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Model Reference Controller (MRC) for contribution of Variable Speed Wind Generators (VSWG) in inertial response of Electrical Power System (EPS) is presented and analyzed in this paper. MRC is synthesized based on a model of Generating Unit With non-Reheat Steam Turbine (GUNRST) thus enabling VSWG to emulate GUNRST response during the initial stage of dynamic frequency response ie inertial phase. Very important property of conventional steam generating units is that its contribution to inertial phase response is independent from the initial generating power. By using MRC in VSWG it is accomplished that in most common wind speed region (3-12m/s) VSWG inertial support is almost independent from wind speed. Since in most EPSs VSWG replaces conventional steam generators, application of MRC algorithm provides that the characteristics of EPS in terms of inertial response are preserved, regardless of the growing trend of introducing VSWG. Evaluation analysis of the proposed MRC is performed on modified nine bus power system when VSWG with MRC is connected to one of the power system buses. K e y w o r d s: wind generator, inertial support, model reference controller The increase of variable speed wind generators (VSWG) in electrical power system (EPS) brings their system operation support possibilities to primary focus of interest. In order to maintain the safety and integrity of a power system, and also to maintain the frequency value within allowable range limit, continuous balance of generation and consumption is of a vital importance. Grid codes of different countries are continuously revised and their requirements are adjusted to the needs of possible participation of wind power plants in control of power system response during disturbances. Evaluation of impact assessment of wind power plants on EPS is especially important in isolated island systems [1]. Additionally, with the increase of integration rate of wind power plants the issues related to their impact on power system operation also becomes important in large interconnections. Modern EPS with integrated wind power plants implies changes in the EPS structure since wind power plants replace conventional generating units, mainly conventional thermal power plants [2,3]. Since inertia of VSWG is partially or fully decoupled from power system via electronic converter, the total power system inertia is decreased. In order to provide the inertial support of modern VSWG, several different control concepts have been proposed which can be generally grouped into: inertial control, droop control, de-loading control or their combination [4-15]. Main challenge in VSWG inertial (and droop) control is “shaping” of the response of active power delivered to the rest of the EPS as well as the speed recovery of the VSWG after the frequency disturbance. This paper presents a MRC concept that provides VSWG to “behave” as the conventional generating unit with nonreheat steam turbine (GUNRST) in the first seconds after an active power disturbance [16]. This approach provides that regardless of the higher participation of VSWG in EPS its capability in frequency stabilization during first several seconds after the power system disturbances are preserved. Further, with the proposed MRC concept it is provided that VSWG truly emulates the behavior of the conventional steam generators since inertial support, in most common wind speed region (3-12m/s), is almost independent from the wind speed hence from the initial mechanical power of wind turbine, which is very important characteristics of the conventional steam turbines. |
