Electric Power Steering Dead Time Compensation
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Solution Overview
Problem
Conventional electric power steering systems face challenges in compensating for inverter dead time, leading to current waveform distortion, torque ripple, and steering sound issues, particularly at low load and low speed conditions, requiring tuning operations that are complex and prone to chattering.
Innovation Solution
The system estimates 3-phase voltages from motor terminal voltages, calculates loss voltages due to dead time, and feeds back dead time compensation values to voltage command values, automatically calculating compensation amounts to minimize chattering and optimize dead time compensation without the need for tuning operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional dead time compensation methods are used, then dead time can be compensated, but current waveform distortion and torque ripple occur due to the need for tuning operations
Solution Approach 1:
The system automatically calculates dead time compensation values based on motor terminal voltages without requiring external tuning operations. The control unit self-adjusts the compensation values by detecting terminal voltages and calculating the difference from command voltages, eliminating the need for manual tuning while maintaining accurate dead time compensation.
Solution Approach 2:
The system uses feedback from motor terminal voltage measurements to automatically adjust dead time compensation values. By comparing detected terminal voltages with command voltages and using the difference as compensation values, the system creates a closed-loop feedback mechanism that eliminates tuning requirements while maintaining compensation accuracy.
2Reliability
If dead time compensation is applied, then inverter dead time effects are reduced, but chattering occurs in low load and low speed conditions
Solution Approach 1:
The system calculates dead time compensation values based on the actual motor terminal voltages rather than applying fixed or ideal compensation values. This partial action approach, where compensation is proportional to the actual voltage conditions, prevents over-compensation in low load and low speed conditions that would cause chattering, while still providing effective dead time compensation when needed.
3Reliability
If ideal dead time compensation values are used, then dead time can be compensated, but the compensation values do not match actual motor terminal voltages
Solution Approach 1:
The system replaces ideal or theoretical dead time compensation calculations with actual measurements from motor terminal voltages. By using voltage detection and calculation based on real terminal voltage data rather than ideal models, the system achieves compensation values that accurately reflect actual motor conditions, improving both reliability and measurement precision.
Data Source
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AI summary
[Problem] An object of the present invention is to provide an electric power steering apparatus of a vector control system that compensates a dead time of an inverter without tuning operation, improves a distortion of a current waveform and a responsibility of a current control, and suppresses a steering sound, a vibration and a ripple. [Means for solving the problem] The present invention is the electric power steering apparatus of a vector control system that converts dq-axes current command values calculated based on at least a steering torque into 3-phase voltage command values, converts the 3-phase voltage command values into duty command values, driving-controls a 3-phase brushless motor by an inverter of a PWM control, and applies an assist torque to a steering system of a vehicle, wherein 3-phase detection voltages are estimated based on 3-phase motor terminal voltages, wherein loss voltages due to a dead time of the inverter are estimated from differences between 3-phase command voltages calculated from the duty command values and the 3-phase detection voltages, and wherein a dead time compensation of the inverter is performed by feeding-back dead time compensation values obtained by compensating the loss voltages to the 3-phase voltage command values.