A Distributed Power Supply System is a large-capacity power supply system composed of several small-Capacity Power Supply Modules. It is a relatively small Power Supply Module Made of new power theory and technology, combined into a modular, intelligent high-power supply system. More and more power supply systems use the parallel technology of modules and flexibly combine multiple Switching Power Supply Modules in parallel into a high-power distributed power supply system, which is the main way to achieve high power switching power supply. In the field of Distributed Power Research and Development, the United States, Germany, Britain, Japan and other countries are in the leading position in technology. Many of their power generation equipment production companies work with power companies, conduct commercial experiments on distributed power technology. In Europe, the policy of popularizing distributed power is being studied, and the Research on Distributed Power in China is still in its infancy.
Nowadays, DC distributed power systems are widely used in the communication field due to their high redundancy and flexible control. A Distributed Power Supply Design Scheme for modern communication networks based on microgrid technology is proposed.
1. Power Supply Mode of the Communication Network
Communication network for the power supply is the basic requirement of continuous power supply, so its power supply mechanism is generally composed of AC-DC, batteries and distribution equipment, an uninterruptible power supply system with a nominal value of-48 VDC or 24 VDC, then the DC-DC converter converts the voltage nominal value of-48 VDC or 24 VDC into various voltages required by the circuit board, such as 12 VDC and/or 5 VDC. From the development history of the communication network power supply mode, it mainly goes through three stages: centralized power supply, distributed power supply and distributed power supply.
(1) centralized power supply. A high-power uninterrupted power supply system with one or more backups provides various voltages required by the entire communication network. Such power supply methods have been basically eliminated.
(2) distributed power supply. A high-power uninterrupted power supply system provides a unified-48 VDC or 24 VDC, and then centrally supplies it to the communication network. In the communication network, each frame of the device rack has one or more medium power supply board (DC-DC converter), The-48VDC or 24 VDC bus voltage is converted into one or more types of voltage, the circuit board that supplies the frame.
(3) distributed power supply. A high-power uninterrupted power supply system provides a unified-48 VDC or 24 VDC, and then centrally supplies power to the communication network. Each circuit board of the device rack has one or several small power supplies (DC-DC converters) each, which convert the bus voltage of-48 VDC or 24 VDC directly to the voltage required by the circuit board.
Relatively speaking, the centralized power supply cost is the lowest, but the reliability is the worst. The distributed power supply features high reliability, flexibility, good scalability, and versatility, but the cost is high; the performance and cost of distributed power supply are between the two. At present, most of the major communication operators use fixed telephone and mobile communication systems, such as distributed power supply. To improve system reliability, the power board is backed up in 1 + 1 mode or N + 1 mode. Currently, distributed power supply is the most cost-effective power supply mode.
With the emergence of a new generation of digital chips, the operating voltage of communication devices in modern communication networks is continuously decreasing. To speed up the chip and reduce power consumption, the use of 12 VDC and 5 VDC is decreasing, while the use of 3.3 VDC and 2.5 VDC or even 1.8 VDC is increasing. Therefore, when the voltage is low, the voltage drop caused by the DC voltage resistance increases significantly. At this time, the use of distributed power supply to become the only solution, because the DC-DC power dispersion is higher, the lower the working current, the lower the power supply pressure drop, which is more suitable for low-voltage applications. Modern communication networks are increasingly using ultra-large-scale integrated circuits. Currently, the mainstream distributed power supply methods cannot meet the requirements. The ideal solution is distributed power supply, where each circuit board is powered by an independent power supply.
2. Features of Distributed Power Supply
Distributed power supply is the development direction of communication network power supply. Its main advantages include:
(1) good performance and high efficiency. On the one hand, because low voltage and high current DC output lines are reduced, low line loss will inevitably increase the system efficiency. On the other hand, the power supply required for each load is generated locally, and the load is close to the power supply, this reduces the impact of line Impedance On the adjustment performance and the impact of interference signals on the load. Therefore, the output voltage stability is better. In addition, the modular and standardized power supply design improves the stability and consistency of the power supply system.
