UPS equipment and DVR equipment

Abstract:

Taking voltage sag control equipment as the object, this paper analyzes the differences between UPS equipment and DVR equipment in application field, working mode, governance object, energy storage components and other aspects, and proposes the governance scheme of voltage sag and test wave pattern of dynamic voltage restorer products.


Nowadays, transmission and distribution system is becoming more and more complete, modern industrial equipment is approaching integration and precision, amounts of high-tech precision equipment that are sensitive to voltage sag , and they are applied in factories of various manufacture industries, such as optoelectronics, integrated circuits, petroleum and petrochemicals, semiconductor industry, workshop assembly. In the standard of IEEE, voltage sag is defined as the voltage drop process is when the effective value of the voltage drops to 10%~90% of the nominal value and the duration is 10ms to 1min. At present, it is generally believed that the voltage sag is caused by short-circuit faults in the system, switching of large motor equipment, and no-load excitation of large transformers;Voltage sags can cause problems such as failure, outage, and damage of sensitive loads, and can even cause huge economic losses to users.The contradiction between the inevitable voltage sag event and sensitive equipment in the power system has become increasingly prominent, making the voltage sag problem the most important and urgently-resolved power quality problem in industry and academia.


With the rapid development of high-power electronics, computers, and communication technologies, large-capacity uninterruptible power systems (hereinafter referred to as UPSs) and dynamic voltage restorers (DVRs) have been used tosolve the problem of voltage sag. UPS and DVR select similar devices in the aspect of structure , including high-power inverter, digital control chip ,backup energy storage element, and bypass isolation system, but each has some differences, here are the differences application field, working mode, governance object, energy storage components and other aspects, and offering reference for industry solve scheme and practical application selection.


1. Application areas:

Original designed UPS is used as backup UPS for single electrical equipment ( computer), which can cope with short-term power failure caused by power supply system, nowadays it is mainly used in commercial area as telecommunication, internet, bank, government , and industrial area like precision manufacturing, petroleum and petrochemicals and power station.Picture 1 is schematic diagram of online UPS. Operation mode of online UPS can be divided into three categories, which are normal operation mode, back-up mode and bypass operation mode, the features of three modes are as below.

① Normal operation mode, rectifier equipment conveys AC power from mains input to inverter through rectifier output DC power; inverter converters DC power from rectifier to AC power, which is transformed to load equipment to make sure the normal operation of equipment.

② Back-up mode, UPS equipment is directly connected to DC system, DC system immediately outputs DC power to the inverter to replace the interrupted rectifier output power. In the output process, there is no consequence to load voltage.

③ Bypass mode, it is divided into two kinds, which is backup bypass and maintenance bypss mode, backup bypass is mainly used in inverter that is in abnormal situation, such as over temperature, short circuit, abnormal output voltage or overload, inverter stops work in case of damage; maintenance bypass is used when the UPS equipment needs to be maintained or repaired, users can make is into maintenance bypass mode to ensure the uninterrupted operation of system and the safety of maintenance personnel.

DVR belongs to voltage sag suppression device aiming at keep the whole electric system safe, its main function is to prevent the impact of voltage fluctuations on the load effectively, which is suitable for protecting normal work of whole manufacturing line. it is used in petrochemical industry, semiconductor precision manufacturing, automobile manufacturing industry. Picture 2 is working theory diagram of DVR. DVR can be connected between power supply circuits and load in parallel, its operation mode includes grid voltage power supply mode and inverter power supply mode, the features of two modes are as below.

① Grid voltage power supply mode, inverter will be backup and stops load power supplying when the mains are in normal situation, system is in the situation of electric bypass, AC power is supplied to load by electronic bypass switch.

② Inverter power supply mode, when mains are in abnormal situation, energy saving component such as super capacitor output AC power by inverter, DVR releases complete voltage with the same amplitude and phase as drop voltage in typical response time 2ms, replace the original voltage value provided by mains so as to guarantee the continuity of system output.



2. Working mode:

Working mode of DVR is in electronic bypass mode wen voltage input of system is normal, it is in compensation mode when voltage sag happens, thus DVR has the prominent characteristic of low energy consumption, its efficiency can be up to 99%. UPS is supplied power by inverter no matter is mains is normal, whose sequence is mains input, rectifier, inverter, and output. Its efficiency is 92% without considering battery loss.Take 800kVA UPS equipment and DVR equipment commonly used in the integrated circuit industry as an example,2.878 million yuan electricity fee can be saved in ten-year life if counted as 0.8yuan per KWH, replacement fee of DC energy saving component can be saved about 3.072 million yuan, details are as below.

