Unlike grid-following inverters (GFLIs) that serve as current sources, grid-forming inverters (GFMIs) act as voltage sources, capable of providing voltage support and inertia support to the power grid. By controlling the magnitude and angle of voltage, it is possible to achieve active (P) and reactive (Q) power transmission along the line. However, conventional algorithm such as virtual synchronous generator (VSG) exhibits coupling between P and Q loops. To address this issue, this article first establishes dynamic models for active and reactive power, which indicate that coupling becomes severe when the grid impedance or the power angle increases. Subsequently, a hybrid control method based on active disturbance rejection control (ADRC) and H∞control is proposed to decouple the P and Q loops in GFMIs. This strategy employs a data-driven H∞ controller as the inner loop for preliminary decoupling of the system, and uses ADRC control as the outer loop, with an extended state observer (ESO) to treat the undecoupled part as a disturbance for secondary decoupling of the system. As a result, the robustness of system decoupling is significantly enhanced. The decoupling performance of this controller has been verified through experiments, which demonstrates the effectiveness and superiority of this method.

Complex power electronic topologies, such as modular multilevel converter (MMC), frequently experience broadband oscillation. To reveal the theoretical mechanism, this article models MMC based on linear-time-periodic-variable (LTPV) approach and obtains analytical expression of its ac-side admittance explicitly, formulated as a six-degree polynomial fraction. Three intrinsic oscillation modes of MMC topology are then estimated, and Foster-type circuit corresponding to the impedance is synthesized, revealing the root cause of multiple oscillation modes. It is found that due to the existence of arm capacitors, MMC impedance presents multiple LC oscillations. Increasing the capacitance can mitigate the oscillation, making the output impedance close to the filter inductor of two-level converter. The derivation and analysis are extended to single-loop grid-forming control, current control, and multiple-loop control. Correctness of the impedance model and oscillation frequency estimation is verified through impedance measurement and hardware-in-the-loop test.

The integration of large-scale distributed photovoltaic (PV) units into a microgrid poses critical challenges to transient stability. Developing an effective model of distributed PV generation systems is essential for stability analysis. However, detailed modeling of individual PV units leads to prohibitive computational costs. To address this issue, this paper proposes an equivalent model for distributed PV generation systems in a microgrid. By thoroughly analyzing the PV units’ responses during the low voltage ride-through (LVRT) process, the dominant active power responses are identified, and two segmentation thresholds for clustering are analytically derived. To improve engineering applicability of the proposed clustering method, one voltage-dip-dependent segmentation threshold is approximated. Moreover, for PV units exhibiting post-fault active power ramp recovery, an additional clustering based on average pre-fault steady-state active power is introduced to better represent the dynamic behaviors of actual distributed PV generation systems. On this basis, a four-machine equivalent model is proposed, which captures key dynamic characteristics while ensuring both computational efficiency and modeling accuracy. Extensive simulations under various operating conditions and fault scenarios verify the effectiveness of the proposed equivalent model in reproducing transient behavior of distributed PV generation systems in a microgrid.

We demonstrate an approach for improving the spectral linewidth of a spin torque nano-oscillator (STNO). Using He + ion irradiation, we tune the perpendicular magnetic anisotropy (PMA) of the STNO free layer such that its easy axis is gradually varied from strongly out-of-plane to moderate in-plane. As the PMA impacts the non-linearity N of the STNO, we can, in this way, control the threshold current, the current tunability of the frequency, and, in particular, the STNO linewidth, which dramatically improves by two orders of magnitude. Our results are in good agreement with the theory for nonlinear auto-oscillators, confirm theoretical predictions of the role of the nonlinearity, and demonstrate a straightforward path toward improving the microwave properties of STNOs.

We demonstrate field and current controlled magnetodynamics in nanocontact spin-torque nano-oscillators based on orthogonal magnetic tunnel junctions. We systematically analyze the microwave properties (frequency f, linewidth Delta f, power P, and frequency tunability df/dI) with their physical origins-perpendicular magnetic anisotropy, dampinglike and fieldlike spin transfer torque (STT), and voltage-controlled magnetic anisotropy (VCMA). These devices present several advantageous characteristics: high emission frequencies (f>20 GHz), high frequency tunability (df/dI=0.25 GHz/mA), and zero-field operation (f similar to 4 GHz). Furthermore, detailed investigation of f(H, I) reveals that df/dI is mostly governed by the large VCMA [287 fJ/(V m)], while STT plays a negligible role.

