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In this paper, a dual half-bridge LLC resonant converter with magnetic control is proposed for the battery charger application. The primary switches are shared by two LLC resonant networks, and their outputs are connected in series. One of the LLC resonant converters is designed to operate at the series resonant frequency, which is also the highest efficiency operating point, and the constant output voltage characteristic is achieved at this operating point. The second LLC resonant converter adopts magnetic control to regulate the total output current and voltage during both constant current charge mode and constant voltage charge mode. Meanwhile, the function decoupling idea is adopted to further improve the system efficiency. The significant amount of the power is handled by the LLC resonant converter operating at the series resonant frequency, whereas the second LLC resonant converter fulfills the responsibility to achieve closed-loop control. By carefully designing the resonant networks, the zero-voltage switching for primary switches and zero-current switching for secondary diodes can be achieved for whole operation range. A 320-W experimental prototype is built to verify the theoretical analysis, and the maximum efficiency is measured about 95.5%. [ABSTRACT FROM AUTHOR]

The Cuk dual resonance core (DRC) realizes overlapped dual resonance to regulate its output voltage. However, the DRC configuration was only applied to the Fibonacci switched-capacitor converter (SCC), series–parallel SCC, and voltage doubler. In this paper, the Cuk DRC is modified and then is extended to the Dickson SCC to form a multi-resonance-core-based (MRC) Dickson resonant switched-capacitor converter. All charging and discharging loops achieve soft charging, and so the inherent capacitor charge sharing loss and the high current transient spikes are eliminated. The modular configuration makes the MRC Dickson easy to be extended to a higher voltage level. The on-time fixed frequency modulation is adopted, all transistors being turned on with zero-current-switching (ZCS) operation and all diodes being turned off with ZCS operation. Most importantly, the conversion ratio of the MRC Dickson can be regulated continuously, widely, and efficiently even at light load condition, which is a huge advantage over the traditional Dickson SCC with limited control headroom. A comprehensive analysis of the operation principle, voltage-gain curve, component stress analysis, and output characteristic is provided. The converter operation principle and regulation capability were verified by both simulation and experiment. [ABSTRACT FROM AUTHOR]

In this paper, a bidirectional dc–dc converter with coupled inductor is proposed. The proposed converter can achieve a wide voltage-gain range by turning the ratios of windings of the coupled inductor. Furthermore, the voltage stresses across the power switches are reduced. By employing a low-current ripple structure, a tiny input/output current ripple can be achieved, which can avoid larger filters. In addition, the common ground structure between the grounds of the input and the load sides can avoid extra du/dt issues. A prototype rated at 400 W/300 V has been developed and the maximum efficiency of the proposed converter was measured as 94.2%. Experimental results are presented to validate the effectiveness of the proposed converter. [ABSTRACT FROM AUTHOR]

Load-independent output characteristics of inductive power transfer (IPT) systems are increasingly popular in battery charging. This paper proposes a novel variable-parameter T-circuit (VT) for an IPT system charging a battery with constant current (CC) or constant voltage (CV) output. The VT can transfer a CC/CV input to a CC or CV output by using an ac switch and a passive component (inductor or capacitor). An IPT system with a VT for CC–CV charging can reduce the number of passive components and ac switches. Besides, the proposed VT merits more design freedom of charge current/voltage with the constraints imposed by the loosely coupled transformer parameters compared to that of the traditional one. In addition, there are three kinds of VTs for various IPT charging systems with different requirements. A 400 W laboratory-scale prototype with a 150 mm air gap was built to verify the theoretical analyses. Both electronic load and lead-acid battery are utilized to verify the charging profile of the proposed method. The experimental results of the IPT system indicate that the fluctuation of the charging current in CC mode is less than 2%, and the change rate of charging voltage in CV mode is within 2.9%. The maximum overall efficiency 93.93% of the charging system is achieved from a dc 110 V input to a dc 100 V output. [ABSTRACT FROM AUTHOR]

This paper proposes the design of gray wolf optimizer (GWO) algorithm-based fractional order proportional integral (FOPI) controller for power factor correction (PFC) using interleaved dc–dc single ended primary inductance converter converter with improved performance characteristics such as speed, accuracy, and stability. The detailed analysis and modeling of the proposed converter are presented. The optimal parameters of FOPI controller are obtained using GWO algorithm to improve the speed of response of the system. FOPI controller provides better performance in terms of robustness and stability since it has one more adjustable parameter than the conventional proportional integral (PI) controller. The cascade control strategy is implemented for the proposed converter with GWO-based FOPI controller as inner current and outer voltage controllers for PFC and load voltage regulation. The performance characteristics of the proposed system are analyzed and compared with conventional and other optimization techniques using MATLAB/Simulink software. A prototype of the proposed converter controlled by TMS320C2000 microcontroller for an output power of 200 W is tested and validated with the simulation results. The proposed system is used for powering devices like robots in critical applications such as military, space craft, etc., where stability, speed, and accuracy are major concerns. [ABSTRACT FROM AUTHOR]

