Haitham Zaki Azazi

In the dominion of power systems, voltage sags and swells are transient disturbances that can significantly impact the performance and stability of the grid. This issue must be addressed with robust control techniques to have good performance, with low harmonic and stable operation of the power system. Many techniques for instance, dynamic voltage restorers (DVRs) and series active power filters were proposed based on conventional theories having merits and demerits. This research aims to provide a comprehensive comparison between two DVR control techniques. The First technique is the modified instantaneous reactive power theory (PQ), whereas the second is modified synchronous stationary frame (DQ) method under various sag and swell voltage conditions. The extracted components of the grid voltage positive sequence and load current negative sequence form the basis of the improved approaches. to detect the disturbance and generate the control signal of the DVR. The study encompasses Unbalanced load voltage with 80% sag, unbalanced load voltage with 70% swell, balanced 80% voltage sag, and a 50% balanced load change are the four different operating conditions. Both control approaches, with their modified versions, are mathematically represented and evaluated under different specified severe power quality conditions. The methods are performed in MATLAB/Simulink environment and implemented experimentally using DSPACE DS1104 controller-based system to provide a comparison analysis and validate the system's voltage profile and harmonic distortion performance study. The obtained results and analysis illustrate the effectiveness of the proposed two control methods. Each technique demonstrates their effectiveness for addressing the power quality issue.

In today’s power system, power quality is a critical topic having several impacts on customers and utilities. In the current electric power system, the integration of renewable energy sources, smart grid technologies, and significant usage of power electronics equipment has generated a slew of issues. The sensitive equipment might be damaged by harmonics, voltage sag, and swell. These devices are vulnerable to Interference with other elements of the system resulting in input voltage changes. As a result, in the contemporary period, Power quality is becoming more important as the number of sensitive and costly electronic devices grows. To overcome the challenges of non-standard voltage, the Dynamic Voltage restorer (DVR) device has been extensively utilized to keep the load voltage stable. To have a dynamic and fast response of the DVR a modified instantaneous reactive power (PQ) theory is proposed to control DVR under extreme transient voltage circumstances. The proposed technique is based on the extraction of the positive sequence component of grid voltage and the negative sequence component of load current for generating a voltage reference signal. The power system network with the proposed PQ control scheme is investigated and assessed under various scenarios to compensate for severe balanced, unbalanced (voltage sags and swells), and load change. MATLAB/Simulink is used to verify the mathematical models of the conventional PQ and proposed PQ control system for DVR. The complete system is implemented experimentally using a dSPACE 1104 based laboratory system to validate the presented control scheme. The simulation and experimental results are correlated, demonstrating the efficacy of the suggested modified PQ control technique.

Nowadays, power quality under the excessive implementation of power electronics devices is quite challenging issue. The compensation of non-sinusoidal; reactive and harmonic; components is the main role for power quality devices which highly depend on the robustness of the control system. Some common control systems are implemented using Synchronous Stationary Frame (DQ) theory. This paper proposes a new version of DQ control technique to control dynamic voltage restorer under severe transient voltage conditions. The power system network with the new DQ control technique is studied and analyzed under different scenarios to compensate for severe balanced and unbalanced voltage sags and swells. This new scheme is based on extraction of positive sequence components to implement the control algorithm. A mathematical model of the dynamic voltage restorer (DVR), hysteresis voltage control, converter controller model, new DQ scheme with complete system equations are carried out and verified using Simulink / MATLAB. The proposed system is validated experimentally using DSpace 1104 based laboratory system. The obtained results of the proposed compensation algorithm are compared with the results obtained from the traditional DQ method. Simulation and experimental results are correlated and show effectiveness of the proposed DQ control scheme.

This paper proposes a single-stage three-phase boost inverter for Photovoltaic (PV) applications. The proposed circuit topology is directly step-up the input low level DC voltage to a high-level output AC voltage in only one stage, using an inductor and six switches. A new control methodology is introduced to regulate the AC output voltage and current and is suitable for grid-connected and stand-alone applications. The proposed circuit uses only six switches of a simple type of switches that achieve the desired objectives easily without additional antiparallel diodes. The circuit topology is extensively analysed and the overall performance including total harmonic distortion (THD) is obtained by computer simulation and presented under different conditions. A DSP-based laboratory model is built to assess the proposed single-stage three-phase boost inverter when fed from a PV source. The experimental results confirm the simulation, illustrating the successful operation of the proposed circuit topology to produce three-phase AC output from the low DC voltage of the PV source.

A novel approach for optimized feedback gains of a stable sensorless induction motor (IM) drives at low speeds in the regenerating mode is presented. The proposed approach depends on the rough set (RS) and genetic algorithm (GA) in a cascading construction. The RS is used to obtain the most dominant machine parameters that affect the stability of the sensorless IM drive at very low speeds in the regenerating mode. The parameter's values are randomly selected to investigate their influence on the stability. Then, a reduction is obtained for the most dominant machine parameters affecting the stability. GA is applied to search for the optimal design of the observer feedback gains under the dominant parameter deviation. The proposed RS theory and GA guarantees a stable speed estimate and efficient sensorless IM drive at very low speeds in the regenerating mode. Theoretical analysis, design procedure, and simulation work of the proposed approach are presented. A sensorless IM drive is executed in the laboratory using the digital signal processor (DSP)-DS1104 control board. Extensive results in the different operating conditions to verify the efficacy of the proposed approach are presented and compared with previous works.

This paper proposes a transformerless/non-isolated, high-gain DC-DC converter required to increase low voltages in renewable energy applications. The converter topology uses only a single-switch with minimum voltage stress over the semiconductors. The design is obtained by integrating both the boost and the quadratic boost converter topology. Operating principles of the converter circuit topology are detailed, and the steady-state performance is analysed. The design results in lower switching voltage that significantly improves the efficiency of the controlled switches. The results obtained by computer simulation demonstrate that the high voltage gain is obtained at lower values of duty ratio with an efficiency of more than 94%. The merits of the proposed converter are given in comparison with other high-gain DC-DC converters. Finally, a laboratory model is built using the digital signal processor [dSPACE (DS-1104)] to verify the converter theory. The theoretical, simulation and experimental results that indicate the claimed converter performance and capability are given.

This paper introduces a Four-Switch Three-Phase Shunt Active Power Filter (FSTP-APF) based on One Cycle Control (OCC) technique for compensating the currents of three phase non-linear loads. The power stage of FSTP-APF uses only four semiconducting switches which leads to reduce the overall cost of APF. The proposed technique retains the advantages of the conventional OCC, such as no reference current calculation, no need for using Phase-Locked Loop (PLL), very simple control circuit and constant switching frequency. In addition, the modification reduces the number of semiconductor switches, reduces the filter output inductances, reducing the number of sensors to only four sensors, two of them for measuring supply currents and the others for measuring DC-link voltages, and the control algorithm becomes simpler. The feasibility and performance of the proposed technique are demonstrated through the simulation and experimental verifications.

This article presents an accurate computational technique for estimating the photovoltaic (PV) cell parameters from experimental measurements of the current‐voltage ( I – V ) characteristics. The technique is based on using various evolutionary algorithms (EAs) and the double‐diode eight‐parameter cell model to precisely estimate unknown parameters. The proposed technique is implemented to extract the PV cell parameters of different manufacturer's modules by minimising the summation of absolute square errors between theoretical and measured I – V output characteristics obtained under different irradiation levels. The effectiveness and robustness of the proposed technique are demonstrated via a comparative assessment of the measured output I – V characteristics and those obtained by computer simulation, using Matlab SIMSCAPE library components. The good agreement obtained between theoretical and experimental results endorses the proposed approach to determine precisely the PV parameters required for power system studies. The proposed technique is useful power system studies with penetration of photovoltaic sources.

In this paper, a new control strategy for an induction motor (IM) drive system fed from threephase pulse width modulation (PWM) AC chopper is proposed. The main objective of the proposed control scheme is to achieve input power factor correction (PFC) of the IM drive system under different operating conditions. PFC is achieved by continuously forcing the actual three-phase supply currents with the corresponding reference currents, which are generated in phase with the supply voltages, using hysteresis band current control (HBCC) technique. The proposed control strategy has two loops; inner and outer loop. Output of the outer loop is the magnitude of the supply reference current resulting from either speed controller or startup controller, whereas output of the inner loop is PWM signals of the AC chopper. The proposed AC chopper features a smaller number of active semiconductor switches; four IGBTs, with only two PWM gate signals. As a result, the proposed system is simple, reliable, highly efficient and cost-effective. Mathematical analysis of the drive system is presented. Components of the input LC filter are designed using frequency response. The IM drive system is modeled using MATLAB/SIMULINK and a laboratory prototype was built and tested. Simulation and experimental results confirm validity and robustness of the proposed control strategy.