Delta DC/DC Converters for PV String Voltage Optimization
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Solution Overview
Problem
Photovoltaic (PV) systems connected in parallel often operate at a common voltage, which is not optimal for each string, leading to reduced efficiency and power output due to shading issues and uneven temperature distribution, resulting in up to 15% lower production.
Innovation Solution
A system with delta DC/DC converters connected to each PV string, which adjust the voltage to the optimal string voltage by comparing the DC link voltage to the optimal voltage for each string, allowing each string to operate at its maximum power point, thereby maximizing overall system power output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If PV strings are connected in parallel to a common DC link, then the system can supply more current and operate simpler, but all strings must operate at the same voltage which prevents each string from operating at its optimal voltage, reducing power output by up to 15%
Solution Approach 1:
The patent divides the PV system into independent string-level control units, with each string having its own DC/DC converter that can independently adjust its operating voltage. This segmentation allows each string to operate at its optimal voltage point without being constrained by other strings, thereby resolving the contradiction between maintaining simple parallel connection and achieving individual optimal operation.
Solution Approach 2:
The patent introduces DC/DC converters as intermediary devices between the PV strings and the common DC link. These converters act as mediators that decouple the voltage constraints of the parallel connection from the optimal operating voltages of individual strings, allowing each string to operate independently at its optimal voltage while still contributing to the common DC link.
2Productivity
If individual DC/DC converters are added to each PV string to enable independent voltage control, then each string can operate at its optimal voltage and maximize power output, but the device complexity and hardware investment increase
Solution Approach 1:
The patent applies local quality by implementing voltage optimization at the string level rather than requiring complex array-level control. Each DC/DC converter is sized and controlled specifically for its associated string's characteristics (shading, temperature), providing localized optimization that achieves high productivity with relatively simple, modular hardware.
Solution Approach 2:
The patent employs dynamic voltage adjustment through controlled DC/DC converters that can adapt each string's operating voltage in real-time based on environmental conditions. This dynamic control allows the system to maintain optimal power output under varying conditions without requiring overly complex static hardware configurations.
3Ease of operation
If all PV strings operate at a common DC link voltage determined by the inverter, then the system operation is simplified, but strings with different optimal voltages (due to shading, temperature) cannot achieve maximum power extraction
Solution Approach 1:
The DC/DC converters serve as intermediary devices that maintain the simple common DC link architecture while enabling individual string optimization. They translate the common DC link voltage into appropriate string-specific voltages, preserving system operational simplicity while achieving high power extraction efficiency.
Solution Approach 2:
The patent changes the voltage parameter at the string level using DC/DC converters, allowing each string to operate at its optimal voltage while maintaining a common DC link voltage. This parameter transformation resolves the contradiction by decoupling the DC link voltage from the string operating voltage.
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 increases the maximum power output of the PV system by allowing each string to operate at its individual optimal voltage, potentially increasing production by up to 15% with minimal additional hardware investment.
Implementation Method 1
Each DC/DC converter receives the DC link voltage from the DC link and is configured to provide a tuning voltage to the DC link voltage at which its respective PV string operates in order to bring the string voltage for that PV string to its optimal string voltage
Data Source
AI summary
A PV system includes a plurality of PV strings each having an optimal string voltage at which a string output power is maximized. The PV strings are connected to a DC link in a parallel arrangement such that each PV strings operates at a variable DC link voltage. A PV inverter is connected to the DC link to receive a DC output, with the PV inverter controlling the DC link voltage. Delta DC/DC converters are connected to the PV strings, with each DC/DC converter receiving the DC link voltage from the DC link and providing a tuning voltage to the DC link voltage at which its respective PV string operates in order to bring the string voltage for that PV string to its optimal string voltage. The tuning voltage of each delta DC/DC converter is the difference between the DC link voltage and a respective optimal string voltage.