Solar String Shutoff Circuit to Prevent Relay Chattering
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Solution Overview
Problem
Solar power generation systems face instability due to power fluctuations and noise generation from switching devices, particularly when the power generated by solar cell modules is insufficient or unstable, leading to repeated switching between ON and OFF states.
Innovation Solution
The system incorporates a dual shutoff device configuration with semiconductor switching units that are turned ON before the primary switching units, ensuring stable operation by reducing noise and chattering, and includes a bypass mechanism to maintain system stability during power fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a switching device (relay) is used to cut off the electric path in the solar power generation system, then the rapid shutdown function can be achieved to protect firefighters from electric shock, but noise including surge is generated when opening and closing the contact
Solution Approach 1:
The patent replaces the mechanical relay contact with a semiconductor switching device (such as a MOSFET or IGBT). This substitution eliminates the mechanical contact opening and closing action that generates noise and surge, while maintaining the rapid shutdown functionality. The semiconductor device switches electronically without mechanical movement, thus achieving the safety function without the harmful noise and surge generation.
2Extent of automation
If the switching device is driven by power from solar cell modules, then the system can operate autonomously, but when the generated power is smaller than required or unstable, the switching device repeatedly switches between ON and OFF states
Solution Approach 1:
The patent introduces a preliminary action by adding a startup circuit that pre-charges the capacitor before the semiconductor switching device is activated. This preliminary charging ensures that sufficient energy is available in the capacitor to drive the switching device reliably, preventing the repeated ON-OFF switching that occurs when power is insufficient or unstable. The startup circuit acts in advance to prepare the necessary energy storage.
3Device complexity
If a single shutoff device is used, then the system structure is simple, but the system stability during power fluctuations is insufficient
Solution Approach 1:
The patent segments the shutoff function into two independent devices: a first shutoff device connected between the string and inverter, and a second shutoff device connected to the solar cell module group. This segmentation allows each device to independently handle shutdown operations, improving system stability during power fluctuations. If one device experiences issues, the other can still perform the shutdown function, enhancing overall reliability without significantly complicating the system structure.
Data Source
AI summary
A solar power generation system includes a string, an inverter, a first shutoff device, and a second shutoff device′. The string includes a plurality of solar cell modules connected in series. The first shutoff device cuts off the string and the inverter in response to a first control signal from the inverter. The second shutoff device cuts off a solar cell module group including one or more among the plurality of solar cell modules and either another solar cell module or the inverter in response to a second control signal from the first shutoff device. The second shutoff device includes a first switching unit that includes a first open and close unit and a first semiconductor switching device connected in parallel with the first open and close unit. The first semiconductor switching device is turned ON before the first open and close unit is operated.