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This paper proposes a new methodology for automated design of power electronic systems realized through the use of artificial intelligence. Existing approaches do not consider the system's reliability as a performance metric or are limited to reliability evaluation for a certain fixed set of design parameters. The method proposed in this paper establishes a functional relationship between design parameters and reliability metrics, and uses them as the basis for optimal design. The first step in this new framework is to create a nonparametric surrogate model of the power converter that can quickly map the variables characterizing the operating conditions (e.g., ambient temperature and irradiation) and design parameters (e.g., switching frequency and dc link voltage) into variables characterizing the thermal stress of a converter (e.g., mean temperature and temperature variation of its devices). This step can be carried out by training a dedicated artificial neural network (ANN) either on experimental or simulation data. The resulting network is named as $\text{ANN}_{1}$ and can be deployed as an accurate surrogate converter model. This model can then be used to quickly map the yearly mission profile into a thermal stress profile of any selected device for a large set of design parameter values. The resulting data is then used to train $\text{ANN}_{2}$ , which becomes an overall system representation that explicitly maps the design parameters into a yearly lifetime consumption. To verify the proposed methodology, $\text{ANN}_{2}$ is deployed in conjunction with the standard converter design tools on an exemplary grid-connected PV converter case study. This study showed how to find the optimal balance between the reliability and output filter size in the system with respect to several design constraints. This paper is also accompanied by a comprehensive dataset that was used for training the ANNs. [ABSTRACT FROM AUTHOR]

With the increasing proliferation of variable speed drive, the demand for the more reliable drive is also on the rise. Despite the growing interest on more advanced motors like permanent magnet and flux switching motors, three-phase induction motors (3ph-IMs) are still the main workhorse in the industry and hence the fault-tolerant control of these motor drives remains an interesting and important topic. In this paper, a simple fault-tolerant field-oriented control technique for 3ph-IMs is presented. It is shown that by injecting zero-sequence compensation voltage in a feedforward manner, open-circuit faults can be effectively tolerated. Compared to the previous feedforward fault-tolerant control methods, the proposed approach does not require the knowledge of the magnetizing inductance, which is tricky to be obtained in induction motors. Furthermore, the unified feedforward approach allows the same control structure to be used for different fault-tolerant 3ph-IMs drive topologies, with minor modifications to the feedforward terms. In addition, the effect of inverter non-idealities on the performance of the proposed control method is also highlighted and addressed. The effectiveness of the proposed controller is verified using MATLAB simulation and further validated using experimental tests. This paper is accompanied by a video demonstrating the experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a new class of bidirectional partial-resonance power converters is presented. The proposed family can be configured to interface single- or multi-port dc, single- or multi-phase ac systems at input-side and/or output-side. The proposed family offers a very modular structure, which can lead to cost reduction from a common designed module. In this converter, which accomplishes power conversion in a single stage, a small inductor placed in series with the input and output switch-bridges forms the link. This small link inductor is responsible for transferring power between different ports of the system. The proposed topologies can operate in buck, boost, and buck–boost modes of operation to step up and/or step down the voltage. In buck–boost mode of operation, the converter is controlled such that the power is entirely transferred through the link inductor; whereas, in buck or boost modes of operation only a fraction of the power is transferred through the link inductor, and the remaining power is directly transferred from input phases to the output phases. Galvanic isolation, which is typically a prominent factor contributing to power density of a converter, can be provided by means of a compact and lightweight single-phase high-frequency transformer added to the link. In comparison with earlier generations of partial-resonance inductive-link power converters, in the proposed converter, the level of link peak current and consequently power-loss, as well as voltage and current stress of switches are dramatically decreased. A very small film capacitor can be placed in parallel with the link inductor to facilitate zero-voltage-switching (ZVS) operation for all the switches/diodes. Apart from increasing the overall efficiency, minimized dv/dt stress and improvement in power density are achieved by adding the link capacitor. The proposed converter employs four-quadrant switches, i.e., bidirectional-conducting bidirectional-blocking switches, and charges the link inductor in both positive and negative directions in each cycle. In view of this, better utilization of the link inductor and lower total harmonic distortion (THD) are offered. Furthermore, two distinct switching algorithms are developed for the proposed family of converters. In this paper, the detailed behavior of the proposed family is investigated analytically, and simulation and experimental results are presented to evaluate the performance and effectiveness of the proposed converter. A low-power proof-of-concept prototype with input voltage of 59 V/161 V, load voltage of 178 V/73.5 V, maximum switching frequency of 4.9 kHz/3.65 kHz at 215 W/450 W in a step-up/step-down operation is considered for the experimental verification. [ABSTRACT FROM AUTHOR]

This paper proposes a methodology for active thermal control of power electronic modules in ac applications, which includes a loss manipulation unit, a thermal observer structure, and an active thermal cycle reduction algorithm. It aims to reduce the thermo-mechanical strain in the inter-connects of the module in order to enhance its reliability and lifetime. The loss manipulation unit operates in a minimally invasive manner by manipulating adaptive gate resistances and the pulsewidth modulation frequency. This allows the individual thermal control of multiple devices within a power module, which has not been achieved in prior work. A thermal observer structure that estimates averaged junction temperatures by combination of a thermal model and sensor information is introduced. The observer technology makes this paper the first to realize closed-loop control of averaged temperatures achieving an increased robustness and insensitivity to modeling errors. A key element of the active thermal cycle reduction algorithm is the virtual heat sink that derives feasible and stress-relieving thermal trajectories. The trajectories are applied with a unique thermal feedback control that smoothly manipulates the averaged junction temperature of the power module even in the presence of loss manipulation limits. The active thermal control methodology is evaluated experimentally with a state-of-the-art insulated-gate bipolar transistor (IGBT) power module. [ABSTRACT FROM AUTHOR]

In this paper, a novel high-conversion-ratio isolated bidirectional dc–dc converter for distributed energy storage systems is proposed. In the buck mode, the proposed converter is equivalent to that of a cascade consisting of an isolated buck–boost converter and a buck converter, thus achieving a high step-down ratio. Likewise, in the boost mode, the converter is equivalent to the cascaded structure consisting of a boost converter and an isolated buck–boost converter, and then, a high step-up ratio is achieved. Therefore, the proposed topology exhibits a high conversion ratio with low transformer turns ratio, improving the efficiency of high-frequency transformers and the integration and reliability of the control system. In addition, voltage spikes caused by the leakage inductance can be avoided as the leakage inductance energy is released to capacitors in a high-voltage side or a low-voltage side. Moreover, a zero-voltage-switching (ZVS) operation reduces switching losses and improves the conversion efficiency. The operating principles and theoretical derivations of the proposed converter along with ZVS implementations are discussed in detail in this paper. Furthermore, the validity and performance of the proposed converter are verified using a prototype with 600-V high voltage, 48-V low voltage, and 2-kW output power. [ABSTRACT FROM AUTHOR]

