IEEE 30-bus Power System Research Articles

Risk-Averse Generation Maintenance Scheduling With Microgrid Aggregators

This paper presents risk-averse long-term generation maintenance scheduling in the power systems with a considerable installed capacity of microgrids. Microgrid aggregators facilitate the participation of microgrids in the wholesale market. In this paper, the effect of microgrids as controllable demand entities on the generation maintenance scheduling practices in the power system is investigated. The uncertainties in the marginal cost of generation in microgrids, the generation capacity installed within the microgrids, and the system electricity demand are captured using respective nominal values and uncertainty intervals. Moreover, the contingencies in transmission network are addressed by introducing additional variables. A two-stage robust optimization problem is formulated to determine a trade-off among the performance and conservativeness of the procured solution in the long-term operation horizon. The problem is formulated as a mixed integer linear programming problem and column-and-constraint generation procedure is used to solve the problem. The master problem minimizes the maintenance cost of the generation units subjected to generation units’ constraints in the long-term operation horizon and the sub-problems determine the worst realization of the uncertainties and generate additional constraints in the master problem. The proposed methodology is applied to two case studies for a 6-bus and IEEE 118-bus power systems.

Distributed Finite-Time Consensus Control for Heterogeneous Battery Energy Storage Systems in Droop-Controlled Microgrids

This paper presents a novel distributed finite-time control scheme for heterogeneous battery energy storage systems (BESSs) in droop-controlled microgrids. In contrast to the existing centralized methods, the proposed control strategy is fully distributed so that each BESS only requires its own information and the information from its neighbors through a sparse communication network. Our novel consensus-based method is implemented to achieve energy level balancing, active/reactive power sharing, and voltage/frequency synchronization of energy storage devices by using inter-BESS communications, where both the heterogeneous nature of batteries and the hierarchical control structure are taken into consideration. Furthermore, the proposed design is shown to improve the synchronization performance and exhibit more accurate robustness against time-varying communication topologies and load changes. Simulation results on a modified IEEE 57-bus power system are provided to verify the effectiveness of the proposed consensus strategy.

Electrical LeaderRank method for node importance evaluation of power grids considering uncertainties of renewable energy

Node importance evaluation of power grids plays an important role in the safe operation and planning of power systems. This paper proposes an electrical LeaderRank (ELR) method to identify the important nodes in complex power grids, considering the renewable energy uncertainties, system topological structure, transmission power flow and the loss of loads caused by cascading failures. The proposed method uses an ELR value function to represent the importance of a system node, which can be derived iteratively from the weighted distribution strategy of its in-linked nodes. Furthermore, the uncertainties of wind and solar energy generation are modelled as interval numbers, and the interval power flow calculation is employed to obtain the interval power in transmission lines, direct adjacent matrix, and finally the interval ELR values. The performance of ELR method has been fully tested and benchmarked on the IEEE 118-bus power system and the Western Liaoning Power Grid of China. Comparative results on four performance criteria have not only demonstrated the validity and superiority of the proposed method, but also confirmed its capability to cope with the node importance evaluation of practical power grids.

Implementation of the power transistor‐assisted Sen transformer in steady‐state load flow analysis

The wide use of power flow controllers (PFCs) in transmission and distribution grids is becoming imperative. Power transistor-assisted Sen transformer (TAST) is a very recently introduced novel PFC that bridges the gap between most versatile flexible AC transmission systems controllers. It proved to possess closely comparable technical characteristics to that of the unified power flow controller (UPFC) at an installation cost that is less than the half. It is thus an attractive substitute of the UPFC for many utility applications. Nonetheless, since the TAST is a newly introduced PFC, it is of great importance to develop its steady-state model for its implementation in modern power systems analysis. The main contribution of this study is presenting two accurate steady-state models of the TAST: a simplified Simulink model (SSM) and a comprehensive Newton–Raphson model (CNRM) for its representation in the load flow analysis. The presented SSM and CNRM of the TAST are novel. A standard five-bus system and a modified IEEE-30 bus power system are used for demonstration of the effectiveness and validation of the SSM and the CNRM. Very closely comparable results are obtained when a TAST or more is used to increase and decrease the power flow in transmission lines.

