Three Phase Inverter Circuit

The post discuses a 3 phase inverter driver 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.


The Request

i would like to build an inverter for 3-phase (380V) submersible pumps. The pump is rated 5.5kW and is used in a borehole...Can u help

The Design

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 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 555 IC is configured as a PWM generator which sets the RMS of the 4047 output to the required degree by chopping the output transistor base signals. 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 NPN/PNP transistor 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 explained below.
This signal generator uses a single 12V supply and not a dual supply.

Complete explanation of this 3 phase signal generator can be read HERE




The circuit below shows a 3 phase mosfet driver stage 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. 







PLENTY OF ISSUES IN THE ABOVE DESIGN
The above circuits are not entirely correct and needed a few serious corrections.

After reassessing the circuits I have come up with the following revised diagrams of a 3-phase inverter circuit.

Presently it's a square wave type, I'll soon explain how it could be converted into a modified pure sine wave simply by inserting a dimesioned PWM input to the shut down pins of the half bridge driver ICs.

The ground rail of all the circuits should be terminated into a common line.




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