Motor Control Interpolation for Peak Torque Linearity
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Solution Overview
Problem
Conventional motor control systems experience errors in interpolation when operating near peak torque, especially when the actual DC voltage lies between pre-stored tables, leading to inaccuracies in current command calculations due to the non-linear nature of torque versus voltage curves.
Innovation Solution
A modified interpolation technique that uses extrapolated torque commands from the upper table to improve torque linearity by interpolating between the maximum torque limit of one table and a revised torque value from the adjacent table, allowing for accurate current command computation even when the torque command exceeds the lower table's limit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional linear interpolation is used between two DC voltage tables, then the system can operate at intermediate voltages, but torque accuracy deteriorates due to non-linear torque-Vdc characteristics
Solution Approach 1:
The patent changes the interpolation parameter from voltage-based linear interpolation to torque-based interpolation. Instead of interpolating current commands directly based on voltage ratio, the system calculates an extrapolated torque command that accounts for the non-linear torque-Vdc relationship, then uses this corrected torque value for current command interpolation. This parameter transformation resolves the contradiction by maintaining torque accuracy while preserving intermediate voltage operation capability.
Solution Approach 2:
The patent introduces an intermediary calculation step involving extrapolated torque command. Before performing the final current command interpolation, the system computes a corrected torque value that serves as an intermediary parameter. This intermediary torque command compensates for non-linear effects and enables accurate current command determination at intermediate voltages, resolving the accuracy issue while maintaining system adaptability.
2Force
If the torque command exceeds the peak torque limit of the lower Vdc table, then the system can handle higher torque demands, but interpolation errors occur because only valid operating commands are available in the upper table
Solution Approach 1:
The patent performs preliminary action by calculating an extrapolated torque command before the interpolation step. When the torque command exceeds the lower table's peak torque limit, the system proactively computes a corrected torque value that accounts for the non-linear relationship between torque and DC voltage. This preliminary torque correction ensures that subsequent current command interpolation uses accurate reference values, preventing interpolation errors while maintaining high torque command capability.
3Adaptability or versatility
If multiple look-up tables are stored for different DC voltages, then the system can cover a wide voltage range, but memory requirements and computational complexity increase
Solution Approach 1:
The patent simplifies the control algorithm by changing the interpolation approach from direct voltage-based current command interpolation to torque-based interpolation. The modified method uses a single extrapolation formula that works across all intermediate voltages, reducing the need for complex conditional logic and multiple interpolation paths. This parameter transformation maintains wide voltage range coverage while reducing algorithmic complexity and computational burden.
Data Source
AI summary
In a motor controller, a modified interpolation technique uses an extrapolated torque command for the upper table to improve torque linearity under certain conditions. When the torque command input is greater than the max torque limit of a first look-up table, but less than the maximum torque limit of a second, adjacent look-up table, the desired current command is computed by interpolating between the maximum torque limit of the first table and a revised torque value for the second look-up table, wherein the revised torque value is determined by extrapolating from the maximum torque limit of the first look-up table through a torque value based on the torque command input.