In modern power systems, the increasing penetration of renewables and power electronics, particularly inverter-based wind and solar power generation, is altering power system dynamics and bringing new stability concerns. One challenging issue that is attracting considerable attention is the wide range of power oscillations associated with multiple parallel grid-connected inverters. In such systems, the characteristics in terms of resonance and oscillation are significantly different from single-inverter systems. This paper investigates the mutual interaction and stability issues of multiple grid-interfacing inverters with LCL-filters in power-electronics-based power systems under various grid conditions. The investigation reveals that such interactions between power inverters and the grid may excite multiple resonances at various frequencies under certain grid conditions. The nodal admittance matrix concept, which was originally from power systems engineering, is adopted here. Moreover, this paper further develops an Interaction-Admittance model that can effectively describe these mutual interactions in terms of a physical network admittance. We apply our model to various scenarios such as stiff grid conditions and inductive grids with/without power factor correction capacitors. The results with the proposed framework demonstrate an intuitive interpretation of multi-inverter system resonance and instabilities. Finally, simulations and experiments on a lab-scale system are provided to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper describes a dc-link voltage control method of a single-phase back-to-back cascaded H-bridge inverter (SBCI) for a medium-voltage motor drive system. The main advantage of the SBCI topology over the conventional regenerative cascaded H-bridge topology with a three-phase active front-end (AFE) is a simple system structure, which is composed of an input transformer, a power cell, a current sensor, etc. However, the challenging points of the SBCI are larger voltage ripple in the dc-link capacitor and imbalance of dc-link voltages of each phase. The asymmetric dc-link voltage of each power cells could cause unstable operation such as over-modulation due to the lack of the dc-link voltage of a particular phase and result in over-voltage or under-voltage faults. In this paper, the control strategy of the dc-link voltage for the SBCI that uses the negative-sequence voltage of the converter is described. The proposed control method is verified with a computer simulation whose target is a 6.6-kV–1.25-MW medium-voltage drive system. Also, through the experimental setup with the prototype SBCI whose power rating is 16.2 kVA, the dc-link voltage of each AFE has been controlled within a 0.5% error of its reference value at the full load. [ABSTRACT FROM AUTHOR]

This paper presents the first experimental validation of the stability analysis based on the online measurement of harmonic impedances exploiting the linear time-periodic (LTP) approach applied to ac networks of power converters. Previous studies have provided the theoretical framework for the method, enabling the stability assessment of an unknown system adopting a black-box approach, relying only on injected perturbations and local measurements. The experimental case study considered in this paper comprises two single-phase converters, one acting as source subsystem and the other as load subsystem. A third converter, the stability measurement unit, is controlled to inject small current perturbations at the point of common coupling (PCC). From the measured small-signal perturbations of PCC voltage, source current, and load current, the harmonic impedances of source and load subsystems are calculated. The LTP Nyquist criterion is then applied to the ratio of the two harmonic impedances in order to assess the stability of the whole system. Theoretical and experimental results from a 5-kW laboratory prototype are provided and confirm the effectiveness of the method. In addition, the measurements do not require sophisticated equipment or control boards and can be easily performed from data sampled by commercial micro-controllers. [ABSTRACT FROM AUTHOR]

This paper studies the high power density bidirectional dc–dc converter with interleaving, soft-switching, and near critical conduction mode (near-CRM) operation. Systematic design and control methods are proposed to enhance the effectiveness of passive currents balancing between multiple interleaved phases without using individual phase current feedbacks. This paper first analyzes the zero voltage turn-on operation, including the turn-off energy diversion by the added snubber capacitor and the turn-off resonance models. Second, the intrinsic inverse co-relation between the phase current deviation and the resulting effective duty cycles variation is quantitatively formulated and modeled as a closed-loop mechanism that balances the currents passively. Then, the design constraints of the system parameters including the snubber capacitance, dead time, and valley currents of the near-CRM mode are formulated to guarantee the effectiveness of counteracting the current unbalance. Finally, a variable switching frequency control is proposed to actively control the valley current and maintain the current balancing effectiveness throughout the operating range. An IGBT-based 20-kW three-phase interleaved prototype with the maximum efficiency of 99.1% is constructed to verify the proposed design and control methods. [ABSTRACT FROM AUTHOR]

In this paper, a new non-isolated two-input single-output dc–dc converter with high voltage gain is proposed. In the proposed converter, there are two three-winding coupled inductors used to achieve a high voltage gain and ripple-free input currents. The proposed converter has two switches, and their control pulses are the same as the control pulses of the two-phase interleaved converters with a phase shift equal to $\text{180}^{\circ} $. The voltage stresses of switches and diodes are reduced and are always lower than the high output voltage. The proposed converter is extendable to a four-input single-output converter in which the switches have the control pulses the same as those in four-phase converters with phase shifts equal to $\text{90}^{\circ} $. In this paper, the proposed topology is analyzed in all operating modes, and the values of current and voltage stresses of all switches and diodes, voltage gain, and required conditions for input current ripple cancelation are calculated during a switching period. Finally, the accuracy performance of the proposed converter is reconfirmed through experimental results for 225- and 298-W prototypes. [ABSTRACT FROM AUTHOR]

This paper proposes a cooperative mechanism for detecting potentially deceptive cyber attacks that attempt to disregard average voltage regulation and current sharing in cyber-physical dc microgrids. Considering a set of conventional cyber attacks, the detection becomes fairly easy for distributed observer based techniques. However, a well-planned set of balanced attacks, termed as the stealth attack, can bypass the conventional observer based detection theory as the control objectives are met without any physical error involved. In this paper, we discuss the formulation and associated scope of instability from stealth attacks to deceive distributed observers realizing the necessary and sufficient conditions to model such attacks. To address this issue, a novel cooperative vulnerability factor (CVF) framework for each agent is introduced, which accurately identifies the attacked agent(s) under various scenarios. To facilitate detection under worst cases, the CVFs from the secondary voltage control sublayer is strategically cross coupled to the current sublayer, which ultimately disorients the control objectives in the presence of stealth attacks and provides a clear norm for triggering defense mechanisms. Finally, the performance of the proposed detection strategy is simulated in MATLAB/SIMULINK environment and experimentally validated for false data injection and stealth attacks on sensors and communication links. [ABSTRACT FROM AUTHOR]

