Energy Storage Ground Fault Detection Across the Electrical Midpoint
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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 and control unit that utilize co-phasal harmonic components measured at the AC and DC sides to detect ground faults by monitoring increases or decreases in these components, combined with pole unbalance voltage to locate the fault, and incorporate converters to generate reference harmonic voltages for comparison.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional ground fault detection based on pole voltage is used, then ground faults near DC poles can be detected, but ground faults near the electrical midpoint cannot be detected
Solution Approach 1:
The patent transitions from single-dimensional pole voltage measurement to multi-dimensional measurement by incorporating both AC side phase voltages and DC side pole voltages, and further extends to frequency domain analysis by extracting harmonic components. This dimensional expansion enables detection of ground faults at any location including the electrical midpoint that was invisible to conventional single-point measurement
Solution Approach 2:
The patent changes the detection parameter from fundamental pole voltage to co-phasal harmonic components (particularly 3rd, 5th, 7th harmonics). By transforming the measurement parameter to harmonic frequency domain, the system gains sensitivity to ground faults near the electrical midpoint, as these faults create characteristic harmonic patterns that differ from normal operating conditions
2Device complexity
If only pole voltage measurement is used, then the detection method is simple, but detection accuracy for midpoint faults is insufficient
Solution Approach 1:
The patent segments the detection system into three independent measurement channels: AC side phase-to-ground voltage measurement, DC side pole-to-ground voltage measurement, and harmonic component extraction. Each segment processes specific frequency components and spatial information, allowing comprehensive fault detection while maintaining modular simplicity in implementation
Solution Approach 2:
The patent introduces co-phasal harmonic components as an intermediary parameter that bridges the gap between AC side and DC side measurements. These harmonic components serve as a mediator that captures coupling effects between AC and DC sides, enabling indirect detection of ground faults that do not directly manifest in pole voltage but create characteristic harmonic patterns
Data Source
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AI summary
There is disclosed herein a method (100) for detecting a ground fault in an energy storage system (20) comprising at least one string (21) having a plurality of energy storage modules (22). The string is connected between a first direct current, DC, pole (12) and a second DC pole (14). The first DC pole and the second DC pole are connected to an AC side through a respective converter (10A, 10B). The method comprises determining (110) a first co-phasal harmonic component based on at least one phase-to-ground voltage (112A-112C) measured at the AC side, determining (120) a second co-phasal harmonic component based on at least one pole-to-ground voltage (122A, 122B) measured at the DC side, and determining (130) 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.