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Fast settling phase locked loops (PLLs) play a pivotal role in many applications requiring rapid attainment of a stable frequency and phase. In modern communication standards, these PLLs are extensively utilized to guarantee precise compliance with dynamic resource allocation requirements. In processors, these PLLs manage dynamic voltage frequency scaling. Moreover, the fast-settling PLLs expedite the scanning of frequency spectra in sophisticated electronic radar set-ups, proving particularly advantageous for imaging and scanning radar applications. The rapid response exhibited by these PLLs is also harnessed in quantum technologies, catering to the urgent need for precise frequency adjustments to manipulate qubit states effectively. The strategies employed to attain fast-settling PLLs are primarily classified into five broad techniques in this article: enhanced phase frequency detection, hybrid multiple subsystems, VCO start-up, gear shift, and look-up table or finite state machine. This article explores the fundamental operational principles encompassing these techniques and presents optimal settling times for each method reported in the literature. Finally, the architectures utilizing these techniques will be evaluated based on their figure of merit (FoM), settling time, and tuning range. [ABSTRACT FROM AUTHOR]

This paper introduces a newly designed reactive power control method for single-phase photovoltaic (PV) inverters. The control focuses on easy application and autonomous actions. The regulation is designed with regard to the effective network operation and the saving of reactive power with the functionality of voltage control and optimization of active losses. This paper proves the easy application of the newly proposed control design using the implementation of a control algorithm into a dynamic photovoltaic power plant (PVP) model and supply point with PSCAD software. The long-term benefit of this control is illustrated by the MATLAB/Simulink case study of a one-week simulation over the CIGRE LV European benchmark four-wire network using data from smart meters and measured PVP generation, which was provided by the Distribution System Operator (DSO). The case study showed the benefits of the newly designed regulation in terms of saving reactive energy supply from the upstream system by up to 64% (the regulation contributes to the self-sufficiency of the LV network in terms of reactive power), a positive effect on the reduction of active losses by up to 1.5% and a simultaneous improvement of the voltage profile at the nodes of the modelled network is also observed. The case study also reveals the risks of autonomous control of $Q = f(V)$ single phase inverter on the voltage unbalance depending on its definition.

This paper proposes an ac fault ride-through (FRT) method for high-voltage dc (HVDC) transmission systems that serve as an interconnector between the onshore ac grid and an islanded offshore ac grid. In conventional HVDC systems for offshore wind farms FRT is realized by consuming excess power with braking resistors. However, the same method cannot be applied if the offshore ac grid includes not only wind farms but also various loads, which are being considered for integration into multipurpose interconnectors or energy islands. In this article, a novel FRT method based on voltage control for HVDC interconnectors operating with bidirectional power flow is proposed. The proposed method curtails the ac voltage formed by the offshore converter according to the converter’s dc current and voltage. The effectiveness of the proposed FRT method is established through experiments on a mini model.

In the transition towards sustainable energy systems, microgrid (MG) plays a pivotal role, especially in the context of variable-inertia MGs that integrate renewable energy sources (RESs) and distributed energy resources (DERs). Maintaining stable voltage control within such grids is imperative for reliable operation. This paper presents an adaptive data-driven control technique for the voltage control loop of grid-forming converters in variable-inertia MGs. The primary objective is to enhance control performance while accommodating the unpredictable nature of renewable energy sources. The approach utilizes advanced data-driven algorithms to continuously monitor and adjust control parameters based on real-time grid conditions. This adaptability allows for effective management of varying inertia and load demand, ensuring optimal grid performance. The data-driven nature of the approach enables self-adaptability, making it suitable for the dynamic MG environment. This new approach is a noteworthy advancement in controlling RESs and DERs to maintain stable voltage in MGs, without needing precise knowledge of the MG’s parameters. Simulation tests and real-world examples confirm that the adaptive data-driven control method effectively optimizes voltage control in MGs with variable inertia, especially those with a high presence of RESs and DERs.

Neutral point clamped inverters, such as NPC, ANPC, or T-Type inverters, have emerged as competitive solutions for specific automotive traction applications due to the increase in DC-link voltage levels up to $800 \,\mathrm{V}$. Besides improved harmonic performance, certain 3-level inverter structures can provide a reconfigured failure mode operation in case of a semiconductor failure by applying a permanent neutral point connection in the faulty phase leg. This feature is a vital factor in the design of traction inverters, particularly in the context of fault-tolerant autonomous vehicles. During failure mode operation, none of the neutral point balancing techniques found in current literature are practical. Addressing this issue is crucial since the neutral point stress is high in this mode of operation. Therefore, this paper investigates the impact of stationary and dynamic neutral point voltage deviations on the motor flux in electric machines and offers a compensatory strategy for these errors. Furthermore, a new neutral point control method is presented that balances stationary neutral point voltage deviations by using a phase angle dependent voltage shift in the $\alpha / \beta$-plane. All proposed strategies are first discussed theoretically and then verified by simulation and measurements on an $800 \,\mathrm{V}$ IPMSM machine test bench.