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Ideal Institute of Technology, Ghaziabad
Electronics & communication Engineering Department
SVPWM CONTROLLED INVERTER FOR POWER CODITIONING
Muneer Ahamed Khan
(Assistant Professor)
INTRODUCTION
1.1
The growing use of non-linear and time-varying loads has led to distortion of voltage and current
waveforms and increased reactive power demand in ac mains. Harmonic distortion is known to be source
of several problems, such as increased power losses, excessive heating in rotating machinery, and
harmonic resonances in the utility, significant interference with communication circuits, flicker and
audible noise, incorrect operation of sensitive loads [1,2].
Traditionally, LC tuned passive filters have been used to absorb harmonic currents generated by nonlinear
loads. Their main advantage is high reliability and low cost. However, passive filters have several
drawbacks, which may cause harmonic interaction with the utility problems with the utility system, in the
presence of stiff utility sharp tuning of the LC filter is required and may not meet the specified harmonic
current limits [3, 4]. This provides the motivation for investigation of an active filter topology, which is
practically viable, cost effective and can meet the recommended standard for high power nonlinear loads.
For high-power applications, the active filters are not cost effective due to their large rating and high
switching-frequency requirement of the Pulse Width Modulation (PWM) inverter.
1.2 PWM TECHNIQUE
Because of advances in solid state power devices and microprocessors, switching power
converters are used in industrial application to convert and deliver their required energy to the motor or
load. PWM signals are pulse trains with fixed frequency and magnitude and variable pulse width. There is
one pulse of fixed magnitude in every PWM period. However, the width of the pulses changes from pulse
to pulse according to a modulating signal. When a PWM signal is applied to the gate of a power
transistor, it causes the turn on and turns off intervals of the transistor to change from one PWM period to
another PWM period according to the same modulating signal. The frequency of a PWM signal must be
much higher than that of the modulating signal, the fundamental frequency, such that the energy delivered
to the motor and its load depends mostly on the modulating signal. The advantage of PWM based
switching power converter over linear power amplifier is:
1 Lower power dissipation
2 Easy to implement and control
3 No temperature variation and aging-caused drifting or degradation in linearity
4 Compatible with today’s digital micro-processors
Fig. 1.1 Symmetric and Asymmetric PWM Signals
Fig 1.1 shows two types of PWM signals, symmetric and asymmetric. The pulses of a symmetric PWM
signal are always symmetric with respect to the center of each PWM period. The pulses of an asymmetric
PWM signal always have the same side aligned with one end of each PWM period.
It has been shown that symmetric PWM signals generate fewer harmonics in the output currents
and voltages. This literature is considers three popular PWM techniques for the mostly used three phase
voltage source power inverter applications.
This is the most popular method of controlling the output voltage and this method is termed as
Pulse-Width Modulation (PWM) Control.
The advantages possessed by PWM techniques are as under:
The output voltage control with this method can be obtained without any additional
components. With this method, lower order harmonics can be eliminated or minimized along
with its output voltage control. As higher order harmonics can be filtered easily, the filtering
requirements are minimized.
The main disadvantage of this method is that SCRs are expensive as they must possess low turnon and turn-off times. PWM techniques are characterized by constant amplitude pulses. The
width of these pulses is however modulated to obtain output voltage control and to reduce its
harmonic content. The different PWM techniques are as under:
a) Single-pulse modulation
b) Multiple pulse modulations
c) Sinusoidal pulse width modulation (Carrier based Pulse Width Modulation Technique)
1.3 SVPWM TECHNIQUE
SVPWM technique was originally developed as a vector approach to pulse width modulation for
three-phase inverters. The SVPWM method is frequently used in vector controlled applications. In vector
controlled applications this technique is used for reference voltage generation when current control is
exercised. It is a more sophisticated, advanced, computation intensive technique for generating sine wave
that provides a higher voltage with lower total harmonic distortion and is possibly the best among all the
pulse width modulation techniques. It confines space vectors to be applied according to the region where
the output voltage vector is located. Because of its superior performance characteristics, it is been finding
wide spread applications in recent years. The main aim of any modulation technique is to obtain variable
output voltage having a maximum fundamental component with minimum harmonics. Many PWM
techniques have been developed for letting the inverters to posses various desired output characteristics to
achieve the wide linear modulation range, less switching losses, lower harmonic distortion. The SVPWM
technique is more popular than conventional technique because of its excellent features.

