Medium Frequency Transformer Inductive Coupling Parasitic Currents
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Solution Overview
Problem
Medium-frequency transformers in medium-voltage converters experience significant parasitic ring currents due to stray magnetic fields, leading to unbalanced current distribution, reduced copper fill factor, and increased losses, which are exacerbated by the difficulty in twisting wires with larger cross-sectional areas.
Innovation Solution
The implementation of inductive coupling between coil branches using toroidal cores to compensate for parasitic current flows, allowing for complete or partial cancellation of these currents without the need for wire twisting, thereby optimizing space utilization and reducing winding losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of stationary object
If multi-core wires are used for coil windings to reduce transformer size at high operating frequencies, then the transformer size is reduced, but parasitic ring currents are generated due to stray magnetic fields
Solution Approach 1:
The patent utilizes the stray magnetic fields that cause harmful ring currents to instead induce compensating currents through inductive coupling. By strategically positioning wires and creating controlled inductive coupling, the previously harmful stray fields are converted into a beneficial mechanism that generates compensating currents to cancel out the parasitic ring currents, thereby eliminating the harmful effect while maintaining the reduced transformer size.
Solution Approach 2:
The patent introduces inductive coupling as an intermediary mechanism between the stray magnetic fields and the coil windings. This inductive coupling acts as a mediator that transforms the harmful direct induction of ring currents into a controlled process where compensating currents are generated through controlled inductive links, thereby reducing the harmful parasitic effects.
2Object-generated harmful factors
If wires are twisted to compensate for current imbalance and reduce ring currents, then parasitic current flows are reduced, but mechanical stress damages wires and increases production difficulty
Solution Approach 1:
The patent replaces the mechanical wire twisting method with an electromagnetic solution based on inductive coupling. Instead of mechanically deforming the wires to achieve current balance, the invention uses controlled inductive coupling to generate compensating currents that electronically balance the current distribution, thereby eliminating the mechanical stress and production difficulties associated with wire twisting.
Solution Approach 2:
The patent changes the approach from mechanical parameter modification (wire twist geometry) to electromagnetic parameter control (inductive coupling strength and configuration). By adjusting the inductive coupling parameters such as coupling coefficient and magnetic path geometry, the current balance is achieved without mechanical wire deformation, simplifying manufacturing while effectively reducing parasitic currents.
3Object-generated harmful factors
If inductive coupling is implemented to compensate parasitic currents, then ring currents are reduced, but additional inductance is added to the transformer
Solution Approach 1:
The patent merges the inductive coupling structure with the existing transformer core and coil winding assembly. The inductive coupling elements are integrated into the transformer's magnetic circuit rather than being added as separate external components. This merging allows the compensating inductance to be combined with the transformer's existing inductance, minimizing the net additional inductance while maintaining the current compensation effect.
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 parasitic ring currents, maintains efficient power output, and minimizes additional inductance added to the transformer, while simplifying production and avoiding mechanical stress on wires.
Implementation Method 1
an inductive coupling in order to inductively couple the coil branches to one another in pairs in such a way that parasitic branch currents in the coil branches are compensated for
Implementation Method 2
The inductive coupling between two wires in each case can have a toroidal core, through which the various coil branches are crossed, so that they run through the toroidal core in mutually opposite directions with respect to the winding direction of the coil branches
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The invention relates to a transformer (2), in particular a medium-frequency transformer, for use in a converter (1), comprising: - a transformer core (21), - a multi-core winding (22) with several wires (22a, 22b) wound around the transformer core (21), each of the wires (22a, 22b) forming a coil branch (24a, 24b); - terminals (23) at which the corresponding ends of the wires (22a, 22b) are electrically connected to each other; - an inductive coupling (5) to inductively couple the coil branches (24a, 24b) in pairs so that parasitic branch currents in the coil branches (24a, 24b) are compensated.