Electric Power Steering Dead Time Compensation
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Solution Overview
Problem
Conventional electric power steering systems face challenges in accurately compensating for dead time in inverters, leading to distorted current waveforms, reduced control responsibility, and issues like torque ripple, sound, and vibration, especially during high-speed steering and low-load maneuvers, due to the need for tuning operations and potential chattering.
Innovation Solution
The system employs plural dead time compensating functions that switch based on steering states, using both a dead time compensating function based on motor rotational angle and another based on current command value models, allowing for optimal dead time compensation without tuning operations, improving steering performance and waveform distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single dead time compensating function is used, then the device complexity is reduced, but the manufacturing precision of current waveform control deteriorates due to inability to compensate across all steering states
Solution Approach 1:
The dead time compensation system is segmented into multiple functions: a first dead time compensating function for low-speed steering and a second dead time compensating function for high-speed steering. This segmentation allows each function to be optimized for specific operating conditions, improving current waveform control precision without requiring a single complex universal compensator.
Solution Approach 2:
The system dynamically switches between different dead time compensating functions based on the steering state. The switching mechanism adapts the compensation approach in real-time according to motor rotational speed and steering conditions, enabling precise current waveform control across all operating ranges while maintaining manageable system complexity.
2Ease of operation
If dead time compensation is performed without tuning operations, then the ease of operation is improved, but the measurement precision of dead time compensation deteriorates
Solution Approach 1:
The system uses parameter changes based on motor rotational speed to determine which dead time compensating function to apply. By automatically adjusting the compensation parameters according to the operating state rather than requiring manual tuning, the system achieves both ease of operation and maintained precision through adaptive parameter selection.
Solution Approach 2:
The dead time compensation system performs self-adjustment by automatically selecting appropriate compensation functions based on detected steering conditions. This self-service capability eliminates the need for manual tuning operations while maintaining compensation accuracy through built-in state-dependent parameter selection.
3Productivity
If dead time compensation is optimized for high-speed steering, then the productivity of high-speed steering control is improved, but the reliability of low-speed steering control deteriorates
Solution Approach 1:
The compensation system is divided into distinct functions for different speed ranges. The first dead time compensating function specifically addresses low-speed steering conditions to ensure stability and reliability, while the second function optimizes for high-speed performance. This segmentation prevents high-speed optimization from compromising low-speed reliability.
Solution Approach 2:
The system dynamically selects the appropriate compensating function based on real-time motor rotational speed detection. This dynamic switching ensures that low-speed steering always receives the stability-optimized first function while high-speed steering receives the performance-optimized second function, maintaining both reliability and productivity across all operating conditions.
4Manufacturing precision
If multiple dead time compensating functions are switched based on steering state, then the manufacturing precision of current control is improved, but the device complexity increases
Solution Approach 1:
The switching between multiple dead time compensating functions is driven by dynamic detection of steering state parameters such as motor rotational speed. This dynamic, state-based switching mechanism achieves precise current control across all operating conditions while maintaining relatively simple system architecture through automated condition-based selection rather than complex multi-layer compensation structures.
Data Source
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AI summary
[Problem] An object of the present invention is to provide an electric power steering apparatus that has plural dead time compensating functions to compensate the dead time of the inverter without the tuning operation, compensates with the feed forward method by switching the dead time compensating functions corresponding to the steering state, improves the steering performance, improves the distortion of the current waveform and the responsibility of the current control, and suppresses the sound, the vibration and the torque ripple. [Means for solving the problem] The present invention is the electric power steering apparatus of vector control system that calculates steering assist command values of dq axes based on at least a steering torque, calculates dq-axes current command values from the steering assist command values, converts the dq-axes current command values into 3-phase 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 the electric power steering apparatus has plural dead time compensating functions of which efficiencies to respectively perform a dead time compensation of the inverter are different each other, and performs the dead time compensation by switching from one of the plural dead time compensating functions to an another dead time compensating function with a predetermined condition.