Of course, as a power supply guarantee system, the requirements for the reliability and anti-interference ability of UPS are very high. Firstly, the UPS system should have the ability to provide a continuous high-quality power supply of 365×24. This means that in the operation of the UPS power supply system, no instantaneous power interruption/outage accidents are allowed, nor is it allowed for ordinary mains power to directly supply power to the user load through the AC bypass (except for system failure without power outage maintenance). Generally speaking, the failure rate of a single UPS is extremely low. Currently, the average time between failures (MTBF) of UPS products is mostly between 200000 and 400000 hours. The reliability of a highly fault-tolerant “N+1” type redundant parallel UPS system is higher (for example, the typical MTBF value of a “1+” type redundant parallel UPS system can reach 1.4 to 2 million hours). On the other hand, UPS must also have high anti-interference capability. A large amount of operational practice has shown that power interference is one of the important reasons for the decrease in the “availability” of electronic devices. It should be noted that power interference not only comes from the ordinary mains power grid, but also from the poorly designed UPS itself and the user’s equipment itself. This is because the servers, disk array machines, switches, and other equipment configured in the computer room are all equipped with switch power supplies. This rectification and filtering type nonlinear load will reflect 3-23rd order low harmonic interference to the UPS power supply system, which may result in a decrease in network quality. Practice has proven that excessive and excessive power interference can lead to a decrease in transmission rate, an increase in data packet loss rate of network servers, and other hidden faults, resulting in devices being forced into a “reduced usage” state. In severe cases, it can cause network paralysis.
Classification of UPS
With the development of UPS, it has been refined into many categories, and we can classify them according to different standards. According to the output power (capacity) S, we can divide UPS into four types: micro, S<1KVA; Small, 1KVA ≤ S<5KVA; Medium size, 5kVA ≤ S<30KVA; Large, S230KVA。 According to the input and output methods, there are single-phase inputs and single-phase outputs; Two phase input and two phase output; Three phase input and output (including three-phase three wire system and three-phase four wire system); Three phase input and single-phase output are commonly used in micro and small UPS systems, while medium and high-power UPS systems often use three-phase input/single-phase output and three-phase input/three-phase output. According to the output voltage waveform, there are three types: square wave, step wave, and sine wave. According to the length of the delay time t, there are two types: short delay power supply (t ≤ 30min) and long delay power supply (0.5h<t<10h). In short-term power supply, there are generally two standard backup times for UPS: 10 minutes and 30 minutes. For long delay models, the power supply time can be selected according to actual needs. Of course, in more cases, we classify UPS according to its working principle:
1. Backup type
It is the earliest static UPS, consisting of a battery, charger, inverter, automatic voltage regulator circuit, and transfer switch. Early backup UPS systems were powered directly to the load through AC bypass and transfer switches when the mains power supply was normal. The AC bypass was equivalent to a wire, and the inverter did not work. At this time, the power supply efficiency was high but the quality was poor. In recent years, backup UPS systems have often been equipped with AC voltage stabilization circuits and filtering circuits on the AC bypass for improvement. When the mains power is abnormal (the mains voltage and frequency exceed the input range allowed by the backup UPS or the mains power is interrupted), the backup UPS switches to battery power supply through the conversion switch, and the inverter enters the working state. At this time, the output waveform is AC sine wave or square wave. Backup UPS has a switching time, usually 4 milliseconds to 10 milliseconds, but it will not affect the operation of general computer equipment. Due to the fact that the output waveform of backup UPS is mostly square wave during operation, the stability and accuracy of the output voltage are relatively poor, and the power is generally small, mostly below 2000 watts, with a maximum not exceeding 3KVA. But backup UPS products have a price advantage, are relatively cheap, and are suitable for use in small office enterprises and home users with low requirements.