The 3rd National Graduate Conference (NatGrad2015), Universiti Tenaga Nasional, Putrajaya Campus, 8-9 April 2015.
Process Optimization for AC/DC Conversion
Solution based on Open Source Software
Ho Kai Fatt
College of Graduate Studies, Universiti Tenaga Nasional, Malaysia. Email: richardhkf@gmail.com
Ahmad Qisti bin Ramli
College of Engineering, Electrical Power Department, Universiti Tenaga Nasional, Malaysia. Email: qisti@uniten.edu.my
Abstract - This paper proposes a new method using an open
source software that receives user input and selects and compares
an optimized solution for a DC backup power system. This
solution comprises of a rectifier system which converts AC to DC
power and a battery system which provides the DC backup power.
The open source software will derived the solution based on the
input and produce an optimized and cost effective solution. The
algorithm on how to choose the correct rectifier model and battery
model is written in an open source software, namely SCILAB. The
rectifier system and battery selection optimization is analyzed
according to the entered load and backup time with respect to
lowest cost. This open source software solution is intended for
technical personnel who requires a fast and effective way to
propose standard solution product options in their manufacturer’s
rectifier and battery system domains respectively.
Keywords—Battery charger; AC/DC Conversion; Battery
backup system; rectifier; Power conversion; Battery charging;
SCILAB; open source software; Optimization; conversion; AC-DC
Power converters; single-power conversion
I.
INTRODUCTION
Telecom energy systems around the globe are powered
by DC Power. They have been traditionally powered by either
24VDC or 48VDC and has a typically back up time of between
2 to 8 hours of battery power. It may also be coupled with a
diesel generator to provide seamless uninterrupted DC power
supply during outages of the utility mains [1]. This energy
system plays an important role in supporting and maintaining a
constant availability of direct current power to the
telecommunication network equipment around the region.
Therefore a downtime is not acceptable by telecom operators as
they will lose revenue by the minutes if it happens.
A technical personnel of a DC power system company
often have too many different system sizing tools in terms of
spreadsheets and customized calculators to do their system
sizing. Some may even use a simple excel spreadsheet to do
their system sizing. By using too many templates one can cause
inefficiency in searching and comparing the best optimize
solution to offer to the end user and thus waste time.
This paper provides a more efficient way to optimize
the power system in terms of cost, selection of battery models
and selection of manufacturer’s equipment all rolled into one
optimization tool which runs on an open source software,
namely Scilab. Scilab was chosen because it’s an open source
software with an impressive numerical computation in the
domains of scientific and engineering applications. [4]
II.
AC/DC POWER CONVERSION
A. AC to DC Power Conversion Architecture
Fig. 1, shows the typical block diagram of a backup
power application. It consists of two major components such as
the rectifier which converts the incoming AC power to DC
power, powers the load and charges the battery. The other major
component which is the battery, functions as an energy storage
device which powers the load when there is a failure in the
incoming AC power [2]. The red arrows in Fig. 1 shows the
current flow from the main AC input through the converter to
the load whereas the green arrows shows the current flow from
the backup power to the equipment load in the event the AC
input fails.
`
Fig. 1. Block diagram of AC to DC Conversion current flow.
B. Rectifier System
The function of the AC to DC converter is to rectify
and reverse the AC current into one direction, which is label as
direct current (DC). In a typical telecom architecture the
commonly used voltage is -48VDC. The reason being negative
is that the battery positive side is grounded and the negative
polarity is used. There are a few manufacturers of rectifier
systems notably Emerson Network Power. In this solution, the
process optimization software will use a few types of this
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The 3rd National Graduate Conference (NatGrad2015), Universiti Tenaga Nasional, Putrajaya Campus, 8-9 April 2015.
manufacturer’s rectifier to optimize and produce a cost
effective DC power solution. [3]
C. Battery System
The battery bank operates according to the voltage of
48VDC. By providing 24 cells of 2V batteries in series we can
meet this voltage requirement [2]. These battery cells have a
range of between 100Ah to 6000Ah from a variety of
manufacturers around the globe. However in this paper we will
take 3 commonly used batteries namely Narada batteries,
Vision batteries and Sacred Sun batteries. These battery brands
will be used in the software whereby it will intelligently select
the cost effective battery according to user load input.
