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Dual active bridge (DAB) converter is the most suitable converter to transfer high power with bidirectional power flow capability and isolation. However, it has the drawbacks of circulation power flow (CPF) and limited range of zero voltage switching (ZVS). To overcome these drawbacks, several modulation strategies have been proposed; however, the CPF can be eliminated either at input or output voltage ends. In order to eliminate the CPF at both input and output sides, a novel front and rear end switch DAB (FRS-DAB) bidirectional dc–dc converter has been proposed in this paper. It has the advantages of lower current stress, extension of ZVS range, higher power transfer capacity, and improved efficiency compared to the conventional DAB converter. The paper presents the detailed operating modes and analysis of power flow control for the proposed FRS-DAB converter. The operation and analytical results of the proposed converter have been verified through the experimental results using an FPGA Spartan 3AN processor.

This paper applies finite control set model predictive control (FCS-MPC) for dynamic reactive power compensation using a hybrid active power filter (HAPF). The FCS-MPC uses a model based on LCL -filter equations to predict the system behavior and optimize the control action. In fact, the application of FCS-MPC in grid-connected converters with LCL -Filter is quite recent. This algorithm is a very promising control technique for power electronics converters and its use for reactive power control of hybrid filter has not been reported in the literature yet. This paper uses the FCS-MPC in a multivariable structure along with an adaptive notch filter to damp resonance. The main purpose is to improve the dynamic response of the HAPF. Simulation as well as practical results prove the feasibility of FCS-MPC application in HAPF reactive power control. The dynamic response of the equipment was significantly improved and represents the main contribution of this paper. As a result, the FCS-MPC allows tracking fluctuations and abrupt changes in load reactive power.

© 1982-2012 IEEE. An important bottleneck in the design, operation, and exploitation of mechatronic powertrains is the lack of accurate knowledge of broadband external loading. This is caused by the intrusive nature of regular torque measurements. This paper proposes a novel nonintrusive approach to obtain torsional load information on mechatronic powertrains. Online coupled state/input estimation is performed through an augmented nonlinear Kalman filter. This estimation approach exploits general lumped-parameter physics-based models in order to create a widely applicable framework. This paper considers both extended (EKF) and unscented Kalman filtering approaches. Contrary to previous works, no considerable difference in accuracy is obtained from experiments, with a considerably lower computational load for the EKF. This paper reveals the benefits of including rotational acceleration measurements from a theoretical perspective, which is demonstrated through the experimental validation. This drastically increases the broadband accuracy. The result of this paper is an accurate and noninvasive virtual torque sensor with a sufficiently broad bandwidth for use in condition monitoring, control, and future design optimization. ispartof: IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS vol:65 issue:3 pages:2378-2387 status: published

This paper addresses the problem of load identification in nonintrusive monitoring application when using load signatures in transient signals. The study presents a systematic approach to design a set of wavelet filters to be used as matching patterns for load identification in nonintrusive monitoring. The effect of different higher order wavelet filters and the signal length on the classification accuracy are investigated. The concepts of wavelet clustering and wavelet-signal matching are introduced and are developed in this paper. Machine learning classifiers are used to automate the load classification process using co-testing. The introduced concept is evaluated on a real test system and the results of the experimental work have shown that 1.5 cycle may suffice to achieve a 97.25% classification accuracy. Moreover, the results have shown that the proposed approach is effective in detecting loads with more electronic components and not previously categorized in the assembly.

In this paper, we propose an approach for integrating a series filter inductance in a coaxially wound transformer (CWT) as a potential alternative to conventional solenoidally wound transformers (SWT) for high-power isolated soft-switching dc–dc converters. The critical elements that determine the size and the performance of soft-switching dc–dc converters are the isolation transformer and the filter elements. While conventional SWTs using a stray magnetic field as a filter inductance often suffer from a considerably increased loss, heat congestion, and electromagnetic interference, a CWT is rarely affected by high frequency and fringing effects. The desired properties are still valid while the required filter inductance is fully integrated with an isolation transformer using the proposed method. In addition, the evenly distributed magnetic fields in a concentric geometry enable accurate electrical and mechanical analysis and a specific application-oriented design. In this paper, the operating principles, design procedure, and loss modeling of a CWT with an integrated filter inductance are introduced. Its functionality and suitability for high-frequency applications were proven by theoretical analysis and experiments. A prototype transformer with an integrated inductance 4 mH was facilitated and evaluated in a 15 kV-SiC mosfet -based 6 k–400 Vdc stage for a solid-state transformer of up to 6.5 kW at a switching frequency of 20 kHz.

High dc voltage utilization is one of the important requirements in a three-phase inverter. Under some carrier-based pulse width modulations (PWMs), the dc voltage utilization can reach the same maximum as that under the space vector modulation. But the third harmonic component of common-mode voltage (CMV) will be increased markedly while using these carrier-based PWMs in inverters. To improve the situation, this paper proposes that a midpoint-fluctuation carrier (MFC) scheme should be used in the three-phase inverter. The MFC is formed by adding a midpoint-fluctuation signal on the standard symmetrical triangular carrier. By analyzing the linear modulation region of the midpoint-fluctuation signals, a minimum fluctuant signal in the linear modulation region is designed in the paper. Compared with the use of other conventional schemes in the three-phase inverter, the use of minimum MFC scheme has higher fundamental amplitude in the output line voltage and smaller magnitude of the third harmonic in the CMV. The feasibility and validity of the MFC are proved by experiment results in a three-phase inverter.

