Bidirectional DC-DC Converters for Mismatched PV Source Balancing
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Solution Overview
Problem
Existing power systems with interconnected DC power sources face inefficiencies due to voltage and current mismatches, leading to reduced power output, particularly in arrays of solar photovoltaic panels and battery packs, where shading, varying chemistries, and material degradation cause imbalances.
Innovation Solution
A power conversion system utilizing a nested arrangement of bidirectional DC-DC voltage converters that implement feed-forward and feed-backward power flow concepts to balance current and voltage across DC power sources, allowing for optimal power processing and bypassing converters when no mismatch exists, thereby stabilizing power output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If DC power sources are interconnected in series-parallel combination, then power output can be increased, but voltage and current mismatch among individual sources degrades overall power output
Solution Approach 1:
The system segments the power processing function by introducing individual DC-DC converters for each DC power source. Each converter independently processes power from its associated source, allowing voltage and current matching to be performed separately for each source rather than requiring all sources to operate at identical parameters. This segmentation enables the system to maintain high power output while minimizing energy loss due to mismatch.
Solution Approach 2:
DC-DC converters serve as intermediary devices between individual DC power sources and the load. These converters act as mediators that transform and regulate voltage and current from each source, enabling mismatched sources to operate together efficiently. The converters buffer the mismatch effects, allowing each source to operate at its optimal point while delivering coordinated power to the load.
2Reliability
If bypass diodes are used to prevent hotspots in PV panels, then power delivery is maintained at reduced voltage, but multiple peaks in power-voltage characteristics require complex MPPT algorithms
Solution Approach 1:
DC-DC converters are introduced as intermediary devices between PV panels and the load, replacing the need for complex MPPT algorithms. The converters actively regulate voltage and current, maintaining optimal operating points for each panel regardless of mismatches. This intermediary approach simplifies the control strategy compared to traditional MPPT methods while preserving reliability and preventing hotspots.
Solution Approach 2:
The system dynamically changes operating parameters (voltage and current) for each PV panel through individual DC-DC converters. Rather than relying on fixed-point MPPT algorithms that struggle with multiple peaks, the converters continuously adjust parameters to maintain optimal power extraction from each panel, effectively navigating complex power-voltage characteristics without requiring complex control logic.
3Power
If full power processing DMPPT systems are implemented, then maximum power can be extracted from each DC power source, but conversion losses increase due to processing all power through electronics
Solution Approach 1:
The system applies partial power processing by using DC-DC converters only when and where needed to correct mismatches. Rather than forcing all power through conversion electronics, the system allows direct power transfer for matched sources while applying conversion only to the extent necessary to balance mismatches, thereby reducing overall conversion losses while maintaining maximum power extraction.
Solution Approach 2:
The power processing approach applies local quality by treating each DC power source individually with its own DC-DC converter. Each converter is sized and controlled according to the specific needs of its associated source, applying conversion locally only where mismatches exist. This localized approach minimizes unnecessary conversion losses while ensuring maximum power extraction from each source.
4Power
If multiple DC-DC converters are used to balance mismatched power sources, then power output is stabilized, but system complexity and cost increase
Solution Approach 1:
The system uses segmentation by deploying individual DC-DC converters for each DC power source, allowing independent control and stabilization of each source's output. This modular segmentation enables straightforward scaling - additional converters are added only when additional power sources are introduced, keeping system complexity proportional to the number of sources rather than requiring complex centralized control for the entire system.
Data Source
AI summary
Disclosed examples relate to a power conversion system configured to provide a power output from an arrangement of direct current (DC) power sources. One example power conversion system includes multiple power sources PV(n), n=1 to x, connected in a series. For each power source PV(n) for n=1 to x−1, the power conversion system includes an intermediate bidirectional voltage converter VC(n) connected to a first terminal of the power source PV(n), a first terminal of power source PV(x), and a second terminal of power source PV(1). Each intermediate bidirectional voltage converter VC(n) includes a first switch operable in a pulsed mode to boost a power output by power source PV(n) and a second switch operable in a pulsed mode to reduce a power output by power source PV(n). The power conversion system also includes a balancer VC(x) connected to the first terminal of PV(x) and to a load.