Principle Of Operation - SamplexPower PST-300-12 Manuel Du Propriétaire

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seCtIOn 5 |

These inverters convert DC battery voltage to AC voltage with an RMS (Root Mean

Square) value of 120 VAC, 60 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 120 VAC, 60 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 120 VAC, 60 Hz system, it slowly rises in the positive direction

from 0V to a peak positive value "Vpeak" = + 168.69V, slowly drops to 0V, changes the

polarity to negative direction and slowly increases in the negative direction to a peak

negative value "Vpeak" = - 168.69V and then slowly drops back to 0V. There are 60 such

cycles in 1 sec. Cycles per second is called the "frequency" and is also termed "Hertz

(Hz)".

TIME

Fig. 5.1: 120 VAC, 60 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 120 VAC, 60 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.

14 | SAMLEX AMERICA INC.