This paper proposes a coordinated control strategy for the rotor-side converter (RSC) and the grid-side converter (GSC) of an LC-filtered doubly fed induction generator (DFIG) under distorted grid voltage condition, to eliminate the distortion of the total output current (including the stator current, the GSC current, and the filter capacitor current). For an LC-filtered DFIG connected to a distorted grid, the low-order current harmonics can freely flow into the filter capacitor thereby polluting the total output current, even when the stator current and the GSC current are both controlled as sinusoidal. Although this problem can be addressed by measuring the output current or the capacitor current, the extra current sensors are undesired in industrial applications. In this paper, a novel hybrid virtual impedance method is implemented in both the RSC and the GSC, to reshape the parallel impedance of the stator, the GSC and the filter capacitor to nearly infinite for low-order harmonics, thus, the freely flowing output current harmonics can be mitigated. Meanwhile, the low-order current harmonics required by the output current compensation can be flexibly distributed between the stator and the GSC according to their operating conditions, to disperse the side-effects on the drive train and the GSC, thereby better protecting the whole system. The effectiveness of the proposed strategy is theoretically analyzed and verified with both simulation and experiment. [ABSTRACT FROM AUTHOR]

This paper proposes a novel active-clamp forward converter (ACFC) with a lossless-snubber on the secondary-side, which combines a resonant capacitor and a clamping diode with an output inductor in parallel. The conventional ACFC achieves zero-voltage-switching on switches of the primary-side during dead time for reducing the switching loss and voltage spike. Unfortunately, on the secondary-side of transformer, the voltage spike damages the free-wheeling diode and rectifier diode due to the reverse recovery current and junction-capacitor of the diode and leakage inductance of the transformer. This paper proposes a lossless-snubber on the secondary-side operation for reducing the voltage spike on the free-wheeling diode and forward-rectifier diode. Therefore, the converter proposed in this paper is suitable for high-output-current applications. Experimental results are shown to verify the analysis and design procedure of the proposed forward converter. [ABSTRACT FROM AUTHOR]

This paper is concerned with combined power-source sizing and energy management optimization for multi-motor-driven electric powertrains. Existing studies focus mostly on adopting heuristically determined battery and motor sizes for such powertrains, without a sufficient exploration of the coupling between power-source dimension and energy management strategy. To address this research gap, this paper aims at presenting an alternative, convex programming based method to optimize the multi-power-source integration problem, for vehicular economy maximization. Specifically, for the first time, we leverage this method to optimize an electric bus powertrain configuration with front-and-rear-axle dual motors and a clutch, as a case study. Numerous analysis results, as well as comparisons with common design/control practice, demonstrate the effectiveness and computational benefit of the proposed scheme. [ABSTRACT FROM AUTHOR]

The photovoltaic (PV) output voltage varies over a wide range depending on operating conditions. Thus, the PV-connected converters should be capable of handling a wide input voltage range while maintaining high efficiencies. This paper proposes a new series resonant dc–dc converter for PV microinverter applications. Compared with the conventional series resonant converter, a dual-mode rectifier is configured on the secondary side, which enables a twofold voltage gain range for the proposed converter with a fixed-frequency phase-shift modulation scheme. The zero-voltage switching turn-on and zero-current switching turn-off can be achieved for active switches and diodes, thereby, minimizing the switching losses. Moreover, a variable dc-link voltage control scheme is introduced to the proposed converter, leading to a further efficiency improvement and input-voltage-range extension. The operation principle and essential characteristics (e.g., voltage gain, soft-switching, and root-mean-square current) of the proposed converter are detailed in this paper, and the power loss modeling and design optimization of components are also presented. A 1-MHz 250-W converter prototype with an input voltage range of 17–43 V is built and tested to verify the feasibility of the proposed converter. [ABSTRACT FROM AUTHOR]

The instantaneous output power of the two-stage single-phase grid-connected photovoltaic (PV) inverter pulsates at twice the line frequency ($2f_{{\text{o}}}$), generating second harmonic current (SHC) in the front-end dc–dc converter and PV panel, which will affect the maximum power point tracking operation and deteriorate the overall conversion efficiency. The generating mechanism of the SHC is analyzed in this paper and it is pointed that in order to eliminate the SHC in the front-end dc–dc converter and PV panel, the voltage loop gain of the front-end dc–dc converter should be high enough at $2f_{{\text{o}}}$. Since there is a −180° phase abrupt at the resonant frequency of the input side filter capacitor and the inductor, the system may be unstable. To cope with this problem, the inductor current feedback active-damping scheme (ADS) is adopted. For further improving the loop gain at $2f_{{\text{o}}}$ , proportional–integral–resonant regulator with ADS (PIR + ADS) is proposed in this paper. Besides, a step-by-step closed-loop parameters design method is presented. Finally, a 3-kW two-stage single-phase grid-connected PV inverter has been fabricated and tested, and the experimental results verify the feasibility of the proposed control schemes. [ABSTRACT FROM AUTHOR]

This paper proposes a predictive zero-voltage-switching (ZVS) control with improved ZVS time margin and limited variable switching frequency range for a 99% efficient megahertz (MHz) GaN totem-pole power-factor-correction (PFC) rectifier. The conventional ZVS control methods for totem-pole PFC may lead to zero ZVS time margin and ultra-wide switching frequency range. This paper proposes that the synchronous rectifier (SR) turn-off current is a new degree of freedom for the ZVS control. Thus, the proposed cycle-by-cycle predictive ZVS control method controls the SR turn-off currents to extend the ZVS time margin and to reduce the maximum switching frequency. With the proposed ZVS control, the minimum ZVS time margin and a limited maximum switching frequency can be realized in a MHz GaN-based totem-pole PFC. With the improved ZVS time margin, the reliability for realizing ZVS is significantly improved. With the limited maximum frequency and the limited frequency range, the difficulty in high-speed current sensing and digital control is reduced, and the frequency-related loss is also reduced, which is important for improving the light-load efficiency. To accurately extract the current and timing parameters for the proposed ZVS control, an analytical model for the ZVS totem-pole PFC is proposed. The proposed ZVS control and analytical model are applicable over the full input and output voltage range, and over the full load range. In addition, a hybrid current control is proposed and implemented based on the proposed ZVS control. Finally, a 3.2-kW MHz GaN totem-pole PFC prototype is developed and tested with full-range ZVS, minimum ZVS time margin, limited switching frequency range, 99% peak efficiency, and 130-W/in3 power density based on the proposed ZVS control and system control strategy. The realized efficiency, power level, and power density are among the best ever reported for the GaN-based totem-pole PFC. [ABSTRACT FROM AUTHOR]

This paper proposes a control method for a switching power converter. This converter is connected to a dc-link of a dc microgrid system via an LC input filter. This control method is based on a Lyapunov stability analysis; all state variables are acquired for evaluating stability analysis, including the output current for calculating the load resistance. To reduce a number of sensor counts, the input current is estimated. Moreover, loss occurrence in the converter is observed to reduce static errors of the controlled state variables, especially the output voltage. The losses are modeled as a series input voltage source observed from the dc–dc converter and a parallel current source. The latter enables us to eliminate the output current sensor. Using information from the estimated current source, a load resistance can be calculated. A Lyapunov function candidate is chosen to ensure that the system, including the observer, operates in a stable manner. Based on evaluating the time-derivative of the chosen Lyapunov function, we obtain the switching command that makes the system operate stably in each sampling cycle. In this paper, the proposed technique is applied to a boost converter. The simulation and as well experimental results validate the proposed control. [ABSTRACT FROM AUTHOR]

