---

---

One of the serious concern of grid connected distributed resources is islanding problem. This condition should be prevented due to several reasons concerning such as personnel and equipment safety. This paper investigated a passive islanding detection method using wavelet transforms analysis. The proposed method is based on Rate of change of Frequency (RoCoF) measurements and processing of this signal with analysis of a Symlets wavelets transform. The presented studies are based on time-domain simulations using MATLAB, and its feasibility is evaluated with an experimental analysis in comparison with the recently reported method based on Daubechies wavelet transform. The experimental system parameters are the same as those of the simulated system. The results evaluation confirm that the proposed islanding detection method succeeds in detecting islanding mode both in the experimental and simulated systems and is superior to the Daubechies wavelet transform based detection method.

---

An approach for assignment of the optimal location and tap changer adjustment related to Flux-Lock type Superconducting Fault Current Limiter with Tap Changer is used in this paper by debating the reduction of fault current flowing from each device and enhancement of reliability varying with customer type in a distribution network connected with Distribution Generation (DG). Three objective functions based on reliability index, reduction of fault current and number of installed MSFCL is systematized and a Nonlinear Time-Varying Evolution (NTVE) based Multi-Objective Particle Swarm Optimization (MOPSO) style is then formed in searching for best location and tuning of tap changer of MSFCL to meet the fitness requirements. A decision-making procedure based on Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) is used for finding best compromise solution from the set of Pareto-solutions obtained through MOPSO-NTVE. In a distribution network as Bus 4 of Roy Billinton Test System (RBTS), comparative analysis of the results obtained from application of the Resistive SFCL (RSFCL) and MSFCL is presented. The results show that optimal placement of MSFCL than RSFCL can improve reliability index and fault current reduction index with less number.

---

Polymer electrolyte membrane fuel cells (PEMFC) have been considered by researchers due to their high efficiency, low pollution, and high-power density in distributed generation systems. In this paper, the connected PEMFC fuel cell power recovery system with an LCL filter is evaluated in the harmonic Grid. LCL filters, despite their greater ability to attenuate harmonics, can lead to system resonance and instability. In this research, a transformer has been used to connect the fuel cell inverter to the Grid and its leakage inductance has been used as the inductor on the network side. Besides, for optimal resonance damping, and attenuation of current ripple caused by grids voltage harmonics, capacitor voltage through feedback control has been used. Complete control of capacitor voltage feedback includes proportional, derivative, and second-order components. In the proposed control scheme, the capacitor voltage derivative component opposes the capacitor current feedback due to identical and symmetrical loop gain. Therefore, both of them can be deleted. Thus, the capacitor current sensor is saved. Instead, the LCL filter resonance is damped by a proportional component and a second-order derivative of the capacitor voltage. A low-pass filter is also added to the second-order derivative in the controllable frequency range to ensure system stability. The simulation results of the PEMFC power recovery system in different conditions confirm the proper attenuation of the grid-connected inverter, the injection of current of suitable quality into the contaminated and harmonic grid, the stability, and the appropriate dynamic response of the proposed system.