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Presents a listing of the best papers and distinguished reviewers for this publication in 2020.

In this paper, the influence of the stiffness and damping of real elastic shafts on the behavior of a multidrive system driving a tissue paper machine is investigated. The drive system consists of four DC motors, where two of them drive the Yankee drying cylinder and the other two drive the presses section. Six-pulse thyristor bridge power converters that are connected to the same power transformer supply the motors. The inertias of the motors and the driven machines, in conjunction with the shaft stiffness, form mechanical resonators. Thus, resonance phenomena may occur, which may lead to undesirable results. This particular case results to two three-mass and one five-mass systems. This paper presents an analysis of the resonance frequencies of two sections of the machine during startup and machine production, considering the shaft stiffness (shaft diameter, length, and thickness). The elastic shafts eliminate the ripple of the motor electromagnetic torque, which is transferred to the driven machine. The behavior of elastic shafts with different stiffness in the transmission system is studied. Moreover, the steady state and dynamic behavior of the system considering the influence of the elastic shafts and vibration analysis were investigated using simulation. A model algorithm for system simulation was developed using the MATLAB/SIMULINK software. Characteristic simulation results are presented and are expressed in terms of speed and torque response. Considering the resonance frequency analysis and simulation results, mechanical design guidelines can be given for the most significant drive components in order to avoid torsional oscillation resonance phenomena and minimize torsional oscillations of the drive system.

The design rules of winding configurations and stator-pole/rotor-tooth (SP/RT) number combinations of doubly-fed flux-switching permanent magnet (DF-FSPM) machines are investigated in this paper based on coil-EMF vectors. The relationships between the components of stator and rotor coil-EMF vector diagrams are unveiled at first, including the numbers of stator and rotor phases, and the numbers of stator and rotor spokes. Then, the SP/RT number combinations are derived considering feasible stator/rotor phase number combinations and different winding configurations. The SP/RT number combinations are optimized considering the winding factors, magnetic field harmonics, unbalanced magnetic forces and machine diameter. It is shown that both of the stator and rotor pitch factors increase when the SP and RT numbers get closer. Furthermore, the influence of winding configurations and SP/RT number combinations on electromagnetic performances of DF-FSPM machines are analyzed by finite-element method. Finally, the analysis results are validated by experiment.

Low-speed drive is one of the challenges for modular multilevel converters (MMCs) due to large capacitor voltage fluctuation. In this paper, a cascaded MMC and cycloconverter (CCV) based machine drive system is proposed to ensure stable operation of medium- -voltage and low-speed machine. The MMC provides medium-frequency ac voltage for the CCV, and the CCV converts the medium-frequency ac input to low-frequency ac output required by the machine. Detailed analysis about MMCs operation frequency, device current stress and submodule (SM) capacitance are given in this paper. Proposed drive system can operate at zero/low frequency under rated load torque, while the SM capacitance is much smaller than that in existing methods. Simulation and experimental studies are conducted, and the results verify the effectiveness of proposed system.

This paper studies the problem of controlling a multi-robot system to achieve a polygon formation in a self-organized manner. Different from the typical formation control strategies where robots are steered to satisfy the predefined control variables, such as pairwise distances, relative positions and bearings, the foremost idea of this paper is to achieve polygon formations by injecting control inputs randomly to a few robots (say, vertex robots) of the group, and the rest follow the simple principles of moving towards the midpoint of their two nearest neighbors in the ring graph without any external inputs. In our problem, a fleet of robots is initially distributed in the plane. The socalled vertex robots take the responsibility of determining the geometric shape of the entire formation and its overall size, while the others move so as to minimize the differences with two direct neighbors. In the first step, each vertex robot estimates the number of robots in its associated chain. Two types of control inputs that serve for the estimation are designed using the measurements from the latest and the last two time instants respectively. In the second step, the self-organized formation control law is proposed where only vertex robots receive external information. Comparisons between the two estimation strategies are carried out in terms of the convergence speed and robustness. The effectiveness of the whole control framework is further validated in both simulation and physical experiments.

In this paper, a converter-based multi-bus DC microgrid (MG) in series is studied, in which the trade-off between voltage recovery and current equalization has been a hot topic of interest. To solve this problem, a distributed learning-based high-order fully actuated (DL-HOFA) secondary control is proposed in this paper, and the simple structure of this control technique facilitates its application in various modern DC MGs with different configurations. Before designing the secondary control protocol, this paper provides a comprehensive description of DC MGs in advance. In the suggested control strategy, the controller design is tightly related to the underlying physical characteristics of the MG, and this prominent feature represents a significant improvement in its adaptability. In addition, the DL-HOFA control obtains fast dynamic and accurate current sharing performance by virtue of the high-order fully actuated DC MG model. The effectiveness of the proposed control method is verified on a real photovoltaic- and battery-based hardware system with maximum power point tracking (MPPT) controller.