Recently, a series elastic actuator (SEA) has emerged as a potential actuator system for various robotic applications where safe and precise interactive force control is required. Even though lots of research has been conducted on the mechanical/controller design and the development of applications for SEAs, the accurate force observation issue has not been highlighted much. Only the simple law, that is, the spring in an SEA can measure interactive force has been repeatedly mentioned and utilized. However, this is not true when the load-side dynamics affects the spring deformation significantly. This paper tackles this problem by demonstrating the imprecise force observation of the spring deformation and proposing two types of external force observers to address the problem. A reaction force-sensing SEA (RFSEA) is adopted in this paper, and its dynamic characteristic is analyzed in detail using the Lagrangian mechanics. Based on the analyzed dynamics, force observers are designed and verified through simulations and experiments. An XY stage driven by RFSEAs is developed so that the stage can be force controlled, and the proposed force observers are applied to this. Human interactive forces on the developed XY stage, the impedance of which is controlled in several ways, are estimated and compared with a force plate. Various experimental results validate the performance and potential of the proposed force observer for SEA systems.

To address the lack of reliable power supplies for lightning current measurement systems (LCMS), this paper proposes a novel self-powered LCMS. The required operation power of a LCMS can be provided by harvesting the surge current that is measured using a power coil such that the system can be energized to complete a single-cycle measurement and data recording. In this manner, the stand-alone LCMS is triggered by lightning currents, and, hence, the signal acquisition can be activated automatically. In particular, this paper designs a two-channel passive peak-holding circuit as a low-power substitution to the conventional high-speed sampling modules. The polarity, current peak, and trigger time can be measured and ultimately be stored in a nonvolatile memory. The theoretical and simulation studies are presented in detail to determine the structure, size, and number of winding turns of the power and signal coils. The circuitry design of the power supply and signal conditioning units are also addressed. Experimental results verify that the proposed LCMS can accurately measure the amplitudes of lightning currents, achieving an accuracy of a maximum error of 4%, while the LCMS is fully self-powered to satisfy the energy demand from the measurement and data acquisition tasks.

A novel hybrid pulse width modulation (PWM) technique is proposed in this paper for two parallel interleaved, two-level, three-phase voltage source inverters (VSIs). The two parallel interleaved VSIs are analyzed as a three-level (3L) inverter. A 3L inverter provides minimum line current ripple when nearest three voltage vectors are applied. In this paper, a novel carrier-based PWM technique is developed that ensures the application of nearest voltage vectors, keeping average circulating current to zero over a switching period. For carrier-based implementation of the proposed PWM, generalized common-mode (CM) offsets are derived in terms of maximum and minimum values of reference signals. Each 3L space-vector sector is divided into seven subsectors. For each subsector, a CM offset is calculated, addition of which to reference signals ensures the minimum line current ripple and zero average circulating current. Simulation and experimental results are provided to validate the proposed technique.

The phase-shifted full-bridge (PSFB) converter is widely employed in high-power applications. However, circulating current, narrow range of zero-voltage switching (ZVS), duty-cycle loss, and secondary parasitic oscillation are the main drawbacks of the traditional PSFB converter. This paper proposes an improved full-bridge converter to solve the drawbacks of the traditional PSFB converter. In the proposed converter, a coupled inductor with three windings is introduced to adjust the available ZVS energy and to transfer power to the output side during freewheeling period. Due to this structure, output filter requirement, circulating current, the required ZVS energy, and secondary voltage oscillation can be reduced. Thus, the proposed converter can obtain higher conversion efficiency than the traditional PSFB converter. In this paper, the detailed operation principles and experimental results are presented.

The aim of this paper is to study the dynamics of a permanent magnet direct current (PMDC) brushed motor while two crucial space-domain effects, namely, slotting effect and commutation phenomenon are taken into account. Semi-analytical dynamic time-domain PMDC brushed motor model inclusive of these space-domain effects is used to analyze and investigate the dynamics. Pulse width modulation operated discontinuous current PMDC brushed motor drive with steady duty cycle is employed to acquire the bifurcation patterns. The chaotic nature due to slotting effect and commutation is identified from the bifurcation patterns and reported. It also has to be admired that such nonlinear dynamical behavior with the same set of parameters at similar operating condition has not been observed when a conventional PMDC brushed motor dynamic model is considered. These space-domain effects, namely, slotting effect and commutation also have a prominent impact to make some time-domain states of a PMDC brushed motor drive chaotic. The role of slotting effect and commutation phenomenon to analyze the chaos over time-domain state variables of the PMDC brushed motor drive is investigated and validated experimentally in this paper.

The traditional evaluation method of vehicle noise can no longer meet the requirements of electric vehicle as the sound character of electric powertrain (E-PT) is totally different from that of internal combustion engine vehicles. This paper presents a complete investigation of the sound quality of an E-PT. An acoustic test is conducted to analyze the sound character of E-PT, based on which the acoustic origins of E-PT including electromagnetic noise, gear whine, and inverter switching noise are studied. After that the sound quality of E-PT is investigated by objective and subjective evaluations. Subsequently, a sound quality model of E-PT based on support vector machine is established. The relative error testifies the effectiveness of the prediction model. The influence of the main noise origins on the sound quality of E-PT is determined. Finally, the structure of gearbox housing is redesigned based on topology optimization to improve the sound quality. The main original contributions of this paper are not only the sound quality method developed for E-PT but also improvement feasibility of sound quality.

