3 Phase IGBT Inverter - LC Filter and Capacitor ground selection

[suri007]

Hello,

I am working on 3 phase IGBT inverter project in unbalanced condition so that i can use the Phases independently. As the Load would not be a Motor and i am using 3 phases independently to control 3 resistive loads (bulbs) I know to generate a Neutral point at the output common for three phases.


Below are my queries

1) From where should i take the Neutral point / How to generate the Neutral point if there is any pre-existing method

2) Design of LC filter - How to select it for an Output freq of 50HZ

3) The capacitor one end will be connected to Inductor, Other end of capacitor should be connected to which point?

I hope you guys can help me over come this problem


Regards,
Suresh

 

[tcmtech]

Is it even necessary?

 

[Misterbenn]

In an unbalanced 3phase system the neutral point will have a voltage. As it is simply the sum of the 3phase voltages, so if the voltages aren't balanced the neutral point will not be 0. However that doesn't mean your idea wont work, just don't go connecting neutral to earth!

As for how to generate your 'neutral' - which I'll refer to as the star point from here on in - your trying to create a Wye system. See here https://en.wikipedia.org/wiki/Three-phase_electric_power#mediaviewer/File:3-phase_flow.gif.
So your load in this case the bulbs need to have one terminal connected to a phase and the other terminals of all bulbs joined together to create your start point.

there are two types of capacitor arrangements, one where they are form a star point (i.e one terminal connected to phase, the other terminal of all caps are joined) these are termed Y caps.
The other arrangement has 3 capacitors connected phase to phase, so A-B, A-C & B-C.
If the capacitors fail it can be very dangerous so over-rate the capacitors significantly in terms of voltage, current and temperature.