In this paper a finite control set model predictive control is used to track a current reference in a power converter connected to an RL load. An artificial intelligence (AI) approach is presented for real-time determination of the weighting factor that regulates the average switching frequency, independently of the operating point. The paper focuses on the design, training, and digital implementation of an artificial neural network (ANN) that can be developed in a low-cost control platform. It is presented a sampling and offline ANN training procedure, together with a low-cost hardware implementation based on integer quantization of the ANN. The above approach provides a standalone application, serving as a framework for development of ANN applications for power-converters. The main advantage of the presented approach is that the ANN inference is executed in real-time. In this way, the weighting factor is automatically updated in real-time, allowing the system to quickly adapt to any reference step changes, and consequently provide the desired behavior. Executing the setup in laboratory prototype confirmed the theoretical analysis and successful tracking of the reference frequency.

This paper investigates the effects of the signal average power and the ambient temperature on the behavioral modeling and pre-distortion of high-power amplifiers concurrently. The measurement results showed that in addition to the signal average power, the behavior of a high-power PA is a function of ambient temperature as well. This paper proposes a novel smart Digital Pre-Distortion (DPD) model that considers both average Power and Temperature (PTI-DPD). The PTI-DPD is implemented using Artificial Intelligence (AI) based model and it benefits from sets of data formats containing the signal, its delayed versions, signal average power, and ambient temperature. The devised apparatus provides an uninterrupted linearization across the ambient temperature and signal average power span without need for any feedback or multiple models. A series of measurements have been conducted to study the PTI-DPD performance across the temperature and average power range. According to the results, the PTI-DPD achieves an average of -48.5 dBc Adjacent Channel Power Ratio (ACPR) across the average power and temperature span.

This paper proposes a low-profile coplanar magnetic coupling resonance wireless power transfer system, which can be expanded segment by segment to power more receivers over a long distance with load-independent constant current output. Due to the low structural profile, it can easily conform to the environment such as desktops, floors, and walls, occupying a small space. By placing low-profile ferrite plates on or under the junctions of adjacent coplanar coils, the main coupling coefficients of the adjacent coils are significantly enhanced and therefore the power transmission efficiency (PTE) of the system is greatly improved. With the fixed operating frequency, load- independent current characteristics, simple structure, coplanarity with the environment, good scalability and high PTE, the system can be easily utilized in various medium and long-range multi- load WPT applications. The paper describes its principle in detail and clarifies the influence of losses on system performance such as output current characteristics, PTE and the maximum number of the charging segments. The experimental platform with two and three receivers was established to verify the theory, and the measurement results are in good agreement with the theoretical analysis. The maximum measured PTE reached 93.8% and 93.6% for two and three receivers, respectively.

Ring and meshed dc distribution grids have attracted increasing interest lately. Their multi-point and multi-terminal structure facilitates flexible operational control and reliable power supply across the network. However, the systems implemented with existing power converters lack sufficient control freedoms for proper power flow adjustment; therefore, it is necessary to develop additional dc power flow controllers (DCPFCs) to be added to these grids for improved power flow control capability. Specific to multi-terminal dc networks built with modular multilevel converters (MMCs), this paper proposes an embedded DCPFC (e-DCPFC) directly integrated in the MMC topology. Unlike previously proposed solutions, the e-DCPFC configuration is derived from the conventional MMC and does not need any isolation transformers or external power supply. Its other main features include modular construction, convenience for multiport extension and bipolar regulating capacity. In this paper, the topology, working principle, and the coordinated control strategy for e-DCPFC and its host MMC are elaborated. Experimental results from a lab prototype verify the proposed topology and its performance under typical working conditions.

In this paper, a hybrid Modular multilevel converter (MMC) topology is proposed, in which two of the submodules (SMs) are based on SiC MOSFET, while others are based on Si IGBT. In the proposed hybrid topology, the capacitor voltage of SiC SM is controlled to be half of that of Si SM, which reduces the requirement for the SiC devices. Whats more, this paper improves the modulation scheme to move most of the switching actions from Si SMs to the two SiC SMs, which strengthens the merits and avoids the shortcomings of SiC MOSFET. Besides, to solve the voltage imbalance problem caused by the change of topology and modulation scheme, a specialized voltage balancing scheme is proposed. Finally, the simulation and experiment result proves the feasibility of the hybrid MMC and control scheme, and the comprehensive analysis verifies that the hybrid MMC can achieve a better balance among cost, loss and feasibility compared with others.

This paper proposes a straightforward and effective control strategy to reduce the periodic speed ripple of the permanent-magnet synchronous motor (PMSM). The control strategy can be described as injecting current harmonics whose amplitude and phase can be adjusted automatically to compensate for periodic speed ripple. Compared with the resonant controller with the Tustin transform, the method proposed in the paper can track speed ripple frequency without frequency displacement, realizing no steady-state error. Besides, the system stability is analyzed, and the phase compensation scheme is proposed to increase the phase stability. Moreover, the equivalence between the harmonic injection module and the resonant controller has been analyzed, which provides a simple way to understand the phase compensation of the resonant controller. The theoretical analysis and experimental results are presented to verify the feasibility of the proposed harmonic injection method.

This paper addresses the problem of proper flicker severity assessment by smart energy meters. Flicker severity occurs for a typical voltage clipped cosine distortion caused by operation of power electronic devices in the power grid. The voltage distortion caused only by higher harmonics does not cause voltage fluctuations, and therefore does not cause flicker. This paper presents the research results for some models of Advanced Metering Infrastructure (AMI) smart meters, for which irregularities are observed in the voltage variation severity assessment if the typical voltage distortion occurs in the power grid. Possible mistakes in implementation of flickermeter signal chain as defined by International Electrotechnical Commission (IEC) in smart meters that influence the measurement results have been explained. The analysis of the influence of typical voltage distortion on the indicator Pst measurement has been carried out analytically and in numerical simulation studies using the modeled flickermeter signal chain.

