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Theory of Operation
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2.0 THEORY OF OPERATION
2.1 General Component Descriptions
The UPS system includes all of the equipment necessary to continuously provide computer-grade AC
power to a critical load, even when there is an interruption of the utility power. It consists of the UPS
modules and a back-up battery plant. Refer to Figure 2.
UPS Module
The UPS module consists of system controls, a rectifier/charger, an inverter, protective devices and
other accessories.
System Controls: The system control logic automatically manages critical bus operation and moni-
tors performance of the UPS module. Microprocessor technology and dedicated firmware provide
advanced logic control and a comprehensive display of information. The UPS module status is dis-
played locally. Optional ports permit communicating with external devices.
Rectifier/Charger: The rectifier/charger converts utility power from AC to DC to charge the battery
and provide the DC input to the inverter. Its design limits reflected harmonic current distortion to
source power and provides low-ripple DC power for charging batteries.
Inverter: The inverter converts DC power into the precise AC power required to supply a sensitive
critical load. The inverter converts DC power into a pulse-width-modulated (PWM)/six-step waveform
that is easily filtered into a clean sine wave output. The PWM waveform also minimizes the harmonic
voltage distortion caused by typical switching power supplies and other non-linear load components
used in computers and related electronics.
Static Bypass Switch: The static (solid-state) bypass switch logic independently monitors the out-
put voltage and current on the UPS critical load bus. It immediately transfers the load from the
inverter to the bypass AC power source in the event of a severe overload on the system or a failure
within the UPS. This transfer takes place without any interruption of the power supplied to the load.
Fuses are installed in series with the static bypass circuit to ensure reliable overload protection in the
unlikely event of a catastrophic output condition (e.g., a dropped wrench) electrically close to the out-
put of your UPS system. The static switch SCRs themselves are rated to easily handle the fuse-blow-
ing current.
Bypass Circuit: The bypass circuit consists of motor-operated circuit breakers and associated syn-
chronizing and control circuitry to transfer the load to/from the bypass source.
Battery Plant
The battery is used as the alternate source of power to supply DC power to the inverter if the AC sup-
ply voltage is outside the acceptable range. The battery supplies power to the inverter until the utility
power is restored or until an alternate power source is available. If AC source power is not restored or
an alternate power source is not available, the battery can be sized to provide power long enough for
an orderly shutdown of the load.