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In recent years, very high frequency (VHF) converter has attracted much attention. However, with rich parasitic parameters and complex resonance links, there are some great difficulties to the modeling of such systems. Taking the on-off controlled VHF resonant boost converter as an example, this paper presents an accurate modeling and analysis method that considers multiple parasitic parameters. First, the closed-loop VHF converter system is divided into a main network and a parasitic oscillation network. Then, based on the operation analysis, an equivalent circuit model characterized by a time-varying input voltage source and two variable duty-cycle controlled switches is proposed. It worth noting that both the time-varying input and the controlled switches take into account the influences of the parameters. Furthermore, the periodic approximate analytical solution of the output voltage in the on stage is obtained by using the equivalent small parameter method to the proposed circuit model. And then combining the solution of the parasitic oscillation network and on-off state switching conditions, the steady-state waveform of output voltage can be obtained quickly. Finally, a prototype with operating frequency of 21.44 MHz is built to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This article develops a series of improved Z-source dc–dc converters to realize additional voltage pumping and high power density through two propositions. Proposition 1 develops two improved positive- and negative-connected Z-source dc–dc converters (IPZSC and INZSC), using the same number of components as in the existing voltage pumping Z-source converter. Based on Proposition 1, Proposition 2 proposes four novel embedded Z-source dc–dc converters (EZSCs) by placing the source in a specifically designed position, which realizes lower voltage stresses across capacitors. Various technical aspects of the proposed EZSCs, including operations, power losses, and small signal stability analyses are detailed in this paper. Besides, comparisons between the proposed series of improved Z-source dc–dc converters and other existing Z-source dc–dc converters are thoroughly made to demonstrate the better performance of the EZSCs. Finally, experiments are conducted to well validate the effectiveness and superiority of the proposed converter circuits. [ABSTRACT FROM AUTHOR]

Parallel dc–dc converters are commonplace in applications such as computing power supplies, point of load systems, and dc microgrids. The presence of multiple converters in such systems allows for switch interleaving and ripple cancellation. One class of existing ripple reduction methods depends on central controllers that require communication among the converters. These approaches compromise system scalability and reliability. When it comes to decentralized methods, the state-of-the-art is limited to uniform conditions and cannot handle mismatches in physical parameters and operating points among converters. In this article, we address these shortcomings with fully decentralized controller that robustly drives the pulsewidth modulation carriers of a collection of heterogeneous converters to the phase-shifts that give minimized ripple. More precisely, the proposed controller eliminates the dominant fundamental switching harmonic from the output current and voltage using only local voltage feedback. After outlining a comprehensive analytical model, we experimentally validate our approach on a system of five parallel-connected buck converters under a variety of parametric and operational mismatches. Measurements show ripple reduction of more than $4\times$ in the output voltage and the fundamental switching frequency harmonic is attenuated by more than 30 dB compared to conventional symmetric interleaving. [ABSTRACT FROM AUTHOR]

In this article, a novel method is proposed to reduce the dc-link capacitance of the brushless dc motor (BLDCM) system. In the proposed strategy, the charging mode of dc-link capacitor is designed to improve the energy stored by dc-link capacitor in the charging process instead of reducing the discharge time of dc-link capacitor used in previous article. The new modulation strategy and controller is designed to pump the dc-link capacitor voltage and ensure that it exceeds the ac voltage peak. The proposed modulation strategy has three vectors. The charging vector is used to improve the dc-link capacitor voltage, and the effective vector and zero vector are used to adjust the motor speed. For practical application, we provide an engineering calculation method to get the dc-link capacitance, and prove that the dc-link voltage can exceed the average voltage of the BLDCM. The experimental results verify the correctness of the theoretical analysis and the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

The current-fed isolated dc/dc converters are suitable solutions for applications requiring low high-frequency current ripple and convenient current control, such as fuel cells and Li-ion batteries. The existing current-fed isolated dc/dc converters are combined with a current-fed bridge-type terminal and a voltage-fed bridge-type terminal, which can only partially obtain the merits of the current-fed terminals. In this article, a dual-current-fed dual-active-bridge dc/dc converter is proposed with the inductor connection on both terminals. Hence, low high-frequency current ripple and convenient current control can be realized on both sides. Besides, it can also realize the voltage spike suppression without snubber circuits and has the inherent soft-switching operation and voltage boost function. Then, the operation principle, design process, and loss analysis of the proposed converter are presented in detail. The experimental results based on a proof-of-concept laboratory prototype are given to verify the steady-state and dynamic performance of the proposed converter. [ABSTRACT FROM AUTHOR]

In this article, a high efficiency and high power density Regulated dc Transformer (RDCX) is proposed for on-board charger (OBC). In this circuit, high input and output voltages are undertaken by series connected low-voltage devices. Owing to the low new figure of merit (NFoM, Rdson×Coss)(Il-Jung et al., 1995), (Wu and Shi, 2020) characteristic of low-voltage devices, the conduction loss of switches can be reduced. Mathematical modeling and verification are also carried out. In addition, by applying cascaded buck as the regulation part of RDCX, the volt-second of buck inductor can be reduced compared with the traditional two-level buck circuit. As a result, the size of the inductor can be reduced. Furthermore, since all dc buses of the cascaded buck converter are from the rectifiers whose windings are coupled to the same transformer, those bus voltages can be naturally balanced. A 2.3 kW prototype based on 60V device with 388–412 V input and 250–450 V output voltage range is built up to verify the analysis, achieving 98% peak efficiency and 910 W/in3 power density. [ABSTRACT FROM AUTHOR]

The dual-active-bridge (DAB) is a typical topology of dc–dc converter for bus connection, voltage conversion, power transmission, and electrical isolation in dc power grids. The open-circuit switching fault (OCSF) may threaten the safe operation of DAB and should be eliminated in time. However, the researches on parasitic parameters mainly focus on traditional dc–dc converters, and there are still few discussions on parasitic parameters in the high-frequency dc–dc converter such as DAB. The power components are usually considered without parasitic parameters in OCSF analysis and tolerant control, leading to deviations in modality analysis and practical control for DAB. To solve this issue, the modality analysis considering parasitic parameters during OCSF in DAB is investigated, and the sneak circuits and electrical characteristics with parasitic parameters are discussed in this article. Besides, to realize fault tolerance for DAB during OCSF considering parasitic parameters, a new fault tolerance control strategy including modeling, topology transformation principle, and practical control architecture are also proposed. Compared with conventional fault tolerance strategy, the proposed strategy will be more efficient, rapid and feasible for DAB during OCSF process. The experimental results in DAB prototype verify correctness and effectiveness of analysis and proposed strategy. [ABSTRACT FROM AUTHOR]

