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In this paper, a reduced order thermal observer with disturbance estimation is applied for temperature monitoring in a power electronics module. Although accurate thermal models of power electronics assemblies are widely available, based e.g. on computational fluid dynamics (CFD) solvers, their\ud computational complexity hinders the application in real-time temperature monitoring applications. This paper proposes a reduced order state space observer to provide a real-time estimation of temperature in power electronics modules. The observer is coupled with a disturbance estimator, to minimize the error caused by uncertainties in the model and unknown operating conditions.

Short-term household electricity load forecasting is important for utility companies to ensure reliable power supplies. Traditional methods for load forecasting relied on historical records from one single data source and have limitations with insufficient or missing data. Recently, an emerging family of machine learning algorithms, multitask learning (MTL), has been developed and has the potential for load forecasting. By MTL, the electricity consumption data from multiple communities can be fused to improve forecasting accuracy. However, appropriate modeling of the relatedness to enable the between-community knowledge transfer remains a challenge. This paper proposes an improved MTL algorithm for a Bayesian spatiotemporal Gaussian process model (BSGP) to characterize the relatedness among the different residential communities. It hypothesizes on the similar impacts of environmental and traffic conditions on electricity consumption in improving short-term load forecasting. Furthermore, this paper proposes a low-ranked dirty model along with an iterative algorithm to improve the learning of model parameters under an MTL framework. This paper uses a real-world case study from two residential communities in Tallahassee, Fl, USA, to demonstrate the method effectiveness. The proposed method significantly outperforms state-of-the-art forecasting methods and effectively captures the relatedness to provide between-community knowledge transfer compared with other MTL methods.

The concept of energy Internet (EI) is very promising due to its ability to integrate distributed generators and storage devices. Energy routers (ERs) enable highly efficient, reliable, and flexible power system operation. To dynamically control and optimize energy flow in EI, an extensive communication is required. Considering the diversity of generators and ERs, it is crucial that such communication is achieved in a standardized and interoperable way. In this paper, an improved energy routing algorithm and its impact in EI operation are demonstrated. Furthermore, a full communication solution is developed for ERs and their interaction with grid operator. This paper proposes an International Electrotechnical Commission (IEC) 61850 communication-based power routing algorithm in microgrids. Optimal selection of source and routing path is achieved according to the proposed algorithm and communicated to the ERs via IEC 61850 based communication. The effectiveness of the proposed IEC 61850 communication-based routing algorithm is verified on network emulation platform comprising of IEC 61850 emulator tools and network simulator tool.

This paper reports the application of silicon bipolar junction transistor (BJT) modeling techniques to the modeling of dynamic behavior of high-voltage 4H-SiC BJTs, and the experimental validation thereof. High-voltage silicon BJTs are impractical due to their low current gain that requires a bulky base driver. Emergence of high-voltage 4H-SiC vertical NPN BJTs with a tenfold higher gain enables the application of efficient drivers, with ratings close to those of IGBTs. This paper demonstrates the advantages offered by 4H-SiC BJTs by means of wide-scale measurements at 800 V and 10 A in a range of temperatures up to 175 °C and adjusted base driver switching rates. This paper shows that the turn- off storage delay in the SiC BJT is two orders of magnitude lower than that of the silicon device. It also shows that the turn- on switching transients of SiC device are by an order of magnitude and the turn- off transients are by two orders of magnitude faster than that of its silicon counterpart, resulting in a tenfold reduction of the switching energy. It also demonstrates the temperature dependence of switching transients of the silicon BJT, and the relative temperature-invariance of the SiC device's performance. This paper concludes with validation of the transient models for the 4H-SiC NPN BJT, showing that the model is sufficiently accurate for transient switching and loss calculations.

Smart buildings form an integral part of the smart grid that lowers electricity cost. This objective can be achieved by using suitable enhanced algorithms and techniques. The motivation of this paper is the request for an economical decision-making system from a commercial company in Singapore. This paper presents an economical building management system (EBMS) concept inspired by the building management system and machine learning. EBMS improves the decision-making process through rule-based algorithm within the system. Machine learning algorithm is included as part of EBMS to enhance the computational calculation for the electricity distribution. It includes the function of self-making decision for purchasing electricity based on forecasting system for electricity price or real-time electricity price data when facility managers are not present. EBMS uses multiagent system to communicate, interact, and negotiate with multiple agents for energy supply and demand in the building. Simulation studies have shown the potential of EBMS concept to provide a cost reduction solution up to 61.42% savings for smart buildings. Better electricity purchasing contract option can be decided based on the forecasting system for building power consumption.

In multi-phase AC power systems, e.g. aircraft electric power systems (EPS), the proximity effect between the feeder cables can be severe and complex due to the tightly wired cable bundles. Simulation software is widely used to analyze such effects in order to guarantee proper system operation, but it is highly time consuming and requires extensive computational resources. Accordingly, this paper proposes an analytical calculation method for estimating the ac resistance of closely bundled power cables, namely multi-conductor cables. Simulation and experimental tests are performed to validate the effectiveness and accuracy of the method, showing that the algorithm developed in this paper is easy to implement with a minimum accuracy of 92% in all the tests. It allows online estimation of cable resistances, which can be beneficial for advanced system monitoring and management to enhance safety and reduce losses. Aircraft EPS and cables are used as the example in this paper, while the proposed method is also applicable for other applications, such as shipboard EPS, renewable energy parks, or microgrids where multi-conductor cables are used.

