Electric energy can be converted into chemical energy, potential energy, kinetic energy, electromagnetic energy and other forms for storage. So far, people have developed various forms of energy storage systems, which can be divided into physical, electromagnetic, electrochemical, and phase-change storage systems according to their specific methods. There are four types of ability. Among them, electromagnetic energy storage includes superconducting, supercapacitor, and high-energy-density capacitor energy storage; below we will talk about the specific characteristics of electromagnetic energy storage:
(1) Superconducting energy storage system
Superconductor Magnetics Energy Storage (SMES) uses coils made of superconducting wires to store the magnetic field energy generated by the grid-powered excitation, and then send the stored energy back to the grid or use it for other purposes when needed.
Superconducting energy storage systems usually include superconducting coils placed in a vacuum adiabatic cooling container, cryogenic and vacuum pump systems, and power electronic devices for control. The current circulates continuously in the closed inductance formed by the superconducting coil and will not disappear.
Compared with other energy storage technologies, superconducting energy storage has significant advantages:
①Because the energy can be stored for a long time without loss, the energy return efficiency is very high;
②The energy release rate is fast, usually only a few seconds;
③The use of SMES can make the grid voltage, frequency, active and reactive power easy to adjust. The development of high-temperature superconducting technology and power electronics technology has promoted the application of superconducting energy storage devices in power systems, which have been applied to wind power generation systems in the 1990s. SMES’s fast power throughput and flexible four-quadrant adjustment capabilities enable it to effectively track fluctuations in electrical quantities and improve the damping of the system. Various studies have shown that SMES devices have excellent performance in improving the stability of wind farms.
At present, in distributed power generation systems, SMES energy storage units are often used in island-type wind power generation systems and photovoltaic power generation systems. With the development of wind power generation to large-scale and industrialization, and the reduction of equipment costs, SMES will also be connected to the grid. A large number of applications in wind power systems. The main research directions of superconducting energy storage in the future are: converters and control strategies, reducing losses and improving stability, developing high-temperature superconducting wires (HTS), quench protection technology, etc.
In addition, superconducting energy storage technology can also be used for voltage support, power compensation, frequency adjustment of the distribution network, and to improve system stability and power transmission capacity.
(2) Super capacitor energy storage system
The supercapacitor is developed based on the theory of electrochemical double layer, which can provide powerful pulse power. When charging, the electrode surface is in the ideal polarization state. The charge layer constitutes an electric double layer capacitor. Due to the very small distance between the charge layers (generally less than 0.5mm) and the use of a special electrode structure, the surface area of the electrode has been increased tens of thousands of times, resulting in a great electric capacity. A farad-level capacitance is achieved in a small volume; no special charging circuit and control discharging circuit are required; compared with batteries, overcharge and overdischarge do not have a negative impact on their life; from the perspective of environmental protection, it is a A kind of green energy; super capacitors can be welded, so there is no problem such as weak battery contact; due to low dielectric withstand voltage and leakage current, its energy storage and retention time are limited; compared with aluminum electrolytic capacitors, its internal resistance is larger Therefore, it cannot be used in AC circuits and must be used in series to increase the volume of the charge and discharge control circuit and the system. In the power system, it is mostly used for short-time, high-power load balancing and adjustment of power quality, high peak power and other occasions.