Existing studies about the harmonic analysis of grid-connected converters (GCCs) mainly focus on the frequency range below Nyquist sampling frequency (NSF) or switching frequency (SF) to make full use of linearization. However, in some actual high-power industrial applications, e.g. electric railways or wind power generation, harmonic problems are challenging in a wide frequency that can be as high as thousands of hertz. This is much higher than the NSF and SF. In order to bridge the gap, this paper extends the harmonic analysis frequency to the entire frequency range by addressing the aliasing effect and sideband effect. These two effects can be neglected at the low frequency for simplification while they will make great differences at the high-frequency, as demonstrated in this paper, due to the frequency coupling and nonlinear characteristics. In this regard, a regression method based on an artificial neural network (ANN) is used to map the in-out relation of the pulse width modulation (PWM) process. By adopting the methodology of this paper, harmonic performances of GCCs can be analyzed comprehensively and explicitly in terms of harmonic instability, harmonic resonance, harmonic overvoltage, filter design and so on. Finally, Experiments are presented to verify the effectiveness and accuracy of the analysis.

In this paper, a novel optical rotary sensor based on laser self-mixing interferometry is developed for the full-circle rotation measurement. The proposed sensor is convenient to use for it does not need any contact with the target or a cooperative mirror. A prototype is fabricated and tested. The measured results demonstrate a good performance compared with other optical rotary sensors, in terms of the 0.1 μrad resolution, the 2.33×10-4 linearity and 2 μrad stability over one hour. Additionally, the repeatability error is below 14.66 mrad under 9-group full-circle tests, which exhibits the potential to be instrumentalized reliably. Error analysis and limitation discussion have been also carried out. Although the accuracy needs further improvement compared with the best rotary sensor, this method has its unique advantages of high resolution, non-cooperative target sensing and electromagnetic immunity. Hence, the proposed optical rotary sensor provides a promising alternative in precise rotation measurement, tremor tracing and nano-motion monitoring.In this paper, a novel optical rotary sensor based on laser self-mixing interferometry is developed for the full-circle rotation measurement. The proposed sensor is convenient to use for it does not need any contact with the target or a cooperative mirror. A prototype is fabricated and tested. The measured results demonstrate a good performance compared with other optical rotary sensors, in terms of the 0.1 μrad resolution, the 2.33×10-4 linearity and 2 μrad stability over one hour. Additionally, the repeatability error is below 14.66 mrad under 9-group full-circle tests, which exhibits the potential to be instrumentalized reliably. Error analysis and limitation discussion have been also carried out. Although the accuracy needs further improvement compared with the best rotary sensor, this method has its unique advantages of high resolution, non-cooperative target sensing and electromagnetic immunity. Hence, the proposed optical rotary sensor provides a promising alternative in precise rotation measurement, tremor tracing and nano-motion monitoring.

This paper focuses on solving the problem of precise peg-in-hole assembly. This paper aims at realizing the insertion assembly tasks of cylindrical or prismatic objects with clearance or interference fit. First, a feature space and a response space are constructed according to the relative pose and equivalent forces and moments. Then the contact states are segmented in the feature space and the segmentation boundaries are mapped into the response space. Further, a feature-based compliance control (FBCC) method is proposed based on boundary mapping. In FBCC method, a direction matrix is designed to execute accurate adjustment and an integral element is applied to eliminate residual responses. Finally, the simulations and experiments demonstrate the superiority and robustness of FBCC method.

This paper proposes a primary-side linear control strategy to realize the constant current (CC)/voltage (CV) charging for the wireless power transfer (WPT) system, based on the LCC-N circuit. Different from the conventional compensation topology used in control strategies, this paper combines magnetic integration structure on the primary side and non-compensation topology on the secondary side. Firstly, the LCC-N magnetic integration and non-compensation topology is introduced. An improved parameters identification method considering the non-pure resistive input impedance characteristics of the rectifier is proposed to identify the current, voltage and equivalent resistance of the load, based on the LCC-N topology. In the process of identification, the relationship between the input impedance of the rectifier and the load is needless. Then, according to the LCC-N output characteristics and identified load parameters, the relationship between the input voltage and load current and voltage is simplified to linear through the linear superposition of fundamental wave and third harmonic. A linear control strategy on the primary side is proposed to achieve CC/CV output. Finally, a 1 kW WPT prototype is built. The experimental results show that the maximum error of the output current and voltage are 1.8% and 1.2% during the CC and CV charging, respectively.

