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In recent years, wide voltage range DC/DC converters have been widely used in telecom power, solar generation and electric vehicle charger applications. Based on this, a new multi‐resonant converter with wide input voltage is proposed here. Compared with the traditional LLC converter, the proposed converter can maintain the output voltage within a narrow frequency regulation range in both under‐resonance and over‐resonance areas. Thus, a wide voltage range can be realized without additional switch components or complex control strategies. The topology and the corresponding working principle of the proposed converter are introduced. In addition, the equivalent model by considering the fundamental wave is established and the influence of the resonance parameters on the voltage gain characteristic is analysed in detail. With these considerations, the resonance parameters are designed. Finally, a 500 W experiment platform is established to verify the effectiveness and feasibility of the proposed converter. [ABSTRACT FROM AUTHOR]

Oil-filled motors (OFMs) are widely used in deep-sea exploration and oil well extraction. During motor operation, the rotor stirs the oil in the air gap, causing viscous loss. Viscous loss affects the temperature distribution inside the motor. Accurately calculating the viscous loss and temperature rise in OFMs can provide a basis for optimizing the motor's structural design. Motor structural parameters, including the rotor's outer diameter, air gap, and slot opening, have a significant impact on viscous loss. The working conditions of OFMs, such as rotor speed and environmental temperature, also affect viscous loss. The viscosity of hydraulic oil is highly influenced by temperature, and changes in viscosity can lead to changes in viscous loss. These changes in viscous loss, in turn, alter the temperature distribution. Therefore, the coupling relationship between viscous loss and temperature must be considered. Additionally, when Taylor vortices occur in the fluid, the surface roughness of the rotor also has a significant influence on viscous loss. Currently, both domestic and international research on viscous loss and thermal analysis struggle to simultaneously consider the coupling of viscous loss and the temperature field, rotor surface roughness, and the effect of motor structure. This paper summarizes the methods used in recent years for studying viscous loss and thermal analysis, and puts forward some suggestions for future research on the coupling of the OFM temperature field and viscous loss. [ABSTRACT FROM AUTHOR]

Photovoltaic power generation and energy storage technology are current hotspots in the clean energy industry. As a core piece of equipment, an inverter is subjected to higher demands for its voltage regulation range and output performance. A differential boost inverter features a boosting function not found in traditional inverters, effectively widening the input voltage range, with characteristics of a single-stage structure and simple modulation. However, the differential boost inverter faces the issue of high common-mode voltage. Considering that the magnitude of the common-mode voltage changes with different modulation methods, a novel modulation strategy with a flexible common-mode voltage is proposed, which can effectively suppress the common-mode voltage under the same gain without affecting the output power quality. This article first introduces the topology, working principle, and traditional modulation methods of the differential boost inverter. Then, the new modulation strategy is defined, and the gain equation is derived. The new modulation method's applicable scenarios are discussed and compared to other modulation methods based on the gain curve, concluding that the new method has advantages in terms of common-mode voltage amplitude and power quality under low boost gain. Finally, the effectiveness of the proposed method is verified through simulation and experiments. [ABSTRACT FROM AUTHOR]

In a simultaneous wireless power and data transfer (SWPDT) system using common coils, achieving high-speed communication in high-power wireless charging systems is challenging due to power transfer interference on communication. Based on high-frequency data carrier-based SWPDT (HFDC-SWPDT) technology, this paper proposes an orthogonal-frequency simultaneous wireless power and data transfer (OF-SWPDT) method to minimize interference where the data carrier frequency is orthogonal to the power carrier frequency and its harmonics. In addition, a guard band is inserted between the spectra of power harmonics and data in order to further separate the power and data spectra. Thus, a high-power, high-speed SWPDT system is achieved. Finally, an 11 kW prototype with 64.125 kbps full-duplex communication is developed to validate the proposed method. [ABSTRACT FROM AUTHOR]

A modular Sigma DC/DC converter with wide input voltage range is proposed in this paper. The proposed converter is combined with a traditional LLC converter and two multi-resonant converters via Sigma architecture. Among them, the traditional LLC converter operates as a DC transformer (DCX) at resonant frequency to achieve maximum efficiency. Meanwhile, one of the multi-resonant converters, the DC to DC (D2D) part of the Sigma structure, is responsible for voltage regulation over a wide input voltage range. In addition, the other multi-resonant converter has two operation modes, including DCX and D2D. When it operates in the DCX mode, the Sigma converter has better performance and higher efficiency. When it operates in the D2D mode, the Sigma converter can handle a wider input voltage range. For each submodule, the operation principle and characteristics of the proposed Sigma converter are analyzed in detail. In addition, some key points of the parameter design for each part are also demonstrated. Finally, an experimental prototype with an input voltage of 540~1100 V is built to verify the effectiveness of the proposed converter. [ABSTRACT FROM AUTHOR]

With the recent revolution in the green economy, agricultural solid waste resource utilization has become an important project. A small-scale laboratory orthogonal experiment was set up to investigate the effects of C/N ratio, initial moisture content and fill ratio (vcassava residue: vgravel) on the maturity of cassava residue compost by adding Bacillus subtilis and Azotobacter chroococcum. The highest temperature in the thermophilic phase of the low C/N ratio treatment is significantly lower than the medium and high C/N ratios. The C/N ratio and moisture content have a significant impact on the results of cassava residue composting, while the filling ratio only has a significant impact on the pH value and phosphorus content. Based on comprehensive analysis, the recommended process parameters for pure cassava residue composting are a C/N ratio of 25, an initial moisture content of 60%, and a filling ratio of 5. Under these conditions, the high-temperature conditions can be reached and maintained quickly, the organic matter has been degraded by 36.1%, the pH value has dropped to 7.36, the E4/E6 ratio is 1.61, the conductivity value has dropped to 2.52 mS/cm, and the final germination index increased to 88%. The thermogravimetry, scanning electron microscope, and energy spectrum analysis also showed that the cassava residue was effectively biodegraded. Cassava residue composting with this process parameter has great reference significance for the actual production and application of agriculture. [ABSTRACT FROM AUTHOR]

