Parallel Shutdown Units for PV Array Voltage Reduction
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Solution Overview
Problem
Existing photovoltaic power generation systems face challenges in rapidly and safely shutting down high-voltage photovoltaic arrays during emergencies, as current shutdown devices experience heat generation and reduced lifespan due to continuous high current flow, and require high voltage and current endurance, leading to large size and high costs.
Innovation Solution
A photovoltaic power generation system with shutdown units connected in parallel to the photovoltaic arrays and inverter, using a control unit to detect a power-off state and generate a signal for short-circuiting the arrays, reducing power transmission and voltage to near zero, thereby minimizing risk and extending device lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shutdown device is connected in series between photovoltaic arrays and inverter, then shutdown function is achieved, but disconnecting element experiences large heat generation and reduced lifespan due to continuous high current flow
Solution Approach 1:
The patent inverts the conventional series connection to a parallel connection. The shutdown device is connected in parallel with the photovoltaic array, with the disconnecting element connected between the positive terminal of the array and the positive high-voltage wire. During normal operation, the disconnecting element remains open and carries no current. During shutdown, it closes to create a short circuit, diverting current away from the inverter and protecting the system without subjecting the disconnecting element to continuous thermal stress.
2Reliability
If shutdown device is connected in series, then shutdown capability is provided, but high voltage and current endurance requirements increase device volume and cost
Solution Approach 1:
By connecting the shutdown device in parallel rather than series, the disconnecting element only needs to withstand the array's open-circuit voltage when open, and carries full current only briefly when closing to create the short circuit. This eliminates the need for continuous high voltage and current endurance, significantly reducing the size and cost of required components.
3Reliability
If DC switch in junction box is used for shutdown, then inverter input is disconnected, but photovoltaic panels still maintain high open-circuit voltage causing electric shock risk
Solution Approach 1:
The patent extracts the shutdown function from the inverter input side (DC switch) and places it at the photovoltaic array output side. The disconnecting element is positioned on the array side to directly short-circuit the array terminals, actively reducing the open-circuit voltage to near zero. This ensures that both the inverter is protected and the array voltage is actively managed to eliminate electric shock hazards.
4Reliability
If conventional series shutdown arrangement is used, then shutdown is achieved, but disconnecting element is in closing state for long time causing heat generation
Solution Approach 1:
The patent inverts the operational state of the disconnecting element. In the parallel connection, the element remains open (not conducting) during normal operation and only closes briefly during shutdown. This is the opposite of series connection where the element must remain closed continuously to maintain power flow. The inverted state dramatically reduces thermal generation and extends component lifespan.
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
The system efficiently, stably, and simply shuts down photovoltaic arrays during emergencies, reducing the risk of electric shock and extending the lifespan of shutdown units by avoiding continuous current flow, while using conventional disconnecting elements like thyristors to lower volume and cost.
Implementation Method 1
the disconnecting element is closed to short-circuit the photovoltaic array, so the output voltage of the photovoltaic array decreases to nearly zero
Data Source
AI summary
A photovoltaic power generation system includes a plurality of photovoltaic arrays, a plurality of shutdown units and an inverter. The shutdown unit is adjacent to the corresponding photovoltaic array, connected in parallel with the corresponding photovoltaic array, and electrically connected to the inverter via high voltage wires; the photovoltaic power generation system further includes a control unit configured to receive a detection signal indicating a state of the AC side of the inverter, monitor whether the AC side of the inverter is in a power-off state according to the detection signal, and generate a first power-off signal when the AC side of the inverter is in the power-off state; and the shutdown units are configured to receive the first power-off signal, and stop a power transmission from the photovoltaic arrays to the inverter according to the first power-off signal.