Non-Linear Behavioral Modeling for DC-DC Converters and Dynamic Analysis of Distributed Energy Systems

In modern distributed energy systems (DES), there is a shift in focus from conventional centralized approach to more advanced distributed architecture. Modeling and analysis of these complex systems is more challenging, as multiple energy sources are connected with different loads through power electronics converters. Due to vastly different dynamic characteristics of these converters, it is necessary to model their behavior before integration into DES, to avoid various issues, e.g. instability. This paper presents behavioral modeling methodology for a three phase AC-DC converter system based upon the measurement of frequency responses. The frequency responses are measured using a black-box approach, i.e. independent of system's internal design and parameters. For verification, the dynamic analysis is performed for the actual switching model and compared with the developed behavioral model. The matching of results from the switching model and frequency response measurements based behavioral model serves to verify the accuracy of the methodology used for frequency response measurements and behavioral modeling.

The optimal location of renewable distributed generations (DGs) into a radial distribution system (RDS) has attracted major concerns from power system researchers in the present years. The main target of DG integration is to improve the overall system performance by minimizing power losses and improving the voltage profile. Hence, this paper proposed a hybrid approach between an analytical and metaheuristic optimization technique for the optimal allocation of DG in RDS, considering different types of load. A simple analytical technique was developed in order to determine the sizes of different and multiple DGs, and a new efficient metaheuristic technique known as the Salp Swarm Algorithm (SSA) was suggested in order to choose the best buses in the system, proportionate to the sizes determined by the analytical technique, in order to obtain the minimum losses and the best voltage profile. To verify the power of the proposed hybrid technique on the incorporation of the DGs in RDS, it was applied to different types of static loads; constant power (CP), constant impedance (CZ), and constant current (CI). The performance of the proposed algorithm was validated using two standards RDSs—IEEE 33-bus and IEEE 69-bus systems—and was compared with other optimization techniques.

The relationship of stress and strength gradients must be considered simultaneously in analysis of a particular type of fracture. This chapter discusses the principal elastic stress distribution in members of various shapes under different types of pure loads. A basic understanding of both the stress and strength gradients of metal parts with and without stress concentrations and under different types of loading is provided. The chapter also describes the effect of service conditions on applied stresses.

A physical theory of the structure of uniaxially oriented polymers is used to propose a new mechanical model that makes it possible to predict deformation processes in polymers. Polycaproamide-film fibers are used as an example to illustrate the use of the model to predict deformation and relaxation in polymers. Making optimum use of both new and traditional polymers in different sectors of industry would be impossible without proper study of their viscoelastic properties. Such studies can be performed by mathematically modeling the deformation processes which take place in these materials. In practice, an attempt is made to quantitatively predict the behavior of polymers by using various methods that involve mathematical modeling and numerical projection [1-5]. However, as is known, these methods are valid for a relatively narrow range of mechanical loads, strains, and temperatures and cannot predict certain features of the materials’ behavior. In addition, such methods do not embrace or explain all of the processes that take place in synthetic fibers and filaments because the physical features of polymers are not accounted for in the integral equations of viscoelasticity [1-12]. Thus, in this article we propose to model deformation and relaxation processes by using a nonlinear mechanical model that includes physical properties. This will make it possible to determine the mechanical characteristics of polymeric materials under conditions that correspond to different types of loading, which in turn will allow the materials’ properties to be predicted within a wide range of loads and temperatures. The supermolecular structure of oriented amorphous-crystalline polymers is variegated and complex. Thus, the polymers can be in different quasi-equilibrium states when loaded. The viscoelastic component of deformation is a subject worthy of special attention when studying the deformation of materials of the given class. In accordance with modern physics, materials may undergo viscoelastic deformation due to the rearrangement of different stable structures (clusters) which are in different states separated by energy barriers. These clusters or active conformation elements (ACEs) [13] - the nature of which is not germane to mechanical descriptions - can be in one of two stable states. The stable state in which the linear dimension is minimal - state 1 - will be referred to as being conditionally convolute and will be represented as . We will call the second stable state - state 2 - conditionally involute and will represent it as . For example, an elastic spring can either be convolute or involute. On the one hand, this element is elastic. On the other hand, it is also nonlinear. Thus, instead of using classical mechanical models in the form of Hookean springs, dampers, and combinations thereof, i.e. classical linear Maxwell elements, Kelvin-Voigt elements, etc., we are proposing to use a nonlinear model (elastic spring) which is based on energy barriers. These barriers will be represented in the form of the energy diagram shown in Fig. 1. In accordance with the proposed physical and mechanical model, an unloaded cluster can be in one of two stable states - state 1 or state 2. These states are separated by an energy gap of the width U and a barrier of the height H. A deformation

