Fundamentals of Power Electronics
Second edition
Robert W. Erickson
Dragan Maksimovic
University of Colorado, Boulder
Fundamentals of Power Electronics
1
Chapter 1: Introduction
Chapter 1: Introduction
1.1.
Introduction to power processing
1.2.
Some applications of power electronics
1.3.
Elements of power electronics
Summary of the course
Fundamentals of Power Electronics
2
Chapter 1: Introduction
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
Fundamentals of Power Electronics
3
Chapter 1: Introduction
Control is invariably required
Power
input
Switching
converter
Power
output
Control
input
feedforward
feedback
Controller
reference
Fundamentals of Power Electronics
4
Chapter 1: Introduction
High efficiency is essential
1
η=
Pout
Pin
η
0.8
1 –1
Ploss = Pin – Pout = Pout η
0.6
High efficiency leads to low
power loss within converter
Small size and reliable operation
is then feasible
Efficiency is a good measure of
converter performance
0.4
0.2
0
0.5
1
1.5
Ploss / Pout
Fundamentals of Power Electronics
5
Chapter 1: Introduction
A high-efficiency converter
Pin
Converter
Pout
A goal of current converter technology is to construct converters of small
size and weight, which process substantial power at high efficiency
Fundamentals of Power Electronics
6
Chapter 1: Introduction
+
–
Devices available to the circuit designer
DT
Resistors
Capacitors
Fundamentals of Power Electronics
Magnetics
7
T
s
s
Linearmode
Switched-mode
Semiconductor devices
Chapter 1: Introduction
+
–
Devices available to the circuit designer
DT
Resistors
Capacitors
Magnetics
T
s
s
Linearmode
Switched-mode
Semiconductor devices
Signal processing: avoid magnetics
Fundamentals of Power Electronics
8
Chapter 1: Introduction
+
–
Devices available to the circuit designer
DT
Resistors
Capacitors
Magnetics
T
s
s
Linearmode
Switched-mode
Semiconductor devices
Power processing: avoid lossy elements
Fundamentals of Power Electronics
9
Chapter 1: Introduction
Power loss in an ideal switch
Switch closed:
Switch open:
v(t) = 0
+
i(t) = 0
In either event: p(t) = v(t) i(t) = 0
Ideal switch consumes zero power
Fundamentals of Power Electronics
10
i(t)
v(t)
–
Chapter 1: Introduction
A simple dc-dc converter example
I
10A
+
Vg
100V
Dc-dc
converter
+
–
R
5Ω
V
50V
–
Input source: 100V
Output load: 50V, 10A, 500W
How can this converter be realized?
Fundamentals of Power Electronics
11
Chapter 1: Introduction
Dissipative realization
Resistive voltage divider
I
10A
+
Vg
100V
+
–
+
50V –
Ploss = 500W
R
5Ω
V
50V
–
Pin = 1000W
Fundamentals of Power Electronics
Pout = 500W
12
Chapter 1: Introduction
Dissipative realization
Series pass regulator: transistor operates in
active region
+
I
10A
50V –
+
Vg
100V
+
–
linear amplifier
and base driver
Ploss ≈ 500W
Pin ≈ 1000W
Fundamentals of Power Electronics
–+
Vref
R
5Ω
V
50V
–
Pout = 500W
13
Chapter 1: Introduction
Use of a SPDT switch
I
10 A
1
+
Vg
100 V
+
2
+
–
vs(t)
R
–
vs(t)
v(t)
50 V
–
Vg
Vs = DVg
switch
position:
Fundamentals of Power Electronics
DTs
0
(1 – D) Ts
t
1
2
1
14
Chapter 1: Introduction
The switch changes the dc voltage level
vs(t)
switch
position:
Vg
Vs = DVg
D = switch duty cycle
0≤D≤1
DTs
0
(1 – D) Ts
t
Ts = switching period
1
2
1
fs = switching frequency
= 1 / Ts
DC component of vs(t) = average value:
Vs = 1
Ts
Ts
vs(t) dt = DVg
0
Fundamentals of Power Electronics
15
Chapter 1: Introduction
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
R
v(t)
–
Pin ≈ 500 W
–
Ploss small
Pout = 500 W
•
Choose filter cutoff frequency f0 much smaller than switching
frequency fs
•
This circuit is known as the “buck converter”
Fundamentals of Power Electronics
16
Chapter 1: Introduction
Addition of control system
for regulation of output voltage
Power
input
Switching converter
Load
+
vg
+
–
i
v
H(s)
–
Transistor
gate driver
Error
signal
ve
δ(t)
dTs Ts
Fundamentals of Power Electronics
–+
Pulse-width vc G (s)
c
modulator
Compensator
δ
Sensor
gain
Hv
Reference
vref
input
t
17
Chapter 1: Introduction
The boost converter
2
+
L
1
Vg
+
–
C
R
V
–
5Vg
4Vg
V
3Vg
2Vg
Vg
0
0
0.2
0.4
0.6
0.8
1
D
Fundamentals of Power Electronics
18
Chapter 1: Introduction
A single-phase inverter
vs(t)
1
Vg
+
–
+
2
–
+
v(t)
–
2
1
load
“H-bridge”
vs(t)
t
Fundamentals of Power Electronics
19
Modulate switch
duty cycles to
obtain sinusoidal
low-frequency
component
Chapter 1: Introduction
1.2 Several applications of power electronics
Power levels encountered in high-efficiency converters
• less than 1 W in battery-operated portable equipment
• tens, hundreds, or thousands of watts in power supplies for
computers or office equipment
• kW to MW in variable-speed motor drives
• 1000 MW in rectifiers and inverters for utility dc transmission
lines
Fundamentals of Power Electronics
20
Chapter 1: Introduction
A laptop computer power supply system
Inverter
iac(t)
vac(t)
Display
backlighting
Charger
Buck
converter
PWM
Rectifier
ac line input
85–265 Vrms
Fundamentals of Power Electronics
Boost
converter
Lithium
battery
21
Microprocessor
Power
management
Disk
drive
Chapter 1: Introduction
Power system of an earth-orbiting spacecraft
Dissipative
shunt regulator
+
Solar
array
vbus
–
Battery
charge/discharge
controllers
Dc-dc
converter
Dc-dc
converter
Payload
Payload
Batteries
Fundamentals of Power Electronics
22
Chapter 1: Introduction
An electric vehicle power and drive system
ac machine
Inverter
ac machine
Inverter
control bus
battery
µP
system
controller
+
3øac line
Battery
charger
50/60 Hz
DC-DC
converter
vb
–
Low-voltage
dc bus
Inverter
Inverter
ac machine
ac machine
Vehicle
electronics
Variable-frequency
Variable-voltage ac
Fundamentals of Power Electronics
23
Chapter 1: Introduction