Understanding critical conduction mode converters

[AlienCircuits]

What is critical conduction mode? All of the stuff I find online assumes that the reader already knows about it, and my book Fundamentals of Power Electronics doesn't say anything on it.

Is this related to resonant converters (ZVS)?

 

[mtwieg]

CCM converters sense inductor current and always switch on when that current falls to zero, thereby forcibly achieving zero current switching (when switching on, not off). CCM converters are always variable frequency converters, and can work by modulating peak inductor current or switch on time. However they're not resonant converters, and the turn off is always hard switched.

 

[FvM]

Critical conduction mode (CRM) means to operate a switched mode converter (e.g. buck or boost) at the boundary between continous conduction mode (CCM) and discontinuous conduction mode (DCM). The term should be clear with a few clicks on your internet browser.

CRM can serve different purposes, soft switching (ZVS or ZCS) seems to be among it according to literature.