III.
battery is done seamlessly using SCILAB software. This paper
proposes the use of a newly develop optimization software for
any rectifier manufacturer. It is flexible and more efficient in
generating a solution proposal which is optimized and cost
effective. The technical personnel can use this proposal as an
additional document attachment to be submitted to the
customer. Once the solution proposal is generated it will show
available options that the user can choose in terms of safety
margin and cost.
Fig. 3, shows the overview of the algorithm flow of the
developed software.
SINGLE LINE DIAGRAM
In telecom networks, the rectifiers used are modular.
Which means reliability is achieved by implementing an N+1
configuration in the system. N refers to the number of rectifiers
intended for the load and an extra spare rectifier which will be
on standby if any of the rectifiers in the system fails.
Fig. 2, shows a typical single line diagram of an AC to
DC power system whereby rectifiers are arrange in parallel with
an N+1 configuration. The battery banks are connected via DC
MCB’s and powered the load in the event there is an AC mains
failure. The load distribution may consist of different types of
MCB ratings or fuses suitable for the load.
Fig. 3. Overview of Software Solution
Fig. 2. Single line diagram of a typical AC/DC Power conversion system.
IV.
SOLUTION OPTIMIZATION
A. Optimization approach using open source software
Technical personnel from business units of large
companies who manufacture DC Power systems require tools
to do their equipment sizing. One typical example is using the
commonly available excel template and customizing it to do the
rectifier and battery sizing according to the manufacturers
product line. By doing this it can consume a lot of time. If there
is more than 10 projects at hand which requires solution
optimizing in terms of cost, it will be a challenge. This can be
daunting in respect to the time constraint that these technical
personnel face, as these pre-tenders have a limited timeline for
submission.
With respect to this issues faced by these employees,
the amount of process optimization in sizing the rectifier and
Step by Step features are explained here
1) User enter predefined parameters.
2) Scilab Phase 1 will then work in the background
to size the rectifier and extract battery data based
on these input parameters.
3) Read data from library – Scilab will read the
battery data in terms of hours and do a
comparison, it will then smartly selects the best
three battery models AH base on optimized
criteria.
4) Formulate Solution – Input data is analyzed with
library data to produce a solution.
5) Technical proposal will then be generated by
Scilab and it will show the bill of quantity
required by the solution in terms of cost and safety
margin.
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The 3rd National Graduate Conference (NatGrad2015), Universiti Tenaga Nasional, Putrajaya Campus, 8-9 April 2015.
B. Battery Selection Process
In selecting the correct battery model and type for
indoor or outdoor solutions, we need to choose the correct type
of batteries. Valve regulated lead acid batteries are commonly
used as energy storage for telecommunication applications due
to their high energy concentration, long service life and their
high cycling ability. Another advantage would be its small
space size and with this reason it can be deployed into smaller
sites effectively [5]. In this software, 3 major battery brands
with competitive prices are used. These type of batteries are
completely sealed and leak proof at a nominal voltage of 2V
each.
Fig. 4, shows the process flow on how the algorithm
obtains and selects the correct battery brand in terms of load and
cost.
load and 4 hours backup time is used as an
example. The formula used to calculate battery
banks is as below :
= /
(1)
= Battery Banks
= Equipment W/Cell
= Battery W/Cell
4) Once the battery banks are calculated, if the value
is greater than one it requires more than one bank
of batteries. Values obtained less than one
requires only one battery bank.
5) The ratio accuracy of the solution is also
calculated to ensure the battery selected and used
is optimized. Ratio accuracy formula is shown as
below:
=
× 100%
(2)
= Ratio Accuracy
= Equipment W/Cell
= Battery W/Cell
6) Once all this are completed, the battery solution
portion will display the amount of battery banks
required, brand, model and price. User can
compare these in a table.
The battery constant power discharge table is shown
in Table I, compares three battery brands in terms of W/Cell
versus battery type and price. The end of discharge voltage is
typically selected as 1.80V per cell for discharging of more than
1 hour. This is because if the battery voltage falls below 1.8V
threshold it might damage the equipment and also the battery
cells [6].
TABLE I.
CONSTANT POWER DISCHARGE TABLE OF 3 BATTERY
BRANDS
Hours
Fig. 4. Battery solution process flow
Step by Step explanation on how it flows here
1) Users enter the items required in the “Parameters
Input”.
