Asynchronous Generator Stator Current Calculation via Rotor Measurement

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Solution Overview

Problem

In electric circuits with asynchronous generators, stator current measurement can be inaccurate or incorrect during power grid faults, leading to control errors and potential system instability.

Innovation Solution

The stator current is calculated from the measured rotor current using parameters of the asynchronous generator, such as transmission ratio, allowing for accurate stator current calculation even during power grid faults, using the equation [iS_aiS_r]=Xh*XSRS2+XS2⁡[-1RSXS-RSXS-1]*[iR_aiR_r+iμ⁢⁢0] to ensure consistent control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Difficulty of detecting and measuring

If stator current is measured directly during power grid faults, then measurement is simple, but measurement accuracy deteriorates

Engineering Contradiction:

Improvestator current measurement simplicityVSAvoidstator current measurement accuracy

Core Design Contradiction:

Difficulty of detecting and measuringVSMeasurement precision

Solution Approach 1:

The patent uses rotor current as an intermediary measurement to indirectly determine stator current. Instead of measuring stator current directly (which becomes inaccurate during grid faults), the system measures rotor current through sensors and calculates the corresponding stator current value using the transformer relationship, thereby obtaining accurate stator current information without direct measurement

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces direct electrical measurement of stator current with a calculation-based approach. By substituting the direct measurement system with a computational system that uses rotor current measurements and generator parameters, the system achieves accurate stator current determination during fault conditions

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Duration of action of stationary object

If stator current measurement is used for control during power grid faults, then control continuity is maintained, but control accuracy deteriorates

Engineering Contradiction:

Improvecontrol continuityVSAvoidcontrol accuracy

Core Design Contradiction:

Duration of action of stationary objectVSMeasurement precision

Solution Approach 1:

The patent implements a feedback mechanism where rotor current measurements are continuously monitored and used to calculate updated stator current values. This feedback loop ensures that control decisions are based on accurate, real-time calculations rather than potentially erroneous direct measurements, maintaining both continuity and accuracy of control during grid faults

Inventive Principle:

Principle #23Feedback

3Device complexity

If direct stator current measurement is used, then device complexity is low, but reliability during faults deteriorates

Engineering Contradiction:

Improvemeasurement system complexityVSAvoidsystem reliability during power grid faults

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent makes the measurement system multi-functional by using the rotor current measurement infrastructure to serve dual purposes: direct rotor current control and indirect stator current determination. This universal approach allows a single measurement system to provide reliable information for both normal and fault conditions, enhancing overall system reliability without proportionally increasing complexity

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS9190943B2Electric circuit for generating electric power

Publication Date: 2015.11.17 GE ENERGY POWER CONVERSION TECHNOLOGY LTD(GB)

AI summary

An electric circuit is described for generating electric power. In this circuit, an asynchronous generator includes a stator and a rotor. On the stator side, the asynchronous generator is coupled to a power grid. The rotor current flowing to the rotor of the asynchronous generator can be measured. A control device is designed such that, in case of a fault in the power grid, the stator current flowing to the stator of the asynchronous generator is calculated from the measured rotor current as a function of parameters of the asynchronous generator.