Evaluation Of Transient Performance Research Articles

Comparative analysis and optimal allocation of virtual inertia from grid‐forming and grid‐following controlled ESSs

AbstractA broad consensus of neutralizing the carbon dioxide emissions facilitates the transition to the renewable energy power system. Meanwhile, the concerns about the volatility of renewable energies are growing as the rotational inertia of power system becomes inadequate. To maintain the frequency stability of power system, some studies for configuring inertia energy storage systems (ESSs) are carried out, mainly focusing on the allocation of virtual inertia from grid‐forming ESS. In contrast, the allocation of virtual inertia from grid‐following ESS has not been well elaborated and the differences in virtual inertia provided by these two modes are yet to be revealed. Based on ‐norm and Kron reduction, firstly, the state‐space model of post‐disturbance system is established, together with the transient performance evaluation. Then the inertia characteristics of both grid‐forming and grid‐following devices are formulated, followed by the unified gradient descent optimization method for allocating virtual inertia. A modified IEEE 39‐bus system and its time‐domain simulations help in the verification of the contribution of this paper. Through the comparative analysis of corresponding optimal results, the conclusions from two aspects are drawn: in terms of transient frequency support, the grid‐forming devices can provide no less than better inertia support; with the higher power capacity and similar energy capacity, the grid‐forming devices can relieve the response pressure of other generators by approximately .

A transient performance evaluation of a porous evaporative cooler for preservation of fruits and vegetables

A transient performance of a porous evaporative cooling system was carried out using mathematical models developed from the first principles. The models are based on energy and mass balance analysis on different sections of the evaporative cooler. The developed models were solved using a FlexPDE computational fluid dynamics analyzer, based on the finite element, to generate numerical solutions. The models developed were validated using experimental data from a properly designed, constructed, and tested an evaporative cooler and subsequently used to determine the evaporative cooler performance during four different periods of the year covering the two major climatic seasons experienced in Nigeria. Results obtained showed a reduction in the storage chamber temperature by up to 9 °C from the ambient air condition which was within the range of 22–33 °C. Furthermore, it was observed that it performs best during the dry seasons as compared to the wet season. However, during both seasons, the cooling chamber temperature significantly remained below the ambient value. Thus, the evaporative cooler can serve as an effective means of reducing heat-induced post-harvest losses incurred by farmers while also helping in combating climate change since it uses only water and does not require any external energy input.

Dual core processors: Coupled queues: Transient performance evaluation

High-Performance Computing (HiPC) systems routinely employ multi/many – core processors. Specifically, dual – core processors find many applications in pervasive computing devices. Dual–core processors employ buffers for queueing the incoming jobs. Traditionally, the queues at the processors are assumed to be independent and the queueing system is analyzed in equilibrium for tractability purposes. Queues are modeled using Continuous Time Markov Chains (CTMC's) and the equilibrium performance measures are determined to analyze as well as design the queueing systems. In most interesting cases, the incoming jobs are routed to the queues using the Join the Shortest Queue (JSQ) policy. Thus, with such an adaptive routing algorithm, the two queues are evidently coupled and are not statistically independent. Hence traditional equilibrium performance evaluation doesn't provide realistic performance measures. In this research paper, the two queues associated with buffers in dual-core processors are considered to be coupled. The Coupled Queues are modeled using a Quasi – Birth – and – Death (QBD) process. Using traditional results related to QBD processes, equilibrium performance measures are determined. More interestingly, we demonstrate the tractability of the computation of transient probability distribution of a QBD process. In the research literature, transient analysis of the QBD process was shown to be tractable in the Laplace transform domain. But in this research paper, we prove that the matrix exponential eQt arising in transient analysis (where Q is the generator matrix of the QBD process) can be computed directly in the time domain rendering efficient transient analysis of QBD process. Using the transient probability mass function of queue length, estimation of transient performance measures such as expected queue length, average delay, and tail distribution can be determined. Further, optimal adaptive routing algorithms for coupled queues can be designed.

A one-dimensional modelling methodology of printed circuit heat exchangers for steady, off-design and transient feasibility in a supercritical CO[formula omitted] power block

As the most widely-used heaters and recuperators in supercritical CO2 (sCO2) power cycles, the Printed Circuit Heat Exchangers (PCHEs) have received considerable interest to investigate their steady, off-design and transient behaviour mainly by simulations, which remains a challenging task accounting for various application scenarios. After an introduction and comparison about the state-of-art PCHEs numerical approaches, this paper presents a generic one-dimensional (1D) numerical PCHE modelling methodology featured by (1) ability fulfilling the steady, off-design and transient simulation; (2) precise capture of the non-linear local variations in the thermo-physical properties of sCO2; (3) feasibility for a wide range of flow patterns, working fluids, and operation conditions. The off-design prediction via the proposed 1D PCHE modelling methodology is justified by validating its Modelica implementation against previous literature. Later, one optimal Nusselt correlation out of five candidates is identified to reproduce two typical transient power cycle operations, i.e., ‘shutdown and startup’ and ‘ramp-up’ scenario. These scenarios are validated by experiments at the Pinjarra Hills High Pressure Loop (PHPL) of the University of Queensland. The proposed 1D PCHE model successfully follows the changing rules of the time-varying temperature of both hot- and cold-side working fluids, though a slight time lag is observed between the simulation and experiment, which is caused by the modelling assumptions. In general, the presented 1D PCHE modelling methodology is credited for the steady, part-load and transient performance evaluation of sCO2 power blocks and the corresponding control strategy development. Several crucial future work is summarized for guidance.

