The present paper deals with the new opportunities deriving from the interconnections of the European and North African transmission systems. In order to achieve a single international market for electricity exchanges, interconnections between networks in different countries are becoming increasingly important and Sicily, for its geographical position in the middle of the Mediterranean Sea, will undoubtedly play an important role as an electrical bridge between Europe and the North Africa in the near future. The paper, presenting the actual electro-energetic context of Tunisia, reports the new important interconnection already realized in South Italy (in particular in Sicily) and describe the planned interventions of the near future. In the second part of the paper, using the Neplan software package (10.7.4, NEPLAN AG, CH-8700 Kusnacht (ZH), Switzerland) for simulating the grid, some load flows are carried out to check some operating scenarios (2020 and 2025) considering energy flows from north to south, avoiding system violations.

New energy corridors in the euro-mediterranean area: The pivotal role of sicily

A social cost benefit analysis of grid-scale electrical energy storage projects: a case study

The modern power system is becoming more complicated due to the ever increasing penetration of power electronics, which is referred to as a power-electronics-dominated system (PEDS). In this case, the analysis, control, and operation of the entire power system should tone with the energy-paradigm transition pace, where the challenges should be properly tackled. After the brief introduction of grid-connected converters, this article explores stability challenges of PEDSs, especially on the low inertia issue and multitimescale characteristics, as well as the dynamics when connected to weak grids. The low inertia issue is considered as one of great challenges that power electronics introduce to the conventional power grid. Accordingly, the stability issues of PEDSs are discussed. The exploration reveals that the multitimescale coupling among various control loops and the mutual effects of multiple converters demand much more attention than ever before. The coordinated control of converters for the global stability of PEDSs is also summarized, part of which offers the possibility to solve the inertia problem. This article serves as an inspiration on potential solutions to these issues. In order to provide a more intuitive impression of the inertia problem in PEDSs, a case study is exemplified to highlight the analysis and discussion.

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On the Stability of Power Electronics-Dominated Systems: Challenges and Potential Solutions

The price of solar energy: Comparing competitive auctions for utility-scale solar PV in developing countries

The power system is experiencing an ever-increasing integration of photovoltaic power plants (PVPPs), which leads to the demand on the power system operators to force new requirements in order to sustain quality and reliability of the grid. Subsequently, a significant quantity of flexible power point tracking (FPPT) algorithms have been proposed in the literature to enhance functionalities of PVPPs. The intention of FPPT algorithms is to regulate the PV power to a specific value imposed by the grid codes and operational conditions. This will inevitably interfere the maximum power point tracking (MPPT) operation of PV systems. Nevertheless, the FPPT control makes PVPPs much more grid-friendly. The main contribution of this article is to comprehensively compare available FPPT algorithms in the literature from different aspects and provide a benchmark for researchers and engineers to select suitable FPPT algorithms for specific applications. A classification and short description of them are provided in this article. The dynamic performances of the investigated algorithms are compared with experimental tests on a scaled-down prototype. Directions for future studies in this area are also presented.

/pdf/extended-functionalities-of-photovoltaic-systems-with-39h2aakbm0.pdf

Extended Functionalities of Photovoltaic Systems With Flexible Power Point Tracking: Recent Advances

Photovoltaic (PV) systems are gradually replacing conventional synchronous generators. However, reduced system inertia and lack of dynamic grid support from PV are the main issues that could have a detrimental impact on the transient response in power systems when critical contingencies arise. In this study, the authors modelled and analysed transient and small-signal stability for a representative transmission system with realistic loading scenarios and high PV penetration levels. First, system eigenvalues were calculated to identify critical modes. Thereafter, the results of the small-signal analysis were further expanded by performing transient simulations after critical contingencies. Such contingencies detrimentally excited the critical modes of the system. To carry out this analysis, they implemented a positive-sequence dynamic model of a utility-scale PV unit (USPVU) in the open programming environment MATLAB/Simulink. This dynamic model is based on a Western Electricity Coordinating Council (WECC) generic model (full converter model), which is suitable for electromechanical transient studies. Also included was the model of the PV array, dc-dc converter, and associated control systems. The most critical factors pertaining to the detrimental or beneficial impact of USPVUs on stability were the unit commitment and dispatch strategy and the protection/control strategy during voltage swell and dip events for equivalent PV penetration and loading scenarios.

Stability assessment for transmission systems with large utility-scale photovoltaic units

This research presents a model of a utility-scale photovoltaic unit (USPVU) enhanced with an embedded hybrid energy storage system (HESS), suitable for stability studies in transmission systems. The main goal of this model is the simultaneous provision of primary frequency control and dynamic grid support. The primary frequency control includes both droop response (achieved by the frequency sensitive mode [FSM] operation) and inertial response (IR). To obtain these grid support functions, the research designed a suitable voltage and frequency (V–f) control, which coordinates the photovoltaic (PV) maximum power point tracking control, HESS converter control, and PV inverter control. Firstly, a midterm assessment of energy requirements in the sized HESS, based on frequency data, validated the energy availability of the enhanced USPVU for primary frequency control, according to new prequalification rules for energy-constrained units. Then, transient stability assessments were performed on a representative transmission system to check the performance of the added FSM and IR in USPVUs with dynamic grid support. The results of the frequency phenomena in the IEEE 39-bus system showed that the enhanced USPVU shared primary frequency control responsibilities with the conventional generation. This was achieved with two criteria to dispatch and commit conventional units by USPVUs.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-rpg.2016.0714

Enhanced utility-scale photovoltaic units with frequency support functions and dynamic grid support for transmission systems

Photovoltaics is replacing an important portion of conventional generation. Therefore, the newest network codes endow utility-scale photovoltaic units (USPVUs) with frequency control functions similar to that of conventional synchronous generation, i.e., frequency sensitive mode (FSM) and inertial response (IR). Moreover, new prequalification rules for energy-constrained units participating in ancillary services market state the sizing of frequency containment reserves (FCR). In this context, the study presents from a previous authors' model an enhanced USPVU model with a V-f control algorithm which coordinates the maximum power point tracking (MPPT) control, the charging and discharging control of an embedded hybrid energy storage system (HESS), and the inverter control. The whole controls working together provide an equivalent V-f control capacity in the USPVU to that of conventional generation. Short-term and midterm simulations based on historic frequency measurements demonstrated the benefits of the added mandatory FSM enhanced with the IR in USPVUs on frequency stability.

Pedro G. Bueno

Papers

Stability assessment for transmission systems with large utility-scale photovoltaic units

Enhanced utility-scale photovoltaic units with frequency support functions and dynamic grid support for transmission systems

Large photovoltaic systems providing frequency containment reserves