Download H5CPE2

Power Electronics 2 (H5CPE2)
Dr Christian Klumpner
Power Electronics, Machines and Control Group
School of Electrical and Electronic Engineering, UoN
Tower Building, 508
email: [email protected]
Module webpage: www.eee.nott.ac.uk/teaching/h5cpe2
Introduction
Line-side Converter
Motor-side Converter
DC
AC
AC
DC
DC-link
Typical AC/DC/AC power conversion (Adjustable Speed Drive)
• AC/DC converter (Rectifier): fixed voltage&frequency to DC voltage
• DC/AC converter (Inverter): DC voltage to variable voltage/variable frequency
Why AC/DC/AC? Electrolytic capacitors (compact and cheap), only unipolar devices
available (transistors)
Operation of rectifier, stress on devices ($), design of filter ($), operation of inverter
Introduction
Pre requisites
Circuit theory and electronics at first year undergraduate level, knowledge of
switching regulators and single phase rectification (controlled and uncontrolled) such
as that provided by module H5BPE1.
Aims and objectives of the module
The aim of this module is to provide an in depth knowledge of power electronics
at a level suitable for final year undergraduate students.
Since power electronics is a rapidly growing subject the course tries to reflect this by
covering the well established and widely used technologies (such as three phase
rectification) as well as more recent developments such as resonant converters.
The increasing importance of power quality is also addressed and various high
power factor utility interface circuits are discussed.
Inverter circuits employing pulse width modulation (PWM) are studied due to their
very widespread use in variable speed drives and power supply systems. High power
(multi-level) converter structures are then discussed.
Throughout the course, emphasis is placed on circuits and their applications
rather than on the technology of power switching devices.
Lecture course syllabus
Lecture
TOPIC
1
Introduction to the course, review of 3-phase supplies and the associated waveforms.
2-3
3-phase uncontrolled (diode) rectifiers. Basic mode of operation and waveforms.
Concept and importance of power factor, displacement factor and distortion factor
applied to power electronic equipment.
Overlap in diode rectifiers, waveforms and calculations. Introduction to thyristor
characteristics.
3-Phase controlled rectification, waveforms and calculations, effect of overlap. Power
4-5
6-7
8-9
10-12
13-15
16-17
18-20
factor calculations. Inversion.
Smoothing circuits. Capacitive smoothing, waveforms and analysis. Inductive
smoothing, waveforms and analysis, discontinuous current. Multiple converter circuits
and HVDC.
Resonant converters, review of hard switching, introduction to soft switching and
different types of resonant switches and converters. Forward converter employing zero
voltage switching, analysis and waveforms.
Single phase inverters, the H-bridge circuit and its operation, applications, quasi-square
wave and PWM techniques for voltage and frequency control, typical frequency spectra,
relationship between AC and DC side harmonics.
3-phase PWM inverters, High power (multi-level) converter structures.
High power factor utility interface circuits, single switch boost converter with input
current wave shaping. PWM rectifiers (pulse converters), control strategies.
Recommendations
Booklist
There are no essential books for this course. However, the following book is
excellent and covers most of the material in this course and the second year power
electronics course.
POWER ELECTRONICS: Converters, Applications and Design (2-ed) by Mohan,
Undeland and Robbins, Wiley publishing
Another book worth looking at for power electronics in general, rather than
specifically this course is:
ELEMENTS OF POWER ELECTRONICS, by Philip T Krein, Oxford University Press
- familiarize yourself with emergency exits (fire alarm) in the building
- don’t get late (not more than 5 minutes) into the classroom
- switch off mobile phones
- attend to the course equipped with a ruler, 4 or more colored pens/markers
- if you have a computer at home, install a simulation pack (PSPICE, Simcad)
Review of 3-phase supplies (1)
Why sinusoidal voltage?
Behavior of passive components
Resistor
Inductor
Capacitor
v
i
R
1
i   v  dt
L
dv
iC
dt
Proportional
Integrative
Rectangular Current
Triangular Current
Derivative
Rectangular Voltage:
Pulse Current
Production, transport & distribution system = Resistors + Inductors + Capacitors
We need to preserve the voltage waveform
Review of 3-phase supplies (2)
We need a supply voltage waveform which preserves its
shape when is derivated or integrated  sinusoidal
Behavior of
passive
components
i
v
R
Proportional
Sinusoidal Voltage
v  E  sin t 
Inductor
Resistor
E  sin  t 
i
R
Sinusoidal Current
i
1
v  dt

L
Integrative
E
cos  t  
L
E



sin   t  
L 
2
i
Sinusoidal Current
Capacitor
iC
dv
dt
Derivative
i  C  E    cos(t )

 C  E    sin(t  )
2
Sinusoidal Current
Review of 3-phase supplies (3)
Assume a “STAR” connected supply
In practice, the 3 voltage sources represent the voltages generated by 3 coils
(physically displaced by 120O from each other) in an AC rotating machine (Alternator)
Line A
A
Phasor diagram
Phase
voltage
Neutral
Line to
line
voltage
VCA
VAN
VAB
VCN
N
VBN
VBC
C
B
“Line to line” voltage
often called “line voltage”
Review of 3-phase supplies (4)
Assuming the peak phase voltage is E (a convention used throughout the course) then:
B lags A by 120O, C lags B
by 120O etc
VAN  E sin(t )
VBN  E sin(t  2 / 3)
VCN  E sin(t  4 / 3)  E sin(t  2 / 3)
This is for “phase sequence” A-B-C, A-C-B is also possible – we will always assume
A-B-C
Drawing a phasor diagram and converting back to time functions, it is easy to show
that the line voltages are given by:
VAB  3E sin(t   / 6)
VBC  3E sin(t   / 2)
VCA  3E sin(t  5 / 6)
3-phase supplies are specified using the RMS line voltage. Hence “a 415V, 50Hz,
3-phase system” means:
3E
 415V,
2
  100
Review of 3-phase supplies (5)
Why three-phase voltage systems (120O displaced)?
EI
p  v  i  E  sin  t   I sin  t    
sin  2 t     cos( ) 
2
Displacement angle = 0O
Displacement angle = 90O
Necessity to deliver - smooth power (require less filtering)
- smooth torque in a motor (less mechanical stress, noise)