Sensorless Electric Power Steering Motor Control via Inductive Voltage Correction
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Solution Overview
Problem
Electric power steering systems using sensorless control face challenges in maintaining motor synchronism due to fluctuations in axial force, leading to reduced assist torque and increased likelihood of reverse rotation, as they struggle to accurately estimate and maintain the current vector's alignment with the q-axis direction without a rotational angle sensor.
Innovation Solution
The system incorporates a permanent magnet synchronous motor with a rotational angle sensor, sensor anomaly detection, electrical angle estimation, and motor control means that switch between d-q and γ-δ coordinate systems, using inductive voltage to correct the estimated electrical angle and maintain the current vector's alignment, thereby enhancing synchronism robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sensorless control is used to eliminate the rotational angle sensor, then device complexity is reduced, but measurement precision of the electrical angle deteriorates
Solution Approach 1:
The system uses feedback control by detecting the γ-axis inductive voltage and using it to correct the estimative electrical angle through estimative-electrical-angle correction means, thereby improving the accuracy of electrical angle measurement in sensorless control mode
Solution Approach 2:
The patent replaces the mechanical/physical rotational angle sensor with an electrical-based estimation system that uses inductive voltage detection and coordinate system transformation to determine the electrical angle, eliminating the need for physical sensors
2Use of energy by moving object
If the current vector is maintained to coincide with the q-axis direction for efficient motor driving, then use of energy is improved, but reliability of motor synchronism deteriorates under axial force fluctuation
Solution Approach 1:
The system applies preliminary correction to the estimative electrical angle by detecting the γ-axis inductive voltage and adjusting the angle before control is applied, preventing the current vector from leading the q-axis and thereby preventing loss of synchronism before it occurs
Solution Approach 2:
The system performs preliminary detection of the γ-axis inductive voltage and calculates the electrical angle difference in advance, then applies correction to ensure the current vector remains properly aligned with the q-axis under varying axial force conditions
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
This approach effectively corrects the electrical angle to prevent reverse rotation and maintain motor synchronism, even under sharp axial force fluctuations, ensuring robustness and efficient torque generation in sensorless control scenarios.
Implementation Method 1
a permanent magnet synchronous motor (20) provided in a steering mechanism (10) and adapted to generate steering assist torque
Implementation Method 2
electricity is supplied to U-phase, V-phase, and W-phase coils through switching control of an inverter. The brushless DC motor is driven through current vector control
Implementation Method 3
a rotational angle sensor (22, 120) for detecting an electrical angle of the permanent magnet synchronous motor
Implementation Method 4
electrical angle estimation means (110), operable when the anomaly of the rotational angle sensor is detected by the sensor anomaly detection means, for estimating the electrical angle of the permanent magnet synchronous motor on the basis of an inductive voltage generated in the permanent magnet synchronous motor
Data Source
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AI summary
An electrical angle estimation section 110 calculates an estimative electrical angle θeb' on the basis of an inductive voltage e generated in a motor 20, and obtains an estimative electrical angle θeb by correcting the estimative electrical angle θeb' by an electrical angle correction amount Δθc. On the basis of a detection value eγ/e which represents the difference in electrical angle between the q-axis and the δ-axis calculated by an electrical-angle-error detection section 117, an electrical-angle-correction-amount computation section 118 calculates an electrical angle correction amount Δθc such that the electrical angle of the δ-axis falls within a prescribed angular range A, which lags behind the q-axis in terms of electrical angle. Thus, when sensorless control is performed, a phenomenon in which the motor 20 loses synchronism can be restrained.