Vector Control of Permanent Magnet Synchronous Motor (4)-Three closed-loop position control system

4. Three closed loop position control system

4.1 What is a three-loop control system?

On the basis of double closed loop (speed loop and current loop) control, a position outer loop is added outside the speed outer loop. The main function of this position outer loop is to make the motor follow the position setting accurately, so it is also called position closed loop system. The principle is similar to the double closed-loop system. The difference between the target position and the actual position of the motor is used to obtain the deviation as the speed setting of the speed regulator. The greater the position deviation, the greater the corresponding speed setting.

The biggest difference between the three-closed -loop control system and the double-closed-loop control system is that the three-closed-loop mainly solves the problem of where the motor turns, while the double-closed-loop mainly solves the problem of how fast it rotates .

4.2 The control principle and construction of the three closed loop system

The principle block diagram is shown in the figure above. On the basis of the basic double closed loop control, adding a position loop, we can regard the double closed loop as a speed control module, and the position regulator sets the difference between the given position signal and the actual position detection signal as the control module The speed is given to control the motor to rotate according to the desired speed and direction, thereby controlling the position of the motor.

For example: if the given position is $\tiny 350^{\circ}$ there and the actual position is there $\tiny 50^{\circ}$ , if you want the motor to rotate to the target position angle, you need to rotate the motor clockwise $\tiny 300^{\circ}$ . At this time, the position regulator will output an instruction to control the forward rotation of the motor, and the speed loop will receive the instruction, rotate clockwise, and stop rotating after reaching the target position.

4.3 Design Ideas of Position Loop Parameters

The first step: double closed loop parameter design. It makes the motor speed following performance superior, the step response effect is better, and the system speed is better. As mentioned above, the basis of the three closed loops is the dual loop control. For a good position control system, the effect of the dual loop control must be adjusted to the optimal value.

Step 2: Position loop parameter design. Introduce position feedback and position regulator, give input signal, and adjust position loop parameters.

Signal given: It is recommended that the initial given input signal is a ramp signal with a small slope.
Regulator setting: It is recommended that the regulator be set to a pure P regulator, because most position control does not allow overshooting, and the initial parameters of the position P regulator can be set slightly larger, and the test can be started from 500.
Limit value setting: It is recommended to set the output limit value of the position regulator to the rated speed of the motor (the dual closed-loop PI parameter meets the speed and stability of the rated speed of the motor).

summary:

The goal of three-loop position control is where the motor turns, while the goal of double-loop control is how fast it turns. There is a big difference between the two.
The position regulator sets the difference between the given position signal and the actual signal detection signal to the speed setting of this control module, thereby controlling the motor to rotate according to the desired speed and direction, thereby controlling the position of the motor.
Double loop is an important basis for position control. Before position control, the first condition is to adjust the performance of the double loop system to the best.