University of Manitoba
Department of Electrical & Computer Engineering
ECE 4600 Group Design Project
Final Project Report
Design and Implementation of a Low Power Line-Commutated
Converter (LCC)
by
Group 14
Chen Chen
Li Hang
Motluk Lyle
Huo Yingyang
Liu Jingwei
Final report submitted in partial satisfaction of the requirements for the degree of
Bachelor of Science in Electrical and Computer Engineering in the
Faculty of Engineering of the University of Manitoba
Academic Supervisor(s)
Dr.Aniruddha Gole
Department of Electrical and Computer Engineering
University of Manitoba
Industry Supervisors
Arash Darbandi – Manitoba HVDC Research Center
–
Date of Submission
March 4, 2015
Copyright © 2015 Chen Chen, Huo Yingyang, Li Hang, Liu Jingwei, Motluk Lyle,
Low Power LCC
Abstract
High Voltage Direct Current (HVDC) converters are used in power transmission to convert high
voltage alternating current (AC) to high voltage direct current. HVDC provides an alternative to
AC for electrical energy transmission over long distances or between multiple AC power systems
of different frequencies. This project will focus on HVDC-LCC systems that are implemented
where very high power capacity and efficiency are required. 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 low power line commutated converter 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 208V 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. The lower power HVDC-LCC was designed using
PSCAD software before transferring the controllers to real time digital simulation (RTDS) software
and assembling the final design on Lab-Volt equipment.
i
Low Power LCC
CONTRIBUTIONS
•
◦
•
◦
•
• Lead task ◦ Contributed
ii
◦
◦
◦
Motluk Lyle
Liu Jingwei
Li Hang
•
PSCAD Design
Drive Circuit Design
Controller Design
RSCAD Design
Hardware Assembly
RTDS Interfacing
Entire System Testing
Legend:
Huo Yingyang
Chen Chen
Contributions
•
◦
•
•
◦
◦
◦
◦
◦
•
◦
◦
Low Power LCC
ACKNOWLEDGEMENTS
Acknowledgements
The team would like to thank the following people for their support in this project:
ˆ Dr.Aniruddha Gole, the project advisor, for offering and introducing the topic,and for all the
time he spent with us designing and troubleshooting our design.
ˆ Arash Darbandi from the Manitoba HVDC Research Center for the problem solving and
guidance he provided through out the course of this project.
ˆ Behzad Kordi, Dan Card and Aidan Topping for helping on revisions and feedback on our
reports and presentations, Erwin Dirks from the power system group at the University of
Manitoba for ordering of parts and general technical help.
ˆ Christian Jegues from RTDS Technologies Inc. for advising the team with RTDS interfacing.
ˆ All graduate and PhD students that who helped us, Qi Yi, Li Tan, and Zhao Hengfeng.
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Low Power LCC
TABLE OF CONTENTS
Table of Contents
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
i
Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ii
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
iii
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
vi
List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii
Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ix
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
2 PSCAD Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
2.1
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
2.2
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
2.3
Testing of PSCAD performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
3 Filter Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
3.1
Harmonic Filter Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
3.1.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
3.1.2
Algorithm for the parameters of AC filter . . . . . . . . . . . . . . . . . . . . 10
3.1.3
Testing of AC filter performance . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.1.4
DC filters and DC smoothing reactors . . . . . . . . . . . . . . . . . . . . . . 15
3.1.5
Testing of DC filers and DC reactor . . . . . . . . . . . . . . . . . . . . . . . 16
iv
TABLE OF CONTENTS
Low Power LCC
4 Control System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.1
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.2
Control system design and testing in PSCAD . . . . . . . . . . . . . . . . . . . . . . 22
5 Gate Drive Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.1
Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.2
Optocoupler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.3
DC-DC converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.4
Silicon-Controlled Rectifier (SCR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.5
DESIGN PARAMETER
5.6
Testing and Troubleshooting
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
6 RTDS Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
6.1
RSCAD design and RTDS interfacing . . . . . . . . . . . . . . . . . . . . . . . . . . 32
6.2
RSCAD circuit design and simulation . . . . . . . . . . . . . . . . . . . . . . . . . . 32
6.3
RTDS interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Appendix A Budget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Appendix B Hardware Componntes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Appendix C Curriculum Vitae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
v
Low Power LCC
LIST OF FIGURES
List of Figures
2.1
Detailed image of the rectifier designed in PSCAD . . . . . . . . . . . . . . . . . . .
2.2
DC voltage waveform at the rectifier output prior to improvements to the control
5
system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
2.3
DC voltage waveform at the rectifier output post improvements to the control system
7
2.4
Detailed image of the inverter designed in PSCAD . . . . . . . . . . . . . . . . . . .
8
2.5
Overview of the complete HVDC design in PSCAD . . . . . . . . . . . . . . . . . . .
8
3.1
The configuration of a double tuned filter and two single tuned filters with the same
performance
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2
Double-tuned filter for order of 5th and 7th harmonics . . . . . . . . . . . . . . . . . 14
3.3
Double-tuned filter for order of 11th and 13th harmonics . . . . . . . . . . . . . . . . 14
3.4
Double-tuned filters built in PSCAD . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.5
AC side current waveform before adding AC filters . . . . . . . . . . . . . . . . . . . 16
3.6
AC side current waveform after adding AC filters
3.7
DC filters on DC side to reduce voltage and current ripples . . . . . . . . . . . . . . 18
3.8
DC voltage waveform before adding DC filters and DC reactor . . . . . . . . . . . . 18
3.9
DC voltage waveform after adding DC filters and DC reactor . . . . . . . . . . . . . 19
. . . . . . . . . . . . . . . . . . . 17
3.10 DC current waveform with DC filter and DC reactor . . . . . . . . . . . . . . . . . . 19
4.1
A brief diagram for HVDC transmission system . . . . . . . . . . . . . . . . . . . . . 20
4.2
Simple rectifier current control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.3
Simple extinction angle control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
vi
LIST OF FIGURES
Low Power LCC
4.4
A block of PI controller designed in PSCAD
. . . . . . . . . . . . . . . . . . . . . . 22
4.5
The controllers response to the change of reference current
4.6
DC current response after tuning the controller . . . . . . . . . . . . . . . . . . . . . 23
5.1
Optocoupler symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.2
Optocoupler symbol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.3
structure circuit of six-pulse bridge rectifier . . . . . . . . . . . . . . . . . . . . . . . 26
5.4
DC-DC converter (ROE-0505S)
5.5
Characteristic of SCR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.6
SCR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.7
Mutilsim simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
5.8
Testing circuit
6.1
Draft circuit built in RSCAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.2
The waveform of the output of firing pulse generator
6.3
DC current waveform in RSCAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.4
Controller and firing pulse generator for interfacing with external circuit
6.5
The current transducer for DC current measurement . . . . . . . . . . . . . . . . . . 43
. . . . . . . . . . . . . . 23
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
B.1 Three single phase ACME Transformers.
