The first class of functions in the above list is characterized by the fact that
switching is controlled by a function depending solely on time, h ¼ H(t), or
external actions. The corresponding converters are simple to model and analyze.
For example, this is the case of buck converters with continuous conduction
controlled at variable duty ratio.
As regards the second class, some functions hi may only depend on time,
whereas others may depend on the system state. For example, the buck converter
operating in discontinuous conduction and a thyristor-based rectifier belong to this
class. Finally, the third class is illustrated by a diode-bridge rectifier connected to
the grid or by a current-controlled buck converter.
One can note that a given configuration may belong to different classes
according to the manner in which it operates.
It appears that analysis and control methods will be more suited to one of the
above mentioned families rather than to another one. Thus, for example, as shown
later in this book, the classical averaged model is a simple tool, easy to use for
converters belonging to the first family, but it is unsuitable for the other two classes.
The same holds for variable-structure control and associated sliding modes