This document provides an overview of power electronics topics including semiconductor devices, controlled rectifiers, DC choppers, inverters, and AC choppers. It discusses various semiconductor devices used in power electronics like power diodes, transistors, BJTs, MOSFETs, IGBTs, SITs, thyristors, SCRs, TRIACs, and GTOs. It covers the structures, characteristics, and applications of these devices. It also compares different semiconductor devices and discusses switching and safe operating areas.
The document discusses insulated gate bipolar transistors (IGBTs). It describes IGBTs as having MOSFET-like input characteristics and bipolar junction transistor-like output characteristics. The document summarizes IGBT structure, working principles, characteristics including transfer and switching characteristics, and methods of connecting IGBTs in series and parallel. It also discusses protection of IGBTs from overvoltage, overcurrent, high dv/dt, and overheating.
The inverter is a static device. It can convert one form of electrical power into other forms of electrical power. But it cannot generate electrical power. Hence the inverter is a converter, not a generator.
A chopper is a static device that uses pulse width modulation or variable frequency control to obtain a variable DC output voltage from a constant DC input voltage. Choppers are widely used to control motors and regenerate braking energy. The document describes different types of choppers - Type A chops the input voltage to produce positive output voltage and current. Type B allows regenerative braking by producing negative current. Type C operates in both quadrants while Type D's output voltage can be positive or negative.
This article discusses different power electronics devices that are in use like power diodes, power thyristors, power transistors, IGBT, GTO, IGCT and others. This article will give a basic view of these devices and their operations.
This ppt provides a brief overview on thyristors commonly known as SCRs. V- I characteristics curve, triggering methods, protection methods, series and parallel operations of SCRs, applications are discussed in this slide.
The document discusses insulated gate bipolar transistors (IGBTs). It describes IGBTs as having MOSFET-like input characteristics and bipolar junction transistor-like output characteristics. The document summarizes IGBT structure, working principles, characteristics including transfer and switching characteristics, and methods of connecting IGBTs in series and parallel. It also discusses protection of IGBTs from overvoltage, overcurrent, high dv/dt, and overheating.
The inverter is a static device. It can convert one form of electrical power into other forms of electrical power. But it cannot generate electrical power. Hence the inverter is a converter, not a generator.
A chopper is a static device that uses pulse width modulation or variable frequency control to obtain a variable DC output voltage from a constant DC input voltage. Choppers are widely used to control motors and regenerate braking energy. The document describes different types of choppers - Type A chops the input voltage to produce positive output voltage and current. Type B allows regenerative braking by producing negative current. Type C operates in both quadrants while Type D's output voltage can be positive or negative.
This article discusses different power electronics devices that are in use like power diodes, power thyristors, power transistors, IGBT, GTO, IGCT and others. This article will give a basic view of these devices and their operations.
This ppt provides a brief overview on thyristors commonly known as SCRs. V- I characteristics curve, triggering methods, protection methods, series and parallel operations of SCRs, applications are discussed in this slide.
The MOSFET is a four-terminal semiconductor device used for switching and amplifying electronic signals. It comes in two basic forms, P-channel and N-channel, and two modes, depletion and enhancement. MOSFETs exhibit three operating regions - cut-off, where no current flows; ohmic or linear, where current increases with drain-source voltage; and saturation, where current reaches a maximum. MOSFETs are voltage-controlled, unipolar devices that can switch or amplify depending on their operating region.
Electrical fault is the deviation of voltages and currents from nominal values or states. Under normal operating conditions, power system equipment or lines carry normal voltages and currents which results in a safer operation of the system.
This document discusses different types of integrated circuit voltage regulators. It describes fixed voltage regulators like the 78XX and 79XX series, which provide positive and negative fixed output voltages, respectively. Adjustable voltage regulators like the LM317 allow the output voltage to be varied. Switching regulators like the MC1723 and LM723 are also covered. Key features and applications of IC voltage regulators are explained, along with basic regulator circuits and their operating principles. Performance parameters like line and load regulation are defined.
Static relays use electronic components like semiconductors instead of mechanical parts to detect faults and operate. They have components like rectifiers to convert AC to DC, level detectors to compare values to thresholds, and amplifiers and output devices to trigger trips. The document discusses the components, types, and applications of various static relays like overcurrent, directional, differential, distance and instantaneous relays used in power system protection.
An inverter is a device that converts DC power from batteries into AC power. It allows appliances that run on AC power to operate from a DC power source. There are different types of inverters based on their output waveform: square wave, modified sine wave, and pure sine wave. Square wave inverters are the cheapest but produce a less stable output. Modified sine wave inverters produce a three-step waveform and are suitable for basic appliances. Pure sine wave inverters have the best waveform quality but are the most expensive. Inverters are commonly used in UPS systems, with solar panels, for backup power, and in HVDC transmission.
Transmission lines have four parameters that characterize them: resistance, inductance, capacitance, and conductance. These distributed parameters determine the power carrying capacity and voltage drop across the line. Short lines only consider the series resistance and inductance, while medium and long lines must also account for the distributed shunt capacitance. The resistance of overhead transmission lines is affected by factors like skin effect, temperature, bundling of conductors, and proximity effect between phases.
This document discusses protection methods for SCRs, including overvoltage, overcurrent, dv/dt, and di/dt protection. It explains that dv/dt protection is needed to prevent false triggering of the SCR from high rates of change of the anode-cathode voltage. This is achieved using an RC snubber network across the SCR. It also notes that SCRs generate heat from current conduction, so a heatsink is required to dissipate this heat and prevent failure.
This document outlines the syllabus for a Power Electronics course. It covers key topics like power semiconductor switches, AC-DC converters, DC-DC converters, AC-DC inverters, and AC-AC converters. Specific units will discuss power switching devices, phase controlled rectifiers, choppers/SMPS, inverters, and voltage regulators. The course aims to develop skills for designing power converters for drive and power system applications and to understand commercial and industrial power electronics applications.
The document discusses different types of choppers, which are static devices that produce a variable DC voltage from a constant DC source. It describes step-down and step-up choppers and the principles of their operation. Various chopper control methods and classifications are covered, including Class A through Class E choppers and their characteristics. Load and source inductance effects are also summarized.
Nowadays, it is very important to maintain voltage level. Controlling of that voltage is also important. This Presentation contains methods of voltage control.
The document discusses the construction and operating principles of an Insulated Gate Bipolar Transistor (IGBT). It describes how the IGBT was developed from earlier power semiconductor devices like the IGT and COMFET. The IGBT cell contains a parasitic thyristor structure that must be controlled to prevent latchup. In operation, the IGBT behaves like a MOSFET for gate control and can block high voltages while supporting medium frequencies and current levels, making it suitable for replacing bipolar junction transistors in applications like motor drives and power supplies.
Inverter is a device which convert a DC input supply voltage into symmetric AC voltage of desired magnitude and frequency at the output side. It is also know as DC-AC converter.
Ideal and practical inverter have sinusoidal and no-sinusoidal waveforms at output respectively.
