EPS Motor Field-Weakening Control Using q-Axis-Coupled d-Axis Adjustment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional motor control devices for three-phase brushless motors during field-weakening control fail to adequately suppress noise and vibration caused by changes in the q-axis current command value, which are not addressed by limiting the change rate of the d-axis current command value alone.
Innovation Solution
A motor control device that includes a torque command/current command converter, a field-weakening controller, a d-axis current final value calculator, a current controller, and a d-axis current adjuster, which adjusts the d-axis current command based on the q-axis current command value to suppress the frequency component of the q-axis current command in a specific frequency band, thereby reducing noise and vibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If field-weakening control is performed by limiting the change rate of the d-axis current command value, then the motor speed response is improved, but noise and vibration caused by q-axis current command changes are not adequately suppressed
Solution Approach 1:
A d-axis current adjuster is introduced as an intermediary component between the field-weakening controller and the current controller. This adjuster modifies the d-axis current command final value based on the q-axis current command value, effectively mediating the interaction between d-axis and q-axis current controls to suppress noise and vibration while maintaining speed response performance
Solution Approach 2:
The d-axis current adjuster uses the q-axis current command value as feedback to dynamically adjust the d-axis current command final value. This feedback mechanism allows the system to respond to changes in q-axis current and suppress the resulting noise and vibration in real-time during field-weakening control operation
2Speed
If the d-axis current command value changes rapidly to increase motor speed during field-weakening control, then the motor's ability to operate at high speed is improved, but noise and vibration occur due to the interaction with q-axis current changes
Solution Approach 1:
The d-axis current adjuster performs preliminary anti-action by pre-adjusting the d-axis current command final value based on anticipated or concurrent changes in the q-axis current command value. This proactive adjustment prevents the harmful interaction between d-axis and q-axis current changes before it can generate significant noise and vibration
Solution Approach 2:
The d-axis current adjuster serves as a mediator that coordinates the relationship between d-axis and q-axis current controls during high-speed operation. By adjusting the d-axis current command based on q-axis current command value, it enables rapid speed response while filtering out the harmful interactions that would otherwise generate noise and vibration
Data Source
AI summary
A field-weakening controller determines a d-axis current command correction value in field-weakening control according to a modulation factor that correlates with the ratio of the voltage amplitude applied to the inverter to the power supply voltage. A d-axis current final value calculator outputs a d-axis current command final value calculated using a d-axis current command value and a d-axis current command correction value. A Current controller performs feedback control of the d-axis current command final value and the q-axis current command value. A d-axis current adjuster adjusts the d-axis current command final value based on the q-axis current command value so as to suppress an influence of the frequency component of the q-axis current command value in a specific frequency band for which at least a lower limit frequency is determined.