In the general case, any power electronic device may be regarded as a control plant (Figure 3.1). One characteristic of such components is that they have two inputs.

1. A power input, to which supply voltages ek (k = 1,…,K) are supplied. These voltages must be converted into output voltage or current signals in accordance with the particular control problem. For the sake of simplicity, they may be expressed in the form of the supply voltage vector ( )E e e e eK KT | |= −1 2 1… . Superscript T denotes transposition; in reality, this vector is a column one.