Technical Impacts of High Penetration Levels of Wind Power on Power System Stability [chapter]

Damian Flynn, Zakir Rather, Atle Rygg Årdal, Salvatore D'Arco, Anca D. Hansen, Nicolaos A. Cutululis, Poul Sorensen, Ana Estanqueiro, Emilio Gómez-Lázaro, Nickie Menemenlis, Charles Smith, Ye Wang
2019 Advances in Energy Systems  
With increasing penetrations of wind generation, based on power-electronic converters, power systems are transitioning away from well-understood synchronous generator based systems, with growing implications for their stability. Issues of concern will vary with system size, wind penetration level, geographical distribution and turbine type, network topology, electricity market structure, unit commitment procedures, and other factors. However, variable-speed wind turbines, both onshore and
more » ... ted offshore through DC grids, offer many control opportunities to either replace or enhance existing capabilities. Achieving a complete understanding of future stability issues, and ensuring the effectiveness of new measures and policies, is an iterative procedure involving portfolio development and flexibility assessment, generation cost simulations, load flow and security analysis, in addition to the stability analysis itself, while being supported by field demonstrations and real-world model validation. Wind energy is being rapidly integrated into many power systems across the globe, with a total installed capacity of 370 GW, and with 51 GW added in 2014 alone 1 . As the penetration of wind generation increases, the impact on power system dynamics is becoming increasingly apparent, and will become a more integral part of system planning and renewables integration studies 2 . Historically, power systems have been based around large synchronous generators connected to a strongly meshed transmission network, with the dynamic characteristics of such systems being well understood. However, renewable generation, particularly in the form of wind and solar generation, is increasingly universally connected via power electronics interfaces, may well be connected to the distribution network, or weaker parts of the network, may offer new control capabilities, and, of course, is subject to the variability and uncertainty associated with local and regional weather patterns 3,4 . The time variability and non-dispatchable nature of wind generation may pose substantial challenges, particularly at higher levels of penetration, including an increase in regulation costs and incremental operating reserves, but can also lead to increased opportunities for energy storage, demand-side response, cross-border interconnections and other flexibility measures. In addition to onshore wind power installations, which are already saturating in some countries, such as Denmark, a large number of offshore wind power plants have been developed recently, and this trend is likely to continue into the future 5 . Increasingly, such plants will be sited further offshore, in the form of larger wind farms, and will be connected onshore either individually through a HVDC connection, or as part of an interconnected DC grid 6 . Wind generation, by its mere presence, does not necessarily worsen the stability of a system, but it does change its characteristics, and through intelligent co-ordination of power electronic based controls, system capabilities could even be enhanced in some situations 2,7 . System stability issues range from the ability to maintain generator synchronism when subject to a large disturbance (transient stability); the ability to restore steady-state conditions (voltage, current, power) after being subject to a small disturbance (small-signal stability); the ability to recover and maintain system frequency following a major generation-load imbalance (frequency stability); and the ability to maintain an acceptable voltage profile after being subjected to a disturbance (voltage stability) 8-10 . Those issues of concern for a particular system will depend on system size, wind distribution relative to the load and other generation, along with the unit commitment / economic dispatch (UC/ED) decisions and network configuration. However, they are likely to be first observed during the night or seasonal low-demand periods when instantaneous wind penetration may be high 11 , say greater than 20%, or alternatively when wind exports across a region are high, even in cases when the annual (wind) energy contribution to the system is comparatively low. So, for example, during periods of high instantaneous wind penetration, with reduced numbers of conventional (synchronous) generators online, frequency stability may be affected due to the reduction in governor response 12, 13 , and, particularly for smaller systems, by the reduction in synchronous inertia [14] [15] [16] [17] . For example, the All-Island system of Ireland would be insecure, without additional measures being taken, for approaching 30% of the year 2020 due to a lack of adequate synchronous inertia 18 , as shown in Fig. 1. Similarly, a study of the Electricity Reliability Council of Texas (ERCOT) system observed a decline in its frequency response, based on frequency event records taken over a span of four years with increased wind penetration 17 . The transient stability of a system may also be reduced when synchronous units are de-committed and replaced with wind generation connected at lower voltage levels, and hidden behind a relatively large impedance 19,20 . However, transient stability impacts are largely affected by the turbine technology. For example, a study performed by Transpower (New Zealand) reported that 'old' technology, fixed speed induction generators (FSIG), worsen the transient stability of the system, as they absorb reactive power during and after a fault, and are generally not voltage ride through (VRT) compliant 21 . On the other hand, variable speed wind turbines (doubly fed induction generators and direct drive full converters) have VRT capability, and can improve
doi:10.1002/9781119508311.ch3 fatcat:vlexpun6yfbetkt7apdo5bwdu4