Morad Mohamed Abdelmageed Abdelaziz

A Novel and Generalized Three-Phase Power Flow Algorithm for Islanded Microgrids Using a Newton Trust Region Method

A new formulation is required to provide a proper power flow analysis in islanded microgrids taking into consideration their special philosophy of operation. In this paper, a novel and generic three-phase power flow algorithm is formulated for islanded microgrids. The algorithm is novel since it adapts the real characteristics of the islanded microgrid operation; i.e., 1) some of the distributed generation (DG) units are controlled using the droop control methods and their generated active and reactive power are dependent on the power flow variables; 2) the steady-state system frequency is considered as one of the power flow variables. The proposed algorithm is generic, where the features of distribution systems, i.e., three-phase feeder models, unbalanced loads and load models have been taken in consideration. Further, all possible operation modes of DG units (droop, PV, or PQ) have been considered. The problem has been formulated as a set of nonlinear equations. A globally convergent Newton-trust region method has been proposed to solve this set of nonlinear equations. The proposed algorithm is a helpful tool to perform accurate steady state studies of the islanded microgrid. Different case studies have been carried out to test the effectiveness and the robustness of the proposed algorithm.

Voltage and Reactive Power Impacts on Successful Operation of Islanded Microgrids

This paper proposes a probabilistic technique to evaluate the success of islanded microgrids taking into consideration the impacts of voltage and reactive power constraints and the special features and operational characteristics of both dispatchable and wind distributed generators in islanded microgrids. New adequacy and reliability indices are proposed to account for the effect of voltage and reactive power constraints. To facilitate these studies, the proposed technique employs a microgrid model that reflects the special characteristics of microgrid operation. Simulation studies have been carried out to validate the proposed technique. The simulation results show that voltage and reactive power constraints have considerable effects on the microgrids successful operation.

Optimum Reconfiguration of Droop-Controlled Islanded Microgrids

This paper proposes a new formulation for the optimum reconfiguration of islanded microgrid (IMG) systems. The reconfiguration problem is casted as a multi-objective optimization problem, in order to: 1) minimize the IMG fuel consumption in the operational planning horizon for which islanded operation is planned; 2) ensure the IMG capability to feed the maximum possible demand by enhancing its voltage instability proximity index taken over all the states at which the islanded system may reside; and 3) minimize the relevant switching operation costs. The proposed problem formulation takes into consideration the systems operational constraints in all operating conditions based on the consideration of the uncertainty associated with renewable resources output power and load variability. Moreover, the proposed formulation accounts for droop controlled IMG special operational characteristics as well as the availability/unavailability of a supervisory microgrid central controller (MGCC). The formulated problem is solved using non-dominated sorting genetic algorithm II (NSGA-II). MATLAB environment has been used to test and validate the proposed problem formulation. The results show that the implementation of appropriate IMG reconfiguration problem formulations will enhance the performance of IMG systems and facilitate a successful integration of the microgrid concept in distribution networks.

Estimation of induction motor single-cage model parameters from manufacturer data

This paper proposes a new method for estimating the induction motor single-cage model parameters from the manufacturer data. A multidimensional single-objective nonlinear optimization problem is formulated to minimize the deviation between the values of the performance characteristics provided by the manufacturer and their corresponding estimates. By introducing variable slip dependency parameters in the optimization problem, the proposed method gives a single-cage motor model that is capable of simultaneously predicting the induction motor characteristics at high and low slips, both with high accuracy. The proposed method has been tested on a sample of eight induction motors of different sizes, rated voltages and manufacturers. The results show the effectiveness of the proposed method in providing single-cage induction motor models that are capable of accurately estimating the different motor external quantities along the entire slip domain.

The effects of renewable energy resources on the implementation of Distributed Resources Islanded Systems

This paper assesses the impacts of the penetration level of renewable energy resources on the successful implementation of Distributed Resources (DR) Islanded Systems. A probabilistic analytical approach has been developed to facilitate the proposed study. The probabilistic approach takes the special features and operational characteristics of DR islanded systems in islanded mode. The probability of successful islanding and the corresponding load points reliability indices have been calculated at different penetration levels of renewable energy resources. Simulation studies have been carried out to verify the effectiveness of the proposed probabilistic approach.

