Design of monitoring system for electric vehicle charging station based on MCGS

1 Introduction

Due to the renewable and clean nature of fuel, electric vehicles have gradually become the object of the country's vigorous development in the new energy vehicle industry. Electric vehicle charging stations are the infrastructure that must be built after the large-scale industrialization of electric vehicles. From the discussion in literature [2], [3], and [6], it can be seen that in the construction of charging stations, achieving efficient, safe, and intelligent management has become the mainstream. The charging station monitoring system, as the core of the charging station automation system, is an important topic and hot spot in the current research of the electric vehicle charging station construction industry.

This paper first introduces the structural design of the charging station monitoring system based on the dedicated parking lot, designs the functions implemented by the monitoring system according to national standards, and finally introduces the implementation of the charging station monitoring system based on MCGS technology.

2 Charging station monitoring system structure design

Referring to the State Grid Corporation's Guiding Opinions on Electric Vehicle Charging Facilities [7][8], Typical Design of Electric Vehicle Charging Facilities [9], and the technical implementation route and development trend of power monitoring systems, the charging station monitoring system is designed by combining c/s and b/s, as shown in Figure 1.

Figure 1 Structure diagram of the charging station monitoring system

The entire monitoring system is connected by industrial Ethernet . The charger, BMS (battery management system) and smart meter are connected to Ethernet and communicate with the host computer after protocol conversion by the communication controller . The power distribution monitoring system also communicates with the monitoring system through Ethernet . These parts adopt the c/s structure; the upper monitoring system communicates with the local monitoring system through Ethernet, and this part adopts the b/s structure; the server is responsible for storing various data information in the charging station, and the gps clock provides local clock calibration function. The monitoring system can access various types of chargers through industrial Ethernet and monitor the chargers and battery management systems. In addition, the local monitoring system can communicate with multiple upper monitoring systems through Ethernet to achieve hierarchical and remote monitoring. This structure makes the system highly scalable and can meet the requirements of the continuous expansion of the scale of charging facilities.

3 Monitoring system function design

The core function of the charging station monitoring system is the charging monitoring function, that is, the monitoring of various working conditions of the charger and the rechargeable battery. In addition, some auxiliary functions are included to enhance the system robustness and intelligent management.

3.1 Data collection function

The system collects the charger working status (charging mode), temperature, voltage (output voltage, DC bus voltage), current (output current, DC bus current), power and fault signals (input voltage overvoltage, input voltage undervoltage, input current overcurrent, output voltage overvoltage, output current overcurrent, module temperature is too high, input phase loss, communication interruption, fan failure, etc.); collects the battery pack temperature, SOC , terminal voltage, terminal current, battery connection status and battery fault signals (including single battery working parameters, such as normal working voltage, temperature, capacity, energy, battery voltage upper and lower limit alarm limits, temperature alarm upper limit, maximum charging current and current alarm upper limit, voltage difference maximum alarm upper limit, charging times, battery health index); collects the switch status, protection signal, voltage and current, active power, reactive power and power factor uploaded by the charging station distribution system monitoring.

3.2 Control and adjustment function

The monitoring system can send control instructions to the charger, remotely control the charger to start and stop, calibrate the time, perform emergency shutdown, remotely set charging parameters, and control the opening and closing of the distribution system circuit breakers and switches.

3.3 Data processing and storage functions

The monitoring system classifies and stores the data in the charging station according to its nature and importance. When the data volume is large, it can ensure the real-time transmission of important information according to predetermined strategies. It provides centralized storage and query functions for real-time and historical data such as charger and battery pack telemetry, telesignaling, and alarm events. In addition, the system has operation records, system fault records, charging operation parameter abnormality records, and battery pack parameter abnormality records.

4 Implementation of Charging Station Monitoring System

4.1 GPS clock system

The system uses the K806-D satellite synchronous clock of Shanghai Ruicheng Co., Ltd. In addition to the universal serial port, the clock also provides 2-way network timing signals. The system has strong self-maintenance capability (better than 0.6us/min), supports multiple operating systems and network devices such as routers, switches, and intelligent controllers based on the NTP protocol, supports power interruption and GPS out-of-step dry contact signal alarm, and has stable operation and easy operation. In the charging station monitoring system, the time format used by the GPS clock timing is shown in Figure 2.

Figure 2 GPS clock timing format

4.2 Communication Controller

The charger uses the CAN bus to transmit data , which does not provide conversion between CAN bus signals and Ethernet signals. The upper-level monitoring computer uses industrial Ethernet communication, so a communication controller is used between the monitoring computer and the charger to be monitored to complete the conversion. The controller mainly includes hardware platform design and software system design.

