Non-Isolated DC Fast Charger Topology for Leakage Current Mitigation
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Solution Overview
Problem
Electric vehicle charging infrastructure faces challenges due to the bulkiness, high cost, and low efficiency of line frequency transformers used in fast charger schemes, which also lead to leakage current issues that affect grid quality and safety.
Innovation Solution
The proposed system includes a bank of parallel capacitors and inductors coupled to an AC voltage source, with a neutral point connected to DC ground, and a controller to mitigate leakage currents by controlling the voltage of the capacitors, stabilizing the zero component voltage, and driving the zero component current through the inductors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a line frequency transformer is used in the fast charger, then isolation and safety are improved, but the size, cost, and efficiency deteriorate
Solution Approach 1:
The patent removes the line frequency transformer from the charging system entirely, extracting the isolation function and replacing it with a non-isolated topology that uses active control to mitigate leakage currents. This eliminates the bulky, inefficient transformer while maintaining safety through alternative means.
Solution Approach 2:
The patent changes the operating parameters by using high-frequency switching (20-100 kHz) instead of line frequency (50-60 Hz), which enables the use of smaller magnetic components and eliminates the need for large line frequency transformers while maintaining isolation and safety functions.
2Reliability
If a line frequency transformer is used in the fast charger, then isolation and safety are improved, but the size and cost deteriorate
Solution Approach 1:
The patent removes the line frequency transformer from the charging system entirely, extracting the isolation function and replacing it with a non-isolated topology that uses active control to mitigate leakage currents. This eliminates the bulky, inefficient transformer while maintaining safety through alternative means.
3Reliability
If a line frequency transformer is used in the fast charger, then isolation and safety are improved, but the cost deteriorates
Solution Approach 1:
The patent removes the line frequency transformer from the charging system entirely, extracting the isolation function and replacing it with a non-isolated topology that uses active control to mitigate leakage currents. This eliminates the bulky, inefficient transformer while maintaining safety through alternative means.
4Weight of stationary object
If the transformer is removed from the charging system, then size and cost are improved, but leakage currents and grid quality deteriorate
Solution Approach 1:
The patent implements an active control system with feedback that monitors the neutral point voltage and adjusts the switching of power electronic devices to maintain the neutral point at a stable potential. This feedback mechanism actively counteracts leakage currents and maintains grid quality without requiring a transformer.
Solution Approach 2:
The patent introduces an intermediary control system that mediates between the power electronic switching and the grid connection. This control system uses voltage balancing techniques to prevent leakage currents from flowing to the grid, effectively acting as a mediator that protects grid quality without physical isolation.
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 solution effectively reduces leakage currents, improving grid current quality and safety while potentially reducing the size and cost of fast charging units by eliminating the need for bulky transformers.
Implementation Method 1
a rectifier electrically coupled to and downstream from the one or more parallel inductors, wherein the rectifier converts the AC voltage source to a DC voltage
Implementation Method 2
a bank of one or more inductors per phase electrically coupled to the one or more parallel capacitors
Implementation Method 3
a bank of one or more parallel capacitors per phase electrically coupled to an AC voltage source
Data Source
AI summary
A system may mitigate leakage currents in charging stations for electric vehicles. The system may include a bank of one or more parallel capacitors per phase electrically coupled to an AC voltage source, wherein a neutral point of the one or more parallel capacitors is electrically coupled to a DC ground; a bank of one or more inductors per phase electrically coupled to the one or more parallel capacitors, wherein each inductor is in series with and downstream from one capacitor; a rectifier electrically coupled to and downstream from the one or more parallel inductors, wherein the rectifier converts the AC voltage source to a DC voltage for supply to a battery; a DC bus electrically coupled to the rectifier; and a controller, wherein the controller is configured to mitigate leakage currents by controlling a voltage of at least one of the bank of one or more parallel capacitors.