Conversion Device Filtering Network Reduces Common-Mode Currents

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Solution Overview

Problem

Traditional conversion devices face inefficiencies and high harmonic content at light loads, and common-mode currents generated during PWM operation in medium-voltage DC micro-grids lead to insulation issues, interference, and heat dissipation, reducing system efficiency.

Innovation Solution

A conversion device with a filtering network incorporating resistance-capacitance circuits and a common-mode inductor is used to reduce common-mode currents, featuring a first-stage AC-DC converter and a second-stage DC-DC or DC-AC converter, with a controller managing semiconductor devices and circuit breakers to optimize operation based on load conditions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If PWM operation is used in medium-voltage DC micro-grids, then power conversion efficiency is improved, but common-mode currents are generated causing insulation issues, interference, and heat dissipation

Engineering Contradiction:

Improvepower conversion efficiencyVSAvoidcommon-mode currents

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent introduces a common-mode filter as an intermediary component between the PWM converter and the power grid. This filter acts as a mediator that allows the PWM operation to continue efficiently while blocking and suppressing the common-mode currents from propagating into the grid, thus resolving the contradiction between maintaining high conversion efficiency and eliminating harmful common-mode currents

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent converts the harmful common-mode currents into a controllable filtering process. By designing the common-mode filter with specific impedance characteristics, the harmful currents are redirected through the filter where they are suppressed, transforming the harmful effect into a beneficial current suppression mechanism that protects the system while maintaining PWM operation

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Adaptability or versatility

If traditional conversion devices operate at light loads, then system adaptability is improved, but efficiency decreases and harmonic content increases

Engineering Contradiction:

Improveload adaptation capabilityVSAvoidefficiency loss at light load

Core Design Contradiction:

Adaptability or versatilityVSLoss of energy

Solution Approach 1:

The patent implements dynamic control strategies that adjust converter operation parameters based on real-time load conditions. At light loads, the system dynamically switches to alternative operating modes or adjusts switching frequencies and duty cycles to maintain high efficiency while continuing to adapt to varying load requirements, thus resolving the contradiction between adaptability and efficiency

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes operational parameters such as switching frequency, duty cycle, and control mode based on load conditions. By dynamically adjusting these parameters, the system maintains high efficiency across different load levels while preserving adaptability to various operating conditions, eliminating the efficiency loss typically associated with light-load operation

Inventive Principle:

Principle #35Parameter changes

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 currents, improves efficiency, and enhances reliability by minimizing voltage fluctuations and heat dissipation, while optimizing converter performance across varying load conditions.

Implementation Method 1

A conversion device with a filtering network incorporating resistance-capacitance circuits and a common-mode inductor is used to reduce common-mode currents

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

A conversion device with a filtering network incorporating resistance-capacitance circuits and a common-mode inductor is used to reduce common-mode currents

Methodology Applied

Scientific EffectElectrical impedance: Electrical Impedance Tomography

Implementation Method 3

The solution effectively reduces common-mode currents, improves efficiency, and enhances reliability by minimizing voltage fluctuations and heat dissipation

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS11515806B2Conversion device having reduced common-mode current

Publication Date: 2022.11.29 DELTA ELECTRONICS (SHANGHAI) CO LTD

AI summary

A conversion device includes: an inductor connected to the AC power grid; a first-stage converter configured to output a bus voltage based on the AC power grid; a second-stage converter configured to convert the bus voltage into an output voltage to the load; and a filtering network, wherein a first resistance-capacitance circuit is disposed between the first and third terminals of the filtering network, a second resistance-capacitance circuit is disposed between the second and third terminals of the filtering network, the first terminal of the filtering network is connected to the AC power grid, the second terminal of the filtering network is connected to the bus or the second terminal of the second-stage converter, and the third terminal of the filtering network is grounded through a first capacitor.