. . . . . . . . . . . . . . . . . 40
. . . . . . 42
. . . . . . . . . . . . . . . . . . . . . . . . 48
B.2 Lab-Volt Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
B.3 RTDS equipment in the machine lab.
. . . . . . . . . . . . . . . . . . . . . . . . . . 52
B.4 Wire wrap board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
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Low Power LCC
LIST OF TABLES
List of Tables
2.I
System Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
viii
4
Low Power LCC
NOMENCLATURE
Nomenclature
Symbol
Description
α
Valve Ignition Delay Angle (firing angle)
µ
Overlapping Angle
β
Advanced Angle
γ
Extinction Angle
Vdc
DC Voltage
Idc
DC Current
AC
Alternative Current
DC
Direct Current
HV DC
High Voltage Direct Current
SCR
Silicon Controlled Rectifier
LED
Light Emitting Diode
CCA
Current Control Amplifier
LCC
Line-Commutated Converter
PI
Proportional Integral
I/O
Input and Output
P LL
Phase Lock Loop
RT DS
Real Time Digital Simulation Machine
GT AI
Analog Input Card for RTDS
GT DO
Digital Output Card for RTDS
GP C − 2
Giga-Processor Card in RTDS
RSCAD
A software for interfacing to the RTDS Simulator hardware
P SCAD
A simulation software for analyzing power systems transients
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Low Power LCC
Chapter 1
Introduction
High Voltage Direct Current (HVDC) converters are used in power transmission to convert high
voltage alternating current (AC) to high voltage direct current. HVDC provides an alternative to
AC for electrical energy transmission over long distances or between multiple AC power systems
of different frequencies. Two categories of HVDC converters exist: line-commutated converters
(LCC) and voltage-sourced converters (VSC). This project will focus on HVDC-LCC systems that
are implemented where very high power capacity and efficiency are required.
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 transmission is more energy efficient than transmission with AC voltages over large distances
because power losses are minimized due to the transmission line skin effect, and a reduction voltage
drop due to the line inductance.
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 because
the equipment is not rated for voltages of that magnitude and the health risk to the operator.
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
1
Low Power LCC
power HVDC-LCC will first be designed using PSCAD software before transferring the controllers
to real time digital simulation (RTDS) and assembling the final design on Lab-Volt equipment.
The HVDC is broken down into two main parts a rectifier that converts the 3-phase AC source
voltage into a steady DC voltage at the output, and an inverter, which preforms the reverse function
of converting DC voltage back to AC. In practical operation the transmission of electrical power
takes place between the rectifier and inductor, which are separated, by very long distances. Both
components are constructed with AC and DC filters, a transformer, a pulse rectifier and a control
system. The correct performance of each component allows the HVDC to operate.
This project was chosen because HVDC systems are widely used in the high voltage industry
therefore the completed HVDC line commutated converter will demonstrate valuable insight into
equipment that electrical engineers are constantly constructing, monitoring and improving. 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.
2
Low Power LCC
Chapter 2
PSCAD Design
2.1
Overview
The object of the PSCAD software design is to simulate a HVDC design optimized to convert a
3-phase 208 V line-to-line source into 2 A DC current for transmission and then reverse the initial
conversion in order to output the original 3-phase 208 V AC power source. The PSCAD design
will be implemented in RTDS for use in the final product therefore it is essential that the PSCAD
design be optimized.
The low power line-commutated converter consists of a rectifier and an inductor.The primary
role of the rectifier is to control the load voltage at the output. The load voltage is controlled
by the firing angle alpha. The rectifier components include input alternating current that is step
down with a high voltage transformer from 205V to 52 V in order to comply with the operational
performance of the lab equipment and the safety of the operator. A series of AC filters are installed
in parallel to the AC source in order to remove harmonics that are generated by the converter. A
6-pulse gate drive circuit constructed with six thyristors is responsible for converting AC voltage
to DC voltage by passing the positive polarity through three of the thyristors and the negative
polarity through the last 3 thyristors that are orientated in the opposite direction. This results in a
unidirectional pulsating DC current at the output of the rectifier. In order to establish a constant
voltage a DC filter is added to the output of the rectifier. A constant current controller that limits
3
Low Power LCC
2.2 Specifications
the maximum DC current to 2 amps controls the 6-pulse gate drive circuit. Control of the gate
drive circuit is achieved by manipulating the firing angle of the thrysistors that make up the gate
drive circuit.
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. The design for the inverter consists of the same components as the rectifier but
orientated in reverse order. An extinction angle controller controls the 6-pulse gate drive circuit
for the inverter in order to reduce the incidence of commutation failures.
2.2
Specifications
The specifications of the project were determined by discussing the feasibility of building high
voltage system. CIGRE developed a benchmark for HVDC-LCC system, which will help us to
understand the operation of HVDC-LCC. However, the developed model is in the range of MW
and kV, which are not suitable for laboratory application. The input AC voltage is three-phase,
208V line to line. Design requirement for DC bus voltage is in the range of 306 Volts to 374 Volts.
All system specifications are summarized in the table below.