In voltage-source converter systems, utilization of filter inductors with deep saturation characteristics is often advantageous because of the improved size, cost, and efficiency. However, with the use of conventional current regulation methods, the inductor saturation results in significant dynamic performance loss and poor steady-state current waveform quality. This paper proposes the saturation compensation with resistive decoupling (SCRD) method to overcome these performance issues. The method converts the nonlinear inductor of the plant to a fictitious linear inductor such that linear current regulators can perform satisfactorily. The steady-state and dynamic performances of SCRD are investigated in detail in comparison with other methods and advantageous performance attributes of SCRD are demonstrated on a 1.5-kW grid-connected system via simulations and laboratory experiments. In addition, identification of L–R parameters is performed, parameter sensitivity issues are addressed, and satisfactory performance is demonstrated. [ABSTRACT FROM AUTHOR]

This paper proposes a constrained modulated model-predictive control (M $^{2}$ PC) scheme for an LC-filtered voltage-source converter (VSC). To tackle the coupling effects of the state variables in a second-order LC filter, a dual-objective cost function (CF) is used to explicitly track both capacitor voltage and inductor current references, which can achieve an improved voltage quality. To handle the state and control input constraints of VSCs, a constrained M $^{2}$ PC scheme is proposed with an “online post-correction” constraint-handling technique. First, the unconstrained optimal voltage vector (OVV) is derived. It is generated by seeking the minimum analytical solution of the CF offline, simplifying the online implementation. Then, an “online post-correction” strategy is employed by reconsidering the constraints to correct the precalculated OVV online, which guarantees the future states within the allowed range. Finally, the corrected OVV is synthesized by the space vector modulation, resulting in a fixed switching frequency and low harmonics. Compared with the typical constrained model-predictive control, the presented scheme has the advantages of improved steady-state performance, flexible constraint-handling ability, and lower computational cost. Additionally, design procedures for weighting factor selection in the CF are given. Comparative experiments are investigated to verify the presented control strategy. [ABSTRACT FROM AUTHOR]

This paper presents novel single-phase single-stage buck–boost inverters. The proposed inverters provide buck–boost operation for a wide variation of the input dc voltage. In addition, the proposed inverters are bidirectional and provide reactive power. Further, they require only one inductor. The proposed inverters also eliminate the common-mode leakage current by connecting the output neutral to the midpoint of input capacitors or directly to input voltage sources. Therefore, they are well suitable for photovoltaic applications. Although six switches are required, two switches are working at line frequency, resulting in negligible switching loss. Of the four remaining switches, only two are switching at high frequency at a time. The circuit operations are demonstrated through the analysis of the proposed inverters. A 120 Vrms/60 Hz/400 W hardware prototype was constructed and tested. The experimental results verified the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper proposes a new modulation strategy with balanced power device currents for the full-bridge three-level dc/dc converter. The proposed modulation strategy has two working patterns, which cannot only realize zero-voltage switching (ZVS) but also satisfy the wide input voltage range. More significantly, the two working patterns of the proposed strategy can balance the currents both among the power switches and clamping diodes in comparison with the conventional control strategies which cause current imbalances among the power switches and clamping diodes. Consequently, the proposed strategy can balance the thermal stresses among the power switches and clamping diodes, which would, thus, improve the converter's reliability. Finally, the experimental results, obtained using a built 1.5-kW experimental prototype, verify almost zero current difference and zero thermal-stress difference among the inner power switches, outer power switches, and clamping diodes under the proposed strategy. [ABSTRACT FROM AUTHOR]

This paper analyzes and compares available measurement techniques that can be used to assess the effect of parasitics on the impedance of capacitors and inductors within the frequency range, where most electromagnetic compatibility regulations impose limits to conducted emissions of power converters. Direct measurement of impedance is compared with measurement of the transmission coefficient of the component. For impedance measurement, a criterion is identified to determine whether cables and test fixtures used to connect the component to the measuring device will have an impact on the measurements. It is shown that this criterion is more restrictive than the well known requirement of electrically short cable. We also show that, by contrast with direct impedance measurement, the measurement of the magnitude of the transmission coefficient is not affected by the cables in the frequency range of interest. Therefore, to carry out compensation previous measurements are not required. This permits us to quickly evaluate the effect of parasitics on the impedance of inductors and capacitors and also allows us to readily construct a circuit model for the component, which can be used to improve accuracy in the prediction of conducted emissions of power converters by simulation. Experimental validation is presented for practical capacitors and inductors. [ABSTRACT FROM AUTHOR]

In the flexible dc grid, the dc fault propagates extremely fast. It requires the dc protection and the dc circuit breaker (DCCB) can identify and isolate the fault line very quickly, for the healthy network ride-through, especially in the multi-terminal dc grids. However, the existing protection and DCCB techniques for flexible dc grid can still not match the dc fault propagation speed. Therefore, a novel current-commutation-based fault current limiter (FCL) is proposed in this paper. It can limit the dc fault current effectively, to guarantee the converter continuous operation and healthy network ride-through after dc faults, so the requirement on the protection and DCCB acting speed can be decreased. Compared with the existing fault current limiting methods, the proposed FCL has tiny negative influence on the system transient response speed, operation stability, and DCCB isolating speed. The experiment tests and simulation case studies are carried out to verify the working principle and superiorities of the proposed novel FCL.3 [ABSTRACT FROM AUTHOR]

