Alvaro Ortega

Generalized Model of VSC-Based Energy Storage Systems for Transient Stability Analysis

This paper presents a generalized energy storage system model for voltage and angle stability analysis. The proposed solution allows modeling most common energy storage technologies through a given set of linear differential algebraic equations (DAEs). In particular, the paper considers, but is not limited to, compressed air, superconducting magnetic, electrochemical capacitor and battery energy storage devices. While able to cope with a variety of different technologies, the proposed generalized model proves to be accurate for angle and voltage stability analysis, as it includes a balanced, fundamental-frequency model of the voltage source converter (VSC) and the dynamics of the dc link. Regulators with inclusion of hard limits are also taken into account. The transient behavior of the generalized model is compared with detailed fundamental-frequency balanced models as well as commonly-used simplified models of energy storage devices. A comprehensive case study based on the WSCC 9-bus test system is presented and discussed.

Modeling, Simulation, and Comparison of Control Techniques for Energy Storage Systems

This paper describes the modeling and formulation of a variety of deterministic techniques for energy storage devices, namely the PI, H-infinity, and sliding mode controllers. These techniques are defined based on a general, yet detailed, energy storage device model, which is accurate for transient stability analysis. The paper also presents a thorough statistical comparison of the performance and robustness of the considered control techniques, using stochastic dynamic models and a variety of disturbances and scenarios. The case study is based on a 1479-bus model of the all-island Irish transmission system and an energy storage device actually installed in the system.

Design of a control limiter to improve the dynamic response of energy storage systems

This paper proposes an effective control scheme to improve the transient behavior of VSC-based energy storage systems facing energy saturations. This control is aimed to reduce abrupt transients following energy saturations of the storage device. The WSCC 9-bus test system is used for validating and discussing the proposed controller. In particular, the dynamic response of a battery energy storage undergoing energy saturations is tested considering deterministic as well as stochastic load variations. Simulation results shows that the proposed control scheme allows reducing installation costs while ensuring an adequate dynamic reponse of energy storage systems.

Comparison of different control strategies for energy storage devices

This paper compares three control strategies for energy storage devices. Detailed formulations and implementation procedures of PI, sliding mode, and H-infinity controllers are presented and discussed. The dynamic performance of each control technique is also studied and compared. With this aim, the paper duly discusses a comprehensive case study based on the IEEE 14-bus test system with inclusion of a wind power plant and an energy storage device.

Model Predictive Control based AGC for multi-terminal DC grids

With increasing DC grid connections between non-synchronous AC systems it is desirable that DC connections would take a role in frequency regulation for connected AC grids. A number of primary and secondary P and PI based controllers have been designed previously for this purpose. Here Model Predictive Control is proposed for including DC power controllers in the provision of Automatic Generation Control.

Comparison of bus frequency estimators for power system transient stability analysis

The paper presents a study on the dynamic response of power system frequency control devices considering different approaches to estimate bus frequencies in power system simulators. The frequency signals considered in this paper are obtained based on the center of inertia, a commonly-used washout filter that approximates the derivative of the bus voltage phase angle, and a frequency divider formula developed by the authors. The dynamic behavior of frequency control devices such as thermostatically regulated loads is compared considering the three signals above. Different scenarios are discussed based on the IEEE 14-bus and New England 39-bus, 10-machine test systems.

Impact of variability, uncertainty and frequency regulation on power system frequency distribution

This work originates from the observation of the frequency distribution of the Irish system as obtained from a Frequency Disturbance Recorder lent to the last author by the University of Tennessee. The probability density function of such a distribution appears to be bimodal. The paper first investigates how stochastic sources, in particular, load and wind power estimation errors, impact on the distribution of the frequency of a high-voltage transmission system. Then, possible routes to obtain a bimodal distribution of the frequency are explored and the most likely cause that leads to the observed behaviour of the Irish system is identified. Finally, the paper presents a comparison of different frequency regulation strategies and their impact on the distribution of the frequency. A sensitivity analysis of wind speed and load parameters is presented and discussed based on the IEEE-14 bus system.

Stochastic Transient Stability Analysis of Transmission Systems With Inclusion of Energy Storage Devices

The letter provides a thorough stochastic analysis of the impact of energy storage systems on the transient stability of transmission grids. This impact is evaluated considering the combined effect of different energy storage technologies, fault clearing times, and network topologies. The latter concerns the relative positions of faults, storage devices, and synchronous machines. The case study consists of stochastic time-domain simulations carried out for the all-island, 1479-bus model of the Irish transmission system that includes a real-world hybrid storage device. Results lead to some nonintuitive conclusions.

Design of MPC-based controller for a Generalized Energy Storage system model

This paper presents a control strategy based on Model Predictive Control for Energy Storage Systems. The mathematical formulation of this controller is outlined, and the procedure for applying this controller to a Generalized Energy Storage model is then documented. The dynamic performance of the control strategy presented is compared with that of a PI-based control technique. A comprehensive case study based on the New England 39-bus 10-machine test system with the inclusion of Energy Storage Systems is presented and discussed.

Stability-constrained unit commitment with water network loads

The paper presents an analysis of the economical and technical impact of Water Network Loads (WNLs) on the operation of power systems. The paper also proposes an iterative technique to solve both a unit commitment problem with the inclusion of conventional power generation, wind power and WNLs and a N-1 contingency analysis based on time-domain simulations. At each iteration, if the WNLs schedule in a given period is not acceptable for some of the considered contingencies, the unit commitment problem is solved again constraining the amount of dispatchable WNLs. The proposed technique is tested using the New England 39-bus 10-machine system adapted to include wind generation and WNLs.