In this paper, a nonisolated dc–dc converter with high voltage gain is presented. Three diodes, three capacitors, an inductor, and a coupled inductor are employed in the presented converter. Since the inductor is connected to the input, the low input current ripple is achieved, which is important for tracking maximum power point of photovoltaic panels. The voltage stress across switch S is clamped by diode D 1 and capacitor C 1. Therefore, a main switch with low on-resistance RDS (on) can be employed to reduce the conduction loss. Besides, the main switch is turned on under zero current. This reduces the switching loss. The steady-state analysis of the proposed converter is discussed in this paper. Finally, the proposed converter prototype circuit is implemented to justify the validity of the analysis.

Underground localization is considered a key technology for controlling underground equipment, such as directional drilling equipment. However, most sensors for localization such as vision sensors, range sensors, and wireless sensors cannot be utilized in an underground environment. Moreover, vibration by the drill bit and distortion of the geomagnetic field by the surrounding material adversely affect localization performance. To accurately estimate the pose for directional drilling, a resilient underground localization method using concurrent normalized cross correlation (CNCC) and magnetic field vector is proposed in this paper. In the underground environment, a different magnetic field is distributed at each region. Since the drilling system moves only inside the borehole, the magnetic field distribution can be re-measured. Therefore, the constraint between the poses is detected by comparing the magnetic field distribution. A comparison method based on CNCC is proposed to resolve the ambiguity of the magnetic field. Moreover, to reduce the orientation error, magnetic field vector matching is used. The constraint can correct the pose estimation of the system using pose graph optimization. To validate the performance of the proposed method, two types of field tests are carried out in this paper.

The general trend toward more intelligent energy-aware ac drives is driving the development of new motor topologies and advanced model-based control techniques. Among the candidates, pure reluctance and anisotropic permanent magnet motors are gaining popularity, despite their complex structure. The availability of accurate mathematical models that describe these motors is essential to the design of any model-based advanced control. This paper focuses on the relations between currents and flux linkages, which are obtained through innovative radial basis function neural networks. These special drive-oriented neural networks take as inputs the motor voltages and currents, returning as output the motor flux linkages, inclusive of any nonlinearity and cross-coupling effect. The theoretical foundations of the radial basis function networks, the design hints, and a commented series of experimental results on a real laboratory prototype are included in this paper. The simple structure of the neural network fits for implementation on standard drives. The online training and tracking will be the next steps in field programmable gate array based control systems.

Isolated high output current dc/dc converters are critical for power supplies in information technology industries. LLC converters with a matrix transformer are suitable for these applications due to their high efficiency and high power density. By pushing switching frequency up to MHz with GaN devices, planar matrix transformers with printed circuit board (PCB) windings are advantageous over conventional transformer designs, but the large interwinding capacitance of the PCB windings provides a critical coupling path for common-mode (CM) noise. In order to analyze the CM noise, the interwinding capacitance of the PCB windings is analyzed, and a related CM noise model is provided in this paper. To suppress the CM noise, shielding layers can automatically be inserted into the PCB windings between the primary and secondary windings in the fabrication process. This paper proposes a novel shielding technique, in which half of the shielding serve as the primary winding. The proposed shielding technique not only suppresses CM noise but improves the efficiency as well. The proposed shielding is verified by experiments on 1-MHz 400 V/12 V 800-W LLC converters with a peak efficiency of 97.7% and a power density of 900 W/in3. The proposed shielding reduces CM noise by 30 dB and improves full-load efficiency by 0.2%.

Small power home appliances (refrigerator compressor motor drives) demand ever better efficiency at moderate initial cost. An efficiency of 85% has been already reached at 100 W, 2930 r/min, with line-start split-phase capacitor induction motors (IMs). To boost performance, the present paper models and analyses a split-capacitor IM with regular rotor cage plus two flux barriers filled with permanent magnets to also exploit the reluctance of such torque for 100 W, 3000 r/min and, thus, raise efficiency to 90% for a 4.22-kg motor. The present paper introduces a circuit model for asynchronous operation; a magnetic nonlinear equivalent circuit model to assess synchronous magnetization inductances ${\rm{L}}_{{\rm{dm}}}$ , ${\rm{L}}_{{\rm{qm}}}$ ; a circuit dq model in rotor coordinates for transients; and finite element method (FEM) validation of ${\rm{L}}_{{\rm{dm}}}$ and ${\rm{L}}_{{\rm{qm}}}$ to fully model the machine and offer digital simulation for the case study. Then, an optimal design methodology based on the modified Hooke–Jeeves algorithm and a multicriterion objective (cost) function that includes machine materials + capacitor + energy loss capitalized cost, as well as penalties for starting torque, synchronizing torque, and power un-realization, is unfolded and applied for same 100 W, 3000 r/min case study. Finally, a prototype was build and tested to validate the developed modeling and optimal design methodologies.

For power converters with inductive loads, a freewheeling path is needed for the current due to reactive power. The MOSFET synchronous rectification (SR) is widely used to reduce the conduction loss during the freewheeling period. Due to the wide band gap of silicon carbide (SiC), the intrinsic body diode of SiC MOSFET exhibits a high voltage drop. Hence, an antiparallel SiC Schottky diode is normally implemented to eliminate its conduction. However, the external SiC Schottky diode is not fully utilized as it only works during the dead time. In this paper, the hard-switching SR is investigated in an SiC three-phase inverter and compared with a conventional inverter using freewheeling diode (FWD). An improved power loss model for the two inverters has been developed. It is found that the inverter using SR has higher efficiency due to the smaller switching loss. A 7-kW prototype of SiC three-phase inverter is built, which achieves a peak efficiency of 98.8% (±0.15%) and 98.5% (±0.15%) at 40 kHz using SR and FWD, respectively. This paper confirms that the SiC MOSFET is an ideal candidate for the SR. NRF (Natl Research Foundation, S’pore)

