Power line communication technology is a communication method that uses power lines to transmit data and voice signals. The technology loads the high-frequency signal carrying information onto the power line, transmits the data by wires, and modulates and demodulates the power line through a dedicated power line, and separates the high-frequency signal from the power line and transmits it to the terminal device [1]. Based on the wide distribution of distribution network in China, this paper studies and designs a system for controlling street lamps by means of power line carrier transmission.
1 system design
Since the signal attenuation is large when the power line is transmitted across the transformer, the GPRS wireless network communication may be transmitted according to actual requirements or the inter-area data communication may be realized by routing access to the wide area network. The management personnel only need to operate the computer and transmit data through the power line, and can control the switch state of the street lamp and query the running state of the street lamp to realize timely and effective management and control of the street lamp.
1.1 Design ideas
The street light control system consists of three main parts: the main control center, the street light intelligent control center and the street light control box. The distribution transformer has a blocking effect on the power carrier signal, so the power carrier signal can only be transmitted within a distribution transformer area. The main control center can realize data transmission through the GPRS wireless communication network or the router and the street lamp intelligent control center. 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 voltage and current abnormal alarm, street lamp fault alarm, super high temperature alarm, etc. to the main control center. In order to achieve the purpose of management control of each street light. As shown in Figure 1.
1.2 Hardware Design
It mainly designs the interface of the controller module of the street lamp control system and the power line transmission module and the power line transmission module.
1.2.1 MI200E Power Line Carrier Chip
The power transmission module selects the MI200E power line carrier communication chip produced by Shanghai Miya Micro Co., Ltd., which adopts the complex quadrature modulation principle. This principle has great advantages in power line transmission with severe signal attenuation changes. Compared with the current main narrowband communication method, spread spectrum communication method, and orthogonal frequency multiplexing technology, it can more effectively prevent the negative effects caused by the correlation between phase and orthogonality. The MI200E is a highly integrated, high-performance power line carrier communication chip optimized for low-voltage power lines. It has the characteristics of reliable communication and strong anti-interference ability. Users can easily embed modules into the system [2].
1.2.2 Controller Module
The LM3S6916's 32-bit ARM processor is used as the controller of the intelligent control center. It supports the ARM Cortex-M3 core with a maximum frequency of 50 MHz. The integrated nested vector interrupt control is the biggest advantage of other controllers. 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 WAN through the router, and the communication can be realized by configuring the IP address, or the GPRS wireless network module can also be used for data communication. The controller and the power line transmission module use an SPI interface, which does not require addressing operations and is full-duplex communication, simple and efficient, with a maximum rate of several Mb/s. The interface hardware schematic is shown in Figure 2.
The CPU of the controller LM3S6916 is powered by a 6 MHz, 3.3 V power supply. The 25 MHz crystal is used for network data transmission. The system uses a button 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 the instruction is read, the chip select signal CS is set to low frequency. At this time, SDO is in a high impedance state, serial data is input by SDI, and the rising edge of the clock signal SCK is latched. When an instruction is written, data is output by SDO on the falling edge of the clock signal SCK. After the PLC_AC is powered on, the data is transmitted and received through the transmission mode of the power line carrier.
1.2.3 Power Transmission Module
The controller of the intelligent control center realizes data transmission through the power carrier module and the sub-control box power carrier module. Due to the high integration of the MI200E power line carrier chip, its peripheral circuit design is very simple. Therefore, this design uses MI200E as the power line carrier communication chip. The circuit schematic is shown in Figure 3.
The MI200E's analog power supply AVDD and digital power supply DVDD are connected to a 10μF electrolytic capacitor and a 100 nF capacitor to filter the power supply. In the circuit design, the magnetic beads are connected in series between the digital power DVDD and the analog power supply AVDD, which reduces the interference of the digital signal on the analog signal. In order to reduce the impact of 220 V voltage on the power carrier chip, the design is also connected to the power line after connecting 5.1 MΩ and 220 kΩ resistors on VAC+ and VAC- respectively. The MI200E can select different carrier speeds according to different requirements. This design uses a transmission rate of 1 920 b/s and a crystal frequency of 12 MHz. The PA and PB output a carrier signal of 76.8 kHz. The carrier signal is sent to the coupling circuit. power line. RAI+ and RAI- receive the 76.8 kHz carrier signal on the power line, and the MI200E carrier chip demodulates the data signal for corresponding data processing.
2 software design
The software design uses Keil uVision3 as the programming development tool of LM3S6916. The main program sets the time interrupt and queries the internal registers of MI200E every 2 ms. When transmitting data, the MI200E first transmits the frame header, baud rate and data length at a rate of 200 b/s. The user can then reconfigure the mode register as required to change the baud rate of the transmitted data. The MI200E has a hardware auto-verification function that reads the comparison value directly from the register. When receiving data, first write the baud rate and data length set when the data is sent to the register. After the hardware completes the CRC check, check whether the received data is correct. The system always defaults to receiving data status, and 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. Through the network debugging assistant, the intelligent control center and the sub-control box have been tested by power line carrier communication several times, and the reliable communication between the two is realized. The main control center realizes the requirements of monitoring and controlling the street lamps by forcibly turning on the lights, turning off the lights, uploading the system time, and uploading the running parameters of the street lights through the power line carrier mode. The local port number is the default 4 374, the local IP address is 192.168.1.55, and the server is the intelligent control center with the port number of 5,000 and the IP address of 192.168.1.191. Through the network port debugging assistant, the intelligent control center and the sub-control box have been tested by power line carrier communication several times, and the mutual communication between the two is realized. The system network test is shown in Figure 5.
The Ethernet frame transmission protocol test result shows that uploading the forced turn-on or turn-off command, the street light sub-control box returns the data SGGOPL "1KPGO00000000 means that the 1st street light is turned on or off successfully. The upload system time command returns the data 0001UTGO, corresponding to the 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, indicating 2010 Thursday, December 2, 2:16:46. The upload street light running parameter command returns the data 0002UPGO, corresponding to the 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 operating parameter is F1 46 46 00 0000 00 01 01 DE, converted to decimal number is 241 70 70 0 0 0 0 1 1 222, indicating relay switch state 241, street light operation mode 70, street light forced / automatic mode 70, street light brightness value 0, ambient brightness 00, ambient temperature 01, CPU Temperature 1222.
The power line is a widely-existing network. By taking advantage of this, there is no need to re-establish the network for the street lamp system. As long as the existing distribution network can be used for data transmission, this greatly reduces the infrastructure and maintenance. cost. The MI200E selected in this paper is a power line carrier communication module, which can realize stable and reliable data transmission. Based on this, a system based on power line carrier is controlled and designed to control street lamps. The realization of the system shows that the scheme design is feasible, the performance is stable and reliable, and it can provide reference for the future “low carbon†economy [4].
The handheld addresser is used to program the address of the monitoring module offline. When in use, connect the two output wires of the handheld encoder to the communication bus terminal (terminal label 1, 2) of the monitoring module, turn on the black power switch on the right side upwards, and press "ten Add", [Subtract ten", [Add one place" and [Subtract one place" to program the address.
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