Thilo Krause

Multiple-Energy Carriers: Modeling of Production, Delivery, and Consumption

This paper presents a generic framework for the modeling of energy systems comprising multiple-energy carriers, such as electricity, heat, gas, biomass, etc. The modeling framework is based on the so-called energy hub approach. The core idea of the energy hub is the definition of a conversion matrix capable of describing the interactions of production, delivery, and consumption in multiple-energy carrier systems. Based on the energy hub concept a broad spectrum of modeling extensions and applications is presented, such as a multiple-energy carrier optimal power flow, risk management and investment analysis tools, agent-based control schemes for decentralized generation units as well as the possibility to analyze the influence of plug-in hybrid electric vehicles (PHEVs) on future energy systems. The paper is concluded with a section presenting the key benefits of the energy hub modeling framework, followed by a discussion on the main design principles generality, scalability, and modularity as well as a discussion on the possibility to follow top-down or bottom-up modeling strategies.

Evaluating congestion management schemes in liberalized electricity markets using an agent-based simulator

In this paper we compare different congestion management schemes in liberalized electricity markets using an agent-based simulator. By modelling market participants as adaptive agents in oligopolistic structures, we consider the possibility of strategic behavior and the existence/exercise of market power. Generation companies submit their bids to the market place in order to maximize their payoffs, where we apply reinforcement learning as behavioral agent model. The market is then cleared taking into account specific congestion management methods, such as locational marginal pricing (LMP), market splitting and flow-based market coupling. We demonstrate the functionality of the simulator using a test network, illustrating that different congestion management methods lead to different market dynamics and/or equilibria. Additionally, we assess the effects on the distribution of the surplus for producers and consumers as well as overall social welfare

Modeling interconnected national energy systems using an energy hub approach

This paper describes an approach to model interconnected national energy systems using the concept of energy hubs. Each country is modeled as an energy hub, characterized by the national generation infrastructures for heat and electricity, the demand for heat and electricity as well as properties detailing mobility demand. Countries are interconnected via electricity and gas networks, i.e. it is possible to import or export electricity and/or gas. The paper gives a short introduction to the concept of energy hubs and describes the extensions of the concept to account for national multi-carrier energy systems. In a subsequent part the network model is introduced. The different constituents (generation, demand, transmission infrastructures) form an optimization problem, where a numerical solution approach is combined with particle swarm optimization. Furthermore, it is described how the relevant data concerning demand, generation and network infrastructures was obtained. The paper is concluded with three case studies demonstrating the applicability of the proposed approach.

Closure of “a unified analysis of security-constrained OPF formulations considering uncertainty, risk, and controllability in single and multi-area systems”

This paper presents a variety of different Security Constrained Optimal Power Flow formulations addressing four power system operation and planning problems: (a) forecast uncertainty of Renewable Energy Sources (RES) in-feed and load, (b) security criteria based on contingency risk, (c) corrective control offered through High Voltage Direct Current (HVDC) lines and flexible demand, (d) operation of multi-area systems with limited data exchange. A comprehensive probabilistic Security Constrained Optimal Power Flow (SCOPF) framework based on scenario-based methodologies is presented. This approach provides a-priori guarantees regarding the probability of the constraint satisfaction. In this paper, we show how HVDC lines, flexible demand, and novel risk-based operational paradigms can be used to handle outage uncertainty and the fluctuating in-feed from RES. Our analysis is extended by introducing a distributed probabilistic SCOPF algorithm for multi-area systems involving different levels of data exchange. The applicability of the methods is demonstrated on the three-area Reliability Test System (RTS-96). Results are compared based on operating costs and maximum wind power penetration.

Corrective Control to Handle Forecast Uncertainty: A Chance Constrained Optimal Power Flow

Higher shares of electricity generation from renewable energy sources and market liberalization is increasing uncertainty in power systems operation. At the same time, operation is becoming more flexible with improved control systems and new technology such as phase shifting transformers (PSTs) and high voltage direct current connections (HVDC). Previous studies have shown that the use of corrective control in response to outages contributes to a reduction in operating cost, while maintaining N-1 security. In this work, we propose a method to extend the use of corrective control of PSTs and HVDCs to react to uncertainty. We characterize the uncertainty as continuous random variables, and define the corrective control actions through affine control policies. This allows us to efficiently model control reactions to a large number of uncertainty sources. The control policies are then included in a chance constrained optimal power flow formulation, which guarantees that the system constraints are enforced with a desired probability. By applying an analytical reformulation of the chance constraints, we obtain a second-order cone problem for which we develop an efficient solution algorithm. In a case study for the IEEE 118 bus system, we show that corrective control for uncertainty leads to a decrease in operational cost, while maintaining system security. Further, we demonstrate the scalability of the method by solving the problem for the IEEE 300 bus and the Polish system test cases.

