Photovoltaic Inverter Shutdown Control via Average Input Current
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Solution Overview
Problem
Existing methods for controlling photovoltaic inverter shutdown based on power or voltage lead to frequent operations of the grid-connected relay, reducing its service life.
Innovation Solution
A method that determines shutdown by calculating a first average input current of the photovoltaic inverter's direct current side over a predetermined duration, disconnecting the grid-connected relay when the current falls below this average, thereby avoiding repeated disconnections and extending the relay's service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If shutdown control is based on power or voltage threshold, then shutdown decision is simple, but relay operates frequently reducing service life
Solution Approach 1:
The system performs preliminary sampling of input current at startup to establish a baseline average value before normal operation begins. This preliminary action creates a reference threshold that reflects actual operating conditions, preventing premature shutdown decisions based on transient low-power states.
Solution Approach 2:
The shutdown threshold is dynamically adjusted based on the sampled average input current rather than using a fixed power or voltage threshold. The system continuously compares real-time input current against this adaptive threshold, allowing the shutdown decision criterion to evolve with changing environmental conditions and panel characteristics.
2Device complexity
If shutdown control is based on input voltage threshold, then voltage monitoring is straightforward, but relay disconnects frequently on cloudy days
Solution Approach 1:
The control parameter is changed from voltage to current-based measurement. By sampling the input current at startup and using its average value as the shutdown threshold, the system adapts to varying environmental conditions including cloudy days, where voltage thresholds would cause excessive relay operations.
3Measurement precision
If fixed power threshold is used for shutdown, then shutdown criterion is clear, but relay disconnects and closes repeatedly affecting service life
Solution Approach 1:
The system implements feedback by continuously monitoring the input current and comparing it against the dynamically determined threshold based on sampled average current. This feedback mechanism prevents repeated relay operations by adapting the shutdown criterion to actual system performance and environmental conditions.
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 approach effectively prevents the premature wear caused by frequent relay operations, ensuring the photovoltaic inverter operates within a stable duration range and prolongs the service life of the grid-connected relay.
Implementation Method 1
a photovoltaic panel is used to absorb solar energy and convert the solar energy into direct current
Data Source
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AI summary
A method for controlling shutdown of photovoltaic inverter, a system thereof, and a photovoltaic power generation system are provided. Input current of the direct current side of the photovoltaic inverter is obtained when the grid-connected relay is closed, the first average input current is determined. If the duration for which the input current of the direct current side is less than or equal to the first average input current reaches a first predetermined duration, the grid-connected relay is disconnected, to stop the grid-connected operation of the photovoltaic inverter. In the solution, by determining whether the duration for which the input current of the direct current side of the photovoltaic inverter is less than or equal to the first average input current reaches the first predetermined duration, it is determined whether to stop the grid-connected operation of the photovoltaic inverter. Thus, the duration of the grid-connected operation of the photovoltaic inverter reach a certain range, repeatedly disconnecting and closing the relay are avoided. The problem of the reduction of service life of the relay caused by repeatedly disconnecting and closing the relay in conventional technology is solved.