Dickson-type dc–dc converters have gained renewed interest in recent years due to their best-in-class volt-amp switch utilization. In addition, “hybrid” switched-capacitor (HSC) structures increase passive component utilization while avoiding the slow-switching limit (SSL), and yet, most HSC work to date has done little to assess large signal voltage ripple behavior and subsequent passive utilization limits. This work contributes a comprehensive review of contemporary Dickson-type HSC converters before introducing eight fundamental reduced HSC Dickson structures, including three that are proposed here. Analysis allowing characterization of large signal operating points, capacitor sizing regimes, switching schemes, and maximum allowable power throughput is introduced. The analysis for “split-phase” switching is also presented in detail, without making small ripple approximations. Furthermore, an expression for large ripple flying capacitor energy density utilization is derived, assisting with optimal topology selection and revealing that split-phase operation may be preferable for conversion ratios greater than 6:1. All analysis is verified in simulation, with an additional discrete hardware prototype further validating a complex case of resonant split-phase timing. The analytical results of 17 distinct Dickson variations are recorded, assisting with topology selection and design. [ABSTRACT FROM AUTHOR]

In this article, we proposed a bidirectional dual active bridge (DAB) converter adopting a boost-up function. The proposed converter can be implemented by adding only one capacitor to the high voltage side without additional active components. By utilizing the boost-up function, the proposed converter can achieve higher output power than the conventional DAB converter under the same leakage inductance condition. In comparison with the resonant converter in addressing the output power limitation, the proposed converter can reduce the switching and conduction losses due to the low turn-off and circulating currents, and complex control is not required to drive the synchronous rectifier. Furthermore, the direction of the output power can be easily changed with a simple control circuit. Experimental results from the proposed converter with a 3 kW rated power, 28-V low-side voltage, and 600-V high-side voltage are demonstrated to verify the proposed works. [ABSTRACT FROM AUTHOR]

Multisource switched-capacitor multilevel inverters are proper topologies when multiple dc sources are available as renewable energy sources. However, these multilevel inverters have the main drawbacks of requiring a large number of power semiconductors and capacitors and a low boost factor to achieve a large number of voltage levels, which complicate control, reduce performance, and raise the cost. This article presents two configurations for multisource switched-capacitor multilevel inverters. First, a basic multisource switched-capacitor topology is proposed with a small number of capacitors and semiconductors that produce a zero voltage level and a large number of positive voltage levels. The input dc sources are operated in an asymmetric trinary algorithm, while the capacitors are charged/discharged in a binary algorithm using parallel/series modes (without the need for any circuit balancing). Based on the proposed basic topology, two multilevel inverter topologies are proposed, which create bipolar output voltage levels using two different circuits at the output. The first proposed topology uses a standard H-bridge inverter at the output of the basic topology, while the second topology uses an extra switched-capacitor (self-balancing) circuit. The comparison indicates that both the proposed topologies have advantages over most of the reported multisource switched-capacitor multilevel inverters, such as a small number of capacitors, a small number of power semiconductors, low voltage stress, and high boost factor. Furthermore, the proposed topologies decrease the low cost factor in comparison to other topologies. The capacitors' capacitance, power losses, and voltage ripple losses are all measured and evaluated in detail. Theoretical research is validated with the use of laboratory prototypes to validate the performance of the proposed topologies. [ABSTRACT FROM AUTHOR]

This article proposes a control and modulation strategy for medium-voltage (MV) drives that exhibits excellent steady-state and transient behavior. Specifically, optimized pulse patterns (OPPs) and direct model predictive control are employed so that the associated advantages of both, such as minimum stator current total demand distortion (TDD) and fast transients, respectively, are fully exploited. To do so, the current reference trajectory tracking and modulation problems are addressed in a coordinated manner in the form of a constrained optimization problem that utilizes the knowledge of the stator current evolution—as described by its gradient—within the prediction horizon. Solving this problem yields the optimal real-time modification of the offline-computed OPP, which guarantees that very low—and close to its theoretical minimum value—stator current TDD is produced at steady state, and very short settling times during transients. To highlight the effectiveness of the proposed strategy, a variable speed drive system consisting of a three-level neutral point clamped inverter and an MV induction machine serves as a case study. [ABSTRACT FROM AUTHOR]

In this article, the performance of gradient-based predictive pulse pattern control (GP $^{3}$ C) is evaluated for a medium-voltage variable-speed drive consisting of a three-level neutral-point-clamped (NPC) inverter and a medium-voltage induction machine. To this end, real-time tests are performed in a hardware-in-the-loop (HIL) environment, which, along with extensive simulation studies, elucidate the potential of performance gains achieved with GP $^{3}$ C. As shown, by manipulating offline-computed optimized pulse patterns (OPPs) in real time such that the stator current of the machine follows a precalculated optimal current trajectory, superior steady-state and transient performance can be achieved. Specifically, the current total demand distortion (TDD) is significantly reduced compared with established control methods, such as field-oriented control (FOC) with space vector modulation (SVM), while shorter settling times during transients are achieved. Finally, to complete the assessment of the control method of interest, real-time implementation aspects are discussed in detail. [ABSTRACT FROM AUTHOR]

Interfacing low voltage dc to medium voltage three-phase ac grid is often based on series-stackable modular converter architectures. To minimize energy storage requirements, it is advantageous to employ a quadruple active bridge (QAB) stage operating as a “dc transformer” in each stackable module. The QAB stage offers three isolated dc link voltages, which then allow for flexible stacking of three single-phase dc-to-ac inverter stages. Each of the module phases processes a pulsating power having a component at twice the line frequency. This presents a challenge in maintaining zero voltage switching (ZVS) on the secondary sides of the QAB during low-power portions of the line cycle. This article is focused on the design of the QAB stage. A detailed analysis of ZVS switching waveforms is presented, including effects of nonlinear device capacitances. It is shown how ZVS can be achieved at all times using a relatively small circulating current provided by the magnetizing inductance of the high-frequency transformer. Analytical expressions are given for the optimal values of the magnetizing inductance and the dead times of the QAB primary and secondary bridges. The approach is verified by experimental results on a 1 kV, 10-kW SiC-based prototype, demonstrating a relatively flat efficiency curve with a peak efficiency of 97.1% at 75% load. [ABSTRACT FROM AUTHOR]

