Active Filter for Reducing Common Mode Current in Vehicle Circuits
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Solution Overview
Problem
The existing solutions for reducing common mode current between an electrical circuit and ground, particularly in vehicles with electrical propulsion, face challenges such as high costs and complexity in integrating isolation transformers and overheating issues with Power Factor Corrector components, while existing active filters may not accurately measure and effectively reduce common mode currents at high frequencies.
Innovation Solution
A method that involves making a toroid go through a complete cycle of magnetization and demagnetization to reach magnetic saturation, improving the accuracy of current measurement in the electric line, and applying an electrical quantity, such as voltage or current, to inject a counter-current that opposes the common mode current, using an electronic component with an integrator-comparator module and a magnetic core to measure and compensate the flux, thereby reducing the common mode current effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an isolation transformer is used to reduce common mode current, then safety and compliance with standards are improved, but cost and device complexity increase
Solution Approach 1:
The patent replaces the mechanical/isolation transformer system with an electronic active filter system that uses electronic components (operational amplifiers, capacitors, resistors) to generate a counter-current. This substitution reduces physical complexity and cost while maintaining the safety function through electronic current cancellation rather than physical isolation.
Solution Approach 2:
The patent introduces an intermediary active filter circuit between the power line and ground that generates a counter-current through electronic measurement and amplification. This intermediary system measures the common mode current and produces an opposing current to cancel it, achieving safety without requiring a direct isolation transformer connection.
2Reliability
If PFC component strategies are implemented to reduce common mode current, then compliance with standards is improved, but overheating and device complexity occur
Solution Approach 1:
The patent replaces thermal-based PFC component strategies with an electronic active filter system that uses operational amplifiers and electronic feedback to generate counter-current. This electronic approach avoids the overheating issues inherent in power electronic PFC components while achieving the same compliance objective through current cancellation rather than power factor correction.
Solution Approach 2:
The patent implements a feedback mechanism where the common mode current is measured through a magnetic core sensor, amplified by an operational amplifier, and used to control the generation of counter-current. This closed-loop feedback system continuously adjusts the counter-current to match the measured common mode current, ensuring compliance without the overheating problems of open-loop PFC strategies.
3Object-generated harmful factors
If active filters are used to reduce common mode current at high frequencies, then common mode current reduction is improved, but measurement precision deteriorates
Solution Approach 1:
The patent employs a feedback-based measurement system using a magnetic core sensor that accurately detects common mode current at high frequencies. The measured signal is fed back through an operational amplifier to generate the counter-current, creating a closed-loop system that maintains measurement precision while effectively reducing common mode current across a wide frequency range including high frequencies.
Solution Approach 2:
The patent creates a universal active filter system that handles both measurement and current reduction functions through a single integrated circuit using operational amplifiers. This multi-functional approach maintains measurement precision across different frequency ranges while simultaneously achieving effective common mode current reduction, unlike specialized high-frequency filters that may compromise 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 approach significantly improves the accuracy of common mode current measurement and reduces the common mode current by generating a counter-current that effectively cancels out the existing current, meeting or exceeding 50-95% of the common mode current, thus enhancing safety and compliance with standards like European standards for admissible common mode current.
Implementation Method 1
making a toroid go through a complete cycle of magnetization and demagnetization to reach magnetic saturation
Implementation Method 2
a secondary winding, wound around said core, to generate a magnetic flux from a reference current
Implementation Method 3
applying an electrical quantity, such as voltage or current, to inject a counter-current that opposes the common mode current
Implementation Method 4
using an electronic component with an integrator-comparator module and a magnetic core to measure and compensate the flux
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The invention relates to a method for reducing the common-mode current flowing between the internal ground of an electrical circuit, in particular an electrical circuit of a motor vehicle, and ground, when electrical energy is exchanged between an electrical energy storage unit of the electrical circuit and an external electrical energy source. The method is such that: • an electrical quantity at least equal to the common-mode current is applied at an injection point of the circuit using an electronic component, said electrical quantity being applied so as to reduce the common-mode current; • the value of the common-mode current is obtained using a measuring device (124) comprising: - a magnetic core (128) configured to be traversed by an electrical line through which said electrical energy is exchanged, said electrical line forming a primary winding (127);- a secondary winding (130), wound around said toroid (128), to generate a magnetic flux from a reference current; - an oscillator (132) to generate the reference current through the secondary winding (130), the reference current being configured to saturate said toroid (128); the common-mode current corresponding to the value of the power line current obtained from the average value of the current in the secondary winding (130) over an oscillation period covering a complete magnetization and demagnetization cycle of the toroid (128).