Abdelmomen Mahgoub

Multiphysics circuit of a magnetostrictive energy harvesting device

Kinetic energy harvesting devices based on magnetostrictive materials are composed of several parts, for dealing with multiphysics, including mechanical, magnetic, and electric quantities. An effective method to simulate the effects of different working conditions is important to fully exploit such devices. The aim of this paper is to present an equivalent circuit that can be identified with standard measurements on the device and simulated with a standard circuit simulator, such as Spice. The circuit is a nonlinear three-port circuit, related to the mechanical, magnetic, and electrical parts of the device. Unlike many of the published papers on the subject, the magneto-mechanical modeling is quite realistic and exploits nonlinear functions and the full coupling among the involved physical quantities of the employed magnetostrictive material. The nonlinear equivalent circuit is preliminarily validated on a concept device with permanent magnets biasing on a Stress Annealed Galfenol rod. Experimental data with different resistive loads and magnetic biasing are considered and compared with simulation outputs, in terms of the RMS voltage and harvested power.

Enhancing Shielding Efficiency of Separate Shell Magnetic Shield Using Two Independent Controllers

A new strategy using two independent controllers to cancel both static and time varying magnetic fields is introduced. Two sets of coils are utilized for active compensation in the y-direction. The system shielding efficiency improved to 800 at 30 Hz from 20 in the case of passive shield only. The performance of the shield is further investigated by optimally selecting the relative position between the feedback and measuring sensors. Also, the distribution of y-component of magnetic field inside the shell along x-direction under different shell separation is investigated. The results show that the new controller was able to reduce the noise at 1 Hz to 20 pT/√ Hz, and the noise at 60 Hz is reduced more than 100×, with a noise floor of 3 pT/√ Hz.

Desktop Shielding System

A new active shielding system, which can be operated on a desktop, is developed with two identical separate magnetic shells: cap shell and cup shell. Shells are axis-symmetric and made of fiber-reinforced plastic (FRP) layers and 20 layers of magnetic sheets sandwiched with the FRP layers. A ring coil for the active compensation is attached to both of the shells so that the axial component of the magnetic field can be shielded at the center space between two shells. This shielding system may be useful in such a case where a single component of the magnetic field from samples needs to be measured for detecting important information. Furthermore, due to the opening at all along the shell edge, samples can be continuously conveyed to the measurement point in the shield. The shielding performance has been investigated numerically for various design parameters and confirmed experimentally. The shielding factor (SF) achieved at low frequency is very high as it reaches 3162 at 1 Hz and it is as high as 100 at 100 Hz.

Control of space-vector modulated solar grid-tied quasi-Z-source Inverter

This paper proposes a control system design for quasi-Z-Source Inverter in photovoltaic grid-tied applications. The control system is designed based on the dynamical characteristics of the converter and comprises three cascaded controllers. Firstly, output current controller designed in the synchronous rotating frame. The second is DC-link voltage controller. Sampling and measurement of the DC-link voltage signal is discussed using modified space-vector modulation. The last is maximum power point tracking in which a new strategy is proposed to provide wide operating range of DC-link voltage and shoot-through duty ratio, minimize the voltage stress on the inverter bridge, and prevent overlap between shoot-through duty ratio and modulation index. Simulation results are presented to validate the controllers design.

Inverter dead-time and non-linearity rejection using a wide bandwidth current controller for PMSM drives with a speed sensor

The dead-time and the other inverter nonlinearities known as the inverter non-idealities affect the output voltage and current distortions especially at low output voltages. The inverter non-idealities could be modeled as disturbances acting on the plants (motors) input. This paper discusses the effect of current controller design on the rejection of inverter non-idealities induced disturbances acting on the motors terminals. Compensating for the inverter non-idealities through wide bandwidth current controller without the need of any additional compensation scheme is proposed, studied and verified experimentally at challenging operating conditions. The method is shown to be very suitable for permanent magnet synchronous motors (PMSM) drives with speed sensor as they do not rely on any estimation based on the reference voltage signal unlike sensorless vector induction motors (IM) and sensorless PMSM drives in general. Different design methods for PI current controllers are investigated along with a proposed current controller based on internal model control. The different current controller design techniques are then compared analytically and experimentally to highlight the most suitable one.

The effect of overcompensation on magnetic field gradients in a separate shell magnetic shield

In this paper the concept of overcompensation is introduced. The effect of overcompensation on reducing the gradient of the vertical component of magnetic field inside the separate shell magnetic shield is studied for the operation of a first order SQUID gradiometer. The results show that slight increase in the active compensation current used is capable of eliminating the gradient of By component at the area of interest. Finally, A practical implementation is introduced to achieve overcompensation inside the shield.