Electric Power Steering Dead Time Compensation Switching
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Solution Overview
Problem
Conventional electric power steering apparatuses face issues with dead time compensation in inverters, leading to current waveform distortion, torque ripple, and adverse steering feelings due to nonlinear dead time, which affects steering performance and causes noise and vibration.
Innovation Solution
The apparatus employs a vector control system with multiple dead time compensation functions that switch based on steering state and temperature, using conditional branches and gradual-changing switches to optimize dead time compensation, ensuring accurate and precise voltage command compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If dead time compensation is applied to the inverter, then current waveform distortion and torque ripple are reduced, but the system complexity increases due to multiple compensation functions and switching mechanisms
Solution Approach 1:
The dead time compensation function is segmented into multiple independent compensation functions (first, second, and third compensation functions), each handling specific aspects of dead time compensation under different operating conditions. This segmentation allows the system to apply appropriate compensation strategies selectively, reducing overall distortion while managing complexity through modular design.
Solution Approach 2:
The system dynamically switches between different dead time compensation functions based on real-time operating conditions such as motor rotational velocity and steering state. This dynamic adaptation enables the system to optimize compensation effectiveness across varying operational ranges without requiring a single complex fixed compensation mechanism.
2Reliability
If multiple dead time compensation functions are used, then steering performance is improved, but the switching between functions may cause torque ripple and vibration
Solution Approach 1:
The system performs preliminary determination of the appropriate dead time compensation function based on predicted operating conditions (motor rotational velocity and steering state) before actual switching occurs. This preliminary action allows for smooth transition preparation, preventing abrupt changes that would cause torque ripple and vibration during function switching.
Solution Approach 2:
The control unit acts as an intermediary that smoothly manages the switching between different dead time compensation functions. It monitors operating conditions and orchestrates transitions in a way that maintains continuous and stable compensation, preventing discontinuities that would manifest as torque ripple and vibration.
3Object-generated harmful factors
If dead time compensation is applied, then noise and vibration are suppressed, but the control responsibility and computational load increase
Solution Approach 1:
The dead time compensation is applied selectively based on local operating conditions (specific ranges of motor rotational velocity and steering state) rather than uniformly across all operations. This local quality approach ensures noise and vibration suppression is applied precisely where needed, reducing unnecessary computational load in conditions where compensation is not required.
4Measurement precision
If temperature compensation is implemented, then compensation accuracy is maintained across varying temperatures, but the device complexity and calibration requirements increase
Solution Approach 1:
The system adjusts dead time compensation parameters based on detected temperature conditions. By changing compensation parameters dynamically according to temperature, the system maintains accurate compensation across varying thermal environments without requiring complex hardware modifications, achieving temperature compensation through software-based parameter adaptation.
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 (DT) compensation functions to compensate the dead time (DT), compensates the DT by switching the DT compensation functions depending on the steering state and the functions, improves the steering performance, the distortion of the current waveform and the responsibility of the current control. [Means for solving the problem] The present invention is the electric power steering apparatus of a vector control system that drives and controls a motor by an inverter and applies an assist torque to a steering system of a vehicle, comprising the first compensation function to perform a dead time (DT) compensation based on respective phase motor terminal voltages and respective phase duty command values, the second compensation function to perform a DT compensation based on steering assist command values, the third compensation function to perform the DT compensation based on dq-axis current command values, and a temperature detecting section to detect temperature of ECU, wherein the correction of the DT compensation is performed based on the temperature, wherein switches of the compensation functions are performed by using a conditional branch due to software and a gradual-changing switch, wherein the dq-axis DT compensation values after the conditional branch and the gradual-changing switch are performed are calculated, and wherein the dq-axis voltage command values are compensated by the dq-axis DT compensation values.