Centralized MPPT Control for Photovoltaic Inverters
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Solution Overview
Problem
Photovoltaic inverters face decreased MPPT efficiency due to deviations in maximum power points of individual photovoltaic strings from the overall maximum power point, leading to reduced conversion and MPPT efficiency when illumination intensity changes.
Innovation Solution
A method for photovoltaic inverters that involves performing individual MPPT control on each string, determining standard values for maximum power points based on DC chopper circuit types, and restarting DC chopper circuits with voltage differences exceeding a preset threshold to maintain optimal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If MPPT centralized mode is used to improve system conversion efficiency, then overall conversion efficiency is improved, but MPPT efficiency decreases due to voltage deviations of individual strings from the overall maximum power point
Solution Approach 1:
The patent divides the photovoltaic system into multiple independent string groups, each with its own DC chopper circuit and MPPT control. This segmentation allows each group to operate independently at its own maximum power point while maintaining overall system efficiency through selective parallel connection to the DC bus.
Solution Approach 2:
The patent implements dynamic switching between centralized and individual MPPT modes based on real-time voltage deviations. When voltage differences between strings exceed a threshold, the system dynamically transitions from centralized MPPT to individual string MPPT control, and vice versa, optimizing both conversion efficiency and MPPT accuracy adaptively.
2Loss of energy
If DC chopper circuits are stopped to connect photovoltaic strings directly in parallel to improve conversion efficiency, then conversion efficiency is improved, but the system loses adaptability when illumination intensity changes cause maximum power point deviations
Solution Approach 1:
The system dynamically adjusts the operating state of DC chopper circuits based on real-time monitoring of voltage deviations. When illumination changes cause maximum power point shifts exceeding a threshold, the system dynamically activates the relevant DC chopper circuits to enable individual string MPPT control, restoring adaptability while minimizing impact on conversion efficiency.
Solution Approach 2:
The patent implements a feedback mechanism that continuously monitors the voltage of each photovoltaic string and compares it with the DC bus voltage. Based on this feedback, the control system determines whether to activate or deactivate DC chopper circuits, ensuring the system maintains optimal performance under varying illumination conditions.
3Measurement precision
If individual MPPT control is performed on each photovoltaic string to maintain high MPPT efficiency, then MPPT efficiency is improved, but system conversion efficiency decreases due to operation of low-efficiency DC chopper circuits
Solution Approach 1:
The patent segments the photovoltaic system into multiple independent string groups, each capable of individual MPPT control when needed. This segmentation allows the system to apply individual MPPT control only to specific strings that require it, rather than forcing all strings through inefficient DC chopper circuits, thereby maintaining both MPPT efficiency and overall conversion efficiency.
Solution Approach 2:
The patent applies different control strategies to different string groups based on their specific conditions. Strings with voltage deviations within the threshold operate in centralized mode for high conversion efficiency, while strings with larger deviations operate in individual MPPT mode for high MPPT efficiency. This local quality approach ensures optimal performance for each string without compromising the whole system.
Data Source
AI summary
Disclosed is a centralized MPPT exiting method for a photovoltaic inverter comprising multiple DC chopper circuits and one inverter circuit. The method comprises: when the photovoltaic inverter is in a centralized MPPT mode, MPPT control is implemented independently for each photovoltaic cell in a photovoltaic component and the maximum power point for each photovoltaic cell is obtained; a reference value of the maximum power point for each photovoltaic cell is determined according to the type of the multiple DC chopper circuits; whether the voltage difference between the other maximum power points and the reference value goes beyond an allowable voltage difference is judged and the operation of the DC chopper circuits connecting to the photovoltaic cells with a voltage difference beyond the allowable voltage difference is recovered.