Active Switching Filter for Common Mode Current Suppression

Solution Overview

Problem

Conventional low-pass power line filters for reducing common mode disturbances in power electronic systems are often large and costly, especially when high common mode currents or significant attenuation at switching frequencies are required.

Innovation Solution

The method involves a low-pass power line filter with series inductive and shunt capacitive elements, where shunt common mode capacitance is replaced by a network of capacitors and diodes that maintain the load node voltage near the reference potential, reducing the time integral of the load node voltage and thus the current in the series common mode inductance, using switches or amplifiers to control the capacitive elements for efficient energy transfer and discharge.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a conventional low-pass power line filter with shunt capacitance is used to reduce common mode current, then common mode attenuation is improved, but the filter size and cost increase prohibitively

Engineering Contradiction:

Improvecommon mode currentVSAvoidfilter size

Core Design Contradiction:

Object-affected harmful factorsVSVolume of stationary object

Solution Approach 1:

The invention extracts and eliminates the shunt common mode capacitance from the traditional filter topology. By removing this component, the filter size is significantly reduced while maintaining common mode current suppression through an alternative mechanism using series capacitors and active switching that controls load node voltage to remain near the reference potential

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention introduces dynamic control through active switching elements (MOSFETs or IGBTs) that continuously adjust the load node voltage to stay near the reference potential. This dynamic voltage control replaces the static shunt capacitance function, enabling common mode current reduction without requiring large physical filter components

Inventive Principle:

Principle #15Dynamics

2Object-affected harmful factors

If a conventional low-pass power line filter with shunt capacitance is used to reduce common mode current, then common mode attenuation is improved, but the filter cost increases prohibitively

Engineering Contradiction:

Improvecommon mode currentVSAvoidfilter cost

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

The invention extracts and eliminates the shunt common mode capacitance from the traditional filter topology. By removing this component, the filter size is significantly reduced while maintaining common mode current suppression through an alternative mechanism using series capacitors and active switching that controls load node voltage to remain near the reference potential

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The active switching elements in the invention serve multiple functions: they control the load node voltage to suppress common mode current, they replace the function of shunt capacitance, and they can be integrated with existing power electronic device control circuits. This multi-functionality reduces the need for additional dedicated filter components, thereby reducing overall system cost

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Object-affected harmful factors

If series common mode inductance is used to restrict interference current flow, then common mode attenuation is improved, but magnetic saturation and system losses increase

Engineering Contradiction:

Improveinterference currentVSAvoidsystem losses

Core Design Contradiction:

Object-affected harmful factorsVSLoss of energy

Solution Approach 1:

The invention introduces dynamic control through active switching elements (MOSFETs or IGBTs) that continuously adjust the load node voltage to stay near the reference potential. This dynamic voltage control replaces the static shunt capacitance function, enabling common mode current reduction without requiring large physical filter components

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The invention substitutes the passive magnetic field-based common mode inductance with an active electronic control system using voltage-switching elements. This replacement eliminates the magnetic saturation issues and energy losses associated with large inductors, as the active electronics can achieve the same current suppression function without magnetic field effects

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 approach reduces the size and cost of the filter while effectively minimizing common mode current, maintaining voltage isolation, and preventing self-resonance between inductance and capacitance, thereby reducing system losses and magnetic saturation.

Implementation Method 1

A first capacitive element is coupled in series to a first one-way conductor that allows current flow in one direction. The first one-way conductor and the first capacitive element are coupled between a load node and a reference potential.

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

charging the first capacitive element and the capacitive means positive by one positive voltage transition of the load node, transferring energy to the first capacitive element and the capacitive means

Methodology Applied

Scientific EffectEnergy transfer:

Implementation Method 3

The one-way conductor may be diodes. A second capacitive element is coupled in series to a further one-way conductor that allows current flow in the opposite direction.

Methodology Applied

Scientific EffectDiode rectification: Diode

Implementation Method 4

A first switch connects between a potential node that is between the first one-way conductor and the first capacitive element, and the load node. The switches may be switched by means of a switch control, for example, between a conducting state allowing current flow and a non-conducting state with no current flow.

Methodology Applied

Scientific EffectSwitching:

Data Source

PatentUS10454272B2Electronic devices and method for filtering common mode disturbances from power electronic devices

Publication Date: 2019.10.22 TDK ELECTRONICS AG

AI summary

An electronic device and a method for filtering common mode disturbances from a power electronic device are disclosed. In an embodiment the device includes a first capacitor coupled in series to a first one-way conductor, the first one-way conductor allowing current flow in one direction, wherein the first one-way conductor and the first capacitor are coupled between a load node and a reference potential and a second capacitor coupled in series to a second one-way conductor, the second one-way conductor allowing current flow in an opposite direction, wherein the second one-way conductor and the second capacitor are coupled between the load node and the reference potential. The device further includes a third capacitor being coupled between the load node and the reference potential, a first switch bypassing the first one-way conductor and a second switch bypassing the second one-way conductor.