Flux Offset Compensation for Rotating Electrical Machines
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Solution Overview
Problem
In rotating electrical machines, especially those with long motor feeds, it is challenging to accurately measure and control flux and torque due to errors in resistive voltage drop estimation, gain and offset errors, and frequency changes, leading to inaccurate flux and torque calculations.
Innovation Solution
A method that determines an inverter voltage vector and current vector, calculates an estimated flux vector, and compensates for errors by adjusting its length based on a comparison with a reference flux magnitude, allowing for effective error correction even when frequency changes occur.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If open loop scalar control is used for long motor feeds, then the control system can operate over long distances, but the resistive voltage drops cannot be estimated accurately leading to flux and torque calculation errors
Solution Approach 1:
The patent implements a feedback mechanism where the estimated flux magnitude is continuously compared with a reference flux magnitude, and the difference is used to compensate for errors in the flux estimation. This closed-loop approach corrects the flux calculation errors that arise in long motor feed applications using open loop scalar control.
Solution Approach 2:
The patent changes the parameter being controlled from the flux vector direction to the flux magnitude scaling factor. By adjusting only the length of the estimated flux vector based on the comparison with reference flux, the system compensates for errors without requiring complex changes to the control algorithm or additional measurements.
2Measurement precision
If minimum and maximum flux level estimates are used for correction, then flux error compensation is achieved, but the correction is not accurate when motor frequency is changing
Solution Approach 1:
The patent uses a dynamic reference flux magnitude that is calculated based on the current motor frequency and voltage. This allows the reference flux to adapt automatically to frequency changes, ensuring accurate flux error compensation across varying operating conditions without requiring separate correction algorithms for different frequency ranges.
3Reliability
If various error sources are present (measuring gain errors, offset errors, inverter losses), then comprehensive error compensation is needed, but the system complexity increases
Solution Approach 1:
The patent introduces an intermediary reference flux magnitude that serves as a mediator between the measured electrical quantities and the actual flux. This reference flux acts as a benchmark against which the estimated flux is compared, and the difference compensates for multiple error sources simultaneously without requiring separate compensation mechanisms for each error type.
Data Source
AI summary
A method is provided for compensating the flux drift caused by measurement and/or calculation errors when controlling a rotating electrical machine. The flux drift of the estimated flux vector may be compensated for by comparing the length of the flux vector with a reference flux magnitude which already has been determined for controlling the inverter. Depending on the comparison, the length of the estimated flux vector may be lengthened or shortened.