A novel modulation scheme for a bidirectional isolated pulsewidth modulation active-clamp (PAC)-Ćuk converter is presented in this article. In the PAC-Ćuk converter, the clamping circuit consisting of a capacitor, a series inductor, and an active device enables zero-voltage-switching (ZVS) turn-on capability of all the active devices. This additional circuit equips the converter with three independent control parameters. This article discusses power transfer, ZVS region, and circulating current dependency on the control parameters across the converter gain. Minimal circulating current is generally desired to decrease the conduction losses. With the help of the proposed modulation technique, the optimization of the control parameters to achieve lower circulating current while ensuring ZVS operation is also discussed. A 2-kW experimental converter is also designed and fabricated to validate the analysis. [ABSTRACT FROM AUTHOR]

This article proposes a novel 5-D switching-table-based direct torque control (5D-DTC) strategy for asymmetrical six-phase induction machines (6PIMs). As is well-known, classical DTC of 6PIM is penalized by significant stator current harmonics, which are mapped into the nonenergy subspace ($x-y$ subspace). The concept of virtual voltage vectors (VVs) has been frequently perceived as able to tackle the problem of $x-y$ currents. Such a concept maintains zero average volt-second in the $x-y$ subspace, which in turn suppresses current harmonics due to discrete pulsewidth modulation implementation to a great extent compared to the classical DTC. However, it still cannot effectively compensate for $x-y$ currents, mainly arising from dead band effect and machine/converter asymmetry, due to lack of dedicated regulators for $x-y$ currents. Indeed, the $x-y$ currents can be fully suppressed only in the presence of active control over them. This article incorporates additional hysteresis regulators of $x-y$ currents into the direct torque control strategy. In the proposed 5D-DTC scheme, there are in total five indexes for optimal selection of VVs as torque, stator flux, $x-y$ currents, and stator flux position indexes. In this way, a clustering method is developed for synthesizing VVs to cover all possible cases of the switching table. A beneficial feature in comparison with 3-D switching-table-based DTC is effective suppression of $x-y$ currents with a rather simple structure, without increasing the switching frequency, and without decreasing dc-link utilization. Experimental results confirm the effectiveness of the proposed technique. [ABSTRACT FROM AUTHOR]

Modular multilevel converter (MMC) faces challenges ofcost and footprint in medium and high voltage grid applications. By adding a three-phase switching bridge on the basis of MMC, this article proposes a three-phase multiplexing arm modular multilevel converter (TPMA-MMC) with high power density and small volume. The multiplexing principle for TPMA-MMC is investigated, showing the multiplexing arm can be multiplexed for one-third fundamental period. After that, the subsection modulation scheme is further proposed for energy balance purpose. Compared with MMC, the number of submodules (SMs) and power devices are reduced by 22.8% and 13.83%, respectively, resulting in lower construction cost. Meanwhile, the SMs’ capacitance and the total capacitor energy storage of TPMA-MMC reduce greatly with the subsection modulation, which can greatly reduce the footprint and improve the power density. Moreover, the proposed TPMA-MMC outperforms the MMC in terms of efficiency. Finally, the topology and proposed modulation scheme are verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

This article presents dynamic voltage-domain stacking, which incorporates the attractive efficiency benefits of voltage-domain stacking into a wide-input-range conversion system. This is achieved by combining two novel switched-capacitor converter topologies with an integrated finite-state machine into a highly reconfigurable system. First, a zooming gearbox converter efficiently enables a wide input range while only implementing three conversion ratios. Second, a reconfigurable ladder converter continuously compensates for imbalance between the dynamically stacked voltage domains. A prototype has been fabricated in a 40-nm baseline CMOS technology to provide a stable supply voltage to four loads across an input voltage range from 4 V down to 0.55 V. Measurements show a best-in-class average efficiency of 80.1% and a peak efficiency of 92.1%. [ABSTRACT FROM AUTHOR]

In this article, a new inverter unit is proposed. It is a compact switched-capacitor-based inverter, which is combined of four switches, two diodes, and four capacitors. Since this inverter unit is a mid-point-clamped inverter, it can mitigate the capacitive leakage current in many applications. One of the main applications of the proposed inverter is in grid-tied photovoltaic systems, where the common-mode current brings many challenges. Other than the mentioned feature, the proposed inverter includes the following advantages: 1) spontaneous balancing of the voltage across the capacitors without needing any control system or auxiliary circuits; 2) capability of full reactive power transfer; 3) low voltage stress on the capacitors compared to common three-level inverter topologies (NPC, T-type-NPC, FC, etc.); and 4) symmetric switching sequence, which causes a continuous input current. The feasibility and versatility of the proposed inverter unit is validated by experimental tests, which are conducted by using a lab-scale prototype. [ABSTRACT FROM AUTHOR]

This article introduces the measurement and analysis of the transient electric field (E-field) derived from the switching operation of the modular multilevel converter (MMC) and the high voltage direct current (HVdc) circuit breaker (CB) in a 200 kV converter station constructed in the Zhoushan Islands, China. It is revealed that the switching transient E-field in the converter station is a quasi-static field. Although the switching E-field pulse is a kind of electromagnetic interference to the secondary electronic circuit of the converter station, it can be used to accurately monitor the action moment of the MMC and the CB. The action moment of the MMC and the CB can be measured with an error of less than 0.005 ms based on the steep pulse front of the switching E-field pulse. This result, which is far more accurate compared to the measurement using the voltage recording system that comes with the converter station. This is of significance to the relay protection of the HVdc transmission system whose fault rapidly develops. Additionally, this method has the advantage of being noninvasive, flexible, and low cost. It has potential application value in the condition monitoring of the MMC and the HVdc CB. [ABSTRACT FROM AUTHOR]

A silicon/silicon carbide (Si/SiC) hybrid switch (HyS), comprised of a high-current Si insulated gate bipolar transistor and a low-current SiC metal oxide semiconductor field effect transistors, gains attention because it offers lower on-state loss under both light and heavy loads. However, the dynamic overcurrent stress experienced by the HyS under the heavy load has to be coped with to avoid reliability degradation and the maximum current rating limitation. This article comprehensively studies how gate resistances regulate the dynamic behavior of the HyS under the heavy load condition. Experiments and analyses are conducted for both turn-on and turn-off processes. It is found that the gate resistance is important for not only the dv/dt control but also the overcurrent suppression. Moreover, the lower switching loss can be achieved by adjusting gate resistances when the HyS operates at a heavy load, compared with the gate timing control. A guideline is developed for the design of the gate resistances. This study offers an insight into the role of gate resistances in switching performances of the HyS and an alternative way of coping with the dynamic overstress stress. [ABSTRACT FROM AUTHOR]

