Analysis Of Transient Characteristics Research Articles

Synthesis of a fractional-order PIλDμ-controller for a closed system of switched reluctance motor control

The relevance of creating high-quality control systems for electric drives with a switched reluctance motor (SRM) was substantiated. Using methods of mathematical modeling, transient characteristics of the process of turn-on of SRMs with various moments of inertia were obtained. Based on analysis of the obtained transient characteristics, features of the SRM turn-on process determined by dynamic change of parameters of the SRM during its turn-on were shown. Low accuracy of SRM identification using a fractionally rational function of rat34 class was shown. Regression coefficient of the resulting model was 85 %. Based on analysis of transient characteristics of the SRM turn-on process, a hypothesis was put forward about the possibility of identifying the SRM by means of a fractional-order transfer function. Using the methods of mathematical modeling, transient characteristics of the process of turning-on the SRMs with various moments of inertia were obtained. Using the FOMCON MATLAB Toolbox, identification of the SRM turn-on process with the help of a fractional-order transfer function of second order was performed. Regression coefficient of the resulting model was 93–96 %. For the obtained fractional-order transfer functions, a method of synthesis of a fractional-order PI λ D μ controller optimized in terms of minimum integral square error of the transition function of the closed system of fractional-order control of objects was implemented. The FOMCON MATLAB Toolbox was used for synthesis of the PI λ D μ controller. Comparative analysis of the SRM turn-on processes in both open and closed control systems with a classical integer-order PID controller and with a fractional-order PI λ D μ controller was made. Use of the fractional-order PI λ D μ controller in comparison with the classical integer-order regulator makes it possible to reduce overshoot from 13.3 % to 2.64 %, increase speed of the closed ACS, decrease regulation time from 1.48 s to 0.53 s while reducing variability of transient characteristics. The study results can be used to improve performance of closed systems for controlling angular velocity of the SRM

Transient thermal characteristic analysis and charging state estimation of lithium batteries for Automated Guided Vehicle during discharge

The lithium batteries and their health management for automated guided vehicle power supply system are studied in depth in this paper. First, the transient heat generation for the discharge process of a lithium battery will cause it to work in an unhealthy state and non-linear conditions, seriously affecting the life expectancy. The thermal behavior for lithium battery discharge is studied in depth, and a reliable thermal model is constructed to provide a theoretical basis for designing a lithium battery health management system. Secondly, the accurate and reliable residual state estimation of the lithium battery cannot only provide visualized battery residual capacity, but also reflect the aging status of the lithium battery and other related information, and is one of the important functions to ensure the healthy operation of the lithium battery pack. A new support vector machine is proposed on account of the analysis of the equivalent circuit model of lithium battery, which combines genetic algorithm with particle swarm optimization to enhance the parameters of hybrid kernel function, to analyze accurately the charging status. Finally, the state-of-charge simulation of lithium batteries with variable current discharge is conducted, which proves that the support vector machine algorithm proposed in this paper can accurately judge the charging state of lithium batteries.

Transient Characteristics Analysis of 500kV Parallel Circuit Breaker Based on Highly Coupled Split Reactor

With the continuous expansion of power system capacity, parallel high-voltage circuit breakers with a Highly Coupled Split Reactor (HCSR) have a potential application for limitation of high short-circuit current. However, as the parallel circuit breakers open at different time, the residual voltage of the split reactor on the post-open circuit breaker is higher and the stray capacitors of HCSR form high-order oscillating circuits, which may lead to serious transient recovery voltage (TRV). Therefore, it is necessary to analyze and simulate the transient characteristics of 500kV HCSR. Firstly, the equivalent model of HCSR circuit breakers is built in EMTP simulation plat-form, and its TRV generation is analyzed. Then, the TRV of parallel circuit breakers under different operating conditions and fault types is simulated and calculated. Finally, according to the statistical calculation results, the protection measure of 0.2uF shunt capacitance to limit rise rate of TRV is proposed.

