Introduction to UPS and its working principle
UPS is the abbreviation of English Uninterruptible Power Supply, which means "uninterruptible power supply". It is an energy storage device (commonly Battery), a constant voltage and constant frequency uninterruptible power supply with an inverter as the main component. It can solve the existing power outages, low voltage, high voltage, surge, noise and other phenomena, making the computer system run more efficiently. Safe and reliable. Now it has been widely used in computer, transportation, banking, securities, communications, medical, industrial control and other industries, and is rapidly entering the home.
Now, let us briefly understand the working principle of UPS.
When we do not use UPS, PCs, printers and other terminal equipment are directly connected to the mains power. With UPS, PCs, printers and other terminal equipment are connected to the UPS for use. The UPS is then connected to the mains power. When the mains input is normal, the UPS stabilizes the mains voltage and supplies it to the terminal equipment (compared to UPS, we call these terminal equipment loads). At this time, the UPS is an AC mains voltage regulator. At the same time, it also charges its own built-in battery; when the mains power is interrupted (such as a power outage), the UPS immediately uses the power of the built-in battery to continue to supply 220V AC power to the load through inverter conversion, so that the load can maintain normal operation and protect the load. Software and hardware systems are not damaged.
2. The impact of mains power on household PCs and their terminal equipment
If our PCs, computer networks and other equipment do not use UPS, what will be the impact? Many people have a common misconception that the mains power we use is continuous and constant except for occasional power outages. Not really. As a public power grid, the mains power system is connected to thousands of various loads. Some of the larger inductive, capacitive, switching power supply and other loads not only obtain electric energy from the power grid, but also in turn The power grid itself has an impact, deteriorating the power supply quality of the power grid or local power grids, causing mains voltage waveform distortion or frequency drift. In addition, unexpected natural and man-made accidents, such as lightning strikes, open circuits or short circuits in the power transmission and transformation system, incorrect plugging and unplugging of power plugs, etc., will endanger the normal supply of power and thus affect the normal operation of the load. In particular, it needs to be pointed out that PCs, network equipment, communication systems, medical equipment, etc. are all very sophisticated electronic equipment, and their impact is particularly prominent.
For PCs, both the monitor and the host require normal power supply. Memory, in particular, has higher power requirements. It is a storage device that relies on electrical energy and requires constant refreshing actions to maintain stored content. Once the power is cut off, the saved content will disappear immediately. If there is an abnormal power outage and the information in the memory is not saved to a storage device such as a hard disk, the information will be completely lost or incomplete and lose its value, thus wasting a lot of work energy and time; and like UNIX, Linux If such an operating system (many computer enthusiasts use this operating system now) is shut down abnormally, the system information in the memory will not be written back to the hard disk, which may cause the system to crash and make it impossible to start again; in addition, the computer Although the hard disk uses magnetic storage media and will not lose information due to power outages, a sudden power failure will damage the physical head of the hard disk that is performing read and write work, or the system file will cause file allocation when maintaining the file system. table errors, resulting in bad sectors on the hard disk. In severe cases, it may even cause the entire hard disk to be scrapped. In addition, most current operating systems can set up virtual memory. Due to a sudden power outage, the system has no time to cancel the virtual memory, causing the hard disk to be damaged. The "information fragments" in the computer not only waste hard disk storage space, but also cause the machine to run slowly; the computer power supply is a rectified power supply, and excessive voltage may cause the rectifier to burn out. Interferences such as voltage spikes, transient overvoltages, and power supply noise may enter the motherboard through the rectifier, affecting the normal operation of the machine, or even burning the host circuit.
Under normal circumstances, the standard sine wave (220V, 50Hz) is an ideal state, but in actual situations, according to tests by power experts, it often occurs in the power grid and causes interference or damage to computers or precision instruments. Damage situations mainly include the following: surges, high-voltage spikes, transient overvoltage, voltage sags, wire noise, frequency drift, continuous low voltage, mains interruption, etc.
