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Old 12-08-2014, 11:20 AM   #1388 (permalink)
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Originally Posted by MPaulHolmes View Post
I would be interested!! I don't really understand though. so, you have a 300v dc input. You pwm that input to make it look like a pwm version of a sine wave. Then you pwm another one with the complement. Then you subtract the results? How do you subtract them?

The requirement is instead of having complementary PWM outputs for each timer, one needs to have a dedicated output, rather than a complementary mode as they now have.

By default thats not possible with the PIC, but perhaps with a bit of smart coding we could use the interrupts and a look up table to disable one of the channels, so that only the positive or the negative switch can be active at a given time.

For example, assuming an h bridge:
During the positive half cycle, PWM is sent to the high Igbt of leg 1 and the low IGBT of leg 2, so that the voltage is positive (DC-LINK)

During the negative half cycle PWM is sent to the low IGBT of leg 1 and the high IGBT of leg 2, so that the voltage is negative (-DC-LINK)

Here's an example for a single phase inverter using this topology

Last edited by cts_casemod; 12-08-2014 at 12:10 PM..
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