Real-Time Event Identification Through Low-Dimensional Subspace Characterization of High-Dimensional Synchrophasor Data

This paper proposes a data-driven real-time event identification method based on the measurements of Phasor Measurement Units (PMUs). The central idea is to characterize an event by the low-dimensional subspace spanned by the dominant singular vectors of a data matrix that contains spatial–temporal blocks of PMU data. The subspace representation is robust to system initial conditions and characterizes the system dynamics. A dictionary of subspaces that correspond to different events are established offline, and an event is identified online with the most similar event in the dictionary through subspace comparison. The compact subspace representation reduces the dictionary size and the computational time of the event identification method. Numerical experiments on both simulated events in an IEEE 68-bus power system and the recorded data in New England validate the proposed method.

A Topological Investigation of Power Flow

This paper combines the fundamentals of an electrical grid, such as flow allocation according to Kirchhoff's laws and the effect of transmission line reactances with spectral graph theory, and expresses the linearized power flow behaviour in slack-bus independent weighted graph matrices to assess the relation between the topological structure and the physical behaviour of a power grid. Based on the pseudoinverse of the weighted network Laplacian, the paper further analytically calculates the effective resistance (Thevenin) matrix and the sensitivities of active power flows to the changes in network topology by means of transmission line removal and addition. Numerical results for the IEEE 118-bus power system are demonstrated to identify the critical components to cascading failures, node isolation, and Braess’ paradox in a power grid.

On Reliability Analysis of Smart Grids under Topology Attacks

Building an efficient, smart, and multifunctional power grid while maintaining high reliability and security is an extremely challenging task, particularly in the ever-evolving cyber threat landscape. The challenge is also compounded by the increasing complexity of power grids in both cyber and physical domains. In this article, we develop a stochastic Petri net based analytical model to assess and analyze the system reliability of smart grids, specifically against topology attacks under system countermeasures (i.e., intrusion detection systems and malfunction recovery techniques). Topology attacks, evolving from false data injection attacks, are growing security threats to smart grids. In our analytical model, we define and consider both conservative and aggressive topology attacks, and two types of unreliable consequences (i.e., system disturbances and failures). The IEEE 14-bus power system is employed as a case study to clearly explain the model construction and parameterization process. The benefit of having this analytical model is the capability to measure the system reliability from both transient and steady-state analysis. Finally, intensive simulation experiments are conducted to demonstrate the feasibility and effectiveness of our proposed model.

Saddle Node Bifurcation Point Analysis of Voltage Stability of IEEE 30-BUS Power System for Removal of Generation through Bacteria Foraging Optimization Algorithm

This paper deals with the identification of instability nodes of IEEE 30 BUS power system to generation removal. Optimal sizing and locations of reactive power compensations are obtained. Firstly one of the generators is assumed to be removed from service and the saddle node bifurcation (SNB) point voltages are evaluated without reactive power compensation. Secondly two generators are assumed to be removed from service and the saddle node point voltage magnitudes are obtained without reactive power compensation. For both cases the study is conducted by placing optimal reactive power compensations at optimal locations using Bacterial Foraging Optimization Algorithm (BFOA).

Optimal reactive power dispatch using water wave optimization algorithm

This paper presents water wave optimization (WWO) algorithm to solve the optimal reactive power dispatch (ORPD) problem with the continuous and discrete control variables in power system. The ORPD problem is defined as a complex, discrete, constrained nonlinear combinatorial optimization problem. The WWO algorithm is utilized to find the optimized values of control variables such as generator voltages, tap positions of tap changing transformers and the amount of reactive compensation devices to achieve minimized value of active power losses. The WWO algorithm not only effectively avoids the shortcomings of local search and poor calculation accuracy, but also accelerates the convergence rate to find the global optimal solution. The WWO algorithm is implemented on standard IEEE 30-bus power system that is to verify the effectiveness and feasibility of the WWO algorithm to tackle with the ORPD problem. Compared with other algorithms, the WWO algorithm can find the set of the optimal solutions of control variables. The simulation experiment indicates that the WWO algorithm has better overall performance to reduce the real power losses.

Application of Differential Evolution Algorithm for Optimal Placement of UPFC for Improved Voltage Stability

The Unified Power Flow Controller (UPFC) is one of the versatile and most effective Flexible AC transmission System (FACTS) devices which can provide full dynamic control of a transmission line parameters, bus voltage, line impedance and phase angle for improved system security. However, the extent that performance of UPFC can be brought out; it’s greatly dependents upon the location of the device in the system. The present work is a Differential Evolution (DE) based algorithm for optimal placement of the UPFC device under steady state (normal, moderate and critical) conditions and is aimed at voltage profile enhancement of an interconnected power system. The proposed method is applied on an IEEE 14-bus power system which is demonstrated through MATPOWER simulation tool. The results obtained indicate that DE is robust based on the facts that the voltage profile was kept within the acceptable limit. Installing UPFC in the optimal location determined by DE can significantly enhance the security of power system through improvement of bus voltage limit violations.

