TITLE
PROPORTIONAL RESONANT CURRENT CONTROLLER FOR 7-LEVEL
MULTILEVEL INVERTER WITH REDUCED SWITCHING
ABDUL KHAIRI BIN ABDUL RAHMAN
A project submitted in partially fulfilment of requirement for the award of the
Degree of Master of Electrical Engineering
Faculty of Electrical and Electronic Engineering
University Tun Hussein Onn Malaysia
JANUARY 2018
iii
ACKNOWLEDGEMENT
Alhamdulillah, thanks to Allah for his greatness and graciousness and all
praise to Allah SWT for the sources and guidance and I managed to complete this
report as scheduled.
I would like to take this opportunity to express my sincere appreciation to my
supervisor Dr. Shamsul Aizam Bin Zulkifli, for generously spending his precious
time and offering his evaluable and encouragement during the completion of this
project.
I am also expressing my deepest appreciation to my beloved parent Abdul
Rahman Haji Ahmad and Dayang Khabibah Awang Sallam for their help and morale
support during the time I need it the most.
Apart from this, my sincere thanks to all my friends, especially my classmate
for supporting me and cheering me during hard times and always there for me when
they are needed.
iv
ABSTRACT
This project is describing the recently introduced Proportional Resonant (PR)
controller and its performance in the application of 7-level multilevel inverter
controller system. The performance of the PR controller is [u2]measured based on the
ability of the controller to reduce the harmonic distortion in the inverter system with
non-linear load connected at the output of the inverter. This is because of the ability
of the PR controller system to have additional selective harmonic compensator. In
this project, a new topology of 7-level multilevel inverter is used to prove the
efficiency of this topology to provide a symmetric 7-level multilevel inverter with
has low Total Harmonic Distortion (THD) due to the reducing of the number of
switches used in the inverter circuit. This project consists of the simulation process
of the PR controller for symmetric 7-level multilevel inverter with non-linear load.
The system is then also been implemented in a hardware setup with the application
of Texas Instrument (TI) C2000 microcontroller as the controller of the inverter
circuit. The simulation and the downloading process of the PR controller system to
the microcontroller is done by using MATLAB/Simulink software[u3]. The result of
the multilevel inverter simulation in MATLAB/Simulink shows that the
implementation of the PR controller in the inverter system reduce the total harmonic
distortion cause by the system load and the harmonic distortion form the inverter
system itself. The hardware result shows that the PR controller system is applicable
and functioning.
v
ABSTRAK
Projek ini membincangkan tentang sistem pengawal resonan berkadar dan
prestasinya dalam aplikasi untuk system kawalan untuk inverter bertingkat 7-tingkat.
Prestasi pengawal resonan berkadar diukur berdasarkan kemampuan pengawal untuk
mengurangkan herotan harmonic dalam system sistem inverter yang disambungkan
pada bukan linear pada keluaran inverter tersebut. Ini kerana pengawal resonan
berkadar mampu menggunakan pemampas harmonic untuk harmonic yang tertentu.
Di dalam projek ini, topologi baru untuk inverter bertingkat 7-tingkat digunakan
untuk membuktikan topopogi tersebut mampu menurunkan kadar total herotan
harmonik dsebabkan oleh pengurangan bilangan suis separa pengalir yang
digunakan. Projek ini mempunyai bahagian simulasi untuk inverter bertingkat 7-
tingkat dengan pengawal resonan berkala yang disambung dengan beban tidak linear.
Sistem tersebut kemudiannya diimplimenkan ke dalam litar sebenar dengan bantuan
mikropengawal Texas Instrument (TI) C2000 dimana sistem pengawal inverter
diprogramkan kedalamnya. Proses simulasi dan transaksi sistem kedalam litar
sebenar dilakukan dengan bantuan perisian MATLAB/Simulink. Hasil dari simulasi
di dalam perisian MATLAB/Simulink, penggunaan sistem kawalan resonan berkala
di dalam sistem inverter bertingkat 7-tingkat telah mengurangkan kadar total herotan
harmonic yang disebabkan oleh beban pada sistem dan herotan harmonic dari dalam
sistem inverter tersebut sendiri. Hasil daripada eksperimen ke atas sistem yg telah
diadaptasikan ke dalam litar sebenar menunjukkan bahawa sistem kawalan resonan
berkala berfunsi.
