>6.3 INVERTER
The DC/AC Converter (Inverter) converts the direct current into a stabilised sinusoidal alternating current to
power the load. When the UPS is in ON-LINE mode, the load is always powered by the Inverter.
The Inverter is an IGBT (Insulated Gate Bipolar Transistor) based three-phase design; the IGBT is a transistor that
allows high commutation frequencies (>18 kHz) and, as a result, the Inverter provides a high quality output
voltage, with low noise levels and high operating efficiency. In addition, the DSP microprocessor controls,
guarantee static and dynamic performance under any operating condition:
Voltage adjustment
The output voltage can be adjusted using the independent phase control and DSP microprocessor; this enables
a better static and dynamic response. In detail:
a) static condition: the Inverter output voltage remains within ±1% for all variations of the input voltage within
the accepted limits;
b) dynamic condition: for load variations from 0 to 100%, the output voltage remains within ±3%, (within the
values defined by class 1 of the EN 62040-3 standard).
Frequency adjustment
The Inverter output frequency is generated autonomously by an internal oscillator, in synchronisation with the
bypass supply. Frequency stability is operating condition dependent:
a) Frequency stability
a. With mains power present: the internal oscillator follows any frequency variations in the bypass supply
and in relation to the preset value - normally ±5% (configurable from ±0,25% to ±10%).
b. With no supply present: the Inverter autonomously generates the frequency of the output voltage with
a stability of ±0,01%.
b) Frequency variation speed
The maximum Inverter output frequency variation (to lock to that of the bypass supply) is 1 Hz/s (adjustable
from 0,5 to 2 Hz/s).
Distortion of the output voltage
Inverter output waveform distortion with a linear load is maintained within ±1%. Within a non-linear load, as
defined by the EN 62040-3 standard, output voltage distortion does not exceed 3%.
Overload
The Inverter is sized to provide a power overload for a limited length of time (see the limits indicated in the
“Technical specifications table”).
When the time period or power limits are exceeded, the load is transferred to the bypass supply.
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