Analysis of Stationary- and Synchronous-Reference Frames for Three-Phase Three-Wire Grid-Connected Converter AC Current Regulators

The current state of the art shows that unbalance and distortion on the voltage waveforms at the terminals of a grid-connected inverter disturb its output currents. This paper compares AC linear current regulators for three-phase three-wire voltage source converters with three different reference frames, namely: (1) natural (abc), (2) orthogonal stationary (αβ), and (3) orthogonal synchronous (dq). The quantitative comparison analysis is based on mathematical models of grid disturbances using the impedance-based analysis, the computational effort assessment, as well as the steady-state and transient performance evaluation based on experimental results. The control scheme devised in the dq-frame has the highest computational effort and inferior performance under negative-sequence voltage disturbances, whereas it shows superior performance under positive-sequence voltages among the reference frames evaluated. In contrast, the stationary natural frame abc has the lowest computational effort due to its straightforward implementation, with similar results in terms of steady-state and transient behavior. The αβ-frame is an intermediate solution in terms of computational cost.

Order-Reduced Dynamic Decoupling Approach for Performance Evaluation of Multitype and Small-Batch-Based Serial Lines With Adjustments and Resets

In the existing literature, extensive investigations focus on evaluating the performance of production systems that typically assumed to be operating under rigid production mode. Mass production as well as single type of products is the representative characteristics of this production mode. However, by applying prompt equipment adjustments and resets, modern production lines are capable of making different products in small batches with varying processing requirements. This is referred to as flexible manufacturing mode. With the flexible manufacturing mode, which has been widely used in recent years, real-time performance evaluation and prediction, small-batch-based real-time scheduling, and management of such systems, etc., are having important research significance. In this article, by considering adjustments and resets on serial production lines with multitype and small-batch-based production, the transient performance evaluation problem is studied. Specifically, for the system with machines having the Bernoulli reliability model and buffers having finite capacities, the mathematical model is formulated first. Then, we develop a Markovian model and a computational procedure for evaluating various system real-time performance indicators, such as production rates and completion times of different batch-based production tasks, etc. In addition, an order-reduced dynamic decoupling approach is proposed to approximate system real-time performance with high accuracy and computational efficiency. Finally, theoretic properties of the system under the flexible manufacturing mode are discussed.

Small Signal Analysis and Control of Snubberless Naturally-Clamped Soft-Switching Current-Fed Push-Pull DC/DC Converter

This article presents detailed small-signal modeling and closed-loop control design for transient performance evaluation of a high-frequency snubberless isolated current-fed push-pull dc-dc converter. The topology attains the natural commutation of semiconductor devices through zero current switching. The state-space averaging technique is employed to derive the transfer functions. A two-loop average current controller is designed and implemented on a digital signal processor to evaluate and demonstrate the transient performance of the converters. A complete procedure for a closed-loop control design is illustrated. Simulation results using PSIM 11.1.64 with the designed controller are shown to validate the stability of the system. Experimental results demonstrated satisfactory transient performance at various load conditions of the converter and validated the derived model and the control design.

Investigation on NBTI-induced dynamic variability in nanoscale CMOS devices: Modeling, experimental evidence, and impact on circuits

With the downscaling of CMOS devices, dynamic variability induced by negative bias temperature instability (NBTI) has become a critical issue. In addition to the time-dependent device-to-device variation (DDV) of NBTI degradation, the cycle-to-cycle variation (CCV) originated from random trap occupation is found non-negligible and should be added into the total dynamic variation. This paper summarizes our recent studies on NBTI-induced dynamic variability, focusing on the CCV effect, with more details on the statistical modeling, circuit reliability simulation methodologies and experimental results. By adding the random trap occupation into consideration, a statistical model for total dynamic variation (DDV+CCV) is proposed. The effective occupancy probability peff is introduced as a key parameter for modeling and circuit reliability simulation. With the statistical trap response (STR) method and modified on-the-fly method, the proposed model is validated by the experimental evidence under both DC and AC NBTI. According to the model and experimental results, circuit reliability simulation framework is proposed for both long-term quasi-static and short-term transient performance evaluation with the additional impact of CCV. Two representative digital circuit units, ring oscillator (RO) and SRAM cell, are simulated under different conditions, indicating it necessary to consider the evident influence of the CCV in accurate circuit reliability evaluation. The results are helpful for the reliability/variability-aware circuit design in nanoscale technology.

