Download UPS GUIDE SPECIFICATIONS

2.3.2 Inverter
The term inverter shall denote utilizing the latest IGBT switching Vector Controlled DC – AC
converter (also known as Space Vector Pulse Width Modulation) that provides the second
conversion phase, which is, convert DC from the rectifier/charger or battery to provide AC
power to the critical load. The inverter shall be solid-state, capable of providing rated output
power. The inverter shall be of Vector Controlled design using the latest DSP and utilize
insulated gate bipolar transistors (IGBTs), switching at high frequency in order to minimize
output voltage distortion and cross currents in redundant configuration.
A. Overload Capability: The inverter shall be able to sustain an overload across its output
terminals up to 150% with ±5% output voltage regulation. The inverter shall be capable of
supplying at least 150% current under short circuit conditions for 5 seconds if the Bypass
source is not healthy. If the bypass supply is healthy, inverter should transfer the load to
bypass during a short circuit current overload beyond 150% and disconnect itself from critical
bus.
B. Output Frequency: The inverter shall track the bypass mains supply continuously providing
the bypass source maintains the rated frequency (of either 50 or 60Hz). The inverter will
change its frequency at 0.1Hz per second (adjustable from 0.1 to 1.0Hz per second) to
maintain synchronous operation with the bypass. This shall allow make-before-break manual
or automatic transfers of the load between the inverter and the bypass mains supply. If the
bypass mains supply frequency falls outside of these limits, the inverter shall revert to an
internal digital oscillator and hold the inverter output frequency to within ±0.01Hz of the rated
frequency for steady state and transient conditions. Drift shall not exceed 0.1% during any 24
hour period. Total frequency deviation, including short time fluctuations and drift, shall not
exceed 0.1Hz from the rated frequency.
C. Phase-to-Phase Balance: System logic (DSP) shall provide individual phase voltage
compensation to obtain phase balance of ±1% under all conditions including up to 100% load
unbalance.
D. Fault Sensing and Isolation: Fault sensing shall be provided to isolate a malfunctioning
inverter from the critical load bus to prevent disturbance of the critical load voltage beyond the
specified limits. The inverter output static switch shall be switched off to isolate a
malfunctioning module from the critical load.
E. Battery Protection: The inverter shall be provided with monitoring and control circuits to
protect the battery system from damage due to excessive discharge. Shutdown of the inverter
shall be initiated when the battery has reached the end of discharge (EOD) voltage. The
battery EOD voltage shall be calculated and automatically adjusted for reduced load
conditions to allow for extended autonomy periods without damage to the battery. Automatic
shutdown control shall not be a function of discharge time.
F. Self-Ageing: The inverter shall be able to provide up to 80% load to the UPS system itself
to test its complete functionality. This shall be done via the service software parameters
setting. The UPS system shall display all values such as input & output voltages, input &
output kW, frequency, currents, etc. This self-ageing mode shall be done to replace the
traditional “resistive load testing” of the UPS system at the installation site.