Table 2.I: System Specifications
Parameter
Rectifier AC side input volatge
Rectifier DC side output voltage
DC bus current and power
4
Values
208 ± 10%V
340 ± 10%V
2 ± 10%and680 ± 10%W
Low Power LCC
2.3
2.3 Testing of PSCAD performance
Testing of PSCAD performance
The PSCAD design stage for the project was broken down into two parts,designing and testing the
rectifier (Fig 2.1)and inverter(Fig 2.4) individually and testing the complete design as a unit. Once
the individual components for the rectifier were designed, the greatest problem that occur when
testing the rectifier was developing a controller with a minimized percent overshoot and minimal
the response time. (Fig 2.2)
Fig. 2.1: Detailed image of the rectifier designed in PSCAD
The initial design consisted of a controller with an average response time of 2 seconds and a
percent overshoot of 60%. Recalibrating the performance values of the controller, the response time
was reduced to 0.2 seconds and the present overshoot was reduced to 5% (Fig 2.3)
5
Low Power LCC
2.3 Testing of PSCAD performance
Fig. 2.2: DC voltage waveform at the rectifier output prior to improvements to the control system
The design of the inverter consisted of reusing the 6-pulse gate drive circuit and transformer
that were used to construct the rectifier. The filters for both AC and DC voltages had to be
calculated specifically for the inverter design in order to remove the resulting AC harmonics and
steady the inconsistent DC current. Similar to the design of the rectifier, the control systems of
the inverter was the component responsible for the primary issue that needed to be corrected.
Finally the rectifier and inverter were placed in series in the final design to complete the HVDC
(Fig. 2-5). As a result of the time spent optimizing the design and individual performance of the
rectifier and inverter, the performance of the complete design required no modifications.
6
Low Power LCC
2.3 Testing of PSCAD performance
Fig. 2.3: DC voltage waveform at the rectifier output post improvements to the control system
7
Low Power LCC
2.3 Testing of PSCAD performance
Fig. 2.4: Detailed image of the inverter designed in PSCAD
Fig. 2.5: Overview of the complete HVDC design in PSCAD
8
Low Power LCC
Chapter 3
Filter Design
3.1
3.1.1
Harmonic Filter Design
Introduction
The operation of a converter will generate harmonic currents and voltages on both AC and DC
sides. The harmonics have an essential impact on the performance of the entire HVDC transmission
systems. Filters are installed on each side of the converter to restrain harmonics distortion and
to compensate reactive power to the system. At the output of the rectifier of the converter, DC
smoothing reactors on the DC line for reducing the DC current ripple.
In the project, a 6-pulse converter is used as a rectifier and inverter. A converter with a pulse
number of p generates harmonics having the order of n*p1 (n=1,2,3)[1]. Therefore, on the AC side
of the rectifier (input of the rectifier), a 6-pulse converter will generate harmonics with order 5, 7, 11
and 13. On the DC side of converter, harmonics with order n*p (n=1,2,3) is generated. Therefore,
a double-tuned filter will be the ideal solution to restrain two harmonics at one time. Based on
researches, there are two types of double-tuned filters: conventional type and damped-types [2].
A conventional type harmonic filter is a LC circuit. However, damped-type filter has a resistor
in parallel with inductors and capacitors which provides a protection to the transmission system.
Finally, damped-type double tuned filters are selected in the project.
9
Low Power LCC
3.1 Harmonic Filter Design
As mentioned, a damped-type double tuned filter can easily restrain harmonics at two frequencies. For example, the goal of filter design is to reduce harmonic distortion at certain frequencies.
In the project, the 6 pulse bridge rectifier generates 5th, 7th, 11st and 13th harmonics to the AC
side, which means that the goal can be achieved by simply adding two set of double tuned filters
on the AC side of the converter. However, the algorithm for the parameters of double tuned filters
is not introduced widely. Another approach is to use four single tuned filters instead of two sets
of double tuned filters. The advantage of using single tuned filter is that the algorithm for the
parameters of single tuned filter is well known and easy to implement. However, the drawback is
that in practice two single tuned filters occupy more space than a double tuned filter type, but the
results are the same. More room occupied will also have a higher cost. Therefore, double tuned
filter is a more practical selection.
3.1.2
Algorithm for the parameters of AC filter
After comparing and testing several IEEEs research papers, an algorithm was demonstrated that
can be used to calculate the parameters of the filters. The idea of the algorithm is basically
transform the parameters of two paralleled singled tuned filters into a double tuned filter. The
figure below shows the configuration of two parallel single tuned filters and one double tuned filter
with the same performance.
Fig. 3.1: The configuration of a double tuned filter and two single tuned filters with the same
performance
10
Low Power LCC
3.1 Harmonic Filter Design
Fig. 3.1
The inputs of such an algorithm are the reactance power compensation (Q), the bus voltage
(U1), the order of harmonics (N=5, 7, 11, 13) and the rated DC current (Idc=2A). The detail of
the calculation is introduced as follow. The parameters below are identical with the parameters
indicated in the above figure. Calculation Procedure: Firstly, calculating the parameters of two
single-tuned filters based on the inputs. Qc is the total power needed from the system:
Qc= w · Ca ·
N12
· U12 = U1 · I1 = 416V ar
N12 − 1
(3.1)
Harmonics current of order 5, 7, 11 and 13 are calculated as follow:
√
2 3
· Idc = 0.441A
I5 =
5π
(3.2a)
√
2 3
I7 =
· Idc = 0.315A
7π
(3.2b)
I11
√
2 3
=
· Idc = 0.2A
5π
(3.2c)
I13
√
2 3
=
· Idc = 0.17A
5π
(3.2d)
Reactive power compensated by each individual filter:
Q1 = Qc ·
Q2 = Qc ·
I5
5
I5
5
+
I7
7
+
I9
9
+
I11
11
I9
9
+
I11
11
I7
5
I5
5
+
I7
7
+
11
= 127.55V ar
(3.3a)
= 113.83V ar
(3.3b)
Low Power LCC
3.1 Harmonic Filter Design
Q3 = Qc ·
Q4 = Qc ·
I9
5
I5
5
+
I7
7
+
I9
9
+
I11
11
I9
9
+
I11
11
I11
5
I5
5
+
I7
7
+
= 45.99V ar
(3.3c)
= 33.08V ar
(3.3d)
Ca is the capacitance of one of the capacitors for the two single-tuned filters:
Ca =
Q1 · (N12 − 1)
= 7.5µF
w · N12 · U1 2
(3.4)
La is the inductance of one single-tuned filter:
La =
w2
1
= 37.49mH
· N12 · Ca
(3.5)
Cb is the capacitance of one of the capacitors for the two single-tuned filters:
Cb =
Q1 · (N22 − 1)
= 6.84µF
2
w · N22 · U1
(3.6)
Lb is the inductance of one single-tuned filter:
Lb =
w2
1
= 21.00mH
· N12 · Ca
(3.7)
Secondly, performing parameter transformation based on the algorithm [3].
