PV Relay Fault Detection Using Inverter Phase-Gated Shutdown
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Solution Overview
Problem
Existing photovoltaic systems face challenges in accurately detecting faulty relays, leading to potential risks due to undetected stuck relays, which are often misidentified as alternating current grid-to-ground short circuits.
Innovation Solution
A photovoltaic system with a controller that synchronizes the frequency and phase of the filter capacitor voltage with the alternating current grid voltage, stops the inverter's switch transistor action within a preset phase range, and sends fault alarms based on a voltage difference threshold to accurately detect relay faults.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the controller stops sending PWM driver gating signals to the inverter to detect relay faults, then relay fault detection capability is improved, but false detection as AC grid-to-ground short circuit increases due to low grid-to-ground voltage
Solution Approach 1:
The controller performs preliminary actions by stopping the PWM driver gating signals before detecting relay faults. This preliminary action prepares the system in a specific state where the relay can be accurately detected without false positives from low grid-to-ground voltage conditions
Solution Approach 2:
The controller changes the operating parameters of the inverter by adjusting the PWM driver gating signals. By modifying these parameters, the system transitions to a detection mode that enables accurate relay fault identification while avoiding the condition that causes false short circuit detection
2Measurement precision
If the controller stops driving switch transistors in the inverter within a preset phase range, then relay fault detection accuracy is improved, but system operation is interrupted
Solution Approach 1:
The controller implements periodic action by stopping the driving of switch transistors only within a preset phase range during detection periods. This periodic interruption allows accurate relay fault detection while minimizing impact on overall system operation, as the interruption is limited to specific phases rather than continuous operation
Data Source
AI summary
A photovoltaic system, a relay detection method, and a power supply system. When a fault, for example, sticking of the relay is detected, the controller stops sending a PWM driver gating signal to the inverter, and stops driving of a switch transistor in the inverter, and the inverter stops outputting power, and then determines whether a voltage difference between two ends of the relay is greater than a preset value, to determine whether the relay is faulty. The controller stops sending the PWM driver gating signal to the inverter only within a preset phase range of a voltage of the filter capacitor, to ensure that the voltage of the filter capacitor has a large value. Because the voltage of the filter capacitor is large, an alternating current grid-to-ground voltage is pulled up, to avoid detecting the fault as an alternating current grid-to-ground short circuit.