If the input dc is a voltage source, the inverter is called a Voltage Source Inverter (VSI). One can similarly think of a Current Source Inverter (CSI), where the input to the circuit is a current source. The VSI circuit has direct control over ‘output (ac) voltage’ whereas the CSI directly controls ‘output (ac) current.
Inverter is a device which convert a DC input supply voltage into symmetric AC voltage of desired magnitude and frequency at the output side. It is also know as DC-AC converter.
Ideal and practical inverter have sinusoidal and no-sinusoidal waveforms at output respectively.
If the input dc is a voltage source, the inverter is called a Voltage Source Inverter (VSI). One can similarly think of a Current Source Inverter (CSI), where the input to the circuit is a current source. The VSI circuit has direct control over ‘output (ac) voltage’ whereas the CSI directly controls ‘output (ac) current.
1. A document discusses fault analysis in power systems, including symmetrical and unsymmetrical faults. Common fault causes include insulation failure, mechanical issues, over/under voltage, and accidents.
2. Key concepts are introduced, such as different types of reactance (subtransient, transient, steady-state) and how fault current transients have both AC and DC components.
3. Two examples are provided to demonstrate how to calculate fault current and MVA for given systems using per unit calculations and reactance values.
Thyristors are semiconductor devices that act as electrically controlled switches. The document discusses the thyristor family including SCRs, TRIACs, DIACs, and GTOs. It focuses on SCRs, providing details on their construction, V-I characteristics, and triggering methods like gate triggering. SCRs are used in applications like AC-DC converters and inverters as high power switches. TRIACs and DIACs are also briefly introduced.
Introduction to Power Electronics, Power Diodes, Thyristors and Power Transistors. Different types of Power Converters, Applications of Power Electronics and Peripheral effects.
The document discusses synchronous generators and their operation. It covers:
- The two reaction theory which separates the armature mmf into direct and quadrature axis components.
- How phasor diagrams can be used to represent the direct and quadrature axis reactances (Xd and Xq).
- The slip test method to measure Xd and Xq by taking voltage-to-current ratios with the armature mmf aligned to each axis.
- Important cautions for the slip test including keeping slip extremely low to avoid errors from damper windings or open circuit voltages reaching dangerous levels.
This document discusses cycloconverters, which are devices that convert input power at one frequency to output power at a different frequency in a single stage. It describes the types of cycloconverters including step up, step down, single phase to single phase, and three phase. It provides details on the principles and operation of single phase cycloconverters including mid-point and bridge types for step up and step down conversion. It also discusses three phase to single phase and three phase to three phase cycloconverters. Applications mentioned include speed control drives and induction heating.
Thyristor devices like silicon controlled rectifiers (SCRs) can control large amounts of power using very low control power. SCRs are 4-layer devices turned on by a positive gate signal when the anode is positive to the cathode. Commonly used thyristor families include SCRs, GTOs, triacs, diacs, SCSs, and MCTs. SCRs are widely used in power electronics due to their fast switching, small size, and high voltage/current ratings. SCRs have three terminals and require interrupting the anode current to turn off. Thyristors can be connected in series and parallel to increase voltage and current ratings using techniques like equal
The document discusses various types of power semiconductor devices used in power electronics. It covers power diodes, power transistors including BJTs, MOSFETs, IGBTs, and SITs. It also discusses thyristors such as SCRs, triacs, GTOs, and their characteristics. The key devices covered in detail include their structure, V-I characteristics, switching characteristics, and applications. Comparisons are made between different power devices like BJTs and MOSFETs, and IGBTs. Triggering methods for thyristors such as forward voltage, gate, dv/dt, temperature and light triggering are also summarized.
The document provides information about various power semiconductor devices. It begins with an overview of topics covered, which include semiconductor devices, controlled rectifiers, DC choppers, inverters, and AC choppers. It then discusses numerous power semiconductor devices in detail, including their structures, characteristics, and applications. Devices covered include power diodes, power transistors (BJTs, MOSFETs, IGBTs, SITs), thyristors (SCRs, triacs, GTOs, SITHs, MCTs), and provides comparisons of their performance and specifications. The document aims to educate about the operating principles and applications of important power electronics components.
The MOSFET is a four-terminal semiconductor device used for switching and amplifying electronic signals. It comes in two basic forms, P-channel and N-channel, and two modes, depletion and enhancement. MOSFETs exhibit three operating regions - cut-off, where no current flows; ohmic or linear, where current increases with drain-source voltage; and saturation, where current reaches a maximum. MOSFETs are voltage-controlled, unipolar devices that can switch or amplify depending on their operating region.
Electrical fault is the deviation of voltages and currents from nominal values or states. Under normal operating conditions, power system equipment or lines carry normal voltages and currents which results in a safer operation of the system.
This document discusses different types of integrated circuit voltage regulators. It describes fixed voltage regulators like the 78XX and 79XX series, which provide positive and negative fixed output voltages, respectively. Adjustable voltage regulators like the LM317 allow the output voltage to be varied. Switching regulators like the MC1723 and LM723 are also covered. Key features and applications of IC voltage regulators are explained, along with basic regulator circuits and their operating principles. Performance parameters like line and load regulation are defined.
Static relays use electronic components like semiconductors instead of mechanical parts to detect faults and operate. They have components like rectifiers to convert AC to DC, level detectors to compare values to thresholds, and amplifiers and output devices to trigger trips. The document discusses the components, types, and applications of various static relays like overcurrent, directional, differential, distance and instantaneous relays used in power system protection.
An inverter is a device that converts DC power from batteries into AC power. It allows appliances that run on AC power to operate from a DC power source. There are different types of inverters based on their output waveform: square wave, modified sine wave, and pure sine wave. Square wave inverters are the cheapest but produce a less stable output. Modified sine wave inverters produce a three-step waveform and are suitable for basic appliances. Pure sine wave inverters have the best waveform quality but are the most expensive. Inverters are commonly used in UPS systems, with solar panels, for backup power, and in HVDC transmission.
Transmission lines have four parameters that characterize them: resistance, inductance, capacitance, and conductance. These distributed parameters determine the power carrying capacity and voltage drop across the line. Short lines only consider the series resistance and inductance, while medium and long lines must also account for the distributed shunt capacitance. The resistance of overhead transmission lines is affected by factors like skin effect, temperature, bundling of conductors, and proximity effect between phases.
This document discusses protection methods for SCRs, including overvoltage, overcurrent, dv/dt, and di/dt protection. It explains that dv/dt protection is needed to prevent false triggering of the SCR from high rates of change of the anode-cathode voltage. This is achieved using an RC snubber network across the SCR. It also notes that SCRs generate heat from current conduction, so a heatsink is required to dissipate this heat and prevent failure.
This document outlines the syllabus for a Power Electronics course. It covers key topics like power semiconductor switches, AC-DC converters, DC-DC converters, AC-DC inverters, and AC-AC converters. Specific units will discuss power switching devices, phase controlled rectifiers, choppers/SMPS, inverters, and voltage regulators. The course aims to develop skills for designing power converters for drive and power system applications and to understand commercial and industrial power electronics applications.
