Operating instructions

Operation with only one supply frequency inverter

MICROMASTER 420 / 440 – DC link coupling between several

Frequency inverters

4.3.1 Connecting the DC link coupling at the frequency inverter

The DC link couplings are connected at terminals DC + und DC – of the

frequency inverter. Terminals DC + are connected with DC + and DC – with

DC – of the frequency inverter. If frequency inverters whose rated powers

differ significantly, are coupled with one another, then it should be noted

that the small cable cross-sections of the lower rating frequency inverter

may not be directly connected to the higher rating frequency inverter at the

DC link. In this case, a suitable reduction should be used.

Note:

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

not interchanged as otherwise the connected frequency inverters could be

destroyed.

4.3.2 Cable cross-sections required and implementing the DC link

couplings

The cable cross-sections required are obtained from the power rating of the

frequency inverters connected to the supply inverter. The cable cross-

section is selected starting from the supply inverter corresponding to the

sum of the powers connected there and the resulting sum of all of the DC

link currents. The cable cross-section can be lower the greater the distance

to the supply point if the total connected power of the frequency inverters in

the particular section of the line is lower. As an alternative, a DC bus bar,

connected to the supply inverter can be used.

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

operating point) are specified above under Point 2.3. The sum of the DC

link currents of the frequency inverters connected to the supply inverter are

then used to select the cable cross-section of the DC link connection. In

addition, the type of cable routing and ambient temperature must be taken

into account.

The DC link couplings must be appropriately implemented for the voltages

which occur. The voltage strength required is as follows:

o 450V DC for a line supply voltage of 1/3-ph. 200-240V AC

o 900V DC for a line supply voltage of 3-ph. 380-480V AC

In order to reduce EMC noise, shielded cables must be used for the DC link

coupling. The shield should be connected at both ends through the largest

possible surface area. For frequency inverter sizes A, B and C, the optional

A&D SD Page 12/32