Common-Mode Transformer for Parallel DC/AC Converters
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Solution Overview
Problem
Photovoltaic installations face issues with electromagnetic compatibility (EMC) and electric risks due to high-frequency voltage variations between input terminals and ground, which can damage insulation and pose safety hazards, especially when multiple DC/AC converters are connected in parallel without transformers, leading to increased costs and reduced system output.
Innovation Solution
A control method for multi-converter systems connects all converters to a single transformer with a single primary winding, using pulse width modulation (PWM) and an auxiliary device to match common-mode voltages generated by each converter, ensuring these voltages fall mainly on the transformer, thus maintaining constant voltage at input terminals with respect to ground and reducing EMC issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If multiple DC/AC converters are connected in parallel without individual transformers, then installation cost is reduced and system efficiency is improved, but high-frequency voltage variations occur between input terminals and ground causing insulation damage and EMC problems
Solution Approach 1:
The patent introduces a single common-mode transformer as an intermediary component that all DC/AC converters share. This transformer mediates the common-mode voltages from multiple converters, providing a unified reference potential and preventing high-frequency voltage variations between input terminals and ground. The transformer acts as a mediator that maintains galvanic insulation and voltage stability without requiring individual transformers for each converter.
Solution Approach 2:
The patent merges multiple individual transformer functions into a single common-mode transformer that serves all DC/AC converters in parallel. By combining the galvanic insulation and common-mode voltage reference functions into one shared transformer, the system reduces overall cost and complexity while maintaining the necessary protection against high-frequency voltage variations.
2Object-affected harmful factors
If individual transformers are used for each DC/AC converter, then high-frequency voltage stability is maintained, but system size, weight, and cost increase significantly
Solution Approach 1:
The patent combines multiple individual transformer functions into a single common-mode transformer that serves all DC/AC converters. This merging approach maintains high-frequency voltage stability through the transformer's galvanic insulation and common-mode reference, while dramatically reducing system weight by eliminating redundant transformer components.
Solution Approach 2:
The common-mode transformer is designed to perform multiple functions simultaneously: providing galvanic insulation for all converters, establishing a common reference potential, and suppressing high-frequency voltage variations. This multi-functional approach replaces what would otherwise require multiple separate transformers, reducing overall system weight.
3Reliability
If individual transformers are used for each DC/AC converter, then galvanic insulation and voltage stability are ensured, but installation price increases considerably
Solution Approach 1:
The patent merges the galvanic insulation function across multiple converters into a single common-mode transformer. This shared transformer provides the necessary electrical isolation and voltage stability for all converters while reducing the total component count and installation cost compared to using individual transformers for each converter.
Solution Approach 2:
The common-mode transformer is designed to provide universal galvanic insulation and voltage reference for all DC/AC converters in the system. This multi-functional design ensures reliability through maintained galvanic insulation while reducing installation price by eliminating the need for multiple separate transformer units.
4Productivity
If individual transformers are used for each DC/AC converter, then system output is reduced due to increased losses, but removing transformers improves efficiency
Solution Approach 1:
The patent combines the magnetic core functions of multiple individual transformers into a single common-mode transformer, which reduces total core losses and copper losses. The shared magnetic path and optimized winding configuration improve overall conversion efficiency and system output compared to using multiple separate transformers.
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 eliminates insulation and safety risks, reduces costs, and enhances system output by ensuring common-mode voltages are managed effectively, resulting in a more robust and efficient power conversion system.
Implementation Method 1
This transformer provides galvanic insulation between the installation and the grid
Implementation Method 2
The converter is made up of power transistors that switch at high-frequency to convert the direct current provided by the photovoltaic generator into alternating current
Implementation Method 3
the photovoltaic generator has a parasitic capacity between the active terminals (positive and negative) and the ground (CPV), this parasitic capacity being proportional to the area
Data Source
AI summary
A control method for multi-converter systems wherein all DC/AC converters (1.1-1.n) are connected to a single transformer (2) via a single primary winding. The method of the present invention stands out mainly because it controls the common-mode voltage generated by the different DC/AC converters (1.1-1.n) so that said voltage falls mainly on the transformer (2).