This paper presents the circuit design and magnetic integration of push–pull class-E inverters for wireless power transfer (WPT) up to megahertz. The design criterion for achieving zero-voltage switching (ZVS) of a class-E inverter with coupled windings is derived mathematically. The approaches of magnetic integration for push–pull class-E inverters are analyzed and compared. Then, a new magnetic structure with hybrid magnetic materials is proposed to build the integrated inductors with either coupled windings or uncoupled windings. A 3-MHz WPT system is built to verify the analysis. The detailed comparison of the class-E inverters with magnetic integration is presented in terms of switch voltage, efficiency, harmonic currents, and thermal distribution. In the optimized design example, the switches keep ZVS over the entire load range without using any closed-loop control. The system efficiency reaches 87.1% at 350-W output power. [ABSTRACT FROM AUTHOR]

Improving the power density of a power converter has many benefits for systems integration. Aspects such as thermal management, weight, conformation to mounting locations, and the footprint of the converter all become critical factors as systems continue to scale down in size. The flying capacitor multilevel converter topology is of interest because it has characteristics which contribute to high power density. This paper presents a quasi-square-wave zero-voltage switching (ZVS) multilevel dc–dc converter. ZVS greatly reduces switching losses and enables high-frequency operation of the converter. A hardware prototype is implemented, built on a flexible polyimide substrate circuit board. Experimental results show a peak system efficiency above 98.1%, an effective switching frequency of up to 3 MHz, and a power output of 250 W. [ABSTRACT FROM AUTHOR]

In this paper, two single-phase single-stage split-inductor buck–boost inverters are proposed: type-I and II. The proposed type-I is unity power factor inverter, while the proposed type-II inverter is suitable for any power factor. Both topologies remove the shoot-through problem. Furthermore, the reverse recovery issues for all switches are eliminated; therefore, mosfets are used to obtain higher efficiencies. The proposed inverters operated at higher switching frequencies confer the additional benefit of smaller passive components. The current stresses of the two switches in the proposed type-I and II inverters are lower of the conventional boost inverter. The dead time can be eliminated at both the high and line switching frequencies. In addition, the inductor conduction loss is minimized to improve efficiency. Moreover, the voltage stresses of the two switches in the type-I inverter can be much lower of its counterpart boost inverter. Most importantly, unlike the conventional high-reliability inverters, the magnetic volume of the proposed high-reliability type-I and II inverters is same of its counterpart boost inverter. The experimental results obtained for 500 W, 110 Vrms, 60 Hz hardware prototypes verify the analysis. [ABSTRACT FROM AUTHOR]

Analysis and design of a single-switch high step-up coupled-inductor boost converter are presented in this paper. With the aid of the coupled inductor, the proposed converter can achieve high-voltage gain without extreme duty cycle. Also, low switch voltage stress can be achieved, thus low-voltage-rating mosfet is allowed to lower the conduction loss. Moreover, the proposed converter features continuous input current, which is desirable and friendly to the battery, fuel cell, and photovoltaic applications. In addition, the reverse recovery problem of the diodes can be alleviated and leakage energy can be recycled. The operation principles and characteristics of the proposed converter are discussed. Experimental results are provided to verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

When the interleaved boost power-factor correction (PFC) converter operates in a light load (<15% of nominal load), the phase-shedding control is commonly used to increase the converter's efficiency. If the inductors are coupled for high power density applications, because of the strong mutual effects of the coupled inductor, the switching of the operation phase may lead to a current flowing in the non-operation phase. In this paper, a two-phase interleaved boost PFC converter with a coupled inductor in the single-phase operation was analyzed. The operation modes of the converter in a switching cycle and a half line cycle were presented, and the modes’ variation with the load changes, as well as the power distribution, was provided. A 1-kW prototype was built to verify the analysis, and it was shown that the non-operation phase also delivers some power, which may worsen the converter's efficiency and distort the average input current waveform. [ABSTRACT FROM AUTHOR]

This paper presents a self-adapting synchronized-switch harvesting (SA-SSH) interface circuit to extract energy from vibration-based piezoelectric energy harvesters (PEHs). The implemented circuit utilizes a novel switching technique to recycle optimum amount of harvested charge on piezoelectric capacitance to strengthen the damping force, and simultaneously achieve load-independent energy extraction with a single inductor. Charge recycling is realized by adjusting extraction time, and optimized through a maximum power point tracker based on charge-flipping dissipation. The circuit has been implemented using 180 nm HV CMOS technology with 0.9 × 0.6 mm2 active area. Self-adapting SSH circuit has been validated with both macro-scaled and MEMS PEHs with different inductor values. The interface circuit provides maximum energy extraction for the full storage voltage range of 1.8–3.7 V. The implementation harnesses have 500% more power compared to an ideal full-bridge rectifier, and output 3.4 μW for 2.24 V peak-to-peak open-circuit piezoelectric voltage from MEMS PEH excited at its resonant frequency. [ABSTRACT FROM AUTHOR]