Vernier reluctance machine with DC field coils in stator is a competitive rare-earth-free design for variable-speed industrial applications due to its robust structure and controllable excitation, while its torque density is relatively disadvantageous. To address this issue, this paper proposes a new armature winding design method for VRM with DC field coils across two stator teeth. The key is to break the traditional winding design principle based on the flux modulation effect of fundamental DC field harmonic, and instead, reconstruct a novel harmonic winding to enhance the utilization factor of the modulated high-order DC field harmonics. By this means, the torque density can be improved by 75.6% compared to the existing poor counterpart. In this paper, the machine structure and operation principle are introduced, with emphasis on the high-order DC field harmonics distribution rule and its influence on the armature winding design. By finite element design and optimization, a comparative study is performed to evaluate the machine performance using two different winding configurations with variable slot pole combinations. A prototype is fabricated and tested, and the results agree well with finite element analysis, which verifies the feasibility and advantages of the proposed winding design method.

Following the continuous development of wide bandgap (WBG) devices and multilevel converter technology, medium voltage (MV) active front ends (AFEs) are becoming promising in future high-power-density and high-power applications. However, the cost issue is one of the major drawbacks, which stops the WBG devices from being widely applied in high-power areas. This paper proposes a silicon carbide (SiC) and silicon (Si) hybrid five-level unidirectional rectifier. It requires only four SiC MOSFETs with relatively low blocking voltage and four Si diodes. Meanwhile, by adding snubber capacitors, all the Si devices are with low-speed switching, and the voltage stresses of fast SiC MOSFETs are minimized. In this paper, operational analysis and carrier-based phase-disposition PWM scheme for this circuit are discussed in detail. The capacitor voltage balancing and unity power factor are both realized. Simulation and scaled-down experimental results are demonstrated to verify the proposed rectifier. Furthermore, the comparison of the hybrid five-level rectifiers is given to show the advantages of the proposed rectifier in terms of voltage stress, efficiency, and cost.

This paper presents a partial-power post-regulated LLC resonant converter. In the proposed topology, the input power is first transferred to the secondary side of the transformer through the LLC-DCX converter to achieve galvanic isolation and voltage conversion functions. Then, most of the power is directly transmitted to the load side, and only a small portion of the power is converted to the output side by the partial-power processing converter (PPC). Therefore, unlike the two-stage solution, the converter proposed in this paper achieves output voltage regulation while minimizing the efficiency loss caused by the two-stage conversion. The operating principle of the proposed converter is analyzed, and the system prototype is constructed. Experimental result validates the correctness of the analysis and proves the feasibility of the proposed converter.

This paper proposed a simplified flying capacitor voltage (FCV) control strategy based on hybrid clamped three-level boost converter (HC-TLBC). Compared with the traditional control method, the proposed method does not need the sampling of the FCV and the extra FCV control loop. Hence, the software and hardware resources, like sampling circuits and control algorithm, can all be saved significantly especially in high voltage photovoltaic system (HVPS) with multiple dc inputs. In this paper, the balancing mechanism and control parameter design of the proposed method are presented in detail. With the proposed strategy, the FCV can be controlled around half of the bus voltage with error less than 2%. Besides, a pre-charge strategy for flying capacitor is also provided in this paper. The performance and analysis of the proposed strategy are verified by the experiments at last.

The three-phase dual active bridge (3p-DAB) is a popular topology suitable for high power DC-DC isolated conversion. This converter features bi-directional power flow, zero-voltage switching capability, and reduced transformer and filter volume. These features meet the requirements of several applications, such as solid-state transformers. But when operating under light load the resulting converter efficiency is highly degraded by the loss of soft-switching capability. This paper introduces the use of a Wye-extended-Delta (Y-e) transformer winding in the 3p-DAB converter, which increases the efficiency under light load, keeping the simplicity of phase-shift control. The framework developed allows a complete analysis of the converter, including the determination of the power and rms current, zero-voltage switching boundaries and the impact of the selected phase-shifting angle in the transformer design. Additionally, this paper presents a negative sequence modulation scheme, allowing maximum efficiency under light loads to be achieved for both direct and reverse power flows. The performance of the 3p-DAB with Y-e transformers is compared with previously reported winding options for 3p-DAB. The experimental results show a converter efficiency increase, up to 10\% for direct power flow and up to 9\% for reverse power flow, when operating at light load (10\% of nominal power).

Automotive applications demand high efficiency, good reliability, and a wide operating speed range within limited DC bus voltage constraints. In this paper, a zero degree displacement dual three-phase PMSM is derived from an original 3-phase PMSM to enhance the power rating as well as the operating speed range. The proposed topology can be used as an alternative to the conventional configuration of three-phase PMSM with a bidirectional DC-DC converter for electric vehicles. Even though the commonly used dual three-phase PMSM with split-phase winding eliminates the sixth harmonic torque pulsation, a large circulating current is generated during six-step operation, which results in additional stator copper loss. In this paper, six-step operation of the symmetric dual three-phase PMSM with zero degree winding displacement is proposed to achieve maximum inverter utilisation. Both harmonic circulating current and torque pulsation were observed to be within satisfactory levels using this configuration. A changeover algorithm is also proposed to enable a smooth transition between closed-loop current vector control during low and medium speed operation to open-loop six-step voltage angle control for high speed operation. The performance of the proposed method is experimentally validated on a 3kW dual three-phase PMSM drive.