The document discusses different types of choppers, which are static devices that produce a variable DC voltage from a constant DC source. It describes step-down and step-up choppers and the principles of their operation. Various chopper control methods and classifications are covered, including Class A through Class E choppers and their characteristics. Load and source inductance effects are also summarized.
Nowadays, it is very important to maintain voltage level. Controlling of that voltage is also important. This Presentation contains methods of voltage control.
The document discusses the construction and operating principles of an Insulated Gate Bipolar Transistor (IGBT). It describes how the IGBT was developed from earlier power semiconductor devices like the IGT and COMFET. The IGBT cell contains a parasitic thyristor structure that must be controlled to prevent latchup. In operation, the IGBT behaves like a MOSFET for gate control and can block high voltages while supporting medium frequencies and current levels, making it suitable for replacing bipolar junction transistors in applications like motor drives and power supplies.
Inverter is a device which convert a DC input supply voltage into symmetric AC voltage of desired magnitude and frequency at the output side. It is also know as DC-AC converter.
Ideal and practical inverter have sinusoidal and no-sinusoidal waveforms at output respectively.
If the input dc is a voltage source, the inverter is called a Voltage Source Inverter (VSI). One can similarly think of a Current Source Inverter (CSI), where the input to the circuit is a current source. The VSI circuit has direct control over ‘output (ac) voltage’ whereas the CSI directly controls ‘output (ac) current.
Inverter is a device which convert a DC input supply voltage into symmetric AC voltage of desired magnitude and frequency at the output side. It is also know as DC-AC converter.
Ideal and practical inverter have sinusoidal and no-sinusoidal waveforms at output respectively.
If the input dc is a voltage source, the inverter is called a Voltage Source Inverter (VSI). One can similarly think of a Current Source Inverter (CSI), where the input to the circuit is a current source. The VSI circuit has direct control over ‘output (ac) voltage’ whereas the CSI directly controls ‘output (ac) current.
1. A document discusses fault analysis in power systems, including symmetrical and unsymmetrical faults. Common fault causes include insulation failure, mechanical issues, over/under voltage, and accidents.
2. Key concepts are introduced, such as different types of reactance (subtransient, transient, steady-state) and how fault current transients have both AC and DC components.
3. Two examples are provided to demonstrate how to calculate fault current and MVA for given systems using per unit calculations and reactance values.
Thyristors are semiconductor devices that act as electrically controlled switches. The document discusses the thyristor family including SCRs, TRIACs, DIACs, and GTOs. It focuses on SCRs, providing details on their construction, V-I characteristics, and triggering methods like gate triggering. SCRs are used in applications like AC-DC converters and inverters as high power switches. TRIACs and DIACs are also briefly introduced.
Introduction to Power Electronics, Power Diodes, Thyristors and Power Transistors. Different types of Power Converters, Applications of Power Electronics and Peripheral effects.
The document discusses synchronous generators and their operation. It covers:
- The two reaction theory which separates the armature mmf into direct and quadrature axis components.
- How phasor diagrams can be used to represent the direct and quadrature axis reactances (Xd and Xq).
- The slip test method to measure Xd and Xq by taking voltage-to-current ratios with the armature mmf aligned to each axis.
- Important cautions for the slip test including keeping slip extremely low to avoid errors from damper windings or open circuit voltages reaching dangerous levels.
This document discusses cycloconverters, which are devices that convert input power at one frequency to output power at a different frequency in a single stage. It describes the types of cycloconverters including step up, step down, single phase to single phase, and three phase. It provides details on the principles and operation of single phase cycloconverters including mid-point and bridge types for step up and step down conversion. It also discusses three phase to single phase and three phase to three phase cycloconverters. Applications mentioned include speed control drives and induction heating.
Thyristor devices like silicon controlled rectifiers (SCRs) can control large amounts of power using very low control power. SCRs are 4-layer devices turned on by a positive gate signal when the anode is positive to the cathode. Commonly used thyristor families include SCRs, GTOs, triacs, diacs, SCSs, and MCTs. SCRs are widely used in power electronics due to their fast switching, small size, and high voltage/current ratings. SCRs have three terminals and require interrupting the anode current to turn off. Thyristors can be connected in series and parallel to increase voltage and current ratings using techniques like equal
The document discusses various types of power semiconductor devices used in power electronics. It covers power diodes, power transistors including BJTs, MOSFETs, IGBTs, and SITs. It also discusses thyristors such as SCRs, triacs, GTOs, and their characteristics. The key devices covered in detail include their structure, V-I characteristics, switching characteristics, and applications. Comparisons are made between different power devices like BJTs and MOSFETs, and IGBTs. Triggering methods for thyristors such as forward voltage, gate, dv/dt, temperature and light triggering are also summarized.
The document provides information about various power semiconductor devices. It begins with an overview of topics covered, which include semiconductor devices, controlled rectifiers, DC choppers, inverters, and AC choppers. It then discusses numerous power semiconductor devices in detail, including their structures, characteristics, and applications. Devices covered include power diodes, power transistors (BJTs, MOSFETs, IGBTs, SITs), thyristors (SCRs, triacs, GTOs, SITHs, MCTs), and provides comparisons of their performance and specifications. The document aims to educate about the operating principles and applications of important power electronics components.
The document discusses various types of power semiconductor devices used in power electronics. It covers power diodes, power transistors including BJTs, MOSFETs, IGBTs, and SITs. It also discusses thyristors such as SCRs, triacs, GTOs, and their characteristics. The key devices covered in detail include their structure, V-I characteristics, switching characteristics, and applications. Comparisons are made between different power devices like BJTs and MOSFETs, and IGBTs. Triggering methods for thyristors such as forward voltage, gate, dv/dt, temperature and light triggering are also summarized.
The document discusses various power semiconductor devices. It covers topics such as power diodes, power transistors including BJTs, MOSFETs, IGBTs, and SITs. For each device type, it discusses the basic structure, V-I characteristics, and applications. It also covers thyristors such as SCR, TRIAC, GTO, and their working principles including forward and reverse blocking modes, and triggering methods. The document contains detailed information on the structural features and operating characteristics of various important power semiconductor devices.
The document provides information about various power semiconductor devices. It begins with an overview of topics covered, which include semiconductor devices, controlled rectifiers, DC choppers, inverters, and AC choppers. It then discusses numerous power semiconductor devices in detail, including their structures, characteristics, and applications. The key devices covered are power diodes, power transistors (BJTs, MOSFETs, IGBTs, SITs), thyristors (SCRs, triacs, GTOs), and their switching behaviors. Comparisons are made between the performance and ratings of different power devices.
The document discusses various types of power semiconductor devices used in power electronics. It covers power diodes, power transistors including BJTs, MOSFETs, IGBTs, and SITs. It also discusses thyristors such as SCRs, triacs, GTOs, and their characteristics. The document provides details on the structure, working, V-I characteristics and applications of these different power semiconductor devices.
