Lou van der Sluis

From transportation patterns to power demand: Stochastic modeling of uncontrolled domestic charging of electric vehicles

This paper presents a Monte Carlo simulation approach for the modeling of the power demand of electric vehicles under the scenario of uncontrolled domestic charging. A detailed transportation dataset for the Netherlands is used to derive the stochastic characteristics of the behavior of vehicles. The stochastic variables are the start/end-time of each trip and the respective travelled distance while the battery state of charge at the beginning of charging is derived by the consideration of the distance traveled since the last charging and the charging history. The stochastic variables are modeled using normal copula function based on the respective correlations and marginal distributions. The total load due to electric vehicles is computed based on the combination of the simulated commuting pattern with the charging profile of a typical electric vehicle battery. The results show that the EV power demand reaches the highest value during the evening peak hours for the residential load, however the peak is significantly lower than maximum which is mainly caused by the low charging time due to a generally low mean traveled distance.

Advantages of ARMA-GARCH wind speed time series modeling

This paper presents the advantages of using wind speed time series models from ARMA-GARCH class. The models are found using good statistical practice and are able to capture the most important characteristics of the data like distribution, time dependence structure and periodicity in a satisfying manner. It is shown that the models offer several crucial advantages. The artificial wind speeds simulated from the obtained models are statistically indistinguishable from the wind speed time series measurements recorded in other years than the original data. Moreover, models can contribute to the considerations of extreme scenarios of wind power generation by simulating wind speeds characterized by a very high energy content. Thanks to the use of continuous cdf transformations, the synthetic time series do not possess the measurement error.

Towards Faster Solution of Large Power Flow Problems

Current and future developments in the power system industry demand fast power flow solvers for larger power flow problems. The established methods are no longer viable for such problems, as they are not scalable in the problem size. In this paper, the use of Newton-Krylov power flow methods is proposed, and a multitude of preconditioning techniques for such methods are discussed and compared. It is shown that incomplete factorizations can perform very well as preconditioner, resulting in a solver that scales in the problem size. It is further shown that using a preconditioned inner-outer Krylov method has no significant advantage over applying the preconditioner directly to the outer iterations. Finally, algebraic multigrid is demonstrated as a preconditioner for Newton-Krylov power flow and argued to be the method of choice in some scenarios.

Outline of a New Hierarchical Agent-Based Voltage Instability Protection System

In the Dutch power system the power consumption is increasing while the transmission and distribution system capacity is not increasing at the same rate. Furthermore due to the increasing amount of decentralized generation, by for example micro-CHP units and wind turbines, the power flows in the power system are changing. In weak sub-transmission and distribution grids an increase in the number of voltage stability problems is expected. However: with the large share of decentralized generation we have the solution for voltage problems already there. In this paper we propose a new Hierarchical Agent Based Instability Protection System. In this paper the idea is described and a theoretical justification is given, in a later stage of the project we will verify the system with the Real-time Digital Simulator and external controls.

Modern state estimation methods in power systems

State estimation is an important tool for system operators. The state of the power system is defined by the voltage magnitudes and phase angles at all buses. The state estimator (SE) determines this state based on a set of redundant measurements.

Black Box Modeling of Low-Voltage Circuit Breakers

In this paper, we propose a black box model for low-voltage arcs. This model is based on the classical theory with the addition of a corrective term to better fit the small current phase, which is seen to be crucial in determining arc extinction. The model is physically consistent, accounting for nonequilibrium effects in a cold plasma. A mathematical algorithm is proposed for model parameter identification, solving a constrained optimization problem by suitably coupling gradient moves with heuristic search methods. Black box modeling is applied to industrial circuit breakers and very good agreement between model predictions and experiments is observed.

Fast Newton load flow

The Newton-Raphson method is widely used to solve load flow problems. Traditionally a direct solver is used to solve the linear systems within this method. In this paper we explore the use of an iterative method to solve the linear systems, leading to an inexact Newton-Krylov method. The main parameters of this method are the preconditioner and the forcing terms. Several candidate choices for these parameters are discussed and tested. With the proper preconditioner, and forcing terms, the inexact Newton-Krylov method is shown to greatly improve on using a direct solver.

Voltage stability consequences of decentralized generation and possibilities for intelligent control

Many decentralized generation technologies are mature today. For the Dutch power system it is expected that in 2020 Decentralized Generators (DGs) form a major (about 35 %) part of the total production capacity. This expectation is true all over the world. A large share of DG will influence the voltage stability of the system. The objective of this paper is to give a clear overview of the consequences of DGs for typical voltage stability problems encountered at transmission level. No particular DG will be studied, but an overview will be given what happens if a DG is based on a certain generator type. Based on theoretical expectations the simulations done in this study show for a typical transmission system that adding DG is generally beneficial for the voltage stability. Mainly three factors are important for the consequence DG has on voltage stability: active power support, reactive power consumption, and voltage support. Taking these benefits into account requires intelligent control of the DGs.

Current-Zero Characteristics of a Vacuum Circuit Breaker at Short-Circuit Current Interruption

High resolution measurements on the post-arc current in vacuum circuit breakers reveal a period, immediately following current-zero, in which the voltage remains practically zero. The most widely used model for simulating the interaction between the post-arc current with the electrical circuit lacks a proper explanation for this event, and hence it needs to be complemented. We demonstrate that the breakers electrical behaviour during this zero-voltage period can be explained by using the theory of a Langmuir probe. Such probes are used to investigate plasma properties, such as the ion density and the electron temperature, and we extrapolate its theory to the vacuum circuit breaker. The simulation results obtained with this model are in good agreement with measured data

Smart grid emergency control strategy for Load Tap Changers

In this paper a strategy is introduced for emergency control of Load Tap Changers (LTCs) to prevent the system from voltage collapse. The method is based on the fact that the power consumed by constant current and constant impedance loads can be lowered by decreasing the secondary voltage of the LTC. This idea is used to develop a method of indirect load shedding. This method calculates, based on a model of the connected load, the voltage set-point of the secondary side of the LTC for a given amount of load that needs to be shed. With simulations it is demonstrated that a LTC can be applied for load relief using the proposed method. A sensitivity analysis is done to study the effect of an error in the load model parameters. Furthermore it is proven that the method can be used to prevent the power system from a typical voltage instability. Finally a proposal for the implementation in a smart grid multi-agent system is presented.