MODELING & SIMULATION OF VOLT/HZ SPEED CONTROL FOR INDUCTION MOTOR USING DSPACE PLATFORM

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International Journal of Electrical Engineering & Technology (IJEET)
Volume 7, Issue 3, May–June, 2016, pp.145–156, Article ID: IJEET_07_03_012
Available online at
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© IAEME Publication
MODELING & SIMULATION OF VOLT/HZ
SPEED CONTROL FOR INDUCTION
MOTOR USING DSPACE PLATFORM
Manisha M. Patel
M. Tech Scholar, Department of Electronic Instrumentation & Control Engineering
Institute of Engineering & Technology,
Alwar-301030 (Rajasthan), India
Dr. Anil Kumar Sharma
Professor & Principal, Department of Electronics & Communication Engineering
Institute of Engineering & Technology,
Alwar-301030 (Rajasthan), India
ABSTRACT
The rapid adoption of automation techniques in industry has increased the
requirement for better process control. This has resulted in many new
applications for AC variable speed drives (VSDs) to control the speed and
torque of driven machinery. Variable speed drives (VSDs) are also used to
meet particular starting and stopping requirements. The objective of this
thesis is development of Voltage Source Inverter (VSI) using the dSPACE
DS1104 DSP controller board for speed control of a phase induction motor.
The board enables the linking of the MATLAB/Simulink model to the real time
hardware. We have the feasibility of injecting real time analog and digital
data into the MATLAB/Simulink model, process it to suit our model
requirements, do the simulation, study the response in MATLAB/Control Desk
and at the same time get real time analog and digital output from the DSP
controller board. The standalone VSI control system is implemented in the
DS1104 board, which in our case, utilizes the constant Volts/Hz. strategy to
generate & stabilize its sinusoidal AC output voltages. The Simulink model
generates the sinusoidal pulse-width modulation (SPWM) control signals for
the switching of the VSI’s power devices, MOSFET’s. This research paper
addresses the study of steady-state and dynamic control of 3 phase induction
motor supplied from a power converter and its integration to the load. In the
due course, the design of the controller and its implementation is considered.
Control algorithms and analysis has been developed to facilitate dynamic
simulation with personal computers.
Key words: Control Desk, dSPACE, Induction Motor, VSD, VSI.

Manisha M. Patel and Dr. Anil Kumar Sharma
Cite this Article: Manisha M. Patel and Dr. Anil Kumar Sharma, Modeling &
Simulation of Volt/Hz Speed Control For Induction Motor Using Dspace
Platform. International Journal of Electrical Engineering & Technology, 7(3),
2016, pp. 145–156.
http://www.iaeme.com/ijeet/issues.asp?JType=IJEET&VType=7&IType=3
1. INTRODUCTION
An induction or asynchronous motor is a type of AC motor where power is supplied
to the rotor by means of electromagnetic induction, rather than a commutator or slip
rings as in other types of motor. In certain texts, a machine with only amortisseur
windings is called an induction machine. The distinguishing feature of an induction
motor is that no DC field current is required to run the machine. These motors are
widely used in industrial drives, particularly polyphase induction motors, because
they are rugged and have no brushes. Their speed is determined by the frequency of
the supply voltage, so they are most widely used in constant-speed applications,
although variable speed versions, using variable frequency drives are becoming more
common. The most common type is the squirrel cage motor, and this term is
sometimes used for induction motors generally. Although it is possible to use an
induction machine as either a motor or a generator, it has many disadvantages as a
generator and so is rarely used in that manner. For this reason, induction machines are
usually referred to as induction motors [1]. A state observer is a subsystem that
models a real system in order to provide an estimate of its internal state, given
measurements of the input and output of the real system. It is typically a computer-
implemented mathematical model. In this paper the state observer is designed for the
Induction motor and its performance is checked with the Voltage/frequency (V/f)
speed control methods.
Recently, software tools for real-time control became available. Using these
software tools it is possible to output values while the simulation program is running,
and also to add signals obtained from external sensors. This scheme is known as
“hardware in the loop” simulation. Control and supervisory strategies are designed
graphically in the Simulink block diagram environment. Then, control algorithms are
downloaded to a real-time prototyping system, instead of designing specific hardware.
However, a complete and integrated environment is required to support a designer
throughout the development of a control system, from initial design phase until the
final steps of code generation. In response, several rapid control prototyping modules
have been proposed using MATLAB/Simulink. Controller board like dSPACE
DS1104 is appropriate for motion controls and is fully programmable from the
MATLAB/Simulink environment. The dSPACE uses its own real-time interface
implementation software to generate and then down load the real-time code to specific
dSPACE boards. It enables the user to design digital controller simply by drawing its
block diagram using graphical interface of Simulink. In the paper the model of the
plant and the control algorithm is developed using MATLAB/Simulink module. The
code for the dSPACE board is generated using the Real Time Workshop toolbox. The
Real-Time Workshop produces code directly from Simulink models and
automatically builds programs that can be run in a variety of environments, including
real-time systems and stand-alone simulations. After downloading the software in the
real time platform the data and system parameters can be observed and modified
using ControlDesk. The software allow to create graphic user interfaces using
predefined objects like plots, buttons, sliders, labels, etc.. The main features of this

