Industry News

Does UPS have a response time?

The effective value of the voltage at the input end of the UPS power load circuit (imaginary instantaneous value of the effective value), where the unshaded part is the effective value of the voltage during the mains supply time, and the shaded part is the effective value of the load input during inverter power supply. When t=0, the UPS is powered by the mains. When t=t1, the mains drops to the lowest allowable mains voltage V2. The mains detection and conversion control circuit in the UPS immediately responds, and the mains drops to V2. Hereinafter, the mains-inverter conversion control circuit in the UPS power supply sends a signal at t2 to start the switching element. It takes a certain period of time. This time is called the abnormal response time of the mains and is recorded as Tf. The current UPS power supply The concept of abnormal mains power often refers to mains power failure, undervoltage, overvoltage, distortion, etc. Some lower-grade UPSs only have one or more of these requirements. The method where the electric zero-crossing time exceeds a given time is used for rapid detection of mains power failure or undervoltage. The general method of rectifying and filtering the voltage cannot meet the requirements of rapid detection.

The definition of the conversion time is: the time from when the conversion control circuit in the UPS power supply sends a signal to when the inverter output is actually connected to the input end of the UPS power load, it is called the conversion time, which is recorded as Ts, small offline type (also known as backup type) UPS power supplies generally use fast relays as switching elements, and the contact action time is 2~4ms. In order to shorten the conversion time Ts, bidirectional thyristors are used in higher-end UPS power supplies, or bidirectional silico-connected static relay contacts in parallel The static switch is used as the switching element. Of course, the use of online UPS is an effective method.

The recovery time is defined as the time from the UPS power switch to the inverter power supply and the time required for the inverter output of the UPS to reach 90% of the rated output voltage, denoted as T. The reason for the recovery time is:
1) The resistance and capacitance characteristics of the load, the internal resistance of the battery, transformer, and inverter components, etc.
2) The inverter output is not synchronized with the mains phase.
3) Slow recovery circuit.

In order to shorten T, a battery with a large capacity, good quality, and capable of instantaneously discharging a large current should be selected, and the parameters of the filter components should be reduced. The variable components select components with fast switching speed and reduced saturation voltage. For the second point, in some larger capacity UPS power supplies, the mains synchronization circuit is used. For the third) point, it is a circuit designed by the UPS designer. The function is to control the UPS inverter output voltage to rise according to the prescribed law to prevent excessive inrush current from burning the UPS inverter components.

The utility power has actually returned to normal, and the UPS power supply should be switched to the utility power supply state, but the UPS is not in a hurry to respond, and has to wait for a period of time before sending a control signal to switch to the utility power at t6. In order to eliminate jitter and synchronization time, it is recorded as Tu. The reason why UPS reserves jitter and synchronization time T is: the normal operation of the mains power is often the mains closing operation, from the moment the knife is just turned on to the completion of the connection. During this period of time, due to the mechanical jitter of the knife, the mains electrode is unstable and changes irregularly in the range of 0~220V. If the UPS has no debounce circuit, the UPS power supply is between mains and inverter at the moment of closing. Constantly changing, this kind of frequent beating back and forth is very easy to burn the UPS, and the quality of the power obtained from the load of the UPS power supply is very poor. Another reason for the dynamic and synchronization time Tu. is: some UPS have a mains synchronization circuit, When the mains power returns to normal, the inverter output frequency and phase in the UPS should be synchronized with the mains first, and then the UPS is switched to the mains power supply state, that is, synchronous switching, which can reduce the inrush current and shorten the power interruption time .