  The complex representation of real-valued instantaneous power may be written
as the sum of two complex powers, one Hermitian and the other non-Hermitian, or
complementary. A virtue of this representation is that it consists of a power
triangle rotating around a fixed phasor, thus clarifying what should be meant
by the power triangle. The in-phase and quadrature components of complementary
power encode for active and non-active power. When instantaneous power is
defined for a Thevenin equivalent circuit, these are time-varying real and
reactive power components. These claims hold for sinusoidal voltage and
current, and for non-sinusoidal voltage and current. Spectral representations
of Hermitian, complementary, and instantaneous power show that,
frequency-by-frequency, these powers behave exactly as they behave in the
single frequency sinusoidal case. Simple hardware diagrams show how
instantaneous active and non-active power may be extracted from metered voltage
and current, even in certain non-sinusoidal cases.
