Dead Time Constant of IGBT

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raf23 Active Contributor Join Date: Feb 2010 Location: cochin,kerala Posts: 18	Dead Time Constant of IGBT 04/02/2013 5:07 AM
	Hi I'm working on a project to control single phase ac induction motor in which i planned to use two IGBTs ,one for switching the pwm to the motor(for AC chopping and pwm frequency is fixed @16khz) and one for freewheeling the motor. A symbolic circuit is included here. I know the dead time of IGBTs is going to have some effect on the system. I want to know how worst the system is going to be effected because of this dead time and what are the remedies with respect to hardware and software. what will happen if i completely ignore the dead time . Any help would be deeply appreciated.
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	Pathfinder Tags: AC motor induction motor speed control

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Yahlasit Guru Join Date: Dec 2008 Location: Cd. Juarez, Chihuahua, Mexico. Posts: 1023 Good Answers: 69	#1 Re: Dead Time Constant of IGBT 04/02/2013 9:33 AM
	Before you worry about "dead time", you have to understand the very basic principle of operation of a frequency inverter, a grosso modo: It rectifies the incomming supply voltage, then it uses "H" transistor bridges in order to alternate the polarity of the PWM current applied to the load. In your tiny drawing, I see you're using a single phase motor, just make sure it is a shaded pole or a synchronous motor, because one with a start winding just won't open the centrifugal switch at low RPMs, leading to overheating. Forget about AC chopping, it would only work with a universal motor. Before you embark on this project, I strongly sugest that you read about electric motors. I know you're excited about your project, but you can't force things to work the way you want it, the electric motor theory has been here for over a century, learn it. __________________ No hay conocimiento ni herramienta que sustituya al sentido comun.
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tcmtech Guru Join Date: Jun 2009 Location: South of Minot North Dakota Posts: 8376 Good Answers: 775	#2 Re: Dead Time Constant of IGBT 04/02/2013 12:34 PM
	Your circuit will not work with a alternating current motor of any design. What yo have there would only work with a direct current motor. As mentioned earlier you clearly have a lot of learning ac motors and power to do first.
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Snave Power-User Join Date: Oct 2007 Location: S. California, USA Posts: 279 Good Answers: 12	#3 Re: Dead Time Constant of IGBT 04/03/2013 11:48 AM
	The two above comments are right on. By the way, a universal motor is a bit of an odd motor in that it can be powered from either a DC or AC source.
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