Volume 63 (2012): Issue 4 (July 2012)

This contribution describes the method of harmonic modulation of a velocity set-point signal in control to reduce undesirable oscillations. Especially the combination of this method with the well known input shaping method is of interest. Such a solution seeks for instance to a control structure used for servomechanisms equipped with a gear-box or namely mechatronic drives (MDs); where undesirable oscillations in transient- as well as semi-steady-states could arise. The combination of the methods has been proofed under real conditions in an experimental setup. Based on this, simulations regarding different industry demands and the proper choice of the modulation signal types will be introduced. Further it will be discussed which modulation signal should be used for the corresponding ie industrial demands. Both proposed methods are in the category of feed-forward-control which led to a practical implementation where no additional sensor (for measuring these undesirable effects) is needed to improve the system dynamics.

This paper proposed a multi-objective genetic algorithm (MOGA) based approach for determining the steady-state performance characteristics of three-phase self-excited induction generators (SEIGs) operating in parallel and supplying an unbalanced load. The symmetrical component theory is used for the transformation of a complex three-phase generators-capacitances-load system to a simple equivalent circuit. The MOGA has been employed for the determination of unknown variables by minimizing the impedance module of the equivalent circuit. Using this approach, effects of various parameters on the terminal voltage control characteristics are examined for two parallel SEIGs with C2C connection under a single phase load.

Ultrasonic piezoelectric motor technology is an important system component in integrated mechatronics devices working on extreme operating conditions. Due to these constraints, robustness and performance of the control interfaces should be taken into account in the motor design. In this paper, we apply a new architecture for a fault tolerant control using Youla parameterization for an ultrasonic piezoelectric motor. The distinguished feature of proposed controller architecture is that it shows structurally how the controller design for performance and robustness may be done separately which has the potential to overcome the conflict between performance and robustness in the traditional feedback framework. A fault tolerant control architecture includes two parts: one part for performance and the other part for robustness. The controller design works in such a way that the feedback control system will be solely controlled by the proportional plus double-integral PI2 performance controller for a nominal model without disturbances and H_∞ robustification controller will only be activated in the presence of the uncertainties or an external disturbances. The simulation results demonstrate the effectiveness of the proposed fault tolerant control architecture.

In this paper, a new method for robust PSS design based on the power system pole placement is presented. In this stabilizer, a feedback gain matrix is used as a controller. The controller design is proposed by formulating the problem of robust stability in a Linear Matrix Inequality (LMI) form. Then, the feedback gain matrix is designed based on the desired region of the closed loop system poles. This stabilizer shifts the poles of the power system in different operational points into the desired regions in s-plane, such that the response of the power system will have proper damping ratio in all the operational points. The uncertainties of the power system parameters are also considered in this robust technique. Finally, in order to show the advantages of the proposed method in comparison with conventional PSS, some simulation results are provided for a power system case study in different operational points.

Pull-in voltage Evaluation is significant for the design of electrostatically actuated MEMS devices. In this work simple closed form models are derived for computation of pull-in voltage of cantilever beams. These models are obtained based on five different capacitance models suitable for wide range of dimensions. Using these models pull-in voltages are computed for a range of dimensions and the results are compared with the experimentally verified 3D finite element analysis results. The results show that, for every given range of dimension, choice of the model changes for the evaluation of the pull-in voltage with a maximum deviation of 2%. Therefore for a given range of dimension appropriate closed form model is to be chosen for accurate computation of pull-in voltage. Computation of pull-in voltage of microgripper further validates the closed form models. The results again show that for a given range of dimension only a particular model evaluates the pull-in voltage with less error.

In this paper, a multiple model approach is proposed for the identification of synchronous generators. In the literature, the same structure often is used for all local models. Therefore, to obtain a precise model for the operating condition of the synchronous generator with severely nonlinear behavior, many local models are required. The proposed method determines the complexity of local models based on complexity of behavior of the synchronous generator at different operating conditions. There are two choices for increasing model precision at each iteration of the proposed method: (i) increasing the number of local models in one region, or (ii) increasing local model complexity in the same region. The proposed method has been tested on experimental data collected on a 3 kVA micro-machine. In the study, the field voltage is considered as the input and the active output power and the terminal voltage are considered as the outputs of the synchronous generator. The proposed method provides a more precise model with fewer parameters compared to some well known methods such as LOLIMOT and global polynomial models.

The fault is inevitable in any complex systems engineering. Electric power system is essentially a typically nonlinear system. It is also one of the most complex artificial systems in this world. In our researches, based on the real-time measurements of phasor measurement unit, under the influence of white Gaussian noise (suppose the standard deviation is 0.01, and the mean error is 0), we used mainly nonlinear principal component analysis theory (NLPCA) to resolve fault identification problem in complex electrical engineering. The simulation results show that the fault in complex electrical engineering is usually corresponding to the variable with the maximum absolute value coefficient in the first principal component. These researches will have significant theoretical value and engineering practical significance.

This work presents the simulation of a shunt active filter using seven-level cascaded inverter. The ultimate objective is to bring out the influence of multiple carrier level shifted PWM techniques on the performance of a shunt active filter. Classical disposition PWM techniques such as PD, POD and APOD have been used to generate the gating signals for the inverter active switches. A comparison is presented to substantiate the effect of these techniques in filtering. The comparison is made from the perspective of reduction in THD of source currents after filtering. For compensation current extraction synchronous detection method has been used. The harmonic reduction is achieved in source currents as well as source voltages.

The article presents a way of improvement the important performances of an electronic low resistance comparator. The practical usage of a realized instrument prototype shows some disadvantages: the time until the result appears at the display is to long (the stationary state establishing sequence should be shorter) because of the negative influence of parasitic voltages. Modification of output voltage hold circuit gives quite convenient instrument response time. The parasitic voltage disturbance is decreased to acceptable value, even though the comparator is modified for multirange measurement. The paper describes some details of a solution and its conformation in practical usage.

We have studied La_0.67Sr_0.33MnO₃ (LSMO) thin films with temperature of metal-insulator (T_MI) transition enhanced to above 400 K, and we estimated characteristic electrical transport mechanisms for these films. We have fitted the measured resistivity vs. temperature ρ(T) dependence in a wide temperature range 4-500 K using different mechanisms of the electrical transport in different parts of ρ(T). In addition to the narrow temperature range around T_MI very well agreement was found. We found out that the Debye's temperature was also increased (Θ_D ≈ 840 K) probably due to the change in crystallization of LSMO films.