Offset Voltage Source for PV Power Plant Ground Loop Avoidance
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Solution Overview
Problem
Large PV power plants face inefficiencies and potential damage due to grounding requirements, which can lead to ground loops, corrosion, and electromagnetic interference, especially in systems with thin film or back-contact modules, and existing solutions often rely on expensive transformer-based inverters or labor-intensive grounding configurations.
Innovation Solution
A PV power plant design incorporating an offset voltage source that controls the DC potential at the AC outputs, allowing non-negative or non-positive potentials at PV module terminals without grounding, thus avoiding ground loops and enabling the use of transformer-less inverters, with the offset voltage source being programmable and adaptable to different PV string types and conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If grounding is implemented to comply with regulations and prevent corrosion, then reliability is improved, but ground loops and electromagnetic interference occur
Solution Approach 1:
The patent introduces an offset voltage source as an intermediary component between the PV string and ground. This offset voltage source shifts the potential of the PV string terminals relative to ground, allowing the system to maintain defined potentials without direct grounding connections, thereby preventing ground loops and electromagnetic interference while still ensuring regulatory compliance and corrosion prevention.
2Object-affected harmful factors
If transformer-based inverters are used to separate DC and AC sides galvanically, then electromagnetic interference is reduced, but device complexity and cost increase
Solution Approach 1:
The offset voltage source acts as a mediator that enables the use of simpler transformer-less inverters by providing the necessary potential reference without requiring galvanic isolation transformers. This intermediary component allows the system to achieve electromagnetic interference reduction through potential control rather than physical isolation, thereby reducing device complexity and cost.
3Reliability
If PV modules are grounded to prevent corrosion and detect isolation faults, then reliability is improved, but module efficiency decreases due to static charge buildup
Solution Approach 1:
The offset voltage source serves as an intermediary that references PV module terminals to a shifted potential rather than directly to ground. This approach maintains the benefits of fault detection and corrosion prevention while avoiding direct grounding connections that cause static charge buildup, thereby preserving module efficiency.
4Device complexity
If transformer-less inverters are used to reduce cost and weight, then device complexity is reduced, but ground loops and potential control issues arise
Solution Approach 1:
The offset voltage source is introduced as an intermediary component that enables transformer-less inverters to operate without ground loops. By providing a shifted potential reference, it allows the inverter to control PV string potentials relative to ground without requiring direct grounding connections, thus eliminating ground loops while maintaining the cost and weight advantages of transformer-less design.
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, reduces costs and weight by eliminating the need for transformer-based inverters, prevents damage to PV modules, and allows for adaptive control of potentials to mitigate degradation and interference issues, while simplifying the installation and maintenance of PV power plants.
Implementation Method 1
an offset voltage source, which controls the DC potential at the AC outputs. Thereby, the DC potential at the DC input will be indirectly controlled
Implementation Method 2
the PV modules, which convert the solar energy into electrical energy
Data Source
AI summary
In large PV power plants, grounding of individual PV modules may lead to problems. The present invention overcomes such problems. The basis for the invention is a PV power plant comprising one or more PV generators, each comprising a PV string and an inverter with a DC input and an AC output. The PV string comprises at least one PV module and is electrically connected to the DC input of the inverter. The inverter comprises means for controlling the DC potential at the DC input depending on the DC potential at the AC output. The AC outputs of the inverters are coupled in parallel. The novel feature of the invention is that the PV power plant further comprises an offset voltage source, which controls the DC potential at the AC outputs. Thereby, the DC potential at the DC input will be indirectly controlled, and it is thus possible to ensure that the potentials with respect to ground at the terminals of the PV modules are all non-negative or all non-positive without grounding the PV modules. Ground loops can be avoided, and there is no need for the use of transformer-based inverters.