More efficient use of DC supply voltage

15% more output voltage then conventional modulation

Lower Total Harmonic Distortion (THD)

Prevent un-necessary switching hence less commutation losses
1.4 PRINCIPLE OF SVPWM
Firstly model of a three-phase inverter is presented on the basis of space vector representation. The threephase VSI is reproduced in Fig. 1.2. S1, to S 6, are the six power switches that shape the output, which are
,
,
controlled by the switching variables a, a , b , b ,
c and c , When an upper transistor is switched on, i.e.,
,
,
,
the corresponding a , b , , or c is 0 . Therefore, the on and off states of the upper switches S1, S3, S5,
can be used to determine the output voltage.
+
S1
a
Vdc
C
+
S5
c
Va
-
Vab
Vb
a’
S4
-
S3
b
b’
S6
Vc
c’
S2
Vca
N
Vbc
Load
Fig. 1.2 Power circuit of a three-phase VSI
The relationship between the switching variable vector [a b
c ]t and line-to-line voltage vector [ Vab, Vbc,
Vca ] is given by (5.6) in the following:
Vab 
 1  1 0  a 
V   V  0 1  1 b 
dc 
 bc 
 
Vca 
 1 0 1   c 
(1.1)
Also, the relationship between the switching variable voltage vectors [ Vab, Vbc, Vca ]t can be expressed
below.
Van 
V   Vdc
 bn 
3
Vcn 
 2  1  1 a 
 1 2  1 b 

 
 1  1 2   c 
(1.2)
.One simple method of approximation is to generate the one simple method of approximation is to
generate the average output of the inverter in a small period, T to be the same as that of V ref in the same
period. . The angle of the reference voltage is hold for each switching period so that its value does not
change during time calculation. A ramping time signal is generated using repeating sequence block.
CHAPTER 2
Simulink Model : In following figure different simulink model using PWM & SVPWM technique
have been discussed . Their result have been compared also.
Fig. 2.1Simulink model of PWM technique for nonlinear load condition with APF
Fig 2.2Source current waveform with PWM technique for nonlinear load condition with
APF
0
-10
0
0.2
0.4
0.6
0.8
1
Time (s)
Mag (% of Fundamental)
Fundamental (50Hz) = 8.793 , THD= 13.26%
30
25
20
15
10
5
0
0
5
10
Harmonic order
15
20
SVPWM technique for nonlinear load (rectifier with R load) condition with APF
Fig. 2.3 Simulink model of SVPWM technique for nonlinear load condition with APF
Selected signal: 50 cycles. FFT window (in red): 2 cycles
10
0
-10
Fig. 2.4 Source Current waveform with SVPWM technique for nonlinear load condition with APF
0
0.2
0.4
0.6
0.8
1
Time (s)
Fundamental (50Hz) = 6.964 , THD= 5.47%
Mag (% of Fundamental)
4
3
2
1
0
0
5
10
Harmonic order
15
Fig. 2.5 Harmonic spectrum of SPWM technique for nonlinear load condition with APF
20
SVPWM technique for nonlinear load (rectifier with R load) condition with APF
Fig. 2.8Simulink model of SVPWM technique for nonlinear load condition with APF
Fig. 2.9 Source Current waveform with SVPWM technique for nonlinear load condition with APF
0
-10
0
0.2
0.4
0.6
0.8
1
Time (s)
Fundamental (50Hz) = 6.964 , THD= 5.47%
Mag (% of Fundamental)
4
3
2
1
0
0
5
10
Harmonic order
15
20
Fig. 2.10 Harmonic spectrum of SPWM technique for nonlinear load condition with APF
1.7 SIMULATION RESULT ANALYSIS AND DISCUSSIONS
From the simulated results of different cases without and with active filter are shown in following tables.
Table1.1 Result Analyses for non linear System.
Without APF
THD Source Site
PF
30.28%
0.92
Non Linear Load
PWM Technique with APF
THD Source Site
PF
13.26%
0.94
SVPWM technique with APF
THD Source Site
PF
5.47%
0.95
From Table 1.1 show the simulation of harmonic spectrum of linear three phase balance and
unbalance load. is shown in fig harmonic spectrum of the current before compensation on the load side.
The source current total harmonic distortion (THD) is 0.00%. It should be noted that no harmonic
generated in linear three phase balance system. From Table 1.1 shows the simulation of harmonic
spectrum of linear three phase unbalance load. is the harmonic spectrum of the source current before
compensation on the source side. The source current total harmonic distortion (THD) is 0.00%. It should
be noted that no harmonic generated in linear three phase unbalance system.
From aboveTable shows the simulation of harmonic spectrum of APF with PWM Technique and
SVPWM Technique used for non linear load used when the non-linear is a three-phase diode bridge
rectifier with resistance-inductive load. is the harmonic spectrum of the source current before
compensation on the source side. The harmonic spectrum of the source current shows that magnitude of
the 5th, 7th, 11th and 13th harmonics are evidently reduced after compensation. The source current Total
Harmonic Distortion (THD) is 30.21%, before compensation and after compensation the supply current
THD is 13.26% when PWM Technique used this is shown by Fig. . When the SVPWM technique used
the supply current Total Harmonic Distortion (THD) is 5.47%, this is shown by Fig.
It should be noted that the higher frequency harmonics caused by APF in mains current can be
canceled easily by a small passive filter and there are pulses in main current at the points, where di
dt
of
load current is large, because fixed switching frequency restrict the tracking capability of APFfrom the
above results the performance of balanced linear load, unbalanced linear load and non linear load with the
proposed control algorithm is observed. The three-phase source voltage is made in phase with source
current for balanced linear load. The three-phase source current is made equal in magnitude when an
unbalanced linear load is simulated. The harmonic spectrum shows that reduction of higher order
harmonics in three-phase source current when non-linear load is simulated.
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