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UPS, or uninterruptible power supply, is usually one of the subsystems of a weak current room project. It connects the battery to the host device and is mainly used to provide a stable and uninterrupted power supply to the device.
When the AC power input is normal, the UPS stabilizes the AC power and supplies 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 AC power is interrupted (power outage), the UPS immediately uses the battery's DC power to continue to supply 220V AC power to the load through inverter switching, so that the load maintains normal operation and protects the load's software and hardware from damage.
UPS devices usually provide protection against overvoltage or undervoltage. Let's take a look at the basics of UPS.
The basic principles 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 (AC) power to user equipment when there is a power outage or other grid failure.
Why do you need a UPS?
The electricity supply provided by the municipal power grid appears normal, but it is unreliable: the electricity that appears normal is actually fraught with dangers.
Power outages, data loss, communication interruptions, business opportunities delays...
—— Direct losses are 5,000-100,000 yuan per minute
Equipment stopped working, instruments failed, operations were interrupted...
—— Indirect economic losses are incalculable
Power pollution
Transient spikes, power surges, high voltage pulses
Cause hardware damage to servers, routers, disk arrays, etc.
Harmonic pollution, line noise, frequency drift
This causes a significant increase in the network transmission bit error rate and a low data transmission speed.
Four major functions of UPS
No power outage function - solve the problem of power outage
AC voltage stabilization function——can solve the problem of severe fluctuations in network voltage
Purification function - solving the problem of power grid and power supply pollution
Management function - solving AC power maintenance problems
UPS system structure
The monitoring platform is also one of the most important components of UPS
UPS main technical parameters
Input characteristics:
1. Input voltage range A wide input voltage range can reduce the chance of battery discharge and extend battery life.
2. Input power factor: If the power factor is low, the input reactive power will be large, and the harmonic current will pollute the power grid, affecting and interfering with other equipment.
3. Allowable range of main power supply 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-sized.
2. Output transient characteristics: 5% for large and 8% for medium and small.
3. Output overload capacity. (eg: overload 125% 5MIN; 150% 10S)
4. Output power factor. (0.8, 0.9, 1)
5. Output voltage harmonic distortion: typically within 3%.
UPS related configuration and calculation
The UPS system basically consists of the following parts:
UPS host, mandatory functional parts (such as BCB BOX, etc.), batteries, matching battery cabinets/racks, battery switches, etc., functional options (such as lightning protection, monitoring, harmonic control, upper output lines, etc.)
Calculations to be performed:
UPS host capacity calculation and selection
UPS backup battery capacity calculation and selection
UPS capacity calculation and selection
First, obtain the total power consumption of the load and unify the unit to KVA
For example: the load of a general personal computer is about 200VA, the load of a small server is about 1500VA, and the load of a large or medium-sized server is about 3000VA
The conversion relationship between current I (ampere) and power consumption W (watt) and VA
VA = I*220
VA = W/0.8 (When calculating, it is usually considered that below 20KVA is 0.7, and above 20KVA is 0.8)
Considering that the UPS operates in the range of 60-80% is the best operating state, it is generally recommended to divide the above result by 0.8 and enlarge it again when calculating, and then select the closest power product in the product manual and use the constant power mode calculation method
W/cell = PL/(N×6×η)
Introduction to UPS power supply solutions
Centralized power supply mode:
Advantages: It can realize equipotential control of network equipment resources and reduce transmission bit error rate.
Disadvantages: large initial investment and large impact of single machine failure.
Distributed power supply mode:
Advantages: flexible solution layout and small impact of failures.
Disadvantages: If the entire device cannot maintain the same ground line, it is easy to cause interference.
Single machine power supply
The simplest type of UPS solution, the AC power supply system capacity of each dispersed location is usually less than 6KVA, and each AC load is independently powered and protected by a UPS.
The mains power is usually input from the nearest socket, and the master and slave machines are connected in series for "hot backup". It is suitable for small and medium-sized networks, server clusters, offices, instruments and other applications. It consists of a UPS host, a UPS slave, a battery system, and a power distribution system. The power distribution design and engineering construction are simple.
advantage:
1. Two or more UPS are basically in a relatively independent and non-interfering operating state.
2. The requirements for UPS synchronization tracking performance are relatively low.
3. Use UPS of different models and capacities to form a series hot backup mode.
shortcoming:
1. The slave machine is in no-load operation for a long time and has low efficiency.
2. The slave battery pack is in floating charge state for a long time, and there are few opportunities for regular load discharge maintenance, which will affect the battery life.
3. The slave must have good step load capability.
For long-term operation, the host inverter = good static bypass conversion function is the key
1. No expansion function.
2. Compared with the "parallel" redundant system, the mean time between failures is relatively low.
Modules in parallel power supply
1. All AC loads are centrally powered by a modular parallel UPS
2. Modular UPS includes: rack, parallel-connectable power modules, parallel-connectable battery modules, charging modules, etc.
3. Suitable for small and medium-sized networks, server clusters, offices, instruments and other applications
4. It consists of a rack, UPS power module, battery module, and power distribution system
5. The power module is configured as N+1 redundancy, reducing MTTR
6. Shared input, output, parallel battery system, control system
N+1 direct parallel redundancy
1. Suitable for medium and large networks, data centers, centralized power supply for buildings, industrial plants and mines, etc.
2. It consists of N+1 UPS units connected in parallel, battery modules, and power distribution systems.
3. System N+1 redundancy, reliability is higher than single UPS
4. Easy to expand and maintain, it is the most widely used solution
advantage:
1. Perfect phase-locked synchronization technology ensures that the load current can be evenly shared when multiple UPS are directly connected in parallel.
2. Good expansion performance (N+1)
3. Avoid the shortcomings of the "series" hot backup method.
shortcoming:
1. High requirements for the synchronous phase-locking technology of the equipment itself
2. High requirements on equipment manufacturing technology - output impedance is close.
3. High requirements for inverter output voltage regulation performance - phase regulation
4. UPS must be of the same model and capacity.
5. When multiple units are connected in parallel, the bypass also needs to add a "current sharing inductor"
Double busbar
Solve the single-point "bottleneck" problem of single-busbar operation mode. Further improve system reliability. The system configuration is complex, the investment is large, and the installation and debugging requirements are high.
Disclaimer: This article is compiled from the Internet. Interested engineers are welcome to correct and supplement it and make progress together!
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