Miloš Cvetković

An Integrated Dynamic Market Mechanism for Real-Time Markets and Frequency Regulation

The intermittent and uncertain nature of renewables represents a major challenge for large scale adoption of sustainable energy resources. Of particular concern is the need to maintain both quality of grid frequency and low costs of regulation reserves in the face of increasing fluctuations in renewables. To this end, we propose an integrated dynamic market mechanism (DMM), which combines real-time market and frequency regulation allowing market players, including renewable generators and flexible consumers, to iteratively negotiate electricity prices at the wholesale level while using the most recent information on the available wind power and the quality of grid frequency. Main features of the integrated DMM are as follows: 1) a Newton-Raphson-based method, which leads to fast convergence to the optimal dispatch; and 2) use of an aggregated frequency error as a feedback signal for the negotiation process, which leads to reduced regulation capacity requirements. The benefits of this DMM are illustrated via simulations on the IEEE 118 bus system.

PMU based transient stabilization using FACTS

Phasor Measurement Units (PMU) and Flexible AC Transmission Systems (FACTS) have great potential for stabilizing response of the power grid to the large disturbances. A combination of both technologies can result in very powerful near-real time sensing and control capable of monitoring and counteracting the effects of very fast disturbances. In this paper we propose fast switching of FACTS devices which is guaranteed to transiently stabilize the system using very fast and accurate PMU measurements. The nonlinear control law proposed in this paper is based and designed upon understanding the physical system-wide effects of a fault. The control law can be interpreted in terms of controling stored energy flow dynamics and it is also derived using energy-based high gain control methods for nonlinear systems. As such, it is entirely scalable and applicable to any size system. The location of PMUs and the design of systemwide communications for given locations of FACTS devices is directly determined using the designed control law. FACTS control of this type would not be possible without having the accuracy and sampling rate of PMUs.

Ectropy-Based Nonlinear Control of FACTS for Transient Stabilization

This paper concerns a novel approach to the modeling and control design for transient stabilization of electric power systems using Flexible Alternating Current Transmission System (FACTS) devices. A nonlinear dynamic model of general interconnected electric power systems in the ordinary differential equation (ODE) form is proposed in terms of time-varying phasors of all dynamic components. This model captures previously unmodeled fast dynamics of inductors and capacitors of FACTS. Additionally, it allows us to observe the active power which is flowing through FACTS during transients. Using the derived model, an ectropy-based FACTS controller is proposed. The proposed controller regulates the active power through FACTS in order to shift the increment in energy created by disturbances. The energy increment is directed from generators into FACTS, preserving the synchronization between generators during disturbances. Simulation results obtained on the IEEE 14-bus system demonstrate the potential of this controller. The controller is shown to increase critical clearing time of the system in the case of a fault.

Physics-based foundations for cyber and market design in complex electric energy systems

In this paper we propose a Dynamic Modeling and Decision Systems (DyMonDS) framework for modeling, simulating and designing cyber in the changing electric energy systems. The approach is fundamentally physics-based, which helps identify the relevant multi-layered structure of their complex dynamics. The common thread throughout the paper is the idea that coupling within a complex interconnected system can be represented using energy stored in different components and the rate of energy exchange with the rest of the system. This idea supports modeling in a transformed state space which makes it possible to systematically design interactive cyber for managing dynamics of energy exchange for provable performance in the evolving multi-physics energy systems. We describe a general scalable DyMonDS simulator currently under the development by our group for demonstrating potential of newly proposed cyber.

A two-level approach to tuning FACTS for transient stabilization

Transient stability of power systems is becoming increasingly important as the grid evolves toward adopting smart, distributed and renewable technologies. The steady state methods, such as (N-1) reliability-related methods and Remedial Action Schemes (RAS), do not guarantee stable system behavior during transients. Additionally, these methods are centralized, while the new technologies, namely fast communications and power-electronically-controlled devices, provide potential for distributed stabilization. In this paper, we propose an approach to designing dynamical controllers for transient stabilization of interconnected power systems. This approach is based on modeling and stabilization of interaction variables which describe how different parts of the system interact. The approach is applicable to large scale systems and different controlling devices. We illustrate it on a simple system with a converter-based Flexible Alternating Current Transmission System (FACTS) device as a controller.

