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University of ManitobaDepartment of Electrical & Computer Engineering

ECE 4600 Group Design Project

Final Project Report

Design and Implementation of a Low Power Line-Commutated

Converter (LCC)

byGroup 14

Chen Chen Huo YingyangLi Hang Liu Jingwei

Motluk Lyle

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 EngineeringUniversity of Manitoba

Industry Supervisors

Arash Darbandi – Manitoba HVDC Research Center

–

Date of Submission

March 4, 2015Copyright © 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

Contributions

Ch

enC

hen

Hu

oY

ingy

ang

Li

Han

g

Liu

Jin

gwei

Mot

luk

Lyle

PSCAD Design • •Drive Circuit Design • Controller Design • RSCAD Design •Hardware Assembly • RTDS Interfacing •Entire System Testing •

Legend: • Lead task Contributed

ii

Low Power LCC ACKNOWLEDGEMENTS

Acknowledgements

The team would like to thank the following people for their support in this project:

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.

Arash Darbandi from the Manitoba HVDC Research Center for the problem solving and

guidance he provided through out the course of this project.

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.

Christian Jegues from RTDS Technologies Inc. for advising the team with RTDS interfacing.

All graduate and PhD students that who helped us, Qi Yi, Li Tan, and Zhao Hengfeng.

iii

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

Low Power LCC TABLE OF CONTENTS

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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

5.6 Testing and Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . 5

2.2 DC voltage waveform at the rectifier output prior to improvements to the control

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 . . . . . . . . . . . . . . . . . . . 17

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

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

Low Power LCC LIST OF FIGURES

4.4 A block of PI controller designed in PSCAD . . . . . . . . . . . . . . . . . . . . . . 22

4.5 The controllers response to the change of reference current . . . . . . . . . . . . . . 23

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) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

5.5 Characteristic of SCR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

5.6 SCR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

5.7 Mutilsim simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

5.8 Testing circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

6.1 Draft circuit built in RSCAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

6.2 The waveform of the output of firing pulse generator . . . . . . . . . . . . . . . . . 40

6.3 DC current waveform in RSCAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

6.4 Controller and firing pulse generator for interfacing with external circuit . . . . . . 42

6.5 The current transducer for DC current measurement . . . . . . . . . . . . . . . . . . 43

B.1 Three single phase ACME Transformers. . . . . . . . . . . . . . . . . . . . . . . . . 48

B.2 Lab-Volt Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

B.3 RTDS equipment in the machine lab. . . . . . . . . . . . . . . . . . . . . . . . . . . 52

B.4 Wire wrap board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

vii

Low Power LCC LIST OF TABLES

List of Tables

2.I System Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

viii

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

HVDC 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

PLL Phase Lock Loop

RTDS Real Time Digital Simulation Machine

GTAI Analog Input Card for RTDS

GTDO Digital Output Card for RTDS

GPC − 2 Giga-Processor Card in RTDS

RSCAD A software for interfacing to the RTDS Simulator hardware

PSCAD A simulation software for analyzing power systems transients

ix

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 op-

erations 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 Values

Rectifier AC side input volatge 208± 10%V

Rectifier DC side output voltage 340± 10%V

DC bus current and power 2± 10%and680± 10%W

4

Low Power LCC 2.3 Testing of PSCAD performance

2.3 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


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


Fig. 2.3: DC voltage waveform at the rectifier output post improvements to the control system

7


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 Harmonic Filter Design

3.1.1 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 frequen-

cies. 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 sameperformance

10


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 ·N2

1

N21 − 1

· U21 = U1 · I1 = 416V ar (3.1)

Harmonics current of order 5, 7, 11 and 13 are calculated as follow:

I5 =2√

3

5π· Idc = 0.441A (3.2a)

I7 =2√

3

7π· Idc = 0.315A (3.2b)

I11 =2√

3

5π· Idc = 0.2A (3.2c)

I13 =2√

3

5π· Idc = 0.17A (3.2d)

Reactive power compensated by each individual filter:

Q1 = Qc ·I55

I55 + I7

7 + I99 + I11

11

= 127.55V ar (3.3a)

Q2 = Qc ·I75

I55 + I7

7 + I99 + I11

11

= 113.83V ar (3.3b)

11


Q3 = Qc ·I95

I55 + I7

7 + I99 + I11

11

= 45.99V ar (3.3c)

Q4 = Qc ·I115

I55 + I7

7 + I99 + I11

11

= 33.08V ar (3.3d)

Ca is the capacitance of one of the capacitors for the two single-tuned filters:

Ca =Q1 · (N2

1 − 1)

w ·N21 · U1

2= 7.5µF (3.4)

La is the inductance of one single-tuned filter:

La =1

w2 ·N21 · Ca

= 37.49mH (3.5)

Cb is the capacitance of one of the capacitors for the two single-tuned filters:

Cb =Q1 · (N2

2 − 1)

w ·N22 · U

2

1

= 6.84µF (3.6)

Lb is the inductance of one single-tuned filter:

Lb =1

w2 ·N21 · Ca

= 21.00mH (3.7)

Secondly, performing parameter transformation based on the algorithm [3].

C1 = Ca + Cb = 14.34µF (3.8a)

L1 =La · Lb

La + Lb= 13.43mH (3.8b)

C2 =Ca · Cb · (Ca + Cb) · (La + Lb)

2

(Ca · La − Cb · Lb)2= 133.05µF (3.8c)

12


L2 =(Ca · La − Cb · Lb)

2

(Ca + Cb)2 · (La + Lb)= 1.573mH (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.

