Assessment of imbalance settlement exemptions for offshore wind power generation in Belgium

This article deals with a specific support mechanism exempting offshore wind power generators partially from their balancing responsibilities by means of a tolerance margin. This specific support mechanism was enforced in Belgium as from 2009 and is defended by its proponents in view of the lower power output predictability at offshore locations. Although policies accommodating offshore developments may be seen as important to tap better wind resources, this contribution stresses the importance of full balancing responsibility for variable renewables. After a detailed evaluation of the support mechanism and its impact on the balancing costs for wind power generators, the use of current applied production support mechanisms is recommended. These can be used to acquire the same financial effect without increasing market complexity and harming the operation of the balancing market. The first part of the study deals with the specific implementation of the tolerance margin in the Belgian context. Secondly, its underlying motivation is quantitatively assessed, namely the relatively higher offshore prediction errors. Finally, the total offshore subsidy resulting from the measure is determined. Expressed in €/MWh, this subsidy is currently determined at €1.4–1.7/MWh, which represents the required increase of production support in order to replace the regulation.     

Fluctuations in instantaneous clearness index: Analysis and statistics

Solar radiation is characterized by short fluctuations introduced by passing clouds. An analysis of these fluctuations with regard to solar energy applications should focus on the instantaneous clearness index. Its probability distribution for a given mean clearness index is, as a first approximation, independent from the season and partly also from the site. This is verified for four annual datasets from three different sites.An analysis of fluctuations in solar radiation must focus on their amplitude, persistence, and frequency of occurrence rather than their location in time. The Fourier analysis cannot satisfactorily provide this information since time series of the instantaneous clearness index exhibit no periodicity. Instead, a localized spectral analysis based on wavelet bases rather than on periodic-ones has been applied. This analysis allows the decomposition of the fluctuating clearness index signal into a set of orthonormal subsignals. Each of them represents one specific scale of persistence of the fluctuation.The annual mean square values of all subsignals have been analysed, permitting the allocation of the signal’s power content to the different scales of persistence of a fluctuation. These annual mean values agree well for the different datasets, indicating the existence of statistically significant mean square values of the fluctuations as a function of their persistence.The analysis offers a valuable tool for the estimation of power flow fluctuations introduced by direct solar energy systems. With further elaboration it may be applied by power system operators for network planning in distribution grids with a high density of embedded generation.     

Calculation of the flux density and the unbalanced pull in two pole induction machines

Contents In this paper, the relationship between the homopolar flux generated by a statically eccentric rotor and the unbalanced magnetic pull in two-pole induction motors is considered. We will show that due to this kind of eccentricity, a homopolar flux is generated having the supply frequency, yielding a vibrational component of the unbalanced magnetic pull with the double supply frequency.

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Die Ermittlung der Induktionsverteilung und der Radialkräfte in zweipoligen Asynchronmaschinen

Übersicht In der vorliegenden Arbeit wird auf die Verknüpfung der Unipolarflüsse mit den Radialkräften bei 2poligen Drehstromasynchronmaschinen näher eingegangen. Es wird nachgewiesen, daß sich bei statisch exzentrischer Verlagerung des Läufers in zweipoligen Drehstromasynchronmaschinen netzfrequente Unipolarflüsse ausbilden können, die Rüttelkräfte von doppelter Netzfrequenz zur Folge haben.

     

Distributed control of renewable generation units with integrated active filter

Due to the current concern about the environment, there is a growing interest in distributed generation from renewable energy sources. Usually a power electronic converter is required to interface renewable generation units with the utility grid. The power electronic converters can be designed to provide nonactive power in addition to active power supply in order to compensate distorted currents. This paper proposes a distributed control method for converter-interfaced renewable generation units with active filtering capability. Agent-based communication makes coordination between the generation units possible. Experimental results are included to demonstrate the validity of the proposed method.     

Investigating performance, reliability and safety parameters of photovoltaic module inverter: Test results and compliances with the standards

Reliability, safety and quality requirements for a new type of photovoltaic module inverter have been identified and its performance has been evaluated for prototypes. The laboratory tests have to show whether the so-called second generation photovoltaic module inverter can comply with the expectations and where improvements are still necessary. Afterwards, the test results have been compared with the internationals standards.     

Servo motor selection criterion for mechatronic applications

Modern mechatronic applications often involve complex motions, resulting in highly dynamic motor loads. The selection of an appropriate motor is based on the characteristics of the load, besides other technical, as well as economic, considerations. However, motor characteristics, such as rotor inertia, affect the motor load, which complicates the analysis. The selection criterion presented in this paper separates the motor characteristics from the load characteristics and its graphical representation facilitates the feasibility check of a certain drive and the comparison between different systems. In addition, it yields the range of possible transmission ratios. The method is illustrated with an industrial case study     

3D optimization of average torque of electrostatic micromotors

The paper presents a technique to optimize electrostatic micromotors. The finite element technique is combined with different types of optimization strategies, one of them, a version of the evolution strategy is discussed. It further involves an automated generation of 3D meshes where the dimensions and rotor positions of the motor models can be chosen arbitrarily. It also involves constructing equivalent circuit models for the electrostatic motors. Both, the automated 3D mesh generation and the construction of the equivalent circuit model are treated in detail in this paper. The possibilities of producing powerful tools in the field of optimization are described, but also some warnings and limitations concerning the automated optimization are mentioned.     

Transmission of bulk power

The transmission of bulk power through HVDC is growing. Expansion of the HVDC network over large distances across the developing countries poses new challenges. The classic HVDC remains a cost effective alternative for such cases. The recent progress in power electronics heralded a new era for the HVDC technology. The VSC HVDC is believed to be a strong contender for the flexible transmission system and certainly has a promising future in the ever increasing number of applications.     

Determining optimal electricity technology mix with high level of wind power penetration

Notwithstanding its variability and limited controllability, wind power is expected to contribute strongly to electricity generation from renewable energy sources in the coming decades. Treating wind power as non-dispatchable by subtracting its output from the original load profile, results in a net load profile, which must be covered by conventional power generation. The screening curve methodology is a first approximation to find the optimal generation technology mix, based on relative cost levels. However, increased variability of the net load profile, due to wind power generation, strongly influences system operation. Therefore a static linear programming investment model is developed to determine the optimal technology mix. This alternative methodology shows a reduced capacity of inflexible generation after including operational constraints to properly account for net load variability. In order to illustrate this methodology, an example is set up, showing the sensitivity with respect to ramp rates of conventional generation, transmission interconnection and energy storage. The comparison of those different sources of system flexibility suggests that energy storage facilities better facilitate the integration of wind power generation.