Midpoint-to-Ground Voltage Detection for High Resistance Ground Networks
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Solution Overview
Problem
Conventional methods for detecting ground faults in high resistance ground networks are inaccurate and complex, especially in power conversion circuits, due to low fault currents and inability to differentiate between faults and load changes.
Innovation Solution
A system utilizing a midpoint-to-ground voltage detection circuit that measures and analyzes the midpoint-to-ground voltage to detect and locate ground faults, including line side, DC bus, and load side faults, through components such as a monitoring and analysis circuit, processor, and filters to identify fundamental frequency, DC offset, and output frequency components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional simplified impedance models are used for ground fault detection, then the detection method is simple, but the accuracy is insufficient when applied to systems containing power converters
Solution Approach 1:
The patent changes the detection parameter from simplified impedance models to midpoint-to-ground voltage measurement. By measuring the voltage at the midpoint of the DC bus relative to ground and analyzing its fundamental frequency component, the system achieves accurate ground fault detection in power converter systems while maintaining practical implementation simplicity.
2Reliability
If output phase to ground voltage measurement is used for ground fault detection, then ground faults can be detected, but the technique is complicated and can identify only output phase to ground fault
Solution Approach 1:
The patent extracts the essential detection information by measuring only the midpoint-to-ground voltage at the DC bus, rather than measuring all output phase-to-ground voltages. This single measurement point provides sufficient information to detect and locate all types of ground faults (line side, DC bus, and load side) while significantly simplifying the detection system.
3Reliability
If ground fault detection is performed on high resistance ground networks, then ground faults can be detected, but the fault current is small and negligible making it difficult to reliably separate faults from large changes of the load
Solution Approach 1:
The patent focuses on detecting only the fundamental frequency component of the midpoint-to-ground voltage, which is sufficient to identify ground faults. By analyzing specifically the fundamental frequency (e.g., 60 Hz or 50 Hz) rather than the entire voltage spectrum, the system can reliably distinguish ground faults from load changes even in high resistance ground networks where fault currents are small.
Data Source
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AI summary
A method is provided for detection of a ground fault in a high resistance network in a voltage source power conversion circuit comprising a power converter that converts incoming AC power to DC power applied to a DC bus and an inverter that converts DC power from the DC bus to output AC power. The method includes detecting a midpoint-to-ground voltage between a low side of the DC bus and a ground potential and detecting the presence of a ground fault in a high resistance network based upon the detected midpoint-to-ground voltage.