Modularization design has been widely used to reduce the detent force of permanent magnet linear synchronous motor (PMLSM). For modular PMLSM, ideally, unit motors are independent of each other and the detent force of the whole motor is the sum of that for unit motors; thus, the whole motor's detent force can be suppressed by adjusting the phase difference among the unit motors’ detent forces. But actually, there is coupling effect between adjacent unit motors, which has adverse effect on the detent force suppression. The coupling effect changes the magnetic field distribution, which is often neglected in current research. Hence, this paper carries out the research on magnetic field analysis and flux barrier design for modular PMLSM considering the coupling effect: the influence of the coupling effect on the air gap magnetic field is clarified through magnetic field analysis; the coupling force is isolated by finite element analysis, and then the effects of key parameters are discussed; the whole motor's detent force model considering the coupling effect is established, and an optimal design method of adjusting the flux barrier length is presented to suppress the detent force. Finally, a prototype is made to test the detent force characteristics with different flux barrier lengths, which verifies the research theory in this paper. The research results in this paper can provide guidance and reference for the design of modular PMLSMs.

Series-connected-based offshore wind farms can eliminate bulky central offshore converters, transformers, and platforms. In a series-connected-based offshore wind farm, the dc voltage of the converters should be changed within a large range to control the dc-link voltage (grid side) and maximize wind power acquisition (generator side). In this paper, the full-bridge-based modular multilevel converter (FB-MMC) is proposed as grid- and generator-side converters. The dc voltage of the FB-MMC can vary in a large range because the full-bridge submodule (FBSM) is used. The control method of the FB-MMC in a series-connected-based offshore wind farm is different from those of traditional ones. The dc current control and capacitor voltage balance control are proposed in this paper, with which the FB-MMC can operate normally in the series-connected offshore wind farm. Moreover, the capacitor ripple voltage in the generator-side FB-MMC is studied. The result shows that the capacitor in the FBSM can be designed in rated power and frequency, and it will be feasible when the power and frequency decrease. Simulation and experiment results verify the feasibility of the proposed configuration and the corresponding control algorithm.

Nanorobotic manipulation technique has been regarded as one of the most dominating approaches to upgrade the functions of microscope benefits from its complex and precise operation system. At the current stage, although atomic force microscopy (AFM) is capable of mapping specimens on a two-dimensional/partial three-dimensional (3-D) plane, a full orientation of 360 $^{\circ }$ characterization still remains a challenge for AFM. Taking advantage of a nanorobotic manipulation system (NMS), 360 $^{\circ }$ mapping and 3-D reconstruction of topography and nanomechanical properties are presented in this paper. Compared with recent advances of AFM mapping techniques, our proposed method is able to realize effective, large area characterization and integral results can be directly perceived through 3-D reconstruction. In this paper, a six degrees-of-freedom NMS assembled inside AFM and task specification are first proposed. Second, home positioning method for effective specimen rotation scanning is introduced. Third, 3-D reconstruction methods for the topography and nanomechanical properties of the specimen are presented. After that, 360 $^{\circ }$ characterization of three different types of specimens, human hair (anisotropic biological material), trapezoidal cantilever, and conical micropipette (isotropic inorganic material) are adopted to demonstrate the feasibility and practicability of our proposed system. Finally, the 3-D reconstruction results of selected specimens are analyzed. This paper fills the blank of current AFM topography and nanomechanical characterization methodologies, which is expected to give a long-term impact in the fundamental nanomaterial research and practical micro/nano characterization.

This paper proposes a family of single-stage converters consisting of three different converters, each of which is able to produce a variety of waveforms through the waveform-subtraction technique. We brand this converter family as waveform-subtraction based single-stage converter (WSSC). By using only a single-stage converter, the proposed waveform generation technique is able to realize dc–dc–ac conversions and suppress input current ripple, meeting the needs of modernized power grid with renewable energy sources. At the same time, converters in this WSSC family are capable of generating a range of shapes, such as triangular, rectangular, and sawtooth waveforms, with simple structures, demonstrating its suitability of being applied in the electrochemical industry, e.g., in the electroplating process. Furthermore, the proposed family converters also realize substantially better input current ripple suppression compared to other conventional converters. In order to prove the validity and efficacy of the proposed WSSC and the theory underpinning it, in this paper, extensive simulations and analyses are conducted to verify the theoretical foundation of the proposed WSSC strategy, and the prototype of a converter from the proposed converter family is built and tested in our laboratory, which validates the functionality of the WSSC.

With the proliferation of distributed generation in distribution networks, quickly and smoothly converting to a state of regional autonomy in the case of distribution network failure is one of the main challenges for the stable operation of a multimicrogrid (MMG). To address the aforementioned problem, this paper proposes coordinated control of the passive transition from grid-connected to islanded operation for a three/single-phase hybrid MMG. Under the premise of fully considering the constraints on the tie-line transfer power undertaken by the master power supply (MPS), the following two scenarios regarding safety and emergency are formulated: 1) when the output power of the MPS is in the safe range, the proposed strategy coordinates the energy storage (ES) in each submicrogrid (SMG) to achieve power balance; 2) when the output power is in the emergency range, this paper proposes a three-phase balance method based on a bubble sort to realize the combination optimization of the single-phase source-load-storage (SLS) and a fast power regulation method based on implicit enumeration for the SLS to reduce the tie-line transfer power, which could prevent failure of the mode transition from power overload. The test results verify the effectiveness and feasibility of the proposed coordination strategy.

This paper presents the development of a Class-D full-bridge zero-voltage switching (ZVS) inverter, applicable to wireless power transfer (WPT) systems, operating at 13.56 MHz switching frequency with dynamic dead-time control (DDTC). Resonant-coupled WPT systems are being designed at ultrahigh switching frequencies to reduce the size of the wireless link and the passive components. Maintaining ZVS while controlling the output power delivered to a fixed or variable load is one of the major challenges of designing inverters at multi-MHz switching frequencies. DDTC is the approach deployed in this paper to sustain soft switching of a Class-D full-bridge inverter over the full range of output power while regulating the input dc bus voltage. Simulation results are presented to show that dynamically controlling the dead-time during input dc bus voltage variations reduces switch-node voltage overshoot, prevents large current spikes in the switching devices, and reduces associated high switching loss. Practical results obtained show that DDTC reduces switch-node voltage overshoot, increases the inverter efficiency, and reduces the steady-state temperature of the inverter during output power regulation.

