EV Charging
E
lectric vehicles (EVs) are no longer just a futuristic dream; they’re becoming a part of our everyday lives. As more people make the switch to electric, one of the most critical aspects of owning an EV is understanding charging technology. Think of EV charging technology as the fuel station for your electric car, but instead of pumping gas, you’re plugging in to recharge. In this article, we’ll explore how EV charging technology works, what’s new on the horizon, and what challenges we face. Buckle up as we dive into the electrifying world of EV charging!
Electric Vehicle Charging Equipment Requirements
Electric vehicle charging equipment refers to equipment that is connected to electric vehicles or power batteries and provides them with electrical energy. It is the most important equipment in electric vehicle charging stations. Electric vehicles have the following requirements for charging equipment:
Safety: When charging electric vehicles, ensure the personal safety of personnel and the safety of the battery pack.
Easy to use: Charging equipment should be highly intelligent and should not require operators to intervene too much in the charging process.
Cost-effective: Cost-effective and low-priced charging equipment helps to reduce the overall cost of electric vehicles, improve operating efficiency, and promote the commercialization of electric vehicles.
High efficiency: High efficiency is one of the most important requirements for modern charging equipment, and the efficiency has a significant impact on the energy efficiency of the entire electric vehicle.
Less pollution to the power supply: Charging equipment using power electronics technology is a highly nonlinear device that will produce harmful harmonic pollution to the power supply network and other electrical equipment. Moreover, due to the low power factor of the charging equipment, when the load of the charging system increases, the impact on its power supply network cannot be ignored.
Types of Electric Vehicle Charging Equipment
There are many types of electric vehicle charging equipment, generally divided into non-onboard chargers, on-board chargers, AC charging piles, DC charging piles and AC/DC charging piles, etc. On-board chargers and AC charging piles are the most important and widely used charging equipment for electric vehicles.
Off-board charger: Off-board charger refers to a special device installed outside the body of an electric vehicle, which converts the AC power of the power grid into DC power and uses conduction to charge the power battery of the electric vehicle. Off-board chargers are generally composed of high-frequency switching power supply modules, monitoring units, human-machine operation interfaces, electrical interfaces with electric vehicles, metering systems, and communication interfaces.
On-board charger: An on-board charger is a special device that is fixedly installed on an electric vehicle and converts AC power into DC power. It uses conduction to charge the power battery of the electric vehicle. The on-board charger consists of an AC input interface, a power unit, a control unit, a DC output interface, etc. During the charging process, the on-board charger provides low-voltage power for the battery management system, charging contactor, instrument panel, cooling system, etc.
AC EV Charger: AC EV Charger refers to a special power supply device that is fixed outside the electric vehicle and connected to the AC power grid. It uses conduction to provide AC power to electric vehicles with on-board charging devices. AC charging piles only provide power output and have no charging function. They need to be connected to an on-board charger to charge electric vehicles. AC EV Chargers consist of three parts: pile body, electrical module and metering module.
DC EV charging station: A DC EV charging station is a power supply device that is fixed outside an electric vehicle and connected to an AC power grid, and can provide a low-power DC power supply to the power battery of an off-board electric vehicle. A DC charging station is mainly composed of a monitor, a card swiping area, a charging indicator light, a gun plug interface, and a charging pile body.
AC/DC charging pile: AC/DC charging pile adopts an integrated structure, which can realize both DC charging and AC charging. When there are many charging services during the day, DC charging is used for fast charging. When there are few users at the charging station at night, AC charging can be used for slow charging.
Electric Vehicle Charging Method
The main methods for charging electric vehicle batteries are constant current charging, constant voltage charging and constant current limited voltage charging. Modern intelligent battery chargers can be set with different charging methods.
Constant Current Charging
a method that keeps the charging current constant during the charging process.
Advantages: Constant current charging has greater adaptability and can easily fully charge the battery, which is beneficial to extending the battery life.
Disadvantages: During the charging process, the charging voltage needs to be adjusted according to the gradually increasing battery electromotive force to keep the current constant, and the charging time is longer.
