Mohammad Shahidehpour

Security-Constrained Unit Commitment With Volatile Wind Power Generation

This paper presents a security-constrained unit commitment (SCUC) algorithm which takes into account the intermittency and volatility of wind power generation. The UC problem is solved in the master problem with the forecasted intermittent wind power generation. Next, possible scenarios are simulated for representing the wind power volatility. The initial dispatch is checked in the subproblem and generation redispatch is considered for satisfying the hourly volatility of wind power in simulated scenarios. If the redispatch fails to mitigate violations, Benders cuts are created and added to the master problem to revise the commitment solution. The iterative process between the commitment problem and the feasibility check subproblem will continue until simulated wind power scenarios can be accommodated by redispatch. Numerical simulations indicate the effectiveness of the proposed SCUC algorithm for managing the security of power system operation by taking into account the intermittency and volatility of wind power generation.

Stochastic Security-Constrained Unit Commitment

This paper presents a stochastic model for the long-term solution of security-constrained unit commitment (SCUC). The proposed approach could be used by vertically integrated utilities as well as the ISOs in electricity markets. In this model, random disturbances, such as outages of generation units and transmission lines as well as load forecasting inaccuracies, are modeled as scenario trees using the Monte Carlo simulation method. For dual optimization, coupling constraints among scenarios are relaxed and the optimization problem is decomposed into deterministic long-term SCUC subproblems. For each deterministic long-term SCUC, resource constraints represent fuel and emission constraints (in the case of vertically integrated utilities) and energy constraints (in the case of electricity markets). Lagrangian relaxation is used to decompose subproblems with long-term SCUC into tractable short-term MIP-based SCUC subproblems without resource constraints. Accordingly, penalty prices (Lagrangian multipliers) are signals to coordinate the master problem and small-scale subproblems. Computational requirements for solving scenario-based optimization models depend on the number of scenarios in which the objective is to minimize the weighted-average generation cost over the entire scenario tree. In large scale applications, the scenario reduction method is introduced for enhancing a tradeoff between calculation speed and accuracy of long-term SCUC solution. Numerical simulations indicate the effectiveness of the proposed approach for solving the stochastic security-constrained unit commitment

Price-based unit commitment: a case of Lagrangian relaxation versus mixed integer programming

This paper formulates the price-based unit commitment (PBUC) problem based on the mixed integer programming (MIP) method. The proposed PBUC solution is for a generating company (GENCO) with thermal, combined-cycle, cascaded-hydro, and pumped-storage units. The PBUC solution by utilizing MIP is compared with that of Lagrangian relaxation (LR) method. Test results on the modified IEEE 118-bus system show the efficiency of our MIP formulation and advantages of the MIP method for solving PBUC. It is also shown that MIP could be applied to solve hydro-subproblems including cascaded-hydro and pumped-storage units in the LR-based framework of hydro-thermal coordination. Numerical experiments on large systems show that the MIP-based computation time and memory requirement would represent the major obstacles for applying MIP to large UC problems. It is noted that the solution of large UC problems could be accomplished by improving the MIP formulation, the utilization of specific structure of UC problems, and the use of parallel processing.

Security-constrained unit commitment with AC constraints

In a restructured power market, the independent system operator (ISO) executes the security-constrained unit commitment (SCUC) program to plan a secure and economical hourly generation schedule for the day-ahead market. This paper introduces an efficient SCUC approach with ac constraints that obtains the minimum system operating cost while maintaining the security of power systems. The proposed approach applies the Benders decomposition for separating the unit commitment (UC) in the master problem from the network security check in subproblems. The master problem applies the augmented Lagrangian relaxation (LR) method and dynamic programming (DP) to solve UC. The subproblem checks ac network security constraints for the UC solution to determine whether a converged and secure ac power flow can be obtained. If any network violations arise, corresponding Benders cuts will be formed and added to the master problem for solving the next iteration of UC. The iterative process will continue until ac violations are eliminated and a converged optimal solution is found. In this paper, a six-bus system and the IEEE 118-bus system with 54 units are analyzed to exhibit the effectiveness of the proposed approach.

Market-based transmission expansion planning

Restructuring and deregulation has exposed transmission planner to new objectives and uncertainties. Therefore, new criteria and approaches are needed for transmission planning in deregulated environments. A new market-based approach for transmission planning in deregulated environments is presented in this paper. The main contribution of this research is: i) introducing a new probabilistic tool, named probabilistic locational marginal prices, for computing the probability density functions of nodal prices; ii) defining new market-based criteria for transmission expansion planning in deregulated environments; and iii) presenting a new approach for transmission expansion planning in deregulated environments using the above tool and criteria. The advantages of this approach are: i) it encourages and facilitates competition among all participants; ii) it provides nondiscriminatory access to cheap generation for all consumers; iii) it considers all random and nonrandom power system uncertainties and selects the final plan after risk assessment of all solutions; and iv) it is value based and considers investment cost, operation cost, congestion cost, load curtailment cost, and cost caused by system unreliability. The presented approach is applied to IEEE 30-bus test system.