This article presents an efficient and fast echelon battery equalization method based on wide voltage range bidirectional converter combined with DBSCAN (density-based spatial clustering of applications with noise) clustering control strategy. Thanks to the wide voltage range and bidirectional buck-boost characteristics of the four-switch bidirectional converter, the battery energy can be reasonably redistributed between the battery and the super capacitor. The converter operating in synchronous rectification mode can not only achieve bidirectional energy flow in a wide voltage range, but also has a high energy conversion efficiency. The DBSCAN clustering algorithm is used to divide all battery cells into groups, and each group may contain one or more adjacent and nonadjacent battery cells. First, the nonadjacent single cells are balanced and integrated into adjacent group with the closest voltage. Then, the groups with different voltages are balanced by group-to-group, thereby realizing rapid balance of the entire battery pack. In order to verify the effectiveness of the proposed method, simulations and experimental verification were carried out. The experimental results show that, comparing with traditional battery balancing methods, the proposed method achieves shorter balancing time and higher balancing efficiency. [ABSTRACT FROM AUTHOR]

The lack of uniform production of panels in photovoltaic (PV) systems and snowball effects in fuel cell (FC) systems led us to use a separate dc–dc converter. In addition, in the PV and FC systems, the output voltage is low. Hence, dc–dc boost converters are commonly used in a series connection. Each small unit of a PV or FC operates independently. Therefore, another problem arises in the system that uses the series connection of the converter's output. Owing to the unequal electricity production of the cells, a voltage imbalance occurs at the output terminals. To create voltage balance, a modular structure grounded on a three-level boost converter was investigated. The main objective of this article is to design the control of a modular topology, allowing perfect control of the dc-bus voltage, even with mismatched input powers. The proposed control strategy ensures dynamical properties independent of the operating point, voltage balance, and robust control of the dc output voltage with respect to load perturbations. To ensure the balance of voltages and the control of currents, a sliding mode controller based on indirect synthesis was used. To control the dc–bus voltage, an energy controller is proposed that ensures dynamical performance independent of the operating conditions. The performance in terms of tracking and regulation, as well as its effect on the voltage balance of the output capacitors, was validated through simulations and experimental results. A comparison with a classical proportional integral (PI) approach for controlling the dc-bus voltage was performed. [ABSTRACT FROM AUTHOR]

Class-E power amplifiers are widely used in megahertz frequency power conversion systems due to their high efficiency, which can further be enhanced by virtue of wide-bandgap devices such as GaN high-electron-mobility transistors. Here, a GaN-based cross-quadrant mode Class-E amplifier is proposed, which addresses one of the major challenges for such amplifiers, i.e., to achieve both high power and high efficiency with low-voltage-rating devices. By utilizing the reverse conduction of GaN transistors, a cross-quadrant mode Class-E amplifier with small dc-feed inductance is constructed, whose circuit model is derived by virtue of the Laplace transform technique. We demonstrate an experimental prototype operating at 3.11 MHz with a 100-V GaN transistor, achieving an output power of about 6 W with the efficiency being almost 90% when the input voltage is 10 V and the load resistance is 28 $\mathrm{\Omega }$. Compared with conventional Class-E amplifiers, the power conversion capability of the proposed amplifier is increased up to three times from 0.49 to 1.69 with a slight reduction in efficiency. Such cross-quadrant mode amplifiers can be used to improve the power conversion capability and to reduce the peak switch voltage at the same output power level. [ABSTRACT FROM AUTHOR]

In this article, a novel soft switched interleaved boost structure with a simple auxiliary circuit is proposed which is suitable for stand-alone loads or ac grid applications. In this topology, coupled inductors and switched capacitor cells of parallel modules are merged to obtain high voltage conversion ratio. The converter also has the capability of adding extra switched capacitor cells to attain very high voltage gain. To provide soft-switching condition in the wide range of output power, a new zero-voltage transition auxiliary circuit is employed which is responsible for soft switching of both phases and benefits from low conduction losses, the minimum number of semiconductor elements, and only one auxiliary gate-driver. These merits provide very high efficiency at both full-load and light loads. More importantly, no auxiliary magnetic components are utilized by taking advantage of the leakage inductance of coupled inductors for the resonant network. All semiconductor components operate under soft switching alleviating the reverse recovery problem and switching losses. Besides, the converter benefits from common ground between input and output which simplify voltage feedback. The experimental results of the interleaved converter prototype with 400-V output voltage at 400 W and 100 kHz switching frequency are provided. The full load efficiency of 98% was achieved and the power density was observed 1.9 W/Cm3. [ABSTRACT FROM AUTHOR]

LLC resonant converters are typically unsuitable to be applied for wide voltage-transfer ratio applications. With a full-bridge inverter, however, they can be operated in a variety of different modulation modes to extend the operating range. Most notably, by permanently turning on one switch and turning off the other switch of the same bridge leg, the LLC can be operated in half-bridge mode reducing the gain by a factor of two. In this modulation, however, the switch that is permanently turned on is stressed by the complete resonant current while exhibiting no switching losses. This article proves that the frequency-doubler modulation can better balance the losses among all switches and should be the preferred mode of operation favored over the conventional half-bridge modulation. This article analyzes the beneficial loss distribution and proposes an on-the-fly morphing modulation to the frequency-doubler modulation and reverse. Furthermore, the morphing magnetizing current offset of the morphing is analyzed to show that the offset can be influenced by the design of the magnetizing inductance and through the morphing modulation itself. Finally, an improved morphing modulation is presented showing that the morphing flux offset can be reduced substantially. Experimental measurement results on a 1.8 kW prototype show that by employing the frequency-doubler modulation, the maximum inverter temperature can be reduced by about 20 K and that the maximum transformer flux deviation during morphing can be reduced significantly on average by 78%. Both results enable the use of switches with a lower on-state resistance and the application of transformers with a smaller core cross-section. [ABSTRACT FROM AUTHOR]

