Yunfeng Wen

Enhanced Security-Constrained Unit Commitment With Emerging Utility-Scale Energy Storage

We introduce emerging utility-scale energy storage (e.g., batteries) as part of the set of control measures in a corrective form of the security-constrained unit commitment (SCUC) problem. This enhanced SCUC (ESCUC) leverages utility-scale energy storage for multiple applications. In the base case, the storage units are optimally charged and discharged to realize economic operation. Immediately following a contingency, the injections of storage units are adjusted almost instantly to alleviate short-term emergency overloads, thereby avoiding potential cascading outages and giving slow ramping generating units time to adjust their output. The ESCUC is a large two-stage mixed-integer programming problem. A Benders decomposition has been developed to solve this problem. In order to achieve computational tractability, we present several acceleration techniques to improve the convergence of the proposed algorithm. Case studies on the RTS-79 and RTS-96 systems demonstrate the effectiveness of the proposed approach.

Enhanced Security-Constrained OPF With Distributed Battery Energy Storage

This paper discusses how fast-response distributed battery energy storage could be used to implement post-contingency corrective control actions. Immediately after a contingency, the injections of distributed batteries could be adjusted to alleviate overloads and reduce flows below their short-term emergency rating. This ensures that the post-contingency system remains stable until the operator has redispatched the generation. Implementing this form of corrective control would allow operators to take advantage of the difference between the short- and long-term ratings of the lines and would therefore increase the available transmission capacity. This problem is formulated as a two-stage, enhanced security-constrained OPF problem, in which the first-stage optimizes the pre-contingency generation dispatch, while the second-stage minimizes the corrective actions for each contingency. Case studies based on a six-bus test system and on the RTS 96 demonstrate that the proposed method provides effective corrective actions and can guarantee operational reliability and economy.

Frequency Dynamics Constrained Unit Commitment With Battery Energy Storage

The decline of system inertia due to the increasing displacement of synchronous units by renewable units has introduced a major challenge on the frequency dynamics management of a power system. This paper discusses how fast-response battery energy storages can be used to maintain the frequency dynamic security. Immediately following a generation loss, the injections of batteries are adjusted instantly to ensure minimum power imbalance in the system. This control strategy is included in a novel formulation of the frequency dynamics constrained unit commitment, in which the impact of wind uncertainty is dealt with using interval-based optimization. The reformulation-linearization technique is applied to reformulate the original nonlinear model as a mixed-integer linear programming problem. Case studies on a six-bus system and the modified RTS-79 system demonstrate that the proposed method guarantees frequency security while still preserving economy without curtailing wind generation.

Risk-oriented preventive control of transmission lines overload

Traditional preventive control strategies do not take into account the likelihood of each potential contingency, thus the dispatch results may often be conservative or radical. Aiming to achieve a reasonable tradeoff between economy and security, this paper develops a risk-oriented preventive control (ROPC) strategy. A three-state weather model is introduced to reflect the impact of weather conditions on the failure rate of transmission lines. Using the multi-objective optimization (MO) method, system security level associated with overload risk can be controlled in advance. A distance based multi-objective particle optimization (DSMOPSO) algorithm is adopted to solve the MO problem. Simulation results obtained on a six-bus system are analyzed in comparison with OPF and PSCOPF to show that the proposed ROPC could provide a useful decision-making tool to keep an optimal balance between system operational cost and overload risk in different weather conditions.

Synergistic Operation of Electricity and Natural Gas Networks via ADMM

The increasing growth in the installation of natural-gas fired units has raised necessitates on synergy between the electricity and natural gas networks. This paper discusses how synergistic operation of electricity and natural gas networks can be achieved in a distributed fashion using alternating direction method of multipliers (ADMM). A standard ADMM approach and a consensus-based ADMM approach are developed, respectively, to solve the gas-electric integrated optimal power flow problem with and without a coordination operator. In both cases, the optimization formulation for each operator is modeled, and the solution procedure as well as data exchange among multiple decision-makers are explained. Case studies on both small and large gas-electric integrated systems show that the two ADMM-based distributed approaches have significant efficiencies over the traditional Lagrange relaxation (LR) and augmented LR-based methods.

