Question:
Is it possible to operate two asynchronous motors in parallel at one drive 8400 StateLine in operating mode SLVC (sensorless vector control) or V/f + encoder? Which are the relevant parameters during commissioning?
Answer:
The operation of two asynchronous motors connected to one drive 8400 StateLine in operation mode SLVC (C0006/0 = 4) as well as V/f linear + encoder (C0006/0 = 7) is possible. The following conditions apply:
- The asynchronous motors must be of identical type.
- In case of gear boxes the gear ration needs to be identical as well.
- Both motors must be coupled friction-locked.
- The two motors being connected in parallel are detected as one big motor (summation of the two single motors) by the drive.
- Only one speed feedback is to be connected to the drive (applies for V/f + encoder) .
- Temperature switches can be wired in series.
- In principle a serial connection of PTCs is possible as well. Please note that the addition of the resistances causes the temperature monitoring to trip at a slightly lower temperature. Alternatively an external temperature monitoring needs to be installed for the second motor.
The following procedure is recommend for the setting of parameters:
Selection of a motor with a rated power, which corresponds to the summation of the rated powers of the single motors, so that the corresponding standard settings for the control parameters (speed controller in SLVC) can be loaded.
Thereafter the following parameters needs to be adjusted differently from the nameplate data of a single motor:
- C0081 - Rated motor power: Double the value
- C0088 - Rated motor current: Double the value
- C0022 - Maximum current: to be adapted in accordance of requirements (usually double the value)
The following parameters are to be taken from the nameplate of one single motor and do not change for parallel operation:
- C0087 - Rated motor speed
- C0089 - Rated motor frequency
- C0090 - Rated motor voltage
- C0091 - cos phi of motor
Carry out motor identification run. This is vital for operation in SLVC. In V/f + encoder the concentricity is improved but apart from this it is not vital.
In case the motor identification run cannot be performed get the following motor data for the single motor and do adjustments for parallel operation:
- C0082 - Motor rotor resistance: Halve in value
- C0084 - Motor stator resistance: Halve in value
- C0085 - Motor stator leakage inductance: Halve in value
- C0092 - Motor main inductance: Halve in value
- C0095 - Motor magnetising current: Double the value
After parameter setting a check of the current controller setting is recommended. The same instructions as for operation of single motors apply. Therefore the details are not given in this document and can be taken from the documentation.
Since both parallelly connected motors are detected as one sum motor, the following changes in displaying the motor's torque apply:
- C0057 - Maximum motor torque: Value still dependent on C0022; doubling of C0022 leads to doubling of C0057.
- C0097 - Rated motor torque: Double the value
Idle running:
If two asynchronous motors are operated in parallel and in idle running, even without friction-locked coupling, the motor without speed feedback is expected to run without problems.
Synchronous motors:
Parallel operation of two synchronous motors connected to one drive 8400 StateLine is not possible.