Four Constant Current Charging Methods
Trickle charge: a charging method that maintains the battery in a fully charged state and just offsets the battery’s self-discharge. Its charging rate is harmless to long-term charging of a fully charged battery, but the current is too small to charge a fully discharged battery.
Minimum current charging: refers to a method of adjusting the charging current to the minimum possible while effectively restoring the battery capacity of a deeply discharged battery.
Standard charging: that is, charging at a standard rate, the charging time is 14h.
High-rate (fast) charging: a method of fully charging the battery within 3 hours. This charging method requires an automatic control circuit to protect the battery from damage.
Constant Voltage Charging
Constant voltage charging refers to a charging method that keeps the charging voltage constant during the charging process. The charging current decreases as the battery electromotive force increases. A reasonable charging voltage should make the charging current approach 0 when the battery is about to be fully charged. If the voltage is too high, the charging current will be too large and overcharged in the early stage of charging. If the voltage is too low, the battery will be undercharged. If the charging current is too large in the early stage of charging, the charging voltage should be appropriately lowered, and the charging voltage should be adjusted to the specified value after the battery electromotive force increases.
Advantages: short charging time, no need to adjust voltage during charging, more suitable for supplementary charging.
Disadvantages: It is not easy to fully charge the battery, and the large current in the initial stage of charging will have an adverse effect on the plates.
Constant Current and Voltage Limiting Charging
First, charge with constant current. When the battery terminal voltage rises to the voltage limit value, the charger automatically switches to constant voltage charging until charging is completed.
Electric Vehicle Charging Methods Classification
The main charging methods for electric vehicles include conventional charging, fast charging, battery replacement, wireless charging and mobile charging.
Conventional Charging Method
Conventional charging uses a traditional constant voltage and constant current charging method to charge electric vehicles. The corresponding charger operation and installation costs are relatively low. Electric vehicle home charging facilities (on-board chargers) and small charging stations mostly use this charging method.
On-board charger: The charger is fixed on the car or placed in the trunk as standard. You only need to plug the plug of the on-board charger into the power socket in the parking lot or at home to charge, so the charging process is generally completed by the customer independently. It directly draws power from the low-voltage lighting circuit, the charging power is small, and it is powered by a standard grid power supply with a specification of 220V/16A. The typical charging time is 8~10h (the SOC value reaches more than 95%). This charging method has no special requirements for the grid, as long as the power supply quality can meet the lighting requirements, it can be used. Since charging at home is usually at night or during the low electricity period, it is conducive to the effective use of electricity.
Small charging station: Small charging station is one of the most important charging methods for electric vehicles. Charging piles are set up on the street, in supermarkets, office buildings, parking lots, etc. The charging is done with conventional charging current. The electric car driver only needs to park the car at the designated location of the charging station and connect the wires to start charging. The charging method is coin or card. The charging power is generally 5~10kW, and it uses a three-phase four-wire 380V power supply or a single-phase 220V power supply. The typical charging time is 1~2 hours for replenishment and 5~8 hours for full charge (SOC value reaches more than 95%).
Advantages and Disadvantages of Conventional Charging Methods
Advantages: The charging technology is mature, the technical threshold is low, it is easy to use and easy to promote; the charging facilities are simple to configure, occupy a small area, require little investment, the battery charging process is gentle, and the battery can be deeply charged; the battery heats up gently during charging, and it is not easy to have high-temperature short circuit or leakage and explosion hazards, and the safety is relatively high; the interface and related standards are low; the charging power is relatively low, the requirements for the distribution network are reduced, and the demand for supporting infrastructure is small; generally choose to charge at night to avoid the peak electricity consumption in the evening, and the energy-saving effect is better.
Disadvantages: long charging time, limited driving range, and restricted use; used in parking places with slow power demand, such as residential parking lots, social public parking lots, etc.
