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Author Topic: Which is better in AC Control ? -- Phase Angle Control or Pulse Skipping?  (Read 2871 times)
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tAhm1D
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« on: July 25, 2009, 12:44:08 12:44 »

Hi,
In different Projects, where AC has to be controlled like Battery Charging, Heater Control, Ac Motor control,Electronics/Electrical Appliance control etc., Phase Angle Control and Pulse Skipping (sometimes known as Burst Fire Triac/SCR AC Control) methods are used randomly. Earlier,different types of ICs were mainly used for this purpose. But with the advent of Microcontroller, the system became easier and very small Microcontrollers(like 8 pin- pic 12F675) can now be used for this job, which earlier use to be done by Trac/Diac, IC and OPAmp etc.etc.
Out of this 2 Method, for AC Control, which one is better and preferable? Why?
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myheadhurts
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« Reply #1 on: July 25, 2009, 03:13:16 15:13 »

If you are constrained by emc/emi requirements then Burst Fire is a good choice if the load can support it .As you are giving complete phases to the load and switching at zero current the emc/emi  is reduced quite significantly and so its great for slow systems such as heaters etc..
The downside of burst firing is when using a fast changing  load such as a tungsten filament light bulb ...so thats where you'll need Phase Angle Control.

Burst Fire does simplify emc/emi ..
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tAhm1D
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« Reply #2 on: July 25, 2009, 03:59:14 15:59 »

Hi,
you are correct. Pulse skipping/Burst fire is done just after the Zero xing and hence emi/emc problem reduced. Moreover sine shape is not disturbed.In phase Angle Control, the Sine Shape is distorted and hence lot of problem in its use. In an Application Note of Toshiba, I have seen they advocate to use Burst Fire for Single Phase Ac Motor control. I have not use Burst Fire so far and not sure whether can be applied in Ac Motor control or not. However,I used phase angle control for Battery Charging. However,use of these requires lot of Practical Application Knowledge.
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myheadhurts
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« Reply #3 on: July 25, 2009, 09:10:07 21:10 »

"However,use of these requires lot of Practical Application Knowledge."

Amen to that one... Burst fire could have become forgotten and "old hat" if it werent for EMI issues and testing regimes now being a fundamental design hoop to go through.

There was a great chip by plessey ..the tda2086a... for phase Angle Control of  AC motors /battery charging etc...
plesseys demise and the subsequent loss of this chip was a prime mover for me to move over to cplds / microcontrollers from analog/cmos discrete designs.

Rob
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tAhm1D
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« Reply #4 on: July 28, 2009, 07:38:37 19:38 »

Hi,
There are some good chips are there in the market. One that produced by Atmel is good. But I think now a days people prefer Microcontroller to use for this purpose. Small Micros with lot of internal features made the task easy and simple. I also prefer to do with Microcontroller.

I have not used Burst Fire technique but now a days I am working with it and find it very useful. This technique can be used in lot of Applications I hope and one important aspect of it is immune from EMI disturbances.
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darwin
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« Reply #5 on: December 02, 2009, 05:59:41 17:59 »

Hi,

What type of AC motor are you trying to control. If it's a 3 phase AC motor then a good control method is field oriented control also know as vector control. If you want more information on the subject send me a replay and I'll post some info.
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tAhm1D
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« Reply #6 on: December 03, 2009, 04:58:04 16:58 »

Hi,
Actually I want to use current control in smps welding machine with AC phase angle control/pulse skipping method. I have applied these processes with the help of Pic Microcontroller and came to a conclusion that, Phase Angle Control is better. This is exclusively my personal opinion. Hope to get your opinion to formulate a concrete Idea.
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darwin
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« Reply #7 on: December 10, 2009, 04:33:05 16:33 »

It seems I probably need some more information on your system. How are you sensing the load on the welder?
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