Application note Controller gain scheduling for improved performances

Controller gain scheduling

Controller gain scheduling 1 - TUNING LEVEL SCHEDULING Select Scheduling operation = Tuning level reduction at standstill. This scheduling operation concern the axis positioning in Profile Position mode or in Sequences mode. The normal tuning level is applied during the axis displacement. It can be increased for better dynamic performances. The low tuning level is applied at standstill and in low-speed movements to get stable and smooth behavior. If low tuning level value is greater than the normal tuning level value, the normal tuning level is maintained at standstill. The switching delay duration...

Controller gain scheduling Examples of scheduling operation are described below. Drive operation in position mode: When the velocity set point value is lower than the velocity threshold value, and the switching delay is over, the low tuning level is applied as shown below. When the switching delay duration is greater than the rest time between two movement, the normal tuning level is maintained during the rest time as shown below. Tuning level scheduling

Controller gain scheduling Drive operation in speed mode: When the velocity set point value is lower than the profile velocity limit, and the switching delay is over, the low tuning level is applied as shown below. When the switching delay duration is greater than the low-speed operating time duration, the normal tuning level is maintained. Tuning level scheduling

Controller gain scheduling 2 - HIGH SPEED GAIN SCHEDULING Select Scheduling operation = Gains reduction at high speed. This scheduling concern all the drive modes. In this case, the controller gain values are reduced when the motor speed is increasing. Motor speed limit defines the maximum motor speed value for the controller gains reduction. When the motor speed is greater than this parameter value, the gains reduction is limited to 75% (standstill gain value / 4). When this parameter value is set to 0, the gain reduction is deactivated. High speed gain scheduling

Controller gain scheduling 3 - APPLICATION EXAMPLE OF TUNING LEVEL SCHEDULING 3.1 - APPLICATION REQUIREMENTS Many positioning applications requires fast movement execution and short servo loop response time, to reduce the axis positioning cycle and increase the machine feed rate. However, in case of low resolution, or noisy position sensor feedback, it is necessary to increase the servo loop filtering and reduce the servo loop gain to have a stable and quiet behavior at standstill. This result in poor dynamic performances when the axis is moving. 3.2 - CONTROLLER ADJUSTMENT FOR HIGH DYNAMIC Increasing...

Controller gain scheduling OINFRANOR3.3 - CONTROLLER ADJUSTMENT FOR REDUCED NOISE AT STANDSTILL Reducing the tuning level value to 40% results in quiet and stable behavior of the motor at standstill. But, because of the lower gain value, in movement, tracking error and settling time are dramatically increased. T Scheduling operation select Tuning level reduction parameters (Positioning mode) Velocity threshold for standstill detection (inc/s) [Standstill switching delay (ms) l Normal tuning level (movement) By using the tuning level scheduling, high gain (100%) can be applied when the axis is...

Controller gain scheduling OINFRANOR 4 - APPLICATION EXAMPLE OF HIGH-SPEED GAIN SCHEDULING Position measurement error over one motor shaft revolution is inherent to resolver feedback. The same error can be observed with hallow shaft encoders in case of large concentricity tolerances. These measurement errors generate motor current ripples when running at high speed. Current ripples cause undesirable motor heating and vibration in the machine mechanical structure. For reducing the current ripples amplitude, it is necessary to reduce the servo loop low pass filter cut off frequency and consequently...

Controller gain scheduling 4.3 - CONTROLLER ADJUSTMENT FOR LOW CURRENT RIPPLES Bandwidth level set to 60% with tuning level set to 60% reduce dramatically the current ripple amplitude. This is due to the low value of the servo loop low pass filter cut off frequency and consequently the low value of the servo loop gain. But the axis stiffness and stability at standstill are also dramatically reduced. Stiffness and stability at standstill are reduced Current ripple amplitude is divided by 4 4.4 - CONTROLLER WITH HIGH-SPEED GAIN SCHEDULING By using the high-speed gain scheduling, the auto-tuning...

Controller gain scheduling 5 - CONCLUSION The “Gain scheduling” feature on the servo loop tuning allows to improve the servo loop performances in case of controller gain limitation due to the position sensor resolution, position sensor noise, position sensor error, or mechanical disturbances (backlashes, elasticity, frictions). The optimal gain value is switched in the controller according to the drive operating condition: standstill / movement, or high speed / low speed. Application examples described in this document have shown the real gain in the servo drive dynamic performances.