PV Converter Shutdown Isolation for Safe Series Strings
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Solution Overview
Problem
Photovoltaic power generation systems face safety hazards due to high voltages remaining in arrays during shutdown, as existing solutions cannot disconnect photovoltaic components connected in series, violating safety standards like NEC 2017 which requires voltages within a safe range after shutdown.
Innovation Solution
A converter system with a switching transistor that disconnects photovoltaic units in series during shutdown, ensuring no dangerous high voltage exists in the array, using a controller to manage the switching transistor and power circuit to limit output voltage and current, and an auxiliary power supply for continuous operation monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple photovoltaic components are connected in series to obtain high output voltage, then the output voltage is improved, but dangerous high voltage remains in the photovoltaic array during shutdown
Solution Approach 1:
The photovoltaic array is segmented into multiple strings, each with its own converter. During shutdown, each converter can independently disconnect its associated photovoltaic string from the common DC bus, isolating the high voltage segments and allowing safe shutdown of individual modules while maintaining system architecture flexibility.
Solution Approach 2:
A common DC bus serves as an intermediary between multiple photovoltaic strings and the inverter. This bus allows individual strings to be connected or disconnected without affecting other strings, enabling selective isolation of high voltage segments during shutdown while maintaining the ability to aggregate power from multiple strings during normal operation.
2Productivity
If multiple photovoltaic components are connected in series to maximize power generation efficiency, then energy loss from parameter mismatches is reduced, but safety hazards increase due to inability to disconnect during shutdown
Solution Approach 1:
The system dynamically reconfigures the photovoltaic array topology based on operational state. During normal operation, multiple strings are connected in series through the common DC bus to maximize power generation efficiency. During shutdown, the converter switches to disconnect individual strings, dynamically adapting the system configuration to meet safety requirements while preserving performance optimization capabilities.
Solution Approach 2:
Each converter module independently manages its associated photovoltaic string, performing self-service shutdown by disconnecting only its own string from the common DC bus when shutdown is required. This distributed control approach ensures safety without requiring system-wide reconfiguration, allowing each module to autonomously protect itself while maintaining overall system functionality.
Data Source
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AI summary
This application provides a converter, a method, and a system applied to a photovoltaic power generation system. The converter includes a controller and at least one switching transistor. The converter supports access of at least two photovoltaic units, the at least two photovoltaic units are connected in series inside the converter by using the switching transistor, and the photovoltaic unit is formed by at least one photovoltaic component connected in series and in parallel. The controller is configured to: when a shutdown instruction is received or a heartbeat instruction is lost within a preset time period, control the switching transistor to be disconnected, so that any two photovoltaic units connected in series are disconnected. According to the converter provided in this application, any two photovoltaic units connected in series can be disconnected when the photovoltaic power generation system is shut down. In this way, no dangerous high voltage exists in a photovoltaic array formed by the photovoltaic units, thereby improving safety of the photovoltaic power generation system.