User Manual

Table Of Contents
Induction Motor Parameters Calculation
Advanced Digital Motor Controller User Manual 141
to set motor RPM to 800 on channel 1 when MaxSpeed is set to 1000 RPM. Correspond-
ing if MaxSpeed is set to 2000 RPM, any value on the slider will give 2 times RPM.
Speed can be also set as an absolute RPM value using the S command from Serial, USB,
CAN or Microbasic.
Speed Limiting in FOC Torque Mode
AC Induction Controllers provide a way of smoothly limiting the speed in FOC torque
mode to prevent motor runaways. The method for limiting the speed is based on PID
speed over-ride control which provides very smooth motor output but requires PID tuning.
The speed loop PID tuning can either be done in “FOC torque mode” at the speed limit or
in “FOC Speed Mode” by looking at the response time.
When in “FOC Torque Mode, command some torque to the motor and cause the
motor to spin to the speed limit. Some low frequency ripple will be noticed in the
speed which should be minimized by increasing PID gains. Increase the PID gains
to a point where no ripple is seen.
If in “FOC Speed Mode, tune the speed PID gains by looking at the response time
of the motor. And then move to case 1) to check the ripple in the speed.
Induction Motor Parameters Calculation
The motor parameters of Induction Motors are crucial when the Field Oriented Control
Close loop torque/speed control is needed. More specifically, the rotor induced flux abso-
lute position is determined mathematically using known speed, voltage and current, and a
model representation of the motors main parameters shown in the figure below.
FIGURE 9-8. Electrical Representation of ACIM for motor characteristics calculation
These parameters include per phase rotor resistance ‘R
r
, rotor leakage inductance ‘L
lr
’,
mutual inductance ‘L
m
’ and rotor leakage inductance ‘L
lr
’ (core losses R
c
are neglected).
Furthermore, in order to set the FOC (Flux and Torque) PID gains, the Stator Resistance
(R
s
) and Stator Inductance (L
ls
) needed, according to the method as described in chapter
“FOC Gains Tuning” at Section 8. The most common ways, to manually estimate induc-
tion motor parameters through the controller, are to test induction motor under no-load
and locked rotor conditions.
No load testing
The no-load test, like the open circuit test on a transformer, gives information about ex-
citing flux I
d
current, the magnetizing inductance L
m
and rotational losses. The test is per-