Sensorless AC Motor Speed Estimation Using Torque Error Filtering
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Solution Overview
Problem
Existing methods for estimating the position and speed of an AC motor without sensors face challenges, particularly at low driving frequencies, where the signal-to-noise ratio is reduced due to noise and nonlinearity, leading to increased speed estimation errors.
Innovation Solution
A control apparatus and method that includes a pulse width modulation controller, a motor model computing unit, a current detector, a stator frequency computing unit, a torque error computing unit, and a speed estimator, which computes motor magnetic flux, estimated current, stator frequency, torque error, and speed, using proportional control to reduce torque error and eliminate high-frequency components, enabling reliable speed estimation without sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the induced voltage method is used for speed estimation at low frequencies, then the method can be applied without inductance characteristic data, but the signal-to-noise ratio is reduced and speed estimation error increases
Solution Approach 1:
The patent introduces a high-frequency signal injection mechanism as an intermediary method. When the induced voltage method becomes unreliable at low frequencies, the system switches to injecting a high-frequency signal and detecting the resulting current response. This intermediary approach allows the system to maintain accurate speed estimation across all frequency ranges by selecting the appropriate measurement method based on operating conditions.
Solution Approach 2:
The patent dynamically changes the measurement parameters based on the operating frequency. At low frequencies where induced voltage is insufficient, the system transitions to using high-frequency signal injection with different detection parameters. This parameter adaptation allows the system to overcome the signal-to-noise ratio problem by operating in a frequency range where the injected signal dominates over noise and nonlinearity effects.
2Device complexity
If sensorless control is implemented, then cost and complexity are reduced, but speed estimation accuracy deteriorates at low frequencies
Solution Approach 1:
The patent implements a dynamic control strategy that adapts the estimation method based on real-time operating conditions. The system continuously monitors the driving frequency and automatically switches between the induced voltage method and the high-frequency signal injection method. This dynamic adaptation maintains high estimation accuracy across the entire operating range while preserving the sensorless control architecture's simplicity and cost-effectiveness.
Solution Approach 2:
The patent employs periodic high-frequency signal injection to maintain accurate speed estimation at low frequencies. By superimposing a periodic high-frequency signal on the fundamental drive signal and analyzing the periodic current response, the system can extract accurate speed information even when the fundamental induced voltage is too weak. This periodic action effectively separates the measurement signal from noise and nonlinearity effects.
Data Source
AI summary
An alternating-current motor control apparatus includes a stator frequency computing unit configured to compute a stator frequency of a motor magnetic flux; a torque error computing unit configured to compute a torque error by using the motor magnetic flux, an estimated current, and a motor current; and a speed estimator configured to estimate a speed of the alternating-current motor by using the stator frequency and the torque error. The speed estimator includes a proportional controller configured to reduce the torque error to zero, and an adaptive filter configured to eliminate a high-frequency component of the torque error.