This document provides an overview of power semiconductor devices taught in a course at S.M.D.R. Government Polytechnic in Dhule, India. It covers various topics including semiconductor devices like power diodes, transistors, thyristors, and their characteristics. Specifically, it discusses the structures, symbols, V-I characteristics, and applications of power diodes, BJTs, MOSFETs, IGBTs, SITs, thyristors, SCRs, and triacs. It provides comparisons of the key features of BJTs vs MOSFETs and IGBTs vs MOSFETs. The document aims to educate students about important power semiconductor devices and their working principles
This document provides an overview of power semiconductor devices taught in a course at JCT College of Engineering & Technology. It covers topics like power diodes, transistors, thyristors, and other devices. For each device, it discusses structural features, characteristics like V-I and switching, and examples. It compares features of power BJT, MOSFET, IGBT, and provides applications of devices like thyristors, IGBTs and SITs. The document aims to educate students about key power electronics components through detailed technical explanations and diagrams.
The document discusses power semiconductor devices used in power electronics. It covers various types of semiconductor devices including power diodes, transistors, thyristors and their characteristics. Specifically, it describes the structural features and V-I characteristics of power diode, power BJT, power MOSFET, IGBT, SIT and thyristors like SCR. It provides comparisons of the key parameters of these devices and their applications in power electronics circuits.
This document discusses various power semiconductor devices used in power electronics, including power diodes, thyristors, SCRs, and TRIACs. It provides details on their structural features, characteristics, and operating principles. Thyristors like SCRs can conduct current in either direction but only be turned on by a gate signal, while TRIACs can conduct bidirectionally and be turned on by a gate pulse of either polarity.
This document discusses the gate turn-off thyristor (GTO). It begins with an introduction explaining that a GTO is a type of thyristor that can be turned on and off through its gate terminal. The construction of a GTO is then described, including the heavily doped n+ and p+ layers. The operation involves turning on through forward gate bias and turning off by applying reverse gate bias. Applications of GTOs include AC drives, DC drives, AC power supplies, and induction heating. In comparison to regular thyristors, GTOs have faster switching but higher on-state voltage drop and require more gate current.
The document discusses various power semiconductor devices used as switches in power electronics applications. It describes power diodes, thyristors, power transistors, and other devices. Key points covered include:
1. Power diodes conduct current in the forward direction and block voltage in the reverse direction. Thyristors can conduct in both directions but require a gate signal to turn on.
2. Thyristors like SCRs have four alternating layers of p-type and n-type semiconductor material. They can latch on in the conducting state once triggered by a gate signal.
3. Other power semiconductor devices discussed include power MOSFETs, IGBTs, and GTO thyristors. Each
A gate turn-off thyristor is a special type of thyristor, which is a high-power semiconductor device. It was invented by General Electric. GTOs, as opposed to normal thyristors, are fully controllable switches that can be turned on and off by their third lead, the gate lead. http://bit.ly/2PIOIQM
The document summarizes several types of power semiconductor devices used in power electronics applications. It describes thyristors, gate turn-off thyristors, reverse-conducting thyristors, power transistors, power MOSFETs, insulated-gate bipolar transistors, and MOS-controlled thyristors. It provides brief explanations of the characteristics and operating principles of each device type.
This document provides an overview of power electronics devices including power diodes, transistors, MOSFETs, IGBTs, thyristors, and triacs. It discusses the basic structures and characteristics of these devices. It also covers topics such as thyristor triggering methods, gate control, commutation, and applications. The document is intended as an introductory guide to understanding various power semiconductor devices used in power electronics applications.
Contents of this presentation:
General Introduction to IGBT
IGBT Equivalent Circuit
IGBT Output Characteristics
IGBT usage as a Switch
IGBT Datasheet
IGBT Applications
IGBT Power Losses
Some FAQs about IGBTs
Introduction to IGBT & its losses with videos demonstration Zeeshan Akhtar
Contents of this presentation:
General Introduction to IGBT
IGBT Equivalent Circuit
IGBT Output Characteristics
IGBT usage as a Switch
IGBT Datasheet
IGBT Applications
IGBT Power Losses
Some FAQs about IGBTs
along with some demonstration videos from different sources
Thyristors are four-layer semiconductor devices that can efficiently control and convert large amounts of power in AC or DC systems. They have higher power handling capabilities than diodes and transistors. A thyristor is turned on by applying a voltage at its gate terminal and remains on until the current drops to zero. Thyristors are used in applications that require switching or controlling high currents like speed control, voltage regulation, and circuit protection. They can be connected in series and parallel configurations to achieve higher voltages and currents.
Similar to Unit-1 Power Semiconductor devices (20)
Necessity of starter in induction motorjohny renoald
The starter is a device required for three-phase induction motors to limit the high starting current, which can be 6 to 8 times the full load current and damage the motor windings. A starter works by controlling the induced electromotive force in the rotor circuit and thereby controlling the rotor current during start-up. Common types of starters include stator rheostat starters, autotransformer starters, star-delta starters, and direct on line starters.
This document discusses three phase induction motors. It describes their operating principle of rotating magnetic fields produced by three phase currents in the stator. Key points include:
- Induction motors operate on rotating magnetic fields and can run on single or three phase power, with three phase preferred.
- Advantages over DC motors include low maintenance, ruggedness, low cost, and ability to operate in harsh environments.
- Speed is controlled by varying supply frequency using variable frequency drives to maintain constant flux.
- Starters like star-delta are used to limit starting current and torque by initially applying reduced voltage.
This document discusses special electrical machines, specifically permanent magnet synchronous motors (PMSM). It describes PMSM as a brushless DC motor with permanent magnets on the rotor that create magnetic poles instead of a field winding. The document outlines the basic construction and working principle of PMSM, noting that a rotating magnetic field from the stator interacts with the permanent rotor magnets to produce torque. Applications mentioned include servo drives, robotics, traction systems, and railway transportation.
This document contains a presentation on transformers given by Dr. B. Gopinath, Professor of Electrical and Electronics Engineering. It discusses the principle of operation of transformers, their basic construction, equivalent circuit, regulation and efficiency. It provides equations for transformer operation and covers topics like single phase transformer referred to primary and secondary, transformer losses, practical transformer equivalent circuit, and components like conservator tank, silica gel breather, and Buchholz relay.
The document discusses different methods for triggering an SCR (silicon controlled rectifier) to turn on. There are four main triggering methods: forward voltage triggering, thermal/temperature triggering, radiation/light triggering, and gate triggering. Forward voltage triggering involves applying an additional forward voltage until avalanche breakdown occurs. Thermal triggering relies on increased temperature reducing the depletion layer. Radiation triggering uses light to generate charge carriers. Gate triggering, the most common method, injects charge carriers from the gate terminal to reduce the depletion layer thickness.
This document discusses DC-DC converters, which convert a fixed DC source into a variable DC source like an AC transformer. It describes step-down converters, which use a switch like a BJT, MOSFET, or IGBT to alternately connect and disconnect the voltage source to produce a lower average output voltage. Key concepts covered include duty cycle, pulse-width modulation, modes of operation, generation of the switching signal, and analysis of a step-down converter with an RL load in continuous conduction mode.
1) There are several methods to control the output voltage of single phase inverters including external control of AC output voltage, external control of DC input voltage, and internal control of the inverter.
2) Internal control of the inverter through pulse width modulation is commonly used as it requires no additional components. Pulse width modulation controls the output voltage by adjusting the ON and OFF periods of the inverter components.