Grid forming (GFM) control strategy has been increasingly used in grid-connected converters to regulate system frequency and mimic the inertia of synchronous generator. However, the description of its power angle dynamics under large disturbances is still lacking up to date, which may pose great challenges to stable operation and economic configuration of grid-connected converters in the future power system. To overcome the aforementioned obstacle, a Krylov–Bogoliubov–Mitropolsky (KBM) asymptotic method with the perturbation theory is presented first in this article to derive an analytical solution for power angle trajectory under large disturbances. Considering that the antiderivative problem is usually unsolvable due to the complicated perturbation function, a tailored integral method is further proposed to address this problem and simplify the final result, which facilitates the KBM asymptotic method to the analysis and calculation of power angle trajectory. As a result, an explicit and accurate time-domain expression is obtained, and it reveals the quantitative relationships between control parameters and dynamic characteristics, which may provide a good potential for system transient stability analysis and GFM converter design. In the end, the effectiveness and accuracy of the proposed method are verified by both simulations and control-hardware-in-loop experiments. [ABSTRACT FROM AUTHOR]

The medium-voltage dc (MVDC) system are intensely investigated by both industry and academy. However, how to realize a lower power circuit directly fed by MVDC is an important but easily neglected problem, which seriously affects the reliability of the dc system. The current high step-down circuits are mostly suitable for high-power applications, while the circuits for low-power applications are designed case by case. To address the obstacle, a generalized buck-boost type high step-down converter (BHSC) structure is proposed in this article. The submodules of BHSC are derived from basic dc–dc converter. As a result, the features of high modularity, simple structure, and low cost can be obtained, and each submodule operates independently without communication and synchronization to achieve voltage balance. Furthermore, a submodule strategy with Bang-Bang control, instead of hardware modification, is proposed to overcome the limitation of BHSC generality in medium-voltage (MV) and high-voltage (HV) applications, due to the operating current difference in different submodules of the cascaded structure. Therefore, BHSC can be easily extended to MV or HV by increasing the number of submodules. Finally, an experimental evaluation of a 1 kV/80 W prototype converter is presented, which can be applied as auxiliary power supply for high-power converter. [ABSTRACT FROM AUTHOR]

Carboxylated styrene‐butadiene latex (XSBL), attributed to its insufficient adhesion and poor water resistance, cannot be widely popularized in the adhesive industry. Herein, a novel XSBL‐based resin with high‐strength yet water‐resistant was reported, in which the butadiene macromolecular chains were grafted with acrylonitrile (AN) and acrylic acid‐2 hydroxyethyl ester (HEA) molecules, the crosslinking sites were esterified and expanded to construct a branched network structure, and the matrix was filled with nano‐SiO2 particles treated by blending silane coupling agents. We show that the new resin, having a dual curing mechanism at low and high temperatures, can be glued under different conditions. At room temperature, the sample group with a doping level of 1.33 wt% could achieve an overload shear strength of 3.17 MPa after curing, which is 233.7% higher than the XSBL; in the high temperature curing regime, the glue strength reached 1.21 MPa, much higher than the standard for the use of GB Class I plywood (≥0.7 MPa). The physicochemical properties meet the requirements for potential industrialization, for which the property–structure relation has been extensively explored. Further DSC and TG tests provide evidence for their wide application in the hot pressing process of man‐made plywood. [ABSTRACT FROM AUTHOR]

In this letter, an internal electric field shielding layer for high voltage winding of medium voltage high frequency transformer used in a modular cascaded medium voltage solid state transformer is proposed. Without breaking the litz wire insulation layer, the high electric field is effectively shielded by a semiconducting layer and an unclosed copper foil spiral, which are electrically connected together. Not only the electric field in the main wall insulation is uniformed but also the peak value of the internal field is greatly reduced, which will help to achieve lower partial discharge and higher insulation reliability. With this structure, the difficulties of pouring process and electric field estimation for the litz wire winding are both avoid. Finally, a no partial discharge 100 kW medium voltage high frequency transformer prototype with 75 kV base insulation level is built and verified with the insulation tests. [ABSTRACT FROM AUTHOR]

Following the continuous development of wide bandgap (WBG) devices and multilevel converter technology, medium voltage active front ends 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 article 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 article, operational analysis and carrier-based phase-disposition pulsewidth modulation 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. [ABSTRACT FROM AUTHOR]

Switching ripple communication (SRC), which modulates the PWM carrier with digital data and takes the switching ripple as a signal carrier, helps power electronic converters to transfer digital data along with power. This article discusses the theory and implementation of SRC technology. It proves that the modulation using square wave and sinusoidal wave carriers is compatible. The fundamental principles of frequency hopping–differential phase shift keying (FH–DPSK) modulation are then analyzed in detail, and an improved FH–DPSK scheme is proposed to suppress output voltage disturbances, thereby maintaining power quality, reducing communication noise, and separating power control and data modulation. Furthermore, to evaluate the reliability of the communication technique, the effect of power conversion on communication is discussed in detail. Finally, a buck converter with a switching frequency of 100/83.3 kHz is set up, and the experiment achieves a 16.7 kbps bit rate using quaternary modulation, demonstrating the correctness of the scheme. [ABSTRACT FROM AUTHOR]

