Photovoltaic Inverter Switching Frequency Control for LCL Stability
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Solution Overview
Problem
Photovoltaic inverters face efficiency losses and grid-connected stability issues due to improper switching frequency matching with LCL filter parameters, leading to potential shutdowns and damage.
Innovation Solution
A photovoltaic inverter with a data sampling module and control module that dynamically adjusts the switching frequency based on instantaneous current values, setting upper and lower frequency limits to ensure the frequency is greater or lesser than the previous period accordingly, thereby adapting to filter parameters and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the switching frequency of the photovoltaic inverter is increased, then the conversion efficiency is improved, but the switching loss of the switch component increases
Solution Approach 1:
The patent implements dynamic switching frequency adjustment by introducing a switching frequency control module that continuously monitors grid conditions and adapts the switching frequency in real-time. The control module adjusts the switching frequency within a predetermined range based on grid impedance characteristics, power factor, and active/reactive power output requirements, transforming the static switching frequency into a dynamic parameter that optimizes efficiency while controlling losses.
Solution Approach 2:
The patent changes the switching frequency parameter dynamically based on operating conditions. By adjusting the switching frequency within a predetermined range according to grid impedance, power factor, and power output requirements, the system optimizes the balance between conversion efficiency and switching losses, converting a fixed parameter into a variable one that adapts to different operating scenarios.
2Productivity
If the switching frequency is improperly matched with LCL filter parameters, then the conversion efficiency may be high, but the grid-connected stability deteriorates causing oscillation and potential damage
Solution Approach 1:
The patent implements a feedback control mechanism where the switching frequency control module continuously monitors grid-connected status, impedance characteristics, and resonance conditions. Based on this feedback, the system dynamically adjusts the switching frequency to maintain stability while preserving conversion efficiency, preventing oscillation and potential damage to the inverter.
Solution Approach 2:
The patent makes the switching frequency a dynamic parameter that adapts to grid conditions in real-time. By continuously adjusting the switching frequency within a predetermined range based on grid impedance and resonance characteristics, the system maintains both high conversion efficiency and grid-connected stability, avoiding the fixed frequency limitations that cause oscillation and damage.
3Productivity
If the switching frequency is dynamically adjusted, then the conversion efficiency is improved, but the device complexity increases due to additional control modules
Solution Approach 1:
The patent designs the switching frequency control module to perform multiple functions: monitoring grid impedance characteristics, detecting resonance conditions, calculating optimal switching frequency, and adjusting the switching signal. By consolidating these functions into a single multi-functional control module, the patent reduces the overall system complexity while achieving dynamic switching frequency adjustment and improved conversion efficiency.
Data Source
AI summary
A photovoltaic inverter is provided, including an inverter circuit, a data sampling module, and a control module. The inverter circuit includes a switch component and an alternating current output terminal. The data sampling module is configured to collect, from the alternating current output terminal, an instantaneous current value at each sampling point moment in target sampling duration and an instantaneous value of each-phase current at a target moment. The control module is configured to: determine a valid current value of the target sampling duration based on the instantaneous current value at each sampling point moment, determine an upper switching frequency limit and a lower switching frequency limit of an Nth switching period based on the valid current value, and determine a target instantaneous current value IN based on the instantaneous value of each-phase current at the target moment.