Why my igbt circuit fail with inductive load

Thread Starter

Tinsae

Joined Jan 8, 2015
72
Dear all,
I have built igbt dimmer circuit which works fine with resistive load but when I change the load to inductive load the dimming (speed variation of 100 watt universal motor) became barely noticeable. Even when I switch back to the resister load the igbt failed to operate normal. I didnt use any external snubber circuit assuming that the inductive load current is only below 5amps and the igbt I uses is well above this 75amps and 1200v so I guessed the internal free wheeling diode copes with spikes produced. Amazingly very small mosfet works fine irf740 but why not that huge igbt works. I have attached the circuit
 

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Marc Sugrue

Joined Jan 19, 2018
130
I can only assume the avalanche rating of the Mosfet is zenering the back emf from the load spike whilst the IGBT is getting overvolted and getting damaged.
 

crutschow

Joined Mar 14, 2008
24,969
I guessed the internal free wheeling diode copes with spikes produced.
Wrong guess.
The internal transistor diode does not attenuate the spike as it's in the wrong location and polarity for that purpose.
You must use a diode clamp across the motor load to minimize the inductive spikes, as those spikes could exceed the transistor rating.
 
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Thread Starter

Tinsae

Joined Jan 8, 2015
72
I can only assume the avalanche rating of the Mosfet is zenering the back emf from the load spike whilst the IGBT is getting overvolted and getting damaged.
Dear Marc, the igbt used is 1200V do u think 100watt universal motor with less than 5amp could generate a spike over 1200V?
 

Thread Starter

Tinsae

Joined Jan 8, 2015
72
Wrong guess.
The internal transistor diode does not attenuate the spike as it's in the wrong location and polarity for that purpose.
You must use a diode clamp across the motor load to minimize the inductive spikes, as those spikes could exceed the transistor rating.
Exactly I didn't noticed that u are right I should use external diode across the load and test it again. Thanks
 

Thread Starter

Tinsae

Joined Jan 8, 2015
72
Dear all,
as Crutschow said adding diode across the load solve the problem. the same type of igbt now works fine with the circuit attached before


Thank you everybody thank you Crutschow
 

MaxHeadRoom

Joined Jul 18, 2013
20,700
One thing to keep in mind is that a Universal motor operates in a run away condition and rpm is limited by voltage and load, so a 220v motor on rectified AC and with smoothing is operating now on a 300VDC supply, where there is also no limiting due to reduced (non) inductive reactance..;)
Max.
 
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Vivan

Joined Feb 17, 2019
5
One thing to keep in mind is that a Universal motor operates in a run away condition and rpm is limited by voltage and load, so a 220v motor on rectified AC and with smoothing is operating now on a 300VDC supply, where there is also no limiting due to reduced (non) inductive reactance..;)
Max.
Thank you for the reply.
Can you suggest me what better can be done to achive speed regulation of celing fan ? I am currently using Triac with zero cross detector but there is a humming noise created. Cant get it right. So I thought by using an IGBT this may solve the problem and also easy to provide PWM. Now the Microcontroller is busy in Interupts made my by the zero corss detector to fire the triac for phase angle control.
So as you said 300v DC , if i limit the voltage to 220 v dc by controlling the PWM , will it work? Will it be harmful on long run ? Or should i stick with the triac version? Or how can I reduce the humming noice ?
Thank you in advance.
 

MaxHeadRoom

Joined Jul 18, 2013
20,700
It appears you are using a typical PWM with 555, what PWM frequency are you using?
Are you sure it is a Universal motor, usually fans are either shaded pole or small PSC (induction) motors.
Humming usually exists with Triac/phase angle control.
OOps I though you were the OP!
Not good to Hikjack a thread.
Max.
 

Vivan

Joined Feb 17, 2019
5
It appears you are using a typical PWM with 555, what PWM frequency are you using?
Are you sure it is a Universal motor, usually fans are either shaded pole or small PSC (induction) motors.
Humming usually exists with Triac/phase angle control.
Max.
I am using an nodemcu to control the triac. Sorry i am not aware of the PWM frequency. I dont have an access to an oscilloscope .
But again the nodemcu is busy in delay function for firing the triac at proper timing. And is causing problems in other parts of the problem. So i want to switch over to IGBT. But i am not sure this will help me or not. The fan is Std. 220v 50hz 40-50w (INDIA) motor. I had once disassembled it and got to see a magnet fixed to the hub and the stator fixed.
I don’t know much about fan and it’s windings.
By the way how to remove the humming noise ? Is it anything to do with the snubber ciruit ?

I guess using IGBT will ease the work of the nodemcu and work smoothly with other parts if the code easily, because not it need not keep track of zero crossing.

What do you suggest? Should i use IGBT or not ? Will it not damage the windings by heating up or cause problems on long run ?
I made quite bit of research on the internet but couldn’t find a solution. Can you please help me out of this problem?
 

MaxHeadRoom

Joined Jul 18, 2013
20,700
If using Triac control of 50hz/60hz buzz sound is pretty much inevitable.
And if an induction motor your control methods are pretty much limited to Triac control.
Max.
 

Vivan

Joined Feb 17, 2019
5
If using Triac control of 50hz/60hz buzz sound is pretty much inevitable.
And if an induction motor your control methods are pretty much limited to Triac control.
Max.
But in this post i read saying adding an diode across the load will resolve the problem. But i was not sure on the load used .
By using IGBT is there any problem?
 

MaxHeadRoom

Joined Jul 18, 2013
20,700
But in this post i read saying adding an diode across the load will resolve the problem. But i was not sure on the load used .
By using IGBT is there any problem?
You hijacked a thread by an OP that mentioned using a Universal motor!
If yours is Induction motor then it is another ball game.
Max.
 
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