Passive Grid Research Articles

Design approach and performance analysis of trap filter for three-phase PV grid integration systems using evolutionary search algorithms

The main objective of this article is to provide an efficient design approach of passive grid filters based on evolutionary search algorithms. The case study is conducted on a passive trap filter (one of modern high order passive filters that can provide better performance compared with first order scheme) to be incorporated with a three-phase grid-tied inverter fed from PV array and a battery bank, forming a typical PV grid integration system. The filter design approach is mainly based on particle swarm optimization technique (PSO) as one of the efficient evolutionary search algorithms meanwhile Genetic Algorithm (GA) has been utilized as well for comparison purposes. The developed PSO algorithm searches for the optimum numerical values of filter passive components that can optimize a customized objective function of multiple terms. Unlike single-term objective function, the adopted approach has the advantage of involving multiple items in the customized objective function, such as harmonic attenuation factor and the numerical values of passive filter elements to be minimized. Moreover, the evolutionary search-based design approach is characterized by offering several groups of solutions for the same optimization problem. Thus, the obtained solution is not unique. Consequently, the choice between those solutions depends on the system designers who can select the most convenient solution among several alternatives based on component availability in market, the overall cost of the filter and the desired upper limit of THD of grid currents. The obtained results of this study demonstrate also the capability of evolutionary search approach to get optimum values of filter components that achieve good harmonic attenuation and satisfy the related grid codes such as the IEEE standard 519. Compared with traditional filter design method, the obtained results indicate that the PSO technique achieves lower numerical values of filter parameters in the most of parameters, resulting in an overall reduction in the size and cost of the passive grid filter. In addition, the employed GA succeeded to provide satisfactory numerical values of trap filter as well. However, the PSO technique is better than GA in several terms such as lower final value of objective function and lower numerical values of filter elements and convergence to the optimal solution(s) irrespective the initial guess values.Matlab® has been employed as a simulation platform for PSO and GA algorithms. While the overall grid integration system has been modelled and studied using professional version of PSIM software®.

Integrating reliability and resilience to support the transition from passive distribution grids to islanding microgrids

Reliability and resilience are the main drivers for the transition of distribution networks from passive systems to active microgrids; as such, quantifying the potential benefits of microgrids in the design phase can support the transition of passive distribution networks into microgrids. To support this transition, this paper presents a mathematical optimization model which integrates techno-economic, resilience and reliability objectives. Storage and distributed generation are optionally installed to complement renewable generation, enabling the microgrid to supply priority demands during stochastic islanding events with uncertain duration. Islanding due to external events is combined with a detailed model of internal faults for comprehensive quantification and optimization of microgrid resilience and reliability. Minimizing the interruption costs yields optimal capacities and placements of distributed energy resources and new lines for reconfiguration. The proposed method produces microgrid designs with up to 95% reliability and resilience gain and moderate cost increase in two benchmark distribution networks using data from the United States Department of Energy. The developed methodology is scalable to large networks owing to the tailored Column-and-Constraint-Generation approach, reducing the computational time by 92% compared to state-of-the-art Benders decomposition for a 123 bus network.

Effective sensitivity-based method for N-1 contingency analysis of VSC-based MTDC power grids considering power generation droop speed controls

This paper introduces a sensitivity-based approach for the efficient calculation of the post-disturbance, steady-state conditions in VSC-based MTDC power grids subject to generation outages and VSC disconnections. This approach is useful for the N-1 contingency analysis, a crucial tool in power system control centres. In order to maintain a high degree of fidelity, the approach considers state-of-the-art VSC control strategies: converters with DC voltage regulation, power-injection control, DC voltage/power droop control, and converters imposing frequency regulation on passive grids. The speed-governing response of power plants is also considered, enabling accurate calculations of AC/DC power flows and AC system frequencies. Indeed, the derived sensitivity factors permit the primary frequency response of the AC systems and DC grid to be efficiently assessed, something that would require several hours of simulation by standard electromagnetic transient (EMT) simulators. Evidently, this novel approach allows a much faster calculation of the AC/DC network’s post-disturbance conditions than is possible with dynamic simulation tools. A formulation with such modelling versatility and practicality does not currently exist elsewhere.The usefulness of this novel formulation has been confirmed using an MTDC system comprising six VSC-connected AC grids and a 13-bus DC grid. The disconnections of VSC units and power plants have also been evaluated. The study shows that the post-disturbance, steady-state conditions computed by the sensitivity-based approach agree well with those obtained by full dynamic simulations, because the relative errors between the two fundamentally different methods are smaller than 0.1% for the AC system frequencies and smaller than 4% for the AC and DC transmission line power flows.

