Power Electronics

Natural or Line commutation is a Class-F SCR commutation technique in which, a thyristor is turned off due to natural current zero and voltage reversal after every half cycle. This commutation method is only applicable for AC circuit and mostly used in Phase-Controlled Converters, Line-Commutated Inverters, AC voltage controllers and Step-down cycloconverters.  Principle of Class-F … Read more

Class-E Commutation is one of the forced commutation method to turn off an SCR / Thyristor. An external current pulse is used in this technique to commutate SCR. This is the reason, Class-E commutation is also known as External Pulse Commutation. This external current pulse is obtained form a separate voltage source. . Condition for … Read more

Class-D Commutation is a commutation method used to turn off thyristor in a DC circuit by the application of a sudden reverse voltage across the terminals of SCR. This is the reason, it is also called Impulse Commutation. A Class-D commutation circuit consists of Main Thyristor T1, Auxiliary Thyristor TA, Capacitor C, Diode D and … Read more

Class-B or Resonant Pulse Commutation is a forced commutation technique to turn off an SCR. In this technique, thyristor or SCR is turned off by gradual build-up of resonant current in the reverse direction i.e. from cathode to anode of SCR. This technique is also known as current commutation and occurs in DC circuit not … Read more

Load commutation of SCR is a forced commutation technique in which SCR is forced to turn off. Turning off an SCR essentially requires its anode current to fall below holding current and a reversed biased voltage must be present across SCR for sufficient time so that SCR may regain its blocking state. Load Commutation of … Read more

Commutation in Power Electronics refers to the process of commutation of SCR. Whenever we talk of commutation in power electronics, we simply mean the process to turn off an SCR. This article details about the commutation of SCR, Natural Commutation, Forced Commutation and various types of Forced Commutation techniques. What is Commutation of SCR? Commutation … Read more

There are various methods to turn-on a Silicon Controlled Rectifier (SCR) or thyristor. But the most common way to turn-on an SCR/Thyristor is the application of Gate Signal to a forward biased SCR. This method of turning on an SCR is called Gate Triggering. In this post, we will discuss the various condition required to … Read more

Whenever the load current requirement is more than the current carrying capacity of a single SCR, two or more SCRs are connected in parallel to form a string. By having parallel connection of SCR, it is expected that individual SCR shall share load current equally and hence the string efficiency is unity. But there are … Read more

Series connection of SCR is required where we want to meet the increased voltage requirement by using various SCRs.  Let us make it easier to understand. Suppose the SCR available with us is having a voltage rating of 600 V but the voltage rating required for our application is 2400 V. In this case, if … Read more

String Efficiency of SCR: String Efficiency of SCR is the degree of capacity utilization of individual SCRs in a string of series / parallel connected SCRs. String efficiency is always less than 1. Series or parallel connection of SCR is required to meet the higher voltage / current requirement in industrial application. Though the rating … Read more