Introduction to Electrical Power and Power Electronics

23AC Power Fundamentals

1.6 AC POWER IN COMPLEX FORM

For a general form of ac power delivered from a source or absorbed in a load,

we consider V∠θ

v

and I∠θ

i

phasors shown in Figure 1.11. The ac power is given

by the product of the voltage and the complex conjugate of the current pha-

sor. Therefore, the power is also a phasor, a complex number, hence the name

+

jX



–

jX



0

Z



+θ

Z

*



–θ

R







FIGURE 1.10 Complex conjugate of phasor is its own mirror image in reference axis.

I

θ

θ

i

θ

v

Reference axis

V

˜

˜

FIGURE 1.11 Product of



V

and Ĩ 

*

gives complex power in ac.

24 Introduction to Electrical Power and Power Electronics

complex power. For average power, we use ...