Brushless Motor Control Unit Eliminates Resolver for Steering Systems
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Solution Overview
Problem
Existing motor control units for brushless motors, particularly in vehicle steering systems like electric power steering, face challenges in cost reduction and size minimization due to the high cost and space requirements of rotational angle sensors, and existing sensorless drive methods are not suitable for all applications.
Innovation Solution
A motor control unit that includes a current drive unit, control angle calculation unit, torque detection unit, command torque setting unit, addition angle calculation unit, and command current setting unit, which operates without a rotational angle sensor by using a control angle and load angle to calculate and adjust motor currents based on torque deviations, allowing for efficient steering assistance without a rotational angle sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a resolver is used as a rotational angle sensor, then the motor control precision is improved, but the cost and installation space increase
Solution Approach 1:
The patent extracts and eliminates the resolver (rotational angle sensor) from the motor control system. By using sensorless control methods that estimate rotor position through voltage and current measurements rather than direct sensing, the system removes the physical sensor, its wiring, and associated installation space while maintaining control functionality
Solution Approach 2:
The patent replaces the mechanical/electrical resolver system with an electronic estimation system. Instead of using a physical sensor to detect rotational angle, the system uses computational methods to estimate rotor position based on electrical measurements, substituting a mechanical sensing approach with an electronic calculation approach
2Device complexity
If sensorless drive method is used, then the device complexity is reduced, but the control reliability deteriorates at low speeds and standstill
Solution Approach 1:
The patent applies preliminary action by using different control strategies for different operating conditions. Before entering the sensorless control mode, the system establishes appropriate control parameters and estimation algorithms. For low-speed and standstill conditions, the system prepares specific control methods in advance to ensure reliable motor startup and low-speed operation before transitioning to the primary sensorless control mode
Solution Approach 2:
The patent implements dynamic control adaptation where the control system automatically adjusts its behavior based on operating conditions. The system dynamically switches between different control methods depending on motor speed and load conditions, ensuring optimal performance and reliability across the entire operating range rather than using a single static control approach
3Device complexity
If conventional sensorless control is used, then the cost is reduced, but the adaptability to different applications deteriorates
Solution Approach 1:
The patent creates a universal motor control system that can adapt to multiple applications including vehicle steering systems, industrial drives, and other motor control applications. The control method uses general principles of sensorless control combined with application-specific parameter adjustments, allowing the same basic system architecture to serve different purposes by modifying control parameters rather than requiring application-specific hardware
Data Source
AI summary
A motor is driven by the γ-axis current of a γδ coordinate system that is an imaginary rotating coordinate system. A command current value preparation unit sets the γ-axis command current value based on the command steering torque and the detected steering torque. The command current value preparation unit includes a command current increase/decrease amount calculation unit and an addition unit. The command current increase/decrease amount calculation unit calculates the current increase/decrease amount for the command current value based on the sign of the command steering torque and the deviation of the detected steering torque from the command steering torque. The current increase/decrease amount calculated by the command current increase/decrease amount calculation unit is added to the immediately preceding value of the command current value by the addition unit. Thus, the command current value in the present calculation cycle is calculated.