Modeling & Simulation of Volt/Hz Speed Control For Induction Motor Using Dspace
Platform
environment are: 1) controller code can be generated automatically for hardware
implementation; 2) different languages can be used to describe different parts of the
system; 3) Simulink block diagrams can be used to define the control structure; 4)
controller parameters can be tuned online while the experiments are in progress
without having to rebuild and download a new Simulink model to the DSP board; and
5) ease of operation especially by means of a simple graphical user interface.
2. INDUCTION MOTOR
An induction or asynchronous motor is a type of AC motor where power is supplied
to the rotor by means of electromagnetic induction, rather than a commutator or slip
rings as in other types of motor. In certain texts, a machine with only amortisseur
windings is called an induction machine. The distinguishing feature of an induction
motor is that no DC field current is required to run the machine. These motors are
widely used in industrial drives, particularly polyphase induction motors, because
they are rugged and have no brushes. Their speed is determined by the frequency of
the supply voltage, so they are most widely used in constant-speed applications,
although variable speed versions, using variable frequency drives are becoming more
common. The most common type is the squirrel cage motor, and this term is
sometimes used for induction motors generally. Although it is possible to use an
induction machine as either a motor or a generator, it has many disadvantages as a
generator and so is rarely used in that manner. For this reason, induction machines are
usually referred to as induction motors. [2]- [5]
Speed control is achieved in the inverter driven induction motor by means of
variable frequency. Apart from frequency, the applied voltage needs to be varied, to
keep the air gap flux constant and not let it saturates. This is explained as follows. The
air gap flux induced in an AC machine is given by
E1 = 4.44 kω1 Φm fs T1 (1)
Where,
kω1 = Stator winding factor fs = Supply frequency
Φm = Peak air gap flux T1 = Number of turns per phase in the
stator
Neglecting the stator impedance, the induced emf approximately equals the
supply phase voltage. Hence,
Vph ≈ E1 (2)
The flux is then written as
Φm ≈ Vph / kb fs (3)
Where,
kb = 4.44 kω1 T1 (4)
If Kb is constant, flux is approximately proportional to ratio between the supply
voltage and frequency. This is represented as
Φm α Vph / fs α Kvf (5)
Where Kvf is the ration between Vph and fs .
From Equation (2.5), to maintain the flux constant, Kvf has to be maintained
constant. Therefore, whenever stator frequency is changed to obtain speed control, the
stator input voltages have to be changed accordingly to maintain the air gap flux
constant. Another classification of the control techniques for the induction machine
depends on how the voltage-to-frequency ration is implemented:

1. Scalar control
 Voltage/frequency (V/f) control.
 Stator current control and slip frequency control.
These techniques are implemented through direct measurement of the machine
parameters.
2. Vector Control
 Field orientation control.
 Indirect Method
 Direct Method
 Direct torque and stator flux vector control.
3. VOLT/HZ CONTROL SCHEME FOR INDUCTION MOTOR
In the constant Volts/Hz. control strategy, the air gap flux is kept reasonably constant
over the constant torque region by keeping the ratio of stator voltage to excitation
frequency constant, if the stator impedance is small or the air gap voltage is close to
the input voltage applied to the stator. However, at low frequencies the stator
resistance becomes dominant and the voltage drop across the stator is no longer
negligible. Therefore, at low frequency voltage boost is required to compensate for
the voltage drop across the stator resistance. This control strategy is often referred to
as a scalar control strategy. If a small variation in rotor speed with a change in loading
is tolerable, then a simple open loop control strategy would probably suffice.
However, if the application requires a tighter control over rotor speed and torque
while limiting stator current, then a closed loop control strategy with rotor speed as
feedback is the better alternative. With rotor speed as feedback, the slip speed of the
motor can be regulated. Figure 1 shows an implementation of the constant Volts/Hz
control strategy in open loop mode. The frequency command fs* is enforced in the
inverter and the corresponding DC link voltage is controlled through the front-end
converter. The offset voltage Vo, is added to the voltage proportional to the frequency,
and they are multiplied by a constant gain, as decided by the slope of the voltage and
frequency relationship, to obtain the DC link voltage.
Few issues to be taken care while using this drive scheme are:
1. Motor speed cannot be precisely controlled.
2. The slip speed cannot be maintained as a result because the rotor speed is not
measured in this drive scheme. This can lead to operation in the unstable region of the
torque-speed characteristics.
3. The effect discussed in point 2, can make the stator currents exceed the rated value by
many times, thus endangering the inverter-converter combination.

