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This paper presents a high-level overview of the integration of renewable energy sources (RES), primarily wind and solar, into the electric power system (EPS) in Croatia. It presents transmission system integration aspects for the particular case of this country. It explains the current situation and technical characteristics of the current conventional generation units and currently installed wind energy capacities. Based on the current situation future development scenario is determined and used to evaluate the impacts of the wide-scale integration of renewables. Grid connections aspects, power balancing, market participation, and inertia reduction aspects are considered. Furthermore, some specifics of both solar and wind integration are discussed identifying problems and potential solutions. Primarily through the provision of the inertial response of both solar and wind and through better forecasting of wind production. Finally, the outlook for the Croatian power system is given, that will most probably double its RES capacity in the coming 3-year period and a certain level of investments and changes of current operational practices will need to be provided.
Ninoslav Holjevac; Tomislav Baškarad; Josip Đaković; Matej Krpan; Matija Zidar; Igor Kuzle. Challenges of High Renewable Energy Sources Integration in Power Systems—The Case of Croatia. Energies 2021, 14, 1047 .
AMA StyleNinoslav Holjevac, Tomislav Baškarad, Josip Đaković, Matej Krpan, Matija Zidar, Igor Kuzle. Challenges of High Renewable Energy Sources Integration in Power Systems—The Case of Croatia. Energies. 2021; 14 (4):1047.
Chicago/Turabian StyleNinoslav Holjevac; Tomislav Baškarad; Josip Đaković; Matej Krpan; Matija Zidar; Igor Kuzle. 2021. "Challenges of High Renewable Energy Sources Integration in Power Systems—The Case of Croatia." Energies 14, no. 4: 1047.
Increased wind energy penetration influences the power system dynamic response to transient disturbances. Replacement of conventional production units with converter-connected wind turbines reduces natural power system inertia contained in rotational masses of synchronously connected turbine-generator units, therefore creating low-inertia power systems. Such a transition has an adverse effect on system resilience to disturbances and on the capability to maintain stable operation. This research examines the impact of high regional wind power production on system transient stability in the case of island operation of the Croatian power system. The system is divided into four geographical areas modeled as four centers of inertia with aggregated parameters. The study investigated initial transient RoCoF values in different areas for current and future wind capacity share scenarios, loading data, and primary frequency regulation settings. The modeling and scenario analysis have been performed on a detailed phasor power system model in the MATLAB/Simulink environment.
Josip Đaković; Matej Krpan; Perica Ilak; Tomislav Baškarad; Igor Kuzle. Impact of wind capacity share, allocation of inertia and grid configuration on transient RoCoF: The case of the Croatian power system. International Journal of Electrical Power & Energy Systems 2020, 121, 106075 .
AMA StyleJosip Đaković, Matej Krpan, Perica Ilak, Tomislav Baškarad, Igor Kuzle. Impact of wind capacity share, allocation of inertia and grid configuration on transient RoCoF: The case of the Croatian power system. International Journal of Electrical Power & Energy Systems. 2020; 121 ():106075.
Chicago/Turabian StyleJosip Đaković; Matej Krpan; Perica Ilak; Tomislav Baškarad; Igor Kuzle. 2020. "Impact of wind capacity share, allocation of inertia and grid configuration on transient RoCoF: The case of the Croatian power system." International Journal of Electrical Power & Energy Systems 121, no. : 106075.
Generic dynamic models of hydraulic turbines are unable to capture power oscillations phenomena originating from a torque disturbance on a single runner blade. In this paper, an improved dynamic model of a double-regulated hydraulic turbine which takes into account torque oscillations identified from draft tube pressure measurements was presented. It was experimentally identified that specific power oscillations of a bulb turbine operating with low tailwater level can be connected to cavitation-related phenomena on a single runner blade. Furthermore, it was shown that these oscillations do not originate from grid fault-induced resonance between the turbine rotor and generator, nor from the excitation system. The proposed simulation model was validated against measurement data of hydro power plant Dubrava and the validation shows good agreement between measured and simulated results.
Miljenko Brezovec; Igor Kuzle; Matej Krpan; Ninoslav Holjevac. Improved dynamic model of a bulb turbine-generator for analysing oscillations caused by mechanical torque disturbance on a runner blade. International Journal of Electrical Power & Energy Systems 2020, 119, 105929 .
