Something about online double-conversion UPS
With the rapid development of technologies such as big data, cloud computing, and 5G, data centers have also ushered in a period of rapid change. As an important part of the data center power supply and distribution system, UPS has also begun to change. Online double-conversion UPS appears.
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Quality and performance such as reliability, efficiency, ease of use and maintenance have become the focus of more and more UPS manufacturers and users. This blog mainly discusses online double-conversion UPS.
The online double-conversion UPS converts the power supply twice. Firstly, the AC input and all its voltage spikes, distortions, and other abnormalities are converted to DC. Double-conversion online UPS uses capacitors to stabilize this DC voltage and store the energy drawn from the AC input. Secondly, the DC power is converted back to AC power strictly regulated by the UPS. The AC output can even have a different frequency from the AC input. When there is an AC input, all power supplied to the load equipment goes through this double conversion process.
- Avoid interference. Since the rectifier and inverter isolate the load from the AC power source, various interference of the AC power, such as line noise, overvoltage, lightning, voltage harmonics, and power interruption, are suppressed.
- Fast conversion time. When the AC input power fails, the online double-conversion UPS can instantly switch from the normal mode to the energy storage mode, and the conversion time tends to be zero.
- Long battery life. The battery discharge probability of double-conversion online UPS is smaller than that of any other UPS battery, so the battery life can be prolonged.
- Good input and output voltage performance. The allowable variation range of the input power voltage of the double-conversion online UPS is very wide, and the static and transient accuracy of the output voltage is very high.
- The highest reliability. The rectifier and bypass input of the double-conversion online UPS are generally connected by two independent input terminals, which greatly improves the fault tolerance of the UPS.
However, it is a two-edged sword.
- The structure is complex and the cost is high. Double-conversion online UPS has many components, complicated operation and maintenance, and generally high cost.
- Large energy loss and low efficiency. The energy loss of the double-conversion online UPS in the conversion process is proportional to the number of conversions and the converted power, and the system efficiency is low.
- The harmonic interference at the input end is large. The input end of the double-conversion online UPS generally uses a phase-controlled rectifier, and the input harmonic current generated by this component will cause serious interference to the AC input power.
Online double-conversion UPS mainly has three working modes, namely normal mode, bypass mode, and battery mode. The conventional UPS always works in one of the working modes.
In the normal mode, the rectifier input, circuit breaker is closed; the battery circuit breaker is closed; and the inverter output, contactor is closed.
The alternating current supplies power to the rectifier/charger. The rectifier converts the alternating current to direct current and supplies it to the inverter. The inverter converts the direct current to alternating current to supply the load. At the same time, the rectifier also provides charging current for the battery.
In normal mode, if the UPS detects overload, load failure or UPS internal failure, it will automatically switch to bypass mode.
In the bypass mode, the inverter output contactor is disconnected, and the bypass power supply (AC) directly supplies power to the load through the fuse and static switch.
When the UPS is working in the normal mode, if the AC power is interrupted or the AC power indicator exceeds the specified indicator, the UPS will automatically switch to the battery mode.
In the battery mode, the battery breaker is closed and the inverter output contactor is closed.
The storage battery supplies DC power to the inverter, and the inverter continues to run, supplying power to the load uninterruptedly. The operating time of the UPS system in battery mode depends on the capacity of the battery and the size of the load.
Online double-conversion UPS is mainly used for high-power UPS and important loads. The UPSs above 3kVA on the market are basically this type of UPS.
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