Ulaş Karaağaç

E-mail

ulaskar@metu.edu.tr

Department

Department of Electrical and Electronics Engineering

Theoretical Examination of Small-Signal Impedance Models of Inverter-Based Resources Meng, Lei; Karaağaç, Ulaş; Chan, Ka Wing; Ghafouri, Mohsen; Mahseredjian, Jean (2025-01-01) Various impedance modeling methods have been developed in different reference frames for the impedance-based stability assessment (IBSA) of inverter-based resources (IBRs). In practice, these impedance models are extracted...
Computationally Efficient Impedance Scanning Approach for Inverter-based Resources Ouyang, Chenxi; Furlaneto, Renan M.; Meng, Lei; Jacobs, Keijo; Xue, Tao; Karaağaç, Ulaş; Mahseredjian, Jean (2024-01-01) Impedance-based stability assessment (IBSA) is an effective method to study sub-synchronous control interaction (SSCI) with inverter-based resources (IBRs) in modern power systems. An IBR's required frequency-dependent imp...
State-Space Models for Control Interaction Analysis of DFIG and FSC Wind Parks Kim, Jisoo; Mahseredjian, Jean; Karaağaç, Ulaş; Lesage-Landry, Antoine; Grilo Pavani, Ahda P.; Kim, Chul-Hwan (2024-01-01) This paper presents state-space models for both doubly-fed induction generator (DFIG) and full-scale converter (FSC)-based wind parks (WPs) that can be used to investigate the WP control interaction (CI) problems. The pres...
Analysis of the Influence of Grid Forming Control on Power System Stability Cai, Lijun; Karaağaç, Ulaş; Meng, Xiaogang (2024-01-01) This paper focuses primarily on the impact of phase-locked-loop (PLL) in grid-forming control on power system oscillations and their participation levels. It highlights the determination of PLL parameter ranges for ensurin...
Analysis of the Influence of Grid Forming Control on Power System Oscillations in Large Power Systems Cai, Lijun; Hou, Yanjin; Karaağaç, Ulaş (2024-01-01) This paper focuses on the role of Virtual Synchronous Generator (VSG) control in mitigating oscillation instabilities, which are critical in power systems with high renewable penetration. Through modal analysis and time-do...
A combined <i>dq</i>-MIMO and sequence-SISO impedance-based stability assessment scheme for IBR interfaced system Meng, Lei; Xue, Tao; Karaağaç, Ulaş; Cai, Lijun (2023-11-01) The electromagnetic transient (EMT)-type impedance scanning methods conducted in positive sequence domain and dq-frame (p-scan and dq-scan, respectively) have been widely used for identifying inverter-based resource (IBR) ...
Solid-state transformer modelling in power flow calculation Javid, Zahid; Karaağaç, Ulaş; Kocar, Ilhan; Holderbaum, William (2023-11-01) This article proposes a novel Solid-State Transformer (SST) power flow (PF) model which is implemented with Modified Augmented Nodal Analysis (MANA) formulation using Newton-Raphson (NR) algorithm. Any network topology can...
Unified Power Flow Solver for Hybrid AC/DC Distribution Networks Javid, Zahid; Xue, Tao; Karaağaç, Ulaş; Kocar, Ilhan (2023-10-01) Hybrid ac/dc distribution grids are gaining popularity due to their potential to conflate the benefits of both ac and dc grids. However, the complex structure of these grids imposes new challenges in power flow (PF) calcul...
DC grid load flow solution incorporating generic DC/DC converter topologies Javid, Zahid; Karaağaç, Ulaş; Kocar, Ilhan; Xue, Tao (2023-10-01) This research proposes a load flow (LF) solver with DC/DC converter models for DC distribution. The solver is based on modified-augmented-nodal-analysis (MANA) formulation and is implemented with the Newton-Raphson (NR) al...
A new stationary frame multi-input multi-output EMT-level frequency scanning method for inverter based resources Meng, Lei; Karaağaç, Ulaş; Ghafouri, Mohsen; Stepanov, Anton; Mahseredjian, Jean (2023-10-01) Impedance-based stability analysis (IBSA) is an effective method to identify subsynchronous interaction (SSI) problem between the inverter-based resources (IBRs) and series compensated or weakly tied AC grids. The electrom...

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