A comparative review of three different power inverters for DC–AC applications

This paper presents a comparative review of three different widely used power inverters, namely the conventional six-switch inverter; the reduced switch count four-switch inverter; and the eight-switch inverter. The later inverter can be reconfigured as a neutral-point diode-clamped inverter at the failure of one inverter leg. The three power inverters are compared and discussed with respect to cost, complexity, losses, common mode voltage, and control techniques. The paper is intended to serve as a guide regarding selecting the appropriate inverter for each specific application. Simulation results are presented to demonstrate the performance of the three power inverters, followed by a comprehensive comparison between the three power inverters

Model predictive current control for a low-cost shunt active power filter

Performance of a three-phase shunt active power filter (SAPF) relies on the capability of the controller to track the reference current. Therefore, designing an accurate current controller is crucial to guarantee satisfactory SAPF operation. This paper presents a model predictive current controller (MPCC) for a low-cost, four switch, shunt active power filter for power quality improvement. A four switch, B4, converter topology is adopted as an SAPF, hence offering a simple, robust, and low-cost solution. In addition, to further reduce the overall cost, only two interfacing filter inductors, instead of three, are used to eliminate switching current ripple. The proposed SAPF model MPCC is detailed for the implementation, where simulation and experimental results validate the effectiveness of the proposed control algorithm showing a 20% improvement in total harmonic distortion compared with a conventional hysteresis band current controller

Genetic algorithm based approach of SRM current profiling for torque control and minimal copper losses

This paper presents a novel approach to current profiling for switched reluctance machines that eliminates torque ripple while inherently guaranteeing minimum copper losses, along with linear torque control. Minimization of copper losses increases machine efficiency, while eliminating torque ripple is the pre requisite for SRM use in applications such as traction vehicles. This paper presents theoretical optimal current profiles, initially without consideration of DC link voltage limitations. Utilizing a Genetic Algorithm in conjunction with current profiling limit envelopes, an optimized set of current profiles across the torque ripple free speed range of an exemplary 8/6 SRM is then created. The profiles characteristics are analyzed and compared with commonly used torque sharing function control to confirm the merits of the proposed method

A neutral-point diode-clamped converter with inherent voltage-boosting for a four-phase SRM drive

This paper proposes a new asymmetric neutral-point diode-clamped (NPC) multilevel converter for a four-phase switched reluctance motor drive. The inbuilt NPC clamping capacitors are used for both voltage level clamping and also as dc rail voltage-boosting capacitors to increase the output power of the motor, particularly for high-speed electric vehicle applications. The new converter allows regenerative energy to be recovered back to the dc supply for rapid machine braking, thus increasing overall drive efficiency. Analysis of the different modes of converter operation, along with design equations for sizing the voltage-boosting capacitors, are detailed. The effect of capacitance on boost voltage and increased motor base speed is presented. Simulation and experimental results confirm the effectiveness of the proposed converter

A new torque ripple minimization approach for switched reluctance drives

This paper presents a new torque control function for torque ripple reduction in switched reluctance drives. The approach is based on the maximum utilization of available dc link voltage, extending the zero torque-ripple speed range. The approach is suitable for switched reluctance machines with any number of phases and stator/rotor poles. Soft switching control is deployed, which reduces switching losses. At any instant, only one phase current is controlled, significantly reducing the control complexity. Simulations are carried out on a four-phase 8/6, 4kW SRM in MATLAB/Simulink

Power density improvement due to rotor flux screens in an SRM with a higher number of rotor poles than stator poles

This paper studies the performance of screened switched reluctance motors (SRMs) with a number of rotor poles higher than the number of stator poles. Flux (conducting) screens are electrically conducting, non-magnetic materials like aluminum or copper. These screens fill the interpolar rotor air gaps decreasing the unaligned inductance, and thereby increasing the output torque. In addition, flux screens result in a cylindrical rotor structure which minimizes windage losses especially at high speeds. The paper investigates the effect of the flux screens thickness and material on the SRM performance including output torque, power and phase current. A modified flux tube approach for estimating the unaligned inductance of screened SRM is proposed. Finite element analysis results for different screen cases confirm the effectiveness of conducting screens in improving the torque, hence power capability, of switched reluctance motors

Isolation and Genetic Characterization of Rift Valley fever virus from Aedes vexans arabiensis, Kingdom of Saudi Arabia

An outbreak of Rift Valley fever in the Kingdom of Saudi Arabia and Yemen in 2000 was the first recognized occurrence of the illness outside of Africa and Madagascar. An assessment of potential mosquito vectors in the region yielded an isolate from Aedes vexans arabiensis, most closely related to strains from Madagascar (1991) and Kenya (1997)

The Urologist's View of Male Overactive Bladder: Discrepancy between Reality and Belief in Practical Setting

PURPOSE: In order to gain insight into the physicians' awareness of and attitude towards management of overactive bladder (OAB) in males, we performed a nationwide survey of the current strategies that urologists use to diagnose and manage OAB in male patients. MATERIALS AND METHODS: A probability sample was taken from the Korean Urological Association Registry of Physicians, and a random sample of 289 Korean urologists were mailed a structured questionnaire that explored how they manage benign prostatic hyperplasia (BPH). RESULTS: A total of 185 completed questionnaires were returned. The consent rate in the survey was 64.5%. Eighty-one (44%) urologists believed that of all males with lower urinary tract symptoms (LUTS), 20% or more had OAB and 72 (39%) believed that 10-20% had OAB. Half of the urologists surveyed believed that the most bothersome symptom in male OAB patients was nocturia. Seventy-three percent of respondents reported that they prescribed alpha blockers with anticholinergics for first line management, while 19% of urologists prescribed alpha blocker monotherapy but not anticholinergics for OAB patients. Though acute urinary retention (AUR) was considered the anticholinergic adverse event of most concern, the most frequently observed adverse event was dry mouth (95%). CONCLUSION: The present study provides insights into urologist views of male OAB. There is a discrepancy between the awareness of urologists and actual patterns of diagnosis and treatment of male OAB. This finding indicates the need to develop further practical guidelines based on solid clinical data.ope