vi
TABLE OF CONTENTS
TITLE i
DECLARATION ii
ACKNOWLEDGEMENT iii
ABSTRACT iv
TABLE OF CONTENTS vi
LIST OF FIGURES ix
LIST OF TABLES xii
CHAPTER 1 INTRODUCTION 1
1.1 Introduction 1
1.2 Problem Statement 3
1.3 Project Objectives 3
1.4 Project Scopes 4
CHAPTER 2 LITERATURE REVIEW 5
2.1 Introduction 5
2.2 Multilevel Inverter 5
2.2.1 7-Level Multilevel Inverter 7
2.2.1.1 Cascade H-Bridge Multilevel Inverter 7
2.2.1.2 Symmetric Multilevel Inverter 9
2.3 Proportional-Resonant Controller 11
vii
2.4 Non-Linear Load and Harmonic Distortion 13
2.5 Previous Research Projects 14
2.5.1 Design and Implementation of Proportional-Resonant
Controller for 3-Phase Current Source Inverter In Dspace
DS1104 14
2.5.2 A Proportional-Resonant Current Controller for Selective
Harmonic Compensation in a Hybrid Active Power Filter14
2.5.3 Low-Cost Digital Implementation of Proportional-
Resonant Current Controller for PV Inverter Application
Using Delta Operator 15
2.5.4 Developed Cascaded Multilevel Inverter Topology to
Minimise The Number of Circuit Devices And Voltage
Stresses Of Switch 15
2.5.5 Verification of a low Components Nine-Level Cascaded-
Transformer Multilevel Inverter in Grid-Tie Mode 16
2.6 MATLAB/Simulink 17
2.7 C2000 Texas Instruments Microcontroller 18
CHAPTER 3 METHODOLOGY 20
3.1 Introduction 20
3.2 Master Project Flow Chart 20
3.3 Project Development 22
3.3.1 Hardware setup Flowchart 22
3.3.2 Project Design Specification 23
3.4 Software Development 24
3.4.1 Symmetric 7-Level Multilevel Inverter 24
3.4.2 Proportional Resonant Current Controller 26
3.5 Hardware Development 30
3.5.1 Texas Instrument C2000 Microcontroller 30
3.5.2 7-Level Symmetric Multilevel Inverter 31
viii
3.5.3 Full-wave Bridge Rectifier 32
3.5.4 Gate driver 33
3.5.5 Current Transducer (LA 25-NP) 34
3.5.6 LC Filter 35
CHAPTER 4 RESULTS AND ANALYSIS 37
4.1 Introduction 37
4.2 Simulation Results 37
4.2.1 Open Loop Simulation Result 38
4.2.1.1 Open Loop Simulation without Non-linear
Load 42
4.2.1.2 Open Loop Simulation with Non-linear Load
43
4.2.2 Closed Loop Simulation Result 47
4.2.3 Simulation for Real Application of Inverter 50
4.3 Hardware results 54
4.3.1 Open Loop Inverter System without Non-linear Load 54
4.3.2 Closed Loop Inverter System without Non-linear Load 58
CHAPTER 5 CONCLUSION AND RECOMMENDATION 62
5.1 Conclusion 62
5.2 Recommendation 65
REFERENCE 66
ix
LIST OF FIGURES
1.1 Block diagram of Multilevel Inverter with PR Controller 2
2.1 Power and voltage range of multilevel inverter 6
2.2 Output waveform of 7-level multilevel inverter 7
2.3 Cascade H-Bridge multilevel inverter 8
2.4 Circuit diagram of 7-level symmetric multilevel inverter 10
2.5 PR controller bode graph[14] 12
2.6 Overall Scheme of Proposed Multilevel Inverter Topology 16
2.7 MATLAB 2014 Beta version 17
2.8 Simulink library for Embedded Coder Support Package for TI C2000 18
2.9 TMS320F2835 TI C2000 microcontroller 19
3.1 Master Project Flowchart 21
3.2 Flowchart of Project Setup 22
3.3 Block diagram of multilevel inverter with minimal switching using
proportional resonant current controller 23
3.4 Symmetric 7-level multilevel inverter circuit diagram 24
3.5 POD PWM 25
3.6 PWM generation circuit 26
3.7 Proportional-resonant current controller with third and fifth
harmonics mitigation. 27
3.8 Flowchart of PR controller design 28
3.9 Texas Instrument C2000 Microcontroller Board 30
3.10 Hardware Circuit of 7-level Symmetric Multilevel Inverter 31
3.11 Full wave bridge rectifier hardware circuit 32
3.12 Hardware Circuit of Gate Driver 33
x
3.13 LA 25-NP Current Transducer 34
3.14 LC Filter Hardware Circuit 35
3.15 LC Filter Schematic Circuit 36
4.1 Simulink model of multilevel inverter without non-linear load 39
4.2 Switches Pulse from The PWM and The Inverter Output Voltage 40
4.3 Output Voltage of Inverter without Filter 41
4.4 Output Voltage and Current of Inverter with Filter 41
4.5 Output Voltage and Current of Inverter without Non-Linear Load 42
4.6 FFT Analysis of Inverter System without Non-Linear Load 43
4.7 Full-wave Bridge Rectifier Circuit 44
4.8 Simulink model of multilevel inverter with non-linear load 45
4.9 Output Current of Inverter with Non-Linear Load 46
4.10 FFT Analysis of Inverter System with Non-Linear Load 47
4.11 Closed Loop Simulation Setup 48
4.12 Output Voltage and Current of Inverter with Non-Linear Load 49