Design optimization of magnetic components, which considers both electrical and thermal performance, can help in designing power converters with a high power density. This paper proposes an approximate analytical model for thermal resistance of inductor and transformer windings, including litz wire, which only requires knowledge of thermal properties of constituent materials and geometric dimensions. The model is based on regular square and hexagonal packing of insulated wires and is derived by integration of infinitesimal thermal resistances along a specified heat flow path. The model closely agrees with finite-element analysis (FEA) and can be used in place of time-consuming FEA as part of larger thermal network models for magnetic components. The model is also experimentally validated using a toroidal inductor with a litz-wire winding; the model has less than 12% error compared to the experimental measurement. Application of the model for practical windings, including litz-wire windings, is also discussed. The model can be used during the design process of magnetic components of a switching power converter to evaluate the temperature and potential hot spots. The model provides closed-form results, hence fast computation times, and so can be used in design optimization procedures. [ABSTRACT FROM AUTHOR]

A typical finite-set model predictive control (FS-MPC) scheme for LC-filtered voltage source inverters (VSIs) requires measurements of capacitor voltage and inductor current as well as load current measurement or estimation, which increases the system complexity and cost. To reduce the number of sensors in typical FS-MPC, this paper proposes a new current-sensorless FS-MPC scheme for LC-filtered VSIs. First, based on the inner relationship of the predictive matrices, the predictive model is exactly simplified with the capacitor voltage and its current as the state variables, making it suitable for current-sensorless control. Then, to eliminate the current sensors for cost reduction and reliability enhancement, the dynamic model is reconstructed and an easily implemented capacitor current estimator is designed, which can achieve a comparable performance with typical FS-MPC scheme. Considering the inevitable control delay in digital implementation, the delay compensation is inherently obtained by using the proposed estimator. In addition, the proposed control scheme is flexible to various cost functions and can also reduce the computational cost. The feasibility of the presented control scheme under load variations and model mismatches are verified by the comparative simulation and experimental results with typical FS-MPC. [ABSTRACT FROM AUTHOR]

This paper presents a delta-sigma modulation (DSM) control scheme for noninverting buck–boost (NIBB) converter that features a duobinary encoding for four power switch controls. The proposed scheme converts the single-bit output of the modulator into a 1.5-b signal to enable a three-phase operation comprising the charging, bypassing, and discharging phases. This control method reduces both switching and conduction losses by changing only two switches in each period, thus, achieving high conversion efficiency. A smooth mode transition is provided by the DSM controller, which automatically and continuously determines the operating mode of the converter. Thus, the dead zone can be effectively released with improved transient responses. Furthermore, the spurious tones in the output are effectively eliminated by the robust noise shaping capability of the modulator. The proposed DSM-based NIBB converter was implemented on a 180-nm CMOS. It regulated the output in the range of 2.0–4.6 V with input voltage of 2.5–5.0 V, and the maximal load current was 500 mA. The converter showed a peak efficiency of 94.8% at 90-mA load and the output voltage ripples were maintained under 18 mV. A low noise floor with the first spurious peak located –92 dBc below the signal was achieved across all mode operations. In addition, the converter occupied a small chip area of 1.51 mm2. [ABSTRACT FROM AUTHOR]

In this paper, a novel filter structure to suppress circulating currents is proposed based on the sequence of pulsewidth modulation voltage harmonics for high-power interleaved motor-drive systems. The sideband harmonics can be divided into positive-, negative-, and zero-sequence components. Through 120° interleaving among three paralleled inverters, a majority of positive- and negative-sequence harmonics are phase shifted. By these phase shifts, the differential-mode circulating currents between the paralleled ac–dc converters can be suppressed with the proposed filters, which have an identical structure to the three-phase common-mode chokes. Such a structure highly benefits the design and manufacturability for high-power applications where a choice of magnetic-core shapes is limited. Compared to coupled inductors (CIs) with cyclic-cascade or monolithic configurations, the number of magnetic cores can be reduced by one-third. Peak flux-linkages of the proposed filters and the conventional CIs were compared to estimate the size reduction in case of flux-limited designs. Considering the whole modulation index range, which may be required in the motor-drive systems, the maximum flux-linkage can be reduced by 50%. Prototype filters are built and showed a 33% reduction in weight and size compared to the conventional CIs. The validity of the proposed filter is verified through the simulation and a small-scale experiment. [ABSTRACT FROM AUTHOR]

