Power Conversion Device Leakage Current Cancellation

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Solution Overview

Problem

In multilevel power conversion devices, the varying patterns of potential at different connection points due to alternating current input voltage polarity result in differing leakage currents through parasitic capacitances, making it difficult to cancel these currents simultaneously, thus increasing disturbance voltage.

Innovation Solution

A power conversion device with a voltage potential variation suppression mechanism that injects compensating currents via reactors and ground capacitors to cancel leakage currents at each connection point, depending on the polarity of the alternating current voltage, using a bidirectional switch and a reactor with opposing induced voltages to manage potential variations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If high switching frequency is used to increase efficiency and reduce size, then productivity is improved, but disturbance voltage increases due to higher leakage currents

Engineering Contradiction:

Improveswitching frequencyVSAvoiddisturbance voltage

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful leakage current into a beneficial compensating current. By detecting the leakage current generated by parasitic capacitance during high-frequency switching, the system generates an equal and opposite compensating current that cancels the harmful effect, allowing high switching frequencies to be used without increasing disturbance voltage

Inventive Principle:

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

Solution Approach 2:

The patent introduces an intermediary compensating current path that mediates between the leakage current and the ground. This compensating current, generated through controlled switching elements and capacitors, acts as an intermediary that neutralizes the harmful leakage current before it can create disturbance voltage

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If EMI filter capacity is increased to reduce disturbance voltage, then disturbance voltage is reduced, but device size and cost increase

Engineering Contradiction:

Improvedisturbance voltageVSAvoiddevice size

Core Design Contradiction:

Object-affected harmful factorsVSVolume of stationary object

Solution Approach 1:

The patent extracts the disturbance voltage reduction function from the EMI filter by creating a separate compensating current path. This allows the EMI filter to be downsized while maintaining disturbance voltage reduction performance, as the compensating current mechanism handles the high-frequency leakage current cancellation independently

Inventive Principle:

Principle #2Taking out (Extraction)

3Object-affected harmful factors

If parasitic capacitance is reduced to minimum to lower disturbance voltage, then disturbance voltage is reduced, but layout and wiring become extremely difficult

Engineering Contradiction:

Improvedisturbance voltageVSAvoidlayout and wiring

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

Instead of trying to eliminate parasitic capacitance, the patent accepts it as an inherent feature and converts the harmful leakage current it generates into a useful signal. The compensating current mechanism uses the leakage current information to create an equal and opposite current, turning the parasitic effect into a controllable parameter

Inventive Principle:

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

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 automatically cancels leakage currents based on alternating current voltage polarity, effectively suppressing potential variations and reducing disturbance voltage across the device.

Implementation Method 1

a reactor (62) having a main winding (62m) and an auxiliary winding (62s), one end of the auxiliary winding (62s) being connected to one end on the alternating current input terminal R1 side of the main winding (62m), and the other end of the auxiliary winding (62s) being connected to one end of a first ground capacitor (44) and the other end of the first ground capacitor (44) and the other end of the auxiliary winding (62s) being connected to a ground point via a switch (8)

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS10122281B2Power conversion device for cancelling leakage current

Publication Date: 2018.11.06 FUJI ELECTRIC CO LTD

AI summary

A power conversion device includes a potential variation suppression portion having first and second ground capacitors and a reactor, for suppressing a potential variations at an A point at which switching elements and are connected together and at a B point in a bidirectional switch. The potential variation suppression portion suppresses potential variation at the A point by cancelling a first leakage current, which flows due to the potential variation at the A point at the positive and negative polarities of an alternating current voltage, with a first compensating current flowing via the reactor and ground capacitor, and suppresses the potential variation at the B point by cancelling a second leakage current, which flows due to the potential variation at the B point at the negative polarity of the alternating current voltage, with a second compensating current flowing via the reactor, a switch, and the second ground capacitor.