What are Power Converters?

A power converter is an electrical circuit that converts the electrical energy from one form into the desired form optimized for the specific load. This conversion can be from direct current to alternating current to direct current to increase or decrease the magnitude of the input voltage, invert polarity, or produce several output voltages of either the same polarity as the input, different polarity, or mixed polarity, such as in the computer power supply unit. Converters are available in the form of a simple transformer or may be more complex, depending on the application. This article will discuss what power converters are and their different types.

Table of Content

What is Power converters?

1. Types of Power converters

•    AC-DC Converters

•    DC-DC Converters

•    DC-AC Converters 

•    AC-AC converters

Types of Power Converters

1. AC-DC Converters  (Phase Controlled Rectifiers)

An AC to DC converter is an electrical circuit that transforms alternating current ( AC ) input into direct current ( DC ) output.  These rectifiers use line voltage for their communication. 

AC to DC converter is mainly used in power electronic applications where the power input is a 50 Hz or 60 Hz sine-wave AC voltage that requires power conversion for a DC output. 

It may be fed from a one-phase or three-phase source. It is used in DC drives, metallurgical and chemical industries, excitation systems for synchronous machines, etc.

2. DC-DC Converters (DC Choppers)

A DC-to-DC converter is an electronic circuit or electromechanical device that converts a source of direct current from one voltage level to another. It is also known as DC choppers. 

A DC chopper circuit is needed to force, load, and commute to turn off the thyristors.  Thyristors are replaced by power transistors for the lower power circuit.

Classification of the chopper circuit is dependent upon the types of DC communication and also on the direction of power flow. It finds wide application in DC drives, subway cars, trolley trucks, battery-driven vehicles, etc.

3. DC-AC Converters (Power Inverters)

DC to AC converters is electronic circuits that change direct current ( DC ) to alternating current ( AC ). A DC-to-AC converter is also called a power inverter.  Output current may be variable current and variable frequency. 

This types of converter find wide use in induction motor and synchronous motor drives, induction heating, UPS, HVDC, and transmission etc. 

Power inverters use load, line, or forced commutation for turning off the thyristors. 

At present, the conventional thyristor is also being replaced by high power application and by power transistors in low-power applications.

4. AC-AC converters:

AC to AC converters is electronic circuits that convert an AC waveform to another AC waveform, where the output voltage and frequency can be set arbitrarily. In other words, it converts a fixed AC input voltage into a variable AC output voltage. 

There are two types of AC to AC converters: 

• AC Voltage Controllers 
• Cyclo Converters 

AC voltage controllers convert fixed AC voltage directly to a variable AC voltage at the same frequency. It is based on either thyristors, TRIACs, SCRs, or IGBTs, which convert a fixed voltage, fixed frequency alternating current electrical input supply to obtain a variable voltage in output delivered to a resistive load. 

The output voltage is controlled by varying the firing angle delay, and the turn-off device is obtained by line communication. 

They are widely used for lighting control, speed control of fans, pumps, etc.

Cyclo converters convert AC, power at one frequency into AC power of an adjustable but lower frequency without any direct current. It converts input power at one frequency to output power at a different frequency through one-stage conversion. 

Line commutation is more common in cyclo converters, so that forced and load commuted cyclo-converters are also employed. 

They are primarily used for slow-speed large AC drives like rotary kiln etc.

Auto Transformer Application

An Autotransformer also known as Autoformer, is a unique kind of transformer that only has one isolated winding to increase or decrease voltage. In many situations where low voltage is required, an autotransformer might be an excellent option. There are also benefits and drawbacks of autotransformers. Here Following are some applications for autotransformers.

What are the applications of Auto transformers?

