Essam M. Rashad

Synchronous reluctance motors performance based on different electrical steel grades

Recently, the Synchronous Reluctance Motor (SynRM) has received more attention for many applications, thanks to its rugged construction and low cost [1]. Over the past decades, developments in machine design methodology, high quality magnetic materials, and advanced power electronics allow the machine designers to enhance the performance of the SynRM which depends mainly on the direct and quadrature axis inductances (Ld, Lq). Therefore, considerable attention has been given to improve the saliency ratio of the SynRM, taking into account the core material and its saturation behaviour. Several papers have focused on the rotor geometry design and the saturation effect on the performance of the SynRM [2, 3]. However, the effect of the electrical steel grades on the performance of the SynRM has not been deeply studied.

Maximum power tracking of a grid-connected wind-driven Brushless Doubly-Fed Reluctance Generator using scalar control

This paper presents a scalar volt per hertz (v/f) control technique for maximum power tracking of a grid-connected wind-driven Brushless Doubly-Fed Reluctance Generator (BDFRG). The proposed generator has two stator windings namely; power winding, directly connected to the grid, and control winding, connected to the grid through a bi-directional converter. The presented control technique is based on the abc-axis and dq-axis dynamic model of BDFRG. A detailed abc-axis and dq-axis dynamic model, by which the dynamic behaviour of the BDFRG can be successfully predicted under different operating conditions, is presented. In addition, a soft starting method is suggested to avoid the over-current of the bi-directional converter. The presented simulation results ensure the effectiveness of the proposed control strategy for maximum wind-power extraction under wind-speed variations.

Combined Star-Delta Windings to Improve Synchronous Reluctance Motor Performance

This paper analyzes and compares the synchronous reluctance motor (SynRM) performance for a conventional star winding and for a combined star-delta connected winding under healthy and faulty conditions. The finite element method is used to simulate the SynRM characteristics in case of normal star and in case of combined star-delta connected windings. For the healthy case, it was found that for the same current, the SynRM output power increased by about 5% for the star-delta connected windings compared with the conventional star connection. Moreover, the efficiency increased slightly by 0.20%. Probably the strongest advantage of the combined star-delta winding is observed when a phase fault occurs. When one phase is missing, for the same current, the star-delta connected motor keeps 80% of the rated torque in the healthy case, while the star connected motor only keeps 40%. Furthermore, the torque ripple of the star wound machine is extremely high in case of a missing phase, compared to the star-delta wound machine. Simulation results were validated by experimental results to show the effectiveness of the star-delta connected windings on the SynRM.

A simple CB-PWM technique for five-phase matrix converters including over-modulation mode

This paper presents a simple carrier-based PWM (CBPWM) technique to control a three-phase to five-phase matrix converter (3×5 MC). The proposed technique is based on the indirect configuration of the matrix converter in which the three to five-phase matrix converter is modeled as three-phase rectifier followed by a five-phase inverter. With this representation, CBPWM technique is suggested to control both stages in both linear and over-modulation modes. Using the proposed modulation technique, the maximum possible voltage transfer ratio (VTR) of the converter in the linear and over-modulation modes is achieved. The proposed modulation technique is modeled using Matlab/Simulink software and the overall system algorithms are compiled to a real time system based on DS1104 controller. A sample of the obtained experimental results is presented to support the viability of implemented three to five-phase matrix converter with the proposed modulation technique.

Vector control strategy for maximum wind-power extraction of a grid-connected wind-driven Brushless Doubly-Fed Reluctance Generator

This paper proposes a vector-control (power-winding flux orientation) strategy for maximum wind-power extraction of a grid-connected wind-driven Brushless Doubly-Fed Reluctance Generator (BDFRG) system. The adopted generator has two stator windings namely; power winding, directly connected to the grid, and control winding, connected to the grid through a bi-directional converter. In addition, a unity power-factor operation is also provided based on the proposed vector-control strategy. Moreover, a soft starting method is suggested to avoid the over-current of the bi-directional converter. A sample of the obtained simulation results is presented to check the effectiveness of the proposed strategy.