Contingency-Constrained PMU Placement in Power Networks

In this paper, a model for the optimal placement of contingency-constrained phasor measurement units (PMUs) in electric power networks is presented. The conventional complete observability of power networks is first formulated and then, different contingency conditions in power networks including measurement losses and line outages are added to the main model. The communication constraints which would limit the maximum number of measurements associated with each installed PMU is considered as measurement limitations. The relevant formulations are also proposed to make the model more comprehensive. The IEEE standard test systems are examined for the applicability of proposed model. The comparison of presented results with those of other methods is presented which would justify the effectiveness of proposed model with regards to minimizing the total number of PMUs and the execution time. A large-scale system with 2383 buses is also analyzed to exhibit the applicability of proposed model to practical power system cases.

Impact of Natural Gas Infrastructure on Electric Power Systems

The restructuring of electricity has introduced new risks associated with the security of natural gas infrastructure on a significantly large scale, which entails changes in physical capabilities of pipelines, operational procedures, sensors and communications, contracting (supply and transportation), and tariffs. This paper will discuss the essence of the natural gas infrastructure for supplying the ever-increasing number of gas-powered units and use security-constrained unit commitment to analyze the short-time impact of natural gas prices on power generation scheduling. The paper analyzes the impact of natural gas infrastructure contingencies on the operation of electric power systems. Furthermore, the paper examines the impact of renewable sources of energy such as pumped-storage units and photovoltaic/battery systems on power system security by reducing the dependence of electricity infrastructure on the natural gas infrastructure. A modified IEEE 118-bus with 12 combined-cycle units is presented for analyzing the gas/electric interdependency.

Maintenance scheduling in restructured power systems

List of Figures. List of Tables. List of Symbols. Preface. Acknowledgements. I. Introduction. II. Mathematical Review. III. Long-Term Generation Maintenance Scheduling. IV. Short-Term Generation Scheduling. V. Coordination Between Long-Term and Short-Term Generation Scheduling. VI. Long-Term Transmission Maintenance Scheduling. VII. Coordination Between Long-Term and Short-Term Transmission Maintenance Scheduling. VIII. Coordination Between Generation and Transmission Maintenance Scheduling. IX. Application of Short-Term Scheduling to Photovoltaic-Utility Grid. Appendix. Bibliography. Index.

Short-term scheduling of battery in a grid-connected PV/battery system

We present in this paper a short-term scheduling of battery in security-constrained unit commitment (SCUC). For economical operation and control purposes, electric power users with photovoltaic (PV)/battery systems are interested in the availability and the dispatch of PV/battery power on an hourly basis, which is a cumbersome task due to the complicated operating patterns of PV/battery. The details of battery model in the PV/battery system are presented in this paper. The paper applies a Lagrangian relaxation-based optimization algorithm to determine the hourly charge/discharge commitment of battery in a utility grid. The paper also applies a network flow programming algorithm for the dispatch of committed battery units. The paper analyzes the impact of grid-connected PV/battery system on locational pricing, peak load shaving, and transmission congestion management. An eight-bus test system is used to study the operational pattern of aggregated PV/battery and demonstrate the advantages of utilizing PV/battery systems in the electric utility operation.

Security-Constrained Unit Commitment With Natural Gas Transmission Constraints

The contribution of this paper focuses on the development of a security-based methodology for the solution of short-term SCUC when considering the impact of natural gas transmission system. The proposed methodology examines the interdependency of electricity and natural gas in a highly complex transmission system. The natural gas transmission system is modeled as a set of nonlinear equations. The proposed solution applies a decomposition method to separate the natural gas transmission feasibility check subproblem and the power transmission feasibility check subproblem from the hourly unit commitment (UC) in the master problem. Gas contracts are modeled and incorporated in the master UC problem. The natural gas transmission subproblem checks the feasibility of natural gas transmission as well as natural gas transmission security constraints for the commitment and dispatch of gas-fired generating units. If any natural gas transmission violations arise, corresponding energy constraints will be formed and added to the master problem for solving the next iteration of UC. The iterative process will continue until a converged feasible gas transmission solution is found. A six-bus power system with seven-node gas transmission system and the IEEE 118-bus power system with 14-node gas transmission system are analyzed to show the effectiveness of the proposed solution. The proposed model can be used by a vertically integrated utility or the ISO for the short-term commitment and dispatch of generating units with natural gas transmission constraints.