Controlling the Gates of simple Three phase inverter

[Fatima Ali]

How can i control the output frequency of three phase inverter using a microncontroller ?
I have heard that pwm is used for controlling the output ? The output of inverter can be simple square wave for simplicity purposes .
Describe any procedure or share any helpful notes , i would be thankful

 

[cl10greg]

A three phase inverter is pretty much three half bridges that connect to each phase of the load. The load is isolated from power and ground through 2 switches. So to change the frequency you are setting the PWM frequency that is going to the switch. The PWM is what actives and deactives the load phases. Umm any google search will yield multiple examples of this.

 

[Fatima Ali]

A three phase inverter is pretty much three half bridges that connect to each phase of the load. The load is isolated from power and ground through 2 switches. So to change the frequency you are setting the PWM frequency that is going to the switch. The PWM is what actives and deactives the load phases. Umm any google search will yield multiple examples of this.


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How could i generate those pwm signals for driving the gates of the switches .I will need three pwm signals for driving the six transistors .Those pwm signals should be phase shifted ,am i right about this statement ?

 

[FlapJack]

The waveforms are 120 degrees out of phase from each other adding up to 360 degrees.

 

[Fatima Ali]

The waveforms are 120 degrees out of phase from each other adding up to 360 degrees.

Yes flag jack ,that is the main issue .How can i generate those phase shifted waveforms using microcontroller ?

 

[FvM]

The 3 x 120 degree phase shift will be implemented for the modulating signal, usually a sine wave.
Explained e.g. in this application note: https://ww1.microchip.com/downloads/en/AppNotes/00967A.pdf

You can operate an inverter with a simple phase shifted square waves, the operation mode is called fundamental frequency switching, but it hasn't to do with PWM.

 

[Fatima Ali]

The 3 x 120 degree phase shift will be implemented for the modulating signal, usually a sine wave.
Explained e.g. in this application note: https://ww1.microchip.com/downloads/en/AppNotes/00967A.pdf

You can operate an inverter with a simple phase shifted square waves, the operation mode is called fundamental frequency switching, but it hasn't to do with PWM.

How can i generate those phase shifted square waves using microcontroller .The generation of square waves are possible but i am not getting the idea of phase shifting those square waves .Can u suggest any method or algorithm for implementing this phase shifting in microcontroller ?

 

[FvM]

Use a timer interrupt at 6*fundamental frequency and switch the output pattern at each interrupt respectively. Gate drive deadtimes can be either generated in hardware or by additional software delays.

 

[Fatima Ali]

Use a timer interrupt at 6*fundamental frequency and switch the output pattern at each interrupt respectively. Gate drive deadtimes can be either generated in hardware or by additional software delays.

You mean that , i should interrupt with 6 times the fundamental frequency .Whenever timer overflows interrupt should be called and executed .what is the purpose of using these interrupts ? Tell me how could i generate these delays in microcontroller ?

 

[cl10greg]

You mean that , i should interrupt with 6 times the fundamental frequency .Whenever timer overflows interrupt should be called and executed .what is the purpose of using these interrupts ? Tell me how could i generate these delays in microcontroller ?

Correct. The interrupts are for your PWM signals. You need to turn on the phases using a set sequence for the 6 switches. Look at the application note that was provided by FvM.