Maximum torque, influenced by operating parameters

Question:
How influence mains voltage range, switching frequency and heatsink temperature the maximum possible torque?

Answer:
The maximum possible motor torque results from the motor data (e. g. C0086) and the setting under C0022 (Imax). This calculated maximum torque is indicated under C0057 and serves as reference for the internal processing of torque values (e. g. MCTRL-MSET2).

Dependent on different operating parameters such as mains voltage range, switching frequency and heatsink temperature the drive controllers mentioned in the following carry out an internal derating of the maximum output current:

• EVF9326 ... EVF9333 vector / hoist frequency inverters
• EVS9326 ... EVS9332 servo inverters including the technology functions Servo PLC, Register, CAM, Positioning
• ECS servo controller

The respective drive controller reduces the output current to a permissible value. However, this reduction is not considered under C0057 and in case that an internal current derating is executed a torque setpoint requested may not be reached. As a result, the tensile force set at a winding drive reduces or an additional following error is generated in a drive operating under conditions of angular synchronism.

If the torque is recorded (e. g. by means of an internal oscilloscope via GDC or GDO) the signal sequence may lead to misinterpretations since a torque reserve seems to be available.

When does the behaviour occur?
a) If the parameter setting of the mains voltage range is changed from C00173 = -0-; -1- to C0173 = -2, -3-, -4-
b) If a small rotating field frequency (< 5 Hz) is used

Recommendation:

• The consequences caused by the current derating should be considered during the drive sizing process if possible (e. g. by overdimensioning; especially important in case of vertical drives such as hoists!). In case of hoists it is to be dimensioned on the current which may be reached under must unfavourable operating conditions (e. g. max. ambient temperature or rotating field frequency = 0 Hz)!
• In case of systems which are tested and commissioned on 400 V mains and which are finally to be operated on 460 V / 480 V mains codes C0018, C0022 and C0173 are to be written with the same values which are permissible to be used in the final application.

URL for linking this AKB article: https://www.lenze.com/en-de/go/akb/200509405/1/