C1 = Ca + Cb = 14.34µF
L1 =
La · Lb
= 13.43mH
La + Lb
(3.8a)
(3.8b)
2
C2 =
Ca · Cb · (Ca + Cb ) · (La + Lb )
= 133.05µF
(Ca · La − Cb · Lb )2
12
(3.8c)
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3.1 Harmonic Filter Design
L2 =
(Ca · La − Cb · Lb )2
= 1.573mH
(Ca + Cb )2 · (La + Lb )
(3.8d)
Therefore, the parameters of a double-tuned filter are calculated. This filter is designed to
restrain the order of 5th and 7th harmonics.
By using the same procedure, the parameters for the 11th and 13th harmonic filter can be
calculated. The results are shown below.
3.1.3
C1 = 8.625µF
(3.9a)
L1 = 5.733mH
(3.9b)
C2 = 307.13µF
(3.9c)
L2 = 159.42mH
(3.9d)
Testing of AC filter performance
After calculating the parameters of the two double-tuned filters, a test is done in MATHCAD by
plotting a graph of frequency vs. impedance.
The figure below shows that at 5th , 7th , 11th and 13th harmonics, the impedances of the doubletuned filter are extremely small. This means that the designed filters can successfully restrain
harmonics at certain frequencies. In this case, the frequencies are 300Hz, 420Hz, 660Hz and 780Hz.
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3.1 Harmonic Filter Design
Fig. 3.2: Double-tuned filter for order of 5th and 7th harmonics
Fig. 3.3: Double-tuned filter for order of 11th and 13th harmonics
To further test the entire performance of the filter, a block of AC filters is added to the AC
side of the rectifier on PSCAD case. The filters are shown below.
Initially the AC line current was affected by the harmonics generated from the converter,the current waveform was non-sinusoidal. After adding the filters, the current waveform became smoother
and close to a sinusoid waveform.The resulting waveform demonstrated that the design goal is
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3.1 Harmonic Filter Design
Fig. 3.4: Double-tuned filters built in PSCAD
achieved. The figures below illustrate the AC line current waveform before and after adding the
AC harmonic filters.
3.1.4
DC filters and DC smoothing reactors
The DC side of the converter can also be affected by harmonics. The order of harmonics on DC
side is n*p where n=1, 2, 3 In the project, 6th and 12th harmonic have the most significant impact
on DC current [1]. The harmonics need to be restrained, otherwise the harmonics will increase the
DC current ripple resulting in a varying output voltage and current. On the DC side, a DC filter
along with a DC smoothing reactor is normally used to filter out harmonics.
The DC filters below are designed to restrain harmonics at 360 Hz and 720 Hz, which corresponding to 6th and 12th harmonics. The DC filters are directly connected with the DC line.
The DC smoothing reactor plays an important role on decreasing harmonic voltages and currents in the DC line. Also, DC reactors smooth the ripple in the direct current in order to prevent
the current becoming discontinuous at light load [4]. Normally, a DC smoothing reactor is an
inductor that connected in series with the DC line. The selection of the smoothing reactor in the
project is based on one equation [4].
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3.1 Harmonic Filter Design
Fig. 3.5: AC side current waveform before adding AC filters
This criterion for the sizing of the reactor is the direct current ripple. The inputs of such
equation are the no load DC voltage of the converter (Vdo ), the number of converters connected in
series (s), the frequency of operation, the pulse number (p) and the firing angle of the converter
(1):
ipeak
= (sVd0 /w1 Ld )[1 − (π/p) cot(π/p)] sin α
d
(3.10)
Plugging in all the inputs: ipeak
=2.05A, S=1, Vdo =68 V, W1 = 2π60,p = 60,α = 45◦
d
The resulting: Ld = 5.79mH
3.1.5
Testing of DC filers and DC reactor
The voltage ripple before adding the DC filters and DC reactor is around 17.5 volts which is quite
large and must be get rid of. After adding such a DC filter and DC reactor, the DC voltage ripple
decreased to only 0.034 volts.
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3.1 Harmonic Filter Design
Fig. 3.6: AC side current waveform after adding AC filters
In conclusion, the design of harmonic filters for the line-commutated converter project is successful. The parameters of filters are calculated based on the project specifications and criterion.
For example, the direct current measured in PSCAD is 2A with ripple ±0.03A. The percentage of
ripple is which is within the design criteria:2 ± 10%Amp.However, as the rated direct current in
the system is 2 Amp, to build such filters by hardware is going to be very expensive. As the group
discussed with project supervisor,hardware assembly of harmonic filer was not performed. Therefore, the DC current measured from the real DC output will contain large ripples. To overcome
this problem, we are trying to add a larger smoothing reactor to the DC line to decrease the ripple.
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3.1 Harmonic Filter Design
Fig. 3.7: DC filters on DC side to reduce voltage and current ripples
Fig. 3.8: DC voltage waveform before adding DC filters and DC reactor
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3.1 Harmonic Filter Design
Fig. 3.9: DC voltage waveform after adding DC filters and DC reactor
Fig. 3.10: DC current waveform with DC filter and DC reactor
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Chapter 4
Control System Design
4.1
Overview
The control system is designed to turn on and off the six-phase bridge correctly in order to generate
the correct firing angle to produce good quality DC current. The purpose of the HVDC control
system is to design a control system that will control power flow between the terminals [1]. The
rectifier voltage and inverter voltage are independently controlled. This means the rectifier side
and inverter side will have different values and hence there will be a voltage difference across the
DC circuit.
Fig. 4.1: A brief diagram for HVDC transmission system
There are several types of control systems for a HVDC. The rectifier can be controlled by
constant voltage control or firing angle control (current control) and the inverter can be controlled
by the gamma angle control, voltage control and extinction angle control [1]. After comparison, we
chose constant current control for the rectifier in order to limit the maximum DC current.
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4.1 Overview
The feedback control system for the rectifier will control the rectifier’s firing angle α (Fig 4.2).
