High-Voltage DC Ground Isolation Monitoring via Shunt Resistor Trend Analysis
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Solution Overview
Problem
Existing methods for detecting ground isolation faults in electric motor control circuits are prone to measurement errors and fail to accurately detect faults due to signal limitations and resonance issues, leading to potential capacitor damage and inverter failure.
Innovation Solution
An electrically isolated high-voltage direct-current circuit that monitors the positive and negative DC electric power buses, periodically samples electrical signals, calculates ground isolation indexes, and characterizes trends to detect potential faults by comparing them to expected trends, thereby identifying deviations that indicate ground isolation issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current sensing devices are used to measure electric current through each phase cable and arithmetically sum them to detect ground isolation faults, then fault detection capability is provided, but measurement errors are cumulative and can cause error in the overall current signal
Solution Approach 1:
The patent introduces a high-precision shunt resistor as an intermediary measurement element through which all three phase currents flow. This single shunt resistor replaces multiple current sensing devices, eliminating cumulative measurement errors while maintaining fault detection capability. The shunt resistor serves as a common reference point that accurately reflects the sum of all phase currents without the compounding errors of multiple sensors.
2Measurement precision
If phase current sensors are used with magnetic and electrical response characteristics, then current measurement is enabled, but bandwidth/step response limitations and sensor saturation occur causing missed fault detection
Solution Approach 1:
The patent replaces magnetic-based current sensors with an electrical measurement system using a shunt resistor and voltage measurement. This substitution eliminates the magnetic response limitations and saturation issues inherent in traditional current sensors, providing superior bandwidth and step response characteristics while maintaining accurate current measurement capability.
3Reliability
If data sampling is performed at or near zero crossing to detect ground isolation faults, then fault detection is attempted, but resonance elements in fault impedance cause fault current to be aliased out
Solution Approach 1:
The patent employs continuous monitoring and trend analysis of the shunt resistor voltage signal, comparing actual measurements against expected trends based on inverter switching patterns. This feedback mechanism allows the system to detect ground isolation faults even when individual samples may be affected by resonance aliasing, as the cumulative trend analysis reveals deviations that indicate fault conditions.
4Reliability
If DC voltage sensors are used to measure voltage between positive/negative DC buses and chassis ground, then ground isolation fault detection is enabled, but bandwidth and response time limitations prevent timely fault detection
Solution Approach 1:
The patent uses a low-inductance shunt resistor as an intermediary element that provides a direct electrical path for measuring DC bus voltage deviations. This shunt-based measurement system has superior bandwidth and response time compared to traditional DC voltage sensors, enabling timely detection of ground isolation faults while maintaining measurement accuracy.
Data Source
AI summary
An electrically isolated high-voltage direct-current electric circuit is monitored. Electrical signals are periodically sampled, and ground isolation indexes are calculated. A trend corresponding to trend elements is characterized. The characterized trend is compared with an expected trend with deviations indicative of potential faults.