In this paper, decoupled control of rotor torque and rotor electric power in a reluctance wound rotor brushless doubly fed machine, (BDFM), is presented. The machine stator windings are fed from two ...separate voltage source inverters. The proposed control technique is applied to the inverters such that the BDFM is capable of producing mechanical torque at any desired synchronous speed and simultaneously delivers n-phase rotor electric power through the rotor terminals independent of the mechanical loading. This technique can eliminate the need for slip-rings and can be used in applications such as rotational antennas and turret systems. An existing slip-ring induction motor is modified to build up the proposed prototype BDFM. Simulation and experimental results validate the proposed control technique.
A study is undertaken to determine whether the bonuses paid to executives of firms that switched from FIFO (first in, first out) to LIFO (last in, first out), mostly in 1974, were adversely affected ...by the switch. The analysis is conducted for a period of 4 years, covering the 2 years before the change, the year of the change to LIFO, and the year following the switch. The sample is composed of 176 firms, 88 of which switched to LIFO and 88 of which retained FIFO over the entire 4-year period. Analysis indicates that the switch from FIFO to LIFO did not, on average, adversely affect the income-based performance bonuses for those executives who opted to make the switch. The switch firms apparently adapted their bonus pay to reflect the effect of the LIFO change on income by renegotiating their bonus contracts. The results also suggest that executives of the manager-controlled companies that retained FIFO had a relatively higher income-based bonus compared to the other companies.
MMC encounters serious limitations in the zero and low-frequency operation of variable-speed motor drives. In MMC, the voltage ripples of SubModule (SM) capacitor is inversely proportional to the ...phase current frequency. This paper proposes a new approach to solve the zero-/low- frequency operation technical issue of MMC-based drive systems. The proposed approach utilizes the additional degrees of freedom of multiphase machines to inject secondary-plane current components with certain magnitude and frequency in the load current to enable smooth operation during that interval. A simulation model of a three-level five- phase MMC-based Induction Machine (IM) drive system has been built using MATLAB/Simulink. In this paper, the adopted control strategy is explained and the simulation results are presented.
This paper introduces Hybrid Boost Modular Multilevel Converter (Hybrid Boost MMC) as a suitable candidate for subsea drive systems. The investigated drive system is based on a five-phase Induction ...Machine (IM) in order to enhance system's reliability and to gain other several merits of multiphase machines compared with conventional three-phase IMs. Each arm in the employed Hybrid Boost combines Half-Bridge (HB) and Full-Bridge (FB) Submodules (SMs) with ratio 2:1 respectively. The suggested Hybrid Boost MMC provides boosting capability with a reduced number of switches, which can be employed effectively instead of employing conventional voltage source converter followed by bulky step-up transformer. In addition, voltage balancing of the capacitors in any MMC is crucial in order to ensure proper operation of the converter. A sensor-less capacitor voltage balancing technique is proposed in this paper, employing five-level five-phase MMC with two HB-SMs and single FB-SM per MMC's arm. A simulation case study for the proposed system is investigated using a 1000 Hp five-phase Induction Machine (IM).
Energy storage systems have become an essential pillar in most of electrical engineering applications due to introduced technical and economical merits, particularly following the pronounced ...grid-integration of renewable energy sources. Flywheel Energy Storage Systems (FESSs) have emerged as reliable and cost effective short term storage system. FESS may be used for critical load support or fault ride-through purposes, therefore the FESS reliability must be ensured. In this paper, FESSs are investigated for medium voltage applications where the main concern is the FESS's reliability. The main challenge for medium voltage FESS is the driving machine ratings and interfacing power conversion system. Therefore, two-parallel three-phase Modular Multilevel Converters (MMCs) are proposed to drive an asymmetrical six-phase Induction Machine (IM) in order to reduce the DC link voltage of the medium voltage system into a proper level for the IMs, where each converter is connected to feed each three-phase set of the six-phase machine. The employment of MMCs and an asymmetrical six-phase IM enhances system reliability as well. The machine and converter mathematical models are presented in this paper. Moreover, a simulation case study for FESS control under the proposed configuration is investigated.
This paper introduces space vector modulation (SVM) schemes for reducing the common mode voltage (CMV) of a direct three-to seven-phase matrix converter (3×7 MC) fed a seven-phase induction motor. ...The proposed techniques are based on the indirect SVM (ISVM) in which the 3×7 MC can be modeled as a three-phase rectifier followed by a seven-phase inverter. The CMV reduction is achieved by suggesting three-ISVM schemes that are capable of reducing the peak CMV of the MC by 20%, 38% and 50% respectively compared with the conventional modulation strategy. The selection criterion to the suitable voltage space vectors and their proper arrangement within the switching cycle are described. The proposed ISVM schemes are assessed by simulating a direct 3×7 MC fed seven-phase IM using Matlab/Simulink. The effect of different modulation schemes on the motor phase currents and output torque is also investigated.
The on-line generation of carrier based gating signal for pulse width modulation-current source inverter (PWM-CSI) extends the duality between VSI and CSI. Accordingly, feedback control strategies ...with voltage source inverter, (VSI) such as vector control technique can be applicable with CSI. Moreover, the problems encountered with VSI and its effect on the machine can be avoided. The objective in this paper is to get the benefits from intrinsic advantages of multiphase CSI when engaged with the multiphase induction machine. A vector controlled five-phase PWM-CSI induction motor drive is introduced to study the performance of such system.
Recently, magnetic gearboxes (MGBs) are serious contenders to their conventional mechanical counterparts in terms of reduced maintenance requirements, improved reliability, tolerance to mechanical ...inaccuracies, and inherent overload protection. MGBs are preferably employed in high speed applications and compact harsh environments. One of the challenging design aspects of MGBs is the proper selection of the combination of the number of pole-pairs of both inner and outer rotors, yielding specific gear ratios, to minimize cogging torque magnitude. For any general desired gear ratio, the torque ripple magnitude may be unacceptable. Since MGBs generally belongs to permanent magnet (PM) machines family, the same techniques for torque ripple mitigation can be employed. This paper introduces a new technique for torque ripple reduction in MGB based on step skew technique. In the proposed technique, the MGB is divided into two equal parts along its stack length and the optimum skew angle between the two parts is determined for minimum torque ripple. A conventional 14/4 MGB, which is normally results in a significant cogging torque magnitude, is designed and simulated using 3D finite-element analysis (FEA) for different skew angles. Based on the simulation results, the required optimum skew angle that optimizes torque transmission while minimizes the corresponding cogging torque is recognized.