AMA StyleMiljenko Brezovec, Igor Kuzle, Matej Krpan, Ninoslav Holjevac. Improved dynamic model of a bulb turbine-generator for analysing oscillations caused by mechanical torque disturbance on a runner blade. International Journal of Electrical Power & Energy Systems. 2020; 119 ():105929.
Chicago/Turabian StyleMiljenko Brezovec; Igor Kuzle; Matej Krpan; Ninoslav Holjevac. 2020. "Improved dynamic model of a bulb turbine-generator for analysing oscillations caused by mechanical torque disturbance on a runner blade." International Journal of Electrical Power & Energy Systems 119, no. : 105929.
The paper introduces, describes and analyses the specific power oscillations in hydroelectric power plant Dubrava that can appear in large bulb turbines operating with low tailwater levels. The procedure for the identification of the cause of oscillations is described and it is experimentally shown that the cause of power oscillations is a disturbance on a specific runner blade. The physical background of the cavitation-related phenomena that causes these oscillations is presented. Furthermore, it is shown that neither the automatic voltage regulator nor the transmission network disturbance is the source of oscillations, while the power system stabiliser can only partially damp them. Power oscillations reduce the average power output due to the operation in the unsteady output zone. These oscillations can cause damage to the equipment and reduce its lifespan. The effectiveness of various measures for treatment of these oscillations is discussed. A simple model for simulation of these oscillations is shown and verified against measurements.
Miljenko Brezovec; Igor Kuzle; Matej Krpan; Ninoslav Holjevac. Analysis and treatment of power oscillations in hydropower plant Dubrava. IET Renewable Power Generation 2019, 14, 80 -89.
AMA StyleMiljenko Brezovec, Igor Kuzle, Matej Krpan, Ninoslav Holjevac. Analysis and treatment of power oscillations in hydropower plant Dubrava. IET Renewable Power Generation. 2019; 14 (1):80-89.
Chicago/Turabian StyleMiljenko Brezovec; Igor Kuzle; Matej Krpan; Ninoslav Holjevac. 2019. "Analysis and treatment of power oscillations in hydropower plant Dubrava." IET Renewable Power Generation 14, no. 1: 80-89.
Power converter technology partially or fully electrically decouples the wind energy source from the grid which results in the decrease of system inertia. However, when those units participate in virtual inertial response their electromechanical dynamics become coupled to the grid electromechanical modes. To date, there were no comprehensive studies on how do different elements and parameters of a wind energy conversion system (WECS) impact its virtual inertial response provision. This is important from the standpoint of understanding the expected wind farm response during frequency containment process as well as from the standpoint of developing better inertial response controllers. In this paper we have investigated how do operating point, line-side and machine-side converter, phase-locked loop and pitch angle control impact the inertial response of the total power controlled type III WECS (DFIG) which is one of the most common wind turbine topologies used today. We show that the operating point, pitch angle control and outer loop of the machine-side converter have a visible impact on strength of the inertial response, while other elements do not and some can even be neglected in inertial response studies.
Matej Krpan; Igor Kuzle. Dynamic characteristics of virtual inertial response provision by DFIG-based wind turbines. Electric Power Systems Research 2019, 178, 106005 .
AMA StyleMatej Krpan, Igor Kuzle. Dynamic characteristics of virtual inertial response provision by DFIG-based wind turbines. Electric Power Systems Research. 2019; 178 ():106005.
Chicago/Turabian StyleMatej Krpan; Igor Kuzle. 2019. "Dynamic characteristics of virtual inertial response provision by DFIG-based wind turbines." Electric Power Systems Research 178, no. : 106005.
Adnan Secic; Matej Krpan; Igor Kuzle. Vibro-Acoustic Methods in the Condition Assessment of Power Transformers: A Survey. IEEE Access 2019, 7, 83915 -83931.
AMA StyleAdnan Secic, Matej Krpan, Igor Kuzle. Vibro-Acoustic Methods in the Condition Assessment of Power Transformers: A Survey. IEEE Access. 2019; 7 ():83915-83931.
Chicago/Turabian StyleAdnan Secic; Matej Krpan; Igor Kuzle. 2019. "Vibro-Acoustic Methods in the Condition Assessment of Power Transformers: A Survey." IEEE Access 7, no. : 83915-83931.