4.13 FFT Analysis of Close Loop Inverter System with Non-Linear Load 49
4.14 Output Voltage and Current of Inverter without Non-linear Load for
230Vrms simulation 50
4.15 Current THD level of Inverter without Non-linear Load for 230Vrms
simulation 51
4.16 Output Voltage and Current of Inverter with Non-linear Load for
230Vrms simulation 52
4.17 Current THD level of Inverter without Non-linear Load for 230Vrms
simulation 52
4.18 Output Voltage and Current of Close Loop Inverter with Non-linear
Load for 230Vrms simulation 53
4.19 Current THD Level of Close Loop Inverter with Non-linear Load for
230Vrms simulation 54
4.20 Simulink Block of Open Loop Inverter System 55
4.21 Switching Pulse of the MOSFET 1(yellow) and MOSFET 2(blue)
from gate driver output 55
4.22 Switching Pulse of the MOSFET 2(blue) and MOSFET 3(yellow)
from gate driver output 56
xi
4.23 Switching Pulse of the MOSFET 4(yellow) and MOSFET 5(blue)
from gate driver output 56
4.24 Output Waveform of Multilevel Inverter 57
4.25 Output Waveform of Multilevel Inverter with filter 58
4.26 Simulink Model of Close Loop controller system 59
4.27 The Voltage and Current Waveform of The Close Loop Inverter
System 61
xii
LIST OF TABLES
2:1 Switching scheme for 7-level symmetric multilevel inverter 11
3:1 List of Component for Rectifier Hardware 32
3:2 List of Components for the Gate Driver Hardware 34
4:1 Table of components and values 39
4:2 Table of components and values 45
5:1 Table of THD level before and after implementation of PR controller 63
CHAPTER 1
INTRODUCTION
1.1 Introduction
In a power system, inverter is used especially in AC microgrid where there is
application of renewable energy source. This is because, most renewable energy
source or generator produces a DC voltage. Other than that, the inverters are also
needed in the energy storage system where storage energy is in DC form [1].
There are many type of inverter as inverter varies with the topology used. The
application of the inverter determines the topology used for the inverter as each
topology has its own advantages and disadvantages. Based on numbers of research
paper, a multilevel inverter is the most efficient type of inverter as it solves the
drawback faced by a conventional inverter [2].
However, multilevel inverter needs more numbers of switches compared than
conventional inverter. The switching operation will create harmonics distortion to the
inverter system [3]. In [4], the implementation of PI controller in to control the
current is not effective as the control system will be unstable during the variation of
attenuation and resonant frequency of the filter.
Thus, a more efficient type of controller to be used to reduce the harmonic
distortion in the inverter system is the Proportional Resonant (PR) controller is
2
proposed in this project. With the present of infinite gain at the resonant frequency,
PR controller are able to ensure zero steady-state error which in other hand it will
minimize the load current distortion and harmonic content in the inverter system [5].
Another mitigation that can be done in the reduction process of harmonic
distortion is by decreasing the number of switching pattern used in the multilevel
inverter. The reduction of switches number means a new topology of multilevel
inverter and a new design of inverter circuit. The modulation strategy of the circuit
will be differed from the conventional multilevel inverter. This is to ensure that even
if the inverter circuit is modified to have less number of switches, the inverter must
produce the same desired output waveform which is in staircase waveform. The 7-
level multilevel inverter with the least number of switches used was introduced by
which are the inverter topology of symmetric 7-level multilevel inverter with five
switches [6].
Therefore, this project focuses on the PR current controller strategy and the 7-
level multilevel inverter with minimum switching pattern. In order to analyse the
performance of the PR controller in reducing Total Harmonic Distortion (THD), the
inverter system THD value will be increased until it exceeds more than 2% [u4][k5]of
the previous THD value without non-linear load by connecting the inverter to a non-
linear load. Figure 1:1 shows the block diagram of the overall project setup.
