Predictive Active EMI Filter for PFC Differential Noise Suppression
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Solution Overview
Problem
Existing active EMI filters for PFC circuits rely on noise sensing, which introduces delays and requires additional components, limiting their effectiveness in suppressing electromagnetic interference (EMI) due to their reactive nature.
Innovation Solution
A predictive active EMI filter that injects a compensation current into the inductor current based on the characteristics of the switch control signal, such as duty cycle and frequency, without the need for noise sensing, using a compensation current calculation unit and an EMI noise model to suppress differential mode noise, potentially combined with a passive EMI filter for hybrid suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If noise sensing is used in active EMI filter, then EMI compensation can be achieved, but delay is introduced and additional components are required
Solution Approach 1:
The patent applies preliminary action by calculating the compensation current in advance based on the known switching signal characteristics before the EMI noise actually occurs. The controller computes the compensation current waveform ahead of time using the relationship between the switching signal and inductor current, then injects this pre-calculated compensation current through the compensation current source, eliminating the need for reactive noise sensing and avoiding response delays.
Solution Approach 2:
The patent introduces an intermediary approach by using the switching signal as a reference to predict and calculate the compensation current waveform, rather than directly sensing the EMI noise. This intermediary method allows the system to derive the necessary compensation current information from the switching signal characteristics without requiring additional noise sensing components or waiting for the noise to occur.
2Reliability
If noise sensing is used in active EMI filter, then EMI compensation can be achieved, but additional components are required
Solution Approach 1:
The patent extracts and eliminates the noise sensing stage from the traditional active EMI filter structure. Instead of sensing the EMI noise and then compensating for it, the invention directly calculates the compensation current based on the switching signal characteristics, removing the need for noise sensing components and simplifying the overall filter structure while maintaining EMI compensation effectiveness.
Solution Approach 2:
The system uses the existing switching signal from the PFC circuit as the basis for calculating compensation current, rather than requiring separate noise sensing components. The controller leverages information already present in the system (the switching signal) to generate the compensation current, making the system self-sufficient and reducing component requirements.
3Measurement precision
If reactive noise sensing is used, then EMI can be measured, but response speed is reduced
Solution Approach 1:
The patent calculates the compensation current in advance based on the switching signal characteristics before the EMI noise occurs. By using the known relationship between the switching signal and inductor current, the system predicts the compensation current waveform ahead of time and injects it proactively, eliminating the need to wait for noise measurement and significantly improving response speed while maintaining compensation accuracy.
Data Source
Figure 1~2
AI summary
A PFC circuitry with EMI filter comprises: - A PFC switch having a switch and an inductor, - A control unit controlling, preferably feedback-controlling, the switch via a switch control signal, and - An active EMI filter, arranged between AC supply terminals and the PFC circuitry and having a compensation current unit injecting a compensation current into the current flowing through the inductor, wherein the EMI filter unit further comprises a compensation current calculation unit setting the current of the compensation current unit based on the characteristics, such as e.g. duty cycle and/or frequency, of the switch control signal.