UNIT – I
Power semiconductor devices and commutation
circuits
Introduction to power electronics:
Power Electronics is a field which combines Power (electric power), Electronics and Control systems.
Power engineering deals with the static and rotating power equipment for the generation, transmission
and distribution of electric power. Electronics deals with the study of solid state semiconductor power
devices and circuits for Power conversion to meet the desired control objectives (to control the output
voltage and output power). Power electronics may be defined as the subject of applications of solid state
power semiconductor devices (Thyristors) for the control and conversion of electric power. Power
electronics deals with the study and design of Thyristorised power controllers for variety of application
like Heat control, Light/Illumination control, Motor control - AC/DC motor drives used in industries,
High voltage power supplies, Vehicle propulsion systems, High voltage direct current (HVDC)
transmission.
Power Electronics refers to the process of controlling the flow of current and voltage and converting it to
a form that is suitable for user loads. The most desirable power electronic system is one whose efficiency
and reliability is 100%.
Take a look at the following block diagram. It shows the components of a Power Electronic system and
how they are interlinked.
Figure: 1.1. Block diagram of DC power supply
2|Page
,A power electronic system converts electrical energy from one form to another and ensures the
following is achieved −
Maximum efficiency
Maximum reliability
Maximum availability
Minimum cost
Least weight
Small size
Applications of Power Electronics are classified into two types − Static Applications and Drive
Applications.
Static Applications
This utilizes moving and/or rotating mechanical parts such as welding, heating, cooling, and electro-
plating and DC power.
DC Power Supply
Figure: 1.2. Block diagram of DC power supply
Drive Applications
Drive applications have rotating parts such as motors. Examples include compressors, pumps, conveyer
belts and air conditioning systems.
Air Conditioning System
Power electronics is extensively used in air conditioners to control elements such as compressors. A
schematic diagram that shows how power electronics is used in air conditioners is shown below.
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, Figure: 1.3. Block diagram of Air Conditioning System
Power electronic applications
Commercial applications Heating Systems Ventilating, Air Conditioners, Central Refrigeration,
Lighting, Computers and Office equipments, Uninterruptible Power Supplies (UPS), Elevators, and
Emergency Lamps
Domestic applications Cooking Equipments, Lighting, Heating, Air Conditioners, Refrigerators &
Freezers, Personal Computers, Entertainment Equipments, UPS
Industrial applications Pumps, compressors, blowers and fans Machine tools, arc furnaces, induction
furnaces, lighting control circuits, industrial lasers, induction heating, welding equipments
Aerospace applications Space shuttle power supply systems, satellite power systems, aircraft power
systems.
Telecommunications Battery chargers, power supplies (DC and UPS), mobile cell phone battery
chargers
Transportation Traction control of electric vehicles, battery chargers for electric vehicles, electric
locomotives, street cars, trolley buses, automobile electronics including engine controls
Utility systems High voltage DC transmission (HVDC), static VAR compensation (SVC), Alternative
energy sources (wind, photovoltaic), fuel cells, energy storage systems, induced draft fans and boiler feed
water pumps
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, Types of power electronic converters
1. Rectifiers (AC to DC converters): These converters convert constant ac voltage to variable dc
output voltage.
2. Choppers (DC to DC converters): Dc chopper converts fixed dc voltage to a controllable dc
output voltage.
3. Inverters (DC to AC converters): An inverter converts fixed dc voltage to a variable ac output
voltage.
4. AC voltage controllers: These converters converts fixed ac voltage to a variable ac output voltage
at same frequency.
5. Cycloconverters: These circuits convert input power at one frequency to output power at a
different frequency through one stage conversion.
Power semiconductor devices
i. Power Diodes.
ii. Power transistors (BJT's).
iii. Power MOSFETS.
iv. IGBT's.
v. Thyristors
Thyristors are a family of p-n-p-n structured power semiconductor switching devices
Power diodes
Power diodes are made of silicon p-n junction with two terminals, anode and cathode. P-N junction is
formed by alloying, diffusion and epitaxial growth. Modern techniques in diffusion and epitaxial
processes permit desired device characteristics. The diodes have the following advantages High
mechanical and thermal reliability High peak inverse voltage Low reverse current Low forward
voltage drop High efficiency Compactness.
Power transistors
Power transistors are devices that have controlled turn-on and turn-off characteristics. These devices
are used a switching devices and are operated in the saturation region resulting in low on-state voltage
drop. They are turned on when a current signal is given to base or control terminal. The transistor
remains on so long as the control signal is present. The switching speed of modern transistors is much
higher than that of thyristors and is used extensively in dc-dc and dc-ac converters. However their
5|Page
Power semiconductor devices and commutation
circuits
Introduction to power electronics:
Power Electronics is a field which combines Power (electric power), Electronics and Control systems.
