UPS is an uninterruptible power supply . It is usually one of the engineering subsystems of the weak electric machine room, which connects the battery with the host equipment, and is mainly used to provide stable and uninterrupted power supply to the equipment.
When the mains input is normal, the UPS will stabilize the mains and supply it to the load . At this time, the UPS is an AC voltage stabilizer, and it also charges the battery inside the machine; when the mains is interrupted (accident power outage) , the UPS will continue to supply 220V AC of the battery immediately , so as to maintain the normal operation of the load and protect the software and hardware of the load from damage.
UPS devices usually provide protection against overvoltage or undervoltage. Let's take a look at the basics of UPS.
The basic principle and main technical parameters of UPS
What is a UPS?
An energy conversion device that uses battery chemical energy as backup energy to continuously provide (alternating current) power to user equipment in the event of grid failures such as mains power outages.
Why do you need a UPS?
The power supply provided by the mains grid looks normal, but it is unreliable: the seemingly normal power is actually dangerous.
power outage
Lost data, disrupted communications, delayed business opportunities...
—— The direct loss is calculated at 5,000-100,000 yuan per minute
Equipment outages, instruments malfunctioning, operations interrupted...
—— The indirect economic loss is immeasurable
power pollution
Transient spikes, power surges, high voltage pulses
Cause hardware damage to servers, routers, disk arrays, etc.
Harmonic pollution, line noise, frequency drift
The bit error rate of network transmission is greatly increased, and the data transmission speed is low.
Four functions of UPS
Non-power-off function - to solve the problem of power grid outage
AC voltage stabilization function - can solve the problem of severe fluctuations in network voltage
Purification function - to solve the problem of power grid and power supply pollution
Management function - solve AC power maintenance problems
UPS system structure
The monitoring platform is also one of the most important components of UPS
Main technical parameters of UPS
Input properties:
1. Input voltage range Wide input voltage range can reduce the chance of battery discharge and prolong battery life.
2. Input power factor The power factor is low, the input reactive power is large, and the harmonic current pollutes the power grid, affecting and interfering with other equipment.
3. Allowable range of main power frequency.
4. Input current harmonic components. (PFC, 6/12 pulse transformer )
Output characteristics:
1. Static stability. 1% for large and 2% for small and medium.
2. Output transient characteristics. Large 5%, small and medium 8%.
3. Output overload capability . (eg: overload 125% 5MIN; 150% 10S)
4. Output power factor. (0.8, 0.9, 1)
5. Output voltage harmonic distortion. Typical within 3%.
UPS related configuration and calculation
The UPS system basically consists of the following parts:
UPS host
Required functional parts (such as BCB BOX, etc.)
storage battery
Supporting battery cabinet/rack, battery switch , etc.
Function options (such as lightning protection, monitoring, harmonic control, upper outgoing line, etc.)
Calculations to be performed:
Calculation and Selection of UPS Host Capacity
Capacity Calculation and Selection of UPS Backup Battery
Calculation and selection of UPS capacity
First obtain the total power consumption of the load, and unify the unit to KVA
For example: the load of general personal computer is about 200VA, the load of small server is about 1500VA, and the load of large and medium-sized server is about 3000VA
Conversion relationship between current I (A ampere) and power consumption W (watt) and VA
VA= I*220
VA= W/0.8 (usually consider 0.7 below 20KVA and 0.8 above 20KVA when calculating)
Considering that the UPS operates in the 60-80% range is the best operating state, it is generally recommended to divide the above results by 0.8 and zoom in again when calculating.
Then select the closest power product in the product brochure
Calculation method using constant power mode
W/cell = PL/(N×6×η)
Introduction of UPS power supply scheme
Centralized power supply mode:
Advantages: It can realize the equipotential control of network equipment resources and reduce the transmission bit error rate.
Disadvantages: The initial investment is large, and the impact of a single machine failure is large.
Distributed power supply mode:
Advantages: flexible scheme layout, little impact of failure.
Disadvantages: If the entire device cannot be kept on the same ground line, it is easy to cause interference.
stand-alone power supply
One of the easiest UPS solutions
The capacity of the AC power supply system at each scattered location is mostly below 6KVA
Each AC load is independently protected by a UPS
Mains electricity usually adopts the nearest socket input
Master-slave series "hot backup"
Suitable for small and medium-sized networks, server farms, offices, instruments and other applications
Consists of UPS host, UPS slave, battery system, power distribution system
Simple power distribution design and engineering construction
advantage:
Two or more UPSs are basically in a relatively independent and non-interfering operating state.
The performance requirements for UPS synchronous tracking are relatively low.
Different models and different capacities of UPS are used to form a serial hot backup mode.
shortcoming:
The slave machine is in the no-load operation state for a long time, and the efficiency is low.
The battery pack of the slave machine is in the floating charge state for a long time, and there are few opportunities for regular on-load discharge maintenance, which will affect the battery life.
The slave must have good load capacity with steps.
Long-term operation, master inverter = static bypass transfer function is the key
No expansion function.
Compared with the "parallel" redundant system, the mean time between failures is relatively low.
Modules connected in parallel
Centralized power supply for all AC loads, powered by a modular parallel UPS
Modular UPS includes: rack, parallelable power module, parallelable battery module, charging module, etc.
Suitable for small and medium-sized networks, server farms, offices, instruments and other applications
Consists of rack, UPS power module, battery module and power distribution system
The power module is configured as N+1 redundancy, which reduces MTTR
Shared input, output, parallel battery system, control system
N+1 direct parallel redundancy
Suitable for medium and large networks, data centers, centralized power supply for buildings, industrial factories and mines, etc.
Consists of directly paralleled N+1 UPSs, battery modules, and power distribution systems
System N+1 redundancy, higher reliability than stand-alone UPS
Easy to expand and easy to maintain
is the most widely used solution
advantage:
The perfect phase-locked synchronization technology ensures that the load current can be evenly shared when multiple UPSs are directly connected in parallel.
Good expansion performance (N+1)
Avoid the disadvantages of "tandem" hot backup mode.
shortcoming:
High requirements on the genlock technology of the device itself
High requirements for equipment manufacturing technology - the output impedance is close.
High requirements for inverter output voltage regulation performance - phase-separated regulation
The UPS must be of the same model and capacity.
When multiple units are connected in parallel, the bypass also needs to increase the "current sharing inductance "
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