Performance Analysis of Assembly Systems With Bernoulli Machines and Finite Buffers During Transients

Serial lines and assembly systems are two of the most fundamental production system structures used in practical manufacturing environments. While serial lines have been studied extensively in production systems literature and practice, assembly systems have received much less attention. Among existing results on assembly systems, most are focused on steady state performance evaluation, system properties, and improvement. On the other hand, transient behavior of such systems remains largely unexplored. In the framework of assembly systems with Bernoulli machines and finite buffers, this paper develops a mathematical model for transient analysis and derives closed-form formulas to calculate the real-time production rate, consumption rates, work-in-process, and probabilities of machine starvation and blockage, during transients. Then, an improved computationally efficient algorithm for transient performance evaluation in Bernoulli serial lines is proposed. Based on the improved algorithm, an effective and efficient method for transient performance evaluation in Bernoulli assembly systems is derived. Finally, the method is extended to complex assembly system structures.

Transient performance evaluation of waste heat recovery rankine cycle based system for heavy duty trucks

The study presented in this paper aims to evaluate the transient performance of a waste heat recovery Rankine cycle based system for a heavy duty truck and compare it to steady state evaluation. Assuming some conditions to hold, simple thermodynamic simulations are carried out for the comparison of several fluids. Then a detailed first principle based model is also presented. Last part is focused on the Rankine cycle arrangement choice by means of model based evaluation of fuel economy for each concept where the fuels savings are computed using two methodologies. Fluid choice and concept optimization are conducted taking into account integration constraints (heat rejection, packaging, …). This paper shows the importance of the modeling phase when designing Rankine cycle based heat recovery systems and yields a better understanding when it comes to a vehicle integration of a Rankine cycle in a truck.

Transient Performance Evaluation of Assembly Systems with Bernoulli Machines

Assembly systems are widely used in large volume manufacturing processes, where the final product requires several components. However, investigations of assembly systems have been relatively limited. Moreover, among existing results on assembly systems, most are focused on steady state performance, while transient behavior of such systems remains largely unexplored. In this paper, we study the problem of performance evaluation of assembly systems during transients. Specifically, we assume all machines in the system follow the Bernoulli reliability model and the buffers are of finite capacities. Then, an effective and computationally efficient algorithm for transient performance evaluation in Bernoulli assembly systems is developed and formulas for estimating the real-time production rate, consumption rates, work-in-process, and probabilities of machine starvation and blockage, during transients, are derived. The accuracy of the algorithm is demonstrated using numerical experiments. Finally, the method is extended to complex assembly system structures.

On-Engine Validation of Mean Value Models for IC Engine Air-Path Control and Evaluation

Mean value engine models (MVEM) are well established for the study of IC engine air-path performance. Closed-loop control of the air-path is used to ensure the tracking of reference signals subject to constraints. To meet these requirements model predictive control (MPC) has been applied successfully to several air-path applications. This paper reports on the development of an MVEM and suitable MPC controller for transient performance evaluation which is then applied to the engine. A linearised prediction model is evaluated at each control time step, based on the current operating conditions, which ensures the model remains valid across a wide range of speeds and loads. This linearisation of the nonlinear model allows for the formulation of quadratic programming (QP) problems, which are efficiently solved as part of the proposed MPC algorithm. Special treatment in the measurement and calculation of the states and their derivatives is demonstrated to provide excellent tracking performance and a good match between the model and real-time experimental results. The systematic process of modelling coupled with MPC is shown to closely match test-bed performance, which verifies the methodology for studying air-path hardware alternatives.

EM3-3: Evaluation of Transient Performance of a Diesel Particulate Filter via a Light Scattering Method(EM: Exhaust Emission Control and Measurement,General Session Papers)

EM3-3: Evaluation of Transient Performance of a Diesel Particulate Filter via a Light Scattering Method(EM: Exhaust Emission Control and Measurement,General Session Papers)

Steady-state and transient performance evaluation of a DTC scheme in the low speed range

In this paper, a direct flux and torque control scheme for industrial application is analyzed in order to emphasis the drive performance at standstill and in the low speed range. The control strategy utilizes the torque and rotor flux commands to determine the reference value of the stator flux. In order to improve the low speed performance a closed loop estimator is employed to evaluate the rotor flux. The validity of the control scheme is verified by simulations and experimental tests of an induction motor drive system.

Modeling of the Saturated Leakage Reactance of Induction Motors as a Time Varying Parameter for Transient Computations

ABSTRACT A procedure has been developed for incorporating the saturated leakage reactance of induction motors into starting transient performance evaluation. An empirical formula has been provided for simulating the envelope of the transient current in terms of time. This faciliated to express the transient rmg stator winding current in terms of time. Then saturated leakage reactance is expressed in terms of the transient rms stator winding current, which in turn, made it possible to express the leakage reactance as a time varying parameter. All types of slot openings, i.e., closed slots, semi closed slots and open slots are considered separately. Transient performance of a machine having closed slots on the rotor and semi closed slots on the stator is evaluated using the approach described in this article and the effect of leakage path saturation is demonstrated.