Current
controller
VDC 7-Level
Multilevel
Inverter
Filter Non-linear
Load
PWM
Gate
Driver Io
Figure 1:1: Block diagram of Multilevel Inverter with PR Controller
3
1.2 Problem Statement
In application of inverter, the type of inverter plays an important role especially in
the aspect efficiency. Multilevel inverter is a type of inverter with the efficiency as it
has the ability to produce the best waveform outputs which are close to sinusoidal
waveform. However, the conventional multilevel inverter needs more switches
compare to conventional two-level inverters. Semiconductor switches produce
significant harmonic current as they chop voltage waveforms during their transition
between cut-off and conducting state.
The different circuit configuration of an inverter means a different circuit
modulation strategy. Therefore, a new configuration of PWM system must be created
to allow the inverter circuit to produce the desired staircase waveform.
Even if the total number of switches in the inverter system is reduced, the
harmonic current is still more than one switches needed in the inverter circuit.
Harmonic distortion can still be form from the operation of the switches. Moreover,
the present of non-linear could also lead to the production of harmonic current in the
system [7]. This will eventually increase the THD level of the system. Therefore, the
inverter system must have a type of controller system which can detect the changes
in the output waveform and reduce the harmonic distortion. [u6]
1.3 Project Objectives
Based on the problem statements, there are three objectives that are going to be
achieved. The objectives of this project are;
1. To construct a minimal switching single phase 7-level multilevel inverter
with non-linear load circuit using MATLAB/Simulink.
2. To reduce the THD on the inverter system and non-linear load using
Proportional Resonant (PR) controller.
3. To construct and proof the concept in hardware setup for reduced switching
single phase 7-level multilevel inverter with non-linear load and PR
controller.
4
1.4 Project Scopes
This project is to develop a Proportional Resonant (PR) controller for 7-level
multilevel inverter with minimum switching pattern. The application of the PR
controller in the inverter system is used to reduce the harmonic distortion when a
non-linear load is connected to the inverter system. Thus, PR controller and 7-level
multilevel inverter with minimum switching pattern is proposed to study as stated
below;
• The construction of symmetric 7-level multilevel inverter is using MATLAB/
Simulink.
• The simulation of symmetric 7-level multilevel inverter is be conducted with
and without non-linear load.
• The output current THD level will be analyse and the harmonic produced by
the inverter and non-linear load will be ensured exceed overall THD of at
least 2% higher than the inverter without non-linear load.
• After implementing the PR controller in the inverter system, the output of the
symmetric 7-level multilevel inverter with PR controller will be determined
and analysed to identify the THD value
• The PR controller and the inverter topology will be implement in hardware
using Texas Instrument (TI) C2000 microcontroller.
5
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
This chapter will focus on studies, fact and research project on a topic on this project
title. The chapter will also review on four major themes which frequently emerge
throughout the literature reviewed. These themes are single-phase multilevel inverter,
proportional-resonant controller, software and C200 Texas Instrument
microcontroller.
2.2 Multilevel Inverter
Multilevel inverter is a type of power electronic converter which can provide or
produce desired Alternating Current (AC) voltage level at the output of the converter
using numbers of lower level Direct Current (DC) voltage source as input [8].
Multilevel inverter has a high power and voltage range which is as shown in Figure
2:1. This kind of capability instantly solves the problem faced by the normal inverter
6
which is facing difficulty in connecting single power semi-conductor to the medium-
voltage network.
Figure 2:1: Power and voltage range of multilevel inverter
Multilevel inverter starts from the three-level inverter which was introduced
by Nabae in [9]. There are many types of multilevel inverter as the level of the
inverter increase from three to as many as possible. This chapter will review more on
7-level multilevel inverter as it is going to be the one that will be used in this project.
The variety of multilevel inverter will increase as they are many topologies that are
available. This chapter will review is the common topologies used for 7-level
multilevel inverter which is cascade H-bridge multilevel inverter and the new
symmetric multilevel inverter which is going to be used in this project.
There are many advantages of multilevel inverter. One of them is that this
type of inverter can produce a low distortion output voltage. It also draws input
current with low distortion. Another advantage of this inverter is that it can operate
with a lower switching frequency [10].
7
2.2.1 7-Level Multilevel Inverter
As mention earlier, 7-level multilevel inverter is used in this project. The 7 -level
inverter is chosen as it has moderate number of level which makes the output of the
inverter is almost sinusoidal and only require simple filter to produce smooth
sinusoidal AC current and voltage [2]. There will be two types of 7-level multilevel
inverter that are going to be reviewed in this subtopic. The first one will be the
conventionally used cascade H-bridge multilevel inverter and the new symmetric
multilevel inverter. The staircase waveform of the 7-level multilevel inverter is as
shown in Figure 2:2.
