Brushless Motor Control Device Noise Suppression via Angle Interpolation
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Solution Overview
Problem
Existing motor control devices for electric power steering systems face challenges in suppressing noise and vibration in brushless motors due to noise in interpolated Duty command values, especially at high speeds, and are affected by dead time compensation in inverter control.
Innovation Solution
A motor control device that calculates an interpolated Duty command value using a voltage command value and motor electric angle, with an electric angle interpolation unit estimating an interpolated electric angle through quadratic or linear function interpolation, allowing for switching between interpolation methods based on motor rotation speed, and outputs the appropriate Duty command values to reduce noise and vibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the PWM calculation cycle is reduced to suppress motor vibration and noise, then the noise suppression effect is improved, but the calculation processing amount increases and power consumption increases
Solution Approach 1:
The patent pre-calculates and stores voltage command values at multiple electric angles in advance, so that during PWM control only interpolation and lookup operations are needed rather than full recalculation, reducing real-time computational load and power consumption while maintaining the ability to generate high-frequency PWM signals for noise suppression
Solution Approach 2:
The patent creates interpolated voltage command values by copying and combining pre-calculated voltage command values at different electric angles through interpolation, avoiding the need to recalculate from scratch and reducing computational energy requirements while achieving the desired PWM signal frequency
2Device complexity
If the interpolated Duty command value is calculated using the Duty command value, then the calculation is simple, but the interpolated value includes large noise particularly at high speed steering
Solution Approach 1:
The patent extracts only the essential voltage command value information needed for PWM control, separating it from the noisy Duty command value. By interpolating voltage command values at different electric angles and using these for PWM generation, the system avoids propagating the noise present in Duty command values while maintaining calculation simplicity
Solution Approach 2:
The patent introduces voltage command values as an intermediary between the control system and PWM generation. Instead of directly interpolating noisy Duty command values, the system uses voltage command values at different electric angles as intermediaries, which when interpolated provide cleaner signals for PWM control without the high-frequency noise
3Productivity
If the control cycle is extended to reduce calculation processing, then the processing load is reduced, but the motor vibration frequency remains in the audible range
Solution Approach 1:
The patent segments the voltage command calculation into two parts: pre-calculation of voltage command values at multiple electric angles stored in memory, and real-time interpolation of these stored values. This segmentation allows the system to use a longer control cycle for the interpolation step while maintaining the ability to generate higher frequency PWM signals, reducing audible noise without excessive computational load
Solution Approach 2:
The patent performs preliminary calculation and storage of voltage command values at various electric angles before runtime. During actual PWM control, only interpolation and memory lookup are required, enabling the system to operate with longer control cycles while still generating sufficient PWM frequency to push motor vibration out of the audible range
Data Source
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AI summary
A motor control device for performing PWM control of an inverter for driving a three-phase brushless motor on the basis of a current command value, wherein the motor control device is provided with: a voltage command value computation unit for calculating a voltage command value using the current command value, and a motor rotation speed and a motor electric angle acquired for each control cycle from the three-phase brushless motor; an electric angle interpolation unit for estimating an interpolated electric angle from the motor electric angle at division intervals obtained by dividing the control cycle; a conversion unit for calculating a three-phase Duty command value from the voltage command value and the motor electric angle, and calculating a three-phase interpolated Duty command value from the voltage command value and the interpolated electric angle; and an output setting unit for switching between, and outputting, the three-phase Duty command value and the three-phase interpolated Duty command value so as to match the division intervals.