Impedance-based criteria are often used for assessing the stability of cascaded converter systems. In this paper, it is pointed out that the switching ripple interaction (SRI) between the source converter and the load converter in a cascaded system would change the gain of the pulsewidth modulation of the source converter, causing the cut-off frequency and the phase margin of the source converter to change accordingly. Thus, even if a cascaded system is shown to be stable under an impedance-based criterion, it can, in fact, be unstable due to the SRI. This paper proposes an adaptive modulation sample-and-hold method for eliminating the effect of the SRI. A 48 V–12 V–5 V cascaded system consisting of two buck converters is tested for verification. [ABSTRACT FROM AUTHOR]

The extraction of winding resistance from impedance measurements needs a compensation of undesirable effects, e.g., core loss and distributed winding capacitance. This paper rigorously shows that the core loss (or core-loss resistance) measured with the two-winding method always includes the effect of the winding mutual resistance. At high frequencies, this effect becomes more prominent and can cause an overestimation of the measured core-loss resistance. As a result, the compensated winding resistances can be significantly underestimated. To mitigate this effect, this paper proposes to measure the core-loss resistance on an auxiliary 1:1 transformer with single-turn windings. Consequently, it is scaled to obtain the actual core loss. The proposed analysis and method is applicable to multiwinding systems. For validation, this paper considers a gapped transformer with litz-wire winding for high-frequency operations. The experimental results are validated against the results from its three-dimensional finite-element (FE) model. The litz-wire winding is considered in the FE model by means of a homogenization approach. With the method proposed in this paper, the experimentally extracted winding resistances become more accurate and are in good agreement with the FE results. [ABSTRACT FROM AUTHOR]

This paper proposes a new single-current-sensor (SCS) control method for a permanent-magnet synchronous motor (PMSM) driven by a quasi-Z-source inverter (qZSI). In this method, the sum of two branch currents in the inverter is sampled by an SCS twice for one control period, under actions of two different shoot-through voltage vectors. Then, the three-phase currents of the motor can be reconstructed by these two sample values and can be later used for the current closed-loop control of the PMSM. In this paper, the feasibility of the SCS control method is analyzed thoroughly and a corresponding modulation strategy is given for the qZSI. Compared with the traditional SCS control methods, the new method fully eliminates the measurement dead-zone problem without any additional compensation strategy. The operation range of the PMSM extends and utilization rate of the input voltage improves. In conclusion, the proposed method is easy and convenient to implement, which makes itself a promising application in electrical vehicles. [ABSTRACT FROM AUTHOR]

System identification is fundamental in many recent state-of-the-art developments in power electronic such as modeling, parameter tracking, estimation, self-tuning and adaptive control, health monitoring, and fault detection. Therefore, this paper presents a comprehensive review of parametric, non-parametric, and dual hybrid system identification for dc–dc switch mode power converter (SMPC) applications. The paper outlines the key challenges inherent with system identification for power electronic applications; speed of estimation, computational complexity, estimation accuracy, tracking capability, and robustness to disturbances and time-varying systems. Based on the literature in the field, modern solutions to these challenges are discussed in detail. Furthermore, this paper reviews and discusses the various applications of system identification for SMPCs; including health monitoring and fault detection. [ABSTRACT FROM AUTHOR]

In a three-stage cascaded modular solid state transformer (CMSST), unbalanced dc bus voltages at the output of cascaded multilevel rectifier is a common issue due to inevitable parameter mismatch in stage-2. To balance the dc bus voltages, either voltage balance control (VBC) in stage-1 or power balance control (PBC) in stage-2 is necessary. In this paper, an in-depth theoretical analysis to investigate the input power quality of the CMSST in the presence of voltage and PBC schemes is presented. The grid-side multilevel voltage of the CMSST is analyzed to highlight the limitation of using VBC in stage-1. It is then mathematically proven that the switching frequency based harmonics in the grid current are significantly reduced by using the PBC in stage-2. Simulation studies of a 3.3-kV, 50-kVA CMSST are carried out using the PLECS software to substantiate the proposed analysis. Experimental verifications are performed on a 750-VA single-phase CMSST laboratory prototype for a 20% parameter mismatch in stage-2. It is found that the grid current total harmonic distortion (THD) is reduced from 6.65% to 3.8% at 50% load by using PBC in stage-2. This paper provides guidelines for the designer to choose appropriate balance controllers for the CMSST. [ABSTRACT FROM AUTHOR]

A high-efficiency three-dimensionally (3-D) shaped polymer multi-jet impingement cooler based on cost-efficient fabrication techniques is introduced for the cooling of high-power applications. State-of-the-art highly efficient multi-jet cooling solutions rely on expensive Si or ceramic fabrication techniques, while low-cost cooling solutions have been proposed for less performant single-jet impingement. In this paper, we present the concept, modeling, design, fabrication, experimental characterization, and benchmarking with literature data of a multi-jet impingement based liquid cooling solution, fabricated using low-cost polymer fabrication techniques, targeted to directly cool the backside of high-power devices. For the modeling study, unit cell model and full system level models are used to study the nozzle array scaling trends and thermal and fluidic jet-to-jet interactions. Furthermore, design guidelines for high-power electronics cooling are provided, including geometry selections, material selection, and fabrication techniques. Based on the design guidelines and cooling concept, this paper demonstrates a 3-D-shaped polymer impingement cooler with a 4 × 4 nozzle array, showing a very good thermal performance with low required pumping power. The multi-jet cooler can achieve heat transfer coefficients up to 6.25 × 104 W/m2·K with a pump power as low as 0.3 W. The benchmarking study confirms furthermore that multi-jet cooling is more efficient than single-jet cooling and that direct cooling on the backside of the semiconductor device is more efficient than cooling the substrate or base plate. [ABSTRACT FROM AUTHOR]

The utilization of wide bandgap devices such as silicon carbide (SiC) diode and mosfet can significantly increase the power density and the efficiency of rectifier circuits. However, SiC-based circuits always suffer from the high cost of their power stage. In this paper, a highly efficient low-cost hybrid three-phase three-level rectifier is proposed. Instead of using SiC diode and Si IGBT, it consists of SiC mosfet and Si diode. It presents extremely low switching losses because the reverse recovery losses of all the Si diodes are eliminated. At the same time, the total device cost of this rectifier is much lower than the all-SiC-based rectifiers. Furthermore, half-bridge modules can be used to comprise the rectifier circuit, which makes it suitable for high-power applications. In this paper, the circuit operational analysis, simulation, and experimental results are given. A comparison is given to show the advantages of the proposed rectifier. [ABSTRACT FROM AUTHOR]

