PWM Motor Control Timing for Axial Voltage Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In three-phase motor systems, simultaneous voltage fluctuations between the output shaft and motor case can lead to noise and electrolytic corrosion due to matching switching timings of PWM signals, causing rapid axial voltage changes.
Innovation Solution
A motor control device that adjusts the timing of voltage fluctuations between two-phase connection terminals by delaying one and advancing the other, ensuring their occurrence times do not overlap, thereby preventing simultaneous switching and reducing axial voltage fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If switching timings of PWM signals are synchronized for efficient motor control, then motor control precision is improved, but instantaneous axial voltage fluctuations increase causing noise and electrolytic corrosion
Solution Approach 1:
The control unit predicts whether voltage fluctuations will occur simultaneously based on duty command values before actual PWM switching occurs. When simultaneous fluctuations are predicted, the control unit preemptively adjusts the switching timing of at least one phase to prevent overlap, thereby eliminating axial voltage fluctuations before they can occur while maintaining synchronized control.
2Use of energy by moving object
If PWM switching signals are generated with matching timings for efficient power conversion, then power conversion efficiency is improved, but noise and electrolytic corrosion in rotor bearing increase
Solution Approach 1:
The control unit continuously monitors duty command values and predicts the timing of voltage fluctuations in each phase. Based on this feedback information, the control unit dynamically adjusts PWM switching timings to prevent simultaneous voltage fluctuations, thereby eliminating the harmful effects of noise and electrolytic corrosion while maintaining efficient power conversion.
3Object-affected harmful factors
If simultaneous voltage fluctuations are prevented by delaying or advancing switching timing of one phase, then axial voltage fluctuations are reduced, but switching timing synchronization is compromised
Solution Approach 1:
The control unit applies timing adjustments selectively only to the specific phases that would otherwise experience simultaneous voltage fluctuations. By locally adjusting the switching timing of affected phases rather than globally desynchronizing all phases, the invention maintains switching timing synchronization for the majority of operations while eliminating axial voltage fluctuations only when necessary.
Data Source
AI summary
A motor control device includes a conversion circuit that is connected to an n-phase motor, and a control unit that controls the conversion circuit based on n-phase duty command values updated at a predetermined update cycle. When the control unit predicts, based on the n-phase duty command values, that voltage fluctuations of at least two-phase connection terminals among the n-phase connection terminals connected to the n-phase motor occur in the same direction and at the same timing, the control unit delays the occurrence timing of the voltage fluctuation of one of the two-phase connection terminals by a first time and advances the occurrence timing of the voltage fluctuation of another connection terminal by a second time. The total value of the first time and the second time is a predetermined time during which predetermined occurrence timings of the voltage fluctuations of the two-phase connection terminals do not overlap each other.