PV DC Combiner Protection Switch for Fast Short-Circuit Isolation
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Solution Overview
Problem
Existing photovoltaic power generation systems face challenges in effectively protecting photovoltaic units and lines from short-circuit currents due to high fusing currents of fuses, leading to prolonged fuse activation times and increased cable costs.
Innovation Solution
Implementing a photovoltaic power generation system with protection switches and DC-DC converters that include a release mechanism to disconnect the switch mechanism when a short-circuit fault occurs, eliminating the need for fuses and reducing cable costs by relocating Y wire harnesses to the photovoltaic unit side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fuse is connected in series to protect the photovoltaic unit and line, then the photovoltaic unit and line are protected from short-circuit current, but the fusing current is relatively high causing long blow time and ineffective protection
Solution Approach 1:
The patent changes the protection parameter from high-current fuse operation to low-current differential protection. By using current transformers to detect small current differences (difference current) that indicate short-circuit conditions, the system achieves rapid protection without waiting for high fusing currents to accumulate, directly resolving the contradiction between protection effectiveness and response time.
Solution Approach 2:
The patent replaces the mechanical/thermal fuse system with an electromagnetic detection and control system. Current transformers electromagnetically detect short-circuit conditions, and a control circuit electronically triggers thyristors to open circuit breakers, substituting the slow thermal-mechanical fuse blowing process with fast electromagnetic detection and electronic control, achieving rapid protection.
2Reliability
If fuses are used for protection, then short-circuit protection is provided, but additional control circuits and complex cable arrangements are required
Solution Approach 1:
The patent makes the existing circuit breaker control system perform dual functions: normal operation control and short-circuit protection. The same control circuit that operates circuit breakers for normal switching also triggers them for protection when short-circuits are detected, eliminating the need for separate protection control circuits and reducing overall system complexity.
Solution Approach 2:
The protection system uses the existing circuit breaker's own control mechanism to provide protection. When current transformers detect a short-circuit, they trigger the circuit breaker's control circuit to open the breaker, making the circuit breaker self-protecting without requiring external protection devices or complex additional control systems.
Data Source
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AI summary
This application discloses a photovoltaic power generation system, a photovoltaic inverter, and a direct current combiner box, and relates to the field of photovoltaic power generation technologies. The photovoltaic power generation system includes a protection switch and a plurality of DC-DC converters. Each DC-DC converter includes a direct current bus, a DC-DC circuit, and at least one input interface. The input interface is configured to connect to a photovoltaic unit. The photovoltaic unit includes at least one photovoltaic module. The input interface is connected to the direct current bus by using the protection switch, the direct current bus is connected to an input end of the DC-DC circuit, and an output end of the DC-DC circuit is an output end of the DC-DC converter. The protection switch includes a release and a switch mechanism that are connected in series. The release is configured to: when a short-circuit fault occurs on a line in which the release is located, control the switch mechanism to be disconnected. By using the photovoltaic power generation system, the photovoltaic unit and the line can be effectively protected when a short circuit occurs on the photovoltaic unit or the line.