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System identification of a Two-Wheeled Robot (TWR) through nonlinear dynamics is carried out in this paper using a data-driven approach. An Artificial Neural Network (ANN) is used as a kinematic estimator for predicting the TWR's degree of movement in the directions of x and y and the angle of rotation Ψ along the z-axis by giving a set of input vectors in terms of linear velocity 'V' (i.e., generated through the angular velocity 'ω' of a DC motor). The DC motor rotates the TWR's wheels that have a wheel radius of 'r'. Training datasets are achieved via simulating nonlinear kinematics of the TWR in a MATLAB Simulink environment by varying the linear scale sets of 'V' and '(r ± ∆r)'. Perturbation of the TWR's wheel radius at ∆r = 10% is introduced to cater to the robustness of the TWR wheel kinematics. A trained ANN accurately modeled the kinematics of the TWR. The performance indicators are regression analysis and mean square value, whose achieved values met the targeted values of 1 and 0.01, respectively. [ABSTRACT FROM AUTHOR]

The aim of this paper is to numerically analyze the hydrothermal behavior of different cross-sectional geometries of microchannel heat sinks (MCHSs) and conduct a comparative analysis of traditional and non-traditional designs using ANSYS Fluent. It is expected that the proposed design discussed in this paper will improve the performance of MCHSs by maximizing the cooling capability and minimizing the thermal resistance and entropy generation rate, thus leading to better energy efficiency. The channel designs include a rectangular microchannel (RMC), a circular microchannel (CMC), an elliptical microchannel (EMC), a trapezoidal microchannel (TMC), a hexagonal microchannel (HMC), and a new microchannel (NMC) which has a plus-like shape. The discussed geometry of the NMC is designed in such a way that it maximizes the cross-sectional area and the wetted perimeter of the channel, keeping the hydraulic diameter constant ( D h = 412 µm). The performance of various channels is compared on the basis of pressure drop, wall temperature, thermal enhancement factor, thermal resistance, thermal transport efficiency, and entropy generation rates. It has been observed that the NMC is capable of cooling effectively and it can achieve a minimum wall temperature of 305 K, thus offering the lowest thermal resistance ( R th ), irreversible heat loss, and entropy generation rate. Moreover, the NMC has achieved the highest value of the thermal enhancement factor, i. e., 1.13, at Re = 1 , 000. Similarly, it has the highest thermal transport efficiency of almost 97 % at Re = 1 , 000 , followed by the TMC and the RMC. Overall, the NMC has achieved the best performance in all aspects, followed by the RMC and TMC. The performance of the EMC, the CMC, and the HMC was found to be the worst in this study. [ABSTRACT FROM AUTHOR]

A system identification of a two-wheeled robot (TWR) using a data-driven approach from its fundamental nonlinear kinematics is investigated. The fundamental model of the TWR is implemented in a Simulink environment and tested at various input/output operating conditions. The testing outcome of TWR's fundamental dynamics generated 12 datasets. These datasets are used for system identification using simple autoregressive exogenous (ARX) and non-linear auto-regressive exogenous (NLARX) models. Initially the ARX structure is heuristically selected and estimated through a single operating condition. We conclude that the single ARX model does not satisfy TWR dynamics for all datasets in term of fitness. However, NLARX fitted the 12 estimated datasets and 2 validation datasets using sigmoid nonlinearity. The obtained results are compared with TWR's fundamental dynamics and predicted outputs of the NLARX showed more than 98% accuracy at various operating conditions. [ABSTRACT FROM AUTHOR]

Analysis of distributed energy systems (DESs) is more challenging, as multiple energy sources are connected with different loads through power electronics converters. Modeling and simulation become an essential step during the design stage, prior to actual implementation. These DESs comprised numerous converters in various configurations, e.g., parallel and cascade. This paper presents behavioral modeling technique for interconnected converters that can be used to predict dynamics of overall system. First models are developed for two converters in parallel and cascade configuration using direct approach (DA). The model derivation using DA becomes too complex for larger systems. A new transformation-based approach (TBA) is proposed, which, unlike DA, is simple and can easily be extended to model N interconnected converters. In this method, the measured g -parameter set is transformed to another domain, equivalent model is computed simply by the addition or multiplication of transformed g -parameters and then the equivalent model is transformed back to g -parameter set. The modeling techniques are implemented in Matlab/Simulink. The results from DA and TBA are compared, and their close agreement suggests that the new TBA can be used for the analysis of interconnected systems, comprised of multiple parallel and cascade converters. [ABSTRACT FROM AUTHOR]

