Advanced techniques of PULSE WIDTH MODULATION.

AUDISANKARA
ADVANCED TECHNIQUES
OF
PULSE WIDTH
MODULATION
Under the esteemed guidance of
A.N.V.K NAVEEN
BY
SUDHEER PUCHALAPALLI
112H1A0279
INSTITUTE OF TECHNOLOGY
H.O.D
M.NAGARAJU
M.Tech.,(Ph.D.,)

CONTENTS
Need for voltage control
Traditional methods for inverter voltage control
Disadvantages of conventional methods
Pulse width modulation
Classification of pwm
Components used in vsi and csi
Single-pulse width modulation
Multiple-pulse width modulation
Sinusoidal pulse width modulation
Disadvantages with above techniques
Space vector pulse width modulation
Advantages of svpwm
Applications
conclusion

NEED FOR VOLTAGE CONTROL
Light dimming circuits for street lights
Industrial & domestic heating
Induction heating
transformer tap changing
Speed control of Motors (variable torque)
speed control of winding machines, fans
AC magnet controls

TRADITIONAL METHODS FOR INVERTER
VOLTAGE CONTROL
 EXTERNAL CONTROL OF AC OUTPUT VOLTAGE
 EXTERNAL CONTROL OF DC INPUT VOLTAGE
Inverter
AC Voltage
Controller
AC Load
InverterFilter
Fully
Controlled
rectifier
Constant
DC Voltage
Controlled
AC voltage
AC
voltage
Constant
AC Voltage
DC
Voltage
Controlled
DC Voltage
Controlled
AC Voltage

DISADVANTAGES OF TRADITIONAL METHODS
Complexity increases
High cost
Occupies more space
Not flexible in control
Not compatible with user
Not commercial
Requires more floor area
Unique solution to above all problems is PULSE WIDTH MODULATION technique.

PULSE WIDTH MODULATION
The modulating of width of the pulse by
keeping height as constant.
The different time periods or pulses will be
given to power electronics devices.
Although this modulation technique can be
used to encode information for transmission.
Its main use is to allow the control of the
power supplied to electrical devices,
especially to inertial loads such as motors.

COMPONENTS USED IN VSI AND CSI
Silicon control rectifier(SCR)
Gate Turn off Thyristor(GTO)
Thyristors
Transistors
Bi-junction transistor(BJT)
Metal oxide semi-conductor device(MOSFET)
Static induction transistor(SIT)
Insulated gate bi-polar transistor(IGBT)

Pulse Width
Modulation
Single Pulse
Width
Modulation
Multiple Pulse
Width
Modulation
Sinusoidal
Pulse Width
Modulation
CLASSIFICATION OF PWM

SINGLE-PULSE WIDTH MODULATION
Single pulse for half cycle generates from this
techniques.
It consists of a pulse located symmetrical about π/2
and another pulse located symmetrical about 3π/2.
The shape of the output voltage is Quasi-Square wave.

Great deal of harmonic content is introduced in the output voltage.
The amplitude of harmonic content is 0.33 units.
Very poor performance at lower voltages.
CONTD.,

MULTIPLE-PULSE WIDTH MODULATION
It is an extension to single pulse width modulation.
More pulses will exist in an half cycle.
The width of every single pulse is same.
Comparator
Trigger pulse
generator
Triangular wave
Square wave
Trigger
pulses to
scr

lower order harmonics are
eliminated.
The magnitude of higher harmonics
would go up.
This has more applications than
single-pulse width modulation in
olden days.
CONTD.,

SINUSOIDAL PULSE WIDTH MODULATION
Pulses will have
different widths.
The width of the
individual pulse will
be decided
according to the
angular position of
sine wave.

CONTINUE
Height of the pulse is kept as constant
Odd multiple of 3 and even harmonics are suppressed
Popularly accepted pulse width modulation technique.

DISADVANTAGES OF ABOVE
PWM TECHNIQUES
 Lesser utilization of DC supply voltage.
 Higher harmonics
 Lower modulation index
 Less flexibility
 Difficult in manipulation
Unique solution to above all problems is
SPACE VECTOR PULSE WIDTH MODULATION
technique.

