Sensorless Motor Control Unit for Vehicle Steering
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Solution Overview
Problem
The use of resolvers as rotational angle sensors in brushless motor control units for vehicle steering apparatus is costly and space-intensive, and existing sensorless drive methods struggle with estimating rotor position at low speeds.
Innovation Solution
A motor control unit that employs an imaginary rotating coordinate system and a PI control unit to estimate the rotational angle of the rotor without a rotational angle sensor, using a combination of current detection and voltage estimation to control the motor based on steering torque and vehicle speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a resolver is used as a rotational angle sensor, then the motor control accuracy is improved, but the cost and installation space increase
Solution Approach 1:
The patent extracts and eliminates the resolver component from the motor control system. By removing this expensive and space-consuming sensor, the invention achieves cost reduction and compactness while maintaining control functionality through alternative sensorless control methods that estimate rotor position without direct measurement.
Solution Approach 2:
The motor control system performs self-position estimation using only the existing motor windings and control circuits. The controller utilizes current detection and voltage estimation to calculate rotor position internally, making the system self-sufficient without external rotational angle sensors, thereby reducing both cost and complexity.
2Measurement precision
If a resolver is used as a rotational angle sensor, then the motor control accuracy is improved, but the manufacturing cost increases
Solution Approach 1:
The patent replaces the expensive resolver with a cost-effective software-based estimation approach. The controller uses inexpensive current sensors and computational algorithms to achieve the necessary control accuracy, significantly reducing component costs while maintaining functional performance for the intended application lifecycle.
Solution Approach 2:
The patent substitutes the mechanical/electrical resolver system with an electronic/software-based estimation system. By replacing physical sensing components with computational methods that use existing motor parameters and current measurements, the invention eliminates the need for expensive sensors and reduces overall manufacturing costs.
3Device complexity
If sensorless drive method is used to reduce cost, then the installation space is reduced, but the rotor position estimation accuracy deteriorates at low speeds
Solution Approach 1:
The patent implements dynamic adaptation of the control algorithm based on operating conditions. The controller adjusts its estimation method and parameters according to motor speed, providing enhanced accuracy at low speeds where traditional sensorless methods fail, while maintaining the sensorless architecture's space-saving benefits across the entire operating range.
Solution Approach 2:
The patent dynamically changes control parameters including estimation algorithms and gain values based on operating speed. By adapting parameters to match operational conditions, the system maintains high estimation accuracy at low speeds without requiring additional sensors, thus preserving the compact design while improving measurement precision when needed.
Data Source
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AI summary
A motor control unit controls a motor including a rotor and a stator facing the rotor. A current drive unit drives the motor at an axis current value of a rotating coordinate system that rotates in accordance with a control angle that is a rotational angle used in a control. An addition angle calculation unit calculates an addition angle to be added to the control angle. A control angle calculation unit obtains, at every predetermined calculation cycle, a present value of the control angle by adding the addition angle that is calculated by the addition angle calculation unit to an immediately preceding value of the control angle. An angular speed calculation unit calculates an angular speed of the rotor. An addition angle correction unit corrects the addition angle based on the angular speed calculated by the angular speed calculation unit. A filtering unit filters the angular speed calculated by the angular speed calculation unit.