Flywheel battery energy storage technology for electric vehicles

Electric vehicles using chemical batteries have been tested for decades, but have not yet entered the practical stage. Solar energy, wind energy, tidal energy, and wave energy all have storage problems. Currently, they mainly rely on chemical batteries, but they are restricted by the life and efficiency of chemical batteries and have not yet been widely used. The above problems have prompted people to seek a green energy storage device with high efficiency, long life, large energy storage, convenient use, and no pollution. Unexpectedly, the ancient "flywheel" has become the first choice.

The "flywheel" energy storage element has been used by people for thousands of years, from the ancient spinning wheel to the steam engine during the Industrial Revolution. In the past, its inertia was mainly used to balance the speed and pass the "dead point". Because their working cycles are very short, each rotation takes less than one second. In such a short time, the energy consumption of the flywheel can be ignored. Now, if we want to use the flywheel to balance the energy with a cycle of up to 12 to 24 hours, the energy consumption of the flywheel itself becomes very prominent. The energy consumption mainly comes from bearing friction and air resistance. People have reduced bearing friction by changing the bearing structure, such as changing sliding bearings to rolling bearings, liquid hydrodynamic bearings, gas hydrodynamic bearings, etc., and reducing air resistance by vacuuming. The bearing friction coefficient has been reduced to 10-3. Even with such a small amount, 25% of the energy stored in the flywheel is still lost within a day, which still cannot meet the requirements of efficient energy storage. Another problem is that conventional flywheels are made of steel (or cast iron) and have limited energy storage. For example, in order to make a power plant with a generating capacity of 1 million kilowatts generate electricity evenly, the energy storage wheel needs 1.5 million tons of steel! In addition, to complete the conversion of electrical energy into mechanical energy, a complex set of power electronics is also required, so the flywheel energy storage method has not been widely used.

In recent years, the breakthrough progress of flywheel energy storage technology is based on the rapid development of the following three technologies: first, the emergence of high-energy permanent magnet and high-temperature superconducting technology; second, the advent of high-strength fiber composite materials; and third, the rapid development of power electronics technology. In order to further reduce bearing loss, people once dreamed of removing the bearings and suspending the rotor with magnets, but the experimental results failed again and again. Later, a British scholar theoretically explained that it is impossible for an object to be fully suspended by a permanent magnet (Earnshaw theorem), which made the experimenters quite discouraged. Unexpectedly, the dream of fully suspended objects has been realized in superconducting technology, which is really like nature's comfort to explorers.

The principle of superconducting magnetic levitation is as follows: when we align one pole of a permanent magnet with a superconductor and approach the superconductor, an induced current is generated on the superconductor. The magnetic field generated by the current is just opposite to the magnetic field of the permanent magnet, so the two generate repulsion. Since the resistance of the superconductor is zero, the intensity of the induced current will remain unchanged. If a permanent magnet approaches a superconductor in the vertical direction, the permanent magnet will be suspended in the air at a position where its own weight is equal to the repulsive force, and it will resist interference from above, below, left and right. After the interference force is eliminated, it can still return to the original position, thus forming a stable magnetic suspension. If the superconductor below is replaced with a permanent magnet, repulsion will also be generated between the two permanent magnets in the horizontal direction, so the permanent magnetic suspension is unstable.

Using this characteristic of superconductivity, we can put a flywheel with a certain mass on top of the permanent magnet, and the flywheel also serves as the motor rotor. When charging the motor, the flywheel speeds up and stores energy, turning electrical energy into mechanical energy; when the flywheel slows down, it releases energy and turns mechanical energy into electrical energy. Figure 1 is a schematic diagram of an energy storage flywheel device. The superconductor in the figure is made of barium yttrium copper alloy and cooled to 77K with liquid nitrogen. The flywheel cavity is evacuated to a vacuum of 10-8 Torr (Torr is a unit of vacuum, 1Torr (Torr) = 133.332Pa). This flywheel consumes very little energy, only 2% of the stored energy is consumed every day.

mass, v is speed. Since the speed of each point on the flywheel is different, its kinetic energy can also be expressed as:

where ∑ is the representation of "sum", mi is the mass of each point on the wheel, and vi is the speed of each point on the wheel. It can be seen from the above formula that the energy storage of the flywheel is not only related to the mass (weight) of the flywheel, but also to the speed of each point on the flywheel, and it is a square relationship. Therefore, increasing the speed (rotation speed) of the flywheel is more effective than increasing the mass. However, the rotation speed of the flywheel is limited by the material of the flywheel itself. If the speed is too high, the flywheel may be torn apart by the strong centrifugal force. Therefore, the use of high-strength, low-density high-strength composite fiber flywheels can store more energy. The currently selected carbon fiber composite materials have a wheel rim linear speed of up to 1000 meters per second, which is higher than the speed of a bullet. It is precisely because of the advent of high-strength composite materials that flywheel energy storage has entered the practical stage.

