Kostadin Brandisky

Resonant Contactless Energy Transfer With Improved Efficiency

This paper describes the theoretical and experimental results achieved in optimizing the application of the series loaded series resonant converter for contactless energy transfer. The main goal of this work is to define the power stage operation mode that guarantees the highest possible efficiency. The results suggest a method to select the physical parameters (operation frequency, characteristic impedance, transformer ratio, etc.) to achieve that efficiency improvement. The research clarifies also the effects of the physical separation between both halves of the ferromagnetic core on the characteristics of the transformer. It is shown that for practical values of the separation distance, the leakage inductance, being part of the resonant inductor, remains almost unchanged. Nevertheless, the current distribution between the primary and the secondary windings changes significantly due to the large variation of the magnetizing inductance. An approximation in the circuit analysis permits to obtain more rapidly the changing values of the converter parameters. The analysis results in a set of equations which solutions are presented graphically. The graphics show a shift of the best efficiency operation zone, compared to the converter with an ideally coupled transformer. Experimental results are presented confirming that expected tendency.

Electrical field and current distributions in electrochemotherapy.

Electrochemotherapy is a method for cancer treatment consisting in combining intratumor injection of cytotoxic agent with the application of intensive electrical stimuli. Thus transient cell membranes permeabilization is created, allowing the agent to better exercise its destroying effect. Positive results have been published in the treatment of cutaneous malignant formations and other types of cancer are under consideration. The electrode configurations presently used are based mainly on empirical treatment results. In vivo imaging of stimulation currents was attempted in animal models. A preliminary study revealed that having in view the relatively high voltages and currents, there was a virtually resistive load to the electrical source. Assuming a homogeneous medium, potential and current distributions were modeled and studied. The results could help in selection of specific electrode designs, depending on tumor size and location. An optimization of the voltages and/or currents by different electrode arrays can lead to obtaining desired field distribution.

Parallel implementation of evolution strategy optimization algorithm on multicore processors

Purpose – The purpose of this paper is to present a parallel implementation of an evolution strategy (ES) algorithm for optimization of electromagnetic devices. It is intended for multi‐core processors and for optimization problems that have objective function representing a numerical simulation of electromagnetic devices. The speed‐up of the optimization is evaluated as a function of the number of processor cores used.Design/methodology/approach – Two parallelization approaches are implemented in the program developed – using multithreaded programming and using OpenMP. Their advantages and drawbacks are discussed. The program is tested on two examples for optimization of electromagnetic devices.Findings – Using the developed parallel ES algorithm on a quad‐core processor, the optimization time can be reduced 2.4‐3 times, instead of the expected four times. This is due to a number of system processes and programs that run on part of the cores.Originality/value – A new parallel ES optimization algorithm ha...

Comparative Analysis of Three Classes of Experiment Design Applied to Optimization of PM DC Machines

The combination of numerical field calculation with the response surface methodology permits computer simulations to be extended to the design stage, rather than to be used in the analysis of a system. The necessity of using response surface methodology and simplified analytic models stems from the fact that the numerical field computation is very time-consuming, especially for 3D or transient analysis of complicated devices. This makes the direct use of such computer models in optimization algorithms unattractive, because most of them require many evaluations. When using the design of the experiment, a comparatively small number of computer model evaluations are required in obtaining an approximate polynomial model. Moreover, this approach is inherently parallelizable using massively parallel computers.

Comparative analysis of two methods for time‐harmonic solution of the steady state in induction motors (abstract)

The abstract presents two methods of solving induction motor problems using a time‐harmonic approach, taking into account the saturation of the iron material. The first method uses the following algorithm. Initially, two static nonlinear problems are solved: one problem using the real part of the stator currents, and the other using the imaginary part. From both solutions, a reluctivity vector is generated. This reluctivity vector is then used in solving a time‐harmonic problem to calculate the induced rotor currents. These currents are used to solve two new static problems. From the solution, a more accurate reluctivity vector can be generated. Convergence of this method occurs after 4 or 5 steps. The second method is an iterative method of solving nonlinear time‐dependent problems by harmonic representation. It is assumed that H(t) is a sinusoidal function of time. A new sinusoidal Beq is introduced based on energy equivalence with the real nonsinusoidal B. This new Beq is used to calculate the new B‐H ...