Research on protection and drive circuit of high frequency inverter power supply

1. Composition of high-frequency inverter communication power supply system

The high-frequency inverter communication power supply system generally includes a double-circuit 10 kV high-voltage system, a 10 kV/380 V low-voltage power distribution system, an oil-powered generator power supply system, a high-frequency switching power supply system (DC rectification and distribution system), a UPS system, a lightning protection and grounding system, a centralized monitoring system, etc. In the base station power supply system, the 10 kV high-voltage system is generally not included, and the local 220/380 V power supply is usually directly introduced, and the others are basically the same.

2. Main measures to improve the safety and reliability of high-frequency inverter communication power supply

According to the composition of the communication power supply system, although the safety and reliability of the communication system are already very high, it is not easy to ensure long-term uninterrupted power supply for communication equipment. We need to be down-to-earth and do a good job in various safety assurance work. The following describes how to improve the safety and reliability of each major equipment, thereby improving the safety and reliability of the entire mobile communication power supply system.

2.1 High and low pressure systems

(1) Establish a true 10 kV dual-circuit power supply system. To establish a true dual-circuit power supply system, the dual-circuit 10 kV power supply cannot be introduced from the same transformer, but the 10 kV high-voltage power supply should be introduced from different substations. This will provide a more reliable power supply. When one of the 10 kV lines stops working, the other 10 kV line can still supply power in time.

(2) Take backup measures at the bottleneck of power supply for key equipment. Transformers, power switches, fuses, and cables can serve as backup for each other. For example, there should be two circuit breakers for the rectifier and UPS, which can supply power independently. When the main power switch is damaged, the backup switch can be used to quickly supply power.

(3) Separate the three wires and change the down-line to the up-line. When laying cables, the AC power line, DC power line, and signal data line should be separated and not crossed. Because different cables have different withstand voltage levels, insulation and shielding levels, separation can effectively prevent fires and electromagnetic interference. Based on past experience, it has been found that the down-line cable laying method has many safety hazards and should be changed to the up-line method as much as possible.

2.2 Rectification equipment

In the field of communication power supply, high-frequency switching power supply has gradually replaced linear rectification and phase-controlled rectification equipment. Compared with phase-controlled rectifier, high-frequency switching rectifier has the advantages of small size, low noise, high efficiency, high power factor, good dynamic performance, high reliability and low pollution to the power grid. Communication DC power supply generally adopts the positive grounding method, and the voltage is usually -48V.

(1) The positive pole of the rectifier must be reliably grounded, and the DC grounding point must be at least 5 m away from the lightning protection grounding grid to avoid interference from lightning.

(2) Prevent the rectifier monitoring unit from controlling the rectifier module to exit service. If the rectifier exits service, the rectifier output cannot be rectified and can only be maintained by the battery. Once the rectifier exits service, the battery will be discharged quickly, causing the communication network to be paralyzed. The main reason is that there is a problem with the control unit. The control unit often shuts down the rectifier output for protection due to high-voltage shutdown, lightning interference, software/hardware failure, etc., and can only be maintained by a limited battery for 0.5 to 2 hours. After the battery is discharged, if the rectifier still cannot output normally, the communication network is generally paralyzed. The emergency measure is to quickly arrive at the scene, cut off the control line or power line of the control unit, and restart the rectifier modules one by one; then quickly repair the monitoring unit to prevent the rectifier module from outputting abnormally and causing damage to the communication equipment or battery.

(3) Each high-frequency switching power supply system should be equipped with a certain number of switching power supply modules to prevent high voltage or strong electromagnetic intrusion and burning of the modules in use.

(4) The colors of DC cables should be uniform. Usually, the DC positive pole uses a red RVVZ cable, the negative pole uses a blue RVVZ cable, and the protective ground wire uses the internationally accepted yellow-green two-color cable. These seem simple, but some computer rooms do not use uniform colors, which can easily cause major accidents when the equipment is powered on or off.

(5) Avoid using AC power for equipment that can be powered by DC. The safety and reliability of DC power is much better than that of AC power. In addition, with the development of 3G and NGN, the level of equipment refinement is getting higher and higher, and the requirements for electromagnetic interference are also getting higher and higher. Therefore, when purchasing or designing equipment, DC power supply equipment should be used as much as possible.

(6) Adopt a new power supply method, changing centralized placement and centralized power supply to centralized placement and decentralized power supply, that is, separate the power supply for basic transmission, switches, high-level networks or more important networks from general business networks. After separation, the power supply system is relatively small, which is easier to ensure quality, improve safety and reliability, reduce maintenance workload, and prevent global paralysis.

