DC to AC Converter - Inverter - An Introduction
DC to AC Converters - Inverters:
We know that,
The circuit which converts AC into DC is called as Rectifier.
The circuit which converts DC into DC with different voltage level(step up or step down) is called as Chopper.
The circuit which converts AC into AC with different frequency level(increase or decrease) is called as cycloconverter.
In this post, we are going to see the inverter circuits.
The circuit which convert DC power into AC power at desired output voltage and frequency are called as Inverters.
Normally the DC source is a battery or output of the controlled rectifier.
Inverters are widely used in standby power supplies, UPS, induction heating, induction motor drives etc.
- The inverter circuit's output voltage waveform can be square wave, quasi-square wave or low distorted sine wave.
- AC output voltage is built by using SCR as switches. So inverter circuit with fewer components have non sinusoidal output waveform.
- By adding complex circuits, it is possible to obtain sinusoidal output voltages.
- With the help of drives of the switches(SCRs), the output voltage can be controlled (ie, adjustable).
- To control the output voltage of inverters, the pulse width modulation(PWM) techniques are generally used. Such inverters are known as PWM inverters.
- The output voltage of the inverter contain harmonics whenever it is non sinusoidal. These harmonics can be reduced by using proper control schemes.
Classification of Inverter Circuits:
The inverters can be classified as voltage source inverters or current source inverters.
- When input DC voltage remains constant, then it is called voltage source inverter (VSI) or Voltage Fed Inverter (VFI).
- When input supply current is maintained constant, then it is called current source inverter (CSI) or Current Fed Inverter (CFI).
- Some times the DC input voltage to the inverter is controlled to adjust the output. Such inverters are called variable DC link inverters.
- The inverters output can be single phase or three phase.
There are four important inverter circuits.
- Center-tapped DC supply (or) Half bridge inverter
- Inverter with center taped load
- Single phase bridge inverter
- Three phase bridge inverter
Requirements of a Practical Inverter are listed below
- Ability to operate into an inductive load
- Provision for over current protection.
- Controllable output
- Close proximity of the output waveform to sinusoidal waveform
- Ability to work with load disconnected
- Drive rating should not be exceeded
Some of the industrial applications of the inverter circuits are given below
- Standby aircraft power supplies
- High voltage DC Transmission
- Variable frequency AC drives
- Induction heating
- Uninterruptible power supplies for computers
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