Aerodynamic characteristics of variously modified leading-edge protuberanced (LEP) wind turbine blades under various turbulent intensities

A series of wind tunnel tests were performed to investigate the effect of turbulent inflows on the aerodynamic characteristics of variously modified leading-edge protuberanced (LEP) wing configurations at various turbulence intensities. A self-developed passive grid made of parallel arrays of round bars was placed at different locations of the wind tunnel to generate desired turbulence intensity. The aerodynamic forces acting over the baseline straight leading-edge model and the modified small, medium and high LEP wing configurations were obtained from the surface pressure measurements made over the wing at different turbulence intensities using MPS4264 Scanivalve simultaneous pressure scanner corresponding to a sampling frequency of 700Hz. All the test models were tested for a wide range of angles of attack ranging between −45° ≤ α ​≤ ​45° at turbulence intensities varying between 0.51% ​≤ ​TI ​≤ ​4.92%. Results reveal that the time-averaged mean coefficient of lift (CL) increases with the increase in the turbulence intensity associated with smooth stall characteristics rendering the modified LEP test models advantageous. Furthermore, based on the surface pressure coefficients the underlying dynamics behind the stall delay tendency were discussed. Additionally, attempts were made to statistically quantify the aerodynamic forces using standard deviation at both the pre-stall and the post-stall angles.

Study of a Passive Gating Grid for Ion Back Flow Suppression

Space Charge (SC) distortions are some of the main issues for high-resolution Time Projection Chambers (TPC). The two main SC sources are those from primary ionizations and those that result from amplification stages. The gain stages are required to increase the electron (e -) signal above electronics noise levels, but this inevitably creates extra ions. These ions can enter the drift region and distort the electric field, and thus lower the detector performance. We will present a brief motivation for our Ion Back Flow (IBF) studies along with explanations of existing techniques and our simulation results to reduce IBF. We propose several mesh structures along with static bi-polar gating. Further, we discuss position distortions in e - trajectories due to a static bi-polar grid and use these distortions to compensate for non-linear responses of our Zig-Zag pad readout.

Stm32f4 Ve Matlab Kullanılarak Tek Faz Şebeke Bağlantılı Pv İnverterin Hızlı Prototip Geliştirilmesi

In this paper, the program source code of the STM32F407 microcontroller for PV (photovoltaic) inverter circuit was tested using Simulink before applying it to a power electronics circuit. Firstly, a single-phase grid-connected PV (photovoltaic) inverter structure is modeled in Matlab / Simulink environment. In the light of these simulation results, the control blocks of the inverter are programmed using the MicroC ARM compiler for the STM32F407 microcontroller. Before the circuit design stage, a model was developed to work with Matlab / Simulink in order to prevent possible errors and losses of the microcontroller code of the designed PV inverter. This model includes power electronics semiconductors and passive components, PV panels, grid and data communication blocks. The C source code containing the inverter control blocks (MPPT, PLL, DCLinkPI and Current controller) are loaded into the STM32F4 Discovery kit. At each step of the simulation, the current and voltage information obtained from the Matlab model is sent to the STM32F4 kit via serial communication. The current and voltage information is processed in microcontroller software and switching pulses of IGBTs are created and transferred back to Matlab model. In this way, a rapid and secure prototype hardware development method is presented with the joint operation of Matlab and STM32F4. The results obtained from the simulation and Matlab-STM32F4 joint study are given comparatively.

