Neutral Relay Sticking Detection Through Bus Neutral Potential
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Solution Overview
Problem
Existing methods for detecting neutral relays in inverters are ineffective, leading to potential issues with relay sticking during abnormal system conditions.
Innovation Solution
A method for detecting neutral relays by applying a voltage disturbance to the bus neutral point and measuring potential changes relative to the grid neutral point, using a balancing bridge circuit to adjust voltage differences, and determining the sticking state based on potential change information and a threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If common sticking detection methods are used for phase relays, then phase relay detection is effective, but neutral relay detection is ineffective
Solution Approach 1:
The patent changes the detection parameter from phase voltage to neutral point potential. By monitoring the potential change of the neutral point relative to ground when a voltage disturbance is applied, the detection method becomes effective for neutral relays while maintaining high detection accuracy.
Solution Approach 2:
The patent introduces a balancing bridge circuit as an intermediary to apply voltage disturbance to the neutral point and measure the potential change. This intermediary mechanism enables the detection of neutral relay sticking states without directly interfering with the relay operation.
2Measurement precision
If voltage disturbance is applied to detect neutral relay sticking, then detection accuracy improves, but system disturbance increases
Solution Approach 1:
The patent applies a small partial voltage disturbance to the neutral point through the balancing bridge circuit, rather than applying full system voltage. This partial action is sufficient to detect relay sticking states while minimizing the harmful disturbance to the overall system operation.
Solution Approach 2:
The balancing bridge circuit serves as an intermediary that isolates the voltage disturbance from the main power system. It applies only the necessary minimal disturbance to the neutral point for detection purposes, reducing the harmful effects on the broader system.
Data Source
AI summary
Provided is a method for detecting a neutral relay, belonging to the field of inverters. The method for detecting the neutral relay includes: applying a voltage disturbance to the bus neutral point when other neutral relays except a target neutral relay among the at least one series-connected neutral relay are closed; acquiring potential change information of the bus neutral point relative to the grid neutral point within a period during which the voltage disturbance is applied; and determining a sticking state of the target neutral relay based on the potential change information and a target threshold.