Research on LED intelligent lighting system based on centralized DC power supply

Before the 1980s, my country's public lighting equipment was generally in the traditional power grid and manual management mode. The operation status of street lamps was mainly achieved through line and lamp patrols. The disadvantages of this mode are high cost, low automation, and inability to achieve local control and remote monitoring, such as automatic detection, dimming and other intelligent management. The response to faults is slow, and there are factors such as failure to obtain timely maintenance when a fault occurs, causing lighting inconvenience and even safety hazards.

From the late 1980s to the early 1990s, my country began to research and put into use street lamp monitoring and management systems. With the gradual development of technology, intelligent line management and dimming control have been realized. The street lamps have strong monitoring capabilities and can quickly collect and analyze data on system operation conditions, adjust the system according to the conditions specified by the program, and determine fault conditions to locate faults. By reducing the cost of the street lamp system and improving the monitoring capability and automation level of the system, rapid recovery from faults can be achieved, fault time can be reduced, and the reliability of power supply and lighting and the level of system management can be improved.

The centralized power supply LED intelligent lighting system discussed in this article is a management model that emerged under the background of the widespread popularity of LED street lamps and the relatively mature intelligent lighting system. This model aims to supply DC power to several branch LED street lamps around, and achieve safe, reliable and stable power supply and secondary energy saving through intelligent management. Guangdong Product Quality Supervision and Inspection Institute has undertaken the drafting of the Guangdong Provincial Local Standard "Centralized Power Supply LED Intelligent Lighting Interface" and has carried out some preliminary research for this purpose. We welcome the industry to provide valuable opinions.

1. Characteristics and advantages of centralized power supply LED street lamp intelligent lighting control system

(I) Comparison between centralized power supply and traditional power supply system of LED street lamps

1. LED lamps

(1) Traditional AC-powered LED lamps

LED lamps are directly connected to the AC power grid. On the one hand, they are greatly affected by the power grid, such as the EMC impact of the power grid on the lamps and the impact of lightning transmitted from the power grid; on the other hand, each LED lamp needs to have EMC, rectification, power factor correction, filtering, power drive, inverter step-down, voltage stabilization output or re-current stabilization output to the LED light source. The circuit of the lamp control device is complex, with many components, and the cost of the lamp is high. Moreover, safety and EMC issues are relatively prominent. These make the reliability of LED lamps low and affect their lifespan (for example, there are components such as electrolytic capacitors in the lamp that can withstand the power grid voltage).

(2) LED lamps powered by high voltage DC

LED lamps are connected to the DC output end of the power module of the control cabinet. On the one hand, they are basically not affected by the EMC of the AC power grid and the lightning transmitted from the AC power grid (of course, they still need to resist the pulses transmitted from the DC line by lightning strikes); on the other hand, each LED lamp does not need EMC, rectification, power factor correction, filtering, power drive, inverter step-down and other circuits and components. Simple constant voltage types require very few auxiliary components and directly output to the LED light source in series, or add a constant current circuit to output a constant current to the LED light source in series. In this way, the circuit of the lamp control device is very simple, the reliability is very high, and the service life can be very long, which is very beneficial for road and tunnel lighting projects with harsh environmental conditions. More complex intelligent DC LED lamps also need to add intelligent receiving control circuits and internal intelligent control protocol programs. The lamp control device has slightly more components, the circuit is slightly more complex, and the lamp cost is slightly higher. But compared with similar intelligent AC LED lamps, it is still much simpler, more reliable, and has a longer service life, which is still very beneficial for road and tunnel lighting projects.

2. Control cabinet

(1) Traditional AC powered LED lighting control cabinet

High-pressure sodium lamp street light control cabinet generally controls dozens of high-pressure sodium lamp street lights. In the early days, simple control cabinets were used to manually switch high-pressure sodium lamp street lights; slightly more complex energy-saving high-pressure sodium lamp street light control cabinets were used to manually convert transformers to reduce power in the middle of the night; further, some cabinets accept remote control to automatically switch or dim all high-pressure sodium lamp street lights or LED lamps, or to intelligently control each LED lamp individually.

