Droop-based Co-ordination of Grid-Forming and Grid-Following Inverters Ensuring Stability in a Microgrid Riaz, Nida; Peltonen, Lasse; Repo, Sami; Järventausta, Pertti (2025)

 Droop-based Co-ordination of Grid-Forming and Grid-Following Inverters Ensuring Stability in a Microgrid

Riaz, Nida; Peltonen, Lasse; Repo, Sami; Järventausta, Pertti (2025)

Abstract -This paper presents the droop-based co-ordination for active and reactive power-sharing between grid-forming (GFM) and grid-following (GFL) inverters. A 12 MVA inverter-based microgrid with two photovoltaic (PV) systems, 1 km apart is simulated to analyze the impact of different inverter control strategies on power-sharing and microgrid’s frequency response. Three simulation cases are studied for different combinations of GFM and GFL inverters, keeping the total PV headroom same (4 MVA) for regulation in all cases. Two grid-supporting GFM units (2 MVA headroom on each unit) in parallel operation results in 61% RoCoF reduction and 0.54 Hz less frequency nadir as compared to the case when one grid-supporting GFM operates in parallel with a grid-supporting GFL unit. When a GFL unit is operating together with a GFM unit, the choice of droop coefficients, inverter control mode and headroom capacity allocation plays a crucial role in overall frequency response. A grid-supporting GFM unit (4 MVA headroom capacity) in parallel with a grid-feeding GFL unit provides comparatively improved damping and frequency response with 39% reduction in RoCoF and 0.42 Hz improvement in the frequency nadir as compared to the case when both GFM and GFL units in parallel regulate the frequency.

SEE FULL ARTICLE : https://trepo.tuni.fi/handle/10024/231494

Adaptive Grid Forming Control of STATCOM to Improve DC Dynamics in Hybrid AC-DC Microgrid Hikmat Basnet, Henrik Alenius, Tomi Roinila-Department of Electrical Engineering Tampere University Tampere, Finland

 Adaptive Grid Forming Control of STATCOM to Improve DC Dynamics in Hybrid AC-DC Microgrid Hikmat Basnet, Henrik Alenius, Tomi Roinila Department of Electrical Engineering Tampere University Tampere, Finland

 ABSTRACT 

A grid-forming static synchronous compensator (STATCOM) is a power electronic device that regulates voltage, provides active and reactive power support, and stabilizes power systems by mimicking the dynamic behavior of traditional synchronous machines. When integrated with an energy storage system (ESS) from a DC microgrid, it ensures efficient power exchange and enhances system resilience to disturbances. By maintaining the DC-link voltage and synchronizing with the AC grid, a grid-forming STATCOM plays a pivotal role in stabilizing both AC and DC subsystems. However, challenges such as dynamic AC grid impedance variations, transient power fluctuations, and the poor adaptability of conventional controllers can lead to voltage instability and oscillatory behavior, particularly in weak grid conditions. This paper presents a novel adaptive control strategy for a grid-forming STATCOM that dynamically adjusts control parameters in response to real-time AC grid impedance measurements obtained through a broadband perturbation technique. By adaptively tuning the damping coefficient in the virtual synchronous machine (VSM) framework, the proposed method ensures robust voltage regulation, mitigates oscillations, and improves transient performance at the DC-link. Experimental results validate the effectiveness of the proposed approach, highlighting its capability to achieve stable operation under varying grid conditions and enhancing the reliability of DC microgrids.

SEE FULL ARTICLE : https://cris.tuni.fi/ws/portalfiles/portal/147398474/ICDCM_2025_Hikmat.pdf

Frequency Response Analysis of Load Effect on Dynamics of Grid-Forming Inverter Matias Berg , Tuomas Messo, Teuvo Suntio Laboratory of Electrical Energy Engineering, Tampere University of Technology, Tampere, Finland

Frequency Response Analysis of Load Effect on Dynamics of Grid-Forming Inverter Matias Berg, Tuomas Messo, Teuvo Suntio Laboratory of Electrical Energy Engineering, Tampere University of Technology, Tampere, Finland 

Abstract—The grid-forming mode of the voltage source inverters (VSI) is applied in uninterruptible power supplies and micro-grids to improve the reliability of electricity distribution. During the intentional islanding of an inverterbased micro-grid, the grid-forming inverters (GFI) are responsible for voltage control, similarly as in the case of uninterruptible power supplies (UPS). The unterminated model of GFI can be developed by considering the load as an ideal current sink. Thus, the load impedance always affects the dynamic behavior of the GFI. This paper proposes a method, to analyze how the dynamics of GFI and the controller design are affected by the load. Particularly, how the frequency response of the voltage loop gain changes according to the load and, how it can be used to the predict time-domain step response. The frequency responses that are measured from a hardware-in-the-loop simulator are used to verify and illustrate explicitly the load effect.