For grid-connected or interconnected microgrids, the transition to an autonomous and decentralized architecture was hampered by two perplexing issues: how to guarantee voltage-supporting capacity, while fully and controllably utilizing local power generation, and how to switch between islanded and grid-connected modes flexibly and seamlessly. Through a combination of benefits of interlinking converters and switches, the flexible transfer converters (FTCs), positioned at the interfaces between the utility grid and microgrids, are offered as a solution in this article. The basic concepts and classifications of the FTC are first presented, and a general-purpose FTC and a universal control strategy for distributed generations are then proposed as an example, which contribute to appropriate power dispatch and flexible mode transfer in a communication-free design, leading to a fully autonomous microgrid. Simple and economic operation rules, as well as high interoperability with existing assets, makes this solution promising for distributed microgrid applications. Further, generalized small-signal models of the target system are derived for stability analysis and parameter design. Finally, comprehensive case studies in simulations and experiments are provided to validate its effectiveness. [ABSTRACT FROM AUTHOR]

The dual active bridge (DAB) converter operating with a relatively high switching frequency is well suited for deriving a high-power density electric vehicle (EV) charger. In this case, safeguarding the realization of zero voltage switching (ZVS) for a wide operating range becomes crucial to ensure a good performance in terms of efficiency and control reliability. Unfortunately, most modulation schemes available today in the literature require a detrimental compromise in the achievable ZVS range, particularly the ones working mainly toward the minimization of the current stress. Due to the fact a public EV charger will work with multiple vehicles having quite different charging profiles, i.e., with wide operational voltage and currents ratings, the ZVS operation may be prone to fail to undermine the whole cycle charging efficiency. To relieve the issues, this article proposes a new modulation scheme for the DAB converter featuring a maximized ZVS range and a quasi-optimal inductor rms current. Herein, the concept of dynamic settings of the required modulator's ZVS-current is utilized and a straightforward implementation with seamless circuit mode transition is achieved. With the above characteristics, the dynamic and static losses of the component circuits can be reduced together. By adopting the dynamic ZVS-current settings strategy, the turning-on currents of the DAB switches are adjusted in real-time guaranteeing the ZVS operation under various operating conditions. With the seamless transition, the inductor current can be smoothly regulated to ensure system stability. The proposed modulation scheme is introduced, analyzed, validated, and benchmarked in a 4.5 kW/100 kHz SiC-based DAB prototype, whose peak efficiency can reach 96.3% when operated at partial load. [ABSTRACT FROM AUTHOR]

LLC resonant converter has been widely employed in electric vehicle (EV) charging applications. However, conventional frequency-modulated LLC converters generally demand a wide frequency variation range and are difficult to scale up, while the traditional phase-shifted (PS) LLC converters have the issues of ease of losing soft-switching condition and high turn-off current. In response to these challenges, this article proposes a new method for EV charging applications based on the capacitor-clamped LLC converter topology and fixed-frequency PS modulation. Compared with traditional PS LLC converters, the proposed method can achieve 1) smaller phase shift variation range, 2) lower turn-off current, and 3) wider soft switching range, resulting in higher efficiency. An 825-W prototype with 200 V input and 125–210 V output range verified the features of the proposed idea, and the efficiency reaches 97.82% at the maximum output power. [ABSTRACT FROM AUTHOR]

This article proposes a new sliding mode control based on a nonlinear switching surface that provides a suboptimal current-limited start-up response in step-down converters. The main idea behind the design consists in combining different switching surfaces. The first one forces the system trajectories to track a constant current path until the output voltage error is small. A nonsingular terminal switching surface then drives the trajectories to the vicinity of the steady-state operating point. Finally, a first-order switching surface regulates the steady state providing very good rates of load and line regulation. The article presents the design guidelines of the suboptimal sliding mode control and the experimental evaluation that confirms the effectiveness of the proposal. [ABSTRACT FROM AUTHOR]

In this article, a new high voltage gain quasi-Z-source (QZS) dc–dc converter suitable for renewable energy applications is presented. The proposed converter utilizes a zero voltage transition auxiliary circuit with coupled inductors to provide soft-switching conditions for all switches for a wide range of output power. In addition, a switched capacitor circuit is employed to obtain a higher voltage gain and lower voltage stress. The main advantages of the proposed converter include high voltage gain, high efficiency, reduced switch and diode voltage stress, continuous input current, and common ground between the output and input, which are important features for photovoltaic applications. In this circuit, the reverse recovery problem of diodes is alleviated. Operating principles and design considerations of the proposed converter are analyzed. Moreover, to prove the validity of the theoretical analysis, a 200-W prototype of the proposed converter is implemented and the experimental results are shown. [ABSTRACT FROM AUTHOR]

Bidirectional capacitive power transfer technology makes it possible for energy sharing among multiple electronic devices. This article proposes an asymmetrical bidirectional power conversion topology to satisfy different input and output characteristics’ requirements and increase load variation tolerance. A π–T (CLC–LCL) resonant topology is designed for this bidirectional conversion mode with constant output voltage characteristics in both directions. A hybrid power flow regulation strategy is proposed by integrating multiple zero-voltage switching soft-switching operating points switching and phase-shifted mode. This method overcomes the problem of mixing two different type topologies (push–pull and full bridge) with two different power regulation modes (switch soft-switching operating points and phase shift), which provide a way to make two different chargers compatible. Simulation and experimental results verified the proposed method. [ABSTRACT FROM AUTHOR]

New emerging power inverter topologies are aiming at high-power density and efficiency with reliable performance. The recently proposed family of single-phase single-stage buck–boost inverters with output unfolding circuits have promising features for application in different fields. Nevertheless, the incapacity of injecting reactive power by the classical unfolding inverters has been assumed as its main drawback. Thus, our focus is on the reactive power injection capability of the single-stage buck–boost inverters with unfolding circuits. This attribute enables the converter to provide some extra ancillary services for friendly integration of the renewable energy resources and energy storage systems, providing support to the smart grid/microgrid, thus contributing to its power quality welfare. By means of a comprehensive analysis and implementation of proper closed-loop model predictive control, together with an adequate selection of the output capacitor, the single-inductor unfolding buck–boost inverter is capable of delivering reactive power to the utility grid. We used the simulation and experimental tests to validate the theoretical aspects. [ABSTRACT FROM AUTHOR]

The common inductor and common capacitor current sharing technologies with excellent current sharing capabilities and low cost have attracted a lot of attention in recent years. However, these methods have certain limitations when dealing with multiple resonate parameters mismatches of multiphase LLC converters. To solve this problem, this article proposes a unified common inductor and common capacitor scheme. First, the existing common inductor and common capacitor methods are reviewed. Based on the first harmonic approximation (FHA) analysis method, the limitations of these schemes are analyzed, and we find that the current sharing performance is not well when the multiresonant parameters are mismatched, which will cause the one-phase to bear more power, even overpowered and damaged. To realize a better current sharing of multiphase LLC modules, a unified common inductor and common capacitor method is proposed in this article, where the series resonant inductors and resonant capacitors in each LLC converter are connected in parallel. The current sharing performance of the proposed method is analyzed by the FHA analysis method, and the proof-of-concept prototype with a 480 W 24 V two-phase LLC converter was built to verify the effectiveness of the proposed method. Simulation and experimental results show that the current sharing error of the proposed method is 2.1% under half load and 0.9% under full load. [ABSTRACT FROM AUTHOR]

