Electric vehicle charging station – GPRS wireless access solution based on CM3160P/CM3160EP

  1. Introduction to CM3160P/CM3160EP

CM3160P/CM3160EP adopts high-performance industrial-grade embedded processor, uses real-time operating system as software support platform, large memory, and embedded TCP/IP protocol stack with independent intellectual property rights, which can provide users with high-speed, stable and reliable, and data terminals are always online. , A variety of protocol conversion virtual private network. For users with network traffic control, the product supports the functions of voice, SMS, data triggering online and automatic disconnection after timeout, and also supports dual data center backup, and multiple data centers synchronously receive data and other functions. CM3160P/EP is an upgrade and replacement product of CM3150P/EP. CM3160P/EP improves the linking method of the original CM3150P/EP wireless module and improves the stability of the product. The software and hardware are fully compatible with CM3150P/EP.

  1. System composition

The topology of the GPRS wireless access network based on CM3160P/CM3160EP is shown in Figure 1, which is mainly composed of four parts: electric vehicle charging pile, concentrator, battery management system, and charging management service platform.

Figure 1 - Topology of GPRS wireless access network based on CM3160P/CM3160EP
Figure 1 – Topology of GPRS wireless access network based on CM3160P/CM3160EP

(1) On the terminal controller of the electric vehicle charging pile, the user can swipe the card for user authentication, balance inquiry, billing inquiry and other operations, and can also provide a voice output interface to realize voice interaction. Users can choose 4 charging modes according to the instructions on the LCD screen: charging according to the time, charging according to the amount of electricity, automatic charging, and charging according to the mileage.

(2) The electric vehicle charger controller and the concentrator use the CAN bus for data interaction, and the concentrator and the server platform use the wireless GPRS network to exchange data through the wireless transmission terminal CM3160P. For security, electricity billing and amount data are securely encrypted.
(3) The main function of the battery management system is to monitor the working state of the battery (voltage, current and temperature of the battery), predict the power storage capacity (SOC) of the power battery and the corresponding remaining mileage, and manage the battery to avoid excessive battery life. Discharge, overcharge, overheating and severe voltage imbalance between single batteries, maximize the use of battery storage capacity and cycle life.

(4) The charging service management platform mainly has three functions: charging management, charging operation, and comprehensive query.
①Charging management Centralized management of the basic data involved in the system, such as electric vehicle information, battery information, user card information, and charging pile information.
②The charging operation mainly manages the charging of users’ charging.
③Comprehensive query refers to the comprehensive analysis and query of the management and operation data.

  1. Wireless system solution

1) Public network solution
The center uses a server group as the center to receive, uses ADSL to connect to the INTELNET public network, and uses public network fixed IP or public network dynamic IP+DNS resolution services. This kind of scheme needs to apply for broadband services such as ADSL to INTERNET operator first.

(1) Central public network fixed IP. The monitoring point directly initiates a connection to the central fixed IP, and the operation is reliable and stable. This solution is recommended (the fixed IP fee is more expensive).
(2) Central public network dynamic IP+DNS resolution service. Most IPs are dynamic and relatively inexpensive. The user first contacts the DNS service provider to activate the dynamic domain name, the monitoring point first uses the domain name addressing method to connect to the DNS server, and then the DNS server finds the dynamic IP of the central public network and establishes a connection. This method can greatly save the cost of fixed IP on the public network, but the stability is subject to the stability of the DNS server, so it is necessary to find a reliable DNS service provider.

2) Private network solution
(1) According to the special requirements of the user’s intranet for network security, use the special APN form of the GPRS network to access the network.

①Access the GPRS network through a 2M dedicated line, use private IP addresses for wide-area connection between the interconnected routers, and establish an encrypted tunnel between the mobile company authentication router and the user authentication router.
② Allocate a dedicated APN for the user, and ordinary users cannot enter the APN. Only the GPRS special network card can enter the APN to prevent other illegal users from entering.

③ The user establishes a RADIUS server internally as a remote authentication server for internal user access (or enables the local authentication function of the router in the APN router). Only authenticated users are allowed to access to ensure the internal security of users.
④ The user establishes a DHCP server internally (or enables the DHCP function in the APN router), and assigns the user’s internal address to the authenticated user.

⑤ End-to-end encryption, that is, the use of end-to-end encryption between the mobile terminal and the server platform to avoid possible leakage of information during the entire transmission process.
⑥ Both sides are isolated by firewall, and IP address and port filtering are performed on the firewall.

(2) In the APN business process, the terminal of the GPRS private network system accesses the Internet and logs in to the server platform.

①The user sends a GPRS login request, which includes the private network APN specially allocated by the mobile company for the GPRS private network system.
②According to the APN in the request, the SGSN sends a query request to the DNS server, finds the GGSN connected to the enterprise server platform, and encapsulates the user request to the GGSN through the GTP tunnel.

③GGSN sends the user authentication information (including mobile phone number, user account, password, etc.) to Radius through a dedicated line for authentication.
④The Radius authentication server sees the authentication information such as the mobile phone number, confirms that it is a request from a legitimate user, and requests the DHCP server to assign the user address.
⑤After the Radius authentication is passed, the Radius sends the confirmation information carrying the user address to the GGSN.

⑥ After the user gets the IP address, he can carry the data package, inquire about the information of the GPRS private network system and visit the service processing platform.

Read more: Solution based on CAN bus communication for charging station (pile)