Research on dynamic characteristics of gas film of spherical hybrid gas bearings based on computational fluid dynamics

A realizable k–ε turbulence model for spherical spiral groove hybrid gas bearing films was established based on computational fluid dynamics (CFD). A six degrees of freedom passive grid was used to calculate the gas film pressure distribution, bearing capacity, and dynamic characteristic coefficients numerically. The gas flow field dynamic and static pressure coupling mechanism was studied. The effects of the rotation speed, gas film thickness eccentricity ratio, and gas supply pressure on the dynamic and static pressure bearing capacity, and dynamic characteristic coefficients during operation were analyzed as a method of research into the mechanical mechanisms of gas bearing stability. The CFD calculation analysis can simulate the complex gas flow in the transient flow field of the gas film and determine reasonable operation parameters to optimize the dynamic and static pressure coupling effects, which can improve the gas film bearing capacity, dynamic characteristics, and operational stability of gas bearings.

Characteristics of Two Ground Grid Potentials After a Triggered Lightning Stroke

It has been determined that the discharge of lightning current to ground through grounding grid results in high potential at the grounding grid and other nearby grounding grids, which is very destructive. In the present paper, based on artificially triggered lightning technology, the characteristics of the ground potential rise (GPR), the transient effect at the active grid under the transient impulse of lightning current was analyzed. The impulse grounding resistance is found to decrease for large input currents. On the other hand, for small input currents, it usually increases. In addition, the characteristics of the transfer potential of the passive grid which is located 40 m from the active grid were analyzed. It was shown that the peak value of the transfer potential at the passive grid was approximately 5.1% of the peak value of the ground potential at the active grid during the return stroke. The achievements made in this study may contribute toward the optimization of the simulation model.

Shape effects on aerodynamic loading of heliostats

The effect of the shape of the mirror of a heliostat is studied through wind tunnel tests in uniform smooth and turbulent flow conditions. Three shapes are investigated: square (reference case), octagonal and circular geometries. The forces and moments are measured on reduced scale models of heliostats in low, medium and strong turbulence wind conditions in a uniform wind profile. The turbulence intensity of the flow is adjusted in the wind tunnel test section by the adjunction of passive grids upstream the model. The experimental results are presented for several elevation and azimuth angles. The results showed that: in smooth flow conditions, the geometry of the mirror has very limited effect on the mean force coefficient, while impacting the fluctuating part of the aerodynamic loads. In turbulence flow conditions, the circular mirror/panel is advantageous for the aerodynamic design of the elevation drive and mirror support structure.

Multi-objective design approach of passive filters for single-phase distributed energy grid integration systems using particle swarm optimization

This article presents a non-conventional design approach of high order passive filters incorporated with distributed energy grid integration systems based on particle swarm optimization (PSO) as one of multi-objective evolutionary search algorithms. Two topologies of passive grid filters (third order passive damped LCL-filter and trap filter) are chosen as case studies. The presented grid filter design is based searching the optimum values of filter passive elements that can optimize an objective function composed of several terms such as harmonic attenuation factor and size (value) of passive elements (inductors and capacitors). The employed multi-objective design approach has three main advantages: (1) The PSO algorithm offers several groups of solutions to the same optimization problem. Accordingly, the most convenient solution can be chosen based on several factors such as cost of realization, availability in the market and the corresponding THD of grid current. (2) Multi-objective design approach is flexible enough to include other factors in the customized objective function to achieve different design criteria in accordance with new (or updated) versions of grid codes. (3) The PSO algorithm converges to the optimum solution(s) regardless the initial search values (initial guess). Consequently, the algorithm does not need any prior knowledge about filter numerical valuesThe PSO algorithm has been developed in Matlab®, while the overall hardware grid-integration system has been modeled and studied using PSIM® software package. The obtained results demonstrate the effectiveness of the proposed approach to get practical and applicable values of filter components that result in good harmonic attenuation and satisfy the related codes of grid integration such as the IEEE standard 519.The main contribution of this paper is the utilization of evolutionary optimization technique to achieve an optimum design of passive grid filters that can optimize simultaneously several contradictory goals such as achieving the maximum possible harmonic attenuation at the lowest possible filter size. Compared with conventional design approach, the PSO-based filter design approach results in lower numerical values of filter components, which leads to considerable reduction in the size and cost of the passive grid filter. Moreover, grid filter design based on evolutionary search approach permits accommodation of several design criteria in the customized objective function with arbitrary weighting factors upon system design requests and new grid codes constrains.