2.3 Battery

(1) The battery should be mainly valve-regulated sealed lead-acid battery. Its main advantages are: almost no acid spillage during use, almost no pollution and corrosion to the environment and equipment, no need to set up a separate battery room, less maintenance workload, can be placed layer by layer, and occupy less space. Its main disadvantages are: poor uniformity and consistency of battery voltage; strict requirements on ambient temperature and floating charge voltage for service life; some manufacturers' batteries are not technically perfect, with problems such as backward batteries, leakage, rapid corrosion of plates, and bulging; large capacity and long life use still need to be proven in practice.

(2) Batteries are the lifeline of emergency communication power supply and are also an important factor leading to system paralysis, and should be given special attention.

(3) It is necessary to detect lagging batteries in time. Often, the voltage drop of one or two single cells will cause the voltage of the entire system to drop rapidly, resulting in communication interruption.

(4) Pay attention to the floating charge parameters: the general battery charging voltage is 2.23 V/cell (25°C) (53.52 V/24PCS); the maximum charging current is ≤0.25C10; the temperature compensation coefficient is -4 mV/℃·cell (based on 25℃).

(5) Pay attention to the balanced charging parameters: the charging voltage is 2.35 V/cell (25°C) (56.4 V/24PCS); the maximum charging current is ≤0.25 C10; the temperature compensation coefficient is -4 mV/°C·cell (based on 25°C).

(6) Equalizing charging may be considered when one of the following situations occurs: the discharge capacity exceeds the rated capacity by more than 20%; the battery has been left unused for more than 3 months; the battery has been continuously float charged for 3 to 6 months, or a battery with lagging voltage appears in the battery pack.

(7) The main factors that affect the battery life are: ambient temperature, discharge times (frequency), discharge depth and charging voltage (float charge current), etc. Attention must be paid to overcoming the influence of these factors in order to effectively extend the battery life.

(8) The battery must be replaced in a timely manner according to the specifications. The criterion for battery replacement: If the battery voltage is lower than 1.8 V/cell before discharging 80% of its rated capacity (compared with the capacity of the corresponding discharge rate such as C10 and other parameters), it should be considered for replacement.

(9) In order to prevent flood disasters, the power supply room in some areas should not be placed on the first floor or in the basement. This requires that the load-bearing capacity of the floor must be considered when installing the valve-regulated sealed lead-acid battery and load-bearing treatment must be performed.

2.4 UPS equipment

(1) Loads powered by UPS should be analyzed regularly. For equipment that can be powered by DC, it is recommended not to use AC.

(2) UPS system failures often occur at the moment of switching, mainly due to the existence of induced electromotive force. Therefore, the reliability of switching must be ensured and emergency measures should be taken when necessary.

(3) Be aware of the high voltage danger of the UPS battery pack, which can reach over 400 V.

(4) Outdated single cells should be discovered in time.

2.5 Generator

(1) To prevent the starting battery from failing, the starting battery should be checked and maintained regularly, and emergency starting batteries and chargers should be prepared when necessary.

(2) Emergency diesel should be kept in reserve to prevent oil shortages and unexpected disasters.

(3) A backup emergency oil engine interface is required to avoid generator failure or switching failure.

(4) The engine room should be well-lit and well-ventilated, and should be kept clean and free of debris. Necessary noise reduction measures should also be taken in accordance with environmental protection requirements.

(5) The indoor temperature of the engine should not be lower than 5°C. If the room temperature is too low in winter (below 0°C), antifreeze should be added to the water tank of the engine. If antifreeze is not added, the cooling water should be drained when the engine is stopped; at the same time, replace it with -10 diesel.

(6) Tools, parts and other items placed on and near the unit should be cleaned before starting the unit to avoid unexpected dangers during operation of the unit.

(7) When the ambient temperature is below 5°C, the unit should be heated.

(8) Power supply can only be provided after the voltage and frequency (speed) meet the specified requirements and operate stably.

(9) When the unit encounters faults such as low oil pressure, high water temperature, high speed, abnormal voltage, etc., it should be able to shut down automatically or manually.

(10) When the speed is too high (running wild) or other situations may cause personal accident or equipment danger, the oil line and air intake line should be cut off immediately and the machine should be shut down immediately.

2.6 Lightning protection grounding

Lightning overvoltage can produce direct lightning, induced lightning, line waves and ground potential counter-attacks, which can cause serious consequences such as electromagnetic pollution, electromagnetic interference, equipment damage and system collapse, so various lightning protection and grounding measures must be taken.

(1)Multi-level lightning protection measures should be considered in an AC power supply system.

(2) A surge suppressor and lightning protection switch should be installed on the AC input side of the base station.

(3) The rectifiers and controllers of the DC power supply system should be equipped with lightning arresters; the centralized monitoring system equipment itself should also use lightning protection devices.

(4) Measure the ground resistance value (non-wetland) regularly and keep records.

