There are various types of UPS power supplies available in the market today, with output power ranging from 500VA to 4800KVA (multiple units in parallel). UPS power supply can be divided into three categories according to its working principle: backup UPS, online interactive UPS, and online UPS; According to the output waveform, it can be divided into two types: square wave output UPS and sine wave output UPS; Structurally, it can be divided into two categories: DC UPS and AC UPS; From the perspective of backup time, UPS can be divided into two types: standard and long-term. The specific classification can be found below:

Ⅰ.Classified by working principle

1.Backup UPS: When the mains power input is normal, it directly goes through thebypass and supplies power to the load through the conversion switch. The rectifiercharger in the machine is in working mode, and the battery is floating charged. Theinverter is in a stopped state; When the mains power supply is interrupted or outside theinput voltage range of the UPS, the battery supplies power to the inverter of the UPS andprovides stable and frequency stable AC power to the load. The conversion betweenthese is interrupted for several milliseconds (2 to 10 milliseconds). It not only improves thefluctuation amplitude of the mains voltage, but also has little improvement on thefrequency instability, waveform distortion, and interference from the power grid. Theadvantages of backup UPS power supply are high operating efficiency, low noise, and lowprice. It is suitable for situations where there is not much fluctuation in the market andthere are low requirements for power supply quality (such as home computers, salespoints, etc.).

2.Online interactive UPS: When the mains power input is normal, it directly goes throughthe bypass and supplies power to the load through the conversion switch. The inverter ofthe UPS is in reverse operation (i.e. charging the battery pack in a rectifier working state);When the mains power is abnormal, the inverter immediately switches to the inverterworking state, converting the battery pack energy into AC output. Therefore, onlineinteractive UPS also has conversion time, which is an intelligent UPS. Compared withbackup UPS, online interactive UPS has stronger protection function, and the outputvoltage waveform of the inverter is generally sine wave. Its biggest advantage is that it hasstrong software function, which can easily access the internet for remote control andintelligent management of UPS. This type of UPS combines the advantages of highefficiency of backup UPS and high quality of online UPS power supply, but its frequencystability performance is not very ideal and is not suitable for long delay UPS power supply.

3.Online UPS: When the mains power supply is normal, the AC power supply isconverted into a DC power supply through a rectifier, which is then pulse width modulated and filtered. The inverter then converts the DC power supply back into an AC power supply to the load [mains power rectification (while charging the battery) - inverter load]. Once the mains power is interrupted, the battery immediately powers the load through the inverter (DC to AC). Therefore, under normal circumstances, the online UPS power supply is always powered by the inverter of the UPS power supply to the load, regardless of the presence or absence of mains power, thus avoiding all impacts caused by voltage fluctuations and disturbances in the mains power grid. Compared with backup UPS and online interactive UPS, the power quality of online UPS is much higher than the first two because it can achieve stable frequency and voltage supply to the load, and the conversion time from mains power to battery power is zero.

High frequency online type
The power frequency online UPS can also be divided into single input and single output (input~220V/output~220V), three input and single output (input~380V/output~220V), and three input and three output (input~380V/output~380V) according to the input and output voltage working mode, which is commonly referred to as "S11, S31, S33". According to redundancy, it can be divided into:
①The master-slave hot backup is connected in series with this type of UPS, with the hostcarrying 100% load; The slave machine is connected to the bypass of the host machine ina battery floating charge state and supplies power to the host bypass, with a load rate of 0.Once the host inverter fails, the slave machine will switch to the host bypass to continuesupplying power to the load. The capacity of the host must be greater than or equal to thatof the slave. And the main power supply comes from the same bus.
②Redundant parallel connection: Two UPS units each carry 50% of the load, and if oneunit fails, the other unit will be fully loaded. And the capacity of the two UPS should beexactly the same. Their main power supply can come from different busbars, but thebypass power supply must share a common one
Some online UPS power sources have two inputs, one is mains power and the other is from other power grids or generators (large and medium-sized UPS). Online UPS is suitable for industries such as computer, transportation, banking, securities, communication, medical, metallurgical, petrochemical, military, etc.

Ⅱ.Classification by output voltage waveform

1.Square wave UPS: This type of UPS power supply has poor load carrying capacity (theload capacity is only 40-60% of the rated load) and cannot carry inductive loads. If theload carried is too large, the third harmonic component contained in the square waveoutput voltage will increase the capacitive current flowing into the load, and in severecases, it will damage the power filter capacitor of the load. This type of UPS is commonlyused as a backup UPS in the future.
2.Sine wave UPS: The relationship between the distortion of the output voltage waveformand the load of this type of UPS power supply is not as obvious as that of square wave
output UPS power supply. It has relatively strong load carrying capacity and can carry micro inductive loads. This type of UPS is commonly found in online UPS, and some backup UPS outputs are also sine waves.

Ⅲ.Classification by structure

1.DC UPS: composed of two basic units - rectifier and battery.

2.AC UPS: When the mains power is normal, the current is supplied to the load throughthe rectifier/inverter, while the rectifier charges the battery. When there is a power failureor rectifier failure, the control circuit automatically switches to enable the battery to supplypower to the load, and the voltage flow is from the battery to the inverter to the load. TheAC UPS power supply consists of three basic units. They are rectifier, battery, andinverter.
Ⅳ.Classified by backup time
1.Standard type (standard machine): The host is equipped with a battery pack, which canmaintain power supply for a short period of time after a power outage (the delay time isgenerally between 5-20 minutes, depending on the load carried, the smaller the load, thelonger the delay time)
2.Long term (long term): The host does not come with a battery, but a charger is added.Users can connect multiple sets of batteries according to their own needs to extend thepower supply time. Manufacturers will increase the charger capacity or install parallelchargers when supplying. Long delay machines typically operate between 30 minutes and8 hours.
In addition, UPS can be classified into rotating UPS and stationary UPS based on their composition principles; From the application field, it can be divided into commercial UPS (high-frequency machine: output without isolation transformer) and industrial UPS (industrial frequency machine: output with isolation transformer).
With the continuous development of science and technology, UPS technology has also entered another new level. In the future, its purpose and classification will be increasingly understood by users.