Motor Control Device for Torque Ripple Suppression
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Solution Overview
Problem
Conventional motor control devices for three-phase brushless motors with harmonic components in back electromotive voltages face issues with torque ripple and inefficient power supply utilization due to distortion in motor drive voltage waveforms, leading to reduced rotation performance and increased noise in motor-driven power steering systems.
Innovation Solution
A motor control device that actively controls the d-axis current to shape motor drive voltage waveforms, using phase current detection, rotor position sensing, and target current setting to maintain a constant composite voltage vector, effectively utilizing power supply voltage and suppressing torque ripple through lead angle control and d-q axis coordinate-based current control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the torque of a harmonic motor is controlled to be constant using conventional vector control, then the torque stability is improved, but the motor drive voltage waveforms become substantially distorted according to the harmonic waves of the induced voltages, resulting in reduced power supply utilization efficiency
Solution Approach 1:
The invention changes the control parameters by actively controlling the d-axis current to shape the motor drive voltage waveforms. By adjusting the d-axis current component, the system modifies the voltage waveform characteristics to maintain a constant composite voltage vector, thereby resolving the distortion caused by harmonic components while preserving torque stability and improving power supply utilization efficiency.
2Use of energy by moving object
If the motor drive voltage waveforms are shaped by actively controlling d-axis current, then the power supply voltage utilization is improved and torque ripple is suppressed, but the control system complexity increases
Solution Approach 1:
The invention introduces d-axis current control as an intermediary mechanism to indirectly shape the motor drive voltage waveforms. Rather than directly controlling the voltage waveforms, the system uses d-axis current as a mediator that naturally shapes the voltage through the motor's electrical characteristics, thereby achieving waveform shaping and torque ripple suppression without requiring complex direct voltage control circuits.
Solution Approach 2:
The invention replaces complex mechanical or circuit-based waveform shaping mechanisms with electrical control of the d-axis current. By using the motor's own electrical system to generate the desired voltage waveforms through controlled current injection, the invention eliminates the need for additional mechanical waveform shaping devices or complex power electronic circuits.
3Ease of operation
If conventional vector control is used for harmonic motors, then the control implementation is simplified, but the rotation performance is reduced and noise is increased in motor-driven power steering systems
Solution Approach 1:
The invention implements feedback control by continuously monitoring the composite voltage vector and adjusting the d-axis current to maintain its constancy. This feedback mechanism ensures that the voltage waveform distortion is actively compensated in real-time, thereby suppressing torque ripple and reducing noise while maintaining relatively simple control implementation through the use of standard feedback control techniques.
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
The solution enhances motor output, reduces torque ripple, and improves rotation performance by effectively using power supply voltage, resulting in a low-noise, high-power motor-driven power steering system with favorable steering feel.
Implementation Method 1
three-phase brushless motor with back electromotive voltages having harmonic components superimposed therein
Data Source
AI summary
An object of the present invention is to provide a motor control device capable of suppressing voltage composite vector fluctuation to increase the output of a brushless motor, and a motor-driven power steering system using this device. The present control device calculates motor phase current command values based on a target current and a rotor rotational position detection value, calculates voltage command values based on the motor phase current command values and phase current detection values, and supplies phase currents to a three-phase brushless motor based on the voltage command values. The present control device outputs the phase current command values so that the absolute value of a composite vector of respective phase drive voltages is substantially a value √3/2 times the power supply voltage.