Electrical Machine Torque Ripple Control via Angle Error Compensation

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Solution Overview

Problem

Existing methods for reducing torque ripple in electrical machines are either costly due to the need for precise rotor position sensors or ineffective because they do not account for angle errors and DC link voltage limitations.

Innovation Solution

A method for calculating current profiles that adjusts to minimize torque ripple and sensitivity to angle errors, while ensuring the currents can be supplied by the available DC link voltage, using a system of equations and weighting functions to constrain voltage and sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If very accurate encoders or resolvers are used to measure rotor position, then angle error is reduced, but cost increases significantly

Engineering Contradiction:

Improverotor position measurement accuracyVSAvoidcost of transducer

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces expensive, high-precision encoders or resolvers with a low-cost, simple rotor position sensor. The system compensates for the lower measurement accuracy through software-based angle error compensation algorithms, making the expensive transducer unnecessary while maintaining smooth torque output.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The patent substitutes the mechanical/optical precision measurement system (encoder or resolver) with an electrical/software-based compensation system. Instead of relying on hardware precision, the system uses mathematical algorithms to calculate and correct angle errors, replacing physical measurement precision with computational correction.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Object-generated harmful factors

If current profiles are calculated to achieve smooth torque, then torque ripple is reduced, but sensitivity to angle error increases

Engineering Contradiction:

Improvetorque rippleVSAvoidsensitivity to angle error

Core Design Contradiction:

Object-generated harmful factorsVSReliability

Solution Approach 1:

The patent introduces angle error compensation algorithms that continuously calculate the difference between the actual rotor position and the expected position, then use this feedback to correct the current profiles. This feedback mechanism reduces sensitivity to angle error while maintaining smooth torque output.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent modifies the current profile parameters dynamically based on detected angle errors. By adjusting current magnitude and timing parameters in response to measured position deviations, the system compensates for angle errors and maintains reliable torque output despite sensitivity issues.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If current profiles are optimized for zero angle sensitivity, then reliability improves, but adaptability to DC link voltage variations deteriorates

Engineering Contradiction:

Improveinsensitivity to angle errorVSAvoidaccommodation of DC link voltage limits

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent creates a dynamic current profile generation system that continuously adapts to changing DC link voltage conditions. The system calculates optimal current profiles in real-time, adjusting parameters such as current magnitude, phase timing, and waveform shape to maintain both angle error insensitivity and voltage adaptability across varying operating conditions.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes multiple current profile parameters simultaneously (current magnitude, timing, waveform characteristics) to achieve a solution that satisfies both the zero angle sensitivity requirement and the DC link voltage constraints. This multi-parameter optimization allows the system to maintain reliability while adapting to voltage variations.

Inventive Principle:

Principle #35Parameter changes

4Device complexity

If low cost rotor position sensors are used, then device complexity is reduced, but measurement precision deteriorates

Engineering Contradiction:

Improvecost of transducerVSAvoidrotor position measurement accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent converts the apparent disadvantage of low-cost sensor imprecision into a benefit by using the measured position data to calculate and compensate for angle errors. The system treats the limited precision measurements as useful input data that, when processed through compensation algorithms, actually improves torque smoothness compared to using expensive sensors without compensation.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS9024556B2Control of electrical machines

Publication Date: 2015.05.05 NIDEC SR DRIVES

AI summary

In an electrical machine which has time-varying or position-varying disturbances in its output, signals representing the position and values of machine-related parameters are used to solve a model of the machine to calculate the phase currents which are required to minimize the disturbances. The model is able to provide solutions in the presence of limitations of some of the operating conditions of the machine, for example the supply voltage or the error in the signal representing the position.