Steady-state Time-domain Research Articles

ZVS Soft Switching Operation Region Analysis of Modular Multi Active Bridge Converter Under Single Phase Shift Control

Modular multi active bridge (MMAB) converter can provide multiple dc ports using modular H-bridge. When voltage conversion ratios of each port are not equally balanced, zero-voltage-switching (ZVS) turn-on of power semiconductors in the MMAB converter cannot be secured under single phase shift (SPS) control, increasing power loss and leading to lower efficiency. To estimate the efficiency of the converter in various conditions, ZVS operation region of MMAB converters under SPS is comprehensively derived based on steady-state time domain with superposition theorem. Voltage conversion ratios are taken as main variables for ZVS region analysis and influences of them are comprehensively analyzed. Full ZVS regions and constrained ZVS regions are obtained by ZVS discriminants. Simulation and experimental results for a three-port MMAB prototype are given to verify the theoretical analysis of ZVS operation region.

Dynamic Analysis and Extreme Response Evaluation of Lifting Operation of the Offshore Wind Turbine Jacket Foundation Using a Floating Crane Vessel

The jacket is the most widely-used fixed foundation for offshore wind turbines due to its superior strength and low installation cost in relatively deep waters. Floating crane vessels are commonly used to install jacket foundations. However, the dynamic coupling between the jacket and the floating vessel might generate complex dynamic responses under wave action. The complexity of the multi-body system requires comprehensive time-domain simulations and statistical analysis to obtain reliable results, especially for the evaluation of the operational safety of offshore lift installations of a jacket foundation. In this context, this study performs numerical simulations and statistical analyses to predict the extreme responses and the preliminary allowable sea states for guiding the lowering operation of a jacket using a floating crane vessel. First, ANSYS-AQWA is used to obtain the hydrodynamic coefficients of the vessel in the frequency domain. A nonstationary time-domain simulation of jacket lowering with winches is performed to identify several preliminary critical vertical positions of the jacket from the time series in an irregular wave. The extreme responses of a target probability are evaluated by the extreme distribution model after a large number of steady-state time-domain simulations of the critical vertical positions in irregular waves. The most critical vertical position is determined from three preliminary critical vertical positions by comparing the extreme responses. Eigenvalue analysis and spectrum analysis of the most critical vertical position of the jacket are carried out to find the natural periods of the system and the dynamic coupling characteristics between different components. The influence of wave direction, significant wave height, and spectrum peak period on the dynamic responses are also analyzed in the most critical vertical position. Furthermore, the optimal wave direction is determined as the head sea. Preliminary allowable sea states are derived by comparing the calculated dynamic amplification coefficient with the defined operational criteria.

Topology optimization of DC-biased pot-type reactor using design sensitivity in steady state of electromagnetic field with magnetic nonlinearity

Because reactors applied to electric vehicles are typically driven under a DC-biased current, a constant inductance property is required. When a high-performance DC-biased reactor is designed, the topology optimization (TO) is an effective design method owing to the high degree of structural change in the magnetic circuit. However, there exists no report regarding the TO method in the steady-state time domain with magnetic nonlinearity. In this paper, based on the time-domain adjoint variable method, a novel sensitivity analysis approach for the steady-state time domain with thorough consideration of the magnetic saturation is proposed. Through the proposed method, the TO of the iron core and winding structures in a pot-type reactor was carried out to enhance the DC-biased characteristics. Furthermore, the eddy current loss occurring on the aluminum plate installed outside the reactor was suppressed by the multi-objective TO. The interesting structure of a pot-type reactor that enhanced the DC-biased characteristics and reduced the eddy current loss on the outer conductor plate was also illustrated.

Free and forced vibration analysis of pyramid lattice sandwich plate based on the dimensional reduction model

Due to the high porosity and periodicity of a pyramid lattice core, the dynamic behaviors of a pyramid lattice sandwich plate (PLSP) show new characteristics. In this work, the equivalent stiffness of a PLSP was obtained by homogenizing over the unit cell, and input to an equivalent two-dimensional (2D) reduced-order model constructed from the framework of a variational asymptotic method, based on which the calculation of natural frequencies and the frequency domain analysis of forced vibration were carried out. The accuracy and efficiency of the proposed model were verified by numerical examples of free and forced vibration under different boundary conditions, including frequency domain analysis, steady-state time domain analysis, and analysis of the local field recovered from the maximum resonance response at the peak and trough times. We also investigated the influence of the pyramid lattice core’s structural parameters on the first three natural frequencies and the maximum resonance response, which can provide a useful reference for the fatigue life expectation of a PLSP under a periodic load.

Transient beam loading and rf power evaluation for future circular colliders

Interaction of the beam with the fundamental impedance of the accelerating cavities can limit the performance of high-current accelerators. It can result in a significant variation of bunch-by-bunch parameters (bunch length, synchronous phase, etc.) if filling patterns contain gaps that are not negligible compared with the cavity filling time. In the present work, this limitation is analyzed using the steady-state time-domain approach for the high-current option (Z) of the future circular electron-positron collider and for the future circular hadron-hadron collider. Mitigation of transient beam loading by direct rf feedback is addressed with evaluation of additional required generator power.