The SiC bipolar junction transistor (BJT) offers an attractive alternative to the more popular SiC mosfet. It is important to develop an accurate SPICE model for the SiC BJT to enable its use in power electronic applications. The current gain of an SiC BJT may degrade considerably at high current levels and/or at high temperatures largely due to the surface recombination effect. In this paper, an improved SPICE behavioral model that accurately accounts for the current gain depending on the collector current and the junction temperature is proposed for the SiC BJT. In this paper, the conventional Gummel–Poon model is extended to include this important physical effect by adding a diode between the external base and emitter terminals of the BJT. A two-step model parameter extraction method is developed. First, the basic Gummel–Poon model parameters are extracted from low-current measurement data, and then, the new surface recombination model parameters are extracted by observing the difference between the measured high-level base current and the standard Gummel–Poon model prediction. The simulated static and switching characteristics of the new SiC BJT model match the measured data very well. Finally, the new SPICE model is used in the performance assessment of a proportional base driver technique embedded in a 3.6-kW boost converter, demonstrating its validity in helping with the optimum design of power electronic applications based on SiC BJTs. [ABSTRACT FROM AUTHOR]

In this paper, an enhanced fault-tolerant operation approach is developed to maintain continued operation of five-phase grid-tied current-source converters (CSCs) during one-phase supplying wire broken. First, the instantaneous power flow of this system is analyzed based on the sequence decomposition method. It is found that through proper arrangement of positive-, negative-, and pseudozero-sequence components of line current reference and compensation of filter CL current offset, the CSC system can achieve reduction of instantaneous active power fluctuation and minimization of line current magnitude at the same time. Accordingly, multiphase CSCs are able to operate with smaller dc rail current ripples and to obtain more active power transfer capability during fault tolerant operation. In addition, this paper also briefly discusses the control of multiphase systems in the case of complex grid faults with simultaneous wire broken and imbalanced grid voltage dips. It is found that an intentional constant reactive power injection can help to reduce the peak current of the five-phase grid-tied system. Furthermore, it should be noted that the proposed method is realized in a direct current modulation manner. Thus, a large number of line current acquisition devices for conventional multiphase grid-tied converters are removed. Finally, this paper also discusses the modulation method of five-phase CSC with one-phase wire broken. A modified “ampere-second balance” principle is applied to direct obtain the gating signals that can satisfy the constraints of CSCs. [ABSTRACT FROM AUTHOR]

This paper is focused on a dual-loop current control method (grid current loop and fundamental current loop) for digitally controlled LCL-type shunt active power filters (APFs). Normally, a proportional-resonant (PR) unit is used as the fundamental current controller, where the proportional part of PR unit actually serves as the proportional feedback of inverter-side current and provides a certain degree of damping for LCL resonance. However, its valid damping region is only up to one-sixth of the sampling frequency (fs/6), which leads to less robustness to the grid impedance. To address this issue, a delay-compensation control link is proposed in this paper to replace the proportional part of the PR fundamental current controller and widen the effective damping region. As a result, the system robustness is improved without adding extra sensors or introducing an extra active damping loop. Theoretical analysis proves that it can obtain a wider damping region of (0, fs/4). Moreover, a systematic controller parameter design criterion is studied. In particular, a numerical optimization algorithm is developed to optimize damping property, and a design method based on root locus plot and Bode diagram is presented to enhance harmonic compensation accuracy. Finally, experimental results implemented on a 30 kVA APF prototype have validated the feasibility of the proposed current controller and parameter design criterion. [ABSTRACT FROM AUTHOR]

This article proposes a novel bidirectional isolated dc–dc converter with high voltage gain and wide input voltage, which can be applied to bidirectional power conversion systems. The proposed topology is composed of a bidirectional buck-boost converter and a forward-flyback converter; it has the advantage of higher voltage gain and has continuous current characteristic of the low-side port in step-up and step-down mode. In addition, the proposed topology also has the function of leakage inductance energy recovery, which can improve the efficiency of the converter, reduce the voltage surges on switches, and have the characteristics of zero voltage switching on certain switches. Finally, this paper implements a 500-W bidirectional dc–dc converter to verify the feasibility of the proposed topology. The low-side voltage of the proposed topology is 24, 48, and 55 V; the maximum efficiency in step-up mode are 94.2%, 95.6% and 96.9%, and the maximum efficiency are 92.6%, 94.2% and 94.5% in the step-down mode, respectively. [ABSTRACT FROM AUTHOR]

Isolated, zero-voltage-switching dc–dc converter topologies represent attractive solutions in the continuous run toward higher switching frequencies, allowing more compact power supplies. Among them, the asymmetrical half-bridge flyback converter represents an interesting option, featuring simple duty-cycle control at constant switching frequency, as opposed to the popular LLC converter. The majority of papers dealing with this topology consider an approximated voltage gain similar to that of an isolated buck converter operating in continuous conduction mode, i.e., proportional to the duty cycle and, practically, load independent. On the contrary, the true voltage gain is nonmonotonic at high duty-cycle values. Anytime the converter is designed for a resonant operation, as is advisable to eliminate any reverse recovery problem of the rectifier diode, the voltage gain not only increases, but also becomes a function of the switching frequency. This article investigates the converter's voltage gain in detail, deriving a theoretical framework capable of capturing its real behavior and dependencies. The proposed analytical model has been verified through simulations as well as experimental measurements taken on a 160-W prototype working at 400 kHz. [ABSTRACT FROM AUTHOR]

This paper presents a power management unit (PMU) powered by a 1 mm $^{\boldsymbol{2}}$ solar cell on the same substrate to rise up the harvested voltage above 1.1 V. The on-chip solar cell and the PMU are fabricated in standard 0.18  $\mu$ m CMOS technology achieving a form factor of 1.575 mm $^{\boldsymbol{2}}$. The PMU is able to startup from a harvested power of 2.38 nW without any external kick off or control signal. The PMU features a continuous and two-dimensional maximum power point tracking (MPPT) working in open-loop mode to handle a harvested power range from nW to $\mu$ W, by modifying both the charge pump topology and the switching frequency. The MPPT is based on four voltage level detectors that define five working regions depending on the illumination and on a self-tuning reference current for a fine adjustment of the switching frequency. The chip also includes an auxiliary charge pump to generate the voltage level necessary for the control circuit, implemented as a Pelliconi charge pump of eight stages with NMOS transistors in P-well as diodes. A Dickson charge pump with transmission gates as switches and with variable gain and capacitance per stage is also designed as the main charge pump. Finally, two relaxation oscillators are implemented to drive both charge pumps. This paper is accompanied by a video file demonstrating the PMU operation by powering an off-chip nor gate. [ABSTRACT FROM AUTHOR]

