BEE 4101: POWER ELECTRONICS

Introduction

Chapter 1

1
Lecture Outline

2
 Course Outline
course outline

Power Electronic Devices Power Converters

• Diodes • Uncontrolled Rectifiers
• Power Transistors • Controlled rectifiers
• IGBTs • Inverters
• etc. • Converters
• Application circuits

3
 What is power electronics?
1) Definition
• Power Electronics: is the electronics applied to conversion and
control of electric power.

Electric
Power Power
Power
input output
Converter

Control
input
4
 What is power electronics?
A more exact explanation:
• The primary task of power electronics is to process and control
the flow of electric energy by supplying voltages and currents in
a form that is optimally suited for user loads.

5
 Prerequisites
• Power electronics incorporates concepts
from the fields of
– Analog circuits
– Electronic devices
– Control systems
– Power systems
– Magnetics
– Electric machines
– Numerical simulation

6
 Scope
• It is not possible to build practical computers, cell phones, personal
data devices, cars, airplanes, industrial processes, and other
everyday products without power electronics.

• Alternative energy systems such as wind generators, solar power,

fuel cells, and others require power electronics to function.

• Technology advances such as electric and hybrid vehicles, laptop

computers, microwave ovens, flat-panel displays, LED lighting, and
hundreds of other innovations were not possible until advances in
power electronics enabled their implementation.

• Although no one can predict the future, it is certain that power

electronics will be at the heart of fundamental energy innovations.7
The interdisciplinary nature
Bimal’s description

Electronics Power

学
Devices,circuits Static & rotating
power equipment
Power
Electronics

学
Continuous,
discrete

连Control
续、离

Power electronics is the interface

between electronics and power.
8
 • Relation with multiple disciplines

Systems& Signal
Circuit Ct Control theory processing
theory
Control Simulation &
computing
Electric theory Power
machines electronics electronics

electr oni
Power Solid state
systems cs physics
Electromagnetics
electr
Power electronics is currently the most active discipline in
electric power engineering.
9
 Applications: Electric Vehicle
Tesla Model S

Functions of the power electronics:

1. Convert the DC battery voltage to
the variable AC required to drive
the AC motor
• 240 V battery
• Variable-frequency, variable-
voltage AC drives the motor
• AC motor propels the rear axle
• Up to 330 kW (acceleration)
• Up to 60 kW regenerative braking

2. Control charging of the battery

• Interface to 240 V 50 Hz 1φ 100 A circuit in
garage.
• Control AC current waveform to be sinusoidal,
unity power factor.
• Control charging of battery to maximize life. 10
 Applications: Hybrid Vehicles
Prius

Power Electronics Module:

• Convert the DC battery voltage to the
variable AC required to drive the AC
motor.
• Includes dc-dc boost converter and
dc-3φ ac inverter
• Control system can operate in all-
electric mode or in hybrid gas+electric
mode
• Partial-power electronics

Under the hood:

Gas engine
Power electronics module
11
 Applications: Variable-Speed Wind Turbine Systems

• AC generator produces “wild ac”:

frequency and amplitude change
with wind speed.
• Utility operates with constant
frequency (50 Hz) constant voltage
ac.
• Power electronics changes the
frequency and voltage, and also
implements control functions
• Cycloconverter, or
• DC link system: rectifier, boost
dc-dc, inverter

12
 Applications: Photovoltaic Solar Power Systems

Grid-tied solar: inverter converts

dc of solar panels to ac for grid.

Stand-alone solar: dc-dc converter

interfaces solar panels to batteries

Buck-boost DC
PV + Transformer +
converter Output
input (noninverting) 1:8
48 V 400 V to
12- Zero-voltage inverter
100 V – switching –

Controller

13
A standalone photovoltaic power
system

The system constructed in ECEN 4517/5517 Power

Electronics and Photovoltaic Systems Laboratory

14
 Applications: Computer power supply systems

Inverter Display
backlighting

iac(t) Charger
Buck Microprocessor
vac(t) PWM converter
Rectifier Power
management

ac line input Boost Disk

85–265 Vrms Lithium
battery converter drive

Laptop power system

iPhone power system and charger

15
 Trends in Power Supplies
• Two distinct trends drive electronic power supplies, one
of the major classes of power electronic circuits.

– At one end, microprocessors, memory chips, and other

advanced digital circuits require increasing power levels and
increasing performance at very low voltage.

– At the other end, the explosive growth of portable devices

with rechargeable batteries. The power supplies for these
devices and for other consumer products must be cheap and
efficient.

16
 Trends in Power Supplies
• In the past, bulky “linear” power supplies were designed
with transformers and rectifiers from the ac line
frequency to provide dc voltages for electronic circuits.

• In a well-designed power electronics arrangement

today, called a switch-mode power supply, an ac source
from a wall outlet is rectified without direct
transformation.

• The resulting high dc voltage is converted through a dc–

dc converter to the 1, 3, 5, and 12V, or other levels
required.
17
 Trends in Power Supplies
• A personal computer commonly requires multiple
voltage levels. E.g. 3.3-V, 5-V, 12-V supplies, additional
levels, and a separate converter for 1-V delivery to the
microprocessor.

• Only a switch-mode supply can support such complex

requirements with acceptable costs.

18
 Key Characteristics of Power Converter
• All power electronic circuits manage the flow of electrical
energy between an electrical source and a load.
• The parts in a circuit must direct electrical flows, not impede.

• The function of the power converter in the middle is to control

the energy flow between a source and a load.
• A crucial point emerges: to build a power converter, we should
consider only lossless components.
• A realistic converter design must approach 100% efficiency.
19
Devices Available to the circuit designer

20
Devices available to the circuit
designer

Signal processing: avoid magnetics

21
Devices available to the circuit
designer

Power processing: avoid lossy elements

22
 Power loss in an ideal switch

• Switch closed: v(t) = 0 1

• Switch open: i(t) = 0 i
+
• In either event: p(t) = v(t) i(t) = 0
v
• Ideal switch consumes zero power
–
0

23
 Power Electronic Devices
• The power Electronic devices provides the
utility of switching.

• The flow of power through these devices can

be controlled via small currents.

• Power electronics devices differ from ordinary

electronics devices in terms of their
characteristics.
24
 Power Electronic Devices
• Power Semiconductor Devices can be
classified into three groups according to their
degree of controllability.

– Diodes (on and off controlled by power circuit)

– Thyristors (latched on by control signal but must
be turned off by power circuit)
– Controllable Switches (turned on and off by
control signal)

25
 Conversion Examples
• Single-Switch Circuits
– Consider the circuit shown in figure.
– It contains an ac source, a switch, and a resistive load.
– It is a simple but complete power electronic system.

• What if the switch is turned on whenever Vac >0, and

turned off otherwise?
26