Active EMI Filter for Electric Vehicle DC Networks
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Solution Overview
Problem
Existing EMI filters for electric vehicles are bulky, unsuitable for mass production, and struggle with high current requirements, particularly in the powertrain, where high-frequency noise cancellation is ineffective due to delays in active circuits, and passive components like inductors and chokes are not optimized for high current and frequency ranges.
Innovation Solution
An active EMI filter design featuring a sensing section, gain section, and injection section with a coupling capacitance and current transformer, utilizing MgZn core material for stable performance across 150 kHz to 30 MHz, and a feedback configuration to inject cancelling noise into power conductors, reducing phase shift and saturation risks, and allowing for compact construction without winding large cross-section busbars around the core.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If passive EMI filters with inductors and chokes are used, then filtering capability is provided, but the size and weight increase and they are unsuitable for high current applications
Solution Approach 1:
The patent replaces passive mechanical filtering components (inductors and chokes) with an active electronic filtering system comprising sensing circuitry, processing circuitry, and injection circuitry. This substitution eliminates the need for bulky magnetic components while maintaining EMI filtering capability through electronic noise cancellation.
Solution Approach 2:
The invention changes the operating parameters by using active electronic circuits operating at high frequencies to generate cancelling noise signals. The system dynamically adjusts the cancelling signal parameters (amplitude, phase, frequency) to match the detected EMI noise, enabling effective filtering without passive components.
2Object-affected harmful factors
If active circuits are used for high-frequency noise cancellation, then filtering bandwidth is increased, but delays in the active circuit cause the cancelling noise to increase rather than cancel the noise
Solution Approach 1:
The sensing circuitry detects EMI noise and the processing circuitry generates the cancelling noise signal in advance, before the original noise fully propagates through the system. This preliminary action allows the cancelling signal to be properly phased and timed to effectively counteract the incoming EMI.
Solution Approach 2:
The system continuously monitors the EMI noise through sensing circuitry and uses this feedback information to dynamically adjust the cancelling noise signal generated by the processing and injection circuitry. This closed-loop feedback mechanism compensates for circuit delays and ensures the cancelling signal remains properly synchronized with the EMI noise across the extended bandwidth.
3Power
If large cross-section cables or bus-bars are used for high current, then current carrying capacity is increased, but winding them around a magnetic core becomes impractical
Solution Approach 1:
The invention extracts and removes the magnetic core and winding structure from the EMI filtering system. By eliminating these components, the system no longer requires the impractical winding of large cross-section bus-bars, thereby maintaining high current carrying capacity while dramatically improving ease of manufacture and assembly.
4Strength
If nanocrystaline core materials are used to obtain maximal permeability, then magnetic properties are improved, but the permeability is not constant over the frequency range 150 kHz to 30 MHz
Solution Approach 1:
The patent replaces the magnetic core material system with an active electronic filtering system. This substitution eliminates the frequency-dependent permeability issue entirely, as the electronic circuits can dynamically adapt their response across the 150 kHz to 30 MHz frequency range without relying on materials with constant magnetic properties.
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
The active EMI filter effectively cancels noise across a wide bandwidth of 150 kHz to 30 MHz, maintaining stability and immunity to environmental changes, while being compact and lightweight, suitable for high current applications in electric vehicles, and potentially applicable to other DC networks and frequencies.
Implementation Method 1
the sensing section comprises a current transformer to sense the noise current in the first power conductor and/or the second power conductor
Implementation Method 2
the injection section comprises a coupling capacitance configured to inject the cancelling noise in the first power conductor and the second power conductor
Implementation Method 3
the core material has a constant permeability between 150 kHz and 30 MHz
Data Source
AI summary
A power system for a vehicle comprising: a battery; a charging interface for receiving external power to charge the battery; a network connecting the battery and the charging interface, wherein at least a part of the network is a DC network; an active EMI filter between the battery and the charging interface in the DC network.