Review of Voltage and Reactive Power Control Algorithms in Electrical Distribution Networks

The traditional unidirectional, passive distribution power grids are rapidly developing into bidirectional, interactive, multi-coordinated smart grids that cover distributed power generation along with advanced information communications and electronic power technologies. To better integrate the use of renewable energy resources into the grid, to improve the voltage stability of distribution grids, to improve the grid protection and to reduce harmonics, one needs to select and control devices with adjustable reactive power (capacitor batteries, transformers, and reactors) and provide certain solutions so that the photovoltaic (PV) converters maintain due to voltage. Conventional compensation methods are no longer appropriate, thus developing measures are necessary that would ensure local reactive and harmonic compensation in case an energy quality problem happens in the low voltage distribution grid. Compared to the centralized methods, artificial intelligence (heuristic) methods are able to distribute computing and communication tasks among control devices.

Effect of turbulence on the performance of VAWTs: An experimental study in two different wind tunnels

Turbulence is one of the main characteristics of urban flows, but its effect on the performance of small VAWTs (often used in urban wind installations) has not been thoroughly researched. This experimental study focuses in testing a H-Darrieus VAWT prototype in different turbulent conditions inside the wind tunnel, in order to study the influence of turbulence intensity, integral length scales and Reynolds number. Passive grids are used to increase the wind tunnel free stream turbulence up to Iu = 15%, with integral length scales of Lux = 0.18 m and Reynolds numbers of ReD ≈ 300,000. The measurements are repeated in two wind tunnels of different size, which strengthens the results and helps quantify the effect of blockage on the turbine ratings. The results show power coefficient increases up to 20% from smooth (Iu = 0.5%) to turbulent (Iu = 15%) flows, an effect that is enhanced at low λ but that fades as ReD > 400,000. The study of the crossed influence of ReD, Iu and Lux offers valuable data in the process of optimizing the operation of small VAWTs inside urban environments.

An Effective Passive Islanding Detection Algorithm for Distributed Generations

Different issues will be raised and highlighted by emerging distributed generations (DGs) into modern power systems in which the islanding detection is the most important. In the islanding situation, a part of the system which consists of at least one DG, passive grid, and local load, becomes fully separated from the main grid. Several detection methods of islanding have been proposed in recent researches based on measured electrical parameters of the system. However, islanding detection based on local measurements suffers from the non-detection zone (NDZ) and undesirable detection during grid-connected events. This paper proposes a passive islanding detection algorithm for all types of DGs by appropriate combining the measured frequency, voltage, current, and phase angle and their rate of changes at the point of common coupling (PCC). The proposed algorithm detects the islanding situation, even with the exact zero power mismatches. Proposed algorithm discriminates between the islanding situation and non-islanding disturbances, such as short circuit faults, capacitor faults, and load switching in a proper time and without mal-operation. In addition, the performance of the proposed algorithm has been evaluated under different scenarios by performing the algorithm on the IEEE 13-bus distribution system.

Aerodynamic characteristics of unsymmetrical aerofoil at various turbulence intensities

A series of wind tunnel tests were performed to investigate the effect of turbulent inflows on the aerodynamic characteristics of the unsymmetrical airfoil at various turbulence intensities and Reynolds number. To assess the aerodynamic characteristics, surface pressure measurements were made over the unsymmetrical airfoil surface by using a simultaneous pressure scanner MPS4264 of Scanivalve make. Self-generated passive grids made of parallel arrays of round bars were placed at four different locations to generate various Turbulence Intensities (TI) in the wind tunnel. The location of the passive grid has been normalized in terms of considering the distance between the entry of the test section and the leading edge of the model. Based on the wind tunnel results, by comparing the baseline without grid low turbulence case TI = 0.51% with other turbulence generated cases like TI = 4.68%, 4.73%, 6.04% and 8.46% at different Reynolds number, it is found that the coefficient of lift increases with the increase in the turbulence intensity. Results also reveal that the flow featuring turbulence can effectively delay the stall characteristics of an airfoil by attaching the flow over the airfoil for an extended region. Additionally, attempts were made to understand the influence of turbulence on the aerodynamic hysteresis.

