As the economy continues to develop, computers are widely used, and some important places: such as finance, information, communication, and public equipment control, have high requirements for power supply reliability and stability, and industries such as ultra-large-scale integrated circuit manufacturing also have high power requirements.
Voltage offset, voltage waveform distortion, continuous power failure and other power quality degradation will have serious economic losses and social impacts. Most of the key equipment in the above sites are powered by LIPS.
1. The type of UPS power supply
Usually the equipment chooses the UPS power supply as economically as possible according to the requirements of power supply reliability, functional requirements, and ease of use. Choose different types of UPS according to different load characteristics. Starting from practicability and convenient selection, UPS can be divided into three categories:
Single operation, backup operation;
With bypass conversion, without bypass conversion;
Usually the inverter runs. Normally the mains is running.
2. Features of UPS power supply
Single-operation UPS power supply, used for general important loads; used for loads with different output frequencies, or has little effect on the city power, and requires high frequency accuracy.
Backup operation of UPS, using multiple non-stop devices, with backup function, when some parts fail, other normal parts supply power to the load, used for particularly important loads.
There is a bypass conversion UPS, and the load can be supplied by the mains and inverter to improve the reliability of power supply. Most UPSs are bypassed.
No bypass conversion UPS, used for loads with different input and output frequencies, or requiring extremely high frequency and voltage accuracy of the mains.
The inverter runs normally, and the load has high requirements on the quality of the power supply, which is not affected by the commercial power supply, power supply voltage, and frequency.
Usually the city power runs, the load does not have high requirements on power quality, high reliability, and high efficiency without conversion. Three operating modes are used in combination according to the nature of the load.
3. The principle of choosing UPS for power supply system
3.1 Importance of load
Is there any potential abnormality in the power supply? In principle, there is no power supply abnormality and there is no need to set up UPS power supply. Whether the load is important depends on the partial damage to the load caused by the abnormal power supply. Damage includes direct losses and indirect losses. The direct losses include bad products on the production line and the loss of important data for scientific and technological research and development. Indirect losses include the time required to restore power supply and social credibility. According to the size of the damage, the total investment of the UPS system is measured. In order to improve the reliability, whether to use UPS, whether to use backup and bypass of UPS, and determine the operation mode.
3.2 Influence of power quality on load
The influence of power quality on the load includes: the allowable voltage drop range and duration of the power supply voltage; the daily voltage distortion range and frequency accuracy. The load has a strong bearing on the quality of the power supply, which can simplify the system to improve reliability and reduce costs. For example, when adding a bypass, a transient power failure conversion method of generally 0.02 ~ 0.2S is used. Daily voltage distortion, frequency accuracy is generally not a special load, and it is sufficient to operate under the mains power supply, and it is generally not necessary to consider the influence of the power supply on the load. Computers sensitive to instantaneous power supply voltage drop and power outage will have an effect even if the power supply voltage drops by 10% for half a cycle. You need to provide power.
3.3 UPS power supply capacity selection
Select UPS power supply capacity based on the following factors, characteristics, calculated load, inrush current, peak current, overload capacity, and sudden load change.
The effective load capacity is compensated with the following values.
(1) About inrush current
Calculated capacity of UPS that can withstand peak current = effective load capacity X inrush current (maximum value) / UPS rated current, its value is generally 5 ~ 10 times of effective capacity.
The load is put into the power supply and generates a considerable inrush current, especially for computers and peripheral equipment. In order to reduce the capacity of the UPS, in order to reduce the capacity of the UPS, the load is put into or selected for UPS mains operation in sequence; when the current returns below the rated current value, it will be switched to the rectifier and the inverter to supply power without power failure.
(2) About peak current
UPS that can withstand peak current;
Capacity = effective load capacity X peak current (maximum value) / UPS rated current;
Peak capacity is generally twice the effective capacity;
UPS with a peak factor of more than 2.5, the peak current withstand capacity is 250% PA, generally does not exceed the rated capacity of the UPS. It can be directly used without compensation.
(3) About overload
The overload capacity of UPS is generally more than 1.1 times of the effective load, and the UPS should be protected if the overload is more than 1.1 times.
(4) Load mutation
Most UPS loads are abruptly changed within the range of 0 "100%, and the output voltage fluctuation can be controlled within _10% l ~ A. Therefore, the effective load capacity can not be compensated.
(5) Generator-UPS coordination
In some places, the UPS switches to the self-provided generator for power supply after the mains power failure. When the self-provided generator is used for power supply, it should be able to provide a large inrush current when the UPS starts, without affecting the operation of the generator.
A. Choose a lower starting current UPS for rectifier equipment. For example, a 12-pulse rectifier, the capacity of the self-provided generator should be twice that of the rectifier.
B. Select several groups of UPS in parallel, group delay start. It can be combined together with a ramp start function to avoid excessive rush current when all UPSs start at the same time.
C. Choose a UPS with rectifier charger input power control, so that the rectifier charger input part of the power, insufficient power is provided by the battery.
D. Select the UPS with limited charging current function. When starting the generator, limit the charging and set the charging current value to 0 amperes. That is, charging can be stopped while the generator is running, thereby reducing the UPS's absorption of power from the generator.