This paper presents a 5-level inverter topology for open-end induction motor drives by using a single dc source. The open stator windings of the drive are supplied with a 3-level flying capacitor inverter from one end and capacitor-fed 2-level inverter from another end. The voltage ratio of the dc link to the capacitor in 2-level inverter is maintained at 4:1 ratio to generate five-level voltage output. The capacitor in 2-level inverter is balanced by the switching redundant vector combinations from both the inverters while the floating capacitors in the 3-level inverter are balanced by using redundant switching states. The proposed topology gives 5-level operation with less number of floating capacitors and power semiconductor switches compared to other existing topologies. Also, the balancing of the capacitors is independent of load power factor and modulation index. Further, the generalization of the proposed dual inverter scheme for any n -level inverter is also included in this paper. The experimental results and required analysis are also presented to validate the inverter scheme.

Satellite dc–dc power converters are required to have electromagnetic interference (EMI) compatibility as well as high reliability. The requirement of high reliability limits the complexity of the structure as well as the number of low-reliability components. In this paper, a conventional active-clamp-forward (ACF) topology is examined for a satellite converter owing to its relatively simple structure, small number of components, and good clamping capability regarding its switch voltage stress. However, it has a pulsating input current shape, a high di / dt level, and high switch voltage stress, which are disadvantageous with regard to the EMI filter size and high-input-voltage converter applications. To overcome these drawbacks, a new ACF topology with a continuous input current waveform is proposed. In the proposed waveform, the voltage stresses on the main switches are relieved, which is crucial to ensure the reliability of satellite FET switches, by utilizing a two-series connected structure. These features allow the proposed converter to serve as a high-input-voltage, high power-density satellite converter. In this paper, 100 W prototype converters with 50 V inputs operating at 300 kHz are built with a high power density of 47.9 W/in3. Experiments on these prototype converters are carried out to verify the features.

The development of wide band-gap semiconductor devices is rapidly promoting the development of power electronics technology, especially in high frequency (HF) power converter region. A category of HF power converter is switch-mode power amplifier (PA). This paper focuses on the implementation of a multiphase dc–dc PA with high bandwidth and high power rate. When naturally sampled phase-shifted carrier modulation is implemented in the practical digital control system to control this HF power converter, the pulsewidth error problem caused by limited domain frequency of control chip becomes much severer. As a result, dc voltage component of each phase becomes different under several conditions, leading to current imbalance among phase inductors. This paper analyzes this problem and proposes a sensorless control method to solve it, based on the injection of random sequence in reference wave. A four-phase prototype employing GaN devices is fabricated, switching at 1 MHz. Current imbalance and effectiveness of the proposed control method are verified by experimental results. The prototype is capable of uniformly amplifying sine signal within 200 kHz and a 350 kHz bandwidth random signal, with peak output power up to 810 W.

Active magnetic bearing is a core technology for high-speed rotational machines. Power electronics converter as the active magnetic bearing drive is the actuation unit and its topology highly impacts the performance of the bearing system. This paper introduces the progress of topology of active magnetic bearing drive. The initial topology of an H-bridge does not sufficiently utilize the power electronics devices. The topology with half-bridge and shared phase-leg has been proposed as the fundamental topology. In this paper, two approaches of novel magnetic bearing drive topology modification have been developed on the basis of the fundamental topology. In the first approach, central phase-leg for multiaxis magnetic bearing drive can be further shared and the power electronic devices can be globally optimized in the whole system. Further, a topology with current in the reverse direction can reduce the central phase-leg current rating and power losses. In the second approach, fault-tolerant magnetic bearing drive topology has been developed on the basis of the fundamental topology, too. It can ride-through the open-circuit fault of power electronics switch-in operation and keep levitation for the magnetic bearing. The series work of novel topologies can improve the performance of an active magnetic bearing system in application.

The wind energy generating system (WEGS) in this paper, aims to provide the required active peak power without high frequency fluctuations even under variable wind speed conditions. The generator speed is adjusted according to the intermittent wind speeds through two voltage source converters (VSCs) connected back to back, namely, machine-side VSC (MSVSC) and utility grid side VSC (UGVSC) across the dc-link capacitor. In this paper, the hybrid generalized integrator control is proposed for switching UGVSC and providing dc offset rejection and immunity against oscillatory errors due to subharmonics, thereby improving the power quality (PQ). Fuzzy logic controller (FLC) is implemented for the speed control of the salient pole synchronous generator (SG) driven by the wind turbine. The FLC provides the tracking of the reference speed under high overshoot transient conditions and narrow bandwidth. The switching of MSVSC is obtained by field oriented control. The dynamic performance is improved by the wind feed-forward term, which reduces the oscillation, ensuring balanced and sinusoidal grid currents. The generated power from the WEGS is fed to the grid. The weak grid conditions, namely, grid voltage unbalance, voltage sag, voltage swell, and grid voltage distortion, are considered. The performance of the system is tested on a laboratory prototype. Test results provide the effectiveness of the system with increased wind penetration and performance under weak grid conditions. Moreover, improving the PQ, the grid current total harmonic distortion meets the requirement of IEEE-519 standard, and is found to be less than 5%.

This paper improves the position sensorless drive by sensing actual machine phase voltages. A high-bandwidth phase voltage measurement is developed for pulsewidth modulation (PWM) voltage inverters. On the basis, the actual phase voltage is obtained based on the digital integration of PWM voltage using the capture modulator in existing drive microcontrollers (MCU's). Comparing to existing phase voltage measurement, no separated A/D converter and communication hardware are required because PWM pulses are directly measured using MCUs. However, for standard machines without neutral points, only line-to-line ac PWM voltages can be measured for the phase voltage reconstruction. Since the capture based on transistor-transistor logic (TTL) logics receives only digital signals, a preprocess circuit to convert ac PWM line voltages to equivalent digital signals is proposed. This paper clearly explains the voltage sensing hardware using MCU capture modulator. According to experimental results, a 150-MHz sampling rate for phase voltage measurement is achieved based on the proposed capture-based voltage measurement. Although the physical limitation of back electromotive force estimation still appears, the proposed phase voltage measurement substantially enhances the sensorless drive performance at low speed.

