Download V out - UniMAP Portal

EET 423
POWER ELECTRONICS -2
Prof R T Kennedy
1
BUCK CONVERTER CIRCUIT CURRENTS
Ii n
Ids a IL
Ifwd
IL b Iout
L
IC
Ids
Ei n
Ifwd
Prof R T Kennedy
C
R Vout
2
BUCK CONVERTER CIRCUIT VOLTAGES
Vds
a
VL,a-b
b
L
Ei n
Vfwd
Prof R T Kennedy
C
R Vout
3
SUB INTERVAL EQUIVALENT CIRCUITS
VL,a-b= Ein-Vout
Vds = 0
a
L
b
MOSFET
Ei n
ON
Vfwd = -Ein
C
R
Vout
RECTIFIER
OFF
Prof R T Kennedy
4
SUB INTERVAL EQUIVALENT CIRCUITS
Vds = Ein
VL,a-b= -Vout
a
b
L
MOSFET
Ei n
C
OFF
R Vout
Vfwd= 0
RECTIFIER
ON
Prof R T Kennedy
5
Vgs
0
Ein
0
Vds
Ein =Eds + Efwd
0
0
Vfwd
0
VL
Vout
VL + Vout = -Vfwd
0
0
Prof R T Kennedy
6
Vgs
0
Ein =Vds - Vfwd
Ein
0
-Vfwd
Vds
0
0
Vfwd
0
VL
Vout
0
0
Prof R T Kennedy
7
SMPS OPERATION
QUANTIZED POWER/ENERGY TRANSFER
VOLTAGE REGULATION
Prof R T Kennedy
8
VOLTAGE TRANSFER FUNCTION ANALYSIS
• ENERGY BALANCE
• POWER BALANCE
• VOLT-TIME INTEGRAL
Prof R T Kennedy
9
‘IDEAL’ BUCK ANALYSIS
ENERGY BALANCE APPROACH
IL,M
INDUCTOR CURRENT
I L
I L
2
IL,av = Iload
I L
2
I L, M

I out 
I L
2
I L, m

I out 
I l
2
I L, M  I L, m

2  I out
I L, M  I L, m

I L  I out
I L, M 2  I L, m 2
 2  I out  I L
IL,m
0
Prof R T Kennedy
10
SUB-INTERVAL 1
inductor energy from source
JL
load energy from source

1
L ( I L, M 2  I L, m 2 ) 
2
J load , s
input power sub  int erval 1 Pin1
Prof R T Kennedy
L  I out  I L
 Vout  I out  Dsw  T

J load , s
Dsw  T
 Vout  I out
11
SUB-INTERVAL 2
VL  Vout

Vout

L  I L
load energy from inductor
total load energy
J 2,load
J load
L
L
di
dt
I L
(1  Dsw )  T

 Vout  (1  Dsw )  T
 L  I load  I ind

J1,load  J 2,load
Prof R T Kennedy
 Vload  I load  (1  Dsw )  T
 Vload  I load  T
12
switching
total load energy
J load
load power

Pload
period
J1,load  J 2,load

load energy from source
J load
T
 Vload  I load  T
 Vload  I load
J load , s
Prof R T Kennedy
 Vout  I out  Dsw  T
13
FARADAY’S VOLT-TIME INTEGRAL
IM
INDUCTOR CURRENT
Im
current start and finish at same value
0
t
V1
INDUCTOR VOLTAGE
0
t1
t
V2
t2
VL, av

1 T  di 
L
dt
T 0  dt 
VL, av

1 T
L di
T 0
VL, av

L T
I 
T 0
VL, av

L
I 0  IT   0
T
T
EQUAL AREAS
T
0 v(t ) dt
V1  t1
0
 V2  t2
Prof R T Kennedy
14
BUCK and BOOST CONVERTERS
VOLTAGE TRANSFER FUNCTIONS
5
BOOST
4.5
Vout
1

1
Ein 1  Dsw1
4
3.5
Vout
Ein
3
2.5
2
1.5
BUCK
1
Vout
 Dsw1  1
Ein
0.5
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
Dsw1
1
Prof R T Kennedy
15
BUCK-BOOST
BOOST- BUCK CONVERTERS
VOLTAGE TRANSFER FUNCTIONS
1
INVERTED
STEP DOWN (<1)
0
1
2
3
4
Vout
Ein 5
INVERTED
STEP UP (>1)
6
7
8
9
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
1
Dsw1
Prof R T Kennedy
16
PRACTICAL SYSTEMS

Vout
Ein

Vout  I out
Ein  I in, av

 I in, av 

 
 I 
Vout
Vout

 efficiency
Ein practical
Ein ideal
Prof R T Kennedy
17