Application of power electronics

 A whole lot of power electronics applications that we use in our daily

life, such as a fan regulator, air-conditioning, induction cooking, light
dimmer, emergency lights, vacuum cleaners, personal computers,
UPS, battery charges, etc., are the major applications of power
electronics.
 Power electronics are also extensively used in automotive
applications, like hybrid electric vehicles, trolleys, subways, forklifts,
etc. A modern car itself is an example of power electronics that has
some components like windshield wiper control, ignition switch,
adaptive front lighting, electric power steering, interior lighting, etc.
Apart from these, power electronics are widely used in ships and
modern traction systems.
 Power electronics are used in industries since the industries have a
huge installation of high-power motors that are controlled by power
electronic drives, for instance, cement mills, rolling mills, compressor
pumps, fans, elevators, textile mills, blowers, elevators, rotary kilns,
etc. Some other applications consist of arc furnaces, welding, heating
applications, construction machinery, excavators, emergency power
systems, etc.
 Power electronics are used in defence and aerospace to supply
power to aircraft, advance control in missiles, satellites, unmanned
vehicles, space shuttles, and several other equipment of defence.
 Power electronics are used in the generation of renewable energy,
such as solar, wind etc., which needs storage systems and
conversion systems, and power conditioning systems in order to
become usable.
The benefits of power electronic converters are:

 They are highly reliable and have a long life.

 There is very less power loss while using electronic converters.
 Power electronic converters are efficient, and they have a quick
response; they are small in size and less in weight.

Disadvantages of Power Electronics Converters

The drawbacks of power electronic converters are:
  Power electronic converters have low overload capacity.
 Power electronic converters are very expensive.
What is power electronics?
To deliver power that supports a variety of needs, there exists a branch of electrical
engineering called power electronics; this branch basically deals with the
processing of high voltages and currents.
Q2
What is current?
The rate of flow of electrons in a conductor is known as electric current. The SI
Unit of electric current is the Ampere.
Q3
Define voltage.
Voltage can be defined as the difference in electric potential between two points.
The quantity of voltage is generally measured by a unit known as the volt denoted
by V.
Q4
What are the disadvantages of power electronics converters?

 Power electronic converters have low overload capacity.

 Power electronic converters are very expensive.
Q5
How many types of power electronics circuits are there?
There are basically five types of power electronics circuits.

There are basically five types of power electronic circuits; each one is
based on different purposes:

 To convert fixed AC to variable DC such as full wave or half wave

rectifiers – Rectifiers are used.
 To convert fixed DC to variable DC – Choppers are used.
 To convert DC to AC having a variable frequency and amplitude –
Inverters are used.
  To convert fixed AC to variable AC at the same input frequency –
Voltage Regulators are used.
 To convert fixed AC to AC with variable frequency – Cycloconverters
are used.

DC/AC converters (inverters)[edit]

Main article: power inverter
DC to AC converters produce an AC output waveform from a DC source. Applications
include adjustable speed drives (ASD), uninterruptible power supplies (UPS), Flexible AC
transmission systems (FACTS), voltage compensators, and photovoltaic inverters. Topologies for
these converters can be separated into two distinct categories: voltage source inverters and current
source inverters. Voltage source inverters (VSIs) are named so because the independently
controlled output is a voltage waveform. Similarly, current source inverters (CSIs) are distinct in that
the controlled AC output is a current waveform.

DC to AC power conversion is the result of power switching devices, which are commonly fully
controllable semiconductor power switches. The output waveforms are therefore made up of discrete
values, producing fast transitions rather than smooth ones. For some applications, even a rough
approximation of the sinusoidal waveform of AC power is adequate. Where a near sinusoidal
waveform is required, the switching devices are operated much faster than the desired output
frequency, and the time they spend in either state is controlled so the averaged output is nearly
sinusoidal. Common modulation techniques include the carrier-based technique, or Pulse-width
modulation, space-vector technique, and the selective-harmonic technique.[15]

Voltage source inverters have practical uses in both single-phase and three-phase applications.
Single-phase VSIs utilize half-bridge and full-bridge configurations, and are widely used for power
supplies, single-phase UPSs, and elaborate high-power topologies when used in multicell
configurations. Three-phase VSIs are used in applications that require sinusoidal voltage
waveforms, such as ASDs, UPSs, and some types of FACTS devices such as the STATCOM. They
are also used in applications where arbitrary voltages are required, as in the case of active power
filters and voltage compensators.[15]

Current source inverters are used to produce an AC output current from a DC current supply. This
type of inverter is practical for three-phase applications in which high-quality voltage waveforms are
required.

