Design of street lamp control system based on power line carrier

Power line communication technology is a communication method that uses power lines to transmit data and voice signals. This technology loads high-frequency signals carrying information onto power lines, uses wires for data transmission, and separates high-frequency signals from power lines through dedicated power line modulation and demodulation, and transmits them to terminal devices [1]. Based on the widespread distribution of distribution networks in my country, this paper studies and designs a system that controls street lamps using power line carrier transmission.

1 System Design

Since the signal attenuation of power lines is large when transmitting across transformers, GPRS wireless network communication can be used for transmission or cross-regional data communication can be achieved through routing access to the wide area network according to actual needs. Managers only need to operate the computer and transmit data through the power line to control the switch status of the street lamp and query the operating status of the street lamp, so as to achieve timely and effective management and control of the street lamp.

1.1 Design Idea

The street lamp control system consists of three parts: the main control center, the street lamp intelligent control center, and the street lamp control box. The distribution transformer has a blocking effect on the power carrier signal, so the power carrier signal can only be transmitted within the area of ​​a distribution transformer. The main control center can realize data transmission with the street lamp intelligent control center through the GPRS wireless communication network or router. After receiving the command from the main control center, the intelligent control center transmits the command of the monitoring center to the street lamp sub-control box of each branch through the power line carrier. At the same time, the street lamp intelligent control center detects the temperature, brightness, voltage, current and other conditions of each street lamp through the power line carrier module, and sends information such as abnormal voltage and current alarm, street lamp failure alarm, and high temperature alarm to the main control center to achieve the purpose of managing and controlling each street lamp. As shown in Figure 1. 1.2 Hardware Design

The main design is for the interface between the controller module and the power line transmission module of the street light control system and the power line transmission module.

1.2.1 MI200E power line carrier chip

The power transmission module uses the MI200E power line carrier communication chip produced by Shanghai Mia Micro Corporation. It adopts a complex orthogonal modulation principle, which has great advantages in power line transmission with drastic signal attenuation changes. Compared with the current main narrowband communication methods, spread spectrum communication methods, and orthogonal frequency multiplexing technology, it can more effectively prevent the negative impact caused by the correlation between phase and orthogonality. MI200E is a highly integrated, high-performance power line carrier communication chip specially optimized for low-voltage power lines. It has the characteristics of reliable communication and strong anti-interference ability. Users can easily embed the module into the system [2].

