Nidec Unidrive M600 Series

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162 Unidrive M Regen Design Guide

Issue Number: 4

The following should be noted:

1. It is possible that high levels of active current that contain components similar to the injection frequency may cause false detection of an island

condition and this is more likely the higher the injection frequency.

2. The detection system will detect an island condition in a time from 3 to 4 cycles of the injection frequency, therefore a higher injection frequency

gives faster detection.

3. Changing Island Detection Injection Frequency (03.031) while the system is running may cause an Island.1 trip.

The injection frequency used by the island detection system affects the maximum island detection time as given in the table below:

For the island detection system to comply with IEEE 1547 the detection time must be 2 s or less, and so an injection frequency of 2 or 4 Hz must be

used. For the island detection system to comply with VDE 0126-1-1 the detection time must be 5 s or less, and so any of the injection frequencies

may be used.

See Island Detection Enable (03.030).

If Island Detection Synchronization Source Select (03.033) is set to its default value of zero then the frequency of the current injected to detect an

island condition is defined by the Regen system. If Island Detection Synchronization Source Select (03.033) is set to a non-zero value to select an

option module, and the option module provides a suitable clock, then the injected current is synchronized to the clock. This allows the injected current

from a number of Regen systems to be synchronized to a master clock. If the option module does not provide a suitable clock then the frequency is

defined by the Regen system. The source being used is given in Island Detect Synchronization Source (03.034).

See Island Detection Synchronization Source Select (03.033).

Each time a synchronization attempt is made the DC bus voltage is increased because of current that is built up in the inductors connected between

the supply and the Regen system. As the current decays energy is transferred from the supply to the DC bus capacitors, and the energy stored in the

inductors is also transferred to the DC bus capacitors. To prevent an over-voltage trip during synchronization or re-synchronization the system will

prevent this process from starting if the DC bus voltage is above the level defined by Maximum DC bus voltage x Synchronization Headroom

(03.035). For example the full scale DC bus voltage for a 400 V drive is 830 V, so with the default setting of 5 % the DC bus voltage must be less than

830 V x 95 % = 788.5 V before the synchronization process will begin. If the recommended components are connected between the supply and the

Regen system the rise in the DC bus voltage during synchronization requires less than 5 % headroom. If alternative inductors are used that are

significantly larger than the recommended values or the supply inductance is very high it may be necessary to increase the headroom.

Injection frequency Maximum detection time

1Hz 4s

2Hz 2s

4Hz 1s

03.031 Island Detection Injection Frequency

RW Txt US

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1Hz (0), 2Hz (1), 4Hz (2)

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