Transient Simulation Model Research Articles

Simulation analysis and experimental validation of enhanced photovoltaic thermal module by harnessing heat

A novel thermally regenerative electrochemical cycle (TREC) has been developed recently for converting low-grade heat into electricity, which is suitable but rarely researched for harnessing the thermal energy generated by the photovoltaic/thermal (PV/T) module to enhance the electrical performance. This study conducts experimental works on the heat-to-electricity performance of the TREC battery to demonstrate the feasibility and superiority of the PV/T-TREC hybrid system. Based on the experimental results, a detailed transient three-dimensional MATLAB simulation model of the PV/T-TREC system is developed to predict the overall electrical performance. For practical applications, the annual behaviors of the PV/T-TREC system employed in three typical climate areas of Hefei, Beijing, Harbin are simulated and compared. The results show that the electrical performance of the hybrid system is better than the single PV and PV/T module during different areas of various weather conditions except for cold season of February and November in Harbin. In comparison to the PV/T, the hybrid system can generate additional electricity of 45.95 kWh/m2, 50.20 kWh/m2, 29.99 kWh/m2 in the locations of Hefei, Beijing, Harbin annually. To reach the maximum electrical efficiency at different amounts of solar radiation, optimal tank volumes are analyzed and suggested in different months. The optimal working temperatures for the maximum electricity output on ideal theoretical analyses are 72 ℃, 83 ℃, 91 ℃, 100 ℃ at the ambient temperature of 5 ℃, 15 ℃, 25 ℃, 35 ℃ in constant heat cases. This study may provide a feasible plan for designing the water tank and water temperature of the PV/T-TREC for achieving high-efficient annual electricity performance of solar power in different application locations.

Advanced two phase flow model for transient molten salt receiver system simulation

In order to realistically predict and optimize the actual performance of a concentrating solar power (CSP) plant sophisticated simulation models and methods are required. This paper presents a detailed dynamic simulation model for a Molten Salt Solar Tower (MST) system, which is capable of simulating transient operation including detailed startup and shutdown procedures including drainage and refill. For appropriate representation of the transient behavior of the receiver as well as replication of local bulk and surface temperatures a discretized receiver model based on a novel homogeneous two-phase (2P) flow modelling approach is implemented in Modelica Dymola®. This allows for reasonable representation of the very different hydraulic and thermal properties of molten salt versus air as well as the transition between both. This dynamic 2P receiver model is embedded in a comprehensive one-dimensional model of a commercial scale MST system and coupled with a transient receiver flux density distribution from raytracing based heliostat field simulation. This enables for detailed process prediction with reasonable computational effort, while providing data such as local salt film and wall temperatures, realistic control behavior as well as net performance of the overall system. Besides a model description, this paper presents some results of a validation as well as the simulation of a complete startup procedure. Finally, a study on numerical simulation performance and grid dependencies is presented and discussed.

Discrete-time simulation for performance modelling of FIFO single-server queuing system

Optimal queue management is crucial for improving the network operation since packet loss is commonly attributed to the likelihood of buffer overflow at intermediate routers on end-to-end communication path. In this paper, a transient discrete-time simulation model is proposed based on queuing theory served by single-server system and single first-in first-out (FIFO) queue. This queuing service framework effectively enforces the best-effort service to the streams of incoming data packets across the network with disparate quality of service (QoS) requirements. We plot the network performance measures such as queue length, delay, server utilisation and packet lifetime to validate the practical wireless systems. Besides, we employ conventional multiple-objective genetic algorithm to model the trade-off among key queuing system parameters including queuing delay, packet drop rate and network bandwidth. Finally, the efficiency of our queuing optimisation model is significantly compared with previous works in terms of bandwidth utilisation, delay, and packet loss rate.

Dynamic Identification of Equivalent Parameters of Mathematical Models of Power Electrical Equipment of Electromechanical Power Systems

The article describes a method for dynamic identification of AC and DC hybrid power network parameters. The inaccuracy of the parameters of the electromechanical transient simulation model of the power system has caused the obvious difference between the simulation results and the actual measurement, which has restricted its online application. Over the years, the dynamic parameter identification technology based on field test and test has made great progress, but it is far from satisfactory and accurate. There is still a long research journey for the requirements of performance. The online identification method based on the actual dynamic parameters of the power system is a way to solve the problem. The article includes the main microprocessor modules for system parametric identification of load (SIP L) and an overhead power transmission line (SIP TL). The article will analyze the active electrical network and passive electrical network

