Rotor Position Estimation Using State Observers and Signal Injection
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Solution Overview
Problem
Existing methods for controlling synchronous electrical machines lack precision, especially at low speeds, due to the limitations of position sensors and estimation methods, which often require complex calculations or approximations, and are not robust against measurement noise.
Innovation Solution
A method that determines the position and speed of a synchronous electrical machine's rotor using a state observer based on current and voltage measurements, injecting specific signals to make the machine's model observable, even at low speeds, without the need for position sensors, and employs state observers to reconstruct the magnetic flux and rotor dynamics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If position sensors (Hall effect or inductive sensors) are used to determine rotor position, then position information can be obtained, but measurement precision deteriorates at high rotational speeds and the system becomes vulnerable to sensor failure and measurement noise
Solution Approach 1:
The patent replaces physical position sensors with a mathematical observer-based estimation system. The observer uses voltage and current measurements combined with a mathematical model of the synchronous machine to estimate rotor position and speed, eliminating the need for Hall effect or inductive sensors that suffer from precision and reliability issues at high speeds.
Solution Approach 2:
The patent introduces an intermediate mathematical model and observer algorithm that acts as a mediator between electrical measurements (voltage and current) and the desired position information. This intermediary processing layer transforms electrical quantities into accurate position and speed estimates without requiring direct mechanical or magnetic sensing.
2Measurement precision
If precise position sensors (incremental encoders or absolute sensors) are used, then measurement precision improves, but device complexity and cost increase
Solution Approach 1:
The patent replaces complex mechanical position sensors (incremental encoders or absolute sensors) with an electronic observer-based system. This substitution maintains high measurement precision while dramatically reducing device complexity by eliminating mechanical components, moving parts, and complex sensor assemblies.
Solution Approach 2:
The patent creates a virtual copy of the physical system through mathematical modeling. The observer model replicates the machine's electrical behavior and uses this virtual representation to infer position and speed, providing the same information function as physical sensors without the associated complexity.
3Ease of operation
If estimation methods without specific input signals are used, then ease of operation improves, but measurement precision deteriorates at near-zero or low speeds
Solution Approach 1:
The patent applies periodic signal injection at a specific frequency to the machine terminals. This periodic excitation creates measurable effects in the current that are modulated by the rotor position, enabling the observer to extract position information even at low speeds where natural operating signals are insufficient. The periodic action maintains measurement precision across the entire speed range.
Solution Approach 2:
The patent changes the operating parameters by injecting signals at specific frequencies and amplitudes that optimize the observability of the system. By carefully selecting injection parameters, the system maintains high measurement precision at low speeds without compromising the simplicity of the control approach, as the parameter changes are systematically managed by the observer.
4Measurement precision
If hybrid solutions with sensor for low speeds and estimation for high speeds are used, then measurement precision improves across speed range, but device complexity increases due to requiring at least one sensor
Solution Approach 1:
The patent creates a universal observer-based system that functions across the entire speed range without requiring different sensing approaches. The single observer architecture provides both low-speed and high-speed position estimation capabilities, eliminating the need for hybrid solutions and reducing device complexity by removing all position sensors while maintaining precision throughout the operating range.
Solution Approach 2:
The periodic signal injection mechanism enables the observer to maintain high measurement precision at low speeds where conventional estimation methods fail. This approach allows the system to use a single unified method across all speeds, eliminating the need for sensor-based fallback solutions and reducing overall device complexity.
Data Source
Figure 1~2
AI summary
The present invention proposes a method for determining the position and speed of the rotor of a synchronous electric machine (4) based on a current state observer of the electric machine and on signal injection. Thus, thanks to the invention, the position information is accurate, particularly at low speeds, without the use of a position sensor. The invention further relates to a method and a control system (1) for a synchronous electric machine that takes into account the determined position of the rotor (2).