This paper presents a detailed analysis of the electromagnetic force and vibration behavior of an axial flux permanent magnet synchronous machine (AFPMSM). First, the AFPMSM configuration and two types of dual three-phase winding are introduced. Subsequently, the electromagnetic force of the double-stator inner-rotor AFPMSM is investigated. Its spatial and temporal characteristics are derived analytically and validated through two-dimensional Fourier decomposition. A multiphysics model is established to calculate the vibration of the AFPMSM, which includes control, electromagnetic, structural, and vibration model. The accuracy of this multiphysics model is verified by the modal and vibration test. Furthermore, the vibration of the AFPMSM with three winding types considering current harmonics are calculated based on the multiphysics model. The vibration performance of the AFPMSM with three different winding types are compared and the mechanism of vibration is discussed. It was concluded that the novel detached winding could mitigate the vibration of dual three-phase AFPMSMs. Finally, the vibration test is carried out to validate the theoretical analysis and the experimental results agree well-with the simulation results. This paper provides an effective method for double-stator permanent magnet synchronous machine (PMSMs) to reduce vibration.

In this paper, a new modular and active snubber cell, easily applicable, and attractive for converters, especially have many switches proposed. This snubber cell is implemented on the single phase of a grid-connected three-phase T-type three-level inverter (T-3LI). In this new converter, the main switches turn- on under zero-voltage transition and turn- off under zero-voltage switching (ZVS). Also, auxiliary switches turn- on under zero-current switching and turn- off under ZVS. All snubber diodes operate under soft switching (SS). There are no additional current and voltage stresses on the main switches. During an SS operation, the switching energies are transferred to a dc voltage source. Then, these energies are processed to input with an independent dc–dc converter. Thus, all switching energies are recycled. In this paper, the principle operation and steady-state analysis of the modular and active snubber cell for a single-phase T-3LI are presented and experimental results, rated 1 kW and 100 kHz, are provided to verify theoretical analysis.

This paper proposes a mutual calibration strategy for multiple current sensors in an electric vehicle motor drive. The motor drive usually consists of three current sensors, i.e., a dc-bus current sensor and two phase current sensors. Due to the aging effect and harsh operating environment, the accuracy uncertainty issue is inevitable in these crucial sensors, which results in poor driving performance. In this paper, the detection voltage injection (DV-Injection) method is proposed for mutual calibration of the aforementioned current sensors. Two opposite basic vectors are set together to detect and eliminate the offset error of the dc-bus current sensor. Then, both the directly measured phase-current values by the phase-current sensors and the indirectly measured values by the dc-bus current sensor are sampled. These values are utilized for mutual calibration of the phase-current sensor offset errors and scaling error differences among all the current sensors. Meanwhile, the DV-Injection process is only applied in the period of calibration process, whereas in the remaining intervals the space vector pulsewidth modulation technology is utilized. Finally, the effectiveness of the proposed scheme is verified by simulation study in MATLAB/Simulink and experimental results on a 5-kW interior permanent magnet synchronous motor motor prototype.

Active flow control by means of plasma actuators has potential advantages over conventional strategies, e.g., mechanical or hydraulic components may be replaced by lightweight, compact, fast response plasma actuators. In this paper, several designs of dielectric barrier discharge (DBD) plasma actuators are presented for aerospace applications and the focus is on the associated feedback control implementation. The interdisciplinary nature of aerodynamic feedback control with plasma, however, makes direct experimental demonstrating an outstanding challenge. Here, we propose a realistic experimental control implementation afforded by commercial off-the-shelf electric products and the major achievement is the detailed instruction (in both electricity and aerodynamics) and the successful demonstration of the closed-loop design in controlling the dominant modes from a cylinder flow setup. The essence of our approach is to drive DBD plasma actuations by a downstream sensor and excite aerodynamic velocity perturbations, which are further amplified on the shear flow from the cylinder, leading to airflow structures, such as vortex roll-up and randomization, which are measured by the downstream sensor to complete the whole loop. We benchmark our control approach by comparing to the predicted dominant frequencies of the controlled flow system, which can be achieved by the Barkhausen stability criterion after establishing the corresponding transfer function of the whole flow control system. Overall, this paper shall assist a host of new applications in aerospace applications in the near future.

Steel-reinforced concrete has been widely used in the construction of railways because of its robustness and low maintenance cost. This paper focuses on the analysis of unwanted losses in a reinforced concrete track when a high-power online wireless power transfer system is installed on it. Induced dielectric loss in the concrete, and eddy current and hysteresis losses in the reinforcing steel bar are calculated using analytic equations and finite-element analysis. Among the three sources of loss, a dominant one is identified in the first three sections of this paper. It is shown that the dielectric loss in the concrete and the hysteresis loss in the reinforcing bar do not have a critical impact on the efficiency. However, it is found that the eddy current loss of the reinforcing bar is dominant over the other two losses. Furthermore, the eddy current loss of the reinforcing bar overwhelmed the ohmic loss of a transmitter coil if the transmitter coil is not located in a proper position on the concrete track. The theoretical results are evaluated experimentally using a 7-m-long test bed. When the transmitter coil is located 0.14 m above the reinforcing bar, the measured eddy current loss of the steel bar is 3 kW while the Ohmic loss of the transmitter coil is 1.5 kW. As the distance between the transmitter coil and the steel bar increases, the eddy current loss of the bar decreases rapidly. From the simulation and the experimental evaluation of the loss, guidelines for installing a transmitter coil on a reinforcing bar for an in-motion wireless power transfer system are suggested in this paper.