1.2.2 Controller module The

32-bit ARM processor LM3S6916 is selected as the controller of the intelligent control center. It supports the ARM Cortex-M3 core with a maximum main frequency of 50 MHz and integrated nested vector interrupt control. Its biggest advantage over other controllers is that it integrates 100 MHz Ethernet [3]. When the intelligent control center and the main control center are in different local area networks, the computer is connected to the wide area network through a router. Communication can be achieved by configuring the IP address, or a GPRS wireless network module can be used for data communication. The controller and the power line transmission module use the SPI interface, which does not require addressing operations and is full-duplex communication. It is simple and efficient, with a maximum rate of several Mb/s. The interface hardware schematic is shown in Figure 2. The CPU main frequency of the controller LM3S6916 is powered by a 6 MHz, 3.3 V power supply. A 25 MHz crystal oscillator is used for network data transmission. The system uses a key reset operation. CS is the chip select input of MI200E, SDO is the serial data output, SDI is the serial data input, and SCK is the serial clock input. When reading instructions, the chip select signal CS is set to low frequency, SDO is in high impedance state, serial data is input by SDI, and the rising edge of the clock signal SCK is latched. When writing instructions, data is output by SDO at the falling edge of the clock signal SCK. After PLC_AC is powered on, data is sent and received through the power line carrier transmission method. 1.2.3 Power transmission module The controller of the intelligent control center realizes data transmission through the power line carrier module and the power line carrier module of the sub-control box. Due to the highly integrated characteristics of the MI200E power line carrier chip, its peripheral circuit design is very simple. Therefore, this design selects MI200E as the power line carrier communication chip, and the circuit schematic diagram is shown in Figure 3. The analog power supply AVDD and digital power supply DVDD of MI200E are connected to 10μF electrolytic capacitors and 100 nF capacitors respectively to filter the power supply. In the circuit design, magnetic beads are connected in series between the digital power supply DVDD and the analog power supply AVDD to reduce the interference of digital signals on analog signals. In order to reduce the impact of 220 V voltage on the power carrier chip, this design also connects 5.1 MΩ and 220 kΩ resistors in series to VAC+ and VAC- respectively before connecting to the power line. MI200E can select different carrier rates according to different requirements. This design adopts a transmission rate of 1 920 b/s and a crystal frequency of 12 MHz. The carrier signal is output by PA and PB at 76.8 kHz, and the carrier signal is sent to the power line after passing through the coupling circuit. RAI+ and RAI- receive the 76.8 kHz carrier signal on the power line, and the MI200E carrier chip demodulates the data signal and performs corresponding data processing. 2 Software Design The software design uses Keil uVision3 as the programming development tool for LM3S6916. The main program sets the time interrupt and queries the internal registers of MI200E every 2 ms. When sending data, MI200E first transmits the frame header, baud rate and data length at a rate of 200 b/s. Then the user can reconfigure the mode register according to requirements to change the baud rate of the sent data. MI200E has a hardware automatic verification function, which can directly read the verification value from the register. When receiving data, first write the baud rate and data length set when sending data into the register. After the hardware completes the CRC check, check whether the received data is correct. The system always defaults to the receiving data state. The receiving data flow chart is shown in Figure 4. 3 System test The control center module of the system is connected to the intelligent control center module through the network port, and the intelligent control center module is connected to the sub-control box module through the power line. The network debugging assistant has conducted multiple tests on the intelligent control center and the sub-control box through power line carrier communication, and achieved reliable communication between the two. The main control center uses the power line carrier method to force the street lights to turn on and off, upload the system time, and upload the street light operating parameters, realizing the monitoring and control requirements of the street lights. The local port number is the default 4 374, the local IP address is 192.168.1.55, and the server, i.e. the intelligent control center, has a port number of 5 000 and an IP address of 192.168.1.191. Through the network port debugging assistant, the intelligent control center and the sub-control box were tested several times through the power line carrier communication, and the mutual communication between the two was realized. The system network test is shown in Figure 5. The Ethernet frame transmission protocol test results show that when the forced light on or off command is uploaded, the street light sub-control box returns the data SGGOPL<1KPGO00000000, indicating that the No. 1 street light is turned on or off successfully. The upload system time command returns the data 0001UTGO, and the corresponding hexadecimal data is 30 30 30 31 55 54 47 30 20 10 12 02 04 02 16 46 OD OA, that is, the system time is 20 10 12 02 04 02 16 46, which means Thursday, December 2, 2010 2:16:46. The command to upload street light operation parameters returns data 0002UPGO, and the corresponding hexadecimal data is 30 30 30 32 55 50 47 30 F1 46 46 00 00 00 00 01 01 DE OD OA, that is, the street light operation parameters are F1 46 46 00 0000 00 01 01 DE, which is converted into decimal 241 70 70 0 0 0 0 1 1 222, indicating relay switch status 241, street light operation mode 70, street light forced/automatic mode 70, street light brightness value 0, ambient brightness 00, ambient temperature 01, and CPU temperature 1222. Power lines are a widely available network. Taking advantage of this, there is no need to re-establish the network for the street light system. Data can be transmitted by using the existing distribution network, which greatly reduces the cost of infrastructure construction and maintenance. This paper uses MI200E as the power line carrier communication module, which can achieve stable and reliable data transmission. On this basis, a system for controlling street lights based on power line carrier is studied and designed. The implementation of the system shows that the design scheme is feasible, the performance is stable and reliable, and it can provide a reference for the future "low-carbon" economy [4].