University of Manitoba
Department of Electrical & Computer Engineering
ECE 4600 Group Design Project
Project Proposal
Design and Implementation of a Variable-Frequency Drive Using a
Multi-Level Topology
by
Group 03
Kale Ewasiuk
Curtis Shumski
Edwin Ifionu
Matt Szyda
Academic Supervisor(s)
Shaahin Filizadeh
Industry Supervisors
Steven Howell – Manitoba Hydro
Date of Submission
September 26, 2014
Copyright © 2014 Kale Ewasiuk, Edwin Ifionu, Curtis Shumski, Matt Szyda
G03 Proposal 2014
CONTENTS
Contents
1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
2
Project Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2
2.1
Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
2.2
Topology Description
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
2.3
Simulation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
2.4
Component Values Selection
. . . . . . . . . . . . . . . . . . . . . . . . . . .
4
2.5
User Interface and Control System . . . . . . . . . . . . . . . . . . . . . . . .
5
2.6
Switches and Gate Driver Circuitry
. . . . . . . . . . . . . . . . . . . . . . .
5
2.7
Sub-Module Capacitor Voltage and Arm Current Measurement System . . .
5
2.8
Future Provisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
3
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
4
Division of Labour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8
5
GANTT Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
6
Budget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
References
13
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G03 Proposal 2014
1
1 Introduction
Introduction
The development of fully controlled power electronic converters has led to improvements in
variable-frequency drive (VFD) performance and efficiency. Voltage-source converters (VSC) are
a popular type of VFD that use power electronic switches and capacitive energy to emulate an
alternating output voltage from a dc-link. Common VSC topologies use pulse-width modulation
(PWM) with two output levels to achieve an alternating voltage with a desired magnitude and
fundamental frequency. The concept of voltage-source conversion can be extended to produce a
staircase waveform with multiple output voltage levels.
The purpose of this project is to design and implement a small scale VFD using a multi-level
VSC topology. Multi-level converters have shown several advantages compared to conventional
two-level VSCs. Benefits such as improved output waveform quality, reduced switching frequency,
and lower levels of produced interference have been demonstrated[1]. The converter topology to
be designed is the modular multi-level converter (MMC) [2, 3]. The MMC will be used for its
scalability and simplicity of topology compared to the other multi-level converters. The MMC
allows for increasing output levels by adding identical sub-modules (SM)[3] which can reduce switch
and capacitor voltage ratings and improve harmonic performance. This project will contribute to
the practical application of the MMC as it is a relatively new topology that has grown in popularity
over the past few years.
2
Project Details
This section gives specific details of how the project will be implemented, as well as the system
components needed to meet project objectives.
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G03 Proposal 2014
2.1
2 Project Details
Implementation
A basic version of the converter will first be implemented by testing a single SM. Sub-modules
will then be cascaded and their individual control will be tested. Half-bridge SMs will be used
because they allow for simpler control schemes and fewer components compared to full-bridge SMs.
The control system will be simultaneously developed as the circuit complexity and functionality
increases. Real-Time Digital Simulator (RTDS) will be used to simulate firing-pulses to allow for
independent development of the control system if required. The MMC and control system will
be integrated and used to drive an induction motor with open-loop controls upon successful test
results. The performance of the converter will be tested under various load conditions which can
be set by a dynamometer. The system overview is shown in Figure 1.
Modular Multilevel Inverter
Half-Bridge
Sub-Modules (SM)
UV
𝐶𝑑𝑐
+
Induction Motor
𝐿arm
.
.
.
𝑽𝒅𝒄
-
175 W
120 VRMS
𝒊𝒂𝒄
M
+
𝒗𝒂𝒄
𝐿arm
-
𝐶𝑑𝑐
LV
....
....
Sub-module
capacitor voltages
and arm currents
Gate drivers, deadtime generators,
isolators
....
....
Valve controllers (VC) ×2
Reference
wave
controller
(RC)
Frequency and
voltage control
and display
Motor
speed
and
voltage
Speed display
and load
torque
control
Speed and
voltage
control and
display
Speed and
voltage
controller
(MC)
_________
3-phases and
closed-loop speed
control if time permits
Fig. 1: MMC circuit and control system overview
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G03 Proposal 2014
2.2
2 Project Details
Topology Description
In steady state, the converter operates by switching SMs in the upper and lower valve (denoted
UV and LV on Figure 1) such that the potential vac in between them is alternating as described in
equation 1.
vac =
vl − vu Larm diac
−
2
2 dt
(1)
If there are N SM capacitors C inserted in the converter at all times, then their nominal
voltages should be the same at Vdc /N . As current is drawn from the converter, the voltage in each
SM capacitor changes. The arm inductors Larm are used to limit unwanted harmonics in current
deriving from the voltage imbalance between the dc-link voltage Vdc and the sum of the upper and
lower valve voltages. Balanced capacitor voltages will result in minimal deviation from a staircase
waveform and reduced harmonic content in the arm currents [4].
