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Outer-rotor switched reluctance machines (SRMs) have drawn much attention as promising candidates for in-wheel direct-drive motors of future electric vehicles. This article presents a systematic performance comparison of three outer-rotor SRM topologies for in-wheel traction applications in terms of the specific torque, electromagnetic efficiency, torque ripple, radial force, and mechanical aspects. A generalized design optimization framework for SRMs is proposed to enable the fast evaluation of large numbers of designs generated from the differential evolution by incorporating an analytical current profile estimation into the transient finite element analysis. The relationship between the saliency ratio and converter volt-ampere rating is also discussed. The calculations are then benchmarked with the experimental results from an existing prototype. The effectiveness of the performance prediction method and the proposed optimization approach is validated. [ABSTRACT FROM AUTHOR]

Distributed generation sources (DGs) are widely considered as important sources of power generation in distribution systems during the last few decades. Despite the substantial benefits of DGs, increasing the penetration level of the DGs can cause dramatic voltage magnitude fluctuations. Coordination of the use of dynamic reactive power sources such as photovoltaic (PV) inverters and voltage control equipment can mitigate rapid voltage magnitude fluctuations. A coordinated volt-var control method is proposed herein to achieve the optimal expected performance (e.g., system losses) while considering the spatial correlation among PV source powers and constraining the variability of voltage magnitudes throughout the distribution network within permissible ranges. The proposed strategy formulates chance constraints on the voltage magnitude and considers the uncertainty of PV power injections over the interval of interest to maintain voltage magnitudes within acceptable limits. The proposed method has been tested on the IEEE 123-node radial distribution system for validation. Moreover, the simulation results demonstrate that the proposed method can effectively mitigate the fast voltage magnitude deviations with an acceptable reduction in system losses in the presence of intermittent renewable resources. [ABSTRACT FROM AUTHOR]

The computational cost for the simulation of detailed models of machine-rectifier systems is expensive because of repetitive diodes switching. Average-value models (AVMs) of machine-rectifier systems have been developed that can alleviate the computational burden by neglecting the details of the switching of each individual diode while retaining the average characteristics. This paper proposes an alternative formulation of numerical AVMs of machine-rectifier systems, which makes direct use of the natural dynamic impedance of the rectifier without introducing low-frequency approximations or algebraic loops. By using this formulation, direct interface of the AVM is achieved with inductive circuitry on both the ac and dc sides allowing traditional voltage-in, current-out formulations of the circuitry on these sides to be used with the proposed formulation directly. This numerical AVM formulation is validated against an experimentally validated detailed model and compared with previous AVM formulations. It is demonstrated that the proposed AVM formulation accurately predicts the system's low-frequency behavior during both steady and transient states, including the cases where previous AVM formulations cannot predict accurate results. Both run times and numbers of time steps needed by the proposed AVM formulation are comparable to those of existing AVM formulations and significantly decreased compared with the detailed model. [ABSTRACT FROM AUTHOR]

An electrical power system for low-Earth-orbit satellites, which can be reused for a variety of mission requirements with minimal redesign, is proposed. The goals of the proposed power system are achieved by modularizing the subsystems of a small spacecraft and designing them to allow any number of each module to be connected simultaneously. The modularized subsystems include solar energy generation and energy storage. The overall objectives will be accomplished without compromising efficiency or power system stability. The purpose of this paper is to describe the proposed power system and detail the experimental results. The generalized system can be used as a one-size-fits-all solution that only requires basic power systems knowledge to configure and operate. [ABSTRACT FROM AUTHOR]

Brushless excitation systems are widely used for synchronous machines. As a critical part of the system, rotating rectifiers have a significant impact on the system behavior. This paper presents a numerical average-value model (AVM) for rotating rectifiers in brushless excitation systems, where the essential numerical functions are extracted from the detailed simulations and vary depending on the loading conditions. Open-circuit voltages of the brushless exciter armature are used to calculate the dynamic impedance that represents the loading condition. The model is validated by comparison with an experimentally validated detailed model of the brushless excitation system in three distinct cases. It has been demonstrated that the proposed AVM can provide accurate simulations in both transient and steady states with fewer time steps and less runtime compared with detailed models of such systems and that the proposed AVM can be combined with AVM models of other rectifiers in the system to reduce the overall computational cost. [ABSTRACT FROM AUTHOR]

Current consumption measurements are useful in a wide variety of applications, including power monitoring and fault detection within a lithium-ion battery management system (BMS). This measurement is typically taken using either a shunt resistor or a Hall-effect current sensor. Although both methods have achieved accurate current measurements, shunt resistors have inherent power loss and require isolation circuitry, and Hall-effect sensors are generally expensive. This paper explores a novel alternative to sensing battery current by measuring terminal voltages and cell temperatures and using an unknown input observer to estimate the battery current. An accurate model of a LiFePO4 cell is created, validated, and then used to characterize a model of the proposed current estimation technique. Finally, the current estimation technique is implemented in hardware and tested in an online BMS environment. Results show that the current estimation technique is sufficiently accurate for a variety of applications, including fault detection and power profiling. [ABSTRACT FROM AUTHOR]