2.2.1.1 Cascade H-Bridge Multilevel Inverter
Cascade H-bridge multilevel inverter is the one of the basic and commonly used
topology for multilevel inverter. This topology can be used in both single and three
Lvl. 1
Lvl. 2
Lvl. 3
Lvl. 4
Lvl. 5
Lvl. 7
Lvl. 6
Figure 2:2: Output waveform of 7-level multilevel inverter
8
phase system conversion. The inverter circuit consist of H-Bridge (HB) power
converter with DC source and capacitor. This topology gives the inverter the ability
to produce multiple levels of output voltage to form AC output depending the
number of level that are suitable for the system.
Figure 2:3 shows the schematic diagram of cascade HB multilevel inverter.
Each HB cell consists of four switches and four diodes. Different combination of
switch positions determines the level of output voltages. For 7-level multilevel
inverter, three HB cells are required which gives a total of 12 switches that must be
controlled in the process of producing 7 level staircase waveforms.
Figure 2:3: Cascade H-Bridge multilevel inverter
One of the advantages of this inverter is that the number of levels can be
increased simply by increasing the number of HB. As the number of level increase,
the total harmonic distortion can be reduced. The only drawback of doing so is that
the higher the number of levels mean a more complex circuit modulation strategies
[11]. This is due to the increase number of switches that needs to be control. Other
than that, the number increase number of switches also will encourage the presents of
harmonic due to switching process.
9
2.2.1.2 Symmetric Multilevel Inverter
For a 7-level multilevel inverter, designing a system or strategy to control 12
switches could be burdensome. Other than that, high number of switches can also
cause harmonic distortion. Therefore, numbers of researches have been conducted to
reduce the switching number for the 7-level multilevel inverter. This is because the
reduction of the number of switches can reduce the complexity of the circuit
modulation system and reduce the Total Harmonic Distortion (THD).
Basically, reducing switches in multilevel inverter can be done by modifying
the circuit of the inverter. Paper [12] successfully archives the reduction of three
switches which makes only nine switches in needed. An improvement is then made
by Lakshi by reducing the number of switches for 7-level multilevel inverter from
nine to seven [12]. Then, another successful improvement had been made by Rokan
who had successfully reduce the number of switches to six [13]. However, the circuit
design of the 7-level multilevel inverter with the least number of switches was made
by Umashankar. He reduce the number of switches to five switches and at the same
time produce a multilevel inverter with lowest THD value as stated in his research
entitle “ A New 7-Level Symmetric Multilevel Inverter with Minimum Number of
Switches” [6].
A 7-level symmetric multilevel inverter as shown in Figure 2:4 is a
redesigned circuit of an existing 6-switch topology. The switch that are connected
parallel to the load was removed as the production of 7-level staircase voltage
waveform can also be done but with only modifying the modulation of the circuit
strategy.
From the circuit diagram, it is shown that the polarity of the load can be
controlled by giving the polarity reversal role to switch 4 and 5. Generally, the
expression for the output voltage levels is as shown in equation (1) and (2) where m
is the number of output voltage level, n is the number of switches and v is the
number of dc source.
10
𝑚 = (2𝑛 − 3) (2.1)
𝑚 = (2𝑣 − 1) (2.2)
Figure 2:4: Circuit diagram of 7-level symmetric multilevel inverter
Reduced switches had made the circuit compact and simpler. However, the
circuit needs four dc sources in order for the circuit to produce 7-level staircase
waveform.
11
Table 2:1: Switching scheme for 7-level symmetric multilevel inverter
SL no. S1 S2 S3 S4 S5 Output
voltage
1 OFF OFF ON OFF ON +Vdc
2 OFF ON OFF OFF ON +2Vdc
3 ON OFF OFF OFF ON +3Vdc
4 OFF OFF OFF OFF OFF 0Vdc
5 ON OFF OFF ON OFF -Vdc
6 OFF ON OFF ON OFF -2Vdc
7 OFF OFF ON ON OFF -3Vdc
2.3 Proportional-Resonant (PR) Controller
In the operation of the 7-level multilevel inverter, there is a presence of harmonic
distortion in the AC output of the inverter. Conventionally, Proportional Integral (PI)
controller is used in the 7-level multilevel inverter to reduce the total harmonic
distortion at the output of the inverter. However, the PI controller has a limited
bandwidth which unable the controller remove or reduce the low current harmonic
[14].
