The ongoing modernization of the distribution grid involves the high penetration of power electronics (PE). These PE-interfaces are utilized to integrate PV systems, energy storage systems, electric transportation, etc. Microgrids appear as an attractive alternative for enabling an organized implementation of PE-dominated grids which could provide a more efficient, flexible, and resilient operation.

There are still many challenges to accelerate the deployment of microgrids. Two of the most important technical challenges are stability and optimal control systems for microgrids. First, the different features of PE-dominated grids bring new instability issues that cannot be classified in the classical stability e.g., the so-called converter-driven stability which is the dynamic interaction between the control system in PE-interfaces and the grid. Optimal controllers are needed especially in microgrids in island mode and optimal energy management.

CINELDI has contributed to the understanding and mitigating of the converter-driven stability in microgrids. For example, a novel apparent impedance-based adaptive control was proposed [1]. An impedance-based approach is used to improve stability in microgrids in island mode in [2], [3] [4]. Moreover, for helping to understand the complex dynamics involved between converters and distribution grids, a reduced order model was proposed in [5]. This new modeling approach can assist to evaluate the stability in more complex grids with many PE-interfaces. A virtual oscillator that can improve synchronization properties but at the expense of voltage quality was also proposed in [6]. Besides, optimal management of power quality for microgrids in island mode was also proposed in [7]. In the optimal controllers, a model predictive control (MPC) for optimal energy management was proposed in [8]. Uncertainties are systematically incorporated into the MPC problem via adaptive chance-constraints.

There is a great need for tools to analyse the converter-driven stability in distribution grids. CINELDI results have contributed to developing new models and methods (e.g. reduce order models [5] and impedance-based adaptive controllers [1]) that can provide tools for anticipating stability issues in the future distribution grid.

Selected publications from CINELDI:

  1. F. Gothner, R. E. Torres-Olguin, J. Roldan-Perez, A. Rygg, and O.-M. Midtgard, "Apparent Impedance-Based Adaptive Controller for Improved Stability of a Droop-Controlled Microgrid", IEEE Trans. Power Electron., vol. 36, no. 8, pp. 9465–9476, Aug. 2021, doi: 10.1109/TPEL.2021.3050615.
  2. F. Göthner, O.-M. Midtgård, R. Torres-Olguin, and J. Roldan-Perez, "Virtual Impedance Design for Power Quality and Harmonic Sharing Improvement in Microgrids," in 2019 20th Workshop on Control and Modeling for Power Electronics (COMPEL), Jun. 2019, pp. 1–7. doi: 10.1109/COMPEL.2019.8769698.
  3. C. Li, M. Molinas, O. B. Fosso, N. Qin, and L. Zhu, "A Data-driven Approach to Grid Impedance Identification for Impedance-based Stability Analysis under Different Frequency Ranges," in 2019 IEEE Milan PowerTech, Milan, Italy, Jun. 2019, pp. 1–6. doi: 10.1109/PTC.2019.8810402.
  4. W. Zhou et al., "A Robust Circuit and Controller Parameters’ Identification Method of Grid-Connected Voltage-Source Converters Using Vector Fitting Algorithm," IEEE J. Emerg. Sel. Topics Power Electron., vol. 10, no. 3, pp. 2748–2763, Jun. 2022, doi: 10.1109/JESTPE.2021.3059568.
  5. F. Gothner, J. Roldan-Perez, R. E. Torres-Olguin, and O.-M. Midtgard, "Reduced-Order Model of Distributed Generators With Internal Loops and Virtual Impedance," IEEE Trans. Smart Grid, vol. 13, no. 1, pp. 119–128, Jan. 2022, doi: 10.1109/TSG.2021.3120323.
  6. M. Melby, M. Molinas, and O. Fosso, "Impact of Virtual Oscillator Control on the instantaneous properties of VSC output voltage in distorted island grids," in IECON 2019 - 45th Annual Conference of the IEEE Industrial Electronics Society, Lisbon, Portugal, Oct. 2019, pp. 3995–4000. doi: 10.1109/IECON.2019.8926669.
  7. F. Gothner, J. Roldan Perez, R. Torres, and O.-M. Midtgard, "Harmonic Virtual Impedance Design for Optimal Management of Power Quality in Microgrids," IEEE Trans. Power Electron., vol. 36, no. 9, pp. 10114–10126, Sep. 2021, doi: 10.1109/TPEL.2021.3065755.
  8. J. P. Maree, S. Gros, and V. Lakshmanan, "Low-complexity Risk-averse MPC for EMS," in 2021 IEEE International Conference on Communications, Control, and Computing Technologies for Smart Grids (SmartGridComm), Aachen, Germany, Oct. 2021, pp. 358–363. doi: 10.1109/SmartGridComm51999.2021.9632329.