Inverter Neutral Relay Detection Using Bus Neutral-Point Potential
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Solution Overview
Problem
Existing methods for detecting neutral relays in inverters are inadequate, leading to ineffective sticking detection, which is crucial for ensuring normal operation during abnormal system conditions.
Innovation Solution
A method involving applying a voltage disturbance to the bus neutral point of an inverter circuit to detect neutral relay sticking by 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
1Reliability
If common sticking detection methods are used, then detection can be performed on phase relays, but detection on neutral relays is ineffective
Solution Approach 1:
The patent changes the detection parameter from phase voltage to neutral point potential. By measuring 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 reliability in identifying sticking states.
Solution Approach 2:
The patent introduces a balancing bridge circuit as an intermediary to apply voltage disturbance to the neutral point and measure potential changes. This intermediary mechanism enables indirect detection of neutral relay sticking state through potential measurement rather than direct current measurement.
2Measurement precision
If voltage disturbance is applied to detect neutral relay sticking, then detection accuracy is improved, but system disturbance increases
Solution Approach 1:
The patent applies partial action by using a small voltage disturbance (e.g., 10-50V) rather than full system voltage. This partial disturbance is sufficient to generate measurable potential changes at the neutral point for detecting relay sticking, while minimizing impact on the overall system operation.
Solution Approach 2:
The voltage disturbance is applied periodically during specific detection windows rather than continuously. The system applies disturbance only when conditions are appropriate (e.g., when neutral relay should be closed), minimizing overall system disturbance while maintaining detection capability.
Data Source
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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.