3) Harmonic reduction can be achieved through techniques like multiple pulse modulation, sinusoidal pulse modulation, and combining output voltages from multiple inverters with transformer connections. Internal control of the inverter through advanced PWM techniques is effective in minimizing harmonics in the output voltage.
An inverter is a static device that converts DC power from a source like batteries into AC power at a desired output voltage and frequency. There are different types of inverters classified by their commutation method, component connections, and the nature of the DC source. Voltage source inverters have a constant voltage input and output voltage does not depend on the load, while current source inverters have a constant current input and output voltage depends on the load. Common inverter configurations include single phase half and full bridge inverters, and three phase inverters that can operate in 180 or 120 degree modes.
This document discusses different types of phase controlled converters including single-phase and three-phase semiconverters, full converters, and dual converters. It provides equations and diagrams to describe the operation and analyze the performance of single-phase semiconverters and full converters with resistive-inductive loads. It also describes the operation of a three-phase half-wave converter with continuous and constant load current.
This document provides information on a Power System Protection course taught at Vivekanandha College of Engineering for Women. The syllabus covers 5 units: introduction to protection schemes, relay operating principles and characteristics, apparatus protection, theory of circuit interruption, and circuit breakers. It lists textbooks and presents details on each unit, including topics like relay types, transformer/generator/motor protection, arc phenomena, and different circuit breaker types. The last section provides references for textbooks, websites, and presentations on related topics.
This document provides information about a power system protection course, including:
1. The syllabus covers 5 units - introduction to protection schemes, operating principles of relays, apparatus protection, theory of circuit interruption, and circuit breakers.
2. The theory of circuit interruption unit discusses arc phenomena, interruption of DC and AC circuits. It explains the physics behind arc initiation, maintenance and methods of arc extinction.
3. Interruption of capacitive current can produce high transient voltages across the circuit breaker contacts. This occurs when unloaded transmission lines or capacitor banks are switched off.
This document provides information about power system protection for a course. It includes:
1. A syllabus covering introduction to protection schemes, operating principles of relays, apparatus protection, circuit interruption theory, and circuit breakers.
2. Details on apparatus protection including considerations for protecting generators, transformers, and transmission lines with zones of protection.
3. An overview of generator protection including faults that can occur and classifications of protective relays into categories based on their response time.
This document contains information about a power system protection course, including:
1. The syllabus covers 5 units - introduction to protection schemes, operating principles of electromagnetic and static relays, apparatus protection, circuit interruption theory, and circuit breakers.
2. Unit 2 discusses the operating principles of electromagnetic relays like overcurrent, directional, distance, differential and under frequency relays. It also introduces static relays.
3. Directional relays use both current and voltage inputs to operate only for a specific direction of power flow, while non-directional relays operate based only on current.
This document outlines the syllabus for a Power System Protection course, including 5 units: introduction, relay operating principles and characteristics, apparatus protection, theory of circuit interruption, and circuit breakers. It provides an overview of key concepts like faults and fault currents in power systems, the importance of protective schemes, and components of protection systems like relays, circuit breakers, and batteries. The document also shares diagrams to illustrate power system configurations and protective devices.
This document provides an introduction to basic electrical concepts including charge, current, voltage, resistors, and capacitors. It defines each concept, provides examples and analogies to explain them, and discusses how components such as resistors and capacitors are constructed and operate in electrical circuits. Key points covered include that charge is carried by electrons and protons, current is the flow of electrons, voltage is needed to push charge through a circuit, and resistors and capacitors can store and control the flow of electric charge and energy.
This document outlines the roles and responsibilities of teachers as role models for students. It discusses how teachers should develop students' character, values, and skills through their guidance, inspiration, and classroom teaching techniques. The document also provides guidance for teachers to continuously develop themselves as experts in their subject, to adopt modern teaching tools, and to evaluate their own performance to improve.
This document discusses management from several perspectives: as an activity, process, academic discipline, and group. It also covers the nature, importance, and functions of management. Management involves planning, organizing, directing, and controlling resources to achieve organizational goals. There are three levels of management - first-line managers who directly oversee production, middle managers who coordinate activities and set objectives, and top managers who provide overall direction. Different skills are important at each level, including communication, teamwork, planning, and leadership.
This document discusses communication skills and effective communication. It defines communication as a series of senses and describes the most common ways to communicate as speaking, writing, visuals, images, and body language. It then covers types of communication based on organization, flow, and expression. The document also discusses formal channels of communication like downward, upward, and horizontal communication. It identifies barriers to communication such as semantic, emotional, organizational, and personal barriers. Finally, it provides tips for developing good communication skills through exploring related skills, maintaining eye contact, using gestures, practicing, and ensuring communication is two-way, involves listening, utilizes feedback, and is clear and free of stress.
An e-mail is an informal method of communication between colleagues or fellow students. An agenda outlines the contents of an upcoming meeting and is sent with the meeting notice. Minutes are the official record of a meeting's proceedings and decisions, serving as a permanent reference. A circular letter is distributed to multiple customers at once without individual addresses. A bio-data, resume, and CV provide personal and professional details about a person, with the resume focused on qualifications for a specific job application.
This document discusses industry relations and industrial relations. It defines industrial relations as the complex inter-relations between workers, managers, and government in both organized and unorganized sectors. Industrial relations is characterized by both conflict and cooperation and involves studying workplace conditions, management-labor cooperation, laws and regulations. Key aspects of industrial relations include collective bargaining, worker participation, and employment conditions. Successful industrial relations programs require top management support, sound human resource and industrial relations policies and practices, adequate training, and following up on results.
Online train ticket booking system project.pdfKamal Acharya
Rail transport is one of the important modes of transport in India. Now a days we
see that there are railways that are present for the long as well as short distance
travelling which makes the life of the people easier. When compared to other
means of transport, a railway is the cheapest means of transport. The maintenance
of the railway database also plays a major role in the smooth running of this
system. The Online Train Ticket Management System will help in reserving the
tickets of the railways to travel from a particular source to the destination.
Data Communication and Computer Networks Management System Project Report.pdfKamal Acharya
Networking is a telecommunications network that allows computers to exchange data. In
computer networks, networked computing devices pass data to each other along data
connections. Data is transferred in the form of packets. The connections between nodes are
established using either cable media or wireless media.
Covid Management System Project Report.pdfKamal Acharya
CoVID-19 sprang up in Wuhan China in November 2019 and was declared a pandemic by the in January 2020 World Health Organization (WHO). Like the Spanish flu of 1918 that claimed millions of lives, the COVID-19 has caused the demise of thousands with China, Italy, Spain, USA and India having the highest statistics on infection and mortality rates. Regardless of existing sophisticated technologies and medical science, the spread has continued to surge high. With this COVID-19 Management System, organizations can respond virtually to the COVID-19 pandemic and protect, educate and care for citizens in the community in a quick and effective manner. This comprehensive solution not only helps in containing the virus but also proactively empowers both citizens and care providers to minimize the spread of the virus through targeted strategies and education.
