Non-Isolated Bidirectional Charger Residual Current Control
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Solution Overview
Problem
Non-isolated bidirectional battery chargers for electric vehicles face challenges in integrating a ground-fault circuit interrupter (GFCI) due to residual currents, which can lead to unnecessary tripping and safety hazards, especially when operating without galvanic isolation, and require additional components like isolation transformers, increasing weight and cost.
Innovation Solution
A non-isolated high-voltage DC charger is made compatible with a GFCI by controlling the net current difference between forward and return currents using voltage or current sensors, adjusting the power converter to keep residual currents below safety thresholds, eliminating the need for isolation transformers and ensuring safe operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If galvanic isolation is used to ensure safety, then safety is improved, but weight and cost increase due to isolation transformers
Solution Approach 1:
The patent removes the isolation transformer from the system entirely, replacing galvanic isolation with a non-isolated power converter design. This extraction of the heavy isolation component directly reduces weight while maintaining safety through alternative means (controlled residual current management).
Solution Approach 2:
The patent changes the operational parameters of the power converter to actively control and minimize residual currents to below 20mA. By adjusting conversion ratios, switching frequencies, and control strategies, the system maintains safety without requiring galvanic isolation, thus eliminating the weight penalty of isolation transformers.
2Reliability
If galvanic isolation is used to ensure safety, then safety is improved, but cost increases due to isolation transformers
Solution Approach 1:
The patent removes the isolation transformer from the system entirely, replacing galvanic isolation with a non-isolated power converter design. This extraction of the heavy isolation component directly reduces weight while maintaining safety through alternative means (controlled residual current management).
Solution Approach 2:
The patent changes the operational parameters of the power converter to actively control and minimize residual currents to below 20mA. By adjusting conversion ratios, switching frequencies, and control strategies, the system maintains safety without requiring galvanic isolation, thus eliminating the weight penalty of isolation transformers.
3Weight of moving object
If non-isolated chargers are used to reduce weight, then weight is reduced, but residual current causes GFCI tripping and safety hazards
Solution Approach 1:
The patent implements a feedback control system that continuously monitors residual currents and adjusts power converter parameters in real-time to maintain residual current below 20mA. This active feedback mechanism prevents GFCI tripping while maintaining the weight advantages of non-isolated design.
Solution Approach 2:
The patent dynamically adjusts conversion ratios, switching frequencies, and operational parameters of the power converter to minimize residual currents. By changing these parameters adaptively, the system maintains safety compliance without requiring heavy isolation components.
4Power
If residual current is increased above 20mA, then charging power is improved, but GFCI trips and charging is interrupted
Solution Approach 1:
The patent employs dynamic control strategies that adjust power converter parameters in real-time based on operating conditions. By dynamically optimizing conversion ratios and switching frequencies, the system delivers high charging power while continuously maintaining residual current below the 20mA GFCI trip threshold, ensuring uninterrupted charging.
Solution Approach 2:
The patent changes operational parameters such as switching frequency, duty cycle, and conversion ratio adaptively to maximize power transfer efficiency while keeping residual current controlled. These parameter adjustments enable high power delivery without triggering GFCI protection.
Data Source
AI summary
A non-isolated bidirectional high-voltage direct current battery charger is made compatible with a ground-fault circuit interrupter (GFCI) at the DC output by adapting the power converter to control, in response to voltage or current sensors, a net current difference between forward current and return current to remain below a threshold of the GFCI. This can be done without compromising safety in the case of actual ground faults.