Incorporating voltage regulator and load models in unbalanced power flow studies of active distribution systems

One of the most important issues in smart grid is to quantitatively assess the operational issues arising from the shift of the conventional distribution system toward an active distribution system with high penetration of distributed generations. This assessment requires the accurate representation of all distribution system components. This paper presents a new power flow formulation that incorporates accurate models for distribution system components. Three phase, two phase and single phase voltage regulators (SVR) are modeled to satisfy the desired voltage level along the feeder. Different types of loads configurations and modeling are incorporated at the system buses. The distributed generation connected as PQ and PV buses are integrated into the proposed power flow formulation. To test the accuracy of the proposed method, the power flow results have been compared with the results of the IEEE 123 test feeder. The importance of incorporating the voltage regulators at different operation scenarios in active distribution systems has been observed through simulation results.

Economic Droop Parameter Selection for Autonomous Microgrids Including Wind Turbines

Droop control is a key strategy for operating islanded microgrid systems. The droop settings of the different distributed generation (DG) units in an islanded microgrid determine the operational characteristics of the island. This paper presents an algorithm for choosing the optimal droop parameters for islanded microgrids with wind generation in order to minimize the overall island generation costs in the absence of a microgrid central controller (MGCC). A detailed microgrid model is adopted to reflect the special features and operational characteristics of droop controlled islanded microgrid systems. The proposed problem formulation considers the power flow constraints, voltage and frequency regulation constraints, line capacity constraints and unit capacity constraints. Numerical case studies have been carried out to show the effectiveness of the proposed algorithm as compared to conventional droop parameter selection criteria typically adopted in the literature.

Assessment of droop-controlled islanded microgrid maximum loadability

This paper presents an algorithm for determining the maximum loading factor of droop-controlled islanded microgrids. The problem is formulated as an optimization problem to consider both the static voltage stability constraints and the small-signal stability constraints. A detailed microgrid model is adopted to reflect the special features and operational characteristics of droop-controlled islanded microgrid systems. The proposed problem formulation considers the system reactive power requirements and the different possible load characteristics. The optimization problem is subject to different system operational constraints including; the power flow constraints, voltage and frequency regulation constraints and unit capacity constraints. Different numerical case studies have been carried out to test the effectiveness and the robustness of the proposed algorithm.

Determination of worst case loading margin of droop-controlled islanded microgrids

The determination of an islanded microgrid proximity to voltage instability is essential for its operation with an adequate security margin. This paper presents an algorithm for determining the worst case loading margin of droop-controlled islanded microgrids. The problem is formulated as an optimization problem to determine the shortest distance to voltage instability (i.e. the closest saddle node bifurcation point). A detailed microgrid model is adopted to reflect the special features of droop controlled islanded microgrid systems where; 1) the system frequency is a power flow variable, and 2) the power produced by the different DG units is dependent on the system power flow variables and cannot be pre-specified. The optimization problem is subject to different system operational constraints including; the power flow constraints, voltage and frequency regulation constraints and unit capacity constraints. Different numerical case studies have been carried out to test the effectiveness and the robustness of the proposed algorithm.

A globally convergent trust-region method for power flow studies in active distribution systems

This paper proposes a new power flow algorithm for active distribution systems. The proposed algorithm is developed for both radial and meshed topology based on a globally convergent trust-region method. Different types of loads including constant power, constant current and constant impedance are modeled at the system buses. The mathematical model of distributed generation (DG) connected as PQ and PV buses are integrated into the power flow algorithm to simulate the penetration of DGs in the distribution systems. The proposed method has been tested and compared with the IEEE 37 bus unbalanced test feeder result. A 25 bus unbalanced meshed distribution network has also been used to test the effectiveness of the proposed power flow algorithm in case of meshed networks.