Calculation of operating cost savings


UPS

DVR

capacity

800kVA

800kVA

Power factor

0.8

0.8

Load

0.9

0.9

Loss

8%

1%

 One decade

24h/D*360D*10

Electricity fee (RMB/KWH)

0.8

TOTAL (MILLION)

3.185

0.398

DC component replacement costs(MILLION):

28.5(replaced within 10 years)

0(no need to replace)

TOTAL (MILLION)

3.47

0.398

TOTAL SAVING (MILLION):

3.072



3. Governance object:

Main function of UPS is to improve power quality and keep uninterrupted in a short time, battery is the pillar of backup time in UPS system, UPS without battery can only be called CVCF, whose actual application value is none. When Mains is abnormal, inverter directly converts chemical energy in battery into AC power, electrical equipment operates continuously after AC power is outputted. Normally without external power supply, UPS can remain ten minutes to dozens of hours’ power supply depending on different batteries with different capacity. UPS is very suitable for completing computer’s important data backup and maintaining financial system operation. We could see that DVR is mainly applied in large-scale complex manufacturing line and sensitive system links, whose purpose is to prevent it from being effected by voltage fluctuation, it is used for controlling power quality problems as voltage sag , voltage rise and short-time power off, its interruptive capability is not that powerful, and it can only maintain for seconds as backup.



4. Energy storage device

Maintenance-free sealed lead-acid battery is being widely used in UPS power at present, which has much higher maintenance cost. The service life of battery in UPS is about 5 years in it is normally used. There are some points about battery as energy storage device except the factor of cost.

① It needs to work in a suitable ambient temperature, ambient temperature is an important factor influencing service life of battery, service life of battery can be seriously reduced though temperature rise improves the capability of battery discharge, according to the test, the battery is in the best status under the temperature of 20-25℃, Above 25 ° C, the battery life will be reduced by half for every 10 ° C increase.

② The floating charge voltage and discharge voltage in the UPS power supply are set to the rated values at the factory,The size of the discharge current increases as the load increases, and the load should be reasonably adjusted during use,such as control the number of computers and other electronic equipment. Normally the load should not exceed 60% of the rated UPS load. Discharge current of battery will not over discharge in this range. Power supply quality is high as UPS connects with Mains in a long term, and power off rarely happens, battery is in the situation of floating charging in a long time, which will lower conversion active between battery chemical energy and power supply, speed up aging and reduce service life. This is why we discharge it once in 2 or 3 months, discharge time can be confirmed by the capacity and load of the battery. After discharging, the battery needs to be charged for at least 8 hours according to the regulation.

③ At present, batter number equipped in large or medium size UPS ranges from 23 to 80, or even more. Single battery combined as battery group through circuit connection, so as to satisfy the demand for UPS DC power supply. During the continuous operation of UPS, it is inevitable that the performance of some battery degrades and energy store capacity fails to meet the requirements due to differences in performance and quality.When one or some of the batteries in the battery pack are damaged, the maintenance personnel should perform an inspection test on each battery to exclude the damaged battery. Same type of battery from the same manufacturer should be purchased when replacing a new one. It is prohibited to mix acid-proof batteries, sealed batteries, and batteries of different specifications.


UPS once used freewheel as load for power supply before using battery as energy storage device, this kind of UPS is called flywheel or rotary uninterruptible power supply. Rotary uninterruptible power supply consists of rectifier, DC motor, flywheel, diesel engine (or gasoline engine) and generator. DC-driven motor provided by rectifier drives flywheel to rotate when it is supplied power by grid, generator also supplies power for the load, which saves floor space. With the development of lithium battery technology, most UPS is equipped with lithium battery,Compared with lead-acid batteries, lithium batteries can have a significant reduction in energy storage density, equipment weight, and equipment volume, and in terms of charging and discharging times and service life, there are also major technical changes. See Table 2 for comparison of technical performance of energy storage components.

energy storage technology

Energy Density Wh·kg-1

Power Density W·kg-1

Cycle life / time

Technical level

cost

Super capacitor

1-10

10^3-10^5

10^3-10^5

Basically mature

midium

Flywheel Energy Storage

5-50

18-1800

10^4-10^5

developing

high

Lead-acid batteries

20-80

50-200

<1000

Very mature

low

Lithium Ion Battery

100-200

1500-3000

3000-5000

Basically mature

low


DVR selects super capacitor as energy storage component, and discards traditional battery component. DC voltage in super capacitor equipment is inverted to a specific power frequency sinusoidal AC voltage, which provides integrate power supply for load in the way of parallel injection system line, thus ensuring reliability of system. Compared with lead-acid batteries, super capacitor has below advantages.

① Fast charging speed, fulfilling 95% of rated capacitor only needs 10 senconds, 10 minutes at most.

 Long cycle life, high-quality super capacitors can be deeply charged and discharged for up to 1 million cycles;

 High energy conversion efficiency. Large current energy cycle efficiency> 90%;

 High power density. Up to 1000W / kg—50000W / kg, more than 10 times the battery;

⑤ Raw materials are free from pollution during production, use, storage and dismantling, making them ideal green power sources; high safety factor, maintenance-free for long-term use;

⑥ High charge and discharge efficiency. Because the internal resistance is small, the charge and discharge losses are also small, and it has a high charge and discharge efficiency, which can reach more than 90%.

