نشریه مهندسی برق و مهندسی کامپیوتر ایران
سال هجدهم شماره 1 (پیاپی 54، بهار 1399)

In this paper, we proposed solutions for controlling the two-wheel self-balancing robot system in the presence of uncertainties in dynamical equation and without the need for kinematic equations. For this purpose, the dynamical equations of this system are initially transmitted to the domain of error, then these equations are divided into two independent subsystems, one of which is an under-actuated system and the other is fully actuated system. In order to control the under-actuated subsystem, two completely different sliding mode controllers are proposed that are able to provide this subsystem in the presence of structured and un-structured uncertainties with global asymptotic stability. Subsequently, in order to control the fully under-actuated subsystem, a sliding mode control is proposed to provide this subsystem in the presence of existing uncertainties with global asymptotic stability. Since these two subsystems are completely independent of each other, their global asymptotic stability proofs prove the global asymptotic stability of the closed-loop system. The separation of two-wheeled self-balancing robot sub-systems eliminates the need to use the kinematic equations, and this causes the presence of structured uncertainties to have no effect on the accuracy of tracing the closed-loop system state variables. Finally, to evaluate the performance of the proposed controllers and compare their performance results, three-stage simulations are implemented on the two-wheeled self-balancing robot system. Mathematical proofs and simulation results show the desired performance of the proposed solutions.

With the advent of electricity markets and the creation of a competitive environment in power systems, proper allocation of transmission cost among network users (consumers and producers) is essential to help the investment of transmission network, effectively. In this paper, a hybrid method for transmission cost allocation based on the effect of transmission facilities in system reliability and their merchant value is proposed. In the proposed method, first, the users' benefit in the electricity market and in other words, the merchant benchmark in cost allocation has considered. Second, cost allocation considering the effect of facilities in system reliability which are consist of factors of system security and adequacy and the benefit of users with these factors is done. For the implementation of the proposed method, the capacity of all facilities includes lines and transformers are divided into four sections consist of merchant capacity, contingency capacity for maintaining security, future capacity for maintaining adequacy and invalid capacity. The numerical results in a 3-bus and the IEEE 30-bus test system are presented to demonstrate the effectiveness of the proposed method and compare to other methods.

A new structure of multi-port DC-DC converter is proposed which is based on T-Source converter. It can be used for hybrid renewable energy applications. Two input ports includes a solar panel and battery. The main advantages of the converter are including; high voltage gain, continuous input current, independent mode operation of input ports, and high efficiency. Different switching modes are discussed in the relations for steady state operation of the converter are derived. A prototype of the converter is provided and several tests are performed which validates the simulations and theoretical predictions of the converter.

In this paper, a novel observer is designed for online time delay estimation, in SISO linear systems, with variable and unknown time-delay in control input. It is clear that Laplace transfer function of a delayed system includes a time-delay operator (exponential and non-rational). In this article, it is assumed that the only unknown and variable parameter in the system is the system’s time-delay. For designing the proposed observer, first, a Pade approximation is used for exponential operator of time delay to rationalize the system transfer function. Therefore, the new transfer function, which is an approximation of the main transfer function of the system, will include a time-variant delay parameter. After rewriting a state space realization of the mentioned transfer function and considering time delay parameter as an extra state variable, a system with nonlinear state equations will be formed. Eventually, using a Kalman filter, the systems states, such as system time-delay, are estimated. Finally, simulations results show rather desirable performance of the proposed estimator in dealing with unknown and variable time-delays.

The microgrid is a set of local energy producers and consumers that can be utilized with low cost and high reliability. In this paper, a robust multi-objective model is proposed to reduce operating costs and carbon emissions in which a smart grid utilizes a wind turbine and micro-turbine to feed its connected loads. The microgrid also uses a battery to store electrical energy in off-peak hours and to deliver energy in on-peak hours. On the other hand, it is connected to the main grid and can exchange energy with it. Consumers connected to this microgrid are divided into two groups. The first group is uncontrollable loads with certain load pattern and the second group is controllable loads that have certain energy consumption but can be controlled by the operating time. The proposed model is a mixed-integer linear programming problem and is simulated with the CPLEX solver in GAMS software. The results show that when the price of electricity is low, the loads are often supplied by grid electricity, and when the price of electricity is high, they are often fed by micro-turbines, batteries, and wind turbines.

The abundant benefits of Orthogonal Frequency-Division Multiplexing (OFDM) and its high flexibility have resulted in its widespread applications in many telecommunication standards. One important parameter for improving wireless system’s efficiency is the accurate estimation of channel state information (CSI). In the literatures many techniques have been studied in order to estimate the CSI. Nowadays, the techniques based on intelligent algorithms such as genetic algorithm (GA) and particle swarm optimization (PSO) have attracted attention of researchers. With a very low pilot overhead, these techniques are able to estimate the channel frequency response (CFR) properly only using the received signals. Unfortunately each of these techniques suffers a common weakness: they have a slow convergence rate. In this paper, a new intelligent and different method has been presented for channel estimation using gravitational search algorithm (GSA). This method can achieve accurate channel estimation with a moderate computational complexity in comparison with GA and PSO estimators. Furthermore, with higher convergence rate our proposed method is capable of providing the same performance as GA and PSO. For a two-path fast fading channel, simulation results demonstrate the robustness of our proposed scheme according to the bit error rate (BER) and the mean square error (MSE).

In this article, by replacing lowpass filter in Gysel power divider configuration, a power divider with 9 harmonic suppression capability at 930 MHz has been designed analyzed and fabricated. To provide a step by step analysis, the basic resonator of the proposed lowpass filter has been firstly investigated and the location of the first transmission zero of it has been calculated, then, its stopband is extended by using rectangular suppressor. After replacing the designed filter in Gysel configuration, the final circuit has been fabricated and measured. The measured results indicate that the final circuit has 79% size reduction in comparison with a conventional Gysel power divider. Moreover, first port return loss, the second port return loss, the isolation and insertion loss are 16.5, 17, 36, 3.14 dB, respectively.

Silicon on insulator junctionless field effect transistor (SOI-JLFET) includes a single type doping at the same level in the source, channel, and drain regions. Therefore, its fabrication process is easier than inversion mode SOI-FET. However, SOI-JLFET suffers from high subthreshold slope (SS) as well as high leakage current. As a result, the SOI-JLFET device has limitation for high speed and low power applications. For the first time in this study, use of the auxiliary gate in the drain region of the SOI-JLFET has been proposed to improve the both SS and leakage current parameters. The proposed structure is called "SOI-JLFET Aug". The optimal selection for the auxiliary gate work function and its length, has improved the both SS and ION/IOFF ratio parameters, as compared to Regular SOI-JLFET. Simulation results show that, SOI-JLFET Aug with 20nm channel length exhibits the SS~71mV/dec and ION/IOFF~1013. SS and ON-state to OFF-state current (ION/IOFF) ratio of SOI-JLFET Aug are improved by 14% and three orders of magnitudes, respectively, as compared to the Regular SOI-JLFET. The SOI-JLEFT Aug could be good candidate for digital applications.