(2) LED lighting control cabinet with centralized high voltage DC power supply

First, the control cabinet generally controls dozens of LED lamps. First, the AC power of the power grid is converted into a high-voltage DC voltage and output to the LED lamps. The control cabinet contains an intelligent control circuit module so that it can accept remote control, and then control the power module to adjust the output DC voltage to automatically switch and dim all LED lamps in a unified manner. Or a more complex intelligent control system can perform multi-functional intelligent control on each intelligent LED lamp separately.

Second, the power module of the control cabinet can be divided into a single high-power power module or a combination of multiple low-power power submodules. The DC output of the combination of multiple low-power power submodules can be divided into unified output after parallel connection or multiple outputs of each. Since the unified output mode after parallel connection can ensure that when one of the power submodules fails, the hot backup power submodule is immediately connected to the output line, which can not only ensure the reliable operation of the system under the same power output, but also reduce the number of power submodule backups to a minimum. However, the technical requirements are relatively high, for example, the error of the DC output voltage of each power submodule should be as small as possible. The DC output voltage can be divided into high-voltage DC, such as 300V (outputting high voltage can reduce wire line loss and improve the overall efficiency of the system), or safe low voltage, such as below 120V (the electrical safety of the line and lamps to the human body is higher, but the wire line loss will be much greater under the same load, the line itself will generate more heat, and the cost is high).

3. Line

(1) Traditional AC power supply line

Single-phase three-wire (live wire, neutral wire and ground wire), or three-phase five-wire (three live wires, neutral wire and ground wire) power supply line.

(2) Centralized high voltage DC power supply lines

First, the input end of the control cabinet needs to be connected to the AC power grid, which can be divided into single-phase AC input or three-phase AC input. Three-phase AC input can balance the load of the power grid, which is a better way. The output DC power supply line can be three-wire (for the positive, negative and ground wire of >120V high voltage DC), or two-wire (corresponding to the positive and negative poles of ≤120V DC, and meeting the various requirements of safe extra-low voltage). If there is another AC power grid access point in the adjacent LAN of the same intelligent lighting project, the power line of the original AC power grid can be used as the DC output line in the transformation of the LED intelligent lighting system, otherwise it is necessary to lay additional wiring for the output DC power supply line. Similarly, the same is true for new projects. This is easier to achieve in public building intelligent lighting systems than in street lamp intelligent lighting systems, but there are many other issues to consider.

4. Intelligent control protocols and approaches

(1) Between the remote computer and the control cabinet

There are many secondary development protocols based on the Internet, but there is no particularly unified and dedicated one.

(2) The mobile phone is connected to the control cabinet via GPRS

It is only used for system maintenance personnel to set individual data and receive feedback information. It is technically unrealistic to achieve comprehensive, fast and continuous single-lamp control of the system. More importantly, from the perspective of public safety, system maintenance personnel should not be allowed to arbitrarily control public lighting occasions such as street lights, tunnel lights and large buildings with mobile phones.

(3) Between the control cabinet and each lamp

The control cabinet power module is controlled to adjust the output DC voltage to automatically and uniformly switch or dim all LED lamps. At this time, no intelligent control protocol is required between the control cabinet and each lamp (at this time, the lamp cost is the lowest and most reliable, but a single lamp cannot be controlled).

(4) Protocols and paths between the main control device and each lamp

For an intelligent system that can control each lamp individually, there must be a control protocol and path between the main control device and each lamp. The intelligent control path between the control cabinet and each single lamp can be achieved by laying a dedicated control line, or AC carrier, or DC carrier, or wireless Zigbee. If each LED street lamp needs to be intelligently controlled individually, the most commonly used intelligent control protocols are DMX512 and DALI.

DMX512 has many control nodes, fast speed, and long transmission distance, but it can only transmit in one direction (if fault diagnosis feedback is required, other measures must be taken to compensate), and the protocol does not specify specific instructions and processes. The system signal distribution has many points and the use of points is uncertain. Therefore, from the control perspective, it is difficult for the systems and lamps of each enterprise to be interchangeable and universal. It is only suitable for lighting projects where the warranty and maintenance contract period of the enterprise is very long, or the lamps and systems have high reliability and long life. Therefore, from the above analysis, it can be seen that DAX512 is very suitable for centralized power supply DC intelligent lighting, especially for tunnel lighting projects.