• The output voltage of an AC power source can be simply changed with an autotransformer
• It also acts as a voltage regulator
• Widely used in synchronous motor
• It is utilized to correct a voltage drop in a distribution cable
• If you want to listen to an old radio or amplifier that you haven't used in a while, it is preferable to start it up carefully.
• In distribution systems, voltage fluctuations are adjusted by increasing supply voltage.
• An auto transformer is used as a variac in a lab or when a continuous variable with a wide range is needed.
• An Autotransformer can be used to change the AC voltage, which will change the temperature of resistance type heather.
• You can regulate the hot wire temperature and change it in accordance with your needs by using an autotransformer.
• The speed of AC motors can be altered by altering the voltage applied to them.
• With the aid of an autotransformer with numerous taps, synchronous and induction motors are started.
• It acts as a starter to supply the stator of a squirrel cage induction motor with up to 50% to 60 % of the entire voltage when it is first turned on.
• It is used in all electrical appliances
• It is used in power distribution and transmission system

Thank you for reading this article. Still, if you have any questions or queries in your mind on the Autotranformer Application then please ask us in the comment section below.

Power over Ethernet

What is Power over ethernet?

POE stand is a wired ethernet local area network implementation technology that allows the electrical current required to operate each device to be carried by ethernet data cables rather than standard electrical power cords and wiring.

PoE which is used in both smart home applications and business premises uses less expensive Ethernet cabling that can transport both power and data instead of electrical wiring, which only supplies power and requires separate wiring for data. PoE transport both power and data over cable, less wiring is required and existing electrical wiring can be reused.

PoE was created in 2003 to support devices such as wireless access points. Individual vendors previously used various forms of proprietary PoE to provide PoE capabilities. Some of these proprietary PoE devices are still in use. PoE installer must locate these older, proprietary devices because they can be troublesome or incompatible with later released standard PoE devices. Today's standard PoE devices make AP installations simpler and more adaptable in ceilings that can wire for electrical power.  

Why should you use PoE?

Power over Ethernet provide numerous benefits to an installation:

• Saving in time and money -  By reducing the time and cost of installing electrical power cabling. Network cables do not need to be installed by a qualified electrician and can be placed anywhere.
• Flexibility -  Because they are not tethered to an electrical outlet, devices such as IP cameras and wireless access points can be placed wherever they are most needed and easily repositioned if necessary.
• It is intelligent and designed to protect network equipment from overloading, uploading, or incorrect installation.
• Reliability -  Rather than a collection of distributed wall adapters, PoE power comes from a centralized and universally compatible source. It can be powered by an Uninterruptible power supply  or remotely controlled to easily disable or reset devices.
• Scalability - It is having enough power on the network to make installation and distribution of network connection simple and efficient.

Power semiconductor devices

Silicon controlled rectifier called SCR was first introduced in 1957 as a power semiconductor device the same way other semiconductor devices used as switches or rectifier electronic circuits called switch-mode power supplies. This device is also called a power device or some time it will be used in the integrated circuit, called power ICs.

Most of these semiconductor devices are listed below and it along with device and present advantages is maximum ratings.

1. Diode - Voltage or current rating - 5000 V/ 5000 A
2. Full form of SCR(silicon controlled rectifier) - Voltage or current rating - 7000 V/ 5000 A
3. LASCR called (light-activated SCR) - Voltage or current rating - 6000 V/ 3000 A
4. ASCR/RCT called (asymmetrical SCR / reverse conducting thyristor) -Voltage or current rating - 2500 V/ 400 A
5. Full form of GTO called (gate turn off thyristor) - Voltage or current rating - 5000 V/ 3000 A
6. Full form of SITH called (static induction  thyristor) - Voltage or current rating - 2500 V/ 500 A
7. Full form of MCT called (Mos controlled thyristor) - Voltage or current rating - 1200 V/ 40 A
8. Full form of BJT called (bipolar junction transistor) -Voltage or current rating - 1400 V/ 400 A
9. SIT called (static induction transistor)) - Voltage or current rating - 1200 V/ 300 A
10. Full form of IGBT called (insulated gate bipolar transistor) - Voltage or current rating - 1200 V/ 500 A

Based on,

• Turn on and turn off characteristic 
• Gate signal requirement
• Degree of controllability

The power semiconductor devices can be classified as under the following category

1. Diode: This is uncontrolled rectifying devices. Their on and off-state are controlled by a power supply.

2. Thyristor: These have controlled turn on by a gate signal. after thyristor is on they remain latched in on state due to internal regenerative action and gate loses control. These can be turn off by the power circuit.