Numerous models and formulations have been used to study synchronous machines in different applications. Herein, a unified derivation of the various model formulations, which support direct interface to external circuitry in a variety of scenarios, is presented. A synchronous machine model with magnetizing path saturation including cross saturation and an arbitrary rotor network representation is considered. This model has been extensively experimentally validated and includes most existing machine models as special cases. Derivations of the standard voltage-in, current-out formulation as well as formulations in which the stator and/or the field windings are represented in a voltage-behind-reactance form are presented in a unified manner, including the derivation of a field-only voltage-behind-reactance formulation. The formulations are compared in a variety of simulation scenarios to show the relative advantages in terms of time steps, run time, and accuracy. It has been demonstrated that selection of the formulation with the most suitable interface for the simulation scenario has better accuracy, fewer time steps, and less run time. [ABSTRACT FROM PUBLISHER]

The primary existing methods for average-value modeling of hysteresis current controlled three-phase inverters do not accurately portray transient or over-modulation operation. This article presents two new methods for average-value modeling of hysteresis current controlled three-phase inverters: the effective voltage model and the slew-rate limitation model. These models are compared both in simulation and experimentally with the existing perfect hysteresis current control model in a variety of cases. It is shown that the proposed models are better able to predict the transient and over-modulation performance of the inverter than the existing method while retaining the computational efficiency advantages of average-value models. [ABSTRACT FROM AUTHOR]

Power distribution systems are desired to operate at their optimal control settings. These settings typically mean operation at low energy consumption and minimized distribution losses. Renewable energy resources can be very important for efficient operation of the distribution systems. However, when the number of renewables in the distribution system increases, the complexity of the control also increases. Intermittent renewable resources, particularly wind and solar, can cause significant fluctuations in distribution feeder voltages. This article presents a dual-layer control approach for finding the optimal feeder control settings and maintaining the feeder voltages within specified limits between the optimization intervals. The load-tap changer transformers, voltage regulator, capacitor banks, and smart inverters participate in the global control, while the smart inverters deal with the fast changing transients at the local control level. Thus, this control scheme will take full advantage of power-electronics-based smart inverters to reduce or eliminate fast transients, and also reduce the wear and tear of mechanical controllers. Evaluation studies are performed based on the IEEE 37 node radial test feeder under varying load and generation conditions. The results demonstrate that the proposed approach is promising for voltage and VAR control of distribution feeders with intermittent resources. [ABSTRACT FROM AUTHOR]

A synchronous machine model with saturation and cross saturation and an arbitrary rotor network representation that uses a voltage-behind-reactance representation for both the stator windings and the field winding of the machine is proposed. This allows the stator windings and the field winding to be represented as branches in a circuit solver, permitting straightforward simulation with connected circuitry. In particular, the model can be simulated with rectifier loads or with rectifier sources applied to the field winding. The model is validated against experimental data, and its utility is demonstrated in an excitation failure case study. [ABSTRACT FROM PUBLISHER]

In many applications, engineering systems are required to operate acceptably well in hostile environments. In the past, survivability engineering has addressed this requirement using heuristic rule-based design approaches followed by analysis to determine if survivability constraints have been satisfied. The treatment of survivability as a constraint rather than an independent design objective hinders the ability of system engineers to trade off survivability with other design objectives, such as cost and performance. Herein, the survivability problem is posed in terms of maximizing expected performance and minimizing the risk of unacceptable performance. Design metrics that allow optimal selection of systems on the basis of these survivability dimensions are presented. The metrics are part of a systematic approach to system engineering in which survivability concerns are quantified and individual systems and entire classes of systems can be compared objectively. These metrics are a necessary step toward an integrated design process wherein tradeoffs between all design objectives can be identified. This methodology is demonstrated on the design of a notional electric warship integrated engineering plant (IEP) that is subject to hostile disruptions posed by antiship missiles. By use of this method, the performance of the IEP is shown to be improved. [ABSTRACT FROM PUBLISHER]

Many robust design problems can be described by minimax optimization problems. Classical techniques for solving these problems have typically been limited to a discrete form of the problem. More recently, evolutionary algorithms, particularly coevolutionary optimization techniques, have been applied to minimax problems. A new method of solving minimax optimization problems using evolutionary algorithms is proposed. The performance of this algorithm is shown to compare favorably with the existing methods on test problems. The performance of the algorithm is demonstrated on a robust pole placement problem and a ship engineering plant design problem. [ABSTRACT FROM AUTHOR]

In military applications, it is important for a platform (warship, aircraft, etc.) or an installation (airbase, etc.) to maintain war-fighting ability after being damaged. In particular if the unit requires electric power, cooling, or other resources to perform its mission, then these resources must be available following a weapon detonation event. The integrated engineering plant (IEP) is responsible for providing these services to the mission-critical loads in a unit. Novel continuity-of-service metrics for IEPs are set forth herein. These metrics provide a means of predicting the average and worst-case level of service the plant can provide as well as the worst-case scenario over a class of disruptions. This provides a method of making meaningful comparisons between different designs. The computation and meaning of the proposed metrics are explored using a notional warship IEP. [ABSTRACT FROM AUTHOR]