Sensorless Speed Estimation for Asynchronous Induction Motors
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Solution Overview
Problem
Existing methods for controlling asynchronous machines in industrial trucks lack a robust and simple solution for sensorless speed determination, relying on speed sensors or incremental encoders, which can be cumbersome and prone to errors.
Innovation Solution
A method utilizing field-oriented control with an observer module and torque module to calculate speed without explicit internal torque values, using phase currents and voltages to iteratively converge on accurate speed values, allowing for robust and dynamic control without speed sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If speed sensors or incremental encoders are used for speed detection, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The system uses its own existing measurements (conductor currents and line voltages) to calculate speed through the observer module, eliminating the need for external speed sensors. The control system serves itself by deriving speed information from operational parameters already being measured for control purposes.
Solution Approach 2:
The observer module acts as an intermediary that processes existing electrical measurements (currents and voltages) to generate speed information. Instead of directly measuring speed with a sensor, the system uses the observer module to infer speed from electrical parameters through mathematical modeling.
2Ease of operation
If field-oriented control with observer module is implemented, then ease of operation is improved, but device complexity increases
Solution Approach 1:
The speed calculation functionality is merged into the existing field-oriented control system through the observer module. Rather than adding a separate speed measurement system, the speed estimation is integrated into the control algorithm using existing current and voltage measurements already present in the system.
Solution Approach 2:
The observer module serves multiple functions: it calculates speed for control purposes, provides feedback for the field-oriented control, and enables sensorless operation. The same computational infrastructure serves both control and speed estimation functions simultaneously.
Data Source
Figure 1
AI summary
A method for sensorless speed determination of an asynchronous machine, comprising the following process steps: - a field-oriented control module calculates the voltages to be applied to the asynchronous machine based on a setpoint for the speed, at least two measured values for the line current, and a speed calculated by an observer module; - the voltage values from the field-oriented control or the measured voltage values are applied to the observer module, which determines a value for the torque-generating current îsq(t) and an internal torque Mi(t) of the asynchronous machine from the applied values; - a torque module calculates a load torque Ml(t) acting on the asynchronous machine from the difference between the torque-generating currents from the field-oriented control and the observer module; - a speed module calculates the current speed of the asynchronous machine using the load torque of the torque module and the internal torque of the observer module.