Thermal boundary condition optimization of ball screw feed drive system based on response surface analysis

Abstract To improve the simulation accuracy of the traditional transient thermal characteristics analysis model (TCAM) of the ball screw feed drive system (BSFDS), the optimization method of the thermal boundary conditions (TBCs), including the thermal loads, the convective heat transfer coefficient and the thermal contact resistance (TCR), was proposed. A multi-objective and multi-parameter optimization model was established based on the hybrid response surface (HRS) and a multi-objective genetic algorithm (MOGA) was developed to optimize the above TBCs. To simulate the thermal characteristics of the BSFDS under different working conditions, the generality of the method was extended to predict the TBCs under different feed rates. To validate the effectiveness of the method, the thermal characteristic experiments of BSFDS were conducted. The results showed that the simulation error for the temperature field was reduced from 25% to 10% and that the simulation error for the thermal elongation was reduced from 30% to 11%.

Numerical analysis of transient characteristics of a bulb hydraulic turbine during runaway transient process

In this paper, the runaway transient process in a bulb turbine has been investigated by adopting commercial CFD code ANSYS CFX, and transient characteristics in the process have been examined and analyzed in detail. The results show that the predicted maximal runaway rotational speed and flow rate of the turbine are in close agreement with experimental data. During transient process, both the flow rate and rotational speed are rising with time, leading to an increase in both axial and circumferential velocities at the runner outlet. The velocity ratio between them has been diminished greatly at the draft tube inlet, inducing a spiral vortex rope growing with time. The cavitation will shorten the duration and reduce the maximal rotational speed of the runaway process. The runner blade pressure surface is much more critical to cavitation than the suction surface. The amplitude of pressure fluctuation in the runaway process is increasing in the main flow direction. Furthermore, the amplitude of pressure fluctuation reaches up to over 100% of the working head in the draft tube, considerably threatening the safe operation of the turbine.

Analysis of transient current distribution characteristics of Press Pack IGBT

In the switching process of Press Pack IGBT (PPI) module, the phenomenon of nonuniform current distribution invariably happens which reduce the reliability and life time of chips and the module. The uneven current distribution would be caused by some physical reasons such as the clamp force, the temperature; and the electrical reasons including the parasitic inductance of the emitter pillars, the parasitic resistance of the gate connector and the difference of the paralleled chips characteristic, etc. Based on the modeling of two disparate module structures, the parasitic parameter of the emitter pillars and gate connector is extracted in this paper. Then the different equivalent circuits of PPI module are built due to the researches in different factors with the Synopsys Saber software. At last, by comparing the influence of two modules indifferent factors, the simulation results prove the relationship between the pillars distribution and the chip switching losses.

Large-eddy simulation and linear acoustic modeling of entropy mode oscillations in a model combustor with coolant injection

Lean-burn combustor is particularly susceptible to combustion instability and the unsteady heat release is usually considered as the excitation of the self-maintained thermo-acoustic oscillations. The transverse coolant injection is widely used to reduce the temperature of burnt gas, but on the other hand, it will introduce temperature fluctuation inside the combustor. Therefore, it is necessary to consider the influence of the coolant injection on combustion instability, and evaluate its dynamic feature. In this paper, Large-Eddy Simulation (LES) of the self-excited pressure oscillations in a model combustor with coolant injection is carried out. The analysis of transient flow characteristics and the identification of the pressure modes confirm that one of the low frequency pressure oscillations is related to entropy fluctuations, which is known as rumble combustion instability. The LES results show that transient coolant injection is another excitation of temperature fluctuation other than unsteady combustion. The amplitude of the entropy mode oscillation increases with increasing coolant air mass whereas the change of its frequency is insignificant. According to the major feature of entropy wave oscillation caused by coolant injection, a compact coolant injection model is proposed and applied in the One Dimensional (1D) Acoustic Network Method (ANM). Key correlations used in the model match well with LES data in low frequency range. This means that the coolant injection model is a complex one reflecting the interaction of the fluctuating coolant mass, pressure and temperature. Finally, the combustion instability frequencies and modes predicted by acoustic network method are also in good agreement with LES results.

