Stacked Inner-Core Filter Inductor for Stable EMI Filtering
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Solution Overview
Problem
Existing filter inductors in high-power three-phase on-board-chargers suffer from degraded or ineffective EMI signal suppression due to current imbalances in the windings, leading to magnetic saturation and impaired differential mode inductance and impedance.
Innovation Solution
A filter inductor design featuring two independent inner magnetic cores stacked and positioned between adjacent windings, with one core providing magnetic flux paths for differential mode interference signals and the outer core handling common mode interference, ensuring balanced magnetic flux distribution even with unbalanced currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If an integrated differential mode and common mode magnetic core structure is used to reduce size and weight, then the filter inductor provides both differential mode and common mode impedance simultaneously, but when currents are unbalanced, the differential mode magnetic branch becomes saturated due to large magnetic flux, degrading EMI suppression capacity
Solution Approach 1:
The magnetic core is segmented into multiple independent magnetic branches (first differential mode magnetic branch, second differential mode magnetic branch, and common mode magnetic branch). Each branch independently handles specific current paths, preventing magnetic saturation in any single branch when currents are unbalanced, thus maintaining reliable EMI suppression while keeping the overall structure compact.
2Weight of stationary object
If an integrated differential mode and common mode magnetic core structure is used to reduce size and weight, then the filter inductor provides both differential mode and common mode impedance simultaneously, but the differential mode magnetic branch becomes easily saturable due to large magnetic flux from unbalanced currents, seriously affecting differential mode inductance and impedance
Solution Approach 1:
The magnetic core is divided into separate differential mode branches and a common mode branch. This segmentation ensures that unbalanced currents in one phase do not cause excessive magnetic flux in any single differential mode branch, preventing saturation and maintaining stable differential mode inductance values even when current distribution is uneven.
Solution Approach 2:
Each magnetic branch is designed with specific local properties tailored to its function. The differential mode branches are optimized for handling phase currents, while the common mode branch is optimized for common mode interference. This localized optimization ensures that each branch operates within its optimal magnetic flux range, maintaining stable inductance characteristics.
3Device complexity
If a single integrated magnetic core is used, then the device complexity is reduced, but the filter inductor cannot effectively handle unbalanced currents without magnetic saturation
Solution Approach 1:
The magnetic core is segmented into multiple functional branches that are integrated into a single structure. This segmentation provides the adaptability to handle unbalanced currents by directing different current paths through different branches, while the integrated nature maintains relatively simple device complexity compared to using completely separate inductors for differential and common mode filtering.
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 design effectively alleviates magnetic bias and improves the inductor's capacity to suppress EMI signals, maintaining stability and performance under current imbalances.
Implementation Method 1
the outer magnetic core provides a magnetic flux path for common mode magnetic flux generated by a common mode interference signal in the windings
Implementation Method 2
the first inner magnetic core and the second inner magnetic core provide magnetic flux paths for differential mode magnetic flux generated by differential mode interference signals in the windings
Data Source
AI summary
A filter inductor, which includes: an outer magnetic core with a window, an inner magnetic core, and a winding. The inner magnetic core includes a first inner magnetic core and a second inner magnetic core which are located at least partially in the window. The winding includes a first winding, a second winding, a third winding and a fourth winding which are wound around the outer magnetic core at intervals. The first inner magnetic core and the second inner magnetic core are stacked. For the first inner magnetic core, a first end is located between the first winding and the second winding, and a second end is located between the third winding and the fourth winding. For the second inner magnetic core, a first end is located between the second winding and the third winding, and a second end is located between the fourth winding and the first winding.