Platform
Implementation of Volts/Hz Scheme
Figure 1 Implementation of Volts/Hz strategy in inverter fed induction motor drives
4. DSPACE DS1104 DSP CONTROLER BOARD
The dSPACE control platform simplifies the programming task using library block set
and interfacing of control algorithm to run on processor and on-chip peripherals. In
the hardware part open loop simulation has been presented with real time simulation
implementation. This is achieved by using digital signal processor controller.
dSPACE and MATLAB interface is being made to achieve pulse generation.DS 1104
is used for PWM generation by SPWM technique. Description of DS1104 DSP
Controller board is given below.
DS1104 R&D Controller Board: The DS1104 DSP Controller Board upgrades the
host PC to a development system for Rapid Control Prototyping. The DS1104 DSP
Controller Board is a standard board that can be plugged into a PCI slot of a PC. It is a
complete real time control system based on a 603 PowerPC floating point processor
running at 250 MHz. For advanced I/O purposes, the board includes a slave DSP
subsystem based on the TMS320F240 DSP microcontroller. For purposes of rapid
control prototyping (RCP), specific interface connectors and connector panels (listed
below) provide easy access to all input and output signals of the board. [7][9][12]-
[15]

Technical Specifications of the DS1104 Board
Main Processor Timers
• MPC8240 processor with PPC 603e core, 250 MHz CPU
clock
• 4 general purpose timers
• 2 x 16 KB cache • 1 sampling rate timer
• 64 bit floating-point processor • 1 time base counter
A/D Converter Memory
• Resolution
Multiplexed channels : 16-bit
Parallel channels : 12-bit
• Global memory, 32 MB DSRAM
• Flash memory, 8 MB
D/A Converter
• Input voltage range : ± 10 V • Channels : 8 channels
• Conversion Time
Multiplexed channels : 2 µs
Parallel channels : 800 ns
• Resolution : 16-bit
• Output range : ± 10 V
• Settling time: Max. 10 µs
• Signal-to-noise ratio
Multiplexed channels : > 80 dB
Parallel channels : > 65 dB
• Signal-to-noise ratio : > 80 dB
• Imax : ± 5 mA
Digital Incremental Encoder Interface
Digital I/O • Channels : 2 independent channels
• Channels : 20-bit parallel I/O • Position counters: 24-bit resolution
• Voltage range : TTL input/output levels • Sensor supply voltage : 5V / 0.5A
• Iout;max : ± 5 mA Slave DSP
Serial Interface • Texas Inst. TMS320F240 DSP, 16-bit
procc.
• Single UART with FIFO • Clock rate : 20 MHz
• RS232 / RS485 compatibility • Memory : 32 MB flash memory
• Baud Rate : Up to 115.2 kBd (RS232) • I/O channels : 10 PWM o/p, 4 capture i/p
• Baud Rate : Up to 1 MBd (RS422/RS485) • A/D converter voltage range : 0 ... 5 V
Host Interface : Requires one 33 MHz / 32-bit 5V PCI slot • Output current:Max. ±13 mA
Figure 2 Architecture and the functional units of the DS110
CLP1104 Connector Panel: Using an adapter cable you can link your external
signals from the 100-pin I/O connector on the board to Sub-D connectors. Figure 3
shows CLP1104 Connector Panel. The CPL1104 provides easy to use connections
between the DS1104 R&D Controller Board and devices to be connected to it.
Devices can be individually connected, disconnected or interchanged without
soldering via BNC connectors and Sub D connectors. This simplifies system
construction, testing and troubleshooting. For the pin assignment and mapping of I/O
signals, please refer the reference [9]

