Leakage Current Control in Parallel Inverter Systems
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Solution Overview
Problem
In systems with multiple inverters connected in parallel, leakage currents can occur due to differing ground potentials, leading to potential damage and operational issues, which are typically addressed by using costly galvanic isolation measures like multiple windings on LV/MV transformers.
Innovation Solution
Implementing an active control system for leakage currents using current detectors and feedback loops to manage the ground connection between each inverter and its DC energy source, allowing for voltage adjustments across bulk capacitors to minimize leakage currents without the need for shared data or galvanic isolation between inverters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple inverters are connected in parallel with separate ground connections, then each inverter can operate independently with its own DC source, but strong leakage currents are generated due to different ground potentials
Solution Approach 1:
A neutral/ground transformer is introduced as an intermediary device between the inverters and the distribution grid. The transformer provides a common reference potential through its neutral point while galvanically isolating the inverters from direct ground connections, thereby eliminating leakage current paths while maintaining independent operation capability
Solution Approach 2:
The grounding system is segmented into separate galvanically isolated sections for each inverter, with each inverter connected to the transformer's secondary side. This segmentation prevents direct ground current paths between inverters while maintaining individual ground references through the transformer's neutral point
2Object-generated harmful factors
If multiple windings output transformers are used to provide galvanic isolation, then leakage current recirculation is avoided, but the system becomes very complex and costly
Solution Approach 1:
Multiple inverters share a single neutral/ground transformer instead of each inverter requiring its own dedicated transformer winding. The transformer's multiple secondary windings are combined into a common neutral point, providing galvanic isolation for all inverters while simplifying the overall system architecture and reducing component count
Solution Approach 2:
The neutral/ground transformer serves multiple functions simultaneously: it provides galvanic isolation for all inverters, establishes a common reference potential, enables neutral grounding for the distribution grid, and prevents leakage current recirculation. This multi-functionality eliminates the need for separate dedicated isolation devices for each inverter
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 reduces leakage currents to a desired value, such as zero, without the need for costly isolation measures, thereby reducing electrical noise and stress, and enabling multiple photovoltaic fields or sources to be connected at the same ground potential while maintaining AC grid compatibility.
Implementation Method 1
a ground connection branch with a current sensor which supplies a signal proportional to a leakage grounding current measured in said ground connection branch
Implementation Method 2
from said signal supplied by said current sensor a feedback signal is generated to control the leakage current
Data Source
AI summary
There is described an electrical energy conversion system comprising: at least a first inverter (1) and at least a second inverter (2), whose outputs are connected in parallel; at least a first DC voltage source (PV1) connected to the input of the first inverter (1) and a second DC voltage source (PV2) connected to the input of the second inverter (2); a ground connection of the first inverter (1) and a ground connection of the second inverter (2). The ground connection of said inverters comprises a ground connection branch (1G; 2G) with a current sensor (5/1; 5/2) which supplies a signal proportional to a leakage grounding current (Ileak) measured in said ground connection branch (1G; 2G). Through the signal proportional to the leakage current measured a feedback signal is generated to control the leakage current (Ileak).