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2 | P a g e Sunday, 12 October 2014
Power Electronics Lecturer: Dr. Oday A. Ahmed Lecture Note 1: Introduction to Power Electronics
Definition of Power Electronics
Power Electronics (PE) is power processing
It is an application of electronic circuits to control the power between the source
and the load to change the characteristics (voltage and current magnitude and/or
frequency) of electrical power to suit a particular application.
Power electronics encompasses the use of electronic components, the
application of circuit theory and design techniques, and the development
of analytical tools toward efficient electronic conversion, control, and
conditioning of electric power
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
Goal of Power Electronics
Efficient conversion, conditioning, or processing and control of electric power using solid-state semiconductor devices in order to supply high quality power to the load causing minimum pollution of environment and the utility supply circuit.
Block Diagram of a Power Processor
Figure below show the block diagram of the PE system
Power Electronics can be spilt into:
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Power Electronics Lecturer: Dr. Oday A. Ahmed Lecture Note 1: Introduction to Power Electronics
► Power Circuit: convert input power and deliver to output
► Electronics Circuit: controls the converter by measuring the input
and output voltage and or/current and generates for the power
circuit.
Converter has power switching semiconductor devices and energy storing
elements like inductors and capacitors.
Control is done using electronic switches, capacitors, magnetics, and
control systems.
Resistive elements are avoided in converters because they cause power loss
and reduce efficiency.
Controller switches on/off the switching devices present in the converter.
Example of Power Processor is shown below:
A power processor may have more than one stage of power conversion.
This kind of electrical-to-electrical power conversion is normally effected using systems without moving parts. The systems that carry out these conversions are called electronic power converters or power electronics converters, or simply converters.
Converters are classified by the relationship between input and output:
Power electronic converter that can conversion of electric
power from one to another.
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Power Electronics Lecturer: Dr. Oday A. Ahmed Lecture Note 1: Introduction to Power Electronics
The Power Electronic Converter can be classified into five types as shown in the
table below:
Note: AC to AC conversion can be divided into three types:
► AC voltage controller: which can be used to change the input voltage only at the load demand.
► Cycloconverter: which can be used to change the input AC voltage and frequency to the desired level by the load. This converter consist from one stage.
► Frequency converter: which can be used to change the input AC voltage and frequency to the desired level by the load. This converter consist from two stages to give a wide voltage and frequency range.
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Power Electronics Lecturer: Dr. Oday A. Ahmed Lecture Note 1: Introduction to Power Electronics
Power Electronics Vs Signal Processing
In Power Electronics —
■ The focus is on power conversion at the highest possible efficiency using very small control signals.
■ Semiconductor devices work as switches.
Rectifier
Chopper
Inverter
AC voltage controller,
Cycloconverter
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Power Electronics Lecturer: Dr. Oday A. Ahmed Lecture Note 1: Introduction to Power Electronics
■ Power handled may range from a few watts to several mega-watts.
In Signal Processing —
■ Semiconductor devices generally work as controlled sources in the linear region of their characteristics.
■ The focus is on information processing with minimum loss of information. ■ Power handled will be of the order of few milli-watts or few watts.
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Power Electronics Lecturer: Dr. Oday A. Ahmed Lecture Note 1: Introduction to Power Electronics
NOTE:
In electronic circuits, it is difficult to include magnetic elements into
integrated circuit as they are large in size compared to capacitors and
resistors.
In power circuits, resistors and power switches in linear mode are not used
in power circuit due to significant losses generated by current via these
components, which decreases the efficiency, and cause thermal problems.
NOTE:
Changing the output voltage in the PE converter on the account of current
magnitude.
Exercise: A 50Hz fixed AC input voltage is converted to fixed DC voltage and
then is stepped up to a higher DC voltage level. This voltage is converted again
to the same level of AC input voltage but with a higher output frequency. With
the aid of block diagrams, show the power electronic conversion stages that
required to satisfy the system above.
Power Electronics Applications
It should be mentioned here that power electronics technology has now gained
significant maturity after several decades of the dynamic technology evolution of
power semiconductor devices, converters, pulse width modulation (PWM)
techniques, electrical machines, variable-frequency drives, advanced controls and
computer simulation techniques.
According to the estimate of the Electric Power Research Institute (EPRI) of the
United States, roughly 70% of electrical energy in the United States is now
processed through power electronics, which will eventually expand to 100%.
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Power Electronics Lecturer: Dr. Oday A. Ahmed Lecture Note 1: Introduction to Power Electronics
In the present century, we expect to see the significant impact of power
electronics not only in global industrialization and general energy systems, but
also in energy conservation, renewable energy systems, bulk energy storage and
electric vehicles (EVs) and hybrid electric vehicles (HEVs). The corresponding
impact in solving or mitigating climate change problems is expected to be
significant.
With the changes that occurred in electrical power engineering has resulted in
wide spread of PE in a large spectrum of applications.
Figure below shows how electrical energy generation is distributed for the end-
user, showing transmission, distribution, storage, renewable energy sources and
users. In fact, nowadays PE is a key technology for all those sub-systems, and has
spread in many applications, examples including:
► Residential: heaters, home appliances, electronic lighting, equipment
sources;
► Commercial: heaters, fans, elevators, Uninterruptible Power Supply
(UPS), AC and DC breakers, battery chargers;
► Industrial: pumps, blowers, robots, inductive heaters, welding, machine
drive, portable sources;
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Power Electronics Lecturer: Dr. Oday A. Ahmed Lecture Note 1: Introduction to Power Electronics
► Transportation: electrical and hybrid vehicles, battery chargers, railroad
electric system;
► Utility systems: high voltage direct current, generators, reactive
compensators, interface for photovoltaic, wind, fuel cells systems, Flexible
AC Transmission System (FACTS) equipment;
► Aerospace: sources for spacecrafts, satellites, planes;
► Communication: sources, RF amplifiers, audio-amplifiers.
Global energy concerns will provoke a large interest in the increase of the
conversion efficiency and more application of PE in power quality, distributed
generation, energy conservation, and smart grids. The integration of power and
control circuitry into functional modules will result in systems solutions that are
highly integrated into packaged products that will be both more reliable and
affordable.
Some PE converters that used in various applications are shown in the figures
below:
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Power Electronics Lecturer: Dr. Oday A. Ahmed Lecture Note 1: Introduction to Power Electronics
Typical wind power system with two-sided PWM converters
Typical configuration of photovoltaic system
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Power Electronics Lecturer: Dr. Oday A. Ahmed Lecture Note 1: Introduction to Power Electronics
Typical configuration of Electric Elevator
Typical configuration of Electric Vehicle