3. Controllable switches: These devices are turned on and turn off by the application of control signals. The devices which behave as controllable switches areas like BJT, MOSFET, GTO, SITH, SIT, and MCT. 

So the device like GTO, BJT, SIT, SITH, MCT, SCR, IGBT is unidirectional current devices, whereas RCT and Triac posses bi-directional current capability.

Power electronic systems

Power electronics is a technology associated with the efficient conversion, control, and conditioning of electric power by static means from its available input form into the desired electrical output form.

The main component of the power electronic system is shown in the form of a block diagram in a figure. The main power source may be an AC supply system or a DC supply system.

The output from the power electronic circuit, it may be variable DC or AC voltage, or it may be a variable voltage and frequency. In general, the output of a power electronic converter circuit depends upon the requirement of the which type of load.

The feedback component in the figure measures a parameter of the load, says speed in case of a rotating machine and compares it with the command.

The difference between these two, through the digital circuit components and controls the instant of turn-on of semiconductor devices forming the solid-state power converter system.

In this manner, the behavior of the load circuit can be controlled as desired, over a wide range with the adjustment of the command. 

Block diagram of a typical power electronic system

You can check more details about power electronics system: POWER ELECTRONICS 

I - V characteristics of thyristor

The terms thyristor denotes a family of semiconductor devices used for power control in dc and ac system. One of the oldest methods of this thyristor family called silicon control rectifier. An elementary circuit diagram for obtaining static I-V characteristics of a thyristor is shown in the figure.

1. Reverse blocking mode :

• When cathode is made positive with respect to anode with switch S is open. Junction point J1, J3 are seen to bee a reverse biased whereas junction J2 is forward biased.

• A small leakage current of the order of a few mill amperes . This is reverse blocking mode, called the off- state, of the thyristor. In reverse blocking mode to shown in I-V characteristics of thyristor.

• If the reverse voltage is suddenly increased, at a critical breakdown level, called as reverse breakdown voltage VBR, an avalanche occurs at J1 and J3 and the reverse current increase rapidly

2. Forward blocking mode :

• When the anode is positive with respect to the cathode terminal, at that time the gate circuit is to be open and a thyristor is said to be forward-biased as shown in the figure.

• It is seen from this figure J1, J2, J3 are forward biased but J2 is reverse biased.

• As the forward leakage current is small, SCR offers a high impedance. Therefore, a thyristor can be treated as an open switch mode even in the forward blocking mode.

3. Forward conduction mode :

• When anode to cathode forward voltage and it is too much increased with gate circuit open, reverse-biased junction point J2 will have an avalanche breakdown at a voltage called forward break over voltage VB0.

• (This is on-state) after this breakdown occurs, thyristor gets turned on with point shifting to another point and this point anywhere called forward conduction mode.

Application of GTO

GTO is like a conventional thyristor ( CT ) but with added features in it. It can easily be turned off by a negative gate pulse of appropriate amplitude. Nowadays GTO device is now being used in

Application of GTO:

• The high-performance drive system, such as the field-oriented control scheme used in rolling mills, robotics, and machine tools.
• Traction purpose because of their lightweight.
• GTO used in Induction heater.
• Adjustable frequency inverter drive.
• At present, GTOs with rating up 5000 V and 3000 A is available.
• It is used in AC stabilizing power supplies.TO is used in static VAR compensators (SVCs).
• GTO voltage source inverter in a two-terminal HVDC link, which is fed at the sending end by a line-commutated rectifier.
• GTO is used in AC drives.
• GTO is used in DC drives or DC choppers.

Explore more information:

1. GTO vs Thyristor

Thyristor Application

The terms thyristor denotes a family of semiconductor devices used for power control in both DC  and AC system. One of the oldest methods of this thyristor family, called SCR full meaning is silicon control rectifier.

The thyristor is used in many areas of electronics where they find uses in a variety of different applications. 

Application of thyristor :

Transistors are mainly used in electronics applications as voltage and power amplifiers.