The voltage will increase or decrease depending on the firing angle α. For example if ∆Id > 0 and
the firing angleα is increased, increase the Vd will cause the Id increase. The desired current will
be obtained as αo > αmin and if the reaches to αmin , the rectifier side will not need control. For
the rectifier the value of αmin is chosen to be 5 degrees, because we want guarantee the thyristors
will be successfully turned-on.
Fig. 4.2: Simple rectifier current control
For the inverter side, extinction angle control is commonly used, in order to reduce the incidence
of commutation failures.
Fig. 4.3: Simple extinction angle control
The purpose of the extinction angle control is to ensure the extinction angle γ is small as
possible. But as we decrease the extinction angle γ , the probability of commutation failure will be
increased [1]. Therefore, the range of extinction angle is between 15 degrees to 18 degrees.
After the further research, we found that the extinction angle control is much more complicated
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4.2 Control system design and testing in PSCAD
than the constant current control. Compared to measuring the DC current, it is difficult to measure
the extinction angle. In conference with Dr. Gole, he suggested to use the constant current control
at the inverter side due to the similarities with the rectifier side.
4.2
Control system design and testing in PSCAD
The control system of our project is designed in software. As we are using current control, a simple
PI controller can satisfy our design requirement. Initially, the PI controller was built in PSCAD
to test controllers performance. The reason for building control system in PSCAD is because it is
very easy for tuning the performance of the controller by simply adjusting the proportional gain
and time constant of the controller.
Fig. 4.4: A block of PI controller designed in PSCAD
The controller should be able to adjust DC current to the reference current that we set. For
example, if we manually set the reference current to 2 Amps, the controller should adjust the firing
angle so that the DC current equals to the set current. The reference current is 0 Amps initially.
As we set the reference current to 2 Amps, the DC current rises to 2 Amps rapidly.
However, a high percentage of overshoot occurs when reference current was changed. The
current overshoot is a serious problem, because if the current exceeds the actual rating, it may
cause damage and even burn equipment. We carefully consider this problem, and did many retunes
to get a better result. Proportional gain was finally adjusted to 675, and the time constant value
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4.2 Control system design and testing in PSCAD
Fig. 4.5: The controllers response to the change of reference current
was set to 0.001 s. The adjusted PI controller was tested, and the DC current response is shown
as figure below.
Fig. 4.6: DC current response after tuning the controller
A comparison between the first DC current response and the second response, we can see that
the overshoot problem has been optimized. An overshoot of 10-20% is within the acceptable range.
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Chapter 5
Gate Drive Circuit
5.1
Objectives
The purpose of designing gate drive circuit is to control firing pulses sequence of thyristors to
produce DC current from three-phase AC source. There are six thyristors (SCR) in both rectifier
side and inverter side, so for the whole project, we need to build 12 of gate drive circuits to control
each of SCR open. The devices we use for drive circuit to firing SCR are optocoupler, DC/DC
converter, 5V DC source and some certain value of resistors. In the drive circuit, firing pulses are
generated by RTDS to apply on optocoupler, and then use voltage divider to give certain voltage
and current to the gate of thyristor. Optocoupler was used to isolated low power control circuit
and high power main circuit. Finally DC current will tested on the rectifier side.
5.2
Optocoupler
The reason why we use optocoupler is that SCR we use in our project, which is in a sensitive
electronic system. We need to provide isolation between circuits, because we should reduce the
possibility of power line noise being induced into control devices,also to protect SCR failure when
we test.
Optocoupler also known as an opto-isolator, it is an electronic device to connect two separate
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5.2 Optocoupler
Fig. 5.1: Optocoupler symbol
circuits by light. An optocoupler contain a LED light which can convert electrical input signal into
light, there is a light sensor on other side to detect coming light to determine when device allow
current that is provided by the external power supply to pass through. Opto-isolator is an electronic
switch device use to switch an electronic device such as SCR thyristor, and provide isolation between
low voltage control signal and high voltage or current output signal. The advantage of using
optocoupler is to prevent the damage of lower voltage circuit components when higher voltage side
has rapidly changing.
Fig. 5.2: Optocoupler symbol
The optocoupler we choose from DigiKey, the part number is CNY17F-2. On low voltage
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5.3 DC-DC converter
side of circuit, a pulse is provided by external device, pin 1 connect to source and pin 2 connect to
ground, current follow into senor device and this device convert electrical signal to light, when senor
inside receive enough light, another side of current from external device can follow into collector
(pin5) and follow out from emitter (pin4), the external circuit will be connected.
5.3
DC-DC converter
In our project, there are six SCR in six pulse bridge rectifier side, it means we should contain six
gate drive circuit to control SCR, each of thyristor has its own voltage level requirement different
from that supplied by external supply, sometimes higher and sometimes lower than power supply.
Fig. 5.3: structure circuit of six-pulse bridge rectifier
To provide pulse to active thyristors, in our design project, we need to give same level of voltage
to the gates, in figure 3 same voltage should apply between point 3 and point2, also point 2 and
point 1, there is no point for a line have different voltage, so DC-DC converter need to provide to
deal with this problem.
We choose DC-DC converter from DigiKey (part number is ROE-0505S), which is 1:1 input
range, input voltage is 5 V, and output voltage is 5 V. Pin1 (Vin-) connects to ground. Pin 2(Vin+)
connects to 5V voltage source. We provide this converter in each of thyristor to achieve its own
voltage level.
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5.4 Silicon-Controlled Rectifier (SCR)
Fig. 5.4: DC-DC converter (ROE-0505S)
5.4
Silicon-Controlled Rectifier (SCR)
Fig. 5.5: Characteristic of SCR
SCR also known as silicon-controlled rectifier, which is commonly used for controlling power
or high voltage AC and DC circuits. SCRs are unidirectional devices. That means current can
follow in one direction, otherwise SCR acts as open circuit, normally we need to apply a voltage
to the gate of SCR. This is characteristic of thyristor differ from diode. In SCR structure, it has
three terminals, anode, cathode and gate. External power supply connects anode and cathode. A
sub circuit is provides to make the main circuit work. In our project, the main external circuit is
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5.5 DESIGN PARAMETER
six-pulse bridge which is build by six SCRs, in this SCR converters high ac voltages between anode
and cathode of the thyristor, and low voltage level pulses are placed between gate and cathode.
Isolation is necessary between the gate-cathode circuit and the anode-cathode circuit.
