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168 Unidrive M Regen Design Guide
Issue Number: 4
A single time constant thermal model is provided that can be use to estimate the temperature of the Regen inductors connected between the Regen
drive and the supply. The input to the model is the Current Magnitude (04.001). The Inductor Protection Accumulator (04.019) is given by the
following equation.
T = 100.0% x [I / (K
1
x I
Rated
)]
2
x (1 î› e
-t/
)
where:
T = Inductor Protection Accumulator (04.019)
I = Current Magnitude (04.001)
I
Rated
= Rated Current (05.007)
 = Inductor Thermal Time Constant (04.015)
If Rated Current (05.007) îš” Maximum Heavy Duty Rating (11.032) then K
1
= 1.05, otherwise K
1
= 1.01.
Inductor Protection Accumulator Reset
The initial value in the Inductor Protection Accumulator (04.019) at power-up is defined by Inductor Protection Accumulator Power-up Value (04.036)
as given in the table below.
The Inductor Protection Accumulator (04.019) is reset under the following conditions:
Inductor Thermal Time Constant (04.015) is set to 0.0. Note that this is not possible in the standard product as the minimum parameter value is 1.0.
Rated Current (05.007) is modified.
Inductor Protection Accumulator Warning
If [I / (K
1
x I
Rated
)]² > 1.0 then eventually the Inductor Protection Accumulator (04.019) will reach 100% causing the Regen drive to trip. If this is the
case and Inductor Protection Accumulator (04.019) > 75.0% then [Ind Overload] alarm indication is given and Inductor Overload Alarm (10.017) is set
to one.
Reactive Current (04.017) is the instantaneous level of reactive current scaled so that it represents the r.m.s. level of reactive current under steady
state conditions.
Final Current Limit (04.018) is the current limit level that is applied to the active current.
See Inductor Thermal Time Constant (04.015).
04.015 Inductor Thermal Time Constant
RW Num US

1.0 to 3000.0 s

89.0 s
Inductor Protection Accumulator Power-up Value
(04.036)
Inductor Protection Accumulator (04.019) at power-up
Power Down The value is saved at power-down and is used as the initial value at power-up.
Zero The value is set to zero.
Real Time
If a real-time clock is present and if Date/Time Selector (06.019) is set up to select the
real-time clock then the value saved at power-down is modified to include the effect of
the inductor thermal protection time constants over the time between power-down and
power-up. This modified value is then used as the initial value at power-up.
If no real time clock is present then and this option is selected then the value saved at
power-down is used as the initial value.
04.017 Reactive Current
RO Num ND NC PT FI

VM_DRIVE_CURRENT A

04.018 Final Current Limit
RO Num ND NC PT

VM_TORQUE_CURRENT %

04.019 Inductor Protection Accumulator
RO Num ND NC PT PS

0.0 to 100.0 %

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