This paper presents a ground breaking traction drive for fuel cell powered light rail vehicles based on a multilevel cascade converter with H-bridge cells. The converter provides dc-ac power conversion with unique buck-boost capability to compensate for the variation of fuel cell terminal voltage with the load power. In comparison to a conventional boost inverter, based on the cascade connection of a boost dc-dc converter and a voltage source inverter, the proposed converter has the significant benefits of much smaller inductor size, lower dc side current ripple, and multilevel voltage waveforms at the ac output. This paper presents the converter modelling and design of the boost inductor and sub-module capacitors, taking into account the full speed range of the motor. The concept has been fully validated on a bespoke experimental prototype driving a small induction motor, showing the suitability of the proposed converter as a traction drive for hydrogen-powered rail vehicles.

Magnetic bearing is an important part of modern high-speed rotating machinery. The performance of power electronic converter highly determines the quality of magnetic bearing drive. In this paper, a fault-tolerant converter with series-winding topology is introduced. Compared with the traditional topology, the current stress of the phase leg is reduced while the utilization of DC voltage is guaranteed, and fault-tolerant operation can be realized in the case of open circuit fault of the switching device. This paper introduces the characteristics of the series-winding topology and the current control method. Open circuit fault detection methods and countermeasures are also analyzed. Experimental results show the effectiveness of the proposed topology. Fault-tolerant experiments under static suspension and rotation of the rotor demonstrate the performance of the topology. This kind of series-winding topology provides a new scheme with good performance and high reliability for the design of magnetic bearing controllers.

In this paper, an effective solution is presented for efficient robotic object search by leveraging metric-topological map. Based on the reference of objects, we construct a novel metric-topological map that is particularly suitable for object search, where the topological nodes represent the object-related locations in the environment. To effectively determine the creation of nodes on the map, a rapid adjustment method of the robot viewing angle is introduced. Compared with traditional maps, the map built in this paper not only removes redundant nodes irrelevant to objects, but also facilitates the mobile robot to locate the target object. Besides, inspired by human search behavior, a search strategy is proposed by considering the tradeoff between the current position of the robot and the distance from the robot to the promising location of finding the target object, in order to further improve the search efficiency. The effectiveness and efficiency of our solution is verified through comparative experiments in both simulation and real-world environments. Results show that the presented approach always allows the mobile robot to find the target object efficiently and reliably, while achieving human-like search behavior.

In this paper, a novel zero-voltage switching (ZVS) full-bridge converter is proposed to overcome the disadvantages of traditional phase-shifted full-bridge (PSFB) converter. In the proposed converter, a half-bridge (HB) converter with center-tap rectifier (CTR) is integrated into the traditional PSFB converter by sharing the lagging-leg switches and output filter. The HB converter operates with full duty cycle to ensure continuous energy transmission and the output voltage is regulated by adjusting the phase-shifted time of FB converter. The proposed converter has many advantages such as reduced filter requirement, wide ZVS range and low primary circulating current. In addition, the rectifier in the proposed converter is composed of a full-bridge rectifier (FBR) section and a CTR section. This feature makes the proposed converter well appropriate for the medium output voltage applications. Key operation principle and characteristics are fully discussed in this paper. The effectiveness of proposed converter is verified using a 1.2-kW prototype circuit with 280 V input voltage and 60-120 V output voltage.

On-line detection of rotor and load faults in permanent magnet synchronous motors (PMSM) based on spectrum analysis of current or vibration is not capable of identifying the root cause of the fault, since all faults produce identical fault signatures. The sensitivity of fault detection also depends on the motor and controller design making fault detection unreliable. In addition, operation under variable frequency and load limits the effectiveness of spectrum analysis based methods. In this paper, airgap flux monitoring is investigated as an alternative for providing reliable identification of rotor and load faults in PMSMs. Based on the analysis of airgap flux under partial and uniform demagnetization, dynamic eccentricity and load unbalance, an airgap search coil voltage based method for detection and classification of the faults is proposed. The claims made in the paper are verified through experimental testing on an IPMSM under emulated fault conditions along with a comparison to vibration and current spectra-based detection. It is shown that the proposed method provides reliable on-line identification of the faults for cases where conventional spectrum analysis based methods fail.

This paper proposes a coupled-inductor-based soft switching non-inverting Buck-Boost Converter (NIBBC) with reduced auxiliary component count. Instead of using multiple auxiliary passive components to achieve soft switching, the proposed coupled-inductor-based NIBBC uses the coupled inductor as the main inductor, and the auxiliary current generated by the magnetic coupling effect is used to obtain the soft switching for all switches. With simple PWM modulation under fixed frequency, full load range ZVS can be obtained under wide voltage range. Unlike the conventional method utilizing the coupled inductor only to generate non-active power, the coupled inductor of the proposed converter also takes participant in the power transmission. Besides, the added diode can achieve zero current turn-off which avoids the diode recovery issue. The operating principle, the soft switching and parameter designs are analyzed in this paper. Finally, experimental results have verified the effectiveness of the proposed solution.

