Electric vehicle charging station – GPRS wireless access solution

  1. GPRS network

At present, most cities in China have opened GPRS services one after another, which is the mainstream transmission resource adopted by the monitoring system of electric vehicle charging station in the future, and it is the inevitable trend of the communication mode of the monitoring system of electric vehicle charging station. The electric vehicle charging station monitoring and management system adopts the advanced GPRS network and integrates various advanced technologies such as computer, communication, electromechanical, automatic control, etc., and successfully realizes the real-time monitoring and management of the electric vehicle charging station, ensuring efficient, stable and all-weather operation. .

GPRS network has the advantages of always-on, fast login, high-speed transmission, charge-by-volume and free switching, etc. It overcomes the long construction period, large investment scale, poor network coverage, and technical inadequacy of wired communication, wireless trunking, CDMA and other communication methods. The shortcomings of maturity and less terminal support have improved the technological content of the system, ensured the stability of the system, greatly reduced the construction investment and operating costs of the system, and laid a good foundation for future system upgrades. No matter from the function or from the reliability, no wireless network can compare with the GPRS network. The GPRS network has the following advantages.

(1) Cover a wide area. At present, the coverage rate of GPRS network in the whole country reaches more than 95%, and the coverage rate in non-remote areas is almost 100%. GPRS users can distribute and move their own network points at will, without worrying about the maintenance of the line or the interruption of communication caused by the wire transfer. There is no need to lay communication lines in the construction of new monitoring points. Compared with optical fiber or dedicated line systems, the investment is less, and the equipment installation is convenient. The communication distance is long, and a central station can be set up in any occasion. The coverage is better. Compared with multi-wireless data networks (cluster, two-way paging, CDPD, CDMA), its network coverage is the best. The GPRS network has unlimited capacity expansion and unlimited access locations, which can meet the monitoring and management needs of electric vehicle charging stations.

(2) GPRS network access speed is fast, providing seamless connection with the existing data network. Since the GPRS network itself is a packet data network, it supports TCP/IP and X.25 protocols, so it does not need to go through PSTN and other networks, and directly communicates with the packet data network (IP network or X.25 network), and the access speed is Only a few seconds, faster than circuit-type data services. Using TCP/IP protocol, compared with the previous wireless data network (cluster, two-way paging, GSM short message), network access is more direct and convenient. GPRS has real-time online characteristics, small data transmission delay, and supports multi-point simultaneous transmission, so the monitoring center can quickly and real-time conduct two-way communication between multiple monitoring points, which well meets the system’s real-time data collection and transmission. requirements. At present, the actual data transmission rate of GPRS network is about 30kb/s, which can fully meet the requirements of the system data transmission rate (≥10kb/s).

(3) The network reliability is high. First, the network has large redundant equipment and channels; secondly, the equipment is reused; thirdly, once the base station is damaged under special circumstances, the mobile company is very timely to repair it. Through the GPRS data monitoring center, the remote control of the electric vehicle charging station can be realized, such as remote switch control, remote status query, etc.

(4) Good stability. On the one hand, the ability to resist natural interference is strong; on the other hand, the frequency band is dedicated and will not be subject to artificial interference.
GPRS can best support frequent and small burst data services. The communication quality is stable and reliable, and the line will never be dropped. Compared with SMS short message mode, GPRS-DTU adopts connection-oriented TCP protocol communication, which avoids the phenomenon of data packet loss and ensures reliable data transmission. The monitoring center can transmit data simultaneously with multiple monitoring points without interfering with each other. The GPRS network itself has a perfect frequency division multiplexing mechanism, and has strong anti-interference performance, which completely avoids the “collision” phenomenon of multiple frequency bands of traditional digital radio stations.

GPRS network structure
GPRS network structure

(5) GPRS tariff is cheap and charging is reasonable. The monthly GPRS tariff is cheaper than the wired telephone network tariff. The monitoring data collection service of the electric vehicle charging station does not transmit information with a large amount of data, and it is not necessary to use a dedicated line (DDN, frame relay) with high tariffs. GPRS can also charge according to the amount of data communicated and the quality of service provided. In the GPRS network, the user only needs to establish a connection with the network once, and the connection can be maintained for a long time, and the channel is occupied and charged only when the data is transmitted. In this way, the business site does not have to establish connections frequently, nor does it have to pay for transmission gaps. GPRS is a new technology in the mobile communication network, which completes the wireless Internet access. This technology encapsulates the data into each packet during data transmission, and the network capacity is only allocated when needed. Once the packet completes the sending task, Channel capacity is released immediately, so instant connection and efficient transmission are provided, enabling real-time online functionality. Therefore, it is a cost-effective packet data technology.

(6) In terms of networking, both the master and slave devices can use dynamic IP and fixed IP. When forming a small-scale monitoring network, both the master and slave use dynamic IP and use dynamic domain name resolution. Using the public network can save costs (there is no need to rent a dedicated line such as DDN); when forming a large network, the host can use a fixed IP and use a private network to improve the efficiency of the system, but dynamic IP and public network can still be used when conditions are not available. network, the efficiency is only 0.2% lower than that of fixed IP.

(7) The transmission capacity of the system is large and the capacity expansion performance is good. The monitoring center of the electric vehicle charging station should be connected with each charging pile in real time. Due to the large number of charging piles, the system is required to meet the needs of burst data transmission, and GPRS technology can well meet the needs of burst data transmission; because the system adopts a mature TCP/IP communication architecture, it has good expansion performance , a monitoring center can easily support the communication access of thousands of charging piles.

