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praveen_palaparthi
Joined: 15 Feb 2008
Posts: 111
Helped: 1
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 29 Jun 2009 18:15 Help required experts |
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Hi friends i am doing single phase sinusoidal PWM inverter using micro controller.I have generated sine wave at output using sine table.My controller is pic 16f886 output frequency is 50Hz,and swicthing frequency is 20Khz and output at no load is 250 volts rms.I used PWM modules in the controller to generate SPWM.
My problem is when i am switching the load of 200W bulb its output voltage is decreasing to 200V rms.How to correct this voltage.Theory says that by changing modulation index Ma=Ar/Ac Ar=peak amplitude of reference wave,Ac peak amplitude of carrier wave,we can get varaible volta ge but how to implement this in code.I mean how to correct(increase or decrease) the duty cycle.I know by using PI tuning we can get but i dont know how to implement i am not getting the logic can anybody help to get the logic.
can anybody give examples code for this to correct duty cycle using PID tuning
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bobcat1
Joined: 10 Jul 2002
Posts: 1100
Helped: 46
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04 Jul 2009 7:52 Re: Help required experts |
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HI
You need to sample the output voltage (or current) back into the controller and change the PWM acording to load
All the best
Bobi
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praveen_palaparthi
Joined: 15 Feb 2008
Posts: 111
Helped: 1
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06 Jul 2009 13:48 Re: Help required experts |
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| Hello sir for responding to my post.As u know i am doing sinsuoidal inverter using PIC 167886.How to update my duty cycle.sir can u expain me in details as i am new to this type of project.How to vary the duty cycle according to reference value.......
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btbass
Joined: 20 Jul 2001
Posts: 1175
Helped: 111
Location: Oberon
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06 Jul 2009 17:59 Re: Help required experts |
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With sinusoidal control you change the amplitude of the sine wave to vary the output voltage.
Download application note AN1017 from Microchip.
This is an application note for driving a brushless motor with a sinewave, but gives the algorythms for changing amplitude.
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