Rogowski Coil Current Measurement With Temperature Offset Correction
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Solution Overview
Problem
Current measurement apparatuses using Rogowski coils and operational amplifiers face challenges with offset accumulation due to the offset voltage and bias current of the operational amplifier, which are not accurately compensated, especially with temperature variations, leading to measurement errors.
Innovation Solution
A current measurement apparatus that includes a current sensor, integrator, and a corrector with AD converter, first and second correction units to compensate for operational amplifier offsets by calculating and subtracting offset values based on switching frequency and duty cycle, and performing d-q transformation to eliminate temperature-induced errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If manual tuning of variable resistor using offset compensation network is used, then offset compensation is achieved, but manpower is required and temperature-dependent offset changes cannot be accurately compensated
Solution Approach 1:
The system automatically compensates for OP amplifier offset without manual intervention. The corrector circuit continuously adjusts the offset compensation based on real-time detection of offset voltage, eliminating the need for manual tuning while maintaining accurate compensation across temperature variations
Solution Approach 2:
The corrector circuit employs feedback mechanism where the detected offset voltage is fed back to adjust the compensation. The system monitors the actual offset and dynamically adjusts the compensation values, enabling accurate temperature-dependent offset compensation without manual intervention
2Measurement precision
If offset reset for each switching period is implemented, then offset accumulation during switching is reduced, but offset still accumulates during integration period
Solution Approach 1:
The system performs offset compensation before the integration process begins. By detecting and compensating for the OP amplifier offset in advance through the corrector circuit, the system prevents offset accumulation during the integration period, ensuring accurate measurement from the start of the measurement process
Solution Approach 2:
The corrector circuit continuously compensates for offset throughout the entire measurement process, not just at discrete reset points. This continuous compensation ensures that offset is eliminated during both switching and integration periods, maintaining measurement accuracy throughout the entire cycle
3Reliability
If Rogowski coil with OP amplifier is used, then magnetic flux saturation is avoided, but offset voltage and bias current cause measurement errors
Solution Approach 1:
The corrector circuit acts as an intermediary between the Rogowski coil-OP amplifier system and the final measurement output. It detects the offset voltage and bias current introduced by the OP amplifier and provides compensation signals that cancel these errors, allowing the Rogowski coil to benefit from its saturation-free operation while the measurement accuracy is maintained through electronic compensation
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
Accurately measures current by compensating for operational amplifier offsets, reducing measurement errors to within ±0.2 A, even with temperature changes, through real-time offset correction.
Implementation Method 1
a current sensor measuring a rate of change of the measurement target current
Implementation Method 2
an integrator integrating the rate of change and outputting an estimated current amount
Data Source
AI summary
The present invention relates to a current measurement apparatus using a Rogowski coil and an operational (OP) amplifier, the current measurement apparatus being capable of accurately measuring a current by compensating for an offset of the OP amplifier according to a temperature change. The current measurement apparatus that measures a measurement target current having a predetermined switching frequency and an on-duty includes a current sensor measuring a rate of change of the measurement target current, an integrator integrating the rate of change and outputting an estimated current amount, and a corrector including a first correction unit that corrects and outputs a direct current (DC) offset of the estimated current amount based on at least one of the switching frequency or the on-duty.