Power Factor Correction Demo
Objectives:
In this demo we will investigate some properties of the power factor and how it affects
the system. More specifically we will compare a two AC to DC conversion schemes, one without
a power factor correction module and one with one.
Reasons Behind Power Factor Correction:
The main reason to drive the power factor to unity from the utility’s point of view is to
reduce costs. Looking at the power triangle:
In general the utility sells real power to the customer but it must be capable of
transmitting the full apparent power. This means that the lines, transformers and all other
associated equipment must be sized larger than what the utility is actually selling. This increases
the installation and maintenance costs of the whole system. If the power factor were driven to
unity meaning the real power is equal to apparent power the utility would be able to supply the
same amount of power with a smaller system and thus it would reduce costs.
Properties of Power Factor:
The power factor is defined by the ratio of real power to apparent power as shown below.
( )
θ
cos==
S
P
pf
In the case below with no delay between the current and voltage waveforms
∫
≠∂= 0*
1tIV
T
P
so
0≠=
S
P
pf
since
10 ==⇒=⇒°=
S
P
pfSP
θ
1)cos(0
=
=
⇒
°
=
θ
θ
pf
so in this case
)cos(1
θ
==
S
P
In this case there is no delay between the current and voltage waveforms but the current
waveform has a strong second harmonic
∫
=∂= 0*
1tIV
T
P
so
0==
S
P
pf
since
1)cos(0
=
⇒
°
=
θ
θ
so in this case
)cos(
θ
≠
S
P
P
S
Q
θ
But the cos(θ) only holds in a harmonic
free environment as seen below
I
V
I
V
S
θ
P
Q
S = Apparent Power
P = Real Power
Q = Reactive Power