2) Equipment load is divided by 24 cells to obtain
the watt per cell value for the load.
3) This value is taken and compared with the battery
watt per cell table which consists of 3 major
brands mainly Narada, Vision and Sacred Sun.
Table I shows the comparison of the power
discharge table of the three brands. In this battery
solution optimization 83.3W/Cell for equipment
Constant Power Discharge (Watts per cell) at 25
degrees to 1.80 Volts per cell
Brand Type I
Brand Type II
Brand Type III
Brand Type
NARADA
VISION
SACRED SUN
Model Type
EOS-200
CL200
GFM-200C
Price
(USD)
Ratio
Accuracy
Battery
Banks
Required
100 a
102 a
95 a
94%
104%
116%
1
2
2
2
147
126
117
3
108
94.7
89.1
4
89.1
80.3
71.9
12
36.1
32.6
32.2
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The 3rd National Graduate Conference (NatGrad2015), Universiti Tenaga Nasional, Putrajaya Campus, 8-9 April 2015.
Table II shows the summary of the battery brands in
terms of battery model type and price per battery bank. In this
example, 3 battery brands are compared based on three
constraints which is the ratio accuracy, amount of battery banks
and cost per bank.
TABLE II.
When calculating the rectifier modules, the value obtained is
rounded up to the nearest higher value and added with another
extra module to comply with N+1 redundancy. Fig. 5, shows
the process flow on how the algorithm obtains and selects the
rectifier in terms of quantity and cost.
BATTERY TYPE AND PRICE TABLE BASED ON 83.3W/CELL
EQUIPMENT LOAD AND 4 HOURS BACKUP TIME
Solution Details
Battery
Type and
Price
Number
of Banks
Ratio
Accuracy
Battery
Model
Price
(USD)/
per
block
Total
Bank
Price
(USD)
Battery
Solution 1
1
94%
Narada
EOS200
100a
2400a
Battery
Solution 2
2
104%
Vision
CL200
102a
4896a
Battery
Solution 3
2
116%
Sacred
Sun
GFM200C
95a
4560a
a.
Dummy prices shown are for illustration only.
C. Rectifier Selection Process
Once the user has entered the equipment load and the
battery solutions has been selected, the algorithm will proceed
to the rectifier module selection process. It will then select the
appropriate amount of required rectifier modules based on the
total load which includes battery charging and equipment load.
The rectifier needs to be sized based on total load and not
equipment load alone. As the rectifier converts AC to DC
power, it is supplying 48VDC power to the load and also at the
same time charging the battery bank. With this in mind, both
the battery charging and actual equipment load needs to be
taken into account when sizing the amount of rectifier modules
required in the DC system. In this paper, Emerson Network
Power product portfolio of DC power solutions will be used.
Their products consist of rectifiers, controllers, 19 inch standard
subracks and cabinet solutions [7]. In this example subrack
solution is chosen.
The algorithm will calculate and design the solution
based on below formula:
=
=
1 +
2=( )×
1
2
2
Fig. 5. Rectifier quantity selection process flow.
Solution details of rectifier will be displayed as Table III, which
shows the summary of the rectifier model with subrack offered,
price and quantity. In this solution two subracks with different
rectifier modules rating is shown. A safety margin is included
to let the user know the amount of spare power available that
the rectifier modules can provide. The formula to calculate this
safety margin is as below:
α=(
α
(3)
(4)
TABLE III.
(6)
= Safety Margin (W)
= Total load consumption (W)
= Total rectifier required
= Individual rectifier capacity (W)
RECTIFIER TYPE AND PRICE TABLE
(5)
= Total load consumption (W)
= DC Equipment load (W)
= Battery charging load (W)
= Total rectifier modules ( > 1)
= Individual rectifier capacity (W)
= Backup time (hours)
× ) −
Solution Details
Subrack
Type
Netsure
501 A41
Netsure
701 A41
ISBN 978-967-5770-63-0
No of
Rectifier
(N+1)
3
2
Model of
Rectifier
R482000
R483500
Safety
Margin
(W)
Price (USD)/
Unit
Total
Rectifier
Price
(USD)
1040
400b
1200b
540
700b
1400b
b.
Dummy prices shown are for illustration only.
