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Regarding the working principle of UPS, many people should have a vague concept, it is not very clear, what is the specific working principle. And for users who use UPS, it is necessary to understand how it works.

Today, I will introduce the knowledge about UPS working principle in detail here.The working principle of UPS uninterruptible power supply is simple and simple, and it is not difficult to say. Let ’s take CJD Power as an example to briefly talk about its working principle:AC-DC conversion: The AC power from the power grid is stepped down by an autotransformer, full-wave rectified, and filtered into a DC voltage and supplied to the inverter circuit. The AC-DC input has a soft-start circuit, which can avoid the impact on the power grid during startup.DC-AC inverter circuit: It adopts a high-power IGBT module full-bridge inverter circuit, which has a large power margin, has a particularly small output impedance in the output dynamic range, and has fast response characteristics. Due to the use of high-frequency modulation current limiting technology and fast short-circuit protection technology, the inverter can work safely and reliably regardless of power supply voltage transients or load shocks or short circuits.

Control drive: Control drive is the core to complete the function control of the whole machine. In addition to providing detection, protection, synchronization, and various switching and display drive signals, it also completes SPWM sine pulse width modulation control. Due to the use of static and dynamic dual voltage feedback . Greatly improved the dynamic characteristics and stability of the inverter.

Schematic: But UPS power supplies include three types, online , backup and online interactive . Each type of UPS has different working principles. Here we take online and backup as examples to talk about their working principles.The working principle of the on-line UPS is that after the input mains power is rectified and filtered, it becomes a pure 50Hz, 220V AC voltage output after being inverted; on the other hand, the charger outputs DC power to charge the battery pack. The battery pack is converted into 220V, 50Hz AC power output by the inverter circuit, and it automatically converts in zero time, which effectively guarantees uninterrupted power output, comprehensively resolves power failures in city power, and provides high-level power protection.

For the protection of critical systems and important data, it is widely used in data centers, large networks, and industrial systems (finance, post and telecommunications, hospitals, power, aerospace, military, etc.)The backup UPS is directly output by the bypass switch when the mains power is supplied. Only when the mains power is cut off, the battery pack is inverted by the inverter circuit to an AC circuit output of 220V, 50Hz. It is most suitable for protecting a single PC or workstation. It can solve three major faults of common power failures for you, including: power interruption, voltage sag and voltage surge.The working principle of UPS is roughly the same as above.

For a detailed understanding of it, users need to understand it through the user manual and product introduction or the explanation of the merchant. After all, this is only theoretical knowledge, and practice yields true knowledge.

1. UPS Uninterruptible Power Supply Principle-Introduction

UPS (Uninterruptible Power System / Uninterruptible Power Supply) power supply is also called uninterruptible power supply. It is an uninterruptible power supply of constant voltage and constant frequency that contains an energy storage device and an inverter as its main component. Important external equipment for power supply. Strictly speaking, UPS is not a power supply. It does not rely on the conversion of energy forms to provide electrical energy. It only provides an opportunity to switch between two power sources without interruption. This is the main design idea of UPS.

As the name suggests, UPS power supply is such a machine. When the mains power input is normal, the UPS will stabilize the mains power and supply it to the load. At this time, the UPS is an AC mains voltage stabilizer. The internal battery is charged; when the utility power is interrupted (an accidental power outage), the UPS immediately supplies 220V AC power to the load through the inverter conversion method to maintain the load and protect the software and hardware of the load from damage.

Summary: UPS has two main functions in computer systems and network applications: first, emergency use, that is, to prevent sudden power outages, affect the normal operation of electrical equipment, and cause damage to computers. The second is to purify the power supply and eliminate "power pollution" such as surges, electromagnetic interference, instantaneous high and low voltages, wire noise, or frequency shifts on the mains, improving our power quality and providing our computer systems And precision electrical equipment provides high-quality power.

2. UPS uninterruptible power supply principle-composition

From a structural point of view, UPS power can be mainly composed of battery, inverter, rectifier and static switch.

