By-pass MOS Transistor Circuit for PV Panel Power Dissipation
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Solution Overview
Problem
Photovoltaic panels face inefficiencies and potential damage due to sub-illumination of cells, which leads to overheating and power dissipation issues, as conventional by-pass diodes like Schottky diodes result in significant energy loss and reliability concerns.
Innovation Solution
A by-pass device utilizing a power MOS transistor with an oscillator and charge pump circuit, controlled by a protection transistor and gate driving stage, eliminates the need for an inductor, allowing for efficient and controlled operation by minimizing power dissipation through voltage-dependent triggering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Schottky diodes are used as by-pass diodes, then cells are protected from permanent impairment, but power dissipation increases significantly
Solution Approach 1:
The patent changes the electrical parameters of the by-pass device by using a MOS transistor instead of a Schottky diode. The MOS transistor offers lower on-resistance and lower forward voltage drop, reducing power dissipation while maintaining the by-pass function. The transistor's channel resistance can be optimized through doping concentration and geometry to minimize energy loss.
Solution Approach 2:
The patent substitutes the Schottky diode's pn-junction mechanism with a MOS transistor's field-effect mechanism. Instead of relying on the diode's forward conduction, the MOS transistor uses an electric field to control current flow, achieving lower power dissipation and better efficiency in by-passing shadowed cells.
2Loss of energy
If an inductor is used in the by-pass circuit, then power dissipation is reduced, but device complexity and fabrication difficulty increase
Solution Approach 1:
The patent extracts and eliminates the inductor component from the by-pass circuit. By using a MOS transistor with optimized gate control, the circuit achieves efficient by-pass operation without requiring energy storage elements like inductors, thereby simplifying the overall device structure and reducing fabrication complexity.
Solution Approach 2:
The patent merges the by-pass function with the MOS transistor's inherent switching capability. The transistor's gate is controlled by the voltage across the cell string, automatically enabling by-pass when needed without requiring separate control circuits or additional energy storage components, thus reducing overall device complexity.
3Loss of energy
If MOS transistor is used as by-pass diode, then power dissipation is reduced, but control circuit complexity increases
Solution Approach 1:
The MOS transistor's gate is controlled by the voltage across the cell string itself. When the string voltage becomes negative (indicating shadowing), the gate automatically turns on the transistor to enable by-pass. This self-controlled mechanism eliminates the need for external control circuits, sensors, or additional power management components.
Solution Approach 2:
Instead of using active control to turn on the by-pass diode, the patent inverts the approach by using the negative voltage condition as the trigger to turn on the MOS transistor. The normal forward voltage does not activate the by-pass, but the reverse voltage condition automatically enables it, simplifying the control logic.
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 solution reduces power dissipation and enhances the efficiency and reliability of photovoltaic panels by minimizing energy loss and extending the lifespan of the by-pass device, while eliminating the fabrication challenges associated with inductive components.
Implementation Method 1
If the gate voltage of the power MOS transistor exceeds a threshold voltage, the power MOS transistor channels a current flow between a source and a drain
Implementation Method 2
the current generated by the irradiated cells inverts the voltage on the by-pass MOS transistor by flowing in the intrinsic diode of the integrated structure of the transistor
Implementation Method 3
Photovoltaic panels contain a large number of series connected photovoltaic cells
Data Source
AI summary
A by-pass circuit includes a first power MOS with an intrinsic diode, a first conduction terminal coupled to a cathode, a second conduction terminal coupled to an anode, and a control terminal. A tank capacitor is coupled to the anode. A second MOS has a first and second conduction terminals, a control terminal, and a turn-on threshold smaller than that of the intrinsic diode, the first conduction terminal thereof coupled to the cathode and the control terminal coupled to the anode, so the first MOS turns on when the array of cells are sub-illuminated. An oscillator and charge pump are supplied through the second conduction terminal of the second MOS to charge the tank capacitor. A control circuit is coupled to the control terminal of the first power MOS to switch it based upon a voltage of the tank capacitor and sign of the voltage between the cathode and anode.