Current Shunt Parasitic Inductance Compensation
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Solution Overview
Problem
Current shunts, especially at high frequencies, face inaccuracies due to parasitic inductance, leading to over or underestimation of current values, which affects the measurement of switching losses in electrical circuits like IGBTs.
Innovation Solution
A current measurement system that includes a shunt and a controller to measure voltage values over a predetermined interval, derive time-domain admittance through inverse Fourier transform, and output a signal indicative of current by convolving voltage data with the admittance, thereby correcting for parasitic inductance effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional current shunt is used for current measurement, then the measurement is simple and direct, but the measurement precision deteriorates at high frequencies due to parasitic inductance causing over or underestimation of current values
Solution Approach 1:
The system performs preliminary characterization of the shunt's impedance as a function of frequency before actual current measurements. The admittance is converted to a time-domain transfer function and stored for later use. This preliminary preparation enables accurate compensation during subsequent measurements without adding real-time computational complexity.
Solution Approach 2:
The patent introduces an intermediary processing step where the measured voltage signal is convolved with the time-domain admittance transfer function. This convolution operation acts as a mediator that compensates for parasitic inductance effects, transforming the distorted voltage signal into an accurate current representation.
2Ease of operation
If the shunt resistance is reduced to minimize voltage drop and circuit impact, then the circuit operating characteristics are preserved, but the parasitic inductance effects become more significant at high frequencies
Solution Approach 1:
The system uses feedback from the characterized shunt impedance properties to compensate for measurement errors. By measuring the shunt's impedance as a function of frequency and using this information in the convolution process, the system continuously corrects for parasitic inductance effects, maintaining accuracy even with low resistance shunts that have significant parasitic components.
3Productivity
If traditional voltage division method is used to derive current from shunt voltage, then the calculation is simple and fast, but the measurement accuracy deteriorates when the rate of change of current exceeds a predetermined magnitude
Solution Approach 1:
The time-domain admittance transfer function is pre-calculated and stored, containing all the compensation information needed for high-rate-of-change scenarios. During actual measurement, the system simply performs a convolution operation with this pre-prepared function, maintaining both speed and accuracy without real-time iterative calculations.
Solution Approach 2:
The patent replaces the simple algebraic division operation (I = V/R) with a convolution operation in the time domain. This substitution transforms the measurement process from a static calculation to a dynamic operation that accounts for the shunt's frequency-dependent behavior, enabling accurate measurement of rapidly changing currents.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides accurate current measurements, reducing errors associated with parasitic inductance and ensuring precise characterization of switching losses in high-frequency applications.
Implementation Method 1
output a signal indicative of a current flowing through the shunt and derived from a convolution of the voltage values and a time-domain admittance of the shunt
Implementation Method 2
The time-domain admittance may be derived from an inverse Fourier transform
Implementation Method 3
measuring an impedance of a shunt as a function of frequency and converting the impedance to an admittance in a time domain
Data Source
AI summary
A method includes measuring an impedance of a shunt as a function of frequency and converting the impedance to an admittance in a time domain. The method further includes connecting the shunt in a circuit and measuring voltage data across the shunt over a predetermined interval. The method includes outputting a signal indicative of a current through the shunt derived from the voltage data convolved with the admittance. The method may be implemented in a controller configured to interface with the shunt.