Multichip silicon carbide power modules with integrated snubbers are promising for large-capacity converters with high speed and cost efficiency. In the design stage, the parasitic inductance of module layout generally attracts the primary efforts of designers because of its severe impact on dynamic performance, e.g., voltage overshoot and transient current imbalance. However, due to the complexity of the heterogeneous layout, the solution space and development efficiency are always limited by the traditional manual design approach. Thus, this article proposes a generative method to optimize the layout autonomously. First, a graph model is built to describe heterogeneous layouts with all interconnectivity and design constraints retained. Based on the model, integer programming is introduced to generate layout templates with variable geometric topologies. Then, coupled with a self-developed discrete extractor, the Pareto-front is obtained by genetic algorithm, providing a tradeoff boundary for loop inductance and branch mismatch. The proposed method is systematic, flexible, and requires few designers’ expertise. A 1200 V/240 A half-bridge module is designed and fabricated to validate its capability. The experimental results show that the loop inductance of 5.59 nH is achieved, and less than 5% of the transient current imbalance is realized under 6.2 A/ns turn-on in the rated. [ABSTRACT FROM AUTHOR]

In direct current (dc) microgrids, communication between converters is necessary for better power distribution and finer energy scheduling. This article proposes an orthogonal frequency division multiplexing (OFDM) based carrier communication method for dc microgrid applications. The method integrates the communication function in the process of power conversion by modulating data into power control loop. To maximize the communication rate in a narrow band limited by pulsewidth modulation control, OFDM technology is applied in the data modulation process. The data is modulated to multiple low-frequency signal carriers, then the modulated wave is added to the output of the power control loop. Since no additional component is needed for sending data, this method has the advantages of low cost and simple implementation. In order to provide theoretical guidance for system design, the dc microgrid applying the proposed method is modeled. Furthermore, important issues of the communication system are discussed, including data frame format and intersymbol interference problem. At last, a 2 kW dc microgrid experimental platform is established and 9.6 kbps communication rate with a transmission distance of 200 m is achieved, which verifies the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

To commercialize wirelesselectric vehicle charging (WEVC), three critical issues must be resolved: communication between the vehicle assembly (VA) and the ground assembly (GA), metal object detection (MOD) on the GA coil, and position detection (PD) of the VA. This paper proposes a comprehensive system that integrates MOD and PD with VA-GA near-field communication (NFC). A common high-frequency aided carrier is used not only for NFC, but also for MOD and PD. In addition, an array of dual-purpose detection coils is proposed as a sensor for MOD and PD. As a result, the three functions listed above share numerous components and circuits, greatly simplifying the system structure. Furthermore, because the high-frequency aided carrier can operate with or without a power carrier, the preceding three functions are independent of system power status. The proposed method has been validated using a 3.3 kW WEVC prototype operating at 85 kHz. The experimental results show that the proposed system is capable of performing both online and offline NFC, MOD, and PD with high sensitivity while having no impact on wireless charging efficiency. [ABSTRACT FROM AUTHOR]

Different from the typical topology derivation of power electronics converters (PECs) depending on manual effort, this article aims to explore a programmable method based on graph theory for multiport dc–dc converters with reduced switches. By mathematically modeling converters with graph theory and transforming their working criteria into the corresponding graph constraints, the topology derivation can be automatically and conveniently solved with the aid of computer program. In this article, first, the principle of the proposed graph theory-based programmable method is introduced in detail. Then, it is employed to derive multiport 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 criteria 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. [ABSTRACT FROM AUTHOR]

The stitch wire configuration is widely adopted for large-area IGBT chips. However, an inhomogeneous wire current density introduces uneven self-heating and nonuniform chip heating, which exacerbates the chip thermal stress. In this article, a multicellular electro-thermal model considering the stitch-bonding wires is derived to optimize the wire layout parameters. Furthermore, the current density alleviation of wire bonds is investigated to be the most sensitive and effective method to comprehensively mitigate the thermal nonequilibrium and local overheating. Consequently, an improved multitier layout is proposed to further achieve thermal stress suppression without any additional components and advanced materials. Finally, a triple-tier-bonded IGBT module with optimal design parameters is fabricated to validate the thermal mitigation performance. The prototype experimental results demonstrate that the modeling error is less than 3.0%. The multitier layout decreases the current density by 57.6%, hence, the maximum and average chip temperature are reduced by 21.8% and 12.4%, respectively. [ABSTRACT FROM AUTHOR]

Implementation of the series connection of the SiC MOSFETs in medium voltage (MV) high power converters faces a series of challenges, including the electrical/thermal stress imbalance, insulation coordination design, high dv/dt elimination and robustness under variable operating conditions. This paper stresses these challenges and proposes a comprehensive design of a 9.6 kV/200 A power block based on the series connection of SiC MOSFETs. The power block has been verified under the continuous operation, which demonstrates the highly efficient and reliable operation under the variable switching current condition. Afterward, performance screening in a 5 kV/1 MW inverter is conducted to assess the efficiency in MV converters. Compared with the advanced high voltage high power devices, the proposed power block demonstrates fast switching speed and low switching loss, which indicates that the series connection of SiC MOSFETs is a promising technique to expand the operation voltage/power of the SiC MOSFETs to the MV megawatt level. The proposed design can be expanded to other specifications as well. [ABSTRACT FROM AUTHOR]