An In-Depth Exploration of Natural Language Processing: Evolution, Applicatio...DharmaBanothu
Natural language processing (NLP) has
recently garnered significant interest for the
computational representation and analysis of human
language. Its applications span multiple domains such
as machine translation, email spam detection,
information extraction, summarization, healthcare,
and question answering. This paper first delineates
four phases by examining various levels of NLP and
components of Natural Language Generation,
followed by a review of the history and progression of
NLP. Subsequently, we delve into the current state of
the art by presenting diverse NLP applications,
contemporary trends, and challenges. Finally, we
discuss some available datasets, models, and
evaluation metrics in NLP.
Better Builder Magazine brings together premium product manufactures and leading builders to create better differentiated homes and buildings that use less energy, save water and reduce our impact on the environment. The magazine is published four times a year.
Sachpazis_Consolidation Settlement Calculation Program-The Python Code and th...Dr.Costas Sachpazis
Consolidation Settlement Calculation Program-The Python Code
By Professor Dr. Costas Sachpazis, Civil Engineer & Geologist
This program calculates the consolidation settlement for a foundation based on soil layer properties and foundation data. It allows users to input multiple soil layers and foundation characteristics to determine the total settlement.
8. POWER TRANSISTORS
FOUR TYPES
Bipolar junction Transistor(BJT)
Metal Oxide Semiconductor Field Effect
Transistor(MOSFET)
Insulated Gate Bipolar Transistors(IGBT) and
Static Induction Transistor (SIT)
8/1/2019
9. POWER BJT
• Three layer ,Two Junction npn or pnp type
• Bipolar means current flow in the device is
due to the movement of BOTH holes and
Electrons.
8/1/2019
16. POWER MOSFET
• THREE TERMINALS – DRAIN,SOURCE AND
GATE
• VOLTAGE CONTROLLED DEVICE
• GATE CIRCUIT IMPEDANCE IS HIGH (OF THE
ORDER OF MEGA OHM).HENCE GATE CAN BE
DRIVEN DIRECTLY FROM MICROELECTRONIC
CIRCUITS.
• USED IN LOW POWER HIGH FREQUENCY
CONVERTERS,SMPS AND INVERTERS
8/1/2019
21. COMPARISON OF BJT AND MOSFET
S.No BJT MOSFET
1 BIPOLAR DEVICE UNIPOLAR DEVICE
2 LOW INPUT IMPEDANCE(KILO OHM) HIGH INPUT IMPEDANCE (MEGA
OHM)
3 HIGH SWITCHING LOSSES BUT LOWER
CONDUCTION LOSSES
LOWER SWITCHING LOSSES BUT
HIGH ON-RESISTANCE AND
CONDUCTION LOSSES
4 CURRENT CONTROLLED DEVICE VOLTAGE CONTROLLED DEVICE
5 NEGATIVE TEMPERATURE COEFFICIENT
OF RESISTANCE.PARALLEL OPERATION IS
DIFFICULT.CURRENT SHARING
RESISTORS SHOULD BE USED.
POSITIVE TEMPERATURE
COEFFICIENT OF RESISTANCE.
PARALLEL OPERATION IS EASY
6 SECONDARY BREAKDOWN OCCURS. SECONDARY BREAKDOWN DOES NOT
OCCUR.
7 AVAILABLE WITH RATINGS 1200V,800A AVAILABLE WITH RATINGS 500V,140A8/1/2019
22. INSULATED GATE BIPOLAR TRANSISTOR
(IGBT)
• COMBINES THE BEST QUALITIES OF BOTH BJT AND
MOSFET
• HAS HIGH INPUT IMPEDANCE AS MOSFET AND HAS
LOW ON-STATE POWER LOSS AS IN BJT
• OTHER NAMES
MOSIGT (METAL OXIDE INSULATED GATE TRANSISTOR),
COMFET (CONDUCTIVELY-MODULATED FIELD EFFECT
TRANSISTOR),
GEMFET (GAIN MODULATED FIELD EFFECT TRANSISTOR),
IGT (INSULATED GATE TRANSISTOR)
8/1/2019
30. APPLICATIONS OF IGBT
• DC AND AC MOTOR DRIVES
• UPS SYSTEMS,POWER SUPPLIES
• DRIVES FOR SOLENOIDS,RELAYS AND
CONTACTORS
8/1/2019
31. COMPARISON OF IGBT WITH MOSFET
S.No MOSFET IGBT
1. THREE TERMINALS ARE GATE,SOURCE AND
DRAIN
THREE TERMINALS ARE GATE,EMITTER
AND COLLECTOR
2. HIGH INPUT IMPEDANCE HIGH INPUT IMPEDANCE
3. VOLTAGE CONTROLLED DEVICE VOLTAGE CONTROLLED DEVICE
4. RATINGS AVAILABLE UPTO 500V,140A RATINGS AVAILABLE UPTO 1200V,500A
5. OPERATING FREQUENCY IS UPTO I MHz OPERATING FREQUENCY IS UPTO 50KHz
6. WITH RISE IN TEMPERATURE,THE INCREASE IN ON-STATE RESISTANCE IN MOSFET IS
MORE PRONOUNCED THAN IGBT.SO, ON-STATE VOLTAGE DROP AND LOSSES RISE
RAPIDLY IN MOSFET THAN IN IGBT ITH RISE IN TEMPERATURE.
7. WITH RISE IN VOLTAGE,THE INCREMENT IN ON-STATE VOLTAGE DROP IS MORE
DOMINANT IN MOSFET THAN IT IS IN IGBT.THIS MEANS IGBTs CAN BE DESIGNED FOR
HIGHER VOLTAGE RATINGS THAN MOSFETs.
8/1/2019
34. WORKING OF SIT
• SIT IS A NORMALLY ON DEVICE
• IF VGS =0 AND VDS IS PRESENT ,ELECTRONS WOULD FLOW FROM
SOURCE TO n,P+,n-, n+ AND REACH DRAIN.DRAIN CURRENT
FLOWS FROM D TO S.
• IF VGS = NEGATIVE, P+n- JUNCTIONS GET REVERSE
BIASED.DEPLETION REGION IS FORMED AROUND P+
ELECTRODES AND THIS REDUCES THE CURRENT FLOW FROM ITS
VALUE WHEN VGS =0.
• AT SOME HIGHER VALUE OF REVERSE BIAS VOLTAGE VGS ,THE
DEPLETION LAYER WOULD GROW TO SUCH AN EXTENT AS TO
CUT OFF THE CHANNEL COMPLETELY AND LOAD CURRENT
WOULD BE ZERO.
8/1/2019
35. STATIC INDUCTION TRANSISTOR(SIT)
• IT IS A HIGH POWER,HIGH FREQUENCY DEVICE.
• LARGE DROP IN SIT MAKES IT UNSUITABLE FOR GENERAL
POWER ELECTRONIC APPLICATIONS.
• A 1500V,180A SIT HAS A CHANNEL RESISTANCE OF 0.5 Ω
GIVING 90V CONDUCTION DROP AT 180A.AN EQUIVALENT
THYRISTOR OR GTO DROP MAY BE AROUND 2V.
• TYPICAL TON AND TOFF TIMES ARE VERY LOW AROUND 0.35µs.
