Operating instructions

Operation with up to three supply inverters

MICROMASTER 420 / 440 – DC link coupling between several

Frequency inverters

the individual frequency inverters. This can therefore avoid overloading

the rectifier integrated in the frequency inverter. The frequency inverters

which are not used to supply the DC link group do not have to be

overdimensioned and can be dimensioned corresponding to the

connected motor load.

o When engineering the drive system it is important to ensure that the

frequency inverters, connected to the line supply, can have a max. load

which represents 74% of the rated input current on the input side

(overdimensioned by a factor of 1.35x). The drive group must therefore

be engineered so that the complete motoring power of the frequency

inverters does not exceed 74% of the sum of the rated powers of the

frequency inverters connected to the line supply. However, in addition,

frequency inverters connected to the DC link can be operated in the

regenerative mode so that they do not represent a load for the supply

inverter.

o In order not to overload the frequency inverters connected to the line

supply when pre-charging, the maximum load which can be additionally

connected to the DC link is the sum of the rated powers of the supply

inverters. This applies for frequency inverters operating in the motoring

mode as well as in the regenerative mode.

Engineering example to check the required supply power:

DC link coupling with 3 supply inverters and 2 frequency inverters

connected through the DC link.

Motor power of the supply inverters: 11kW, 15kW, 22kW

Motor power of the frequency inverters connected to the DC link: 2 x 7.5kW

The motors of the supply inverters predominantly operate in the motoring

mode, one frequency inverter which is not a supply inverter, (7.5kW)

operates in the regenerative mode and the other frequency inverter which is

not used as supply inverter (7.5kW), operates in the motoring mode.

The following check is necessary because of the necessity to

overdimension the supply inverter by a factor of 1.35:

Sum of the motoring powers:

mottot

= 11kW+15kW+22kW+7.5kW = 55.5kW

Required supply power:

PSUPPLYtot = Pmottot * 1.35 = 55.5kW * 1.35 = 75kW

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