Charging Profile Generator Requirements Theory Of Inverter Operation; W Aveform - Trace Engineering LEGEND II Manual

The Trace Legend Series II inverter/chargers utilize a low frequency power transformer-based
design. This design takes low voltage direct current from a DC source (usually a battery bank) and
produces higher voltage power. High efficiency is achieved by utilizing top quality field effect
transistor switches (FET's) in an "H-bridge" configuration, as well as in-house designed and
manufactured power transformers.
The theory behind inverter operation is to "chop" the DC power up into pulses via the transistor
switches. These pulses are then applied to a power transformer which steps the low voltage DC
pulses up to higher voltage AC. In the Legend Series II inverter, this process is overseen by an
onboard microcomputer. The computer is also responsible for the monitoring and charging of the
battery bank, as well as monitoring and protecting the inverter/charger against damage from heat,
over current, and other potentially hazardous situations.
The output waveform of the inverter is referred to as a modified sine wave. This waveform is suitable
for a wide variety of applications such as induction motors (i.e. refrigerators, drill presses), resistive
loads (i.e. heaters, toasters), and universal motors (i.e. hand tools, vacuum cleaners), as well as
microwave ovens and computers. The modified sine wave waveform could be more accurately
described as a pulse width modulated square wave. The accompanying figure shows the
relationships between square wave, sine wave and modified sine wave formats.
Figure 12, Comparison of Output Waveforms
WK