This paper proposes two power flow control algorithms for a grid-connected voltage source converter used as part of the energy storage for a smart grid under unbalanced voltage conditions. Both ...algorithms are improvements of the dual vector current control algorithm (DVCC). The first proposed algorithm, DVCC_CL, optimizes the method of limiting phase currents for the duration of voltage unbalance. The second proposed algorithm, DVCC_HB, provides high bandwidth control of active and reactive power. Which of the two proposed algorithms is the better choice depends on the grid code requirements and the constraints imposed by the particular energy storage system which the inverter connects to the grid. The operation of both algorithms was verified within the framework of an ultralow-latency hardware-in-the-loop emulator, which makes accurate analysis of converter behavior safe and easy for any grid conditions.
The usage of distributed generation sources and the segmentation of power systems into microgrids brings several advantageous features, such as energy independence, lower transmission losses, and ...improved energy management flexibility. Still, the expected steady abolition of traditional centralized networks and their centralized control schemes introduces several operational difficulties, that can compromise (micro)grid’s stability and reliability. Consequently, several approaches to how microgrids should be operated have been proposed, albeit with several salient deficiencies. Precise power exchange, control of frequency and voltage excursions, applicability on different grid topologies, and the possibility to integrate grid codes, which are very important control aspects, are not jointly enabled in a general case. This paper proposes a novel approach, based on a specific goal function and corresponding decentralized control that addresses the mentioned problems and guarantees the microgrid’s stability by constraining the frequency and node voltage deviations, simultaneously supporting the desired active power exchange between prosumers. Unlike droop-based and droop-derived control schemes, the proposed approach aims to inherently preserve the frequency and voltage levels within the limits defined by the grid operator or future microgrid codes, thus preventing the generation unit’s unwanted disconnection during transients and disturbances. In addition, the control algorithm is independent of network topology, can be applied in both islanded and non-islanded microgrids, and secures system scalability. To confirm the effectiveness of the proposed control strategy, a number of simulation results are presented and thoroughly discussed.
•A novel seamlessly scalable self-stabilizing microgrid control framework is proposed.•Guaranteed upper bounds on deviations of node frequencies and voltages are provided.•Precise active power exchange between nodes is enabled.•Priorities of the proposed scheme can be adjusted according to user preferences.•Comprehensive tests in relevant operational scenarios are performed.
U radu je prikazano istraživanje u podmorju sjevernog Jadrana i priobalja južne Dalmacije unutar naslaga pliocena, pleistocena i holocena. Njime su opisane postojeće litostratigrafske jedinice u ...taložinama rijeke Po u Hrvatskoj i određene takve jedinice u prostoru taloženja rijeke Neretve. Oba taložna prostora bila su pod utjecajem promjena razina mora, posebice tijekom kvartara, što se znatno odrazilo u smanjivanju dubine mora i povećanju površine kopna tijekom oledaba, posebice u sjevernom Jadranu. U hrvatskom dijelu Padske depresije navedene su dvije formacije – Istra (pliocen) i Ivana (pleistocen, holocen). U formaciji Ivana opisana su tri člana, poimence Anamarija, Katarina i Izabela. Dalje prema jugu, u priobalju južne Dalmacije, imenovana je nova formacija Neretvanski kanal (za taložine pliocena, pleistocena i holocena). Ona je zatim podijeljena u pijeske Neretva (koji mogu biti ekvivalent i cijele formacije) te član Malostonski zaljev (kvartarne starosti). Isključivo pliocenski tipski litotip nije opisan.
Prototyping and verification of complex power electronics (PE) systems and control algorithms is a laborious and time-consuming process. Even when a low-power hardware model is assembled, it enables ...only a limited insight into the large number of operating points; changes in system parameters regularly demand hardware modifications and always there is the risk of hardware damage. The ultralow-latency Hardware-In-the-Loop (HIL) platform proposed in this paper combines the flexibility, accuracy, and ease of use of state-of-the-art-simulation packages, with the response speed of small power-hardware models. In this way, PE systems-optimization, code-development, and laboratory-testing can be combined into one step, which dramatically accelerates the pace of product prototyping. Low-power hardware-models also suffer from nonscalability, because some parameters such as electrical machine inertia cannot be properly scaled. However, HIL enables control prototyping that covers all operational conditions. In order to demonstrate HIL-based rapid development, the verification of an active damping algorithm for a permanent magnet synchronous generator (PMSG) cascade is performed. Two goals are set in this paper: to verify the developed HIL platform by means of comparison with a low-power hardware setup and then to emulate the real, high-power system in order to test the active damping algorithm.
