UPS,is an uninterruptible power supply. It is usually one of the subsystems in weak current machine room projects, connecting batteries with main equipment to provide stable and uninterrupted power supply to devices.

When the mains input is normal, the UPS supplies the stabilized mains power to the load, acting as an AC voltage stabilizer, while also charging the internal battery; when the mains power is interrupted (accidental power outage), the UPS immediately supplies the load with the DC power from the battery through an inverter switching method.220V AC power, allowing the load to maintain normal operation and protecting the load's hardware and software from damage.

UPS devices typically provide protection against both overvoltage and undervoltage. Let's take a look at the basic knowledge of UPS.

Basic principles and main technical parameters of UPS

What is UPS?

An energy conversion device that uses the chemical energy of batteries as backup energy to provide (AC) power to user devices continuously during power outages or other grid failures.

Why do we need UPS?

The power supply provided by the mains grid may appear normal, but it is unreliable: seemingly normal power is actually fraught with crises.

 

Power interruption

• Data loss, communication interruption, business opportunity delays......

  —— Direct losses are calculated at 5000-100000 yuan per minute.

• Equipment downtime, instrument failure, surgery interruption......

  —— Indirect economic losses are incalculable.

Power pollution

• Transient spikes, power surges, high voltage pulses

  causing hardware damage to servers, routers, disk arrays, etc.

 

• Harmonic pollution, inter-line noise, frequency drift

  causing a significant increase in the network transmission error rate and slow data transmission speed.

Four main functions of UPS

Uninterruptible power function——solving the problem of power outages.

AC voltage stabilization function——solving the problem of severe voltage fluctuations.

Purification function——solving the problem of grid and power pollution.

Management function——solving the problem of AC power maintenance.

UPS system structure

The monitoring platform is also one of the most important components of the UPS.

Main technical parameters of UPS

Input characteristics:

1. Input voltage range   A wide input voltage range can reduce battery discharge opportunities and extend battery life.

2. Input power factor   A low power factor results in a large amount of reactive power input, harmonic current polluting the grid, and interfering with other devices.

3. Allowable range of main power frequency.

4. Input current harmonic components. (PFC, 6/12 pulse transformer)

Output characteristics:

1. Static stability. Large units are 1%, small and medium units are 2%.

2. Output transient characteristics. Large units are 5%, small and medium units are 8%.

3. Output overload capacity. (e.g., overload 125% for 5 minutes; 150% for 10 seconds)

4. Output power factor. (0.8, 0.9, 1)

5. Output voltage harmonic distortion. Typically within 3%.

UPS related configurations and calculations

The UPS system is mainly composed of the following parts:

•  UPS main unit

• Essential functional components (e.g., BCB BOX, etc.)

• Batteries

• Supporting battery cabinets/racks, battery switches, etc.

• Optional functional components (e.g., lightning protection, monitoring, harmonic treatment, output lines, etc.)

Calculations to be performed:

• Calculation and selection of UPS main unit capacity

• Calculation and selection of UPS backup battery capacity

Calculation and selection of UPS capacity

First, obtain the total power consumption of the load and unify the units to KVA.

For example: a typical personal computer load is about 200VA, a small server load is about 1500VA, and a medium to large server load is about 3000VA.

The conversion relationship between current I (A) and power W (watts) with VA.

• VA= I*220

• VA= W/0.8 (when calculating, it is usually considered that below 20KVA is 0.7, above 20KVA is 0.8)

Considering that the UPS operates best in the 60-80% range, it is generally recommended to divide the above result by 0.8 and then amplify it.

Then select the closest power product in the product manual.

• Using constant power mode calculation method

  W/cell = PL/(N×6×η)

Introduction to UPS power supply solutions

Centralized power supply method:

Advantages: Can achieve equipotential control of network device resources, reducing transmission error rates.

Disadvantages: High initial investment, significant impact from single machine failures.

Decentralized power supply method:

Advantages: Flexible layout of the scheme, small impact from failures.

Disadvantages: If the entire device cannot maintain the same ground line, it is prone to interference.

Single machine power supply

• One of the simplest UPS solutions

• The capacity of the AC power supply system at each dispersed location is mostly below 6KVA

• Each point's AC load is independently powered and protected by a UPS

• The mains power is usually input through nearby sockets

Master-slave machine series "hot backup"

• Suitable for small and medium-sized networks, server clusters, offices, instruments, and other applications

• Composed of UPS main unit, UPS slave unit, battery system, and distribution system

• Simple distribution design and engineering construction

Advantages:

Two or even multiple UPS units are basically in a relatively independent, non-interfering operating state.

Lower requirements for UPS synchronization tracking performance.

Using different models and capacities of UPS to form a series hot backup method.

Disadvantages:

The slave unit is in a long-term no-load operating state, resulting in low efficiency.

The slave unit's battery pack is in a long-term float charge state, with few opportunities for periodic load discharge maintenance, which can affect battery life.

The slave unit must have good step load handling capability.

For long-term operation, the main unit's inverter = static bypass switching function is key.

No expansion capability.

Compared to the "parallel" redundancy system, the average mean time between failures is lower.

Module parallel power supply

• All AC loads are centrally powered by one modular parallel UPS

• Modular UPS includes: rack, parallel power modules, parallel battery modules, charging modules, etc.

• Suitable for small and medium-sized networks, server clusters, offices, instruments, and other applications

• Composed of rack, UPS power module, battery module, and distribution system

• Power module configured for N+1 redundancy, reducing MTTR

• Shared input, output, parallel battery system, control system

N+1 direct parallel redundancy

• Suitable for medium to large networks, data centers, centralized power supply for buildings, industrial plants, and other applications

• Composed of N+1 directly paralleled UPS units, battery modules, and distribution systems

• System N+1 redundancy, reliability higher than single machine UPS

• Easy to expand, convenient maintenance

• The most widely used solution

Advantages:

Perfect phase-locked synchronization technology ensures that multiple UPS units can evenly distribute load current when directly paralleled.

Good expansion performance (N+1)

Avoids the disadvantages of the "series" hot backup method.

Disadvantages:

High requirements for the synchronization phase-locking technology of the equipment itself.

High requirements for equipment manufacturing technology - output impedance is close.

High requirements for inverter output voltage regulation performance - phase adjustment.

UPS must be of the same model and capacity.

When multiple units are paralleled, the bypass must also increase the "current sharing inductance".

Dual bus

Solves the single point "bottleneck" problem existing in single bus operation mode. Further improves system reliability. The system configuration is complex, investment is large, and installation and debugging requirements are high.

 

 

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