• HIGH CONDUCTION DROP WITH VERY LOW TURN-ON AND
TURN-OFF TIMES RESULT IN LOW ON-OFF ENERGY
LOSSES.THIS MAKES SIT SUITABLE FOR HIGH POWER,HIGH
FREQUENCY APPLICATIONS.
8/1/2019
36. APPLICATIONS OF SIT
• AM/FM TRANSMITTERS
• INDUCTION HEATERS
• HIGH VOLTAGE LOW CURRENT POWER SUPPLIES
• ULTRASONIC GENERATORS
• TYPICAL RATINGS AVAILABLE -1200V,300AWITH
TURN ON AND TURN OFF TIMES AROUND 0.25 TO
0.35 µs AND 100KHz OPERATING FREQUENCY.
8/1/2019
37. THYRISTORS
SILICON CONTROLLED RECTIFIER (SCR)
• Three terminal, four layers (P-N-P-N)
• Can handle high currents and high voltages,
with better switching speed and improved
breakdown voltage .
• Name ‘Thyristor’, is derived by a combination
of the capital letters from THYRatron and
transISTOR.
• Has characteristics similar to a thyratron tube
But from the construction view point belongs
to transistor (pnp or npn device) family.
8/1/2019
38. THYRISTORS
• TYPICAL RATINGS AVAILABLE ARE 1.5KA &
10KV WHICH RESPONDS TO 15MW POWER
HANDLING CAPACITY.
• THIS POWER CAN BE CONTROLLED BY A GATE
CURRENT OF ABOUT 1A ONLY.
8/1/2019
41. SCR / Thyristor
• Circuit Symbol and Terminal Identification
SCR
2N3668
ANODE
CATHODE
GATE
8/1/2019
42. SCR / Thyristor
• Anode and Cathode
terminals as
conventional pn
junction diode
• Gate terminal for a
controlling input signal
SCR
2N3668
ANODE
CATHODE
GATE
8/1/2019
43. SCR/ Thyristor
• An SCR (Thyristor) is a “controlled” rectifier
(diode)
• Control the conduction under forward bias by
applying a current into the Gate terminal
• Under reverse bias, looks like conventional pn
junction diode
8/1/2019
44. SCR / Thyristor
• 4-layer (pnpn) device
• Anode, Cathode as for a
conventional pn
junction diode
• Cathode Gate brought
out for controlling input
P
N
P
N
Anode
Cathode
Gate
8/1/2019
46. Apply Biasing
With the Gate terminal
OPEN, both transistors are
OFF. As the applied
voltage increases, there will
be a “breakdown” that
causes both transistors to
conduct (saturate) making
IF > 0 and VAK = 0.
VBreakdown = VBR(F)
IF
IC2=IB1
IF
IC1 = IB2 Q2
BJT_NPN_VIRTUAL
Q1
BJT_PNP_VIRTUAL
ANODE (A)
CATHODE (K)
GATE (G)
Variable
50V
8/1/2019
48. Apply a Gate Current
Q2
BJT_NPN_VIRTUAL
Q1
BJT_PNP_VIRTUAL
ANODE (A)
CATHODE (K)
GATE (G)
Variable
50V
IF
IF
IB2
VG
For 0 < VAK < VBR(F),
Turn Q2 ON by applying a
current into the Gate
This causes Q1 to turn ON, and
eventually both transistors
SATURATE
VAK = VCEsat + VBEsat
If the Gate pulse is removed,
Q1 and Q2 still stay ON!
IC2 = IB1
8/1/2019
49. How do you turn it OFF?
• Cause the forward current to fall below the
value if the “holding” current, IH
• Reverse bias the device
8/1/2019
50. SCR Application – Power Control
When the voltage across
the capacitor reaches the
“trigger-point” voltage of
the device, the SCR turns
ON, current flows in the
Load for the remainder of
the positive half-cycle.
Current flow stops when
the applied voltage goes
negative.
Rload
15ohm
60%25kOhm
Key = a
R
C
0.01uF
Vs
170V
120.21V_rms
60Hz
0Deg
A B
T
G
XSC1
D1
2N1776
8/1/2019
52. SCR OPERATING MODES
FORWARD BLOCKING MODE: Anode is positive w.r.t cathode, but
the anode voltage is less than the break over voltage (VBO) .
only leakage current flows, so thyristor is not conducting .
FORWARD CONDUCTING MODE: When anode voltage becomes
greater than VBO, thyristor switches from forward blocking to
forward conduction state, a large forward current flows.
If the IG=IG1, thyristor can be turned ON even when anode
voltage is less than VBO.
– The current must be more than the latching current (IL).
– If the current reduced less than the holding current (IH),
thyristor switches back to forward blocking state.
REVERSE BLOCKING MODE: When cathode is more positive than
anode , small reverse leakage current flows. However if cathode
voltage is increased to reverse breakdown voltage , Avalanche
breakdown occurs and large current flows.
8/1/2019
53. Thyristor- Operation Principle
• Thyristor has three p-n junctions (J1, J2, J3 from the anode).
• When anode is at a positive potential (VAK) w.r.t cathode with no
voltage applied at the gate, junctions J1 & J3 are forward biased,
while junction J2 is reverse biased.
– As J2 is reverse biased, no conduction takes place, so
thyristor is in forward blocking state (OFF state).
– Now if VAK (forward voltage) is increased w.r.t cathode,
forward leakage current will flow through the device.
– When this forward voltage reaches a value of breakdown
voltage (VBO) of the thyristor, forward leakage current will
reach saturation and reverse biased junction (J2) will have
avalanche breakdown and thyristor starts conducting (ON
state), known as forward conducting state .
• If Cathode is made more positive w.r.t anode, Junction J1 & J3
will be reverse biased and junction J2 will be forward biased.
• A small reverse leakage current flows, this state is known as
reverse blocking state.
• As cathode is made more and more positive, stage is reached
when both junctions A & C will be breakdown, this voltage is
referd as reverse breakdown voltage (OFF state), and device is in
reverse blocking state8/1/2019
54. TRIGGERING METHODS
• THYRISTOR TURNING ON IS ALSO KNOWN AS
TRIGGERING.
• WITH ANODE POSITIVE WITH RESPECT TO CATHODE, A
THYRISTOR CAN BE TURNED ON BY ANY ONE OF THE
FOLLOWING TECHNIQUES :
FORWARD VOLTAGE TRIGGERING
GATE TRIGGERING
DV/DT TRIGGERING
TEMPERATURE TRIGGERING
LIGHT TRIGGERING
8/1/2019
55. Forward Voltage Triggering
• When breakover voltage (VBO) across a thyristor is exceeded
than the rated maximum voltage of the device, thyristor
turns ON.
• At the breakover voltage the value of the thyristor anode
current is called the latching current (IL) .
• Breakover voltage triggering is not normally used as a
triggering method, and most circuit designs attempt to avoid
its occurrence.
• When a thyristor is triggered by exceeding VBO, the fall time
of the forward voltage is quite low (about 1/20th of the time
taken when the thyristor is gate-triggered).