This paper presents the design of a multi-MHz inductive power transfer (IPT) system showcasing lightweight and energy-efficient solutions for non-radiative wireless power transfer. A proof of concept is developed by powering a drone without a battery that can hover freely in proximity to an IPT transmitter. The most challenging aspect, addressed here for the first time, is the complete system-level design to efficiently provide uninterrupted power flow while allowing for variable power demand and highly variable coupling factor. The proposed solution includes the design of lightweight air-core coils that can achieve sufficient coupling without degrading the aerodynamics of the drone, and the design of newly developed resonant power converters at both ends of the system. At the transmitting-end, a load-independent Class EF inverter, which can drive a transmitting-coil with constant current amplitude and achieves zero-voltage switching for the entire range of operation, was developed; and at the receiving-end, a hybrid Class E rectifier, which allows tuning for large changes in coupling and power demand, was used. For the demo, the range of motion of the drone was limited by a 7.5 cm nylon string tether, connected between the center of the transmitting-coil and the bottom of the drone. The design of the IPT system, including all the power conversion stages and the IPT link, is explained in detail. The results on performance and specific practical considerations required for the physical implementation are provided. An average end-to-end efficiency of 60% was achieved for a coupling range of 23%–5.8%. Relevant simulations concerning human exposure to electromagnetic fields are also included to assure that the demo is safe, according to the relevant guidelines. This paper is accompanied by a video featuring the proposed IPT system [ABSTRACT FROM AUTHOR]

This paper presents a novel loss minimization based nonlinear controller for interior permanent magnet synchronous motor (IPMSM) drive to achieve both high efficiency and high dynamic performance. Traditionally, the dynamic performance of the drive is often ignored for any loss minimization controller or, loss minimization is ignored for robust controller. Therefore, in this paper, a loss model based controller is integrated to an adaptive backstepping based nonlinear controller in the design stage. In order to cope with parameter uncertainties, some motor parameters are also estimated online for the proposed loss model based nonlinear controller (LMNC). Moreover, stability of the proposed drive is demonstrated through Lyapunov's stability criterion and global asymptotic stability is assured through the application of Barbalat's lemma. The proposed LMNC-based IPMSM drive is implemented using a digital signal processor board DS1104 for a laboratory 5-hp motor. The performance of the proposed control scheme is investigated in both simulation and experiment at different load and speed conditions. The performance of the proposed LMNC is also compared with the conventional PI as well as nonlinear controller without any loss minimization. It is found that the proposed LMNC is superior to the conventional benchmark PI controller or nonlinear controller. [ABSTRACT FROM AUTHOR]

The six-phase asymmetrical induction motors (SPIMs) are employed for high power medium voltage drive due to its attractive features of reduced stator copper loss, lower torque pulsation, higher torque per ampere, and higher reliability. In this paper, analysis of carrier-comparison-based pulse width modulation (PWM) techniques namely sinusoidal PWM and double zero-sequence injection PWM are carried out from a space vector perspective. Furthermore, new space vector pulsewidth modulation (SVPWM) techniques are developed by modifying the switching sequences of carrier-based PWM techniques. A comprehensive analysis of these PWM techniques is carried out in terms of harmonic flux trajectories, squared harmonic flux, and harmonic distortion factor (HDF). As a result, modified SVPWM technique namely 6ΦSVM3 is found superior to aforesaid PWM techniques, which significantly reduces HDF and provides lower current total harmonic distortion (THD). The experimental results of aforementioned PWM techniques are obtained and verified from six phase asymmetrical induction motor fed by dual two-level 3ΦVSIs. This paper is also accompanied by a video file of experimental test setup recorded while 6ΦSVM2 is running on SPIM. [ABSTRACT FROM AUTHOR]

This paper studies the driving of white light emitting diodes (LEDs) from very low voltages in the 1.2 to 2 V range. The proposed idea is based on replacing the standard Schottky diode used in conventional converter topologies (i.e., buck, buck–boost, and boost) with an LED while shortcutting the output of the converter. In this configuration, the LED works both as the load and the rectifier diode of the converter, hence switching the LED at high frequencies (>100 kHz). Moreover, a thorough analytical study is carried out for the two topologies proposed in this paper, emphasizing in particular their static analysis and the obtaining of the boundaries between the different conduction modes. Finally, the idea is experimentally validated by means of the boost converter variation (i.e., the DL//S ac-LED driver). The DL//S ac-LED driver was also compared with a dc–dc boost converter, showing a better luminous efficacy while disposing of the Schottky diode and the output capacitor. The analysis was carried out when connected to a Li-ion battery using a simple control and integrated circuit for its development. [ABSTRACT FROM AUTHOR]

This paper proposes a novel method to determine and control active and reactive power output of the virtual ocillator control-based inverter in grid-connected mode. An analytical expression is introduced to describe the quasi-steady-state relationship between the parameters of the inverter including its controllers, and the power injection and voltage at the inverter terminals. We introduce a new, complex valued parameter (K) to the conventional virtual oscillator control (VOC) scheme in order to control the inverter output power. We compare analytic and numeric solutions of the above analytical expression with time-domain simulation results, using different K values and line impedances to validate the analytical expression. In the second part of the paper, we design a controller: we use the above expression to derive K for given reference powers and use adaptive integrators to compensate for the remaining errors. We compare this control scheme to a method that uses PI controllers, and also to a simple decoupling method for independent control of active and reactive power. The controller based on the analytical method exhibits very good dynamic and decoupling performance. A single VOC-controlled inverter connected to a nonstiff grid is simulated in MATLAB/Simulink for demonstration, and is also validated using real-time simulations. [ABSTRACT FROM AUTHOR]

In this paper, a generalized droop control (GDC) is proposed for a grid-supporting inverter based on a comparison between traditional droop control and virtual synchronous generator (VSG) control. Both the traditional droop control and VSG control have their own advantages, but neither traditional droop control nor VSG control can meet the demand for different dynamic characteristics in grid-connected (GC) and stand-alone (SA) modes at the same time. Rather than using a proportional controller with a low-pass filter, as in a traditional droop control, or fully mimicking the conventional synchronous generator parameters in a VSG control, the active power control loop of the GDC can be designed flexibly to adapt to different requirements. With a well-designed controller, the GDC can achieve satisfactory control performance; unlike a traditional droop control, it can provide virtual inertia and damping properties in SA mode; unlike a VSG control, the output active power of an inverter with GDC can follow changing references quickly and accurately, without large overshoot or oscillation in the GC mode. Moreover, given specific controller parameters, the GDC can function as both a traditional droop control and a VSG control. The GDC's controller parameter design is more intuitive and flexible, and this paper provides a distinct design process. Finally, the effectiveness of the proposed control method is validated by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