SmartLVGrid Platform—Convergence of Legacy Low-Voltage Circuits toward the Smart Grid Paradigm

The current electrical system is transitioning towards a new technological model called the smart grid. The transition duration between the traditional Electric Power System (EPS) and the full smart grid depends on well-designed strategic plans, implementing transition models that are as close to smart grids as possible, based on the processes and technological resources available at the time, but always considering their economic feasibility, without which no solution thrives. In this article, we present a method for convergence of the traditional power distribution grid to the smart grid paradigm by retrofitting the legacy circuits that compose this grid. Our results indicate that the application of such a method, through a distributed system platform with integrated technological resources added to the legacy infrastructure, converts these passive grids into intelligent circuits capable of supporting the implementation of a smart grid with a broad scope of functionalities. Based on a novel retrofitting strategy, the solution is free from the cost of replacing or significantly modifying the legacy infrastructure, as verified in deploying other currently available solutions.

Power Quality Management of PV Power Plant With Transformer Integrated Filtering Method

This paper presents a new solution of power quality management for the photovoltaic (PV) power plant with the transformer integrated filtering method. The innovation of the PV power plant is that it contains two-stage filtering station, which consists of a box-type transformer with integrated filter and a 110 kV grid-connected transformer based on inductive filtering method. The filtering reactor can be integrated into the box-type transformer as a decoupled winding, so that the modular design of the box-type transformer and the passive filter is realized. Inductive filtering method applied in the grid-connected transformer not only improves the power quality at the point of common coupling, but dampens the harmonic resonance between the passive filter and grid. The hierarchical structure of the PV power plant is introduced firstly. Then, the equivalent circuit model and the mathematical model of the primary and secondary filtering stations are established, respectively. Moreover, the influence of the weak coupling of integrated reactor on the filtering performance is analyzed. The antijamming capabilities of the inductive filtering method and the traditional filtering method are compared under the condition of parameter disturbance. At last, the site tests of the PV power plant with transformer integrated filtering method are made, which show that the PV grid-connected system comprised of the two-stage filtering station has the characteristics of low harmonic emission, high power factor, and stable operation.

Transient Response of Surge Protective Devices During the Potentials Transferred Between Independent Grounding Grids

This paper analyzes the potential transferred between two independent grounding grids located 40 m apart, one of which, called the active grid, was injected with current of rocket-triggered lightning flashes. The transferred potentials in another grid, called the passive grid, and the transient response of the surge protective device (SPD) in the passive grid are evaluated. Observations results benefiting from six nearby triggered flashes, in which a total of 35 return strokes were involved, show that the peak transferred potential in the passive grid ranges from −1.1 to −28.5 kV with a mean of −10.7 kV. These voltages exhibit transient pulses, having a primary peak with a mean duration of 3 μ s, followed by a sub-peak, whose amplitude is averagely 36.6% against the primary one. The average 10%–90% risetime is 0.74 μ s and the average half-peak width is 1.6 μ s. The energy consumed by SPD during transferred potentials is 2.0 J on average, much lower than that of the SPD equipped in nearby overhead power lines. The amplitude of initially injected lightning currents in the active grid is found to be an important determinant of the peak transferred potentials, the peak current flowing through the SPDs, and the energy consumed by the SPD.

