I. Working Principle
Online UPS :
When the mains power is normal, the mains electricity is first rectified into direct current by the rectifier. Then, part of the direct current is supplied to the inverter, which converts it back into alternating current to power the load. Another part of the direct current is used to charge the battery pack. That is to say, the load always obtains power through the rectification, inversion and other processing steps inside the UPS, rather than directly using the mains electricity.
When the mains power is abnormal, the battery pack quickly takes over as the power source and continuously provides stable alternating current to the load through the inverter. The switching process is extremely rapid, basically achieving seamless switching to ensure uninterrupted power supply to the load.
Offline UPS:
When the mains power is normal, the mains electricity directly powers the load, and at the same time, the mains electricity charges the battery pack through the charger.
When the mains power is abnormal, the UPS power supply will quickly switch from mains power supply to battery power supply mode. The inverter will convert the direct current stored in the battery into alternating current to continue powering the load. However, there is a certain time interval in this switching process, usually ranging from a few milliseconds to dozens of milliseconds.
II. Structural Composition
Online UPS :
It includes an input rectifier, which is used to rectify the mains alternating current into direct current.
There is a charger that uses the rectified direct current to charge the battery pack when the mains power is normal.
There is a battery pack, which serves as the backup energy source when the mains power fails.
It is equipped with an inverter that converts direct current into alternating current that meets the requirements of the load.
It has a static bypass switch. In special cases such as UPS self-failure or maintenance, it can switch the load to the mains power supply state.
There is also an output filter, which is used to optimize the quality of the alternating current output by the inverter.
Offline UPS :
It includes a mains input circuit, which is responsible for receiving the mains alternating current.
There is a charger that charges the battery pack when the mains power is normal.
The battery pack is used to provide power when the mains power is abnormal.
It contains an inverter that converts the direct current output by the battery pack into alternating current.
It has an output circuit that transmits the processed electrical energy to the load.
III. Performance Characteristics
Power Supply Continuity:
Online UPS : It has extremely high power supply continuity. Whether the mains power is normal or not, the load can basically obtain stable power continuously. The switching time is extremely short (usually a few milliseconds or even shorter), which can well meet the needs of equipment with extremely strict requirements for power continuity, such as servers in large data centers and key industrial control equipment.
Offline UPS : There is a certain switching time (a few milliseconds to dozens of milliseconds). Relatively speaking, the power supply continuity is slightly worse. For some precision equipment that is sensitive to the switching time, it may cause instantaneous restart and other situations due to the switching. It is suitable for small equipment or scenarios with not particularly high requirements for power continuity, such as home office equipment and small commercial establishment equipment.
Output Voltage Quality:
Online UPS : Through a series of processes such as rectification, inversion and filtering, it can effectively control the parameters such as the voltage, frequency and harmonic content of the output alternating current, and provide stable and pure alternating current to the load, which can avoid equipment failures or performance degradation caused by voltage fluctuations and harmonic interference.
Offline UPS : The output voltage quality is relatively poor. Mainly, when the mains power is normal, it directly outputs the mains electricity. When the mains power is abnormal, although it is converted by the inverter, the overall fine control degree of parameters such as voltage is not as good as that of the online UPS, and there may be certain voltage fluctuations and other situations.
Redundancy Function:
Online UPS : Some high-end products have redundancy functions. They can connect multiple identical UPS units in parallel. When one of the units fails, the other units can continue to undertake the power supply task, further improving the reliability of power supply.
Offline UPS : Generally, it does not have a redundancy function. It mainly relies on its own battery pack and inverter to provide power guarantee when the mains power is abnormal.
Cost:
Online UPS : Due to its complex circuit structure, advanced technology and high requirements for output power quality, the manufacturing cost is high, and the sales price is also relatively expensive, which limits its use in some application scenarios that are sensitive to cost.
Offline UPS : The structure is relatively simple, without a complex online circuit architecture. The manufacturing cost and sales price are usually lower, which is suitable for application scenarios that are sensitive to cost and do not have extremely high requirements for power continuity.
IV. Application Scenarios
Online UPS : It is mainly applied to places with extremely strict requirements for power supply, such as large data centers, key industrial control systems and medical equipment fields. For example, servers in large data centers need continuous, stable and uninterrupted power supply, and online UPS power supplies can meet their needs. Important medical equipment in hospitals (such as CT scanners, NMR scanners, etc.) have extremely high requirements for power continuity and stability, and online UPS power supplies are also applicable.
Offline UPS : It is suitable for small application scenarios with not particularly high requirements for power continuity, such as home office environments, small commercial establishments and backup power supplies for office equipment. For example, personal computers, printers, routers and other equipment in households, cash registers, computers, lighting equipment and other equipment in small stores, and copiers, fax machines, small servers and other equipment in offices.
Online UPS and Offline UPS have obvious differences in working principle, structural composition, performance characteristics and application scenarios. Users can choose the appropriate type of UPS power supply according to their own needs.