The discontinuous conduction mode boost power factor correction converter features zero-current turn-on for the switch, no reverse recovery in diode, and constant frequency operation. With traditional constant duty ratio control, the power transfer in each switching cycle exhibits great difference during a half-line cycle. Consequently, the peak and root mean square values of the inductor current are large, the same goes for the switch and diode. This increases not only the current stress of the power components but also the conduction and switching turn-off loss, and lowers the efficiency of the converter. Introducing third and fifth harmonics into the input current and varying the duty cycle correspondingly can reduce the aforementioned power transfer difference, and provide huge space for the increment of boundary inductance as well. An optimum boundary inductance control concerning limited power factor (PF) is proposed in this paper. For the maximum boundary inductance of the converter within wide input voltage range, the optimum harmonics amounts are analyzed and figured out. The proposed method brings about efficiency improvement, output voltage ripple reduction, and PF increase as well, especially at high input voltages. A prototype has been built and the experimental results are presented to show the validity of the scheme. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) systems having rechargeable batteries are prone to be complex and costly because multiple converters are necessary to individually regulate a load, PV panel, and battery. This paper proposes novel nonisolated multiport converters (MPCs) integrating a bidirectional pulsewidth modulation (PWM) converter and phase-shift-switched capacitor converter (PS-SCC) for standalone PV systems. A PWM converter and PS-SCC are integrated by reducing the total switch count, realizing the simplified system and circuit. In the proposed MPCs, two control freedoms of duty cycle and phase shift angle are manipulated to individually regulate the load, PV panel, and/or battery. The detailed operation analysis was performed to mathematically derive gain characteristics and zero voltage switching operation boundaries. For the battery discharging mode, in which the PV panel is not available and the MPC behaves as a single-input–single-output converter with two control freedoms available, the optimized control scheme achieving the lowest rms current is also proposed to maximize power conversion efficiencies. Various kinds of experimental verification tests using a 200-W prototype were performed to verify the theoretical analysis and to demonstrate the performance of the proposed MPC. [ABSTRACT FROM AUTHOR]

Boost-based converters are used in a variety of non-isolated step-up applications, such as power factor correctors, because of their simplicity. The power density of these converters can be increased in higher switching frequencies, which reduces the size of the magnetic elements. This increases the switching losses, but that can be solved by soft-switching techniques. This paper proposes a resonant bridgeless power factor correction converter that provides soft switching for all of the semiconductors. The proposed structure can provide zero voltage switching for the switches and zero current switching for the diodes. In the proposed structure, the input current is inherently sinusoidal with low total harmonic distortion, even with small inductances. Therefore, a high input power factor is achieved without requiring a current control loop in the circuit. This reduces the complexity of the control circuit. An experimental prototype has been constructed to investigate the validity of the claims. Experimental results show near-unity power factor, as well as $\text{2}\%$ efficiency improvement at full load when compared to a conventional interleaved boost converter with the same components. [ABSTRACT FROM AUTHOR]

LCL resonance complicates the design of a current control loop and can even threaten its stability. Extensive approaches have been proposed to deal with this resonance, among which active damping (AD) schemes based on the feedback of a single filter variable have been shown to be effective and cost-efficient. This paper presents a study of such AD techniques, where a generalized approach to developing an AD controller by relating a control diagram to an equivalent circuit is proposed. Based on this approach, AD controller forms with any one of four commonly used filter variables to realize virtual resistors (VRs) in six different connections to the LCL filter are derived. Comparisons are then made between these 24 AD controller alternatives by considering the implementation complexity of the AD controller, the number of measuring sensors, and the effect of the AD controller on the power stage. Consequently, grid-side current feedback AD to realize a VR in parallel with the filter capacitor is selected as a considered alternative. Next, two issues associated with the practical implementation of the selected grid-side current feedback AD, caused by the second-order differential expression and the digital time delay, are discussed and solved. Finally, the selected AD method is analyzed in the discrete z-domain, and its effectiveness is experimentally verified. [ABSTRACT FROM AUTHOR]

In this paper, a new low-voltage ringing zero voltage transition (ZVT) cell is proposed for a family of non-isolated dc–dc converters. In the proposed converter, all semiconductor devices operate under soft-switching condition at both turning on and off. The proposed ZVT cell resolves the issues appeared in the previous works: no online calculation required to achieve ZVS turn-on of the main switch; no extra voltage stress imposed on the main or snubber components; no floating gate driver required for the main and snubber switches; low component count of the ZVT cell; operation principles and design guideline of the boost converter with the proposed ZVT cell are presented. Also, three different positions of a snubber diode considering its junction capacitor are analyzed to clarify the advantage of the proposed ZVT cell. A 2-kW laboratory prototype of the boost converter with the proposed ZVT cell operating at 100 kHz is built and tested to verify the theoretical analysis. Finally, a comparative analysis is given to demonstrate the superiority of the proposed converter. [ABSTRACT FROM AUTHOR]

This paper presents a new bridgeless buck–boost power factor corrector with the use of the active virtual ground technique, which is named as the Manitoba Rectifier. The proposed topology can convert the grid ac voltage into a wide range of voltage outputs within a single-stage circuit. It is in a bridgeless structure and simple in design. During the operation, an LC filter is generated at the system input, where continuous grid current is guaranteed in a buck–boost characteristic topology. In addition, the filter capacitor helps to clamp the voltage ripple between the grid and the output bus terminal. Both leakage current and common mode noise are kept in a relatively small value. Thus, a single-stage and low common-mode buck–boost converter system is built. The proposed topology is successfully implemented on an 800 W prototype, and the performance is experimentally verified, which shows good agreement with the theoretical findings. [ABSTRACT FROM AUTHOR]

