Professor Farhad Shahnia

An autonomous microgrid (MG) may observe overloading and renewable-based excessive generation. Such issues can lead to unacceptable deviation in the MG's voltage or frequency. These problems can be eased by load-shedding or renewable curtailment. On the other hand, forming provisional neighboring MG clusters and facilitating power exchange among them can also improve the situation more economically and effectively. The power exchange link between the MGs can be in the various forms such as a three-phase ac, a single-phase ac or a dc link. This approach requires power electronics-based converters to interlink the three-phase ac microgrid with the power exchange link and control the power-sharing amongst them. This paper has studied such structures and has proposed a decentralized approach to control the converters of the neighboring MGs to enable power-sharing amongst them. The performance of the proposed control mechanisms is evaluated through simulation studies in PSIM ® .

With the development of technology and ever-increasing integration of renewable energy power generation, the growing problem of the uncertainty of power outputs from renewable energy sources (RESs) has further promoted the progress of the demand-side response (DR) technology. The large industrial customers have high power consumption and high degree of automation, bringing in a higher DR potential. This paper presents a DR strategy for large industrial customers considering the uncertainty in the power outputs from RESs. First, the DR model of large industrial customers has been established considering their characteristics. Then, to deal with the uncertainty of the RES outputs, the methods of scenario sampling and reduction are formed, through which the typical and representative scenarios of RES outputs will be obtained. Next, based on the day-ahead prediction of the power outputs from RESs and real-time electricity price, a day-ahead DR strategy has been established for such customers with an objective of minimizing the overall daily electricity cost. Finally, taking an industrial park with distributed wind power and photovoltaic units as a sample example, the feasibility and effectiveness of the proposed method are demonstrated. In addition, the impacts of different types of loads are evaluated on the DR potentials of customers.

To evaluate the investment effectiveness of and provide decision-making support for a production and technical transformation project (PTTP) in a power system, the concept and methodology of perfect technical transformation (PTT) are presented in this work. The well-established analytic hierarchy process (AHP) is employed to disassemble the evaluation objectives of a PTTP while the weights and scores of indicators at each level can be determined. Then, the comprehensive evaluation result of a PTTP can be obtained by weighted calculation. A perfection percentage index is defined to judge the satisfaction degree of an implemented PTTP. Next, a deviation identification and improvement method is used to accurately locate the poorly implemented parts of the PTTP, and optimize the technical scheme of the PTTP. Finally, an actual PTTP is employed to demonstrate the presented PTT based approach for investment effectiveness evaluation of a PTTP.

For the life-cycle cost management of a power grid project, the maintenance is not only expensive, but also has many impacting factors. Therefore, studying the cost of maintenance stage is important to improve the cost management of power grid enterprises. Based on the life-cycle cost management, this paper analyzes the content and cost composition of various maintenance tasks of power grid engineering. Finally, through the introduction of single factor sensitivity analysis method, combined with specific examples, this paper analyzes in detail the impacts of various kinds of power grid maintenance tasks in life-cycle maintenance.

The ever-declining price of the photovoltaic (PV) modules and governmental supports have contributed to the continued increase of PV system installations and integration into the power systems. There is a growing need to upgrade and stabilize the power system with massive PV integration to address the corresponding technical challenges. At the same time, revising international standards and national grid code requirements to enable a more diverse and robust power system infrastructure is a must. Given this background, this paper presents a comparison of several current grid codes for integrating PV systems and explores future grid code amendments for maintaining power system secure operation.

The availability of solar energy has encouraged the application of renewable energy technologies in the grid-connected power system. A microgrid (MG) system provides electricity to the local areas based on the load requirements and variations of local renewable energy resources. The objective of this study is to assess the technical and economic feasibility of an MG system. The economics of an MG is investigated with the aim of promoting renewable energy technologies such as photovoltaic and battery system. In view of this, the optimal configuration of the proposed MG system is achieved with the application of the HOMER software. In this study, the green technologies are applied in the grid-connected system that serves a medium-sized residential building. It can be seen from the study results that the proposed configuration of the MG system is cost-effective and environmentally friendly. This leads to the improvement in the annual cost savings and reduction of energy purchased, cost of energy, total net present cost and greenhouse gas emissions respectively.

Interleaving of converters is a concept in the power electronics domain, which has been used extensively for dc-dc converters to improve the performance. Interleaving ensures reduction in the peak-to-peak ripple for both input and output currents. This concept also guarantees a reduction in the current stress levels for all the switching components involved in the converter circuit. In this paper, a switchedcapacitor (SC) based single-stage single-phase inverter operating in interleaved configuration has been proposed which is interfaced with a photovoltaic (PV) module and powers a stand-alone load. This inverter uses SC blocks to step-up the PV voltage and then delivers high quality ac voltage to load. A modified version of SC blocks has been used in this work, by ensuring that an equal number of controlled and uncontrolled switches are connected in each SC block, fewer controlled switches are put to use and economy is achieved. To consume maximum power from the PV panel and to operate it at its maximum power point, the Perturb and Observe technique has been employed. Feasibility of the proposed work has been evaluated by simulation studies in MATLAB/Simulink.

An autonomous microgrid is susceptible to the uncertainties in the variations of its demand and the generation of its non-dispatchable renewable sources. Such events can result in the voltage or frequency of the microgrid to exceed beyond their allowed ranges. Some methods are proposed in the literature to predict such events a few minutes ahead. As such, the voltage and frequency violation of a microgrid can be predicted and prevented with the introduction of an appropriately designed preventive controller. The key factor to be considered is the accuracy of the prediction tools, based on which the preventive controller is designed. This paper proposes a look-ahead controller that is complemented by considering various scenarios, as the result of considering the prediction inaccuracies and their probabilities. The sensitivity of the performance of such a preventive controller with respect to the prediction error is also studied in this paper through extensive numerical analyses in MATLAB.

The growing number of intermittent distributed generations units has increased the voltage regulation challenges in distribution networks. This paper proposes a joint voltage regulation in medium voltage and low voltage distribution feeders by employing and coordinating both traditional and emerging approaches. The proposed technique is a three-stage control strategy that suits well the integrated and unbalanced radial distribution networks. In this technique, the reactive power support of delta-connected switched capacitors, installed at the medium voltage feeders, are coordinated with that of the PV inverters, available at low voltage feeders. Factors such as the network's power loss, as well as the voltage magnitude and balance profiles, are aimed to be improved. The effectiveness and superiority of the proposed volt-var optimization model is evaluated by numerical analysis on a real typical distribution network over a 24-hour period.

Battery storage systems used to smooth out solar PV power fluctuations can be integrated with solar PV-diesel microgrids as an enabling technology to increase the penetration of solar PV and aid microgrid stability. This paper compares the moving average and ramp rate control techniques for selecting the optimal capacity of a smoothing battery. The studies are based on a large data set of 1-minute resolution solar irradiance data for a full calendar year and across multiple locations. Results from these tests are used to derive correlations between the optimal smoothing battery capacity and daily variability indices.