نشریه مهندسی برق و مهندسی کامپیوتر ایران
سال نوزدهم شماره 2 (پیاپی 62، تابستان 1400)

One of the main limitations of using renewable energies for electricity generation is the low output voltage of power plants with renewable energies. Therefore, the design of a converter with higher gain voltage and higher efficiency is important in the use of renewable energies. In this paper, a new topology that simultaneously has the structure of a boost converter can minimize switching losses by conventional soft switching methods and is also able to reduce voltage stress on diodes and switches Keep to an acceptable level. A simple boost converter can Increase the output voltage significantly by adding a parallel branch by generating a series resonance and enables zero voltage switching at the same time. Suggested converter without adding active element to converter with simple non-isolated structure at 500 watts and 385 volts it has a voltage gain factor of about 10.8 and efficiency of over 93%. The results show the performance simulation of the proposed converter for different performance modes.

In this paper, Design of a fuzzy sliding mode controller (FSMC) with adaptive extended Kalman filter (AEKF) for controlling a shake table system with electric actuator and ball-screw mechanism. Due to the uncertainties regarding the model parameters and the noise of the data of the two encoder and accelerometer sensors, there are many problems in controlling this system. Therefore, it is crucial to employ a non-precise model-based controller and a nonlinear adaptive filter. The fuzzy sliding mode control and Extended Kalman filter are a good way to control this system. In sliding mode control, chattering at the control input is inevitable. In this paper, a simple fuzzy inference mechanism is used to reduce the undesirable phenomenon of chattering by correctly estimating the upper bound of uncertainty. In the following, a recursive method is used to determine the system and measurement noise covariance matrices. The data of the two encoder and accelerometer sensors are combined in the adaptive extended Kalman filter and the results in noise elimination and parameter estimation are investigated. Linear speed feedback available through the Kalman filter is used to stabilize and control the closed loop system. The end is examined to check the performance of the control structure provided by the seismic table test. The results show that the proposed method is very effective.

With the growth and integration of distributed generation resources in smart grids, net load forecasting is of significant importance. A hybrid optimization method is proposed in this paper for probabilistic net load forecasting using neighborhood component analysis and solving regression problem with the aid of mini-batch LBFGS method. Net load forecasting is suggested in this paper trough forecast combination via adaptive network-based fuzzy inference system. The structure includes a combination of several long-term forecasts, including forecasts of load, the generation of a solar station, and the generation of a wind farm with wind turbines equipped with doubly-fed induction generator. Also, the net load forecasting and the relationship between errors of load, wind and solar predictions are studied in this paper. The simulation results of the proposed method and its comparison with Tao and quantile regression models show that mean absolute percentage error of load forecasting, and the forecasts of solar and wind generations improved by 0.947%, 0.3079% and 0042%, respectively which result to a decrease in net load forecasting error.

In this paper in order to improve the electrical performance of nanoscale SOI-junctionless, a targeted modification has been performed. The proposed structure has been aimed to reduce the OFF current and self-heating effect. To reduce the self-heating effect, the buried oxide thickness has been reduced into the half and a part of it has been replaced by a buffer layer. Increase in the thermal conduction and making an extra depletion layer in the buffer layer/channel region interface are led to improvement of the electrical performance in the terms of DC and AC. In the proposed method, which is based on the energy band modification, the parameters such as IOFF, ION/IOFF, subthreshold swing, lattice temperature, voltage gain, transconductance, parasitic capacitances, power gains, cut-off frequency, maximum oscillation frequency and minimum noise figure have been improved. Also, a designing consideration for the role of buffer layer on the proposed device has been performed. Comparing structures under the study simulated by the SILVACO showed the electrical performance superiority for the proposed device.

This paper presents an EMI reduction technique for switched-mode buck converters. To achieve this, the frequency hopping concept is utilized in asynchronous pulse width modulators (APWM) performing the power conversion with controlling the on-off time of the power switches. The modulator has an oscillatory behavior; such that its oscillation frequency depends on its internal loop delay. Making use of this property and randomly changing the loop delay between 8 distinct random values, its self-oscillation frequency is also changed between 8 different values. As a result, a spur-free spectrum is achieved at the output of the converter. To verify the usefulness of the proposed method, a model-based behavioral simulation was done using MATLAB-SIMULINK. The main advantage of the proposed method over previous works is that the switching frequency controlling mechanism is fully digital. Besides, it can be readily done without causing any disturbance in the carrier signal.

The flying-capacitor modular multilevel converter (FC-MMC) has been introduced as a hardware development of the conventional MMC with the aim of reducing the cell capacitor ripple voltage in the application of electrical drive at low speeds. The capacitor ripple voltage of the cells in this converter is reduced only by injecting high frequency circulating current between the arms. In the conventional control method of this converter, the circulating current component is injected with the aim of complete elimination of the voltage ripple at low frequencies, which leads to an unnecessary increase of the current amplitude in the converter arms. In this paper, the converter control system is modified by finding the relationship between the cell capacitor voltage ripple and the high frequency circulating current amplitude. Then, by injecting the appropriate amplitude of the circulating current, the voltage ripple is controlled in an acceptable range. It is shown that by partial compensation (instead of full elimination of the voltage ripple), in addition to reducing the amplitude of the arm currents, the losses of the electrical system are significantly reduced. The results of simulations and experiments confirm the successful performance of the proposed method.

With the rise in the penetration of inverter based distributed energy sources, grid codes say that converters should not be disconnected during the fault. These sources should also help the grid by reactive power injection. Power system grids are resistive inductive and the converter may be unstable during the fault. Converters use phase locked loop (PLL) to synchronize with the grid. PLL is not able to be stable during severe voltage drop, so converters cannot ride through the fault and should be disconnected. In this paper a novel method based on virtual impedance is proposed to maintain the synchronization during severe voltage drop. This method needs grid impedance estimation and virtually connects the converter to a point that has a stronger connection. By this novel method, during voltage drop, the converter stays connected to the grid and injects reactive power. Simulation results in MATLAB verify the ability of proposed method in improving the transient stability of converter.

In this paper, a wireless powered communication network (WPCN) is considered, in which the hybrid access point (HAP) and the users are equipped with multiple antennas.In the downlink phase, an energy HAP transfers the energy signal to the users and in the uplink phase, users apply the harvested energy to transfer their information to the HAP using spatial division multiple access (SDMA) technology. By considering the nonlinear behavior of energy harvester in system design and aiming to maximize the sum of the rates, we propose an optimal method for designing energy pre-coding matrices, user information pre-coding matrices, and time devoted to the downlink and uplink phases. For this purpose, we rewrite the problem as a convex optimization problem by appropriate change of variables and propose a method to solve it. The simulation results show that in practical scenarios, employing the nonlinear energy harvesting model in the system design could reduce the transmitted energy, increase and the sum rate of the users.