Search

Summary: Bridgeless ac‐dc converters are the optimal choice for many applications, as they offer many advantages such as low distorted supply current, high power factor, and improved efficiency. This paper presents a new topology for a single‐phase bridgeless ac‐dc converter. The proposed hybrid topology is based on integrating the inverting and non‐inverting buck‐boost dc‐dc converters that are connected to the ac supply through an LC filter. To insure sinusoidal supply current, the proposed hybrid bridgeless ac‐dc converter is operated in discontinuous current mode. The proposed converter has many merits, such as a reduced number of components, enhanced efficiency, and soft start‐up capability. The operation modes and design of the proposed converter are presented. In addition, a design method is proposed for the input LC filter to minimize the voltage stress across switches. Moreover, a small signal model for the proposed converter is developed. The proposed converter topology is simulated to evaluate the dynamic behavior and verify the accuracy of the presented small signal model. Furthermore, an 850 W prototype is developed to validate the features of the proposed converter experimentally. Tight voltage regulation, sinusoidal supply current, and near‐to‐unity power factor operation are observed from the results, regardless of supply or load disturbances. [ABSTRACT FROM AUTHOR]

The wide use of communication layers in DC microgrids to transmit voltage and current measurements of each distributed generator unit (DGU) increases the possibility of exposure to cyber-attacks. Cyber-attackers can manipulate the measured data to distort the control system of microgrids, which may lead to a shutdown. This paper proposes distributed mitigation layers for the false data injection attacks (FDIA) on voltages and currents of DGUs in meshed DC microgrids. The proposed control strategy is based on integrating two layers for cyber-attack detection and mitigation to immune the primary and the secondary control loops of each DGU. The first layer is assigned to mitigate FDIAs on the voltage measurements needed for the voltage regulation task of the primary control loop. The second layer is devoted to the mitigation of FDIAs on the DGU current measurements, which are crucial for the secondary control level to guarantee the proper current sharing of each DGU. Artificial neural networks (ANNs) are employed to support these layers by estimating the authenticated measurements. Different simulation and experimental case studies are provided to demonstrate the proposed mitigation layers' effectiveness in detecting and mitigating cyber-attacks on voltage and current measurements. The simulation and experimental results are provided to evaluate the dynamic performance of the suggested control approach and to ensure the accurate operation of DC microgrids despite the existence of cyber-attacks on the measurements employed in the control strategy. Moreover, the control strategy succeeds to keep the maximum voltage error and the maximum error in current sharing within tolerance. [ABSTRACT FROM AUTHOR]

Variable-speed pulsewidth-modulated (PWM) drives allow for precise speed control of induction motors, as well as a high power factor and fast response characteristics, compared with nonelectronic speed controllers. However, due to the high switching frequencies and the high dV/dt, there are increased dielectric stresses in the insulation system of the motor, leading to premature failure, in high power and medium- and high-voltage motors. Studying the degradation mechanism of these insulation systems on an actual motor is both extremely costly and impractical. In addition, to replicate the aging process, the same waveform that the motor is subjected to should be applied to the test samples. As a result, a low-power two-level high-voltage PWM inverter has been built to replicate the voltage waveforms for aging processes. This generator allows for testing the insulation systems considering a real PWM waveform in which both the fast pulses and the fundamental low frequency are included. The results show that the effects of PWM waveforms cannot be entirely replicated by a unipolar pulse generator. Index Terms--High voltage, insulation testing, inverter-fed drive motors, power electronics, pulsewidth modulated (PWM).

The dynamic voltage restorer (DVR) is an effective solution for power quality problems related to voltage. One of the most common control algorithms that are used for the DVR is the symmetrical components method. This paper introduces a new approach for the estimation of the symmetrical components. A modified delta rule structure is proposed and developed which is capable of dealing with multioutput systems for the parameters estimation. An innovative feedforward control, based on the new delta rule structure, is proposed for the series compensator not only to compensate for the zero and negative sequence components, but also to regulate the positive sequence component at the nominal load voltage. One advantage of the proposed control scheme is its insensitivity to parameter variation, a necessity for the series compensator. Experimental verification of the new delta rule algorithm, by using a DSP, is provided. Numerical simulations of the proposed control strategy are conducted to show the robustness, high accuracy, and fast dynamic performance of this novel control algorithm. Index Terms--Delta rule, dynamic voltage restorer (DVR), estimation, flicker, power quality, sag, symmetrical components, voltage regulation.