ZVS Soft Switching Operation Range Analysis of Three-Level Dual-Active Bridge DC–DC Converter Under Phase Shift Control Strategy

The switches of three-level dual active bridge (3L-DAB) dc–dc converter under phase shift control may operate with hard working especially when the voltage conversion ratio is not equal to one, which will lead to high power loss and low system efficiency. A comprehensive analysis of the ZVS soft switching operation range of 3L-DAB is presented for the first time. The power characteristics of 3L-DAB operating under phase shift control is analyzed. Then, the ZVS operation range of the switches in the primary and secondary sides varied with phase shift ratios and voltage conversion ratio is deduced. The ZVS operation range is obtained by using steady-state time domain analysis under two conditions, without and with considering the junction capacitance of the semiconductor, and the comparative analysis are carried out later. Finally, simulation and experimental results obtained from a 3L-DAB prototype verify the discussed theoretical analysis.

Application of entropy in identification of breathing cracks in a beam structure: Simulations and experimental studies

A cantilever beam with a breathing crack is studied to detect the crack and evaluate the crack depth using entropy measures. During the vibration in engineering structures, fatigue cracks undergo the status from close-to-open (and open-to-close) repetitively leading to a crack breathing phenomenon. Entropy is a measure, which can quantify the complexity or irregularity in system dynamics, and hence employed to quantify the bi-linearity/irregularity of the vibration response, which is induced by the breathing phenomenon of a crack. A mathematical model of harmonically excited unit length steel cantilever beam with a breathing crack located near the fixed end is established, and an iterative numerical method is applied to generate accurate time domain vibration responses. The steady-state time domain vibration signals are pre-processed with wavelet transformation, and the bi-linearity/irregularity of the vibration signals due to breathing effect is then successfully quantified using both sample entropy and quantized approximation of sample entropy to detect and estimate the crack depth. It is observed that the method is capable of identifying crack depths even at very early stages of 3% of the beam thickness with significant increment in the entropy values (more than 200%) compared to the healthy beam. In addition, experimental studies are conducted, and the simulation results are in good agreement with the experimental results. The proposed technique can also be applied to damage identification in other types of structures, such as plates and shells.

Modelling and analysis of a capacitively coupled contactless power transfer system

Capacitively coupled contactless power transfer (CCPT) technology has been proposed as a new contactless/wireless power transfer method recently. By employing electric field as the energy transfer medium, CCPT has advantages of being able to transfer power across metal barriers and reduced electromagnetic interference. However, there is very limited understanding and experience in the CCPT system modelling and analysis. This study models a typical CCPT system and analyses its performance under steady-state operations. An accurate non-linear circuit model is established and the stroboscopic theory is extended to determine the zero-voltage switching (ZVS)-operating frequency of the system. The tuning inductance for achieving exact ZVS operation is derived, and the effects of the coupling and load variations on the system performance are analysed. A prototype CCPT circuit is built, and practical measurements show that the steady-state time domain waveforms and efforts of coupling and load variations calculated from the theoretical model are in good agreements with experimental results. The power efficiency predicted is slightly higher than the practical results, particularly at heavy loads, because ideal power semiconductor switches and wires are used in the theoretical model.

Electric machinery parameters and torques by current and energy perturbations from field computations. I. Theory and formulation

In this first of a two-part article, the well-established energy/current (E/C) perturbation method of computation of machine winding inductances is reviewed. The method's efficacy in machine performance calculations is delineated and verified in a companion paper by comparison to experimental results. The critical role that winding inductance parameters have in modeling and simulation of the nonsinusoidal steady state time-domain (forced response) performance of electric machinery is demonstrated using state models in both the winding flux linkage and current-based frames of reference. The computed machine performance characteristics include profiles of winding inductances, induced terminal voltage waveforms, and instantaneous torque profiles that contain all the ripples due to the significant space harmonics in a machine. The method and associated formulations and techniques are shown to be very effective in both 2D-FE and 3D-FE electric machinery field solutions involving substantial degrees of saturation and complexity of construction. The machines analyzed in the comparison paper include a 15-HP permanent magnet brushless DC motor, a 1.2-HP three-phase induction motor, and a 14.3 kVA three-phase modified Lundell alternator possessing very complex magnetic circuit geometries. The well-posedness of the method held true for all these cases, as well as many other case-studies briefly reviewed here.

Electric machinery parameters and torques by current and energy perturbations from field computations. II. Applications and results

For pt.I see ibid., vol.14, no.4, p.1507-13 (1999). The theoretical developments and formulations of part I of these two-part companion papers are applied here to three practical examples, namely a 15-HP permanent magnet brushless DC machine, a 1.2 HP three phase induction motor, and a 14.3 kVA modified Lundell alternator. The excellent correlation between computed and test results for inductance profiles, steady-state terminal voltage waveforms and steady-state time-domain developed torque profiles verify the reliability and well posedness of the energy/current perturbation approach in electric machinery problems involving both 2D-FE and 3D-FE magnetic field solutions.

Applications of the current state space model in analyses of saturated induction machines

Main flux saturation in induction machines plays an important role in a number of operating regimes and therefore has to be accounted for in the process of modelling. The current state space model of a saturated induction machine has gained substantial popularity recently as an excellent tool for transient and steady-state time domain analysis of induction motor drives when the main flux saturation has to be considered. This paper discusses different applications of the model. First, the self-excitation process in single-cage and double-cage (deep-bar) induction generators is addressed. Switch-off and reclosing transients of an induction motor with capacitor reactive power compensation are dealt with next. Two inverter fed induction motor drives, namely, the current-source and resonant parallel inverter fed induction machines, are elaborated further. The last application described here is the rotor flux oriented control of an induction machine. The elaborated cases are illustrated with simulation and experimental results.