Electric Power Steering Dead Time Compensation
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Solution Overview
Problem
Existing electric power steering apparatuses face issues with dead time compensation, leading to current distortion, torque ripple, and instability due to temperature changes in the inverter switching elements, which are not adequately addressed by current methods that do not consider both steering conditions and temperature variations.
Innovation Solution
A control device that calculates a dead time compensation value based on the temperature of the inverter and steering status, using a dead time characteristic section, steering status determining section, gain section, polarity determining section, and temperature sensor to adjust the dead time compensation dynamically, ensuring accurate compensation regardless of temperature changes and steering conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dead time compensation is applied using fixed values, then current distortion is reduced at normal temperature, but torque ripple increases and stability deteriorates when inverter temperature changes
Solution Approach 1:
The patent applies dynamics by making the dead time compensation value variable rather than fixed. The compensation value dynamically changes based on inverter temperature and steering status (turning/returning). This resolves the contradiction by adapting the compensation to actual operating conditions, maintaining current accuracy across temperature ranges while preventing torque ripple and instability.
Solution Approach 2:
The patent changes the parameter of dead time compensation value based on temperature and steering status. By adjusting this parameter according to actual conditions, the system maintains precise current control without causing torque ripple or instability, thus resolving the contradiction between current distortion reduction and steering stability.
2Measurement precision
If dead time compensation is increased to reduce current distortion, then voltage distortion decreases, but torque ripple increases due to temperature variations
Solution Approach 1:
The system dynamically adjusts the dead time compensation value based on inverter temperature and steering status. This prevents excessive compensation that would cause torque ripple while still reducing voltage distortion, thus resolving the contradiction between voltage distortion reduction and torque ripple prevention.
Solution Approach 2:
The patent changes the compensation parameter according to temperature and steering conditions. This adaptive approach reduces voltage distortion without generating harmful torque ripple, resolving the contradiction by optimizing the compensation level for each operating condition.
3Reliability
If temperature-based dead time correction is applied, then steering stability improves, but system complexity increases due to additional sensors and control logic
Solution Approach 1:
The system uses the inverter's own temperature sensor (already present in the system) to automatically adjust dead time compensation. This self-service approach improves steering stability without requiring external sensors or complex external control systems, thus resolving the contradiction between stability improvement and system complexity.
Solution Approach 2:
The patent makes the existing temperature sensor serve multiple functions: monitoring inverter temperature for thermal management and providing feedback for dead time compensation adjustment. This multi-functionality improves steering stability without adding dedicated temperature monitoring systems, reducing the net increase in complexity.
4Object-generated harmful factors
If steering status-based gain adjustment is applied, then torque ripple is reduced during returning, but current distortion increases during turning
Solution Approach 1:
The patent applies different compensation gains for different steering statuses (turning vs. returning). By tailoring the compensation characteristics to the specific steering phase, the system reduces torque ripple during returning while maintaining current accuracy during turning, thus resolving the contradiction through localized optimization.
Solution Approach 2:
The system changes the compensation gain parameter based on steering status detection. This adaptive parameter adjustment reduces torque ripple in returning mode while preserving current distortion reduction in turning mode, resolving the contradiction by optimizing for each operational phase.
Data Source
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AI summary
[Problem] An object of the present invention is to provide a control apparatus for an electric power steering apparatus that suppresses disaccord between the dead time and the dead time compensation value by correcting the dead time compensation value based on the temperature of the switching element and reduces the distortion of the motor current and the occurrence of the torque ripple, and simultaneously reduces the occurrence of noises by performing a dead time compensation corresponding to steering conditions and obtains good steering performances even under an environment from low temperature to high temperature. [Means for solving the problem] The present invention comprises a dead time characteristic section that calculates a dead time characteristic value; a steering status determining section that determines a steering status; a gain section that varies a gain of the dead time characteristic value in accordance with a determination of the steering status; a polarity determining section that switches polarity determining methods in accordance with the determination of the steering status and determines a polarity on the basis of a detected current of a motor, a current command value or a model current; a temperature sensor that detects a temperature of an inverter; a dead time temperature correction value calculating section that calculates a dead time temperature correction value corresponding to the temperature; and a calculation processing section that calculates and processes the dead time temperature correction value with respect to a dead time compensation value with polarity based on an output of the gain section and outputs a dead time compensation value.