This paper proposed a method for one step fabricating the continuously variable multi-permeability (CVMP) toroid core by applying a specific gradient sintering temperature from the inner wall to the outer wall, i.e., along the radius direction, of a toroid core in a tube furnace using a high-temperature resistant stainless steel pipe which is used for flowing the cooling medium. The sintering temperature gradient was designed based on the relationship between permeability and sintering temperature. A CVMP core with the permeability gradually increasing continuously along the radius could be made in this way. It is beneficial for improving the uniform distribution of magnetic flux density of the core by this way. The distribution of magnetic flux density and the inductance was analyzed in theoretical calculation and finite-element analysis. A CVMP core and a single-permeability core were fabricated to evaluate their performance using an 8-V input, 1-V output dc–dc converter. The results show that the CVMP core is possible to balance the inductance and improve the output efficiency compared with a single-permeability core employed in a dc–dc converter at heavy load. It can be concluded that the CVMP core has the capacity of taking higher current than a single-permeability core. [ABSTRACT FROM AUTHOR]

In motor drive system, ear-piercing acoustic noise caused by high-frequency vibration from motor becomes unacceptable in sensitive environments, due to the application of pulsewidth modulation (PWM) and consideration of switching losses. In this paper, a novel method which associates a presented dual three-phase permanent magnet synchronous motor (PMSM) called dual-branch three-phase PMSM with carrier phase-shift technique is implemented to completely reduce odd-order PWM frequency vibration. The proposed motor has two no phase-shift three-phase windings, whose coils wind on the same teeth; it is driven by paralleled inverters with magnetically coupled inductors. With carrier phase shifting $\pi $ , the odd-order carrier frequency current harmonics with the identical amplitude in two windings are opposite in phase, and therefore the produced magneto-motive-force (MMF) harmonics in the air gap offset with each other. The experimental results are provided to verify the validity of the proposed method in vibration reduction. Compared with the previous work of vibration reduction for dual three-phase PMSMs, the proposed method can achieve total elimination of odd-order PWM frequency vibration. [ABSTRACT FROM AUTHOR]

The three-level full-bridge (TLFB) dc−dc converter has been widely used in high-voltage, high-power applications. In the experimental test, the neutral-point voltage deviation appears; moreover, it has also been found out that if the flying capacitors are introduced, the input capacitor voltages could realize self-balance even if no active balancing solutions are adopted. In the previous publications, the role of flying capacitors is generally considered to extend the range of soft switching; however, the self-balance ability has not been mentioned or investigated in any publications thus far. In order to fill this gap, this paper provides the detailed mode operation analysis of the TLFB converter and reveals the cause of the imbalance. In addition, the mechanism of the self-balance ability provided by the flying capacitors is explained in detail, which gives a deep insight into the converter. At last, the influence factor of the voltage error in steady state has been analyzed, and the specific expression of the voltage error is also derived. The feasibility of the theoretical analysis is verified by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a family of three-port three-level converters (TPTLC) composed of asymmetrical bidirectional half-bridge modules is proposed, which offers the benefits in terms of a simple control scheme, extended soft switching over a wide range of operating conditions, and reduced voltage stress across switches. The proposed converters take advantage of a pulsewidth modulation plus phase shift control technique to regulate the output voltage as well as to control the power flow between different ports independently. A stacked TPTLC is taken as an example to be introduced in detail to gain a thorough insight into the proposed family of converters. The stacked TPTLC can provide a high voltage gain along with a wide voltage gain range without using any transformer, resulting in the improvement in the power density. In order to minimize the conduction loss and reduce the current stress of switches, the root-mean-square current of the inductor and the boundary condition of the phase-shift controller in different operation scenarios are studied. Finally, the feasibility of the proposed concept and effectiveness of the design approach are validated based on the experimental results of a 1-kW, 100-kHz prototype of the stacked TPTLC using gallium nitride switches. [ABSTRACT FROM AUTHOR]

A conventional asymmetrical half-bridge (AHB) converter is one of the most promising topologies in low-power applications because of the zero-voltage switching (ZVS) of all switches and the small number of components. However, when it operates with an asymmetrical duty ratio, it has a large dc-offset current in the transformer, which increases the size and core loss of the transformer. Moreover, because the dc-offset current decreases ZVS energy for one of the half-bridge switches, it has low efficiency in a light load condition. In addition, because most of the output current is concentrated in high-voltage-rating diodes that have large forward voltage drops, large conduction loss occurs in the secondary rectifier. To solve these problems, a new AHB converter with a coupled inductor rectifier (CIR) is proposed in this paper. By adopting the CIR structure in the AHB converter, the proposed converter not only eliminates the dc-offset current in the transformer, but it also has equalized current stress in the rectifier diodes. As a result, the proposed converter achieves high efficiency in entire load condition, compared to an AHB converter with a full-bridge rectifier. The effectiveness and feasibility are verified with a 250–400 V input and 100 V/200 W output prototype. [ABSTRACT FROM AUTHOR]