Experiment and finite element analysis of asymmetrical hardness induced by quenching in railway wheel

Excellent properties of railway wheels are of vital significance for adapting to complex and changeable operating environments to reduce maintenance costs and extend service life. This paper presents the results suggesting that the hardness distribution in wheel rim is of obvious inhomogeneity, especially in areas near and away from the flange as ‘on two rim sides’, which undoubtedly affects the subsequent use of the wheel, such as eccentric abrasion and peeling. Product properties (hardness of wheels) are determined, to a certain extent, by temperature and microstructure changes caused by relevant parameters during water–air alternate spraying process. It leads to differences in heat transfer between the surface and the medium or internal heat conduction. To fully investigate such a complicated quenching, a thermo-phase modeling of wheel quenching was used with transient heat transfer, phase change and hardness calculation taken into account. It was found that unsynchronized cooling on both sides of the rim alters the phase behavior of bainite and martensite, especially in stage III of spraying. However, as the depth from the tread increases, the hardness difference becomes almost less obvious. In this condition, the angle of spraying becomes the key parameter influencing temperature–time process during cooling. The calculated results reveal that the hardness is gradually unified on two rim sides by adjusting the deflection angle of spraying that was simultaneously applied to the tread and the rim. The effect of the adjustment was verified experimentally through subsequent actual wheel production. The test analysis mode combined with transient thermal simulation model can be used to effectively and rapidly optimize parameters for intelligent heat treatment process.

Evaluation of Green's Functions for PEEC Models in the Air and Lossy-Ground Space

This article presents the numerical evaluation of Green's functions for the generalized partial element equivalent circuit (PEEC) formulation in the air and lossy-ground space. Both the source and field points can be located in any layer of the air–ground space. Green's functions are expressed using Sommerfeld integrals (SIs), which have highly oscillating and slowly decaying integrands. As a robust and easy-implemented approach, the direct real-axis integration is presented with the techniques for removing the singularity and accelerating the convergence. Closed-form expressions are derived for the quasi-static and asymptotic approximation of SIs. The results are compared with numerical electromagnetics code NEC2, and good agreements were observed. An image model is developed for quasi-static SIs. Greens’ functions can then be contributed by the source and/or its image. This model is used to derive the frequency-invariant PEEC model for fast transient simulation in the time domain. The proposed numerical procedure can be applied to generate lookup tables of SIs, which are indispensable in the evaluation of PEEC circuit parameters for massive wire segments.

DVR Transient Analysis with Saturated Iron-Core Superconducting Fault Current Limiter

Abstract: The saturated iron-core super conducting fault current limiter exceeds all other fault current limiters in terms of technical performance. Based on the real structure, magnetic structures have been proposed. Simulated current limiting inductance was calculated using the Newton iteration method and the fundamental magnetization curve. Sagging and soaring current levels occurred frequently during the faulting process. Short circuits and voltage fluctuations are two of the most typical grid-related issues.. The use of the SISFCL and DVR in this project resulted in a reduction in the amount of fault current and voltage variation. With the help of Matlab/Simulink and theoretical insights from previous research, we were able to construct an electromagnetic transient simulation model. The transient behavior of these devices during simulation tests demonstrates the accuracy and validity of the suggested strategy. Keywords: Analysis of transient electromagnetic waves in a saturated iron core using a Newton iteration method. Fault current limiter (SISFCL), dynamic voltage restorer (DVR), pulse width modulation (PWM)

Expanding the measuring range via S-parameters in a EHV voltage transformer modelling for reliable GIS VFT simulations

The customary approach to modelling voltage transformers (VT) at gas insulate substations (GIS) subject to Very Fast Transients Overvoltages (VFTOs) consists of using a capacitive element. However, this simplistic approach is unable to reproduce characteristic resonances and predict how transients propagate to the VT’s secondary winding. Multiport black-box passive rational models built upon frequency-domain measurements are instrumental to overcome these challenges. The adoption of S-Parameters is an alternative to black-box approaches based on Y-Parameters so as to consistently expand the measurement frequency range which is required to accurately capture the dynamics involved in VFTO phenomena up to 50 MHz at GIS facilities. We validate our results using an strategy that entails measuring, modeling and simulation upon a multiport extra-high voltage (EHV) VT. The proposed approach using S-Parameters leads to increased accuracy compared with the customary approaches using Y-Parameters or capacitive elements.We build two models estimated upon distinct frequency ranges to highlight the importance of extending the measurements into the MHz range so that time-domain simulations better reproduce VFTO characteristics. The black-box VT model thus obtained is incorporated into an actual 500 kV GIS model for transient simulations enabling the analysis of transient propagation between primary and secondary windings.