In recent years, there has been an increasing interest in hand movements in various application fields. However, the human hand is too dexterous and only has limited space. Developing a proper method to monitor and capture hand motion is meaningful. Conventionally, an optical measurement method is widely used to capture hand gestures. Nevertheless, this method is costly and has the problem of line-of-sight shielding. In this paper, a sensor fusion algorithm is proposed to calculate a more accurate result by calculating acceleration, magnetic field strength, and angular speed from the inertial measurement unit (IMU). The core concept of this algorithm is based on the idea of feedback control. To validate the performance, the active rotary platform is set up to compare the measured results to the references directly. Most of the error results are less than 3°, and the standard deviations are less than 1°. The measurement results ensure the feasibility of the inertial measurement method with the sensor fusion algorithm proposed in this paper.

A high-efficiency, high-power-density Sigma converter for a 48 V rack architecture in data centers is proposed in this paper. The Sigma converter is a quasi-parallel converter that uses a high-efficiency unregulated converter to deliver the bulk power to the load. A small buck converter is responsible for regulating the output voltage with prescribed dynamic responses. A design guideline for Sigma converter with integrated magnetics is provided in this paper. The unregulated converter is an LLC converter designed with a printed circuit board (PCB) winding matrix transformer, a structure which integrates four elemental transformers into one core. The buck converter is designed with discrete gallium nitride (GaN) devices and a PCB winding inductor. The proposed Sigma converter operates at 48 V input and 1 V-80 A output and can achieve a power density of 420 W/in3 as well as a peak efficiency of 94%.

In this paper, a three-dimensional (3-D) motion tracking method is proposed for binocular microscopic vision system to precisely record the motion trajectories of millimeter size objects in the Cartesian space. Primarily two fundamental problems are solved. The first problem arises from the limited depth of field (DOF) of microscope. Considering the motion of the objects, the existing autofocusing methods requiring sequential images either in focus or defocus are not workable. Therefore, a one-shot prior autofocusing approach is desired, which needs to take the motion tendency of objects into account. Besides, the autofocusing process always lags behind the motion of objects, and there inevitably will be prediction deviation on the motion tendency of objects. This leads to the second problem to estimate the 3-D motion states from defocused images. In this paper, we first explain the defocusing process from the perspective of S-Transform, based on which the Bayesian inference inspired method to estimate the depth from defocus from one single image is derived thereafter. Afterwards, a motion states, including both the position and velocity, estimation approach is developed within the Kalman filter framework. The above two aspects mutually supply the necessary information for each other to be functional to accurately realize the DOF tracking and motion tracking of moving objects. Experiments were well-designed to validate the effectiveness of the proposed method, and experiments result showed a tracking precision of 3 μ m was achieved.

This paper presents a new design of round-shaped transformers applied in diode and controllable rectifiers. Despite conventional three-phase transformers, in round-shaped transformers, voltage is induced on the secondary winding by rotating magnetic field. As a result, in the secondary of this transformer, there can be more than three phases with desired shifts. On the other hand, some rectifier systems may use more bridges supplying from the secondary to improve output dc voltage. However, the rectifier systems produce undesirable current harmonics, especially in controllable systems. This paper discusses how the new design of round-shaped transformers can significantly reduce the harmonic contents of the input current by sinusoidal skewing of the secondary core. The new design is investigated in this paper and its analysis confirms that the harmonics of the input currents can be effectively reduced. Experimental results are also provided to validate the analysis carried out in this paper.

The use of vision sensors for noncooperative rendezvous operations is attractive, especially for microspacecraft, because vision sensors are usually of small size, light weight, and low cost but provide rich information. However, vision-based rendezvous operations are extremely challenging. It is difficult for vision sensors to accurately measure the relative distance between a chaser spacecraft and a noncooperative target. In this paper, we propose a systematic angles-only navigation and control scheme for noncooperative rendezvous operations. The scheme is a hybrid framework that combines offline trajectory planning that integrates observability condition and online trajectory tracking based on nonlinear model predictive control. A navigation filter is used in the online trajectory tracking to estimate the relative motion by using only angle measurements. In the scheme, the chaser spacecraft can closely track the desired trajectory and simultaneously guarantee the estimation accuracy of the navigation filter. This paper provides a general and practical framework for angles-only rendezvous operations and the effectiveness is verified by extensive simulations.

Solid state transformer (SST) integrated hybrid dc–ac microgrid (HMG) has wide operating capabilities in presence of dc–ac loads, renewable energy resources, and energy storage. This paper proposes control strategies for localized control of zonal hybrid microgrid, enabled by the SST and centralized energy storage devices (ESD) integrated using dual active bridge (DAB) converter. The control of DAB dc–dc converter is modified for zero circulating power flow (ZCPF) operation in both SST and ESD. Power management and coordination control used in this paper ensures the power supply reliability of the zonal HMG integrated through the SST. Microgrid system, along with its proposed controllers, provides a stabilized low-voltage dc and ac network ports, in both grid feeding and forming modes. The performance of the configured HMG system is evaluated under various power management scenarios using the MATLAB software platform. Further, the SST architecture, with its proposed controller, is tested on FPGA-based hardware platform.

In this paper, a novel decoupling modular permanent magnet flux-switching linear motor (PMFSLM) is proposed. The primary iron core of the motor is a nonsegmented structure without magnetic coupling among different modules. In contrast to a normal PMFSLM driven by a sinusoidal current, the proposed PMFSLM adopts square-wave current driving. On the basis of structure and working characteristics, a piecewise linear permeance model of a single-module PMFSLM is presented, and a specific design method of the novel modular three-phase PMFSLM is proposed. The proposed design method aims at reducing the cogging force and force ripple of a three-phase PMFSLM. Through further electromagnetic analysis, a set of structural parameters is proposed, based on which finite-element analysis (FEA) is conducted. FEA results show that the design aim is realized even with the influence of armature winding commutation. Prototype experiments of a single-module PMFSLM are performed, and experimental results agree well with FEA results. The findings of this paper verify the effectiveness and practicability of the novel modular PMFSLM and the proposed design method.