C1 = 8.625µF (3.9a)

L1 = 5.733mH (3.9b)

C2 = 307.13µF (3.9c)

L2 = 159.42mH (3.9d)

3.1.3 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 double-

tuned 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.

13


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 cur-

rent 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

14


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, 6thand 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 corre-

sponding to 6thand 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 cur-

rents 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].

15


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):

ipeakd = (sVd0/w1Ld)[1− (π/p) cot(π/p)] sinα (3.10)

Plugging in all the inputs: ipeakd =2.05A, S=1, Vdo=68 V, W1 = 2π60,p = 60,α = 45

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.

16


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 suc-

cessful. 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. There-

fore, 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.

17


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

18


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

19

Low Power LCC

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.

20

Low Power LCC 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

21

Low Power LCC 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

22

Low Power LCC 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.

23

Low Power LCC

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

24

Low Power LCC 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

25

Low Power LCC 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.

26

Low Power LCC 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

27

Low Power LCC 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

28

Low Power LCC 5.6 Testing and Troubleshooting

equation

R1 >Vsource − Vmax

Imax=

3.35V

0.06A= 55.8Ω (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

Rtotal =R3 ·Rth

R3 +Rth= 40Ω (5.2a)

Itotal =Vsource

Rtotal +R2=

5V

(40 + 180)Ω= 23mA (5.2b)

VGT = Vsource − Itotal ·R2 = 5− 0.023 · 180 = 0.86V (5.2c)

IGT =VGT

Rth=

0.86V

96Ω= 8.9mA (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

29


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

30


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.

31

Low Power LCC

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

32

Low Power LCC 6.2 RSCAD circuit design and simulation

parameters in the draft circuit are identical to the real components that used in the project.

33

Low Power LCC 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.

34

Low Power LCC 6.3 RTDS interface

6.3 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

35


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

36


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 trans-

ducer, we simply build a circuit with a DC power supply, a 10 resistor in series and the DC line is

37


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 suc-

cessfully 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.

38


Fig. 6.1: Draft circuit built in RSCAD

39


Fig. 6.2: The waveform of the output of firing pulse generator

40


Fig. 6.3: DC current waveform in RSCAD

41


Fig. 6.4: Controller and firing pulse generator for interfacing with external circuit

42


Fig. 6.5: The current transducer for DC current measurement

43

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.

44

Low Power LCC REFERENCES

References

[1] J. Kennedy and R. Eberhart, “Particle swarm optimization,” in Proc., IEEE Int. Conf. onNeural Networks, 1995, vol. 4, November 1995, pp. 1942–1948.

45

Low Power LCC

Appendix A

Budget

46

Low Power LCC

Items Part Number Supplier No. Cost per unit (CAD) Subtotal

Electronic Items

Breadboard U of M 1 50.00 0.00

Transformer ACME Transformer (TB-81216) U of M 3 369.03 0.00

Opto-isolator CNY17F-2 Digi-Key 15 0.67 10.05

Thyristor S8025L-ND Digi-Key 15 3.39 50.85

Resistor180 Ohm69 Ohm10 Ohm

U of MU of MDigi-Key

20201

0.000.004.90

0.000.004.90

CurrentTransducer

LEM LTS 6-NP Digi-Key 2 29.33 58.66

DC-DCConverter

ROE-0505S Digi-Key 15 3.72 55.8

Copper wires U of M 0.00 0.00

Software

PSCAD U of M 1000.00 0.00

RSCAD U of M 0.00 0.00

Multisim U of M 0.00 0.00

Hardware

Wire wrap board U of M 1 5.00 0.00

RTDS U of M 1,000,000.00 0.00

Lab-Volt U of M 0.00 0.00

Micro-controller PIC16F877A Microchip 1 8.39 0.00

Debugger Microchip 1 47.95 0.00

Miscellaneous U of M 0.00 0.00

Shipping 28.00

TOTAL COSTOF PROJECT B/T

208.26

TAXES (13%) 27.07

TOTAL COSTOF PROJECT

235.33

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Low Power LCC

Appendix B

Hardware Componntes

Hardware ComponentsThree 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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The LabVolt equipment was provided by Power System Group from the University of Mani-toba.The LabVolt is used to supply 208 volts three phase source. Also, three blocks of resistive loadare used as voltage divider. A block of smoothing inductors was used as the smoothing reactor inDC line. The rating for such inductor is 0.2 H and 3 Amps DC.

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Fig. B.2: Lab-Volt Equipment

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The Power Group of University of Manitoba also supplied an RTDS machine. RTDS is usedfor interfacing between real circuit and control system. One GTAI board is used for analog inputform three phase voltage sources. A second GTDO board acts as a digital output to generate firingpulses.

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Fig. B.3: RTDS equipment in the machine lab.

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The wire wrap board was used for our entire rectifier circuit assembly. For low voltage anddigital I/O pins we used thin wires with wire wrap technique. For high voltage input and highcurrent output, we used coaxial wires and soldered on the board. Six thyristors, six DC-DCconverters, six opto-isolators, twelve 69ω resistors, six 180ω resistors, one current transducer andcouple connectors are integrated on the board.

Fig. B.4: Wire wrap board

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Documents

Design and Implementation of a Low Power Line …ece.eng.umanitoba.ca/undergraduate/ECE4600/ECE4600/Archive/2014/... · The recti er components include input alternating current that