Search

Environmental concerns have pushed toward electrified technologies for off‐road vehicle actuations that can lower greenhouse gas emissions and reduce energy consumption. Replacing a central diesel engine with a dedicated electric machine (EM) as a prime mover for the hydraulic supply offers several opportunities for so‐called ePumps (aka electric‐driven pumps) to maximize energy efficiency and limit the usage of electric materials. This paper discusses the impact of different choices for the ePumps architecture (i.e., fixed vs. variable displacement pump; variable speed vs. fixed speed electrical machine), and on their main design parameters in terms of size and efficiency. Although the procedure followed in the study could be extended to different types of electric and hydraulic units, the paper particularly considers ePumps based on permanent magnet synchronous machines combined with axial piston machines. The importance of properly considering the ePump drive cycle and its cooling requirements is taken into account while addressing energy efficiency, mass, and overall compactness of the solution. The results show that an ePump based on a variable displacement pump, when compared to fixed displacement ePumps, reduces the electrical machine size both in volume and mass up to 40%, when the high‐pressure demand is not combined with high flow rate demand, thus decreasing the cost of the EM. In all drive cycles, the variable speed EM–fixed displacement pump architecture has a higher efficiency, ranging from 1% to 5%, compared to the case of fixed speed EM–variable displacement pump. Finally, the paper compares the advantages and shortcomings of each ePump architecture presented, based on representative drive cycles. [ABSTRACT FROM AUTHOR]

This paper proposes a design methodology for power-dense and high-efficient electrohydraulic units (EHUs) that can be used to select design specifications for the electric machine (EM) for a given hydraulic machine (HM) architecture. The proposed method evaluates EHU performance considering both electric and hydraulic power losses. The compactness of the EHU is achieved by integrating an axial piston unit as HM inside a permanent magnet EM. The paper provides a sensitivity analysis for important EHU design specifications and discusses the best choices for reducing total mass and energy loss. The study finds that greater aspect ratios promote power-to-weight ratio, while high voltage promotes energy efficiency. The paper also discusses the choice of fixed versus variable displacement HMs, with the finding that a variable displacement unit helps address low efficiency limits of low-speed operation, particularly for low voltage electric machines. Additionally, variable displacement can also be used to reduce EM losses when meeting a flow-pressure demand. The proposed methodology has applications in fields such as off-road vehicles. [ABSTRACT FROM AUTHOR]

Design of electric machinery using population-based optimization requires a highly computationally efficient means of predicting the field distribution as well as the lumped-circuit model parameters. This paper proposes and validates a relatively straightforward analysis appropriate to this end. Index Terms--Automated design, field distribution, lumped-parameter modeling, rotating machinery.

Permanent-magnet synchronous machines can be designed to obtain high efficiency and high torque density. Population-based optimization methods such as genetic algorithms and particle swarm optimization are gaining acceptance as a means of optimizing the design of this class of machines. This paper builds on the literature by utilizing a computationally efficient machine analysis appropriate for use with population-based optimization methods that enables the consideration of a significantly larger search space than previously reported in the literature. It is also unique in that the relative performance of different parameter encoding and objective function formulations are considered. Index Terms--Design automation, genetic algorithms (GAs), optimization methods.

In this paper, we set forth a procedure to perform detailed inductor designs using population-based optimization methods. We chose inductor designs on the basis of design inputs, i.e., the inductor geometry and core material. The method incorporates recent research in magnetic materials characterization, advanced inductor modeling, and hysteresis loss modeling. We present several case studies for both single- and multi-objective optimizations. Index Terms--Automated design, hysteresis, magnetic loss.

This paper sets forth and demonstrates an approach to the design of power electronics based power systems using evolutionary computing techniques. Key features of the paper are the use of evolutionary computing in the context of classical control design, construction of appropriate multievent based performance metrics, and the use of multiobjective evolutionary computing in the selection of control parameters based on system performance versus control effort. The proposed approach is demonstrated in a power electronics based power distribution system similar to those being designed for next generation warships. Index Terms--Evolutionary algorithms (EAs), optimization methods, power electronics, power system controls.

Real-time approximators for continuous-time dynamical systems with many inputs are presented. These approximators employ a novel self-organizing radial basis function (RBF) network, which varies its structure dynamically to keep the prescribed approximation accuracy. The RBFs can be added or removed online in order to achieve the appropriate network complexity for the real-time approximation of the dynamical systems and to maintain the overall computational efficiency. The performance of this variable structure RBF network approximator with both Gaussian RBF (GRBF) and raised-cosine RBF (RCRBF) is analyzed. The compact support of RCRBF enables faster training and easier output evaluation of the network than that of the network with GRBF. The proposed real-time self-organizing RBF network approximator is then employed to approximate both linear and nonlinear dynamical systems to illustrate the effectiveness of our proposed approximation scheme, especially for higher order dynamical systems. The uniform ultimate boundedness of the approximation error is proved using the second method of Lyapunov. Index Terms--Dynamical system, Gaussian RBF (GRBF), radial basis function (RBF), raised-cosine RBF (RCRBF), real-time approximation, self-organizing RBF network, uniform ultimate boundedness.

