نشریه تحقیقات نوین در سیستم های قدرت هوشمند
سال هشتم شماره 1 (پیاپی 17، بهار 1398)

When several parallel inverters are in islands operating mode, the droop control scheme is usually used to control the inverters. The droop control method enables the inverters of a Micro-Grid to control the voltage and frequency of the network in a decentralized regulation behavior. The drop control method also enables the inverters to share the required active and reactive powers of the load between themselves. This paper focuses on some of the limitations of single phase parallel inverters using the drop control characteristic in island operating mode. Some controller algorithms have been proposed to pursue the reactive power sharing constraints and to reduce harmonic voltage disturbances at the PCC in island mode. The empirical results show the suitability of controller algorithms to achieve reactive power sharing and improve voltage harmonic disturbances in PCC.

With the growth of communities and the increasing need for electricity, and because of the many benefits of renewable energy sources, the wind turbine has become a completely commercial and inevitable process, with increasing penetration into the electricity grid. Distribution networks, on the other hand, are subject to fault that cause power fluctuations and outflow of wind units. In order to continue to use these units and not to leave them out of the grid, it is important for them to improve Low voltage Ride-Through. In this paper, two Dynamic Voltage Restorer (DVR) and Superconducting Magnetic Energy Storage (SMES) systems under four different scenarios are used to improve DFIG's low voltage ride-through and uninterrupted performance by maintaining its controllability during the faults. The performance and comparison of the performance of the four scenarios to improve the LVRT and reduce the DC and DC link voltage fluctuations have been studied. The simulation results in the MATLAB/SIMULINK software environment demonstrate the high accuracy and real-time performance of these two equipments in reducing the adverse effects of distribution grids LVRT on wind turbine based DFIG.

In the last decade, the amount of distributed generation connected to the distribution network is increasing. The presence of distributed generation resources in distribution systems has a great influence on its behavior and it is necessary to consider the impact of these resources on the distribution network design. In this study, Optimal Coordinated Voltage Control (OCVC) using wind and solar power plants considering uncertainty of generators for solving multi-objective optimization problem, with the aim of minimizing voltage error in pilot bus, reactive power variations and voltage error in generators is presented. Optimal Coordinate Voltage Control uses Pareto optimization to find the optimal voltage. This method is performed using a combination of wind and solar power plants on the IEEE 13-bus and 34-bus test networks and the uncertainty of solar and wind power plants is also modeled by the Monte Carlo method. The obtained results show the effectiveness of proposed method in controlling voltage and reducing losses.

Unified Power Flow Controller (UPFC) is one of the FACTS devices which plays a crucial role in simultaneous regulating active and reactive power, improving system load, reducing congestion and cost of production. Therefore, determining the optimum location of such equipment in order to improve the performance of the network is significant. In this paper, WCA algorithm is used to locate the optimal placement of UPFC. The concepts and ideas underlying this approach are inspired by nature and are based on observations of water and the process of the water cycle and the formation of rivers and streams and their flow to the sea in the real world. This algorithm has a high potential for escaping local optimizations as well as speeding up global optimization. For UPFC modeling, the power injection model has been used and the OPF-UPFC problem has been solved with various objective functions such as generators fuel cost, network losses and system loading, both single-objective and multi-objective. Also, the results obtained from different objective functions are compared with other references. The results acquired show the efficiency and speed of the water cycle algorithm compared to some other intelligent algorithms. The computer program has been written in the MATLAB software environment and implemented on the IEEE 14-bus network.

Unified Power Flow Controller (UPFC) is one of the FACTS devices which plays a crucial role in simultaneous regulating active and reactive power, improving system load, reducing congestion and cost of production. Therefore, determining the optimum location of such equipment in order to improve the performance of the network is significant. In this paper, WCA algorithm is used to locate the optimal placement of UPFC. The concepts and ideas underlying this approach are inspired by nature and are based on observations of water and the process of the water cycle and the formation of rivers and streams and their flow to the sea in the real world. This algorithm has a high potential for escaping local optimizations as well as speeding up global optimization. For UPFC modeling, the power injection model has been used and the OPF-UPFC problem has been solved with various objective functions such as generators fuel cost, network losses and system loading, both single-objective and multi-objective. Also, the results obtained from different objective functions are compared with other references. The results acquired show the efficiency and speed of the water cycle algorithm compared to some other intelligent algorithms. The computer program has been written in the MATLAB software environment and implemented on the IEEE 14-bus network.

The need for more efficient power systems has prompted the use of a new technologies includes Flexible AC transmission system (FACTS) devices. FACTS devices provides new opportunity for controlling the line power flow and minimizing losses while maintaining the bus voltages within a permissible limit. In this thesis a new method is proposed for optimal placement and sizing of Thyristor controlled series compensator (TCSC) and Static VAR compensator (SVC) for improvement power system operation using crow search algorithm. Optimal place for installation of TCSC and SVC is determined based on line’s reactive power flow and voltage collapse proximity indication (VCPI), respectively. Optimal size of FACTS devices as long as reactive power of generating units and optimal tap of transformers is computed by solving an optimization problem. The objective function is defined as minimizing the sum of the network costs includes costs of energy losses and costs of FACTS devices. Crow search algorithm is a novel metaheuristic optimization method that inspired from the intelligent behavior of crows in storing and retrieving foods. That’s this thesis is used for the first time in optimal placement and sizing of TCSC and SVC. The proposed method is simulated on IEEE 30 bus and 57 bus sample networks in MATLAB environment. Simulation results shows that crow search algorithm converges to optimal solution while meets all technical constraints.And Improves the power system efficiency.