Samlex America PST-200S-24E - Manual (Page 14)

14 | SAMLEX AMERICA INC.
seCtIOn 5 | Principle of Operation
These inverters convert DC battery voltage to AC voltage with an RMS (Root Mean
Square) value of 230 VAC, 50 Hz RMS.
The waveform of the AC voltage is a pure sine wave form that is same as the waveform
of grid power (Supplementary information on pure sine waveform and its advantages
are discussed on pages 8 & 9).
fig. 5.1 below specifies the characteristics of 230 VAC, 50 Hz pure sine waveform. The
instantaneous value and polarity of the voltage varies cyclically with respect to time. for
example, in one cycle in a 230 VAC, 50 Hz system, it slowly rises in the positive direction
from 0V to a peak positive value “Vpeak” = + 325V, slowly drops to 0V, changes the
polarity to negative direction and slowly increases in the negative direction to a peak
negative value “Vpeak” = - 325V and then slowly drops back to 0V. There are 50 such
cycles in 1 sec. Cycles per second is called the “frequency” and is also termed “Hertz
(Hz)”.
Fig. 5.1: 230 VAC, 50 Hz Pure Sine Waveform
The voltage conversion takes place in two stages. In the first stage, the DC voltage
of the battery is converted to a high voltage DC using high frequency switching and
Pulse Width Modulation (PWM) technique. In the second stage, the high voltage DC is
converted to 230 VAC, 50 Hz sine wave AC again using PWM technique. This is done by
using a special wave shaping technique where the high voltage DC is switched at a high
frequency and the pulse width of this switching is modulated with respect to a refer-
ence sine wave.
TIME
OV
+
-
-V
PEAK
= -325V
+V
PEAK
= + 325V
V
RMS
= 230 VAC