Digital peak current mode (DPCM) control is widely used for dc–dc converters operating in continuous current mode. However, current tracking delay (CTD) in the system is normally neglected in the modeling stage, which leads to poor compensator design and degraded performance. This paper investigates CTD effect in boost converter with different DPCM controls. Based on dynamic relationship between the reference current and actual inductor current, the CTD transfer functions are derived, which improves the accuracy of small signal model. Since CTD degrades the phase margin of the system, equivalent migration of right half plane zero is proposed to model CTD effect. This method is very simple and straightforward, which facilitates the compensator design. Furthermore, two novel DPCM control strategies with minimized CTD are proposed, and they are based on duty cycle restriction and duty cycle extension, respectively. Both controls greatly reduce the CTD effect and improve the response speed. Besides, the duty cycle extension benefits from an extended pulsewidth modulation (ExPWM). This optimizes the calculation algorithm and speed, while improving the time margin for digital calculations. Combined with the proposed models and controls, the CTD effect is greatly reduced. The effectiveness is verified through detailed simulations and experiments. [ABSTRACT FROM AUTHOR]

A novel PWM full bridge (FB) dc–dc converter for large power industrial applications is proposed in this paper. The soft switching mode of the primary switches can be varied under different input and output conditions to achieve optimum system efficiency. In the zero-voltage and zero-current switching (ZVZCS) mode, the turn-on and turn-off switching loss can be optimized because the soft switching conditions of the turn-on and turn-off instants are well decoupled. In the zero-voltage switching (ZVS) mode, the turn-off switching loss can also be optimized because there is no requirement for light load operation in this mode. Four mosfets with ultra-low on-state resistance are used, thus, the added conduction loss is small. The auxiliary mosfets with high switching frequency are turned on with zero-current and off with zero-voltage, hence, the added switching loss can also be neglected. Furthermore, some drawbacks of the conventional ZVS and ZVZCS converters, e.g., narrow ZVS load range, high primary circulating current, incomplete reset of the primary current, and unreasonable VA rating of the added components, have been well solved. The operation principles and soft switching characteristics are discussed. Experimental results from an 18-kW prototype are provided to verify the proposed converter. [ABSTRACT FROM AUTHOR]

The inductance is an important parameter impacting current ripple calculation, usually with the assumption that the designed inductance performs ideally in most of voltage source inverters (VSIs) applications. However, the initial permeability of magnetic material usually descends when the winding current reaches or goes beyond the saturation limit. In such region of saturation, the implemented inductor does not perform as expected in design stages and its value varies with the bias current. In this paper, analysis and calculation of the current ripple are presented for a three-phase VSI with powder cores-based inductors, which reveals the calculation error of current ripple caused by the soft saturation nature of powder cores. Based on the equivalent single-phase model, the influence of inductance saturation on current ripple can be quantitatively evaluated. Then, a comparison of the current ripple calculation between considering and ignoring inductance saturation of implemented inductors is drawn in detail. Furthermore, under the condition of inductance saturation, the output current ripple peak-to-peak value of three phases is used as the constraint for variable switching frequency pulsewidth modulation (VSFPWM) design. A comprehensive method is developed to compensate the effect of inductance saturation in VSFPWM. At last, the effectiveness of the proposed strategy is verified by the detailed simulation and experiment. [ABSTRACT FROM AUTHOR]

This paper proposes an improved analytical stray capacitance model for inductors. It considers the capacitances between the winding and the central limb, side limb, and yoke of the core. The latter two account for a significant proportion of the total capacitance with the increase of the core window utilization factor. The potential of the floating core/shield is derived analytically, which enables the model to apply not only for the grounded core/shield, but also for the floating core/shield cases. On the basis of the improved model, an analytical optimization method for the stray capacitance in inductors is proposed. Moreover, a global Pareto optimization is carried out to identify the tradeoffs between the stray capacitance and ac resistance in the winding design. Finally, the analysis and design are verified by finite element method simulations and experimental results on a 100-kHz dual active bridge converter. [ABSTRACT FROM AUTHOR]

Owing to a uniform air-gap distribution of the magnetic powder materials, it is found that the conventional structure of a three-phase inductor made of magnetic powder cores will cause the three-phase magnetic flux paths to be unequal, thereby making the three-phase input voltages of a pulsewidth modulation (PWM) rectifier imbalanced. This paper presents a novel magnetic powder core structure applicable to a three-phase inductor for PWM rectifier. An equal magnetic flux path for the inductor core is designed to solve the imbalance problem of three-phase voltages. The proposed design is based on measuring the maximum flux density and the inductance values, modeled with electromagnetic simulation of a three-dimensional finite-element method. Simulation and experimental results of the proposed design show that it reduces the three-phase voltage imbalance to less than 3%. Furthermore, the unit volume of the three-phase inductor is reduced by 34% and 23%, and the efficiency is increased by 1.2% and 0.9%, compared to those of a conventional three-phase silicon-steel core inductor and three single-phase inductors, respectively. [ABSTRACT FROM AUTHOR]

Despite its potential impact on the balancing performance, current literature on the modular multilevel converter (MMC) energy-balancing feedback gain design and tuning process seem incomplete. In order to close this research gap, the energy-balancing feedback gain tuning of an ac current controlled MMC with half-bridge cells and isolated star point is considered in this paper. The tuning is difficult, because each energy error adds its own dedicated component to the circulating current reference that leads to a strong coupling that evades common tuning approaches. This problem is solved in two steps: at first, the relevant error dynamics is extracted and validated to model the time domain behavior of the energy balancing. Second, a theorem from Wu (1975) is invoked to easily calculate the closed-loop eigenvalues that finally allow for an easy optimization of the energy-balancing performance. Despite the radical simplifications during the modeling and error dynamics extraction, the acquired model is able to adequately reproduce the energy errors and the balancing circulating current of the converter. Simulation and measurement results on a grid-side MMC demonstrate a considerable performance improvement in contrast to the traditional gain estimation on the open loop. This is verified with and without a second harmonic in the circulating currents. [ABSTRACT FROM AUTHOR]