This paper proposes a novel primary level controller and coupling LCL filter design methodology for microgrid prosumer units The so-called decentralized peer-to-peer-based power flow control ...algorithm introduces a power exchange communication link between two contractees, namely a prosumer unit and any other unit, on the time scales of primary power flow controller. This can be regarded as feed-forwarding of power flow information between the units in close to real-time in order to attain almost instant power balancing within the system. When coupled with the conventional voltage and frequency droop primary control, as presented in the paper, and tested on a simulation model of one radial microgrid in the off-grid mode of operation, it showed enhanced static and dynamic performance. The study also investigated adverse influence of the communication link time delay. The paper addressed prosumer units microgrid voltage-forming role by proposing design and control methodology for the prosumer units' LCL coupling filter. To that aim, thorough voltage and current harmonic emission analysis has been conducted, taking into account realistic span of a microgrid parameters' values and presence of other units. The study and the simulation model tests revealed that the limited total voltage harmonic distortion becomes critical requirement in the off-grid model of operation.
•Reliable PLL method to cope with grid unbalances.•Real time estimation of voltage symmetrical components and higher harmonics content.•Solution complexity can be tuned to the expected higher ...harmonics order.
In this paper, a novel PLL technique based on Multi-Resonant disturbance Observer (MRO) is investigated. The proposed technique can achieve grid synchronization under distorted voltages and simultaneously quantify grid unbalances, including voltage sags and higher harmonics. Real-time quantification of grid condition is very important in estimating the overall power quality, which in turn has a drastic effect on power regulation. The proposed technique is easily applicable and expandable to any desired number of higher harmonics. In addition, we provide an in-depth analysis of the connection between original grid unbalances in the stationary reference frame and its image under dq transform. Finally, we propose a methodology capable of real-time estimation of positive and negative harmonic sequences based on the observed properties of fundamental and higher harmonics.
New lithostratigraphic units in the Croatian offshore have been recently proposed, and are now used, especially in the Pleistocene and Holocene sediments. Two new formations in the Croatian part of ...the Northern Adriatic have been previously named (Istra and Ivana), as well as recently three new lithostratigraphic members inside the Ivana Formation. In addition, a name change of the Susak Formation has been proposed. Furthermore, in the Southern Dalmatia shallow offshore (i.e., palaeosediments of the Neretva River), the new Neretva Channel Formation has been recently named. It is divided into the Neretva Sands and the Mali Ston Bay Member. Due to the often descriptive task of the definition of the lithostratigraphic units, here the simplification of the task is made possible by the algorithm and the source code which are based on a sufficient number of measured porosity values in a vertical of a lithological unit or a depositional sequence. The algorithm directly defines the procedure for testing the hypothesis of the normal distribution of porosity values, and the code does it numerically and graphically. The normality test is performed with the Shapiro-Wilk test. Depending on the results of the hypothesis test (normal distribution of the measured values), it is simply evaluated if it is a homogeneous, permeable or non-permeable, or a heterogeneous lithostratigraphic unit, that always can be distinguished from the top and the base. Based on the result, and familiarity with the geographical location of the sample, the unit is easily named following the rules of lithostratigraphic nomenclature.
This paper deals with control of wind turbine connected to the grid through
the back-to-back converter in case of unbalanced grid voltages. The
motivation for this research has been found in recent ...transmission and
distribution grid code, which demand modern wind turbines to stay connected
to the grid and supply the highest possible apparent power during the grid
disturbances. In order to comply with these requirements we proposed improved
dual vector current controller to deal with the unbalance imposed by the
electrical grid. Controller provides injection of active and reactive power
to the grid, even if the voltages are lower than the nominal one. The results
are validated using low power prototype and contemporary hardware-in-the-loop
emulation platform. In both cases the controller is based on TMS320F2812 DSP.
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