SECTION 2 |
General Information
10
2.2 OUTPUT VOLTAGE WAVEFORMS
360
320
280
240
200
160
120
80
40
0
40
80
120
160
200
240
280
320
360
TIME
Sine Wave
Pure Sine Wave
crosses Zero Volt
instantaneously
Modified Sine
Wave sits at
ZERO for some
time and then
rises or falls
Modified Sine Wave
Fig. 2.1: Pure and Modified Sine Waveforms for 230 VAC, 50 Hz.
The output waveform of the Samlex SWI series inverters is a Pure Sine Wave like the
waveform of Utility / Grid Power. Please see Sine Wave represented in the Fig. 2.1
that also shows Modified 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 Modified
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 voltage crossing (for timing control) will not work properly from
a voltage that has a Modified Sine Waveform.
Also, as the Modified 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 Modified Sine Wave. For example, a 50 Hz Modified Sine Wave will consist
of Sine Waves with odd harmonic frequencies of 3rd (150 Hz), 5th (250 Hz), 7th
(350 Hz) and so on. The high frequency harmonic content in a Modified Sine Wave
produces enhanced radio interference, higher heating effect in inductive loads like
microwaves and motor driven devices like hand tools, refrigeration / air-conditioning
compressors, pumps etc. The higher frequency harmonics also produce overloading
effect in low frequency capacitors due to lowering of their capacitive reactance by
the higher harmonic frequencies. These capacitors are used in ballasts for fluorescent
lighting for Power Factor improvement and in single-phase induction motors as Start
and Run Capacitors. Thus, Modified and Square Wave inverters may shut down due
to overload when powering these devices.
