Control Techniques unidrive sp Advanced User's Manual page 177

Parameter Keypad and
Menu 10
structure display
Drive voltage rating
200V
400V
575V and 690V
This parameter defines the time period that the braking resistor fitted can stand full braking volts without damage. The setting of this parameter is
used in determining the braking overload time.
Drive voltage rating
200V
400V
575V
690V
10.31 Full power braking period
Drive modes Open-loop, Closed-loop vector, Servo, Regen
Bit SP
Coding
Open-loop, Closed-loop vector, Servo,
Range
Regen
Open-loop, Closed-loop vector, Servo,
Default
Regen
Update rate Background read
This parameter defines the time period which must elapse between consecutive braking periods of maximum braking power as defined by Pr 10.30.
The setting of this parameter is used in determining the thermal time constant of the resistor fitted. It is assumed that the temperature will fall by 99%
in this time, and so the time constant is Pr 10.30 / 5. If either Pr 10.30 or Pr 10.31 are set to 0 then no braking resistor protection is implemented.
The braking resistor temperature is modelled by the drive as shown below. The temperature rises in proportion to the power flowing into the resistor
and falls in proportion to the difference between the resistor temperature and ambient.
Overload
%
accumulator
Pr 10.39
100
0
Pr
10.30
Assuming that the full power braking time is much shorter than the full power braking period (which is normally the case) the values for Pr 10.30 and
Pr 10.31 can be calculated as follows:
Power flowing into the resistor when the braking IGBT is on, P
Where:
Full braking volts is defined in the table and R is the resistance of the braking resistor.
Full power braking time (Pr 10.30), T
Where:
E is the total energy that can be absorbed by the resistor when its initial temperature is ambient temperature.
Therefore full power braking time (Pr 10.30), T
If the cycle shown in the diagram above is repeated, where the resistor is heated to its maximum temperature and then cools to ambient.
The average power in the resistor, P
Where:
Tp is the full power braking period
P = E / T
on on
176
Parameter Parameter
x.00 description format
Parameter default
0.09s
0.02s
0.01s
Full braking volts
390V
780V
930V
1120V
FI DE Txt VM DP ND
1
0.0 to 1500.0 s
2.0s
Pr 10.31
= E / P
on on
= E x R / Full braking volts
on
= P x T / Tp
av on on
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Advanced parameter
Macros
descriptions
RA NC NV PT US RW BU
1 1
t
2
= Full braking volts / R
on
2
Serial comms Electronic
Performance
protocol nameplate
PS
1
Unidrive SP Advanced User Guide
Issue Number: 7
Feature look-
up table