Median Filter Rotor Speed Estimation for AC Machines
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Solution Overview
Problem
Existing speed sensorless approaches for AC machines face reliability issues due to implementation complexity and hardware failures, necessitating improved methods for estimating rotor speed without physical sensors.
Innovation Solution
A computer-implemented method using a median filter to estimate rotor speed by determining stator and rotor flux signals, electrical angle, and frequency, which involves sampling, filtering, and subtracting slip frequency to derive rotor speed, thereby eliminating spikes and offset values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If physical speed sensors are used to measure rotor speed, then measurement accuracy is improved, but device complexity and reliability worsen due to hardware failures and additional information processing requirements
Solution Approach 1:
The patent replaces physical speed sensors (mechanical/electrical hardware) with a sensorless estimation system that uses electrical signals (voltage and current) and signal processing algorithms to estimate rotor speed. This substitution eliminates hardware-based failures while maintaining speed measurement capability through computational methods including flux signal determination, electrical angle calculation, and median filter processing.
2Reliability
If speed sensorless approaches are used to improve reliability, then device complexity increases due to implementation complexity of estimation algorithms
Solution Approach 1:
The patent introduces a median filter as an intermediary processing step between the electrical frequency signal and the final speed estimation. This intermediary component simplifies the overall algorithm by providing a robust method to eliminate spikes and offset values, making the sensorless estimation more implementable while maintaining reliability. The median filter acts as a mediator that processes the electrical frequency signal to produce cleaner speed estimates.
Solution Approach 2:
The patent extracts and removes harmful components (spikes and offset values) from the electrical frequency signal through median filter processing. By taking out these problematic elements, the implementation complexity is reduced as the filtered signal requires less additional processing and correction, making the sensorless approach more practical to implement.
3Speed
If traditional filtering methods are used to process electrical frequency signals, then processing speed is improved, but measurement precision worsens due to inability to eliminate spikes and offset values
Solution Approach 1:
The patent uses the median filter to create a corrected copy of the electrical frequency signal by selecting the median value from a set of sampled values. This copying approach preserves the essential speed information while eliminating spikes and offset values, achieving both processing efficiency and measurement precision. The median copy replaces the problematic original signal values without requiring complex real-time corrections.
Data Source
AI summary
A computer-implemented method for estimating a rotor speed of an alternating current (AC) machine is provided. The method includes determining a stator flux signal based on signals of voltage and current inputs to the AC machine, and determining a rotor flux signal of the AC machine based on the determined stator flux signal. The method includes determining an electrical angle signal based on the determined rotor flux signal, and deriving an electrical frequency signal from the determined electrical angle signal. Subsequently, the method includes sampling the derived electrical frequency signal at a predetermined sampling rate, and storing a predetermined number of sample values. The method further includes evaluating a median value of the predetermined set of electrical frequency sample values, determining a slip frequency value of the AC machine, and determining the rotor speed of the AC machine by subtracting the slip frequency value from the electrical frequency median value.