Different from the continuous-switching behavior of series power electronic devices in converters, the single-switching attribute of dc circuit breakers (DCBs) provides opportunities to integrate metal oxide varistors (MOVs), balancing circuits, and series power devices. This paper proposes a modular design methodology based on discrete MOVs of a DCB with series power electronic devices. The modular dc circuit breaker (MDCB) topology and voltage balance issues, the steep front effect and solution, and the design method are proposed and analyzed in this paper. Compared with the traditional DCB, the MDCB has a self-balancing ability, thereby removing the voltage-balancing circuit and reducing the number of series modules. The standard designed cell can be operated as an independent DCB or compose a high-voltage DCB in series flexibly, which decreases the difficulty of design and commission. Finally, a series experimental platform based on an insulated-gate commutated thyristor, an insulated-gate bipolar transistor, and an injection-enhanced gate transistor is built to verify the correctness and effectiveness of the proposed design methodology.

This paper describes a bipolar pulsed power supply for strategic mineral exploration. Depending on the operating conditions, the bipolar pulsed power supply is capable of delivering the required high voltage and low current or low voltage and high current when operated, respectively, in either the grounded dipole mode or the loop mode. Based on a 500-V 12.5-A unit module, series and parallel connections of four modules are configured to satisfy both the grounded dipole mode (2000 V) and the loop mode (50 A), respectively. A unit module comprising an LCC resonant converter and a full-bridge-based bipolar pulse-switching unit is designed. In order to achieve high power density, the leakage inductance of the transformer is used as a resonant inductor in place of an external inductor. Accordingly, the resonant tank parameters are designed to give the resonant current a trapezoidal shape to reduce conduction loss and provide high efficiency. In addition, a simple gate-driving algorithm that uses the repetitive short pulse to cover the frequency range from dc to 8 kHz is proposed to allow the compact design of a minimized gate transformer. In this paper, the detailed design of the resonant circuit and the transformer of a unit module is described, and the operation is verified through simulation and experimental results. Finally, the developed LCC resonant converter achieves the maximum efficiency of 95%, the maximum power factor of 0.96, and a high power density of 806.5 W/L.

The voltage source converter based high voltage direct current transmission system with the true bipolar wiring mode features higher flexibility and reliability, yet it cannot be without a proper and effective coordinated control strategy, which is the key to the safe and reliable operation of the system as well as the effective and full utilization of renewable energy on a large scale. A step further from the conventional droop control strategy, the coordinated control strategy based on operating point optimization is proposed in this paper. This paper first illustrates and examines the coordinated control method at the system level in view of special wiring and control modes; it then looks into the method of operating point optimization seeking to achieve both safe and cost-effective operation; and the paper finally demonstrates the effectiveness of the coordinated control strategy verified by MATLAB and PSCAD simulations from the perspective of system operating point deviation, security, and cost-effectiveness.

This paper proposes an “isolated soft switching current fed LCC-T resonant dc–dc converter for PV/fuel cell applications.” This converter is able to achieve zero voltage switching for front-end inverter switches and zero-current switching for voltage doubler diodes. The majority of dc–dc converters have compact capacitive (C) filter in output, but high harmonic currents through transformer makes them bulky. The proposed converter attempts to improve harmonic content through a transformer under wide load and input variations as well as it can significantly reduce required turns ratio of transformer to achieve required output voltage. For the above reasons, the proposed converter can offer better footprints and therefore it can be a potential candidate for PV/fuel cell applications. This paper presents basic operating principal, detailed analysis, control, and design of the proposed converter with the help of an example. This converter operates in two modes, i.e., constant duty cycle mode and constant frequency mode, depending on load demand, and is explained through operating curves. Finally, experimental results are included for justifying the proposed theory.

This paper presents data-driven approaches to improving active power output of wind turbines based on estimating their health condition. The main procedure includes estimations of fault degree and health condition level, and optimal power dispatch control. The proposed method can adjust active power output of individual turbines according to their health condition and can thus optimize the total energy output of wind farm. In the paper, extreme learning machine (ELM) algorithm and bonferroni interval are applied to estimate fault degree while analytic hierarchy process (AHP) is used to estimate the health condition level. A scheme for power dispatch control is formulated based on the estimated health condition. Models have been identified from supervisory control and data acquisition (SCADA) data acquired from an operational wind farm, which contains temperature data of gearbox bearing and generator winding. The results show that the proposed method can maximize the operation efficiency of the wind farm while significantly reduce the fatigue loading on the faulty wind turbines.

This paper proposes a modular on-road wireless power transfer system with interoperable power adjustment mechanism. The paper is anticipated to enhance the capability of on-road charging during the movement of automated guided vehicles (AGV), by which the traveling mileage is increased, while the battery volume is decreased. The system design includes an interoperable power adjustment technique based on the detected impedance, and the moving position of AGV can be, hence, comprehended so as to facilitate the adjustment of the output power from each transmission module in a more flexible way. Through the investigation of on-road charging efficiency, all of coil magnetic analysis, misalignment charging evaluation, system stress simulation, and resonant characteristics investigation are performed. Experimental results gained from software simulation and hardware realization are beneficial for AGV charging applications.

DC microgrid has attracted more and more attention due to its unique characteristics, but the development of a dc microgrid is also facing some challenges, such as interruption and isolation of short-circuit fault currents. Therefore, the dc circuit breaker plays an important role in ensuring the normal work of a dc microgrid. In this paper, a novel bidirectional dc solid-state circuit breaker is proposed to realize the bidirectional flow of energy, which ensures the higher operating efficiency of the dc microgrid. Compared with other solid-state circuit breakers, the proposed novel topology has simpler structure, common ground, and fewer components. First, this paper makes a detailed analysis of the different working stages of the circuit when the fault occurs in combination with simulation results of the circuit topology. Then, the standard of selecting the components through the calculation and analysis of the circuit is given in this paper. Finally, the performance of the novel bidirectional solid-state circuit breaker is verified by experiments.

