Inverter Isolation Monitoring via Leakage Current and Resistance
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Solution Overview
Problem
Existing methods for monitoring the isolation of an IT-Grid with respect to ground are slow in detecting small changes and dangerous isolation faults, particularly on the alternating current side of the inverter, due to the need for stable charge distribution and long measurement times, which can lead to delayed recognition of faults and potential safety hazards.
Innovation Solution
Monitoring both the isolation resistance and leakage current via the inverter, using a combination of reference resistors and a current measurement device with an induction coil to quickly detect short circuits and isolation faults by comparing the leakage current with a threshold value, allowing for immediate shutdown or warning, and differentiating between faults on the direct and alternating current sides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If measurement is performed by waiting for stable charge distribution over capacitances, then measurement accuracy is improved, but detection speed deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-charging the reference resistor to the potential of the conductor before measurement. This eliminates the need to wait for stable charge distribution during actual measurement, as the capacitor is already charged to the correct potential. The measurement can immediately begin by switching the reference resistor to the second conductor, achieving both accuracy and speed.
Solution Approach 2:
The patent implements dynamics by using a switchable measurement arrangement that can rapidly reconfigure between measuring different conductors. The system dynamically adapts by pre-charging the reference resistor to match the potential of the currently measured conductor, then quickly switching to measure the next conductor without waiting for charge stabilization. This dynamic reconfiguration enables fast sequential measurement of all conductors.
2Measurement precision
If inverter is deactivated for isolation resistance measurement, then measurement accuracy is improved, but system availability deteriorates
Solution Approach 1:
The patent enables dynamic measurement during inverter operation by rapidly switching between conductors and using pre-charging techniques. The measurement cycle is so fast that it completes before the inverter needs to be deactivated, allowing continuous monitoring without interrupting power conversion. This dynamic approach eliminates the trade-off between measurement accuracy and system availability.
Solution Approach 2:
The patent implements periodic measurement action where isolation resistance is continuously monitored at regular intervals during inverter operation. By using fast switching and pre-charging, each measurement cycle completes quickly, allowing frequent periodic measurements without deactivating the inverter. This ensures continuous monitoring while maintaining high system availability.
3Measurement precision
If measurement time is extended to capture stable charge distribution, then detection accuracy is improved, but response time to faults deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-charging the reference resistor to the potential of the conductor being measured. This eliminates the time-consuming waiting period for charge distribution stabilization during actual measurement. The pre-charged reference resistor can be immediately switched to measure isolation resistance, achieving both high accuracy and fast response to faults.
Solution Approach 2:
The patent implements skipping by rapidly switching between measurement phases without waiting for intermediate stabilization. The system rushes through the measurement process by pre-charging components beforehand and using fast switching transitions, capturing isolation resistance values before charge distribution has time to stabilize naturally. This rushing through the measurement process dramatically reduces fault recognition time while maintaining accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables rapid detection of small changes and dangerous isolation faults on both sides of the inverter, ensuring timely safety measures and accurate identification of fault locations, reducing the risk of harm to humans and equipment.
Implementation Method 1
a current measurement device with an induction coil to quickly detect short circuits and isolation faults
Data Source
AI summary
For monitoring the isolation of an IT-grid with respect to ground, an inverter connecting a direct current side with an alternating current side of the IT-grid and a photovoltaic device on the direct current side of the IT-grid, at least one isolation resistance of the direct current side with respect to ground is monitored for falling below a resistance threshold value while the inverter is running, and additionally a leakage current via the inverter towards ground is monitored for exceeding a current threshold value.