Energy Storage Ground Fault Detection Using Co-Phasal Harmonics
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Solution Overview
Problem
Conventional methods struggle to detect ground faults, particularly near the electrical midpoint of energy storage systems, leading to safety risks and operational disruptions.
Innovation Solution
A method involving the determination of co-phasal harmonic components based on phase-to-ground and pole-to-ground voltages at the AC and DC sides, respectively, to identify ground faults, and optionally using pole unbalance voltage to locate them.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional pole voltage monitoring is used to detect ground faults, then detection is simple for pole-location faults, but ground faults near the electrical midpoint cannot be detected
Solution Approach 1:
The patent transitions from monitoring only pole voltages (1D) to incorporating AC side phase voltages and their harmonic components (adding dimensional complexity). By analyzing the relationship between AC phase voltages and DC pole voltages across multiple dimensions, the system can detect ground faults anywhere in the system, including near the electrical midpoint where conventional single-point monitoring fails.
Solution Approach 2:
The patent creates a universal detection method that works for all ground fault locations by establishing a relationship between AC side phase voltages and DC side pole voltages. The detection system serves multiple functions: it detects pole-location faults, midpoint faults, and faults anywhere in between, making the monitoring system universally applicable throughout the entire energy storage system.
2Reliability
If ground fault detection is improved to cover all locations, then safety is enhanced, but system complexity increases
Solution Approach 1:
The patent employs feedback mechanisms by continuously monitoring AC phase voltages, calculating harmonic components, and comparing them against expected relationships with DC pole voltages. When deviations are detected, the system provides feedback signals to indicate ground fault conditions, enabling reliable detection without requiring overly complex additional hardware.
Solution Approach 2:
The patent uses AC side phase voltage harmonic components as an intermediary to indirectly detect DC side ground faults. Instead of directly monitoring every possible fault location on the DC side, the system uses the AC-DC voltage relationship as a mediator, simplifying the detection architecture while maintaining comprehensive coverage.
Data Source
AI summary
There is disclosed herein a method for detecting a ground fault in an energy storage system comprising at least one string having a plurality of energy storage modules. The string is connected between a first direct current (DC) pole and a second DC pole. The first DC pole and the second DC pole are connected to an AC side through a respective converter. The method comprises determining a first co-phasal harmonic component based on at least one phase-to-ground voltage measured at the AC side, determining a second co-phasal harmonic component based on at least one pole-to-ground voltage measured at the DC side, and determining presence of a ground fault if the first co-phasal harmonic component increases and/or the second co-phasal harmonic component decreases. There is also disclosed herein a control unit and an energy storage system.