In the beginning of conducting, SCR remain off until a certain level of current follow into the
gate to fire it. If thyristor is open, we cannot off it by turning off the gate current or voltage. SCRs
may be turned off by anode current falling below the holding current value or by ”reverse-firing”
the gate, it means applying a negative voltage to the gate.
Fig. 5.6: SCR
The figure shows that thyristor graph and pin location. We used is TO-220AB (LPackage), it
is an isolated mounting tab.
5.5
DESIGN PARAMETER
For design parameter in gate drive circuit. First of all, design a circuit for active optocoupler, from
datasheet of opto-coupler (CNY17F-2) we choose, we apply 0 to 5 V voltage source to the circuit,
the maximum voltage across the left side diode is 1.65 V, so we need a resistor to get some voltage
from source, at the same time, the maximum current follow into the opto-coupler is 60mA. From
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5.6 Testing and Troubleshooting
equation
R1 >
3.35V
Vsource − Vmax
=
= 55.8Ω
Imax
0.06A
(5.1)
which relate to common value of resistor we choose 68Ω. Previous part of circuit is to active
opto-coupler and provides isolation between control circuit and main circuit. Next circuit is to give
a pulse to gate of thyristor and active it. Looking at data sheet of SCR (S8025L), the range of
current to active thyristor is from 1mA to 35mA. The maximum voltage apply to the gate is 1.5
V so we apply a 5 V constant voltage source, than use voltage divider to apply certain value of
current and voltage to the gate, SCR we used have resistance between gate and cathode, measuring
value Rth equal to 96Ω. I choose R2 equal to 180Ω and R3 equal to 69Ω . From equation
R3 · Rth
= 40Ω
R3 + Rth
(5.2a)
Vsource
5V
= 23mA
=
Rtotal + R2
(40 + 180)Ω
(5.2b)
Rtotal =
Itotal =
VGT = Vsource − Itotal · R2 = 5 − 0.023 · 180 = 0.86V
IGT =
0.86V
VGT
=
= 8.9mA
Rth
96Ω
(5.2c)
(5.2d)
Gate voltage is 0.86 V and Gate current is 8.9 mA. Compare with requirement to active SCR.
The results are in an accepetable range.
5.6
Testing and Troubleshooting
First of all, we use the device we need and some of value determined resistors to build circuit in
the multism. This is one drive circuit to control thyristor and testing load we use is 12V DC source
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5.6 Testing and Troubleshooting
Fig. 5.7: Mutilsim simulation
and a lamp, the test result can be easily known, the lamp is light means drive circuit works well.
After that one drive circuit was build on the small breadboard and tested. The load we give 5V DC
source and series with a 35Ω resistor,We measured the current in the load circuit, when we connect
the circuit with DC source there is current came from thyristor, when we plug out off voltage from
gate, the current is still not change. One problem we met is at the beginning of calculating the
value of resistor, the range of turning on opto-coupler is 10mA to 60mA, we use around 15mA as
standard current to choose resistor, but after building the circuit we tested there is not current in
the load, so the problem may be opto-coupler did not active, then choosing 60mA as standard to
calculate resistor value (69Ω) We got current from load circuit. After solving this problem a new
problem happen when you disconnect the gate pulse, the current became zero. It is against the
character of thyrisistor, which is after thyristor is turned on it cannot be turn off except the current
follow into thyristor is zero. The problem may be we choose the load resistor is too big and because
current follow into thyristort is very small, the way to solve the problem is that choose a small
resistor and tested again. The result became what we expected. Overall, testing result shows our
designing one gate drive circuit works well on breadboard, after that, we building whole external
in the testing breadboard.
In testing circuit, gate voltage cannot be applied by DC source any more. In order to DC
current from thyristor, it is necessary to provide pulse to each of SCR in sequence and continually.
To determine when to give pulses to each of thyristor, we use RTDS as controller, the control
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5.6 Testing and Troubleshooting
Fig. 5.8: Testing circuit
system will introduce how it works in RTDS, RTDS will generated six pulses in sequence, we apply
to the gates of six thyristor, the whole system will generate DC current in rectifier side.
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Chapter 6
RTDS Design
6.1
RSCAD design and RTDS interfacing
An important part of the project is to implement a control system and firing pulse generation
in RTDS (Real Time Digital Simulator) and to achieve interfacing between RTDS and the real
6-pulse rectifier. RTDS is a very expensive real time digital simulation machine, so it is important
to isolate the machine with high voltage and high current components. The RTDS implementation
was organized in three stages. The first stage is to build draft circuit in RSCAD to test if the
control system works. Next was to test the hardware that we built, and measured the DC current
output and observe the circuit board functioning correctly. Finally, we interfaced RTDS with our
real circuit.
6.2
RSCAD circuit design and simulation
The first stage was performed on RSCAD. RSCAD includes a Draft module that allows us to
construct a graphical assembly and data input for simulation circuit. The goal at this stage is to
test the function of a controller and firing pulse generator. A circuit designed with a three-phase
generator (line to line voltage:208V), a transformer (ratio: 280:52), a rectifier block with a DC
smoothing reactor (0.005H), a series resistor (10) and a DC voltage source (30 Volts). All the
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6.2 RSCAD circuit design and simulation
parameters in the draft circuit are identical to the real components that used in the project.
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6.2 RSCAD circuit design and simulation
The control system in the case is identical to the one in PSCAD. After tuning the controller in
PSCAD, we finally built it in RSCAD to achieve current control strategy. Another important part
of this circuit is the phase lock loop (PLL) and a firing pulse generator. The inputs of PLL are
the three phase waveform measurements from the secondary side of the transformer; the output
of PLL is a phase angle that tells firing pulse generator when to generate a pulse. The inputs for
the firing pulse generator are the firing angle (delay angle), the phase angle detected by PLL. The
pulse generator can automatically produce a 6 bits firing pulse which looks as figure below.
As we can see from the waveform, it contains six different magnitudes in one pulse, and between
each magnitude there is a small time shift. The time shift is the designed firing interval among six
thyristors. The firing pulse signal is directly connected with the gate of the 6 pulse rectifier to turn
on certain thyristor at a certain time.
