The most comprehensive of uninterruptible power supply knowledge summary for weak current engineering

Time of issue:2021-05-19


Ⅰ.  Why do you need UPS?


The power supply provided by the mains grid looks normal, but it is unreliable: the seemingly normal power is actually dangerous.


1. Power interruption

> Data loss, communication interruption, delay in business opportunities......—— The direct loss is calculated at 5000-100000 yuan per minute,
> Equipment outage, instrument failure, operation interruption......—— the indirect economic loss is immeasurable,


2. Power pollution

> Transient spikes, power surges, high-voltage pulses cause hardware damage to servers, routers, disk arrays and other equipment,
> Harmonic pollution, line-to-line noise, and frequency drift cause the network transmission error rate to increase greatly, and the data transmission speed is slow.

Ⅱ. Four major functions of UPS

> Non-power failure function - to solve the problem of power outages in the power grid.
> AC voltage stabilization function - can solve the problem of severe fluctuations in network voltage.
> Purification function - solve the problem of power grid and power pollution.
> Management function - solve the problem of AC power maintenance.


Ⅲ. UPS system structure

The monitoring platform is also one of the most important parts of UPS,

Ⅳ. UPS main technical parameters

1. Input characteristics:

> Input voltage range Wide input voltage range can reduce the chance of battery discharge and prolong battery life.
> Input power factor The power factor is low, the input reactive power is large, and the harmonic current pollutes the power grid and interferes with other equipment.
> Allowable range of main power frequency.
> Input current harmonic components. (PFC, 6/12 pulse transformer),


2. Output characteristics:

> Static stability. Large is 1%, small and medium is 2%.
> Output transient characteristics. Large 5%, small and medium 8%.
> Output overload capacity. (Such as: overload 125% 5MIN; 150% 10S),
> Output power factor. (0.8, 0.9, 1),
> Harmonic distortion of the output voltage. Typically within 3%.


Ⅴ. UPS related configuration and calculation

1. The UPS system basically consists of the following parts:

> UPS host.
> Mandatory features (such as BCB BOX, etc.).
> Battery.
> Supporting battery cabinet/rack, battery switch, etc..
> Functional options (such as lightning protection, monitoring, harmonic control, on-line outgoing, etc.).


2. Calculations to be performed:

> UPS host capacity calculation and selection.
> Calculation and selection of UPS battery capacity.


3. UPS capacity calculation and selection

> First obtain the total power consumption of the load and unify the unit to KVA.
For example: general personal computer load is about 200VA, small server load is about 1500VA, large and medium server load is about 3000VA.
> Conversion relationship between current I (A ampere) and power consumption W (watt) and VA.
•VA= I*220
•VA= W/0.8 (It is usually considered as 0.7 for less than 20KVA and 0.8 for more than 20KVA in the calculation).
> Considering that the UPS operating in the 60-80% range is the best operating state, it is generally recommended to divide the above result by 0.8 and zoom in again during calculation.
> Then select the closest power product in the product manual.
> Using constant power mode calculation method W/cell = PL/(N×6×η).


Ⅵ. UPS power supply scheme introduction

1. Centralized power supply mode:

> Advantages: It can realize the equipotential control of network equipment resources and reduce the transmission error rate.
> Disadvantages: The initial investment is large, and the single machine failure has a large impact.

2. Distributed power supply mode:

> Advantages: Flexible plan layout and small failure impact.
> Disadvantages: If the entire device cannot maintain the same ground wire, it is easy to cause interference.

3. Stand-alone power supply:

> The simplest one of UPS solutions.
> The capacity of the AC power supply system in each scattered location is mostly below 6KVA.
> Each point of the AC load is independently powered by a UPS to provide power protection.
> Usually, the mains is input by the nearest socket.

4. Master-slave series connection "hot backup":

> Suitable for small and medium-sized networks, server clusters, offices, meters and other applications.
> Consists of UPS host, UPS slave, battery system, and power distribution system.
> Simple power distribution design and engineering construction.



> Two or more UPSs are basically in a relatively independent operating state without interfering with each other.
> Low performance requirements for UPS synchronization tracking.
> Different types of UPSs with different capacities are used to form a series hot backup mode.



> The slave machine has been in no-load operation for a long time, and the efficiency is low.
> The battery pack of the slave machine is in a floating charge state for a long time, and there are few maintenance opportunities for regular on-load discharge, which will affect the battery life.
> The slave must have good step load capacity.
> Long-term operation, host inverter = static bypass conversion function is the key.
> No expansion function.
> Compared with the "parallel" redundant system, the mean time between failures is low.

5. Parallel power supply of modules

> All AC loads are supplied centrally, powered by a modular parallel UPS.
> Modular UPS includes: racks, parallel power modules, parallel battery modules, charging modules, etc..
> Suitable for small and medium-sized networks, server clusters, offices, meters and other applications.
> Consists of rack, UPS power module, battery module, power distribution system.
> The power module is configured for N+1 redundancy, reducing MTTR.
> Shared input, output, parallel battery system, control system.


6. 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 N+1 UPS, battery modules and power distribution system directly paralleled.
> System N+1 redundancy, higher reliability than stand-alone UPS.
> Easy to expand, easy to maintain.
> Is the most widely used program.


> The perfect phase-locked synchronization technology ensures that the load current can be shared equally when multiple UPSs are directly connected in parallel.
> Good expansion performance (N+1)
> Avoid the shortcomings of the "series" hot backup method.


> High requirements for synchronizing phase lock technology of the equipment itself.
> High requirements for equipment manufacturing technology-the output impedance is close.
> High requirements for inverter output voltage regulation performance-split phase regulation.
> The UPS must be the same model and capacity.
> When multiple units are connected in parallel, the bypass also needs to increase "current sharing inductance".

Ⅶ. Double bus

Solve the single-point "bottleneck" problem in the single-bus operation mode. Further improve system reliability. The system configuration is complicated, the investment is large, and the installation and debugging requirements are high.