Wind power generation has reached a significant share in power systems worldwide and will continue to increase. As the converter-connected generation reduces the grid inertia, more and more interest has been given to exploiting the kinetic energy and controllability of variable-speed wind turbine generators (VSWTGs) for frequency support. Consequently, the grid frequency dynamics are changing. Thus, it is necessary to include the frequency response of wind power plants in the system frequency response (SFR) model. A novel approach to low-order SFR modelling of a future power system with a high share of frequency-support-capable VSWTGs has been presented. Low-order model of VSWTGs with primary frequency response and natural inertial response has been developed considering different wind turbine operating regimes and compared to the non-linear model for validation. Low-order model has been presented in a symbolic transfer function form. Model accuracy has been discussed and the impact of VSWTG parameters on frequency response has been analysed. The developed model facilitates studying power system frequency dynamics by avoiding the need for modelling complex VSWTG systems, while retaining a satisfying level of accuracy.
Matej Krpan; Igor Kuzle. Introducing low‐order system frequency response modelling of a future power system with high penetration of wind power plants with frequency support capabilities. IET Renewable Power Generation 2018, 12, 1453 -1461.
AMA StyleMatej Krpan, Igor Kuzle. Introducing low‐order system frequency response modelling of a future power system with high penetration of wind power plants with frequency support capabilities. IET Renewable Power Generation. 2018; 12 (13):1453-1461.
Chicago/Turabian StyleMatej Krpan; Igor Kuzle. 2018. "Introducing low‐order system frequency response modelling of a future power system with high penetration of wind power plants with frequency support capabilities." IET Renewable Power Generation 12, no. 13: 1453-1461.
An increased share of variable speed wind turbines reduces the inertia of the power system due to the decoupling of mechanical rotor frequency and grid frequency. In the recent years, a lot of research has been done about exploitation of the rotating mass of a wind turbine for participation in the primary frequency regulation of the power system. This paper proposes a linearized general variable speed wind turbine model for studying power system frequency changes. First, an overview of different types of wind turbines is given. Then, the mathematical model of frequency regulation capable variable speed wind turbine is linearized. Finally, a simple system frequency response (SFR) model of a power system is simulated in order to examine the influence of variable speed wind turbines on power system frequency.
Matej Krpan; Igor Kuzle. Linearized model of variable speed wind turbines for studying power system frequency changes. IEEE EUROCON 2017 -17th International Conference on Smart Technologies 2017, 393 -398.
AMA StyleMatej Krpan, Igor Kuzle. Linearized model of variable speed wind turbines for studying power system frequency changes. IEEE EUROCON 2017 -17th International Conference on Smart Technologies. 2017; ():393-398.
Chicago/Turabian StyleMatej Krpan; Igor Kuzle. 2017. "Linearized model of variable speed wind turbines for studying power system frequency changes." IEEE EUROCON 2017 -17th International Conference on Smart Technologies , no. : 393-398.
Increase of converter-connected renewable power generation such as variable-speed wind turbines (VSWTs) decreases the system inertia constant, which reduces the frequency stability of the power system. Thus, it will be necessary to include these renewables in the inertial response and primary frequency control (PFC) of future power systems. In this study, the participation of VSWTs in frequency support is studied. First, the importance of inertial response and PFC is discussed. Then, the linearised model of VSWT with inertial and primary frequency response capabilities is presented and compared against the non-linear model. Finally, this model is integrated in a system frequency response model that consists of various power plants. Different operational scenarios are simulated to investigate the impact of wind turbines with and without emulated inertia and primary frequency response on frequency stability.
Matej Krpan; Igor Kuzle. Inertial and primary frequency response model of variable‐speed wind turbines. The Journal of Engineering 2017, 2017, 844 -848.
AMA StyleMatej Krpan, Igor Kuzle. Inertial and primary frequency response model of variable‐speed wind turbines. The Journal of Engineering. 2017; 2017 (13):844-848.
Chicago/Turabian StyleMatej Krpan; Igor Kuzle. 2017. "Inertial and primary frequency response model of variable‐speed wind turbines." The Journal of Engineering 2017, no. 13: 844-848.