This article proposes a fast predictive control method and a small dc-link inductor to minimize the dc-link current in current-source converter (CSC) based solid-state transformer. The dc-link current minimization can significantly reduce power loss and improve efficiency. The challenge of this problem is on improving both steady-state and dynamic performance. PI control methods and large dc-link inductors are conventionally used in the CSC but have limited dynamic performance. A model predictive control (MPC) method is proposed to achieve switching-cycle-level settling time, and the dc-link inductor is sized for 40% ripple to enable fast current change. Importantly, this article also proposes to minimize the dc-link current by varying the current even within a line cycle under single-phase load to improve the steady-state performance, in contrast with the reduction to a constant value in the literature. The proposed MPC features a constant switching frequency without weighting factors. The MPC does not have a high computational burden and is implemented in a regular digital controller for a prototype of soft-switching solid-state transformer (S4T) with reduced conduction loss. The effectiveness of the proposed method has been experimentally verified on the SiC S4T prototype during steady-state and dynamics under different multiport power flow conditions up to 2 kV peak. The dc-link current in the experiments is close to the minimum current with a short zero-vector duration, which further verifies the performance of the proposed method. [ABSTRACT FROM AUTHOR]

A variable-frequency critical-soft-switching (VF-CSS) model predictive control method is developed combining with a modified nonisolated inverter to improve the efficiency. A two-level control structure is developed, including 1) the central-level grid-side inductor current control and zero-sequence voltage control; and 2) the local-level per-phase power module control of VF-CSS model predictive controller with state estimator. Two VF-CSS controllers are proposed, including variable-continuous-frequency critical-soft-switching controller and variable-discrete-frequency critical-soft-switching, to achieve critical soft-switching operation for high efficiency. The combination of MPC and VF-CSS guarantees a complete critical soft-switching operation at full period range of varying frequency and especially during transient. The state estimator provides sampling noise rejection and accurate switch-side inductor current estimations for MPC and VF-CSS. Also, with the help of state estimator, the current sensor cost is reduced by 50%. Meanwhile, the estimator contributes to a more accurate switch-side inductor current reading for MPC implementation with variable continuous frequency controller, especially when the critical soft switching requires huge inductor current ripple. With the proposed control strategies and topology, medium-frequency ($>$ 200 kHz, 45 $\mu$ H) and high-frequency ($>$ 1 MHz, 4.5 $\mu$ H) test benches are validated experimentally. The efficiency is above 99% at a rated power of 15 kW. A power density of more than 10.4 kW/L is achieved. [ABSTRACT FROM AUTHOR]

Bipolar dc grid systems are fast gaining attraction for renewable energy source integration, because of their merits of higher reliability, efficiency, and robustness as compared to the unipolar dc grids. However, the progress in multiport converters, resulting into lower cost and more compact design for bipolar microgrid systems, is fairly slow. Therefore, this article proposes a novel family of five nonisolated multiport dc–dc converter topologies with bipolar symmetric outputs. The performance and key operational features of the proposed converters under varying input voltages, duty cycles and loads are numerically verified and experimentally on an in-house test setup to prove the concept of the proposed converters. In the experimental validation, the operation of the converter under simultaneous and arbitrary individual power transfer from two input ports is tested. Furthermore, the easy integration of the proposed converters with a multilevel inverter to achieve high-quality ac voltages is demonstrated. As compared to the few existing counterparts, the proposed converters have a competitive edge in terms of higher number of input ports and voltage gains. Alongside the possibility of arbitrary independent power flow from the input ports, inherently symmetrical outputs require a simple balance control for asymmetrical members of the family. [ABSTRACT FROM AUTHOR]

This article presents local shielding techniques applied to a half-bridge inverter leg with the aim to reduce the common-mode (CM) current noise at converter’s dc input. The research study is conducted for 650-V enhancement mode Gallium Nitride power transistor switches. Main contributors of parasitic capacitances referred to the inverter-leg middle point node are identified. Then, shielding solutions are proposed to reduce the CM current emission by these capacitances. Respecting the precautions concerning the isolation of CM currents of the half-bridge inverter leg, the electromagnetic compatibility measurement setup is developed. Experimental step-by-step addition of local shielding copper layers to different contributors of middle point capacitance shows progressive attenuation of CM noise spectra. [ABSTRACT FROM AUTHOR]

A fault-tolerant control (FTC) is proposed for enhancing the reliability of power electronic systems. The software-based FTC of parallel-connected three-level T-type converters (3LT2Cs) for suppressing zero-sequence circulating current (ZSCC) induced by a vertical switch open-circuit fault is investigated. A simplified sequential model predictive control (SSMPC)-based FTC technique is developed. Parallel-3LT2Cs and their prediction models are introduced, followed by an SSMPC for the no-fault condition. The model inaccuracies under vertical switch faults are elaborated. For the faulty 3LT2C, two fault-tolerant SSMPC (FT-SSMPC) methods are provided by creating a sequential predictive controller that considers ZSCC suppression and grid current tracking. The control policies for the ZSCC are changed from the standard feedback-free to feedback-based cost function (CF) optimization using the unimproved FT-SSMPC. Furthermore, an improved FT-SSMPC is proposed using a phase-deficient CF, which increases the accuracy of the mathematical relation of the fault condition. After fault diagnosis, the proposed method achieves neutral-point voltage balance and excellent point-of-common-coupling current, effectively suppresses the ZSCC, and increases the control reliability. Finally, experiments demonstrate the effectiveness of the proposed FT-SSMPC under various conditions. [ABSTRACT FROM AUTHOR]

The double-sided inductor capacitor capacitor topology has been proposed in some national standards for wireless charging systems. However, misalignment between the transmitting and receiving coils usually leads to detuning and weak coupling, resulting in low output power and inefficiency. To improve power output under weak coupling, this article proposes a control method based on the variable inductor and capacitor (VLC). First, it is deduced that the zero phase angle input and full output power can be achieved by VLC regulation under certain misalignment. Second, the variable inductor using an EE-shaped core and pulsewidth modulation controlled capacitor are applied to achieve VLC regulation, and the principles and implementation of VLC are analyzed. Third, as the coupling coefficient k can be identified through the primary electrical parameters, a convenient and accurate coupling coefficient identification method is utilized to help VLC regulation. Finally, a prototype with a 3.3 kW output power and an 87.5% maximum system efficiency (dc–dc) is built to validate the proposed method. The experimental results are consistent with the theoretical analysis, proving that the output power is almost constant when k varies from 0.08 to 0.18. [ABSTRACT FROM AUTHOR]

