For example, when the voltage is sin-wave, the current is
cos-wave. Similarly, when the voltage is sal-wave, the
current is cal-wave. Although rectangular-wave voltage
has only first order Walsh harmonics, triangular-wave
current has many Walsh harmonics. In this paper, only
the first order current harmonics is utilized for the
calculation, because the harmonics is the largest of all
the current harmonics. Therefore, it is easy to detect and
insensitive to noise. The relation between Walsh
harmonic components of current and voltage is derived
as follows