One of the solution that can be used to overcome the limitation of the PI
controller operation is by applying the second order Generalized Integrator (GI) as
reviewed in [15]. Xiaoming Yuan conclude that using stationary-frame generalized
integrator based PI controller will give a zero steady-state error for current harmonic.
This project is purposing the application of Proportional-Resonant (PR)
current controller in the 7-level multilevel inverter. The different between PR and PI
controller is that the PR controller has a different way of taking part in integration
12
action. The integrator will integrate the frequencies that are close to the resonance
frequency. The PR current controller is represented by
𝐺𝑃𝑅(𝑠) = 𝐾𝑃 + 𝐾𝐼𝑠
𝑠2+(𝜔0)2 (2.3)
PR controller is quite similar with the common PI controller. From the Bode
plot of PR controller shown in Figure 2:5 shows that PR have very high gain in a
narrow frequency band centred around resonance frequency. Ki which is the integral
time constant will affect the width of the frequency band. The higher the Ki, the
wider the band [16].
Figure 2:5: PR controller bode graph[14]
13
The proportional gain Kp can be tuned the same way to tuned the similar gain
in PI controller. Kp determines the order in harmonic the PR is used for harmonic
compensation. In this case, it can be used to regulate harmonics without disturbing
the stability limit. This can be done by cascading several GI tuned to resonate at the
desired frequency. The most significant affecting harmonics in current spectrum are
3rd, 5th, and 7th. The transfer function in (2.4) is the typical harmonic compensator
transfer function for 3rd and 5th harmonics.
𝐺ℎ(𝑠) = ∑ 𝐾𝐼ℎ
𝑠
𝑠2 + (𝜔. ℎ)2 (2.4)
ℎ=3,5,7
2.4 [u7] Non-Linear Load and Harmonic Distortion
Nowadays, non-linear load can be easily found in common daily appliance. Some of
most commonly used single phase non-linear are rectified input, switching power
supplies and electronic lighting ballasts and so forth.
Non-linear load is a type of load which its impedance varies with the applied
voltage. This means that the current drawn by the load will not be sinusoidal. This
situation also occurs even if the load is connected to and AC voltage source. The
non-sinusoidal current contains harmonic current that interacts with the impedance of
the specific system which creates distortion. This distortion will affect the
distribution system equipment and eventually affect the performance of the elements
in the system.
Harmonic distortion is defined with respect to the fundamental frequency. This
statement is based on IEEE Standard 519. The magnitude of fundamental frequency
is much larger than any individual harmonic frequency. the RMS sum of the
harmonics are also much larger. To measure the level of total distortion in a system,
Total Harmonic Distortion (THD) calculation is usually used. THD is the ratio of
RMS sum of all harmonic frequencies to the RMS value of the fundamental
frequency[17]. The calculation of THD is as shown in equation (2.5).
𝑇𝐻𝐷 =∑(𝐴𝑙𝑙 𝑅𝑀𝑆 𝐻𝑎𝑟𝑚𝑜𝑛𝑖𝑐 𝐹𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑖𝑒𝑠)
𝐹𝑢𝑛𝑑𝑎𝑚𝑒𝑛𝑡𝑎𝑙 𝐹𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 (2.5)
14
2.5 Previous Research Projects
In general, this subchapter covers the literature review from different sources related
to the development of Proportional Resonant Current Controller and Multilevel
inverter.
2.5.1 Design and Implementation of Proportional-Resonant Controller for 3-
Phase Current Source Inverter In Dspace DS1104
This paper [18] presented about the development of Proportional-Resonant (PR)
current controller for 3-phase current source inverter. The objective of the paper is to
prove that the developed PR controller can overcome the lacking in the performance,
characteristic and functionality of PI controller in the purpose application. The
control system of the 3-phase inverter is implemented in Dspace DS1104. The
control system will influence the active and reactive power generation as it is
intended to be used in grid connected operation. The fast tracking [19] and harmonic
compensation capability of PR controller is tested and analyse.
From this paper, the simulation results show that even though the PR
controller capability of fast respond is proved in other previous researches, the
experimental performance is limited by the Dspace DS1104 computational resource.
It is found that the PR controller required a higher sampling frequency compare to PI
controller. However, due to higher sampling frequency, the selection of higher
integration coefficient Ki can be done without effecting the stability of the system.
This will cause the improvement of time respond of the controller.
2.5.2 A Proportional-Resonant Current Controller for Selective Harmonic
Compensation in a Hybrid Active Power Filter
This paper [20] is about the proposing of Proportional-Resonant (PR) controllers in
the application of hybrid active power filter to reduce the reactive power
compensation and reduction of harmonics in medium-voltage industrial networks. A
proportional-resonant multiloop controller system will be implemented in the
simulation design using PSCAD software. The simulation will show the effect of the
15
implementation of proposed controller in the active power filter to the current and
voltage stress over the element of active power filter.
