MOSFET Bypass Switch for Solar Cell String Protection
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Solution Overview
Problem
Large solar energy generating systems face power losses and potential damage to bypass diodes due to high currents passing through them, even when low-loss diodes are used, as they struggle to handle the high currents effectively.
Innovation Solution
Incorporating a switch, such as a metal-oxide semiconductor field-effect transistor (MOSFET), in parallel with the bypass diode to reroute a majority of the bypass current, using a capacitor and latch circuit to control the switch's operation, allowing the current to bypass the diode and reducing heat and power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bypass diodes are used to allow current to bypass malfunctioning or shaded solar cells, then current can continue to run through the string, but large currents cause unwanted power losses and heat, and even bypass diode damage
Solution Approach 1:
The patent introduces a MOSFET as an intermediary device between the solar cell string and the bypass diode. The MOSFET acts as a controllable switch that redirects the majority of bypass current away from the diode, allowing the diode to handle only a minority of the current. This mediator device resolves the contradiction by enabling current continuity while significantly reducing power loss and heat generation in the bypass path.
Solution Approach 2:
The patent employs a dynamic switching mechanism using a MOSFET controlled by a controller that monitors bypass current levels. When bypass current exceeds a threshold, the MOSFET activates to dynamically redirect current flow. This dynamic adaptation allows the system to maintain reliability under fault conditions while minimizing energy loss by actively managing current distribution based on real-time conditions.
2Loss of energy
If low-loss diodes (e.g., Schottky diodes) are used to reduce power losses, then power loss is reduced, but they still cannot overcome the losses, heat, and potential damage from high currents
Solution Approach 1:
The MOSFET serves as an intermediary that protects the bypass diode from high current stress. By placing the MOSFET in parallel with the bypass diode and controlling it to conduct the majority of bypass current, the diode is shielded from thermal damage. This intermediary approach allows the use of bypass diodes without subjecting them to destructive heat levels, effectively resolving the heat management issue.
Solution Approach 2:
The patent replaces the passive diode-based bypass mechanism with an active electronic switching system using MOSFETs. This substitution transitions from a static, always-on bypass path to a dynamically controlled electronic switch that can handle high currents with minimal on-resistance. The MOSFET's electronic switching capability provides superior power loss and heat characteristics compared to traditional diode-based solutions.
3Loss of energy
If a switch is added in parallel with the bypass diode to reroute current, then power loss and heat are reduced, but device complexity increases
Solution Approach 1:
The MOSFET is introduced as a controlled intermediary that, while adding a component, provides intelligent current management. The device includes a controller that monitors bypass current and activates the MOSFET only when needed, adding minimal operational complexity. The benefit of dramatically reduced power loss and heat generation outweighs the added complexity of the switch and control circuitry.
Solution Approach 2:
The system incorporates self-monitoring and automatic activation capabilities where the controller detects bypass current conditions and autonomously controls the MOSFET switching. This self-service approach minimizes the need for external control systems, reducing operational complexity. The device automatically manages its own current distribution, making the added complexity self-regulating and easier to manage.
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 efficiently directs high currents through the switch rather than the diode, minimizing power loss and preventing damage, while maintaining system functionality even when solar cells are shaded or malfunctioning.
Implementation Method 1
A capacitor can be connected to a control of the switch (e.g., the gate of a metal-oxide semiconductor field-effect transistor) through a latch circuit. When the latch is closed or off, the capacitor cannot discharge and close, or turn on, the switch.
Implementation Method 2
By turning the switch on, a majority of the bypass current can be routed through the switch, which is configured to handle larger currents than the bypass diode is designed for
Implementation Method 3
Bypass diodes can be connected in parallel with groups of solar cells (one or more solar cells connected in series) to allow current to bypass groups of solar cells having one or more highly resistive solar cell
Data Source
AI summary
Systems and methods for efficiently allowing current to bypass a group of solar cells having one or more malfunctioning or shaded solar cells without overwhelming a bypass diode. This can be done using a switch (e.g., a MOSFET) connected in parallel with the bypass diode. By turning the switch on and off, a majority of the bypass current can be routed through the switch, which is configured to handle larger currents than the bypass diode is designed for, leaving only a minority of the current to pass through the bypass diode.