  1. Access plan

Since GPRS is a data packet communication network based on IP addresses, the monitoring center computer needs a fixed IP address or a fixed domain name, and each data collection point uses the GPRS module to access the host through the IP address or domain name, so as to conduct data communication.

(1) Public network access plan. The server uses the public network to access the Internet, such as ADSL dial-up, telecom dedicated line broadband Internet access, etc., and applies for a fixed IP address on the public network, which can realize small and medium-capacity data collection applications.

(2) Private network access scheme. The server adopts the DDN dedicated line provided by the mobile communication company, applies for the configuration of a fixed IP address, and is connected to the GPRS network. Since the DDN dedicated line can provide higher bandwidth, if the number of monitoring points increases, the monitoring center can meet the demand without expanding capacity, which can realize large-capacity data collection applications. After receiving the data from the GPRS network, the RADIUS server of the monitoring center first performs AAA authentication, and then transmits it to the computer host of the monitoring center. The data is restored and displayed through the system software, and the data is processed, which further enhances the security performance of the system data communication.

(3) GPRS/GSM mobile data transmission network. The data of the electric vehicle charging pile is decoded and processed by the GPRS/GSM network interface function module, converted into the format of data transmission in the public network, and then transmitted through the GPRS wireless data network of the mobile company, and finally transmitted to the IP address of the monitoring center.

  1. System scheme

Each electric vehicle charging station uses a GPRS transparent data transmission terminal, which is connected to the monitoring center through a mobile GPRS network. Each monitoring point uses a GPRS common data card or an APN special data card, and the monitoring center registers the GPRS terminal number of each point and associates it with the information of the electric vehicle charging pile for identification and maintenance processing. The electric vehicle charging station control center runs the monitoring software to monitor the information of the electric vehicle charging piles, and the authorized monitoring points can use this system.

  1. System Features

SRS-PVL1000GPRS-DTU wireless transparent data transmission terminal is based on GPRS network and has the characteristics of high performance, high reliability and strong anti-interference ability. , PLC, GPS receiver, data concentrator and other connections, with remote diagnosis, testing, supervision functions, to meet the data acquisition and control between the control center and many remote sites. SRS-PVL1000GPRS-DTU wireless transparent data transmission terminal has the following characteristics:

(1) Built-in TCP/IP protocol stack, optimized for GPRS network. Provide GPRS wireless data bidirectional transmission function; provide RS-232/RS-485/RS-422 interface; comply with ETSIGSMPhase2+ standard; support automatic heartbeat, keep permanently online.
(2) Transparent data transmission. Provide bidirectional 100K large-capacity data buffer for user’s data equipment, support large data packet transmission. Automatic dial-up connection, DTU power-on automatically dial-up connection to the network.

(3) Support the client to initiate a command connection or a remote wake-up connection, provide a short message channel, and a built-in Unicode international code conversion table.
(4) Support remote SMS/phone wake-up; real-time monitoring of network connection, with automatic redial function for dropped calls; the support center is fixed IP or dynamic domain name, and the reporting time interval can be set by the user.

(5) Support point-to-point, point-to-multipoint, and multipoint-to-multipoint peer-to-peer data transmission, support APN data private network services, support multiple data centers, and automatically switch.
(6) Flexible installation, convenient and reliable use, suitable for low temperature and high temperature working environment.
(7) EMC anti-interference design, suitable for electromagnetic harsh environment applications, using composite watchdog technology.
(8) Low power consumption technology of the whole machine, online standby current <20mA.

  1. Safety measures

The monitoring system requires high system security and stability. Security is mainly to prevent intentional and unintentional breaches from inside and outside the system. Network security protection measures include channel encryption, source encryption, login protection, access protection, and access protection. , firewall, etc. Stability means that the system can run 24/7 without interruption, even if hardware and software failures occur, the system cannot be interrupted.

The SRS-PVL data center can be accessed through the public network or the mobile private network. The cost of using the public network access method is relatively low, and there is no need to rent a private line. When using a private data line to access, the GPRS data transmission equipment must be authenticated by the Radius server. The data transmission process is encrypted and protected, and the security is relatively high, which can fully guarantee the speed and network service quality.

(1) APN data private network mode. The APN server is configured in the internal network, and the mobile terminal uses the APN data private network. Due to the use of the data private network, the server is isolated from the public network Internet, which can effectively avoid illegal intrusion.

(2) The uniqueness of the SIM card. The user’s SIM card mobile phone number is authenticated and authorized, and the SIM card number and APN are bound on the network side to delineate the scope of the user’s access to a certain system. Only the SIM card mobile phone number belonging to a specified industry can access the dedicated APN. The data center uses the special APN assigned by the mobile company for wireless network access, and the SIM card number of the ordinary mobile phone cannot call the special APN.

(3) The DTUID number and password can be configured separately for each GPRS data transmission device, and the application layer authentication can be performed through the data center when it logs in. Other GPRS devices without the DTUID number and password assigned by the data center will not be able to log in to the system. The security of the system is further enhanced.

(4) Data encryption, which can encrypt and protect the entire data transmission process.
(5) Network access security authentication mechanism. Firewall software is used to set up network authentication and security protection functions to ensure system security.

Read more: How do electric vehicle charging stations work?