Friction Torque Compensation in Permanent Magnet Synchronous Motors
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Solution Overview
Problem
Permanent magnet synchronous motors experience instability in torque transmission due to changes in motor speed, ambient temperature, and variations in DC link voltage and motor parameters, leading to a need for a method to compensate for friction torques effectively.
Innovation Solution
A method and apparatus that estimate motor torque using input current and rotor speed, acquire friction torque from a lookup table, and compensate for friction torque using a proportional integral controller to generate a torque command that stabilizes motor operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If friction torque compensation is implemented using a lookup table based on motor torque and rotor speed, then torque transmission stability is improved, but device complexity increases due to additional compensation mechanisms
Solution Approach 1:
The patent pre-calculates and stores friction torque values in a lookup table during system initialization or offline characterization. The table contains friction torque values corresponding to various combinations of motor torque and rotor speed. During operation, the controller simply retrieves the appropriate friction torque value from the pre-prepared table based on current operating conditions, avoiding real-time complex calculations and improving response speed while maintaining torque stability.
Solution Approach 2:
The patent introduces a friction torque compensation module as an intermediary between the torque command generator and the motor driver. This module acts as a mediator that receives the torque command, retrieves corresponding friction torque values from the lookup table, and generates compensated torque commands. The intermediary handles the complexity of friction compensation separately, allowing the main control system to remain relatively simple while achieving improved torque transmission stability.
2Measurement precision
If friction torque is compensated based on motor torque and rotor speed variations, then torque control precision is improved, but measurement and detection difficulty increases
Solution Approach 1:
Instead of directly measuring the difficult-to-detect friction torque, the patent creates a copy or representation of friction torque characteristics through the lookup table. The table stores friction torque values that were previously measured or calculated under various operating conditions. During operation, the system copies the appropriate friction torque value from the table based on current motor torque and rotor speed, avoiding the need for direct real-time measurement of friction torque while achieving precise compensation.
Solution Approach 2:
The patent performs friction torque characterization and lookup table generation in advance, during system initialization or offline testing. This preliminary action includes measuring friction torque under various motor torque and rotor speed conditions, then storing these values in the lookup table. During normal operation, the pre-prepared table is used directly, eliminating the need for complex real-time friction torque measurement and reducing measurement difficulty while maintaining high precision.
Data Source
AI summary
A method of compensating for a friction torque of a permanent magnet synchronous motor may include: receiving input of a motor current and a rotor speed of the permanent magnet synchronous motor; estimating a motor torque based on the input motor current; acquiring a first friction torque corresponding to the input rotor speed and the estimated motor torque by using a lookup table of friction torques; compensating for a second friction torque of the permanent magnet synchronous motor based on the first friction torque, wherein the compensating is in response to a first torque command input to control driving of the permanent magnet synchronous motor and outputs a second torque command that compensates for the second friction torque; and/or controlling the driving of the permanent magnet synchronous motor based on the second torque command.