Albert Moser

Justified Fault-Ride-Through Requirements for Wind Turbines in Power Systems

In this paper, a novel adaptive strategy to obtain technically justified fault-ride-through requirements for wind turbines (WTs) is proposed. The main objective is to promote an effective integration of wind turbines into power systems with still low penetration levels of wind power based on technical and economical considerations. The level of requirement imposed by the strategy is increased stepwise over time, depending on system characteristics and on wind power penetration level. The idea behind is to introduce stringent requirements only when they are technically needed for a reliable and secure power system operation. Voltage stability support and fault-ride-through requirements are considered in the strategy. Simulations are based on the Chilean transmission network, a midsize isolated power system with still low penetration levels of wind power. Simulations include fixed speed induction generators and doubly fed induction generators. The effects on power system stability of the wind power injections, integrated into the network by adopting the adaptive strategy, are compared with the effects that have the same installed capacity of wind power but only considering WTs able to fulfill stringent requirements (fault-ride-through capability and support voltage stability). Based on simulations and international experience, technically justified requirements for the Chilean case are proposed.

Simulation methods for assessing electric vehicle impact on distribution grids

Against the background of raising noise and exhaust emissions and the tendency of ever-increasing oil prices, there is a growing interest in electric vehicles (EV) as replacement for conventional vehicles with combustion engine. Since the EV affects neither local tailpipe nor remarkable noise emissions, the EV can improve the ecological situation especially in municipal areas all over the world. Furthermore, due to recent technical advancements and extensive political incentives, the supply of renewable energies-especially wind and photovoltaic energy-is increasing. Since existing distribution grids are not designed for high penetration levels of dispersed generation, or for large scale integration of EVs, extensive network expansion is necessary. Therefore, the question arises if EVs can be used as mobile storage devices or standalone energy sources to counter the aforementioned development and relieve the increasing stress on distribution grids. To answer that question a simulation method based on a comprehensive model of the distribution grid, its conventional as well as the aforementioned new costumers is developed to allow an evaluation of systems of large scale at municipal extent with high penetration of dispersed generation and EVs.

Modeling optimal redispatch for the European Transmission grid

The European Electricity System is undergoing fundamental changes in the next decades. Among other reasons the massive increase of electricity generation from renewable energy sources as well as the increasing cross-border power flows can be identified as the main drivers. This development leads to new challenges for the operation of the transmission grid as bulk power transfers over wide distances will increase rather than remain the exception. The current transmission grid on the other hand has not been designed to allow massive wide area power transfers resulting in overloadings and congestions.

Economic potential of power-to-gas energy storages

All over Europe and especially in Germany the expansion of Renewable Energy Sources is quickly proceeding. A possibility to cushion generation volatility (due to the supply dependence of wind and solar power) and to use surplus energy is storage. One of the most promising technologies for long-term energy storage is Power-to-Gas (PtG). This process produces hydrogen and optionally methane from electricity which is then injected into the natural gas infrastructure. Operators can market PtG plants by buying electricity and sell natural gas. Simulations of optimal plant dispatch show that the contribution margins attained today and until 2032 are not sufficient to cover variable and fixed costs. Even with additional marketing of negative tertiary reserve economic efficiency cannot be reached. With regard of upcoming competing technologies, PtG will not be profitable in the near future but can be an important part on the way to a renewable energy system.

Determination of alternative bidding areas based on a full nodal pricing approach

Congestion management and capacity allocation have turned out to be some of the major challenges in the European electricity system. Although it is known that nodal prices, or often called locational marginal prices, would, in theory and from a static efficiency point of view, lead to an optimal congestion management, due to various reasons (e.g. market power and liquidity) this is no feasible solution in the mid-term; therefore, adjusting the current shape of bidding areas based on the physical transmission constraints could provide a preferable interim solution. Consequently, an algorithm to determine bidding areas based on a full nodal pricing simulation is developed and applied to a model of the European electricity system. The results show that the developed method is capable of investigating large power systems including impacts from uncertainties like grid extension or future development of Renewable Energies Sources (RES).

