Service manual

Always On UPS Systems Inc
7
6. INVERTER
The inverter is composed of IGBT’s, inductors, capacitors, highly efficient filters, control
circuitry and protection circuitry. This inverter inverts the DC power received on the DC bus
to isolated, noise-free AC power, which is then supplied to the critical loads. Our PWM wave
generator is switching at a higher frequency well above the human audible range.
The Voltage regulating circuitry limits the output voltage variation to within 1% of the
nominal voltage and special compensation circuitry has been added to eliminate output
distortion. Every component is oversized to accept a wide DC input range (from 285 to
420VDC), allowing the output waveform to remain sinusoidal throughout the entire range.
With the aid of dynamic feedback loop circuits the inverter maintains a true sine wave
output, even if non-linear loads are connected.
The system is designed and incorporates an independent inverter per phase. These inverters
are totally independent of each other preventing the possibility of cascading failures while
allowing the user to connect loads to adjacent inverters without affecting the other inverters.
This connectivity provides high-end voltage regulation under a 100% unbalanced load
situation.
The IGBT is operated in its optimal condition to obtain maximum efficiency, keeping
electrical costs to a minimum.
Usually, most UPS failures are a result of inverter failures. To prevent this occurrence,
Always “On” has included redundant protection circuitry to protect the inverter and increase
its reliability. To enhance this protection we have also added a high efficiency filter designed
to suppress the spikes and noise that can be reflected from the attached loads back into the
UPS system. Specifying oversized and high quality components, additional semi-conductor
fuses and allowing for good ventilation systems within further increase reliability.
Figure 6.1
Inverter La
y
out