مجله کیفیت و بهره وری صنعت برق ایران
سال نهم شماره 2 (پیاپی 19، تابستان 1399)

Reliability enhancement is one of the main objectives of transmission expansion planning (TEP), and reliability evaluating of different planning schemes is one of the greatest challenges in solving the TEP problem. Due to the large scale of networks and high computational burden of the reliability assessment procedure for any network structure, it is almost impossible and impractical to accurately analyze the reliability of all planning schemes during optimization of the TEP problem. In this paper, first, the necessity of performing an accurate analysis on transmission network reliability during multi-objective based optimization of the TEP problem is shown. Then, a practical approach is proposed for solving this problem. The main objective of the proposed approach which is based on classification of events and occurrences of faults, is to make it possible to more accurately analyze the reliability of transmission networks in order to make decisions on the multi-objective TEP, and to achieve a more accurate solution as well; so that the process is not time-consuming and the computational burden is low. To investigate the efficiency of the proposed approach, the modified Garver's network is used and the multi-objective TEP problem is solved using NSGA-II as optimization tool. The results are compared with those of conventional approach. The obtained results show the accuracy of the proposed approach in solving the TEP problem.

Nowadays, presence of photovoltaic systems in distribution network is not without challenge and it may not have economic productivity for the system under the lack of optimal management. Energy storage systems are able to cope with this problem. Therefore, in this paper, a new method is proposed for energy management of the distribution networks in order to show that how presence of the energy storage systems leads to profitability and high quality. In this method, the frequent charging/discharging of the energy storage systems is controlled so as to avoid from reduction of their lifetime. Moreover, in the proposed approach the convex power flow constraints are applied for energy management of the photovoltaic based distribution systems in order to guarantee the obtained results’ optimality and convergence. Furthermore, price responsive loads and interruptible ones are modelled in the optimization problem. The proposed approach for energy management is implemented to the 33-bus distribution network and the computed results demonstrate that how considering the energy storage systems in the distribution networks had been effective on improvement of the quality of the economic and technical parameters of the network. The obtained results with considering the importance of energy storage systems lifetime and without it have been compared.

In this paper, a multi-stage protective scheme is proposed to maintain the fuse and reclosers coordination. The proposed method operates online and proportional to the photovoltaic sources penetration rate. In the first step, a non-standard Current - Time - Voltage curve is used for fuse saving. If the new calculated TDS from the first stage is not implementable to the reclosers, the second stage of the protection scheme will be activated, and the fault current contribution of photovoltaic sources decrease proportional to inverter PCC voltage. It should be noted that the proposed method is a combitionary method that in the first step, the effect of reclosers sensitivity in modifying the reclosers fast characteristics is taken into account in compared to other schemes presented in this regard, and in the second step, there is less limitation on the output power of PV sources under fault conditions than other inverter current control presented equations. It It is noteworthy that in order to implement the proposed protection method, there is no need to telecommunication infrastructure. The ETAP software simulation results validates the proposed scheme effectively.

In this paper, a new strategy based on a dynamic (time-based) model is proposed for expansion planning of electrical energy distribution systems, taking into account distributed generation resources and advantage of the techno-economic approach. In addition to optimal placement and capacity, the proposed model is able to determine the timing of installation / reinforcement of expansion options. The proposed approach is a non-convex optimization problem with a nonlinear nature and mixed integers. In addition, considering uncertainty in the network loads makes the issue of expansion planning increasingly challenging. Hence, a tri-stage algorithm is developed to solve it. In order to model the uncertainty of loads in the proposed approach, the two-point estimation method has been used. An improved harmony search algorithm has been used to achieve the optimal solution. The feasibility and effectiveness of the proposed approach in the expansion planning of electrical energy distribution systems has been demonstrated by two different case studies on the 13.8 kV power distribution system with 27 buses. The results of the simulation obtained indicate the capability and efficiency of the approach proposed in the dynamic planning of the expansion of electrical energy distribution systems.

After restructuring, Iran’s electricity market has become one of the most competitive markets in which generation companies offer their proposed price on several price benches. So, the decisions in this market can use statistical concepts. In this paper, a conceptual model is presented according to simultaneous analysis of probabilistic distribution for historical data of market clearing price and frequency of acceptance of bids. Based on this model, the probable value of market clearing price is measured through the risk of historical data price intervals and the decision is made about bidding strategy. Also, a method is proposed to calculate the probability of acceptance and risk of rejection of bids on the electricity market. The data (Spring 2014) from a power plant as a numerical example have been used to implement the method. The results show that there is no direct relation between the high or low price intervals and the risk of acceptance, but the probable data regarding the distribution of price intervals should be analyzed. Also, due to the risk of the proposed bid prices, this model is capable of applying risk-taking and risk-aversion and finally appropriate bid price is selected based on the risk appetite and acceptable risk level.

In recent years, the penetration of distributed energy resources has been increased dramatically in the power system, however, according to their small capacity, we need to aggregate these resources in an incorporated unit and examine their participation in the energy and ancillary services market. This goal can be achieved using virtual power plants (VPPs) concept. This paper describes the optimal bidding strategy of a VPP in the energy and spinning reserve markets. In order to improve the performance of the VPP, dispatchable distributed generation (DGs) sources, wind turbines (WTs), thermal and electrical energy storages, combined heat and power (CHP) unit and electric vehicles (EVs) have been considered in the VPP structure. The optimization task has also been addressed in the form of a MILP problem with considering the network and unit constraints and smart EVs’ charging. Finally, to evaluate the effectiveness of the proposed method, simulations are performed on a 21-bus VPP. The simulation results show that the VPP profit will increase by 23% by participating in the spinning reserve market.