Forced commutation of thyristor pdf

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-off (commutation) SCR Thyristor 6500V/1500A. Phase control thyristors. In order to turn the thyristor off, the load current must be reduced below its holding . current I. H. for sufficient time to allow all the mobile charge carriers to vacate the junction. This is achieved by "forced commutation" in DC circuits or at the end of the conducting half cycle in AC circuits. (Forced commutation is Forced Commutation 1) Class A commutation Circuit should be under-damped. 4L < — for damped oscillations. Ringing frequency, LC 4L2 Thyristor conducts for a period of = — R (load) Commutating Components . 2) Class-B commutation or current commutation TM peak TA peak Time required to turn OFF TM after T ON • Conduction time of T = : 3T(Jüc = circuit turn off time tCM Where VR = Vs COS This process is called as natural commutation since no external circuit is required for this purpose. FORCED COMMUTATION In case of dc circuits, for switching off the thyristors, the forward current should be forced to be zero by means of some external circuits. The process is called forced commutation. The process of the current flowing through the thyristor is forced to become zero by external circuitry is called as forced commutation. Skip to content Engineering interview questions,Mcqs,Objective Questions,Class Notes,Seminor topics,Lab Viva Pdf free download. 2. Forced Commutation: The thyristor current is reduced to zero by an additional circuit called a commutation circuit and turn off process depends on the load current. Various types of forced commutation are 1. Self commutation 2. Complementary pulse commutation 3. Resonant commutation 4. Auxiliary commutation 5. Line commutation (1) Self Since the thyristor is turned off forcibly it is termed as a forced commutation process. The basic electronics and electrical components such as inductance and capacitance are used as commutating elements for commutation purposes. Forced commutation can be observed while using DC supply; hence it is also called DC commutation. Commutation of SCR is defined as the process of turning off an SCR / thyristor. It is the process by which an SCR or thyristor is brought to OFF state from ON state. We know that, an SCR is turned on by applying a gate signal to a forward biased SCR. Please read " Required Conditions to Turn-on an SCR " for better understanding. Thyristor Commutation Techniques with ckts and discription. half wave, full wave, pushpull single pahse inverter and 3 phase inverter THYRISTOR COMMUTATION TECHNIQUES 5.1 Introduction In practice it becomes necessary to turn off a conducting thyristor. (Often thyristors are used as switches to turn on and off power to the load). The process of turning off a conducting thyristor is called commutation. The principle involved is that either the anode should be made negative with respect to cathode (voltage commutation) or the Thyristor Turn-off OR Commutation Techniques The commutation techniques of thyristors are classified into two types: o Natural Commutation o Forced Commutation Natural Commutation Generally, if we consider AC supply, t