Researchers in Egypt have developed new control strategies for managing frequency fluctuations during the removal of a photovoltaic plant. The proposed methodology combines a proportional integrated controller together with a speed of change from frequency inverter.
A research group led by scientists at Cairo University in Egypt has developed a new control strategy for frequency levels during the removal of PV systems.
“This article evaluates the performance of the conventional PV Deloaded System Controller and shows its limitations,” said the academic. “An important contribution to this study is the proposal of a blended controller that improves both frequency and frequency change (Rocof). Moreover, it is proposed to facilitate a modified controller to facilitate a safe transition to normal Deload levels.”
The proposed strategy combines a proportional integral (PI) controller together with a rocof controller.
The group initially simulated a conventional Deloading check as a reference. The simulation was performed in the Simulink model, set on a PV penetration rate of 30% and a tax variation of 1% or 0.01 PU. The conventional control strategy, also known as PI Droop, enables PV systems to reserve part of the available power to offer dynamic support in both short and long-term frequency scenarios.
“The conventional Deloading operating method shows certain restrictions when it comes to support for various frequencies,” the tests have shown. “Although some improvements have been noticed in terms of frequency -after, the level of change that is seen in the rocof is quite limited, so that the system is unable to return to the usual business state.”
For this reason, the group has proposed its mixed control, which contains a Rocof controller who monitors how quickly the frequency changes, and when it recognizes a rapid fall, it sends a signal to the PV system to increase its power. This ultimately slows down the frequency decrease, while the PI controller gradually adjusts PV power and helps to reduce it to the designated level.
Moreover, the group has developed a modified version of its blended model by adding a recovery mechanism. Initially, the control action stimulates the power of the PV system, followed by a gradual decrease over the remaining duration of the event. The system was able to improve Rocof by 3.11%, compared to 0.2% for the non-modified mixed method.
“The modified controller distinguishes itself because of the ability to maintain the lowest frequency of Nadir and Rocof levels among all controllers considered, while it was still achieved an acceptable location,” concluded the team. “Moreover, this controller is able to restore the system to its normal working point, which guarantees a more stable and reliable processing. The modified controller has a relatively longer location, but it is reasonable with the characteristics of reducing the operating system to the normal working point.”
The method and the test results were presented in “Improved control strategies for managing frequency loads during the unloading of a photovoltaic system“Published in Ain Shams Engineering Journal.
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