• However, a thyristor switches faster with VBO turn-ON than
with gate turn-ON, so permitted di/dt for breakover voltage
turn-on is lower.
8/1/2019
56. dv/dt triggering
• With forward voltage across anode & cathode of a thyristor, two
outer junctions (A & C) are forward biased but the inner junction
(J2) is reverse biased.
• The reversed biased junction J2 behaves like a capacitor because of
the space-charge present there.
• As p-n junction has capacitance, so larger the junction area the
larger the capacitance.
• If a voltage ramp is applied across the anode-to-cathode, a current
will flow in the device to charge the device capacitance according
to the relation:
• If the charging current becomes large enough, density of moving
current carriers in the device induces switch-on.
• This method of triggering is not desirable because high charging
current (Ic) may damage the thyristor.8/1/2019
57. Temperature Triggering
• During forward blocking, most of the applied voltage
appears across reverse biased junction J2.
• This voltage across junction J2 associated with leakage
current may raise the temperature of this junction.
• With increase in temperature, leakage current through
junction J2 further increases.
• This cumulative process may turn on the SCR at some high
temperature.
• High temperature triggering may cause Thermal runaway
and is generally avoided.
8/1/2019
58. Light Triggering
• In this method light particles (photons) are made to
strike the reverse biased junction, which causes an
increase in the number of electron hole pairs and
triggering of the thyristor.
• For light-triggered SCRs, a slot (niche) is made in the
inner p-layer.
• When it is irradiated, free charge carriers are
generated just like when gate signal is applied b/w
gate and cathode.
• Pulse light of appropriate wavelength is guided by
optical fibers for irradiation.
• If the intensity of this light thrown on the recess
exceeds a certain value, forward-biased SCR is turned
on. Such a thyristor is known as light-activated SCR
(LASCR).
• Light-triggered thyristors is mostly used in high-
voltage direct current (HVDC) transmission systems.
8/1/2019
59. Thyristor Gate Control Methods
• An easy method to switch ON a SCR into conduction is to
apply a proper positive signal to the gate.
• This signal should be applied when the thyristor is forward
biased and should be removed after the device has been
switched ON.
• Thyristor turn ON time should be in range of 1-4 micro
seconds, while turn-OFF time must be between 8-50 micro
seconds.
• Thyristor gate signal can be of three varieties.
– D.C Gate signal
– A.c Gate Signal
– Pulse
8/1/2019
60. Thyristor Gate Control Methods
D.C Gate signal: Application of a d.c gate signal causes the flow of gate
current which triggers the SCR.
– Disadvantage is that the gate signal has to be continuously applied,
resulting in power loss.
– Gate control circuit is also not isolated from the main power circuit.
A.C Gate Signal: In this method a phase - shifted a.c voltage derived from
the mains supplies the gate signal.
– Instant of firing can be controlled by phase angle control of the gate
signal.
Pulse: Here the SCR is triggered by the application of a positive pulse of
correct magnitude.
– For Thyristors it is important to switched ON at proper instants in a
certain sequence.
– This can be done by train of the high frequency pulses at proper
instants through a logic circuit.
– A pulse transformer is used for circuit isolation.
– Here, the gate looses are very low because the drive is discontinuous.8/1/2019
61. Thyristor Commutation
• Commutation: Process of turning off a conducting thyristor
– Current Commutation
– Voltage Commutation
• A thyristor can be turned ON by applying a positive voltage
of about a volt or a current of a few tens of milliamps at the
gate-cathode terminals.
• But SCR cannot be turned OFF via the gate terminal.
• It will turn-off only after the anode current is negated
either naturally or using forced commutation techniques.
• These methods of turn-off do not refer to those cases
where the anode current is gradually reduced below
Holding Current level manually or through a slow process.
• Once the SCR is turned ON, it remains ON even after
removal of the gate signal, as long as a minimum current,
the Holding Current (IH), is maintained in the main or
rectifier circuit.8/1/2019
62. Thyristor Turn-off Mechanism
• In all practical cases, a negative current flows through the device.
• This current returns to zero only after the reverse recovery time (trr) ,
when the SCR is said to have regained its reverse blocking capability.
• The device can block a forward voltage only after a further tfr, the
forward recovery time has elapsed.
• Consequently, the SCR must continue to be reverse-biased for a
minimum of tfr + trr = tq, the rated turn-off time of the device.
• The external circuit must therefore reverse bias the SCR for a time toff >
tq.
• Subsequently, the reapplied forward biasing voltage must rise at a dv/dt
< dv/dt (reapplied) rated. This dv/dt is less than the static counterpart.
8/1/2019
64. MOS CONTROLLED THYRISTOR (MCT)
• IT IS BASICALLY A THYRISTOR WITH TWO MOSFETS
BUILT INTO THE GATE STRUCTURE
• ONE MOSFET IS USED TO TURN ON THE MCT AND
THE OTHER FOR TURNING OFF OF MCT.
• IT IS A HIGH FREQUENCY,HIGH POWER,LOW
CONDUCTION DROP SWITCHING DEVICE.
• IN A MCT, THE ANODE IS THE REFERENCE W.R.TO
WHICH ALL THE GATE SIGNALS ARE APPLIED. IN A
SCR,CATHODE IS THE REFERENCE SIGNAL TO THE
GATE SIGNAL.
8/1/2019
67. MERITS OF MCT
• LOW FORWARD CONDUCTION DROP
• FAST TURN AND TURN OFF TIMES
• LOW SWITCHING LOSSES
• HIGH GATE INPUT IMPEDANCE
• LOW REVERSE VOLTAGE BLOCKING CAPABILITY
IS THE MAIN DISADVANTAGE OF MCT
8/1/2019
70. TRIAC
(TRIODE FOR ALTERNATING CURRENT)
• TRIAC is five layer device that is able to
pass current bidirectionally and
therefore behaves as an a.c. power
control device.
• The main connections are simply named
main terminal 1 (MT1) and main terminal
2 (MT2).
• The gate designation still applies, and is
still used as it was with the SCR.
8/1/2019
71. TRIAC (CONTD….)
• it not only carries current in either direction, but the gate
trigger pulse can be either polarity regardless of the polarity
of the main applied voltage.
• The gate can inject either free electrons or holes into the body
of the triac to trigger conduction either way.
– So triac is referred to as a "four-quadrant" device.
• Triac is used in an ac environment, so it will always turn off
when the applied voltage reaches zero at the end of the
current half-cycle.
• If a turn-on pulse is applied at some controllable point after
the start of each half cycle, we can directly control what
percentage of that half-cycle gets applied to the load, which is
typically connected in series with MT2.
• USED for light dimmer controls and motor speed controls.
8/1/2019
73. TRIAC OPERATION
• TRIAC can be considered as two thyristors connected
in antiparallel .The single gate terminal is common to
both thyristors.
• The main terminals MT1 and MT2 are connected to
both p and n regions of the device and the current
path through the layers of the device depends upon
the polarity of the applied voltage between the main
terminals.
• Device polarity is usually described with reference to
MT1, where the term MT2+ denotes that terminal
MT2 is positive with respect to terminal MT1.
8/1/2019