MDPS Hysteresis Removal via Asynchronous Current Sweep
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Solution Overview
Problem
Motor-driven power steering systems experience hysteresis in current sensors, leading to current offset deviations and torque ripples, which are not effectively removed by conventional compensation algorithms, especially at light loads or when the system is powered off, affecting steering performance and reliability.
Innovation Solution
An apparatus and method that apply a current with an asynchronous frequency, not coinciding with the motor's synchronous frequency, to the motor at high speed during key on or off events, utilizing a sweep function to alternate or gradually decrease the current, thereby offsetting hysteresis and reducing torque ripples without altering hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional compensation algorithms are used to remove hysteresis, then the system complexity is reduced, but the hysteresis removal effectiveness is insufficient, especially at light loads or after power off
Solution Approach 1:
The patent applies a preliminary action by performing hysteresis removal through asymmetric current application before the motor operates at light loads or after power on. The ECU executes a specific routine (Operation S20) that applies current in one direction to saturate the magnetic flux in the current sensor, thereby removing hysteresis effects before normal operation begins. This preliminary action ensures that hysteresis is eliminated proactively rather than attempting to compensate for it during operation.
2Measurement precision
If the current sensor measures motor current, then real-time feedback is obtained, but hysteresis remains in the current sensor causing current offset deviation
Solution Approach 1:
The patent converts the harmful hysteresis effect into a beneficial outcome by deliberately applying asymmetric current to saturate the magnetic flux in the current sensor. The ECU applies current in one direction (Operation S20) to drive the magnetic flux to saturation, which eliminates the hysteresis loop. This intentional application of unbalanced current transforms the hysteresis problem into a solution, ensuring that subsequent current measurements are accurate without offset deviations.
3Manufacturing precision
If torque control is performed using current sensor feedback, then motor control precision is improved, but torque ripple increases due to hysteresis
Solution Approach 1:
The patent eliminates torque ripple by performing hysteresis removal as a preliminary action before torque control begins. The ECU executes the hysteresis removal routine (Operation S20) that applies asymmetric current to saturate the magnetic flux, thereby eliminating the source of torque ripple. By removing hysteresis beforehand, the subsequent torque control operates on a clean baseline without the harmful effects of magnetic flux hysteresis, ensuring precise torque control without ripple.
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
Effectively removes hysteresis and associated torque ripples, improving steering feel and system reliability by applying the asynchronous current within a short time, reducing development and maintenance costs through algorithmic solutions.
Implementation Method 1
the current sensor may convert the magnitude of a motor current corresponding to an actual current flowing in the motor into an induced magnetization, and outputs the induced magnetization as a voltage or current
Implementation Method 2
when the current applied to the motor becomes zero by the property of the current sensor, the induced magnetization may not converge to zero, but hysteresis may remain to thereby generate a current offset deviation
Data Source
AI summary
An apparatus for removing hysteresis of motor driven power steering (MDPS) may include: a motor driving unit for rotating a motor; a key on/off sensing unit for sensing a key on/off of a vehicle; and an electronic control unit (ECU) for receiving a key off state of the vehicle from the key on/off sensing unit and repeating a sweep function a preset number of times. The sweep function may include applying a current having an asynchronous frequency, which does not coincide with a synchronous frequency of the motor, to the motor through the motor driving unit.