Rotor Electrical Angle Sensing for Low-Speed Torque Control

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing methods for determining rotor position in direct-drive wind turbine generators with outer rotors are inaccurate and unreliable, especially at low speeds, leading to unpredictable torque and potential structural integrity issues, and require costly sensor solutions.

Innovation Solution

An assembly combining an encoder mounted on the stator with an electrical angle observer to determine the rotor's electrical angle, utilizing relative rotor rotation information and absolute electrical angle, with dynamic gear ratio correction to enhance precision.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If sensorless methods are used for position estimation, then device complexity is reduced, but measurement precision deteriorates at low speeds

Engineering Contradiction:

Improveposition measurement system complexityVSAvoidrotor position precision

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

An encoder wheel is introduced as an intermediary component that contacts the rotor surface to provide mechanical position feedback. This encoder wheel acts as a mediator between the rotor and the stator-mounted encoder, enabling accurate position measurement without requiring sensors on the rotor itself.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces electronic sensor-based measurement systems with a mechanical encoding approach. The encoder wheel with its coded circumference provides mechanical position information that is read by the encoder, substituting complex electronic sensor systems with a simpler mechanical measurement principle.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Device complexity

If incremental encoders are used, then device complexity is reduced, but reliability deteriorates due to lack of absolute position information

Engineering Contradiction:

Improveencoder system complexityVSAvoidposition determination reliability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The system performs preliminary action by using the encoder to establish absolute position reference information during initialization or when the rotor is stationary. This preliminary position information is stored and used as a reference point, ensuring that even if power is lost or signals are interrupted, the absolute position can be recovered without requiring complex redundant sensing.

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If shaft-mounted encoders are used, then measurement precision is improved, but ease of manufacture deteriorates due to installation difficulties

Engineering Contradiction:

Improverotor position precisionVSAvoidencoder installation ease

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

Instead of mounting the encoder on the rotating shaft (traditional approach), the patent inverts the arrangement by mounting the encoder on the stationary stator and having the encoder wheel contact the rotor surface. This inversion simplifies installation since the main encoder body remains stationary while only the lightweight encoder wheel needs to contact the rotor.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the spatial dimension of the measurement system by moving from a shaft-mounted (radial) configuration to a stator-mounted (axial) configuration. The encoder wheel contacts the rotor surface axially, allowing position measurement without interfering with the rotor shaft structure and simplifying manufacturing and installation.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

4Measurement precision

If high-resolution position feedback is implemented, then torque control precision is improved, but device complexity increases

Engineering Contradiction:

Improveelectrical angle determination precisionVSAvoidcontrol system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The encoder wheel creates a mechanical copy of the rotor's angular position through its coded circumference. This coded pattern on the encoder wheel perimeter provides a simplified representation of rotor position that can be read by the encoder, avoiding the need for complex electronic sensors while achieving high-resolution position feedback.

Inventive Principle:

Principle #26Copying

Data Source

PatentEP4441882B1High-precision rotor position determination for use in position and/or torque control at low speed

Publication Date: 2025.10.29 SIEMENS GAMESA RENEWABLE ENERGY AS

Figure 1~2
Figure 3~4
Figure 5

AI summary

There is described an assembly for determining the electrical angle of a rotor in an electrical machine, such as a wind turbine generator. The assembly comprises: (a) an encoder having an encoder wheel configured to contact a surface of the rotor to obtain relative rotor rotation information based on rotation of the encoder wheel, (b) an electrical angle observer configured to provide an absolute electrical angle, and (c) a processing device coupled to communicate with the encoder and the electrical angle observer and configured to determine the electrical angle of the rotor based on the relative rotor rotation information and the absolute electrical angle. Furthermore, a wind turbine generator comprising such an assembly, and a method of determining the electrical angle of a rotor in an electrical machine, such as a wind turbine generator, are described.