Thermal Time Constant; Thermal Protection Mode - Emerson SP1201 Installation Manual

Safety Product
Introduction
Information information
Therefore:
Ki = (K x L x Kc) x 256 x 167µs x R / L = 0.0427 x K x R x Kc
The above equations give the gain values that should give the best response at all switching frequencies with minimal overshoot. If required the gains
can be adjusted to improve performance as follows:
1. The integral gain (Ki) can be used to improve the performance of the current controllers by reducing the effects of inverter non-linearity. These
effects become more significant with higher switching frequency. These effects will more significant for drives with higher current ratings and
higher voltage ratings. If Ki is increased by a factor of 4 it is possible to get up to 10% overshoot in response to a step change of current
reference. For high performance applications, it is recommended that Ki is increased by a factor of 4 from the auto-tuned values. As the inverter
non-linearity is worse with higher switching frequencies it is may be necessary to increase Ki by a factor of 8 for operation with 16kHz switching
frequency.
2. It is possible to increase the proportional gain (Kp) to reduce the response time of the current controllers. If Kp is increased by a factor of 1.5 then
the response to a step change of reference will give 12.5% overshoot. It is recommended that Ki is increased in preference to Kp.
4.15

Thermal time constant

Drive mode Regen
Bit SP FI
Coding
Range Regen
Default Regen
Second motor
Regen
parameter
Update rate Background
4.16

Thermal protection mode

Drive mode Regen
Bit SP
Coding
1
Range Regen
Default Regen
Update rate Background
Pr 4.25 for the standard drive is used to select the Low Speed Thermal Protection Mode. This is not applicable for Regen drive because operation
below 30Hz is not possible as synchronisation to the AC supply is lost. Therefore Pr 4.25 should be left at the default 0.
If the rated current (Pr 5.07) is less or equal to the maximum Heavy Duty rating then the maximum value for K is 1.05, so the regen inductor can
operate continuously up to 105% current across the whole operating frequency range (48Hz to 65Hz).
If the rated current (Pr 5.07) is above the maximum Heavy Duty rating the maximum value for K is 1.01, so the regen inductor can operate
continuously up to 101% current across the whole operating frequency range (48Hz to 65Hz).
When the estimated temperature reaches 100% the drive takes some action depending on the setting of Pr 4.16. If Pr 4.16 is 0, the drive trips when
the threshold is reached. If Pr 4.16 is 1, the current limit is reduced to (K - 0.05) x 100% when the temperature is 100%. The current limit is set back
to the user defined level when the temperature falls below 95%. In servo and regen modes the current magnitude and the active current controlled by
the current limits should be similar, and so this system should ensure that the regen inductor operates just below its thermal limit.
The time for some action to be taken by the drive from cold with constant current is given by:
T = -(Pr 4.15) x ln(1 - (K x Pr 5.07 / Pr 4.01)
trip
Alternatively the thermal time constant can be calculated from the trip time with a given current from
Pr 4.15 = -T / ln(1 - (K / Overload)
trip
For example, if the drive should trip after supplying 150% overload for 60seconds with K = 1.05 then
Pr 4.15 = -60 / ln(1 - (1.05 / 1.50)
The thermal protection system can be used in regen mode to protect the regen inductors. The rated current (Pr 5.07) should be set to the rated
current for the inductors.
The thermal model temperature accumulator is reset to zero at power-up and accumulates the temperature of the regen inductor whilst the drive
remains powered-up. Each time Pr 11.45 is changed, or the rated current defined by Pr 5.07 is altered, the accumulator is reset to zero.
Unidrive SP Regen Installation Guide
Issue Number: 2
System Mechanical
design installation
DE Txt VM DP ND
0.0 to 400.0
89.0
Pr 21.16
FI DE Txt VM DP ND
0 to 1
0
2
)
2
)
2
) = 89
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RA NC NV PT US RW BU
1 1
RA NC NV PT US RW BU
1
Technical
Parameters
data
PS
1
PS
1 1
Component
Diagnostics
sizing
105