This paper presents a three-dimensional (3-D) performance analysis and multiobjective design optimization of coreless-type permanent magnet linear synchronous motors. The average of open circuit magnetic field distribution is analytically predicted by solving two Laplace's equations. The winding factor calculation, which requires an approach different from conventional slotted motors, is provided to evaluate the motor performances. As a result, average thrust and thrust ripple can be obtained without loss of accuracy compared with results of 2-D finite element analysis (FEA). The 3-D leakage influences are subsequently incorporated into the analysis using lumped parameter magnetic circuit model because end effects are not neglected due to a relatively large air gap. Consequently, two meaningful contributions of this paper are summarized as follows: first, 3-D electromagnetic performances can be accurately predicted by the proposed analytical method. Second, with no need for the time-consuming 3-D FEA, differential evolution, a practical approach to global optimization, can simply be employed to search for solutions which belong to the Pareto optimal set. Finally, the validity of the analytical results is confirmed with the experimental results.

The paper develops a technique for arbitrary power sharing among three-phase winding sets of a multiphase generator. Multiple d − q modeling is commonly used when independent control of the winding sets is required. This paper utilizes instead the vector space decomposition modeling as the starting point and combines it with a multiple d − q approach to preserve the advantages of the vector space decomposition, while still enabling independent control over each winding set. The power sharing is achieved by imposing appropriate x − y currents at the fundamental frequency so that the flux and average torque are not affected. The theory is developed initially for the nine-phase machine. A general expression for arbitrary current sharing is derived further for any multiphase machine with multiple three-phase windings. The obtained equations are valid for any possible machine topology (asymmetrical/symmetrical, with single or multiple neutral points). The theory is validated experimentally using an asymmetrical nine-phase induction generator with indirect rotor field oriented control.

This paper presents three unidirectional step-up ac–dc converter topologies with voltage multiplication on their outputs. The first topology is the hybrid boost rectifier and the other two are novel bridgeless structures, all based on the integration of boost rectifier and the ladder switched-capacitor (SC) cell. The new hybrid structures provide high voltage gain with low voltage stress across the switches, high-power factor, and output voltage regulation. This paper presents the principle of operation, steady-state and dynamic analysis, design methodology, and experimental verification. A different approach is also presented for the design methodology of the SC cell and for the analysis of its influence on the dynamic model. Three 1000-W prototypes with a 220-V input voltage, 800-V output voltage, and 100-kHz switching frequency were designed to corroborate the theoretical study. The best efficiency was 97.1 $\%$ in the proposed bridgeless versions and the voltage stress across the switches stands around 400 V. Furthermore, a comparison between the proposed structures and previous topologies is also presented.

This paper presents an optimal design methodology of a dual-mechanical-port bidirectional flux-modulated machine for electric continuously variable transmission in hybrid electrical vehicles. The machine utilizes bidirectional flux modulation effect to combine two rotors and one stator together, aiming to realize electrical and mechanical power flexible split and combination. Due to the complexity of the machine structure, conventional optimization methods using analytical model are inapplicable. Therefore, an effective and practical method that combines the genetic algorithm and finite-element method (GA-FEM) is proposed to optimize the design of the machine in this paper. Since the computational cost increases exponentially with the increasing of number of design parameters, to reduce the computational cost in the optimization process, the design parameters are divided into two levels basing on a sensitivity analysis. And, then, the sensitive parameters are optimized using the GA-FEM coupled method. Finally, a prototype is fabricated to verify the effectiveness of the optimal design.

This paper proposes an analytical design procedure for the LLCL and the LCCL filters for grid integration of high-power voltage-source converters. The low switching frequency and stringent limits on grid-injected harmonics in high-power applications lead to large smoothing filters. In order to reduce the size and weight, high-order filters are already proposed and wise design procedures with the main goal of minimizing the overall filter size are being suggested. In this paper, the parameters of the LLCL and the LCCL filters are designed in the per-unit system to satisfy the requirements on the injected grid current and at the same time minimize the overall filter size through minimizing the total energy stored in the filter components. The experimental results of a downscaled laboratory prototype with a low switching frequency prove the effectiveness of the proposed design procedure.

A prototype of a high-resolution synthesized magnetic field focusing (SMF) system for a possible application to radio frequency (RF) barcodes is proposed in this paper. It was recently found that coordinated control of array coil currents makes it possible to focus magnetic field, which is requisite for medical imaging, wireless power, and RF identification. Different from conventional phased array RF antennas, SMF is independent of frequency, which is quite promising for various applications. In this paper, an array of rectangular air coils is proposed, and various implementation issues, such as accurate control of coil currents and compact RF barcode design, are newly suggested. A prototype of an SMF system composed of a transmitter (Tx), an RF barcode, and a receiver (Rx) was implemented at below 1 MHz operating frequency. The Tx includes modularized control drivers, full-bridge switching converters, and 16 arrayed air coils, where the RF barcodes proposed in this paper include a self-resonating circuit at 20 mm × 20 mm and a tunable resonating circuit at 15 mm × 15 mm. In this way, a 5 mm resolution at a distance of 20 mm was achieved for the Tx arrayed air coils with spacing of 5 mm, which is about four times sharper magnetic field focusing compared to a nonfocusing conventional coil. Furthermore, the proposed SMF system allows the designed 5-bit RF barcode array to be fully distinguishable at a 15 mm distance.

