Integrated Filter Inductor for Power Converter Flux Optimization
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Solution Overview
Problem
Existing filter solutions for power converters, such as LCL filters and series-connected inductors with capacitors, suffer from large and heavy inductive components, high power losses, and difficulties in designing common mode coils for simultaneous differential and common mode current components, leading to increased size and cost, as well as inefficiencies in filtering common mode currents.
Innovation Solution
A filter arrangement with a first inductor for differential mode coils between AC terminals and a second inductor for common mode coils between DC terminals, both magnetically coupled via a common magnetic core structure, along with capacitive coupling between network terminals and a star point, optimizing the magnetic flux to reduce common mode current flow and power losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If LCL filter is used to filter PWM output voltage, then sinusoidal waveform is achieved, but filter size and weight increase remarkably
Solution Approach 1:
The patent combines the common mode coil and differential mode coils into a single integrated inductor structure with a common magnetic core. The common mode windings are wound around a first core leg while differential mode windings are wound around second, third and fourth core legs. This merging eliminates the need for separate LCL filter components, significantly reducing filter weight and size while maintaining effective PWM output filtering.
2Object-generated harmful factors
If common mode coil is added to limit common mode current, then common mode current is reduced, but device complexity and cost increase
Solution Approach 1:
The common mode coil is integrated into the same inductor structure as the differential mode coils, sharing a common magnetic core. The common mode windings are positioned around the first core leg, while differential mode windings are positioned around the second, third and fourth core legs. This integration reduces device complexity and eliminates the need for separate common mode filter components.
Solution Approach 2:
The integrated inductor structure serves multiple functions simultaneously: it provides differential mode filtering through the differential mode coils, common mode current suppression through the common mode coil, and magnetic coupling between the primary and secondary sides of the converter. This multi-functionality reduces the overall number of components required.
3Ease of manufacture
If inductors are placed in series connection, then filtering is improved, but power losses increase due to large inductive components
Solution Approach 1:
The patent merges the common mode and differential mode filtering functions into a single integrated inductor structure with magnetic coupling. This eliminates the need for series connection of separate inductors, reducing the total inductive reactance and associated power losses while maintaining effective filtering performance.
Solution Approach 2:
The magnetic core structure acts as an intermediary that couples the common mode and differential mode windings. This magnetic coupling allows the filter to achieve effective common mode and differential mode rejection without requiring large series-connected inductive components, thereby reducing power losses.
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 proposed filter arrangement is up to 30% more efficient than prior art, particularly at low AC output voltage and high current conditions, reducing power losses and size while effectively filtering common mode currents, and can be applied in various power conversion systems including renewable energy applications.
Implementation Method 1
the first inductor and second inductor are magnetically coupled (LS) via a common magnetic core structure
Data Source
AI summary
A filter arrangement in connection with a power converter for transferring power between a multiphase AC voltage network and a DC voltage network. The filter arrangement comprises a differential mode coil coupled between each AC terminal of an inverter bridge and corresponding AC network phase terminal, and a common mode coil coupled between each inverter bridge DC terminal and corresponding DC network terminal. Both inductors are located in the same magnetic core structure such that each of the differential mode winding is wound around its own phase-specific core leg and all common mode windings are wound around their own single core leg. The winding direction of both AC- and DC-side inductor windings is such that a common-mode current which flows along both inductors in the same direction, induces in each magnetic core leg a flux which reinforces the total flux circulating in the magnetic core.