DC/DC Converter Reverse Current Protection in PV Strings
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Solution Overview
Problem
In photovoltaic generator systems with multiple strings connected in parallel, reverse currents can cause overloading and potential damage, especially when one string is shaded or connected with incorrect polarity, leading to safety risks such as overheating and fire.
Innovation Solution
Implementing a method and device using DC/DC converters with current sensors to detect and inhibit reverse currents, where the control system manages the DC/DC converters to interrupt reverse currents, utilizing buck or boost converter configurations to prevent overloading without additional components, thereby ensuring fail-safe operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple strings are connected in parallel to a common DC link, then the power output and energy generation capability are improved, but the risk of reverse current flow and string overloading increases
Solution Approach 1:
A current sensor is introduced as an intermediary component between the strings and the DC link to detect reverse current flow. The sensor provides measurement data to a control system that can then activate blocking switches to prevent reverse current, thus protecting the strings while maintaining the parallel connection architecture for high power output.
Solution Approach 2:
The system implements feedback control by continuously monitoring the current direction and magnitude through current sensors, and using this information to control blocking switches. When reverse current is detected, the control system activates the appropriate blocking switches to interrupt the reverse current flow, ensuring string protection while allowing normal forward current flow for power generation.
2Reliability
If reverse current blocking diodes are installed in each string, then reverse current protection is improved, but the device complexity and hardware requirements increase
Solution Approach 1:
The blocking switches serve multiple functions: they act as normal switching elements for power conversion operations and simultaneously provide reverse current protection when activated by the control system. This multi-functionality eliminates the need for separate blocking diodes in each string, reducing hardware complexity while maintaining protection capability.
Solution Approach 2:
The patent replaces passive mechanical/physical blocking diodes with active electronic switching elements controlled by an electronic control system. This substitution allows for more flexible and intelligent protection, where the blocking action is activated only when reverse current is detected, rather than being permanently present as with diodes.
3Reliability
If current sensors and control systems are added to detect and inhibit reverse currents, then string protection is improved, but the device complexity increases
Solution Approach 1:
The control system is segmented and distributed, with each string having its own current sensor and associated blocking switch controlled by the central control unit. This segmentation allows for independent monitoring and protection of each string, simplifying the control logic for each individual string while providing comprehensive system-wide protection.
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
This approach effectively prevents reverse current-induced overloading and ensures safe operation of photovoltaic generator systems by minimizing hardware requirements and avoiding unnecessary tripping, thus preventing potential fires and maintaining system integrity.
Implementation Method 1
the current flowing through each of the DC/DC converters is detected
Implementation Method 2
a reverse current flowing through one of the DC/DC converters is inhibited by the control of the DC/DC converter
Data Source
AI summary
In order to protect reverse currents, several strings of a photovoltaic generator, which are connected in small groups respectively via a DC/DC-converter, parallel to a common DC voltage intermediate circuit, the current which flows over each of the DC/DC-converter is detected and if a reverse current is detected flowing through one of the DC/DC converters, the converter is stopped by controlling the DC/DC-converter.