Power Converter Leakage Current Compensation Without Galvanic Isolation
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Solution Overview
Problem
Leakage currents in the protective conductor of electrical power converters, particularly in transformerless battery charging circuits, cause unwanted shutdowns due to residual current devices (RCDs) failing to distinguish between operational and insulation fault-related currents, reducing the availability of the power supply.
Innovation Solution
A method and device that compensate leakage currents by determining a differential current between phase and neutral conductors, generating a compensation current, and using a two-stage compensation process with frequency-selective control to minimize residual leakage, without requiring galvanic isolation, utilizing existing safety circuits and controllers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a measuring transformer and current source are used to compensate leakage currents, then leakage current compensation is achieved, but the device complexity increases and galvanic isolation is required
Solution Approach 1:
The patent extracts the leakage current compensation function from the protective conductor and implements it through differential current measurement in phase and neutral conductors. By measuring the difference between phase and neutral currents, the system identifies leakage currents without requiring direct measurement or isolation in the protective conductor, thereby simplifying the overall device complexity while maintaining compensation effectiveness.
Solution Approach 2:
The patent makes the existing differential current sensor serve multiple functions: it simultaneously measures phase current, neutral current, and indirectly detects leakage current through differential measurement. This multi-functionality eliminates the need for separate measuring transformers and reduces device complexity while achieving the same compensation goal.
2Measurement precision
If galvanic isolation is implemented in the compensation circuit, then measurement accuracy is improved, but the device complexity and cost increase
Solution Approach 1:
The patent creates a virtual copy of the leakage current measurement by calculating the differential current between phase and neutral conductors. Instead of directly measuring leakage current through galvanically isolated sensors, the system computes an equivalent measurement from readily available phase and neutral current measurements, achieving the same information without the complexity of galvanic isolation.
Solution Approach 2:
The patent replaces the physical/mechanical galvanic isolation system (transformers) with a computational approach. By using differential current calculation in the electrical domain, the system achieves measurement accuracy without requiring the mechanical isolation components, thereby reducing device complexity and cost.
3Reliability
If residual current devices are used to detect leakage currents, then safety monitoring is improved, but false shutdowns occur due to inability to distinguish operational from fault leakage currents
Solution Approach 1:
The patent implements a feedback mechanism where the measured differential current (representing leakage current) is continuously monitored and used to generate compensating currents. This closed-loop feedback allows the system to distinguish between normal operational leakage (which is compensated) and actual fault conditions, preventing false shutdowns while maintaining safety monitoring through the RCD.
Solution Approach 2:
The patent applies preliminary anti-action by compensating for operational leakage currents before they can trigger the RCD shutdown. By injecting compensating currents that counterbalance the operational leakage, the system prevents the RCD from detecting harmful current levels, thereby avoiding false shutdowns while maintaining safety functionality.
Data Source
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.