Sensorless Rotor Position Control for Permanent Magnet Machines
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Solution Overview
Problem
Existing methods for controlling permanent magnet synchronous machines at low and zero speeds without position sensors are unreliable, prone to discontinuities, and dependent on accurate motor models, making them unsuitable for applications requiring precise position control, especially in aviation where reliability and cost are critical.
Innovation Solution
A control method that determines the estimated position of the rotor by calculating a coupling term from differences in stator currents when injecting a periodic signal, allowing for the determination of rotor speed and position through integration, without the need for position sensors, and adjusts voltage setpoints to control the machine effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If EMF-based estimation methods are used for sensorless control, then control at medium and high speeds is achieved, but position control at low speeds and when stopped becomes impossible due to zero EMF and measurement noise
Solution Approach 1:
The patent changes the estimation parameter from EMF (which is zero at low speeds) to stator inductance variations. By injecting high frequency voltage signals and measuring the resulting current responses, the method extracts inductance information that remains observable even when the machine is stopped or running at very low speeds, thus extending the usable speed range while maintaining measurement precision.
Solution Approach 2:
The patent employs periodic injection of high frequency voltage signals into the stator windings. This periodic action creates measurable current responses that reveal inductance variations with respect to rotor position, enabling continuous position estimation across all speed ranges including zero speed, where conventional EMF-based methods fail.
2Measurement precision
If high frequency signal injection is performed every ten or twenty PWM periods, then position estimation is achieved, but control discontinuities occur and torque jolts are generated
Solution Approach 1:
The patent performs position estimation using high frequency signal injection in advance, before the main control cycle requires the position information. By completing the estimation beforehand and holding the value, the method ensures continuous control without discontinuities or torque jolts, while still achieving accurate position measurement.
Solution Approach 2:
The patent maintains continuous position estimation by combining periodic high frequency signal injection with interpolation techniques. The estimation process continues uninterrupted by holding values between injection cycles and using interpolation to maintain smooth control signals, eliminating the discontinuities that would otherwise occur during PWM periods dedicated to estimation.
3Measurement precision
If accurate motor models are used for current comparison in position estimation, then convergence is improved, but dependency on parameter uncertainties and variations increases
Solution Approach 1:
The patent implements feedback mechanisms that continuously update the estimated position and use this information to adjust subsequent estimation cycles. By feeding back the estimated position to refine the interpretation of inductance variations, the method achieves convergence without requiring extremely accurate motor models, reducing sensitivity to parameter uncertainties and variations.
Solution Approach 2:
The patent enables the system to self-correct estimation errors by using the measured inductance variations and estimated position to continuously refine the control. The system serves itself by using its own measurements and estimates to improve accuracy over time, reducing dependency on externally provided accurate motor models and making the system more robust to parameter variations.
Data Source
AI summary
A method of controlling a permanent magnet synchronous machine including a stator and a rotor. The method includes determining an estimated position of the rotor, and determining a second in-phase voltage setpoint that, in alternation, is equal either to a first in-phase voltage setpoint or else to the first in-phase voltage setpoint plus a predetermined periodic signal. The determining an estimated position of the rotor includes determining a coupling term, determining a speed of rotation of the rotor as a function of the coupling term, and determining the estimated position of the rotor by integrating the speed of rotation of the rotor.