A major challenge for practical wireless power transfer (WPT) applications is to attain stable power transfer with high and constant transfer efficiency under a dynamic change of coupling condition. In order to address the issue, this paper proposes a novel nonlinear parity-time (PT) symmetric model, wherein the nonlinear saturable gain is provided by a self-oscillating controlled inverter. In this paper, the transfer performance and stability criterion of the nonlinear PT-based WPT system are analyzed based on the coupled-mode theory. The theoretical analysis shows that the proposed system automatically achieves constant output power with constant transfer efficiency against the variation of coupling coefficient. Moreover, based on the gain saturation mechanism, the control strategy for the inverter needs to detect only the current in the transmitter, which eliminates auxiliary circuits of wireless communication for feedback control from the receiver. As a case study of dynamic charging, a drone-in-flight wireless charging platform is improved by applying the nonlinear PT-symmetric model. Experimental results show that when the flying drone hovers in a confined three-dimensional volume of space above the WPT platform, a stable output power is maintained with approximately constant transfer efficiency of 93.6%.

This paper presents research results of voltage gain number control methods of a power electronic resonant zero-current switching dc–dc switched-capacitor (SC) voltage multiplier (SCVM) in a topology with fault tolerance capability (FSCVM). The converters operated under the basic switching patterns are constant-voltage-gain dc–dc series-parallel resonant SC converters. However, this paper presents a method for the output voltage regulation by a special switching strategy. A variable voltage gain is made possible by selecting the number of active switching cells, using an appropriate control method. This creates a set of voltage ratio ranges. In addition, the proposed topology and method of control enable a fault-tolerant operation of the FSCVM under various failures of the device. The paper presents an analysis of the concept, simulation results and an experimental verification in a three-cell FSCVM dc–dc resonant boost converter operating at a 200-watt charge. Issues regarding the selection of components related to the problem of inrush currents that can occur during the voltage ratio increase are also analyzed in this paper, and the design for low inrush currents is demonstrated.

This paper presents a multifunctional control system for interlinking converters interfacing microgrids and ac mains. Applicable standards pose power quality and grid-support function requirements for converters that interface energy resources of dc nature with an ac utility grid. At the same time, the forthcoming smart grid scenario calls for additional functionalities, enabling the effective integration of hybrid (i.e., dc or ac) microgrids, that are applicable to both grid-connected and islanded modes of operation. This requires novel interlinking converter controllers with extended flexibility. The control system described in this paper fulfills both connected and islanded operation needs and provides seamless transitions between the two modes. Such valuable functionalities are attained owing to an underlying, large-bandwidth, triple-loop control organization. The target converter is meant to be connected to a local dc subgrid at the dc side and to a local ac subgrid at the ac side. The controller manages the connection of the ac-side subgrid with the utility grid, ensuring a fast response control of the ac grid current. Therefore, it allows interfacing of renewable sources and loads, aggregated in dc and ac nanogrids or microgrids, with smart power systems, providing enhanced power quality, stability, and flexibility of operation.

In this paper, an optimal design procedure for LCC -series compensation network is proposed for a stationary wireless electric vehicle charger. The main focus of this paper is to optimize the resonant network suitable for a wide range of operation from no-load to full-power operation. The conventional methods only consider the full-load condition to design the resonant network; in contrast, the proposed method employs a time-weighted average efficiency for different coupling conditions to achieve high efficiency over a wide load range including light-load and no-load operation. The resonant network is tuned to realize zero voltage switching for the primary side inverter. Moreover, a finite-element analysis is performed to calculate self- and mutual inductances as well as core losses for magnetic couplers. In order to validate the feasibility of the proposed design, a 1 kW/85 kHz prototype with circular magnetic couplers is implemented. According to simulations and experiments, flat profiles for both efficiency and output voltage against output power variations are achieved. Experimental results demonstrate a 94.8% peak efficiency for the full-load operation.

This paper proposes a new developed switched-capacitor converter to achieve high-voltage pulses with adjustable voltage level and frequency. The proposed topology generates repetitive high-voltage pulses by using low-voltage power supply with reduced number of components, including power semiconductors and capacitor. Therefore, a converter based on switched-capacitor units with high voltage gain and high efficiency can be achieved. Operation principles and design steps of the converter as well as comparative study with conventional converters are described in this paper. Finally, simulation and experimental results of a two-stage structure of the proposed circuit validate the operation principles and features of this topology.

In grounded photovoltaic (PV) systems, dc leakage to earth is formed by the contribution of the PV modules, inverters, and dc circuitry. Ground faults in such systems occur when there is an unintentional connection between any dc-carrying conductor with a grounded surface or earth. On the occurrence of ground faults, dc leakage will be intensified and will flow through the earth or other conductive paths, before returning back to the source. Thus, it is highly probable that some portion of the dc leakage will attempt to return to the source through any low-resistance paths that exist in the nearby vicinity, for example, through nearby buried pipelines. Therefore, unattended dc leakage may induce stray current corrosion concerns on these pipelines. To this extent, this paper presents a detailed dc interference modeling for assessing the dc leakage activity in PV systems-particularly under undetected fault conditions. First, the modeling carried out embraces the topologically accurate consideration of all sources of dc leakage that are associated with the grounded PV systems. A second feature presented in the paper is the modeling of blind-spot dc faults and their impact on third-party infrastructure. 66 4 2935 2945

This paper proposes a novel intelligent fault diagnosis method to automatically identify different health conditions of wind turbine (WT) gearbox. Unlike traditional approaches, where feature extraction and classification are separately designed and performed, this paper aims to automatically learn effective fault features directly from raw vibration signals while classify the type of faults in a single framework, thus providing an end-to-end learning-based fault diagnosis system for WT gearbox without additional signal processing and diagnostic expertise. Considering the multiscale characteristics inherent in vibration signals of a gearbox, a new multiscale convolutional neural network (MSCNN) architecture is proposed to perform multiscale feature extraction and classification simultaneously. The proposed MSCNN incorporates multiscale learning into the traditional CNN architecture, which has two merits: 1) high-level fault features can be effectively learned by the hierarchical learning structure with multiple pairs of convolutional and pooling layers; and 2) multiscale learning scheme can capture complementary and rich diagnosis information at different scales. This greatly improves the feature learning ability and enables better diagnosis performance. The proposed MSCNN approach is evaluated through experiments on a WT gearbox test rig. Experimental results and comprehensive comparison analysis with respect to the traditional CNN and traditional multiscale feature extractors have demonstrated the superiority of the proposed method.

