Photovoltaic Infeed Converter With Shared Inductor For Current Sharing
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Solution Overview
Problem
Photovoltaic power conditioning units face inefficiencies, particularly at low power output levels, especially during early and late day, and overcast conditions, which limits the overall energy yield from solar panels.
Innovation Solution
A power conditioning unit design featuring a dc-to-dc converter with a shared inductor and dc-to-ac converter, utilizing a transformer with a winding tap and series inductor to facilitate current sharing between converters, optimizing efficiency by reducing component tolerance variations and I^2R losses, and incorporating a controller for dynamic operation of converters based on power levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple dc-to-dc converters are connected in parallel to increase power handling capability, then the power output capacity is improved, but current sharing between converters becomes difficult to control and component tolerance variations cause inefficiency
Solution Approach 1:
A current sharing inductor is introduced as an intermediary component connected in series with each parallel dc-to-dc converter. This inductor acts as a mediator that senses and equalizes the current drawn by each converter, forcing them to share the total load current equally despite variations in component tolerances or operating conditions.
2Manufacturing precision
If component tolerances are tightly controlled to improve current sharing, then the manufacturing precision is improved, but the cost and complexity of the system increases
Solution Approach 1:
The current sharing inductor creates a self-regulating system where each converter automatically adjusts its current draw based on the voltage drop across its series inductor. The converter with slightly higher current draw experiences a larger voltage drop, which naturally reduces its current intake, creating a self-balancing effect without requiring complex control circuitry or tight component tolerances.
3Reliability
If oversized components are used to account for component value variations, then the reliability is improved, but the device complexity and cost increase
Solution Approach 1:
The current sharing inductor serves as a compensating intermediary that actively counteracts the effects of component value variations. By introducing this controlled impedance element, the system achieves reliable current sharing without needing to oversize other components, as the inductor itself becomes the primary mechanism for maintaining balance under varying conditions.
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 design enhances efficiency by reducing component stress, losses, and ripple, allowing for accurate resonant frequency control and efficient operation across varying power levels, thereby increasing energy yield from solar panels.
Implementation Method 1
a transformer having an input winding and an output winding
Implementation Method 2
a series inductor connected to said winding tap; and wherein said rectifiers are each connected to said winding tap of said output winding via said series inductor such that said series inductor is shared between said first and second rectifiers
Implementation Method 3
first and second rectifiers, each connected to a respective first and second said portion of said output winding, to said dc link, and to said winding tap
Data Source
Figure 1
Figure 2a
Figure 2b
AI summary
We describe a photovoltaic power conditioning unit comprising: a dc power input; an ac power output; a dc link; at least a first dc-to-dc converter coupled between the dc power input and the dc link; and a dc-to-ac converter coupled between the dc link and the ac power output. The dc-to-dc converter comprises: a transformer having input and output windings; an input dc-to-ac converter coupled between the dc power input and the input winding of the transformer; and an ac-to-dc converter coupled between the output winding of the transformer and the dc link. The output winding of the transformer has a winding tap between first and second portions of the output winding. The ac-to-dc converter comprises: first and second rectifiers, each connected to a respective first and second portion of the output winding, to the dc link, and to the winding tap; and a series inductor connected to the winding tap. The rectifiers are each connected to the winding tap of the output winding via the series inductor such that the series inductor is shared between the first and second rectifiers.