Motor Torque Control Using SAW Sensor Feedback
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Solution Overview
Problem
Existing electric motor control methods, such as field oriented control (FOC) and direct torque control (DTC), face limitations in processing speed and accuracy, particularly in electric vehicles, leading to unsatisfactory vehicle acceleration and torque ripple, which are exacerbated by the need for complex calculations and resolver sensors.
Innovation Solution
Incorporating a surface acoustic wave (SAW) torque sensor to directly measure motor torque, eliminating the need for torque estimation calculations and enabling direct control of the electric motor through pulse width modulation (PWM) adjustments based on actual torque readings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If field oriented control (FOC) is used to achieve smooth and accurate motor control, then motor control accuracy is improved, but processing speed deteriorates due to large amounts of processing power required
Solution Approach 1:
The patent extracts the torque sensing function from the complex FOC calculation system by introducing a dedicated torque sensor that directly measures torque output. This separates the measurement function from the control calculation, allowing the controller to receive direct torque feedback without performing complex mathematical transformations, thereby improving processing speed while maintaining control accuracy.
Solution Approach 2:
The patent replaces the mathematical/mechanical estimation system (FOC calculations based on current sensors and resolver data) with a direct mechanical sensing system (torque sensor mounted on the output shaft). This substitution eliminates the need for complex real-time calculations and resolver sensor processing, significantly improving processing speed while providing accurate torque measurement.
2Speed
If direct torque control (DTC) is used to simplify control arrangement and increase processing speed, then processing speed is improved, but torque ripple increases causing unsatisfactory vehicle control
Solution Approach 1:
The patent implements a feedback mechanism where the torque sensor provides real-time torque measurement data back to the controller. The controller compares the actual torque with the commanded torque and adjusts the inverter switching signals accordingly. This closed-loop feedback eliminates torque ripple by continuously correcting deviations, allowing the system to use simpler DTC while achieving FOC-level accuracy.
3Measurement precision
If resolver sensors and complex calculations are used in FOC, then motor control accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the torque measurement function from the complex FOC system and assigns it to a dedicated torque sensor. This removes the need for complex torque estimation calculations and reduces dependence on resolver sensors, simplifying the overall control system architecture while maintaining accurate torque control.
Solution Approach 2:
The patent employs a relatively simple and cost-effective torque sensor design that can be directly mounted on the motor output shaft. This sensor provides accurate torque measurement without requiring expensive high-precision resolvers or complex calculation hardware, thereby reducing device complexity and cost while maintaining control accuracy.
4Speed
If resolver sensor data processing is performed at high switching speeds, then motor response speed is improved, but processing time lag increases limiting maximum switching speeds
Solution Approach 1:
The patent replaces the electronic data processing system (resolver sensors requiring mathematical transformations) with a direct mechanical sensing system (torque sensor providing immediate torque output measurement). This substitution eliminates the processing time lag associated with resolver data acquisition and FOC calculations, enabling high switching speeds without time delays.
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 allows for rapid and accurate motor control, reducing torque ripple and improving vehicle performance by eliminating the need for complex calculations and resolver sensors, thus enhancing processing speed and reducing costs.
Implementation Method 1
the torque sensor being a surface acoustic wave (SAW) sensor system
Data Source
AI summary
An apparatus includes an electric motor having an output shaft and a stator comprising plurality of windings and including a torque sensor that is a surface acoustic wave (SAW) sensor system, an electric motor inverter drive including a gate high side driver and a gate low side driver for each respective winding, and an electric motor controller that includes a microcontroller and a plurality of pulse width modulators (PWMs), one PWM for each gate high side and low side driver, the microcontroller being programmed to generate PWM signals for the gate drivers that represent requested torque. The output of the SAW sensor system is compared by the microcontroller with the requested torque, and the PWM signals for the gate drivers are modified by the microcontroller according to a difference between the programmed PWM signals (representing requested torque) and the electrical output signal of the SAW sensor system (representing actual torque).