After reading some more on the forum about tuning motor parameters. So i decided to measure the motor parameters:
Rs = Resistance of the stator winding
flux linkage = BEMF Constant
Ld = d-axis inductance of the stator winding
Lq = q-axis inductance of the stator winding
First Rs this is the simple one of the four. Basically stick a multimeter across two wires of the motor and read the result. But because the motors in car are high current devices the simple approach will not work.
The low tech way of doing this is easy. Use a power supply to push multiple amperes through the motor and measure the voltage as close as possible to the motor windings, to avoid adding wire and contact resistance to the measurement.
With this motor I pushed 10A through the motor from phase A to B. the voltage I got whas 228mV. this is the voltage across two windings.
228mV / 2 = 114mV
114mV / 10A = 11.4mΩ
The flux linkage. In a previous post I made a drill adaptor to spin the motor. With a oscilloscope connected across two phase wires we can measure the period time and the peak to peak voltage. With a formula from the appnote (linked below) we can calculate the flux linkage.
V
p-p * T
el / sqr(3)*4*Pi
From the scope shot in the older post I got 14 cycles in 550ms so this is 39.28 ms per cycle.
28V * 0.03928 / 21.766 = 50.53mWb
Next Ld, this is a bit more involved. We need access to the motor shaft, to align the motor with the phase A windings. The appnote suggest to apply DC power to the motor. phase A to the positive an phase B and C to the negative. The motor will "lock" to one of the stable positions. Counting the number of stable positions will give you the number of pole pairs. With the power applied we need to mechanically stop the motor from spinning. I used two pieces of wood with a single bolt, bolted to the face of the motor and the used a clamp to bite down on the motor shaft.
The appnote suggest to apply a voltage to the motor and measure the current. this is fine with a motor with a Rs of 6.4Ω. If I apply 14V to the motor it will pass 614A so that will not work. By adding in a resistor to limit the current we get a RL network.
I used three 10Ω resistors in parallel to get 3.333Ω. This gave a reasonable current at the voltage I used.
τ = L/R is the time constant. With a step response at one τ the current will be at 63% of the maximum.
the maximum current is about 12.4A 63% of that is 7.8A this is reached in 70us.
Ld = 2/3τ * R
Ld = 0.667 * 70us * 3.333Ω = 155.5 uH or 0,155mH
Last the Lq. To measure this we need to do almost the same setup as for the Ld but this time we need to connect the power supply different than before. Phase B to positive and C to negative, Phase A is not connected.
this aligns Phase A with the d-xis. This time it is more important to lock the rotor in place, because the motor will generate torque when power is applied. the test power is applied the same as before positive to phase A and negative to phase B and C.
This time it takes a bit longer to get to 7.8A, 150us
Lq = 2/3τ * R
Lq = 0.667 * 150us * 3.333Ω = 330.2 uH or 0.330mH
So the values i got are this:
Rs = 11.4mΩ
flux linkage = 50.53mWb
Ld = 155.5 uH
Lq = 330.2 uH
Not sure if this accurate, but is is comparable to other motors. It is similar to the outlander rear motor.
It whas fun to measure it anyway. If you see that I made a mistake please tell me.
Bonus thought is the Ld setup, a way to get syncofs. With my roughly tuned syncofs I got 350 degrees.
