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International Journals of Advanced Research in Computer Science and Software Engineering ISSN: 2277-128X (Volume-7, Issue-6)
Research Article
June 2017
© www.ijarcsse.com, All Rights Reserved Page | 123
Closed Loop – PI Control of a Single Phase Induction Motor
Using SPWM Kuheli Ghosh Goswami
EE Department, UCSTA
Assistant Professor, BGI-SDET
Amit Ghosh
Technology Analyst,
Infosys Limited, India
DOI: 10.23956/ijarcsse/V7I6/0169
Abstract— In this paper we discuss the speed control of a single phase induction motor by proportional integral
control. The PI controller fuses the properties of the P and I controllers. It shows a maximum overshoot and settling
time similar to the P controller but no steady-state error. The output of the inverter has been smoothen by using LC
filter. THIPWM techniques have lower total harmonic distortion than the SPWM technique and SVPWM have much
lower THD than that of THIPWM. The THIPWM can increase the fundamental output voltage by 15.5% over the
SPWM technique and SVPWM more than that. SPWM Simulation results are obtained using MATLAB / Simulink
environment for effectiveness of the study.
Keywords— SPWM, ASD, INVERTER DESIGN, PI CONTROL STRATEGIES, MATLAB.
I. INTRODUCTION
Variable Speed Drives (VSDs), also known as adjustable speed drives, are large industrial electric motors whose speed
can be adjusted by means of an external controller. They are used in process control and help saving energy in plants that
use many powerful electric motors.The use of adjustable speed in process control matches the motor speed to the
required tasks and may compensate for changes in the process's variables. The use of adjustable speed for saving energy
is exemplified by the adjusting the speed of a cooling fan motor to match the temperature of the machinery parts it is
cooling.Adjustable frequency drives are a specific type of VSDs; they are controlling the rotational speed of an
alternating current (AC) electric motor by controlling the frequency of the electrical power supplied to the
motor.Sinusoidal PWM is a type of "carrier-based" pulse width modulation. Carrier based PWM uses pre-defined
modulation signals to determine output voltages. In sinusoidal PWM, the modulation signal is sinusoidal, with the peak
of the modulating signal ways less than the peak of the carrier signal.Here a SPWM inverter is designed and DC voltage
is given to it, DC is converted to ac and a single phase induction motor is driven by this ac o/p and speed of this motor is
adjusted by closed loop speed control method. Here PI control strategies has been adopted.
II. THEORITICAL BACKGROUND
Sinusoidal Pulse width modulation (SPWM) generated by comparing amplitude of triangular wave (carrier) and
sinusoidal reference wave (modulating) signal. SPWM switching for three phase inverter is similar to that of a single
phase inverter. Basically, each switch is controlled by comparing a sinusoidal reference wave with a triangular carrier
wave. The fundamental frequency of the output is the same as the reference wave, and the amplitude of the output is
determined by relative amplitudes of the reference and carrier waves. Each pair of switches requires a separate sinusoidal
reference wave. The three phase reference sinusoidal is 120° apart to produce balanced three phase output.
Figure 1: Sinusoidal Pulse Width Modulation
Goswami et al., International Journals of Advanced Research in Computer Science and Software Engineering
ISSN: 2277-128X (Volume-7, Issue-6)
© www.ijarcsse.com, All Rights Reserved Page | 124
Figure 2: Three Phase Voltage Source Inverter
Figure 3: pulse width modulation technique.
Inverter output voltage:
When V control>V tri, V dc/ 2
When V control<V tri,-V dc/ 2
Control of inverter output voltage:
SPWM frequency is the same as the frequency of V tri
Amplitude is controlled by the peak value of Vcontrol
Fundamental frequency is controlled by the frequency of Vcontrol.
Modulation Index (m),
Figure 4: waveforms of three phase spwm inverters
Goswami et al., International Journals of Advanced Research in Computer Science and Software Engineering
ISSN: 2277-128X (Volume-7, Issue-6)
© www.ijarcsse.com, All Rights Reserved Page | 125
BENEFITS OF VVFD
1. Controlled starting current. When an ac motor is started “across the line,” it takes as much as seven-to-eight
times the motor full-load current to start the motor and load. But when using an adjustable speed drive, the
substantially reduced starting current extends the life of an ac motor. The payback is less wear and tear on the
motor, which translates to extended motor life and less motor rewinds.
2. Reduced power line disturbances. Starting an ac motor across the line and the demand for starting current places
an enormous drain on the power distribution system connected to the motor. Typically, the supply voltage sags,
which can cause sensitive equipment connected on the same distribution system to trip. Items such as computers,
sensors, proximity switches and contactors are voltage sensitive and can drop out when a large ac motor is started
nearby. Using an adjustable speed drive eliminates this voltage sag.
3. Lower power demand on start. The power needed to start an ac motor across the line is significantly higher than
with an adjustable speed drive. This is true only at start, since the power to run the motor at load would be equal
regardless if it were fixed speed or variable speed
4. Adjustable operating speed. Using an adjustable speed drive enables process optimization and making changes in
a process. It also allows starting at reduced speed and allows remote adjustment of speed by programmable
controller or process controller.
5. Controlled stopping. Controlled stopping helps reduce product loss due to breakage or mechanical wear and tear
attributed to shocks to the process.