The small satellite (SmallSat) industry has recorded incredible growth recently. Within this class, among mini-, micro-, and nanosatellites, the cube satellite (CubeSat) is primed for an explosion of growth. These satellites are fascinating for remote sensing, Earth observation, and scientific applications. Remarkable attention from the space operators makes it valuable because of its low cost, cubic shape, less manufacturing time, lightweight, and modular structure. Among the various subsystems comprising the SmallSat, the electrical power system (EPS) is the most crucial one because unreliable power supply to the rest is most of the time detrimental to the mission. The EPS is formed by electrical sources, storage units, and loads, all interconnected via different power converters, the operation of which must be closely orchestrated to accomplish efficient use of photovoltaic power, optimal battery management, and resilient power delivery. At the same time, the EPS design must address a series of challenges such as size restrictions, high power density, and harsh space environments (e.g., atomic oxygen, radiation, and extreme temperatures), which significantly impact the EPS electrical and electronic equipment. In terms of power systems, a SmallSat EPS can be considered a space microgrid owing to coordination and control of distributed generation, storage, and loads in a small-scale electrical network. From this point of view, this article reviews and explores SmallSat microgrid's research developments, energy transfer and architectures, converter topologies, latest technologies, main challenges, and some potential solutions, which will enable building a more robust, resilient, and efficient EPS. The research gaps and future developments are underlined before this article is concluded. [ABSTRACT FROM AUTHOR]

In an era where high-frequency flying capacitor (FC) multilevel inverters (MLIs) are increasingly gaining attention in energy conversion systems that push the boundaries of power density, the need for a compact, fast, and accurate FC voltage monitoring system is also increasing. In this article, we designed and developed a new FC measurement system, based on precise sampling of the inverter switching node voltage, through a bidirectional clamping circuit. The deviation of FC voltages from their nominal values is extracted by solving a set of linear equations. With a single sensor per phase and no isolation requirements, as opposed to dozens of sensors in traditional FC monitoring, our approach results in significantly lower cost, complexity, and circuit size. Detailed device-level simulations in LTspice and system-scale simulations in MATLAB validate the accuracy and speed of the proposed measurement system and the balancing strategy in steady-state, abrupt load change, and imbalance conditions. Experiments carried out in a three-phase gallium nitride five-level inverter prototype reveal a gain in precision and bandwidth that is more than 30 times that of conventional methods, at a fraction of their cost and footprint. The recorded performance renders the developed sensor an ideal solution for fast MLIs based on wide-bandgap technology. [ABSTRACT FROM AUTHOR]

The single-switch topologies, e.g., the Class E topology, have the advantages of low component count, no shoot-through problem, simple driving circuit, which make it more suitable for high frequency low/medium-power wireless power transfer (WPT) applications. However, due to the high switch voltage stress, narrow soft switching range, bulky input choke, or ac inductor, its power delivery capability and applications are limited. In order to solve these problems, this article proposed a novel active clamp topology for high cost-performance medium-power WPT systems. The proposed topology offers low component count with no bulky inductor and low switch voltage stress, leading to high power-density, low cost, and compact size, i.e., high cost-performance for WPT applications. And the switch peak voltage can be adjusted and the soft switching operation can be achieved in a wide load range by designing the compensation capacitor and clamp capacitor. In this article, the detailed theoretical analysis and parameter design are discussed and the proposed topology is compared with the existing single-switch topology in terms of voltage stress, cost, and component count. A 120 W and 1 MHz active clamp WPT system is built and a 92.4% system efficiency is achieved with high cost-performance, which validate the feasibility of the proposed topology and the theoretical analysis. [ABSTRACT FROM AUTHOR]

This article proposes a single-ended hybrid resonant converter (SEHRC) for wireless charger to provide a cost-effective solution with high misalignment tolerance. A comprehensive characteristics analysis of the proposed converter is performed in both of time and frequency domain. The analysis discloses that the hybrid compensation performs impedance transformation which maintains the input impedance nearly constant. As a result, the optimum operation of SEHRC, including zero-voltage-switching, low voltage stress, high power transfer capability, and high efficiency can be maintained within a wide range of coupling coefficients. Also, it ensures a stable output current for both load and coupling variations. The design constraints and procedure are given. Furthermore, a zero-voltage-switching and zero-voltage-derivative-switching control scheme is proposed to achieve a higher efficiency and smaller output current fluctuation, as well as reduced peak switch voltage. Finally, a 1.3 kW prototype is built to verify the theoretical analysis. The test results demonstrate that the peak voltage of the proposed SEHRC is less than 2.7 times the input voltage. When the coupling coefficient varies 2.7 times, the output current changes by 1.16 times. [ABSTRACT FROM AUTHOR]

This article proposes a multiport modular single-stage current-source solid-state transformer (SST) for applications like photovoltaic, energy storage integration, electric vehicle fast charging, data center, etc. The 7.2 kV 50 kVA current-source SST consists of five input-series output-parallel modules, each based on 3.3 kV SiC reverse-blocking mosfet-plus-diode modules. The proposed SST has some unique features. First, compared with the voltage-source or matrix converter-based SSTs, the current-source SST has a unique advantage of single-stage isolated ac/dc or ac/ac conversion with an inductive dc link, but no medium-voltage (MV) ac experiments have been reported. This article for the first time demonstrates MV ac current-source SST up to 7.5 kV peak. Second, the multiport SST has a buffer port for active power decoupling (APD) or energy storage integration. The double-line-frequency power ripple from single-phase ac grid normally results in a large capacitor size in MV SSTs. The APD scheme is proposed in MV applications for the first time to enable a reduced dc link and the electrolytic capacitor-less SST with high reliability. Third, for a direct grid-connected converter without line-frequency transformer, insulation and protection are critical. A medium-frequency transformer design passes 55 kV basic-insulation level (BIL) and 60 kV high potential dielectrics withstand test with only 0.09% leakage inductance. Importantly, a lightning protection scheme is presented to protect the SST itself from 90 kV BIL impulse. Fourth, the proposed current-source SST topology is a modular soft-switching solid-state transformer (M-S4T) with full-range zero-voltage switching and controlled dv/dt for low electromagnetic interference. These concepts are verified in a three-port M-S4T prototype with forced oil cooling under single-module, stacked-module, steady-state, and dynamic operations. [ABSTRACT FROM AUTHOR]

