Eva Cosoroaba

Rotor Shape Investigation and Optimization of Double Stator Switched Reluctance Machine

This paper presents an optimal design for the rotor of a double stator switched reluctance machine. The effect of the rotor shape on the torque profile is analyzed first. Due to the nonlinearity of magnetic core and complex geometry, an iterative approach is developed to automatically shape the rotor geometry using static finite element method. The rotor of a 12/8/12 prototype is optimized. Simulation results validate the effectiveness of the optimal design.

Stability analysis and voltage control method based on virtual resistor and proportional voltage feedback loop for cascaded DC-DC converters

This paper proposes a voltage control method based on virtual resistor and proportional voltage feedback loop for cascaded DC-DC converters. The closed-loop DC-DC converter would act as negative impedance load for the front-end converter and might lead to system instability. Based on the analysis of DC-DC converter with distributed parameters, a modified voltage control strategy based on virtual resistor is proposed which is to only add a proportional feedback of inductor current in the control block. Thus, no extra power loss would be generated. However, under some conditions, this method cannot achieve system stabilization. Then, an additional output voltage feedback loop is introduced which can not only stabilize the system under different cases but also improve system performance. Experimental results verified theoretical analysis and feasibility of the proposed control methods.

Comparative study of two winding configurations for a double stator switched reluctance machine

This paper compared the effect of full-pitched and tooth windings on performance of double stator switched reluctance machines. The main scope of the research presented here is to obtain higher power/torque density for an existent double stator switched reluctance machine (DSSRM). The chosen approach is intended to reduce the amount of copper by applying a winding configuration that allows shorter end windings, compared to the commonly used full-pitch windings. Magnetic circuit design alterations are introduced for an effective use of the single-tooth windings. A considerable reduction of weight was achieved and domains were defined in which the use of each of the two winding topology is advantageous, considering static average torque output and copper losses of the two DSSRMs. Furthermore, aspect ratio and torque ripple have been taken into consideration to complete the comparison. Simulation results verify the anticipated effect of the single-tooth windings.

Stability Optimization Method Based on Virtual Resistor and Nonunity Voltage Feedback Loop for Cascaded DC–DC Converters

This paper proposes a stability optimization method based on virtual resistor and nonunity voltage feedback loop for cascaded dc-dc converters. Oscillating phenomenon or instability would occur occasionally with two or more closed-loop dc-dc converters in series. The virtual resistor and nonunity voltage feedback are used to modify the feedback loop instead of only a direct voltage feedback to improve stability and get rid of oscillating behavior. Based on the stability analysis of dc-dc converters with distributed parameters, several cases have been derived. After that, relative to different cases, two modified methods based on virtual resistor and nonunity voltage feedback loop are proposed to stabilize the overall system. With these methods, no extra power loss would be generated, and it is easy to embed them into any conventional control system. Experimental results verified the theoretical analysis and feasibility of the proposed control methods.

Core loss estimation of SPMSM based on field reconstruction method

Traditional core loss estimation is based on the Steinmetz Equation subject to a sinusoidal excitation. The core losses are segregated into three parts: hysteresis loss, eddy current loss and extra loss. The estimation is based on the information of maximum flux density and fundamental frequency and thereby neglecting the effects of harmonics which results in low accuracy. In order to consider the loss caused by harmonics, a field reconstruction method (FRM) is proposed to reconstruct the field density in the laminations. Fast Fourier Transformation (FFT) is applied to obtain the harmonic components of the flux density to calculate the core loss. To verify the validity of the proposed method, both FEA simulation and experiments based on a surface-mounted permanent magnet synchronous machine (SPMSM) are conducted to calculate and measure the core loss. The comparison of core loss results obtained with different methods shows that FRM is both effective and time saving in determining the core loss of a machine.