(5) For stations with ground wire systems that have been in use for more than 20 years, even if the grounding resistance value meets the requirements, a new grounding device should be added. The resistance value of the newly added grounding device should meet the requirements and be connected to the original grounding system. www.dqjsw.com.cn Electrical Automation Technology Network

(6) For stations struck by lightning, the cause should be promptly identified and appropriate measures should be taken to resolve the problem.

(7) The protective ground wire should be a plastic-insulated copper core conductor with alternating yellow and green colors.

(8) It is strictly prohibited to make joints on the protective ground wire, and it is strictly prohibited to install fuses or switches.

(9) The grounding terminal must be treated with anti-corrosion and anti-rust treatment, and its connection should be firm and reliable.

(10) The distance between the communication equipment and the user grounding bar should not exceed 30 m, and the shorter the better. If it exceeds 30 m, the user should be required to re-install the grounding bar nearby.

2.7 Centralized Monitoring

(1) Centralized monitoring is the "eye" that observes many stations. It should have the ability to quickly repair problems, and the system software should have strong resistance to misoperation.

(2) The monitoring system should have a self-diagnosis function to keep track of the operating conditions of each part of the system at all times and be able to respond to faults in a timely manner.

(3) Non-dedicated line method: the number resources used to dial into the monitoring host are not open to the public.

(4) The computer system used by the monitoring system should have system protection such as anti-virus and network attack.

(5) Set different passwords according to different permissions.

3. Several tips to improve the safety and reliability of communication power supply

3.1 “Zero current + hair dryer” power cutover insurance method

In daily maintenance and management, communication power cutover often occurs. Sometimes, due to label or other errors, the wrong power is cut off when the equipment is powered off, causing a man-made power outage. In this regard, the "zero current + hair dryer" power cutover insurance method can be used to solve this problem.

First, test the "zero current". Turn off the device to be powered off, and use a clamp-type ammeter to measure the current at the switch of the distribution cabinet to see if it is approximately "0". If it is not "0", it should be suspected that the switch may not be the switch of the device.

Secondly, use the "hair dryer measurement method". After testing the "zero current" on the device that is about to be powered off, connect the hair dryer again. While doing the on/off experiment of the hair dryer, use a clamp-type ammeter to measure the current change at the switch on the device side: when the hair dryer is turned on, the current increases by about 10 A (taking an AC 2200 W hair dryer as an example); when the hair dryer is turned off, the current drops back to about OA. Then, follow other cutover procedures (Note: if cutting over DC equipment, use a spare DC hair dryer).

This method has a higher insurance factor.

3.2 Water leakage prevention method

(1) "Waterproof dam" water leakage prevention method. Although this method is simple, it is relatively practical and safe. That is, in areas where water supply is relatively concentrated, such as special air conditioners, a circle of about 10 cm high waterproof dam is built, and multiple filtering floor drains are installed inside.

(2) Adding a "sheath" to the waterway. Because there is a high water pressure in the water pipe, once the valve, interface or pipe sprays water, it will rush out of the "waterproof dam". If it sprays towards the equipment, it will cause an accident. Therefore, a "sheath" should be added to almost all waterways to prevent water leakage and splashing. Wrapping the sheath in the waterway can make the leaking water flow into the waterproof dam, avoiding the expansion of the accident.

3.3 Cable Labeling Standards

The communication power supply and transmission, data, and switching professions involve many cables and switches. If there is no unified cable labeling standard, it is easy to confuse the color, format, content, etc. and cause power outage accidents. For this reason, we have formulated cable labeling standards.

For example, the network logic name of Huawei's equipment constructed by Huarui Company is SCP 7, and the power supply of the equipment is drawn from the No. 2 AC distribution cabinet/No. 6 switch in the 3rd row of the computer room. The equipment is located in the 4th column of the A row in the computer room (this power supply is the second power supply of the equipment). www.dqjsw.com.cn

The cable label format is as follows:

Huarui-Huawei-SCP7

AC2/3.6-A4/2

3.4 Surveillance Data Sharing Law

At present, many bureaus (stations) have installed centralized monitoring systems and arranged on-duty personnel for 24-hour monitoring. However, the powerful data reporting function of the monitoring system in some places has not been effectively utilized, and some places only do some simple notifications, observations, operations and simple duty records every day.

The author believes that a monitoring data analysis and sharing mechanism should be established, more equipment performance analysis should be done, and the content of duty records should be reduced. First, the duty personnel should summarize the important data or screenshots of each major bureau (station) on that day; second, the summarized data should be sent to the mailbox before going to work every morning, so that the team leaders, directors or managers in charge can jointly analyze the data, jointly find or deal with equipment hazards, and supervise the maintenance level of each team.

4. Summary

The high-frequency inverter power supply specialty is responsible for many equipments and has great responsibilities, and is receiving more and more attention from leaders and the industry. Therefore, further improving the safety and reliability of communication power supply, improving the ability of early warning, pre-inspection and pre-repair, and reducing the failure rate are the focus and direction of future work.