The development of electric vehicles includes the research and development of electric vehicles and energy supply systems, which are charging infrastructure, power supply, charging and battery systems, and energy supply modes. Electric vehicle charging technology As a new technology field, countries all over the world are engaged in the research of charging technology, and intend to produce charging technology standards, which will take the lead for future enterprise development.
1. Standard development of charging system
Because the current construction of electric vehicle charging stations is small and the number is small, most of the related technologies of electric vehicle charging stations are still in the initial stage of practical application. The international standard for electric vehicle charging systems is mainly IEC61851:2001 issued by IEC. The standard consists of three parts: general requirements, connection requirements for electric vehicles and AC/DC power supplies, electric vehicles and AC/DC charging stations.
According to the development of domestic electric vehicles, China has formulated three standards in 2001. These three standards are equivalent to the three parts of IEC61851. In recent years, the rapid development of electric vehicles and power technology, these standards can not meet the current development needs, and these standards lack communication protocols, monitoring systems and other aspects. At present, the State Grid Corporation has issued six enterprise standards related to electric vehicle charging stations in order to regulate the application of internal electric vehicles.
At present, the lack of research on power supply, charging and battery system application integration technologies and related standards and specifications is still the main weak link in the promotion and application of electric vehicles, which brings great difficulties to the next development of electric vehicles and the unified planning of charging facilities. . There is no mature product for the charging station monitoring system that can ensure the normal operation of large-scale charging stations. There is no uniform standard for communication protocols and communication interfaces between the charging station monitoring system and the charging device, and there is no information connection between charging stations.
2 electric vehicle common charging mode
According to the technology and use characteristics of electric vehicle power battery packs, there are certain differences in the charging mode of electric vehicles. For the choice of charging scheme, there are three modes of conventional charging, fast charging and battery pack quick replacement system.
2.1 General charging
1) Concept: After the battery is terminated, it should be charged immediately (in special cases, it should not exceed 24h). The charging current is quite low and the size is about 15A. This type of charging is called regular charging (normal charging). Conventional battery charging methods use a constant current or constant current charging with a small current, and the charging time is generally 5-8 hours, and even as long as 10 to 20 hours.
2) Advantages and Disadvantages: Because the rated value of power and current used is not critical, the charger and installation cost are relatively low; the power can be fully utilized for charging during the low valley period to reduce the charging cost; the charging efficiency can be improved and the battery life can be prolonged. The main disadvantage of the conventional charging mode is that the charging time is too long and it is difficult to meet the emergency operation requirements.
2.2 Fast charging
Fast charging, also known as emergency charging, is a short-time charging service provided by a large current for a short period of time within 20 minutes to 2 hours of parking the electric vehicle. The general charging current is 150-400A.
1) Concept: The charging method of a conventional battery generally takes a long time, which brings a lot of inconvenience to the actual use. The emergence of fast-charging batteries has provided technical support for the commercialization of pure electric vehicles.
2) Advantages and Disadvantages: Short charging time; long life of rechargeable battery (can be charged more than 2000 times); no memory, can charge and discharge in large capacity, can charge 70%~80% of electricity in a few minutes; In a short period of time (about 10-15 minutes), the battery storage capacity can reach 80%-90%, which is similar to the refueling time. Therefore, the construction of the corresponding charging station is not equipped with a large parking lot. However, compared with the conventional charging mode, fast charging also has certain disadvantages: the charging efficiency of the charger is low, and the working and installation costs are high; the charging current is large, and special consideration is given.
2.3 Mechanical charging
1) Concept: The battery pack quick change system. The purpose of charging it is achieved by directly replacing the battery pack of the electric vehicle. Due to the large weight of the battery pack, the professional requirements for replacing the battery are strong, and professional personnel are required to quickly complete the replacement, charging and maintenance of the battery by means of professional machinery.
2) Advantages and Disadvantages: Electric vehicle users can rent fully charged batteries and replace used batteries, which is beneficial to improve vehicle use efficiency and improve user convenience and speed. Charging, reducing the cost of charging, improving the economics of vehicle operation; solving the problem of charging time and even the amount of stored charge, battery quality, long driving mileage and price; can find the problem of single battery in battery pack and repair it in time Work, the battery maintenance work will have a positive significance, the battery pack's depth of discharge will also help to improve battery life.
3 charging station monitoring system
The electric vehicle charging station is an energy basic service facility that guarantees the normal use of electric vehicles. The electric vehicle charging station monitoring system is a centralized monitoring system for equipment in the charging station. It is very necessary to research and develop an electric vehicle charging station monitoring system. At present, the charging station monitoring system developed in China basically has the following major functions.
3.1 Charging monitoring function
1) Monitoring of the charging pile: monitoring the state of the AC output interface of the charging pile, such as current, voltage, switching state, protection status, etc.; collecting basic information of the electric vehicle connected with the charging pile; controlling the AC output interface of the charging pile Break.
2) Monitoring of the charger: The charger is used as the monitored object, and the monitoring system mainly includes two types of data, the status information of the charger, and the battery status information.
3.2 Power distribution monitoring function
It realizes the monitoring of the power distribution equipment of the electric vehicle charging station, which facilitates unified management and data sharing. It can realize the monitoring and control of the total power, total current, total power, power factor, main transformer state, switch state, reactive power compensation and harmonic control equipment of the whole station.
3.3 Battery Maintenance Monitoring Function
In a large-scale integrated charging station, after the battery is used for a period of time, since the battery module in the battery pack may have a problem of consistency, it is necessary to perform maintenance and evaluation on the battery through a dedicated battery maintenance device to determine whether to reconfigure the battery. group.
3.4 Quickly change device monitoring function
In a charging station with a battery quick-change device, the charging station monitoring system can collect information such as the current track position and device status of the quick-change device, and can issue a specific battery replacement command to the battery quick-change device through the charging station monitoring system: allowing quick replacement The device replaces the battery pack at the specified location on the battery holder at the specified track position.
The system refers to the charging infrastructure, power supply, charging and battery systems and energy supply modes.
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