Finite element models are invaluable for determining expected machine performance. However, finite element analysis can be computationally intense; particularly if a large numbers of studies or high bandwidth studies are required. One method to avoid this difficulty is to extract machine parameters from the finite element model and use the parameters in lumped parameter models. While often useful, such an approach does not represent space harmonics or asymmetries in the motor. A methodology for constructing a state-variable model, based on a magnetic equivalent circuit of the motor is described herein. In addition, the parameters for this model are based solely on geometrical data. This approach is an excellent compromise between the speed of lumped parameter models and the ability of finite element methods to capture spatial effects. Experimental validation of the model is provided. Index Terms--Geometry-based modeling, induction machine modeling, magnetic equivalent circuit (MEC), space harmonics.

There has been considerable research in developing improved induction motor models. One recently developed model simultaneously includes magnetizing path saturation, leakage saturation, and a highly flexible transfer function approach to represent the rotor circuits. This alternate QD model (AQDM) is also computationally efficient in that it is noniterative at each time step. It is considerably more accurate than the classical QD model (CQDM). However, the suggested characterization procedure is complicated and time consuming. This paper proposes a new characterization procedure for the AQDM. The proposed procedure employs a genetic algorithm (GA) as an optimization engine to identify the parameters of the AQDM by simultaneously considering per-phase fundamental frequency impedance and stand-still frequency response (SSFR) impedance. The proposed approach is validated by comparison of current ripple predictions (to validate high-frequency model behavior) and by application to maximum torque per ampere control design (to validate fundamental frequency model behavior). The proposed procedure is significantly more straightforward than the other published method of obtaining AQDM parameters. Index Terms--Genetic algorithms (GAs), induction machines, parameter estimation.

A brushless excitation system model is set forth that includes an average-value rectifier representation that is valid for all three rectification modes. Furthermore, magnetic hysteresis is incorporated into the d-axis of the excitation using Preisach's theory. The resulting model is very accurate and is ideal for situations where the exciter's response is of particular interest. The model's predictions are compared to experimental results. Index Terms--Brushless rotating machines, magnetic hysteresis, modeling, simulation, synchronous generator excitation, synchronous generators.

In this paper, a parameter identification procedure for a recently proposed hysteretic brushless exciter model is discussed. The model features average-value representation of all rectification modes, and incorporation of magnetic hysteresis in the d-axis main flux path using Preisach's theory. Herein, a method for obtaining the model's parameters from the waveforms of exciter field current and main alternator terminal voltage is set forth. In particular, a genetic algorithm is employed to solve the optimization problem of minimizing the model's prediction error during a change in reference voltage level. Index Terms--Brushless rotating machines, genetic algorithms (GAs), magnetic hysteresis, measurement, parameter estimation, synchronous generator excitation.

This work sets forth a nonlinear average value model (NLAM) of a switched reluctance machine. NLAMs are characterized by state variables that are constant in the steady-state facilitating high-speed simulation and control analysis and design. The main difficulties in deriving such a model for the switched reluctance machine arise from nonlinearities due to magnetic saturation, absence of mutual inductance, and a nonsinusoidal self-in. ductance profile which prevents the use of a rotational transformation in arriving at a rotor position-invariant machine description. Herein, these difficulties are overcome by introducing a variable representation that approximates machine variables by the inner product of a vector of basis functions and a time-varying coefficient vector. A set of nonlinear differential equations is derived which governs the behavior of the coefficient vectors. These equations are rotor position invariant and feature state variables which are constant in the steady-state. The resulting model is experimentally validated. Index Terms--Modeling, reluctance machines, reluctance motors, simulation.

This paper sets forth the experimental procedure for obtaining the parameter set of a synchronous machine model with saturation and arbitrary linear network representation for the rotor. The method utilizes a combination of magnetization curves and standstill frequency-response tests. A novel test procedure is proposed for obtaining the turns ratio. The rotor's transfer function and stator leakage inductance are extracted from the frequency response using genetic algorithms. Index Terms--Electric machines, frequency measurement, frequency response, genetic algorithms (GAs), modeling, parameter estimation, synchronous machines, testing, transfer functions.

