Slip Mode Frequency Shift Research Articles

Review, analysis, and performance evaluation of the most common four active methods for islanding detection in grid-connected photovoltaic systems

• The AFD, SFS, SMS, and SVS active islanding detection methods. • The studied methods provide good detection times within the new grid standards. • The methods have good detection times under different parameters and scenarios. • The active methods are studied and compared for the first time in a detailed study. This paper systematically analyzes the islanding performance under different case studies and scenarios of the most well-known active islanding detection methods (IDMs) for single-phase grid-connected photovoltaic (PV) systems. They are named as follows: Active Frequency Drift (AFD), Sandia Frequency Shift (SFS), Slip Mode frequency Shift (SMS), and Sandia Voltage Shift (SVS) anti-islanding detection strategies. The performance of these four active anti-islanding methods has been examined in detail using Matlab/Simulink. Moreover, the quality factor and non-detection zone (NDZ) influence on islanding detection is also analyzed. According to the new grid codes and standards, the studied active IDMs provide good detection times. Furthermore, the case studies illustrate that these active detection techniques can successfully detect the islanding operation mode under different quality factors, types of loads, solar irradiance changes, and fault-ride through (FRT) operation mode.

Anti-Islanding Detector Based on a Robust PLL

As required by international standards, the distributed energy generators, connected to the grid by an inverter, have to detect an islanding condition within a suitable time interval. In this paper, a phase-locked loop (PLL), based on a third-order prediction-correction filter, is proposed to implement an islanding detector with reduced detection time. Such a feature is obtained using the estimation of the grid angular frequency and acceleration provided by the PLL with a negligible time delay. The proposed approach is implemented on an industrial grade DSP and validated through the experimental comparison among different detection methods, such as rate of change of frequency (ROCOF) and Slip Mode frequency Shift (SMS). The combined use of ROCOF and SMS is also illustrated and discussed.

Performance Assessment of Slip Mode Frequency Shift (SMS) Islanding Detection Methods

The awareness concerning the grid connected Photovoltaic (PV) has become vital and a major concern nowadays. Islanding detection is one of the most dominant challenges for distributed generation system connected to the utility grid. In addition, islanding has not been a preferable option as it may pose safety hazard and may cause damage to power generation and power supply facilities as a result of unsynchronized re-closer. Therefore, the islanding detection techniques are needed to ensure safe and reliable system operation. One of the established islanding prevention methods is the Slip Mode Frequency Shift (SMS) islanding method, which has numerous advantages over the other techniques. This paper investigates the active islanding detection methods and specifically focused on the SMS islanding method. The results show that the SMS islanding method successfully detected an unintentional fault and managed to isolate the system within the prescribed time range.

A novel islanding fault detection for distributed generation systems

SUMMARYThis paper proposes a novel islanding fault detection method for distributed generation systems. Islanding fault detection of distributed generation systems in microgrids and smart grids is an essential security technology. The existing methods for islanding fault detection can be classified as passive methods (such as under/over voltage detection, under/over frequency detection, and voltage phase jump detection, based on natural effects of islanding) and active methods (impedance measurement, slip mode frequency shift, Sandia frequency shift and so on). Once the power consumed by a local load matches the power generated by a local inverter, the islanding phenomenon will be not obvious, and traditional passive methods may fail. In contrast, the active methods can overcome this disadvantage. However, active methods create extra disturbances that may degrade the quality of power generated by the inverter. By reducing the harmonics of the inverter output, coupled with the use of a novel filtering method, the proposed approach can be achieved without additional disturbance and does no nondetection zone islanding detection. In this paper, current harmonic compensation is applied to inverter control to minimize the inverter output harmonics, highlighting on the grid harmonics. Set‐membership filter is developed to estimate the voltage harmonics. Islanding condition is detected by the changes of the specific order harmonics. The effectiveness of the proposed method is demonstrated by simulations. A Kalman filter contrast experiment is presented to confirm that the set‐membership filter can more effectively detect islanding. Copyright © 2013 John Wiley & Sons, Ltd.

