Emerson 50 and 60 Hz Introduction, Operation, Single unit block diagram with split-bypass input

Operation

6.0 OPERATION

! WARNING

Hazardous mains and / or battery voltage present behind covers.

No user-serviceable parts are located behind covers that require a tool for their removal. Only qualified service personnel are authorised to remove such covers.

6.1Introduction

The Liebert NXa Uninterruptible Power System is connected between the Mains AC input source and the critical load to provide uninterruptible power to the latter. The power from the UPS is free from voltage and frequency variations and from disturbances experienced at the Mains AC input supply.

This is achieved through high frequency double conversion power pulse width modulation (PWM) associated with full digital signal processing control (DSP).

As shown in Figure 63, the AC input mains source is supplied at Q1 and converted into a DC source. This DC source feeds a DC/DC Bidirectional Battery Converter (that ensures the battery to remain charged at all times) and at the same time feeds the Inverter that converts the DC source into a clean and input independent AC source. The battery powers the load through the bidirectional battery con- verter and through the inverter in case of an AC input mains power failure. In case of Inverter unavailability or excessive overload, the load may also be powered from an external AC Bypass source through input isolator Q2 and the static bypass. Besides this, if maintenance or repair of the UPS is necessary, the UPS can support the load through the internal and manually controlled maintenance bypass isolator Q3. With the exception of the maintenance bypass isolator, all the isolators shown are closed during normal UPS operation.

Figure 63 Single unit block diagram with split-bypass input

Bypass

Mains

Supply

N

Maintenance Bypass Isolator Q 3			UPS Module
Bypass Isolator Q2				Bypass Side
DC Bus	Inverter
		Static Switch
Rectifier

Input

Mains

Supply

Input
Isolator	Input
Q1	Static
	Switch

Battery

Output

Isolator

Q5

UPS

Output

Converter

1

Battery

CB Circuit Breaker

2

Battery

75