PV Module String Fault Detection Using MLSD Switch-On Transients
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Solution Overview
Problem
The open circuit voltage of photovoltaic modules varies with module type, temperature, and sunlight, making it difficult to accurately determine the number of correctly connected modules in a string, especially with Module Level Shutdown Devices (MLSDs), leading to uncertain installation verification.
Innovation Solution
A method and apparatus using Power Line Communication (PLC) to transmit a Permission to Operate (PTO) signal to MLSDs, capturing switch-on transients, analyzing the resulting string voltage waveform to determine the number of correctly installed modules through Discrete Fourier Transform (DFT), and comparing with a predefined set number to verify correct installation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If open circuit voltage measurement is used to determine the number of photovoltaic modules, then the measurement process is simple, but the measurement precision deteriorates due to voltage variations with module type, temperature, and sunlight
Solution Approach 1:
The patent extracts the identification signal from the power cable and uses it separately for module identification purposes, rather than relying on voltage measurement alone. The detector device extracts identification signals from each module through the power line communication, enabling accurate module counting independent of voltage variations caused by different module types, temperatures, or sunlight conditions.
2Device complexity
If conventional voltage-based detection is used, then the device complexity is low, but the reliability of installation verification deteriorates due to inability to verify correct connection
Solution Approach 1:
The patent introduces an intermediary identification signal transmitted through power line communication as a mediator between the modules and detector. This identification signal serves as a reliable indicator of correct module installation and connection, allowing the detector to verify installation reliability without significantly increasing system complexity. The MLSD devices also act as intermediaries by generating and transmitting these identification signals.
3Adaptability or versatility
If module type variations are accommodated, then the adaptability increases, but the measurement precision of module counting deteriorates due to different open circuit voltages
Solution Approach 1:
The patent segments the module identification process by assigning unique identification signals to each module type and detecting these signals individually through power line communication. Instead of relying on aggregate voltage measurements that vary with module type, the system identifies each module's specific identification signal, enabling accurate counting that adapts to different module types while maintaining precision.
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
Provides reliable detection of faulty connections by ensuring accurate counting of installed modules, enabling automatic countermeasures if incorrect installations are detected, and ensuring all modules are correctly connected and operational.
Implementation Method 1
transmitting by the detector device a Permission to Operate, PTO, signal through its string loop interface to a chain of serially connected Module Level Shutdown Devices, MLSDs, of the Photovoltaic Modules string using Power Line Communication, PLC
Implementation Method 2
capturing by the detector device a string voltage waveform applied by the chain of serially Module Level Shutdown Devices, MLSDs, of the Photovoltaic Module string to the string loop interface of the detector device as a result of switch-on transients generated by the Module Level Shutdown Devices, MLSDs
Data Source
AI summary
A method and apparatus are provided for detection of faulty installations of Photovoltaic Modules equipped with associated Module Level Shutdown Devices, MLSDs, connected serially as a chain within a string of Photovoltaic Modules to a string loop interface of a detector device. The method comprises the steps of: transmitting a Permission to Operate, PTO, signal through its loop string interface to the chain of MLSDs, using Power Line Communication, PLC; capturing a string voltage waveform provided by the chain of serially MLSDs of the Photovoltaic Module string to the loop string interface of the detector device as a result of switch-on transients generated by the MLSDs in response to the PTO signal received by the chain of MLSDs from the loop string interface of the detector device, wherein switch-on delays of the generated switch-on transients are spread in a predefined maximum delay time period; and analyzing the captured string voltage waveform, Vstr, provided by the chain of MLSDs of the Photovoltaic Module string to determine a number, N, of Photovoltaic Modules and associated MLSDs within the Photovoltaic Module string being installed correctly within the Photovoltaic Module string.