Flywheel energy storage

Flywheel energy storage means that the flywheel is driven by the motor to rotate at high speed, and then the flywheel is used to drive the generator to generate electricity when necessary. Its technical characteristics are high power density and long service life.

Introduction to flywheel energy storage The idea of flywheel energy storage was put forward as early as 100 years ago, but due to the technical conditions at that time, there was no breakthrough for a long time. It was not until the 1960s and 1970s that the Glenn Research Center of NASA began to use flywheels as energy storage batteries on satellites. After 1990s, breakthroughs were made in the following three aspects, which brought more development space for flywheel energy storage technology.

The appearance of (1) high-strength carbon fiber composites (tensile strength up to 8.27GPa) greatly increased the kinetic energy reserve per unit mass.

(2) The research on magnetic levitation technology and high temperature superconducting technology has made rapid progress. By using magnetic levitation and vacuum technology, the friction loss and wind power loss of flywheel rotor are minimized.

(3) The new progress of power electronics technology, such as the breakthrough of motor/generator and power conversion technology, provides advanced means for the exchange of kinetic energy and electric energy stored in flywheel. Energy storage flywheel is a high-tech mechatronics product, which has broad application prospects in aerospace (satellite energy storage battery, integrated power supply and attitude control), military (high-power electromagnetic gun), electric power (peak shaving), communication (UPS), automobile industry (electric vehicle) and other fields.

The working principle of flywheel energy storage The flywheel energy storage system is an energy storage device for electromechanical energy conversion, which breaks through the limitations of chemical batteries and realizes energy storage through physical methods. Through the motor/generator reciprocating bidirectional motor, through frequency modulation, rectification, constant voltage and different types of load interfaces, the mutual conversion and storage of electrical energy and mechanical kinetic energy of high-speed flywheel are realized.

When storing energy, the electric energy is converted by the power converter to drive the motor to run, and the motor drives the flywheel to rotate at an accelerated speed, and the flywheel stores energy in the form of kinetic energy, thus completing the energy storage process of converting the electric energy into mechanical energy, and the energy is stored in the high-speed rotating flywheel body; After that, the motor keeps constant speed until it receives the control signal of energy release; When releasing energy, the high-speed rotating flywheel drives the motor to generate electricity, and the current and voltage suitable for the load are output through the power converter, thus completing the energy release process from mechanical energy to electrical energy. The whole flywheel energy storage system realizes the process of input, storage and output of electric energy.

Flywheel energy storage structure Flywheel body is the core component of the flywheel energy storage system, which aims to improve the ultimate angular velocity of the rotor, reduce the weight of the rotor and maximize the energy storage function of the flywheel energy storage system. At present, it is mostly made of carbon fiber.

The performance of bearing system directly affects the reliability, efficiency and life of flywheel energy storage system. At present, the flywheel energy storage system mostly adopts magnetic levitation system, which reduces the friction when the motor rotor rotates, reduces the mechanical loss and improves the energy storage efficiency.

The flywheel energy storage system takes the motor/generator and its control as the core to realize the conversion between mechanical energy and electrical energy. The motor/generator integrates a component and operates as a motor when storing energy. The motor is driven by external electric energy to drive the flywheel rotor to accelerate to a set speed. When the energy is released, the motor operates as a generator and outputs electric energy to the outside. At this point, the speed of the flywheel is decreasing. Obviously, a low-loss and high-efficiency motor/generator is the key to efficient energy transmission.

The purpose of power conversion device is to improve the flexibility and controllability of flywheel energy storage system and convert the output electric energy (frequency modulation, rectification or constant voltage, etc.). ) to meet the power supply requirements of the load.

The main function of the vacuum chamber is to provide a vacuum environment and reduce the wind resistance loss when the motor is running.

Flywheel energy storage system is mainly composed of three parts: rotor system, bearing system and energy conversion system. There are also some support systems, such as vacuum, cryogenic, shell and control system.

1. The kinetic energy of the flywheel in the rotor system is directly proportional to the moment of inertia of the flywheel. The moment of inertia of the flywheel is directly proportional to the flywheel diameter and the quadratic square of the flywheel mass (j = (0.5 ~ 1) * m * r 2, 0.5 when the flywheel mass distribution is uniform, and1when the mass is completely concentrated at the edge).

When the super-large and bulky flywheel rotates at high speed, it will be subjected to great centrifugal force, which often exceeds the ultimate strength of flywheel material, which is very unsafe. Therefore, it is limited to increase the kinetic energy of flywheel by increasing its moment of inertia.