Platform
Figure 3 CLP-1104 Connector Panel
How to start the Code Generation
1. Open the Simulink Model.
2. Set the following configuration parameters.
 Sample time
 Simulation type, can be fixed or continuous
 Select the solver type from listed solvers
 Start and Stop time
3. Set the optimization options.
4. While setting RTW build options you have to mention the board type. After setting
all the parameters you have to build the model.
During build process code is generated for Simulink block diagram that include
RTI blocks for RCP and HILS. Code generation begins with a two-step process,
which is followed by two more steps whenever an executable is being compiled. The
four steps (also summarized in the Build Process) are automatically completed when
you click the Build button on the Real-Time Workshop dialog (assuming that Real-
Time Workshop detects no constraints to generating code for the model; if it does, it
will issue warnings).
Real-Time Workshop analyzes the block diagram and compiles it into an
intermediate hierarchical representation called “model.rtw”. The Target Language
Compiler reads “model.rtw” and translates it to C code, which it places in a build
directory in the working directory. The Target Language Compiler constructs a make
file from the appropriate target make file template, and places the basic directory.
5. HARDWARE IMPLEMENTATION
Gate Driver Circuit: The switches in bridge configurations of inverters need to be
provided with isolated gate drive signals. The individual control signal for the
switches needs to be provided across the gate and source terminals of the particular
switch. The gate control signals are low voltage signals referred to the source terminal
of the switch. For MOSFET switches, when gate to source voltage is more than
threshold voltage for turn-on, the switch turns on and when it is less than threshold
voltage the switch turns off. The threshold voltage is generally of the order of +5 volts
but for quicker switching the turn-on gate voltage magnitude is kept around +15 volts
whereas turn-off gate voltage is zero or little negative (around -5 volts).[17]-[19]

Figure 4 Three-Phase Inverter using IRS2110 to drive MOSFETs
MOSFET Gate Drivers: MOSFET can be driven by any circuit capable of providing
the right gate voltages & that is fast enough to ensure that the MOSFET spends the
absolute minimum amount of time in its linear gate voltage region. This is important,
for it’s when the MOSFET is in its linear region that it acts like a resistor & produces
a lot of heat. Most MOSFET turn on at 10-30 V, and need a high current if you plan
to do high speed switching. Therefore you need a MOSFET driver as an interface
between your logic system and MOSFET.
Figure 5 Per phase gate trigger circuit
The IRS2110 are high voltage, high speed power MOSFET drivers with
independent high-side and low-side referenced output channels. They provide very
fast switching speeds and low power dissipation. The floating channel can be used to
drive an N-channel power MOSFET in the high-side configuration which operates up
to 500 V or 600 V. Figure 5, shows the actual per phase, gate trigger circuit,
implemented and fabricated in research work.

Platform
Figure 6 Actual hardware setup in Laboratory
Inverter: Inverter or power inverter is a device that converts the DC sources to AC
sources. The converted AC can be at any required voltage and frequency with the use
of appropriate transformers, switching, and control circuits. Inverters are used in a
wide range of applications, from small switched power supplies for a computer to
large electric utility applications to transport bulk power.
6. SIMULATIONS & RESULTS
Figure 7 Simulation model inn MATLAB with RTI Data
Figure 8 Reference three-phase sinusoidal signals
recorded in ControlDesk for 100% speed reference
Figure 9 SPWM signals for R phase recorded in
ControlDesk for 100% speed reference

Figure 10 Unfiltered AC voltages at the output of the
inverter recorded in ControlDesk for 100% speed
Reference
Figure 11 Filtered AC voltages at the output of the
inverter recorded in ControlDesk for 100% speed
Reference
Figure 12 Two-phase voltages recorded in
ControlDesk for 100% speed reference
Figure 13 PWMPulses from DS1104
7. CONCLUSIONS
From the preceding sections, it is obvious that to understand a motor drive system,
one need to do an extensive study of electrical machines, power converters and
control systems to have a stable motor drive system. From this research, we have
gained a fair degree of experience and have been able to understand the problems
associated with an implementation of an open loop SPWM induction motor drive
system. The research involved two phases, viz.
 First was to simulate and evaluate the performance of the Volts/Hz. Control strategy.
This involved development of mathematical model for induction motor.
 Second was to implement the Volts/Hz. control strategy on the dSPACE DS1104 DSP
controller board.
The benefits and limitations of each algorithm were examined through theoretical
analysis. Verification of the analysis was performed by simulating various strategies
using MATLAB/Simulink toolbox. During the course of the working with MABX-II,
it was observed that since MABX – II is specially designed for in-vehicle
applications; it has limitations with respect to the maximum carrier frequency being
used. We cannot simulate by using higher carrier frequencies, viz. greater than 5 KHz
and at such low carrier frequencies the sine wave available at the output of the
Isolation and Gating Circuit is highly distorted. Fairly good amount of time was eaten

Platform
away before we came to this conclusion. Thereafter, the dSPACE DS1104 DSP
controller board was then used to generate the sinusoidal pulse width modulated drive
signals for a three phase voltage source inverter while operating under Volts/Hz.
control. Designing and implementing the isolation and the power stage of the inverter,
gave a fair idea of the challenges involved, when we have to do practical
implementation of the theoretical concepts and strategies. One needs to have equal
dedication and very high concentration levels while working in real time systems.
Safety aspects should not be ignored, while working on simulator boards and also
while working with PCBs and power devices.
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MODELING & SIMULATION OF VOLT/HZ SPEED CONTROL FOR INDUCTION MOTOR USING DSPACE PLATFORM