Efficient management of excitons in red and white organic light-emitting diodes by employing blue thermally activated delayed fluorescent emitter based acridine/sulfone derivative as the host

Abstract Highly efficient red and white organic light-emitting diodes (OLEDs) employing blue thermally activated delayed fluorescent (TADF) emitter of mSOAD based acridine/sulfone derivative as the host are realized by efficient management for singlet and triplet excitons. The red OLEDs reach a high maximum current efficiency, power efficiency and EQE of 32.7 cd A−1, 31.0 lm W−1 and 20.3%, respectively. And the white OLEDs with different dopant concentrations exhibit ultra-high color stability of ±(0.008, 0.001), ±(0.000, 0.003) and ±(0.002, 0.005), respectively. Meantime, the high efficiencies are also achieved with maximum current efficiencies, power efficiencies and EQEs of 28.2–32.0 cd A−1, 26.3–30.5 lm W−1 and 12.2–17.4%, respectively. The analysis of energy level and transient decay characteristics demonstrate the excellent device performances are mainly stemmed from the sufficient confinement for charges and excitons and efficient energy transfer from the TADF host to dopant.

Two‐step method for identifying photovoltaic grid‐connected inverter controller parameters based on the adaptive differential evolution algorithm

Photovoltaic (PV) grid-connected inverter is the core component of PV generation system; quickly and accurately obtaining the parameters of inverter controller has great significance in analysis of transient characteristics of PV generation system. Parameter identification relies on disturbance signals and measurements selection, and the trajectory sensitivities of inverter controller parameters are calculated with different system outputs as the measurements, the disturbance signals include AC three-phase short-circuit fault and DC voltage reference jump, accordingly, a two-step identification method is proposed, the first step use a three-phase fault to identify all voltage loop parameters and the proportional coefficient of current loop, and the second step consider a DC voltage reference jump disturbance to identify the integral coefficient of current loop and the setting inductance value. The adaptive differential evolution is taken as the identification algorithm, which adopts adaptive strategies for algorithm parameters in order to speed up the convergence and enhances the balance between the global search and local mining. The simulation analysis validates the effectiveness of this method. In addition, the impact of the inductance error on the identification is discussed.

Simulation on Transient Characteristics of Inter-Turn Short Circuit Fault of Dry-type Air-Core Reactor Based on ANSYS Maxwell

Transient characteristic analysis of inter-turn short circuit fault has been done which is paramount for detecting the earlier fault of dry-type air-core reactor. Dynamic physical process of inter-turn short circuit is theoretically analyzed for dry-type air-core reactor from normal running condition to inter-turn short circuit fault condition. Using ANSYS Maxwell, transient field circuit coupling calculation model is set up and the transient characteristic of inter-turn short circuit fault is simulated, which is also verified by experiments. The study shows that the short circuit ring causes a sudden change of magnetic field at the position of short circuit which can be detected by the detecting coils installed on the package of reactor. Inter-turn short circuit fault can be detected in the earlier fault period by the method proposed in this paper.

Transient characteristics of induced polarization in inhomogeneous media (from results of 2D numerical simulation)

This paper presents the results of 2D mathematical modeling of induced polarization (IP) in the cases of profiling and electrical tomography for piecewise homogeneous media containing ore bodies with different structures, sizes, depths, relaxation times, chargeability, and electrical resistivity. The standard and spectral approaches to data analysis are compared. The cases where analysis of transient IP characteristics yields new information of practical importance are considered. The main features of transient IP characteristics in 2D inhomogeneous media are determined from the modeling results. Analysis of transient IP characteristics is found to yield the best results when the depth of occurrence of polarizable bodies is minimal and their electrical conductivity is an order of magnitude lower than that of the host tock.