In this article, the output voltage control strategy of modular multilevel resonant dc converters (MMRDC) for medium-voltage wide-input-range applications is studied. First, the feasibility and influence of the switching frequency regulation and modulation index regulation are investigated in detail. It is found that the switching frequency choice has a significant effect on the voltage stress of arm inductors and the transformer. Then, based on these considerations, the modulation index regulation plus switching frequency regulation based design and control optimization is proposed. With the proposed design and control method, the switching frequency range for adapting to a wide input range is further reduced, especially under light load operating conditions. Besides, the high voltage stress on arm inductors is avoided and the high voltage dv/dt on the transformer is also eliminated. Finally, a laboratory prototype with 8–16 kV input and 375 V/60 kW output has been built and the experimental validation under a wide input range has been done. The efficiency over 96.4% under the wide input range proved the effectiveness of the optimized control methods. [ABSTRACT FROM AUTHOR]

This article proposes a novel power flow tracing method based on power electronic signaling for peer-to-peer (P2P) electricity trading in dc microgrids. It employs a superimposed low-frequency sinusoidal carrier to trace dc power flows according to the bus port impedance characteristics of power converters. In order to support fair and accurate P2P trading, source-to-load power signaling (S2LPS) and source-to-source power verification (S2SPV) methods are presented. Through S2LPS, the P2P dc power flow from a specific distributed source (DS) to a power load (PL) is determined by detecting the carrier's active power at the PLs bus port. The same carrier is used to check the actual output power of the DS by S2SPV. By implementing S2LPS and S2SPV, the power flows of the system are traced, recorded, and verified by each DS and PL. Accurate power flow tracing is achieved on the physical layer, providing reliable data for P2P electricity trading. The principles of the proposed method are deduced in detail. Furthermore, the modifications to the control loops of DSs and PLs are depicted for implementations in dc microgrids. Finally, a 2.5 kW experimental platform is built to validate the correctness and feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

The modularity of a modular multilevel dc converter (MMDC) makes it attractive for medium-voltage distribution systems. Inherent balance of submodule (SM) capacitor voltages is considered as an ideal property, which avoids a complex sorting process based on many measurements thereby reducing costs and enhancing reliability. This article extends the inherent balance concept previously shown for square-wave modulation to a multilevel version for MMDCs. A switching duty matrix dU is introduced: it is a circulant matrix of preset multilevel switching patterns with multiple stages and multiple durations. Inherent voltage balance is ensured with a full-rank dU. Circulant matrix theory shows that this is equivalent to a simplified common factor criterion. A nonfull rank dU causes clusters of SM voltage rather than a single common value, with the clusters indicated by the kernel of the matrix. A generalized coprime criterion is developed into several deductions that serve as practical guidance for design of multilevel circulant modulation. The theoretical development is verified through full-scale simulations and downscaled experiments. The effectiveness of the proposed circulant modulation in achieving SM voltage balance in an MMDC is demonstrated. [ABSTRACT FROM AUTHOR]

This article reveals the significant stray capacitances in inductive power transfer (IPT) coil, and offers two methods for modeling the stray capacitance effect: concentrated model and distributed model. Both analytic formulas and FEM simulation are introduced to estimate the value of parasitic capacitances, and experimental measurements on an 11 kW IPT coil prototype are conducted to verify the correctness of both methods. The common-mode noise propagation circuit of the IPT system is derived and simulated based on these two models. The results show that parasitic capacitance between Litz wire winding and shielding metal on the transmitter side plays a dominant role in CM noise propagation and the distributed model has higher fidelity because of its asymmetric structure. Besides, to mitigate conductive CM noise, an EMI filter, and HF isolation transformer are introduced. Finally, the conductive EMI tests are performed in an 11kW IPT prototype. The experimental results validate the accuracy of the proposed CM noise model with stray capacitances of the IPT coil. And the combination of EMI filter and HF isolation transformer can suppress CM noise greatly and render the CM noise spectrum below the CISPR 32 Class-B limit. [ABSTRACT FROM AUTHOR]

In this letter, a junction-temperature and current extraction method is presented based on the electroluminescence mechanism of the SiC mosfet body diode. Starting from the observation of two characteristic peaks in the emitted light spectrum, we proved that the junction temperature and the drain current can be simultaneously measured. This novel method consists of decoupling the relationship between the intensity of the electroluminescence peaks, the current, and the temperature. Through this optical method with inherent electrical isolation, the junction temperature and current in the SiC chip can be simultaneously measured with high precision. The total error of the junction temperature estimation is within ±3 °C, and the error of the current estimation is about ±0.2 A. [ABSTRACT FROM AUTHOR]

A shunt active power filter (SAPF) is coupled with load admittance in weak grid conditions, which poses a challenge to stability analysis. In this article, the admittance model of the SAPF is developed, which reveals the coupling mechanism between SAPF and load concisely and accurately. On top of that, the stability region of the system is investigated. The passivity region of the load admittance to guarantee the system stability is first explored. However, the passivity region has a very narrowband at a specific frequency, which makes it difficult to achieve. The stability region is then studied and it turns out to be an extension of the passivity region, and especially the narrowband is expanded. Therefore, the stability region is much easier to meet. The stability-oriented design is then summarized in a flowchart. In the end, the effectiveness of the newly defined stability region is verified by experimental results. [ABSTRACT FROM AUTHOR]

Series connection of SiC power MOSFET is an attractive approach to expand the blocking voltage of SiC devices, whereas the dynamic voltage balancing among the series-connected devices is the most critical challenge of the technique. In this article, a simple, fast, and cost-effective dynamic voltage balancing circuit of the series-connected SiC MOSFETs is proposed to suppress the voltage imbalance among the devices. The proposed circuit is composed of a resistor-capacitor (RC) snubber with a coupled inductor to effectively sense the voltage imbalance and add a compensated signal to the gate driving voltage. In the article, the operation principle of the proposed method is described in detail and the parameter selection of the circuit is given. Then the optimized layout of the circuit in a typical half-bridge SiC power module is proposed to reduce the stray parameters introduced by the coupled inductor effectively. The proposed method is verified by experiments under different conditions. Compared with a purely RC snubber balancing strategy, the capacitor can be significantly reduced. Since only passive components are required in the feedback loop, the proposed method demonstrates a reliable and straightforward approach to achieve equal voltage sharing of the series-connected devices. [ABSTRACT FROM AUTHOR]

