research work.
With the development of technology and the increasing energy shortage, China has begun to pay attention to the intelligent adjustment of public lighting to save resources. One problem that is inevitable in the process of retrofitting lighting systems is the problem of physical channel selection between controllers. If the communication cable is re-routed in the streetlight energy-saving project, it is not only troublesome, but also adds a lot of transformation costs. As a technology that can transmit signals through power lines, power carrier technology has highlighted great advantages in energy-saving retrofit projects.
1 Power carrier technology Power carrier communication is a communication technology that loads high-frequency signals onto power lines and transmits data through power lines to realize communication between devices. The use of the power line as a signal transmission channel has a unique advantage. It does not require additional wiring. As long as the power is plugged in, it can directly transmit signals on the existing power network, which can save a lot of cost, especially if it has no additional wiring or wiring. The place is the best choice.
The implementation cost is low, the existing power network is effectively utilized, and no rewiring is required.
The data transmission rate is high, and the PL transmission rate is up to 4, which is convenient to use and can be used when plugged in.
Wide range, civil power line is the most popular network, PLC can easily penetrate into every family, providing a broad space for the development of modern home intelligence and the development of the Internet.
However, the power carrier also has its inevitable shortcomings 21, mainly reflected in large interference and large attenuation. There are a large number of devices on the power network, which will generate pulse interference when turning on and off. Motors, generators and other devices will generate background noise interference. At the same time, due to the impedance on the power line, various loads, etc., the signal will be greatly attenuated when transmitted to the target device.
At present, many enterprises and research institutes at home and abroad are studying power carrier technology. There are also many power carrier chips on the market. Domestic companies that do power carrier chips include Neusoft, Fuxing Xiaocheng, and Changsha Hsinchu Digital. Foreign companies doing this are Echelon, Inellcn, and National Semiconductor. Power carrier chips produced by domestic companies are generally used in the field of automated meter reading, but they are rarely used in industrial control because they cannot guarantee instant and reliable communication. The PL series power carrier chip produced by ECelcn is used for the industrial control network. It adopts BPS modulation and demodulation technology, dual-carrier communication and various fault-tolerant and error-correcting technologies to automatically switch to the auxiliary frequency band when the main channel interferes greatly. This paper introduces a power carrier intelligent dimming controller designed by ECeOn's P3120 chip. It can receive control commands from ECelon's Smart Serve through power carrier mode, adjust the street light opening degree, and realize intelligent energy saving.
2ECeOn's power carrier chip PL3120 PL120 is one of Echelon's latest intelligent power carrier chip series, which realizes point-to-point communication through LWk network. It differs from previous ECelo's neuron chips in that it integrates a power carrier receiving and amplifying circuit, and only requires an external coupling circuit for power carrier communication, which is specifically developed for use in the power carrier field.
PL3120neu chip input clock frequency has two, one is 6.5536MHZ working in A-band, the communication speed is 3.6Kb/s, the other is 10MHz working in C-band, the communication speed is 5.4Kb/s - the general industrial application field of domestic rot industry Using C-segment communication, A-band communication is used in the field of automated meter reading. Each band has a primary and secondary frequency. The PL3120 has a built-in signal transmitter and receiver amplifier. The PL120 Smart Transceiver architecture is shown.
The coupling circuit PL3120 adopts a narrow-wave BPSK weekly signal, a dual-carrier communication mechanism, and good fault tolerance, error correction mechanism and anti-interference ability. Thereby achieving communication in a noisy power line network.
When the acknowledgment packet can be received, the PL120 smart transceiver initially operates at the primary frequency point. When the transceiver detects that the acknowledgment information is lost, the meter communicates with the secondary frequency point.
The noise signal in the channel will destroy the integrity of the data packet. The PL3120 Smart Transceiver overcomes the packet error problem by a high reliability, low overhead forward error correction algorithm (FEC) plus cyclic redundancy check.
P! The intelligent transceiver has output impedance, and the 1A peak-to-peak signal current output capability enables low-impedance circuit high-level signal transmission while maintaining extremely weak output signal distortion, which fully meets the international EMC standard. The PL Smart Transceiver is processed using DSP technology to overcome signal attenuation and noise interference with a transmit signal power amplifier with a small output impedance and a wide range of signal receivers (> 80dB).
3 energy-saving controller design 31 hardware design The controller includes 5 parts: power supply circuit, processor core, coupling circuit, dimming circuit and detection circuit. The power supply circuit provides the required voltage for the controller, and the processor core is a carrier control chip. The coupling circuit is responsible for coupling the signal to the low voltage power line and receiving the signal from the power line. The detection circuit is mainly for displaying the working state of the circuit, and the dimming circuit is responsible for Receive PL3120 control information through the UART port, adjust the street lamp opening degree and feedback to the working status of the P3120 street light. The overall structure is as shown.
The key part of the hardware design is the design of the coupling circuit. The design of the coupling circuit must be as small as possible so that the signal is not consumed by the output impedance. Since the line impedance may be less than ia, the impedance of the entire transmission channel must be less than the input impedance of the ia. It must be large enough to ensure that the signal is not substantially separated by the line impedance. The coupling circuit design principle is as shown.
The coupling circuit design T is a communication coupling transformer, which functions to isolate the power network from the internal circuit and is also part of the input impedance of the coupling circuit to improve the input impedance and reduce signal loss due to voltage division. TXOUTRXN is the transmit/receive pin on PL3120. The transmit signal is protected by two diodes from T3 through C3 to suppress the surge voltage of the circuit. The function of C2 is to prevent the DC bias voltage of rnur from being loaded on the RXN pin. . R5 is both a part of the input impedance and provides a discharge path for T and C3. F1 and F2 provide overcurrent and overvoltage protection.
In order to achieve the low impedance requirement of the signal line, the signal line width between the transmit amplifier output and the AC power source must be greater than 1.27 mm and the length cannot be greater than 15 to prevent excessive impedance from being introduced.
32 software design communication board sends control information to the dimming board through the serial port. The overall logic of the program is: PL3120 receives the adjustment command from the SnanSevr road controller through the network variable. When the predefined time is up, PL3120 checks whether the command status is Whether to wait for the write command, yes, send a control command to the dimmer through the serial port, set the timeout period, and then wait for the dimmer to return the information. If the feedback message is received before the timeout period, the format is checked and the information is updated. And send to the corresponding network variable, otherwise call the watchdog update, and adjust the command state to wait for the write state. Also set a clock to calculate the energy saving control time. The LnWk task scheduling structure first checks the task with high priority, then selects a check according to a certain algorithm in the low priority task, and executes if there is an event, otherwise returns a task with a high priority and then a low priority task. Select another task check to ensure that high priority tasks get more execution chances. The program structure is as shown.
4 Conclusion This paper introduces a control board design based on power carrier technology, in the laboratory through the PLA-22 power line protocol analyzer for signal strength test and communication test with satsevr connection, the test results show that the communication is very good. The PCA-22 power line protocol analyzer has a receiving strength of 0 dB (ie, the received signal strength sends a signal strength = 1 indicating that the signal has almost no attenuation). The controller can correctly receive the control command to adjust the street light opening and return status information.
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