1) Accumulator: It is mainly used as a UPS power storage device. It has several batteries connected in series, and its capacity determines the length of emergency power consumption. Its main function is to convert electrical energy into chemical energy and store it in the battery. When a power failure is required, it can invert the chemical energy in the battery into electrical energy and provide it to our electrical equipment.

2) Inverter: In general, an inverter is a device that converts DC power into AC power. It consists of a filter circuit, a control logic, and an inverter bridge.

3) Rectifier: Rectifier and inverter are opposite, it is a device that converts AC power into DC power, it has two main functions, one is to convert AC power into DC power and provide it to load equipment or inverter after filtering process, and One role is to act as a charging voltage for the battery, like a charger.

4) Static switch: also known as a static switch, it is a kind of non-contact switch, which is formed by two thyristor directions connected in parallel, and its closing and opening are controlled by a logic controller. There are two types of parallel type and conversion type, and the parallel type switch is mainly used for parallel inverter and mains power supply, or multiple inverters. The converter switch is mainly used for power supply of two power sources to realize automatic switching from one channel to the other.

3. The principle of UPS uninterruptible power supply-working process

When the mains power is normally 380/220VAC, the main DC circuit has a direct current voltage, which is supplied to the DC-AC AC inverter to output a stable 220V or 380V AC voltage. At the same time, the mains power is charged after rectification. When the mains voltage is unstable or suddenly loses power at any time, the battery pack feeds power to the DC link through the isolation diode switch. There is no switching time from grid power supply to battery power supply. When the energy of the battery is about to be exhausted, the uninterruptible power supply sends out an audible and visual alarm, and the inverter stops working at the lower limit of the battery discharge, and a long alarm sounds. The uninterruptible power supply also has an overload protection function. When an overload occurs (150% load), it jumps to the bypass state and automatically returns when the load is normal. When a severe overload occurs (more than 200% of the rated load), the uninterruptible power supply immediately stops the inverter output and jumps to the bypass state. At this time, the front input air switch may also trip. After eliminating the fault, as long as the switch is closed, restart the work and resume work.

4. UPS uninterruptible power supply principle-working principle

UPS can be roughly divided into three types: backup (Off Line), online (On line) and online interactive (Line interactive), the following editors explain the working principle of various UPS one by one

1) On-Line UPS

On-Line UPS (On-Line UPS) operation mode is "mains and power equipment are isolated, the mains will not directly supply power to the equipment", but will be converted into DC power when the UPS, and then divided into two Battery, the other way is to charge the battery, and the other way is to switch back to alternating current to supply power to the electrical equipment. When the quality of the mains power supply is unstable or there is a power outage, the battery is switched from charging to power supply. The entire process of electricity use is involved throughout." The UPS power supply keeps its inverter in working state, converts external AC power into DC power through a circuit, and then converts DC power into high-quality sine wave AC power through a high-quality inverter and outputs it to the computer.

The main function of the online UPS under power supply conditions is to stabilize the voltage and prevent radio wave interference; in the event of a power outage, a backup DC power supply (battery pack) is used to power the inverter. Since the inverter has been working, there is no problem of switching time, which is suitable for occasions with strict requirements on the power supply. One of the advantages of online UPS power supply is that it is different from the backup type in that the power supply lasts for a long time, usually a few hours, and some more than a dozen hours. Its main function is to allow you to work as usual in the event of a power outage. It is more suitable for industries such as computers, transportation, banking, securities, communications, medical care, and industrial control, because computers in these fields are generally not allowed to experience power outages.

2) Back-up uninterruptible power supply (Off Line UPS)

The back-up uninterruptible power supply is just a "backup" UPS. The mains power directly supplies electricity to the electrical equipment and also charges the battery (Normal Mode). Once the mains power supply quality is unstable or the power fails, the mains circuit will be automatically cut off. The DC power of the battery will be converted into an AC power supply task (Battery Mode), until the mains power returns to normal, "UPS will not intervene in the power supply until the mains power is cut off", but the AC power converted from DC power is a square wave, limited to power supply For capacitive loads, such as computers and monitors.