The oscillation frequency of the point of common coupling (PCC) voltage is proposed as a new detecting freedom for dc-based islanding events in this article. In the presented method, the voltage positive feedback with a frequency selection is applied to a distributed generator to make the PCC voltage oscillate at the selected frequency when islanding events occur. With the frequency information, islanding events can be identified by the small-amplitude oscillation superimposed on the normal dc voltage without the necessity of voltage amplitude to be shifted out of the normal range. Thus, the islanding events can be effectively distinguished from other abnormal conditions that lead to large voltage fluctuations, and so, the accuracy of islanding detection is improved. Also, the power quality at islanding events is enhanced, which provides important benefits for seamless transfer from the unintentional islanding conditions to the controlled islanding conditions. Moreover, the frequency selection is designed to only transfer the voltage signal at the sensitive frequency band of the islanding condition. As a result, the deterioration of stability caused by the voltage positive feedback can be relieved under the grid-connected condition compared to the existing methods. Finally, the effectiveness of the proposed method has been verified by both time-domain nonlinear simulation and experimental results. [ABSTRACT FROM AUTHOR]

Visible light communication (VLC) system integrates LED lighting with wireless communication. Conventionally, power conversion and communication are designed separately. The circuitry added for communication helps to achieve a high bit rate, but increases costs and impacts the efficiency. On the other hand, power conversion and communication can also be designed together by applying switching ripple communication (SRC), where no additional devices are needed. However, SRC is usually achieved by broadband modulation methods, which means that the bandwidth is much lower than the switching frequency. By applying information theory to pulsewidth modulation, this article proposes a novel VLC scheme that applies baseband modulation to SRC in order to achieve a high bit rate with a relatively low switching frequency. In addition, power control and communication are decoupled, so that they do not influence each other. In the experiments, GaN MOSFETs are used to achieve a 1.25 Mb/s VLC system with a code error ratio of less than 10–6. Moreover, the scheme shows good performance under the duty cycle from 70% to 30%, and under the output power from 100% to 7.5% of the rated value. [ABSTRACT FROM AUTHOR]

DC transformers based on power electronics are key items of equipment for medium voltage dc (MVDC) distribution systems. Both high and low step-ratio dc–dc conversions are required to interface dc links at different voltages to form an integrated dc distribution system. The transformer-coupled resonant modular multilevel dc–dc converter (RMMC) is well-suited to high step-ratio connection between an MVDC network and a low voltage dc network but it is not suitable in low step-ratio conversion for linking two MVDC networks with similar but not identical voltages. This article presents a circuit evolution of the high step-ratio transformer-coupled RMMC into its low step-ratio transformer-less RMMC counterpart. These two RMMCs share the same structure and the same resonant process within the resonant submodule stack giving rise to the same operational advantages. Also, the circuit design experience can be readily transferred from one to the other. From these two base RMMC circuits, a family of RMMCs with further configurations is elaborated that provide a wider variety of connection options for MVDC distribution systems. In this circuit family, each high step-ratio transformer-coupled RMMC has a low step-ratio transformer-less RMMC counterpart and one can be transformed into the other via the circuit evolution process presented. The theoretical analysis for both high and low step-ratio RMMCs has been verified through full-scale simulations of medium voltage examples and further verified through down-scaled experiments on laboratory prototypes. [ABSTRACT FROM AUTHOR]

In this article, the arm phase-shift conducting modulation (PSCM) is proposed for the alternate arm multilevel converter (AAMC). With the PSCM strategy, the half-bridge (HB) structure could be applied as the submodule (SM) topology to reduce the circuit complexity of the full-bridge submodule based AAMC. First, the phase-shift angle is introduced to match the voltage modulation ratio and power factor of ac grid. The energy stored in the submodule capacitors are balanced by regulating the phase-shift angle. Then, the design criteria and operation performance for HBSM-AAMC with the proposed PSCM strategy are analyzed and presented. Compared with HBSM-modular multilevel converters (MMC), 18% HBSMs and 9% power devices are reduced with the proposed topology and modulation, resulting in the lower construction cost. Furthermore, the loss distribution is analyzed, and the operating losses of HBSM-AAMC are smaller than that of HBSM-MMC. Finally, the simulation and experiment are performed to verify the effectiveness of the derived topology and the proposed modulation strategy. [ABSTRACT FROM AUTHOR]

Nowadays, due to the growing demands of data centers, the traditional line frequency transformer based data center power distribution system (DC-PDS) is becoming bulky and inefficient. Although SST-based DC-PDS dramatically improves the system efficiency, the traditional multicell SST with input-series output-parallel architectures has limitations. Using high-voltage devices to develop single-cell SST improves system performance, however, its application is limited by high-voltage power devices. As an alternative solution, achieving high blocking voltage through the series connection of low-voltage devices brings several advantages. Nevertheless, the series connection brings about two main problems, namely the voltage imbalance among devices and the increment of switching loss. This article proposes a medium voltage series resonant converter (MVSRC) with series-connected SiC MOSFETs. By adding snubber capacitor to each SiC MOSFET and working at LLC resonant soft-switching mode, the voltage imbalance is reduced and switching loss is decreased. Due to snubber capacitors, there are differences between MVSRC and traditional LLC converter, hence the analytical model of MVSRC is established. Moreover, the voltage imbalance model is established and the voltage imbalance sensitivity is defined to guide the snubber parameter selections. Then, a design example of the 99% efficient 5-kV/400-V prototype is presented. Last, the experimental results show that the voltage imbalance is reduced effectively and the switching loss is decreased dramatically, verifying the validity of proposed methods and the accuracy of analysis. [ABSTRACT FROM AUTHOR]