The Hybrid Power Electronic Transformer (HPET) has been proposed as an efficient and economical solution to some of the problems caused by Distributed Energy Resources and new types of loads in existing AC distribution systems. Despite this, the HPET has some limitations on the control it can exert due to its fractionally-rated Power Electronic Converter. Various HPET topologies with different capabilities have been proposed, being necessary to investigate the system benefits that they might provide in possible future scenarios. Adequate HPET models are needed in order to conduct such system-level studies, which are still not covered in the current literature. Consequently, this article presents a methodology to develop power flow models of HPET that facilitate the quantification of controllability requirements for voltage, active power and reactive power. A particular HPET topology composed of a three-phase three-winding Low-Frequency Transformer coupled with a Back-to-Back converter is modeled as an example. The losses in the Back-to-Back converter are represented through efficiency curves that are assigned individually to the two modules. The model performance is illustrated through various power flow simulations that independently quantify voltage regulation and reactive power compensation capabilities for different power ratings of the Power Electronic Converter. In addition, a set of daily simulations were conducted with the HPET supplying a real distribution network modeled in OpenDSS. The results show the HPET losses to be around 1.3 times higher than the conventional transformer losses over the course of the day. The proposed methodology offers enough flexibility to investigate different HPET features, such as power ratings of the Power Electronic Converter, losses, and various strategies for the controlled variables. The contribution of this work is to provide a useful tool that can not only assess and quantify some of the system-level benefits that the HPET can provide, but also allow a network-tailored design of HPETs. The presented model along with the simulation platform were made publicly available.

The optimal design of grid-connected distributed energy systems (DES) has been previously investigated, but most studies exclude nonlinear multiphase optimal power flow (MOPF) constraints which capture imbalances in alternating current (AC) distribution networks. Previous DES design studies considering AC power flow assume balanced loads and networks, which is an assumption that does not hold for distribution networks that are often inherently unbalanced. This is the first study to present an optimisation framework for designing grid-connected DES while simultaneously considering multiphase optimal power flow (MOPF) constraints to accurately represent unbalanced low-voltage distribution. This study proposes a new algorithm for obtaining DES designs subject to nonlinear multiphase power flow constraints with regularised complementarity reformulations for operational constraints containing binary variables. DES design models with either MOPF or OPF are tested using an unbalanced distribution network, where rooftop solar, gas boilers, and battery storage are considered as distributed resources. Despite the increased complexity, DES design with MOPF obtains the best solution, with 81% greater solar capacity and 6% lower total annualised cost when compared to DES with OPF. Designs from a commonly-used linear DES design framework based on direct current (DC) approximations produce the highest costs (8% more than initially predicted) when tested with MOPF. The proposed algorithm with complementarity reformulations achieves a 19% improvement in the objective value over a previous two-stage decomposition for DES with OPF, where the entire binary topology in the nonlinear model is fixed. The study therefore enables the acquisition of DES designs that can work symbiotically within unbalanced distribution networks.

This paper shows the variation of different power system parameters for a grid-tied Distributed Generation system during the situation of islanding under different types of load conditions. Parameters that have been taken into account here are RMS voltage, RMS current, Active Power, Reactive Power, Apparent Power, Impedance and Frequency at the Point of Common Coupling (PCC). A fundamental assumption considered here is that the load remains fixed for all the load cases discussed in the result section. The simulation results show the variations in the above parameters for different values and types of loads when islanding occurs in the grid-tied DG power system.

This paper presents an analytical and experimental research programme’s results regarding material nonlinearity’s influence on reinforced concrete beams’ immediate deflections. Six full-size laboratory beams were tested under different type of loads in the experimental programme. The ANSYS finite element software nonlinear material model was used for simulating the beams’ analytical behavior. Comparing ANSYS nonlinear material model results, ACI 318 equations and the results of the tests made revealed that a beam’s structural behavior is strongly influenced by material nonlinearity.

PurposeThe present work aims to explain how the nonlinear average model can be used in power electronic integration design as a behavioral model.Design/methodology/approachThe nonlinear average model is used in power electronic integration design as a behavioral model, where it is applied to a voltage source inverter based on IGBTs. This model was chosen because it takes into account the nonlinearity of the power semiconductor components and the wiring circuit effects, which can be formalized by the virtual delay concept. In addition, the nonlinear average model cannot distinguish between slow and quick variables and this is an important feature of the model convergence.FindingsThe paper studies extensively the construction of the nonlinear average model algorithm theoretically. Detailed explanations of the application of this model to voltage source inverter design are provided. The study demonstrates how this model illustrates the effect of the nonlinearity of the power semiconductor components' characteristics on dynamic electrical quantities. It also predicts the effects due to wiring in the inverter circuit.Research limitations/implicationsMore simulations and experimental analysis are still necessary to improve the model's accuracy, by using other static characteristic approaches, and to validate the applicability of the model to different converter topologies.Practical implicationsThe paper formulates a simple nonlinear average model algorithm, discussing each step. This model was described by VHDL‐AMS. On the one hand, it will assist theoretical and practical research on different topologies of power electronic converters, particularly in power integration systems design such as the integrated power electronics modules (IPEM). On the other hand, it will give designers a more precise behavioral model with a simpler design process.Originality/valueThe nonlinear average model used in power electronic integration design as behavioral model is a novel approach. This model reduces computational costs significantly, takes physical effects into account and is easy to implement.

