Discussion on communication power supply technology
Communication power supply consists of DC power supply system, AC power supply system, grounding system, monitoring system and lightning protection system. The security and reliability of power supply are important conditions to ensure the normal operation of communication system. Battery pack, high-frequency switching power supply and UPS are important components of communication power supply.
Battery pack; Battery pack; High frequency switching power supply; UPS
China Library Classification Number: TN86 Document Identification Number: Part A Number:1671-7597 (2013)18-0035-02.
1 battery pack
1. 1 Structure and working principle of battery
Battery usually refers to lead-acid battery, which is a kind of battery and belongs to secondary battery. Its working principle is: when charging, external electric energy is used to regenerate the internal active substances, and the electric energy is stored in the form of chemical energy, which is converted into electric energy again when it needs to be discharged.
1. 1. 1 battery charging
When the battery is charged, hydrogen will be released from the negative electrode and oxygen will be released from the positive electrode. The precipitated oxygen reaches the negative electrode and reacts with the negative electrode as follows. When the charge of the anode reaches 70%, the anode begins to evolve oxygen.
Charging process 2PbSO4+2H2O=Pb+PbO2+2H2SO4
1. 1.2 battery discharge
As an emergency backup energy source, the value and performance of the battery are realized by discharging. Chemical reaction during battery discharge;
Discharge process Pb+PbO2+2H2SO4=2PbSO4+2H2O.
1.2 battery maintenance
During maintenance, always check the appearance and pole of the battery. If it is found that the battery tank and cover are damaged, electrolyte leaks from the joint, and acid creeps around the pole, the battery should be replaced in time. In the first five years after the 2 V battery is put into operation, and in the first two years after the 12 V battery is put into operation, an inspection and discharge test should be conducted once a year with actual load to release 30%-40% of the nominal capacity. From the sixth year after the 2 V battery was put into operation, and from the third year after the 12 V battery was put into operation, the capacity test should be conducted once a year.
2 high frequency switching power supply
2. 1 principle of switching rectifier monitoring unit
Single chip microcomputer circuit of switching rectifier monitoring unit collects power supply parameters in real time. The open-phase detection and grid voltage detection circuit performs open-phase detection and grid voltage detection on three-phase AC input, and the detected open-phase signal and grid voltage signal are sent to the single chip microcomputer circuit for processing. Single-chip microcomputer accepts keyboard instructions and displays real-time data and control menu of power supply with LCD. The auxiliary power supply provides all kinds of power needed by the internal control circuit of the switching rectifier. The temperature detection circuit detects the temperature of the main radiator and sends it to the single chip microcomputer system. The single chip microcomputer system controls the working state of the fan through the fan control circuit according to the temperature of the main radiator.
2.2 the concept of load sharing
A high-frequency switching power supply system needs at least two high-frequency switching power supply modules to work in parallel, and a large-scale system even needs dozens of power supply modules to work in parallel, which requires that the power supply modules working in parallel can share the load current equally, that is, share the load current equally. At present, all high-frequency switching power supplies adopt PWM current sharing mode, which is a digital current sharing mode. It has the advantages of high current sharing accuracy, good dynamic response characteristics, good anti-interference and many module controls.
2.3 the principle of load sharing
US is the system sampling voltage and Ur is the system reference voltage. After comparison, an error voltage UD is generated. Compared with triangular wave, UD generates pulse width modulated square wave signal, and its wave width is controlled by UD. This square wave signal is sent to each rectifier module, which is an optocoupler, isolated, shaped, amplified and compared with the module current. Then the comparison signal is superimposed with the preset reference voltage value in the module to adjust the output current of the module and change the output voltage of the module to make the output current of each module equal.
3 UPS power supply
Uninterruptible power supply system (UPS) is an important power supply equipment, which can continuously and stably supply power to loads. Broadly speaking, UPS includes AC uninterruptible power supply system and DC uninterruptible power supply system. For a long time, people used to call the AC uninterruptible power supply system UPS.
3. 1 uninterruptible power supply principle
The input of AC main power supply is converted from rectifier to DC power supply. The inverter converts this DC power supply from the battery or DC power supply into alternating current and provides it to the load. When the commercial power is interrupted, the battery provides backup power to the load through the inverter. The commercial power supply can also supply power to the load through static bypass. When the UPS needs maintenance, the load can be continuously switched to the maintenance bypass power supply.