4.2.1 Hardware Design

The hardware platform is based on the AT91RM9200 chip of Atmel. This industrial-grade chip has an embedded network controller and includes Ethernet MAC control. Therefore, only an external 10/100M physical layer chip DM9161E is needed to provide an Ethernet access channel. The CAN bus interface is composed of the CAN controller chip MCP2515 and the high-speed CAN bus transceiver TJA1050 [1]. The connection between MCP2515 and AT91RM9200 is realized through the standard serial peripheral interface SPI (embedded in AT91RM9200). It supports the CANv2.0b technical specification, can send and receive standard and extended information frames, and has the functions of receiving filtering and information management. TJA1050 is a high-speed CAN bus transceiver matched with MCP2515. It is responsible for the task of receiving and sending level conversion between nodes and buses . In addition, in order to enable the hardware platform to provide an efficient software running environment, the system also designed a storage circuit (16MB NOR flash, mainly used to store the system bootloader, kernel, and file system; 64MB NAND flash, used to store data; 32MB SDRAM, providing running space for the kernel and application programs), reset circuit, JTAG debugging interface, and RS485 expansion serial port. The system structure is shown in Figure 3.

Figure 3 Communication controller hardware structure diagram

4.2.2 Software Design

The communication controller uses Linux as the system software platform. The development work mainly includes the establishment of cross-compilation environment, configuration of u-boot, cutting and transplantation of Linux kernel, production of jffs2 (journalling flash file system version 2) file system and design of protocol conversion software.

4.3 Charging Station Server

The server stores and manages data information within the charging station, records abnormal events, and provides user authority management, remote access, and GPS time calibration functions.

4.3.1 Hardware platform construction

In the charging station, the server stores and processes a large amount of data, has a long running time and requires a short system response time, so the performance requirements of the system hardware platform are very high. In addition, the hardware platform needs to adopt mainstream products in the international computer market, conform to the development direction of the computer industry, and adapt to the application environment of the power industry. The reference configuration is shown in Table 1.

Table 1 Reference configuration of hardware platform

4.3.2 Software Design

The server stores and manages a large amount of data information in the charging station, and the logical relationship between the data is complex. The workstations in the station require the server to quickly respond to various requests and provide data services, and the remote client can access the data on the server through the browser. Therefore, it is necessary to develop a data management system and web service program for the charging station. According to the functions implemented by the server, the architecture of the entire software system is shown in Figure 4.

Figure 4 Charging station server software system architecture

The entire software system adopts a layered and modular structure, which is convenient for system maintenance and software upgrades, and improves the scalability of the server. The system implements the server's hardware platform management, data storage, data management and remote access functions through the corresponding software. The operating system manages the server hardware, improves the operating efficiency and stability of the hardware platform, provides an operating platform for the upper-level software, facilitates the expansion of the server software functions, and provides data security protection and server user rights management. The server stores a large amount of data, and the logical connection between the data is close. Compared with the file system, the database can improve the efficient storage of information in the charging station on the hardware equipment, and improve the efficiency and security of operations such as data query and modification. The database provides a large number of interfaces for the application program, which is convenient for the secondary development of the system. In addition, the database also provides user rights management, provides secondary protection for the data on the server, and improves the security of the server data. The charging station data management system is responsible for the communication between the upper-level software and the local database, responds to the upper-level software's request to query, store, and modify the data in the database and provides corresponding services. Provides user rights management for the server and manages the communication protocol in the charging station. The charging station provides remote monitoring function. The remote client can access the charging station remotely through the web server. The client user only needs to install IE6 or IE7 browser, enter the URL of the charging station web server, log in, query and operate the data within the authority after identity verification. The web service program provides a graphical display of data and can output and print reports.

4.4 Monitoring Software Design

This design uses the configuration software development system mcgs (monitor and control generated system) developed by Beijing Kunlun Tongtai Software Company. This system can quickly construct and generate host computer monitoring software, with high modularity, efficient and stable operation, and friendly operation interface. According to the functional design of the monitoring system, the operation interface design of the monitoring software is shown in Figure 5.

Figure 5 Charger monitoring interface

5 Conclusion

This paper analyzes and discusses the design of a charging station monitoring system, and constructs the entire system by combining c/s and b/s.

Different from the previous monitoring software design method, this paper introduces a new, efficient and reliable design method, that is, using mcgs configuration software for rapid design. With the implementation of the national policy of vigorously supporting the electric vehicle industry, the construction of charging station monitoring system will be put on the agenda. I hope this article can provide strong support and reference for the development of this industry.