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Need Help In Fiter Designing Of Three Phase Inverter...:(

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How long are your wires between the hcpl and the gate? How are you doing the supply voltage for the hcpl output? Please show the complete schematic.
Also, why do you have a 220nF cap across the gate? That makes no sense and sure will ruin your edges.
 
Actually my wires are too long from hcpl to mosfet.maybe 1 foot or more...
And I have a separate isolated supplies from ferrite core..converting 48vdc to 4 isolated supplies...for 6 fets
(3-phase bridge).
220n is to supress any noise on gate...
 
The HCPL should be as close as possible, definitely don't use that capacitor.
 
It scommon practice for industrial inverters to regen, a bias is applied to the windings and the motor used as a generator, a voltage monitor is also placed across the dc bus, if the regen bumps up the volts too much a transistor dumps the excess across a braking resistor.
If you need a brake to stop motion very quickly, or to hold something at zero speed, you can get dc brakes that fit on the back of standard frame size motors.
 
One very simple and rather effective variable braking method for induction motors is to inject DC power into one of the phases. Depending on the current applied the braking effect can be easily adjusted from near nothing to well over the motors normal running torque.

Downside is you are dissipating all the mechanical energy directly into heat in the motors rotor.
 
Hello,

You need to look over your gate drive circuit more carefully. For one thing, you can not connect a capacitor from gate to source and expect to see clean sharp waveforms on the output. It's hard enough to overcome the effect of the already present input capacitance (often goes by the 'gate charge') with the driver so adding another cap can only make matters worse.
The gate drive has to rise sharply, and when it is time to turn off it has to fall sharply. Anything else will cause output voltage ramping which eats up power and could overheat the MOSFET.
 
Yes back in the 80's dc injection braking units were popular on machine tools, they were effective some machine manufacts said you could only stop the machine using the emergency brake 3 times before something broke.
 
Thaks all...
One more ques...howw can I measure the voltage...wether its overshooting dc bus or not..
Maybe scope on the dc bus?
 
Since I have no data about motor...
How can I set my v/f ratio for max torque...
Is there any hit and trial method...
At the moment
I start my motor at 18Hz...and almost 7v between two phases and max motor voltage is 30v rms...starting current at above stated freq is almost 30amps which settels at 15amps...
 
To detect overvoltage you could use an analogue circuit that switches a mosfet or igbt with pwm, the more overvoltage the bus goes the wider the pulse width.
This does however cry out for a microcontroller, most have atod and pwm modules.
 
Hmm will try thi....
I am more interested about breaking at the moment....
Can't I apply same phase to all winding(3)
So that it may stall the motor..although gradually due to momentum of the truck.
What I am doing is I m soft stopping the motor but it takes too long to stop...
I am gradually decreasing the amplitude of my output to zero....
One more thing ..how long should be the soft start period...as at the moment my soft start period is also long...
I have already mentioned it takes almost 30 amps to start motor and then setteles at 15amps...
Thanks
 
Hi,
I am stuck at v/f ratio as i mentioned earlier i don't have much data about motor.
please tell me some ways to estimate the best ratio for my application and what should be the max and min freq limits of my motor.
p = 2.6kw
v = 30v
AT26A2 printed on the frame which i searched over the net but couldn't get a clue.
60min printed in plate..thats all info i have please help me to chose right freq and voltage to start the motor..
i use to start the motor at 20Hz and it takes almost 40amps to start and after starting current settles at 30amps its not very smooth sometimes stalls at 20Hz so i adjust the freq..
i doubt my v/f is not optimal for the correct operation of motor...
i roughly assumed my max freq to be 75Hz which i don't know why is did that i have no experience on three phase motors...
Need you help..
Thanks.
 
Hi,
I am stuck at v/f ratio as i mentioned earlier i don't have much data about motor.
please tell me some ways to estimate the best ratio for my application and what should be the max and min freq limits of my motor.
p = 2.6kw
v = 30v
AT26A2 printed on the frame which i searched over the net but couldn't get a clue.
60min printed in plate..thats all info i have please help me to chose right freq and voltage to start the motor..
i use to start the motor at 20Hz and it takes almost 40amps to start and after starting current settles at 30amps its not very smooth sometimes stalls at 20Hz so i adjust the freq..
i doubt my v/f is not optimal for the correct operation of motor...
i roughly assumed my max freq to be 75Hz which i don't know why is did that i have no experience on three phase motors...
Need you help..
Thanks.
 
Hi,

I regret that i can not remember the details of how we did this back in the 1980's. It was a long time ago and i had to hand over all my notebooks when i left the company, for obvious reasons.
On the other hand it may depends on the motor being used too, so you probably have to ask the manufacturer. If they can help you, then you are suck with experimenting until you find a workable solution. You would have to be able to apply mechanical loads to the motor shaft too in order to do these kinds of tests.

One thought that comes up is that maybe you can incorporate some feedback. Measuring various parameters might tell you what is best, and that could feed back to the control circuit. For one simple example, you could measure the shaft speed and if it goes too low then increase some parameter, measure current, look for power used, decide what is best. I would think that a minimum power solution would be good.
 
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