3 Phase inverter design

[demetal]

Hi,


can anyone just give me some ideas to design a 3 Phase inverter to run a 10 HP motor... Also i would like to know whether it is made from three different single phase inverters drive at 120 degree phase difference....? i prefer a 38v input supply from battery.... so what AH rating should i choose to run this motor for 1 hour...?

Thank You.

 

[BradtheRad]

When a 10 HP motor is running at full load, it draws 7500 watts (converting HP to watts).

Your battery will need to provide 197 A continuously. ( 7500 / 38 )
Add 15 percent for losses through the inverter.

To do this for an hour is possible, if the battery is rated large enough.

When putting out so much current, there is a large power loss through the battery. Taking losses into consideration, you ought to make it 300 AH minimum.

 

[demetal]

When a 10 HP motor is running at full load, it draws 7500 watts (converting HP to watts).

Your battery will need to provide 197 A continuously. ( 7500 / 38 )
Add 15 percent for losses through the inverter.

To do this for an hour is possible, if the battery is rated large enough.

When putting out so much current, there is a large power loss through the battery. Taking losses into consideration, you ought to make it 300 AH minimum.

Thank you for the reply... So what about the inverter design....?

 

[BradtheRad]

At the bottom of this page is a list of threads with similar titles. However the ones I see only contain a few posts (according to the number in parentheses).

It suggests that a 3-phase inverter will not be easy to make. I think it will involve what you stated, that you will need to construct 3 separate inverters, controlled by a single clock which is coordinated so they operate at 120 degrees phase difference.

- - - Updated - - -

Fortunately there are many threads about constructing an inverter.

It will be a question what waveform you desire: sine wave, modified sine, or square waves.

And a question whether you wish to purchase or construct three transformers.

I believe each inverter will need to be 2500 watts.

 

[demetal]

i would like to know which waveform should i use to get it most efficient...? i have heard that using square wave inverters can produce humming noise in inductive loads... I have searched treads for 3 phase inverter but didn't able to find... all of them were talking about single phase inverter... :|

 

[Tahmid]

You should use sine wave. Have you decided which controller you'll use? There are thorough well-explained application notes available using dsPIC and AVR controllers.

 

[BradtheRad]

Yes, there is more buzz from a motor when it is driven with square-ish waves.

Motors run about 10 percent more efficiently on a sinewave.

I don't know how much difference there will be in these regards, due to having 3 waveforms simultaneously.

A sinewave is best to run a motor, but a sinewave inverter is harder to build than a squarish wave inverter.

 

[Tahmid]

You should go through these:

ww1.microchip.com/downloads/en/DeviceDoc/93004A.pdf
ww1.microchip.com/downloads/en/appnotes/00955a.pdf
ww1.microchip.com/downloads/en/appnotes/00843a.pdf
https://ww1.microchip.com/downloads/en/AppNotes/00889b.pdf
www.atmel.com/Images/doc7546.pdf
www.atmel.com/Images/doc7545.pdf

Hope this helps.
Tahmid.

 

[RONY CHAKRABORTY]

Dear dmatel, if u really want to make a 3 phase inverter for drive a motor the best policy would be using microchip 18Fxx31 series. Because they have:
Build in 6 complimentary Hardware PWM with Programmable dead time control. Simultaneous ADC scan of 4 channel at a time. Quad encoder input for motor speed control. Hardware Multiplier etc.

download AN900 from here: **broken link removed**

This is a great App note ever i found about 3 phase Motor control. you will fined the method and hole source code with PID algorithm there

Enjoy!!!