Distributed Generation (DG) is used widely in the modern distribution systems. This paper proposes a novel functionality of the interface between DG and the utility network to mitigate the voltage flicker and to regulate the voltage at the Point of Common Coupling (PCC) in addition to its main function of controlling the power flow. A new control algorithm for the DG interface based on the Hilbert transform (HT) is presented. The HT is employed as an effective technique for tracking the voltage flicker levels in distribution systems. The mathematical simplicity of the proposed technique, compared with the commonly used algorithms in the literature, renders them competitive candidates for the on-line tracking of voltage flicker. The accurate tracking of the HT facilitates its implementation for the control of flicker mitigation devices. Simulation results are provided to verify the tracking capabilities of the HT and to evaluate the performance of the proposed DG interface for multifunction operation. Index Terms--Distributed generation interface, envelope tracking, flicker mitigation, Hilbert transform, power quality, voltage control.

Envelope tracking has many important applications in electrical distribution systems for either flicker meters or flicker compensators. This paper presents a novel control technique for flicker mitigation. This technique is based on the instantaneous tracking of the measured voltage envelope. The ADAptive LINEar neuron (ADALINE) algorithm, and the Recursive Least Square (RLS) algorithm are introduced for the flicker envelope tracking. The ADALINE algorithm is characterized by a light computational demand, unlike that of existing techniques; the RLS algorithm outperforms the ADALINE algorithm by its fast convergence and robust tracking performance. Both the ADALINE and the RLS algorithms give accurate results even under rapid dynamic changes. The paper investigates the effects of different parameters on the performance of the ADALINE algorithm and that of the RLS algorithm. Extensive simulations of the proposed flicker tracking algorithms are conducted to evaluate their performance for the tracking and mitigation of voltage flicker. The ADALINE and the RLS algorithms are examined by tracking and mitigating the flicker produced by a resistance welder and an arc furnace in a simple distribution system simulated in the PSCAD/EMTDC package. Index Terms--Adaptive estimation, envelope tracking, flicker mitigation, least mean square methods, power quality, recursive estimation, voltage control.

Distributed Generation (DG) exists in distribution systems and is installed by either the utility or the customers. This paper proposes a novel utilization of the existing DG nonlinear interface not only to control the active power flow, but also to mitigate unbalance and harmonics, and to manage the reactive power of the system. The proposed Flexible Distributed Generation (FDG) is similar in functionality to FACTS, but works at the distribution level. Moreover, a novel ADAptive LINEar neuron (ADALINE) structure is presented. The new structure is applied to multi output (MO) systems for parameter tracking/estimation, and is called MO-ADALINE. It is dedicated to symmetrical components estimation. The control loop combines a Fuzzy Logic Controller (FLC) for voltage regulation, and a processing unit-based ADALINE to deal with unbalance, harmonics and reactive power compensation. One advantage of the proposed control system is its insensitivity to parameter variation, a necessity for distribution system applications. Simulations of the suggested FDG based control algorithm are conducted to evaluate the performance of the novel system. Index Terms--Adaptive estimation, distributed generation, fuzzy control, harmonic distortion, power quality, reactive power control, voltage control.

Symmetrical components as well as harmonic tracking are of great importance in many applications in power systems such as power quality and protection. This paper introduces a novel Adaptive linear combiner (ADALINE) structure for symmetrical components estimation. This structure is capable of dealing with multi-output systems for parameter tracking/estimation rather than the existing ADALINE, which deals only with single output systems. As the new topology deals with Multi-Output systems, it is called MO-ADALINE. Moreover, the paper presents a new processing unit, which can estimate symmetrical and harmonic components from the measured current signals. The advantages of this proposed unit are its independence of the voltage waveform and its ability to give information about the reactive component of the resolved current. Simulation results are given to validate the proposed algorithms. Index Terms--ADALINE, adaptive estimation, algorithms, harmonic distortion, least mean square methods, power quality, relays, symmetrical components.