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.,)
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
AUDISANKARA
ADVANCED TECHNIQUES
OF
PULSE WIDTH
MODULATIONUnder 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
InverterAC Voltage
ControllerAC Load
InverterFilterFully
Controlled
rectifier
Constant
DC Voltage
Controlled
AC voltage
AC
voltage
Constant
AC VoltageDC
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.
ComparatorTrigger 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
tdc
ca
bc
ab
c]b[avectorvariableswitchingwhere,
c
b
a
101
110
011
V
V
V
V
c
b
a
211
121
112
V3
1
V
V
V
dc
cn
bn
an
Output voltages of three-phase inverter (2)
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)
Output voltages of three-phase inverter (3)
The eight inverter voltage vectors (V0 to V7)
Output voltages of three-phase inverter (4)
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
30
2
1
2
11
3
2
V
V
frequency)lfundamentaf(where,
t2ππtω)V
V(tanα
VVV
s
ssd
q1
2q
2dref
Fig. Voltage Space Vector and its components in (d, q).
cnbnan
cnbnq
cnbnan
cnbnand
V2
3V
2
3V
cos30Vcos30V0V
V2
1V
2
1V
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)
60α0
6)toSector1is,(that6through1nwhere,,
3
1cossin
3
1sincos
3
3
1sin
3
sin3
coscos3
sin3
3sin
3
3
1
3sin
3
210
2
1
TTTT
nn
V
refVT
n
V
refVTT
nn
V
refVT
n
V
refVT
n
V
refVTT
z
dc
z
dc
z
dc
z
dc
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)
Fig. Space Vector PWM switching patterns at each sector.
(c) Sector 3. (d) Sector 4.
Step 3. Determine the switching time of each transistor (S1 to S6) (2)
Fig. Space Vector PWM switching patterns at each sector.
(e) Sector 5. (f) Sector 6.
Step 3. Determine the switching time of each transistor (S1 to S6) (3)
Table 1. Switching Time Table at Each Sector
Step 3. Determine the switching time of each transistor (S1 to S6) (4)
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.
Any queries…
Related Documents
