Coupled Transformer Balance Windings for Primary Current Sharing
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Solution Overview
Problem
Current imbalance among primary currents in multi-rail power converters due to differences in input voltages and component values leads to efficiency loss and potential converter failure, particularly in high-density packaging applications.
Innovation Solution
A multi-limb transformer core with balance windings wound around outer limbs and coupled in series with primary windings, utilizing mutual inductance to counteract current imbalance by creating flux-aiding or flux-opposing relationships between windings, reducing leakage inductance and promoting current sharing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sufficient leakage inductance is introduced in the main transformer to reduce circulating current, then current imbalance is reduced, but transformer performance decreases and size increases
Solution Approach 1:
The patent divides the leakage inductance function into two separate components: the main transformer maintains tight coupling for high performance, while dedicated balance windings on outer limbs provide the necessary leakage inductance for current balancing. This segmentation allows each component to be optimized independently.
Solution Approach 2:
The balance windings act as intermediary elements that mediate between the primary windings and the core. These windings provide the necessary leakage inductance to balance circulating currents without requiring the main transformer to have reduced coupling or increased size.
2Reliability
If additional leakage inductance is added to prevent circulating current, then current imbalance is reduced, but converter efficiency decreases
Solution Approach 1:
The patent segments the inductance functions by placing balance windings with specific turns ratios on outer limbs, allowing precise control of leakage inductance values. This enables optimization of current balancing while minimizing the impact on converter efficiency by carefully designing the balance winding parameters.
Solution Approach 2:
The patent utilizes parameter changes in the balance winding turns ratios to control the amount of leakage inductance introduced. By adjusting these ratios, the system optimizes the balance between current equalization and efficiency, preventing excessive energy losses while achieving current balance.
3Productivity
If tight coupling is used in the main transformer for high performance, then transformer performance increases, but circulating current imbalance increases
Solution Approach 1:
The patent segments the coupling characteristics by maintaining tight coupling in the main transformer for high performance while introducing separate balance windings on outer limbs that provide controlled leakage inductance. This allows the main transformer to operate at peak efficiency while the balance windings correct current imbalances.
Solution Approach 2:
The balance windings serve as intermediary elements that introduce the necessary magnetic coupling asymmetry to balance circulating currents. These windings mediate between the tightly coupled main transformer and the core, providing the leakage inductance needed for current balance without degrading the main transformer's 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
The solution effectively reduces or eliminates current imbalance, enhancing converter efficiency and reducing size, while allowing for tailored output voltage and magnetizing flux parameters.
Implementation Method 1
The first and second balance windings are coupleable together via mutual inductance in response to first and second currents flowing therethrough
Data Source
AI summary
A voltage transformer comprises a multi-limb transformer core having a central limb, a first outer limb, and a second outer limb. The voltage transformer also comprises a first primary winding wound about the central limb, a second primary winding wound about the central limb, a first secondary winding wound about the central limb, and a second secondary winding wound about the central limb. A first balance winding is wound about the first outer limb and coupled in series with the first primary winding, and a second balance winding is wound about the second outer limb and coupled in series with the second primary winding. The first and second balance windings are coupleable together via mutual inductance in response to first and second currents flowing therethrough.