Adel Gastli

Modular Multilevel Converter Circulating Current Reduction Using Model Predictive Control

Modular multilevel converter (MMC) is a promising new topology for high-voltage applications. The MMC is made of several identical submodules. For proper operation, each submodule can be considered as a controlled voltage source where capacitors voltage should be maintained at a certain level. Besides, the minimization of the circulating current, which does not flow to the load, is crucial for achieving stable and efficient operation of the MMC. The interrelations among the load current, circulating current, and capacitor voltages complicate the MMC control. This paper aims to achieve stable and balanced voltage and current control with reduced circulating current in various operating conditions. The proposed control uses weighted model predictive control based on a normalized cost function to select the inverter switching patterns, which control the load current, while minimizing voltage fluctuation and circulating current. The weighting factors were selected based on minimizing the load-current total harmonic distortion (THD) and circulating current. The analysis is conducted on a low-power case study of single-phase four-cells MMC with possible extension to higher number of cells. The low-power three-level prototype is designed and built to validate this proposed method. Theoretical analysis, simulation, and experimental results are presented and compared. Parameter sensitivity analysis was also conducted. They all confirm the effectiveness of the proposed control method.

Conductors of a linear induction motor

In this paper, the joint effect on the thrust and attraction forces of a linear induction motor is discussed and a control algorithm to compensate for such effects is presented. The algorithm is based on the vector control technique and takes into account the variation of the secondary resistance of the LIM when a joint enters the active zone of the LIM. The algorithm was tested by simulation on a sample of linear motor elevator system. Simulations have shown that the fluctuations of the thrust and attraction forces where decreased significantly.

Stator flux controlled V/f PWM inverter with identification of IM parameters (induction motors)

A V/f PWM inverter control algorithm based on controlling the stator flux vector of an induction motor is presented. The algorithm permits an automatic boost of inverter voltage in such a way that the stator flux magnitude is kept constant. The voltage autoboost method is based on knowledge of the IM equivalent circuit parameters and given load characteristics. An offline auto measurement of the equivalent circuit parameters using a PWM inverter is described. The technique consists of performing the no-load and single-phase tests when the motor is connected to the inverter. The complete control system has been constructed and tested and the experimental results have been found satisfactory. The proposed method has achieved a considerable improvement of IM torque-speed characteristics under optimal slip frequency operation. >

Evaluating solar photovoltaic system performance using MATLAB

This paper focuses on the modeling of solar photovoltaic (PV) cell and the performance of typical solar PV panels in selected areas in the Sultanate of Oman. An accurate solar PV cell electrical model is based on the junction diode equations. The model consists of a photo-current current source, a single diode junction and a series resistance, and takes into account temperature and solar irradiation dependence. The model is developed using MATLAB/Simulink and is used to investigate the variation of the maximum power point for different temperatures and solar irradiation levels. Finally, the model is experimentally validated for a typical 30 Watt solar module connected to a variable load.

Investigation of the dependence of DC insulation resistivity of ultra-clean polyethylene on temperature and electric field

The present work aims at determining the dependence of the DC insulation resistivity on temperature and electric field for a super-clean low density polyethylene (LDPE) used in manufacturing modern high voltage AC cables. Resistivity measurements were made using relatively thick (/spl sim/2 mm) samples at different temperatures and DC electric fields. Based on the present experimental data, a mathematical model for the relationship between the insulation resistivity of the polymer, temperature and electric field was determined using: (i) computer curve fitting techniques, and (ii) artificial neural networks (ANN) method. Comparison between the present results and previous measurements, using less clean grades of LDPE, indicates that the inherent dependence of the DC insulation resistivity of LDPE on temperature and electric field has not been appreciably improved by using an ultra-clean polymer. It is concluded that the successful utilization of LDPE for HVDC cables will require the modification of such dependence.

Asymmetrical constants and effect of joints in the secondary conductors of a linear induction motor

In this paper, one method of identification of the linear induction motor (LIM) constants is presented. Beside the asymmetrical nature of the LIMs constants (because of finite winding lengths) it was noticed that when a joint in the secondary conductor moves inside the active area of the LIM it creates variation and fluctuation of the secondary resistance of the LIM. The variation and fluctuation of the secondary resistance affects the thrust of the LIM which also fluctuates. These fluctuations of the thrust are not acceptable in some applications such as linear motor elevators in which the riding comfort is very demanding. A hardware solution to diminish the fluctuations of the thrust is proposed. It consists of adding a secondary joint at half pole pitch distance from the primary joint. This second joint creates another fluctuation that opposes the fluctuation caused by the primary joint. Thus, the secondary joint cancels the fluctuation effect caused by the primary joint. Several experiments were performed to confirm this solution.

Factors affecting transient overvoltages of electric submersible pumps

This article presents a theoretical simulation and analysis of all possible factors due to transient overvoltages (TOVs) that could contribute to electrical failures of electric submersible pump (ESP) motors used in oil fields. A transient calculations software package PSCAD is used to simulate a single cable-fed, 3.3-kV induction motor including the mains of the 33-kV distribution system. The factors studied are cable length, earthing resistance and parameters (insulation permittivity and permeability), opening time of CB and its location, switching via pre-insertion resistance, characteristics of the TVSS and its internal structure, and transformer connections and ratings

Siting of large PV farms in Al-Batinah region of Oman

This paper presents the results of a research study conducted on solar energy resource assessment for Al-Batinah region in Oman. GIS-based spatial multi-criteria evaluation approach, in terms of the FLOWA module was used to assess the land suitability for large PV farms implementation in Oman. The tool used applies fuzzy quantifiers within ArcGIS environment allowing the integration of a multi-criteria decision analysis. Land suitability analysis for large PV farms implementation was carried out for the case study of Al-Batinah region in Oman. The highly suitable land areas exceeding 2.5km2 of minimum surface were selected. Different PV technologies were considered for implementation in the selected areas. It was found that PV technologies provide very high technical potential for implementing large solar plants. In fact, if all highly suitable land is completely exploited for CPV implementation, it can produce almost 24.5 times the present total electric energy demand in Oman.

Improved field oriented control of an LIM having joints in its secondary conductors

This paper presents a primary-flux-control algorithm suitable for applications in short-primary long-secondary linear induction motor drive systems. The advantage of the proposed control algorithm is that is more robust than the conventional vector control algorithm to the variation of the secondary resistance caused by the effect of joint in the secondary conductors, which can be made of several pieces of aluminum plates or rails joined together. The algorithm was tested by simulation on a sample of linear motor disk drive system. The simulation results were compared to those obtained by a conventional vector control algorithm. Simulations and experiments have shown that the fluctuations of the thrust and attraction forces obtained with the proposed primary-flux control algorithm were significantly less than those obtained with the conventional vector control algorithm.

V/f PWM inverter with motor parameter identification and voltage auto-boost capabilities

A V/f control algorithm is presented that is based on constant air-gap flux control with inverter output voltage autoboost. This algorithm permits the realization of variable-voltage-variable-frequency (VVVF) control with a simple system configuration. In addition, as a result of the sine wave modulation of the inverter output voltage, there is a decrease of the torque ripple, an improvement of the efficiency, and a reduction of vibrations and noise. The algorithm permits an automatic boost of the voltage which maintains the same air-gap density. The voltage autoboost method is based on knowledge of the load characteristics and equivalent circuit parameters of the induction motor. An offline automeasurement technique for these parameters is described. The complete control system has been constructed and tested. The test results have been found satisfactory with the use of simple 8 bit microprocessors.<<ETX>>