6. Energy savings. Centrifugal fan and pump loads operated with adjustable speed drives reduce energy
consumption. If the speed of a fan is cut in half, the horsepower required to run the fan is cut by a factor of eight.
The energy savings could relate to a return on investment of less than two years.
ADVANTAGES OF SPWM
The main advantage of SPWM is that power loss in the switching devices is very low. When a switch is off there is
practically no current, and when it is on,there is almost no voltage drop across the switch. Power loss, being the product
of voltage and current, is thus in both cases close to zero. SPWM also works well with digital controls, which, because of
their on/off nature, can easily set the needed duty cycle.
DISADVANTAGES OF SPWM
There are two significant drawbacks with sinusoidal PWM.
(i) Available output voltage
Assuming that the DC voltage is created using a diode rectifier and capacitor dc link , the maximum available DC
voltage is given by
where VLLS is the line-line supply voltage. The maximum output using sinusoidal PWM (ma=1) is
a sinusoidal PWM drive cannot produce a line-line output voltage as high as the line supply. One option to mitigate this
discrepancy is to use higher supply voltages (e.g. 480V supply, 460V motor; 600V supply, 575V motor).
(ii) Short Pulses If the output is to be truly sinusoidal PWM, it is important to include very small pulses when the peak modulation signal
is close to the peak carrier voltage. These small pulses can contribute significantly to inverter losses, while not
significantly effecting the output voltage. In addition, small pulses may be impractical due to the time required to switch
one device off and another device on. Most industrial drives "drop" small pulses to improve efficiency.
III. SOFTWARE IMPLEMENTATION & EXPERIMENTAL RESULTS
The main aim of any modulation technique is to obtain variable output having maximum fundamental component with
minimum harmonics. The objective of Pulse Width Modulation techniques is enhancement of fundamental output
voltage and reduction of harmonic content in Three Phase Voltage Source Inverters. In this paper different PWM
techniques are compared in terms of Total Harmonic Distortion (THD). Simulink Models has been developed for
Sinusoidal PWM (SPWM), Space vector PWM (SVPWM), and Space vector PWM switching Patterns. Simulation work
is carried in MATLAB 13.0/Simulink. The simulation parameters used are: Fundamental frequency 50 Hz
Switching frequency 2 kHz
Amplitude modulation index 1.0
DC voltage 600 Volt
ph. Asynchronous machine: 415 V, 0.5 HP.
ODE Solver ode23tb
Goswami et al., International Journals of Advanced Research in Computer Science and Software Engineering
ISSN: 2277-128X (Volume-7, Issue-6)
© www.ijarcsse.com, All Rights Reserved Page | 126
Figure 5: Circuit diagram for PI Control of a single phase induction motor
Figure 6: Unipolar SPWM output without Filter
Figure 7: Unipolar SPWM output with LC Filter
Goswami et al., International Journals of Advanced Research in Computer Science and Software Engineering
ISSN: 2277-128X (Volume-7, Issue-6)
© www.ijarcsse.com, All Rights Reserved Page | 127
Figure 8: SPWM Technique
Figure 9: Motor speed and Torque
IV. CONCLUSIONS This report introduced adjustable speed drive system of a single phase induction motor. We presented SPWM inverter
and control its speed. When we are changing the load, the voltage and frequency are changed, but voltage upon
frequency ratio is constant so speed is remaining constant. Thus we have adjusted the speed and we have designed
adjustable speed drive system incorporating SPWM Technique.
But, while doing the project we got some error, LOSS OF VOLTAGE- 17.26%
Actual voltage- 230V Practical value- 190.3V Harmonics are present.
Harmonic voltages produce magnetic fields that rotate at speeds corresponding to the harmonic frequencies, resulting in
increased losses, motor heating, mechanical vibrations and noise, pulsating torques, increased eddy current and hysteresis
losses in stator and rotor windings, reduced efficiency, reduced life, and voltage stress on motor winding insulation.
Proper speed control means that we need to vary both the motor voltage and frequency to control slip and keep it in a
sweet zone in relation to the actual rotation speed. This is what Variable Speed Drives do, for single phase induction
motors this idea does not really work.With just one phase, we get a pulsing voltage only. For this reason single phase
motors artificially create a second phase to create the rotation. This second phase can be created in many ways using
auxiliary windings and phase shift capacitors or coils.All proper variable speed drive controlled induction motors are 3
phase, as are the outputs of the variable speed drives. 3 phase shifted voltages is the minimum required to create a
rotating field.
But still for harmonic reduction tuned banks will be needed to totally divert all harmonics away from the system.
For better approach PLC, fuzzy logic can be used.
Goswami et al., International Journals of Advanced Research in Computer Science and Software Engineering
ISSN: 2277-128X (Volume-7, Issue-6)
© www.ijarcsse.com, All Rights Reserved Page | 128
ACKNOWLEDGMENT
I would like to express my gratitude to my professors for their guidance, support and suggestion. I am extremely grateful
to the “Applied Physics Dept., University of Calcutta” and EE department of Brainware Group of Institutions. I humbly
express my sense of gratitude to the faculty members, Laboratory staff, Library staff and administration of the institute
for providing me a congenial working environment.
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