A relatively new class of inverters, called multilevel inverters, has gained widespread interest. The
normal operation of CSIs and VSIs can be classified as two-level inverters, due to the fact that
power switches connect to either the positive or to the negative DC bus. If more than two voltage
levels were available to the inverter output terminals, the AC output could better approximate a sine
wave. It is for this reason that multilevel inverters, although more complex and costly, offer higher
performance.[16]

Each inverter type differs in the DC links used, and in whether or not they require freewheeling
diodes. Either can be made to operate in square-wave or pulse-width modulation (PWM) mode,
depending on its intended usage. Square-wave mode offers simplicity, while PWM can be
implemented in several different ways and produces higher quality waveforms. [15]

Voltage Source Inverters (VSI) feed the output inverter section from an approximately constant-
voltage source.[15]
The desired quality of the current output waveform determines which modulation technique needs to
be selected for a given application. The output of a VSI is composed of discrete values. In order to
obtain a smooth current waveform, the loads need to be inductive at the select harmonic
frequencies. Without some sort of inductive filtering between the source and load, a capacitive load
will cause the load to receive a choppy current waveform, with large and frequent current spikes. [15]

There are three main types of VSIs:

1. Single-phase half-bridge inverter

2. Single-phase full-bridge inverter
3. Three-phase voltage source inverter

AC/AC converters[edit]
Main article: AC/AC converter
Converting AC power to AC power allows control of the voltage, frequency, and phase of the
waveform applied to a load from a supplied AC system .[18] The two main categories that can be used
to separate the types of converters are whether the frequency of the waveform is changed. [19] AC/AC
converter that don't allow the user to modify the frequencies are known as AC Voltage Controllers, or
AC Regulators. AC converters that allow the user to change the frequency are simply referred to as
frequency converters for AC to AC conversion. Under frequency converters there are three different
types of converters that are typically used: cycloconverter, matrix converter, DC link converter (aka
AC/DC/AC converter).

AC voltage controller: The purpose of an AC Voltage Controller, or AC Regulator, is to vary the

RMS voltage across the load while at a constant frequency.[18] Three control methods that are
generally accepted are ON/OFF Control, Phase-Angle Control, and Pulse-Width Modulation AC
Chopper Control (PWM AC Chopper Control).[20] All three of these methods can be implemented not
only in single-phase circuits, but three-phase circuits as well.

 ON/OFF Control: Typically used for heating loads or speed control of motors, this control
method involves turning the switch on for n integral cycles and turning the switch off for
m integral cycles. Because turning the switches on and off causes undesirable
harmonics to be created, the switches are turned on and off during zero-voltage and
zero-current conditions (zero-crossing), effectively reducing the distortion.[20]
 Phase-Angle Control: Various circuits exist to implement a phase-angle control on
different waveforms, such as half-wave or full-wave voltage control. The power electronic
components that are typically used are diodes, SCRs, and Triacs. With the use of these
components, the user can delay the firing angle in a wave, which will only cause part of
the wave to be in output.[18]
 PWM AC Chopper Control: The other two control methods often have poor harmonics,
output current quality, and input power factor. In order to improve these values PWM can
be used instead of the other methods. What PWM AC Chopper does is have switches
that turn on and off several times within alternate half-cycles of input voltage. [20]
Matrix converters and cycloconverters: Cycloconverters are widely used in industry for ac to ac
conversion, because they are able to be used in high-power applications. They are commutated
direct frequency converters that are synchronised by a supply line. The cycloconverters output
voltage waveforms have complex harmonics with the higher-order harmonics being filtered by the
machine inductance. Causing the machine current to have fewer harmonics, while the remaining
harmonics causes losses and torque pulsations. Note that in a cycloconverter, unlike other
converters, there are no inductors or capacitors, i.e. no storage devices. For this reason, the
instantaneous input power and the output power are equal.[21]

