Common-Mode Transformer Segmentation for Compact Noise Filters
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Solution Overview
Problem
Existing common-mode reduction circuits for power converters require larger core sizes due to increased phase currents, necessitating larger diameters for cables and cores, which complicates assembly and increases size.
Innovation Solution
A noise filter comprising a voltage detector, voltage divider circuit, and multiple common-mode transformers connected to power lines, with an injection waveform generator generating an output voltage to superimpose an opposite polarity voltage, reducing common-mode voltage using small-size transformers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the diameter of three-phase cables is increased to handle large phase currents, then the current carrying capacity is improved, but the inner diameter required for the core is increased, making the core larger
Solution Approach 1:
The patent divides a single common-mode transformer into multiple common-mode transformers (e.g., two or more) that are connected in parallel. Each transformer handles a portion of the total phase current, allowing the use of smaller cable diameters and smaller core sizes while maintaining the required current carrying capacity. This segmentation resolves the contradiction by distributing the current load across multiple smaller units rather than requiring one large transformer.
2Object-affected harmful factors
If a single common-mode transformer is used to handle large currents, then the common-mode voltage reduction is achieved, but the transformer size becomes large due to increased core requirements
Solution Approach 1:
The common-mode voltage reduction function is distributed across multiple smaller common-mode transformers connected in parallel. Each transformer contributes to the overall common-mode voltage cancellation while maintaining a compact size. This approach achieves effective common-mode noise reduction without requiring a large single transformer core.
Solution Approach 2:
Multiple common-mode transformers are combined in parallel configuration to achieve the cumulative effect needed for large current applications. The combined system provides sufficient current handling capability and common-mode voltage reduction performance while each individual transformer remains small in size.
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 common-mode voltage while using smaller common-mode transformers, even with high output currents, by employing multiple transformers and controlled voltage injection, thereby downsizing the transformer core and improving assembly efficiency.
Implementation Method 1
a common-mode transformer whose secondary coils, namely, secondary windings, are interposed in three-phase cables that connect the inverter with a motor
Data Source
AI summary
A noise filter includes: a voltage detector that detects a common-mode voltage; a voltage divider circuit that outputs a divided voltage divided from the common-mode voltage; multiple common-mode transformers that are connected separately to respective power lines of multiline systems connected in parallel relation to each other to an input or output of the power converter, and that superimpose a superimposing voltage having an opposite polarity to the common-mode voltage on each of the power lines of multiline systems; and an injection waveform generator that generates at least one output voltage to be outputted to primary sides of the multiple common-mode transformers, on the basis of the divided voltage. The injection waveform generator generates as the output voltage, a voltage with which a difference between the superimposing voltage to be super-imposed on each of the power lines and the common-mode voltage is within an allowable value.