Towards a Versatile Cyber Physical Power System Testbed: Design and Operation Experience

The present trends in the area of smartgrids indicate that future transmission and distribution systems will heavily rely on digital and on communication technologies to operate. Indeed, the power systems are evolving progressively towards what is denoted as a cyber-physical system. This transition challenges the classical approaches for experimental testing and requires the development of testing platforms for cyber-physical systems able to capture the interactions between physical components, control and monitoring software and the communication infrastructure. This paper presents general considerations and requirements for a cyber-physical testing platform for power systems. The paper provides also examples of a testing platform specifying the characteristics of the major components and a summary of the experience matured in its setup and configuration. Finally, an example of an experiment on a notional smartgrid and the related results are reported.acceptedVersio

Impedance-compensated grid synchronisation for extending the stability range of weak grids with voltage source converters

This paper demonstrates how the range of stable power transfer in weak grids with voltage source converters (VSCs) can be extended by modifying the grid synchronisation mechanism of a conventional synchronous reference frame phase locked loop (PLL). By introducing an impedance-conditioning term in the PLL, the VSC control system can be virtually synchronised to a stronger point in the grid to counteract the instability effects caused by high grid impedance. To verify the effectiveness of the proposed approach, the maximum static power transfer capability and the small-signal stability range of a system with a VSC HVDC terminal connected to a weak grid are calculated from an analytical model with different levels of impedance-conditioning in the PLL. Such calculations are presented for two different configurations of the VSC control system, showing how both the static power transfer capability and the small-signal stability range can be significantly improved. The validity of the stability assessment is verified by time-domain simulations in the Matlab/Simulink environment.Peer ReviewedPostprint (published version

Generalized Voltage-based State-Space Modelling of Modular Multilevel Converters with Constant Equilibrium in Steady-State

This paper demonstrates that the sum and difference of the upper and lower arm voltages are suitable variables for deriving a generalized state-space model of an MMC which settles at a constant equilibrium in steady-state operation, while including the internal voltage and current dynamics. The presented modelling approach allows for separating the multiple frequency components appearing within the MMC as a first step of the model derivation, to avoid variables containing multiple frequency components in steady-state. On this basis, it is shown that Park transformations at three different frequencies ($+\omega$, $-2\omega$ and $+3\omega$) can be applied for deriving a model formulation where all state-variables will settle at constant values in steady-state, corresponding to an equilibrium point of the model. The resulting model is accurately capturing the internal current and voltage dynamics of a three-phase MMC, independently from how the control system is implemented. The main advantage of this model formulation is that it can be linearised, allowing for eigenvalue-based analysis of the MMC dynamics. Furthermore, the model can be utilized for control system design by multi-variable methods requiring any stable equilibrium to be defined by a fixed operating point. Time-domain simulations in comparison to an established average model of the MMC, as well as results from a detailed simulation model of an MMC with 400 sub-modules per arm, are presented as verification of the validity and accuracy of the developed model

Emlékállítás és felejtés. A „málenkij robot” emlékezete a szatmári sváboknál

Commemorative practices and oblivion mechanism. The memory of the deportations of the Satu Mare Swabians) In 1945, a series of violent events took place, bringing the greatest individual and collective trauma in the history of the Satu Mare Swabians. The paper presents the various communication situations in which deportation narratives were drafted and transmitted. I wanted to reveal all the channels in which the commemoration of the deportations (both private and public) took/take place, paying special attention to changes in commemoration forms, as historical phenomena, and also making a comparison between the approaches in the Swabian villages from Romania and Hungary. In commemorating practicesof the deportations I distinguished four levels: individual memory, memory of generations, communicative memory and collective memory, all four having different functions and contexts

Windowed PWM: a Configurable Modulation Scheme for Modular Multilevel Converter Based Traction Drives

This article introduces a modulation technique for modular multilevel converter (MMC) in variable speed traction drives for electrical transportation referred as windowed pulsewidth modulation (W-PWM). The windowed PWM (W-PWM) is derived by blending the principles of operation of conventional modulation schemes for MMC based on the nearest level control (NLC) and on PWM with the aim of combining their inherent strengths and offering a higher degree of flexibility. This can reduce switching losses compared to classical PWM schemes and lower the current harmonic distortion compared to NLC schemes. The window in which the PWM is applied can be seen as an additional degree of freedom that allows a dynamic optimization of the performance of the traction drive depending on its operating characteristics. The performance of the W-PWM technique is assessed in this article for several operating conditions and compared with conventional schemes based on NLC and on the phase opposition disposition PWM with both numerical simulation and experimental verification on a small-scale prototype. Results demonstrate the flexibility of the W-PWM and its potential for applications in electrical traction drives. © 1986-2012 IEEE.acceptedVersio

P-HiL Evaluation of Virtual Inertia Support to the Nordic Power System by an HVDC Terminal

This paper provides an assessment of the effect from virtual inertia provided by an HVDC converter terminal on the Nordic power system. The analysis is based on results from Power-Hardware-in-the-Loop (P-HiL) tests with a laboratory-scale Modular Multilevel Converter (MMC) representing an HVDC terminal interfaced with a real-time phasor simulation of the Nordic grid. The applied control method for providing virtual inertia is utilizing the derivative of the locally measured grid frequency to adapt the power reference for the studied converter terminal. The power injection provided by the converter and the resulting impact on the frequency dynamics of the power system are investigated as a function of the emulated inertia constant and the frequency droop gain. The results demonstrate how the HVDC converter can effectively support the dynamic response of the power system when exposed to large load transients by improving the frequency nadir and reducing the Rate-of-Change-of-Frequency (ROCOF). Keywords: HVDC Transmission , Power-Hardware-in-the-Loop , Real-time Simulation , Virtual InertiaacceptedVersio

A modular approach to large-signal modeling of an interconnected AC/MTDC system

Y. Susuki, N. Kawamoto, Y. Ohashi, A. Ishigame, T. Funaki and S. D’Arco, "A Modular Approach to Large-Signal Modeling of an Interconnected AC/MTDC System," 2020 IEEE PES Innovative Smart Grid Technologies Europe (ISGT-Europe), The Hague, Netherlands, 2020, pp. 945-949, doi: 10.1109/ISGT-Europe47291.2020.9248890

A wave-to-wire model for grid integration studies of oscillating-body wave energy converters

Wave energy converters (WECs) are still at an earlier stage of development when compared to variable renewable energy systems based on wind or solar power. Indeed, only a few WECs have exported power to electric grids until recently. Thus, the development of mathematical models able to represent essential aspects of the system and its connection to the grid becomes fundamental to assess the impact of integrating wave power to grids. This work develops a fully integrated wave-to-wire model, where the electrical model has re-configurable dynamic models of rotary and linear generators (with controllers) to accommodate different types of oscillating-body systems. Such an electrical model is interfaced with the WEC hydrodynamic and mechanical models. A complete wave-to-grid model is presented by integrating the generator system model, an electrical grid interface unit and a network equivalent for the receiving grid in a unified simulation environment with the WEC-Sim, an open-source tool for simulating the dynamic behaviour of WECs. Numerical simulation studies are presented considering different operating conditions for the grid integration of a floating body that is connected to either an hydraulic power take-off system or a direct-drive system.A wave-to-wire model for grid integration studies of oscillating-body wave energy convertersacceptedVersio