3.2 Characteristics of Uninterruptible Power Supply System
The hardware and software of parallel UPS are completely consistent with the stand-alone mode. The configuration of machine system can be realized by parameter setting software. The parameter setting requirements of each single machine in the machine system are consistent. The machine control cable forms a closed-loop connection, which provides reliability and redundancy for the system. The dual-bus control cable is connected between any two UPS stand-alone machines with two buses. Intelligent computer logic provides users with maximum flexibility. For example, you can shut down or start up the machines in the machine system in any order. Seamless switching between normal mode and bypass mode can be realized, and it can be automatically restored. That is, after the overload is eliminated, the system will automatically return to the original operation mode. You can query the total load of the machine system through the LCD of each stand-alone machine.
3.3 UPS single machine parallel requirements
A UPS system composed of several single machines in parallel is equivalent to a large UPS system. But it has higher system reliability. In order to ensure the same use of each stand-alone machine and meet the relevant wiring regulations, the following requirements shall be met.
1) All stand-alone machines must have the same capacity and be connected in parallel to the same bypass power supply.
2) The bypass power supply and the rectification input power supply must be connected to the same neutral input terminal.
3) If the leakage detector (RCD) is installed, it must be correctly set and installed in front of the neutral input terminal. Or the equipment must monitor the protective grounding current of the system.
4) The outputs of all UPS stand-alone machines are connected to the same output bus.
3.4 UPS special working mode
3.4. 1 bypass mode
In normal mode, the static switch will switch the load from the inverter side to the bypass power supply side in case of inverter failure, inverter overload or manual shutdown. In this case, the inverter phase is not synchronized with the bypass phase, and the static switch switches the load from the inverter output to the bypass power output, but the load power supply will be interrupted for a short time. This function can avoid the large circulation caused by the parallel connection of asynchronous AC power supplies. The interruption time of load power supply can be set, usually less than 3/4 cycle. For example, when the frequency is 50 Hz, the interruption time is less than15 ms; When the frequency is 60 Hz, the interruption time is less than12.5 ms.
Parallel redundancy mode
In order to improve the system capacity or reliability, or both, multiple UPS stand-alone machines can be directly connected in parallel, and the control logic in each UPS stand-alone machine ensures that all stand-alone machines can automatically share the load. The machine system can be composed of four single machines in parallel at most.
Frequency converter mode
UPS can be set to inverter mode. Provide a stable output frequency of 50 Hz or 60 Hz. The input frequency range is 40 Hz -70 Hz. In this mode, the static bypass is invalid and the battery is optional. Whether to choose a battery depends on whether it needs to run in battery mode.
Automatic boot mode
UPS provides automatic power-on function, that is, the inverter will be turned off after the battery is discharged to the termination voltage for a long time. If the power is restored, UPS will start automatically after a delay. This function and automatic start delay time can be set by the debugging engineer.
Battery mode
The operation mode in which the battery provides standby power to the load via the inverter through the battery boosting circuit is the battery mode. When the main power supply fails, the system will automatically switch to battery mode. The load power supply will not be interrupted. After that, when the commercial power is restored, the system automatically switches back to the normal mode without any manual intervention, and the load power supply is not interrupted.
3.5 UPS advanced functions
UPS provides battery maintenance test function. The battery will automatically discharge at regular intervals, with each discharge amount being 20% of the rated capacity of the battery, and the actual load must exceed 20% of the rated capacity of UPS. If it is less than 20%, automatic discharge maintenance cannot be carried out. 30 -360 days automatic discharge interval can be set by yourself. The battery self-test can be prohibited.
In on-line UPS, whether the commercial power is normal or not, it is powered by the inverter, so the output of UPS will not be interrupted when the commercial power fails. In addition, because online UPS is equipped with input EMC filter and output filter, it can greatly attenuate the interference from the power grid.
refer to
[1] Sun Fawen. Discussion on the selection of UPS in power supply system of chemical production [J]. Medium Nitrogen Fertilizer, 2005.
[2] Kim. Design and research of series-parallel online compensation UPS based on DPS [D]. Hunan University, 2004.
Zeng Jianhua. Achieve the best performance of valve-regulated sealed lead-acid battery [J]. Battery, 2006.
[4] Liu Nanping. Communication power supply [M]. Xidian university Publishing House, 2005.
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