Virtual Oscillator Control of Multiple Solar PV Inverters for Microgrid Applications

This paper proposes the inverter control strategy for multiple solar PV generation sources based on the two-stage converters with a combination of the modified virtual oscillator control (VOC) and the cascaded sliding mode control (SMC). With this proposed control strategy, the load power-sharing in proportion to the inverter rating is guaranteed when the solar PV output satisfies the power-sharing requirement. On the other hand, the control algorithm autonomously forces the solar PV to operate at the maximum power point if the solar PV output is lower than the power-sharing requirement. Various operating scenarios have been simulated to appreciate the effectiveness of the proposed control scheme for ensuring the load-power sharing and maintaining the voltage and frequency stability of the islanded microgrid containing a 100% solar PV generation

On the Coupling of Power-Related and Inner Inverter Control Loops of Grid-Forming Converter Systems

In the last decade, different control concepts for the synchronisation of voltage-controlled power converters have been proposed in order to form converter-based power systems. The interoperability of these grid-forming power controls is often analysed based on reduced-order models covering only the slow controls or modes. In this article, the coupling of the outer, power-related and inner, inverter output-related control of multiple grid-forming power converter systems is analysed, based on a minimal working example. The elementary study cases each consist of a different grid-forming converter coupled with an external (and passive) grid. Here, the investigated stability problems are already manifested in the simplest possible setup. The analysis of these coupling effects is performed by modelling the system in impedance-based, state-space and phase portrait-based frameworks. In particular, small coupling impedances, like short transmission lines or small short circuit impedances, can be challenging for the controller stability of grid-forming converters while the inner controls can even enhance this issue. The impact of this phenomenon and the participating subsystems are identified in this work. Thus, recommendations concerning modelling techniques and their legitimate assumptions are given. Laboratory experiments validate the performed analysis by indicating a close correlation between analytical models and experimental results. CCB

Advanced Synchronization Control for Inverters Parallel Operation in Microgrids Using Coupled Hopf Oscillators

A simple high-performance decentralized controller based on Hopf oscillator is proposed for three-phase parallel voltage source inverter (VSI) in islanded Microgrid. In aß frame, the oscillators equations corresponding output current and com-mon bus voltage as feedbacks are designed according to coupled oscillator synchronization properties. The enough common bus information is considered to realize external synchronization, and the current feedback is to achieve internal synchronization between VSIs. Then, the controller employs Hopf evolution dynamics to integrate their both. Therefore, a larger phase error can be eliminated when additional inverter connects, and the pre-synchronization item is proposed to be close to synchronize with the operational inverters. In addition, an integrated small-signal states pace based on averaged model for two parallel VSIs is developed, and the root locus shows the large stability margin and low sensitivity of parameters. Simulation and experiment results verifi ed the effectiveness of the proposed method in aspects of the fast dynamics response and precise current sharing performance.Peer ReviewedPostprint (published version

Improvement of Power System Frequency Stability With Universal Grid-Forming Battery Energy Storages

Large-scale integration of inverter-based renewable generation leads to the reduction of power systems’ natural inertia. Therefore, the dynamics of the future power systems will be more sensitive than in the traditional systems with high-inertia rotating synchronous generators. This development is a potential risk for frequency stability and requires utilization of rapidly controllable resources for dynamic frequency stability support. Simultaneously, development of new synchronization and control methods for inverter-based resources is needed in order to ensure the frequency and synchronization stability of future power systems. In this paper, a grid-forming and supporting universal frequency-locked-loop -based control and grid synchronization for inverter-based resources is utilized to improve the frequency stability of a small high-voltage network. The simulations are done with PSCAD software and the main focus is on the battery energy storages to evaluate the effect of their location, enhanced control schemes as well as operation mode on frequency stability. In the studies, for example, the effect of battery storages location, active power response related control parameters, communication time delay and input frequency determination on frequency support are studied during charging and discharging of the batteries. Based on the simulations, also new solutions to improve the frequency stability of future variable inertia power systems with universal grid-forming battery storages are proposed.©2023 Author. Published by IEEE. This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/fi=vertaisarvioitu|en=peerReviewed

Output Global Oscillatory Synchronization of Heterogeneous Systems

International audienceThe global output synchronization problem for heterogeneous nonlinear systems having relative degree 2 or higher is studied. The proposed approach consists in two steps. First, a partial projection of individual subsystems into the Brockett oscillators is performed using a sliding-mode control. Second, the network of these oscillators is synchronized using the global synchronization results of a particular second order nonlinear oscillator model from Ahmed et al. (2019). Our approach is based on output feedback and uses a higher order sliding mode observer to estimate the states and perturbations of the synchronized nonlinear systems. Along with numerical simulations, the performance of the proposed synchronization scheme is experimentally verified on a network of Van der Pol oscillators