Some of the more common applications for them are outlined given below : 

• AC power control (including motors, lights, etc)
• AC power switching.
• AC dimmer. 
• Ideal for switching applications.
• Used in Over voltage protection crowbar for power supplies.
• Control elements in phase angle triggered controllers.
• They are used in photographic flashlights where they act as the switch to discharge a stored voltage through the flash lamp, and then cut it off at the required time.
• They are used in making various gates like AND, NOT etc in digital logic circuits.
• It used in audio and radio frequency amplifiers.
• Used in DC regulators and microprocessors.
• Variable speed motor drives.
• High power inverter and traction.
• Fast heater switching.
• High-temperature oven, glass, ceramics, high-temperature alloys.
• To control variables resistance heater.

What is Thyristor

Meaning of thyristor :

The terms thyristor denotes a family of semiconductor devices used for power control in DC as well as AC system. One of the oldest methods of this thyristor family called silicon control rectifier.

SCR is a four-layer, three junctions, P-N-P-N semiconductor switching device and also have three terminal named: anode (A), a cathode (C) and gate (G).

At present, the use of SCR called thyristor is so vast that over the years, the word thyristor has become synonymous with SCR device. It appears that the terms thyristor is now becoming more common than the actual term of SCR.

The definition of thyristor was decided as under :

Thyristor has constituted three or more p-n junctions. It has two stable states as known as ON state, and OFF state, and it can change its state from one to another.

As per this definition, thyristor now includes a large variety of different semiconductor devices having similar basic characteristics.

Thyristors are used in many applications like light dimmers, motor speed controls, AC power switching, pressure-control systems, and liquid-level regulators.

The silicon controlled rectifier is one of the most popular members of the thyristor family. There are several other members of thyristor family-like PUT, SUS, SCS, Triac, diac etc.

Types of thyristor

• The terms thyristor include all four-layer P-N-P-N devices used for control of power in AC and DC systems.
• The silicon controlled rectifier is the most popular member of the thyristor family. There are several other members of the thyristor family-like GTO, ETO, PUT, SUS, SCS, TRIAC, DIAC, etc.

Depending on the turn-off and turn-on capabilities and hence the physical structure, we categorize the thyristor into the following categories :

Major types of Thyristors :

• Silicon controlled thyristor or SCRs
• Bidirectional phase-controlled thyristor or BCTs
• Fast switching thyristor or SCRs
• Bidirectional triode thyristor or BCTs
• Light-activated silicon controlled rectifiers or LASERs
• Reverse conducting thyristor or RCTs
• FET controlled thyristor or FET-CDs
• Gate turn off thyristor or GTOs
• Emitter turn off thyristor or ETOs
• MOS turn off thyristor or MTOs
• Integrated gate commutated thyristors or IGCTs

In recent years, most development effort has gone into both continued integration of the gating and the control electronics into thyristor modules and the use of MOS technology to create gate structures integrated into the thyristor itself.

• Many variations of this theme are being developed and some technologies should rise above in the others in the years to come.

1. PUT :

• PUT full form is Programmable Uni Junction Transistor is a P-N-P-N device like SCR full meaning, but the major difference is that the gate is connected to n-types material near the anode as shown in the figure.
• PUT is used mainly in time delay, logic and also have SCR trigger circuits. Circuit symbol and I-V characteristics of a PUT are shown in the figure.
• In a PUT, Gate is always biased positive with respect to the cathode. When the anode voltage exceeds the gate voltage by about 0.7 V around, Junction j1 point gets forward biased and PUT turn on. When anode voltage becomes less than apply gate voltage, PUT is become turn off.

2. SUS :

• SUS full form Silicon Unilateral Switch is similar to a PUT  but with an inbuilt low voltage avalanche diode between gate and cathode as shown in the figure.
• Because of the presence of diode, SUS turns on for a fixed anode to cathode voltage unlike an SCR whose trigger voltage and/or current vary widely with changes in ambient temperature.
• SUS is used mainly in timing, logic, and trigger circuits. Its rating is about 20 V and 0.5 A. circuit symbol, equivalent circuit and I-V characteristic of a SUS are shown in the figure.