This paper presents a method for small-signal dynamic studies of power systems including utility-scale PV energy systems considering the effects of dc-side components. Existing methods commonly model a PV energy system as a dc source connected to a grid-tied inverter. This paper shows that the dc components of a PV energy system can also contribute in the dynamics of the power system in the range of small-signal studies. The paper first develops the model of a PV energy system by merging the submodels of dc- and ac-side components. Then, a method to obtain the augmented model of the power system including a PV energy system will be explained using a study system. The study system consists of a PV energy system in parallel with a synchronous generator connected to a grid. Then, based on eigenvalue analysis, verified by time-domain simulations, it is shown that the dc-link capacitor, front-end converter, and its controller can introduce oscillatory modes in subsynchronous range of frequencies. Furthermore, it is shown that the damping of the sensitive modes can significantly vary with respect to the parameters of the dc-side components.

This paper presents the multiphysics optimization of a new class of nanopositioning actuators, termed as flexure-based electromagnetic linear actuator (FELA). The optimization is carried out analytically based on the derived closed-form magnetic field, force, and thermal models, while its objectives include the maximizing of force generation and minimizing of thermal generation, which are both crucial for the nanopositioning actuators. The optimization results show that the new version of FELA achieved 67.3% improvement in force generation for certain current and 46.2% thermal reduction for certain output force, compared to the previous version of FELA with the same size, which was optimized using the numerical methods. The optimization results are also validated by the experiments of the new version FELA prototype, where 56.2% improvement in current–force sensitivity and 43% above reduction in thermal power are demonstrated experimentally. Furthermore, by utilizing the established modeling framework, several fundamental questions on the design of FELA are answered theoretically in this paper, such as the effect about the uniform and radial magnetization of the permanent magnet and the performance tradeoff between the different number of magnet segments.

The smart transformer (ST), a solid-state transformer with control and communication functionalities, that interfaces medium voltage (MV) and low voltage (LV) grids, enables the control of the frequency in the LV grid independently from the MV one. In a ST-fed distribution grid, the ST can interact with the droop controllers of local generators and loads frequency characteristic to control the LV power demand. However, most of the existing controllers for power converters cannot guarantee good harmonic control under variable frequency condition. To address this issue, a frequency-adaptive control scheme based on the fractional-order repetitive control and the frequency-adaptive phase-locked loop are proposed in this paper. The proposed scheme provides fast online parameter tuning capability in order to be highly adaptive to variable frequencies, and it can be easily implemented in the power converters controllers of a ST-fed distribution grid. Moreover, the stability analysis of the frequency-adaptive system considering the effect of synchronization has been investigated in this paper. Simulation and experiments have been carried out to verify the effectiveness of the proposed scheme as well as the considered scenarios.

The heat transfer coefficient (HTC) is a critical parameter that is required for accurate thermal modelling of electrical machines. This is often achieved from empirical correlations of ideal geometries or computational fluid dynamics (CFD) simulations. This paper presents a novel technique using double-sided thin film heat flux gauges for measuring the HTC from a direct oil-cooled electrical machine with segmented stator. While thin film gauges are often used in transient measurements of the HTC on gas turbine components, their application to electrical machines has been largely unexplored. This is the topic of this paper. Due to the large viscosity of the coolant, the transient technique was found to be inadequate and a steady state adaptation for oil-cooled machines was developed. This paper explores the challenges linked with this measurement technique when applied to oil-cooled machines, and develops new nondimensional correlations of the Nusselt number with Reynolds number. These correlations are applicable to machines with different geometries, flow and coolant properties. The experimental results were compared to CFD simulations and existing pipe flow correlations. It is shown that these underpredict the HTC by approximately 60% at Re = 20. The discrepancy gradually decreases to around 10% at Re = 200.

In this paper, a coordinated adaptive droop control is addressed for DC microgrid to optimize its power distribution. The optimal solution for economical dispatch problem (EDP) of the microgrid is found through a fully distributed hierarchical control. The consensus-based economical regulator calculating the optimal solution for the generator is fully distributed. Thus, it eliminates the requirement of centralized coordinator. The droop controller receives the reference from the economical regulator and ensures the output power converging to the reference while maintaining the power balance of the system. Moreover, the economical regulator can estimate the load information of the system based on the characteristics of droop control. Thus, the information from load or renewable energy source is no longer required to solve the EDP that consequently decreases the number of communication nodes. This will reduce infrastructure cost, enhance the reliability, and fasten the converging speed of algorithm. The dynamic model is established and parameter selection guideline are given in this paper. A low-voltage dc-microgrid prototype platform is utilized to validate the effectiveness of the proposed control.

Thermoelectric generators (TEGs) convert thermal energy directly into electrical energy using thermoelectric materials, with attractive advantages such as a lack of noise and pollution, considerable reliability, and a long lifetime. Because of the low output power and low output voltage of each TEG module, conventional thermoelectric generation systems are constituted by a centralized converter with series-connected multiple TEG modules. Power mismatch usually occurs in this system configuration due to the unbalanced temperature difference distribution, which results in lower conversion efficiency. In this paper, two solutions based on differential power processing (DPP) have been proposed to enhance the output power and conversion efficiency of the TEG system: the centralized-distributed hybrid structure and the cascaded power transfer structure, both of which realize the maximum power point tracking of each TEG module. The circuit designs and control strategies of the two proposed systems are here presented. Experimental results have demonstrated the feasibility and effectiveness of these two solutions; they have higher output power and better efficiency than the conventional TEG system. Each of these two solutions exhibits its own features and has suitable application situations. If the temperature difference distribution of all TEG modules has significant variations, the centralized-distributed hybrid structure outperforms the cascaded power transfer structure on the output power. While the temperature difference distribution is comparatively stable, the cascaded power transfer structure is superior to the centralized-distributed hybrid structure. With detailed evaluation and comparison between the two structures, the overall design for DPP-based TEG systems with different connection types has been proposed in this paper, which is the reference for the future implementation of practical TEG applications.