In this paper, an improved postfault strategy is introduced for modular multilevel converters, which utilizes the remaining healthy capacity of the converter more efficiently and increases the line voltage amplitude under these circumstances. Previous works proposed to use the neutral point shift in ac side and dc side of the converter simultaneously. This paper adds a comprehensive and coherent formulation, deep analyzation, and experimental validation. The main improvement of the proposed method is maximizing the line voltage amplitude using the optimum dc component and the best neutral point position. Indeed, fewer restrictions in fault numbers, fewer restrictions in load power factor, and fewer nonsolution conditions are among other improvements of a combined dc and neutral-shift method. Comparative simulation and experimental results verify the effectiveness of the proposed method.

This paper develops a comprehensive dynamic-phasor-based small-signal model for the modular multilevel converter (MMC) system under unbalanced grid conditions, which takes into consideration the dynamics of the MMC system under a balanced grid condition as well as the other emerging internal harmonics produced by the unbalanced grid components and more complex controllers. The small-signal model is validated by comparing the time-domain responses from a detailed electromagnetic transient (EMT) simulation in PSCAD/EMTDC. Based on the eigen-analysis and PSCAD-based time-domain simulation studies, this paper reveals the poorly damped modes that cause unstable oscillations in MMC system under the unbalanced grid conditions. From the results, more poorly damped modes involved in the internal harmonics are emerging under unbalanced grid conditions compared with the modes under the balanced grid conditions, and can highly impact the system dynamic behaviors by the selection of the control parameters. It is also shown that, under the unbalanced grid conditions, the feasible region of the control parameters of the vector current control gets narrowed indicating the reduction of the stability margin, smaller (larger) value of proportional (integral) gain of the circulating current suppressing controller can enhance the system stability, and larger values of the proportional and integral gains of the negative-sequence current suppressing control can result in the harmonic instability of the MMC system. Besides, the parameters of multiple complex-coefficient filters for positive- and negative-sequence components extraction also have a big impact on the small-signal stability of the MMC system and are required to be properly selected.

In this paper, an efficient indoor localization algorithm based on the confidence-interval fuzzy model is presented. The width of the confidence interval is essential within the proposed fingerprinting method for calculating weights, which are then taken into account while searching for the $K$ nearest neighbors in the database of fingerprints. For each beacon in the test room, a new confidence-interval fuzzy path-loss model composed of several local linear models is constructed. The map of fingerprints is then constructed of a set of confidence-interval fuzzy models. By their consideration, the localization accuracy is significantly improved in comparison with other commonly used path-loss models. The most important novelty of this paper is the introduction of the confidence interval within the fingerprinting method, which additionally improves localization results. The platform of the localization system is developed on the basis of a smartphone and Bluetooth beacons. Therefore, the localization algorithm has to be optimized in order to be computationally efficient, which is essential for real-time processing and low energy consumption on a smartphone.

This paper presents two capacitor voltage balancing (CVB) strategies for modular multilevel converter (MMC) applications. Both balancing schemes are based on model predictive control and are designed to efficiently solve a constrained optimal control problem, where the predicted capacitor voltage errors are included in the cost function with the demanded output voltage of a cluster being forced through an equality constraint. The first method proposed in this paper computes specific modulation indexes for each module using the explicit solution of a relaxed version of the original optimization problem. The second approach proposed in this paper reduces the complexity of the original problem by linearizing the objective function and using an optimal sorting network based on a greedy algorithm to solve this approximation. Considering the structures of both solution approaches, they are integrated into modulation schemes based on phase-shifted and level-shifted pulsewidth modulation algorithms, respectively. Experimental results obtained from a nine-cell single-phase MMC prototype demonstrate the good performance achieved with the proposed methodologies, as well as the implementation simplicity offered by the proposed CVB algorithms.

This paper develops a modulation based fault-tolerant (FT) strategy for restoring the operation of three-phase modular multilevel converters (MMCs) with faulty switches. This FT strategy is based on a proposed modified space vector modulation (SVM) technique that generates balanced line-to-line (line) voltages even in the case of a fault occurrence. In the postfault operation, the proposed strategy is able to restore the fundamental amplitude of the line to the neutral (load) voltages to that of the normal operation condition with a slightly increased voltage stress over the switches in the faulty phase. In this paper, first a brief background about MMCs and SVM technique is provided. Then, the proposed FT strategy and the modified SVM technique are presented. Finally, several simulation and experimental results are provided to validate operation of the proposed strategy.

Increasing penetration level of distributed generation (DG) units necessitates their participation in supporting power system stability and providing ancillary services. This paper highlights the necessity of supporting the connection voltage by these units under short-term unbalanced voltage sags. To address this, a new regulation scheme, named asymmetrical ride-through (ART), is proposed in this paper. The proposed scheme enforces DG units to properly regulate the voltage within the dynamic limits for three important voltage parameters: positive sequence, negative sequence, and phase voltage magnitude. The main advantages of applying the ART scheme are avoiding unnecessary outages due to temporary unbalanced faults and enhancing the grid stability. As the second contribution, an advanced dynamic voltage support method is also proposed to accurately address the specifications determined in the ART scheme. The successful results of the ART regulation scheme and the proposed dynamic voltage support method are verified using simulation and experimental test cases.