Sensorless Control For Synchronous Machines - Baumuller b maXX BM3000 Operating Manual

4.8
Operating Modes

4.8.10 Sensorless control for synchronous machines

NOTICE!
The motor can make unintentional movements at faulty parameterization, because
there is no encoder available.
The drive controller b maXX 3300 makes the operation of a synchronous machine in the
speed control (operation mode "speed control") without rotary encoder or position encod-
er (sensorless encoder) possible. A position-controlled operation (operating modes posi-
tion control, synchronous operation, positioning), is not implemented at the moment.
The sensorless control procedure accepts the measured currents and the specified volt-
age set values from the current controller. On this basis, it calculates the electrical angle
and the motor speed. This calculation is the basis of the voltage model of the synchro-
nous motor. The motor data must be exactly known for this or must be determined with
the help of the self-optimization, in order to do this.
In the range of low speed or of standstill or if the voltage is too low or even zero, which
was induced in the motor, the voltage model is expanded by the injection procedure or it
is replaced by the controlled procedure. The use of the magnetic anisotropy of the ma-
chine or the difference between the direct axis and of the cross-current axis is the basis
of the injection procedure (Ld and Lq). This is caused by the iron saturation due to the
field of permanent magnets. The orientation of this anisotropy is analyzed with the help
of high-frequent (HF) injection. The HF-voltage signal is injected in the motor, the HF-cur-
rent is filtered, and it is demodulated according to a certain algorithm and is routed to a
specific tracking controller. It controls the orientation of the d-axis or the electrical angle
in such a way, that the estimated d-axis aligns to the physical axis of the permanent mag-
net field.
A constant current is set in Id-direction at controlled operation. The rotor adjusts itself to
the load and splits the constant current in a torque current and a reactive current. This
partition is estimated via a special procedure. At the transition to the voltage model this
information is assumed in form of a electric angle shift, so that a jerk-free transition to the
voltage model is possible.
The constant current at controlled operation can be set in Z133.22–. The constant cur-
rent can be increased to maximum current at speed set value unequal 0 via bit 4 of
Z133.1–. The ramp-up time in the ramp function generator must be parameterized so
that the motor can follow the acceleration ramp. In order to improve the transition to the
voltage model, it is recommended to switch off the consideration of the dLi/dt terms (bit 8
of Z133.1–).
NOTICE!
If there is a faulty parameterization, it cannot be guaranteed, that the motor reaches
the desired speed!
On principle the dead time compensation should be used at the sensorless control, so
that the non-linearity of the power unit can be compensated, in order to improve the ex-
actness of the voltage model. However the dead time compensation can affect the injec-
tion procedure. This must be tested in each case.
646 Parameter manual b maXX BM3000
Document no.: 5.12001.07
of 820
Baumüller Nürnberg GmbH