Correlation analysis of transient heat transfer characteristics for air precooling aggregate

In dam works, air precooling of aggregate is a common and effective method to avoid temperature cracks in concrete structure. In order to offer a reliable design theory for the air precooling process to avoid unreasonable energy consumption, the transient heat transfer characteristics of the aggregate are intensively analyzed. The combined structure of the aggregate and the interstitial space in the hopper is treated as a porous structure, and the space-average method is used to simulate the transient heat transfer process. Simulation results show that size of the hopper and the average air velocity in the cross section have great influence on the transient heat transfer process of the aggregate, while the porosity in the range of 0.4‒0.5 has little influence. Nomograms are abstracted from simulation results, and then correlations of the compared excess temperature are precisely fitted to predict the air precooling transient heat transfer process of the aggregate.

CARACTERÍSTICAS TRANSITORIAS Y ESTRATEGIA ÓPTIMA DE CONTROL DE UN REACTOR CONTROLABLE SUPERCONDUCTOR

Superconducting controllable reactor (SCR) is a promising device for reactive power compensation to improve the voltage stability and reliability of power system. Given the special structure and complex magnetic circuit of SCR, the transient characteristics and control strategy, which have an important effect on the performance of SCR, lack comprehensive analysis. In this study, transient characteristics analysis and an optimal control strategy are proposed. First, the basic operating principle and the impedance of the analytical model of SCR were presented. Second, the transient characteristics on the DC component and the overvoltage of SCR were analyzed in detail, and an optimal control strategy based on circuit breaker and anti-parallel thyristors was proposed. Finally, the principle and performance of proposed methods were validated through electromagnetic simulation and experiments of 380V/30kVar prototype. The simulation and experimental results demonstrate that the DC component and overvoltage will be produced in the transient process. When the switching angle of superconducting winding is 90°, the DC component and overvoltage become small. The optimal control system proposed can avoid producing the DC component and overvoltage that damage the superconducting windings. The results obtained in this study can be applied to the optimal performance design of SCR. Keywords: Superconducting controllable reactor, Optimal control strategy, DC component, Overvoltage

A Calculation Method and Analytical Formula of the Earth High Frequency Zero Sequence Impedance

This paper puts forward a method of calculating the high-frequency zero sequence impedance, and deduces the earth high frequency analytic calculation formula for the zero sequence impedance. In order to verify the validity of analytical formulas, this paper combined with a large field trial data. Analytic calculation formula in this paper, with simple forms and convenient application, will contribute to the analysis and calculation of lightning and transient characteristics of overhead transmission lines.

Seamless measurement technology of transient signals based on approximate entropy.

The acquisition of waveforms and the analysis of transient characteristics of signals are the fundamental tasks for time-domain measurement, while the reduction of the measuring gap till seamless measurement is extremely important to the acquisition, measurement, and analysis of transient signals. This paper, aimed at the seamless time-domain measurement of non-stationary transient signals, proposes an approximate entropy-based characteristic signal extraction algorithm on the basis of information entropy theories. The algorithm quantitatively describes the complexity (amount of information) of sampled signals using the approximate entropy value, self-adaptively captures characteristic signals under the control of the approximate entropy in real time, extracts the critical or useful information, and removes redundant or useless information so as to reduce the time consumption of processing data and displaying waveforms and realize the seamless time-domain measurement of transient signals finally. Experimental results show that the study could provide a new method for the design of electronic measuring instrument with seamless measurement capability.

Optical digital coherent detection technology enabled flexible and ultra-fast quantitative phase imaging.

Quantitative phase imaging has been an important labeling-free microscopy modality for many biomedical and material science applications. In which, ultra-fast quantitative phase imaging is indispensable for dynamic or transient characteristics analysis. Conventional wide field optical interferometry is a common scheme for quantitative phase imaging, while its data acquisition rate is usually hindered by the frame rate of arrayed detector. By utilizing novel balanced-photo-detector based digital optics coherent detection techniques, we report on a method of constructing ultra-fast quantitative phase microscopy at the line-scan rate of 100 MHz with ~2 μm spatial resolution.

