Simple 3 Phase Inverter Circuit

In this post I have explained how to make a 3 phase inverter circuit which can be used in conjunction with any ordinary single phase square wave inverter circuit. The circuit was requested by one of the interested readers of this blog.

UPDATE: Looking for an Arduino based design? You may find this one useful:

Arduino 3 phase inverter

The Circuit Concept

A 3 phase load can be operated from a single phase inverter by employing the following explained circuit stages.

Basically the involved stages can be divided into three groups:

• The PWM generator circuit
• The 3 phase signal generator circuit
• The mosfet driver circuit

The first diagram below shows the PWM generator stage, it may be understood with the following points:

The Oscillator and the PWM Stage

The IC 4047 is wired as a standard flip flop output generator at the rate of the desired mains frequency set by VR1 and C1.

The dimensioned push-pull PWM now becomes available at the E/C junction of the two BC547 transistors.

This PWM is applied to the input of the 3 phase generator explained in the next section.

The following circuit shows a simple three phase generator circuit which converters the above input push-pull signal into 3 discrete outputs, phase shifted by 120 degrees.

These outputs are further bifurcated by individual push-pull stages made from a NOT gates stages. These 3 discrete  120 degree phase shifted, push pull PWMs now become the feeding input signals (HIN, LIN) for the final 3 phase driver stage I have explained below.

This signal generator uses a single 12V supply and not a dual supply.

Complete explanation can be found in this 3 phase signal generator article

The circuit below shows a 3 phase inverter inverter circuit stage using H-bridge mosfets configuration which receives the phase shifted PWMs from the above stage and converts them into corresponding high voltage AC outputs for operating the connected 3 phase load, normally this would be a 3 phase motor.

The 330 high voltage across the indivdual mosfet drivers sections is obtained from any standard single phase inverter integrated across the shown mosfets drains for powering the desired 3 phase load.

The 3-Phase Full-Bridge Driver Stage

In the above 3 phase generator circuit (second last diagram) using a sine wave doesn't make sense because the 4049 would ultimately convert it into square waves, and moreover the driver ICs in the last design employ digital ICs which will not respond to sine waves.

Therefore a better idea is to use a 3 phase square wave signal generator for feeding the last driver stage.

You may refer the article which explains how to make a 3 phase solar inverter circuit for understanding the 3 phase signal generator stage functioning and implementation details.

Using IC IR2103

A relatively simpler version of the above 3 phase inverter circuit can be studied below, using the IC IR2103 half bridge driver ICS. This version lacks the shut down feature, therefore if you do not wish to incorporate the shut down feature, you can try the following simpler design.

Simplifying the Above Designs

In the above explained 3-phase inverter circuit, the 3-phase generator stage looks unnecessarily complex, and therefore I decided to look for an alternative easier option for replacing this specific section.

After some searching I found the following interesting 3 phase generator circuit which looks pretty easy and and straightforward with its settings.

Therefore now you can simply replace the earlier explained IC 4047 and the opamp section entirely and integrate this design with HIN, LIN inputs f the 3 phase driver circuit.

But remember you will have to still use the N1----N6 gates between this new circuit and the full bridge driver circuit.

Making a Solar 3 Phase Inverter Circuit

So far we have learned how to make a basic 3 phase inverter circuit, now we'll see how a solar inverter with a 3 phase output can be built using very ordinary ICs and passive components.

The concept is basically the same, I have just changed the 3 phase generator stage for the application.

Inverter Basic Requirement

For acquiring a 3 phase AC output from any single phase or a DC source we would require three fundamental circuit stages:

1. A 3 phase generator or processor circuit
2. A 3 phase driver power stage circuit.
3. A boost converter circuit
4. Solar Panel (appropriately Rated)

To learn how to match a solar panel with battery and inverter, you can read the following tutorial:

Calculate solar Panels for Inverters

One good example may be studied in this article which explains a simple 3 phase inverter circuit

In the present design we too incorporate these three basic stages, let's first learn regarding the 3 phase generator processor circuit from the following discussion:

How it Works

The diagram above shows the basic processor circuit which looks complex but actually it's not. The circuit is made up of three sections, the IC 555 which determines the 3 phase frequency (50 Hz or 60 Hz), the IC 4035 which splits the frequency into the required 3 phases separated by a phase angle of 120 degrees.

R1, R2 and C must be appropriately selected for acquiring a 50 Hz or 60 Hz frequency at 50% duty cycle.

8 numbers NOT gates from N3 to N8 can be seen incorporated simply for splitting the generated three phases into pairs of high and low logic outputs.

These NOT gates may be acquired from two 4049 ICs.

These pairs of high and low outputs across the shown NOT gates become essential for feeding our next 3 phase driver power stage.

The following explanation details the solar 3 phase power mosfet driver circuit

Note: The shut down pin must be connected to the ground line if not used, otherwise the circuit will not work

As may be seen in the above figure, this section is built across 3 separate half bridge driver ICs using IRS2608 which are specialized for driving high side and low side mosfet pairs.

The configuration looks quite straightforward, thanks to this highly sophisticated driver IC from International rectifier.

Each IC stage has its own HIN (high In) and LIN (low In) input pins and also their respective supply Vcc/ground pins.

All the Vcc are required to be joined together and connected with the 12V supply line of the first circuit (pin4/8 of IC555), so that all the circuit stages become accessible to the 12V supply derived from the solar panel.

Similarly all the ground pins and lines must be made into a common rail.

The HIN and LIN should be joined with the outputs generated from the NOT gates as specified in the second diagram.

The above arrangement takes care of the 3 phase processing and amplification, however since the 3 phase output should be at the mains level and a solar panel could be rated at a maximum of 60V, we must have an arrangement that would enable boosting this low 60 volts solar panel to the required 220V or 120V level.

Using IC 555 Based Flyback Buck/Boost Converter

This can be easily implemented through a simple 555 IC based boost converter circuit as may be studied below:

Again, the shown configuration of the 60V to 220V boost converter looks not so difficult, and can be constructed using very ordinary components.

The IC 555 is configured as an astable with a frequency of approximately 20 to 50 kHz. This frequency is fed to the gate of a switching mosfet via a push pull BJT stage.

The heart of the boost circuit is formed with the help of a compact ferrite core transformer which receives the driving frequency from the mosfet and converter the 60V input into the required 220V output.

This 220V DC is finally attached with the previously explained mosfet driver stage across the drains of the 3 phase mosfets for achieving the 220V 3 phase output.

The boost converter transformer can be built on any suitable EE core/bobbin assembly using 1mm 50 turns primary (two 0.5mm bifilar magnet wire in parallel), and secondary using o.5 mm magnet wire with 200 turns