Development of power factor correction (PFC) technology
Switching rectifiers generally adopt a two-stage conversion form. First, the AC input is converted to DC through the AC-DC rectifier and filter circuit, and then converted to the corresponding DC through the DC-DC link. Since the rectifier and filter circuit in the front stage are a combination of nonlinear components and energy storage components, from the grid side, the switching rectifier is equivalent to a capacitive load, which will cause serious distortion in the grid power supply, and the sinusoidal frequency will cause harmonic pollution when the single base is long. It will cause noise, malfunction, vibration, overheating and even burning accidents, increase the losses in the distribution system and transformers, increase the neutral current (harmonics), and seriously interfere with the normal operation of various wireless communications. In addition, the power factor on the grid side is generally 0.5 to 0.7, which brings additional burden to the grid, causes a lot of energy waste, and reduces the operating efficiency of power generation and transmission and transformation equipment.
In order to reduce the noise caused by harmonic currents at the input end of the AC-DC converter circuit and the harmonic "pollution" to the power grid, ensure the power quality of the power grid, improve the efficiency of the power supply of the power system to improve the reliability of power, and at the same time improve the power factor at the input end to achieve energy saving effects and advocate "green power supply", power electronics research institutes in various countries have begun to research ways to improve the power factor at the input end. Since the 1960s, two main types of solutions have been proposed: passive filters and active power factor correctors (APFCs). Passive filters are power frequency filter inductors connected in series between the rectifier circuit and the filter capacitor, or resonant filters connected on the AC side, and their main advantages are simplicity, low cost, and small EMI. Size, weight, and the difficulty of achieving a high power factor (usually below 0.9), the operating performance is related to the frequency, load changes, input voltage, etc. Active power factor correctors are a technology developed over the past 20 to 30 years that use a DC-DC closed-loop switching converter connected between the rectifier and the load. With values of 0.97 to 0.99 and even close to 1, the THD is small, it operates over a wide input voltage range and a wide frequency band, and the output voltage can be kept constant.
Applications of valve-regulated sealed lead-acid batteries
In traditional open-type batteries, water evaporates and decomposes at the end of charging, so distilled water needs to be frequently replenished. In addition, at the end of charging, when hydrogen and oxygen come out of the negative and positive plates, dilute sulfuric acid is taken out and acid mist is formed, which pollutes the environment and must be removed in a timely manner. This brings great burdens to maintenance personnel.
The positive and negative plates and electrolyte of valve-regulated sealed lead-acid batteries are the same as those of ordinary lead-acid batteries, but they have the following characteristics:
Unlike open-type batteries, which have a high degree of sealing and allow the electrolyte to flow freely, the electrolyte is absorbed into a gel-like (colloidal type) or high-porosity separator plate (liquid-lean type).
The electrode grid uses antimony-less or antimony-free lead alloys with low self-discharge.
The positive and negative plates are all surrounded by insulating plates, so the active components are not easily dropped off and have a long service life.
The good sealing property makes it difficult for moisture to evaporate, and the positive electrode absorption method is used to absorb oxygen by utilizing the surplus negative electrode capacity relative to the positive electrode capacity, suppressing gas generation. The amount of hydrogen generated is also small, so there is no need to add distilled water.
Since the valve-regulated sealed lead-acid battery has the above characteristics, the maintenance work of the battery by workers is greatly reduced, and it is called a "maintenance-free battery." And it is widely used in communication systems.
Centralized network monitoring of power supply
In the field of communication power supply monitoring, it is inevitable to manage communication power supply and communication equipment with advanced, centralized and automated maintenance management methods. The purpose of centralized monitoring is to remotely control, telemeter and telesignal distributed power supply and other equipment, monitor the operation status of equipment in real time, record and process relevant data, detect faults in time, and notify personnel to handle, so as to improve the reliability of power supply system.
The purpose of power and environment intelligent monitoring network is to monitor the operation status of system and equipment in real time, detect and handle faults, record and process relevant data. Power management is the key to the safe and reliable operation of communication network. Without a comprehensive power management system, power interruption or catastrophic accident may occur. Power and environment intelligent monitoring network is particularly important for DC power supply system with distributed power supply mode, because the distributed power supply system is divided into several small units, which requires more redundant rectifiers, battery packs and split air conditioners. Therefore, only through network monitoring can the advantages of high power supply reliability be reflected and the goal of maintenance management with few or no people can be achieved.
General requirements of communication equipment for power supply system
The general requirements of communication equipment for power supply system are: reliable, stable, small and efficient.
In order to ensure smooth communication, in addition to improving the reliability of communication equipment, the reliability of power supply system must also be improved. Usually, the power supply system needs to power many communication equipment, so when the power supply system fails, it has a great impact on communication. To ensure reliable power supply, in the DC power supply system, the rectifier and battery are connected in parallel to float charge. Switching rectifiers use multiple rectifier modules in parallel, so that when a module fails, it will not affect the power supply.
Various communication equipment requires stable power supply voltage and cannot exceed the allowable range of variation. If the power supply voltage is too high, the electronic components in the communication equipment will be damaged. If the power supply voltage is too low, the communication equipment cannot work normally. In addition, the pulsating noise in the DC power supply voltage must also be lower than the allowable value, otherwise, it will also seriously affect the communication quality.
With the rapid development of integrated circuits, it is moving towards miniaturization and integration. In order to adapt to the development of communication equipment, power supply devices must also be miniaturized and integrated. In addition, various mobile communication devices and communication equipment in aviation and aerospace devices require power supply devices to be small in size and light in weight. In order to reduce the size and weight of power supply devices, switching power supplies without industrial frequency transformers have been increasingly widely used.
As the capacity of communication equipment increases, the load of the power supply system continues to increase. In order to save energy, it is necessary to find ways to improve the efficiency of power supply devices. The main energy-saving measure is to use high-efficiency communication power supply equipment. In the past, most communication equipment used phase-controlled rectifiers, which had low efficiency (<70%) and large transformer losses. The efficiency of high-frequency switching power supplies can reach more than 90%, so the use of high-frequency switching power supplies can save energy.
