Mikael Amelin

Congestion-management schemes: a comparative analysis under a unified framework

The restructuring of the electricity industry has spawned the introduction of new independent grid operators (IGOs), typically called transmission system operators (TSOs); independent system operator (ISOs); or regional transmission organizations (RTOs), in various parts of the world. An important task of an IGO is congestion management (CM) and pricing. This activity has significant economic implications on every market participant in the IGOs region. The paper briefly reviews the CM schemes and the associated pricing mechanism used by the IGOs in five representative schemes. These were selected to illustrate the various CM approaches in use: England and Wales, Norway, Sweden, PJM, and California. The authors develop a unified framework for the mathematical representation of the market dispatch and redispatch problems that the IGO must solve in CM in these various jurisdictions. They use this unified framework to develop meaningful metrics to compare the various CM approaches so as to assess their efficiency and the effectiveness of the market signals provided to the market participants. They compare, using a small test system, side by side, the performance of these schemes.

Comparison of Capacity Credit Calculation Methods for Conventional Power Plants and Wind Power

Several methods for computing capacity credit values of power plants have been presented over the years. This paper uses an empirical approach to investigate and compare different properties of four typical capacity credit definitions. It is shown that the choice of definition indeed can have a significant impact on the results. Concerning three of the analyzed methods, it is found that important factors that influence the capacity credit are the overall generation adequacy and the penetration factor of the power plant; this means that the same generating unit will generally have a higher capacity credit if added to a system with high loss of load probability, and the unit will have a higher capacity credit if its installed capacity is small compared to the total installed capacity of the system. The results of the fourth method only depend on the size and availability of the generating units.

Risk Estimation of Critical Time to Voltage Instability Induced by Saddle-Node Bifurcation

Prevention of voltage instability in electric power systems is an important objective that the system operators have to meet. Under certain circumstances the operating point of the power system may start drifting towards the set of voltage unstable operating points. If no preventive measures are taken, after some time the operating point may eventually become voltage unstable. It will thus be preferable to have a measure of the risk of voltage collapse in future loading states. This paper presents a novel method for estimation of the probability distribution of the time to voltage instability for a power system with uncertain future loading scenarios. The method uses a distance from the predicted load-path to the set of voltage unstable operating points when finding an estimate of the time to voltage instability. This will reduce the problem to a one-dimensional problem which for large systems decreases the computation time significantly.

Load modeling using the Ornstein-Uhlenbeck process

In this paper we show how to model the load in an electric power system using the Ornstein-Uhlenbeck process and use the method developed by Lehmann to find the distribution of the maximum of the load process in a bounded time interval. A numerical example showing how to find an upper confidence bound for the maximum of the maximum of the load process in a bounded time interval using the proposed method will also be given.

A study of electricity market design for systems with high wind power penetration

This literature review investigates the influence of intermittent wind power on the electricity market pointing out the importance of the market design along with presenting the Nordic, the German and the Spanish electricity wholesale market. Adaptations in the market design could improve the performance of systems with high wind power penetration levels. As a conclusion promising key-issues are listed.

The state-of-the-art of the short term hydro power planning with large amount of wind power in the system

The amount of wind power is growing significantly in the world. Large scale introduction of wind power in the power system will increase the need for improved short term planning models of hydro power, because additional variations are introduced in the system. This huge amount of uncertainties in the power system will cause changes in the power market and there will be a value of advanced planning techniques, that will allow more flexibility in hydropower generation by taking into account stochastic nature of spot and regulating markets, water inflow, future water value and so on. The application of multi-stage stochastic optimization in the planning of the daily production of hydro power is not wholly discovered and requires further research. The complexity of the mathematical programming of the short term hydro power production including several type of uncertainty, while keeping the problem size solvable, challenges the power system researchers. This paper overviews the literature in the field of short term hydro power planning in power systems with large amount of wind power.

A Comparative Analysis of Congestion Management Schemes under a Unified Framework

The restructuring of the electricity industry has spawned the introduction of new independent grid operators or IGOs, typically called transmission system operators (TSO), independent system operator (ISO) or regional transmission organizations (RTO), in various parts of the world. An important task of an IGO is congestion management (CM) and pricing. This activity has significant economic implications on every market participant in the IGOs region. The paper briefly reviews the congestion management schemes and the associated pricing mechanism used by the IGOs in five representative schemes. These were selected to Illustrate the various CM approaches in use: England and Wales, Norway, Sweden, PJM and Califomia. We develop a unified framework for the mathematical representation of the market dispatch and redispatch problems that the IGO must solve in CM in these various jurisdictions. We use this unified framework to develop meaningful metrics to compare the various CM approaches so as to assess their efficiency and the effectiveness of the market signals provided to the market participants. We compare, using a small test system, side by side, the performance of these schemes.

Taking Credit : The Impact of Wind Power on Supply Adequacy-Experience from the Swedish Market

This article presents some general concepts about capacity credit values, which are illustrated by theoretical examples as well as practical experience from the Swedish electricity market. The capa ...

Multi-Station Equivalents for Short-Term Hydropower Scheduling

Hydropower scheduling in day-ahead electricity markets is complex due to uncertainty in the electricity price. Internal cascade dependency of hydro power plants can also increase this complexity. One way to overcome this complexity is to replace the original hydropower system by an equivalent system, which provides simulation results sufficiently close to the ones of the original system. This paper presents a method to obtain multi-station equivalent models using a bilevel optimization problem, where the objective is to minimize the difference in outcomes between the original and the equivalent models. This bilevel problem is then transformed into a single-level optimization problem that can be solved using standard optimization techniques. Finally, the errors between the simulation results of the original and equivalent hydropower models are computed and analyzed for a Swedish system to show the accuracy of different multi-station equivalents.

Constructing Bidding Curves for a CHP Producer in Day-ahead Electricity Markets

The operation of Combined Heat and Power (CHP) systems in liberalized electricity markets depends both on uncertain electricity prices and uncertain heat demand. In the future, uncertainty is going to increase due to the increased intermittent power induced by renewable energy sources. Therefore, the need for improved planning and bidding tools is highly important for CHP producers. This paper applies an optimal bidding model under the uncertainties of day-ahead market prices and the heat demand. The problem is formulated in a stochastic programming framework where future scenarios of the random variables are considered in order to handle the uncertainties. A case study is performed and conclusions are derived about the CHP operation and the need for heat storage.