2. The bearing system supports the bearings of the rotor, supports the movement of the rotor, reduces the friction resistance, and makes the whole device run with minimum loss.

3. There is a built-in motor in the flywheel energy storage device of the energy conversion system, which is both a motor and a generator. When charging, it acts as a motor acceleration flywheel; When discharging, it acts as a generator to supply power to peripherals, and at this time, the speed of flywheel decreases continuously; When the flywheel idles, the whole device runs with minimum loss. There is no chemical active substance and no chemical reaction in the flywheel energy storage device. When the flywheel rotates, it is purely mechanical, and the kinetic energy when the flywheel rotates is:

E = 1/2Jω/2, where: j is the moment of inertia of the flywheel and ω is the angular velocity of the flywheel.

The technical advantages of flywheel energy storage are high technical maturity, unlimited charging and discharging times and no pollution. The energy density of flywheel energy storage is not high enough, and the self-discharge rate is high. If you stop charging, the energy will run out in a few to dozens of hours. It is suitable for power grid frequency modulation and power quality guarantee.

Application of flywheel energy storage 1, Battery-free magnetic suspension flywheel energy storage UPS (1) When the input of commercial power is normal, or the input of commercial power is low or high (within a certain range), UPS uses its internal active dynamic filter to stabilize and filter the commercial power, providing high-quality power guarantee for load equipment, and charging the flywheel energy storage device at the same time. UPS uses the built-in flywheel energy storage device to store energy. (2) Under the condition that the input quality of commercial power can't meet the normal operation requirements of UPS, or the input of commercial power is interrupted, UPS converts the mechanical energy stored in the flywheel energy storage device into electrical energy, and continues to provide high-quality uninterrupted power guarantee for load equipment.

(3) Under the condition that the internal problems of UPS affect the work, UPS switches to bypass mode through its internal static switch, and the commercial power directly provides uninterrupted power supply to the load equipment.

(4) When the input of commercial power is restored to power supply, or the input quality of commercial power is restored to meet the normal operation requirements of UPS, immediately switch to the mode of commercial power supply through UPS, continue to provide high-quality uninterrupted power guarantee for load equipment, and continue to charge the flywheel energy storage device.

2. Electric vehicle battery With the improvement of environmental awareness and the intensification of global energy supply and demand contradiction, it is an important trend for the development of the world automobile industry to develop energy-saving and environment-friendly vehicles and adopt alternative energy sources to reduce environmental pollution. The automobile manufacturing industry has turned its attention to the development of electric vehicles. Finding a new battery with high energy storage density, short charging time and reasonable price is the key to whether electric vehicles can have greater mobility and compete with gasoline vehicles. Flywheel battery has the characteristics of cleanliness, high efficiency, rapid charge and discharge, and no pollution to the environment, and has been widely valued by the automobile industry. It is predicted that flywheel battery will be the research hotspot of electric vehicle industry in 2 1 century.

3. Uninterruptible power supply Uninterruptible power supply is widely used in communication hubs, national defense command centers, industrial production control centers and other places because it can ensure uninterrupted power supply and power supply quality. At present, uninterruptible power supply is composed of rectifier, inverter, static switch and battery pack. However, at present, there are usually requirements for working temperature, working humidity, input voltage and discharge depth, and frequent opening and closing of batteries are not allowed. Flywheel has the advantages of large energy storage, high energy storage density, fast charging and unlimited charging and discharging times, and has a good application prospect in the field of uninterruptible power supply system.

4. Uninterrupted power supply of wind power generation system brings difficulties to wind power generation users due to unstable wind speed. The traditional way 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. The wind often breaks for a few seconds and minutes. Diesel engines are not only started frequently, but also their service life is affected. Moreover, after the fan is restarted, the diesel engine will act at the same time, which will cause excess power. Considering the large amount of energy stored in the flywheel. Charging is fast, so many foreign scientific research institutions introduce energy storage flywheel into wind power generation system. The United States introduced the flywheel into the wind power generation system to realize the overall peak regulation. The generating power of the flywheel group 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 that the launch vehicle can only be used once and reduce air pollution, the United States is studying a kind of magnetic suspension linear motor bracket (also known as space elevator) to launch the space shuttle, which requires a power supply with huge power but extremely short discharge time, so it is obviously unreasonable to reduce the energy provided by a storage system with huge capacity. This can be achieved by using a flywheel energy storage system. Brief Introduction of Flywheel Energy Storage Working Principle Composition Structure Flywheel Energy Storage Application @20 19