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The 3rd National Graduate Conference (NatGrad2015), Universiti Tenaga Nasional, Putrajaya Campus, 8-9 April 2015.
D. Expected Output
Once the process optimization is complete for battery
and AC-DC converter system, the output solution options will
be shown in Table IV. It will show the overview of the optional
solutions that the user can choose based on three battery
solutions and 2 models of rectifier modules. If the user is not
satisfied with the solution obtained, the process can be repeated
again from the beginning to produce a more preferable solution.
The total cost of solution is calculated based on below formula:
= + +
(7)
= Total Cost
= Total rectifier cost
= Total subrack cost
= Total battery bank cost
TABLE IV.
DC POWER
SOLUTION
Model Name
Number of Rectifier
Modules
Safety Margin (W)
Total Rectifier Cost
(USD)
Rack Cost (USD)
Subrack Total
Cost (USD)
Subrack Total Cost
+ Battery Solution 1
(USD)
Subrack Total Cost
+ Battery Solution 2
(USD)
Subrack Total Cost
+ Battery Solution 3
(USD)
Description
Netsure 501 A41
Netsure 701 A41
3
2
540
c
1,400.00 c
2,000.00 c
3,000.00 c
3,200.00 c
4,400.00 c
5,600.00 c
6,800.00 c
8,096.00 c
9,296.00 c
7,760.00 c
8,960.00 c
c.
CONCLUSION
In this paper, the process of optimizing the selection
process to produce an AC/DC Power conversion solution is
based on SCILAB. The usage of Scilab is due to its simplistic
interface and straight forward numerical computation. In using
this open source software, it has been proven it simplifies and
automates the optimization process in terms of the battery
banks, subracks, and rectifier modules. It also provides an
overview of the options available for the solution in terms of
cost.
[1]
Solution Details
1,200.00
V.
REFERENCES
SOLUTION DETAILS TABLE
1040
type and safety margin versus the price. The use once acquired
the solution details table can make a decision on which solution
option to choose. The intended software for the user when
develop is meant to automate the optimization process which
was done manually.
Dummy prices shown are for illustration only.
The cost effectiveness of this solution is based on
comparing the total solution prices of different rectifier module
types and the type of battery brands. The selection of the battery
solution is mainly based on the amount of battery banks and
ratio accuracy versus the price. On the other hand, the rectifier
solution selection is based on the number of modules, subrack
Michel Fraisse, and Laurent Buchsbaum, “Environment Friendly High
Quality, High Availability Telecom Power Plant Architecture,” IEEE
Telecommunications Energy Conference 2002. INTELEC, pp. 463469, 2002.
[2] “The Power of DC in Rural Telecom Systems,”
http://ecmweb.com/design/power -dc-rural-telecom-systems, January
24, 2015.
[3] “Rectifier,” http://en.wikipedia.org/wiki/Rectifier, January 23, 2015.
[4] “About Scilab,” https://www.scilab.org/scilab/about, December 25,
2014.
[5] Bruce Fountain, “Telecommunications – VRLA Battery Maintenance,
Testing and Replacement,” December 2014.
[6] “Battery Sizing,”
http://www.openelectrical.org/wiki/index.php?title=Battery_Sizing,
January 3, 2015.
[7] “Netsure 501, High Density DC Systems for Small Telecom
Applications,” http://www.emersonnetworkpower.com/enASIA/Products/DCPower/ensys_ACDCPowerSystems/SmallDCSyste
ms/Pages/NetSure501.aspx, January 2, 2015.
[8] “Part 8- How to ensure your UPS batteries don’t fail,”
http://www.upssystems.co.uk/knowledge-base/the-it-professionalsguide-to-standby-power/part-8-how-to-ensure-your-batteries-dont-fail/,
January 15, 2015.
[9] “Stored energy solutions for a demanding world, Narada, Eos-200,”
http://en.naradapower.com/products/SLA/battdata/pdffiles/Eos/Eos200.pdf, November 30 , 2014.
[10] “CL200 2V 200Ah (10hr) Vision,”
http://www.solarguru.com.au/PDFs/CL200.pdf, November 1 , 2014.
[11] “Sacred Sun, GFM-C Series/GFM-200C 2v200Ah,” http://sacredsun.com/pdf/GFM-200C.pdf, November 18 , 2014.
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