Consensus Control for Energy Storage Systems

In this paper, consensus integral control is applied for energy storage in microgrids to synchronize the state-of-charge (SoC) and power levels of batteries with limited information exchange. Both local information (SoC and power level) and neighbors’ information (SoC and power level) will be fed into an integral control installed at every battery converter. The design is based on consensus control and takes into consideration of real-world battery coordination requirements, e.g., all batteries should work in the same charging or discharging mode. Compared with the consensus control in the existing literature for voltage consensus or battery SoC/power consensus, this paper offers a simple design. The major assumption of this paper is that each converter should possess an integral control. This assumption is valid since indeed integral controls exist if converters are equipped with secondary frequency control. The designed consensus control is validated by simulations on 14-bus microgrid and IEEE 57-bus power system. Simulation results demonstrate the effectiveness of the consensus integral control for variety modes of operation: 1) charging; 2) discharging; and 3) load variation.

Distributed Estimation of Power System Oscillation Modes Under Attacks on GPS Clocks

Phasor measurement units (PMUs) are playing an increasingly important role in wide-area monitoring and the control of power systems. PMUs allow synchronous real-time measurements of voltage, phase angle, and frequency from multiple remote locations in the grid, enabled by their ability to align to global positioning system (GPS) clocks. Given that this ability is vulnerable to GPS spoofing attacks, which have been confirmed easy to launch, in this paper, we propose a distributed real-time wide-area oscillation estimation approach that is robust to GPS spoofing on PMUs and their associated phasor data concentrators. The approach employs the idea of checking update consistency with histories and across distributed nodes and can tolerate up to one third of compromised nodes. It can be implemented in a completely decentralized architecture and in a completely asynchronous way. The effectiveness of the approach is confirmed by numerical simulations of the IEEE 68-bus power system models.

A two-stage stochastic programming approach for reliability constrained power system expansion planning

Probabilistic realizations of outages and their effects on the operational costs are highly overlooked aspects in power system expansion planning. Since the effect of randomness in contingencies can be more prominent especially when transmission switching is considered, in this paper we introduce contingency-dependent transmission switching concept to ensure N-1 criterion. To include randomness of outages and the outputs (i.e. flow on the lines/generation amounts) during the outages, we represent each contingency by a single scenario. Status of transmission lines, generation amounts and power flow decisions are defined as recourse actions of our two-stage stochastic model, therefore, expected operational cost during the contingencies are taken into account in a more accurate manner. A solution methodology with a filtering technique is also proposed to overcome the computational burden. The model and the solution methodology are tested on the IEEE Reliability Test System and IEEE 118-bus power system and the results show that the solution method finds the solutions for these power systems in significantly shorter solution times. The solution method is also tested on a new data set for the 380-kV Turkish transmission network. Suggestions for possible extensions of the problem and the modifications of the solution approach to handle these extensions are also discussed.

Comparison of all-side risk and down-side risk constrained probabilistic dispatch models considering wind power

This paper, for the first time, compares the probabilistic optimal power flow (POPF) models targetingdifferent objectives -- minimizing the expected generation cost (EGC) and all-side risk (AR) or down side risk (DR)simultaneously. In the POPF models, wind power generation isconsidered in dispatching, the uncertainty of which can be explained by building a model to describe the stochasticcharacteristic of the forecast error. The distribution of the forecast error can be obtained by sampling from the historical error time series. The POPFsaresolvedusinggroup search optimizer with multiple producers (GSOMP), and a decision-making method TOPSIS is used to select the most suitablesolution. Simulation studies are conducted on a modified IEEE 118-bus power system with wind farms integrated, and the results show that the EGC-DR modelfind better solution compared tothe EGC-AR model.

Power quality monitor placement in power systems considering channel limits and estimation error at unobservable buses using a bi-level approach

The aim of this paper is to propose a new method for locating power quality monitors (PQMs) in a power system at different depths of unobservability. In this method, the placement problem is solved in two levels, taking into account the limitation on the number of measuring channels of these devices. At the first level of this method, different combinations of connecting lines are selected, while the second level determines the best location of monitors for each combination, at different unobservability depths. In addition, the second level also identifies the critical buses and considers their effects on the number and location of monitors. The proposed method also minimizes the voltage phasor estimation error at unobservable buses as well as the cost of these devices as the main objectives. Therefore, this method will find the best location for installing monitors and the minimum number of channels required by these devices to make all power quality parameters, i.e. voltage and current phasors, observable. The results of applying the new method on IEEE 14-bus and IEEE 30-bus power systems and the Iranian south east regional grid (ISERG) demonstrates the performance of proposed method.