This article proposes a novel interleaved three-phase pulsewidth modulation (PWM) single-stage resonant ac–dc converter with high-frequency isolation. The proposed converter comes from an interleaved three-phase power factor correction (PFC) semistage and a three-phase LLC resonant dc–dc semistage. Soft-switching commutation can be achieved on the power switches in this converter including zero-voltage-switching-on on the primary side power switches and zero-current-switching-off on the secondary diodes. The LLC resonant tank in the dc–dc semistage serves as a bandpass filter that attenuates the line-frequency ripple and keeps the switching frequency component passing through the transformer. The high frequency transformer keeps in a small size. Steady-state analysis of the resonant dc–dc semistage for PWM control is proposed to analyze the dc-link voltage stress. Moreover, the dc-link capacitor value can be greatly reduced without affecting the PFC operation. A prototype that converts a wide three-phase input voltage to 300 V dc output voltage is built and tested. The experimental results present an almost unity power factor with a conversion efficiency as high as 96.3% with total harmonic distortion as low as 3.86% at a full-load condition. [ABSTRACT FROM AUTHOR]

This article aims to improve the sensorless control performance of surface-mounted permanent magnet synchronous machine drives in the whole speed range. Based on the thought of speed partition optimization and smooth transition, a hybrid sensorless control strategy integrating with an improved flux linkage observer and the current–frequency (I–f) starting method is proposed. At zero–low speed, the I–f control method is utilized for the stable startup and strong antijamming capability. At medium–high speed, an improved flux linkage observer based on the sliding-mode compensator is designed for the closed-loop sensorless operation. Taking advantage of the sliding-mode compensator, not only the position estimation errors caused by the adopted filter can be compensated effectively without any speed iteration to improve the system stability, but also the suitable cutoff frequency of the filter can be selected for the fast system dynamic response. Meanwhile, the influence of machine parameter variations on the rotor-position estimation accuracy is discussed. Furthermore, in order to achieve the smooth operation between two different control schemes, an adaptive transition algorithm is described in detail. Experimental results indicate that the proposed hybrid sensorless control strategy can show an excellent performance for both steady-state and dynamic operations during full-speed range. [ABSTRACT FROM AUTHOR]

A modular multilevel resonant (MMR) dc–dc converter, its modulation, and control are proposed in this article. The MMR converter inherits the desirable features of both the modular multilevel converter and LLC resonant converter, such as high voltage capability, easy fault-tolerant operation, and soft switching. Besides, the MMR can regulate the output voltage over a wide input voltage range with much narrower frequency range compared to conventional resonant converters. By constantly inserting certain number of submodules into the arm according to the input voltage, the resonant tank voltage can be regulated with a relatively constant amplitude regardless of the wide input variation. This modulation technique is acted as a feedforward loop to roughly regulate the output according to the input voltage, and the feedback loop in the control system precisely regulates the output by varying the switching frequency. Simulations on a 200-kW MMR that converts 9–15 kV to 750 V are provided to verify the effectiveness of the proposed topology and control method. Experimental results on an MMR prototype are also given to demonstrate the feasibility. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive solution to mitigate the sub-synchronous oscillation (SSO) in wind farms connected to series-compensated transmission lines. The concept of motion-induction amplification (MIA) is introduced to reinterpret the physical root cause of the negative resistance in doubly-fed induction generators (DFIGs). Based on this new interpretation, a novel control scheme called motion-induction compensation (MIC) is proposed to counteract the MIA effect. The MIC control eliminates the negative resistance in DFIGs across the entire frequency range, and makes the Type-III (DFIG) generator behave like a Type-IV generator in dynamics. The proposed solution provides wide-range SSO damping and also shows excellent robustness against model and measurement errors. [ABSTRACT FROM AUTHOR]

This letter proposes an online capacitance estimation method for the modular multilevel converter. In the prevalent methods, the inherent second-order circulating current or the injected low-frequency current/voltage component is utilized to calculate the submodule (SM) capacitance. In this letter, the relationship between the voltage variation of an SM capacitor in one fundamental period and the driving signals switching angle under the nearest level modulation scheme is revealed. The voltage variation of each SM capacitor is a direct component and has no relationship with the second-order harmonic current and voltage ripples. Accordingly, an online capacitance estimation method for HVdc applications is proposed by simply monitoring the SM capacitor voltage variations at fundamental frequency. In the proposed scheme, neither the current/voltage injection nor the inherent circulating current is required, which reduces the estimation complexity. The recursive least squares algorithm is also adopted to guarantee the accuracy of the estimation method. Effectiveness of the proposed online capacitor estimation method is verified by the experimental results. [ABSTRACT FROM AUTHOR]

Energy storage units (such as battery or ultracapacitor) can help to reduce the power fluctuation in the impedance source network converter applications such as the photovoltaic (PV) and fuel cells systems. Due to the unknown dynamic characteristics of the energy stored impedance network, the unexpected oscillation and inrush currents in dynamic process might threaten the storage device safety. In this article, an energy stored quasi-Z-source converter with the battery is modeled and analyzed including the transient capacitor current. The impact of the network internal resonance on the battery current control loop is mathematically explored. The resulted conflict between the zero steady-state error and bandwidth requirement is revealed. That yields the sacrifice and limitation of the closed-loop dynamic performance in the conventional methods. An active damping technique is then proposed to ensure the extended bandwidth and better dynamic performances under different state of charge (SOC) occasions. The theoretical analysis and performance are both verified by the simulations and experiments. [ABSTRACT FROM AUTHOR]

