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Discussion on Technical Requirements and Technical Indexes of AC Uninterruptible Power Supply

Feb 22, 2021

Discussion on Technical Requirements and Technical Indexes of AC Uninterruptible Power Supply

AC uninterruptible power supply technical requirements and technical indicators

1. Technical requirements for AC uninterruptible power supply system


(1) During normal and accidental operation, provide the uninterruptible power supply system load with sinusoidal AC power with stable voltage and frequency.



(2) Provide uninterrupted power to the load of the AC uninterruptible power supply system when the normal/accidental AC power supply (ie, security power supply) disappears.


(3) Isolate the load of the AC uninterruptible power supply system from the transient process generated by the auxiliary power system.


(4) The AC uninterruptible power supply should have sufficient capacity so that it will not adversely affect the system when it bears the inrush current of the connected load and cuts out the line fault.


2. Technical index of AC uninterruptible power supply device


(L) The range of output voltage amplitude stability is ±2%.


(2) The output frequency stability range is ±0.5%.


(3) Harmonic distortion is less than 5%.


(4) The switching time is required to be within 5ms.




AC uninterruptible power supply operation mode

1. Normal operation


The input power of the AC uninterruptible power supply system (UPS) has three channels: one is taken from the factory power 400V security section MCC, input to the rectifier and output 250V DC voltage to the inverter, and output AC single-phase 230V through the inverter (Or three-phase 400/230V), and then output to the UPS main distribution panel through the static transfer switch, which is called the normal working power supply; the other is taken from the DC bus of the DC 230V battery, and the blocking diode is connected with the rectifier circuit to output the DC parallel input To the inverter, this circuit is a DC backup power supply; the third circuit is taken from another 400V security section MCC of factory power, and it becomes a single-phase 230V (or three-phase 400/230V) power supply through an input isolation transformer, which serves as an inverter External AC (standby) power supply for the device.


2. Abnormal operation


The abnormal operation mode of AC uninterruptible power supply is as follows:


(1) When the rectifier circuit fails or the normal working power supply loses power, the DC bus of the DC 230V battery will input DC power to the inverter through the blocking diode to ensure that the inverter continues to output AC power.


(2) When the inverter fails or the output voltage drops below 90% of the rated voltage, it is automatically switched to the external AC (standby) power system through the static transfer switch, and the power supply to the main distribution panel is still kept uninterrupted; In this case, when the inverter or static transfer switch needs to be repaired, the manual bypass switch can be switched to "full bypass" to supply power to the main distribution panel. This switching is also uninterrupted. When the inverter output voltage recovers to above 90% of the rated voltage, the static transfer switch automatically switches from manual (standby) power supply to inverter power supply.