Photovoltaic String Voltage Limiting Circuit with Dynamic Section Control
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Solution Overview
Problem
Existing photovoltaic string voltage limiting technologies often result in performance penalties due to short-circuiting of strings, which can lead to reverse current situations that damage equipment, and fail to independently manage string voltage across multiple parallel strings effectively.
Innovation Solution
A circuit and method that divide a photovoltaic string into sections, using a bypass switch and circuit breaker controlled by a controller to dynamically adjust threshold values based on module voltage, allowing for independent voltage limiting of each string without causing reverse currents, and enabling seamless transition between long and short states to maintain optimal power generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a portion of the string is short-circuited to reduce voltage, then the string voltage is reduced below the maximum permissible value, but power is lost due to the short-circuiting of modules
Solution Approach 1:
The string is divided into multiple sections with individual control capability. Each section can be independently disconnected or bypassed, allowing selective voltage reduction without short-circuiting entire modules. This segmentation enables precise voltage management while maintaining power generation from unaffected sections.
Solution Approach 2:
The circuit configuration is made dynamic through controllable switches that can change the circuit topology in real-time. The system dynamically adjusts between series and parallel connections of string sections based on voltage conditions, enabling adaptive voltage control without permanent power loss.
2Stress or pressure
If parallel strings are short-circuited to limit voltage, then voltage is reduced, but reverse current can flow from longer strings damaging the shortened strings
Solution Approach 1:
Each string is segmented into independently controllable sections with individual switching devices. This allows each string to be managed separately, preventing reverse current flow between strings by isolating shortened sections through dedicated switches rather than common short-circuiting.
Solution Approach 2:
Controllable switches act as intermediary elements between string sections and the inverter. These switches mediate the connection state, allowing voltage control while preventing harmful reverse current by controlling the connection path rather than direct short-circuiting.
3Stress or pressure
If the string length is limited to avoid exceeding maximum voltage, then voltage is kept within permissible range, but the number of modules that can be connected in series is reduced
Solution Approach 1:
The effective string length is made dynamic through controllable switches. The system can extend the string to full length when voltage conditions permit, maximizing power generation. When voltage exceeds limits, the system dynamically shortens the effective length by disconnecting or bypassing sections, maintaining voltage control while preserving maximum productivity when possible.
4Stress or pressure
If disconnect switches are used to separate string sections, then voltage can be controlled, but the circuit complexity increases
Solution Approach 1:
Multiple functions are merged into a single integrated circuit design. The bypass and disconnect switches are controlled by a unified control logic that manages both voltage limitation and power loss prevention. This merging reduces overall system complexity compared to separate control systems for each function.
Data Source
Figure 1
Figure 2
Figure 2a
AI summary
A circuit (1) for limiting the voltage of a photovoltaic string (20), which is divided into a first section (21) and a second section (22) of a series arrangement of solar modules (24), comprises a first terminal (13) for connecting to a first end of the first section (21), a second terminal (14) for connecting to a first end of the second section (22) and a third terminal (15) for connecting to a second end of the second section, as well as a bypass switch (12), which is connected at one end to the first terminal (13) and at the other end to the third terminal (15), and an isolating switch (11), which is connected at one end to the first terminal (13) and at the other end to the second terminal (14). The circuit comprises a controller (10) for controlling the bypass switch (12) and the isolating switch (11), wherein the controller (10) is configured to determine a first threshold value Uui_ and a second, smaller threshold value U|j_i as a function of a switch voltage Uoc which drops across the isolating switch (11) in an open state and taking into account the number of solar modules in the first section (21) and in the second section (22). The invention further relates to a photovoltaic field having such a circuit and to a method for voltage limitation.