Simulation Model for Prediction of Transient Performance Characteristics of Single–Phase Shaded Pole Motor

Abstract Paper proposes mathematical model of single phase shaded pole motor suitable for analysis of motor dynamic behavior. Derived mathematical model from d–q reference frame theory is applied at motor simulation model. Derived simulation model enables analysis of transient performance characteristics of motor currents, speed and electromagnetic torque under different operating regimes. Obtained results from the simulation are compared with data from analytical calculations based on method of symmetrical components and data from experiment for the purpose of verification of the simulation model. Simulation model is useful for studying the effect of parameters on motor starting and running characteristics at different types of loads.

Voltage phase angle jump characteristic of DFIGs in case of weak grid connection and grid fault

In the condition of connecting large scale doubly-fed induction generators (DFIGs) into weak grid, the closely coupled interactions between wind generators and power grid becomes more severe. Some new fault characteristics including voltage phase angle jump will emerge, which will influence the power quality of power system. However, there are very few studies focusing on the mechanism of voltage phase angle jump under grid fault in a weak grid with wind turbine integration. This paper focuses on the scientific issues and carries out mechanism studies from different aspects, including mathematical deduction, field data analysis and time domain simulation. Based on the analysis of transient characteristics of DFIGs during the grid fault, this paper points out that the change of terminal voltage phase angle in DFIGs is an electromagnetism transition process, which is different from conventional synchronous generator. Moreover, the impact on transient characteristics of voltage phase angle are revealed in terms of fault ride through (FRT) control strategies, control parameters of current inner-loop of rotor-side converter and grid strength.

Transient fault tolerant control for vehicle brake-by-wire systems

Brake-by-wire (BBW) systems that have no mechanical linkage between the brake pedal and the brake mechanism are expected to improve vehicle safety through better braking capability. However, transient faults in BBW systems can cause dangerous driving situations. Most existing research in this area focuses on the brake control mechanism, but very few studies try to solve the problem associated with transient fault propagation and evolution in the brake control system hierarchy. In this paper, a hierarchical transient fault tolerant scheme with embedded intelligence and resilient coordination for BBW system is proposed based on the analysis of transient fault propagation characteristics. In this scheme, most transient faults are tackled rapidly by a signature-based detection method at the node level, and the remaining transient faults, which cannot be detected directly at the node level and could degrade the system performance through fault propagation and evolution, are detected and recovered through function and structure models at the system level. To jointly accommodate these BBW transient faults at the system level, a sliding mode control algorithm and a task reallocation strategy are designed. A simulation platform based on Architecture Analysis and Design Language (AADL) is established to evaluate the task reallocation strategy, and a hardware-in-the-loop simulation is carried out to validate the proposed scheme systematically. Experimental results show the effectiveness of this new approach to BBW systems.

RTDS-based Model Component Development of a Tri-axial HTS Power Cable and Transient Characteristic Analysis

The transient characteristics of the tri-axial High Temperature Superconducting (HTS) power cable are different from those of a conventional power cable depending on whether the cable is under a steady or transient state due to the quench. Verification using simulation tools is required to confirm both the characteristics of the cable and the effect of the cable when it is applied to a real utility. However, a component for the cable has not been provided in simulation tools; thus the RTDSbased model component of the tri-axial HTS power cable was developed, and a simulation was performed under the transient state. The considered properties of model component include resistance, reactance and temperature. Simulation results indicate the variation of HTS power cable condition. The results are used for the transient characteristic analysis and stability verification of the tri-axial HTS power cable. In the future, the RTDS-based model component of the cable will be used to implement the hardware-in-the-loop simulation with a protection device.