Analysis of the Cooling Concept of the Braking System of a Formula Student Racing Car Using CFD Simulation and 1D Simulation

In order to guarantee the performant operation of the braking system of a racing car under high load an optimized thermal design of the braking system is an important factor. Especially in motorsports, a lot of braking energy is converted into heat due to short and intense braking events. Therefore, a suitable cooling concept is a crucial point to ensure a reliable thermal management of the braking system to dissipate the generated heat. In this work, the braking system of the formula student racing car of the UAS Esslingen is analysed using the racing car of the season 2019. A transient 1D simulation model of the heat balance of the braking system is created. For the determination of the heat transfer coefficients a steady 3D Conjugate Heat Transfer (CHT) simulation model is set up. The logging data of a real race are used for the validation of the presented model (s). The heat balance of the braking system, its entire heat flows as well as the time-dependent temperature evaluation of the brake disc are analysed and compared. The results of this analysis are used to create a cooling concept for the racing car’s braking system, to ensure an optimized braking performance over the entire race. Several different (geometrical) variants of the thermal design of the braking system are investigated using the above mentioned numerical models and the results are presented. Furthermore, the implementation of a cooling duct for the braking system is studied.

Virtual prototype model of circuit breaker movement characteristic with permanent magnetic actuator

ABSTRACT For solving the problem of fission simulation in the simulation of a permanent magnet actuator used in a vacuum circuit breaker and improving the accuracy of simulation results, the virtual prototype model of a movement characteristic of a permanent magnet actuator used in a circuit breaker is constructed through software combination technology in this paper. The transient field simulation model of the permanent magnet actuator is established on the Ansoft Maxwell software platform, the multi-physical movement simulation model of circuit breaker is established on the Adams software platform, and the control and data transfer model of the circuit breaker is established on the Ansoft Simplorer & Matlab Simulink software platform. On this basis, the static holding force, system reaction force, equivalent mass, and contactor arc in the model are calculated, and the specific modeling parameters are determined. Combined with the test data, the accuracy of the joint simulation is verified.

Control-oriented model for air-based BIPV/T systems

This study presents the development of a control-oriented model for Building Integrated Photovoltaic Thermal (BIPV/T) systems. Model-based control strategies could optimize their coupled operation with the building Heating Ventilation and Air-Conditioning (HVAC) system and maximize the heat utilization. Two transient simulation models (1st order and 2nd order) are developed using Python, validated with experimental data and compered to each other. Finally, simulation results are presented where the range of possible outlet air temperatures for different mass flow rates are identified.

A detailed study of the transient behavior of dual-skin chest-freezer with R290

• Detailed transient behavior of dual-skin chest-freezer operating with R290 is described. • Two mathematical models for freezer transient simulation are developed. • Experimental results of transient system operation are provided in Excel file. • Thermal load influence is simulated with a maximum relative error of 2.7%. • The optimum refrigerant charge of 200g of R290 is calculated. This work reports on a numerical and experimental study of the transient behavior of a dual-skin chest-freezer refrigeration system, operating with R290. A simpler dynamic mathematical model, called thermal, and a more sophisticated one, called capacitive, which models the mass distribution in the systems components, were evaluated. The experiments provided measured data for the characterization of the transient operation of the appliance, supply of models’ input data, and validation of the models. Comparisons between simulation and experimental results showed a very good agreement for both transient and time-averaged systems behavior and performance. The maximum relative error for temperatures at pull-down and on/off operations was 5.5 % . The capacitive model simulated the transient experimental behavior of the refrigeration system well when goods were inserted in the freezer’s cabinet, showing a 2.7 % maximum relative error for the systems performance parameters. Moreover, it yielded a parametric analysis of the refrigerant charge, determining a 200g mass of R290 for the optimum performance. The thermal model is an excellent feature for a first design, simulating 100 min of a real operation in few seconds. The capacitive model provides more complex results, and is a very good tool for a detailed systems design. The experimental data can be used by other researchers for validating their simulations and experimental studies. The paper provides new findings for a system operating with R290, a fluid that has been widely used in small scale refrigeration systems for household applications.

