Rogowski Coil Current Sensing With PWM-Based Offset Compensation
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Solution Overview
Problem
Conventional methods for sensing switching currents in power semiconductors, such as MOSFETs, in motor driving inverters and DC-DC converters face issues with magnetic flux saturation, size, and cost, particularly due to the use of Hall sensors, and require manual tuning to compensate for offset voltages and bias currents in Op-Amp integrators.
Innovation Solution
The implementation of a Rogowski coil and Op-Amp integrator system with automatic offset calibration software that generates an offset value table based on PWM duty values, allowing real-time compensation of switching current sensing signals without manual tuning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Hall sensor using a magnet core is used to sense switching current, then magnetic flux saturation occurs, but the sensor size and price increase
Solution Approach 1:
The patent extracts and removes the magnet core from the sensing system, replacing it with a Rogowski coil that measures current through electromagnetic induction without requiring a magnetic core. This eliminates magnetic flux saturation issues while keeping the sensor size compact.
Solution Approach 2:
The patent replaces the mechanical/magnetic Hall sensor system with an electrical sensing system using a Rogowski coil and Op-Amp integrator. This substitution eliminates the need for magnet cores and resolves the trade-off between measurement precision and sensor size.
2Measurement precision
If manual tuning using a variable resistor is applied to minimize offset in Op-Amp integrator output, then offset is reduced, but labor costs increase
Solution Approach 1:
The patent implements self-service through automatic offset calibration. The system automatically measures and compensates for offset voltages in the Op-Amp integrator without requiring manual intervention. This is achieved through software-based calibration routines that eliminate the need for manual variable resistor tuning, thereby reducing labor costs while maintaining measurement precision.
Solution Approach 2:
The patent changes the approach from manual physical adjustment of resistor parameters to automated software-based parameter calibration. The system dynamically adjusts offset compensation parameters through digital processing, eliminating manual labor while achieving precise offset minimization.
3Measurement precision
If manual tuning is used for offset compensation, then initial offset is minimized, but the system cannot respond to offset changes due to component deterioration
Solution Approach 1:
The patent implements continuous feedback-based offset calibration. The system periodically measures the actual offset in the Op-Amp integrator and automatically compensates for it, creating a closed-loop system that adapts to component deterioration over time. This feedback mechanism ensures ongoing measurement precision without manual intervention.
Solution Approach 2:
The patent transitions from static manual tuning to dynamic automatic calibration. The offset compensation is no longer a one-time setup but an ongoing adaptive process that responds to changing component characteristics, enhancing the system's ability to maintain precision despite component deterioration.
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 reduces labor costs, adapts to component deterioration, eliminates the need for magnetic cores, and effectively compensates for offsets in real-time, enhancing the accuracy and efficiency of switching current sensing.
Implementation Method 1
a Rogowski coil configured to detect a switching current flowing through switching elements to output a differentiated value
Implementation Method 2
an integrator configured to integrate the differentiated value received from the Rogowski coil
Data Source
AI summary
The present disclosure relates to an apparatus and method for compensating for an offset in switching current sensing in an improved method using a Rogowski coil and an Op-amp. According to the present disclosure, when a Rogowski current sensor and an Op-Amp integrator are used to sense a switching current of a motor driving inverter, a DC-DC converter, or the like, the fact that an offset value of an output of the integrator varies depending on a duty value of a pulse-width modulation (PWM) control signal is used, so that offset calibration software is applied to automatically generate an offset value table at the beginning of power up of a controller and compensate for a sensed value of the current in real time by referring to the value. As a result, there is no need to perform conventional manual tuning.