Problems needing attention in choosing UPS power supply
Time of issue:2023-01-06
When choosing a UPS power supply, it is necessary to consider the issues that need to be paid attention to from various aspects.
1. Regarding the synchronous switching function.
At present, except for the offline UPS power supply with square wave output whose rated output power is less than 500VA, which still adopts the conversion control without mains synchronization function, all UPS power supplies with an output power of 1KVA and above are powered from the mains to the inverter. During the conversion operation, it should have the function of synchronous switching of mains power to ensure that the inverter and bypass power supply have the same phase and same frequency output characteristics. The phase-locked synchronous control circuit has a strong ability to capture the phase-locked synchronization of the input voltage of the mains, which is mainly manifested in that the sine wave of the mains can control the sine wave output by the inverter within the wide range of the input voltage of the UPS power supply. The waves are controlled synchronously.
When the UPS power supply is switching, the phase difference between the AC bypass power supply and the inverter power supply should be as small as possible. The frequency stability of the power supply network in the application should be considered. If the mains power is used, the same control circuit of the general online UPS power supply can meet the requirements. For small power grids with large frequency fluctuations, in order to successfully realize synchronous switching operations, it is necessary to choose a UPS power supply with corresponding functions.
2. Shock resistance to capacitive loads.
For the rectified and filtered load, since the rectifier is connected with a large-capacity filter capacitor, it requires the peak current provided by the UPS power supply to be much greater than the peak current required to drive the resistive load. The index to measure the capacity of capacitive load is crest factor. Its definition is: the ratio of the maximum capacitive peak current that occurs when using the same sine wave AC power supply with a rectified and filtered load to the maximum peak current that occurs with a purely resistive load. The premise of the above comparison is that the capacitive load and the resistive load have the same impedance value.