In this paper, we design a linear time-invariant two-input-two-output controller for the permanent magnet synchronous motor (PMSM). First, the nonlinear system of a PMSM is approximated using a linear system with structured uncertainties according to the geometric structures of PMSM. We then design a linear controller for the approximated linear system using a standard $\mu$ -synthesis robust control method. The main contribution of this paper is that we recognize that the nonlinear PMSM can be reduced to a linear system to apply the mature modern control theory, without referring to classical PID control, thus largely reducing the design effort. The newly designed robust controller is not only easy to calculate, it is also easy to implement and requires less sensors. By virtue of modern robust control theory, it responds fast to exogenous inputs, and robust against parameter uncertainties as well. The applicability of the designed robust controller is both numerically simulated and experimentally verified on a TMS320 F28335 based control board, with performance further compared with the widely used field-oriented controller.

This paper presents a robust observer–controller scheme for sensor fault-resilient control in dc servomotor drive-based applications (such as antennae control for satellite tracking, radio telescopes, and conveyor belt systems). In contrast to the earlier works on abrupt faults, this paper considers incipient sensor faults and detects using the higher order sliding mode (HOSM) observer, followed by a tracking controller, which maintains the acceptable drive performance. A robust output tracking controller based on fractional integral terminal sliding mode surface with HOSM terms is developed to ensure faster and finite-time convergence of the error trajectory. Moreover, various slopes of incipient faults are considered to analyze the detection delay, and switching strategy reconfigures the system with the estimated speed whenever the residual crosses the threshold. The closed-loop performance in the presence of most common faults (abrupt, incipient, and intermittent) is experimentally validated on a dc motor-based industrial mechatronic drives unit with belt-drive inertial load (which exhibits nonlinear friction, torque variations, and other disturbances).

This paper shows a synchronization technique of power converters based on a limit cycle oscillator (LCO) and a frequency-locked loop (FLL), which makes the system frequency adaptive. The proposed technique LCO-FLL offers a high degree of immunity and robustness against swells, sags, harmonics, and phase-frequency shift. Furthermore, the LCO-FLL has the advantage of performing the synchrony with the grid from any initial condition set for LCO, ensuring an acceptable transient onto the synchronization process. Other advantages of the proposed scheme are that it does not require a phase-locked loop or trigonometric functions and it gives useful information to estimate the positive- and negative-sequence components in a three-phase system with a highly polluted grid scenario. In this paper, a local stability analysis of the LCO-FLL is presented. The behavior and performance of the proposed technique are compared with synchronization techniques by means of experimental results. Furthermore, a three-phase application of the synchronization technique is evaluated experimentally.

Design and optimization of synchronous reluctance machine for medium-speed flywheel energy storage system (FESS) applications is presented in this paper. High efficiency and high torque density are the main design criteria of the motor/generator system for electromechanical storage systems. Moreover, high salience ratio and appropriate stator design are required to achieve a high torque density and acceptable efficiency in synchronous reluctance machine. In this paper, the effects of key design parameters on the performance of the motor/generator system are investigated and an optimization procedure based on response surface methodology coupled to finite-element model is performed to achieve optimum value for stator and rotor parameters. The finite-element simulation results confirm that the performance of FESS improves significantly in comparison with initial design, by using the proposed design procedure. Finally, a prototype motor/generator system is implemented and experimental results are presented.

This paper proposes and validates model predictive control as an alternative control strategy for H-bridgeneutral-point-clamped (H-NPC) converters for single-phase grid-tied string photovoltaic (PV) systems. The presented control scheme achieves good quality current waveforms with unity power factor, dc-link voltage control, and neutral-point voltage minimization. Furthermore, the predictive controller has been further enhanced by including an average device switching frequency restriction and a $dv/dt$ mitigation. The main contribution of this paper is the avoidance of the potential leakage current due to parasitic capacitance of the PV modules by using a predictive model based control technique instead of modulated schemes and eliminating high-frequency common-mode voltage components. Experimental results during steady state and dynamic operation are presented to illustrate the behavior of the H-NPC converter commanded by the proposed control scheme.

The Fuzzy ARTMAP is a supervised learning method, providing high accuracy in many classifications. In this paper, we explore the role of hardware accelerators in remote sensing classification missions. We focus on the designing and implementing a massively parallel hardware architecture on a field-programmable gate array (FPGA) of the performance phase's algorithm. The implementation is mapped on Xilinx Virtex 6 XC6VLX240T FPGA chip for an embedded system using Xilinx ISE 14.5 software. Embedded blocks dedicated to digital signal processing (DSP) and blocks memories are used. DSP48E1 is part of Virtex-6 FPGAs devices. It boasts of increased capability over previous generations, and is highly customizable, a key feature of this primitive that has motivated and enabled the work presented in this paper. We illustrate the application of this methodology to the valuation of various schemes involving embedded elements. This paper also presents a summary of the performance cost with regard to the speed, power, and required computational resources.

This paper introduces a new class of microwave sensor architecture using direct conversion principle to eliminate data processing and provide low-power smart sensor nodes. Using a six-port circuit as the modulator, the sensing data are up-converted directly to a microwave frequency and sent by an antenna. At the receiver, a six-port circuit is used as a demodulator to down-convert the received signal and extract the sensing data. To predict the communication channel of the sensor network and provide a robust connection, a pilot sequence is sent along with the sensor data which is used in the calibration procedure at the receiver for accurate extraction of sensing data and making sensors smarter. Any kind of microwave sensors based on the variation of impedance can be used in the proposed structure. In this paper, the capacitive loading is used as a material sensor. By variation of material in the sensing area, the impedance of the load and reflection coefficient ( $\Gamma$ ) are changed. Then, the amplitude and phase of $\Gamma$ are transmitted via the six-port circuit, received in the network base station, and analyzed to find the material changes. As an example, a system is fabricated and evaluated at 2.45 GHz.

