# What is the difference between commutation number and pulse number in?

My question is about bridge rectifiers in power electronics. I guess the jargons are too vague, so i quote the exact definitions from my book which i don't understand at all:

m represents the commutation number. This is the number of commutations per period in a group commutating cells.For the Graetze bridge, m = 3 for both left and right diodes. In most cases, the commutation number equals the number of phases.

and here is the definition of pulse number:

The pulse number is the total number of non- simultaneous commutations per period.5 For the three-phase bridge, p = 6 as the commutations of the upper and lower diodes are not coincident. In general, for a bridge rectifier with m odd, p = 2m. For a bridge with m even, p = m holds

It would be great if someone can clarify the definitions above.

• What's your question, exactly? They're two different things and you have a clear definition of both. – Finbarr Apr 10 at 12:18
• @Finbarr maybe i wasn't clear before, i don't understand the jargon at all, what does the term 'group commutating cells' means for instance? What does the term 'commutation' here means? Does it mean the number of power takeovers per periode? Why the pulse number is 6 and the other is 3 – Sam B Apr 10 at 12:32
• I'll admit that the book could certainly be better written. Do you know what a commutation is? – Finbarr Apr 10 at 14:24
• @Finbarr from linguistic aspect, i guess, it means when one of diodes switches on, but that's just a guess, i read the book from the very beginning up to this point, and the glossary is almost don't exist. – Sam B Apr 10 at 15:00
• @Mattman944, i assume that the load is highly inductive to keep the current constant. – Sam B Apr 10 at 19:06

A converter configuration can be defined by the basic commutation group and the number of such groups connected in series and/or parallel. This is true for uncontrolled rectifiers, controlled rectifiers or inverters.

simulate this circuit – Schematic created using CircuitLab

Commutation group

A commutation group is essentially a leg which may be comprised of a number of devices in series or parallel to block the voltage or handle the current

Commutation number

the number of parallel connected commutation groups

Pulse number

Output pulse number is the number of pulses in the output voltage that occur during one ac input cycle, of frequency fs

Commutation cell

A commutation cell is the entire commutation block

• Nicely done Jon. I hate textbooks that seem to be more interested in getting you to learn terms than to get you to understand what is going on with the circuit. Sam: do you have a working simulation? Put current probes in series with the diodes. I'm not sure what the load at the bottom is trying to represent, i would first simulate with a plain resistive load. – Mattman944 Apr 10 at 15:13