What is supercapacitor energy storage and its application areas？
2024-12-27
Supercapacitor energy storage refers to the technology of storing electrical energy using capacitors. The mechanism of supercapacitor energy storage is double-layer capacitance and Faraday capacitance. Its main form is supercapacitor energy storage. The supercapacitor energy storage device is mainly composed of a supercapacitor group and a bidirectional DC/DC converter and a corresponding control circuit. Its technical core lies in the voltage-sharing topology and control strategy inside the supercapacitor group and the topology and control strategy of the bidirectional DC/DC converter.
Supercapacitor energy storage has been widely used in electric vehicles, wind and solar power generation energy storage, power quality regulation in power systems, pulse power supplies, etc.
Introduction to supercapacitor technology
The mechanism of supercapacitor energy storage is double-layer capacitance and Faraday capacitance. Its main form is supercapacitor energy storage. Supercapacitor energy storage is a new type of electrochemical energy storage device between traditional capacitors and batteries. Compared with traditional capacitors, it has higher energy density, and the electrostatic capacity can reach thousands of farads to ten thousand farads; compared with batteries, it has higher power density and ultra-long cycle life. Therefore, it has the advantages of both traditional capacitors and batteries and is a chemical power source with broad application prospects. It mainly uses the double layer formed by the charge separation at the electrode/electrolyte interface, or the Faraday "quasi-capacitor" generated by the rapid redox reaction on the electrode surface and inside to realize the storage of charge and energy.
Therefore, supercapacitor energy storage has the characteristics of fast charging speed, good high current discharge performance, ultra-long cycle life, and wide operating temperature. The supercapacitor energy storage device is mainly composed of a supercapacitor group, a bidirectional DC/DC converter, and a corresponding control circuit.
Classification of supercapacitor energy storage
Double-layer supercapacitor energy storage
Is generated by the confrontation of charges caused by the directional arrangement of electrons or ions at the electrode/solution interface. For an electrode/solution system, a double layer will be formed at the interface of the electron-conducting electrode and the ion-conducting electrolyte solution. When an electric field is applied to the two electrodes, the anions and cations in the solution migrate to the positive and negative electrodes respectively, forming a double layer on the electrode surface; after the electric field is removed, the positive and negative charges on the electrodes attract the oppositely charged ions in the solution to stabilize the double layer, and a relatively stable potential difference is generated between the positive and negative electrodes.
At this time, for a certain electrode, an opposite ion charge equal to the charge on the electrode will be generated within a certain distance (dispersion layer), so that it remains electrically neutral; when the two poles are connected to an external circuit, the charge on the electrode migrates and generates a current in the external circuit, and the ions in the solution migrate into the solution to be electrically neutral, which is the charging and discharging principle of double-layer supercapacitor energy storage.
Faraday pseudocapacitor
The theoretical model was first proposed by Conway. It is that the electroactive material is deposited at an underpotential on the electrode surface and near the surface or in the bulk phase in a two-dimensional or quasi-two-dimensional space, and highly reversible chemical adsorption and desorption and redox reactions occur, producing a capacitance related to the electrode charge potential.
For Faraday pseudocapacitor, the process of storing charge includes not only the storage on the double electric layer, but also the redox reaction between the electrolyte ions and the electrode active material. When the ions in the electrolyte (such as H+, OH-, K+ or Li+) diffuse from the solution to the electrode/solution interface under the action of an external electric field, they will enter the bulk phase of the active oxide on the electrode surface through the redox reaction on the interface, so that a large amount of charge is stored in the electrode. During discharge, these ions that enter the oxide will return to the electrolyte through the reverse reaction of the above redox reaction, and the stored charge will be released through the external circuit. This is the charging and discharging mechanism of Faraday pseudocapacitor.
Application fields of supercapacitor energy storage
Supercapacitor energy storage systems have been widely used in electric vehicles, wind and solar power generation storage, power quality regulation in power systems, pulse power supplies, etc.
Application in electric vehicles
Supercapacitor energy storage is used in hybrid electric vehicles. Since the vehicle often needs to accelerate or decelerate during driving, the acceleration motor requires a large starting current, which will cause great damage to both the battery and the fuel cell. When the vehicle is decelerating and braking, according to research, the energy required for braking accounts for 50% of the driving energy. If a supercapacitor energy storage device is added to manage the energy of the vehicle's startup acceleration and braking deceleration, it can not only reduce the damage to the battery or fuel cell in the electric vehicle, but also recover excess energy and extend the driving range of the electric vehicle.
Application in wind and solar power generation and energy storage
Solar energy and wind energy are the most convenient and cleanest energy sources. At present, batteries are widely used as energy storage or buffer devices. The biggest problem is that the operation and maintenance costs are high and the service life is short. Supercapacitor energy storage has the characteristics of more than tens of thousands of charge and discharge cycle life, complete maintenance-free, and high reliability, making it an inevitable trend to replace the storage drive shaft motor generator supercapacitor energy storage device output mechanical energy input mechanical energy discharge rechargeable battery. Supercapacitor energy storage absorbs energy when the sun is sufficient or the wind is strong during the day, and discharges at night or when the wind is weak to maintain the balance of the system.
