Researchers from the GLA University in India have developed a series of harmonic mitigation techniques for islanding conditions.
“The novelty of this work lies in its unique combination of passive and active detection strategies, optimized through adaptive control mechanisms that enhance both reliability and scalability,” the research's lead author, Sanchari Deb, told pv magazine. “This approach represents a significant advancement over existing methods, which tend to favour either accuracy or scalability, but rarely both. The proposed method is preferable for its ability to provide high detection accuracy with minimal notice to deviate for zero (NDZs), all while maintaining system stability and power quality, making it an ideal choice for future PV system deployments.”
Islanding occurs in distributed generation systems when there are disruptions in the power grid. Under these conditions, PV systems continue to inject power into the grid with negative consequences for the power quality and the risk of potential damage to electrical equipment.
“Understanding the intricacies of islanding events is paramount for devising effective solutions that ensure the seamless integration of PV systems without compromising grid performance,” the scientists stated. “During islanding events in grid-connected PV systems, the presence of harmonics can exacerbate power quality issues, affecting both the grid and connected loads.”
In the paper “A novel technique to detect and mitigate harmonic during islanding in grid connected PV system,” published in Energy Reports, the research group investigated the main factors that lead to islanding events – grid fluctuations, inverter behavior, and system impedance. Their analysis sought to analyze the specific harmonic frequencies generated by PV systems during islanding events and identify critical system parameters.
The proposed set of techniques, which the scientists described as a combination of passive and active detection strategies, includes control algorithms and filter designs, as well as modulation strategies to suppress harmonics during islanded operation. It also integrates advanced signal processing with adaptive control mechanisms. Compared to conventional approaches, it reportedly achieves faster detection times by leveraging real-time data analytics and dynamically adjusting to changing grid conditions.
Image: GLA University, Energy Reports, Common License CC BY 4.0
“Unlike existing methods, this technique is designed with scalability in mind,” the academics said. “The decentralized control structure allows for seamless integration into large-scale PV networks, while the adaptive algorithms ensure that the system can adjust to changing grid conditions in real-time.”
The researchers also presented theoretical principles behind islanding detection and focused, in particular, on two islanding detection techniques such as the Slip Mode Frequency Shift (SMS) and Phase Jump Detection (PJD). They also offered a new approach to analyze how impedance mismatches can impact harmonic suppression during islanding.
The proposed method was validated under PV system sizes ranging from 5 kW to 100 MW and was found to achieve a total harmonic distortion (THD) reduction of approximately 3%, which compares to 4.5 % for existing hybrid methods.
“This reduction aligns with IEEE 519 standards, making the system more compliant with grid regulations while maintaining higher power quality,” the scientists emphasized. ” The proposed method consistently maintained an average error margin of less than 2 % in detection accuracy, compared to a 5–7 % error in traditional methods.”
The team said crucial for their work was selecting appropriate detection thresholds and response times for different grid conditions. “By optimizing these parameters, it is possible to balance the trade-off between detection speed and system stability, ensuring reliable anti-islanding protection across a wide range of operating scenarios,” they concluded.
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