Photovoltaic power plant with a compensated voltage source controlling the dc potential at the output of the converter

Abstract

In large PV power plants, grounding of individual PV modules may lead to problems. The present invention overcomes such problems. The PV power plant (34) comprises an offset voltage source (14), wich controls the DC potential at the AC outputs (19). 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 (15) at the terminals of PV modules (5) 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 (4).

Description

technical field [0001] The present invention relates to a photovoltaic (PV) power plant. Background technique [0002] In larger PV power plants with DC / AC converters (converters), the power plant is typically connected to the grid via a dedicated isolation transformer that connects the lower voltage PV generator system to the medium voltage grid. One of the reasons for this is that PV modules that convert solar energy into electricity generally must have a defined potential with respect to ground. This is generally accomplished by grounding all or some of the PV modules. [0003] Grounding is usually done to comply with local regulations, to detect insulation defects of the PV modules, and / or to avoid corrosion and / or yield reduction of the PV modules. [0004] In larger systems, it may be difficult to detect insulation defects because of the considerable leakage currents of individual PV modules, especially under wet conditions. Leakage current can be monitored by grou...

AI Technical Summary

Problems solved by technology

[0014] A disadvantage of this type of power station is the requirement that the ground connection 32 needs to be physically connected to either the positive input 7 or the negative input 8 of the converter 24

This requires additional assembly labor and hardware

Furthermore, changing PV module types at a later date may involve physical disconnection and / or reconnection of ground connection 32, a labor-intensive process and thus a disadvantage

Additionally, if Image 6 If two or more PV generators 23 are shown connected in parallel, and one input of each inverter 23 is grounded as described above, problems can arise if the characteristics or irradiance of each PV string 3 are not the same

This can lead to unwanted voltages and consequent ground loop currents

[0015] In all the prior art power plants described above, it can be seen that although the potential of one or more PV strings with respect to ground is an important parameter for operating the power plant in an efficient manner and does not lead to damage, but this is often only achievable with expensive hardware or laborious assembly of additional hardware

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