design and implementation of a low power linecommutated...
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ECE 4600 Group Design Progress Report
Group 14 Chen Chen
Lyle Motluk Hang Li
Jingwei Liu Yingyang Huo
Academic Supervisor Dr. Aniruddha Gole
Electrical and Computer Engineering Department University of Manitoba
Industrial Supervisor
Arash Darbandi Manitoba HVDC Research Centre
Date of Submission January 12nd, 2015
Design and Implementation of a low power Line-Commutated Converter
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Table of Contents
Glossary of Terms .......................................................................................................................... 2 1 Introduction ........................................................................................................................ 3
2 Project Summary ............................................................................................................... 3 2.1 PSCAD circuit design (Lyle,Hang) .......................................................................... 4 2.2 AC filter design (Hang) ........................................................................................... 4 2.3 Thyristor drive circuit (Yingyang,Jingwei) .............................................................. 5 2.4 Control system (Jingwei,Hang) ............................................................................... 6 2.5 Human Machine Interface (Chen) .......................................................................... 6 3 Future Work ....................................................................................................................... 7 3.1 Control System ......................................................................................................... 7 3.2 Gate Drive Circuit .................................................................................................... 7 3.3 Human Machine Interface ........................................................................................ 7 3.4 Construction and Testing of Complete Design ........................................................ 7
4 Conclusion .......................................................................................................................... 7 5 Gantt Chart ........................................................................................................................ 8
6 Budget ................................................................................................................................. 9
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1. Introduction
The goal of this project is to develop an accurate low power HVDC system to represent
the concepts of a HVDC and implement the design with standard laboratory equipment (Lab-
Volt). HVDC-LCC systems implemented in power transmission require voltage and power in the
kilovolt and megawatt range, which cannot be implemented safely in laboratory settings.
Therefore the low voltage HVDC-LCC design will represent a scaled down version of the
CIGRE (International Council on Large Electric Systems) developed model of an HVDC-LCC.
The lower power HVDC-LCC will first be designed using PSCAD software before transferring
the controllers to RTDS and assembling the final design on Lab-Volt equipment. The final
product will provide instructors an accurate model to educate students on HVDC systems with
the goal of improving the design in a safe low power lab environment to be implemented in
industry.
This project was divided into modular tasks, which allowed individual members of the
team to complete different sections of the project simultaneously. This process has ensured that
although problems arouse and delayed certain sections, the entire project was not derailed. The
report breaks down the problems and progress that occur since the beginning of the school year.
2. Progress Summary
The design portion of the project is complete. The remaining work pertains to assembling
the components and testing the overall system. This project is divided into five sections (I)
PSCAD design, (II) AC/DC filters, (III) Gate Drive Circuit, (IV) Control Systems, and (V)
Human Machine Interface.
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2.1. Design in PSCAD
The low power line-commutated converter was designed using PSCAD, power systems
simulation software. The LP-LCC consists of a rectifier and an inductor. The rectifier
components include input alternating current that is step down with a high voltage transformer
from 205V to 52 V, a series of AC filters that remove harmonics, a gate drive circuit responsible
for converting AC voltage to DC voltage, a controller that regulates a consistent 2 amp DC
current. Presently the rectifier design in PSCAD is complete. The inductances, resistances, and
capacitances have all been determined through calculation and optimizing the controller by
reducing the percentage overshoot and transfer time that is required for the controller to regulate
the DC current is complete. The next step for the rectifier will be to transfer the PSCAD design to
RTDS and begin simulation and optimization test on the lab equipment.
The second half of the PSCAD design consists of an inverter that preforms the reverse
operations of the rectifier in order to converter the DC power (used for transmission) to AC
power for applications. Currently the overall design for the inverter is functioning correctly and
ready to be transferred to RTDS however the controller for the inverter has yet to be optimized.
The percent overshoot needs to be reduced in order to reduce possible issues when testing the
inductor on the Lab Volt equipment.
2.2 AC filters
During the operation of converter, it generates harmonic currents and voltages on both AC
and DC side. Based on the requirement of the project, we are going to design and implement the
AC filters. Due to the high cost of these specific resistors, capacitors and inductors, the
implement of AC filters is not practical. As the decision of our supervisor, we are going to discuss
our design of AC filters in the final report and show the testing results on PSCAD.
The design of AC harmonic filters including choosing certain types of filters and
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calculating parameters. First of all, the goal of AC filter is to restrain certain order of harmonics.
In our case, the main harmonics have the order of 5, 7, 11 and 13. Based on the research, double-
tuned filters are widely used in industry because of less cost. So far I have obtained the
parameters of two double-tuned filters, and tested the filter performance. To calculate the
parameter of double-tuned filters, I basically treat one double-tuned filter as two parallel single-
tuned filters, because the algorithm for the parameters of single-tuned filters is widely introduced
in many research papers. After collecting parameters, I built these AC filters in PSCAD model
and tested. Based on the observation, the current waveform did not improve significantly, which
indicates that the resistance of 3-phase transformer is too low, so the harmonic current goes to the
source directly without going through the AC filters. Therefore, I need to increase the impedance
of the source.
