Nthyristor commutation techniques pdf

The forced commutation technique is further divided into five categories which are class a, b, c, d, and e. Forced commutation applied to dc circuits choppers inverters. Scr turn off methods natural, forced, dynamic electronics hub. Similarly, there are various techniques to turn off a thyristor, these techniques are called thyristor commutation techniques. Classification of forced commutation methods nptel. The commutation techniques of thyristors are classified into two types. Forced commutation natural commutation line commutation generally, if we consider ac supply, the current will flow through the zero crossing line while going from positive peak to negative peak. It can be done by bringing the thyristor back into the forward blocking state from the forward conduction state. The first scr silicon controlled rectifier or thyristor was invented and. Commutation of thyristor or silicon controlled rectifier. Classification of thyristor commutation techniques elprocus. Commutation techniques in power electronics slideshare. Thyristor commutation techniques with ckts and discription.

As we know that once a thyristor starts conducting then it continue to conduct till the current flowing through it reduced below the holding current. The process of turning off a conducting thyristor is called commutation. The six distinct classes by which the scr can be turned off are. In practice it becomes necessary to turn off a conducting thyristor. Commutating elements such as inductance andcapacitance are used for commutation purpose. Commutation achieved by reverse biasing thescr or by reducing the scr current belowholding current value. Commutation is the process by which we can turn off a thyristor. Such external circuits are said to be forced commutated circuits. These forced commutation techniques are generally used in dcdc applications and dcac. So the commutation circuit does this job by reducing the forward current to zero so as to turn off the scr or thyristor. The turn off process of an scr is called commutation.

This commutation is possible with line commutated inverters, controlled rectifiers, cyclo converters and ac voltage regulators. The term commutation means the transfer of currents from one path to another. The process used for turning off a thyristor is called as commutation. To bring the thyristor into forward blocking state, forward current is reduced below the holding current level. By the commutation process, the thyristor operating mode is changed from forward conducting mode to forward blocking mode. To turn off the conducting scr the below conditions must be satisfied. Thyristor commutation techniques electronics tutorial. The transformer is designed with sufficient iron and air gap so as not to saturate. Self commutation or load commutation or class a commutation commutation by resonating the load under damped condition using l,c in series with load results in oscillating currents. So the process of switching off a thyristor or scr is known as commutation. Often thyristors are used as switches to turn on and off power to the load. The forced commutation can be classified into different methods as follows. It is capable of carrying the load current with a small voltage drop compared with the supply voltage. This results in turning off an scr when the current through load is zero.