Multi-Phase AC Motor Control Device for Electric Power Steering
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Solution Overview
Problem
Conventional control devices for multi-phase AC motors in electric power steering systems cannot completely eliminate the unpleasant sound caused by harmonic components, particularly eleventh- and thirteenth-order harmonics, which affect the driver's experience, as they primarily focus on reducing torque ripple through a fixed 30° phase difference between AC voltages.
Innovation Solution
A control device with independent first and second inverters and a control unit that adjusts the phase difference between AC voltages applied to the multi-phase winding wire sets within a control range, including a reference phase difference of 30°, to reduce specified-order harmonic components, while considering the motor's characteristics or causing fluctuations in current supply, thereby addressing the sound issue.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed phase difference control is used, then control simplicity is maintained, but adaptability to different operating conditions and resonant frequencies is poor
Solution Approach 1:
The control system transitions from static to dynamic by continuously adjusting the phase difference based on real-time operating conditions. The control unit monitors motor speed, current, and other parameters, and dynamically modifies the phase difference accordingly. This maintains relative control simplicity while dramatically improving adaptability to different operating conditions and resonant frequencies.
Solution Approach 2:
The patent implements feedback control where the control unit continuously monitors operating conditions and adjusts the phase difference based on this feedback. By using feedback from sensors monitoring motor current, speed, and position, the system adapts to different operating conditions automatically, maintaining simplicity while achieving high adaptability across varying loads and speeds.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively reduces the unpleasant sound for the driver by dynamically managing the phase difference based on steering speed or current, balancing torque ripple reduction and harmonic component mitigation, enhancing the overall driving experience.
Implementation Method 1
The first inverter and the second inverter are electrically independent from each other. The first multi-phase winding wire set and the second multi-phase winding wire set provide a stator of the multi-phase AC motor, and generate a rotating magnetic field in a rotor.
Data Source
AI summary
A control device for controlling a multi-phase AC motor generating a steering assist torque in an electric power steering device of a vehicle, includes: first and second inverters in first and second systems that output first and second alternating current voltages to first and second multi-phase winding wire sets, respectively; and a control unit that controls a phase difference between the first and second alternating current voltages. The first and second multi-phase winding wire sets provide a stator of the motor, and generate a rotating magnetic field in a rotor. The control unit sets a control range including a reference phase difference, which reduces a specified-order harmonic component, and changes the phase difference within the control range according to a characteristic required of the motor, or so as to cause a fluctuation in the energization of the motor.