Phase-to-neutral voltage or neutral-to-virtual neutral voltage zero-crossing points (ZCPs) detection method is usually used for sensorless brushless dc motor commutation control. Unfortunately, neither of them can be realized in lower speed range. In this paper, a simple commutation point detection method is proposed based on detecting inactive phase terminal to dc-link midpoint voltage. It eliminates the requirement of neutral wire or virtual neutral voltage and provides an amplified version of back electromotive force at the ZCPs which makes the lower speed range detection possible. As the speed increases, commutation point error is enlarged due to the low-pass filter. Utilizing the symmetry of the terminal to midpoint voltage, the phase error can be corrected. However, due to the nonlinear relationship between the detected voltage difference and phase error, it is difficult to regulate the error fast and robustly. Therefore, a novel phase regulator based on fuzzy neural network is proposed in this paper with simple structure and learning ability. The validity of the proposed ZCPs detection method and commutation instant shift correction method are verified through experimental results. [ABSTRACT FROM AUTHOR]

This paper introduces a primary pad for wireless charging applications, which is able to transfer high power over large air gaps and is tolerant to lateral displacements suitable for electric vehicle charging applications. The developed pad is an improved solenoid designed specifically to address issues such as flux leakage and loss while retaining good coupling. It is a hybrid structure that consists of a combination of rectangular- or square-shaped coils and a central solenoid, all connected in series. When energized, it produces a single-sided, polarized flux similar to the flux pattern of the solenoid and double D (DDP) pads. The power transfer capability of this pad is investigated through finite-element analysis simulations. The results are compared first to a similar sized solenoid from which it was derived, and also a DDP primary pad and are verified through measurements on prototype systems in the laboratory. The aim of this paper is to provide an improved hybrid solenoid pad showing higher coupling factors and lower stray field emissions with a performance (coupling and stray field emissions) similar to that of DDPs. [ABSTRACT FROM AUTHOR]

Due to inherent high reliability and low maintenance cost, the brushless doubly fed induction generator (BDFIG) has become a promising candidate in offshore wind energy generation systems and dc/ac/hybrid microgrids. This paper proposes a novel BDFIG based system targeting at dc power generation (BDFIG-DC), which features interfacing the power winding (PW) and the dc grid through an uncontrolled rectifier and common dc link. Compared to conventional BDFIG systems fed by ac grid, the BDFIG-DC system offers an alternative to integrate the BDFIG into the dc transmission system with a simpler structure and lower cost. Due to the constraint imposed by the dc-side diode bridge, torque ripple reduction emerges as an urgent issue as a result of the distorted flux and current. To achieve the smooth dc-connected operation of the BDFIG, an improved vector control strategy is proposed in this paper, where the control of the system is divided into three parts: torque ripple reduction, frequency regulation, and average torque control. Based on the investigations into the electromagnetic torque reduction and small-signal model of the PW flux linkage, average torque and PW frequency are successfully controlled with torque ripple effectively suppressed. The effectiveness of the proposed system, along with the associated control strategy, is validated by the experimental results of a 10-kW 2/1 dual-stator BDFIG (DS-BDFIG) prototype. [ABSTRACT FROM AUTHOR]

Synchronverters have gained interest due to their capability of emulating synchronous machines, offering self-synchronization to the grid. Despite the simplicity of the control structure, the adoption of an LCL filter makes the overall model complex again, posing questions regarding the tuning of the synchronverter and its robustness. The multi-inputs multi-outputs (MIMO) formulation of the problem requires multivariable analysis. In this paper, the effects of control parameter and grid conditions on the stability of the system are investigated by means of structured singular values (or $\mu$ -analysis). A step-by-step design procedure for the control is introduced based on a linearized small-signal model of the system. Then, the design repercussions on the stability performance are evaluated through the performed robustness analysis. The developed linearized model is validated against time-domain simulations and laboratory experiments. These have been carried out using a power hardware-in-the-loop test bench, which allows as to test the synchronverter under different grid conditions. As a conclusion, this paper offers a simple guide to tune synchronverters but also a theoretical solid framework to assess the robustness of the adopted design. [ABSTRACT FROM AUTHOR]

This paper presents the design and control of an advanced unidirectional dc–dc modular multilevel converter (MMC), which enables the integration of off-shore windfarms with the high-voltage direct current (HVdc) transmission system. The proposed converter consists of a single-phase MMC inverter, coupled with series-connected rectifier modules through a medium frequency transformer of multiple secondary windings. The modularity feature of the proposed converter enables scalability for different voltage levels. In addition to the galvanic isolation, the transformer also provides stepping gain to the output voltage. The proposed converter shows superior performance in terms of efficiency, losses, and devices utilization, when compared with the most competitive unidirectional cascaded dc–dc converters such as input series output series and input parallel output series. Furthermore, unlike the conventional d-q control method, which involves multiple transformations, this paper employs a simple proportional resonant control strategy that directly acts on the ac output of the MMC, under the stationary reference frame. The analytical design along with the simulation and experimentally validated results, confirmed the excellent performance of the proposed converter. [ABSTRACT FROM AUTHOR]

This paper presents a method to enhance the dc-bus voltage-control loop of a single-phase grid-connected dc/ac converter, which improves its responses in terms of oscillation on its dc-bus voltage as well as its output ac current. Conventionally, the double-frequency (2-f) ripple is reduced by using a large electrolyte capacitor, which increases the cost and size of the system. A state-of-the-art approach is to use a notch filter (NF) to block the 2-f ripple in the voltage-control loop. This can significantly reduce the capacitor size. The existing presentations of this method, however, do not integrate the internal dynamics of the NF into consideration. This paper proposes a new way of implementing the NF, which allows integration of its internal variables into the control loop. The resulted system exhibits enhanced transient responses at both the dc-bus voltage and the output ac current. The proposed method is analyzed in detail and its effectiveness is verified through simulations and experimental results. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) devices are capable of high switching speeds and also enable high switching frequency in power electronic converters. However, this feature poses substantial challenges to packaging, especially limiting the loop inductance. The traditional wire-bonding packaged power module has large parasitic inductance, which will cause voltage overshoot, oscillation, parasitic turn-on, and EMI issues. In order to reduce the parasitic inductance, this paper proposes a flexible printed circuit board (FPCB) based full SiC half-bridge power module with a novel low inductive hybrid packaging structure and three-dimensional (3-D) integration method. This hybrid packaging structure has an ultrathin FPCB substrate stacked on a direct bonding copper (DBC) substrate, which forms a multilayer 3-D power loop. The SiC chips are soldered on the DBC substrate for good thermal dissipation through a cavity in the FPCB substrate. After power loop optimization, the power loop inductance of a 1200-V/120-A SiC power module is only 0.79 nH. The power module consists of three submodules, which are connected by the bendable FPCB substrate. The bendable power module enables maximum utilization of 3-D space. The gate drive, decoupling capacitors, and dc-link capacitors are also integrated and 3D-structured using rigid-flexible PCBs. Moreover, the cooling system is a high-efficiency three-sided cooling structure for the bendable power module. The simulation results show that the three-sided cooling structure reduces the heatsink volume by 50%. Applying this method, the converter can be designed as a system-in-package and a 3D-structured compact system. The power density of a 20-kW three-phase inverter will reach 19.3 kW/L based on this power module. In this paper, the 1200-V/120-A power module fabrication and assembly processes are given. Finally, the static and dynamic experimental comparisons are done for a commercial power module and the proposed power module. The experiment results show that the voltage overshoot of the proposed module reduces about 5.8 times and are consistent with the simulation results. Meanwhile, the proposed power module switching speed is 1.8 times faster than the commercial module under zero external gate resistors and the switching loss can reduce by about 60%. [ABSTRACT FROM AUTHOR]