Comprehensive decoupled risk-limiting dispatch

Risk-limiting dispatch (RLD) is a promising approach to deal with the increasing uncertainty in both supply side and demand side of power systems. However, the conventional RLD has two drawbacks: i) it is difficult to set the value of acceptable risk level; ii) it has limitations to address the scenario with more realistic but non-Gaussian and heavy-tailed renewable output forecasting errors. To resolve these drawbacks, a conceptual framework of comprehensive decoupled risk-limiting dispatch (CDRLD) is proposed in this paper. We consider the severity level and the probability level of operating risk in a unified framework. The acceptable probability level which corresponds to the loss of load probability (LOLP) is extended to an interval number, while the acceptable severity level is consistent with the expected demand not supplied (EDNS). The whole dispatch problem is solved in a decoupling scheme, in which the severity level of operating risk is guaranteed through the severity feasibility check. Numerical simulations indicate the effectiveness of the proposed CDRLD for enhancing the economic benefits without loss of operating reliability.

Software implementation of risk-based dispatch

In this paper, the implementation of a risk based dispatch system (RBDS) for identifying, assessing and controlling system operational risk associated with weather & natural disasters is illustrated. Firstly, a risk-based dispatch framework is presented, then SOA based software architecture of RBDS is discussed. Practical experiences show RBDS could be a useful decision-making tool for operators.

Enhancing Frequency Stability of Asynchronous Grids Interconnected with HVDC Links

Frequency stability management of asynchronously interconnected grids is becoming a great challenge. This paper investigates how asynchronous sending- and receiving-end grids can be operated in a synergistic and interactive manner to guarantee frequency stability following the worst case HVDC bipole block while still ensuring operational economy. A novel enhanced frequency stability constrained multiperiod optimal power flow model (EFOPF) with flexible fast-acting HVDC corrective control is proposed. EFOPF dynamically schedules the distribution of primary reserves and HVDC corrective actions to simultaneously handle postcontingency over- and under-frequency disturbances occurring in the sending- and receiving-end grids, respectively. An alternating direction method of multipliers based distributed algorithm was developed to solve this problem. A case study of a modified two-area RTS-96 system demonstrates the effectiveness of the proposed EFOPF.

Enhanced security-constrained unit commitment with emerging utility-scale energy storage

We introduce emerging utility-scale energy storage (e.g., batteries) as part of the set of control measures in a corrective form of the security-constrained unit commitment (SCUC) problem. This enhanced SCUC (ESCUC) leverages utility-scale energy storage for multiple applications. In the base case, the storage units are optimally charged and discharged to realize economic operation. Immediately following a contingency, the injections of storage units are adjusted almost instantly to alleviate short-term emergency overloads, thereby avoiding potential cascading outages and giving slow ramping generating units time to adjust their output. The ESCUC is a large two-stage mixed-integer programming problem. A Benders decomposition has been developed to solve this problem. In order to achieve computational tractability, we present several acceleration techniques to improve the convergence of the proposed algorithm. Case studies on the RTS-79 and RTS-96 systems demonstrate the effectiveness of the proposed approach.

Decentralized synergetic dispatch of prosumer-based interconnected microgrids

Conventional centralized dispatch has inherent drawbacks to handle the increasing penetration of distributed generation in distribution systems. This paper discusses a decentralized synergetic dispatch paradigm for prosumer-based interconnected microgrids, in which a prosumer is defined as an autonomous agent that can produce, consume, and store electricity. We consider a double-sided market mechanism and propose a two-level optimization approach to realize the decentralized synergetic dispatch paradigm. In the lower-level, each microgrid (MG) calculates its own local marginal price (LMP) and exchanges the supply or demand curve with adjacent microgrids for synergetic operation. In the upper-level, a primal-dual interior-point method is employed to optimize the injection powers of MGs and the flows through the tie-lines. The validity and effectiveness of the proposed approach are demonstrated on a medium-voltage 18-bus distribution system.