Power Electronics Types of Inverters - Power Electronics

What are the types of inverters in power electronics?

Inverter is a power electronic device which will convert power in DC form to AC form at the required frequency and voltage output.

Inverters can be classified into two major categories

  • Voltage Source Inverter (VSI) − Voltage source inverter will have stiff DC source voltage, which means that the DC voltage will have limited or zero impedance at the inverter input terminals.
  • Current Source Inverter (CSI) − Current source inverter will be supplied with a variable current from a DC source which has high impedance and as a result of this, current waves will not be influenced by the load.

Single Phase Inverter

Single phase inverters are of two types− full bridge inverter and half bridge inverter.

Half Bridge Inverter

Half Bridge inverter is the basic building block of a full bridge inverter which consists of two switches and each of its capacitors will have a voltage output equal toPETI . Additionally, switches will be complementing each other i.e. if one is switched ON the other will go OFF.

Full Bridge Inverter

Full Bridge inverter circuit used to convert DC to AC and it uses the closing and opening the switches in the right sequence for the conversion. It includes four types operating states according to the closed switches.

Three Phase Inverter

A three-phase inverter is used to convert the DC input into a three-phase AC output. The main three arms of three phase inverter are delayed by an angle of 120° while creating a three-phase AC supply. Her each inverter switch will have a ratio of 50% and switching will happen for each T/6 of the time T (60° angle interval). Switches S1 and S4, S2 and S5 and switches S3 and S6 are depending on each other.
Following images provides a picture of the circuit for a three phase inverter which appears like three single phase inverters held at the same DC source. Pole voltages in a three phase inverter is similar to the pole voltages in single phase half bridge inverter.

3_phase_inverter.jpg

Above two types of inverters will have two modes of conduction − 180° mode of conduction and 120° mode of conduction.

180° mode of conduction

Let’s find that the180° mode of conduction of each device will be in held in the conduction state for 180° as they are switched ON at 60° intervals. While terminals A, B and C are called as the output terminals of the bridge which connected to the three-phase delta or star connection of the load.
Remaining star connected load operation will be explained as mentioned in the below image. Points S1, S5 and S6 will be in conduction mode for the period 0° − 60°. Terminals A and C of the load will be connected to the source at its positive point and terminal B will be connected to the source at its negative point. Additionally, resistances R/2 will be among the neutral and the positive end whereas resistance R will be among the neutral and the negative terminal.

180_mode_of_conduction.jpg

The load voltages are gives as follows;

VAN = V/3,

VBN = −2V/3,

VCN = V/3

The line voltages are given as follows;

VAB = VAN − VBN = V,

VBC = VBN − VCN = −V,

VCA = VCN − VAN = 0

Waveforms for 180° mode of conduction

180_mode_waveform.jpg

120° mode of conduction

While the 120° conduction mode, each device will be in a conduction state for 120°. This mode is applicable for a delta connection in a load which will result in a six-step type of waveform of its phases. So only two devices will act as a each device and each device can conduct at only 120°.

On the load, terminal A will be connected to the positive end whereas terminal B will be connected to the negative end of the source. Terminal C on the load will be in a state which is known as floating state. Additionally, phase voltages will be equal to the load voltages as shown below.

Phase voltages = Line voltages

VAB = V

VBC = −V/2

VCA = −V/2

Waveforms for 120° mode of conduction

120_mode_waveform.jpg

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