LCL-type grid-connected inverters face problems including complex modeling, sampled current distortion from harmonics and negative-sequence components, and reduced control accuracy of conventional deadbeat predictive current control (DPCC) due to its heavy reliance on precise system parameters. To solve these issues, this paper proposes a model-free DPCC (MF-DPCC) using an adaptive-gain extended state observer (AGESO). Firstly, an ultra-local model is established to avoid dependence on accurate mathematical models. Secondly, an AGESO is designed to overcome conventional ESO drawbacks (initial differential peaking, inflexible bandwidth tuning, and tracking-noise immunity trade-off) by adopting adaptive gains to real-time estimate the ultra-local model’s lumped disturbance and state variables. Finally, a double second-order generalized integrator (DSOGI) purifies sampled currents and extracts fundamental positive-sequence components, reducing harmonic disturbance on the AGESO, allowing for higher bandwidth operation without excessive noise amplification, and indirectly enhancing resonance suppression by including LCL resonance-induced disturbance in the lumped term.
The proliferation of Inverter-Based Resources (IBRs) necessitates the enhancement of control systems to ensure dependable operation, particularly in suboptimal grid conditions. Conventional control methods, such as Phase-Locked Loop (PLL)-based Grid-Following (GFL) and droop-based Grid-Forming (GFM) strategies, often exhibit suboptimal performance under substantial grid disturbances. This paper introduces a novel Model Predictive Universal Control (MPUC) scheme for a single-stage three-phase inverter that effectively integrates both Grid-Forming (GFM) and Grid-Following (GFL) characteristics. The MPUC is designed with a cascaded predictive architecture, wherein the outer loop uses Finite-Control-Set Model Predictive Control (FCS-MPC) for power and voltage regulation, while the inner loop uses Continuous-Control-Set Model Predictive Control (CCS-MPC) for current tracking. The methodology includes a delay-compensation mechanism and a dynamic virtual impedance loop, aimed at improving the feasibility of digital implementation and stabilizing Grid-Forming (GFM) systems. The proposed MPUC is thoroughly assessed, compared with conventional dual-loop PI and droop control methodologies, in MATLAB/Simulink across a range of challenging conditions, including balanced and unbalanced voltage sags and frequency fluctuations. The simulation results indicate a 60% reduction in settling time, a decrease in Total Harmonic Distortion (THD) of the grid current from 4.8% to 2.0% under non-linear loads, as well as a consistent fault ride-through capability. The MPUC provides a cohesive and efficient strategy for enhancing the resilience of next-generation power systems primarily governed by power electronic converters.
M. Bou-Rabee, Mayar Abdelaziz· Clean Energy Science and Tec...· 0 citations
Dual-Quadrature Signal Generator (D-QSG) based Phase lock loop (PLL) has been recently proposed to handle the nonideal grid voltage conditions. However, selecting the parameter for D-QSG based controller has been a great challenge, especially for higher-order systems. Inappropriate parameter selection tends to increase settling time both in terms of amplitude as well as harmonics attenuation. Hence, in the proposed work, the main focus is on parameter selection to achieve a faster response. Here, a fourth-order Quasi-Synchronous Generator has been realized by cascading the two nonidentical second order generalized integrators (NISOGIs). Furthermore, the parameters of both the NISOGIs are selected in such a way that gives a faster envelope around the 2\% settling time threshold in 24.4 ms. This method provides a more condensed distance within a Fourth-Order transfer function's poles, which eventually results in a faster reaction time. A suggested method has been used to regulate an EV charger during harmonics and voltage sag/swell instead of interfering with regular operation. Furthermore, the EV charger can readily adjust the level of active and reactive power in accordance with the established benchmarks while compensating for load harmonics. Both MATLAB/Simulink and Real-time platform provided by OPAL-rt prove the effectiveness of this approach.
Gaurav Yadav, Sudhanshu Mittal, Vineet Kumar et al.· Turkish Journal of Electrica...· 0 citations
This paper aims to address stability issues from dynamic short-circuit ratio (SCR) variations caused by high distributed energy penetration. The limitations of soft open points using single control strategies, which are challenged by varying grid strengths, are overcome and severe transients experienced during direct control mode switching are mitigated.
An adaptive smooth-switching control strategy based on dynamic SCR identification is proposed. First, small-signal models under two control modes are established, and the stable operating boundaries are analyzed. Second, a nonintrusive impedance identification method using secondary-side virtual disturbance is introduced for real-time SCR estimation. Finally, continuous phase angles and current references during transitions are ensured by a switching mechanism incorporating phase pre-synchronization and state tracking.
