The Herschel-Heterodyne Instrument for the Far-Infrared (HIFI): instrument and pre-launch testing

This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI), to be launched onboard of ESA's Herschel Space Observatory, by 2008. It includes the first results from the instrument level tests. The instrument is designed to be electronically tuneable over a wide and continuous frequency range in the Far Infrared, with velocity resolutions better than 0.1 km/s with a high sensitivity. This will enable detailed investigations of a wide variety of astronomical sources, ranging from solar system objects, star formation regions to nuclei of galaxies. The instrument comprises 5 frequency bands covering 480-1150 GHz with SIS mixers and a sixth dual frequency band, for the 1410-1910 GHz range, with Hot Electron Bolometer Mixers (HEB). The Local Oscillator (LO) subsystem consists of a dedicated Ka-band synthesizer followed by 7 times 2 chains of frequency multipliers, 2 chains for each frequency band. A pair of Auto-Correlators and a pair of Acousto-Optic spectrometers process the two IF signals from the dual-polarization front-ends to provide instantaneous frequency coverage of 4 GHz, with a set of resolutions (140 kHz to 1 MHz), better than < 0.1 km/s. After a successful qualification program, the flight instrument was delivered and entered the testing phase at satellite level. We will also report on the pre-flight test and calibration results together with the expected in-flight performance

Operation and Control of Power Systems with Low Synchronous Inertia

Power systems are facing some tremendous challenges for the next decades to come. While dealing with an ageing infrastructure and an ever increasing demand for electric power, the projected increase of electricity generation coming from renewable energy sources will put an even higher stress to the already highly loaded power systems. From a system perspective, renewable electricity generation behaves quite differently from traditional, centralized generation facilities equipped with synchronous generators. Contrary to these generators, most of the renewable energy units do not contribute to the total inertia perceived by the system. This inertia is often considered as one of the vital system parameters upon which the synchronized operation of current day power systems is based. It determines the frequency response with respect to inequalities in the overall power balance. The lower the inertia, the more nervous the grid frequency reacts on abrupt changes in generation and load patterns. As it can be expected that more and more conventional power plants will be replaced by renewable energy generation, such as photovoltaic installations and wind farms, the power system will evolve to a system that will have to be less dependent on this physical inertia. New approaches to control the grid and its components are therefore required. This work covers the complete transition from a traditional power system towards an inertialess, converter based system. The focus lies in understanding the role of synchronous inertia and to provide potential pathways to improve overall system behaviour. To this end, both the quantification and measurement of inertia, together with its impact on the different forms of power system stability, are assessed in detail. Furthermore, distinct control strategies for low inertia systems as a whole, as well as for the provision of so-called ‘virtual inertia’ by renewable energy sources, are presented and evaluated. By applying these advanced controllers to deliver virtual inertia, the use of the otherwise masked (kinetic) energy stored in converter connected units is facilitated in order to improve system stability. Finally, also future approaches for the operation and control of large-scale power systems with zero synchronous inertia are given.status: publishe

The Relevance of Inertia in Power Systems

© 2015 Elsevier Ltd. The inertia of today's power system decreases as more and more converter connected generation units and load are integrated in the power system. This results in a power system which behaves differently from before which causes concerns for many grid operators. Therefore, a detailed study is needed to investigate the relevance of this inertia in the operation, control and stability of the system. Moreover, a new definition of the term system inertia is necessary since is it expected that in the future also the renewable electricity generation units will deliver the so-called virtual (synthetic) inertia. In this paper a review of the research related to inertia in a power system is given. Both the challenges as the solutions from an operator point of view to control a system with low inertia are discussed. Also a new definition of inertia is proposed to incorporate the different forms of inertia which are each described in more detail. From recent studies, it can be concluded that the influence of reduced inertia on frequency stability is generally considered as the main challenge for system operators, but with the additional measures listed in this paper, this impact can be mitigated.publisher: Elsevier articletitle: The relevance of inertia in power systems journaltitle: Renewable and Sustainable Energy Reviews articlelink: http://dx.doi.org/10.1016/j.rser.2015.11.016 content_type: article copyright: Copyright © 2015 Elsevier Ltd. All rights reserved.status: publishe

Grid Inertia and Frequency Control in Power Systems with High Penetration of Renewables

With increasing power generation out of renewable energy sources, there is a rising interest to investigate their impact on the power system and its control. In this paper, both the impact on frequency control and the capability to deliver frequency support by renewables is presented. A test grid is used to also investigate the variation of system inertia as a function of time. It is shown that by integrating renewables in the generation mix, the frequency support deteriorates, but through additional control, the frequency support can be improved. Finally the control of an inertialess grid is shortly described and some recommendations for future research are given.status: publishe

Penetration of renewables and reduction of synchronous inertia in the European power system - Analysis and solutions

info:eu-repo/semantics/publishe

Configurations and Earthing of HVDC Grids

HVDC grids are considered to be essential building blocks for the future upgrade of the existing AC power system and as a means to transport the expected massive amounts of renewable energy from remote sources to the load centers. HVDC systems exist for over 50 years, yet meshed DC grids do not exist so far. For point-to-point HVDC connections, there is a certain freedom in choosing the configuration and earthing scheme. For a grid, different converter arrangements and earthing schemes can be considered. The choices made will influence how the grid will look like, the components in the grid and their rating, the operating principles, the protection philosophy, the degree to which the grid is extensible and the overall reliability and inherent redundancy. Clearly, it will influence investment and operating costs as well. This paper provides a qualitative overview of potential grid configurations for DC grids (symmetrical monopole, asymmetrical monopole, bipolar schemes, with and without metallic return and combined systems). The possible earthing options for a meshed HVDC grid are part of this discussion. The extensibility and reliability of the HVDC grid are specifically dealt with.status: publishe

Damping Controller Design of TCSC Based on Wide-Area Monitoring and Supplement Torque Components

In this paper, the effectiveness of a Thyristor Controlled Series Capacitor (TCSC) using wide-area measurements to damp oscillations is considered. Based on a small-signal stability analysis of a single-machine infinite bus system with TCSC, a detailed theoretical framework is developed to design a Power Oscillation Damping (POD) controller modulated by a remote input signal. Phasor Measurement Units (PMUs) are used to measure real-time remote signals and transfer them to the TCSC stability control loop. The optimal controller design of the TCSC based on the supplement torque components is determined. Test cases show the improvement of the small-signal stability by using a remote control signal instead of a local one. Furthermore, the results demonstrate the practical application capability of wide-area measurements for the improvement of power system stability. © 2012 IEEE.status: publishe

Overview of Grounding and Configuration Options for Meshed HVDC grids

This paper provides an overview and comparison of the possible grounding and configuration options for meshed HVDC grids. HVDC grids are expected to play a key role in the development of future power systems. Nevertheless, the type of grounding and the base configuration for the grid have not yet been determined. Various studies related to multiterminal HVDC or meshed HVDC grids often assume one specific configuration and grounding scheme and take it for granted. However, since a large number of options exist, an overview is needed to balance the pros and cons. In this paper, the influence of the different grounding options on fault behavior is investigated for point-to-point connections. Furthermore, the impact of the grounding type on the system fault behavior is investigated with electromagnetic transient simulations. Next, the suitability of a configuration to serve as a base configuration in a meshed dc grid is investigated and compared in terms of extensibility and flexibility. In this evaluation, the grounding type, the number, and location of grounding points in a grid are considered as well. Finally, an overview of the most important conclusions is given in a summarizing table.status: publishe