Bus Bar Current Measurement with Active Magnetic Field Compensation
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Solution Overview
Problem
Existing current measurement apparatuses for bus bars are impaired by external magnetic fields, particularly in electric vehicles, which can saturate fluxgate magnetometers and disrupt the accuracy of current measurement, as they often fail to compensate magnetic common mode fields exceeding 2 mT effectively.
Innovation Solution
An apparatus with a compensation coil and a magnetic field sensor is used, where the compensation coil generates a field to counteract both internal and external magnetic fields, ensuring the magnetic flux density at a specific point does not exceed a threshold, utilizing a differential fluxgate magnetometer to maintain accurate current measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fluxgate magnetometer is used to detect magnetic flux density for current measurement, then measurement capability is provided, but external magnetic common mode fields cause saturation and disrupt measurement accuracy
Solution Approach 1:
A compensation coil is introduced as an intermediary element that generates a compensating magnetic field to counteract external magnetic common mode fields. The coil receives control signals and produces an opposing field that neutralizes the harmful external fields, allowing the fluxgate magnetometer to operate within its linear range and maintain measurement accuracy.
Solution Approach 2:
The system employs feedback control where the fluxgate magnetometer continuously monitors the magnetic flux density, and based on this measurement, a control signal is generated to adjust the compensation coil current. This closed-loop feedback mechanism dynamically compensates for external magnetic fields, ensuring the total magnetic flux density remains within the operational range of the magnetometer.
2Reliability
If differential fluxgate sensors are used to compensate external magnetic common mode fields up to 2 mT, then compensation capability is improved, but compensation of fields exceeding 2 mT is insufficient
Solution Approach 1:
The compensation system transitions from a static differential sensor approach to a dynamic active compensation system. The compensation coil current is dynamically adjusted based on real-time magnetic field measurements, allowing the system to adapt to varying field strengths beyond the fixed 2 mT limitation of differential sensors. This dynamic adjustment enables effective compensation across a broader range of external field conditions.
Solution Approach 2:
The system changes the operational parameters of the compensation mechanism by varying the coil current based on the measured magnetic field strength. Instead of relying on fixed sensor characteristics, the compensation field strength is continuously modified to match the external field conditions, enabling effective compensation for fields exceeding the original 2 mT limit of differential fluxgate sensors.
3Measurement precision
If magnetic screening is used to reduce the effect of external magnetic common mode fields, then measurement accuracy is improved, but device complexity and cost increase significantly
Solution Approach 1:
The patent replaces the mechanical/magnetic screening approach with an active electromagnetic compensation system. Instead of using physical magnetic shields that add structural complexity and cost, the system uses a compensation coil to generate opposing magnetic fields, achieving the same protective function through electromagnetic means that are simpler to implement and adjust.
Solution Approach 2:
The compensation coil acts as an intermediary that actively manages magnetic field interference, replacing the need for complex passive magnetic screening structures. This intermediary element provides a more straightforward solution that reduces device complexity while maintaining measurement accuracy.
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 solution effectively compensates for external magnetic common mode fields up to 3 mT, preventing saturation of the magnetometer and maintaining the proportionality between the output signal and the current strength, thus ensuring accurate electric current measurement through the bus bar.
Implementation Method 1
The compensation coil is disposed in the through-hole and generates a compensation field
Implementation Method 2
The magnetic field sensor is disposed in the through-hole and detects the magnetic flux density of the resulting magnetic field at the predetermined position
Data Source
AI summary
An apparatus for measuring an electric current through a bus bar comprises a compensation coil and a magnetic field sensor. The bus bar has a through-hole dividing the electric current flowing through the bus bar into at least two partial currents flowing around the through-hole. The compensation coil is disposed in the through-hole and generates a compensation field. The compensation field compensates a plurality of magnetic fields generated by the partial currents and/or an external magnetic field such that a magnetic flux density of a resulting magnetic field at a predetermined position of the through-hole does not exceed a predetermined threshold. The magnetic field sensor is disposed in the through-hole and detects the magnetic flux density of the resulting magnetic field at the predetermined position. The magnetic field sensor emits an output signal corresponding to the detected magnetic field.