We experimentally study the auto-oscillating spin-wave modes in Ni(80)Fc(20)/beta-W constriction-based spin Hall nano-oscillators as a function of bias current, strength of the in-plane applied field, and azimuthal field angle in the low-field range of 40-80 mT. We observe two different spin-wave modes: (i) a linearlike mode confined to the internal field minima near the edges of the nanoconstriction, and only weakly dependent on the bias current and the applied-field angle, and (ii) a second, lower-frequency mode with significantly higher threshold current and stronger dependence on both the bias current and the externalfield angle. Micromagnetic modeling qualitatively reproduces the experimental data and reveals that the second mode is a spin-wave bullet and that the spin Hall nano-oscillator mode hops between the two modes, resulting in a substantial increase in linewidths. In contrast to the linearlike mode, the bullet is localized in the middle of the constriction and shrinks with increasing bias current. Using intrinsic frequency doubling at zero field angle, we can reach frequencies above 9 GHz in fields as low as 40 mT, which is important for the development of low-field spintronic oscillators with applications in microwave-signal generation and neuromorphic computing.

Magnetic droplets are nontopological dynamical soli tons that can be nucleated in nanocontact based spin torque nano-oscillators (STNOs) with perpendicular magnetic anisotropy free layers. While theory predicts that the droplet should be of the same size as the nanocontact, its inherent drift instability has thwarted attempts at observing it directly using microscopy techniques. Here, we demonstrate highly stable magnetic droplets in all-perpendicular STNOs and present the first detailed droplet images using scanning transmission X-ray microscopy. In contrast to theoretical predictions, we find that the droplet diameter is about twice as large as the nanocontact. By extending the original droplet theory to properly account for the lateral current spread underneath the nanocontact, we show that the large discrepancy primarily arises from current-in-plane Zhang-Li torque adding an outward pressure on the droplet perimeter. Electrical measurements on droplets nucleated using a reversed current in the antiparallel state corroborate this picture.

For the first time, nanoporous Al2O3 templates with smoothed surface relief characterized by flattened interpore areas were used in the fabrication of Co/Pd and Co/Pt multilayers (MLs) with strong perpendicular magnetic anisotropy (PMA). Alternating gradient magnetometry (AGM) revealed perfectly conserved PMA in the Co/Pd and Co/Pt porous MLs (antidot arrays) with a ratio of remanent magnetization (Mr) to saturation magnetization (MS) of about 0.99, anisotropy fields (Ha) of up to 2.6 kOe, and a small deviation angle of 8° between the easy magnetization axis and the normal to the film surface. The sufficient magnetic hardening of the porous MLs with enhanced coercive field HC of up to ∼1.9 kOe for Co/Pd and ∼1.5 kOe for Co/Pt MLs, as compared to the continuous reference samples (∼1.5–2 times), is associated with the pinning of the magnetic moments on the nanopore edges. Application of the Stoner–Wohlfarth model for fitting the experimental M/MS(H) curves yielded clear evidence of the predominantly coherent rotation mechanism of magnetization reversal in the porous films.

We investigate how the Oersted field affects the magnetic droplet nucleation boundary in spin-torque nano-oscillators based on orthogonal spin-valve stacks with a perpendicular magnetic anisotropy Co/Ni free layer and an easy-plane anisotropy Ni80Fe20 fixed layer. The current-field nucleation boundary is determined experimentally using both microwave signal and dc resistance measurements. The Oersted field can, in principle, have an impact on droplet nucleation. This effect is considered approximately using an analytical equation for the nucleation boundary, which is extended to cover fields larger than the fixed-layer saturation field. We test the accuracy of this approach by comparing with micromagnetic simulations. Finally, we carry out a numerical fit to experimental data and find good agreement.

A dissipative magnetic soliton, or magnetic droplet, is a structure that has been predicted to exist within a thin magnetic layer when non-linearity is balanced by dispersion, and a driving force counteracts the inherent damping of the spin precession. Such a soliton can be formed beneath a nano-contact (NC) that delivers a large spin-polarized current density into a magnetic layer with perpendicular magnetic anisotropy. Although the existence of droplets has been confirmed from electrical measurements and by micromagnetic simulations, only a few attempts have been made to directly observe the magnetic landscape that sustains these structures, and then only for a restricted set of experimental parameter values. In this work we use and x-ray holography technique HERALDO, to image the magnetic structure of the [ Co/ Ni] x4 multilayer within a NC orthogonal pseudo spin-valve, for different range of magnetic fields and injected electric currents. The magnetic configuration imaged at -33 mA and 0.3 T for devices with 90 nm NC diameter reveals a structure that is within the range of current where the droplet soliton exist based on our electrical measurements and have it is consistent with the expected size of the droplet (similar to 100 nm diameter) and its spatial position within the sample. We also report the magnetisation configurations observed at lower DC currents in the presence of fields (0-50 mT), where it is expected to observe regimes of the unstable droplet formation.