 Single-Phase to Single-Phase Cycloconverters: Single-Phase to Single-Phase

Cycloconverters started drawing more interest recently[when?] because of the decrease in
both size and price of the power electronics switches. The single-phase high frequency
ac voltage can be either sinusoidal or trapezoidal. These might be zero voltage intervals
for control purpose or zero voltage commutation.
 Three-Phase to Single-Phase Cycloconverters: There are two kinds of three-phase to
single-phase cycloconverters: 3φ to 1φ half wave cycloconverters and 3φ to 1φ bridge
cycloconverters. Both positive and negative converters can generate voltage at either
polarity, resulting in the positive converter only supplying positive current, and the
negative converter only supplying negative current.
With recent device advances, newer forms of cycloconverters are being developed, such as matrix
converters. The first change that is first noticed is that matrix converters utilize bi-directional, bipolar
switches. A single phase to a single phase matrix converter consists of a matrix of 9 switches
connecting the three input phases to the tree output phase. Any input phase and output phase can
be connected together at any time without connecting any two switches from the same phase at the
same time; otherwise this will cause a short circuit of the input phases. Matrix converters are lighter,
more compact and versatile than other converter solutions. As a result, they are able to achieve
higher levels of integration, higher temperature operation, broad output frequency and natural bi-
directional power flow suitable to regenerate energy back to the utility.

The matrix converters are subdivided into two types: direct and indirect converters. A direct matrix
converter with three-phase input and three-phase output, the switches in a matrix converter must be
bi-directional, that is, they must be able to block voltages of either polarity and to conduct current in
either direction. This switching strategy permits the highest possible output voltage and reduces the
reactive line-side current. Therefore, the power flow through the converter is reversible. Because of
its commutation problem and complex control keep it from being broadly utilized in industry.

Unlike the direct matrix converters, the indirect matrix converters has the same functionality, but
uses separate input and output sections that are connected through a dc link without storage
elements. The design includes a four-quadrant current source rectifier and a voltage source inverter.
The input section consists of bi-directional bipolar switches. The commutation strategy can be
applied by changing the switching state of the input section while the output section is in a
freewheeling mode. This commutation algorithm is significantly less complex, and has higher
reliability as compared to a conventional direct matrix converter.[22]

DC link converters: DC Link Converters, also referred to as AC/DC/AC converters, convert an AC

input to an AC output with the use of a DC link in the middle. Meaning that the power in the
converter is converted to DC from AC with the use of a rectifier, and then it is converted back to AC
from DC with the use of an inverter. The end result is an output with a lower voltage and variable
(higher or lower) frequency.[20] Due to their wide area of application, the AC/DC/AC converters are
the most common contemporary solution. Other advantages to AC/DC/AC converters is that they are
stable in overload and no-load conditions, as well as they can be disengaged from a load without
damage.[23]

Hybrid matrix converter: Hybrid matrix converters are relatively new for AC/AC converters. These
converters combine the AC/DC/AC design with the matrix converter design. Multiple types of hybrid
converters have been developed in this new category, an example being a converter that uses uni-
directional switches and two converter stages without the dc-link; without the capacitors or inductors
needed for a dc-link, the weight and size of the converter is reduced. Two sub-categories exist from
the hybrid converters, named hybrid direct matrix converter (HDMC) and hybrid indirect matrix
converter (HIMC). HDMC convert the voltage and current in one stage, while the HIMC utilizes
separate stages, like the AC/DC/AC converter, but without the use of an intermediate storage
element.[24][25]

Applications: Below is a list of common applications that each converter is used in.

 AC voltage controller: Lighting control; domestic and industrial heating; speed control of
fan, pump or hoist drives, soft starting of induction motors, static AC
switches[18] (temperature control, transformer tap changing, etc.)
 Cycloconverter: High-power low-speed reversible AC motor drives; constant frequency
power supply with variable input frequency; controllable VAR generators for power factor
correction; AC system interties linking two independent power systems.[18]
 Matrix converter: Currently the application of matrix converters are limited due to the
non-availability of bilateral monolithic switches capable of operating at high frequency,
complex control law implementation, commutation, and other reasons. With these
developments, matrix converters could replace cycloconverters in many areas.[18]
 DC link: Can be used for individual or multiple load applications of machine building and
construction.[23]

Applications[edit]
Applications of power electronics range in size from a switched mode power supply in an AC
adapter, battery chargers, audio amplifiers, fluorescent lamp ballasts, through variable frequency
drives and DC motor drives used to operate pumps, fans, and manufacturing machinery, up to
gigawatt-scale high voltage direct current power transmission systems used to interconnect electrical
grids.[27] Power electronic systems are found in virtually every electronic device. For example:

