Inverter: Types, Circuit Diagram and Its Applications
Table of Contents
A power electronic device known as an inverter transforms power from DC form to AC form at the required output frequency and voltage.
Inverters are classified into two main categories −
- Voltage Source Inverter VSI − The voltage source inverter has a stiff DC source voltage, meaning the DC voltage at the inverter input terminals has little to no impedance.
- Current Source Inverter CSI − A DC source with high impedance provides a variable current to a current source inverter. The load has no effect on the current waves that result.
Single Phase Inverter
There are two types of single phase inverters − full bridge inverter and half bridge inverter.
Half Bridge Inverter
A full bridge inverter’s fundamental building block is this kind of inverters. It has two switches and capacitors with voltage outputs that are equal to Vdc/2. Additionally, the switches work in tandem; that is, when one is turned ON, the other turns OFF.
Full Bridge Inverter
Using an inverter, DC is changed into AC. It accomplishes this by properly closing and opening the switches. It operates in four different modes depending on which switches are closed.
Three Phase Inverter
An inverter produces a three-phase AC output from a DC input. The three arms of this device are typically delayed by an angle of 120° to produce a three-phase AC supply. Every T/6 of the time T 60°angle interval, an inverter switch with a ratio of 50% will switch. Switches S1 and S4, S2 and S5, and S3 and S6 all work in concert with one another.
The figure below shows a circuit for a three phase inverter. It is nothing but three single phase inverters put across the same DC source. The pole voltages in a three phase inverter are equal to the pole voltages in single phase half bridge inverter.
The two types of inverters above have two modes of conduction − 180° mode of conduction and 120° mode of conduction.
180° mode of conduction
Every device in this mode of conduction spends 180 degrees in the conduction state before turning ON every 60. The three-phase delta or star connection of the load is connected to the bridge’s output terminals A, B, and C. The diagram below explains how a balanced star connected load works. The points S1, S5, and S6 are in conduction mode from 0° to 60°. The load’s terminals A and C are connected to the source’s positive point. The negative end of terminal B is where the source is connected. Resistance R/2 is located between the neutral and the positive terminal, whereas resistance R is located between the neutral and the negative terminal.
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
120° mode of conduction
Each electronic component is in a conduction state for 120 degrees in this mode of conduction. It produces a six-step waveform across any of its phases, making it ideal for a delta connection in a load. Because each conducts at only 120°, there are never more than two devices conducting at once. The positive end of the source is connected to the load’s terminal A, and the negative end is connected to the load’s terminal B. The load’s terminal C is in a state known as floating state. Additionally, as shown below, the phase voltages match the load voltages exactly.
Phase voltages = Line voltages
VAB = V
VBC = −V/2
VCA = −V/2