SECTION 5 |
Principle of Operation
16
5.1 GENERAL
These inverters convert DC battery voltage to AC voltage with an RMS (Root Mean
Square) value of 230 VAC, 50 Hz RMS.
5.2 PURE SINE WAVE OUTPUT WAVEFORM
The waveform of the AC voltage is a pure Sine Waveform that is same as the
waveform of Grid / Utility power (Supplementary information on pure Sine
Waveform and its advantages are discussed in Sections 2.2 to 2.4).
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)”. The Time Period of 1 Cycle is 20 ms.
TIME
0V
Peak Negative Voltage
- V
PEAK
= - 325V
V
RMS
= 230 VAC
Peak Positive Voltage
+ V
PEAK
= + 325V
Voltage (+
)
Voltage (-)
20 ms
Fig. 5.1: 230 VAC, 50 Hz Pure Sine Waveform.
5.3 PRINCIPLE OF OPERATION
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 reference sine wave.