The following is an introduction to the progress of flywheel energy storage abroad.

In 1994, the Argonne National Laboratory (ANL) in the United States used carbon fiber to test a flywheel for energy storage: 38 cm in diameter, 11 kg in mass, superconducting magnetic suspension, and the flywheel linear speed reached 1000 m/s. The energy it stores can light 10 100-watt light bulbs for 2 to 5 hours. The laboratory is currently developing a 50-kilowatt-hour energy storage wheel, with the ultimate goal of making it a 5000-kilowatt-hour energy storage flywheel. A power plant with a generating capacity of 1 million kilowatts requires about 200 such energy storage wheels.

In 1992, the American Flywheel Systems (AFS) developed an electromechanical battery (EMB) for automobiles. Each "battery" is 18 cm long, 23 cm in diameter, and weighs 23 kg. The core of the battery is a carbon fiber flywheel that rotates at 200,000 rpm. Each battery stores 1 kilowatt-hour of energy. They put 12 "batteries" on the IMPACT car, which can enable the car to travel 480 kilometers at a speed of 100 kilometers per hour. The electromechanical battery weighs 273 kilograms in total, and if lead-acid batteries are used, the total weight is 396 kilograms. The energy stored in the electromechanical battery is 2.5 times that of the lead-acid battery, and the service life is 8 times that of the lead-acid battery. In addition, its "specific power" (i.e., explosive power) is extremely high, 25 times that of the lead-acid battery and 10 times that of the gasoline engine. It can accelerate the car from rest to 100 kilometers per hour in 8 seconds.

Japan once used the high "specific power" characteristics of the flywheel to design a device that triggers controlled thermonuclear fusion, as shown in Figure 2. The flywheel of the device has a diameter of 6.45 meters, a height of 1 meter, and a weight of 255 tons. The energy it stores is equivalent to the energy of a train with 150 carriages traveling at a speed of 100 kilometers per hour. Therefore, releasing this energy in a very short time is enough to trigger nuclear fusion.

China's research on flywheels began in 1993, and considerable progress has been made in theoretical analysis and model experiments. The feasibility of using flywheels as energy storage devices is no longer doubted. Although there are still many technical problems to be solved for large-scale industrial applications, it is only a matter of time.

In the 21st and 22nd centuries, solar energy (including its derived wind energy and wave energy) may become the only energy source allowed to be used. With the help of flywheel energy storage, solar power plants can provide all-weather energy. At this time, and only at this time, the sky of the global village will become blue, the water will be clear, and the human dream of "green energy" will be completely realized. Flywheel batteries

are new concept batteries proposed in the 1990s. They break through the limitations of chemical batteries and use physical methods to achieve energy storage. As we all know. When a flywheel rotates at a certain angular velocity, it has a certain amount of kinetic energy. Flywheel batteries convert kinetic energy into electrical energy. High-tech flywheels are used to store electrical energy, much like standard batteries. There is a motor in the flywheel battery. When charging, the motor operates as an electric motor. Driven by an external power source, the motor drives the flywheel to rotate at high speed, that is, the flywheel battery is "charged" with electricity, which increases the speed of the flywheel and increases its function; when discharging, the motor operates as a generator, outputs electrical energy to the outside under the drive of the flywheel, and completes the conversion of mechanical energy (kinetic energy) to electrical energy. When the flywheel battery outputs electricity, the speed of the flywheel gradually decreases. The flywheel of the flywheel battery operates in a vacuum environment with an extremely high speed (up to 200,000 r/min), and the bearings used are non-contact magnetic bearings. It is said that the flywheel battery has a specific energy of up to 150W·h/kg, a specific power of 5000-10000W/kg, a service life of up to 25 years, and can provide electric vehicles with a driving range of 5 million kilometers.

Flywheel batteries that have been commercialized abroad, this is a photo of a 150WH flywheel battery.

Current product specifications are:

FLB-E 150 Wh

FLB-E 500 Wh

HB-B 2.5 kwh

FLC-B 25 kwh

FLB-D 200 kwh

Let's take a look at the structure inside.

Flywheel battery schematic diagram Flywheel energy storage technology is an emerging energy storage technology. Like superconducting energy storage technology and fuel cell technology, it is an energy storage technology that has emerged in recent years and has great development prospects. Although chemical battery energy storage technology has been developed very maturely, it has problems such as limited charging and discharging times, serious environmental pollution, and high operating temperature requirements. This has made emerging energy storage technologies more and more valued by people. In particular, flywheel energy storage technology has begun to be more and more widely used in many industries at home and abroad.