Despite attractive thermal and electrical characteristics, wide band-gap semiconductor devices such as SiC MOSFET have struggled to penetrate in aircraft applications because of reliability issues in earlier releases. The second and third generation SiC MOSFETs have achieved improved reliability using high quality oxides and innovative fabrication process. This paper presents a failure rate model for SiC MOSFET based on the accelerated test data at a given operating condition. The proposed model enables the system level reliability analysis of second generation SiC MOSFET-based converters. The reliability of SiC two-phase synchronous boost converter has been evaluated at two different operating conditions: 10 and 16 A load condition. To predict the life time of the converter even after a chain of component failures, Markov's reliability model of the converter is developed. The state transition probabilities and mean time to failure (MTTF) of SiC converter are compared against its Si counterpart which shows that second generation SiC MOSFETs are for aircraft applications with high reliability. [ABSTRACT FROM AUTHOR]

This paper presents an improved average model and evaluation of an 18-pulse autotransformer rectifier unit (ATRU) in differential delta configuration. Average models remove the switching behavior of diode rectifiers and high bandwidth transients, which not only facilitates simulation of power systems by reducing computational cost but also enables impedance-based stability analysis for large complex power systems. To experimentally validate the proposed average model, a 2-kW, 18-pulse ATRU has been tested and the results of the derived model are compared with those of the switching model and experimental prototype. Computed transfer function of load impedance from the proposed average model closely resembles those of the switching model and the experimentally measured results validate the modeling procedure. Furthermore, stability analysis of the 18-pulse ATRU may be executed based on the return ratio of source and load impedance. [ABSTRACT FROM AUTHOR]

Switching models possess discontinuous and nonlinear behavior, rendering difficulties in simulations in terms of time consumption and computational complexity, leading to mathematical instability and an increase in its vulnerability to errors. This issue can be countered by averaging detailed models over the entire switching period. An attempt is made for deriving improved dynamic average models of three phase (six-pulse) and nine phase (18-pulse) diode rectifiers by approximating load current through first order Taylor series. Small signal AC/DC impedances transfer functions of the average models are obtained using a small signal current injection technique in Simulink, while transfer functions are obtained through identification of the frequency response into the second order system. For the switch models in Simulink and the experimental setup, a small signal line to line shunt current injection technique is used and the obtained frequency response is then identified into second order systems. Sufficient matching among these results proves the validity of the modelling procedure. Exact impedances of the integral parts, in interconnected AC/DC/AC systems, are required for determining the stability through input-output impedances. [ABSTRACT FROM AUTHOR]

This paper discusses the measurement of frequency response functions for various dc-dc converters. The frequency domain identification procedure is applied to the measured frequency responses. The identified transfer functions are primarily used in developing behavioral models for dc-dc converters. Distributed power systems are based upon such converters in cascade, parallel and several other configurations. The system level analysis of a complete system becomes complex when the identified transfer functions are of high order. Therefore, a certain technique needs to be applied for order reduction of the identified transfer functions. During the process of order reduction, it has to be ensured that the system retains the dynamics of the full order system. The technique used here is based on the Hankel singular values of a system. A systematic procedure is given to retain the maximum energy states for the reduced order model. A dynamic analysis is performed for behavioral models based on full and reduced order frequency responses. The close agreement of results validates the effectiveness of the model order reduction. Stability is the key design objective for any system designer. Therefore, the measured frequency responses at the interface of the source and load are also used to predict stability of the system. [ABSTRACT FROM AUTHOR]

This paper addresses the design and implementation of a droop controlled three phase bidirectional AC-DC converter for more electric aircraft (MEA) applications. A unified control strategy using a droop characteristic is presented to achieve the bidirectional power flow between the AC and DC source while maintaining a stable DC output voltage. Based on the rigorous control design, the converter is capable of operating over a wide frequency range with a unity power factor. The key findings obtained from the theoretical analysis are confirmed by simulation studies and further validated by a scaled down laboratory prototype. The practical results show good performance of the bidirectional converter and demonstrate the effectiveness of the proposed control strategies. [ABSTRACT FROM AUTHOR]

The remarkable progress of power electronic converters (PEC) technology has led to their increased penetration in distributed energy systems (DES). Particularly, the direct current (dc) nanogrid-based DES embody a variety of sources and loads, connected through a central dc bus. Therefore, PECs are required to be employed as an interface. It would facilitate incorporation of the renewable energy sources and battery storage system into dc nanogrids. However, it is more challenging as the integration of multiple modules may cause instabilities in the overall system dynamics. Future dc nanogrids are envisioned to deploy ready-to-use commercial PEC, for which designers have no insight into their dynamic behavior. Furthermore, the high variability of the operating conditions constitute a new paradigm in dc nanogrids. It exacerbates the dynamic analysis using traditional techniques. Therefore, the current work proposes behavioral modeling to perform system level analysis of a dc nanogrid-based DES. It relies only on the data acquired via measurements performed at the input–output terminals only. To verify the accuracy of the model, large signal disturbances are applied. The matching of results for the switch model and its behavioral model verifies the effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

