ABSTRACT:
A voltage source inverter is commonly used to supply a three-phase
induction motor with variable frequency and variable voltage for variable speed
applications. A suitable pulse width modulation (PWM) technique is employed to
obtain the required output voltage in the line side of the inverter. The
different methods for PWM generation can be broadly classified into Triangle
comparison based PWM (TCPWM) and Space Vector based PWM (SVPWM). In TCPWM
methods such as sine-triangle PWM, three phase reference modulating signals are
compared against a common triangular carrier to generate the PWM signals for
the three phases. In SVPWM methods, a revolving reference voltage vector is
provided as voltage reference instead of three phase modulating waves. The
magnitude and frequency of the fundamental component in the line side are
controlled by the magnitude and frequency, respectively, of the reference
vector. The highest possible peak phase fundamental is very less in sine
triangle PWM when compared with space vector PWM. Space Vector Modulation (SVM)
Technique has become the important PWM technique for three phase Voltage Source
Inverters for the control of AC Induction, Brushless DC, Switched Reluctance
and Permanent Magnet Synchronous Motors. The study of space vector modulation
technique reveals that space vector modulation technique utilizes DC bus
voltage more efficiently and generates less harmonic distortion when compared
with Sinusoidal PWM (SPWM) technique. In this paper first a model for Space
vector PWM is made and simulated using MATLAB/SIMULINK software and its
performance is compared with Sinusoidal PWM. The simulation study reveals that
Space vector PWM utilizes dc bus voltage more effectively and generates less
THD when compared with sine PWM.
KEYWORDS:
1. PWM
2. SVPWM
3. Three
phase inverter
4. Total
harmonic distortion
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Figure-1. Block
diagram of SPWM inverter fed induction motor.
EXPECTED SIMULATION RESULTS:
Figure-2a. Response
of line voltage in SPWM.
Figure-3. Response of line
voltage in SPWM.
Figure-4a. Response
of line current in SPWM.
Figure-5b. Response of line current in SPWM.
Figure-6. Response
of rotor speed in SPWM.
Figure.7. Response
of torque in SPWM.
Figure-8. Response
of line voltage in SVPWM.
Figure-9. Response
of line current in SVPWM.
Figure-10. Response
of rotor speed in SVPWM.
Figure-11. Response of torque in SVPWM.
CONCLUSION:
Space vector Modulation Technique has become the most popular and
important PWM technique for Three Phase Voltage Source Inverters for the
control of AC Induction, Brushless DC, Switched Reluctance and Permanent Magnet
Synchronous Motors. In this paper first comparative analysis of Space Vector
PWM with conventional SPWM for a two level Inverter is carried out. The
Simulation study reveals that SVPWM gives 15% enhanced fundamental output with
better quality i.e. lesser THD compared to SPWM. PWM strategies viz. SPWM and
SVPWM are implemented in MATLAB/SIMULINK software and its performance is
compared with conventional PWM techniques. Owing to their fixed carrier
frequencies cfin conventional PWM strategies, there are cluster
harmonics around the multiples of carrier frequency. PWM strategies viz.
Sinusoidal PWM and SVPWM utilize a changing carrier frequency to spread the
harmonics continuously to a wideband area so that the peak harmonics are
reduced greatly.
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