DALI can transmit bidirectionally, has comprehensive function definitions and program flow, and there are continuous protocol addresses between lamps. However, DALI controls few lamps, has slow speed, and has a short transmission distance. Although there are many clearly defined control functions and instructions, it makes it easy for various companies' systems and lamps to be interchangeable and universal from a control perspective. However, the internal protocol program is complicated, which is a waste of resources in lighting projects such as road lighting that do not require multiple control functions, resulting in high lamp costs. Therefore, it is not suitable for road lighting, including tunnel intelligent lighting.

(II) Advantages and disadvantages of centralized DC power supply LED intelligent lighting control system

The control devices of all lamps (commonly known as driving power supplies) do not need the "AC-stable DC" conversion function, but are all replaced by multiple high-power power modules concentrated in the control cabinet. This makes it easy to make the power modules highly reliable, long-life, and high-quality, and can make the lamps and systems very efficient, reducing the overall system cost.

The control device (drive power supply) circuit of the lamp can be very simple, with few components, and the lamp cost is low. More importantly, all lamps can be without drive power supply. The drive power supply is separated from the LED lamp, which reduces the heat of the lamp. At the same time, the ambient temperature of the drive power supply itself is greatly reduced. These make the lamp reliability very high, the life span can be very long, there is no power factor problem, and the power supply line loss is reduced. These are very beneficial for the use of street lamps and tunnel projects in harsh environments.

The disadvantage is that in street lamp applications, unless there is an additional AC power supply access point every few kilometers, in addition to the power line of the original AC power supply grid, a DC output power line needs to be laid out separately. Indoor applications also have similar problems. In addition, if each lamp needs to be further intelligently controlled separately, unless a carrier is used (there is an AC carrier method, but it is not suitable for centralized DC power supply; there is a DC carrier method, but there are currently few dedicated ICs), or wireless communication is used, otherwise a dedicated control line needs to be laid out separately.

As can be seen from the above, the biggest advantage of the centralized DC power supply intelligent lighting control system is that the LED lamps can be made very simple and easily interchangeable in structure, so they have the advantages of low cost, high reliability and long life. For applications such as roads and tunnels managed by professionals, if another adjacent control cabinet several kilometers away has another AC power supply grid access point and it is allowed, the power line of the original AC power supply grid can be directly used to convert it into a DC output line in the transformation of the LED street lamp intelligent lighting system, reducing the wiring trouble and cost. Otherwise, it is necessary to wire the output DC power supply line separately, which is a problem to be solved, which is also its biggest disadvantage.

For indoor applications, considering that other home appliances such as refrigerators must use AC, for indoor home lighting, unless the newly built building has pre-buried DC lines for lighting, the implementation of a centralized DC-powered LED intelligent lighting control system can be very convenient. However, what needs to be considered more importantly is that DC LED lamps and DC LED lamps should be strictly structurally ensured not to be mixed with current AC lamps and AC lamps, otherwise it will easily lead to major safety problems.

Therefore, considering all aspects comprehensively, the centralized DC-powered intelligent lighting control system is most suitable for professional applications such as tunnel lighting applications.

2. Working principle and key technical points of centralized power supply LED road and tunnel intelligent lighting control system

(I) Working principle (workflow)

The procedure for normal operation of the system is as follows: the host computer system sends the default or set initialization parameters of the system to each sub-network, and retains the working status of the last system memory (including fault status and other information), and then sends requests to each sub-network controller and receives collected data, and judges the received data according to the condition judgment program. When it is determined that a fault has occurred, the fault diagnosis program is imported to accurately analyze the fault type and locate the fault. After the judgment is completed, the control instruction is modified and sent to the specified terminal. The terminal that receives the fault instruction performs the corresponding state switching or switch action. At the same time, the system display information is updated synchronously. During normal operation, various data collection and program analysis, program judgment and instruction sending are continuously performed at specified time intervals to monitor the entire system to work according to the predetermined program until the system is shut down.

(II) Data Communication

The data communication of the centralized power supply LED road and tunnel intelligent lighting control system can be carried out through the GPRS wireless network in addition to the above-mentioned wired data communication between the host computer system and each sub-network system through the Internet. In addition, mobile phones can also communicate data through the host computer system manager, GPRS server, or directly through the sub-network main controller (power controller) with GPRS function and the terminal controller (LED street light or tunnel light fixture controller).