A Fast Local Search Scheme for Adaptive Coordinated Voltage Control

A fast effective local search technique is developed for the adaptive coordinated voltage control scheme presented previously in the work of Ma and Hill. A set of effective controls is first extracted from Pareto solutions, which in turn are obtained by considering coordinated voltage control as a multiobjective optimization problem. The search space can be reduced into a limited area in which only effective control solutions are found. Within this reduced search space, a local search is then developed to get an online control. Computational complexity analysis indicates that it is a very effective and fast way to achieve emergency voltage control. At the same time, a discussion on the impact of system performance by exploring a larger set of nondominated solutions is presented. Numerical simulation on the IEEE 118-bus power system is used for demonstration of performance.

Nonlinear Adaptive Excitation Control for Structure Preserving Power Systems

The paper proposes a decentralized excitation controller to improve the stability of large power systems. Extended Lyapunov-like energy function and equivalent expressions of stator transient voltages are utilized to design a nonlinear adaptive excitation controller. The proposed controller only requires local machine measures and parameters. The performance of the designed excitation control system is evaluated on the well-known IEEE 118-bus 54-unit power system and compared with conventional exciter controls.

A new coordinated design of sectionalizing scheme and load restoration process considering reliability of transmission system

One of the most important processes during load restoration is to use a suitable sectionalizing scheme to enhance the stability, especially when two islands are synchronized. In this regard, this paper provides a new scheme for the coordination of sectionalizing and load restoration to enhance the power system performance before and during the synchronization of islands. In doing so, there will be contradictory objective functions including maximizing the quality of sectionalizing process, minimizing the maximum standing phase angle (SPA) between islands, and minimizing the sum of energy not supplied (ENS) with unavailable energy capability (UEC) between all N-1 contingencies. Therefore, a multi-objective problem is defined as a mixed integer non-linear problem (MINLP). Also, a reliability-based index is defined to determine the quality of each island. Then, the θ-based water cycle algorithm (θ-WCA) is used to obtain the best Pareto optimal set. Two IEEE 39-bus and 118-bus power systems are used for validating the proposed method. The simulation results imply that the system can benefit from this scheme not only to have the good quality of sectionalizing, but also to enhance the power system performance during load restoration and the synchronization of islands.

Quasi-Monte Carlo Based Probabilistic Optimal Power Flow Considering the Correlation of Wind Speeds Using Copula Function

Wind farms commonly cluster in regions rich in wind resources. Thus, correlation of wind speeds from different wind farms should not be ignored when modeling a power system with large wind energy penetration. This paper proposes a probabilistic optimal power flow (POPF) technique based on the quasi-Monte Carlo simulation (QMCS) considering the correlation of wind speeds using copula functions. In this paper, a copula function is used to model the dependent structure of random wind speeds and their forecast errors. QMCS is employed in the sampling procedure to reduce computation burden. The proposed method is applied in probabilistic power flow (PPF). Furthermore, the PPF is used in the POPF problem that aims at minimizing the expectation and downside risk of fuel cost simultaneously. Simulation studies are conducted on a modified IEEE 118-bus power system with wind farms integrated in two areas, and the results show that the accuracy and efficiency are improved by the proposed method.

Robust optimization for improving resilience of integrated energy systems with electricity and natural gas infrastructures

The integration of natural gas in electricity network requires a more reliable operating plan for increasing uncertainties in the whole system. In this paper, a three-stage robust optimization model is proposed for resilient operation of energy system which integrates electricity and natural gas transmission networks with the objective of minimizing load curtailments caused by attacks. Non-convex constrains are linearized in order to formulate the dual problem of optimal energy flow. Then, the proposed three-stage problem can be reformulated into a two-stage mixed integer linear program (MILP) and solved by Benders decomposition algorithm. Numerical studies on IEEE 30-bus power system with 7-node natural gas network and IEEE 118-bus power system with 14-node natural gas network validate the feasibility of the proposed model for improving resilience of integrated energy system. Energy storage facilities are also considered for the resiliency analysis.