Electric Power Steering Rotor Position Estimation
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Solution Overview
Problem
Existing electric power steering systems using three-phase synchronous motors face challenges in estimating rotor position at low speeds, leading to potential malfunctions and increased costs due to hardware limitations, especially when traditional rotational position detectors fail.
Innovation Solution
A control device that estimates rotor position using either a neutral point potential or a virtual neutral point potential, allowing for continuous operation and assistance in steering, even at zero speed or low speeds, without increasing hardware costs by integrating a rotational position estimation unit and a command signal computing unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If rotational position estimation means based on induced voltage is used, then the three-phase synchronous motor can be driven continuously, but it is unable to detect the position at low speeds below 10% of rated speed
Solution Approach 1:
The patent segments the speed range into high-speed range (above 10% rated speed) and low-speed range (below 10% rated speed), using different position estimation methods for each segment. At high speeds, induced voltage-based estimation is used, while at low speeds, neutral point potential-based estimation is used, ensuring accurate position detection across the entire operating range.
Solution Approach 2:
The patent changes the estimation parameter from induced voltage (which is insufficient at low speeds) to neutral point potential (which remains effective at low speeds). This parameter substitution allows the system to maintain position estimation accuracy across different operating conditions, particularly enabling reliable low-speed operation.
2Measurement precision
If the number of rotational position detectors is increased to two or more, then detection accuracy at zero speed is ensured, but hardware cost and loading space increase
Solution Approach 1:
The patent replaces the mechanical/hardware solution of adding multiple rotational position detectors with a software-based neutral point potential estimation method. This substitution achieves the same goal of ensuring position detection accuracy at zero speed while avoiding the increased hardware cost, complexity, and loading space that would result from adding multiple detectors.
3Reliability
If traditional rotational position detectors are used, then position detection is reliable at high speeds, but the system fails or malfunctions at zero speed or low speed
Solution Approach 1:
The patent creates a universal position estimation system that functions reliably across the entire speed range from zero to high speeds. By implementing the neutral point potential estimation method that works at both zero speed and high speed, the system achieves multi-functionality, eliminating the need for separate detection mechanisms for different speed ranges and ensuring continuous reliable operation.
Data Source
AI summary
An object of the present invention is to provide an electric power steering apparatus capable of improving reliability of a drive device for a three-phase synchronous motor without increasing a cost of the drive device. A control device for controlling an electric power steering apparatus according to the present invention is a control device for controlling an electric power steering apparatus using a three-phase synchronous motor as a force assisting in a steering operation, includes: a rotational position estimation unit that estimates a position of a rotor of the three-phase synchronous motor on the basis of a neutral point potential or a virtual neutral point potential of the three-phase synchronous motor; and a command signal computing unit that computes a command signal to the three-phase synchronous motor on the basis of the position of the rotor estimated by the rotational position estimation unit.