2.3
Simulation
A simulation case will be developed as the project progresses to ensure that the design choices
made are met. Power systems CAD (PSCAD/EMTDC) will be used to simulate a high-level
representation of the circuit topology and control system with the goal of accurately reflecting the
designed system. A key part of the converter simulation is to aid in component selection decisions.
2.4
Component Values Selection
The components in the MMC circuit to be selected are the sub-module switches and capacitors,
dc-link capacitors, and arm inductors. The voltage ratings of the components depend on the dc-link
voltage and the number of active SMs in the converter. The dc-link capacitors will be selected to
allow for an acceptable sag in voltage. The SM capacitor and arm inductor will be chosen based
on equations developed in references [5] and [6] respectively. The selected component values will
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G03 Proposal 2014
2 Project Details
be finalized depending on their performance through simulation and availability for purchase.
2.5
User Interface and Control System
An interactive control system will be implemented for the design of the overall system. The
user is allowed two inputs via a 4x4 keypad; the ac-voltage magnitude and frequency. This information is sent to a reference waveform controller (RC) in the form of a modulation index and
reference frequency. The reference controller calculates and passes a time-varying reference wave
with the integer number of SMs to be inserted in the upper and lower arms to their respective
valve controllers (VC). The VCs will perform a sort and balance routine that is used to determine
the correct number of SMs to be inserted based on their respective voltage levels and direction
of current. The VCs will then be responsible for sending the firing signals to the respective gate
drivers.
2.6
Switches and Gate Driver Circuitry
The gate driver circuit is the interface between the control system and the high power switches
of the converter. MOSFETs have been chosen over IGBTs for the design due to their efficiency
at lower power levels[7]. A gate driver circuit with a floating channel will be used to alleviate
changing MOSFET source voltages and allow for bootstrap operation. Optocouplers will be used
between the controller and the other gate driver circuitry to provide electrical isolation from the
high voltage gate driver circuit. A dead-time generator will be used to delay the firing pulse of each
SM switch to avoid short circuiting during finite switching time.
2.7
Sub-Module Capacitor Voltage and Arm Current Measurement System
The voltage across the capacitor in each sub-module has to be measured continuously to
determine the switching routine. The voltage will be measured with a voltage divider or DC/DC
converter to produce a scaled voltage with a maximum output of 5V (logic level). The valve
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G03 Proposal 2014
3 Specifications
controller will serially acquire the measured voltage through an analog multiplexer. The current
through each arm will be measured with a hall effect sensor with a digital output directly connected
to the valve controller.
2.8
Future Provisions
The system design will allow for additional features such as scaling up to a three-phase
converter with a closed-loop speed control system. The controls will include functionality that
allows for user input of speed; the main controller determines the appropriate magnitude and
frequency of the output ac voltage that will achieve the desired motor speed to a certain accuracy
(that is not specified at this time).
3
Specifications
The designed converter is required to meet the specified distortion level under the nominal
conditions listed in Table 1. The properties and ratings of the motor to be driven is listed in Table
2.
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G03 Proposal 2014
3 Specifications
Table 1: Project specifications
Paramater
Value or Range
DC-link voltage
350 V
Converter requirements
Nominal power output
100 W
Nominal voltage range
80-120 VRM S
Nominal frequency range
40-60 Hz
Total distortion for harmonic orders < 15th
3%
Number of sub-modules per arm
3 (minimum)
Table 2: Motor properties
Motor properties
Model
Lab-Volt 8251-00
Type
Single-phase capacitor start
Power rating
175 W
Voltage rating
120 VRM S
Operating frequency
1-60 Hz
Maximum speed
1715 rpm
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G03 Proposal 2014
4
4 Division of Labour
Division of Labour
The tasks for this project have been divided into four sections: simulation, circuit, control,
and user interface. Each section has several milestones that are associated with it. Table 3 shows
how the milestones have been divided between the team along with an estimated completion date.
Table 3: Division of labour
Task
P.I.C.
E.D.O.C
Development of basic simulation model with capacitor voltage balancing
K&M
09/28/2014
Development of advanced simulation model with converter controls
E&K
01/19/2014
Selection and implementation of passive components, switches and gate
driver circuit
K&M
12/10/2014
Implemention of a working cascaded sub-modules prototype with batteries as capacitors
K&M
11/23/2014
Design and implementation of arm current and capacitor voltage measurement system
E&K
12/22/2014
Physical building, testing, and troubleshooting of the single-phase converter
ALL
01/18/2015
Design of control system
C&E
02/11/2014
Implemention of reference controller with variable voltage and frequency
C&E
11/16/2014
Implemention and interfacing valve controller with cicruit measurement
system
E&M
12/22/2014
Interfacing of control system with gate-drivers
C&M
01/11/2015
C
12/22/2014
Design and implementation of three-phase converter
ALL
08/02/2015
Design and implementation of motor speed closed-loop control system
ALL
02/15/2015
Simulation
Circuit
Controls
User Interface
Implementation of converter voltage and frequency control and display
Design Expansions
NOTE: C = Curtis,
E = Edwin,
P.I.C = Person(s) in Charge,
K = Kale,
M = Matt
E.D.O.C = Expected Date of Completion
-8-
GANTT Chart
The GANTT chart shown in Figure 2 divides the project milestones into more detailed sections with an estimated
work timeline.