Energy-based transient stabilization using facts in systems with wind power

This paper considers the problem of transient stability in networks with wind power. The effects of large and sudden wind changes are considered and their impact on system stability is analyzed. Next, a nonlinear control logic referred to as the energy-based nonlinear control is introduced as a possible means of stabilizing the system during such disturbances. It is shown how the proposed energy-based nonlinear control applied to Flexible AC Transmission Systems (FACTS) can attenuate disturbances and increase system resilience in response to large disturbances. Potential impact of such FACTS control on system stability is illustrated on a real-world example of Flores Island in Portugal.

Transient stability analysis by reachable set computation

We present a formal technique for verifying the stability of transient responses of power systems. The procedure uses reachability analysis to compute the complete set of possible transient responses starting from a set of initial states, subject to a dynamics specified by differential-algebraic equations. The method is constructive and fully automatic, two properties that are often hard to achieve with direct Lyapunov methods when the differential-algebraic equations are not simplified. Reachability analysis is computationally expensive, but this work presents new techniques that make it possible to verify the stability of a transient response of the IEEE 14-bus benchmark power system network.

Nonlinear Control for Stabilizing Power Systems During Major Disturbances

Abstract In this paper we revisit state-of-the-art methods for stabilizing the dynamics of electric power systems during major changes. A modeling framework which lends itself to energy function-based transient stabilization is introduced for purposes of stabilizing kinetic energy in generators by means of managing stored energy in Flexible AC Transmission System (FACTS) devices embedded in the transmission system. This approach sets the basis for placement of Phasor Measurement Units (PMU) and communications architecture between the generators and FACTS devices capable of transiently stabilizing system dynamics. It is shown that this approach greatly improves the critical clearing time when compared to other proposed methods. This work opens a new direction toward using fast PMUs and communications to transiently stabilize the system.

Foundations of Infrastructure-CPS

Cyber-physical systems are now becoming increasingly prevalent and possibly even mainstream. Infrastructures have been around as long as urban centers, supporting a societys needs for its planning, operation, and safety. As we move deeper into the 21st century, these infrastructures are becoming smart - they monitor themselves through sensor-networks, communicate through a layered architecture, and most importantly self-govern through multiple agents, resulting in a complex integration and interaction between cyber and physical components. With the basics of CPS in place, such as stability, robustness, and reliability properties at a systems level, and hybrid, switched, and event-triggered properties at a network level, we believe that the time is right to go to the next step, of the analysis and synthesis of cyber-physical systems that are present in an infrastructure. We denote such systems as Infrastructure-CPS, which form the focus of the proposed tutorial. We discuss three different foundations of Infrastructure-CPS, (i) Human Empowerment, (ii) Transactive Control, and (iii) Resilience. This will be followed by two examples, one on the nexus between power and communication infrastructure, and the other between natural gas and electricity, both of which have been investigated extensively of late, and are emerging to be apt illustrations of Infrastructure-CPS.

A graph-theoretic approach to modeling network effects of phase shifters on active power loop flows

This paper proposes a new method for modeling effects of phase shifters in “DC” electric power networks. The new model, based on the diakoptics algorithm, provides intuitive graph-theoretic insights on how phase shifters affect real power line flows. The effect of a phase shifter is modeled with loop flows in every basic loop of a meshed graph representing an electric power system. The model can be used to analyze the active power line flows as the superposition of the loop flows caused by a phase shifter and the loop flows created by power injections. Compared to the conventional distribution matrix-based approach, this method provides a straightforward interpretation of power flow redistribution by means of phase shifters. The new modeling technique is illustrated on an example along with a potential application for loop flow reduction.