Inverters convert DC to AC. They are commonly used to power devices that require AC from DC sources like batteries or renewable energy. Inverters can be classified by their input source (voltage source inverters take DC voltage while current source inverters take DC current), connection type (series, parallel, bridge), output waveform (square, quasi-square, PWM), and commutation method (line commutated uses zero crossings while force commutated requires an external source to turn devices off).

1. Inverters

2. Inverters
 A device which converts DC into AC is known as
Inverter. Most of the commercial, industrial, and residential
loads require AC sources.
 Alternating current is converted into direct current (DC) for
storage purposes. The polarity of DC sources doesn’t
change with time like AC sources so, DC can be stored
in batteries and ultra-capacitors.
 Whenever AC is required to run AC appliances, DC is
converted back into AC to run AC appliances. Also, Inverters
have gained much attention due to rise in renewable energy
technologies
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3. Types of Inverters
 Inverters are classified into many different categories based on the
applied input source, connection wise, output voltage wise etc.
Input Source Wise Classification
 The inverter can be defined as the device which converts DC input
supply into AC output where input may be a voltage source or current
source.
Voltage Source Inverter (VSI)
 The inverter is known as voltage source inverter when the input of the
inverter is a constant DC voltage source. The input to the voltage
source inverter has a stiff DC voltage source. Stiff DC voltage source
means that the impedance of DC voltage source is zero.
 VSI are assumed to be supplied with ideal voltage sources (very low
impedance sources).
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4. Types of Inverters
Current Source Inverter (CSI)
The inverter is known as current source inverter when the input of
the inverter is a constant DC current source. Stiff current is
supplied to the CSI (current source inverter) from the DC source
where the DC source have high impedance.
Types of inverters based on connections:
Series and parallel inverters, and bridge type inverters
Classification based on Waveshape of output voltage:
Square wave inverter, Quasi Square wave inverter, and PWM
inverter
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5. Commutation
 Process of turning off a conducting SCR
 Commutation can be natural (AC source) or forced
(DC source). The latter has further two types i.e.,
current commutation and voltage commutation
Forced Commutation:
 Current Commutation: if SCR is turned off by reducing
its anode current below the holding current value, the
commutation is called current commutation
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6. Commutation
Forced Commutation:
 Voltage Commutation: if SCR is turned off by applying a
large reverse voltage across it, it is called voltage
commutation.
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7. Types of Inverters
Commutation Wise Classification:
 Silicon controlled rectifiers are mainly divided into two main
types according to commutation techniques. Line
commutated and force commutated inverters
Line Commutated:
The device is turned off when the current in SCR experience
zero characteristics. This commutation process is known as
line commutation while inverters working on this principle are
known as Line commutated Inverters.
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8. Types of Inverters
Force Commutated
 The supply does not experience zero points in this type of
commutation. That’s why some outside source is needed
to commutate the device. This process of commutation is
known as force commutation while inverters based on this
process are known as Force commutated inverters.
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