Application in power system
The application of supercapacitor energy storage system in power system is currently mainly for power quality regulation. In the actual power supply system, due to the widespread application of nonlinear loads and the sudden start and stop of large motors, the grid voltage harmonics will increase, waveform distortion, voltage drop and other problems will occur, which will cause damage to the power supply equipment that requires high quality. In order to improve the power supply quality, supercapacitor energy storage system has been widely used as an energy storage element to improve power quality. It is mainly divided into: dynamic voltage restorer (DVR), distribution static synchronous compensator (D-STATCOM), unified power quality conditioner (UPQR), uninterruptible power supply (UPS).
Application in pulse power supply
Mobile communication base stations, satellite communication systems, radio communication systems and military equipment, especially field equipment, cannot be directly powered by the public power grid, but need to be equipped with power generation equipment and energy storage devices. In the future, pulse power systems of new concept weapons such as laser weapons, particle beam weapons, microwave weapons, and electromagnetic guns will absorb energy from the power grid through the charging system. For example, medium-energy lasers and high-power microwave weapons require 100kW to 500kW of pulse power and release pulse power at high power within milliseconds. The research direction of pulse power source technology is often to pursue how to generate higher instantaneous output power and improve efficiency. The core technical problem of high-power power supply is to study pulse power storage systems with high energy storage density (kJ/kg) and high power density (kW/kg). The high power density output characteristics of supercapacitor energy storage can meet the power requirements of these systems.
Advantages and Disadvantages of Supercapacitor Energy Storage
The advantages of supercapacitor energy storage include fast charging speed, high power density, long cycle life, etc., but the energy density is relatively low and it is not suitable for long-term energy storage. Energy storage batteries have high energy density and can store energy for a long time, but the charging speed is relatively slow and there is a service life limit.
The relationship between supercapacitor energy storage and energy storage batteries
Although supercapacitor energy storage and energy storage batteries are both energy storage devices, their working principles and application scenarios are significantly different. Supercapacitor energy storage is not an energy storage battery, but a new energy storage device between traditional capacitors and batteries. They each have their own advantages in the field of energy storage and can complement each other and jointly promote the development of energy storage technology.
In summary, supercapacitor energy storage does not belong to energy storage batteries. They have obvious differences in definition, working principle, application scenarios, advantages and disadvantages, etc. In the field of energy storage, supercapacitor energy storage and energy storage batteries each play an irreplaceable role and jointly promote the development and application of new energy technologies.
Technical route of supercapacitor energy storage
The technical core of the supercapacitor energy storage device lies in the voltage-sharing topology and control strategy inside the supercapacitor energy storage group and the topology and control strategy of the bidirectional DC/DC converter.
Series and parallel connection of supercapacitor energy storage
The rated voltage of a supercapacitor is generally 2.3V, 2.5V or 2.7V, which is very low compared to other energy storage devices. Therefore, it is necessary to connect them in series to increase the voltage level of the supercapacitor energy storage group. According to the circuit principle, the capacitance is smaller as it increases. In actual use, in order to take into account the voltage level and capacity requirements, supercapacitor energy storage is usually connected in series and parallel to form a supercapacitor energy storage group.
Commonly used series voltage equalization circuits for supercapacitor energy storage
The series voltage equalization methods for supercapacitor energy storage can be divided into two categories: one is the method of consuming energy through resistive devices, such as the voltage regulator method and the switch resistor method; the other is the method of transferring energy through energy storage devices, such as the DC/DC converter method.
The voltage stabilizing tube method and the switch resistor method achieve voltage balance of the capacitor by consuming energy, which will inevitably reduce the efficiency of the supercapacitor energy storage system. Moreover, when the charging current of the supercapacitor energy storage is large, it will be difficult to achieve the voltage balance requirement by using the voltage stabilizing tube or the switch resistor method. On the one hand, the high-power resistive device increases the volume and is inconvenient to install. On the other hand, the energy consumption increases and the temperature is too high, which will bring safety hazards to the energy storage system and reduce the reliability of the system.
In addition, the voltage stabilizing tube method and the switch resistor method can only achieve voltage balance during the charging process, which has certain limitations. The energy transfer type voltage balance method uses energy storage devices for voltage balance, which is the current development direction of supercapacitor energy storage series voltage balance technology.
Topology of bidirectional DC/DC converter
As an energy storage element, it is connected to the power grid system through a grid-connected converter. There are two ways to connect the supercapacitor to the DC bus of the grid-connected converter: one is to connect directly to the DC bus of the inverter; the other is to connect to the DC bus through a power converter.
Supercapacitor energy storage charging control circuit
The main circuit is a voltage-type inverter with AC/DC energy conversion mode. Because there is a large-capacity capacitor energy storage circuit between the rectifier and inverter circuit, and because the voltage across the capacitor cannot change suddenly, in the initial stage of power-on, the capacitor device is like a "short circuit", which will form a huge surge charging current, which will cause a large current impact on the rectifier module and damage it, and will also cause the air circuit breaker connected to the inverter power supply end to trip due to overcurrent.
The conventional treatment method is to connect a charging current limiting resistor and a charging contactor (relay) in series between the rectifier and the capacitor energy storage circuit.
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