UPS Classification and Working Principle
The working principle of a UPS is to use the chemical energy of a battery as backup energy. When the AC power fails and is interrupted, the UPS can provide power to the equipment without interruption. It is generally composed of a rectifier, inverter, static switch, and battery.
UPS Classification
Based on their working principle, they can be divided into: offline and online.
According to the power supply method, they are divided into: single-phase input single-phase output, three-phase input single-phase output, and three-phase input three-phase output.
Based on power, they are divided into: small units below 10kVA, medium units between 10kVA and 100kVA, and large units above 100kVA.
Based on the output waveform, they are classified as: square wave, trapezoidal wave, and sine wave.
Working principles of standby and online UPS
1) Standby UPS (Offline UPS)
When the mains power is normal, the equipment is directly powered by the mains power. When the mains power is disconnected, the equipment is powered by the battery inverter.
Its characteristics are: simple structure, small size, and low cost, but narrow input voltage range, switching time, and unsuitability for devices with high power quality requirements. It is usually used in personal computers.
2) Online Interactive UPS
When the mains power is normal, the mains power is rectified to supply DC power to the inverter, which then directly supplies AC power to the equipment. Simultaneously, the charger charges the battery to maintain its full capacity. The inverter is always operational, ensuring uninterrupted output with no switching time. This is suitable for equipment with high power quality requirements.
EPS Classification and Working Principle
The working principle of an EPS (Electric Power Supply) is similar to that of a standby UPS. It generally consists of a charger, inverter, battery, automatic switching device, and control system. Its characteristics include simple structure, no noise, and long lifespan. It is suitable for inductive, capacitive, and mixed loads.
EPS Classification
Based on the type of load they carry, they can be divided into: 1) Emergency lighting type; 2) Hybrid emergency lighting and power type; 3) Power type.
The difference between UPS and EPS
1) Differentiate between UPS and EPS based on output
UPS systems primarily supply power to computer and network equipment, which typically have relatively low load characteristics. Currently, the power factor for UPS output is specified as 0.8. EPS systems, on the other hand, are mainly used for emergency power backup, usually for inductive or capacitive loads. Some loads require activation only after a power outage, so all EPS systems must be able to provide a large inrush current, typically requiring continuous power supply for at least 10 minutes at 120% load. UPS rated capacity is measured in KVA, while EPS rated capacity is measured in KW.
2) Functional differences between UPS and EPS
Both EPS and UPS have mains bypass and inverter circuits, but EPS only has continuous power supply function and does not have high requirements for inverter switching time. Most EPS now also have battery cell detection function. EPS only starts inverter output after the mains power is interrupted, resulting in high computer utilization.
UPS systems generally emphasize three main functions: frequency and voltage stabilization of mains power; power supply for equipment with extremely tight switching time requirements; and mains power purification. Daily operation typically relies on a double-conversion circuit for rectification and inversion, resulting in low energy utilization. However, UPS systems do more than just invert power during power outages; they can also provide stable power output when the mains power experiences large voltage deviations or surges—features that EPS systems lack.
3) Differences in application scope between UPS and EPS
EPS is mainly used for fire protection loads and some equipment that does not have high requirements for switching time but requires continuous power supply.
UPS is mainly used for loads such as computers and digital information systems that have high requirements for power quality.