Comparative Study of a New Coil Design With Traditional Shielded Figure-of-Eight Coil for Transcranial Magnetic Stimulation

Transcranial magnetic stimulation (TMS) is a non-invasive neuro-stimulation based on the principle of electromagnetic induction that uses brief, strong magnetic pulses of electric current delivered to a coil placed on the subject’s head to induce an electric field in the brain. This electric field could stimulate and modulate neural activity. Induced E-field inside brain generated by repetitive TMS (rTMS) can produce changes in neural activity that extends beyond the period of stimulation. Therefore, rTMS can be used as a probe for exploring higher brain functions and as potential treatment technique for psychiatric and neurological disorders. However, based on the chosen shape of the excitation coil, there exists a tradeoff between the excitation focality in the brain and the depth to which the field penetrates. In this paper, a new design of TMS coil is proposed to enhance the performance of the traditional figure-of-eight (FOE) coil. 3-D finite-element method has been used to simulate and compare the electric field induced inside the model of a human brain under the influence of both coil designs. An experimental verification was then followed to validate the advantages of the proposed coil design over the classic FOE coil.

On the proximity effects of high-energy magnets on M-19 magnetic steel core

Permanent magnet synchronous motors (PMSM) and asynchronous induction motors (IM) are widely used in the industry for a diverse set of applications. Although the use of induction motors is increasing for industrial applications due to cost inconsistency in rare earth magnets, PMSM motors are still being used because of their compact size, high power density, and greater efficiency. In interior permanent magnet synchronous motor (IPMSM) and surface mounted permanent magnet synchronous motor (SPMSM), the non-oriented silicon steel core is in continuous contact with high-energy rare earth magnets. This paper focusses on the effects of these high-energy magnets on the magnetic properties of M-19 steel core. It is observed that the relative permeability of the M-19 steel decreases when it is kept in contact with three sintered Neodymium (NdFeB), grade N45 permanent magnets. This leads to decrease in the inductance of the motor. It thus depicts a very important concept which is generally ignored while designing motors especially for electric propulsion and industrial applications where the effects can be significant.

Magnetohydrodynamics in thermal to electric energy conversion

When technologies reach maturity, their energy and power conversion efficiencies can be only improved minimally. Therefore, research efforts need to be invested into finding useful applications for conversion losses, thus improving the systems overall energy consumption. The most common conversion loss manifests itself as waste heat of low-, medium- and high temperatures. This paper aims to introduce an innovative thermal to electric energy conversion system, using magnetohydrodynamics (MHD) at its core. Determined overall efficiencies exceed the efficiencies of thermocouples, the most common thermal to electric energy converter. Furthermore, an MHD prototype is introduced.

Performance improvement and comparison of concentrated winding segmental rotor and double stator switched reluctance machines

Switched reluctance machine (SRM) is well known for its simple and robust design as well as its good high speed performance. On the other hand, its shortcomings are the moderate power/torque density, high torque ripple and high acoustic noise. Having one of the simplest mechanical designs, these machines have potential for a significant improvement. Accordingly, segmental rotor and double stator SRM (DSSRM), which also has a segmental rotor shared by two stators, are designed to improve the performance of SRM. Both of these machines have full pitch or concentrated windings topologies. Among these, concentrated winding topology is highly preferable due to reduced amount of copper and modular winding design. However, this requires a careful magnetic design optimization. This study introduces new magnetic design aspects for segmental rotor SRMs. Consequently, the advantages of DSSRM structure in terms of energy conversion efficiency and torque/power density are addressed in detail.

Temperature dependence of efficiency in renewable magnetohydrodynamic power generation systems

Magnetohydrodynamic (MHD) power generation is based on Faradays law: a magnetic field induces electron movement into a passing, conductive fluid. If captured, these electrons are the source of magnetohydrodynamically generated power. Combustion gas and liquid metal (LM) have been used as work fluid in the research of the 60s, but to gain renewable energy source properties, liquid gallium is used in a circular channel to allow the use of lower temperature thermal energy as the main input. This paper focuses on the detailed description of the proposed renewable system, the efficiency derivation as well as the study of the efficiency sensitivity considering loading conditions, generator dimension, and metal temperature. Conclusions and outlook on specific applications of LM-MHD are given.