Sandia Frequency Shift Method Research Articles

Performance of a new hybrid approach for detection of islanding for inverter-based DGs

This paper proposes a new hybrid method for islanding detection and minimizes the Non-Detection Zone (NDZ), for an inverter-based grid-connected distributed generation (DG) system. The proposed hybrid method is an integration of the modified active Sandia Frequency Shift (SFS) method and the passive reactive power variation technique. The modified active SFS method is obtained by adaptive tuning of the gain parameter Ksfs, using the Adaptive Particle Swarm Optimization (APSO) technique. The proposed hybrid method produces a significant reduction of NDZ and is suitable for more accurate detection of islanding condition. The effect of NDZ for the proposed hybrid method has been derived analytically and the system performance has been assessed, under various power mismatch conditions for a DG-grid interface. The overall system performance has been found to be superior under the presence of constant power control strategy. The effect of frequency and voltage variations at the common coupling point during islanding have also been considered. Finally, the performance of the proposed method under the IEEE standard 1547 islanding test condition has been investigated for different load factors and load variations.

Proposed Sandia frequency shift for anti-islanding detection method based on artificial immune system

Sandia frequency shift (SFS) is one of the active anti-islanding detection methods that depend on frequency drift to detect an islanding condition for inverter-based distributed generation. The non-detection zone (NDZ) of the SFS method depends to a great extent on its parameters. Improper adjusting of these parameters may result in failure of the method. This paper presents a proposed artificial immune system (AIS)-based technique to obtain optimal parameters of SFS anti-islanding detection method. The immune system is highly distributed, highly adaptive, and self-organizing in nature, maintains a memory of past encounters, and has the ability to continually learn about new encounters. The proposed method generates less total harmonic distortion (THD) than the conventional SFS, which results in faster island detection and better non-detection zone. The performance of the proposed method is derived analytically and simulated using Matlab/Simulink. Two case studies are used to verify the proposed method. The first case includes a photovoltaic (PV) connected to grid and the second includes a wind turbine connected to grid. The deduced optimized parameter setting helps to achieve the “non-islanding inverter” as well as least potential adverse impact on power quality.

Accurate SFS Parameter Design Criterion for Inverter-Based Distributed Generation

The Sandia frequency-shift method, among all frequency-based active islanding detection methods (IDMs), is one of the most effective methods for inverter based distributed generators (DGs). The nondetection zone (NDZ) of the Sandia frequency shift (SFS) highly depends on its design parameters. If the design parameters are not properly tuned, they may result in failure of the method or deterioration of the system power quality (PQ) through injection of a high amount of harmonics. The main objective of this paper is to propose a new algorithm for SFS method parameter determination, which would add precision to the previous parameter design criterion. In this paper, also a new formula for multi-DG applications is proposed which results in optimally setting of all SFS parameters to eliminate NDZ. Using the new criterion, the negative impact of the conventional criterion on PQ is reduced, and the efficiency of the SFS IDM is increased. The simulation results show that the proposed algorithm results in more accurate detection of the islanding phenomenon in the shortest possible time. All of the simulations and NDZ analysis are carried out in the MATLAB environment.

Scheduled Perturbation to Reduce Nondetection Zone for Low Gain Sandia Frequency Shift Method

It is known that the choice of gain ( ${K}$ ) in the Sandia frequency shift (SFS) scheme has direct impacts on the stability of a system with grid-connected distributed generations (DGs). In this paper, a scheduled perturbation technique is proposed to reduce the stability impact of ${K}$ . In the proposed technique, chopping fraction ( cf ) is used to compensate for reduction in the value of ${K}$ , where higher cf values are used to achieve zero nondetection zone (NDZ) under low gain SFS. It is shown by analysis that theoretical reduction of NDZ can be always achieved for a nonzero value of cf . Simulations for single- and multi-DGs systems are performed to verify the analytical analysis. It is shown that an appropriate design of scheduled signal duty cycle ( ${d}$ ) is of critical importance to realize the proposed reduction in NDZ. While close synchronization of perturbation signals for multi-DG system is required, a delay of 0.33 s is shown to be tolerated for a two-DG system. Synchronization can be achieved either through locally synchronized timers or by limited communication among DGs. The proposed technique provides an attractive option for systems with high DG penetration by reducing the negative impact of ${K}$ on stability.

