Samlexpower PST-1500-12 Owner's Manual - Section 2 |
10 | SAMLEX AMERICA INC.
2.2 OUTPUT VOLTAGE WAVEFORMS
TIME
180
160
140
120
100
80
60
40
20
0
20
40
60
80
100
120
140
160
180
Modified Sine
Wave sits at
ZERO for some
time and then
rises or falls
V
PEAK
= 169.68V
Modified Sine Wave
Sine Wave
Pure Sine Wave
crosses Zero Volt
instantaneously
V
PEAK
= 140 to 160V
V
RMS
= 120 VAC
VOL
TS (+)
VOL
TS (
–)
16.66 ms
Fig. 2.1: Pure and Modifi ed Sine Waveforms for 120 VAC, 60 Hz
TheoutputwaveformoftheSamlexPSTseriesinvertersisaPureSineWavelikethe
waveformofUtility/GridPower.PleaseseeSineWaverepresentedintheFig.2.1that
also shows Modifi ed Sine Waveform for comparison.
In a Sine Wave, the voltage rises and falls smoothly with a smoothly changing phase
angle and also changes its polarity instantly when it crosses 0 Volts. In a Modifi ed Sine
Wave, the voltage rises and falls abruptly, the phase angle also changes abruptly and
it sits at zero V for some time before changing its polarity. Thus, any device that uses a
control circuitry that senses the phase (for voltage / speed control) or instantaneous zero
voltagecrossing(fortimingcontrol)willnotworkproperlyfromavoltagethathasa
Modifi ed Sine Waveform.
Also, as the Modifi ed Sine Wave is a form of Square Wave, it is comprised of multiple
Sine Waves of odd harmonics (multiples) of the fundamental frequency of the Modifi ed
SineWave.Forexample,a60HzModifiedSineWavewillconsistofSineWaveswith
oddharmonicfrequenciesof3rd(180Hz),5th(300Hz),7th(420Hz)andsoon.Thehigh
frequency harmonic content in a Modifi ed Sine Wave produces enhanced radio interfer-
ence,higherheatingeffectininductiveloadslikemicrowavesandmotordrivendevices
likehandtools,refrigeration/air-conditioningcompressors,pumpsetc.Thehigher
frequency harmonics also produce overloading effect in low frequency capacitors due to
lowering of their capacitive reactance by the higher harmonic frequencies. These capaci-
tors are used in ballasts for fl uorescent lighting for Power factor improvement and in
single-phase induction motors as Start and Run Capacitors. Thus, Modifi ed and Square
Wave inverters may shut down due to overload when powering these devices.