1.1 Introduction to Power Processing!
Power
input
Switching
converter
Power
output
Control
input
Dc-dc conversion:
Ac-dc rectification:
Dc-ac inversion:
!Change and control voltage magnitude!
!Possibly control dc voltage, ac current!
!Produce sinusoid of controllable
magnitude and frequency!
Ac-ac cycloconversion: !Change and control voltage magnitude
and frequency!
The switching converter is the “brain” of the power system, allowing
conversion of voltage and current levels with high efficiency, plus control!
2!
Control is invariably required!
Power
input
Switching
converter
Power
output
Control
input
Feedforward
Feedback
Controller
Reference
3!
•  Traditional analog
feedback!
•  Sophisticated control
using inexpensive digital
microcontrollers!
High Efficiency is Essential!
=
Pout
Pin
Ploss = Pin – Pout = Pout 1 – 1
•  High efficiency leads to low
power loss within converter
•  Small size and reliable operation
is then feasible
•  A good measure of converter
performance is the ratio of
output power to loss:
Pout
=
Ploss 1 –
Converters generally are losslimited, and technologies that
can produce large output power
while incurring small loss result
in small size and low cost
Pin
Converter
Large input power
10!
Small
converter
Pout
Large output power
+
–
Devices available to the circuit designer!
DT
Resistors
Capacitors
Magnetics
11!
T
s
s
Linearmode
Switched-mode
Semiconductor devices
+
–
Devices available to the circuit designer!
DT
Resistors
Capacitors
Magnetics
Signal processing: avoid magnetics!
12!
T
s
s
Linearmode
Switched-mode
Semiconductor devices
+
–
Devices available to the circuit designer!
DT
Resistors
Capacitors
Magnetics
Power processing: avoid lossy elements!
13!
T
s
s
Linearmode
Switched-mode
Semiconductor devices
Power loss in an ideal switch!
1
Switch closed: !v(t) = 0
Switch open:
+
!i(t) = 0
In either event: !p(t) = v(t) i(t) = 0!
i
v
–
Ideal switch consumes zero power!
14!
0
A simple dc-dc converter example!
I
10 A
+
Vg
100 V
+
–
Dc-dc
converter
R
5
V
50 V
–
Input source: 100V!
Output load: 50V, 10A, 500W!
How can this converter be realized?!
15!
Dissipative realization!
Resistive voltage divider!
I
10 A
+
Vg
100 V
+
–
+
50 V –
Ploss = 500 W
R
5
V
50 V
–
Pin = 1000 W
Pout = 500 W
16!
Dissipative realization!
Series pass regulator: transistor operates in
active region!
I
10 A
+ 50 V –
+
Vg
100 V
+
–
Linear amplifier
and base driver
Ploss 500 W
–+ Vref
R
5
V
50 V
–
Pin 1000 W
Pout = 500 W
17!
Use of a SPDT switch!
I
10 A
1
+
Vg
100 V
+
2
+
–
vs(t)
R
–
vs(t)
–
Vg
Vs = DVg
switch
position:
DTs
0
(1 – D) Ts
t
1
2
1
18!
v(t)
50 V
The switch changes the dc voltage level!
vs(t)
Vg
Vs = DVg
switch
position:
DTs
0
(1 – D) Ts
t
1
2
1
DC component of vs(t) = average value:!
19!
D = switch duty cycle!
!0 ≤ D ≤ 1
Ts = switching period!
!
fs = switching frequency!
= 1 / Ts
Addition of low pass filter!
Addition of (ideally lossless) L-C low-pass filter, for
removal of switching harmonics:!
i(t)
1
+
Vg
100 V
+
–
+
L
2
vs(t)
C
–
Pin
500 W
Ploss small
R
v(t)
–
Pout = 500 W
•
Choose filter cutoff frequency f0 much smaller than switching
frequency fs
•
This circuit is known as the “buck converter”!
20!
Addition of control system"
for regulation of output voltage!
Power
input
Switching converter
Load
+
+
–
v
H(s)
–
Transistor
gate driver
Error
signal
ve
Pulse-width vc G (s)
c
modulator
Compensator
(t)
dTs Ts
–+
vg
i
Reference
vref
input
t
21!
Hv
Sensor
gain
The boost converter!
2
+
L
Vg
1
+
–
C
R
V
–
5Vg
4Vg
V
3Vg
2Vg
Vg
0
0
0.2
0.4
0.6
D
22!
0.8
1
A single-phase inverter!
1
Vg
+
–
vs(t)
+
–
+
v(t)
2
–
2
1
Load
vs(t)
“H-bridge”!
t
23!
Modulate switch
duty cycles to
obtain sinusoidal
low-frequency
component!