نشریه مهندسی برق و مهندسی کامپیوتر ایران
سال پانزدهم شماره 1 (پیاپی 42، بهار 1396)

Microgrid (MG) supplied its local load with distributed energy resources at the low voltage system in distribution networks. Microgrid can be used in parts that are not allowed access to the electricity network with low investment cost. The used islanding MG in this research includes wind turbine and photovoltaic systems as renewable energy sources and hydrogen storage system (HSS). This paper proposes a new energy management strategy (EMS) for MG in the presence of the HSS considering the power uncertainties of renewable energy sources. The objective of proposed EMS is to minimize the operating costs of batteries, HSS and the costs associated with excess and undelivered energy considering the supplied load constraints. The considered technical constraints in this paper contain renewable energy sources limits and battery and HSS constraints. HSS includes electrolyzer (EL), hydrogen tanks and fuel cell (FC). Demand response program (DRP) is used to flat the load curve and optimal operation of MG. The proposed model on a MG is been implemented in GAMS software. The simulation results show that the operation cost of MG reduced by using of HSS and DRP.

Load taps, laterals, and sub laterals are different branches of power distribution (PD) networks. In PD systems, reliability indices and their efficiency are improved using an accurate method in fault locating. In this paper, a new combined method for locating single, double and three phase faults to ground is proposed in PD networks. In this article, for finding the possible fault locations, an impedance based fault-location algorithm is used. Then, for determining the faulty section, the new method is proposed using voltage sag matching algorithm. In this method, the possible fault locations are determined, after occurrence of single and double phase faults to ground, using an algorithm which is impedance based fault-location algorithm. Separately, the same fault is simulated in possible locations. Then, at the beginning of a feeder, the voltage is saved and the amplitude and angle of the voltage differences are determined and accordingly, an online data bank is generated. Then, the obtained and recorded amplitude and angle of the voltage differences (at the beginning of the feeder) is compared with that data bank, for the actual fault. By the matching value of each possible fault location, the real location of fault is determined. Compared to the other counterparts, the proposed method is more accurate in locating faults and less sensitive to the fault resistance.

This paper presents a new intelligent algorithm, named binary real genetic algorithm (BRGA) to design parameters of PSS and STATCOM controller simultaneously. The proposed algorithm has a strong search capability and high speed convergence to find the global optimum points. The objective function used in this paper to be minimized is the time integral absolute error (ITAE). The objective will be minimizing the deviations of rotor speed () and the voltage of the bus in which STATCOM has been installed. The simulations are carried out on a two-area four-machine power system to show the superior performance of the proposed method, when compared with GA and PSO algorithms.

The grid tied PV systems without transformer have some benefits such as low cost, weight and size and also increases the overall efficiency. The galvanic connection between the grid and PV system causes leakage current in the transformerless inverter to flow through parasitic capacitors between the PV system and ground and causes personal safety problems, increases the output harmonic spectrum, and system losses. This paper introduces a modified single phase two stage transformerless inverter for grid connected photovoltaic systems with low leakage current. The neutral of the grid is directly connected to the negative terminal of PV panel that eliminates leakage current without complex control strategy. In this paper, a Proportional Resonant (PR) control strategy is used to control the injected current. The performance of the transformerless inverter is analyzed and its structure has been simulated in PSCAD/EMTDC and the obtained results tested experimentally.

The production of the lightning impulse current is very important for research and Standard quality control tests. Conduction of IEC standard type tests on metal-oxide high voltage surge arresters needs a lightning impulse current generator system that is able to produce both lightning impulse current and simultaneous several kV residual voltage. This paper describes the design and manufacturing of a one million volt residual voltage, 10 kA lightning current generator system and the innovation in design of an integrated high voltage air core reactor. Experimental laboratory tests show the good performance of the manufactured generator and its capability to perform standard type test on metal-oxide high voltage surge arresters.

This paper introduces a new sensorless rotor position detection technique with the mechanical load asymmetric error determines ability for switched reluctance motor drives. In presented paper combination of pulse injection technique and digital pulse position modulation are employed for control of SR motor. In this method, a single high-frequency pulse is injected in an idle phase to determine the rotor position and estimates the rotor position through analysis of the resultant current after voltage pulse injection. Since the number of injected pulses is constant, in terms of the proper functioning of the motor, output bit stream has a fixed length and is proportional to the mechanical load torque. In the event of mechanical failure as a result of fluctuations in the mechanical load, the number of bits according to the error rate will change, which counts the number of output bits detection circuit , errors in mechanical load is determined. Proposed method decrease the injuries caused by asymmetry error in mechanical load connected to the motor shaft. The proposed sensorless method has been simulated using Matlab-Simulink and implemented on an experimental setup in real time to validate its performance. The results obtained demonstrate the feasibility and practicability of the method.

In this paper instantaneous electromagnetic torque computation is done for axial flux permanent-magnet brushless DC (BLDC) motor using Lorentz force theorem. In this method, back electro motive force (EMF) and currents of phases should be defined. A novel method is presented for calculation of back EMF harmonics using analytical method (AM). The analytical results are compared with results obtained from the finite element method (FEM). A good agreement is between AM and FEM. Computational time in AM is much less than FEM. Finally, for torque ripple reduction, some motor geometric parameters are optimized using AM.

In this paper a new method for identification of interharmonic producing loads in a power system is proposed which is capable of evaluating the contribution of each individual load in the point of common coupling. This method is based on using the superposition and projection method which needs the norton equivalent circuit of loads and supply network. Also in the proposed method, a two-stage adaptive linear neuron is used for determining the interharmonic components of a signal. The effectiveness of the proposed method has been shown through simulation studies in the MATLAB/SIMULINK software. The simulation results show the capability of the proposed method for identification and contribution evaluation of interharmonic sources in a power system.