Normally, it is in the battery charging state, and the inverter switches to the working state in an emergency, and the DC power provided by the battery is converted into a stable AC power 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 fluctuation is not large and the power supply quality is not high, which is more suitable for family use.

3) Online interactive uninterruptible power supply (Line interactive UPS)

The basic operation mode of the online interactive uninterruptible power supply is the same as that of the backup type. The difference is that although the online interleaved type is not like the online type full intervention power supply, it is always monitoring the power supply status of the commercial power supply. It has boost and decompression compensation itself. Circuit, when the power supply condition of the city power is not ideal, it can be corrected immediately to reduce unnecessary "Battery Mode" switching and extend battery life.

This is an intelligent UPS power supply. The so-called on-line interactive UPS means that when the input of the mains power is normal, the inverter of the UPS is in reverse operation (that is, the rectifier working state) to charge the battery pack; when the mains power is abnormal When the inverter immediately switches to the inverter working state, the battery pack power is converted into AC power output, so the online interactive UPS also has a conversion time. Compared with backup UPS, online interactive UPS power supply has stronger protection function, inverter output voltage waveform is better, generally sine wave, and its biggest advantage is that it has strong software functions and can be easily connected to the Internet. Remote control and intelligent management of UPS.

The working principle of solar inverters mainly includes the following steps:

Here are some key points to consider when choosing a solar inverter:

When selecting a UPS system, the up-front cost necessarily comes into question and this can lead organisations sometimes buying a lesser product at a lesser cost. However, it is essential to check the small print to ensure you have chosen a modular system that it really will do the job intended: protect the critical power of your datacentre with the highest level of availability. Interestingly, with some of the higher quality UPS systems, cost savings are often realised over the long-term through increased efficiency, resulting in lower running costs and a lower overall total cost of ownership (TCO) so doing a full cost analysis is usually worth calculating.

So, as their primary goal, how can datacentres select a UPS to maximise availability? Essentially, there must be no potential single points of failure. Understanding the configuration and the definition of a modular system carefully, before the deal is done, is critical.

At the most basic level, a single standalone UPS unit that protects a critical load is known as an N system configuration. However, a standalone UPS lacks any resilience in the event that the unit develops a fault or is offline for preventative maintenance. Paralleling a second standalone UPS unit of the same rating, provides resilience and is known as an N+1 configuration. It would be possible parallel several standalone units together of an individual smaller rating to give the same philosophy.

Another definition of modular is a standalone UPS designed and manufactured in a modular format. The main component parts of rectifier, inverter and static switch are modular. If there is a problem with say the rectifier for example, it can be swapped easily. The challenge with this configuration is that if one component does fail the whole UPS functionality goes down with it. It may be a modular system, but its level of availability will not be reliable.

A better solution is what we term: a true modular UPS. This is where several individual UPS modules are contained within a frame. All the individual modules are UPSs in their own right, all containing a rectifier, inverter and static switch and all operating online in parallel with each other. For example, six 50kW UPS modules may typically be contained within a single frame offering a resilient configuration of 300KWs N+1. If required, it takes moments (around 30 seconds) to ‘hot-swap’ a module while the rest of the modules continue to protect the critical load. 
At no point does the system need to be transferred to maintenance bypass and hence on raw mains.

Some other modular systems include the rectifier and inverter within their modules, but the static switch is centralised and separate. This results in a potential single point of failure. It may only take a few moments to replace a separate static switch, but, depending on location, getting to the site to replace it may take a maintenance engineer several hours. During that time the system cannot transfer to static bypass. With a true modular system, where the static switch is included in each module, the rest of the modules in the UPS frame continue to protect the load until it can be replaced. This increases the level of availability dramatically.

We have developed our latest generation true modular UPS system which offers power factory of more than 0.99 , with low total cost of ownership (TCO) through its Maximum Efficiency Management (MEM) and low losses of energy. Our design team has been working with data centres for many years at the forefront of technological development.