Adaptive Fuzzy Sandia Frequency-Shift Method for Islanding Protection of Inverter-Based Distributed Generation

Sandia Frequency Shift (SFS) is one of the active islanding detection methods that rely on frequency drift to detect an islanding condition. Recently, SFS has been widely applied to inverter-based distributed generations due to its small Non-Detection Zone (NDZ). The NDZ in SFS method highly depends on its design parameters. Improper tuning of these parameters may result in failure of the method. In the proposed method in this paper, the load parameters are estimated online and the SFS parameter is adaptively tuned to eliminate NDZ using fuzzy load parameter estimation (FLPE) method. Simulation results verify the excellent performance of the proposed method.

Impact of Load Frequency Dependence on the NDZ and Performance of the SFS Islanding Detection Method

Sandia frequency shift (SFS) falls under the active islanding detection methods that rely on frequency drift to detect an islanding condition for inverter-based distributed generation. Active islanding detection methods are commonly tested on constant <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> loads where the load's active power is directly proportional to the square of voltage and is independent on the system frequency. Since the SFS method relies primarily on frequency to detect islanding, the load's active power frequency dependence could have an impact on its performance and the nondetection zone (NDZ). In this paper, the impact of the load's active power frequency dependence on the performance of the SFS method, during an islanding condition, is analyzed. A NDZ model that takes into account the load's frequency dependence parameter is derived mathematically and validated through digital simulation. The results show that the load's frequency dependence has a significant impact on the NDZ of the SFS method and thus is an important factor to consider when designing and testing this method.

Sandia frequency shift parameter selection for multi-inverter systems to eliminate non-detection zone

Among frequency drift islanding detection methods, Sandia frequency shift (SFS) is considered as one of the most effective methods in detecting islanding conditions for grid connected photovoltaic (PV) inverters. The performance of the SFS method during an islanding condition and its non-detection zone (NDZ) depends to a great extent on its parameters. Furthermore, the capability of the SFS method to detect an islanding condition deteriorates with multiple PV inverters. A mathematical formula is derived to aid protection engineers in determining the optimal setting of the SFS islanding detection parameters with multiple inverter-based distributed generation (DG), such as PV systems, to eliminate the NDZ. The derived formula is applied to multiple DG systems equipped with the over frequency/under frequency protection, active frequency drift and SFS islanding detection methods and is verified through NDZ analysis and simulation results on PSCAD/EMTDC. The derived formula provides an effective guideline for designing frequency drift methods in multi-inverter-based DG systems.

Design methodology for the frequency shift method of islanding prevention and analysis of its detection capability

Islanding protection is one of the most important sources of discrepancy in grid-connected photovoltaic systems. Even when islanding is not very likely to happen, regulations demand the photovoltaic inverters to implement effective protection methods. Due to its several advantages, the frequency shift method of islanding prevention, commonly known as Sandia Frequency Shift, is one of the most important active methods. This method implements a positive feedback of the frequency that tends to move it outside the trip limits in case of islanding. The method shows a very high detection capability, which depends on both the values of the method parameters and the characteristics of the load that remains in the same power section after islanding. This paper develops a mathematical analysis of the Sandia Frequency Shift method and proposes a new methodology to design its parameters as a trade-off between the detection capability, which is evaluated as a function of the load characteristics, and the distortion that the method could introduce in the grid as a consequence of transitory frequency disturbances. The ability of this methodology to design the method parameters and achieve the highest detection capability is satisfactorily proved by means of both simulation and experimental results on a commercial photovoltaic inverter that implements the method once its parameters have been designed with the proposed methodology. Copyright © 2005 John Wiley & Sons, Ltd.