This paper states that, in the implementation of proportional current
controller in the hybrid active power filter system allow for the saving in terms of
computational burdens as each pair of harmonics are filtered by one controller. Other
than that, the proper selection of parameters in the controller ensure high selectivity
and improves the transient performance of the hybrid active power filter.
2.5.3 Low-Cost Digital Implementation of Proportional-Resonant Current
Controller for PV Inverter Application Using Delta Operator
The implementation of proportional-resonant current controllers for application of
PV inverter in presented in this paper [21]. The proportional-resonant current
controller is applied in the delta based filter approach in the inverter system. The
main goal of the proposed implementation is to reduce the total harmonic distortion
(THD) better then PI controller [22] in the PV inverter system.
Based on the result of the paper, it can be concluded that proportional-
resonant controller enables a harmonic compensation up to 7th harmonics. With only
3rd harmonic compensation, the total harmonic distortion is above 5%. As the
harmonic compensator is turn on to 7th harmonics, the THD value decrease
drastically to 1.2%.
2.5.4 Developed Cascaded Multilevel Inverter Topology to Minimise The
Number of Circuit Devices And Voltage Stresses Of Switch
A new novel structure for cascade multilevel inverter is presented in this paper [23].
The purposed topology is suitable in the application of photovoltaic system due to is
viability of several isolated DC sources as n-isolated DC voltage sources is used
where n is even and more than 4. The scheme of the proposed inverter topology is
shown in Figure 2:6.
16
Figure 2:6: Overall Scheme of Proposed Multilevel Inverter Topology
Asymmetric multilevel structure enables the reduction of cost and number of
element of switches. The proposed scheme can be obtained when different value of
DC voltage sources is defined. From the results of comparison between traditional
and proposed inverter topology, it is shown that the proposed topology reduces
converter losses due to the reduction of switches number.
2.5.5 Verification of a low Components Nine-Level Cascaded-Transformer
Multilevel Inverter in Grid-Tie Mode
Similar to previous reviewed paper, the problem that are going to be solves in this
paper [24] is to proposed a new multilevel inverter topology to reduce the number of
elements in the inverter circuit to reduce the cost complexity and volume. The
suggested topology in this paper is able to halve the number of element in the
inverter circuit. The circuit is then tested under two condition which is with
supplying load and with current control strategy. Based on the experiment, the
performance of the proposed topology is identical to the conventional inverter
topology despite the reduction of the element inside the circuit. As a conclusion, this
topology managed to reduce the number of switches inside the 9-level multilevel
inverter circuit from 16 to 8. This shows that the number of switches for 7-level
multilevel inverter can be reduced to 6 switches using this topology However,
another paper had proposed a topology which used lesser number of switches in the
inverter circuit which is the symmetric 7 level multilevel inverter [6] that are going
to be used in this project.
17
2.6 [u8]MATLAB/Simulink
MATLAB/Simulink is a software package for modelling, simulating and analysing
dynamic system. This software support both linear and non-linear system, which can
be modelled in continuous time mode, sample time mode or the hybrid of the two.
Simulink have a user friendly Graphical User Interface (GUI) which allow the user to
easily build models as block diagrams as easy as click-and-drag mouse.
Figure 2:7 MATLAB 2014 Beta version
Another reason why MATLAB/Simulink is chosen to be the main software of
this project design software is that it also has the ability to implement the design
system or model into the C2000 TI microcontroller. This software can support the
interface process with the microcontroller just by simply download and install plugin
and support package for the embedded coder. The support package includes the
block diagram for the microcontroller input or output port.
There are no needs of programming and declaration of port as the block
models are already provided with just click-and-drag of the block diagram to the
Simulink model before setting the port channel in the graphical user interface
provided. The library of the block diagram for the support package of the
MATLAB/Simulink is as shown in Figure 2:8.
18
Figure 2:8: Simulink library for Embedded Coder Support Package for TI C2000
2.7 C2000 Texas Instruments Microcontroller
Texas Instrument (TI) C2000 microcontrollers family are equipped with 32-bit
architecture, DSP processing and advanced control peripherals. It provides and
uncompromising performance for real-time control application especially in
electrical drives and power electronics devices.
This microcontroller is also equipped with feature-filled peripherals
complement the core performance with industry-leading PWM generation, enhanced
capture unit and most important specification needed in this project which is the
unparalleled Analogue-to-Digital Converter (ADC) conversion. The advantages of
the microcontroller will be it does not require any external component for analogue
to digital conversion as there are already build-in 16 channels of 12-bit ADC. The
model of TI C2000 microcontroller used in this project is TMS320F2833X Delfino
Microcontroller as shown in Figure 2:9.
