DC Bus Ground Fault Detection Without Isolation Transformers
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Solution Overview
Problem
Existing DC energy distribution networks face challenges in detecting ground faults without incurring significant cost and efficiency losses due to the need for galvanic isolation, which is essential for preventing ground fault currents but increases costs and reduces energy transmission efficiency.
Innovation Solution
A power conversion topology and control method for a DC bus that uses a DC-DC power stage with active current control to drive differential current to zero and a separate voltage control loop to maintain desired differential bus voltage, allowing for ground fault detection without galvanic isolation, thereby preventing ground fault currents while optionally continuing to operate the DC bus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If galvanic isolation using an isolation transformer is used to detect ground faults, then ground fault detection capability is improved, but system cost increases and energy transmission efficiency decreases
Solution Approach 1:
The patent extracts the ground fault detection function from the galvanic isolation structure. Instead of using an isolation transformer to detect ground faults, the invention monitors the voltage of the DC bus with respect to ground directly, separating the detection function from the power transmission path and eliminating the need for isolation transformers.
Solution Approach 2:
The patent introduces a high-impedance path to ground as an intermediary element. By connecting a high-impedance resistor from the DC bus to ground, the system creates a controlled reference path that enables voltage monitoring without requiring galvanic isolation, thus maintaining energy efficiency while enabling fault detection.
2Reliability
If galvanic isolation using an isolation transformer is used to detect ground faults, then ground fault detection capability is improved, but system cost increases
Solution Approach 1:
The patent removes the isolation transformer component from the system architecture. By extracting this expensive component and replacing it with simple voltage monitoring circuitry and high-impedance resistors, the invention significantly reduces system cost while maintaining ground fault detection capability.
Solution Approach 2:
The patent replaces the expensive, complex isolation transformer with inexpensive, simple components such as high-impedance resistors and voltage monitoring circuits. These simpler components achieve the same functional goal at a fraction of the cost.
3Measurement precision
If the DC bus is allowed to float with high impedance to ground for monitoring, then ground fault detection is enabled, but ground fault current prevention capability is reduced
Solution Approach 1:
The patent applies preliminary anti-action by pre-establishing a high-impedance path to ground before any fault occurs. This predetermined high-impedance path limits the magnitude of ground fault currents that can flow during a fault condition, preventing hazardous current levels while still enabling voltage monitoring.
Solution Approach 2:
The patent changes the impedance parameter of the ground connection from low (direct ground) to high (through a high-impedance resistor). This parameter change simultaneously enables accurate voltage monitoring and limits ground fault current to safe levels, resolving the contradiction between measurement capability and hazard prevention.
Data Source
AI summary
A power conversion topology and control method intended for use with a DC bus is disclosed, providing a means to prevent the flow of ground fault current while detecting a fault condition and optionally continuing to operate the DC bus. In one control configuration, a DC-DC power stage with an active current control loop drives differential current to zero, and a separate voltage control loop maintains the desired differential bus voltage. Absolute bus voltage with respect to ground is monitored in order to detect fault conditions. In another configuration, the absolute voltage of the bus with respect to ground is controlled and differential bus current is monitored to detect ground fault conditions.