Advancing the

Power Curve

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Paralleling Capability of SynQor®

Rack Mount System Products

Application Note

Introduction

SynQor rack mount system products can include an optional feature that allows combining the units

to build complex systems. The units with this bulit-in functionality can synchronize their outputs to

deliver higher power through paralleling for split-phase or 3-phase multiple unit configurations. Some

of these products have multiple output ports that can be paralleled. This application note includes a

quick reference summary table that describes the paralleling capabilities and the paralleling algorithms

used for the output ports available on rack mount system products with built-in paralleling features.

Note that some systems may have different types of paralleling capabilities for their output ports. For

example, some rack mount system products may have AC output or DC output or both AC and a number

of DC output ports. AC ports use a digital load sharing method while some parallelable DC output ports

may use the droop method and some the digital method. The DC1 output ports in rack mount system

products do not current share and should not be interconnected.

Contents

Description of paralleling algorithms: .................................................2

I - AC Output Current Share (“-F” and “-R” type units only): ...............................2

II – DC Output Current-Share: ........................................................4

Quick Reference Guide to Paralleling Capabilities of SynQor Rack Mount System Products .......5

Summary

This application note provides an overview of the paralleling

capabilities of the SynQor Rack Mount System Products.

Application Note Paralleling Capabilities of SynQor Rack Mount System Products

Advancing the

Power Curve

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Description of paralleling algorithms:

I - AC Output Current Share (“-F” and “-R” type units only):

The rack mount system products support two different paralleling schemes for the AC output: standard

paralleling “-F” and expanded paralleling or redundant paralleling “-R”. Only floating neutral “F” or “R”

option system products can be paralleled to deliver higher power in different system configurations,

like single-phase, split-phase or 3-phase output. The “G” type option system products have their output

neutral internally connected to ground and must not be used in parallel application to avoid neutral

currents from being able to flow in the ground connections of the paralleled system products. The

system products will only parallel with the floating neutral “F” or “R” option to prevent any neutral

currents from being able to flow in ground connections. If a parallel system consisting of floating –F or

–R units must be grounded, then the ground connection can be made externally.

To parallel the AC or DC output ports of multiple rackmount system products, the units must be of the

same model, power rating and type. The paralleling algorithm does not support paralleling of units

whose models, power rating, output voltage, output frequency and types differ. For example, to parallel

the AC port output of a set of UPS-1500-S-1U units, they must all be of the same type “-F” or “-R”, they

must have the same output voltage and the same output frequency. Paralleling of UPS-1500 units with

UPS-3000 units is not allowed.

AC output port paralleling implementation uses a master-slave digital current sharing algorithm. In this

paralleling algorithm, the master broadcasts its output current reference and phase angle, the backup

and slave units then try to deliver the same amount of current as the master at the intended phase

angle. Typically, the master/slave roles are defined when the units exchange information when they are

first powered “ON”. A series of handshaking messages are exchanged during startup, the units elect

a master for the group from the available units. They also elect the backup master unit. If the master

becomes unavailable, the backup unit will then assume the responsibilities of the master without the

system output shutting down, assuming that the remaining units can still deliver the required amount of

power to the load. When a backup unit assumes the role of a master, a new backup unit is also elected

from the remaining operational units. If a slave unit fails, the system will continue to power the load,

assuming the remaining units can still supply the required power.

The digital load sharing method used by the AC output ports, allows not only for the creation of single-

phase paralleled output systems, but complex output configurations as well, like split-phase (two units)

and 3-phase output system (multiples of 3 units) by using an appropriate configuration cable. In a split

phase system, the two outputs are 180 degrees out of phase. In three-phase output systems the relative

phase angles of the three output voltage waveforms are shifted 120 degrees apart. The phase rotation

of the three-phase configured units is determine by the connectors of configuration cable connected

to the units. Redundancy in these complex systems can be achieved by using “R” type units and adding

additional units to each phase group.