This paper systematically studies a new kind of PM machines with both stator and rotor PM excitations, namely, dual-PM excited machines. The key is to rely on the PM-iron structure in the machine to provide both PM excitation and flux modulation. Besides the fundamental field component in the air-gap, some other predominant harmonics introduced by the flux modulating effect can also contribute to the electromagnetic torque production. Therefore, this kind of machines can be designed with high torque density. Four dual-PM excited machine concepts with the same rotor configuration but different stator structures are comparatively studied, which include double-stator PM machine, stator multitooth-PM machine, stator slot-PM machine, and stator tooth-PM machine (STPM). Based on the flux modulating effect, the general design principle of the dual-PM machines is proposed in this paper. Through analytically investigating the air-gap field harmonics, the physical insight of the dual-PM machines is brought forward. All the four machines are optimized using an improved Tabu search coupled with finite element method, and their electromagnetic performances are comprehensively studied and compared. A prototype of STPM is manufactured. Experimental tests are conducted and the results well verify the electromagnetic design.

The main aim of this paper is the imposition of constraints for the multiobjective optimizations of magnetic gears. In order to reduce the computational effort, a semianalytic design procedure is adopted, providing a fast simulation tool that can be embedded within an optimization loop. Magnetic, thermal, and mechanical constraints are discussed and embedded into a stochastic algorithm, in order to identify immediately infeasible geometries. The algorithm that has been developed provides a useful initial design tool that can be adopted to locate the optimal solutions in the search space. This paper also presents the multistage magnetic gear topology as the counterpart of the multistage mechanical gearboxes.

This paper presents a new magnetic-gear pole-changing hybrid excitation machine (MG-PCHEM), which can provide high torque density and improved flux-weakening ability. The key is to flexibly change the pole-pair number of inner excitation sources by injecting variable dc field currents, and, hence, regulate the dominant pole-pair flux components to realize an effective magnetic field adjustment. In the following paper, the machine configuration and its operation principle of flux control are introduced first. Then, the influences of some leading design parameters are analyzed including the slot-pole combination and other dimension parameters, and after which a comparative study is carried out with traditional single-stator topology. Based on the optimal design, electromagnetic performance of the MG-PCHEM is further evaluated by using the finite-element method. Finally, a prototype is designed, manufactured, and fully tested. Relevant experimental results verify the feasibility of this new hybrid solution as well as the finite-element predictions.

This paper deals with an analysis of a middle-frequency resistance spot-welding (RSW) system with a dc welding current controlled by a pulsewidth modulated inverter, which supplies a welding transformer with a full-wave rectifier mounted at the secondary. Welding transformers in the automotive industry are usually mounted on the arm of a moving robot, so the weight is important. To achieve the same welding power with a large welding current, the transformer's weight can be reduced with a higher PWM switching frequency. This higher frequency allows a reduction in the transformer's iron-core cross section with shorter primary and secondary windings. Unfortunately, the leakage inductances prevent the RSW system from achieving the same nominal welding current at higher frequencies. The frequency-dependent maximum welding current is a characteristic behavior of the RSW system, which can be determined by sophisticated and time-consuming simulations or with the expensive measurements. The third option presented in this paper is determination of an analytical solution, which allows calculation of the maximum welding current as function of frequency or any parameter of the RSW system circuit model. The analytically calculated frequency-dependent function of the maximum welding current was completely confirmed by measurements on an industrial RSW system and by numerical simulations.

Industrial Wireless Sensor Networks (IWSNs) allow the use of battery-operated nodes to provide easy deployment, even in harsh environments, and are low maintenance. The optimal network design can be difficult because several constraints and requirements must be considered among all the power consumption. For this reason, specific approaches, also based on soft computing methods, can be applied in such a way as to further decrease the energy consumption in IWSNs. To this end, this paper proposes a fuzzy logic based mechanism that, according to the battery level and the ratio of throughput to workload, defines the sleeping time of sensor devices in an IWSN based on IEEE 802.15.4 protocol. A particle swarm optimization (PSO) algorithm is introduced to obtain the optimal values and parameters of the proposed fuzzy logic controller (FLC), i.e., optimizing the membership functions, by varying their range, to achieve the best results regarding the battery life of sensor nodes. This paper provides a detailed description of the FLC configuration, a logical analysis of the PSO algorithm for the derivation of best performance conditions values, and simulative assessments obtained through MATLAB simulations.

Measurement and control of electric power quality (PQ) parameters in off-grid systems has played an important role in recent years. The purpose is to detect or forecast the presence of PQ parameter disturbances to be able to suppress or to avoid their negative effects on the power grid and appliances. This paper focuses on several PQ parameters in off-grid systems and it defines three evaluation criteria that are supposed to estimate the performance of a new forecasting model combining all the involved PQ parameters. These criteria are based on common statistical evaluations of computational models from the machine learning field of study. The studied PQ parameters are voltage, power frequency, total harmonic distortion, and flicker severity. The approach presented in this paper also applies a machine learning based model of random decision forest for PQ forecasting. The database applied in this task contains real off-grid data from long-term one-minute measurements. The hyperparameters of the model are optimized by multiobjective optimization toward the defined evaluation criteria.

