PV String Fault Isolation With Shared Protection Switches
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Solution Overview
Problem
The existing photovoltaic power generation systems face a high cost issue due to the high number of protection switches required in fault isolation circuits, which increases the cost and volume of the protection switch unit without effectively reducing the withstand voltage level.
Innovation Solution
The proposed solution involves a fault protection method and device that reduces the number of protection switches by sharing protection switches between co-positive and co-negative power conversion units, allowing at most two photovoltaic strings to be connected in parallel, and using at least three protection switches to disconnect corresponding photovoltaic strings, thereby maintaining a low-voltage protection switch with a lower cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a direct current switch with disconnection function is used in the fault isolation circuit, then fault isolation between photovoltaic strings and power conversion units is achieved, but the cost and volume of the protection switch unit increase
Solution Approach 1:
The system divides photovoltaic strings into multiple groups (first group, second group, third group) with dedicated protection switches for each group. This segmentation allows selective disconnection of specific string groups during faults, reducing the need for high-voltage rated switches across all strings and lowering overall protection switch unit cost and volume while maintaining fault isolation capability
Solution Approach 2:
Different protection switch configurations are applied to different string groups based on their connection characteristics. The first protection switch controls first and second photovoltaic strings, while the second protection switch controls the third photovoltaic string. This localized approach optimizes switch ratings and reduces total cost while ensuring adequate fault isolation for each group
2Reliability
If multiple protection switches are used to disconnect photovoltaic strings, then fault isolation is improved, but the number of protection switches increases cost
Solution Approach 1:
Multiple photovoltaic strings are merged into groups that share common protection switches. The first protection switch manages disconnection for both first and second photovoltaic strings, while the second protection switch manages the third photovoltaic string. This merging reduces the total number of protection switches needed while maintaining effective fault isolation through coordinated control
Data Source
AI summary
Provided are a photovoltaic power generation system and a fault protection method and device thereof, a combiner box, and an inverter. The method includes: disconnecting, when there are co-positive power conversion units or co-negative power conversion units in the plurality of power conversion units and the protection switch units corresponding to the co-positive power conversion units or the co-negative power conversion units share a protection switch when connected to their corresponding photovoltaic string units, part or all of the plurality of protection switch units in response to detecting a fault in the photovoltaic power generation system, such that at most two photovoltaic strings in each of the corresponding photovoltaic string units are connected in parallel. When the protection switch units corresponding to the co-positive power conversion units or the co-negative power conversion units are disconnected, their corresponding photovoltaic strings are disconnected separately by at least three protection switches.