3. SCS :

• SCS full form silicon control switch. For example Four electrons thyristor. It has two gates, one anode gate (AG) like a PUT device and another cathode gate (KG) like an SCR.
• In other words, SCS is a four-layer, four terminal P-N-P-N devices; with anode A, cathode K, anode gate called AG, and cathode gate called KG to shown in the figure.
• SCS can be turned on by either gate. Circuit symbol and also I-V characteristics of an SCS are shown in the figure.
• When a negative pulse is applied to gate anode (AG), junction J1 is forward biased and at that time SCS is turned on.  A positive pulse at AG will reverse bias junction j1 and turn off the SCS.
• A positive pulse at gate kathode  (KG) turns on the device and a negative pulse at KG turns it off. 
• The application includes the timing, logic and triggering circuit, pulse generators, voltage sensors, oscillators.

4. Light-activated thyristors :

• The circuit symbol and I-V characteristics light activated thyristors, are also called LASCR, are shown in the figure. 
• LASCR is turned on by throwing a pulse of light on the silicon wafer of the thyristor. The pulse of the appropriate wavelength is guided by optical fibers to the special sensitive area of the wafer.
• If the intensity of light exceeds a certain value, the excess electron-hole pair is generated due to radiation and forward biased thyristor gets turned on.
• The primary use of light fired thyristor is in high voltage, high current application and also static reactive power compensation etc.
• A light fired thyristor has complete electrical isolation between the light triggering source and the high voltage anode-cathode circuit.
• Light-activated thyristors are available up to 6 kV and also 3.5 kA, with on state voltage drop of about around 2 V and with light triggering requirement of 5mW.

5. Diac ( Bidirectional thyristor diode) :

• Across-sectional view of a DIAC showing all its layers and junction is depicted shown in the figure.
• If voltage V12, with terminal 1 positive with respect to terminal 2, exceeds break over voltage  VB01, then structure P-N-P-N conducts. 
• The term Diac is obtained from capital letters called, DIode that can work on AC. To show in figure Diac has symmetrical breakdown characteristics.
• Its leads are interchangeable. Its turn on voltage is about 30 V.  When conducting, It acts like a low resistance with about 3 V drop across it to shown in figure.
• When not conducting, it acts as an open switch. A DIAC is sometimes called a gate less TRIAC.

6. SCR :

SCR stands for silicon controlled rectifier. It is basically four layered current controlling solid state device. SCRs can conduct current in only one direction, SCR can be triggered normally by the current which is applied to the gate terminal. To know more about SCR follow the link to know more about SCR (thyristor). I-V characteristics of a thyristor

7.Triac :

• SCR full form Silicon Control Rectifier is a unidirectional device that can conduct from anode to cathode only and not from cathode to anode while A Triac can conduct in both the directions. 
• A TRIAC is thus bidirectional thyristor with three terminals MT1, MT2, and Gate. It is used extensively for the control of power in the AC circuit. 
• The word Triac derived by combining the capital letters from the word TRIode and AC. When in operation, a Triac is equivalent to two SCRs connected in anti-parallel. The circuit symbol and its characteristics are shown in the figure.

What is power transistor

Basic information : 

The power transistor is a transistor that used in high power amplifier and power supplies. Power transistors are suited for application where a lot of power is being used current and voltage. It is a junction transistor, is designed to handle high current and power and also used in audio and switching circuits. 

The power transistor is three terminal semiconductor device used to amplify and switch electronic signals and electrical power. They come in NPN, PNP, and Darlington (NPN or PNP) forms.

The structure and construction of a power transistor are entirely different from that of a single transistor but their characteristics and operation are almost the same. 

Power transistors, however, possess controlled characteristics. These are turned on when a current sign is given to base, or control, terminal. The transistor remains in the on-state so long as a control signal is present. When this control signal is removed, a power transistor is totally turned off.

There are four types of power transistor :

• Bipolar junction transistors (BJTs)
• Metal-oxide-semiconductor field-effect transistors (MOSFETs)
• Insulated gate bipolar transistors (IGBTs) 
• Static induction transistors (SITs)

How does a power transistor work? 

A power transistor can mainly do two different jobs such as work as an amplifier or as a switch. When it works as an amplifier, it takes in a tiny electric current at the input and produces a much bigger electric current at the output. 

