Name: Emerson unidrive sp
Brand: Emerson
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Regen

Unidrive SP Advanced User Guide 85

Issue Number: 10 www.controltechniques.com

The sinusoidal rectifier unit will attempt to hold the DC bus at the level specified by this parameter. The bus voltage must always be higher than the

peak of the line to line supply voltage if the unit is to operate correctly. The default values can be used with most supplies giving a reasonable level of

control headroom. However, with higher voltage supplies the set-point must be raised.

When the drive is operated as a regen unit it uses a DC bus voltage controller with inner current controllers as shown below.

The gains of the voltage and current controllers affect the stability of the regen unit control system and incorrect gain settings can result in over-

voltage or over-current trips. In many applications the default gains given for the current controllers (Pr 4.13 and Pr 4.14) will be suitable, however, it

may be necessary for the user to change these if the inductance or resistance of the supply plus the regen inductors varies significantly from the

expected values.

Setting the current controller gains

The most critical parameter for stability is the current controller proportional gain (Pr 4.13). The required value for this is dependent on the regen unit

input inductance. If the inductance of the supply is a significant proportion of the recommended regen inductor (i.e. 60/I

mH per phase, where I

is equivalent to Kc), then the proportional gain may need to be increased. The supply inductance is likely to be negligible compared to the regen

inductor value with small drives, but is likely to be significant with larger drives. The proportional gain should be adjusted as described for Pr 4.13

(closed-loop modes) using the total inductance per phase. The current controller integral gain is not so critical, and in a majority of cases the default

value is suitable. However, if it is necessary to adjust this parameter it should be set up as described for Pr 4.14 (closed-loop modes) using the supply

resistance for one phase.

Setting the voltage controller gain

Even when the gains are set correctly there will be a transient change of DC bus voltage when there is a change in the load on any drive connected

to the regen unit. This can be reduced substantially by using an analog input for power feed forward compensation (see Pr 3.10). The following

discussion relates to a system without power feed-forward compensation.

If the power flow from the supply is increased (i.e. more power is taken from the supply or less power is fed back into the supply) the DC bus voltage

will fall, but the minimum level will be limited to just below the peak rectified level of the supply provided the maximum rating of the unit is not

exceeded. If the power flow from the supply is reduced (i.e. less power is taken from the supply or more power is fed back into the supply) the DC bus

voltage will rise. During a rapid transient the bus will rise and then fall as shown below.

3.05

Voltage set-point

Drive modes Regen