Three-Phase Current Sensor Gain Error Detection at Rotor Standstill
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Solution Overview
Problem
Current methods for detecting amplification errors in current measuring devices of electrical machines with three-phase stator windings are inadequate, especially when the rotor is at standstill, as they fail to accurately determine unbalanced gain errors that affect each phase differently.
Innovation Solution
A method involving the application of a sensor voltage with perpendicular voltage vectors to detect current values across all phases, calculating a sum current vector, and comparing it to a reference vector to determine gain errors, allowing for the identification of uncompensated amplification errors and unbalanced gain errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional current measurement methods are used during rotor operation, then gain errors can be detected during rotation, but gain errors cannot be detected when the rotor is at standstill
Solution Approach 1:
The patent applies preliminary action by performing gain error detection before the rotor starts rotating or during standstill conditions. The method uses voltage pulses applied to the phases while the rotor is stationary to determine gain errors in advance, enabling correction factors to be established before actual operation begins. This resolves the contradiction by making detection possible in the preliminary state (standstill) rather than only during operation.
2Measurement precision
If conventional single-phase current detection is used, then the measurement process is simple, but unbalanced gain errors affecting different phases cannot be accurately determined
Solution Approach 1:
The patent applies segmentation by dividing the gain error detection process into separate evaluations for each phase. Instead of detecting all phases simultaneously or using a single composite measurement, the method processes current values from each phase (U, V, W) independently through voltage pulse applications. This allows unbalanced gain errors in individual phases to be identified and corrected, resolving the contradiction by making the measurement process sufficiently complex to achieve high precision without making the overall system unnecessarily complex.
Solution Approach 2:
The patent applies local quality by treating each phase's gain error characteristics as unique and requiring separate correction factors for each phase. The method determines gain errors locally for each phase rather than applying a global correction, allowing unbalanced errors where different phases have different gain characteristics to be accurately measured and corrected. This resolves the contradiction by adapting the measurement precision to match the local characteristics of each phase.
3Power
If amplification is applied to increase current values, then the output signal is greater than the input signal, but gain errors occur during the amplification process
Solution Approach 1:
The patent applies feedback by using the detected gain errors to calculate and apply correction factors that compensate for the amplification errors. The system measures the actual gain error through the voltage pulse method, then feeds this information back to adjust the correction factors used in current measurement. This closed-loop approach resolves the contradiction by maintaining the beneficial amplification effect while using feedback to correct the resulting measurement inaccuracies.
Data Source
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AI summary
The invention relates to a method for determining a gain error of at least one current measuring device (8, 9, 10) of a sensor unit (7) of an electric machine (1), wherein the machine (1) has a stator winding (2) having at least three phases (U, V, W) and a rotor (5) which is mounted so as to be rotatable about an axis of rotation (6). According to the invention, an electric sensor voltage (11) is applied to the phases (U, V, W), the sensor voltage (11) having at least a first voltage pulse (12) of a first voltage vector and a second voltage pulse (13) of a second voltage vector, the first voltage vector and the second voltage vector being oriented in different directions in each case perpendicularly to the axis of rotation (7), at least one first current value of a first of the phases (U), at least one second current value of a second of the phases (V) and at least one third current value of a third of the phases (W) are detected during the application of the sensor voltage (11), a sum current vector is determined on the basis of the detected current values of all of the phases (U, V, W), and the sum current vector is compared with at least one determined or stored reference current vector, at least one gain error being determined on the basis of the comparison.