Electric Motor Torque Stabilization at Stall Conditions
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Solution Overview
Problem
Electric motors experience transient torque ripple and oscillatory torque output at low operational speeds approaching stall conditions, leading to jerky vehicle movements, which existing control systems fail to mitigate effectively.
Innovation Solution
A system comprising a sensor for detecting rotor position, a data processor to adjust direct-axis and quadrature-axis current commands based on torque and speed thresholds, and a current adjustment module to maintain a fixed ratio between these commands, ensuring a constant shaft torque output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional motor control systems are used at low speeds, then the motor can operate, but transient torque ripple and oscillatory torque output occur causing jerky vehicle movements
Solution Approach 1:
The patent applies parameter changes by modifying the current commands based on motor speed and torque conditions. Specifically, when the motor operates in the low-speed range (below 100 rpm) with high torque demand (above 80% of maximum torque), the system adjusts the q-axis current command using a scaling factor derived from lookup tables that account for rotor position. This dynamic parameter adjustment compensates for the non-linear motor characteristics at stall conditions, eliminating torque ripple and oscillations while maintaining reliable torque output.
2Speed
If the motor operates at low speeds near stall conditions, then vehicle propulsion is maintained, but torque oscillations cause jerky movement
Solution Approach 1:
The patent implements feedback control by continuously monitoring the motor speed and torque demand, then adjusting the current commands accordingly. The system uses lookup tables stored in memory that contain pre-calculated correction factors based on rotor position, speed, and torque conditions. This closed-loop feedback mechanism detects when the motor enters the problematic low-speed high-torque regime and automatically applies the appropriate compensation, ensuring smooth vehicle movement across the entire operating range including stall conditions.
3Device complexity
If standard current control is applied, then motor operation is simple, but torque output varies at low speeds
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction factors in lookup tables during the design phase. These tables contain the optimal current adjustment parameters for various combinations of rotor position, speed, and torque demand. During operation, the controller simply retrieves the appropriate correction factors from memory based on current operating conditions and applies them to the current commands. This approach eliminates the need for complex real-time calculations while ensuring consistent torque output, as the optimal control parameters have already been determined and stored.
Data Source
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AI summary
A data processor determines whether a composite torque command Is larger than a preset torque threshold for a time Interval |S302). The composite torque command is convertible into a direct-axis current command and a quadrature-axis current command (S302). The data processor determines whether a rotor speed of the motor is less than a preset speed threshold for the lime interval (S3Q4), The data processor, the current adjustment module, or the current shaping module adjusts the direct-axis current command and the quadrature-axis current command to obtain a revised direct-axis current command and revised quadrature-axis current command for the time interval if the composite torque command Is larger than the preset torque threshold and If the rotor speed is less than the preset speed threshold (S308){ where the revised current commands vary by the detected rotational position of the rotor to achieve a generally constant shaft torque output.