DC Combiner Box Multipole Switching for PV Reverse Fault Isolation
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Solution Overview
Problem
In photovoltaic systems, reverse connection faults in strings can cause backflow currents, damaging photovoltaic modules due to the limited current-carrying capacity of antiparallel diodes, and existing solutions are complex and costly, with high hardware requirements.
Innovation Solution
A photovoltaic system with a fault isolation circuit using a multipole switch that connects photovoltaic strings in groups to reduce the number of switches, allowing the entire switch to turn off in case of a reverse connection fault, thereby protecting the system and simplifying the hardware structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple photovoltaic strings are connected in parallel to increase capacity, then the power generation capacity increases, but the risk of backflow current damage increases when reverse connection occurs
Solution Approach 1:
The patent applies preliminary action by equipping each photovoltaic string with an isolation switch before parallel connection. These switches are opened in advance to prevent backflow current from damaging reversely connected strings, while allowing normal operation when properly connected. This proactive measure enables safe parallel connection of multiple strings to increase capacity without the harmful backflow effect.
2Reliability
If individual isolation switches are installed for each photovoltaic string to prevent backflow, then fault isolation capability improves, but the hardware complexity and cost increase
Solution Approach 1:
The patent merges multiple individual isolation switches into a single multipole switch that can simultaneously control multiple photovoltaic strings. This unified switch structure provides the same fault isolation capability as individual switches but with reduced hardware complexity and lower cost, while maintaining the ability to isolate reversely connected strings effectively.
Solution Approach 2:
The multipole switch serves multiple functions: it acts as an isolation switch for each photovoltaic string, a protection device against backflow current, and a control element that can be uniformly managed. This multi-functional design replaces multiple specialized components with a single universal device, reducing overall system complexity while maintaining reliability.
3Device complexity
If a multipole switch is used to reduce the number of switches, then hardware complexity decreases, but the requirement for linkage operation increases
Solution Approach 1:
The multipole switch is designed with automatic linkage operation capability, where the control system automatically coordinates the opening and closing of all poles simultaneously. This self-service feature eliminates the need for manual coordination of multiple switches, making the reduced hardware configuration equally easy to operate while maintaining effective fault isolation.
Data Source
AI summary
This application discloses a photovoltaic system, a direct-current combiner box, and a fault isolation method. The photovoltaic system includes a fault isolation circuit and a DC/DC conversion circuit. A first end of the fault isolation circuit is connected to N photovoltaic strings, and a second end of the fault isolation circuit is connected to an input end of the DC/DC conversion circuit. The fault isolation circuit includes a multipole switch, and each group of photovoltaic strings in the N photovoltaic strings is connected to an input end of a power conversion circuit through one pole of switch in the multipole switch. Each group of photovoltaic strings includes at least two photovoltaic strings. When a reverse connection fault occurs in the N photovoltaic strings, the entire multipole switch is turned off in linkage.