Low-voltage multi-terminal DC system is one of the important forms in distribution network. Its stability issue has drawn worldwide attention for the characteristics of low inertia and weak damping. This paper aims to analyze the interactive behavior between the voltage source converter (VSC) and the oscillation mode of the DC network. First, this paper proposed a modeling method for DC voltage control loop considering the time-lag effect of inductor energy storage behavior on the AC side of the VSC. Based on this model, the interactive behavior between VSC and DC network including the influence of droop coefficients and load power under DC voltage-AC power (Vdc-Pac) droop control mode and under DC voltage-DC power (Vdc-Pdc) droop control mode is studied. Then, the overall state-space model of the system is established. Furthermore, the stability of a low-voltage three-terminal DC system under different control modes and parameters is compared and detailed analyzed. Finally, the corresponding simulation and experimental verification validate the theoretical analysis. The research results show that under the same capacity and control parameters, Vdc-Pac mode can better improve the capability of power regulation and system stability. This research can provide an effective method for system control modes design.

This paper presents a high-performance radio frequency (RF) power amplifier (PA) module for which an optimum chip-level packaging structure is proposed to reduce the operating temperature of the RF PA monolithic microwave integrated circuit (MMIC). Because the output power (Pout) and the efficiency of a RF PA module are strongly affected by the thermal characteristics of the PA MMIC, various types of heat spreader materials and thermal interface materials have been examined to implement the PA chip-level packaging structure, and the optimum combination is proposed for a performance enhancement of the PA module in this paper. In addition, the optimum form-factor of the heat spreader was suggested based on a thermal simulation. To verify the proposed PA chip-level packaging structure, a 10 W 618 GHz RF PA MMIC using a commercial 0.25-m gallium nitride high electron mobility transistor process was designed and implemented for radar applications. The operating temperature of the PA MMIC on the proposed chip-level packaging structure shows a dramatic reduction of 24.8 C, and accordingly, the average Pout and average power-added efficiency are enhanced by up to 9.2% and 2.8%, respectively, when compared with a PA module using the conventional chip-level packaging structure.

This paper focuses on the modeling and stability analysis of the typical single-phase phase-locked loop (PLL) based on second-order generalized integrator (SOGI). Traditionally, SOGI-based PLL (SOGI-PLL) is linearized as the linear time-invariant (LTI) model for the stability analysis and parameter design. Yet, the PLL has periodical nature due to the periodical variation of the grid voltage. The traditional LTI model for PLL thereby reduces the precision of stability analysis. For addressing this problem, an accurate linear time-periodic (LTP) model of the single-phase SOGI-PLL is proposed in this paper. The proposed model can precisely characterize the coupling nature of phase, frequency, and amplitude estimated by SOGI-PLL. A precise stability region of SOGI-PLL thereby can be derived from the proposed LTP model. The effectiveness of the proposed LTP model for SOGI-PLL is verified by simulation and experimental tests.

Railway power conditioner (RPC) can provide comprehensive reactive power, unbalanced current, and harmonics compensation in the traction power supply system (TPSS). Under full compensation (FC), RPC can increase the three-phase power factor (PF) to unity but leads to high current rating and operation loss. In previous studies, partial compensation (PC) for the reduction of RPC current rating was proposed. An analytical solution of partial compensation coefficients was used, which limits design freedom since identical PF is required at three-phase. This uniform power factor partial compensation (UPFPC) limits RPC in achieving a further reduction in its current rating. This paper proposes a nonuniform power factor partial compensation (NPFPC), which can further reduce RPC current rating within the acceptable power factor region and under the voltage unbalance threshold. However, determining an analytical solution under NPFPC is complicated, considering three degrees of freedom. This is achieved so in this paper by defining the lower boundary of grid side PFs and optimizing by particle swarm optimization (PSO). It is found through investigations that NPFPC can effectively reduce the compensating current rating by 56% compared to FC mode and 53% compared to UPFPC. Simulation and experimental results verify the validity of the proposed NPFPC.

Different from the typical topology derivation of power electronics converters (PECs) depending on manual effort, this paper aims to explore a programmable method based on graph theory for multi-port dc-dc converters with reduced switches. By mathematically modelling converters with graph theory and transforming their working criterions into the corresponding graph constraints, the topology derivation can be automatically and conveniently solved with the aid of computer program. In the paper, principle of the proposed graph theory based programmable method is firstly introduced in detail. Then, it is employed to derive multi-port dc-dc converters with reduced switches and a diversity of new topologies are simultaneously excavated, among which a favorable one is selected to be theoretically introduced and experimentally verified. The proposed method remains relatively simple with the increasing number of ports, as the graph constraints of working criterions are almost the same for different number of ports. More importantly, because PECs can be essentially regarded as graphs with different components and their connecting relationships, the proposed method is applicable for many various converters.

In this paper, two novel approaches for identifying the synchronous generator (SG) parameters are presented. The proposed approaches use an experimentally obtained armature current during the short-circuit test as input data. Both approaches are simple, cost-effective, and practical since they do not require any additional equipment for signal generation nor applying any of the advanced control techniques. The first approach relies on fitting the analytical total armature current waveform with the experimental one, while the second approach relies on matching the observed waveform with an analytical waveform of asymmetrical and alternating components. Instead of traditional graphical methods typically used in standardized procedures, this paper also proposes a novel hybrid metaheuristic algorithm to identify the SGs parameters. The experimental verification of the proposed methods is carried out on 100 MVA SG at the Bajina Basta hydropower plant (HPP) in Serbia.

