Search

Islanding is one of the important challenges in power networks in the presence of distributed generation which is considered an undesirable incident due to the possibility of damage to operators, network equipment, and consumers. Therefore, it is necessary to quickly detect islanding and make a decision regarding the connection status of local distributed generation units in the network. In this paper, a passive islanding detection method is proposed using adaptive threshold-based instantaneous frequency droop characteristic. The proposed threshold limit is dynamically changed depending on under-studied conditions to discriminate the island from load changes, capacitor bank switching, motor start-up, and short circuit types. Two medium voltage networks of Cigre and 34-bus IEEE are used to evaluate the proposed method. The simulations are performed in Digsilent software and the proposed method is implemented in MATLAB software. The simulation results indicate that the island is correctly detected with appropriate accuracy in a short period of time from other disturbances in the presence of wind, solar and diesel types of distributed generations. [ABSTRACT FROM AUTHOR]

In this paper, a single-stage soft-switching power-factor-correction (PFC) converter is proposed for driving two strings of LEDs. In the proposed driver, a transformer is added to an asymmetric series resonant half bridge converter to shape the input current. Also, zero-current-switching condition (ZCS) and zero-voltage-zero-current-switching (ZVZCS) condition are provided for switches at turn-on and turn-off, respectively, and near-unity power-factor is achieved for the converter. Moreover, the output currents are equal and independent of the output voltages which eliminates the need for current feedback or active current sharing method. Besides, the proposed driver provides minimum voltage for DC-bus capacitor and also switches voltage stress, while attaining low THD. Therefore, low voltage rating semiconductors with low on resistance and lower voltage capacitors with lower volume can be used. To validate the proposed driver features, operating principle of the proposed LED driver is presented, design considerations are discussed and experimental results of a laboratory prototype for supplying two 50 W/70 V strings of LED modules from 220 Vrms/50 Hz ac main is reported in this paper. [ABSTRACT FROM AUTHOR]

In this paper, a new method based on Adaptive Neuro-Fuzzy Inference System (ANFIS) is proposed for locating the switched capacitor banks in distribution systems. To train the proposed ANFIS model, an index based on current transient is introduced, which is calculated either offline by using data or online by real time simulation. The proposed method uses only current transient waveforms, immediately before and after the switching instant. Since only the current signal is used which is available in several locations, the method is simple and can be applied online. The method uses wavelet to determine the capacitor switching instant, which is needed for the ANFIS model to locate the switching capacitor. The method is simulated using PSCAD. Through various simulations, it is shown that other power quality disturbances such as voltage dip, unbalances and harmonics cannot disturb the method. Moreover, the size and connection type of the capacitor bank do not affect the method accuracy. The proposed algorithm is validated by simulating the IEEE 13-bus distribution system. According to the simulation results, the method is reliable enough to be applied to real systems. [ABSTRACT FROM AUTHOR]

Islanding is one of the important challenges in power networks in the presence of distributed generation which is considered an undesirable incident due to the possibility of damage to operators, network equipment, and consumers. Therefore, it is necessary to quickly detect islanding and make a decision regarding the connection status of local distributed generation units in the network. In this paper, a passive islanding detection method is proposed using adaptive threshold-based instantaneous frequency droop characteristic. The proposed threshold limit is dynamically changed depending on under-studied conditions to discriminate the island from load changes, capacitor bank switching, motor start-up, and short circuit types. Two medium voltage networks of Cigre and 34-bus IEEE are used to evaluate the proposed method. The simulations are performed in Digsilent software and the proposed method is implemented in MATLAB software. The simulation results indicate that the island is correctly detected with appropriate accuracy in a short period of time from other disturbances in the presence of wind, solar and diesel types of distributed generations. [ABSTRACT FROM AUTHOR]

Lack of coordination between the operation of capacitors and OLTC to voltage control is one of the basic problems in distribution networks, which can cause problems in the control function. In this paper, a new control method is proposed to create coordination between the operation of capacitors and OLTC. The criterion of this coordination is based on fuzzy logic to determine the status of transformer and capacitor function, which reduces unnecessary switching. In this method, the control function is considered with more accuracy such that the quantity of voltage and power factor are set within the range of 0.98 to 1.02 p.u and between 0.95 lag and lead, respectively. Another advantage of the proposed method is that it is automatic and eliminates human resources to adjust the position of the transformer and capacitors. Simulation results are done on the 14-bus network by using two software MATLAB and DIGSILENT, that these results show the accuracy of the proposed method in the desired performance in distribution networks. [ABSTRACT FROM AUTHOR]

Today, dual-input DC-DC converters are used for various purposes, including simultaneous use of two sources to solve the challenge of the intermittent nature of the renewable energy sources. In this paper, a novel structure of a semi-isolated dual-input dc-dc converter based on the impedance network along with a controlling approach is proposed. In the proposed converter, quasi-Z source network has been utilized and the voltage gain has improved dramatically with the use of switched capacitors and coupled inductor techniques. Due to the necessity of an appropriate controller to improve the performance indicators of these type of converters, a twolayer intelligent adaptive control structure is proposed. In the first layer of the controller, the proposed converter is investigated based on the analysis of multivariate systems, and then in the second layer, in order to achieve a robust performance for the converter responses against the uncertainties such as abrupt inputs voltage change and disturbances, a self-tuning adaptive controller is used. Also, the proposed controller structure has fast transient convergence in different situations for output voltage stability, which makes it a good candidate for renewable energy sources and fuel cells. Simulation results from MATLAB\Simulink have examined the performance of the proposed topology. Finally, experimental evaluation validates the claimed advantages. [ABSTRACT FROM AUTHOR]