Common-Mode Transformer Injection for Low-Frequency Noise Filtering
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Solution Overview
Problem
Existing common mode suppressing circuits face challenges in reducing common mode voltage when the switching frequency is low, leading to the need for larger core sizes in common mode transformers.
Innovation Solution
A noise filter design that includes a voltage detector, a voltage division circuit, and multiple common mode transformers with an injection waveform generator that adjusts output voltages to ensure the difference between the common mode voltage and the total injection voltage is within an allowable value, allowing for the use of smaller transformers even at low switching frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the switching frequency is low, then the time product of magnetic fluxes generated in the core is increased, but the core size of the common mode transformer becomes larger
Solution Approach 1:
The patent divides a single common mode transformer into multiple common mode transformers (e.g., two transformers instead of one). Each transformer handles a portion of the common mode voltage suppression task, allowing each individual transformer to have a smaller core size while collectively achieving the required suppression performance even at low switching frequencies.
2Device complexity
If a single common mode transformer is used, then the structure is simpler, but the transformer size must be larger to handle low switching frequencies
Solution Approach 1:
The patent segments the transformer function across multiple common mode transformers with smaller cores, trading increased component count for reduced individual component size and overall system flexibility.
Solution Approach 2:
The patent introduces an injection waveform generator that dynamically adjusts the output voltages to each common mode transformer based on the detected common mode voltage. This dynamic control allows the system to optimize performance across varying operating conditions while maintaining compact transformer sizes.
3Volume of stationary object
If the core size is reduced, then the noise filter becomes more compact, but the ability to suppress common mode voltage at low switching frequencies deteriorates
Solution Approach 1:
Multiple smaller transformers work together to provide the total suppression capability needed, with each transformer contributing a portion of the overall common mode voltage cancellation.
Solution Approach 2:
The patent employs a feedback mechanism where a detector detects the common mode voltage and provides this information to the injection waveform generator, which then adjusts the injection voltages to maintain effective suppression despite the reduced size of individual transformers.
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 design effectively reduces common mode voltage using smaller common mode transformers, avoiding the need for larger core sizes and enhancing the efficiency and compactness of the noise filter.
Implementation Method 1
a plurality of common mode transformers 11a and 11b that superimpose injection voltages Vs (Vsa and Vsb) each having a polarity opposite to a polarity of the common mode voltage Vci onto an output from or an input to the power converter 2
Data Source
AI summary
A noise filter includes: a voltage detector which detects a common mode voltage generated by a power converter; a voltage division circuit which outputs a division voltage obtained by dividing the common mode voltage detected by the voltage detector; a plurality of common mode transformers which superimpose injection voltages each having a polarity opposite to a polarity of the common mode voltage onto an output from or an input to the power converter; and an injection waveform generator which generates, on the basis of the division voltage, output voltages to be outputted to primary sides of the plurality of common mode transformers. The injection waveform generator generates the output voltages such that a difference between the common mode voltage and a total injection voltage obtained by summing the injection voltages to be superimposed by the plurality of common mode transformers is equal to or smaller than an allowable value.