A non-segmented PSpice model of silicon carbide metal-oxide semiconductor field effect transistor (SiC mosfet) with temperature-dependent parameters is proposed in this paper, which can improve the model's convergence and temperature characteristics. The non-segmented equations and the parameter-extraction method for the proposed SiC mosfet PSpice model are introduced first. Simulation and experiment results are given to verify the correctness of the model while considering the temperature-dependent parameters. The static characteristics of the model are verified by comparing the simulation curves with the static characteristic curves in the SiC mosfet's datasheet, and its dynamic characteristics are verified by comparing the simulation results with experimental results under different ambient temperatures (25, 75, and 125 °C) based on a double-pulse test platform. Moreover, the proposed non-segmented model, the conventional segmented model, and the model from the manufacturer are adopted and simulated in a full-bridge inverter. The simulation results show better convergence of the proposed non-segmented model. Therefore, an accurate and practical simulation model of SiC mosfet is provided for circuit design in this paper. [ABSTRACT FROM AUTHOR]

Flux-linkage based sensorless control method is well-known and has been widely used in the control of electrical machines. The closed-loop flux observer (CLFO), which is the adaptive combination of the machine voltage and current models, is commonly adopted. It can cover a wide speed operation range and was considered to be able to solve the dc drift and initial value problem associated to the pure integrator used in the observer. However, it is reported in this paper that this popular CLFO cannot always work as expected. In some situations, dc-offsets cannot be removed by this flux observer, causing large system oscillation at fundamental frequency and is very harmful to the drive system. This important issue has not been reported and discussed in the existing literatures of the CLFO. In this paper, this phenomenon is experimentally illustrated and solution to damp this harmful oscillation is proposed and verified experimentally on a synchronous reluctance machine drive system. [ABSTRACT FROM AUTHOR]

One promising topology for solid state transformer (SST) is a modular multilevel cascaded converter, in which submodule is composed of dual active bridge (DAB) and H-bridge. For SST application in PV system, the efficiency could be severely affected especially for DAB due to the wide voltage and power range of PV panels. Thus, the motivation of this paper is to deal with the control strategy to improve DAB efficiency inside SST for PV application. Instead of utilizing time-domain based analysis method, which requires complex modeling process, this paper models DAB under frequency domain by fully considering the effect of both fundamental and harmonic frequency component. To achieve high efficiency operation, a multiorder reactive-current suppression (MRS) strategy is proposed by controlling phase shift angle as well as the duty cycles of primary and secondary side H-bridges. In terms of DAB controller design inside SST, the small signal model under MRS is established and a notch filter is implemented to suppress the second order line frequency fluctuation in the control loop. Finally, a 10 kV/1 MW SST prototype is introduced along with the system control structure and implementation method. The experiment of the submodule and SST confirms the effectiveness of proposed method. [ABSTRACT FROM AUTHOR]

Inductor current is an important feedback parameter in synchronous buck converters (SBCs). It is used for overcurrent protection, current sharing among interleaved modules, and current-mode feedback regulation, among others. While implementing a digital controller, inductor current is sensed and fed into the controller through a high sampling frequency analog to digital converter (ADC). As the switching frequency of the converter becomes higher, the need for an even higher sampling frequency ADC also goes up, which is a distinct disadvantage in terms of the overall cost. This paper discusses a simple current estimation technique that avoids use of any expensive current sensor and high sampling frequency ADCs. The paper shows that in a buck converter, inductor current can be estimated by tracking the width of the switch node voltage. Implementation and limitations of the proposed current estimation scheme are discussed in detail. The proposed method is validated using a 3.3 V–15 A SBC prototype and results show the estimation technique is accurate within 5% with a converter switching frequency of 800 kHz. In order to prove the effectiveness of the technique in feedback regulation, the current estimation technique is used to implement average current mode and hysteretic current mode control on a SBC. To prove the effectiveness of the proposed current estimation scheme, it is used in closed-loop control of the SBC to verify the dynamic responses, such as start-up transient, step change in load, and reference. [ABSTRACT FROM AUTHOR]

This paper presents two high-voltage direct-current circuit breakers that have the capability of interrupting a short-circuit current within several milliseconds. They consist of a current-limit inductor, a current-control inductor, one or two mechanical switches, and a multilevel converter with phase-shifted-carrier pulsewidth modulation. The two breakers can commutate an almost zero current from the main branch to the auxiliary branch. This paper proposes an original breaker with low-voltage and high-voltage mechanical switches connected in series, followed by a simplified breaker with a single high-voltage mechanical switch. Finally, this paper includes experimental verification by two slightly different downscaled breakers rated at 300 Vdc and 150 Adc, as well as confirmation of an actual original breaker by circuit simulation using the “PSCAD/EMTDC” software package. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) are solid-state devices with specific $v$ – $i$ characteristics. In this paper, we study the basic requirement of the driving circuits and discuss the proper approach to drive LEDs in view of their characteristics. We compare voltage source driving and current source driving, and discuss their relative advantages and constraints. We specifically introduce the use of circuit duality principle for developing new current-source-mode (CSM) drivers that are less known but are theoretically more versatile compared to their conventional voltage-source-mode counterparts. The study highlights the effects of the choice of driving circuits in terms of the number and size of circuit components used, duty cycle variation, sensitivity of control, nonlinearity and control complexity of LED drivers. We propose a CSM single-inductor multiple-output (SIMO) converter, which demonstrates the advantage of having inductorless and easily controlled current-source drivers, and present a comparison of the CSM SIMO converter with the existing SIMO converters. We further illustrate that a high-voltage-step-down ratio can be naturally achieved by the CSM high-voltage-step-down converter without the use of transformers. This paper presents a systematic and comparative exposition of the circuit theory of driving LEDs, with experimental evidence supporting the major conclusions. [ABSTRACT FROM AUTHOR]