2.3 Gate drive circuit for SCR
The main purpose of designing a gate drive circuit is to control six-pulse bridge converter.
There are six thyristors in the six-pulse bridge rectifier, in order to turn on the thyristor to apply
pulse to the gate of thyristor; the part number of SCR chip we choose is S8025L. The maximum
voltage gate trigger is 1.5V and the maximum current gate trigger is 35mA. First of all, we design
a manually control circuit by using switch and ac power supply to achieve that, than we built the
circuit and tested in Multisim circuit design software. In the future we need use the control
system to control the gate drive circuit, then rebuild the circuit by using a new type of switch
called opto-isolator (CNY12F-2). In the circuit we apply 5V to the chip opto-isolator and add a
resistor to allow a certain range of current to follow into the opto-isolator to turn it on. On the
output, one side connect VCC, another side connect to the gate of thyristor, when we turn on
opto-isolator, use voltage divider we choose two certain resistors. 1.5V will apply on the thyristor
and let SCR on.
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So far, the gate drive circuit had been built on Multisim, test results meets our expectation
and parts have been ordered for the gate drive circuit to be built on a project board.
2.4 Control Systems
There are two control systems in our project. The rectifier side (AC-DC) we use RCC
(rectifier current control) method, and the inverter side (DC-AC) we use extinction angle control.
The PI controller is chosen for our project, the objective for PI controllers is to control the output
of both rectifier and inverter stages.
For the rectifier side, the firing angle is controlled with a feedback control system, the DC
voltage of the rectifier increases or decreases is according to compare the difference between the
measured current and reference current. The error will be sent into the PI controller to control the
firing angle of thyristor, so that we can get the expected DC current. The minimum of the firing
angle is typically chosen to 5°, because the voltage need to be large enough to make sure turn-on
for firing angles beyond this value. The Inverter part is almost the same as the rectifier side.
Instead of comparing the currents, we compare the extinction angles; the error will be sent into PI
controller to control the firing angle. We spent two months for doing the research.
First stage, we found that it is easy to build RCC, but with our knowledge that, it is hard
to build system to measure the extinction angle, Dr.Gole suggest us to use current control for the
inverter side first. If the current control works well, we can try to build the system to measure the
extinction angle if time available.
After doing the research, we have built the two systems in the PSCAD; both of them work
well in PSCAD. This took us about 1 month to finish this task.
2.5 Human Machine Interface
The human machine interface has been programmed the basic functions based on our
current inverter and rectifier. A schematic that includes the AC/DC and DC/AC transformers, 6-
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pulse rectifier, and voltage and current displays have developed. However, the programmed HMI
need to improve after implemented with the entire system.
There is a challenge that the HMI programming cannot meet one of our design goals that
the main menu can login different parameters interface. It shows voltages and currents on the
main loop.
3.0 Future Work
3.1 Control System
Build the control system in RSCAD and test in RTDS.
3.2 Gate Drive Circuit
Construct the physical components for the gate drive circuit based on the Multisim design
after the thyristors parts are received. The construction and implementation will take one week.
3.3 Human Machine Interface
Programming needs to improve after both rectifier and inverter sides are finalized; meet
all design goals; approximately three weeks including programming and testing
3.4 Construction and Testing of the Complete Design
Complete assembly and testing of the low voltage line-commutated converter will be
done in three stages. First the rectifier and inverter will be assembled and tested separately.
Finally the rectifier will be connected to the inverter to be tested and optimize the overall
performance. It is expected to take three weeks to complete.
4.0 Conclusion
The design of all the components for the low power line-commutated converter in
PSCAD and Multisim is complete. The remaining work for the project consists of constructing
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the gate drive circuit, programming the microcontroller and finally testing and tuning the
complete low power line-commutated converter. Although the Gantt chart had to be altered
during the course of the project, the project will be completed by the end of February.
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6.0 Appendix C: Budget The University of Manitoba supplies most of the equipment for free. The total budget for
the project is $45.64.
Table 3. Project budget Items Part
Number Supplier No. Cost per
unit (CAD) Sub-‐total
Electronic Items
Breadboard U of M 1 50.00 0.00 Transformer ACME
Transformer (TB-‐81216)
U of M 1 123.01 0.00
Opto-‐isolator CNY17F-‐2 Digi-‐Key 15 0.67 10.05 Thyristor S8025L-‐ND Digi-‐Key 6 3.39 20.34 Resistor 350 Ohm
60 Ohm 190 Ohm
Digi-‐Key Digi-‐Key Digi-‐Key
15 15 15
TBD TBD
Copper wires U of M 0.00 0.00 Software PSCAD U of M 1000.00 0.00 Hardware RTDS U of M 1,000,000.00 0.00 Lab-‐Volt U of M 0.00 0.00 Miscellaneous U of M 0.00 0.00 Shipping 10.00 TOTAL COST OF PROJECT B/T
40.39
TAXES (13%)
5.25
TOTAL COST OF PROJECT
45.64