Current Sensor Gain Calibration for Stationary Electric Machines
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Solution Overview
Problem
Current methods for ascertaining gain errors in current measuring devices of electrical machines with multiple phases are inadequate, especially when the rotor is stationary, and fail to accurately detect unbalanced gain errors that affect each phase differently.
Innovation Solution
A method involving the application of a sensor voltage with perpendicular voltage vectors to multiple phases, allowing for the acquisition of current values to calculate sum and partial sum current vectors, which are then compared to reference vectors to determine gain errors, including unbalanced ones, using a two-axis coordinate system and oscillating voltage pulses for precise evaluation.
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 normal operation, but gain errors cannot be reliably detected when the rotor is stationary
Solution Approach 1:
The patent applies preliminary action by performing gain error calibration using voltage pulses applied to the phases before normal operation begins. The calibration process uses a voltage source to apply test voltage pulses to the phases and measures the resulting currents through the current measuring devices, allowing gain errors to be detected and corrected in advance regardless of rotor position or motion state.
Solution Approach 2:
The patent introduces an intermediary calibration process that uses a voltage source and test voltage pulses as mediators between the power supply and the current measuring devices. This intermediary calibration sequence allows the system to characterize the current measuring devices' gain errors independently of the rotor's operational state, enabling reliable detection both when stationary and during operation.
2Measurement precision
If standard amplification is applied to current values, then the output signal is enhanced for better measurement, but gain errors occur during amplification that deviate from the ideal function
Solution Approach 1:
The patent implements feedback by measuring the actual current output from the current measuring devices during voltage pulse application, comparing it to the expected ideal current values, and using this information to determine and correct gain errors. The calibration process establishes the actual transfer function of each current measuring device, creating a feedback mechanism that compensates for amplification inaccuracies.
Solution Approach 2:
The patent applies parameter changes by systematically varying the voltage pulse parameters (amplitude, duration, phase) during the calibration process to characterize the current measuring devices' response across different operating conditions. By changing the input voltage parameters and measuring the corresponding current outputs, the system determines the actual gain characteristics and error parameters of each measuring device.
3Measurement precision
If gain calibration is performed using positive sequence components during rotor operation, then balanced gain errors can be detected, but unbalanced gain errors affecting individual phases cannot be identified
Solution Approach 1:
The patent applies segmentation by calibrating each phase's current measuring device independently through separate voltage pulse applications. Instead of using aggregate sequence components that mask individual phase errors, the system applies voltage pulses to each phase individually or in specific combinations, measures the corresponding currents, and determines gain errors for each phase separately, thereby detecting unbalanced errors that affect individual phases differently.
Solution Approach 2:
The patent uses partial action by applying voltage pulses to specific phase combinations rather than requiring all three phases to be active simultaneously. The calibration process can use pairs of phases or individual phases with appropriate voltage pulse applications, allowing the system to isolate and measure each current measuring device's performance independently without requiring balanced three-phase operation.
Data Source
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.