Investigation and evaluation of active frequency drifting methods in multiple grid-connected inverters

As the development of distributed generation goes on, more grid-connected inverters are being inevitably connected to the same local electrical power system and the perturbations exerted by each inverter for islanding detection might interfere with each other. The islanding detection principle of commonly used active frequency drift (AFD), sandia frequency drift and slip-mode frequency shift are comprehensively investigated and improved algorithms are proposed as well for better detection performance. Moreover, the interaction of these strategies applied in multiple-inverter systems especially with frequency measurement errors is systematically analysed. The corresponding detection performance is summarised, which can also serve as an effective guideline for designing AFD methods in multi-inverter systems. Finally, simulation and experimental results are provided to verify the islanding detection performance of these methods under multiple-inverter operation.

Improved SMS islanding detection method for grid-connected converters

Islanding detection is a mandatory function for grid-connected converters. The popular slip mode frequency shift (SMS) and auto phase shift active islanding detection methods are investigated and an improved (IM)-SMS strategy is proposed in this study. In the proposed method, additional phase shift is introduced to help in stimulating the action of the islanding detection and the algorithm is simplified as well. When the utility grid is disconnected, the algorithm keeps the frequency of the converter output voltage deviating until the frequency protection relay is triggered. The working principle of the method is introduced and the guidance of parameters selection and optimisation is also provided. The islanding detection performance is evaluated through theoretical analysis and verified by digital simulation and experimental results. The IM-SMS method exhibits features of simplicity, easy implementation and high reliability.

A combined active anti-islanding method for photovoltaic systems

In a modern power system, photovoltaic as distributed generated source is growing larger and it can cause a variety of problems. The most important problem is that of the islanding phenomenon. In order to prevent islanding phenomenon, three kinds of active islanding detection methods have been studied. These are, respectively, to change magnitude, frequency, and the start phase of inverter output current. Among those, both a frequency variation method and a start-phase variation anti-islanding method make the islanding frequency drift away from the trip window of the frequency relay if islanding occurs. This paper presents a novel combined active anti-islanding method, which consists of a frequency variation method active frequency drift (AFD) and a start-phase variation method slip-mode frequency shift (SMS). Clearly, the proposed anti-islanding method shows the islanding detection ability to IEEE 1547 Standard. To validate the performance of the proposed method, simulations and experiments were performed. Possible islanding conditions are implemented with a unity quality factor by the IEEE Standard 1547. The methodology presented can be extended to the other active anti-islanding methods.

Modeling and design of phase shift anti-islanding method using non-detection zone

Islanding phenomenon of a grid-connected independent generator like a photovoltaic (PV) system occurs when a section of a utility system is disconnected from the main utility voltage source, but the independent generator continues to energize the utility lines in the isolated section. Since islanding causes a safety hazard to utility service personnel and damage to power supply facilities as a result of unsynchronized reclosure, PV inverter is required to have anti-islanding function. In order to prevent this phenomenon, various anti-islanding methods have been studied. Even though phase shift anti-islanding method including slip mode frequency shift (SMS) method and reactive power variation (RPV) method has been regarded as a highly effective anti-islanding method, the analytical design method of that has not been cleared. This paper proposes a design guideline of the phase shift anti-islanding method based on non-detection zone (NDZ). As leading phase shift anti-islanding methods, both SMS and RPV methods are discussed to verify the validity of the proposed method. Both methods are derived analytically through the modeling and verified visually by simulation and experiment under IEEE Std. 929-2000 test condition. It is shown that both methods designed by the proposed method have effectiveness to detect islanding within 2 s and good power quality above 0.99 power factor. The presented methodology in this paper can be extended to design other active anti-islanding methods.

