Dynamic Effect of Input-Voltage Feedforward in Three-Phase Grid-Forming Inverters -Berg, Matias; Roinila, Tomi (2020)-Electrical Engineering, Tampere University, 33720 Tampere, Finland; tomi.roinila@tuni.fi

 ABSTRACT

Grid-connected and grid-forming inverters play essential roles in the utilization of renewable energy. One problem of such a converter system is the voltage deviations in the DC-link between the source and the inverter that can disrupt the inverter output voltage. A common method to prevent these voltage deviations is to apply an input-voltage feedforward control. However, the feedforward control has detrimental effects on the inverter dynamics. It is shown that the effect of the feedforward in the input-to-output dynamics is not ideal due to the delay in the digital control system. The delay affects the input-to-output dynamics at high frequencies, and only a minor improvement can be achieved by low-pass filtering the feedforward control signal. Furthermore, the feedforward control can remarkably affect the inverter input admittance, and therefore, impedance-based stability problems may arise at the DC interface. This paper proposes a method based on linearization and extra element theorem to model the effect of the feedforward control in the inverter dynamics. Experimental measurements are shown to demonstrate the effectiveness of the proposed model. 

 LINK :https://trepo.tuni.fi/handle/10024/217417

Design and Implementation of New Oscillating Power Compensator With Improved Control Method Applied to Single-Phase Solar Inverter Pichan, Mohammad; Mousavi, Ameneh; Hafezi, Hosein; Kianifar, Ali (2025-07-13)

 

Design and Implementation of New Oscillating Power Compensator With Improved Control Method Applied to Single-Phase Solar Inverter Pichan, Mohammad; Mousavi, Ameneh; Hafezi, Hosein; Kianifar, Ali (2025-07-13) 

ABSTRACT

 Single-phase power systems inherently exhibit second-harmonic power oscillations, which can degrade photovoltaic (PV) system performance by reducing efficiency, shortening panel lifespan, and increasing AC current harmonic distortion. Conventional compensation techniques often rely on the main inverter topology, require additional passive components, or involve complex control strategies with limited robustness. This paper proposes a fully independent parallel compensator, implemented as a voltage-controlled current source, to effectively suppress PV current ripple. A hybrid control strategy is introduced, combining a proportional-resonant (PR) controller for steady-state error elimination with a Dead-Beat (DB) controller to ensure fast dynamic response. Additionally, a robust LMI-based PR controller is designed to enhance system performance under varying operating conditions. Simulation results demonstrate that the proposed system reduces current ripple from 10 to 0.5 A, offering a simple, efficient, and inverter-independent solution for PV ripple compensation.

SEE FULL ARTICLE: https://trepo.tuni.fi/handle/10024/229699

Hardware-in-the-Loop Methods for Stability Analysis of Multiple Parallel Inverters in Three-Phase AC Systems Alenius, Henrik; Roinila, Tomi; Luhtala, Roni; Messo, Tuomas; Burstein, Andrew; de Jong, Erik; Fabian, Alejandra (2020)

Hardware-in-the-Loop Methods for Stability Analysis of Multiple Parallel Inverters in Three-Phase AC Systems Henrik Alenius , Member, IEEE, Tomi Roinila , Member, IEEE, Roni Luhtala , Member, IEEE, Tuomas Messo , Member, IEEE, Andrew Burstein, Member, IEEE, Erik de Jong, Senior Member, IEEE, and Alejandra Fabian

Abstract—Modern electric distribution systems typically contain several feedback-controlled parallel inverters that together form a complex power distribution system. Consequently, a number of issues related to stability arise due to interactions among multiple inverter subsystems. Recent studies have presented methods where the stability and other dynamic characteristics of a paralleled inverter system can be effectively analyzed using impedance measurements. This article presents implementation techniques for comprehensive online stability analysis of grid-connected paralleled inverters using power hardware-in-the-loop measurements based on an OPAL-RT real-time simulator. The analysis is based on simultaneous online measurements of current control loop gains of the inverters and the grid impedance, and aggregated terminal admittance measurements of the inverters. The analysis includes the measurement of the inverters’ aggregated output impedance, inverters’ loop gains, global minor loop gain, and grid impedance. The presented methods make it possible to rapidly evaluate the system on both global and local levels in real time, thereby providing means for online stability monitoring or adaptive control of such systems. Experimental measurements are shown from a high-power energy distribution system recently developed at DNV GL, Arnhem, The Netherlands.

SEE FULL ARTICLE WEB : https://trepo.tuni.fi/handle/10024/217660

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