How to get the PMSM motor rotor position Offset value
PMSM's English full name is Permanent-magnetSynchronousMotor, which is literally translated as permanent magnet synchronous motor.
It needs to meet several characteristics:
(1) The AC voltage of a phase difference of 120 degrees between the three-phase stators generates a stator magnetic field of a rotational motion.
(2) The rotor is excited by permanent magnets, regardless of whether the excitation material is AlNiCo, ferrite or NdFeB; whether it is embedded or surface-mounted, it is designed by special stator and rotor shape, and finally in the air gap space. A sinusoidal array of NS magnetic fields is present.
(3) Based on the above two points, the back EMF must be a sine wave, which is the biggest difference between PMSM and BLDC (back EMF trapezoidal wave).
Since the rotor of the PMSM has been solidified, the problem of how to control the motor can be simplified very simply: What kind of way can the rotor shaft of the motor generate a certain rotational torque?
(1) If I came from a relatively old age and unfortunately crossed into modern times, in my time I learned the knowledge: magnets have two polarities, N and S, and the same sex repels each other, and the opposite sex attracts;
I will think that I am taking another magnet close to the rotor, and then let the magnet in my hand draw a circle around the stator, then there will be a force between the magnet and the rotor in my body to make the rotor rotate;
(2) If I came from a little closer, in those days the great Mr. Oster and Mr. Ampere had discovered that electricity can be magnetized, and the sinusoidal alternating current can generate a circular magnetic field in space motion (this does not Is it the same effect that I used to draw a circle with a magnet?), then my work is simple, as long as the stator coil is placed around the rotor, the alternating current on the stator coil can cause the rotor to be subjected to magnetic field forces. Exercise
(3) If I came from a more recent era, Mr. Park and Mr. Clark, who were smart in that era, have already started research work. They found a problem that the three-phase alternating current with a constant speed standard of 120° phase difference has only two degrees of freedom, and if the three-phase voltage is observed at the angle of the moving magnetic field generated by the three-phase voltage, It is found that the projection generated in the vertical direction of the magnetic field and the magnetic field does not change with time, which brings great convenience to the solution of the control.
Gossip is a bit long, but in any case, both (2) and (3) use the motor corners to produce alternating stator voltages.
The standard simplest permanent magnet synchronous motor control algorithm block diagram is as follows:
The block diagram of this control algorithm looks complicated, but says a thousand and ten thousand, its purpose can be described in the following words:
(1) Because there is a moving magnetic field in the air gap, the stator coil generates a counter electromotive force when the rotor rotates;
(2) The easiest way to establish the stator magnetic field The inverter defines a voltage at the same phase angle as the back EMF. The stator magnetic field generated by the stator current after overcoming the back EMF interacts with the rotor magnetic field to perform external work.
To put it bluntly, the so-called motor control algorithm is nothing more than creating three stator voltages. The algorithm requires that the generated sinusoidal voltage be in phase with the back EMF generated by the stator cutting magnetic lines in phase.
(Why should we say the "easiest" three words, because the differential equations of motor control actually have infinite solutions, and what we use in engineering is only one of its special solutions. Too much to say, people are actually in There are countless combinations of given voltages on the stator coils that enable the rotor to output the same amount of torque at a constant speed. The most easily available method is used in engineering applications.)
So there are several ways to determine the initial position angle of the motor controller with regard to the motor position:
(1) Back EMF method
a) The motor phase line is not connected to the ECU, the motor position signal is connected to the ECU, and the software in the ECU only needs the software for angle calculation, and other control software is not needed;
b) Rotate the motor shaft by hand, and the motor angle signal observed in the software should change from 0 to 360 degrees;
c) Use the servo motor or other equipment to drag the motor under test to rotate at a constant speed, and measure the back electromotive force. The back electromotive force and the motor rotation angle after software processing should have the following corresponding relationship (0 degree corresponds to A opposite potential from positive 0 to negative 0, 120 degrees corresponds to B opposite potential from positive 0 to negative 0, 240 degrees corresponds to C opposite potential from positive 0 to negative 0).
d) If the correspondence between the back EMF and the motor rotation angle is not satisfied, the following means shall be adopted to conform to the relationship. :
i. Adjust the motor position angle Offset in the software
Ii. Change the definition of the motor ABC phase (replace the wiring sequence)
(2) Rotor drag method