1. Power Surges: Refers to the effective value of the output voltage being 110% higher than the rated value and lasting for one or several cycles. Surges are mainly due to the high voltage generated by the sudden unloading of the power grid when large electrical equipment connected to the power grid is shut down (such as when a common household air conditioner is turned off) (we all have this personal experience: from 6:00 to 9 pm: The time period around 00:00 is the peak period of electricity consumption. The mains voltage is generally low, and the lighting in the home is relatively dim. After the peak period of electricity consumption, for example, around 10:00 in the evening, you will find that the lighting in the home is dim. Suddenly flashes and lights up a lot. This is the most common power surge phenomenon we see in our daily lives).
2. High Voltage Spikes: refers to a voltage with a peak value of 6000v and a duration from one ten thousandth of a second to one half period (10ms). This is mainly caused by lightning strikes, arc discharges, static discharges or switching operations of large electrical equipment.
3. Transient overvoltage (Switching Transients): refers to a pulse voltage with a peak voltage as high as 20,000V but a duration ranging from one millionth to one thousandth of a second. The main causes and possible damage are similar to high-voltage spikes, but the solutions are different.
4. Voltage sags (Power Sags): refers to a low-voltage state in which the effective value of the mains voltage is between 80% and 85% of the rated value, and lasts for one to several cycles. Turning on large equipment, starting large motors, or plugging in large power transformers can cause this problem.
5. Electrical Line Noise: refers to radio frequency interference (RFI), electromagnetic interference (EFI) and other various high-frequency interferences. The operation of the motor, the action of the relay, the work of the motor controller, broadcast emissions, microwave radiation, and electrical storms will all cause line noise interference.
6. Frequency Variation: refers to the change in the mains frequency exceeding 3Hz. This is mainly caused by the unstable operation of emergency generators or by power supplies with unstable frequency.
7. Continuous low voltage (Brownout): refers to the effective value of the mains voltage being lower than the rated value and lasting for a long time. Causes include: large equipment startups and applications, main power line switching, starting large motors, and line overloading (a problem found in many areas of our country).
8. Power Fail: This is the power outage we usually encounter. The causes include tripping of the circuit breaker on the line, interruption of the mains supply, and grid failure.
3. Classification of UPS
UPS has developed from a rotating generator in the 1960s to today's intelligent static fully electronic circuit, and it continues to develop. At present, UPS generally refers to static UPS, which can be divided into three categories: backup type, online interactive type and online type according to its working method.
1. Backup UPS: When the mains power is normal, the mains power is directly supplied to the load. When the mains power exceeds its working range or there is a power outage, it switches to the battery inverter power supply through the transfer switch. Its characteristics are: simple structure, small size, low cost, but the input voltage range is narrow, the output voltage stability accuracy is poor, there is switching time, and the output waveform is generally a square wave.
The schematic diagram is as follows:
2. Online interactive UPS: When the mains power is normal, the mains power is directly supplied to the load. When the mains power is low or high, the voltage is stabilized through the UPS internal voltage stabilizing circuit. Output, when the mains power is abnormal or has a power outage, it is converted to battery inverter power supply through the transfer switch. Its characteristics are: a wide input voltage range, low noise, small size, etc., but there is also a switching time. However, compared with general backup UPS, this model has stronger protection function and the inverter output voltage waveform is smaller. Okay, generally a sine wave. The schematic diagram is as follows:
3. When the mains power is normal, the online UPS rectifies the mains power to provide DC voltage for the inverter to work. The inverter provides AC power to the load. When the mains power is abnormal, , the inverter is powered by the battery, and the inverter is always working to ensure uninterrupted output. Its characteristics are that it has an extremely wide input voltage range, no switching time and high output voltage stability accuracy. It is especially suitable for occasions with high power supply requirements, but the cost is high. At present, UPS with power greater than 3KVA are almost all online UPS. The schematic diagram is as follows:
According to the output capacity, UPS is divided into small capacity below 3KVA, small and medium capacity 3KVA~10KVA, and medium and large capacity above 10KVA.
UPS can be divided into three categories according to the input/output mode: single-phase input/single-phase output (referred to as single-in and single-out), three-phase input/single-phase output (referred to as three-in and single-out), three-phase Phase input/three-phase output (referred to as three in and three out).