Energy and Economic Sustainability of a Trigeneration Solar System Using Radiative Cooling in Mediterranean Climate

The spreading of nearly zero-energy buildings in Mediterranean climate can be supported by the suitable coupling of traditional solar heating, photovoltaics and radiative cooling. The latter is a well-known passive cooling technique, but it is not so commonly used due to low power density and long payback periods. In this study, the energy performance of a system converting solar energy into electricity and heat during the daytime and offering cooling energy at night is assessed on the basis of a validated model of a trifunctional photovoltaic–thermal–radiative cooling module. The key energy, CO2 emission and economic performance indicators were analyzed by varying the main parameters of the system, such as the spectral emissivity of the selective absorber plate and cover and thermal insulation thickness. The annual performance analysis is performed by a transient simulation model for a typical residential building and two different climates of the Mediterranean area (Trapani and Milano). For both climates, glass-PVT–RC is the best solution in terms of both overall efficiency (electric + thermal) and cooling energy capacity, even better with a thicker insulation layer; the annual electrical, heat and cooling gains of this system are 1676, 10,238 and 3200 kWh for Trapani, correspondingly (1272, 9740 and 4234 kWh for Milano, respectively). The typical glass-PVT module achieves a performance quite similar to the best ones.

A Two-Level Simulation-Assisted Sequential Distribution System Restoration Model With Frequency Dynamics Constraints

This paper proposes a service restoration model for unbalanced distribution systems and inverter-dominated microgrids (MGs), in which frequency dynamics constraints are developed to optimize the amount of load restoration and guarantee the dynamic performance of system frequency response during the restoration process. After extreme events, the damaged distribution systems can be sectionalized into several isolated MGs to restore critical loads and tripped non-black start distributed generations (DGs) by black start DGs. However, the high penetration of inverter-based DGs reduces the system inertia, which results in low-inertia issues and large frequency fluctuation during the restoration process. To address this challenge, we propose a two-level simulation-assisted sequential service restoration model, which includes a mixed integer linear programming (MILP)-based optimization model and a transient simulation model. The proposed MILP model explicitly incorporates the frequency response into constraints, by interfacing with transient simulation of inverter-dominated MGs. Numerical results on a modified IEEE 123-bus system have validated that the frequency dynamic performance of the proposed service restoration model are indeed improved.

Miniaturization design of closing electromagnet for fast contact mechanism of DC circuit breaker in power grid

The newly designed DC circuit breaker closing electromagnet must meet the requirements of small size and fast action. This article focuses on the design index of the electromagnet, and carries on the preliminary design based on the empirical formula. On this basis, with the smallest volume as the objective function, a steady-state simulation design is carried out using BOBYQA's optimization algorithm. The design results are input into the transient simulation model to solve and analyze the characteristic changes of the solenoid coil voltage and current. Simulation and prototype test results show that under AC220V 50Hz full-wave rectification excitation, the moving iron core starts to move in 18.8ms and completes a 6mm stroke in 30.8ms; the peak coil current during the continuous flow is 4.15A, which meets the design index requirements of the electromagnet. The new scheme provides a reference for the design of DC circuit breaker closing device.

Strategies to Increase the Transient Active Power of Photovoltaic Units during Low Voltage Ride Through

Due to a limitation in the magnitude of the three-phase output inverter currents, the output active power of the photovoltaic (PV) unit has been de-rated during low voltage ride through, which brings great instability risk to the power system. With the increase in the penetration rate of new energy, the impact of the power shortage on the system transient stability increases. It is of great significance to analyze the impact of this transient power shortage on system stability. This article explores methods to improve the active power output capability of photovoltaic units during low-breakthrough periods. A transient simulation model of a grid-connected PV generator with low-voltage ride-through (LVRT) capability is presented, under the condition of meeting the overcurrent capacity of the PV inverter and the requirement of dynamic reactive power support supplied by the PV generator specified in the China grid codes (GB/T 19964-2012) during grid fault. An example system with high PV penetration is built. The change principle and influencing factors of PV transient active power output are analyzed. The simulation model is designed in PowerFactory/DIgSILENT, and several types of three-phase voltage sags are performed in simulation to assess the impact of the active current reference calculation method and the maximum inverter output current (Imax) limit value on the PV active power output. According to the three indexes, namely the maximum active power of PV unit during the fault, the power improvement gradient and the power surge after the fault is cleared. Simulation results showed that using the orthogonal decomposition method to calculate the active current reference can make full use of the current capacity of the converter. Setting Imax to 1.1 rated current of photovoltaic inverter (IN) can reduce the cost-effectiveness ratio of the transient active power output of the PV unit. Therefore, we aim to improve the unit’s transient active power output capacity and realize the optimal effect of improving the transient active power shortage of the system.