G03 Proposal 2014
5
-9Fig. 2: GANTT Chart for converter design project.
5 GANTT Chart
G03 Proposal 2014
6
6 Budget
Budget
The proposed budget for the project is shown below in Table 4. The predicted costs are based
off of preliminary research, and both cost and parts are subject to change. The approved budget
for the project is $400.00, and any additional costs will be provided by team members, the project
supervisor Dr. Shaahin Filizadeh, or further contributions from the Department of Electrical and
Computer Engineering.
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G03 Proposal 2014
6 Budget
Table 4: Estimated budget
Item
P/N
Supplier
QTY
Cost
SubTotal
DC-link capacitors
WBR150-150A
Digikey
2
$12.70
$25.40
Sub-Module capacitors
UHE2A221MHD
Digikey
10
$1.04
$10.40
Arm inductors
C-49U
Digikey
2
$38.36
$76.72
Half-bridge switches (includes diodes
IRFI4019HG-117P
Digikey
10
$4.72
$47.20
Gate drivers
IR2110STRPBF
Digikey
10
$4.30
$43.00
Gate driver capacitors
N/A
U. of Manitoba
20
$0.00
$0.00
DC/DC converter for gate supply
VIBLSD1-S5-S15-SIP
Digikey
10
$5.78
$57.80
DC/DC converter for logic supply
VIBLSD1-S5-S5-SIP
Digikey
10
$5.78
$57.80
Optocoupler
H11L2SM
Digikey
10
$1.34
$13.40
Dead-time generators (3 phase)
IDXP630PI
Digikey
4
$5.33
$21.32
Reference controller
PIC16F877A
Digikey
1
$7.10
$7.10
Valve and speed controllers
PIC16F87
Digikey
2
$3.50
$7.00
PICkit-3 in-ciruit debugger
PG164130
Digikey
2
$57.40
$114.80
6-pin connector header
GRPB061VWVN-RC
Digikey
2
$0.75
$1.50
Analog multiplexer
ADG5408BRUZ
Digikey
2
$7.28
$14.56
Resistors
N/A
U. of Manitoba
20
NHD-0216XZ-FSW-
Digikey
1
$13.17
$13.17
27899
Digikey
1
$6.99
$6.99
Single-phase induction motor
Lab-Volt 8251-00
U. of Manitoba
1
$0.00
$0.00
Dynamonmeter
Lab-Volt 8960-10
U. of Manitoba
1
$0.00
$0.00
$50.00
$50.00
and mosfet)
Controls components
Measurement components
User interface
LCD screen (for speed display)
GBW
Keypad
Equipment
Other
Contingency
Machine shop time
8 hrs
Subtotal $568.16
Taxes
$73.86
TOTAL $642.02
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G03 Proposal 2014
7
7 Conclusions
Conclusions
This proposal discussed the basic theory and the design of an MMC for the application of
a VFD. The proposed design incorporates user input which allows the product to be used for
various applications that require different voltages and frequencies. The proposed design allows for
expansion to a three-phase MMC with advanced closed-loop controls.
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G03 Proposal 2014
REFERENCES
References
[1] L. Tolbert, F. Z. Peng, and T. Habetler, “Multilevel converters for large electric drives,” Industry
Applications, IEEE Transactions on, vol. 35, no. 1, pp. 36–44, Jan 1999.
[2] A. Lesnicar and R. Marquardt, “An Innovative Modular Multilevel Converter Topology Suitable
for a Wide Power Range,” in Power Tech Conference Proceedings, 2003 IEEE Bologna, vol. 3,
June 2003, pp. 6 pp. Vol.3–.
[3] R. Marquardt, in Power Electronics Conference (IPEC), 2010 International, title=Modular
Multilevel Converter: An Universal Concept for HVDC-Networks and Extended DC-BusApplications, June 2010, pp. 502–507.
[4] D. Siemaszko, A. Antonopoulos, K. Ilves, M. Vasiladiotis, L. Angquist, and H.-P. Nee, “Evaluation of control and modulation methods for modular multilevel converters,” in Power Electronics
Conference (IPEC), 2010 International, June 2010, pp. 746–753.
[5] K. Ilves, S. Norrga, L. Harnefors, and H.-P. Nee, “On energy storage requirements in modular
multilevel converters,” Power Electronics, IEEE Transactions on, vol. 29, no. 1, pp. 77–88, Jan
2014.
[6] Q. Tu, Z. Xu, H. Huang, and J. Zhang, “Parameter design principle of the arm inductor in
modular multilevel converter based hvdc,” in Power System Technology (POWERCON), 2010
International Conference on, Oct 2010, pp. 1–6.
[7] A. Dubhashi and B. Pelly, “A comparison of igbts and power mosfets for variable frequency
motor drives,” in Applied Power Electronics Conference and Exposition, 1989. APEC’ 89. Conference Proceedings 1989., Fourth Annual IEEE, Mar 1989, pp. 67–74.
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