SPACE VECTOR PULSE WIDTH MODULATION
 Output voltages of three-phase inverter (1)
where, upper transistors: S1, S3, S5
lower transistors: S4, S6, S2
switching variable vector: a, b, c

t
dc
ca
bc
ab
c]b[avectorvariableswitchingwhere,
c
b
a
101
110
011
V
V
V
V






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






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






c
b
a
211
121
112
V
3
1
V
V
V
dc
cn
bn
an
 S1 through S6 are the six power transistors that shape the ouput voltage
 When an upper switch is turned on (i.e., a, b or c is “1”), the corresponding lower
switch is turned off (i.e., a', b' or c' is “0”)
 Line to line voltage vector [Vab Vbc Vca]t
 Line to neutral (phase) voltage vector [Van Vbn Vcn]t
 Eight possible combinations of on and off patterns for the three upper transistors (S1, S3, S5)

 The eight inverter voltage vectors (V0 to V7)

 The eight combinations, phase voltages and output line to line voltages

 Principle of Space Vector PWM
 This PWM technique approximates the reference voltage Vref by a combination
of the eight switching patterns (V0 to V7)
 The vectors (V1 to V6) divide the plane into six sectors (each sector: 60 degrees)
 Vref is generated by two adjacent non-zero vectors and two zero vectors
 Coordinate Transformation (abc reference frame to the
stationary d-q frame)
: A three-phase voltage vector is transformed into a vector in the
stationary d-q coordinate
frame which represents the spatial vector sum of the three-phase
voltage
 Treats the sinusoidal voltage as a constant amplitude vector rotating
at constant frequency

 Basic switching vectors and Sectors
Fig. Basic switching vectors and sectors.
 6 active vectors (V1,V2, V3, V4, V5, V6)
 Axes of a hexagonal
 DC link voltage is supplied to the load
 Each sector (1 to 6): 60 degrees
 2 zero vectors (V0, V7)
 At origin
 No voltage is supplied to the load

 Comparison of Sine PWM and Space Vector PWM (2)
 Space Vector PWM generates less harmonic distortion
in the output voltage or currents in comparison with sine PWM
 Space Vector PWM provides more efficient use of supply voltage
in comparison with sine PWM
 Voltage Utilization: Space Vector PWM = 2/3 times of Sine PWM

 Realization of Space Vector PWM
 Step 1. Determine Vd, Vq, Vref, and angle ()
 Step 2. Determine time duration T1, T2, T0
 Step 3. Determine the switching time of each transistor (S1 to S6)



































cn
bn
an
q
d
V
V
V
2
3
2
3
0
2
1
2
1
1
3
2
V
V
frequency)lfundamentaf(where,
t2ππtω)
V
V
(tanα
VVV
s
ss
d
q1
2
q
2
dref




Fig. Voltage Space Vector and its components in (d, q).
cnbnan
cnbnq
cnbnan
cnbnand
V
2
3
V
2
3
V
cos30Vcos30V0V
V
2
1
V
2
1
V
cos60Vcos60VVV




 Step 1. Determine Vd, Vq, Vref, and angle ()
 Coordinate transformation
: abc to dq

Fig. Reference vector as a combination of adjacent vectors
at sector 1.
 Step 2. Determine time duration T1, T2, T0 (1)

 Switching time duration at any Sector
 Step 2. Determine time duration T1, T2, T0 (3)



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60α0
6)toSector1is,(that6through1nwhere,
,
3
1
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1
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TTTT
nn
V
refVT
n
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T
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refVT
n
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refVT
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z
dc
z
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z
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z
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z
dc
z







Fig. Space Vector PWM switching patterns at each sector.
(a) Sector 1. (b) Sector 2.
 Step 3. Determine the switching time of each transistor (S1 to S6) (1)

(c) Sector 3. (d) Sector 4.

(e) Sector 5. (f) Sector 6.

Table 1. Switching Time Table at Each Sector

APPLICATIONS
Power converters
Motor control
Ac machines control
UPS
Low power applications

CONCLUSION
Space vector pulse width modulation
is the best technique which is ruling
the world now.
Still a lot of research is going on this
svpwm.
It should be available with low cost
for household purpose.

Advanced techniques of PULSE WIDTH MODULATION.

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