Why Does Asynchronous Motor Rotor Stay Fixed with Constant Angle in Open Loop Vq Control?

Dear Forum
we have a asincronous motor connect to a SWPWM ,and with a encoder that read the angle.

The motor is in a closed loop, controlling the speed; the loop is the tipical composition i find
in lecterature named I.F.O.C..Schematic is in the figure I upload.


All math and block are realized via a DSP.

Before close the loop, i did test in open loop..

I used only 3 block,from the inverse park to motor. The input are Vd,Vq and Angle
(al set in my software..no from encoder or loop).

With this 3 input variable, I forced in my algoritm:

-Vq=0.1
-Vd=0
-Angle teta= N poits fix in time

-Result_1:-

I noted that if I set a Angle to a certain value, the rotor goes in a position,and
stay there. Increasing the angle, rotor move in this new angle.

If I put angle in a timer, rotor turn.


-Result_2:-

Increasing Vq dont change the rotor position.


What i dont understand is why rotor stay fix, if angle is fix . Equation says that Vq
create a tourque ,so, motor must rotate alwais.

So question are:

-Why rotor dont continue to move when i set a fix angle?

-If motor stay fix in such angle, and changing Vq dont change the rotor, how
Vq can change speed or position in closed loop ?

Thanks for your time and reply in this long question.

Roberto

Dear Roberto,

Where are the forward and inverse Clarke transforms? Usually they are shown transforming from 3-phase to 2-phase AC signals, both in the stationary frame, then from 2-phase to dq DC signals in the rotating frame. I imagine you have included them in the Park transform blocks (but then they should not be called simply Park blocks).

You are commanding theta? Theta should be coming from the encoder so that when the rotor turns, theta gets updated and the angle of the voltage that the FOC algorithm generates changes, causing the rotor to continue to change position (rotate).

I would suggest starting by opening the velocity loop at iq_dem1 and getting the current loop to work well first. When you command a small iq_dem1, the motor should produce a small torque. With no load it should accelerate up to the no-load speed (limited by the supply voltage). With more current it should produce higher torque. You should lock the rotor and tune the REGcur D 1 and REGcur Q 1 gains (I assume these are PI controllers (proportional and integral gains) )for good step response (fast rise time, minimal overshoot, no steady-state error), no oscillations (screeching). Then you should close the velocity loop and tune it with the targeted load on the motor.

When in your open loop mode and commanding angle, the controller is responding by turning the motor to the commanded angle as it should, so it appears to be working (at least somewhat). Once you close the angle part of the loop, it should spin on its own when you command current. The reason that nothing happens when you increase voltage with the loop open is because the motor has turned to an angle where it cannot produce torque. When it is there, try turning the shaft of the motor away from that position. You should notice that with a small voltage it will be easy to turn move it away from equilibrium. With a larger voltage it should be harder. Now it is in a position where it can produce torque. Once the encoder is correctly connected in the loop, the motor rotation should correlate better with Vq but I think it will make the most sense to you when both the current and the velocity loops are closed.

I hope this helps. Best! -JD