The performance of fault diagnosis and prognosis (FDP) relies greatly on the model that describes the fault behavior and dynamics under study. In the past decades, many researches focused on establishing reliable, robust, and accurate models to describe fault growth dynamics. However, uncertainties in modelling process severely affect the accuracy and precision of FDP results. A major challenge in FDP is how to deal with the uncertainties that affect the performance of the system. For commonly used state space model, uncertainties exist in both the state transition equation and the measurement equation. In this paper, the influence of uncertainties on FDP results are studied and compared in terms of accuracy and precision. Furthermore, this paper proposes a differential model decomposition approach, which can automatically acquire appropriate model parameters and uncertainties for state space model. The effectiveness and advantages of the proposed method are verified and demonstrated with three different application scenarios, including comparison studies on public data and online experimental verification.

In this paper, we propose the dynamic coverage control method based on K-means. In the traditional coverage control, Voronoi partition method is used to assign the coverage positions for intelligent units. However, the Voronoi partition method requires that the space to be covered is compact and convex, and it is difficult to realize the coverage control of high-dimensional space. Therefore, in this paper we propose a dynamic coverage planning algorithm based on K-means, which relaxes the requirements on the coverage objects and can calculate the optimal coverage positions of the intelligent units. In addition, we also design a dynamic coverage control law based on discrete sliding mode control to drive the intelligent units to the optimal coverage positions. Through the combination of planning algorithm and control law, the optimal coverage control performance can be achieved for the specified targets and the specified area, which can be discrete, non-convex and high-dimensional. The stability of the planning algorithm and the control law are proved by theoretical deduction. And the effectiveness and superiority of the dynamic coverage control method are verified by two examples.

In this paper, an optimal structure for a high step-up, non-isolated dc-dc converter is proposed. In this topology, the required high voltage gain can be obtained with low number of elements. Furthermore, by implementing an auxiliary circuit, zero voltage switching (ZVS) condition for the switches is provided, input current ripple has been reduced to almost zero, and all of the power diodes turn off and on under zero current conditions. In the proposed structure, to regulate voltage gain, the extendable number of diode-capacitor voltage multiplier (DCVM) stages are combined with a coupled inductor. Voltage stresses across the semiconductors can be regulated by the number of the DCVM stages and the turns-ratio of the coupled inductor. Thus, it provides two degrees of freedom for the designer to use low rated semiconductors, which increases the converter efficiency. In this paper, the performance of the proposed converter, in terms of voltage stress, voltage gain, and efficiency, has been analyzed, and a comprehensive comparison between the presented topology and other similar topologies presented. Finally, to verify the performance of the proposed topology, a 500 W (40 V/400 V) laboratory prototype has been developed and tested. The experimental results confirm its superiority and suitability.

This paper analyzes the conventional dq-frame model-based deadbeat predictive current control (DBPCC) methods for high-speed permanent magnet synchronous machine (PMSM) drives with low switchingtofundamental frequency ratios (SFRs). It shows that the state-of-the-art compensation schemes of control delay and rotor movement effect can improve the control performance but the problem would still arise at very high speeds with very low SFRs. Therefore, this paper presents a novel DBPCC method for high-speed PMSM drives. The proposed method tracks the machine stator flux vector in the stationary frame to achieve deadbeat control of the dq-axis currents. The control delay and rotor movement effect are both precisely considered. Consequently, the control performance and stability of the proposed DBPCC can be guaranteed at high speeds. Extensive simulations and experiments have been performed on a prototype high-speed PMSM drive. The effectiveness of the proposed method and its superiorities against the field-oriented control (FOC) and the conventional DBPCCs have all been demonstrated.

This paper proposes and implements an output-controllable efficiency-optimized wireless power transfer scheme using hybrid modulation. The key is to combine pulse frequency modulation (PFM) and on-off keying (OOK) modulation and to utilize feedback control. Among them, PFM is used for the output voltage regulation of the inverter to adjust the rectified output voltage on the receiver side, while OOK modulation is adopted to convert the load resistance to be close to the optimal resistance value so that the system efficiency can be effectively optimized. When the relationship between the input and output voltages reaches a ratio related to system parameters, it can be considered that the load resistance has reached the optimal state. Hence, the feedback output voltage is utilized to help convert the load resistance into an optimal value and only one voltage acquisition circuit is needed. In this paper, theoretical analysis and practical experimentation (using the LED lamp as a nonlinear load and the 102- resistance as a linear load) are both given to verify that the proposed scheme can help to maintain high system efficiency during the output voltage regulation process.

In this paper, we investigate a novel multi-sensor odor detection system (electronic nose) for low concentration volatile organic compounds (VOCs). In order to break through the limitation for detecting low concentration volatile organic compounds, we design a conformal symmetric pre-concentration unit structure based on the finite element method. A typical application for exhaled breath is developed to investigate the proposed scheme. The designed pre-concentration system can increase the concentration of the concentrated substance, so that the sensor can detect it. Besides, we choose the alveolar gas at the bottom of the human lung, which can better represent the health status of the human body, to carry out the effectiveness test of the system. In order to combine the gas acquisition system with the pre-concentration system, this paper further designs a cost-effective alveolar gas collection device by a doubled adaptive Pulse Width Modulation (PWM) operation. Finally, the effectiveness of the pre-concentration system is judged by the detection results of gas chromatography-mass spectrometry (GC-MS). We also use the classical algorithm to classify lung cancer and non-lung cancer patients, which proves the effectiveness of our proposed integrated design system and shows the potential of practical application of the system.