(2) high reliability. On the one hand, the distributed power supply can be used as a backup power supply to provide power for uninterrupted power supply users, improving the reliability of the power grid. At the same time, due to the independence of the distributed power supply, it can be disconnected from the power grid, the distributed power supply is used to form an "island" for separate power supply. On the other hand, because each part of the power supply is relatively independent, redundancy technology or backup battery is more convenient, and local power supply is less powerful, heat Dissipation and security protection measures are also easy to implement. Some power supply failures do not affect the normal operation of the system.
(3) strong adaptability. As the entire power supply system is dispersed, various power supply options are flexible and easy to achieve optimal configuration. In addition, a slight modification to the same design scheme can be used in other systems. In particular, if you need to modify the scheme in the later stage of the system design, you do not have to re-design the entire system, making it easy to reconstruct the system and reduce unnecessary waste.
(4) Excellent electromagnetic compatibility. Because the power supply is scattered, the solution to suppress electromagnetic interference is easy to implement. For example, large current loads are isolated from small current loads, and large current fluctuations do not affect small current power supplies. In addition, the system control function can be used to enable the startup of several high-power loads at a time, reduce the impact of high current of the system.
(5) good scalability. The Modular Design of Distributed Power Supply facilitates the expansion of system functions.
(6) Good heat dissipation. Because the power of each power supply is small and the calorific value is low, and the calorific value of the power supply is evenly distributed in the chassis of the system, the heat dissipation is easier and the effect is better than that of the centralized power supply, the power supply is more reliable at low temperature. The higher the dispersion of the power supply, the smaller the impact scope of the power supply in the event of a fault, and the more reliable the system.
(7) The overall cost is low. The Distributed Power Supply removes the power room and battery room, so that the DC power supply equipment is closer to the communication load, which not only reduces the loss of DC power transmission, but also improves the system reliability, at the same time, the cost of installation, operation and maintenance is greatly reduced.
Although the distributed power system has many advantages, it still has the following shortcomings:
(1) The system design is complicated. The distributed system requires multi-level transformation. The voltage and current between the front and back stages are matched, and the average stream among the conversion modules at the same level must be carefully calculated. As the system transformation level increases, the O & M and management tasks of the power supply system increase.
(2) components and other materials are expensive. Because each conversion level is a complete conversion module, the material cost of the power supply system will inevitably increase. However, distributed power supply is much cheaper than centralized power supply. From the perspective of service costs, the centralized power supply is higher than the distributed power supply. If the centralized power supply fails, the entire power supply must be replaced, while the distributed power supply only needs to replace some modules. If the centralized power supply fails, the entire system will be shut down, however, distributed power supply is less likely to be shut down. In addition, the average MTBF of a centralized power supply is 1x105 h, while the power supply of a high-density module is generally 1x106 h. Obviously, the maintenance cost of the centralized power supply is high.
3 Distributed Power Supply Design
3.1 power supply requirements
Modern communication networks require wider bandwidth, higher data rates, stricter confidentiality measures, higher performance updates, and wider user and user business features, higher requirements are put forward for the power supply system, including: (1) continuous power supply to meet the requirements of Power Supply Reliability Indicators. (2) When no-load or full-load Load circuit surges or mains voltage and frequency fluctuations occur, the voltage value is within the range of tolerance. (3) ripple, that is, the AC components attached to the DC power supply, which meets the specifications and shall not exceed the prescribed limits. (4) Real-time Monitoring, with four remote functions: Remote Control, telemetry, remote control, and remote control. (5) cost-effectiveness, good scalability, and strong versatility. (6) AC-DC rectification module and DC-DC converter with high performance, high conversion efficiency, high power density, low price, easy to install and maintain.
