Techniques to stop overvoltage-induced inverter disconnections

Jul 31, 2020 10:09 AM ET
  • Australian scientists have actually recognized 7 methods to avoid PV losses when overvoltage-induced inverter disconnections happen. The techniques consist of battery storage space, responsive power inverters, export restrictions, distribution static synchronous compensators, the replacement of old conductors in power grids, load reconfiguration, as well as dynamic voltage repair.
Techniques to stop overvoltage-induced inverter disconnections
Image: BLACKDOTENERGY, pixabay

Researchers at the University of South Australia have actually identified a collection of strategies that can be executed to stop solar energy losses when overvoltage-induced inverter interferences happen, due to voltage restriction violations.

The study team said on-load tap changers (OLTC) and shunt activators-- 2 conventional technologies that are used to attend to the overvoltage issue-- are not specifically efficient for PV generated overvoltages, as a result of the recurring nature of solar power itself. OLTCs are used to control power transformers in electric energy networks and commercial applications, by enabling voltage law and stage moving by differing the transformer ratio under tons without interruption. Shunt reactors are related to high-voltage power networks to maintain the voltage throughout lots variations.

7 more technologies can be utilized in conjunction with the existing options. They include battery storage space, inverters that can give responsive power, export limitations, circulation static synchronous compensators, the replacement of old conductors in power grids with larger ones, load reconfiguration, and also vibrant voltage reconstruction (DVR).

Batteries as well as inverters

The very first of the proposed services is considered extremely reliable, especially if carried out with appropriate sizing, siting and also power management. Existing storage space prices, however, are determined as the major barrier to mainstream deployment in the short-term.

" However, recent patterns reveal a decrease in battery expenses and also this pattern is expected to continue," the scientists claimed.

Nations such as Germany as well as Australia have actually introduced rules in recent years to allow inverters to provide reactive power support. "However, allowing this mode either minimizes active power generation or boosts the size of the inverter," the scientists stated.

This option, which is taken into consideration a legitimate alternative for medium-voltage grids, is thought about much less reliable for low-voltage networks. In such grids, responsive power variations have a reasonably limited impact on voltage.

" Therefore, solar inverters aren't highly effective in lowering the PV curtailment problem," the group concluded, adding that they are just reliable in minimizing PV curtailment if they are integrated with storage.

Export limits

Using a 5-kVA limitation on single-phase inverters to restrict excessive reverse power circulation is a procedure that has been applied by Australian energies. Nevertheless, this strategy must define an export restriction that can attend to the overvoltage issue without excessive degrees of PV curtailment.

Circulation fixed concurrent compensators (DSTATCOM) are taken into consideration especially effective during solar energy generation peaks. The technology can give constant reactive power assistance, yet it is ruled out ideal for reactive power compensation.

Bigger conductors

Bigger conductors are one feasible means to boost grid capacity and make it possible for even more solar energy without voltage changes. "Increasing the cross-sectional area of the conductors can reduce the voltage goes down," the scientists said. "However, this option is costly."

Defined as a strategy than demands extra research study, the reconfiguration of PV installations can aid to improve voltage profiles. "It will certainly enable utilizing the network framework better without much extra framework expense," the scientists discussed.

The last of the 7 services-- using a vibrant voltage conservator (DVR)-- is considered a low-priced, small-sized and reliable method. The device is described as a power digital controller counting on a voltage resource inverter, a filter, and also a capacitor as a storage unit." It is generally a collection compensator whose output is connected in series with the distribution feeder," the scientists said. "It can control the voltage by injecting a voltage of required magnitude and stage angle into the feeder." The remedy is expected to end up being a sensible option in the future, specifically if incorporated with storage. "With using the battery the dimension of the DVR can also be decreased," the scientists claimed.

Potential impacts

The scientists offered the 7 modern technologies in "Effects of high solar photovoltaic infiltration on circulation feeders as well as the economic influence," which was recently published in Renewable and Sustainable Energy Reviews. They evaluated the influences of PV infiltration in regards to reverse power circulation, overvoltage and also undervoltage events at a real 11 kV circulation feeder in South Australia, where the PV infiltration degree is around 21.72%.

They approximated optimal feasible PV generation losses, in addition to the resulting monetary losses, pertaining to inverter shutdowns activated by overvoltage issues.

" At this level of infiltration, the overvoltage events cause nearly a thousand 'nominal voltage violation' circumstances at the inverters causing a minimum of 625 MWh of PV generation loss due to inverter disconnections," the scientists clarified. "For the clients, this stands for an annual monetary loss of over $106,000 because of the loss of power export earnings."