Superconducting magnetic energy storage (SMES) systems are getting increasing interest in applications of power flow stabilization and control in the transmission network level. This trend is mainly supported by the rising integration of large-scale renewable energy power plants into the high-power utility system and by major features of SMES units. In a SMES system, the power conditioning system (PCS) is the crucial component for controlling the power exchange between the superconducting coil and the ac system. The dynamics of the PCS directly influences the validity of the SMES in the dynamic control of the power system. This paper describes a novel PCS scheme of SMES to simultaneously perform both active and reactive power flow controls. Moreover, a detailed model of the SMES unit is derived and a three-level control scheme is designed, comprising a full decoupled current control strategy in the d-q reference frame with a novel controller to prevent PCS dc bus capacitors' voltage drift/imbalance. The dynamic performances of the proposed systems are fully validated by computer simulation.

Improved Superconducting Magnetic Energy Storage (SMES) Controller for High-Power Utility Applications

Major milestones in the development of high voltage direct current (HVDC) technologies and concepts were achieved in 1950s. Thanks to the high power thyristor switches (1960–70s), the HVDC technologies reached a significant degree of maturity in 1980s. The classical HVDC uses thyristor-based current-sourced line-commutated converter (LCC) technology. The advent of power semiconductor switches in 1980–90s, with turn on-off capabilities especially the IGBTs and IGCTs, and the on-going progress in this field, have introduced the conventional (two-level) voltage-source converter (VSC) technology and its variety of configurations, multi-level and multi-module VSCs, also as viable converter technologies for power system applications. The DC system is experiencing significant degree of re-emergence due to its potential to either directly address, or to facilitate resolving a large number of existing and anticipated interconnected AC power system steady-state and dynamic issues. HVDC technology made possible to transfer bulk power over long distances. In part I of this two-parts paper, comparative evaluations, studies, and review of HVDC versus HVAC transmission systems, are presented. Applications, different schemes of HVDC systems are also outlined.

High voltage direct current transmission - A review, part I

The transmission system is becoming ever more complex. Furthermore, demand for reliable supply of electricity is growing, increasing the need for a higher level of system reliability. A solution might be to incorporate controllable power components within the system. One such component is the HVDC link. However, in the domain of reliability models for HVDC and the component's impact on the overall transmission system reliability, there is still much work to be done. This is an important issue in future grid planning, especially with an increasing penetration of HVDC links within synchronous transmission systems acting as "firewalls". These links may prevent disturbances propagating in the system, which is a common cause of blackouts. This paper provides a broad introduction to the HVDC technology and a literature review of reliability assessments published within this area. It gives a background to and motivation for the technology. Published reliability assessments of the HVDC technology have been reviewed and categorized. One conclusion is that a large number of models and methods for the reliability evaluation of the HVDC system itself have been published, but very few on its impact on the composite system reliability. One future challenge to be solved is how the "firewall" properties of the HVDC can be quantified in a reliability assessment.

Introduction to HVDC Technology for Reliable Electrical Power Systems

In general, a large percentage of the electric power produced is generated in huge generation centres far from the consumption, and with centralized transmission and distribution systems, where the weak point of this scheme is the efficiency with high energy losses in the form of heat. This problem has been increased in the last years due to the significant growth of electric energy demand and in the case of structures of weakly meshed electrical grids, due to the high vulnerability in cases of faults that can originate frequently severe transient and dynamic problems that lead to the reduction of the system security (Dail et al., 2007). Many large blackouts that happened worldwide in the last decade are a clear example of the consequences of this model of electric power. These problems, far from finding effective solutions, are continuously increasing, even more impelled by energy factors (oil crisis), ecological (climatic change) and by financial and regulatory restrictions of wholesale markets, which causes the necessity of technological alternatives to assure, on one hand the appropriate supply and quality of the electric power and on the other one, the saving and the efficient use of the natural resources preserving the environment. An alternative technological solution to this problem is using small generation units and integrating them into the distribution network as near as possible of the consumption site, making this way diminishing the dependence of the local electrical demand, of the energy transmission power system. This solution is known as in-situ, distributed or dispersed generation (DG) and represents a change in the paradigm of the traditional centralized electric power generation (El-Khattam & Salama, 2004). In this way, the distribution grid usually passive is transformed into active one, in the sense that decision making and control is distributed and the power flows bidirectionally. Here it is consolidated the idea of using clean non-conventional technologies of generation that use renewable energy sources (RESs) that do not cause environmental pollution, such as wind, photovoltaic (PV), hydraulic, biomass among others (Rahman, 2003). At present, perhaps the most promising novel network structure that would allow obtaining a better use of the distributed generation resources is the electrical microgrid (MG) (Kroposki et al., 2008). This new paradigm tackles the distributed generation as a subsystem formed by distributed energy resources (DERs), including DG, RESs and distributed energy storage (DES) and controllable demand response (DR), also offering significant control

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Dynamic Modelling and Control Design of Advanced Energy Storage for Power System Applications

SUMMARY

In this paper, we consider two methods for solving differential and algebraic Lyapunov equations in the time and frequency domains. Solutions of these equations are finite and infinite Gramians. In the first approach, we use the Laplace transform to solve the equations, and we apply the expansion of the matrix resolvent of the dynamical system. The expansions are bilinear and quadratic forms of the Faddeev matrices generated by resolvents of the original matrices. The second method allows computation of an infinite Gramian of a stable system as a sum of sub-Gramians, which characterize the contribution of eigenmodes to the asymptotic variation of the total system energy over an infinite time interval. Because each sub-Gramian is associated with a particular eigenvector, the potential sources of instability can easily be localized and tracked in real time. When solutions of Lyapunov equations have low-rank structure typical of large-scale applications, sub-Gramians can be represented in low-rank factored form, which makes them convenient in the stability analysis of large systems. Our numerical tests for Kundur's four-machine two-area system confirm the suitability of using Gramians and sub-Gramians for small-signal stability analyses of electric power systems. Copyright © 2013 John Wiley & Sons, Ltd.

Stability analysis of large‐scale dynamical systems by sub‐Gramian approach

A brief overview of modern transmission technologies and how they may be effectively used to enhance system dynamic performance in response to major system disturbances is presented. In this way, some of the risks of potential cascading outages and islanding of the system can be mitigated. The application of these devices requires proper coordination and tuning of controls to ensure robust performance. The key benefit is the ability to effect fast and automatic response to system disturbances, thereby enhancing damping in power oscillations, transient stability margins, and smooth voltage recovery and regulation following major system disturbances

W. Wong

Papers

Modern countermeasurus to blackouts