Volts/Hertz Control (V/Hz) - Siemens SINAMICS PERFECT HARMONY GH180 Function Manual

Determining motor speed
SMC avoids the need to scan the motor frequency to determine motor speed. The control uses
information from the rotor-induced speed voltages on the stator to determine rotor speed. The
drive begins, in the magnetizing state, by giving a field current command that is equal to the no-
load field current setting to the exciter. This lasts for a time equal to the programmable flux ramp
time that is entered through the menu system.
After this period of time, the drive goes into the run state. In most cases, the regulator in the
field exciter is slow, and the drive applies magnetizing current, through the stator windings to
assist the exciter in establishing rated flux on the motor. At the same time, the speed regulator
commands a torque-producing current to accelerate the motor to the demanded speed. Once
the field exciter establishes the required field current to maintain flux in the motor, the
magnetizing component of stator current reduces to zero. From this point onward, the drive
provides torque-producing current, for acceleration or deceleration that is in-phase with the
drive output voltage. That is, under steady state conditions, unity power factor condition is
automatically maintained at the drive output. The field current command is provided to the field
exciter with the use of an analog output signal.
Summary of differences between SMC and OLVC
• The motor no-load current parameter represents the field no-load current value in SMC.
• With SMC, the flux loop gains are slightly lower than with OLVC.
• Spinning load is always enabled with SMC.
• The drive magnetizing current regulator uses only the proportional gain for the flux exciter.
• Only Stage 1 auto-tuning can be used with synchronous motors.
• When you are performing Stage 1 auto-tuning, you must short the field winding to get a
proper setup of the stator resistance.
4.7.7

Volts/Hertz Control (V/Hz)

Volts/Hertz (V/Hz) control is used when the drive is connected to multiple motors in parallel. The
control algorithm is similar to OLVC, except that it does not use some of the motor parameters
in its control algorithm that OLVC does. High starting torque mode is available in this control
mode.
Note
Many of the features available with OLVC, such as fast bypass, spinning load, and slip
compensation, are not available with this mode, as individual feedback and control of each
motor is not possible.
NXGPro+ Control Manual
Operating Manual, A5E50491925A
CAUTION
Incorrect use of Stage 2 auto-tuning will lead to drive instability.
Never use Stage 2 auto-tuning with synchronous motors.
Only use Stage 1 auto-tuning with synchronous motors.
NXGPro+ Control Description
4.7 Control Modes
53