This paper proposes a torque distributed control strategy for the multiphase machines in the hybrid energy storage system application. Different with the conventional energy current regulation method, the system energy management is researched by the machine torque distribution in different sets of windings. The load power is then afforded by the energy storage devices connected with the windings through the inverters. The principle of the distributed torque operation is explored with a dual three-phase permanent-magnet synchronous machine model and the asymmetrical windings operation is explained with the flux vector diagram. The windings decoupling compensation, flux observer, and parameter identification methods are presented. Based on the proposed strategy, a power frequency dividing coordinated regulation is achieved. The hybrid energy storage devices can directly respond to the average or instantaneous parts in the load torque and power fluctuation. Simulation and experiments are demonstrated with different operation cases. [ABSTRACT FROM AUTHOR]

Medium-voltage high-speed drive is promising in applications, such as the centrifugal compressors and electrified transportation. However, it raises lots of design challenges for the converters, which drive the motors. A SiC and Si hybrid ANPC converter is developed to address these challenges. In this article, the essence of this hybrid structure is investigated to clearly show the derivation process of the hybrid active neutral-point-clamped (ANPC) converter and inspire future research on these hybrid topologies. A dedicated space vector modulation (SVM) scheme is proposed for the hybrid ANPC converter, which enables the three-phase hybrid ANPC converter operating with SiC mosfets in high frequency and Si IGBTs in fundamental frequency. A neutral point (NP) voltage balancing scheme is added to the SVM scheme to balance the NP voltage imbalance under low-frequency modulation index. All these efforts make the hybrid ANPC converter become a high power density and fairly low-cost solution. A 400 Hz fundamental frequency, 3.6 kHz switching frequency, medium-voltage high-speed drive system is assumed and tested by the scaled-down experimental results. The effectiveness of the proposed SVM and NP voltage balancing method have both been verified. [ABSTRACT FROM AUTHOR]

The thermal management plays an important role in improving the reliability and lifetime of high power converters, especially for the high voltage direct current (HVdc) transmission system. In the voltage source converter based HVdc systems (VSC-HVdc), the hybrid modular multilevel converters (MMCs) are taken as the excellent candidates due to their dc short-circuit fault ride-through ability and less submodule (SM) devices. Furthermore, the voltage modulation index of hybrid MMCs can be promoted to achieve higher power rating and efficiency. However, in this article, it is revealed that thermal stress distribution inside the SMs becomes more unbalanced under a high voltage modulation index, which would lead to serious thermal fatigue. To overcome this problem, the active bypass with thyristor for half-bridge submodules (HBSMs) and symmetrical modulation for full-bridge submodules (FBSMs) based active thermal control strategies are employed. With the presented thermal control strategies, the junction temperature of the most stressed devices in both HBSMs and FBSMs is reduced enormously. Besides, the thermal control strategy does not bring negative influence on the steady-state output performance of hybrid MMC. Finally, the theoretical analysis and effectiveness of the proposed control methods are verified based on a laboratorial MMC prototype. [ABSTRACT FROM AUTHOR]

In this letter, a compact silicon carbide (SiC) power module featuring low stray inductance and balanced thermal resistance is proposed. To make full utilization of SiC devices in high-frequency and high-power-density applications, the laminated busbar and double-sided cooling heatsinks are directly packed as parts of the SiC power module. To balance the mechanical and thermal stress on the chips, a press-pack-like package technology is adopted. The electrical and thermal experiments of the prototype are evaluated to validate the design of low inductance and balanced thermal distribution. [ABSTRACT FROM AUTHOR]

The crosstalk voltage on the gate-source terminal of SiC power mosfets in a phase-leg circuit is composed of the gate–drain capacitor introduced voltage and the common-source inductor introduced voltage. The mathematical model of the crosstalk voltage indicates that to suppress two types of crosstalk voltage, there exists a contradictory requirement on the off-state gate loop impedance. This challenge reduces the effectiveness of conventional crosstalk elimination methods. As an improvement, a crosstalk voltage suppression circuit that synchronously eliminates the crosstalk voltage of gate–drain capacitance and the common-source inductance is proposed. In this article, instead of creating low-impedance gate loop in the off-state, a high-impedance gate loop is formatted to eliminate the voltage drop on the common-source inductance. Meanwhile, the potential false turn-on or the negative voltage spikes caused by gate–drain capacitance is eliminated by the precharge voltage in the gate-source capacitor. The required prestored charge is analyzed considering the nonlinear behavior of the junction capacitance of the SiC mosfets. The proposed gate driver is experimentally verified in different switching conditions. [ABSTRACT FROM AUTHOR]

A novel control scheme is proposed in this paper for the sensorless control of interior permanent magnet synchronous machines (IPMSMs) with the automatic tracking of the maximum-torque-per-ampere (MTPA) trajectory. Differing from the conventional method that the estimation of the rotor position and the tracking of MTPA trajectory are two separate processes, the proposed control scheme can achieve sensorless MTPA control of IPMSMs in one step by defining and constructing a proper virtual q-axis inductance to directly calculate the current space vector angle along the MTPA trajectory rather than the rotor position, which greatly simplifies the whole implementation process. Meanwhile, considering that the virtual q-axis inductance is changing with the machine parameters and the applied load, a simple signal processing technique based on the virtual high-frequency signal injection is developed for the real time and accurate acquisition of the virtual q-axis inductance. Furthermore, in order to ensure the reliability and stability of the proposed control scheme, the effective range of the virtual q-axis inductance is analyzed in detail. Finally, the experimental results on an IPMSM demonstrate the proposed control scheme can achieve the high-performance sensorless control with accurate MTPA self-tracking operation. [ABSTRACT FROM AUTHOR]

