Analysis of AC Servo Motor Vector Control Technology
The three-phase AC value is obtained from the current sampling of AC Motor, converted into two-phase coordinates (αβ) by Clark, and then the static αβ coordinate is replaced by the dq coordinate of the rotation by Park transform to form a feedback value, and the command value of dq is calculated.
Through the calculation result of the PI controller, we can obtain the voltage command value of dq two-phase, and the dq command value of the rotating coordinate is transformed by inverse Park to obtain αβ of the stationary coordinate, and then the three-phase voltage driving command is obtained by inverse Clark conversion. Controls the output of the SVPWM.
In addition, the d-axis corresponds to the torque generated by the excitation, and the q-axis corresponds to the torque generated by the permanent magnet. We can make the d-axis command value 0 when controlling the SPM motor. However, in the IPM motor control, both the d-axis and the q-axis are utilized, so the output of the two commands is required in the speed loop.
The following is a forward Clark transform and a Park transform to calculate how to coordinate transformation:
We set the U and α axes to be the same, and assume that k is the vector amplitude ratio coefficient of the three-phase and two-phase. Through the above illustration we can get:
Due to the three-phase balance, we can have:
Bring the above formula to get: k=2/3
We assume that there is an angle of θ between the αβ axis and the dq axis, and decompose αβ onto the dq axis, and then use the trigonometric formula to get:
The inverse transformation of the rotated coordinates and the stationary coordinates is the same as above, and is omitted here.
Above we talked about coordinate transformation and vector control structure. The purpose of vector control is to control the servo while making the current and voltage levels consistent to improve the efficiency of power efficiency and motor torque. Let's take a look at the servo control structure including vector control.
The above structure can be simplified as follows: position control loop, speed control loop, vector (current) control loop.
The vector control of AC motor is analyzed. In the actual control of AC motor using frequency converter, due to the influence of external disturbance, temperature, high frequency and so on, the motor control algorithm is more and more complicated and the accuracy is higher and higher, but we only need Mastering the most basic methods described above helps to understand other developmental algorithms.