1 system overview
In order to realize the optimal management of street lamps, the street lamp monitoring system needs to collect the status and environmental information of each street lamp, collect it into the computer terminal, and optimize the processing to control the output light of each street lamp. The block diagram of the implementation of the entire system is shown in Figure 1.
In 1, the street lamp monitoring system mainly includes a street lamp node, i.Lon Sma rtSever (power line network manager) and street lamp monitoring software running at the computer terminal. The streetlight monitoring software controls all streetlight nodes in the LonWorks control network via the Internet; each LonWorks control network is equivalent to a site on the Internet, with an IP address, access to the LonWorks control network by accessing the IP address.
i. Lon SmartSever manages the LonWorks control network in a master-slave manner and can access the Internet via dial-up via the Ethernet interface or GPRS communication module. In this way, the control center passes with i.
Lon SmartSever performs data exchange and can monitor every node on the LonWorks control network. In addition, the i. Lon SmartSever comes with multiple I/O ports for collecting environmental information (illuminance, humidity, etc.) of the road as a basis for dimming.
In the monitoring center, the street lamp monitoring software continuously checks the status of each street lamp node, displays the working status and output power of each street lamp, and can manually control the light flux of each lamp, and can also automatically adjust the street lamp illumination according to a certain algorithm.
Auto dimming can be used in the following situations, including:
The illuminance is adjusted according to the set time period, for example, in the latter half of the night, the half-load power output is adjusted.
Turn on or off the light or adjust the output light according to the weather conditions and the sunshine conditions in different periods.
Adjust the output light according to the special lighting conditions. For example, in the case of urban tunnel lighting, in order to avoid visual incompatibility when entering or leaving the tunnel, the street light of the tunnel opening is separately adjusted to make the light passage gradually change.
Set the output light according to the special section. For example, when an accident occurs on a certain road section, the maximum luminous flux is output for accident handling and road safety is improved.
2 street light node design
The street lamp node designed by the system includes a power line communication part, an intelligent electronic ballast part and a high pressure sodium lamp part, and the power line communication part and the intelligent electronic ballast part exchange data through the I 2 C interface. Its hardware circuit implementation block diagram is shown as 2.
2. 1 power line communication
2. 1. 1 hardware design
The power line communication control circuit is mainly responsible for the reliable transmission of data on the power line. The main chip is Echelon's PL3120. The PL3120 is a neuron chip dedicated to the power line system. It integrates three processor units and one power line transceiver. The power line transceiver adopts narrow-band BPSK modulation and has dual-carrier frequency. When the main frequency is interfered, it automatically switches to the preparatory frequency, which greatly enhances the anti-interference ability of the system.
As shown in 3, the power line communication control circuit includes a high-pass coupling circuit, a power amplification filter circuit, and a PL3120 and its peripheral circuits; the high-pass coupling circuit extracts a high-frequency signal in the mains line, and is filtered by the band-pass filter circuit and transmitted to the PL3120. Adjust the communication data. At the same time, the PL3120 will transmit data for BPSK modulation, which is coupled to the grid after power amplification. The PL3120 samples the output voltage of the power amplifier circuit through the TXSENSE pin. The resulting value is used to adjust the current on the TXBIAS pin to control the transmit power.
In order to ensure the reliable operation of the power line communication circuit, the high-pass coupling circuit must be optimized to make the high-pass coupling circuit filter out the 50Hz mains component, and have a large input impedance and a small output impedance to reduce the signal degradation. In 3, the capacitors C 1 and C2 and the transformer T1 form a transmission path, and the transformer ratio is 1:1, which serves as an isolation function; to reduce the AC output impedance of the transmission path, it is necessary to select a larger C 1 , C 2 . C 2 is a DC blocking capacitor, which can be made larger; but C 1 is directly connected to the power line. Increasing the capacitance will increase the volume and increase the loss. Therefore, by properly designing the leakage of the transformer without increasing C 1 The sense L k resonates with the capacitor C 1 in the carrier frequency range, reducing the output impedance. In the input path, C 1 and L m filter out the 50 Hz mains component, and the high frequency signal component passes through the C 3 and L 2 resonant circuits to amplify the received signal to obtain a stronger received signal. In the actual circuit, L m is taken as 1 mH, L k is taken as 12 μH, capacitor C 1 is taken as 0. 1 μF, C 3 is taken as 1. 5 nF, and L 2 is taken as 820 μH.
