نشریه تحقیقات نوین در سیستم های قدرت هوشمند
سال دهم شماره 2 (پیاپی 26، تابستان 1400)

Using Distributed Generation (DG) in electrical distribution networks brings many advantages and thus, optimal placement and sizing of these units become important. Most of the researches in this field neglect the effect of transmission system on distribution section. These researches also ignore the effect of Flexible Alternating Current Transmission Systems (FACTS). This thesis proposes a new method for optimal placement and sizing of distributed generation considering FACTS devices. In this method, Thevenin’s equivalent model is used to model transmission section include FACTS devices and the results are compare to integrated transmission-distribution network and slack bus models. Thyristor Controlled Series Capacitor (TCSC) and Static VAR Compensator are used for this goal. As an innovation, uncertainty of electrical load is considered using scenario tree method. Optimisation problem is defined as minimizing a combinatory objective function which includes power loss, voltage deviation and voltage stability indexes. As another innovation, optimization problem is solved using hybrid sine-cosine algorithm and particle swarm optimization (HSCA-PSO) method. Simulation is carried out on IEEE 9 and 16 bus transmission-distribution test system in MATLAB software. Simulation results show that using FACTS in transmission section and DG in distribution section both leads to objective function reduction and therefore improves network performance in the terms of losses, voltage deviation and voltage stability indexes. Results indicate that Thevenin’s equivalent model has better performance in the comparison to slack bus model in modeling transmission section and FACTS devices. Results also illustrate that uncertainties increase the installed capacity of DG units and ignoring uncertainty can leads to wrong solutions.

The noise interferes with the measuring equipment installed in transformer stations and results in technical challenges for utility engineers. Sensors are mounted on transformers, to measure partial discharge (PD) signals, but the noise deforms the PD signals. In this paper, the noise removal from PD signal of power transformers is performed by a radial basis function (RBF) neural network. The CST software is used to simulate a transformer, PD and noise. Also, a laboratory model is used to generate the PD and noise signals. The simulation and measurement results are presented and discussed. It is shown that the proposed method is a good technique for noise removal from PD signals.

Due to the need to use clean energy sources and the existence of different single/three phase consumers, the maximum use of single/three phase distributed generation (DG) units in the distribution system becomes crucial. The presence of DG units in the network, because of the need to inverters for exchanging power with the network and nonlinear structure of the inverters, requires control methods with high dynamic and steady-state performance with respect to sudden changes and disturbances.  In this paper, a robust current controller based on the sliding mode control (SMC) in the synchronous dq reference frame is introduced for controlling active and reactive powers of a single phase inverter connected to the infinite bus with constant voltage. By modelling the single phase inverter as a virtual balanced three phase inverter and using the dynamic phasor of the inverter output current, decoupled control of active and reactive powers of the inverter is possible. The performance of the controller for various scenarios of step changes, uncertainty of parameters and external disturbances is evaluated through computer simulations in the MATLAB environment.

One of the serious issues related to these sources is the effect of system errors on their transient stability, which due to the low inertia of the generators and the slow performance of protection equipment in distribution systems, their transient instability is quite possible. In this paper, first the dynamic behavior of scattered sources on system errors and then the sensitivity of scattered sources to system parameters are investigated. In the next step, some practical protection settings are explained, which are used as voltage relays, and their advantages and disadvantages are mentioned. Finally, based on the results of sensitivity analysis, a new protection method has been proposed to maintain the stability of scattered resources in the event of an error in the distribution network. The proposed method separates scattered resources from the distribution network according to an active time-power relationship. For all cases under review, the error clearance time is less than the critical clearance time. The simulation results also show that the proposed method is resistant to system transitions.

Voltage instability is one of the most important issues in power systems. In recent years, with the restructuring of power systems, system operators to operate the system at a point near the border of stable conditions to maximize profits and reduce costs. When an event occurs in the power system, if the power system is not able to maintain voltage in its various parts, the phenomenon of voltage instability in the power system has occurred which can lead to widespread blackouts in the system. In addition to causing great economic losses, these blackouts will also cause customer dissatisfaction with the electricity network. Therefore, identifying the voltage instability in the network, which can be followed by deciding on control measures, will play an important role in increasing the quality and security of the system. In this paper, various methods of voltage stability and control are introduced, studied and reviewed.

Transformer design is an issue it is a non-linear and complex combination. Accuracy in the answers obtained and the speed of reaching the answers are the two basic criteria in the process of transformer design. The various optimization methods presented so far have had problems such as ignoring some design limitations, reaching a minimum local response, not considering all the variables involved in optimization, or being unable to search the entire space due to their random nature. The surest way to reach the absolute optimal point is to use search algorithms He is all space. But the requirement for all-space search methods to reach the absolute optimal point is that the search space is discrete and limited, and therefore a smart user is needed. Since the problem of optimizing the power transformer has a large number of independent variables and extensive search space, the full space search method will face the problem of lack of computer memory and low program execution speed. In this article, to eliminate this weakness and reach the absolute optimal point, by modifying the Power transformer design process and presenting a new innovative algorithm called pruned tree algorithm to solve the problem of optimal economic design of power transformers and reduce electromagnetic forces, to the optimal point we move absolutely. JMAG‐Designer and Ansys Maxwell software is used for the finite element analysis  in this research.