Voltage and frequency control of a stand-alone wind-energy conversion system based on PMSG

This paper presents a control strategy for a standalone wind-energy conversion system using Permanent Magnet Synchronous Generator (PMSG). The presented control strategy aims at regulating the load voltage in terms of magnitude and frequency under different operating conditions including windspeed variation, load variation and the unbalanced conditions. The wind generating-system under study consists of a wind turbine, PMSG, uncontrolled rectifier, DC-DC boost converter and voltage source inverter. The presented control strategy is based firstly upon controlling the duty cycle of the boost converter in order to convert the variable input dc-voltage, due to different operating conditions, to an appropriate constant dc-voltage. Hence, a sinusoidal pulse width modulated (SPWM) inverter is used to regulate the magnitude and frequency of the load voltage via controlling the modulation index. In order to verify the performance of the employed wind generating-system, a sample of simulation results is obtained and analyzed. The presented simulation results show the effectiveness of the employed control strategy to supply the load at constant voltage and frequency under different operating conditions.

Control of five-phase induction motor under open-circuit phase fault fed by fault tolerant VSI

Five-phase induction motor drive systems have gained much popularity due to the numerous advantages that they offer when compared to their three-phase counterparts. In principle, the supply to five-phase drive system is given from five-phase voltage source inverter (VSI). In this paper, a fault-tolerant control strategy for five-phase VSIs has been suggested. The conventional five-phase inverter consists of only five legs. The proposed strategy forces the faulty phase to connect to the midpoint of the DC-link via the additional dc-bus midpoint inserting Thyristors. The proposed inverter provides tolerance to both short-circuit and open-circuit faults of the switching devices. The performances of the post-fault as well as the normal pre-fault operation are discussed. The fault tolerance of the inverter is verified using vector control of a five-phase induction motor. The complete control scheme is implemented in real-time using digital signal processor (DS1104) for a prototype 1.5 hp motor. Experimental results of the proposed drive verify the proposed control scheme.

Influence of rotor flux-barrier geometry on torque and torque ripple of permanent-magnet-assisted synchronous reluctance motors

The rotor design has a large effect on the performance of Permanent-Magnet-Assisted Synchronous Reluctance Motors (PMaSynRMs). An optimized rotor geometry is necessary in order to obtain higher motor torque with minimum torque ripple. This paper investigates the influence of the flux-barrier design which is the most important rotor geometry parameter regarding the torque and torque ripple of PMaSynRMs. The flux-barrier parameters are angle, width, and position, as well as the length. Starting from the optimized rotor of a SynRM without magnets, a PMaSynRM is created by inserting permanent-magnets inside the center of the flux-barriers. For a prototype SynRM, experimental results have been obtained to validate the FEM results and to validate the strategy for choosing the rotor parameters.

Indirect space-vector PWM technique for three to nine phase matrix converters

This paper develops indirect space vector modulation technique for a three- to nine-phase matrix converter. The proposed technique is based on the double-stage configuration in which the matrix converter is modeled as three-phase rectifier followed by a nine-phase inverter. Both rectifier and inverter stages are controlled using space-vector modulation technique. In the rectifier stage, the modulation is based on input currents space-vectors. However, the modulation of the inverter stage is based on output voltages space-vectors. Two different schemes are suggested to control the inverter stage. In the first scheme, only largest space vectors are used in order to achieve maximum voltage transfer ratio of the inverter stage. In the second scheme, eight active vectors are used in each sector in order to minimize the switching stresses and to give a sinusoidal output voltage. It is observed that, using the first scheme results in achieving a higher value of the maximum overall voltage transfer ratio. However, the output voltages contain a significant amount of lower order harmonics. On the other hand, sinusoidal output voltages with a reduced value are obtained by second scheme. A sample of the obtained simulation results is presented to support the viability the proposed technique.

Assessing the effect of design parameters on optimal size of isolated PV systems for residential utilizations

This paper investigates the effect of varying different operating and design parameters on the sizing and economics of standalone PV systems for residential utilization. Each subsystem is sized using simplified mathematical expressions considering the effecting parameters as input variables. Thus, the sizing and economics of the entire system can be investigated in a generic form. The cost of each system component is analyzed based on international prices and aggregated to obtain the overall cost of energy (COE). The study is based on a 5 kWh/day residential load. A peak load power of 1300W is considered when sizing the inverter capacity. Among the design factors, the battery bank voltage, charge controller type, the solar irradiation and the depth of discharge (DOD) are investigated to examine their effect on the system economy. The analysis results show that the COE relies heavily on both the size and the selected design voltage of the battery bank, which in turn depend on the storage hours, charger size, the (DOD) value and solar irradiation.