We have already learned how to make a simple solar inverter circuit, in this article we'll see how a solar inverter with a 3 phase output can be built using very ordinary ICs and passive components.
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:
- A 3 phase generator or processor circuit
- A 3 phase driver power stage circuit.
- A boost converter circuit
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 the Circuit 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
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