After building such a circuit, the circuit is compiled. During compiling some errors are detected
by the software, so couple adjustments are made to troubleshoot the problem. For example, initially
on the DC line a 0.005 H inductor and a 10ω resistor are connected. However, the DC current
waveform is not correct. During troubleshooting, the block of rectifier has already contained the
reactor and resistor in its setting. The external inductor and resistor on the DC line was removed,
which corrected the problem. In the RunTime page, I observed the new DC current waveform as
shown below.
By tuning the reference current, the resulting DC current response is slow, but after certain
settling time it approaches to the reference value. The results show that both the control system
and the firing pulse generator work well. Therefore, the controller and firing pulse generator are
ready to be used to interface with the external rectifier circuit.
The second stage testing is focused on the external circuit. As we have to make sure the rectifier
circuit along with the drive circuit are absolutely correct before we can interface with RTDS. The
detail of external circuit testing is discussed in drive circuit design section.
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6.3
6.3 RTDS interface
RTDS interface
The third stage is RTDS interfacing with external rectifier circuit. After many testing to RSCAD
and external circuit, we are finally at the stage for interfacing. Couple adjustments are made to
the RSCAD circuit to set up the four input pins (DC current measurement, three phase waveform
measurements) and six output pins (six pulses signals to fire the drive circuit). The new circuit is
shown as figure below.
The firing pulse output from the firing pulse generator is a 6 bits integer. Therefore, these
firing pulses are digital output from RTDS. For three phase AC source inputs and DC current
input, these are analog signals. In the project, we assigned one GTAI board used for four analog
input signals; the inputs limitation is +10 volts and -10 volts. One GTDO board is assigned for
the six digital outputs to fire the thyristors. These pins are digital, so we can connect to thyristors
gate directly. Both I/O boards are using the same processor, which is GPC-2.
The RTDS will grab the DC current measurement from the hardware, and compare this value
to the reference current. Then the controller generates a firing angle. Next, the three phase scaled
down voltage will input to RTDS, and PLL reads these analog signals and outputs a phase angle.
This phase angle along with the firing angle is going to input to the firing pulse generator in RTDS.
Then the firing pulse generator automatically produces a 6 bits pulse signal to the GTDO board
where allows us to interface RTDS signal with hardware. Finally, these pulse signals will lead the
DC current to reach reference current.
One problem in this stage is the voltage input from secondary side of the transformer to the
RTDS. As the rated voltage level is 52 volts line to line for the secondary side of the transformer
and the phase voltage is 30 volts, the RTDS cannot accept such high voltage. As mentioned
in previous paragraph, the limitation for the analog inputs of RTDS is +10 volts and -10 volts.
Therefore, a simple voltage divider is designed to step down the voltage comes into the RTDS. The
voltage divider contains a 1200ω resistor in series with two paralleled 200ω resistors. The reason
for choosing these resistors is simply because the LabVolt equipment provides such an option so
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6.3 RTDS interface
we don’t need to order high power rated resistors and cost money. The equivalent resistance of the
two paralleled resistors is 100ω. The voltage divider is connected with each phase of the secondary
side of the transformer. The rated voltage of the secondary side of the transformer phase voltage is
30 volts, hence the voltage on these two paralleled resistors will be 30 divided by 13, which equals
to 2.3 volts. For RTDS machine, 2.3 volts is a reasonable input value that will not damage the
machine.
The rated DC current is 2 Amps, which cannot be directly connect to the RTDS. In the
project, a current transducer was used. The module that we used is LEM LTS 6-NP. This current
transducer is a through hole transducer that can be used to measure both AC and DC current.
The real module is shown in figure below.
The output voltage of such current transducer is 2.5 volts, which can make sure that RTDS is
not damaged.
Final measurements that need to be performed before we actually hook up our circuit with
RTDS. The first priority in the project is to ensure safety for human and machine. First of all,
we tested our three phase transformer and the voltage divider. In order to do that, we connected
LabVolt three phase voltage source to three transformers. The scale we used is 4 to 1, which mean
by applying 120 phase voltage to the primary side we will receive 30 volts on the secondary side.
We measured the voltages using LabVolt and read the results from PC. The voltage meters clearly
indicate that the transformers are connected correctly as we received exactly 30 volts phase voltage
on the secondary side.
Then we tested our voltage divider. The results show that the voltage on the 100ω resistor is
2.3 volts, which is also as our expected.
Secondly, it is important to ensure the GTDO (Digital Output) board on RTDS is assigned
correctly. To demonstrate the validity, a 32 bits switch is built in RSCAD and assign to a 64 bits
GTDO chip. Then I compiled the case and preformed a real time simulation. At the digital output
board, an oscilloscope was used to observe the digital output. In the project, we are going to use
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6.3 RTDS interface
the first six output pins, so only the first six pins are tested. By turning on and off the switch in
RSCAD, we observed a pulse on oscilloscope. We tested all six pins, and each pin can export a
pulse signal. This means the outputs are assigned correctly in RSCAD.
Last of all, since a GTAI (Analog Input) board is used as well, we must make sure the input
pins are inerrant. To do that, a function generator is used to provide a 5 volts peak to peak sinusoid
waveform with 60 Hz. We plugged the output of the function generator into the analog input pins
of RTDS, and observe these input pins waveforms. Four input pins are tested because we used
three pins for three phase voltage input and one pin for DC current measurement input. From
RSCAD, the waveform of each input pin shows an exact 5 volts peak to peak sinusoid waveform,
which indicates the analog input pins are assigned correctly.
To sum up, test results show that the I/O boards are assigned correctly. Also, the voltage
divider can make sure the input voltage to RTDS is within the limitation. The current transducers
output is 2.5 volts which is within the limitation as well. Therefore, we demonstrated the feasibility
of interfacing between real circuit and RTDS. The protection to RTDS machine is successful.
Since the I/O pins are checked assigned correctly through tests, we are ready to connect our
circuit to the RTDS. However, before we actually interface the circuit to RTDS, we need to measure
the four analog inputs to RTDS is with the limitation.
First test we did is voltage divider testing. The phase A voltage we measure on the 100ω
resistor is 2.176 volts. Phase B voltage of the output of voltage divider is 2.23 volts. Phase C
voltage is 2.14 volts. As these values are inputs to the RTDS, but in real simulation. We used
these phase voltage as 30 volts phase voltage. So the scaling factor for such inputs is 13.63. After
multiplying 2.2 volts to 13.63 the RSCAD will read a value around 30 volts which is in the same
level as the designed circuit. Due to the voltage inputs to RTDS are around 2.2 volts so RTDS will
not be damaged.