A SGAM-Based Test Platform to Develop a Scheme for Wide Area Measurement-Free Monitoring of Smart Grids under High PV Penetration

In order to systematically shift existing control and management paradigms in distribution systems to new interoperable communication supported schemes in smart grids, we need to map newly developed use cases to standard reference models like Smart Grid Architecture Model (SGAM). From the other side, any new use cases should be tested and validated ex-ante before being deployed in the real-world system. Considering various types of actors in smart grids, use cases are usually tested using co-simulation platforms. Currently, there is no efficient co-simulation platform which supports interoperability analysis based on SGAM. In this paper, we present our developed test platform which offers a support to design new use cases based on SGAM. We used this platform to develop a new scheme for wide area monitoring of existing distribution systems under growing penetration of Photovoltaic production. Off-the-shelf solutions of state estimation for wide area monitoring are either used for passive distribution grids or applied to the active networks with wide measurement of distributed generators. Our proposed distribution state estimation algorithm does not require wide area measurements and relies on the data provided by a PV simulator we developed. This practical scheme is tested experimentally on a realistic urban distribution grid. The monitoring results shows a very low error rate of about 1 % by using our PV simulator under high penetration of PV with about 30 % error of load forecast. Using our SGAM-based platform, we could propose and examine an Internet-of-Things-based infrastructure to deploy the use case.

UWGeodynamics: A teaching and research tool for numerical geodynamic modelling

The UWGeodynamics module facilitates development of 2D and 3D thermo-mechanical geodynamic models (Subduction, Rift, Passive Margins, Orogenic systems etc.). It is designed to be used for research and teaching, and combined the flexibility of the Under- world Application Programming Interface, (Moresi, Dufour, & Muhlhaus, 2002, Moresi, Dufour, & Muhlhaus (2003), Moresi et al. (2007)) with a structured workflow. Designing geodynamic numerical models can be a daunting task which often requires good understanding of the numerical code. UWGeodynamics provides a simple interface with examples to get you started with development of numerical models. Users can start designing their models without any pre-existing knowledge of programming. Expert users can easily modify the framework and adapt it to more specific needs. The code can be run in parallel on multiple CPUs on personal computers and/or High Performance Computing systems. Although UWGeodynamics has been primarily designed to address geodynamic problems, it can also be used to teach fluid dynamics and material mechanics. UWGeodynamics uses the flexibility of the Python language and the Jupyter Notebook environment, which allows leveraging the wide range of scientific libraries available from the Python community. It also facilitates the coupling with existing scientific Python modules such as Badlands (Salles, Ding, & Brocard, 2018). The functionalities include: • Dimensional input values, using user’s choice of physical units. • Automated and transparent scaling of dimensional values. • Sets of predefined geometries that can be combined to define the initial geometry of a model. • Handles Newtonian and non-Newtonian rheologies (Viscous, Visco-plastic and Visco-elasto-plastic). • Database of common rheologies used in geodynamics, which can be personalised / extended by users. • Simple definition of kinematic, stress, and thermal boundary conditions. • Lithostatic pressure calculation • Thermal equilibrium (steady-state) calculation. • Pseudo Isostasy using a range of kinematic or stress boundary conditions. • Partial melt calculation and associated change in viscosity / heat production. • Simple definition of passive tracers and grid of tracers. • Simple Phase changes • 2-way coupling with the surface processes model pyBadlands (Salles et al., 2018). UWGeo comes with a series of examples, benchmarks and tutorial setups that can be used as cookbook recipes. They provide a wide range of teaching materials useful to introduce numerical geodynamic modeling to students. New functionalities are constantly being added to the code and contributions are more than welcomed. You can access the full documentation online at https://uwgeodynamics. readthedocs.io

Extended control strategies of voltage source converter stations linked to converter dominated systems

The state of the art of control strategies of modular multi-level converter based high-voltage DC systems can be categorised into two classes according to the connecting system, i.e. the active control strategies such as the vector control and the passive control ones such as the voltage and frequency control. These two control modes need to be transformed to each other under some circumstances. The traditional method to deal with this problem is to switchover the control modes. However, this process takes time and there is risk to lose stability during this period. Thus, an extended control strategy to control the converter in both modes is wanted. An extended control strategy is designed by introducing supplementary feedback property into the traditional vector control strategy. The extended and traditional vector control strategies are compared under various cases by simulation. Simulations show that the system controlled by the traditional vector control strategy loses stability when synchronous machines drop out. However, the extended vector control strategy is superior under weak or even passive grid conditions.