Maximizing exergy efficiency in multi-carrier energy systems

In this paper a model for maximizing exergy efficiency in multi-carrier energy systems is introduced. Based on modeling concepts developed in the project “Vision of Future Energy Network”, e.g. the Energy Hub concept, exergy is modeled in the context of energy systems that involve multiple energy carriers such as electricity, natural gas and heat. In the context of this integrated consideration of multiple energy carriers, the exergy approach allows to take into account the quality of different energy carriers. Hence this modeling approach provides the possibility to identify from a system perspective how the available energy content of different energy carriers can be exploited as efficiently as possible to satisfy a given demand for final energy carriers. In order to illustrate the proposed exergy analysis method, we compare it with a previously developed cost optimization and apply both methods to an example system consisting of an electricity and natural gas system interconnected by Energy Hubs.

Flexible AC Transmission Systems (FACTS) and power system security — A valuation framework

Considering aging power system infrastructures in conjunction with increased electricity trading activities, there is a strong need for future investments in electricity grids. Technological progress has made available a number of different investment alternatives, ranging e.g. from “standard” reinforcements of existing transmission capacities to the installation of Flexible AC Transmission Systems (FACTS). This paper proposes a framework for comparing different investment alternatives. The approach relies on an optimal power flow (OPF), where system security is explicitly considered by means of a novel formulation for a security constrained optimal power flow (SC-OPF). For evaluation purposes several indicators are proposed, such as the loading of transmission lines, the total generation costs and the overall dispatch depending on different consumption levels. In a first case study the installation of shunt and in-series FACTS devices are compared. The paper is concluded with a sample valuation assessing whether to invest in a Thyristor-Controlled Series Capacitor (TCSC) or in a line reinforcement, i.e. additional line capacity.

HVDC line placement for maximizing social welfare — An analytical approach

This paper derives a method for HVDC line placement in order to maximize social welfare. Assuming linear generator costs, it shows that for N congestions, there exist exactly N +1 marginal generators. It then demonstrates that HVDC lines connecting a high-cost with a low-cost marginal generator lead to the maximization of social welfare. The method poses an upper bound on the line installation costs, which could also be used to increase the efficiency of optimization algorithms. At the same time, it shows that an optimal HVDC placement is not necessarily along the overloaded lines. Furthermore, an algorithm for HVDC placement is developed taking into account the line capacity and the generator constraints to estimate expected generation cost savings. The validity of the approach is demonstrated on two case studies: a 10-bus network, and a simplified European network.

Supergrid or local network reinforcements, and the value of controllability — An analytical approach

In this paper, an analytical approach is developed to address network planning questions for meshed AC networks. First, relationships are derived to compare the effectiveness of expansion measures, such as the building of long lines in the form of overlay grids, or local reinforcements along the transmission path in the existing grid. Results show that overlay networks are preferable, transferring more power for the same line-kilometers and line capacity. Second, upper bounds for the maximum utilization of long AC lines over a meshed network are extracted. The derived bounds prove to be significantly limiting in a highly meshed network. This stresses the need for controllable power flows. The obtained relationships are confirmed on the two-area RTS-96 system and through simulations on a single-node per country European network, based on real network data. Controllable flows, through the installation of HVDC lines, can save up to 8 billion Euros/year in comparison with the non-controllable AC technologies.

Impacts of grid reinforcements on the strategic behavior of power market participants

Various trends in power systems increase the need for network investments on the transmission level. In this paper we compare different investment criteria and transmission technologies to determine where and how the network should be reinforced. We deploy an agent-based model taking explicitly into account that generation companies might behave strategically by submitting bids to the marketplace deviating from their true marginal cost. In a subsequent step we formulate the optimization problem of the Independent System Operator relying on the well-known Locational Marginal Pricing market design. In a last step the ISO can decide for transmission investments, by reinforcing existing lines or installing Flexible AC Transmission Systems. We show that the decisions regarding which technologies should be used and what locations are to be chosen are not influenced by the strategic behavior of market participants. Additionally, we demonstrate - both analytically and through simulations - that maximizing social welfare as investment criterion complements the objective of mitigating strategic behavior of individual players.