Operating instructions

Operation with up to three supply inverters

MICROMASTER 420 / 440 – DC link coupling between several

Frequency inverters

5.3.1 Connecting the DC link coupling at the frequency inverter

The DC link connections are connected at the frequency inverter at

terminals

DC + und DC – . Terminals DC + are connected with DC + and DC – with

DC – of the frequency inverter.

Note:

It is extremely important to ensure that the polarity of the DC link

connections is not interchanged as otherwise the connected frequency

inverters could be destroyed.

5.3.2 Cable cross-sections required and fusing of DC link couplings

When selecting the cable cross-sections required, the DC link coupling

differs in two different areas:

a. The cross-sections of the cables used to establish the DC link couplings

of the frequency inverter to the associated DC link fuses are

dimensioned corresponding to the DC link fuses of the frequency

inverter. This applies both for the supply inverters as well as for the

frequency inverters coupled through the DC link. For the supply

inverters, this connection must also be implemented and routed so that it

is short-circuit proof.

b. The cross-sections of the cables after the DC link fuses to connect the

drive inverters with one another are dimensioned so that these

correspond to the sum of the rated currents of the line fuses of all supply

inverters multiplied by a factor of 1.2.

Further, the routing type and ambient temperature of the DC link coupling

must be taken into account. As an alternative to using cables to establish

the DC link coupling, after the DC link fuses, a DC busbar, routed in

parallel, can be used. This low-inductance coupling offers the advantage

that the equalization currents between the supply inverters can be reduced

- thus reducing the load on the inverters. Further, using a DC busbar, it is

easier to reduce the cross-section of the DC link coupling. Starting from the

DC busbar, it is possible to branch to the DC link fuses of the frequency

inverter with a short-circuit proof connection with a lower cross-section.

The DC link currents which flow for each frequency inverter (at the rated

operating point) are specified in Tables 3-1 and 3-2.

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