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[SOLVED] EMI reduction using GTO

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roiberts

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Dear Forum

Now, for regulating the power in owr load, we use a Triac turned ON after some msec from the zero cross of a 220V-50HZ power supply..
So,we create 2 slices ,opposidet sign, each 10msec (50 HZ ).

This bring us to EMI problem, beetwen 150K and 2MHZ.

Question is: could be better to subdivide the sine wave in more slices, using a GTO, with PWM of some MHZ, so, moving the spectral contents more in HF ?

Maybe in this way we can avoid a bigger EMI filter at circuit input.

Any suggestion are nice.

Thanks very much

Roberto
 

GTO switching at MHz? Oops! That's completely unrealistic. Even very fast switches like SiC MOSFET won't be used in this range.

150 kHz to 2 MHz EMI with phase angle control is definitely manageable with filters. The problem is however harmonic currents, thus power quality standards allow it only for lighting purposes.

High frequent pwm control of AC loads may be implemented with IGBT or MOSFET, realistic switching pwm frequencies are 5 to 100 kHz range.
 

Thanks FvM for your reply.

The main question could be : when I move to PWM tecnicr for reduce power, the spectral contents is lower or not ? Is a good idea to slice the sine wave in more than 2 parts (as Triac do) for EMI ?

Thanks again for your time

Roberto
 

Using high frequent PWM (quasi continuous variation of the 50 Hz voltage) eliminates 50 Hz harmonics but adds pwm frequent (fundamental + harmonics) interferences. Looking at the unfiltered modulated voltage and current, the noise power is increased, not reduced.

Consider that the permitted noise level for 150 kHz to 30 MHz conducted interferences is in the mV range, you need > 100 dB attenuation between switcher and supply.
 

yes it sounds like you are doing leading edge dimming.
I think trailing edge dimming may be slightly less EMC noisy.
You can also make the switched egde slower to reduce emc.
If its say a dimmer at the installation input to a big building full of incancescant lamps, then chopping the mains at high frequency would not be good as the HF in the distribution wiring would create a big EMC problem.
 

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