This paper addresses equivalent circuit and magnetic saturation issues associated with synchronous machine modeling. In the proposed synchronous machine model, the rotor equivalent circuits are replaced by arbitrary linear networks. This allows for elimination of the equivalent circuit parameter identification procedure since the measured frequency response may be directly embedded into the model. Magnetic saturation is also represented in both the q- and d-axis. The model is computationally efficient and suitable for dynamic time-domain power system studies. Index Terms--Electric machines, modeling, power system stability, realization theory, rotating machine transient analysis, synchronous generator transient analysis, synchronous machines, transfer functions.

This paper sets forth a new switched reluctance machine model based on a current-dependent inverse inductance representation of the flux linkage versus current and position characteristic. This form permits a particularly simple mathematical description. Based on this relationship, a complete state model is derived. The resulting model is easy to implement and computationally efficient. In addition, both manual and genetic-algorithm-based methods of parameter identification are set forth. The accuracy of the model is tested via comparison to laboratory measurements of the machine's steady-state voltage and current waveforms as well as torque-speed characteristics. The proposed model is shown to be quite accurate. Index Terms--Modeling, reluctance machines, reluctance motors, simulation.

An advanced induction motor model that includes stator leakage saturation, rotor leakage saturation, magnetizing saturation, and distributed system effects in the rotor circuits has been set forth. This model is considerably more accurate than traditional models, particularly in terms of predicting switching-frequency dynamics. The model proposed is very general in terms of the range of magnetic properties that can be incorporated. This paper provides suggestions for specific forms for the leakage and magnetizing characteristics and derives the resulting small-signal impedance and large-signal steady-state equivalent circuit. Based on these results, a test procedure for experimentally characterizing the machine is developed. The application of the procedure to a 50-hp test machine is included as an example. Index Terms--Induction motors, parameter estimation, equivalent circuits, frequency measurement, frequency response, measurement, modeling, transfer functions.

The conventional qd induction motor model typically used in drive simulations is very inaccurate in predicting machine performance, except perhaps for the fundamental component of the current and the average torque near rated operating conditions. Predictions of current and torque ripple are often in error by a factor of two to five. This work sets forth an induction machine model specifically designed for use with inverter models to study machine-inverter interaction. Key features include stator and rotor leakage saturation as a function of current and magnetizing flux, distributed effects in the rotor circuits, and a highly computationally efficient implementation. The model is considerably more accurate than the traditional qd model, particularly in its ability to predict switching frequency phenomena. The predictions of the proposed model are compared with those of the standard qd model and to experimental measurements on a 37-kW induction motor drive. Index Terms--Induction motor drives, induction motors, modeling, simulation, squirrel cage motors.

The distribution transformer has been in use by utilities throughout the twentieth century. Until now, it has consisted of a configuration of iron or steel cores and copper/aluminum coils, with mineral oil serving as both coolant and dielectric medium. Inherent in this type of construction are regulation, significant weight, losses, environmental concerns, and power quality issues. For the 21st century, a new kind of distribution transformer is proposed; one that can be made self-regulating, oil-free, and able to correct power quality problems. A power electronic transformer has been analyzed, simulated, prototyped, and tested. Results of this effort as well as the novel features of this new type of transformer are discussed herein. Index Terms--Converters, power conversion, power electronics, transformers.

Optimized shaping of the stator current in the switched reluctance motor drive can be used to mitigate electromagnetic torque ripple and decrease the rms current. Previously, optimal current waveshaping has been based upon defining the optimal current waveform as a set of discrete points and interpolating intermediate points. In this work, an alternate approach is employed in which the current waveform is treated as a set of harmonic coefficients, rather than as an array of discrete values. This has advantages in terms of computation speed and in programming of the microcontroller. A second feature of this new method is that it incorporates a multiple reference frame estimator/regulator that ensures each harmonic of the current converges to its commanded value thereby avoiding the degradation in performance associated with imperfect tracking that other methods are susceptible to. The experimental and simulated results demonstrate the optimality of the waveforms and the importance of the multiple reference frame estimator/regulator, particularly in mitigating torque ripple. Index Terms--Electric drive, optimal control, switched reluctance, torque ripple.

Alternative voltage control strategies for current-regulated PWM inverters are analyzed, including previously established feedforward and feedforward/feedback controllers and a newly proposed decoupling feedback control strategy. The steady-state and dynamic characteristics of each of these control methods are illustrated and compared for a selected inverter design. It is shown that the feedforward controller exhibits steady-state error and an undesirable overshoot of the output voltages during startup. The addition of a feedback loop eliminates the steady-state error and reduces the overshoot; however, the natural response is underdamped regardless of the choice of feedback gains. A decoupling feedback control strategy that eliminates the disadvantages of the feedforward and feed-forward/feedback controllers is described. Using the decoupling feedback controller, it is possible to eliminate the steady-state error and place the closed-loop poles wherever desired. Moreover, if the closed-loop poles are selected appropriately, it is possible to eliminate the overshoot of the output voltages during startup transients.