The silicon carbide (SiC) MOSFET is characterized by high operating voltage, temperature, switching frequency and efficiency which enables a converter to achieve high power density. However, at high switching frequency, the crosstalk phenomenon occurs when the gate voltage spike introduced by high dv/dt and voltage ringing forces false turn-on of SiC MOSFET which causes a crow-bar current thereby increasing switching losses. In order to increase the immunity against the crosstalk phenomenon in a half-bridge configuration, this paper presents a gate driver for SiC MOSFET capable of generating the negative turn-off voltage without using a negative power supply. In addition, the effect of parasitic inductances on the switching response is analyzed and an RC snubber is designed using high-frequency based circuit reduction technique to dampen the switching ringing. The performance of the proposed gate driver and the designed RC snubber is validated using simulation and experiment at the 1 MHz switching frequency. The results show that the proposed gate driver with RC snubber eliminates crosstalk by maintaining any spurious gate spike below the gate threshold voltage. [ABSTRACT FROM AUTHOR]

A distributed energy system (DES) using controlled power electronics converters delivers power to loads, via conventional, as well as a number of renewable, energy sources. However, stability concerns retard the integration of power electronics converters into an existing DES. Therefore, due to the high penetration of power converters, the overall network analysis of DES is becoming increasingly difficult. Impedance-based DES modeling emerged as an effective technique as it reduces the system into source and load subsystems and offers easier analysis of the dynamic interactions between them. These models can be obtained using either analytical calculations, simulations, or experimental measurements. In this work, firstly, a line-to-line current injection technique is used for the measurement of alternating current (AC) impedances. Since it requires repeated injections, a d q -domain impedance measurement methodology based upon a set of independent perturbations and measurements is proposed. The perturbation is injected via a sweep signal which is preprocessed by the digital signal processor (DSP) prior to injection. The d q reference frame is synchronized with the three-phase AC system using a low-bandwidth phase-locked loop (PLL). The close matching of impedance parameters measured in simulation using the proposed approach with those obtained using analytical expressions and the line-to-line current injection technique verifies the effectiveness of the approach. Furthermore, the method was also implemented experimentally, and the close matching of the results with the analytical and simulation results validates the overall modeling and measurement procedure. [ABSTRACT FROM AUTHOR]

Since the parasitic voltage ringing and switching power losses limit the operation of active devices at elevated frequencies; therefore, a higher-order inductor-capacitor (LC) filter is commonly used, which offers extended attenuation above the cutoff frequency and thus, improves the total harmonic distortion (THD) of the amplifier. This paper applies the concept of integral sliding-mode control to a fourth-order class-D amplifier. Two fixed-frequency double integral sliding-mode (FFDISM) controllers are proposed, where one uses the inductor current while the other involves the capacitor current feedback. Their equivalent control equations are derived, but from the realization viewpoint, the controller using the capacitor current feedback is advantageous and, therefore, is selected for final implementation. The performance of the proposed FFDISM controller for fourth-order GaN class-D amplifier is confirmed using simulation and experimental results. [ABSTRACT FROM AUTHOR]

With the evolution of the More Electric Aircraft (MEA) concept, high pulse converters have gained the attention of researchers due to their higher power quality. Among the high pulse converters, 18-pulse autotransformer rectifier unit (ATRU) offers better power quality level with small size, weight and medium complexity. The conventional topologies of autotransformers that require the use of extra elements such as Inter Phase Transformers (IPT) or Zero Sequence Blocking Transformers (ZSBT), adding to the complexity, weight and size of the overall system, are not considered in the analysis. For 18-pulse rectification, only those topologies of autotransformers which have the intrinsic current harmonic cancellation capabilities are presented here for comparison. These topologies offer current harmonic levels within limits specified by IEEE 519 with reduced weight and size as compared to the conventional multi-pulse converters. A comparison of different differential delta/fork configured 18-pulse autotransformer rectifier units is presented so as to come up with the best among available topologies with respect to weight, size and power quality. Experimental prototypes of each topology were designed and their results are displayed along with the simulation results for comparison. [ABSTRACT FROM AUTHOR]