Performance Assessment of Active Frequency Drifting Islanding Detection Methods

Islanding detection is a mandatory feature for grid-connected inverters. The effectiveness of passive islanding detection methods (IDMs) is usually demonstrated by means of nondetection zones (NDZs) represented in a power mismatch space (/spl Delta/P versus /spl Delta/Q). Active frequency drifting IDMs have been shown to provide improved performance but their theoretical NDZ cannot be described in the /spl Delta/P versus /spl Delta/Q space for a general RLC load. This paper shows that a load parameter space based on the values of the quality factor and resonant frequency of the local load (Q/sub f/ versus f/sub 0/) can be used in these cases. It employs a single curve to represent the NDZ of frequency drifting IDMs for any RLC loads. Equations that represent NDZs of three common active IDMs in the Q/sub f/ versus f/sub 0/ load parameter space are derived and it is shown that the slip mode frequency shift and the Sandia frequency shift IDMs can be designed to guarantee islanding detection for equivalent RLC loads with a quality factor smaller than a design value. The accuracy of the NDZs is verified with simulation and experimental results.

Modeling anti-islanding protection devices for photovoltaic systems

Applications of grid-connected photovoltaic systems are rapidly expanding, providing a viable technology for renewable energy resources. Such systems are utility interactive and one of the major difficulties in their efficient use is related to islanding phenomena connected with a possibility of supplying surplus power back to the utility grid. In detecting and preventing such situations, anti-islanding protection devices play a paramount role. In this paper, we analyze the existing techniques in order to identify a methodology with an optimum combination of characteristics. We implement the chosen methodologies in SIMULINK. Major attention is given to the phase jump detection method (PJD), and to the slip mode frequency shift method (SMS) for which we provide a detailed description of our SIMULINK implementations and their evaluations performed on the basis of their non-detection zones. We develop an experimental iterative scheme to validate the results of computational experiments obtained with the developed models, and report the results of several computational tests.

Predicting islanding operation of grid connected PV inverters

Increasing numbers of photovoltaic arrays are being connected to the power utility through power electronic inverters. This has raised potential problems of network protection. If, due to the action of the inverter or inverters, the local network voltage and frequency remain within regulatory limits when the utility is disconnected, then islanding is said to occur. Many methods to prevent this have been proposed and a SPICE-based model and analysis of the system are presented. Specifically aimed at predicting the effectiveness of two of these. These are: active frequency drift, which causes the inverter current to be generated slightly lower or higher in frequency than the frequency of the terminal voltage; and slip mode frequency shift, which controls the phase angle of the inverter current as a function of the frequency deviation of the terminal voltage from that of the normal network frequency. Experimental verification of the model is provided. Active frequency drift using frequency speed-up rather than speed-down is shown to be preferable for inductive loads, but conditions that resulted in islanding could be predicted. Slip mode frequency shift proved to be a more robust anti-islanding protection technique.

A novel islanding protection system for photovoltaic inverters

AbstractIt is very difficult to detect an islanding condition of a power distribution line with conventional voltage or frequency relays while the output power and the load power of utility interactive PV inverter units are in nearly balanced state in both active power and reactive power. This is because a sufficiently large voltage or frequency change cannot be expected at such a balanced state.Many studies have been reported so far to complement dead bands in combination of active and passive methods to prevent the islanding, but none of them has been successful.This paper presents the principle of a new active method called slip mode frequency shift (SMS). With this method the reactive power between the inverter and the load is made unbalanced intentionally to cause the frequency to shift as if it slips down a slide. The performance when the dead bands are eliminated effectively in the range of practical use has been examined through simulation and experiments.

太陽光発電用インバータの新しい単独運転検出保護

It is very difficult to detect an islanding condition of a power distribution line with conventional voltage or frequency relays while the output power and the load power of utility interactive PV inverter units are in nearly balanced state in both active power and reactive power. This is because a sufficiently large voltage or frequency change cannot be expected at such a balanced state. Many studies have been reported so far to complement dead bands in combination of active and passive methods to prevent the islanding, but none of them has been successful. This paper presents the principle of a new active method called slip mode frequency shift (SMS). With this method the reactive power between the inverter and the load is made unbalanced intentionally to cause the frequency to shift as if it slips down a slide. The performance when the dead bands are eliminated effectively in the range of practical use has been examined through simulation and experiments.