A COMPREHENSIVE DESCRIPTION OF INVERTERS IN POWER ELECTRONICS?

What is inverter in power electronics?

Inverter in power electronics field is defined as a device or circuitry used for conversion of direct current to alternating  current.The reverse process of of this inversion is called rectification performed with the help of rectifier.

inverter(dc to ac)

Nature of phase in invertes?

Normally we always discuss only two types of phase single phase and three phase.Similarly here phase wise inverter is named as single phase inverter and three phase inverter.

Types of dc to ac inverters?

There are mainly three types of dc to ac inverters.
1.voltage fed inverter

                                      This inverter is a sort of inverter where input voltage is contant

2.current fed inverter

                                      The inverter in which input current is constant is called current fed inverter.

3.variable dc linked inverter

                                      This is a special sort of inverter where we are capable of  getting variable output voltage.

Operations performed by inverter?

We can say inverter facilitates us to perform multi  operations  of required scenarion  with the help of this device.We can get variable dc by using inverter. Voltages and currents can be got in a varied form by the applications of inverter whenever we want in different ooperations. Similarly power and frequency variations can be done with the help of inverter.

What is cyclo converter?

Cyclo converter is a converter having special feature of converting one form of ac into an other form of ac in such a way that frequencies of both ac forms before and after modification of form do change according to our desire and requirement. This conversion of ac to ac is possible by using by many other devices and operations but with one limitation that frequency before and after the conversion is same this constant frequency problem is solved using cycloconverter.  

cycloconverter configuaration

Circuit description

Top: Simple inverter circuit shown with an electromechanical switch

and automatic equivalent

auto-switching device implemented with two transistors and split winding auto-transformer in place of the mechanical switch.

Square waveform with fundamental sine wave component, 3rd harmonic and 5th harmonic

Basic design

In one simple inverter circuit, DC power is connected to a transformer through the center tap of the primary winding. A switch is rapidly switched back and forth to allow current to flow back to the DC source following two alternate paths through one end of the primary winding and then the other. The alternation of the direction of current in the primary winding of the transformer produces alternating current (AC) in the secondary circuit.

The electromechanical version of the switching device includes two stationary contacts and a spring supported moving contact. The spring holds the movable contact against one of the stationary contacts and an electromagnet pulls the movable contact to the opposite stationary contact. The current in the electromagnet is interrupted by the action of the switch so that the switch continually switches rapidly back and forth. This type of electromechanical inverter switch, called a vibrator or buzzer, was once used in vacuum tube automobile radios. A similar mechanism has been used in door bells, buzzers and tattoo machines.

As they became available with adequate power ratings, transistors and various other types of semiconductor switches have been incorporated into inverter circuit designs. Certain ratings, especially for large systems (many kilowatts) use thyristors (SCR). SCRs provide large power handling capability in a semiconductor device, and can readily be controlled over a variable firing range.

The switch in the simple inverter described above, when not coupled to an output transformer, produces a square voltage waveform due to its simple off and on nature as opposed to the sinusoidal waveform that is the usual waveform of an AC power supply. Using Fourier analysis, periodic waveforms are represented as the sum of an infinite series of sine waves. The sine wave that has the same frequency as the original waveform is called the fundamental component. The other sine waves, called harmonics, that are included in the series have frequencies that are integral multiples of the fundamental frequency.

Fourier analysis can be used to calculate the total harmonic distortion (THD). The total harmonic distortion (THD) is the square root of the sum of the squares of the harmonic voltages divided by the fundamental voltage: {\displaystyle {\mbox{THD}}={{\sqrt {V_{2}^{2}+V_{3}^{2}+V_{4}^{2}+\cdots +V_{n}^{2}}} \over V_{1}}} \mbox{THD} =  {\sqrt{V_2^2 + V_3^2 + V_4^2 + \cdots + V_n^2} \over V_1}

Advanced designs

H bridge inverter circuit with transistor switches and antiparallel diodes

There are many different power circuit topologies and control strategies used in inverter designs. Different design approaches address various issues that may be more or less important depending on the way that the inverter is intended to be used.

The issue of waveform quality can be addressed in many ways. Capacitors and inductors can be used to filter the waveform. If the design includes a transformer, filtering can be applied to the primary or the secondary side of the transformer or to both sides. Low-pass filters are applied to allow the fundamental component of the waveform to pass to the output while limiting the passage of the harmonic components. If the inverter is designed to provide power at a fixed frequency, a resonant filter can be used. For an adjustable frequency inverter, the filter must be tuned to a frequency that is above the maximum fundamental frequency.

Since most loads contain inductance, feedback rectifiers or antiparallel diodes are often connected across each semiconductor switch to provide a path for the peak inductive load current when the switch is turned off. The antiparallel diodes are somewhat similar to the freewheeling diodes used in AC/DC converter circuits. Courtesy of wikipedia.....