String Inverter IV Scanning With Ripple Current Control
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Solution Overview
Problem
The existing photovoltaic power generation systems experience significant energy yield loss during IV curve scanning due to the need to disconnect photovoltaic strings from inverters, leading to inefficient power transfer and potential overcurrent protection issues in string inverters.
Innovation Solution
A string inverter control method that maintains power transfer to the inverter circuit during IV curve scanning by dynamically adjusting the output voltage and switching frequency of direct current/direct current step-up circuits, ensuring a non-strictly monotonically increasing relationship between input and output voltages to reduce ripple currents and prevent overcurrent protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If IV curve scanning is performed by controlling photovoltaic string output voltage to decrease from open-circuit voltage to short-circuit voltage, then IV curve data can be obtained for health status detection, but power transfer to the inverter circuit is interrupted causing significant energy yield loss
Solution Approach 1:
The patent combines IV curve scanning operations with normal power generation operations by allowing multiple DC-DC conversion circuits to operate simultaneously - some circuits perform IV scanning while others maintain power transfer to the inverter circuit, thus merging measurement and power generation functions
Solution Approach 2:
The inverter system is designed to perform multiple functions concurrently: IV curve scanning for health monitoring and power generation for energy production. The control method enables the system to switch between or combine these functions dynamically, making the system universal in its operational capabilities
2Measurement precision
If IV curve scanning is performed on one DC-DC conversion circuit, then IV curve data can be obtained, but the inverter circuit receives insufficient power causing operation below reference power
Solution Approach 1:
The patent divides the DC-DC conversion circuits into different functional groups: some circuits are dedicated to IV curve scanning while others are dedicated to power transfer. This segmentation allows each group to perform its specific function without interfering with the other, ensuring both scanning accuracy and adequate power supply to the inverter
3Ease of operation
If output voltage of DC-DC conversion circuit is controlled to be constant during IV curve scanning, then control is simplified, but ripple current increases causing overcurrent protection triggers
Solution Approach 1:
The patent implements dynamic control of the output voltage for DC-DC conversion circuits performing IV curve scanning. The output voltage is adjusted according to the input voltage changes, creating a dynamic relationship that reduces ripple current magnitude and prevents overcurrent protection triggers while maintaining reliable operation
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 minimizes energy yield loss and prevents overcurrent protection triggers, ensuring normal operation of the string inverter during IV curve scanning by maintaining stable power transfer and reducing ripple currents.
Implementation Method 1
A string inverter includes one or more first direct current/direct current step-up circuits, one or more second direct current/direct current step-up circuits and an inverter circuit. Output ends of the one or more first direct current/direct current step-up circuits and output ends of the one or more second direct current/direct current step-up circuits are respectively connected to an input end of the inverter circuit.
Data Source
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AI summary
This application discloses a string inverter control method, apparatus, and system, and a storage medium, and belongs to the field of photovoltaic technologies. The method includes: in a process of performing IV curve scanning on one or more first direct current/direct current step-up circuits, controlling a change of an output voltage of one or more second direct current/direct current step-up circuits on which the IV curve scanning does not need to be performed, where a change trend of the output voltage and a change trend of an input voltage of the one or more first direct current/direct current step-up circuits on which the IV curve scanning is performed present a non-strictly monotonically increasing relationship. Therefore, for the direct current/direct current step-up circuit on which the IV curve scanning is performed, a voltage difference between two ends of the direct current/direct current step-up circuit is not always in a relatively high state, so that a ripple current on an input inductor in the direct current/direct current step-up circuit can be reduced. In this way, the following case can be avoided: Overcurrent protection is triggered on the direct current/direct current step-up circuit due to the excessively large ripple current on the input inductor.