2. 1. 2 software design
The biggest advantage of the LonWorks system is that the communication program is designed using the Neuron C language. Based on the standard C, Neuron C provides a large number of hardware interface functions, which can be used by calling the corresponding function. Moreover, the communication between nodes is realized by the binding of network variables, and the communication process is completely The underlying protocol is completed, which facilitates the development of the program.
The power line communication software implementation block diagram system defines an input network variable (i. Lon SmartSever control command for the node) and an output network variable (return data for the node pair i. Lon SmartSever) and the corresponding output on the i. Lon SmartSever , enter the network variable binding. When sending data, the local output network variable is changed, and the value of the input network variable bound to it changes accordingly, and the data transmission process is completely completed by the underlying protocol, which greatly simplifies the development process of the program.
2. 2 electronic ballast
The electronic ballast part of the street lamp node adopts a common two-stage topology, the pre-stage PFC circuit adds the post-stage half-bridge inverter and the resonant trigger circuit, and collects the ballast through the central processor circuit, the sampling circuit and the dimming circuit. Status information and dimming according to the command.
Electronic ballasts have a variety of dimming methods, such as FM dimming, tuning bus voltage dimming, and duty cycle dimming. In the high-power high-pressure sodium lamp, since the frequency of the acoustic resonance is small, a relatively simple frequency modulation method is selected.
The following is an analysis of the effect of frequency changes on output power. For the resonant circuit of the electronic ballast, in order to reduce the crest factor, the operating frequency is usually selected from 4 to 6 times of the resonant frequency, and the component after the higher harmonic is filtered by LC is not considered, and only the fundamental wave analysis is performed on the resonant circuit. .
Fundamental component expression:
Vin=2Ï€V bus(1) where: V bus is the bus voltage of the PFC circuit; R lamp is the equivalent resistance of the lamp during steady operation; output voltage:
VO = V in 1 + Q 2 f 0-f 0 f
2(2) where: Q = 1 R lamp L s Cs(3)f 0 = 1 2πL s Cs(4) Output power according to equations (1), (2): P o = V 2 o R lamp = 2V 2 busπ2 R lamp 1 + Q 2 f 0-f 0 f 2(5) When f > f 0, as f increases, P0 decreases (in order for the switch to operate in the soft-on state, the operating frequency will generally Choose larger than f 0).
The FM dimming circuit is as shown. ATMega8's PB2 pin (counter comparison output pin) outputs PWM wave. After filtering the high frequency component through optocoupler, the reference voltage V ref is obtained. When Vref is changed, the potential of point A changes, and the output current of pin 4 changes. The frequency changes accordingly (the 4th pin of L6574 is a constant 2V voltage, and the frequency is changed by changing the output current value of pin 4); as shown in Equation 5, the frequency of the resonant circuit changes, and the output power also changes. Therefore, changing the duty cycle of the PWM output of the ATMega8 can change the output power of the lamp, and the larger the duty ratio, the lower the output power.
After experimental measurement, the input power-frequency curve is obtained. Since the input power is relatively easy to measure, the change in input power is used to approximate the change in output power.
At full load, the operating frequency is 43 kHz and the input power is 273W. As the frequency increases, the input power decreases approximately linearly. When the frequency reaches 60kHz, the input power is about 100W. In many streetlight applications, the half-load power has been adjusted. Sufficient; and the high-pressure sodium lamp is in the frequency range of 38 kHz to 100 kHz, which is a safe area for acoustic resonance, enabling safe dimming.
3 experimental results
By simulating the scene, 20 streetlight nodes are evenly hung on the 1000 m power line. The experimental results show that each street lamp node can reliably complete the commands issued by the host computer, realize single point dimming, multi-point dimming and timing dimming, etc., and can accurately collect its own status information and display it on the computer. At the same time, i. Lon SmartSever can adjust the output light of each street light node through a specific algorithm without the operation of the upper computer to achieve the desired effect.
4 ends
With the introduction of new urban energy-saving emission reduction requirements, the optimization management of road lighting system has also received more and more attention. The street lighting monitoring system based on LonWorks control network proposed in this paper selects LonWorks technology as the control platform of street lighting monitoring system. The computer terminal monitors the real-time monitoring of each street lamp node; and can adjust the output light channel according to the specific environment in which the street lamp is located, which not only reduces a large amount of manpower, material resources and financial resources, but also achieves more effective illumination.
The system can also be easily applied to other types of street lighting systems. With the maturity of LED-based fourth-generation light sources, many streetlight systems have already adopted LED lights, and the system only needs to replace the high-pressure sodium lamp electronic ballast with an LED driver with a digital interface to work properly. Monitor high pressure sodium lamps and LED lamp nodes.
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