Fast Charging Method
The fast charging method charges the battery in a short time with a high charging current of 150~400A. Compared with the conventional charging method, the installation cost is relatively high. Fast charging can also be called rapid charging or emergency charging. Its purpose is to fully charge the electric vehicle in a short time. Large charging stations (machines) mostly use this charging method.
Large charging station (machine): It is mainly used for charging long-distance travel or when rapid energy replenishment is required. The power of the charger is very large, generally greater than 30kW, and it uses a three-phase four-wire 380V power supply. Its typical charging time is 10~30min. This charging method has a certain impact on the battery life, especially ordinary batteries cannot be charged quickly, because receiving a large amount of electricity in a short period of time will cause the battery to overheat. The key to a fast charging station is the off-board fast charging component, which can output 35kW or even higher power. Due to the high power and current ratings, this charging method has high requirements for the power grid and should generally be used near a 10kV substation or in a monitoring station and service center.
Advantages and Disadvantages of Fast Charging
Advantages: The technology is relatively mature and the interface standard requirements are relatively low; it charges quickly and increases the long-distance endurance of electric vehicles, making it an effective supplementary solution.
Disadvantages: The charging power is large, the interface and power safety are improved, and battery heat dissipation becomes an important factor; the battery cannot be deeply charged, generally about 80% of the battery capacity, which can easily damage the battery life and require more battery depreciation costs; short-term power consumption is large, the distribution network requirements are high, and the infrastructure supporting needs are huge.
Battery Replacement Method
The vehicle’s power can be quickly replenished by replacing the battery, and the battery replacement can be completed within 10 minutes, which theoretically increases the vehicle’s range infinitely.
Advantages: The battery replacement experience is similar to refueling at a traditional gas station; users only need to purchase the bare car, and the battery is leased, which greatly reduces the price of the vehicle; a suitable charging method is used to ensure the health of the battery and the performance of the battery; centralized battery management facilitates centralized recycling and maintenance, reducing environmental pollution; slow charging is selected during the night when electricity consumption is low, which reduces the operating costs of service agencies and plays a role in shifting peaks and filling valleys for the power grid.
Disadvantages: The infrastructure construction cost is high, the site occupied is large, and the supporting grid requirements are high; the problem of convenient battery replacement in electric vehicles needs to be solved, such as the battery design and installation location, the difficulty of battery removal, etc.; strict unification of many standards in the electric vehicle industry is required, including standardization of the battery’s own appearance and various parameters, standardization of the battery and electric vehicle interface, standardization of the battery and external charging device interface, etc.; battery replacement can easily lead to problems such as poor contact of the battery interface, and the safety and reliability requirements for the battery and vehicle interface are increased; battery leasing brings about a series of problems such as asset management, logistics distribution, and pricing and charging, which increase operational complexity and costs.
Wireless Charging Method
Wireless charging for electric vehicles is a new type of charging method that uses wireless power transmission technology to charge batteries. There are mainly electromagnetic induction charging, magnetic resonance charging and microwave charging. Compared with wired charging for electric vehicles, wireless charging is easy to use, safe, reliable, has no risk of electric sparks and electric shock, no dust accumulation and contact loss, no mechanical wear, no corresponding maintenance problems, and can adapt to bad weather and environment such as rain and snow. Wireless charging technology can be used to charge electric vehicles to reduce labor costs, save space, and not affect traffic sight.
Electromagnetic Induction Charging Method
The electromagnetic induction charging method is to transmit power between the power transmission coil and the receiving coil. This is the most practical charging method. When an alternating current passes through the power transmission coil, an alternating magnetic field is generated between the sending (primary) and receiving (secondary) coils, thereby generating an induced electromotive force in the secondary coil that changes with the magnetic field, and outputting an alternating current through the receiving coil end. The problems with this charging method are that the power transmission distance is relatively short (about 100mm), and when there is a large deviation between the power transmission and the power receiving parts, the power transmission efficiency will be significantly reduced; when foreign objects enter, local heating will occur; electromagnetic wave and high frequency protection issues are also difficult to solve; the power size is directly related to the coil size. When high-power power transmission is required, it is necessary to increase investment in infrastructure construction and power equipment.