Motivated by industry needs, this paper focuses on statistical models, descriptive probabilistic data analysis, and data-prescriptive signal processing in smart inertial sensors. These multimode sensors combine physical and cyber components such as solid-state and micromachined motion sensing elements, processing and interfacing integrated circuits, middleware, and software. We develop consistent algorithms and tools based upon cross-cutting engineering science along with substantiation and validation. Fundamental, applied, and experimental results are reported. Our multidisciplinary findings advance fundamental knowledge and enhance transformative technologies. We empower synergetic system-level integration of diverse device physics with descriptive, predictive, and prescriptive analyses. This paper contributes to the design and deployment of the next generation of smart sensors which utilize front-end microelectronic, microelectromechanical system, and processing technologies.

This paper investigates a dc collection grid architecture to process energy from offshore wind turbine generators (WTGs), which can be further interfaced with the shore via a high-voltage dc network. In the proposed approach, WTG output voltage is rectified and converted to medium frequency (MF). Then, a transformer isolation stage is used, followed by a boost rectification stage. The boost rectification stage is controlled to emulate a resistive load, forming a medium voltage dc (MVDC) interconnection. This type of control is simple for varying wind conditions. The operating principles and unique advantages of the proposed approach are documented along with comparison with a conventional benchmark, assuming the turbines are fitted with direct drive technology. System design example, loss/size analysis and transformer finite element analysis are shown in this paper. Simulation results demonstrate the functional capability of the system. Experimental results from a scaled down prototype prove the operation of proposed concept.

This paper proposes a modular multilevel dc-link dc solid-state transformer (MADCT) based on high-frequency dual active phase shift for HVDC grid integration. The proposed MADCT employs one arm of modular multilevel converter as HVDC active front-end interface and dual active bridge as high-frequency power transfer link, which brings many advantages and makes the operation of MADCT quiet different with traditional dc transformers. Compared with the traditional dc transformer schemes, the MADCT not only has good modularity and flexibility but also has good fault handling capacity. Especially, the performances of current stress, power transfer capacitor, and efficiency are improved. The topology, operation principle, voltage, current, power performances, and control and parameter design are presented and analyzed comprehensively in this paper. At last, a MADCT prototype is built and the experimental results verify the correctness and effectively of the proposed solution.

Latterly, multilevel inverters have become more attractive for researchers due to low total harmonic distortion in the output voltage and low electromagnetic interference. This paper proposes a novel single-stage quasi-cascaded H-bridge five-level boost inverter (qCHB-FLBI). The proposed five-level inverter has the advantages over the CHB quasi-Z-source inverter in cutting down passive components. Consequently, size, cost, and weight of the proposed inverter are reduced. Additionally, the proposed qCHB-FLBI can work in the shoot-though state. A capacitor with low voltage rating is added to the proposed topology to remove an offset voltage of the output ac voltage when the input voltages of two modules are unbalanced. Besides, a simple PID controller is used to control the capacitor voltage of each module. This paper presents circuit analysis, the operating principles, and simulation results of the proposed qCHB-FLBI. A 1.2-kVA laboratory prototype was constructed based on a DSP TMS320F28335 to validate the operating principle of the proposed inverter.

One way to incorporate the increasing amount of wind penetration is to control wind turbines to emulate the behavior of conventional synchronous generators. However, the energy balance is the main issue for the wind turbines to be truly dispatchable by the power system operator such as the generators. This paper presents a comprehensive virtual generator control method for the full converter wind turbine, with a minute-level energy storage in the dc link as the energy buffer. The voltage closed-loop virtual synchronous generator control of the wind turbine allows it to work under both grid-connected and stand-alone condition. Power balance of the wind turbine system is achieved by controlling the rotor speed of the turbine according to the loading condition. With the proposed control, the wind turbine system can enhance the dynamic response, and can be dispatched and regulated by the system operator. The sizing design of the short term energy storage is also discussed in this paper. Experimental results are presented to demonstrate the feasibility and effectiveness of the proposed control method.

The increasing penetration of renewable sources, particularly wind energy, has provided the power system with large-scale clean electricity. For integrating gigawatt offshore wind energy, voltage source converter (VSC) based multiterminal HVDC transmission is the prospective technology with flexible control characteristics. Most of the papers so far have dealt with improving the frequency performance caused by an ac system disturbance, and only a few deals with the influence of dc system converter outage on frequency performance. However, the converter outage will bring successive power impulses to the onshore ac grids. This paper presents an optimized power redistribution method to enhance the frequency performance of onshore ac grids. The two scenarios of power redistribution after converter outage are analyzed: self-distributed type and nonself-distributed type. For the self-distributed scenario, the optimized power redistribution method involves three steps: sensitive cluster identification, optimized power redistribution calculation, and dc grid operating point setting. For the nonself-distributed scenario, a combined offshore wind farm control strategy with emulating inertia control and auxiliary pitch angle control is proposed to alleviate the adverse effect of the transferred surplus power on asynchronous grids. Simulation verifications are carried out in a modified New England 39-bus system with seven terminal VSC-HVDC transmission system.

This paper presents a medium-voltage wind energy conversion system with integrated storage that implements power electronics converter based on modular multilevel topology. The proposed converter has a storage system integrated into its modular cell structure. This paper analyzes the proposed topology and presents detail sizing procedure for both converter and storage system in order to meet new grid connection standards and fault ride through (FRT) requirements. In order to verify the system operation, high detail model of the converter leg is used to simulate independent power control on ac and dc sides of the converter needed for the successful implementation of the FRT control.