In this article, a high-performance modified Y-source dc–dc converter is proposed. Comparing with traditional Y-source dc–dc converter, the proposed converter can achieve soft switching characteristics. Due to the discontinuous conduction mode operation of one of the coupled inductor windings and the resonant cell constructed by switch parasitic capacitor, the switch can operate in zero voltage switching (ZVS) and diodes realize zero current switching. Also, the voltage gain of the proposed converter is greatly improved. Meanwhile, the control strategy of hybrid pulsewidth modulation and PFM is adopted to guarantee the ZVS operation within a wide range. A 160 W experimental prototype based on planar coupled inductor is built to verify theoretical analysis and efficiency is up to 94.45% under full load condition. [ABSTRACT FROM AUTHOR]

Promising for applications including renewable energy and electric vehicle fast charging, a medium-voltage (MV) solid-state transformer (SST) typically has multiple modules series stacked, which requires the modules to be single phase. One critical issue of the single-phase SST is the double-line-frequency power ripple. Traditionally, large passives are used to buffer the ripple, resulting in significantly increased volume and cost. This article for the first time proposes active power decoupling (APD) for the SST and a predictive direct dc-link control method, using a current-source (CS) single-stage SST as an example. An electrolytic capacitorless buffer port is used to absorb the ripple, which tolerates up to a 30% voltage ripple for small capacitance. The APD SST control is challenging. First, the CS SST realizes isolation, dc-link, and multiport in a single stage. Second, different from conventional SSTs or APD converters, the low-inertia dc-link in this SST has a 40% switching ripple, which is difficult to stabilize. To address the control challenge, a direct dc-link control architecture and a predictive control method are proposed. Simulation and experimental results verify the proposed control method on an MV SiC modular soft-switching solid-state transformer (M-S4T) prototype. The proposed APD reduces the SST volume by 53.8%. Importantly, the proposed concept is not limited to the M-S4T, but is generic to other SSTs or APD converters. [ABSTRACT FROM AUTHOR]

Power electronic systems employing wide-bandgap GaN transistors promise high efficiency operation and power density but require minimized parasitic circuit elements and an effective cooling concept. This article presents a half-bridge module integrating two 600 V/170 mΩ gallium nitride (GaN) high-electron mobility transistors with their gate drive stages and a fraction of the dc-link capacitance on a patterned multilayer polycrystalline AlN-substrate. The high-voltage isolation at a layer distance of 10 μm and a dense chip-by-chip integration on the GaN half-bridge module enable a compact lateral commutation loop design combined with improved cooling capability of the power transistors. Consequently, the GaN half-bridge module allows for higher load currents at lower device temperature while most parasitic circuit elements are reduced compared to a conventional printed circuit board (PCB) design. The parasitic circuit elements of the GaN half-bridge module and a reference four-layer PCB half-bridge are evaluated using 3D-FEM field simulation and in-circuit measurements. Selected finite element method (FEM) simulation results are validated by S-parameter measurements and further used to parametrize a lumped commutation loop model. The thermal characterization of the GaN half-bridge module validates the improved cooling capability of the GaN half-bridge power module. Transient switching characteristics are studied in hard-switching mode. The device temperature and converter efficiency are evaluated in dc/dc buck-converter operation. [ABSTRACT FROM AUTHOR]

Transformerless inverters, most of which are H-bridge inverters, have been widely used and studied in grid-connected power systems in the last decades. However, the H-bridge inverter is affected by the low- and high-frequency common-mode voltage between the input and output terminals, resulting in a large common-mode leakage current. An alternative solution is to connect the ground of the input terminal to the output load or grid, that is, the dual-grounded inverter. In this case, the low- and high-frequency common-mode voltages can be mitigated or eliminated. As a matter of fact, scholars have made several research results on dual-grounded inverters. However, as of now, there is still no literature that comprehensively and systematically summarizes these research results. To fill this gap, this article classifies different types of dual-grounded inverters from the perspective of topology for the first time, and compares and summarizes their advantages and disadvantages. More than 60 works of literature have been reviewed to identify the practical implementation challenges and research opportunities in the application of dual-grounded inverters. [ABSTRACT FROM AUTHOR]

The proposedisolated buck–boost series resonant dc–dc converter contains two full-bridge hybrid switching cells capable of half-bridge operation. This feature is regarded as topology morphing control. Voltage buck regulation requires special modulations applied to the primary-side hybrid switching cell. In contrast, voltage boost regulation requires special modulations for the secondary-side hybrid switching cell. Combining the topology morphing control with the buck–boost regulation capability, a novel dc–dc converter operating in six different modes was derived. Moreover, the converter is capable of bidirectional operation. This article describes the influence of the topology morphing control on the dc voltage gain of the converter, which results in three boost and three buck modes. The six modes are described, and equations for the converter's dc voltage gain are provided. Based on the selected design guidelines for the power part and the control system, a 350-W prototype was designed and built. Experimental results confirm the theoretical expressions for the converter's dc voltage gain. Experimental efficiency is provided in a wide input voltage range for both energy transfer directions. Operating points with the highest thermal stress of components are analyzed with corresponding power loss breakdown calculations, confirming the measured thermal results. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerator (TENG) is a class of ambient mechanical energy harvesters used to augment the battery life of electronic devices such as sensors in implantables, wearables, and internet of things applications. In this work, the fundamentals of pre-biasing (precharging) the TENG at the start of the operation cycle to enhance the percycle extracted energy is presented. The energy gain is mathematically formulated, and the optimum pre-biasing voltage (equivalently charge) is derived by analyzing the energy exchange between the mechanical and the electrical domain over a periodic cycle. Further, a novel energy extraction circuit (EEC) termed as “pre-biased synchronous charge extraction (pSCE)” is introduced to 1) realize synchronous pre-biasing of TENG using the load battery itself and 2) achieve enhanced energy extraction from TENG. Energy output percycle is derived analytically for the pSCE circuit and compared to the state of the art synchronous charge extraction (SCE) circuit. The experimental implementation is performed for the proposed pSCE circuit that shows a 6.65 fold gain over the full wave rectifier (standard EEC) and 1.45 over the SCE circuit for a 5 V battery load. [ABSTRACT FROM AUTHOR]