When storing energy, it operates as a motor, and the motor is driven by external electric energy to drive the flywheel rotor to accelerate to a certain set speed; when releasing energy, the motor operates as a generator and outputs electric energy to the outside. At this time, the flywheel speed continues to decrease. Obviously, low-loss and high-efficiency motors/generators are the key to efficient energy transmission.
The power converter is to improve the flexibility and controllability of the flywheel energy storage system, and convert the output electric energy into electric energy that meets the load power supply requirements through frequency modulation, rectification or constant voltage.
The main function of the vacuum chamber is to provide a vacuum environment and reduce the wind resistance loss when the motor is running.
Application fields of flywheel energy storage system
1. Battery-free magnetic levitation flywheel energy storage UPS
(1) When the mains input is normal, or when the mains input is low or high (within a certain range), the UPS stabilizes and filters the mains through its internal active dynamic filter to ensure high-quality power supply to the load equipment, and charges the flywheel energy storage system at the same time. The UPS uses the built-in flywheel energy storage device to store energy.
(2) When the mains input quality cannot meet the normal operation requirements of the UPS, or when the mains input is interrupted, the UPS converts the mechanical energy stored in the flywheel energy storage system into electrical energy, and continues to provide high-quality and uninterrupted power supply to the load equipment.
(3) When problems occur inside the UPS that affect the operation, the UPS switches to bypass mode through its internal static switch, and the mains directly provides uninterrupted power supply to the load equipment.
(4) When the mains input is restored, or when the mains input quality is restored to meet the normal operation requirements of the UPS, it immediately switches to the mode where the mains is supplied through the UPS, continues to provide high-quality and uninterrupted power supply to the load equipment, and continues to charge the flywheel energy storage device.
2. Electric vehicle batteries
With the improvement of environmental protection awareness and the contradiction between global energy supply and demand, the development of energy-saving and environmentally friendly vehicles that use alternative energy to reduce environmental pollution is an important trend in the development of the world's automobile industry. The automobile manufacturing industry has turned its attention to the development of electric vehicles. Whether electric vehicles can have greater mobility and compete with gasoline vehicles can be found. The flywheel energy storage system has the characteristics of cleanliness, high efficiency, rapid charging and discharging, and no pollution to the environment, and is widely valued by the automobile industry. It is expected that flywheel batteries will be a research hotspot in the electric vehicle industry in the 21st century.
3. Uninterruptible power supply
Uninterruptible power supply is widely used in communication hubs, national defense command centers, industrial production control centers, etc. because it can ensure uninterruptible power supply and guarantee power supply quality. Uninterruptible power supply consists of rectifier, inverter, static switch and battery pack.
However, batteries usually have requirements for working temperature, working humidity, input voltage, and discharge depth. At the same time, batteries are not allowed to be frequently turned off and on. The flywheel energy storage system has the advantages of large storage capacity, high energy storage density, fast charging, unlimited charging and discharging times, so it has good application prospects in the field of uninterruptible power supply system.
4. Uninterrupted power supply of wind power generation system
Due to the unstable wind speed, wind power generation brings difficulties to wind power users. The traditional approach is to install a diesel generator, but due to the special requirements of the diesel engine itself, it can only be stopped within 30 minutes after starting. And the wind power is often interrupted for seconds or minutes. Not only does the frequent start of the diesel unit affect the service life; but also after the wind turbine is restarted, the diesel engine will work at the same time, which will cause excess electricity. Considering the large energy of the flywheel energy storage system and the fast charging, many foreign scientific research institutions have introduced energy storage flywheels into wind power generation systems. The United States introduced flywheels into the wind power generation system to achieve full peak regulation. The power generation power of the flywheel unit is 300KW, and the energy storage of the large-capacity energy storage flywheel is 277KW per hour.
5. High-power pulse discharge power supply
In order to avoid the huge waste of launch vehicles that can only be used once and reduce air pollution, the United States is studying a magnetic levitation linear motor bracket (also known as a space elevator) to launch the space shuttle. This requires a power supply with huge power but very short discharge time. Therefore, it is obviously unreasonable to build a large-capacity power system to provide energy. The use of a flywheel energy storage system can achieve this.
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