Three-phase current reconstruction techniques with a single current sensor have been studied for permanent magnet synchronous machines (PMSMs) drive system due to its reducing cost and volume. In order to minimize the current reconstruction dead zone in the conventional method with a single dc-link current sensor, a strategy to couple multiple available positions through the single current sensor is proposed in this paper. With the proposed method, two independent equations of the stator currents can be obtained by sampling the single current sensor twice in both zero voltage vectors and active voltage vectors. By solving these two equations, the phase current reconstruction can be achieved accurately, which moves the current reconstruction dead zone toward six corner area of the space vector hexagon. Meanwhile, in order to guarantee the proposed method suitable in the whole linear modulation region, the suitable selection of the pulsewidth modulation switching period is analyzed in detail. Furthermore, the optimal selections of multiple sampling positions are discussed to lower the actual implementation difficulty of the proposed method. Finally, the experimental results on the PMSM demonstrate that the reconstructed phase currents with the proposed method can be always in consistent with the actual measured currents under different working conditions. [ABSTRACT FROM AUTHOR]

Devices and the passive components in the single-phase impedance source network converter are sensitive to the double-line-frequency (DLF) pulsation. Previous research works have studied the power decoupling and the DLF equivalent model for the power pulsation suppression method. This paper explored the DLF transfer routes in the impedance source network. A comprehensive stress derivation of the passive components and switching devices are obtained for the suppression method enhancement and optimization. For the DLF passive suppression method, the explanation for the passive component volume issue is provided from the stress aspect. The component value solution space and corresponding design guidance are presented. For the DLF active suppression method (ASM), a buck-type dc-side ASM suppression method is employed and its optimization is demonstrated with the assistant circuit stress analysis. The total capacitor and inductor values get reduced by 77% and 25%, respectively. The corresponding pulsewidth modulation method implementation and the common-mode leakage current demonstration are also presented. The effectiveness of the theoretical analysis and optimization methods is verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

This letter presents a novel simultaneous wireless power and data transmission (SWPDT) system for wireless electric vehicle (EV) charging. The data carrier is injected and extracted by a plug-and-play toroidal-core inductor. Two data carriers of 5 and 6.25 MHz are adopted to achieve bidirectional and full-duplex communication using frequency-division multiplexing. Differential quadrature phase-shift keying modulation is achieved by a Class-E amplifier in the data transmitter. An analog switch circuit is designed to demodulate the data carrier in the data receiver. The proposed method is verified by a prototype that achieves up to 64 kbps full-duplex data transmission under 3.3 kW power transfer. The bit rate and interference immunity of data transmission are greatly improved compared to the reported SWPDT systems, which makes it possible to realize high-speed simultaneous communication in the kilowatt-level wireless EV charging. [ABSTRACT FROM AUTHOR]

Accurate information of the junction temperature of SiC power mosfets ensures safe operation and helps reliability assessment of the devices. In this paper, an online junction temperature extraction method is proposed based on the electroluminescence phenomenon of the body diode of SiC power mosfets. It is found that during the forward conduction interval of the body diode, visible blue light is emitted around the chip, which ascribes to the radiative recombination in the low doped region of SiC mosfets. Experimental results suggest the light intensity changes linearly with the variation of the temperature and behaves as a temperature sensitive optic parameter (TSOP). Further, an electro-thermal-optic model is proposed to reveal the relationship between the electroluminescence intensity, forward current, and junction temperature. Based on the TSOP, an online junction temperature extraction method is proposed for SiC mosfets and verified in an SiC mosfet based inverter. Compared with state-of-the-art methods, the proposed junction temperature measurement method is contactless and immune from the aging of the package. [ABSTRACT FROM AUTHOR]

Hardware structure is a basic characteristic of a battery management system (BMS), which influences the overall performance of battery packs. This paper presents a novel BMS architecture based on the power/data time division multiplexing transmission technique. In the proposed system, a common bus is employed to transfer power and data simultaneously, so the system wiring is simplified. The system consists of a pack management unit and several cell management units (CMUs). The circuit of the CMU is compact and achieves conventional management functions like status monitoring and active cell balancing; thus, it can be integrated with battery cell to be an intelligent cell. The timing sequence of the system is presented, and the design considerations are discussed in detail, including terminal resistance selection, maximum node number calculation, and power consumption analysis. Finally, a simulation based on MATLAB is carried out and an experimental prototype system with six nodes is built, which verifies the correctness of the architecture and proves the feasibility in practical applications. [ABSTRACT FROM AUTHOR]

In a photovoltaic system, a dc–dc power optimizer (DCPO) is an option to maximize the output power. At the same time, data links among DCPOs are often required for system monitoring and controlling. This paper proposes a novel power line communication method for the DCPOs, in which the data of a DCPO are modulated into the control loop of a power converter, and then transmitted through the series-connected dc power line to other DCPOs. In the process of communication, differential phase-shift keying modulation and discrete Fourier transformation demodulation are employed. To analyze the quality of communication, the communication model of the system is built, based on a small-signal model. Furthermore, the noises of the system, including switching, maximum power point tracking, and additive white Gaussian noise, are discussed and measured to evaluate the signal-to-noise ratio. Lastly, an experimental system including six DCPOs is established and tested, which verifies the feasibility and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]