Detailed explanation of the working principle of UPS power supply

UPS power supply, also known as uninterruptible power supply, is an important external device that can provide continuous, stable and uninterrupted power supply. As the name suggests, UPS power supply is a machine that can maintain power supply for a period of time when the mains power supply stops, so that people have time to save and then calmly shut down the machine.

UPS power supplies are divided into three categories according to their working principles: backup type, online type and online interactive type. UPS power supplies are now widely used in: industry, communications, national defense, hospitals, radio and television, computer business terminals, network servers, network equipment, data storage equipment and other fields.

Working principle of UPS power supply

(1) Online

The operating mode of an online UPS is "the mains power and the power-consuming equipment are isolated, and the mains power will not directly supply the power-consuming equipment." Instead, it is converted into direct current when it reaches the UPS, and then divided into two paths, one for charging the battery, and the other for converting back to alternating current to supply power to the power-consuming equipment. When the mains power supply quality is unstable or there is a power outage, the battery switches from charging to supplying power, and does not switch back to charging until the mains power returns to normal. "UPS is fully involved in the entire process of power consumption." Its advantage is that the output waveform is a sine wave like the mains power, and it is pure and noise-free, and is not affected by the instability of the mains power. It can supply power to "inductive loads", such as electric fans. As long as the UPS output power is sufficient, it can supply power to any equipment that uses the mains power.

The UPS power supply keeps its inverter in working state all the time, converts external AC power into DC power through the circuit, and then converts DC power into high-quality sinusoidal AC power through a high-quality inverter to output to the computer. The main function of the online UPS under power supply conditions is to stabilize the voltage and prevent radio interference; when there is a power outage, the backup DC power supply (battery pack) is used to power the inverter. Since the inverter is always working, there is no problem of switching time, which is suitable for occasions with strict requirements on power supply. A major advantage of the online UPS power supply is that the power supply lasts for a long time, generally for several hours, and sometimes as long as more than ten hours. Its main function is to allow you to work as usual in the case of a power outage. Obviously, due to its special function, the price is obviously much more expensive. This online UPS is more suitable for industries such as computers, transportation, banking, securities, communications, medical care, and industrial control, because computers in these fields generally do not allow power outages.

(2) Backup

The backup type is also called an off-line uninterruptible power supply (Off-Line UPS). It is only a "backup" UPS. The AC power directly supplies power to the power-consuming equipment and also charges the battery (Normal Mode). Once the AC power supply quality is unstable or there is a power outage, the AC circuit will be automatically cut off, and the DC power of the battery will be converted into AC power to take over the power supply task (Battery Mode) until the AC power returns to normal. "UPS will only intervene to supply power when the AC power is out." However, the AC power converted from DC is a square wave, which is limited to supplying power to capacitive loads, such as computers and monitors.

Normally, the battery is in the charging state. When the power is off, the inverter switches to the working state urgently, converting the DC power provided by the battery into a stable AC output. Therefore, the backup UPS is also called an offline UPS. The advantages of the backup UPS power supply are: high operating efficiency, low noise, and relatively cheap price. It is mainly suitable for occasions where the mains power fluctuation is not large and the power supply quality is not required. It is more suitable for home use. However, this UPS has a switching time problem, so it is not suitable for use in critical places where power supply cannot be interrupted. However, in fact, this switching time is very short, generally between 2 and 10 milliseconds, and the computer's own switching power supply should be able to maintain about 10 milliseconds when the power is off, so personal computer systems generally do not have problems due to this switching time. The backup UPS can generally only provide power for a few minutes to tens of minutes, mainly to give you time to back up data and finish the work at hand as soon as possible, and its price is also relatively low. For computer applications that are not too critical, such as individual home users, a low-power backup UPS can be equipped.

(3) Online staggered

The online interleaved UPS is also called the online interactive UPS or the line-interactive UPS. Its basic operation is the same as the offline UPS. The difference is that the online interleaved UPS does not intervene in the power supply throughout the process like the online UPS, but it monitors the power supply status of the AC power at all times. It has its own boost and reduce voltage compensation circuits. When the power supply status of the AC power is not ideal, it will make immediate corrections, reduce unnecessary "Battery Mode" switching, and extend battery life.

[page]This is an intelligent UPS power supply. The so-called online interactive UPS means that when the input mains power is normal, the UPS inverter is in reverse working (i.e., rectifier working state) to charge the battery pack; when the mains power is abnormal, the inverter immediately switches to the inverter working state to convert the battery pack power into AC output, so the online interactive UPS also has conversion time. Compared with the backup UPS, the online interactive UPS power supply has stronger protection function, the inverter output voltage waveform is better, generally a sine wave, and its biggest advantage is that it has strong software functions, which can easily access the Internet for remote control and intelligent management of UPS. It can automatically detect whether the external input voltage is within the normal range. If there is a deviation, the voltage can be stepped up or down by the voltage stabilizing circuit to provide a relatively stable sine wave output voltage. Moreover, it can communicate with the computer through a data interface (such as RS-232 serial port). Through the monitoring software, users can directly monitor the power supply and UPS status from the computer screen, simplifying and facilitating management work, and improving the reliability of the computer system. This type of UPS combines the advantages of high efficiency of backup UPS and high power supply quality of online UPS, but its frequency stabilization characteristics are not very ideal and is not suitable for long-delay UPS power supply.

With the expansion of computer network structure, UPS used in the network is no longer just a simple power supply device, but gradually becomes the power management center of the entire network. UPS has developed from the initial simple uninterrupted power supply to today's intelligent and multifunctional. The new UPS itself integrates a variety of new technologies. UPS is not only a tool for providing uninterrupted power supply, but also when the equipment as the load is unattended, when the mains fails, UPS can shut down in accordance with the pre-agreed sequence, and can even automatically send a page or E-mail to the manager. Modern UPS works with the software on the server, and can also realize event recording, fault alarm, UPS parameter automatic test analysis, adjustment and other functions, providing a complete power management solution. Some UPS can even monitor the ambient temperature, humidity and smoke.

The intelligence of UPS is also reflected in the enhancement of UPS's energy-saving function, the so-called "green UPS". "Green UPS" can reduce the amount of electricity used by the PC system, which not only reduces costs but also protects the environment. For example, when "green UPS" detects that the printer has been idle for a long time, it will turn off the power of the printer. When a print queue request appears, UPS can immediately restore power to the printer. With the emergence of "green UPS", it provides an ideal solution for energy saving.