Active Filter for Low-Frequency Noise Suppression
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Solution Overview
Problem
Existing communications systems face challenges in miniaturization due to the need for large passive filters to suppress low-frequency noise caused by non-linear loads, which leads to increased volume and cost.
Innovation Solution
An active filter is connected in parallel between the power source and conversion circuit, using a main circuit with a full-bridge configuration, inductor, and capacitor, controlled by a circuit that detects harmonic components and generates a compensating current with an opposite phase to cancel out low-frequency noise, thereby reducing the need for large capacitors and passive filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a passive low-frequency filter is used to suppress low-frequency noise, then the filtering effect is achieved, but the volume of the filter becomes huge due to the requirement for very large capacitor capacity
Solution Approach 1:
The patent replaces the passive mechanical filter system (inductor, capacitor, resistor) with an active electronic control system. The active filter uses switching elements (MOSFETs or IGBTs), control circuitry, and energy storage components to generate compensating currents that cancel low-frequency noise, eliminating the need for large passive filter components and achieving miniaturization.
Solution Approach 2:
The patent changes the operating parameters by using active switching elements that can rapidly change their state between on and off, controlled by PWM signals. This dynamic parameter control allows the filter to achieve noise suppression with much smaller component values compared to passive filters, directly addressing the volume reduction goal.
2Object-affected harmful factors
If the inductor and resistor values are increased in a passive filter to improve filtering, then the filtering performance is enhanced, but the loss increases due to series connection in the power bus
Solution Approach 1:
The patent substitutes the lossy passive inductor and resistor with active switching elements and control circuitry. The switching elements have minimal on-resistance, and the control system generates compensating currents without the continuous power dissipation inherent in passive resistive filtering, significantly reducing energy loss while maintaining noise suppression performance.
Solution Approach 2:
The patent converts the harmful effect of load current fluctuations into a useful signal by detecting these fluctuations and using them to generate compensating currents through the control circuit. The control system processes the load current information and produces counter-phase currents that cancel the noise, transforming the problem into a solution.
3Loss of energy
If a passive filter with large capacitor capacity is used to reduce inductor and resistor values, then the loss is reduced, but the volume of the filter becomes even larger
Solution Approach 1:
The patent replaces the entire passive filter architecture with an active filter system that uses switching elements and digital/analog control circuitry. This substitution eliminates the direct relationship between filtering performance and component size, allowing small-volume implementation while maintaining low loss through efficient switching operation and minimal resistive elements.
Solution Approach 2:
The active filter circuit performs multiple functions: it suppresses low-frequency noise, provides power factor correction, and can regulate output voltage simultaneously. The switching elements and control system handle multiple tasks that would otherwise require separate components, reducing overall system volume while maintaining low energy loss.
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 active filter effectively suppresses low-frequency noise, meets the requirement for miniaturization, and reduces interference in communications systems by canceling current fluctuations, ensuring a stable direct current output.
Implementation Method 1
the main circuit is configured to perform, under control of the control signal, conductivity switching on the full-bridge circuit, and thereby control charging or discharging of the inductor and charging or discharging of the capacitor to generate the second current
Data Source
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AI summary
The present invention provides an active filter and a communications system. The active filter includes a main circuit and a control circuit. The control circuit is configured to: detect a first current output by a negative electrode of an input end of a conversion circuit to acquire a harmonic component in the first current, and generate a control signal according to the harmonic component. The main circuit is configured to generate, under control of the control signal, a second current having a phase opposite to a phase of the harmonic component, so that a source current formed after the first current and the second current pass through a power source is a direct current. By using the active filter provided by the present invention, low-frequency noise may be suppressed effectively.