In spite of availability of natural sources, still people are now sitting on the dark zone. Because of the remote area, the grid networking system is very weak. As a result of which power stability may not be assured, which greatly effects to the day-today activities of the people in the reason. Fortunately, technology exist that can give the assurance of quality of electricity in an isolated area which is for away from the regular power network. The preset scenario is the coexistence of both AC and DC micro grids, because of the evolutions of different types of loads. The hybrid microgrid concept assume a cluster of different types of loads and distributed generatoroperating as a controllable system which maintain the quality of power and its stability to its local area. To make the world pollution free environment, renewable energy infrastructure is increasing particularly in the distribution network. It has the advantage that the power generated through distributed generation system is utilized in the grid for other users. The PV cell generates voltage at the distribution level. At the end of distribution line a 1 MVA three phase load is connected. In the absence of the generation from the PV cells, the voltages and currents at various lengths of the line are calculated with a single load of three phase 1 MVA. With the inclusion of PV cells, the improvement in voltage dip is also estimated. This estimate provides the power supplied by the PV cell and improvement in voltages. In order to determine the effect of additional load on voltage profile, a three phase load of 1 MVA was connected to intermediate point in the transmission system. This causes the dip in voltage at various nodes of the distribution line. Several combinations of source and loads have been examined to determine the effect on voltage and power. The above work has been carried out using Electro Magnetic Transient Program (EMTP) Software. In order to simulate the system, 8.98 kV, 5 km long line is divided into 5 sections of 1 km each. The sections are represented in the form of Pi-network by its series inductance, resistance and capacitance to ground. Loads are represented by R and L of appropriate magnitude and through EMTP program the calculations are done. The PV cell is represented by a source stepped up to 8.98 kV system. Both single phase and three phase lines have been examined through the above program. The results obtained for various conditions are presented in the paper.

This paper presents an application of deadbeat control theory in control of the DC/AC single-phase voltage source PWM inverter (VSI PWM). The main object of the article is to ensure a high quality of the inverter output voltage under different types of load (linear and nonlinear). One of the main criteria of the quality of the output voltage is total harmonic distortion (THD). It should be kept as small as possible. This article describes a detailed modelling of the plant and controller design. A novel multi-loop control technique based on deadbeat theory is proposed in order to achieve sinusoidal output voltage. The proposed control scheme consists of current and voltage loop. Theoretical analysis, simulation and practical results have been given to verify the proposed digital control scheme. Proposed control scheme was implemented into the TMS320F28335 DSC controller and tested on 1 kW PWM inverter.

Distribution System consist of different types of loads like linear and nonlinear load. Due to different types of loads, voltage unbalance and other power quality related issues will occur. To overcome this problem, a voltage source inverter based device called distribution static compensator can be used. In this work, an improved voltage controller for distributed static compensator, based on power balancing theory is presented. The improved controller uses only voltage sensors and this controller is developed by considering unbalanced load conditions. Proportional Integral controller is used for maintaining terminal voltage and DC link voltage. The controller is verified for different voltage disturbances such as sag and swell. MATLAB/SIMULINK package is used to verify the controller using simulation. The controller is also verified using Hardware in the loop simulation using DSPACE and results are presented for different voltage disturbances.

Fatigue studies of CoCrFeMnNi high entropy alloy films using nanoindentation dynamic mechanical analyses

In a static problem of the deformed body mechanics, all the forces depending on their availability in the equation resolution system are classified as surface forces P<SUB>i</SUB>, volume forces F<SUB>i</SUB> and distortions or forced strains (xi) . It is known that there is partial equivalence of force which means an identify equality (analogy) of stresses or displacements under the action of different types of loads; in particular, between volume and surface force actions though under very strict limitations. It is easy to demonstrate that by introducing the third constituent -- a forced strain -- it appears to be possible to establish the necessary and sufficient conditions for the analogy. These conditions make it possible to present a forced strain action as the sum of volume and surface force actions; volume forces -- as the sum of surface force effects and forced strains; surface forces -- as the sum of forced strains and volume forces. The analogy in question is very important for the experimental solution of the problem because the realization of every force is limited by modeling technique's possibilities.

In this paper an equivalent complex baseband representation of the analog component related non-linearity of digital transmitters relying on 1-bit complex baseband encoding is derived. By exploiting the properties of the pulsed RF encoding the novel behavioral modeling technique is able to represent accurately the non-linear memory effects of the power amplification stage. Furthermore, a band-limited kernel technique leads to more efficient modeling of the complete digital transmitter, and to relaxed sampling rate. For the parameter estimation the linear regression, common to Volterra model identification, can be employed. According to the simulation and measurement based verification results, the novel modeling technique excels the state-of-the-art in terms of modeling accuracy. It can be assumed that the given methodology serves both as a basis for future behavioral models and for the development of advanced encoding techniques for linearization purposes.