Scenario-based evaluation on the impacts of electric vehicle on the municipal energy supply systems

By improving the ecological situation in the congested urban areas and reducing the dependence on fossil oil imports, a high penetration of electric vehicles (EV) in the automobile market is expected within the next years. Integration of area-wide charging infrastructures rises the challenge for the municipal energy supply systems to fulfill the demand of an increasing number of EV in the near future. Versatile technologies and integration strategies may be implemented in the charging regime, which might have significant impacts on the electrical distribution network. This paper presents the results of a comprehensive investigation in order to evaluate different charging concepts and strategies. Furthermore the resulting consequences on the battery management of the EVs are discussed by means of scenario-based evaluation and demand side management possibilities. The possible impacts on the charging behavior of EV-customers, driven by structurally changed prices for electrical energy due to a rising share of renewables will be also demonstrated.

Optimized positioning of measurements in distribution grids

Due to a massive increase in installed generation capacities in German medium and low voltage networks the number of critical network situations resulting in thermal overloading or voltage band violations is increasing. The knowledge of the system state gains importance if smart grid technologies are to be used to ease critical network conditions. Today only basic state estimation algorithms are used in the medium voltage networks. Their results are vague as there are only few real time measurements. With only few additional measurements the state estimators accuracy can be raised significantly. This paper presents a method for the evaluation of the measurement placements impact on state estimation based on a stochastically approach.

Optimized bidding area delimitations and their impact on electricity markets and congestion management

The delimitation of bidding areas and the overall European congestion management have been heavily discussed in the recent years. Although main evaluation criteria are defined in the network code on congestion management, the question of adequate or optimized bidding area delimitations remains open. Thus, this paper presents an approach for an optimized delimitation of bidding areas based on a clustering of security-constraint nodal prices. Relevant evaluation criteria, like the level of generation and redispatch costs or the level of network security, are derived via a multi-step optimization approach. Results show, that optimized bidding area delimitations differ significantly from the current ones. However, these optimized delimitations yield only small cost savings compared to the current bidding area delimitation.

Expectation-based reserve capacity dimensioning in power systems with an increasing intermittent feed-in

The ongoing transition process of the European electricity sector to an increasing share of renewable electricity generation is in full swing. Unavoidable forecast errors of non-dispatchable energy sources (e.g. wind and solar power) have to be balanced out by reserve capacity power plants. This is normally organized in markets for ancillary services. Whereas the necessary reserve capacity, calculated by the transmission system operator (TSO), was historically dimensioned on a monthly basis, not considering information on the forecasted feed-in of the fluctuating generation from RES, this will change in future. Consequently this paper intents to present a methodology for an expectation-based reserve capacity dimensioning, based on a method currently applied by many of the European TSO. The results show, that by application of the methodology in an exemplary European case study for the year 2022, the necessary average reserve capacity decreases. However, the hourly demand for tertiary reserve capacity is subjected to significant fluctuations, due to volatile wind and solar generation.

Impact of large-scale electric vehicle application on the power supply

Sufficiency and cost-efficiency of energy supply are essential criteria for the economic development of a country. So far, the energy demand as well as the emission of gaseous pollutants in highly developed countries is significantly determined by the number of cars due to dominating combustion engine vehicles (CV). Since the electric drive as an innovative propulsion system effects neither local tailpipe nor remarkable noise emissions, the electric vehicle (EV) can certainly improve the ecological situation in congested areas all over the world. However, questions of global ecological consequences of large-scale introduction of EVs still have not thoroughly been answered since methods for a combined simulation of EV-traffic and power system operation have not yet been available. This paper represents the results of a comprehensive investigation in order to evaluate different strategies and their consequences for EV operations possibilities as well as their effects on power generation and emissions exemplarily for the German power market.