ECE 4600 Group Design Progress Report

Group 14 Chen Chen

Lyle Motluk Hang Li

Jingwei Liu Yingyang Huo

Academic Supervisor Dr. Aniruddha Gole

Electrical and Computer Engineering Department University of Manitoba

Industrial Supervisor

Arash Darbandi Manitoba HVDC Research Centre

Date of Submission January 12nd, 2015

Design and Implementation of a low power Line-Commutated Converter

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Table of Contents

Glossary of Terms .......................................................................................................................... 2 1 Introduction ........................................................................................................................ 3

2 Project Summary ............................................................................................................... 3 2.1 PSCAD circuit design (Lyle,Hang) .......................................................................... 4 2.2 AC filter design (Hang) ........................................................................................... 4 2.3 Thyristor drive circuit (Yingyang,Jingwei) .............................................................. 5 2.4 Control system (Jingwei,Hang) ............................................................................... 6 2.5 Human Machine Interface (Chen) .......................................................................... 6 3 Future Work ....................................................................................................................... 7 3.1 Control System ......................................................................................................... 7 3.2 Gate Drive Circuit .................................................................................................... 7 3.3 Human Machine Interface ........................................................................................ 7 3.4 Construction and Testing of Complete Design ........................................................ 7

4 Conclusion .......................................................................................................................... 7 5 Gantt Chart ........................................................................................................................ 8

6 Budget ................................................................................................................................. 9

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1. Introduction

The goal of this project is to develop an accurate low power HVDC system to represent

the concepts of a HVDC and implement the design with standard laboratory equipment (Lab-

Volt). HVDC-LCC systems implemented in power transmission require voltage and power in the

kilovolt and megawatt range, which cannot be implemented safely in laboratory settings.

Therefore the low voltage HVDC-LCC design will represent a scaled down version of the

CIGRE (International Council on Large Electric Systems) developed model of an HVDC-LCC.

The lower power HVDC-LCC will first be designed using PSCAD software before transferring

the controllers to RTDS and assembling the final design on Lab-Volt equipment. The final

product will provide instructors an accurate model to educate students on HVDC systems with

the goal of improving the design in a safe low power lab environment to be implemented in

industry.

This project was divided into modular tasks, which allowed individual members of the

team to complete different sections of the project simultaneously. This process has ensured that

although problems arouse and delayed certain sections, the entire project was not derailed. The

report breaks down the problems and progress that occur since the beginning of the school year.

2. Progress Summary

The design portion of the project is complete. The remaining work pertains to assembling

the components and testing the overall system. This project is divided into five sections (I)

PSCAD design, (II) AC/DC filters, (III) Gate Drive Circuit, (IV) Control Systems, and (V)

Human Machine Interface.

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2.1. Design in PSCAD

The low power line-commutated converter was designed using PSCAD, power systems

simulation software. The LP-LCC consists of a rectifier and an inductor. The rectifier

components include input alternating current that is step down with a high voltage transformer

from 205V to 52 V, a series of AC filters that remove harmonics, a gate drive circuit responsible

for converting AC voltage to DC voltage, a controller that regulates a consistent 2 amp DC

current. Presently the rectifier design in PSCAD is complete. The inductances, resistances, and

capacitances have all been determined through calculation and optimizing the controller by

reducing the percentage overshoot and transfer time that is required for the controller to regulate

the DC current is complete. The next step for the rectifier will be to transfer the PSCAD design to

RTDS and begin simulation and optimization test on the lab equipment.

The second half of the PSCAD design consists of an inverter that preforms the reverse

operations of the rectifier in order to converter the DC power (used for transmission) to AC

power for applications. Currently the overall design for the inverter is functioning correctly and

ready to be transferred to RTDS however the controller for the inverter has yet to be optimized.

The percent overshoot needs to be reduced in order to reduce possible issues when testing the

inductor on the Lab Volt equipment.

2.2 AC filters

During the operation of converter, it generates harmonic currents and voltages on both AC

and DC side. Based on the requirement of the project, we are going to design and implement the

AC filters. Due to the high cost of these specific resistors, capacitors and inductors, the

implement of AC filters is not practical. As the decision of our supervisor, we are going to discuss

our design of AC filters in the final report and show the testing results on PSCAD.

The design of AC harmonic filters including choosing certain types of filters and

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calculating parameters. First of all, the goal of AC filter is to restrain certain order of harmonics.

In our case, the main harmonics have the order of 5, 7, 11 and 13. Based on the research, double-

tuned filters are widely used in industry because of less cost. So far I have obtained the

parameters of two double-tuned filters, and tested the filter performance. To calculate the

parameter of double-tuned filters, I basically treat one double-tuned filter as two parallel single-

tuned filters, because the algorithm for the parameters of single-tuned filters is widely introduced

in many research papers. After collecting parameters, I built these AC filters in PSCAD model

and tested. Based on the observation, the current waveform did not improve significantly, which

indicates that the resistance of 3-phase transformer is too low, so the harmonic current goes to the

source directly without going through the AC filters. Therefore, I need to increase the impedance

of the source.

2.3 Gate drive circuit for SCR

The main purpose of designing a gate drive circuit is to control six-pulse bridge converter.

