Encoder-less Asynchronous Machine Zero Speed Control
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Solution Overview
Problem
Conventional field-oriented regulation methods for asynchronous machines without rotation-speed encoders become unstable at zero speed due to errors in rotation-speed estimation and field orientation, leading to uncontrolled torque and motor shaft movement, especially when operating at low frequencies.
Innovation Solution
A method that calculates an actuating voltage and adapted rotation speed, models flux and current, and uses a weighted current difference projected onto the model flux to determine a model slip rotation speed, which is then combined with the adapted rotation speed to form a sum signal for controlling the asynchronous machine, effectively compensating for errors and maintaining stable operation down to zero speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If field-oriented regulation is used without rotation-speed encoder, then installation reliability and cost are improved, but operation stability at zero speed deteriorates due to estimation errors
Solution Approach 1:
The patent implements a model monitor that continuously compares measured machine currents with calculated model currents, using the difference as feedback to adapt rotation speed estimates and compensate for drift. This feedback mechanism maintains stability at zero speed by detecting and correcting estimation errors in real-time.
Solution Approach 2:
The patent dynamically adjusts model parameters including rotation speed, slip frequency, and flux linkage based on the difference between measured and calculated currents. By changing these parameters adaptively rather than using fixed values, the system maintains accuracy across the entire speed range including zero speed operation.
2Ease of operation
If conventional field-oriented regulation is used at low frequency, then encoderless operation is achieved, but control precision deteriorates due to bandpass characteristic limitations
Solution Approach 1:
The patent introduces a model monitor as an intermediary that calculates expected machine behavior based on control inputs and compares it with actual measurements. This intermediary system provides accurate reference values for current and flux, enabling precise control even at zero frequency where direct measurement becomes unreliable.
Solution Approach 2:
The patent replaces direct mechanical speed sensing (encoder) with an electrical model-based estimation system. By using mathematical models of machine behavior rather than mechanical sensors, the system achieves precise control at low frequencies without the limitations of bandpass characteristics inherent in conventional approaches.
3Measurement precision
If model error compensation is implemented, then rotation speed estimation accuracy is improved, but system complexity increases due to additional calculation requirements
Solution Approach 1:
The model monitor performs multiple functions simultaneously: it calculates expected currents, compares with measured values, determines slip frequency, adapts rotation speed estimates, and monitors flux linkage. By consolidating these functions into a single integrated system rather than separate components, the patent achieves high accuracy without proportionally increasing overall system complexity.
Data Source
AI summary
In a method for field-oriented operation to zero speed of an encoder-less asynchronous machine, wherein the associated field-oriented regulation device has a monitor with a machine model and rotation-speed adaptation, a model flux and a model current are calculated from a calculated actuating voltage and an adapted rotation speed, from which, in conjunction with a determined machine current, a complex difference is calculated. Also calculated is a model slip rotation speed as a function of the model flux and the model current, which is then scaled. The adapted rotation speed is then superimposed, and the sum is used as the rotation speed actual value which supplied to a rotation-speed regulator. An asynchronous machine without an encoder can therefore be operated to zero speed on a field-oriented basis.