Please verify the logic

I have created a sine look up table and in a timer interrupt of 10ms i am loading one value each upto 256...

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To drive the legs for switching a vague method i have created is calculate the difference between previous voltage to present voltage and increase the duty cycle by some value of 20.

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andre_teprom said:

The concept seems correct at all, I used the same look-up logic with an inverter. I'm assuming you mean by 256 to the maximum allowed value to the duty-cycle register of some PWM module.

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void Sinewave(void)
{
    static int index=0;
    
    if(index <= 256)
    {
         voltage_a= sin(2*PI*index/256);
         voltage_b= sin(2*PI*index+85/256);
         voltage_c= sin(2*PI*index+170)/256);
         index++;
    }
    else
    {
         index = 0;  
    }    
}

There are issues on this method; the most critical is that you are using a constant correction value instead of using some kind of loopback control proportional to the difference.

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void pwm(void)
{
    double diff_phaseA=0.0;

   
   previous_phaseA=present_phaseA;
   present_phaseA=  voltage_a;
   
    if(present_phaseA >  previous_phaseA)
    {
     diff_phaseA= present_phaseA -  previous_phaseA;
     PDC1 += diff_phaseA * 200; /* diff_phaseA is in the range of 0.00 hence multiplying with 200*/
     if(PDC1 >= 500)
         PDC1 = 500;
    }
    else
    {
        
       diff_phaseA = previous_phaseA -  present_phaseA ;
        PDC1 -= diff_phaseA  * 200;
        if(PDC1 <= 2)
            PDC1=2;
    } 
}