Stacked-Core Filter Inductor for Unbalanced Three-Phase EMI
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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 of the three-phase windings are unbalanced, the differential mode magnetic branch experiences large magnetic flux causing saturation, which degrades the EMI suppression capacity
Solution Approach 1:
The magnetic core structure is segmented into separate differential mode magnetic branches and common mode magnetic branches. Each branch is independently designed and positioned, allowing them to handle different current conditions without mutual interference. This segmentation prevents saturation in the differential mode branch while maintaining EMI suppression effectiveness.
Solution Approach 2:
Different parts of the magnetic core structure are designed with different properties optimized for their specific function. The differential mode magnetic branches are configured to handle high current without saturation, while the common mode magnetic branches are optimized for EMI suppression. This local optimization ensures both size efficiency and reliable EMI suppression under unbalanced current conditions.
2Weight of moving object
If an integrated differential mode and common mode magnetic core structure is used, then weight is reduced, but the differential mode magnetic branch becomes easily saturable due to large magnetic flux from unbalanced currents, affecting differential mode inductance and impedance
Solution Approach 1:
The magnetic core is divided into separate differential mode and common mode branches that are spatially separated and functionally independent. This segmentation allows each branch to be optimized for its specific purpose without being affected by the other, preventing saturation-induced instability in the differential mode inductance while maintaining overall weight efficiency.
Solution Approach 2:
The differential mode magnetic branches are specifically designed with properties that prevent saturation under unbalanced current conditions, ensuring stable differential mode inductance. The common mode branches are independently optimized for EMI suppression. This localized optimization maintains inductance stability while keeping the overall structure lightweight.
3Device complexity
If an integrated EMI filter inductor is used to reduce device complexity, then both differential mode and common mode filtering are provided in a single component, but under unbalanced current conditions the differential mode magnetic branch saturates, making the EMI filter ineffective
Solution Approach 1:
The integrated filter inductor uses segmented magnetic core branches where differential mode and common mode filtering paths are separated. This internal segmentation allows the single component to provide both filtering functions independently and effectively, even under unbalanced current conditions, without requiring multiple separate filter components.
Solution Approach 2:
Different magnetic branches within the integrated inductor are designed with locally optimized properties: differential mode branches are configured to prevent saturation and maintain stable inductance, while common mode branches are optimized for EMI suppression. This local quality differentiation ensures the integrated filter remains effective for both differential and common mode interference.
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.