19
Figure 2:9: TMS320F2835 TI C2000 microcontroller
CHAPTER 3
METHODOLOGY
3.1 Introduction
Methodology is a process that includes design, analysis, implant, modify and
collecting the result. Designing processes are including the specifications of the
method that are used for step by step to make a good product at the last stage. In
other word, design model is the product of planning and works. This chapter
generally discusses the planning and method to run this project. The purpose of
doing methodology is to ensure that the project is in the scope and achieve the
objective.
3.2 Project Flow Chart
Initially, the project is started with the idea inspiration to develop a Proportional
Resonant (PR) current controller for single phase 7-level multilevel inverter with
minimal number of switches. The 7-level symmetric multilevel inverter with 5-
switches topology is chosen as it has the design that used the least number of
switches. After exploiting several findings and researches, the project is decided to
21
use C2000 Texas Instrument (TI) microcontroller to be the controller of the project
hardware as it is built with analogue input port which allow the microcontroller to
read analogue input for the controller system. The overall project flowchart is shown
in Figure 3:1.
Yes
No
Yes
No
Yes
No
Yes
No
Start
Design
Specification Design
Requirement
Design
Parameters
Searching for Design Ideas
Ideas Generation
Ideas
Approval
Planning PS-1 Consideration PS-2 Consideration
Software Design
Compile
Error
Simulation
Debug
Hardware Design
Design Circuit
Simulate Circuit
Error Troubleshoot
Build Circuit
Testing
Error
End
Troubleshoot
Figure 3:1: Master Project Flowchart
22
3.3 Project Development
The development of the project divided into two important parts which is the project
hardware setup and project design specification.
3.3.1 Hardware setup Flowchart
The development of the project will start based on several branches which include
the multilevel inverter design and setup, the rectifier setup for the non-linear load,
and the controller setup for the multilevel inverter which is the C2000 TI
microcontroller. Figure 3:2 shows the flowchart of project setup.
Figure 3:2: Flowchart of Project Setup
No
Yes
Yes Yes
No No
Start
Construct
Inverter
Construct
rectifier Construct
Inverter PR
Controller
Circuit
Simulation
Circuit
Testing
End
Circuit
Simulation
Circuit
Testing
Complete 7-level
multilevel inverter with
non-linear load
Hardware
Testing
Simulink Model
PR Controller
Simulation
Implementing PR
Controller Model
in C2000 TI
microcontroller
23
3.3.2 Project Design Specification
The system development starts with the design specification of the proposed design.
Block diagram has been used to outline the proposed design as shown in Figure 3:3.
there are several components that have been identified in these projects which are the
DC supplies, 7-level multilevel inverter, LC-Filer, non-linear load of the system
which is the full wave bridge rectifier and the microcontroller which works as the
controller system of the multilevel inverter. The components inside the
microcontroller software system include the proposed controller which is the
proportional-resonant current controller, the Pulse Width Modulator (PWM) for the
inverter circuit and a pulse generator to generate the switching pulse for the rectifier.
The AC current at the output of the LC-filter will be measured using current
transducer. It will be taken as the feedback signal for the current control system in
the microcontroller.
[u9]
Figure 3:3: Block diagram of multilevel inverter with minimal switching using
proportional resonant current controller
Proportional
Resonant Current
Controller
DC supply 1
DC supply 2
DC supply 3
DC supply 4
7-Level
Symmetric
Multilevel
Inverter
LC-Filter Non-linear
Load
(Rectifier)
Current
Transducer
(LA 25-NP)
PWM
Gate Driver
Pulse
Generator
Gate Driver
Microcontroller Texas Instrument C2000
Io
3.4 Software Development
This section discussed about the important process and parts in the process of
developing the control system of the multilevel inverter together with the inverter it
self by using Matlab/Simulink software.
3.4.1 Symmetric 7-Level Multilevel Inverter
As mention in literature review, symmetric multilevel inverter topology is going to
be used in this project. The circuit of the 7-level multilevel inverter based on the
topology will use 5 switches which in this project, MOSFET is used. Using
MATLAB/Simulink, the circuit of the 7-level multilevel inverter is constructed as
shown in Figure 3:4.
Figure 3:4: Symmetric 7-level multilevel inverter circuit diagram
The inverter circuit will also consist of four DC voltage sources. This
multiple DC sources will be used to form the staircase waveform of the inverter
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[u26]