Power engineering deals with the static and rotating power equipment for the generation, transmission
and distribution of electric power. Electronics deals with the study of solid state semiconductor power
devices and circuits for Power conversion to meet the desired control objectives (to control the output
voltage and output power). Power electronics may be defined as the subject of applications of solid state
power semiconductor devices (Thyristors) for the control and conversion of electric power. Power
electronics deals with the study and design of Thyristorised power controllers for variety of application
like Heat control, Light/Illumination control, Motor control - AC/DC motor drives used in industries,
High voltage power supplies, Vehicle propulsion systems, High voltage direct current (HVDC)
transmission.
Power Electronics refers to the process of controlling the flow of current and voltage and converting it to
a form that is suitable for user loads. The most desirable power electronic system is one whose efficiency
and reliability is 100%.
Take a look at the following block diagram. It shows the components of a Power Electronic system and
how they are interlinked.
Figure: 1.1. Block diagram of DC power supply
2|Page
,A power electronic system converts electrical energy from one form to another and ensures the
following is achieved −
Maximum efficiency
Maximum reliability
Maximum availability
Minimum cost
Least weight
Small size
Applications of Power Electronics are classified into two types − Static Applications and Drive
Applications.
Static Applications
This utilizes moving and/or rotating mechanical parts such as welding, heating, cooling, and electro-
plating and DC power.
DC Power Supply
Figure: 1.2. Block diagram of DC power supply
Drive Applications
Drive applications have rotating parts such as motors. Examples include compressors, pumps, conveyer
belts and air conditioning systems.
Air Conditioning System
Power electronics is extensively used in air conditioners to control elements such as compressors. A
schematic diagram that shows how power electronics is used in air conditioners is shown below.
3|Page
, Figure: 1.3. Block diagram of Air Conditioning System
Power electronic applications
Commercial applications Heating Systems Ventilating, Air Conditioners, Central Refrigeration,
Lighting, Computers and Office equipments, Uninterruptible Power Supplies (UPS), Elevators, and
Emergency Lamps
Domestic applications Cooking Equipments, Lighting, Heating, Air Conditioners, Refrigerators &
Freezers, Personal Computers, Entertainment Equipments, UPS
Industrial applications Pumps, compressors, blowers and fans Machine tools, arc furnaces, induction
furnaces, lighting control circuits, industrial lasers, induction heating, welding equipments
Aerospace applications Space shuttle power supply systems, satellite power systems, aircraft power
systems.
Telecommunications Battery chargers, power supplies (DC and UPS), mobile cell phone battery
chargers
Transportation Traction control of electric vehicles, battery chargers for electric vehicles, electric
locomotives, street cars, trolley buses, automobile electronics including engine controls
Utility systems High voltage DC transmission (HVDC), static VAR compensation (SVC), Alternative
energy sources (wind, photovoltaic), fuel cells, energy storage systems, induced draft fans and boiler feed
water pumps
4|Page
, Types of power electronic converters
1. Rectifiers (AC to DC converters): These converters convert constant ac voltage to variable dc
output voltage.
2. Choppers (DC to DC converters): Dc chopper converts fixed dc voltage to a controllable dc
output voltage.
3. Inverters (DC to AC converters): An inverter converts fixed dc voltage to a variable ac output
voltage.
4. AC voltage controllers: These converters converts fixed ac voltage to a variable ac output voltage
at same frequency.
5. Cycloconverters: These circuits convert input power at one frequency to output power at a
different frequency through one stage conversion.
Power semiconductor devices
i. Power Diodes.
ii. Power transistors (BJT's).
iii. Power MOSFETS.
iv. IGBT's.
v. Thyristors
Thyristors are a family of p-n-p-n structured power semiconductor switching devices
Power diodes
Power diodes are made of silicon p-n junction with two terminals, anode and cathode. P-N junction is
formed by alloying, diffusion and epitaxial growth. Modern techniques in diffusion and epitaxial
processes permit desired device characteristics. The diodes have the following advantages High
mechanical and thermal reliability High peak inverse voltage Low reverse current Low forward
voltage drop High efficiency Compactness.
Power transistors
Power transistors are devices that have controlled turn-on and turn-off characteristics. These devices
are used a switching devices and are operated in the saturation region resulting in low on-state voltage
drop. They are turned on when a current signal is given to base or control terminal. The transistor
remains on so long as the control signal is present. The switching speed of modern transistors is much
higher than that of thyristors and is used extensively in dc-dc and dc-ac converters. However their
5|Page
