Civil Engineering Reference
In-Depth Information
FIGURE 14-8
Harmonic and dynamic source impedance test measurement set-up.
transistors switching on and off. The ripple frequencies are integer multiples
of the switching frequency. The ripples are periodic but not sinewave and
are superimposed on the fundamental wave.
The ripple voltage induced on the bus due to ripple current is given by
the following:
VI
=
⋅
Z
(14-9)
ripple
ripple
d
The ripple is minimized by the capacitor connected to the bus or preferably
at the load terminals of the component causing ripples. The ripple current
is then supplied or absorbed by the capacitor, rather than by the bus, thus,
improving the quality of power.
14.6
Harmonics
The harmonics is the term used to describe the higher frequency sinewave
currents or voltages superimposed on the fundamental sinewave. Phase-
controlled power switching is one source of harmonics. The harmonics are
also generated by magnetic saturation in power equipment. With no satu-
ration present in the magnetic circuit, the generator and the transformer
behave linearly, but not so with saturation. The saturated magnetic circuit
requires non-sinewave magnetizing current.
The usual method of analyzing the system with harmonics is to determine
the performance of the system for each harmonics separately and then to
superimpose the results. The system is represented by the equivalent circuit
for each harmonic.
The fundamental equivalent circuit of the electrical generator is repre-
sented by the d-axis and q-axis.
1-2
In the n
th
harmonic equivalent circuit, the