For users, three-phase power supply makes it easy to distribute mains power and load power. Each phase bears part of the load current. Therefore, medium and high-power UPS mostly use three-phase input/single-phase output. Or three-phase input/three-phase output power supply mode.
Backup UPS is mainly used to provide power protection for a single PC. It has the characteristics of small size, low price and simple operation. It is very suitable for home use. Therefore, when you buy a UPS for your home computer , please choose the backup type.
Online UPS can solve almost all common power problems. When there is mains power, its function is to stabilize voltage and prevent power fluctuation interference. Because its functions are more complete, its cost also increases with its performance. And rising, the price is much more expensive than backup UPS. Online UPS is mainly used for some computer equipment, medical equipment, etc. that have very strict power requirements. It is generally used in series with multiple external batteries to extend the power supply time, and is mostly configured for units.
Intelligent UPS is a major development trend of UPS today. With the application of UPS in network systems, network managers emphasize that the entire network system is the object of protection, hoping that the entire network system will be protected when the power supply system fails. It is still possible to continue working without interruption. Therefore, it is a new trend of UPS to configure microprocessor inside UPS to make it intelligent. The combination of internal hardware and software of UPS greatly improves the function of UPS and can monitor the operation status of UPS, such as: UPS output voltage frequency, grid voltage frequency, battery status and fault records, etc. You can also use software to detect batteries, automatically discharge and charge, and remotely switch on and off, etc. Network managers can analyze the power supply quality based on the information and take appropriate measures based on the actual situation. When the UPS detects that the power supply grid is interrupted, the UPS automatically switches to battery power supply. When the battery power supply capacity is insufficient, it immediately notifies the server to prepare for shutdown and shuts down before the battery is exhausted. The intelligent UPS communicates with the computer through the interface, allowing the network administrator to monitor the UPS, so the function of its management software is extremely important.
What is a backup UPS?
The battery is usually in a charging state. During a power outage, the inverter switches to the working state urgently and converts the DC power provided by the battery into a stable AC output. Backup UPS is also called offline UPS.
Backup UPS has a switching time of 2 to 10 milliseconds and is not suitable for critical power supply locations. In addition, backup UPS generally only lasts for a few minutes to ten minutes.
The advantages of 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 high.
What is an online UPS?
Online UPS: When the online UPS is working, it first converts the mains power into DC power to charge the UPS battery, and at the same time the inverter (see tips) This DC power is inverted into AC power to supply power to the load. Since the mains power has gone through the conversion process from AC to DC and then to AC, the original interference and pulse voltage components in the mains power have been filtered very cleanly. Therefore, the online UPS The voltage produced by the inverter is very stable. Since the inverter circuit is always working, when there is a power outage, the UPS can immediately convert its stored electrical energy into alternating current through the inverter to supply power to the load, thereby achieving the switching goal of zero interruption in output voltage. Double conversion also means that the output voltage of the UPS has undergone two AC and DC conversion processes. High frequency means that the UPS works internally in a high-frequency environment. The advantages of high-frequency UPS are small size, light weight, and high work efficiency. Its disadvantage is poor resistance to overload and impact.
What is an online interactive UPS?
Online interactive UPS: This is an intelligent UPS. The so-called online interactive UPS means that when the input mains power is normal, the UPS The inverter is working in reverse (that is, rectifying working state) to charge the battery pack; when the mains power is abnormal, the inverter immediately switches to inverting working state, converting the battery pack power into AC output, so the online interactive UPS There is also conversion time. Compared with backup UPS, online interactive UPS has stronger protection function and better inverter output voltage waveform, which is generally sine wave. Its biggest advantage is that it has strong software functions and can easily access the Internet and conduct operations. 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 boosted or reduced 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 monitor the power supply and UPS status directly from the computer screen, simplifying and facilitating management work, and improving the efficiency of the computer system. reliability. This kind of UPS combines the advantages of high efficiency of backup UPS and high power supply quality of online UPS, but its frequency stabilization performance is not very ideal and is not suitable for UPS power supply with constant delay.