Lenze 931E/K Small Drives Control - Manual (Page 39)

Commissioning
Torque control
Functions available
5
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39 SW−HB 13.0002−EN 4.1
5.3 Torque control
5.3.1 Functions available
The torque control has the structure of a cascade−shaped control system with an inner
current control circuit and a higher−level speed control circuit. The controllers are designed
as PI controllers. Using the setpoint selectors, you can select setpoints from different
sources for the corresponding controllers. See the chapter "Setpoint selection via setpoint
selectors". (
¶ 46)
The system principles are described in the block diagram on the next page.
With rotor−oriented control, two phase currents and the rotor position will be measured.
Using the Clark transformation, the phase currents will be converted into an imaginary and
a real part first and then transformed into the rotor coordinates by using the Park
transformation. Using PI controllers, the rotor currents can thus be converted into
corresponding rotor voltages and again be inversely transformed into the stator system.
The driver signal generation uses a symmetrical pulse−width modulation for the power
stage in sine commutation with the 3rd harmonic wave.
An integrator monitors the current 2 −time−integral of the controller. If the maximum value
(maximum current for 2 sec) is exceeded, a warning will be sent and the current will be
limited to the rated current.
With torque control, a current setpoint i_set will be selected for the active current
controller. In this case, only the current controller will be active in the servo positioning
controller. Since the torque generated on the motor shaft is more or less proportional to the
active motor current, we can speak of torque control here.
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Note!
ƒ The quality of the torque control mainly depends on the motor and the
sensor technology for the rotor position detection.
ƒ With a good synchronous machine, a high−resolution rotary encoder
(SINCOS encoder) and a good controller setting, the 931E/K can reach a
torque ripple between 1% and 3% referred to the maximum current resp.
the corresponding maximum motor torque.
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Danger!
No speed limitation
In torque control mode, there is no speed limitation!
Possible consequences:
ƒ Death or severe injuries may occur unless appropriate protective measures
are taken.
Protective measures:
ƒ Take protective measures to ensure that the maximum speed will not be
exceeded.