The extensive use of grid-connected power electronics converters in the most different conditions, e.g., grid voltage quality, power level and grid codes, requires a robust synchronization method in order to properly feed other converter controllers with reliable and exact information, namely the phase-angle and the magnitude of the grid voltage. The grid phase-angle is a vital variable used in almost any single- or three-phase converter. The paper proposes a synchronizer based on the Least Squares approach: using the sampled grid voltages to fit a straight line corresponding to the grid phase-angle estimation. An extensive set of simulation results, including comparative results with three other methods, covering steady state and transient conditions, is provided and demonstrates the feasibility of the proposed method. Also, a set of experimental results, obtained with a field programmable gate array platform, complements the validation of the synchronizer and its very good performance in all conditions.

The doubly fed induction generator is particularly appropriate to be used in wind power generation systems. However, in weak grids its stator connection to unbalanced or distorted voltages imposes low frequency and high amplitude rotor current harmonics. Also, the grid side converter must deal with the same voltage conditions. The paper addresses the first issue presenting a voltage harmonics controller in the dq reference frame to be included in the high dynamics rotor current controller. Simulation and experimental results demonstrate the performance of the proposed controller imposing a sinusoidal input current.

Looking toward the future, governments around the world have started to change their energy mix due to climate change. The new energy mix will consist mainly of Inverter-Based Resources (IBRs), such as wind and solar power. This transition from a synchronous to a non-synchronous grid introduces new challenges in stability, resilience, and synchronization, necessitating advanced control strategies. Among these, Grid-Forming (GFM) control techniques have emerged as an effective solution for ensuring stable operations in microgrids and large-scale power systems with high IBRs integration. This paper presents a systematic review of GFM control techniques, focusing on their principles and applications. Using the PRISMA 2020 methodology, 75 studies published between 2015 and 2025 were synthesized to evaluate the characteristics of GFM control strategies. The review organizes GFM strategies, evaluates their performance under varying operational scenarios, and emphasizes persistent challenges like grid stability, inertia emulation, and fault ride-through capabilities. Furthermore, this study examines real-world implementations of GFM technology in modern power grids. Notable projects include the UK’s National Grid Pathfinder Program, which integrates GFM inverters to enhance stability, and Australia’s Hornsdale Power Reserve, where battery energy storage with GFM capabilities supports grid frequency regulation.

Grid-connected voltage source converters using an LCL filter offer reduced harmonics in the grid current. The system modeling results in a multivariable system with cross coupling. Additionally, the system contains three state-variables instead of the one occurring in the case of grid connection using only one inductance. All the three variables must be measured or estimated. Also, the LCL filter has a resonant frequency that can cause unstable behavior. This variable resonant frequency is usually considered using a damping resistor or active damping. The main purpose of the paper is to present a methodology to design a current controller based on the concept of a controller in the complex domain. The complex controller is obtained using the pole placement method and it uses a state observer in order to only measure the grid current as state variable. The simulation results presented clearly demonstrate the validity of the design approach.