Pure sine wave:

Modeified sine wave:

Issues that need to be paid attention to when using the inverter:

• The DC voltage must be consistent

Each inverter has a DC voltage value, such as 12V, 24V, etc. It is required that the battery voltage selected must be consistent with the DC input voltage of the inverter. For example, a 12V battery must be selected for a 12V inverter.

•  The output power of the inverter must be greater than the power used by the electrical appliances, especially for electrical appliances with high power when starting, such as refrigerators and air conditioners, a larger margin should be left.
• The positive and negative poles must be connected correctly

 The DC voltage connected to the inverter is marked with positive and negative poles. Red is positive (+), black is negative (-), the battery is also marked with positive and negative, red is positive (+), black is negative (-), must be connected to positive (red to red), negative Connect negative (black connect black). The diameter of the connecting wire must be thick enough, and the length of the connecting wire must be reduced as much as possible.

• It should be placed in a ventilated and dry place, beware of rain, and have a distance of more than 500px from surrounding objects, away from flammable and explosive materials, and do not place or cover other objects on the machine. The use environment temperature is not more than 40℃ .
• Charging and inverter cannot be performed at the same time. That is, do not insert the charging plug into the electrical circuit of the inverter output during inverter.
• The interval between two startups is not less than 5 seconds (cut off the input power).
• Please wipe with a dry cloth or anti-static cloth to keep the machine tidy.
• Before connecting the input and output of the machine, please ground the casing of the machine correctly.
• In order to avoid accidents, it is strictly forbidden for users to open the case for operation and use.

 When you suspect that the machine is malfunctioning, please do not continue to operate and use it.

• When connecting the battery, make sure that there are no other metal objects on your hands to avoid short circuit of the battery and burn the human body.
• The use environment, based on safety and performance considerations, the installation environment should have the following conditions:

 1) Dry: not soaking or raining;
 2) Shady and cool: the temperature is between 0℃ and 40℃;
 3) Ventilation: Keep no foreign matter within 5cm on the shell, and the other end faces are well ventilated.

If you want to buy a UPS that suits your needs, you have to consider many factors, the most important of which is to determine the power of the UPS, and then determine the type of UPS according to the load and grid environment.

UPS types are divided into: online UPS, interactive UPS, Backup UPS. Choose the installation method according to the use environment, tower UPS and rack UPS.

These are several more important factors. Others can also consider the manufacturer’s service capacity, battery life, etc. I think the right choice The power of the UPS is very important, because if the occasion is small, a high-power UPS will be wasted. For small occasions such as an office or one or two servers, a small power is enough, and there is no need to use too much power.

UPS can be broadly divided into three types: Off Line, Online and Line interactive.

What is an offline uninterruptible power supply (OffLine UPS)

The offline uninterruptible power supply is shown above. Normally, the electricity is supplied directly to the load via a bypass. Only in the event of a power failure does the battery energy convert to AC to provide power to the load through an inverter. Features of offline uninterruptible power supplies:
When the current power is normal, offline UPS does not have any treatment of the power and directly output to the load, so the ability to suppress the electrified noise and surge is poor;
There is a conversion time;
The worst protection performance; Simple structure, small size, light weight, easy control, low cost

What is an on-line uninterruptible power supply (On-Line UPS)

The online UPS is normally powered to the load by an inverter output and is only converted to a bypass output to the load if the UPS fails, overloads, or overheats.
Features of online UPS: The output power is processed by UPS, and the output power supply quality is the highest.
No conversion time;
Complex structure, high cost;
The best protection performance and the strongest resistance to electrified noise and surges.

What is the online interactive uninterruptible power supply (Line interactive UPS)


Online interactive UPS is usually output to the load by bypass transformer, and the inverter is now used as a charger.
When power is lost, the inverter converts battery energy to AC output to the load.
Features of online interactive UPS:
With bidirectional converter design, UPS battery recharge time is short;
There is a conversion time;
The control structure is complex and the cost is high. Protection is between online and offline UPS, and the suppression of electrified noise and surges is poor.

The following are some development trends of portable mobile power supplies: