Adel Khedher

A backstepping control strategy applied to the connected hybrid renewable energy system operated in MPPT

In this paper, an interconnected grid hybrid renewable energy system, HRES, (wind/PV) is studied. The wind energy conversion system, WECS, is constructed aroud a wind turbine coupled to a double fed induction generator, DFIG. The stator of DFIG is directly connected to the grid and the rotor is connected to the grid through back-to-back power converters. To control the wind system, we have applied the adaptive backstepping control strategy for both converters. The PV energy system is composed by PV cell energy and the DC-DC boost converter. To control the DC-DC boost converter, we have applied tow cascade PI control loop. The first one is used to regulate the output current or the second one is used to control the output voltage. We have considered in both control structure the MPPT algorithm. To study the comportment of the HRES against the environment changes, we have considered some simulations scenarios for the wind speed, the irradiance and the temperature. We have studied the dynamic performances of the proposed control strategy.

Nonlinear vector control strategy applied to a variable speed DFIG generation system

We present in this paper the modeling and control designs for a variable-speed constant-frequency wind energy conversion system using double fed induction generator. The aim of this paper is to develop a nonlinear vector control strategy using the second Lyapunov approach for the rotor side converter and a network voltage vector oriented control of the grid side converter and to maximize the energy captured from the wind turbine and injected to the grid. Simulation results of a DFIG generation system have shown good performances of the system under the proposed control strategy.

A sliding mode control approach applied to a photovoltaic system operated in MPPT

In this paper, the modeling and control of a photovoltaic system is presented. A maximum power point tracking (MPPT) algorithm is adopted to maximize the photovoltaic output power. The proposed approach for peak power tracking using the sliding mode control is robust to environment changes (irradiance and temperature). Simulation results using Matlab/Simulink have shown good performances of the photovoltaic system operated in MPPT.

Comparative analysis for various control strategies based MPPT technique of photovoltaic system using DC-DC boost converter

The present research investigates a comparative analysis for various strategies based on Maximum Power Point Tracking (MPPT) technique dedicated for PV systems. The different strategies adjust the duty cycle so as to provide maximum power to the load via a DC-DC boost converter. The two first methods refer to the traditional approach where as the Perturb and Observe (P&O) and the Incremental Conductance (INC) methods. The third and fourth one, based on the artificial intelligence approach, are respectively Fuzzy Logic (FL) and Radial Basis Function Neural Network (RBFNN). The suggested MPPT strategies are tested and validated by using Matlab/Simulink simulation for varying weather conditions. Some concluded remarks are given allowing a best choice of the adequate strategy for a given application, referring to the desired performances and taking into account the required real-time implementation cost.

Performance evaluation of Box-Jenkins and linear-regressions methods versus the study-period's variations: Tunisian grid case

In the aim of forecasting the electricity demand in Tunisia, we have attempted in this paper to evaluate the performances of two traditional methods namely the univariate Box-Jenkins analysis (ARIMA models) and the multiple linear regressions based on economic and demographic variables (gross domestic product per capita and population). Forecasting algorithms are based on historical data period and provide results for a given future period. The evaluation of forecasting errors is calculated regarding the variation of historical data period and the future one. Forecasted results are calculated by means of the ARIMA (Autoregressive Integrated Moving Average) univariate models and their performances are compared to those of regressions models. The influence of historical data and prediction periods on forecasting performance is investigated to evaluate the minimum period that gives acceptable forecasting errors.

Space vector modulation of multilevel inverters: a simple and fast method of two-level hexagon's selection

A commonly used technique to implement the Space Vector Pulse Width Modulation (SVPWM) algorithm of multilevel inverters is based on identifying at any sampling time the appropriate two-level hexagon enclosing the output voltage space vector. The identification method proposed in this paper is based on finding the smallest distance between the reference vector tip point and the center of (n − 1 / 2)2 two-level hexagons covering an entire sector, where n is the number of levels. The effectiveness of this method is confirmed by computer simulations carried out on a numerical model of a five-level Neutral-Point Clamped (NPC) inverter. The obtained results show the high quality of voltages and currents waveforms and reduced common mode voltages (CMV). It was also shown that the real-time computation burden on a Digital Signal Processor (DSP) is less important than the one of a former algorithm using a different identification approach of the appropriate two-level hexagon.

A comparative performances study of different indices for optimal DG placement in distribution system

With the increase of load demand, Distributed Generation (DG) has gained a lot of interest due to its ability to reduce power losses and enhance the system voltage stability. However, a non proper DG allocation and sizing may lead to an increase in power losses and affect the distribution system stability. This paper presents a comparative study for DG placement methods based on four different indices which are voltage drop index (L-index), voltage stability margin index (VSMI), voltage performance index (VPI) and loss sensitivity factor index (LSF). The performances of these indices are evaluated regarding power losses reduction, voltage profile and voltage stability enhancement. Simulations are carried out on the 33-bus radial distribution system. The results have shown that LSF and L-index methods gives better performance compared to the others two DG placement indicators.

PMSM under IOLC introducing a sliding mode position and speed observer

This paper proposes a sliding-mode speed and rotor position observer (SMO) for permanent magnet synchronous motor (PMSM), controlled by Input Output Linearization Control (IOLC) in order to realize the sensorless control. At first step, a mathematical model for PMSM is derived and the IOLC strategy is introduced. Secondly, an observer based on sliding mode is built according to the electromotive force (EMF) model. The stability condition of estimated EMF is studied to prove that the observer is stable in converging to the sliding mode plane. Different performances are improved with MATLAB Simulink. The results demonstrate the efficiency of the IOLC in commanding the PMSM and show the effects of parameters variation. The SMO can effectively estimate the rotor position and speed. It presents robustness and good performances. However, the sensorless PMSM based on SMO and controlled by IOLC is sensitive to parameter variations.

Development of a low cost PV simulator based on FPGA technology

The present paper proposes a low cost photovoltaic simulator with a novel modeling method of PV characteristics in FPGA using MATLAB/XSG toolbox. The main contribution of this work is the utilization of the one-diode model to develop a research platform for rapid prototyping to represent the PV cell. PV emulator systems are used to test different photovoltaic systems under various operating conditions. The model can manage the parameters dependency in the PV panel with respect to solar irradiation and temperature. The input parameters are reduced in order to reduce the calculation time and the values of Rp and R are estimated by an efficient iteration method. The datasheet of the standard PV module gives all the simulator inputs. The proposed emulator system is designed and implemented in the laboratory through XSG in a Virtex 5 FPGA development board. Performance comparison between the software simulation and real-time Hardware in the Loop HIL simulation has been demonstrated. The simulation results prove that the output characteristics of the emulator have good agreement with those of the actual photovoltaic panel.

New MPPT algorithm modeling for photovoltaic emulator designed in FPGA

Photovoltaic Systems are gaining importance rapidly. Their energy production is very intermittent due to the atmospheric conditions variation. So we proceed with an emulator which is an indispensable equipment to develop energy conversion systems in the laboratory. Also, MPPT techniques have a vital role to extract maximum power from the PV systems. This paper deals with a design and implementation of Maximum Power Point Tracking algorithm on FPGA to enhance its efficiency for PV emulator. The PV model is simulated in Matlab/Simulink environment. The P&O algorithm is designed and implemented through XSG toolbox in a Virtex 5 FPGA development board. This control strategy has been validated by interfacing a DC-DC boost converter which is considered as a power conditioning unit for controlling the PV source operating point to improve the overall efficiency of the emulation system.