When it works as switches a tiny electric current flowing through the input of transistor can make a much bigger current flow through the output of transistor. 

Why transistor is used in daily life application?

• High voltage gain
• Require low power supply voltage for operation
• Smaller size 
• No heating problem during operation 
• Solid state device 
• Mechanically so strong
• Easily portable

For detailed information

Read more >>  Power transistor application

Types of power electronics converters

A term power electronics system in electronics science consists of one or more power electronic converters. A power electronic converters are made up of some power semiconductor devices controlled by the integrated circuit.

Broadly speaking power electronic converters can be classified into six types under :

• Diode rectifier
• AC to DC converters
• DC to DC converters
• DC to AC converters
• AC to AC converters
• Static switches

1. Diode Rectifier:

A diode rectifier is an electronic circuit convert AC current known as input voltage which periodically reverses direction to a fixed DC voltage which flows in only one direction. The input alternating voltage may be single phase or three phases. This process is known as rectification. 

Diode rectifiers find wide use in electric traction, battery charging, electroplating, electrochemical processing, power supplies, welding, and uninterruptible power supply systems.

2. AC-DC Converters  ( Phase Controlled Rectifiers ) :

AC to DC converter is electrical circuits that transform alternating current ( AC ) input into direct current ( DC ) output. These rectifier use line voltage for their communication. 

AC to DC converter is mainly used in power electronic applications where the power input is a 50 Hz or 60 Hz sine-wave AC voltage that requires power conversion for a DC output. 

It may be fed from one phase or three-phase source. It is used in DC drives, metallurgical and chemical industries, excitation systems for synchronous machines etc.

3. DC-DC Converters ( DC Choppers ) :

DC to DC converters is an electronic circuit or electromechanical device that converts a source of direct current from one voltage level to another one. It is also known as DC choppers. 

DC chopper circuit is needed to forced, load, commutation to turn off the thyristors. Thyristors are replaced by power transistors for the lower power circuit.

Classification of the chopper circuit is dependent upon the types of DC communication and also on the direction of power flow. It finds wide application in DC drives, subway cars, trolley trucks, battery driven vehicles etc.

4. DC-AC Converters ( Power Inverters ) :

DC to AC converters is an electronic circuit that changes direct current ( DC ) to alternating current ( AC ). DC to AC converter is also called power inverters. Output current may be variable current and variable frequency. 

This types of converter find wide use in induction motor and synchronous motor drives, induction heating, UPS, HVDC, and transmission etc. 

Power inverters use load, line, or forced commutation for turning off the thyristors. 

At present, the conventional thyristor is also being replaced by high power application and by power transistors in low power application.

5. AC-AC converters :

AC to AC converters is an electronic circuit converts an AC waveform to another AC waveform, where the output voltage and frequency can be set arbitrarily. In other words, it converts fixed AC input voltage into a variable AC output voltage. 

There are two types of AC to AC converters : 

• AC Voltage Controllers 
• Cyclo Converters 

AC voltage controllers convert fixed AC voltage directly to a variable AC voltage at the same frequency. It is based on either thyristors, TRIACs, SCRs, or IGBTs which converts a fixed voltage, fixed frequency alternating current electrical input supply to obtain a variable voltage in output delivered to a resistive load. 

The output voltage is controlled by varying the firing angle delay and turn off device is obtained by line communication. 

They are widely used for lighting control, speed control of fans, pumps etc.

Cyclo converters convert AC, power at one frequency into AC power of an adjustable but lower frequency without any direct current. It converts input power at one frequency to output power at a different frequency through one stage conversion. 

Line commutation is more common in cyclo converters so that forced and load commuted cyclo-converters are also employed. 

They are primarily used for slow speed large AC drives like rotary kiln etc.

6. Static switches :

The static switch is an electrical device that switches a load between two sources. Some switches are manual that an operator affects the transfer by throwing a switch, while others are automatic when they sense one of a source has lost or gained power.

The static switches are called AC static switches or DC static switches depending upon the input supply. 

Explore more information:

1. Advantages and disadvantages of power electronics converters