Brushless Motor Control Axis Stabilization Against Noise
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Solution Overview
Problem
Brushless motors experience frequent direction corrections of control axes due to high-frequency noise components in the q-axis current, leading to phase differences near +90° or -90°, which complicates accurate rotor position estimation.
Innovation Solution
A motor control device with an acquisition unit for obtaining q-axis current components, a correction unit to adjust the estimated d-axis based on these components, and a control axis changing unit that alters the d-axis direction by a prescribed angle when the q-axis current magnitude falls below a threshold, helping to separate phase differences from problematic ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the direction of the control axis is corrected based on the q-axis current component when high-frequency noise is present, then the rotor position estimation can be updated, but the phase difference frequently switches between +90° and -90° causing unstable corrections
Solution Approach 1:
The patent introduces a phase difference calculation unit that calculates the phase difference between the voltage vector and current vector as an intermediary parameter. This phase difference serves as a mediator to determine whether correction should be applied, preventing direct correction based on noisy q-axis current alone. The correction unit uses this phase difference information to suppress corrections when the phase difference is near ±90°, thus stabilizing the control axis direction while still enabling accurate rotor position estimation when conditions are favorable.
2Reliability
If continuous correction of the estimated d-axis is performed based on q-axis current, then the direction approaches the actual d-axis, but noise causes frequent switching of correction direction preventing convergence
Solution Approach 1:
The patent implements a feedback mechanism where the phase difference between voltage and current vectors is continuously calculated and fed back to the correction unit. This feedback loop allows the system to assess the effectiveness of corrections and suppress further corrections when the phase difference indicates proximity to ±90°, preventing oscillatory behavior. The feedback-based control enables reliable axis alignment while maintaining manageable complexity through a unified correction control structure.
Data Source
AI summary
A motor control device includes an acquisition unit that obtains a q-axis current component of a current vector generated when electricity is supplied to a brushless motor to generate a voltage vector along a direction of an estimated d-axis; a correction unit that corrects the direction of the estimated d-axis according to the q-axis current component to approach the direction of the estimated d-axis approach to the direction of the actual d-axis; and a control axis changing unit that changes the estimated d-axis direction by a prescribed angle when a magnitude of the q-axis current component is less than a threshold value by the correction of the direction of the estimated d-axis by the correction unit for the first time after the control axis setting control start or when a magnitude of the q-axis current component is less than the threshold value at the control axis setting control start.