⑦ Wide temperature range. It can reach -40~+ 70℃. The reaction rate of the electrode material of the super capacitor is not greatly affected by temperature;

 Convenient detection and control. The remaining power can be directly calculated by the formula E = CV2 / 2. The stored energy can be determined only by detecting the terminal voltage. The calculation of the state of charge (SOC) is simple and accurate, so it is easy to manage and control energy.


In addition to the above differences,UPS uninterruptible power supply equipment and DVR dynamic voltage restorer equipment also have the following same points.

 Both have inverters and output filtering devices, regardless of the difference in device parameter selection under the same specifications, their main structure of the working circuits are the same.

② Both can be equipped with static bypass circuit, and optional manual maintenance bypass. The main role lies in the safety of the system and the safety of maintenance personnel when the main circuit of the equipment fails.

 In design concept, UPS and DVR both use advanced high-tech optical fiber, communication, fully digital computer, humanized operation design and monitoring interface.

④ Equipped with comprehensive protection functions. It can automatically protect the device when overload, over-voltage, under-voltage, or frequency is abnormal (you can set the action value from software).

⑤ Both can be equipped with output and input isolation transformers to meet the needs of industrial applications.



5. Hierarchical governance scheme configuration

Most of the existing voltage sag management measures are based on power electronics technology, governance equipment has high costs, large losses, poor reliability, and limited capacity. It is difficult to adapt to the needs of modern industrial parks with many voltage levels, large user capacity, and many electrical equipment.In view of the above problems, many domestic scholars have proposed a hierarchical voltage sag management scheme based on solid-state switch.According to the four levels of voltage level, voltage sag level, equipment criticality level, and equipment voltage withstand level, the program implements hierarchical management of load equipment.For the low-voltage side, after all the sensitive loads are simply gathered, from the perspective of factory equipment, the dynamic voltage restorer DVR equipment is preferentially configured, and the super capacitor backup time is reasonably selected.For devices that are extremely sensitive to voltage sags and require a certain backup time, priority is given to centralized high-power UPS equipment, and lead-acid batteries, lithium batteries, flywheels and other energy storage equipment are reasonably selected according to time. 

AVR series is the product type of DVR in AVIC-TECH, it is a new type of electronic power device, which connects power and sensitive load. AVR also supplies power for load through outputting rated voltage in a short time when voltage sag, voltage interruption or voltage rise happen in grid voltage,which making sure the continuous operation of equipment. AVR operates in bypass mode when voltage is normal, and its efficiency can be up to 99% that greatly reduces operation loss. Besides , AVR from AVIC-TECH selects super capacitor from world famous brand MAXWELL as short-term energy storage element, it can be guaranteed for 10 years and be charged and discharged for 1 million times, which completely realizes the maintenance-free life cycle and greatly reduces the maintenance cost of the battery.At the same time, the entire AVR footprint is reduced by more than 60% compared with the same power UPS, and no special battery room is required.



6. Conclusion

This article lists the similarities and differences between UPS equipment and DVR equipment, and elaborates the performance comparison among various energy storage components. Hierarchical governance plan for voltage sag not only offer standard configuration for voltage sage governance measurements in modern industrial areas, but also effectively promote grading management ,cooperation and optimization for grid side and user side, which has the characteristics of outstanding technical standards, low construction and operation and maintenance costs, high reliability, high safety, and high practicality.



AVIC-TECH (Xiamen) Electric Power Technology Co., Ltd. is hold by AVIC International group and was founded in 2002 as an innovative company committed to researching, developing, manufacturing and marketing high-end power supply. We are the leading company in China to manufacture industrial uninterruptible power supply (UPS), UPS for electricity industry and new generation of green industrial UPS. Over a decade in manufacturing UPS for industrial use, we always provide professional, efficient and reliable power supply solution to the customers all over the world.



About Avic-tech

Avic-Tech (Xiamen)Electric Power Technology Co.,Ltd is a high-tech enterprise specializing in R&D, manufacture, sales and service of high-end power supply. Our flagship products are industrial UPS (1kVA-800kVA), dynamic voltage restorer (10kVA-2000kVA), and lithium battery system, which are widely used in nuclear power, electric power, petroleum and petrochemical, rail transportation, industrial manufacturing and other fields.

Name: Mia Ling

Email: lwy@avic-tech.com.cn  

Official site: http://www.avic-tech.com

Tel: +86 592-2999 677





Tel: 0592-2999668
E-mail:sale@avic-tech.com.cn
Headquarters: No. 26, Xinlue Road, Haicang District, Xiamen City,China
Home Page|About Us|Products|Projects|News|Marketing|Services