American researchers have studied the sensitivity of photovoltaic inverters to electromagnetic pulses generated by high-altitude nuclear explosions during nuclear weapons testing. Their work suggests several protection strategies aimed at improving the security level of inverters.
High-altitude electromagnetic pulses (HEMPs) generated by high-altitude nuclear explosions caused by nuclear weapons testing can cause destructive current and voltage surges in electrical and electronic systems on Earth, with serious consequences for the systems themselves and for the power grid and power systems. supply.
In 1962, both the United States and the Soviet Union conducted the largest high-altitude nuclear weapons tests. Both tests were reported to have caused severe damage to the network. To this end, several research institutions have in recent years investigated the extent of the impact of electromagnetic pulses on electricity supplies at the national and macro-regional levels to identify possible mitigation solutions.
Using this approach, a team of researchers from the University of Tennessee and the U.S. Department of Energy’s Oak Ridge National Laboratory (ORNL) recently studied the susceptibility of solar inverters to HEMP. “Our work provides deep insight into solar inverter protection and HEMP protection,” said Qiu Wei, lead author of the study, in an interview with Photovoltaics.
The scientists explained that HEMP propagation occurs in three stages, generally classified as E1, E2 and E3, with each stage defined by different spatial and temporal characteristics. “E1 is the start of the explosion and changes rapidly over hundreds of nanoseconds,” they emphasized. “E1 has much higher energy than E2 and E3 and has the greatest impact on the power grid.”
Specifically, the team analyzed the impact of stage E1 HEMP on solar inverters. It uses a pulsed current setup (PCI) based on charge/discharge capacitors and an injection probe to reproduce strong transient electromagnetic interference (which typically occurs when a source emits short pulses of energy) and evaluates three different resistances. kW equipment manufacturer Danfoss Denmark, an 8.2 kW inverter from the Austrian manufacturer Fronius and a custom-made inverter with a capacity of 6 kW.
They chose two “typical” immunity levels, EC5 and EC8, with open circuit voltages of 2000 V and 8000 V respectively.
The researchers also applied a port vulnerability analysis scheme based on three different vector network analyzers (VNAs) with frequencies ranging from 50 Hz to 1.3 GHz. A VNA is a standard test instrument used to measure network parameters for the purpose of making measurements over a wide frequency range. “The vulnerability of a port is assessed by its frequency spectrum and stored energy, and the advantage of the PCI model is the rapid analysis of transients,” they further explained.
The scientists said their analysis showed that the VNAs were consistent with each other, ensuring that the measurements were taken correctly.
“PCI test results show that at immunity levels EC5 and EC8, the maximum voltage and current at EC5 can reach 1500 V and 40 A, respectively, while EC8 can reach 8,000 V and 150 A, respectively, which shows that EC8 can cause serious vulnerabilities “, they said. “Port vulnerability analysis results indicate that the inverter can be damaged by higher voltage or shorter rise time, and also indicate that EC8 is difficult to defend against due to its wider power frequency (from 0.1 MHz to 100 MHz)”.
As a mitigation strategy, they recommend reducing surge voltages for functional and basic insulation, as well as shielding and grounding. “Proper grounding requires low ground resistance and a large number of ground points. Short, flat ground wires should be buried deep underground to reduce resistance and inductance,” they added. “The distance between two adjacent grounding points should be small. Moreover, the grounding point should be as close as possible to the equipment being protected.”
Their findings are published in the paper “Assessing Solar Inverter EMI Vulnerability: Port Testing, PCI Modeling, and Protection Strategies,” published in the journal Measurement.
Oak Ridge National Laboratory conducted a similar study in 2020 on the effects of HEMP on solar panels. These tests showed no significant loss of solar module functionality due to strong electric field transients.
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Post time: Apr-11-2024