Simulation and experimental results demonstrate that real-time SCR variations are accurately identified by the proposed method. Disturbance-free, zero-deviation smooth switching between grid-following and grid-forming modes during transitions across strong and weak grids is enabled, whereby severe voltage/current transients and power fluctuations are effectively eliminated.
The need for extra hardware injection is eliminated by the nonintrusive SCR identification via virtual disturbance. Furthermore, combined with the pre-synchronization loop, an active, impact-free transition mechanism is provided, by which the adaptive support capability and operational robustness of flexible distribution networks are significantly enhanced.
Yutian Zhang, Fan Xie, Bo Zhang et al.· Circuit world· 0 citations
Three-phase grid-tied inverters built around an LCL filter exhibit two intertwined difficulties under weak-grid conditions: resonance-driven instability and inadequate harmonic rejection. This paper develops a joint tuning procedure in which a quasi-proportional-resonant (Q-PR) current regulator is paired with capacitor-current feedback acting as active damping (CCF-AD). The model retains the full third-order LCL dynamics together with the 1.5-sample computation delay of the digital controller, all expressed in the stationary alpha-beta frame. Filter component values are selected for a 10 kW / 750 V / 10 kHz prototype, yielding an LCL resonance near 2.43 kHz. Two candidate gain pairs are then put forward—one (Kp = 0.8, Kr = 80) biased toward fast transient response and the other (Kp = 0.5, Kr = 150) biased toward fundamental tracking accuracy. After comparing their gain and phase margins in the frequency domain, time-domain sweeps over Kp, Kr, and the equivalent grid inductance Lg map out THD, step overshoot, and the onset of instability. An apparently paradoxical result emerges: the parameter set with the larger strong-grid gain margin (6.29 dB versus 3.10 dB) is the first to lose stability when the grid becomes weak, failing already at Lg approximately 22 mH while the other set survives until approximately 25 mH. The mechanism turns out to be straightforward—the resonance migrates downward as Lg grows and eventually crosses into the loop bandwidth—and yields a quantitative robustness rule for Q-PR tuning when the line impedance is uncertain.
Shao-Hua Liu, Zhi-Hao Jiang· 2026 5th International Confe...· 0 citations
In order to address the resonance risk and harmonics suppression issues in LCL-type active power filters (APFs) under distorted background grid voltage conditions, an improved harmonic compensation strategy is proposed in this paper which integrates capacitor current feedback (CCF) active damping, multiple second-order generalized integrator (MSOGI) harmonic extraction, and disturbance observer-proportional-integral (DOB-PI) composite control algorithms. First, CCF active damping is used to suppress the resonance peak of the LCL filter, and a first-order equivalent model is established in the target harmonic frequency range. Then, the 5th, 7th, and 11th harmonic components are accurately extracted by the MSOGI and are treated as lumped disturbances. Finally, a low-order DOB is adopted for real-time estimation and feedforward compensation, while the PI controller is used to eliminate the residual steady-state error. For performance verification, MATLAB/Simulink simulation results are also provided and the results have verified the effectiveness of the proposed method in specific harmonic suppression and grid-connected power quality improvement.
Jiang-Jian Wang, Bin Wang, Hui Zhang et al.· 2026 5th International Confe...· 0 citations
With the widespread adoption of voltage-source converters for grid-connected new energy power generation, the transient stability of VSCs under high penetration of new energy has become a key issue in the construction of modern power systems. Grid-following (GFL) and grid-forming (GFM) controls each have their applicable scenarios and inherent limitations. Traditional hybrid synchronous control uses fixed parameters, making it difficult to adapt to complex and variable grid conditions. Therefore, this paper proposes a control method suitable for an adaptive hybrid synchronous architecture with grid-following and grid-forming dual characteristics, employing a model predictive control strategy to achieve dynamic adjustment of GFL and GFM control ratios in both the synchronization loop and the voltage loop. A simulation model was built in PSCAD/EMTDC to verify the effectiveness and adaptability of the proposed control method under various transient conditions, such as load changes and voltage sags. The simulation results indicate that the method can effectively suppress system frequency and voltage fluctuations, enhance the transient stability of VSCs, and provide a feasible control reference for practical engineering applications.
Guiyuan Li, F. Peng, Yinsheng Su et al.· Electronics· 0 citations
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