 DC/DC converters are used in most mobile devices (mobile phones, PDA etc.) to
maintain the voltage at a fixed value whatever the voltage level of the battery is. These
converters are also used for electronic isolation and power factor correction. A power
optimizer is a type of DC/DC converter developed to maximize the energy harvest
from solar photovoltaic or wind turbine systems.
 AC/DC converters (rectifiers) are used every time an electronic device is connected to
the mains (computer, television etc.). These may simply change AC to DC or can also
change the voltage level as part of their operation.
 AC/AC converters are used to change either the voltage level or the frequency
(international power adapters, light dimmer). In power distribution networks, AC/AC
converters may be used to exchange power between utility frequency 50 Hz and 60 Hz
power grids.
 DC/AC converters (inverters) are used primarily in UPS or renewable energy systems
or emergency lighting systems. Mains power charges the DC battery. If the mains fails,
an inverter produces AC electricity at mains voltage from the DC battery. Solar inverter,
both smaller string and larger central inverters, as well as solar micro-inverter are used
in photovoltaics as a component of a PV system.
Motor drives are found in pumps, blowers, and mill drives for textile, paper, cement and other such
facilities. Drives may be used for power conversion and for motion control.[28] For AC motors,
applications include variable-frequency drives, motor soft starters and excitation systems.[29]

In hybrid electric vehicles (HEVs), power electronics are used in two formats: series hybrid and
parallel hybrid. The difference between a series hybrid and a parallel hybrid is the relationship of the
electric motor to the internal combustion engine (ICE). Devices used in electric vehicles consist
mostly of dc/dc converters for battery charging and dc/ac converters to power the propulsion
motor. Electric trains use power electronic devices to obtain power, as well as for vector control
using pulse-width modulation (PWM) rectifiers. The trains obtain their power from power lines.
Another new usage for power electronics is in elevator systems. These systems may use thyristors,
inverters, permanent magnet motors, or various hybrid systems that incorporate PWM systems and
standard motors.[30]

Inverters[edit]
In general, inverters are utilized in applications requiring direct conversion of electrical energy from
DC to AC or indirect conversion from AC to AC. DC to AC conversion is useful for many fields,
including power conditioning, harmonic compensation, motor drives, renewable energy grid
integration, and spacecraft solar power systems.

In power systems it is often desired to eliminate harmonic content found in line currents. VSIs can be
used as active power filters to provide this compensation. Based on measured line currents and
voltages, a control system determines reference current signals for each phase. This is fed back
through an outer loop and subtracted from actual current signals to create current signals for an
inner loop to the inverter. These signals then cause the inverter to generate output currents that
compensate for the harmonic content. This configuration requires no real power consumption, as it is
fully fed by the line; the DC link is simply a capacitor that is kept at a constant voltage by the control
system.[15] In this configuration, output currents are in phase with line voltages to produce a unity
power factor. Conversely, VAR compensation is possible in a similar configuration where output
currents lead line voltages to improve the overall power factor.[16]

In facilities that require energy at all times, such as hospitals and airports, UPS systems are utilized.
In a standby system, an inverter is brought online when the normally supplying grid is interrupted.
Power is instantaneously drawn from onsite batteries and converted into usable AC voltage by the
VSI, until grid power is restored, or until backup generators are brought online. In an online UPS
system, a rectifier-DC-link-inverter is used to protect the load from transients and harmonic content.
A battery in parallel with the DC-link is kept fully charged by the output in case the grid power is
interrupted, while the output of the inverter is fed through a low pass filter to the load. High power
quality and independence from disturbances is achieved.[15]

Various AC motor drives have been developed for speed, torque, and position control of AC motors.
These drives can be categorized as low-performance or as high-performance, based on whether
they are scalar-controlled or vector-controlled, respectively. In scalar-controlled drives, fundamental
stator current, or voltage frequency and amplitude, are the only controllable quantities. Therefore,
these drives are employed in applications where high quality control is not required, such as fans
and compressors. On the other hand, vector-controlled drives allow for instantaneous current and
voltage values to be controlled continuously. This high performance is necessary for applications
such as elevators and electric cars.[15]

Inverters are also vital to many renewable energy applications. In photovoltaic purposes, the
inverter, which is usually a PWM VSI, gets fed by the DC electrical energy output of a photovoltaic
module or array. The inverter then converts this into an AC voltage to be interfaced with either a load
or the utility grid. Inverters may also be employed in other renewable systems, such as wind
turbines. In these applications, the turbine speed usually varies, causing changes in voltage
frequency and sometimes in the magnitude. In this case, the generated voltage can be rectified and
then inverted to stabilize frequency and magnitude.[15]