 SEE FULL ARTICLE : https://researchportal.tuni.fi/fi/publications/frequency-response-analysis-of-load-effect-on-dynamics-of-grid-fo/

Impedance Measurement of Megawatt-Level Renewable Energy Inverters using Grid-Forming and Grid-Parallel Converters Matias Berg1 , Tuomas Messo1, Tomi Roinila2, Henrik Alenius2 1 Electrical Energy Engineering, Tampere University of Technology, Tampere, Finland 2 Hydraulics and Automation, Tampere University of Technology, Tampere, Finland

 Impedance Measurement of Megawatt-Level Renewable Energy Inverters using Grid-Forming and Grid-Parallel Converters Matias Berg1, Tuomas Messo1, Tomi Roinila2, Henrik Alenius2 1 Electrical Energy Engineering, Tampere University of Technology, Tampere, Finland 2 Hydraulics and Automation, Tampere University of Technology, Tampere, Finland 

 Abstract—Harmonic resonance and power quality problems have been reported in grid-connected photovoltaic and wind power systems. The AC-side impedance of threephase converter is an important characteristic, which can be effectively used as a design parameter to avoid instability and excessive harmonics. A number of methods to measure the three-phase AC impedance have been reported. However, solutions for high power applications such as wind and photovoltaic converters with a power rating of several megawatts, have not been discussed. This paper introduces a new method to measure impedance from high power threephase converter. The impedance is identified by perturbing the converter first by voltage-type injection utilizing highpower grid-forming inverter, and subsequently by currenttype injection by utilizing low-power grid-parallel converter. The main benefit of the proposed setup is the possibility to measure the converter impedance online in its natural operating point both at high and low frequencies. The paper presents a proof-of-concept by validating the method using a switching model.

Medição de impedância de inversores de energia renovável de nível megawatt usando conversores formadores de rede e conversores paralelos à rede. Mathias BergThomas Messo, Tomi RoinilaHenrik Alenius 

Resumo -Problemas de ressonância harmônica e qualidade de energia têm sido relatados em sistemas de energia fotovoltaica e eólica conectados à rede. A impedância do lado CA do conversor trifásico é uma característica importante, que pode ser efetivamente utilizada como parâmetro de projeto para evitar instabilidade e harmônicos excessivos. Diversos métodos para medir a impedância CA trifásica foram relatados. No entanto, soluções para aplicações de alta potência, como conversores eólicos e fotovoltaicos com potência nominal de vários megawatts, não foram discutidas. Este artigo apresenta um novo método para medir a impedância de conversores trifásicos de alta potência. A impedância é identificada perturbando o conversor inicialmente por injeção de tensão utilizando um inversor formador de rede de alta potência e, posteriormente, por injeção de corrente utilizando um conversor paralelo à rede de baixa potência. O principal benefício da configuração proposta é a possibilidade de medir a impedância do conversor online em seu ponto de operação natural, tanto em altas quanto em baixas frequências. O artigo apresenta uma prova de conceito validando o método por meio de um modelo de chaveamento.

SEE FULL ARTICLE: https://researchportal.tuni.fi/fi/publications/impedance-measurement-of-megawatt-level-renewable-energy-inverter/

Overview on Grid-Forming Inverter Control Methods Peter Unruh * , Maria Nuschke *, Philipp Strauß * and FriedrichWelck-Power System Stability and Converter Technology Division, Fraunhofer Institute for Energy Economics and Energy System Technology IEE, 34119 Kassel, Germany

Concept Paper Overview on Grid-Forming Inverter Control Methods Peter Unruh * , Maria Nuschke *, Philipp Strauß * and FriedrichWelck Power System Stability and Converter Technology Division, Fraunhofer Institute for Energy Economics and Energy System Technology IEE, 34119 Kassel, Germany; friedrich.welck@sma.de

 Abstract: In this paper, dierent control approaches for grid-forming inverters are discussed and compared with the grid-forming properties of synchronous machines. Grid-forming inverters are able to operate AC grids with or without rotating machines. In the past, they have been successfully deployed in inverter dominated island grids or in uninterruptable power supply (UPS) systems. It is expected that with increasing shares of inverter-based electrical power generation, grid-forming inverters will also become relevant for interconnected power systems. In contrast to conventional current-controlled inverters, grid-forming inverters do not immediately follow the grid voltage. They form voltage phasors that have an inertial behavior. In consequence, they can inherently deliver momentary reserve and increase power grid resilience 

 SEE FULL ARTICLE : https://www.mdpi.com/1996-1073/13/10/2589