PV String Curtailment Control With Selective MPPT Tracking
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Solution Overview
Problem
In photovoltaic power generation systems, the curtailment phenomenon leads to a power output limited state where all strings are affected, preventing normal maximum power point tracking (MPPT) and accurate prediction of optical power, resulting in reduced utilization and stability of the power grid.
Innovation Solution
A method and apparatus that control a power supply system by selectively enabling some photovoltaic strings to perform MPPT while others are in a power output limited state, allowing for independent control and real-time update of optical power information, using a controller to manage the direct current voltage conversion and inverter units to ensure that only certain strings operate at maximum power point tracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If all photovoltaic strings are placed in power output limited state during curtailment, then power grid stability is improved, but optical power information detection capability deteriorates
Solution Approach 1:
The patent divides the photovoltaic string group into multiple subsets, with each subset independently controlled. During curtailment, some subsets operate in power output limited state while others perform MPPT, segmenting the system to simultaneously achieve grid stability and power information detection
Solution Approach 2:
Different operational states are assigned to different photovoltaic string subsets based on local needs: subsets designated for detection perform MPPT to obtain optical power information, while others maintain power output limitation for grid stability, creating local quality differentiation within the system
2Loss of information
If all photovoltaic strings perform maximum power point tracking, then optical power information is obtained, but power grid stability deteriorates during curtailment
Solution Approach 1:
The system segments photovoltaic strings into different functional groups: one group performs MPPT to capture optical power information while another group implements power output limitation to maintain grid stability during curtailment events
Solution Approach 2:
Instead of applying power output limitation to all strings, the patent applies it partially to only those strings not currently performing MPPT, allowing sufficient strings to operate at maximum power point to maintain detection capability while limiting overall power output to stabilize the grid
3Loss of information
If photovoltaic strings are switched between MPPT and power output limited states, then optical power information detection is improved, but system complexity increases
Solution Approach 1:
The control system is segmented into multiple independent control modules, each managing a subset of photovoltaic strings. This modular approach distributes control complexity across multiple simple units rather than requiring one complex centralized controller
Solution Approach 2:
The system periodically switches between different operational configurations, rotating which string subsets perform MPPT and which maintain power output limitation. This periodic rotation distributes the detection burden across all strings over time while maintaining simple control logic at each moment
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 allows for real-time monitoring and prediction of optical power, reducing power loss and improving system efficiency by enabling quick adjustment to maximum power points after the curtailment state ends, thereby enhancing the stability and utilization of the photovoltaic station.
Implementation Method 1
N photovoltaic strings, configured to convert optical energy into a direct current
Data Source
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AI summary
This application provides a method for controlling a power supply system, including: A controller determines that N photovoltaic strings in the power supply system meet ∑i=1NPmaxi>Pout⋅Pmaxi represents maximum power point power corresponding to each of the N photovoltaic strings in a previous MPPT, and Pout represents scheduling power of an inverter unit. The controller controls a direct current voltage conversion unit to enable X photovoltaic strings in the N photovoltaic strings to be in an MPPT state, and N - X photovoltaic strings to be in a power output limited state. N ≥ 2, 1 ≤ X ≤ N - 1, and the X photovoltaic strings meet ∑i=1XPmaxi≤Pout. According to the method for controlling a power supply system provided in this application, in a light discarding state, power limitations of some photovoltaic strings are separately lifted, so that the photovoltaic strings perform MPPT detection. This may implement independent control on the photovoltaic strings and implement more accurate optical power prediction.