Inverter Grid Fault Detection via Impedance Observation
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Solution Overview
Problem
Existing methods for detecting grid faults in power supply grids, particularly in photovoltaic installations, face limitations as they often disturb the grid and lead to unreliable results or unstable operating states, failing to accurately distinguish between islanding situations and faults that need to be ridden through.
Innovation Solution
A detection method that determines grid impedance and its rate of change over time, comparing these values with predetermined limits to differentiate between islanding situations and faults that require ride-through, using a state observer to emulate the inverter's section and filter input variables with bandpass and band rejection filters to determine grid impedance without affecting the power supply grid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If active methods for detecting islanding are used to distinguish between grid failures and islanding situations, then detection capability is improved, but the methods disturb each other and lead to unreliable results or unstable operating states
Solution Approach 1:
The patent introduces an intermediary approach by using passive impedance measurement instead of active disturbance methods. The inverter measures grid impedance by observing the relationship between grid voltage and current without actively injecting disturbance signals, thereby avoiding interference with other inverters' detection methods while maintaining reliable islanding detection capability
Solution Approach 2:
The patent creates a virtual model of the grid impedance characteristics by measuring and analyzing the relationship between voltage and current. This copied impedance information allows the system to detect islanding situations without physically disturbing the grid, enabling reliable detection while avoiding the instability caused by multiple active methods interacting
2Measurement precision
If active disturbance methods are used to detect grid faults, then detection accuracy is improved, but the power supply grid becomes disturbed and unstable
Solution Approach 1:
The patent uses passive impedance measurement as an intermediary technique that extracts grid fault information without actively disturbing the grid. By analyzing the natural relationship between grid voltage and current, the system achieves accurate fault detection while avoiding the harmful disturbances associated with active injection methods
Solution Approach 2:
The inverter performs self-measurement of grid impedance by observing its own voltage and current measurements. This self-service approach eliminates the need for external disturbance signals, allowing accurate detection of grid faults without introducing harmful disturbances to the power supply grid
Data Source
AI summary
The disclosure relates to a detection method for an inverter for detecting a grid fault in a power supply grid, includes determining a grid impedance (Z) and/or the rate of change thereof with respect to time (dZ/dt) and/or a rate of change of an absolute value of the grid impedance (Z) with respect to time (d|Z|/dt), comparing the absolute value and/or a real part and/or an imaginary part of the grid impedance (Z) and/or the rate of change thereof with respect to time (dZ/dt) and/or the rate of change of the absolute value of the grid impedance (Z) with respect to time (d|Z|/dt) with respective predetermined limit values. The method also includes detecting a grid fault state based on the comparison, wherein a distinction is drawn between an islanding situation (AID) and a fault ride through (FRT) situation, and signaling an existing islanding situation (AID) or a fault ride through (FRT) situation as a grid fault state. The disclosure additionally relates to an inverter that is arranged to perform the method.