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In this letter, a hybrid-type multilevel dual active bridge (HML-DAB) topology is proposed for high and ultrawide input-voltage applications. In addition, a variable-level modulation method is proposed, which can achieve full-range zero-voltage switching (ZVS) of all switches and small, uniform current stress over ultrawide input voltage. The performance of the proposed scheme is verified by experimental results.

This study details an advanced method of algorithm optimization, specifically developed for a novel reservoir computing (RC) architecture to forecast temporal information. Our physical RC is implemented using micro-electro-mechanical systems (MEMSs), ingeniously employing stiffness modulation, wherein the input is manifested as stiffness disturbances within a nonlinear resonator. We have eliminated the discretization of data that was typically required in conventional delay-based RC before it is injected into the reservoir. This allows our sensor to process natural signals directly, significantly reducing system complexity and power consumption. Theoretically, this idea is capable of integrating sensing and computing in a single device. Due to simplifications made at the hardware level, its capacity to handle forecasting tasks was initially compromised. To address this, we have applied software-level optimizations, coupled with nonlinearity tuning, to restore its capability for complex forecasting. We rigorously tested the method using data from three different chaotic systems, as well as with real sensor data for dynamic temperature compensation, all of which yielded impressive results. The proposed architecture demonstrates the concept of an intelligent sensor that can handle a variety of tasks and scenes.

Crowbar is the most widely used low voltage ride-through (LVRT) solution for doubly-fed variable speed pumped storage (VSPS) unit. However, the conventional crowbar solution suffers from excessive crowbar activation period when applied to large-scale VSPS unit, which leads to the disadvantages of high reactive power absorption and huge electromagnetic torque oscillation. To solve the issue, this article analyzes the condition of crowbar release from the perspective of system controllability. Based on it, a hybrid LVRT control strategy combining crowbar and dynamic demagnetizing control is proposed. In this strategy, the crowbar operational duration can be minimized by optimizing the demagnetizing coefficient dynamically. Moreover, the objective of reactive power support or electromagnetic torque oscillation suppression can be achieved to enhance the transient performance of VSPS unit. Finally, the proposed hybrid LVRT control method is validated by the experiments.

This letter proposes a pulse injection modulation (PIM) method for current-fed dual active bridge (CF-DAB). For the first time, the mechanism of zero voltage switching (ZVS) loss in all existing modulation methods of CF-DAB is revealed. PIM redesigns the modulation timing to overcome the inherent flaw of existing modulation methods, thereby achieving full-range ZVS, as well as low inductor current ripple, and voltage stress. The experimental results demonstrate that PIM offers higher efficiency and a wider input voltage range compared to existing modulation methods.

This letter proposes an optimized frequency-locked loop (FLL) for the permanent magnet synchronous generator-based wind turbines to achieve fast inertial response. First, the principle of inertial response is analyzed, finding that changing the FLL output phase can realize inertial response. Then, the optimized FLL is proposed by integrating the estimated angular frequency error and its derivative into the output phase, which enables an instantaneous inertial response. Compared with the classical df/dt inertia control, the proposed optimized FLL reacts to frequency changes faster, and better rate of change of frequency and frequency nadir are obtained. Finally, the proposed method is validated by experiments.

The magnitude of inertia is often used to assess the ability to withstand frequency perturbations. However, the inertia of wind turbines (WTs) is time-varying, equipped with magnitude-phase characteristics. Existing studies have only focused on the magnitude characteristic of WT's inertia but rarely on phase characteristic, which is a limited understanding of WT's inertial response and hard to reveal its effect on system frequency dynamics. Therefore, this article is the first to study the inertial response mechanism of WTs from the perspective of magnitude-phase characteristics. First, the equivalent inertia model of WT is extracted, considering multiple-loop dynamics. Then, the relationship among magnitude-phase characteristics of WT's inertia, active power, and frequency dynamics is revealed according to the definition of equivalent inertia. Furthermore, the extended system frequency response model including the inertia of WT is established and the effect of WT's inertia on system frequency metrics is analyzed. Subsequently, the effects of phase-locked-loop, speed, and reactive power controller parameters on the magnitude-phase characteristics of WT's inertia and frequency metrics are analyzed. Finally, the analysis is verified by hardware-in-loop experiments.

The power boost and response speed are two critical indexes to evaluate the inertia control performances. However, it is hard to obtain the two indexes directly in the time domain for different inertia control methods. How to justify the inertia control performances becomes a critical issue to address. Besides, the issue of whether the inertia control methods of wind turbines can present similar inertia characteristics as synchronous generators also attracts great attention. Targeting the above two questions, this article focuses on the representation, evaluation, and optimization of the inertia characteristics for the doubly fed induction generator (DFIG) based wind turbine. First, the phase motion model and inertia transfer function for the DFIG are established. On this basis, the relations between the inertia control performance in the time domain and the inertia transfer function in the frequency domain are clarified, which is explained through the conventional emulated inertia control. Furthermore, optimization methods for DFIGs to achieve constant inertia, combined with the parameter design guidelines, are demonstrated. Finally, the analysis and the optimized methods are validated by experiments.