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Air‐cored axial‐flux permanent‐magnet synchronous generators (AFPMSGs) are potential candidates for gearless direct‐coupled wind turbines (DCWTs) owing to providing high efficiency and power density. The design of a DCWT generator is so complicated since the generator cost, dimension, and weight affected by gear elimination. Therefore, it is essential to find an optimal AFPMSG design at rated conditions. In this paper, an accurate procedure for the optimal design of an air‐cored AFPMSG applicable for DCWTs is proposed. The genetic algorithm (GA) is used for multi‐objective design optimization to reach the optimal configuration as well as system dimension in order to decrease the weight, increase the power density and enhance the effectiveness of the generator. To validate the efficiency of the suggested optimization proceducer, a 30 kW AFPMSG has been considered as a case study. The results of optimization have been investigated by finite element analysis (FEA). A prototype generator is also fabricated, and the test results are offered and compared with the numerical study. The outcomes show that there exists an acceptable agreement between FEA and experimental outcomes with the error percentage about of 1.35%. [ABSTRACT FROM AUTHOR]

This paper investigates the starting current of an AC/DC/DC converter, consisting of a threephase diode bridge rectifier and a synchronous buck converter. The use of microprocessors in such converters increases the total cost and also reduces reliability due to EMI phenomena. For this reason, by removing the microprocessor, a start-up plan including a limiting starting resistor and then soft starting the switching module is proposed in this paper. By modeling the system under different operating modes, a solution is presented to minimize the circuit startup period, which includes minimizing the bypass time of the startup resistor and reducing the switching soft startup period as possible. The proposed method has been implemented on a 15-kW converter feeding from a three-phase 380 V power grid and provides up to 300 Vdc/50 Adc to supply an electroplating pool. The results show that the sequential startup procedure, including using a 50 ohm/1500 w resistor for 3 seconds, and then bypassing it, then soft start switching after half a second and during 1.5 s, can move this circuit to a steady state in 5 seconds, keeping current in all parts below half rated current. [ABSTRACT FROM AUTHOR]

In a stand‐alone microgrid, voltage control is an important issue to keep the grid balanced under unbalanced load conditions. The other important challenges in microgrids include handling the neutral to the ground voltage (NGV) as well as total harmonic distortion (THD) under its limits due to the IEEE standards. A four‐leg inverter is the best choice for a three‐phase transformerless inverter employed in a stand‐alone microgrid. To control the inverter, sliding mode control (SMC) is a well‐known nonlinear control system to handle unbalanced and nonlinear load conditions as it can provide high sinusoidal load voltage with high performance and fast dynamic response. This paper proposes an enhanced SMC control method for minimizing the NGV and THD in addition to compensating for unbalanced load voltage conditions simultaneously in a three‐phase four‐leg inverter. In order to verify the results of the proposed method, simulation results with MATLAB/Simulink are presented to confirm the effectiveness of the proposed SMC under various load conditions. The proposed method provided fast dynamic response and fixed switching frequency. Further, a significant reduction occurred in NGV and THD. The simulation results of this method compared with the MPC method indicated the better performance of the proposed method against the unbalanced and nonlinear various load conditions. [ABSTRACT FROM AUTHOR]

Power‐Flow (PF) solution in isolated microgrids has attracted notable attention recently, because these systems present various particularities compared with the traditional PF solution in large meshed transmission networks. In this sense, this paper develops a novel Newton‐like PF solver for isolated microgrids. The new proposal is based on the Modified Midpoint method and shows high convergence order with relatively low computational burden. These characteristics bring superior theoretical performance compared with the standard Newton–Raphson (NR) method and other high order techniques, which has been conventionally used. Extensive simulations are performed on various small‐, and large‐scale benchmark Microgrids under different loading conditions and R/X ratios. Results provided serve to confirm the theoretical features of the developed solver, outperforming the NR technique as well as other recently developed solvers in all the studied systems with acceptable reliability even under high stressed conditions. [ABSTRACT FROM AUTHOR]

Doubly fed induction generators are widely used in wind power plants, yet their performance is vulnerable to grid voltage faults. Recent regulations require the wind generator to have the capability of fault crossing to stay connected even in faulty conditions. This paper investigates the problem of stabilizing the rotor current when the stator voltage is affected by the faults that occurred at the nearby grid. The proposed controller consists of 2 terms: the first is responsible for the internal stability of generator dynamics and the second compensates for the effect of the fault on the stator voltage. The stability of generator circuit is verified by using linear quadratic regulator and pole placement criteria. Also, to enhance the performance of the stabilizers, genetic algorithm is used to adjust the stabilizers. To detect the stator voltage disorders and to determine the suitable time for switching in fault stabilizers, a fault observer is also suggested. The fault detection and stabilization structure is simulated and shows higher levels of performance in faulty conditions than in conventional rotor side converter controllers in faulty grid conditions. [ABSTRACT FROM AUTHOR]