A power supply, a power supply line and the LED street lamps or tunnel lamps connected thereto constitute a sub-network system of the system, and a host computer controls such a single or multiple sub-network systems.

The sub-network controller in the sub-network system with two-way communication function (in the control cabinet mentioned above) inquires the working status of each LED street lamp or tunnel lamp in the sub-network through intelligent control means (control dedicated line, or AC carrier; or DC carrier, or wireless Zigbee) at a time period specified by the program (including input and output voltage, current, etc., when the lamp has intelligent and self-test functions), and detects the working status of the power supply (including power input, output voltage and current and power), determines whether there is any abnormality in each component in the sub-network, and then sends the working status information of each LED street lamp or tunnel lamp and power supply in the system (including diagnosed fault information) to the host computer through the Internet or GPRS modem, and receives commands from the host computer at the same time, and sends the results of data information collection and processing to each terminal controller.

3. Example Introduction

(I) System Introduction

The centralized power supply LED street lamp intelligent lighting control system consists of a power module, a controller, a display, a GPRS module, a power collection module, and a cabinet. The input adopts a three-phase four-wire AC power supply plus a protective ground wire. The power module rectifies, filters, and converts the three-phase AC power into a stable DC power. Multiple power modules are connected in parallel to output positive and negative DC power plus a protective ground wire. The power module is hot-swappable and is equipped with a backup hot power module.

The system is a simple centralized DC-powered LED street lamp intelligent lighting control system that achieves the purpose of uniform dimming of all LED street lamps by adjusting the DC voltage. It cannot control a certain LED street lamp individually.

(II) System structure diagram

(III) System electrical interface

Between the power grid and the power distribution control cabinet: 380V (±10%), 50Hz three-phase AC input is provided to each power module, and the input end of each power module has EMC measures; both the input and output ends have complete anti-lightning measures.

The output ends of the power modules are connected in parallel to form a single output, with a maximum DC adjustable voltage of 300V. The voltage level determines the dimming amount.

Between the DC line and the LED street lamp: connect the number of LED street lamps that does not exceed the total power of each power module in the control cabinet to the positive, negative and protective ground wires of the DC line, and connect the positive, negative and protective ground wires.

(IV) System characteristics

1. The combination of power modules enables the system to have a maximum capacity of 15000W and a three-phase 323V~475V wide AC input voltage range.

2. The power module adopts active power factor correction technology, with a power factor ≥ 0.92, reducing the operating costs of the AC power grid.

3. The power module adopts high-frequency soft-switching PWM control conversion technology, which reduces switching losses and improves the overall efficiency (≥92%); low electromagnetic interference and does not affect other control systems installed in the cabinet.

4. The system adopts high-precision current sharing and hot backup technology to improve the reliability of the system and reduce the daily maintenance work of the equipment.

5. The system adopts intelligent air cooling, heating and dehumidification technology to ensure a reliable working environment for electrical components, with low failure rate and high reliability.

6. The power module adopts hot-swappable technology and can be installed or replaced online.

7. The power module has protection functions such as AC input overvoltage, overcurrent, DC output overvoltage, overcurrent and short circuit protection and radiator overtemperature protection.

8. The system adopts programmable controller control, touch screen display and GPRS remote control, which is convenient for users to master, query and set parameters. The system integrates computer technology, intelligent control technology, data acquisition technology and communication technology, which can realize self-testing, automatic diagnosis and automatic control of the system, and can also realize telemetry, telecommunication and remote control of the power supply system.

9. According to the local longitude and latitude, the system can automatically calculate the sunrise and sunset time every day to realize automatic switching of lights. You can also set the brightness value in different time periods to realize the time-sharing dimming function, so as to achieve more humane management and improve energy saving effect.

10. The system uses the GPRS communication function of the mobile operator's platform to promptly feed back system operation information and fault information to customer maintenance personnel, thereby realizing the function of rapid fault handling.

(V) Main technical indicators of power supply system

IV. Conclusion

The centralized DC-powered LED intelligent lighting system discussed in this article is a new power supply technology for LED intelligent lighting. Its advantages are that it improves the reliability of centralized power supply for LED lamps and intelligent lighting systems, reduces operating costs, and realizes the concept of energy-saving and environmentally friendly electricity use through intelligent management.