Magnetic Resonance Charging Method
The magnetic resonance charging method mainly consists of a power supply, power output, power reception, rectifier, etc., and its basic principle is basically the same as that of the electromagnetic induction method. When current passes through the power transmission part, the alternating magnetic flux generated causes the receiving part to generate an electric potential, and outputs current when charging the battery. The difference from the electromagnetic induction charging method is that the magnetic resonance charging method is equipped with two high-frequency driving power supplies and adopts an LC resonance circuit with both coils and capacitors, rather than a simple coil to form the two units of power transmission and reception. The value of the resonance frequency will change with the change of the distance between the power transmission and reception units. When the transmission distance changes, the transmission efficiency will also decrease rapidly like electromagnetic induction. Therefore, the resonance frequency can be adjusted through the control circuit to make the circuits of the two units resonate, that is, “resonance”, and this magnetic resonance state is also called “magnetic resonance”. By changing the transmission and reception frequencies under the action of the control circuit, the power transmission distance can be increased to about several meters, and the resistance of the two unit circuits can be minimized to improve the transmission efficiency. The transmission efficiency is also related to the diameter of the sending and receiving power units. The larger the transmission area, the higher the transmission efficiency. The current transmission distance can reach about 400mm, and the transmission efficiency can reach 95%. The current technical difficulty of magnetic resonance charging is that it is difficult to make it small and efficient. The current technical capability is that a coil with a diameter of 0.5m can provide 60W of power at a distance of about 1m.
Microwave Charging Method
The microwave charging method uses a 2.45GH2 electric wave generator to transmit electricity. The transmitted microwaves are also AC waves, which can be received by antennas in different directions and converted into DC by rectifier circuits to charge the battery of electric vehicles. It can also achieve point-to-multipoint long-distance transmission. To prevent microwave leakage during charging, the charging part is equipped with a metal shielding device. During use, the effective shielding between the power transmitter and the power receiver can prevent microwave leakage. The main problem with this charging method is that the efficiency of the magnetron in generating microwaves is too low, causing a lot of electricity to be converted into heat energy and wasted.
Mobile Charging Method
The ideal situation for electric vehicle batteries is to charge them while the electric vehicle is on the road, which is called mobile charging. In this way, electric vehicle users do not have to find a charging station, park their vehicles and spend time charging. Mobile charging systems are buried under a section of the road surface, the charging area, and do not require additional space.
Contact type: The contact type mobile charging system requires a contact arch to be installed at the bottom of the vehicle body. By contacting the charging element embedded in the road surface, the contact arch can obtain instantaneous high current. When the electric vehicle drives through the mobile charging area, its charging process is pulse charging.
Inductive: The vehicle-mounted contact arch is replaced by an induction coil, and the charging element embedded in the road surface is replaced by a high-current winding that generates a strong magnetic field.
Obviously, due to mechanical losses and the installation position of the contact arch, contact-based mobile charging is not very attractive to people. Current research focuses on inductive charging, which does not require mechanical contact and does not produce large position errors. Of course, this charging method requires huge investment and is still in the experimental stage.
Conclusion
As electric vehicles become more popular, it is critical to understand and accept advanced charging technologies. This article comprehensively introduces the charging technology of electric vehicles, including electric vehicle charging equipment, electric vehicle charging methods, electric vehicle charging methods, etc. This article comprehensively introduces the continuous development of electric vehicle charging. Continued innovation and investment in charging infrastructure will drive the future of electric vehicles, making them more convenient and available to everyone.
Recommended reading: What is an Electric Vehicle Onboard Charger?
Derek Ke
Hi, I’m Derek Ke, founder of Moreday.com, an expert in solar-protected electrical products and electric vehicle charging.
Over the past 15 years, we have helped nearly 500 customers (such as farms, residential, industrial, and commercial) in 60 countries solve new energy and green power problems. We aim to share more knowledge about solar power generation and new energy with everyone so that green electricity can enter thousands of households.
