Non-Isolated DC Fast Charger Zero-Sequence Voltage Control
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Solution Overview
Problem
Electric vehicle charging infrastructure faces challenges due to the bulkiness, cost, and inefficiency of line frequency transformers, which also lead to leakage current issues that affect safety and grid current quality.
Innovation Solution
A system and method that mitigates leakage currents by using a bank of parallel capacitors and inductors coupled with a rectifier and controller, stabilizing zero sequence voltage to eliminate common mode voltage fluctuations, thereby reducing leakage currents without the need for transformers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a line frequency transformer is used for isolation, then safety and grid current quality are improved, but the size, cost, and efficiency of the charging unit deteriorate
Solution Approach 1:
The patent removes the transformer from the charging station system entirely, extracting the isolation function and replacing it with a non-isolated topology that uses semiconductor switches and control circuits to achieve safe operation without the bulky transformer component
Solution Approach 2:
The patent replaces the electromagnetic isolation mechanism (transformer) with an electronic control-based approach using semiconductor devices and control circuits to manage currents and voltages, substituting a mechanical/electromagnetic system with an electronic one
2Reliability
If a line frequency transformer is used for isolation, then safety and grid current quality are improved, but the cost and efficiency of the charging unit deteriorate
Solution Approach 1:
The transformer is completely removed from the system, eliminating its inherent energy losses (typically 2-5% for line frequency transformers) and replacing the isolation function with a more efficient electronic control approach
Solution Approach 2:
The patent changes the operating parameters by eliminating the transformer's electromagnetic coupling and instead using high-frequency semiconductor switching with control circuits to manage power conversion, achieving higher efficiency through reduced resistive and magnetic losses
3Weight of stationary object
If the transformer is removed to reduce size and cost, then the size and cost of the charging unit are reduced, but leakage currents and safety issues worsen
Solution Approach 1:
The patent implements control circuits that continuously monitor system parameters and provide feedback to adjust the operation of semiconductor switches, enabling the system to detect and compensate for leakage currents in real-time, maintaining safety without a transformer
Solution Approach 2:
The patent introduces control circuits and semiconductor devices as intermediary elements between the power source and the vehicle battery, using these intermediaries to manage and control currents in a way that prevents harmful leakage without requiring transformer isolation
4Ease of manufacture
If the transformer is removed to reduce cost, then the cost of the charging unit is reduced, but leakage currents and safety issues worsen
Solution Approach 1:
The expensive transformer is removed from the system, eliminating its cost (which can be thousands of dollars) and replacing the isolation function with more affordable semiconductor devices and control circuits
Solution Approach 2:
The control circuits monitor system operation and provide feedback to prevent leakage currents, enabling the system to operate safely without the expensive transformer while maintaining compliance with safety standards through active control
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 reduces the size and cost of charging units, enhances safety, and improves grid current quality by effectively eliminating leakage currents, making it a cost-effective and efficient solution for electric vehicle charging infrastructure.
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 parallel capacitors per phase electrically coupled to an AC voltage source
Implementation Method 3
a bank of one or more inductors per phase electrically coupled to the one or more parallel capacitors
Data Source
AI summary
A system may mitigate leakage currents in non-isolated 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.