3.2 Design Principles
In modern communication networks, distributed power supply has become the mainstream. In the power supply design, the following principles should be observed, minimize the power supply type. (2) In order to improve power supply efficiency and reduce power supply cost, the input and output voltage difference of the power conversion module should be minimized. (3) the modern communication network uses a large number of ASIC chips, while the voltage and current of the IC are pulse waveforms. Although the average power is not large, the instantaneous power value is considerable, A power supply without a power margin is likely to crash the entire digital system. Therefore, there must be a certain margin during the design, that is, the use of the reduction. (4) design the voltage regulator circuit based on various functional components in the modern communication network, and adopt a function-based Distributed Solution whenever possible. For example, the digital circuit, analog circuit, and high-power output circuit should adopt separate power supply methods to minimize the mutual influence between these power supplies. (5) Minimize the distance between the load and the power supply to reduce the cost of the power supply system and improve the anti-interference and reliability of the power supply system.
3.3 distributed power supply structure design
From a functional perspective, a complete modern communication network consists of a service network, a transmission network, and a support network. The service network includes the fixed telephone network, mobile communication network, FR network, lan ATM network, and Internet. The transmission network includes SDH and optical transmission network. The support network includes the signaling network, management network, and synchronization network.
Based on the functions of the modern communication network and the micro-network technology, a feasible design scheme is to divide the power supply system of the entire communication network into several distributed power supply units (equivalent to the micro-Network) by function ), that is, each service network, transmission network, or support network forms a distributed power supply unit, including Telephone Network Power Supply Unit, mobile network power supply unit, FR Network Power Supply Unit, lan power supply unit, ATM Network Power Supply Unit, Internet power supply unit, SDH power supply unit, optical transmission network power supply unit, signaling network power supply unit management Network power supply units and synchronous network power supply units, 2. When each power supply unit is connected to the grid normally, the grid can run independently when the main grid fails, thus improving the reliability of the system power supply. In addition, battery packs (BAT) can be replaced by other energy storage systems or devices.
In each power supply unit, first several small and medium power AC-DC high-frequency switch rectification module using N + 1 Redundancy parallel, 220VAC or 380 VAC into-48 VDC or 24VDC; it is then connected to one or two groups of small and medium capacity batteries to provide a unified, uninterrupted-48 VDC or 24 VDC, and then through the DC bus, power the DC-DC converter circuit on each circuit board in each frame of each rack, the DC-DC converter circuit converts-48 VDC or 24 VDC to the 12 VDC and/or 5 VDC and/or 3.3VDC and/or 2.5VDC and/or 1.8 VDC required by the circuit board.
The above is a distributed power supply solution based on the functions of modern communication networks, which can meet the power supply requirements of modern communication networks. However, the distribution breadth and depth of the solution are insufficient, and the granularity of the power supply units is too large. In the actual power supply design, you can also consider that each of the above power supply units can be further divided into several smaller-granularity power supply units according to the function. For example, the power supply unit of the fixed telephone network can be further divided into the power supply unit of the user equipment, the power supply unit of the relay equipment, the power supply unit of the switching network and the central control power supply unit. A smaller-granularity distributed power supply solution can also be divided by capacity. For example, the power supply units of your equipment can be further divided into multiple small-granularity power supply units by capacity.
Design of 3.4 DC-DC transform module
When distributed power supply is adopted, the DC-DC transform module becomes the key of the design. The DC-DC conversion module is designed for higher performance, higher conversion efficiency, higher power density and lower prices. Therefore, the most advanced topology and the most advanced soft switch (ZVS and ZCS) Synchronous rectification technology, core technology and MCU/DSP technology must be used. At the same time, because the communication devices in the modern communication network use a large number of large-scale chip, but also take into account the resulting low voltage, high current on the strict requirements of chip power supply, including low internal resistance, low ripple, soft start, anti-surge, anti-switch over-rush, support hot swapping, provide redundant backup, etc, stricter requirements also include upper/lower-Order Control and real-time monitoring.
Distributed power supply is the development direction of modern communication network communication equipment power supply. Aiming at the power supply requirements of modern communication networks and formulating power supply design principles, a distributed power supply structure is proposed to meet the power supply and power supply requirements of modern communication networks. The combination of Distributed Power Supply and micro-network technology is a solution to the new problems in the power supply of communication devices in the future.