Download - Control- and Analysis
Current Mode Control-Functional Basics and
Classical Analysis
Pulsewidth Modulated Dc-to-Dc Power Conversion. By Byungcho ChoiCopyright © 2013 IEEE, Published by John Wiley & Sons, Inc
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22
Chapter Outline
1) Current Mode Control Basics
2) Classical Analysis and Control Design Procedures
3) Closed-Loop Performance of Peak Current Mode Control
4) Current Mode Control for Boost and Buck/Boost Converters
3
33
Voltage Mode ControlC
urre
nt M
ode
Con
trol B
asic
s
2
1
Switch turn-on at beginning of switching periodControl law: turn-off the switch when intersects with .
| ( 0) || ( 0) |
ramp con
O ref
V v
Z j V VZ j
xx
x f �
Ov�
�
Sv
conv
rampV
refV
rampV
conv
2Z
1Z( )q t
( )q t
4
44
Current Mode ControlC
urre
nt M
ode
Con
trol B
asic
s
2
1
Switch turn-on at beginning of switching periodCSN: current sensing networkControl law: turn-off the switch when intersects with .| ( 0) || ( 0) |
I con
O ref
v vZ j v VZ j
xxx
x f �
Li
Sv
refV
CSN
Iv
conv
2Z
1Z
Ov�
�
conv
Iv
( )q t
( )q t
5
55
Propagation of Current Feedback DisturbanceC
urre
nt M
ode
Con
trol B
asic
s
Sub-harmonic oscillation when 0.5D >x
conv
conv
IvIvc
IvIvc
0.5D >
0.5D �
6
66
Addition of Compensation RampC
urre
nt M
ode
Con
trol B
asic
s
SvLi
Ov
�
�
CSN
Iv ��
refV
rampV
conv
2Z
1Z( )q t
conv
Iv
I rampv V�
rampV
( )q t
Control waveformsx
7
77
Addition of Compensation RampC
urre
nt M
ode
Con
trol B
asic
s
SvLi
Ov
�
�
CSN
Iv ��
refV
rampV
conv
2Z
1Z
conv
I rampv V�
I rampv Vc �
Propagation of current feedback disturbancex
8
88
Waveforms of Current Mode ControlC
urre
nt M
ode
Con
trol B
asic
s
Current mode control with unity inductor current sensingx
Equivalent representationx
I Lv i
conv
Li
L rampi +V
rampVrampV( )q t
( )q t
conv
rampV
I Lv i
conv
con rampv V�
( )q t
( )q t
Li
conv
9
99
Waveforms of Current Mode ControlC
urre
nt M
ode
Con
trol B
asic
s
PWM waveforms
Compensation ramp slope
con rampv V�
( )Li k'( 1)Li k' �
sdT'
Li
Lic
conv
nSeS
fS
n sS dT'
f sS dT'
Li
sdT'
e sS dT'
Lic
con rampv V�
( )Li k'
( 1)Li k' �
| ( ) ( )| ( )=
| ( 1) ( 1)| ( 1)=
( 1) 1 for stablity( )
2
L L L n s e s
L L L f s e s
f eL
L n e
f ne
i k i k = i k S dT S dT
i k i k = i k S dT S dT
S Si ki k S S
S SS
c� ' ' � '
c� � � ' � ' � '
�' �� �
' �
�� !
10
1010
Peak Current Mode ControlC
urre
nt M
ode
Con
trol B
asic
s
Sv Ov
�
�
CSN
Iv ��
refV
rampV
conv
2Z
1Z( )q t
rampV
IvI rampv V�conv
( )q t
Block diagram Control waveforms
Peak current mode control senses the switch current.Switch current sensing is functionally identical to the inductor current sensing.Advantages of switch current sensing
i) simple CSN design ii) dc and
xxx
ac sensing for switch current iii) overcurrent protection for switch current
11
1111
Sub-harmonic Oscillation and Compensation RampC
urre
nt M
ode
Con
trol B
asic
s
Sub-harmonic oscillationwithout compensation ramp Effects of compensation ramp
conv
( )d t 0.25
0.57
conv
( )d t 0.25
0.57
12
1212
Current Sensing NetworkC
urre
nt M
ode
Con
trol B
asic
s
1
1CSN gain :
11( ) 1 1
resets the transformer when the switch is open.
and form a noise filter.
R R
Ii sense
Q
tR C H
ramp H HR R R R
z
f f
vR Ri n
VtV t V e V tR C R C
D Q
R C
�
x
§ ·§ ·§ ·¨ ¸ �x � | � ¨ ¸¨ ¸¨ ¸ © ¹© ¹¨ ¸
© ¹
x
x
senseR
pwmV
RRRC
conv
ramp IV v� HV
0
Iv
�
�
rampV�
�
1 : n
Qi
QzD fR
fC
rampV
IvI rampv V�conv
( )q t
Iv
13
1313
Benefits and Issues of Current Mode ControlC
urre
nt M
ode
Con
trol B
asic
s
z Benefits of current mode control
Improved dynamic performance: current mode control is suited for boost and
buck/boost converters with an RHP zero in duty-ratio-to-output
transfer function
Robustness of converter dynamics: current mode control offers good performance
for both CCM and DCM operations
Simple compensation design: current mode control employs a standard two-pole
one-zero compensation for all three basic PWM converters
z Issues of current mode control
Dynamic modeling and analysis of the multi-loop control system
Sampled-data feature (sampling effects) of the control scheme