Active Filter Common Mode Current Reduction Circuit
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Solution Overview
Problem
Existing solutions for reducing common mode current between an electrical circuit and ground, such as using isolation transformers or active filters, are either expensive or complex to implement, especially in constrained spaces like vehicles, and do not effectively address the safety concerns of common mode current at various frequencies.
Innovation Solution
A method involving an electronic component that applies an electrical quantity, such as a voltage or current, at an injection point in the electrical line to generate a counter-current that opposes and reduces the common mode current, using impedance connections and feedback mechanisms to achieve a significant reduction in common mode current across multiple harmonics of the network frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an isolation transformer is used between the rectifier circuit and chassis, then common-mode current is reduced, but cost and device complexity increase
Solution Approach 1:
The patent extracts the common-mode current component from the total current and processes it separately through an active filter. The filter measures the common-mode current, generates an opposing counter-current, and injects it to cancel the harmful component, eliminating the need for isolation transformers while maintaining safety
Solution Approach 2:
The patent introduces an active filter as an intermediary device between the rectifier circuit and chassis. This filter acts as a mediator that processes the common-mode current through measurement and counter-current injection, providing the necessary isolation function without requiring a bulky isolation transformer
2Object-affected harmful factors
If Power Factor Corrector with controllable switches is used, then common-mode current is reduced, but device complexity and overheating risk increase
Solution Approach 1:
The patent implements a feedback mechanism where the active filter continuously measures the common-mode current and adjusts its counter-current injection accordingly. This closed-loop control automatically adapts to varying operating conditions without requiring complex switch control strategies, reducing both device complexity and thermal stress
Solution Approach 2:
The active filter performs self-regulation by measuring its own output and adjusting the counter-current injection to maintain common-mode current cancellation. The system automatically adapts to changing load conditions and grid frequencies without external intervention, simplifying control architecture
3Object-affected harmful factors
If active filter injecting voltage in series is used, then common-mode current at high frequencies is reduced, but device complexity increases
Solution Approach 1:
The patent replaces the mechanical voltage injection approach with an equivalent electrical current injection method. Instead of inserting a voltage source in series (which requires complex isolation and control), the system injects a counter-current in parallel through the active filter, achieving the same cancellation effect with simpler circuitry
Solution Approach 2:
The patent changes the injection parameter from voltage to current. By measuring the common-mode current and injecting an opposing current rather than voltage, the system achieves frequency-independent cancellation across the operating range, simplifying the filter design and reducing component complexity
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 effectively reduces common mode current by generating a counter-current that matches or exceeds the common mode current, thereby minimizing the risk to users and complying with standards without the need for expensive isolation or complex control strategies, and can be implemented without galvanic isolation.
Implementation Method 1
The injection point is connected to the power line via at least one impedance
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The method involve applying an electric quantity (Vs) in an injection point (26) connected through an impedance (28) to a single-phase or three-phase powerline (5) of an electric circuit (4), using an electronic component (21) for exchanging the electrical energy in the powerline, where the electronic component is deprived of a field-effect transistor. The electric quantity is applied to the powerline for reducing a common mode current (i) circulating between an internal mass (13) of the electric circuit and the ground. Independent claims are also included for the following: (1) an electronic component for implementing a method for reducing the common mode current circulating between an internal mass and ground (2) a electric circuit comprising a powerline.