The second test we did is current transducer output test. To test the output of current transducer, we simply build a circuit with a DC power supply, a 10 resistor in series and the DC line is
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6.3 RTDS interface
through the hole of the current transducer. From the output pin of the current transducer, we can
read voltages so we know how much current is in the DC line. As described in the datasheet, when
DC current is 0 Amps, the Vout is 2.5 volts which is the base voltage. As we increase the voltage,
the DC current reaches 2 Amps, and we measured the Vout now is 2.78 volts. We set the scaling
factor as 1. And we found a linear relationship between the input voltage and the DC current.
The relation is that V=0.1*I+2.5, where I is the DC current in simulation and V is the output
voltage of the current transducer. So I set the scaling factor in RSCAD to make sure RSCAD reads
the same current value as that in the circuit. In conclusion, all four analog inputs are within the
limitation and we can make sure the safety for RTDS. Besides, the output of six digital outputs
wont damage the machine so that is not a big issue.
Finally, we connect our real circuit with the RTDS. The primary side of the three single phase
transformers are connected with 208 volts AC source, the secondary is connected with the voltage
divider and directly to the thyristor circuit. The output of the voltage divider is connected to
RTDS analog input pins. The DC output of rectifier circuit is connected to a 10 resistor and a 0.2
H inductor, then to a DC power supply. The DC power supply and the rectifier circuit are both
grounded. We run the RSCAD case and start the RTDS. The three phase source was increased
gently. As we set the initial firing angle to 90 degrees, the initial DC current is the smallest values
which will not damage the RTDS. The DC power supply was set to 30 volts as the beginning voltage.
And we observe the DC current on RSCAD. The current waveform looks similar to the simulation
result which is respective. However, as the interfacing was just successfully demonstrated right
before the submission date. Therefore, some details of demonstrations are not shown here, because
the time is tight. The group will collect the results and plots to be ready for the thesis day.
In conclusion, the interface between RTDS and real circuit is successful. Therefore, we successfully implemented the interfacing for RTDS. During the thesis day, the group will demonstrate
how our project works and some improvements might be made before the thesis day.
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Low Power LCC
6.3 RTDS interface
Fig. 6.1: Draft circuit built in RSCAD
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Low Power LCC
6.3 RTDS interface
Fig. 6.2: The waveform of the output of firing pulse generator
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Low Power LCC
6.3 RTDS interface
Fig. 6.3: DC current waveform in RSCAD
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Low Power LCC
6.3 RTDS interface
Fig. 6.4: Controller and firing pulse generator for interfacing with external circuit
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Low Power LCC
6.3 RTDS interface
Fig. 6.5: The current transducer for DC current measurement
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Low Power LCC
Chapter 7
Conclusions
The report has outlined the design and implementation of a low power HVDC in a laboratory
setting. The low power line commutated converter (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, 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. The
lower power HVDC-LCC was designed using PSCAD software before transferring the controllers
to real time digital simulation (RTDS) software, building the gate drive circuit with hardware
components and assembling the final design on Lab-Volt equipment.
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Low Power LCC
REFERENCES
References
[1] J. Kennedy and R. Eberhart, “Particle swarm optimization,” in Proc., IEEE Int. Conf. on
Neural Networks, 1995, vol. 4, November 1995, pp. 1942–1948.
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Low Power LCC
Appendix A
Budget
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Low Power LCC
Items
Electronic Items
Breadboard
Transformer
Opto-isolator
Thyristor
Resistor
Current
Transducer
DC-DC
Converter
Copper wires
Software
PSCAD
RSCAD
Multisim
Hardware
Wire wrap board
RTDS
Lab-Volt
Micro-controller
Debugger
Part Number
Supplier
No.
Cost per unit (CAD)
Subtotal
ACME Transformer (TB-81216)
CNY17F-2
S8025L-ND
180 Ohm
69 Ohm
10 Ohm
U of M
U of M
Digi-Key
Digi-Key
U of M
U of M
Digi-Key
1
3
15
15
20
20
1
50.00
369.03
0.67
3.39
0.00
0.00
4.90
0.00
0.00
10.05
50.85
0.00
0.00
4.90
LEM LTS 6-NP
Digi-Key
2
29.33
58.66
ROE-0505S
Digi-Key
15
3.72
55.8
U of M
0.00
0.00
U of M
U of M
U of M
1000.00
0.00
0.00
0.00
0.00
0.00
5.00
1,000,000.00
0.00
8.39
47.95
0.00
0.00
0.00
0.00
0.00
0.00
0.00
U of M
U of M
U of M
Microchip
Microchip
PIC16F877A
Miscellaneous
U of M
Shipping
TOTAL COST
OF PROJECT B/T
TAXES (13%)
TOTAL COST
OF PROJECT
1
1
1
28.00
208.26
27.07
235.33
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Low Power LCC
Appendix B
Hardware Componntes
Hardware Components
Three single-phase step down transformers were used in the project with ratio 4:1. The rated
power is 750 VA. The University of Manitoba supplied the transformers.
Fig. B.1: Three single phase ACME Transformers.
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Low Power LCC
The LabVolt equipment was provided by Power System Group from the University of Manitoba.The LabVolt is used to supply 208 volts three phase source. Also, three blocks of resistive load
are used as voltage divider. A block of smoothing inductors was used as the smoothing reactor in
DC line. The rating for such inductor is 0.2 H and 3 Amps DC.
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Low Power LCC
Fig. B.2: Lab-Volt Equipment
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Low Power LCC
The Power Group of University of Manitoba also supplied an RTDS machine. RTDS is used
for interfacing between real circuit and control system. One GTAI board is used for analog input
form three phase voltage sources. A second GTDO board acts as a digital output to generate firing
pulses.
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The wire wrap board was used for our entire rectifier circuit assembly. For low voltage and
digital I/O pins we used thin wires with wire wrap technique. For high voltage input and high
current output, we used coaxial wires and soldered on the board. Six thyristors, six DC-DC
converters, six opto-isolators, twelve 69ω resistors, six 180ω resistors, one current transducer and
couple connectors are integrated on the board.
Fig. B.4: Wire wrap board
53