There are six thyristors in the six-pulse bridge rectifier, in order to turn on the thyristor to apply

pulse to the gate of thyristor; the part number of SCR chip we choose is S8025L. The maximum

voltage gate trigger is 1.5V and the maximum current gate trigger is 35mA. First of all, we design

a manually control circuit by using switch and ac power supply to achieve that, than we built the

circuit and tested in Multisim circuit design software. In the future we need use the control

system to control the gate drive circuit, then rebuild the circuit by using a new type of switch

called opto-isolator (CNY12F-2). In the circuit we apply 5V to the chip opto-isolator and add a

resistor to allow a certain range of current to follow into the opto-isolator to turn it on. On the

output, one side connect VCC, another side connect to the gate of thyristor, when we turn on

opto-isolator, use voltage divider we choose two certain resistors. 1.5V will apply on the thyristor

and let SCR on.

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So far, the gate drive circuit had been built on Multisim, test results meets our expectation

and parts have been ordered for the gate drive circuit to be built on a project board.

2.4 Control Systems

There are two control systems in our project. The rectifier side (AC-DC) we use RCC

(rectifier current control) method, and the inverter side (DC-AC) we use extinction angle control.

The PI controller is chosen for our project, the objective for PI controllers is to control the output

of both rectifier and inverter stages.

For the rectifier side, the firing angle is controlled with a feedback control system, the DC

voltage of the rectifier increases or decreases is according to compare the difference between the

measured current and reference current. The error will be sent into the PI controller to control the

firing angle of thyristor, so that we can get the expected DC current. The minimum of the firing

angle is typically chosen to 5°, because the voltage need to be large enough to make sure turn-on

for firing angles beyond this value. The Inverter part is almost the same as the rectifier side.

Instead of comparing the currents, we compare the extinction angles; the error will be sent into PI

controller to control the firing angle. We spent two months for doing the research.

First stage, we found that it is easy to build RCC, but with our knowledge that, it is hard

to build system to measure the extinction angle, Dr.Gole suggest us to use current control for the

inverter side first. If the current control works well, we can try to build the system to measure the

extinction angle if time available.

After doing the research, we have built the two systems in the PSCAD; both of them work

well in PSCAD. This took us about 1 month to finish this task.

2.5 Human Machine Interface

The human machine interface has been programmed the basic functions based on our

current inverter and rectifier. A schematic that includes the AC/DC and DC/AC transformers, 6-

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pulse rectifier, and voltage and current displays have developed. However, the programmed HMI

need to improve after implemented with the entire system.

There is a challenge that the HMI programming cannot meet one of our design goals that

the main menu can login different parameters interface. It shows voltages and currents on the

main loop.

3.0 Future Work

3.1 Control System

Build the control system in RSCAD and test in RTDS.

3.2 Gate Drive Circuit

Construct the physical components for the gate drive circuit based on the Multisim design

after the thyristors parts are received. The construction and implementation will take one week.

3.3 Human Machine Interface

Programming needs to improve after both rectifier and inverter sides are finalized; meet

all design goals; approximately three weeks including programming and testing

3.4 Construction and Testing of the Complete Design

Complete assembly and testing of the low voltage line-commutated converter will be

done in three stages. First the rectifier and inverter will be assembled and tested separately.

Finally the rectifier will be connected to the inverter to be tested and optimize the overall

performance. It is expected to take three weeks to complete.

 4.0  Conclusion    

The design of all the components for the low power line-commutated converter in

PSCAD and Multisim is complete. The remaining work for the project consists of constructing

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the gate drive circuit, programming the microcontroller and finally testing and tuning the

complete low power line-commutated converter. Although the Gantt chart had to be altered

during the course of the project, the project will be completed by the end of February.

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5.0 Appendix B: Gantt Chart

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6.0 Appendix C: Budget The University of Manitoba supplies most of the equipment for free. The total budget for

the project is $45.64.

Table 3. Project budget Items   Part    

Number  Supplier   No.   Cost   per  

unit  (CAD)  Sub-­‐total  

Electronic  Items  

         

Breadboard     U  of  M   1   50.00   0.00  Transformer   ACME  

Transformer  (TB-­‐81216)  

U  of  M   1   123.01   0.00  

Opto-­‐isolator   CNY17F-­‐2   Digi-­‐Key   15   0.67   10.05  Thyristor   S8025L-­‐ND   Digi-­‐Key   6   3.39   20.34  Resistor   350  Ohm  

60  Ohm  190  Ohm  

Digi-­‐Key  Digi-­‐Key  Digi-­‐Key  

15  15  15  

TBD   TBD  

Copper  wires     U  of  M     0.00   0.00  Software            PSCAD     U  of  M     1000.00   0.00  Hardware            RTDS     U  of  M     1,000,000.00   0.00  Lab-­‐Volt     U  of  M     0.00   0.00              Miscellaneous     U  of  M     0.00   0.00              Shipping           10.00              TOTAL   COST  OF   PROJECT  B/T  

        40.39  

TAXES  (13%)  

        5.25  

TOTAL   COST  OF  PROJECT    

        45.64