Baumuller b maXX BM5800 - Current Prediction; Dead Time Compensation

Controllers
Parameter manual b maXX BM5800
Document No.: 5.16029.03 Baumüller Nürnberg GmbH
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of 814
3.7
3.7.3.1 Current Prediction
The current prediction can be switched off. The voltage equations for the machine form
the starting point for the current prediction.
3.7.3.2 Dead Time Compensation
Since real semiconductor components do not behave ideally, it must be ensured that the
two transistors in a half bridge are never conducting current at the same time, i.e., are
switched on. For this reason, both IGBTs in a half bridge must be switched off for a certain
time, giving rise to dead times which are different for the individual output sections and
furthermore depend on the switching frequency of the power transistors. Due to these
dead times, a part of the theoretical nominal voltage for the PWM is lost. The dead time
effect produces a non-linear distortion in the voltage space vector. The dead time com
-
pensation factor Z47.50– is intended to compensate for the lost voltage.
The required voltages for the dead time compensation are determined from the sign of
the separate phase currents, the Udc actual value and current depending correction table
Z123.15–.
The table Z123.15– can be determined by autotuning (dead time measurement Z123.1–
bit 1 = 1). The measured values are valid for the parameters which are available at the
moment of the measurement: Udc actual value, PWM frequency and locking time (IGBT
dead time
Z129.9–). If the dead time measurement is not executed, the table Z123.15–
has default values defined for Udc = 540 V, PWM frequency = 8 kHz, and locking time =
4
µs.
The effective voltage of the dead time compensation is corrected according to the Udc
actual value (regardless whether the table
Z123.15– includes default values or measured
values).
Basically the correction table Z123.15– is only valid for the device which carried out the
dead time measurement. However the values of the table can be transferred from one
device to another one with the parameter set.
In all probability, the dead time compensation will operate satisfactorily if the device is of
an identical type. However, this must be checked by the user. It is recommended to mea
-
sure the dead time at each device, which requires dead time compensation.
NOTE!
The dead time measurement must be repeated, if the IGBT dead time (Z129.9–) was
changed.
NOTE!
If the correction table Z123.15– is measured from firmware version V01.09 onwards
and the adaption of the dead time compensation according to the PWM frequency is
active (
Z123.1– bit 3 = 1), the effective voltage of the dead time compensation is cor-
rected according to the effective PWM frequency. A new dead time measurement af-
ter a change of the PWM frequency is therefore not necessary. However the best
results are generally reached if the used PWM frequency corresponds to the PWM
frequency at the moment of the dead time measurement.