Flexible Operation of Air Separation Units

AbstractAs part of the Energiewende, the current research on energy‐optimized, flexible operation of air separation units is described. A realistic, pressure‐driven approach for dynamic simulation is presented, which is used to provide a detailed, transient simulation model, a digital twin, of an air separation unit. Extreme operation scenarios, such as start‐up and shutdown of the main heat exchanger, the distillation columns or the entire air separation unit, are described. Since the main heat exchanger experiences repeated temperature changes, its lifetime is investigated in a test rig. The gathered data is used to derive and validate detailed, three‐dimensional simulation models.

Solids back-mixing in the transport zone of circulating fluidized bed boilers

This work investigates the back-mixing of solids in the transport zone of large-scale circulating fluidized bed (CFB) boilers, with the aims of identifying and evaluating the governing mechanisms and providing a mathematical description based on a solid theoretical background rather than on purely empirical correlations. In addition, transient Direct Numerical Simulation (DNS) modeling is used to identify the mechanism that drives migration of the solids from the dilute up-flow in the core region to the down-flow at the furnace walls. Previously published concentration and pressure profiles are collated and analyzed through modeling of the steady-state mass balance of the dispersed solids in the transport zone. The study shows that solids back-mixing at the furnace wall layers is limited (hence governed) by the core-to-wall layer mass transfer transport mechanism rather than by the lateral movement of solids within the core region. The latter is shown by the 3-dimensional (3D) mass balance model, and the transient DNS modeling indicates that this is due to a turbophoresis mechanism. We also show that the use of Pe-numbers to describe the lateral solids dispersion is not straightforward but rather depends on the unit scale, and that Pe-numbers < 26 are needed to yield the solids back-mixing rates measured in large-scale CFB boilers. Finally, we propose a mathematical expression for the core-to-wall layer mass transfer coefficient derived from a Sherwood number (Sh)-correlation fitted to measured values of the characteristic decay constant that result from the solids back-mixing. This expression shows better agreement with the large-scale measurements than do the expressions given in the literature.

Numerical investigation on a double suction twin-screw multiphase pump

Based on the dynamic mesh technology, the moving grids of the double-suction screw multiphase pump were generated by the software SCORG. Then the three-dimensional transient simulation model was established to investigate the two-phase flow mechanism inside the screw pump under different inlet gas volume fraction (IGVF). The results show that the pressure inside the working chamber increases step by step from inlet to outlet and is symmetrical. The pressure drops sharply at the inlet of circumferential clearance and then decrease linearly in the clearance. The curved flow in suction and discharge flow passage causes the gas separation and high gas volume fraction (GVF) area in suction and discharge chamber. Four vortices in cross section of discharge pipe cause four high GVF areas due to the centrifugal force produced by the vortices. The high GVF areas scatter in working chambers and change slightly with the rotation angle except the last chamber under the IGVF 10%. The two-phase leakage flow shows layered flow where the gas concentrates at the bottom of the gap. Thus, the high GVF areas on the surface of the rotors mainly exist at the position of gaps. The work will provide instructions for improving its performance under high IGVF.

Research on Magnetic Field Characteristics in DC Yard of Dinghai Converter Station Under Monopolar Grounding Fault

In Dinghai converter station of Zhoushan VSC-HVDC transmission project, 200 kV hybrid DC circuit breaker is used for the first time to realize DC side fault isolation. When DC side short circuit occurs, its fault current characteristics are different from those of AC substation and HVDC converter station, and the magnetic field interference to secondary equipment in DC yard is still unknown. In this paper, taking the single pole grounding short circuit fault with high probability in flexible DC power grid as an example, the electromagnetic transient simulation model of fault current in Dinghai converter station is established, and the time-domain current waveform is obtained. Then, the magnetic field calculation model of DC circuit breaker and other key electrical equipment is established, and the magnetic field of secondary equipment in DC yard is calculated based on Biot-Savart Law. The results show that the maximum magnetic field strength at the secondary equipment is 59 A/m, the waveform is ms level, and it is aperiodic. The distribution of magnetic field in DC yard varies between 3 and 346 A/m.