Microsoft PowerPoint - Chapter 2_PartB [Compatibility Mode]
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Transcript of Microsoft PowerPoint - Chapter 2_PartB [Compatibility Mode]
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8/12/2019 Microsoft PowerPoint - Chapter 2_PartB [Compatibility Mode]
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SCHMY-MMU, Preliminary Meeting 23rdAugust 2002
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Chapter 2 Part B
Line-Commutated Diode Rectifiers
Uncontrolled Rectifier (Natural Commutating Rectifier)
Controlled Rectifier (Phase Controlled Rectifiers)
Diode
V
t
Constant DC VoltageAC Power Source
Thyristor/SCR
V
t
Variable DC VoltageAC Power Source
AGAIN
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How a Thyristor Works ?
1. ANODE gets more positive voltage
Than Cathode
2. Gate Pulse
PN N P
A K
G
Single-phase, half-wave controlled rectifiers
with pure resistive load,
+
vS(t)
+ vthy(t)
R
i(t)
~
+
vR(t)
+
vo(t)
wt
vS
vS
vthy
vthy
vR
voi
i
0
0
wt
2
)cos1(22
+= VVo
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vL(t)
+
L
+
vS(t)
+ vthy(t)
R
i(t)
~
+
vR(t)
+
vo(t)
iG
Area A
Area B
wt
vS
vS
vthy
vthy
vRvo
vR
vo
i
i
0
0
wtp
2
(2)
Single-phase, half-wave controlled rectifiers
with Inductive load,
)cos(cos2
2
+=
VV
o
Simulation
vL(t)+
L+
vS(t)
+ vthy(t) i(t)
~
+
V1(t)
+
vo(t)
iG
Area A
Area B
wt
vS
vS
vthy
vthy
vo
vo
i
i
0
0
wtp
2
1
V1
V1
vo
(3)
Single-phase, half-wave controlled rectifiers
with Internal DC Voltage,
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Role of free-wheeling diode
To avoid negative voltage when inductive load involved.
vL(t)
+
L
+
vS(t)
+ vthy(t)
R
i(t)
~
+
vR(t)
+
vo(t)
iG
DArea A Area B
wt
vS
vS
vthyvthy
vo
vR
vo
i0
0
wtp
2
D on
LR discharge
purely natural response
Must area A = area B
During < wt < :
vL + vR= voDuring < wt < 2+:
vL
+ vR
= 0
i > 0 (exp decay)
i(t) is expressed in two
separate equations.
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Half Controlled Rectifier with R Load
0 2+
ig
v
Vo
Io
Average Load/Output Voltage
Average Load/Output Current Firing/trigger angle
Note
When= 0, The output is same as uncontrolled rectifier.
V = rms value
Half Controlled Rectifier with RL Load
0 2+
ig
v
Vo
IoAverage Load/Output Voltage
Average Load/Output Current
Firing/trigger angle
2+
Current decay to zero
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Full Controlled Rectifier with R Load
Average Load/Output Voltage
Average Load/Output Current
Firing/trigger angle
If = 0 ,The output will be same as a
Full Uncontrolled Rectifier that uses DIODE.
Full Controlled Rectifier with DC Motor Load
Average Load/Output Voltage
Average Load/Output Current
V
V
Io
Io
Vo
I
I
Vo
S1, S2 S3, S4S1, S2
For 0 < < 90
Ea = armature back emf.
+
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Full Controlled Rectifier with DC Motor Load
Average Load/Output Voltage
Average Load/Output Current
V
V
Io
Io
Vo
I
I
Vo
S1, S2 S3, S4
S1, S2
For 90 < < 180
Ea = armature back emf.
+
V2
VoFor fully controlled rectifier,
The DC Motor operates
in two modes.
1. Rectification
[As Motoring]
2. Inversion
[As Regenerative Braking]
V0 = positive
Ea = Positive
Io= positive
Power Flow (+ve) from input
AC to DC machine
V0 = positive
Ea = Positive
Io= positive
Power Flow (+ve) from input
AC to DC machine
V0 = negative
Ea = negative
Io= positive
Power Flow (-ve) from
DC machine to AC supply
V0 = negative
Ea = negative
Io= positive
Power Flow (-ve) from
DC machine to AC supply
Converter Output Characteristics for continuous load current
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Review on Four Quadrants Operation
< 90
> 90
Review on Four Quadrants Operation Lift Application
< 90
> 90
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What do you mean with
Continues Load Current ?
What do you mean with
Continues Load Current ?
When you have an inductive load as in DC motor,
the load current is subject to the ratio of
Constant)Time(R
Lwhere =
R
L
Larger the ratio will produce almost a constant current,
On the other hand,
small ratio will produce ripple current
Lets look at an example next slide
Vo
Io
Vo
Io
Continuous
Load Current
Discontinuous
Load Current
Vo
Io
Continues and Discontinuous Load Current/Conduction
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Three-phase half-wave
Controlled Rectifier circuit with R load
Vphase
Vo
30
150
Average Load/Output Voltage
VAN= rms value of voltage phase A voltage
Vphase
Vo
Io
IS1
IS4
IA
S1 S3 S5IA
IO
S4 S6 S2
VAN VBN VCN
Vab Vac Vbc Vba Vca Vcb
Three-phase full-wave Controlled
Rectifier circuit with R load
Average Load/Output Voltage
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V63
VoFor fully controlled rectifier,
The DC Motor operates
in two modes.
1. Rectification
[As Motoring]
2. Inversion
[As Regenerative Braking]
V0 = positive
Ea = Positive
Io= positive
Power Flow (+ve) from input
AC to DC machine
V0 = positive
Ea = Positive
Io= positive
Power Flow (+ve) from input
AC to DC machine
V0 = negative
Ea = negativeIo= positive
Power Flow (-ve) from
DC machine to AC supply
V0 = negative
Ea = negativeIo= positive
Power Flow (-ve) from
DC machine to AC supply
Converter Output Characteristics for continuous load current
(Full Converter)
DC Motor Drives
Direct Current
Supply VoltageElectric Motor
Systems used formotion control
AC DC (Rectifier) when Input is AC
DCDC (DC Chopper) when Input is DC
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Control Rectifier Fed DC Drives
Control in either direction
Allow motor control in Q1 & Q4
Control in one direction ONLY
Allow motor control in Q1 ONLY
For Low power application, 10kW, Three phase rectifiers are used.
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Single phase Fully Controlled Rectifier Control of
DC Separately Excited Motor
tVv ms= sin
aa
a
aaa
IKT
KE
RIEV
=
=
+=
Basic equation applicable
to all DC Motors
armatureofspeed
poleperflux
constantmotor
currentarmature
motorbydeveloptorque
emfback
voltagearmature
=
=
=
=
=
=
=
a
a
a
K
I
T
E
V
A 200 V, 875 rpm, 150 A, separately excited dc motor
has an armature resistance of 0.06 . It is fed from a single phase
fully-controlled rectifier with an ac source voltage of 220 V, 50 Hz.
Assuming continuous conduction, calculate the following:
Firing angle for rated torque at 750 rpm.
Motor speed at = 160 and rated torque.
Exercise
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Part B of Chapter 2