As computer application systems have higher and higher power requirements, UPS is receiving increasing attention. UPS has gradually developed into a power protection system with functions such as voltage stabilization, frequency stabilization, filtering, anti-electromagnetic and radio frequency interference, and anti-voltage surfing.
Function
The protective effect of UPS is firstly reflected in stabilizing the mains power supply. The input voltage range of UPS is relatively wide, generally from 170V to 250V, and the quality of the output power supply is quite high. The output voltage of backup UPS is within 5% ~8%, the output frequency is stable at 1Hz; the online UPS output voltage is stable within 3%, and the output frequency is stable at 0.5Hz. When the mains power is normal, the UPS power supply is equivalent to the AC mains voltage stabilizer; at the same time, the mains charges the battery, which is also the charger. In the event of a sudden power outage from the city power supply, the UPS automatically switches to battery power supply, allowing the computer to maintain normal operation and protecting the software and hardware from damage.
Category
(1) Passive backup UPS power supply
It means that the inverter is connected in parallel between the mains and the load and is simply used as a backup power supply. About this type UPS power supply, when the mains power is normal, the load is completely and directly powered by the mains power, while the inverter does not perform any power conversion, and the battery is powered by an independent charger; when the mains power is abnormal, the load is completely powered by the inverter. The device provides electrical energy.
Passive backup UPS has the advantages of simple structure and cheapest price. It is used for certain non-critical loads, such as home computers. However, when the mains power is cut off, the relay switches the inverter to the load. But the switching time is long, usually requiring a few milliseconds of interruption. Therefore, passive backup UPS power supply should not be used for slightly important computer equipment.
(2) Online interactive UPS power supply
It means that the inverter is connected in parallel between the mains and the load to act as a backup power supply. At the same time, the inverter acts as a charger to charge the battery. Through the reversible operation mode of the inverter, it interacts with the mains power, so it is called interactive. This kind of UPS power supply, when the mains power is normal, the load is powered by the improved mains power, and the inverter acts as a charger to charge the battery. At this time, the inverter functions as an AC/DC converter; when the mains power supply during a fault, the load is completely powered by the inverter. Now the inverter functions as a DC/AC converter.
Online interactive UPS has the advantages of simple structure, easy implementation, easy parallel connection, easy maintenance and repair, high efficiency, low operating cost, and high reliability of the whole machine. The performance meets certain load requirements and is especially suitable for systems where some computer equipment in the network uses distributed power supply. The disadvantage of this kind of power supply is that the voltage stabilization performance is not high, especially the dynamic response speed. Secondly, the anti-interference ability is not strong, and the circuit will produce harmonic interference and modulation interference.
(3) Double conversion UPS power supply
It means that the inverter is connected in series between the AC input and the load, and the power supply continuously supplies power to the load through the inverter. The power supply method of this kind of UPS power supply is as follows: when the mains power is normal, the mains power supplies power to the load through the rectifier and inverter; when the mains power is abnormal, the storage battery supplies power to the load through the inverter.
Double conversion UPS is the mainstream product of UPS power supply. It has the advantages of good performance, high voltage stability and frequency stability, strong functions, hot backup connection and parallel redundant connection functions. Its disadvantage is that when the capacity is less than below 10kVA, the overall machine efficiency is not high, generally around 85%.
Technical indicators
Most of the inverters in new UPS use PWM technology, and also use quartz crystal oscillation to control the frequency of the inverter, and ensure the stability of the output voltage through a voltage negative feedback circuit. It has a series of advantages of switching power supply and ensures stable power output by accurately adjusting the pulse width. At the same time, the application of switching power supply technology has also greatly reduced its own losses. The main technical indicators are as follows:
- Rated output power and maximum output power;
- Switching time;
- Output voltage stability, reference value ±0.5%~±2%;
- Output frequency stability, reference value ±0.01%~±0.5%;
- The output waveform is pure (sine wave output), the voltage distortion is less than 1%, and there is no problem of latent wave distortion;
- High efficiency and low loss. The reference index is higher than 90%;
- Trouble-free working hours. Due to the adoption of high technologies such as microprocessor monitoring technology and advanced IGBT driven SPWM, current UPS has reached an extremely high level of reliability. For large-scale UPS power supplies, the average annual trouble-free working time (MTBF) of a single unit has exceeded 200,000 hours. If a multi-machine “redundant” UPS power supply system with dual bus outputs is used, its MTBF can even reach the order of 10 million hours.
