Leakage Current Compensation in Transformerless Power Converters

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Solution Overview

Problem

Transformerless battery charging devices face issues with high leakage currents to ground and through the protective converter, leading to unwanted shutdowns due to the inability of residual current devices to distinguish between operational and fault-related leakage currents, reducing the availability of the power supply.

Innovation Solution

A method and device that compensate leakage currents by determining differential currents between phase and neutral conductors, generating compensation currents without direct measurement in the protective conductor, and using a two-stage compensation system with frequency-selective control to minimize residual leakage, allowing for compact and lightweight design without galvanic isolation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If transformerless charging devices are used to eliminate galvanic isolation, then device complexity is reduced and weight is decreased, but leakage currents increase causing unwanted shutdowns

Engineering Contradiction:

Improvegalvanic isolation structureVSAvoidshutdown frequency

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent applies preliminary anti-action by measuring the differential current that represents leakage current and generating a compensation current in opposite phase before the leakage current causes shutdown. The compensation current is fed into the conductors to counteract the leakage current, preventing residual current devices from triggering unwanted shutdowns while maintaining transformerless operation

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The patent converts the harmful leakage current into a beneficial compensation mechanism. By measuring the differential current (which represents the leakage current) and generating an inverted compensation current, the system transforms the harmful effect into a controlled compensation process that eliminates the shutdown problem while maintaining the transformerless design benefits

Inventive Principle:

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

2Measurement precision

If direct measurement of leakage current in protective conductor is performed, then measurement precision is improved, but device complexity increases requiring galvanic isolation

Engineering Contradiction:

Improveleakage current measurementVSAvoidgalvanic isolation requirement

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent uses an intermediary approach by measuring the differential current between phase and neutral conductors instead of directly measuring the leakage current in the protective conductor. This differential current serves as a mediator that represents the leakage current without requiring galvanic connection to the protective conductor, thus avoiding the need for galvanic isolation in the compensation circuit

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the direct electrical connection (galvanic isolation) with an indirect measurement method. Instead of using a measuring transformer that requires galvanic isolation, the system uses differential current sensors to measure the difference between phase and neutral currents, substituting the mechanical/electrical isolation requirement with a computational measurement approach

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If high precision compensation circuit is designed to minimize residual leakage, then leakage current compensation is improved, but manufacturing cost increases

Engineering Contradiction:

Improveresidual leakage minimizationVSAvoidcompensation circuit tolerance

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent applies partial action by implementing a two-stage compensation approach. The first compensation circuit handles the majority of the leakage current compensation, while a second compensation circuit addresses only the remaining residual leakage. This allows the first circuit to operate with greater tolerance and the second circuit to fine-tune the compensation, reducing overall manufacturing costs while achieving minimal residual leakage

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS20250015626A1Method and device for compensating leakage currents in an electrical power converter

Publication Date: 2025.01.09 DR ING H C F PORSCHE AG

AI summary

A method compensates for leakage currents in a protective conductor of an electrical power converter. The method includes: using a first differential current sensor for determining a differential current depending on a phase conductor current in a phase conductor and a neutral conductor current in a neutral conductor; feeding a compensation current into the phase conductor and/or into the neutral conductor via a first compensation circuit; using a second differential current sensor for capturing a signal representing remaining residual leakage current; converting the signal representing the residual leakage current to a frequency domain; generating a compensation signal for the residual leakage current in a frequency-selective manner; converting the compensation signal to a time domain; supplying the converted compensation signal converted to the first compensation circuit or a second compensation circuit; and feeding a residual compensation current corresponding to the compensation signal into the phase conductor(s) and/or into the neutral conductor.