Transformer Shield Element for Common Mode Noise Cancellation
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Solution Overview
Problem
Existing transformer designs fail to effectively reduce or eliminate common mode (CM) noise, particularly in high power density power converters with printed circuit board (PCB) windings, due to parasitic capacitance between windings and other structures, leading to unpredictable effects and electromagnetic interference (EMI) issues.
Innovation Solution
A shielding method and structure are introduced, where a shield element is interposed between the primary and secondary windings of a transformer, with a voltage distribution that creates complementary currents, resulting in zero net CM current in parasitic capacitance, effectively canceling out CM noise through balanced bridge circuits and voltage distributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If shielding is provided between primary and secondary windings, then common mode noise transmission is reduced, but device complexity increases
Solution Approach 1:
The shield element is nested between the primary and secondary windings, with the shield element forming an integral part of the transformer structure. The voltage distribution along the shield element creates complementary currents that cancel each other, nesting the noise cancellation function within the existing transformer geometry without adding external complex shielding structures.
Solution Approach 2:
The shield element acts as an intermediary between the primary and secondary windings, with its voltage distribution creating complementary currents that mediate the electromagnetic coupling. This intermediary structure provides a controlled path for displacing common mode noise currents while maintaining magnetic coupling between windings.
2Object-affected harmful factors
If voltage distribution is developed in shield element to create complementary currents, then CM noise is eliminated, but manufacturing precision requirements increase
Solution Approach 1:
The invention changes the voltage distribution parameter along the shield element to create complementary currents. By controlling the voltage distribution profile rather than requiring precise physical dimensions, the solution achieves noise cancellation while maintaining manufacturing feasibility. The voltage distribution is developed through the electrical connection to the primary winding rather than through mechanical precision.
3Object-affected harmful factors
If shield element is connected to primary winding, then complementary currents are generated, but transformer efficiency may be impacted
Solution Approach 1:
The invention converts the potentially harmful connection of the shield element to the primary winding into a beneficial effect. The connection generates complementary currents in the shield element that actively cancel common mode noise. The voltage distribution along the shield element transforms what could be a source of additional losses into a noise cancellation mechanism that benefits overall system performance.
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 solution significantly reduces or eliminates CM noise transmission, meeting stringent EMI standards with minimal impact on transformer efficiency and ease of implementation in various transformer configurations, including those with PCB windings, thereby simplifying EMI filtering.
Implementation Method 1
a voltage distribution along a length of the shield element that causes common mode currents between said shield element and another shield element or said second winding of said transformer to be substantially complementary
Implementation Method 2
CM noise can be easily transmitted through the parasitic capacitance between primary and secondary windings of a transformer
Data Source
AI summary
At least one shield member interposed between primary and secondary windings of a transformer and connected to the primary and/or secondary windings forms a distributed parasitic capacitance between the shield member and either the winding to which it is not connected or another shield member connected to that winding. Connections are made to the respective transformer windings such that the voltage distributions thus developed cause complementary common mode noise to be conducted in opposite directions in respective portions of the parasitic capacitance such that net common mode current can be made arbitrarily small without requiring that both sides of the distributed parasitic capacitance have complementary or equal voltage distributions. Such complementary common mode currents can be achieved by dividing opposing shield members or developing a voltage distribution in a single shield member in accordance with Faraday's Law.