This paper analyzes the effect of discretization in the frequency-adaptive flux observer (FAO). Although FAO has structural simplicity and ease of implementation, the discrete-time FAO has phase and gain errors in fundamental flux estimation. As a result, the estimated flux might be erroneous, especially in the high-speed region. For accurate flux estimation, this paper analyzes how the voltage synthesis in the pulse-width-modulation (PWM) affects the stator flux. Through the analysis, the backward Euler method is selected for the primitive stator flux estimation. To mitigate the FAOs discretization error, the proposed FAO utilizes the integrators constructed at the rotor reference frame. Since the discretization error comes from the approximation error of the continuous-time integrator at the operating frequency, the proposed FAO conducts the fundamental flux extraction at the rotor reference frame, where the operating frequency components are treated as a dc signal. Thanks to the coordinate transformation, the FAO can be discretized with no error while keeping the structure of double integrators. The proposed method is verified through the computer simulation and experimental test.

This paper proposes a new combination of correlative statistical analysis and the sliding window technique to detect incipient faults. Compared with the existing monitoring methods based on principal component analysis and transformed component analysis, the combination fully uses the information from the process and quality variables. The sliding window, however, inevitably increases the computation burden due to the repeated window calculations. Therefore, a recursive algorithm is proposed in this paper, which has been shown to have less calculation complexity. Furthermore, a randomized algorithm is proposed to determine the width of sliding window. A numerical example and the thermal power plant process are presented to show the effectiveness and advantages of the proposed method.

In this paper, a nite-time trajectory tracking control problem is studied for a rodless pneumatic cylinder system with disturbance in an inner-outer loop framework. In the inner loop system, the generalized nonlinear extended state observer and the inner-loop controller are designed to estimate and compensate the matched disturbances, respectively. The generalized nonlinear extended state observer designed in this paper achieves desired convergence performance under relaxed existence conditions. In the outer-loop system, a super-twisting extended state observer and an outer loop controller are designed to estimate and compensate the unmatched disturbances, respectively. The super-twisting extended state observer is designed to realize nite-time stable by using the super-twisting technology. Finally, experiment results are shown that finite-time control performances are obtained by the proposed control strategy.

The security of data propagation is a critical challenge for the widespread use of networked control systems (NCSs), while the conventional strategies based on estimation techniques cannot solve this issue well. Furthermore, the contradiction between the security and real-time nature of the control method has not been settled yet. The aim of this paper is to propose a novel real-time control method empowered by blockchain technologies to resolve the security problems of NCSs under potential cyberattack. To facilitate the analysis of blockchain-assisted NCSs, a cyber-authentic-physical system (CAPS) framework is proposed. One of the significant features of CAPS is that the defense of NCSs against attacks is built by introducing a blockchain protocol. Theoretical analysis reveals the relationship among the scale of the peer-to-peer (P2P) network, the security of CAPS, and the latency of NCSs, as well as clarifies the impact of the introduction of blockchain mechanism on the performance of NCSs. With the networked secure control mechanism designed in this paper, the security and stability of NCSs can be achieved simultaneously, and sufficient conditions of which are also given. Finally, simulations and practical experiments are presented to show the efficacy of the suggested secure control strategy.

LLC half-bridge converters have been extensively studied in low power industrial applications. However, the phase shift angle between the voltage and current of the LLC resonant network makes the converter have power circulation, that is, backflow power. The increase of the backflow power will increase the converter conduction loss, which restricts the improvement of the converter efficiency. The existing literature often improves the backflow power from the control aspect, which greatly increases the control complexity. To solve this problem, this paper proposes an LLC half-bridge resonant converter analysis method that takes the backflow power into account. Based on the analysis of operating mode and AC equivalent model of the converter, backflow power is indirectly characterized by the phase-shift angle of the resonant network voltage and current. Based on this, this paper analyzes the internal relationship between resonant parameters and backflow power to reduce backflow power by optimizing resonant parameters. Under the setting operating conditions, converter can achieve ZVS switching, voltage gain conditions and minimum backflow power. Compared with the existing methods, the proposed optimization method avoids additional auxiliary circuits and control complexity, improves the stability of the circuit. Experimental results verify the accuracy and feasibility of the theoretical analysis.

This paper presents an improved current reconstruction technique with current prediction for a permanent magnet synchronous motor (PMSM) drive system. In some conventional single current sensor (SCS) techniques, current fluctuations occur at sector switching period (SSP) due to current holding between two adjacent sampling interval, which can cause current distortion and introduce much current harmonics especially when the motor speed is very high. Focusing on that, a current prediction method is proposed in this paper to prevent the current fluctuation happening at SSP. The SSP is divided into two independent parts for the accurate calculation of output voltage vector and actual three-phase currents at SSP are determined on account of both the predicted dq-axis currents and the measurable ones. As a result, compared with previous current holding strategy, the current fluctuations can be fundamentally eliminated under the proposed method with less current harmonics introduced, further improving the control performance of the whole system. The accuracy and practicability of the proposed method is verified by experimental results.