This paper proposes an interleaved totem-pole bridgeless boost power factor correction (PFC) converter with soft-switching capability. In the proposed converter, an inductor is added compared with the conventional interleaved totem-pole bridgeless boost PFC converter. The added inductor is located between two PFC converter units, and by utilizing the energy of the added inductor, all switches can achieve the zero voltage switching (ZVS). In addition, by applying the phase-shifting control between two PFC converter units, the proposed converter can control the magnitude of the current flowing on the added inductor as an optimal value. Therefore, the proposed converter can achieve the ZVS operation, while minimizing the additional conduction loss and core loss of the added inductor. As a result, the proposed converter can achieve the high efficiency. The feasibility of the proposed converter is confirmed with 180–264 Vrms input and 1.6 kW (400 V/4 A) output prototype. [ABSTRACT FROM AUTHOR]

In this paper, a phase-shifted full-bridge (PSFB) converter employing a new center-tapped clamp circuit is proposed to achieve high efficiency and high power density in electric-vehicle battery charger applications. By using a simple center-tapped clamp circuit, which consists of two diodes and one capacitor, many limitations in conventional PSFB converters are solved. The proposed center-tapped clamp circuit provides the clamping path and allows the secondary voltage stress to be clamped to the secondary-reflected input voltage. This results in a greatly reduced conduction loss in the secondary full-bridge rectifier (FBR) due to the low-forward-voltage drop of low-voltage-rated diodes, and the resistor–capacitor–diode snubber loss is eliminated. In addition, the circulating current in the primary side is removed without any duty-cycle loss. Furthermore, the turn-off switching loss in the FBR is substantially reduced due to the decreased reverse-recovery current and the reduced reverse voltage. With these advantages, high efficiency can be achieved. Besides, the size of the output inductor is considerably reduced with the aid of clamping voltage, resulting in a high power density with saving the cost. In order to confirm the effectiveness of the proposed converter, a 3.3-kW prototype was tested. Experimental results show that the proposed converter achieves high efficiency over the entire conditions with high power density. [ABSTRACT FROM AUTHOR]

The pulse-width modulated (PWM) switching rectification that can achieve a high power factor (PF) for increasing the energy transfer efficiency between an LC resonator and a rectifier and voltage step-up and -down conversion is proposed for a wireless power transfer (WPT) receiver. The proposed method can emulate the switching rectifier as a resistive load by using an inductor and integrated phase synchronizers. Additionally, similar to a switched-inductor converter that controls the duty cycle ratio (D), the proposed PWM rectifier can control the output voltage VOUT when the input is a rectified, wirelessly coupled voltage instead of a constant voltage. Thus, unlike a conventional PWM switching rectifier for ac mains, an additional voltage conditioning circuit would not be needed after the proposed rectifier for WPT. The proposed PWM switching rectification is implemented in the AMS 0.18 μm 1.8 V/5 V CMOS process. PF = 1 is measured, indicating the most efficient energy transfer, compared to only 0.55–0.65 in a peak detection rectifier. Additionally, 88.2% of peak power conversion efficiency of the switching rectifier is achieved, and the maximum output power is 80.3 mW at 500 kHz of the WPT frequency. Moreover, the measured voltage conversion ratios ranging between 0.73× and 2× are demonstrated in this paper. [ABSTRACT FROM AUTHOR]

This paper proposes a high-step-down dc–dc converter with continuous output current which utilizes coupled-inductors. Another main feature of this converter is applying the same number of switches as the synchronous buck converter. The introduced converter is suitable for non-isolated low-voltage high-current applications, especially voltage regulator modules (VRMs) with 12-V-input. Owing to extension of the duty cycle, the main mosfet current stress and the synchronous rectifier switch voltage stress are significantly reduced. However, the discharge of the leakage inductance energy increases the main mosfet voltage stress. By employing a simple lossless clamp/snubber circuit the leakage inductance energy is recovered, the voltage spike across the main mosfet is clamped, and the turn-off switching losses are reduced. There is at least one inductor in all current paths which creates an intrinsic protection against current shoot-through and provides zero-current-switching (ZCS) turn-on for the main mosfet. High efficiency is attained by the proposed converter due to extended duty cycle, low number of switches, and soft switching operation while the converter driver is just like the conventional buck converter. Due to the single-phase structure of the proposed converter, this converter is a viable alternative to the buck VRM. Similar to the other converters using coupled-inductors, the complexity of coupled-inductors design and the space occupied by coupled-inductors can be considered as drawbacks. A prototype of the proposed converter is implemented to verify the converter operation and the theoretical analysis. [ABSTRACT FROM AUTHOR]

Due to its simplicity, the hard-switching boost converter is widely used in many applications, such as renewable energy and power factor correction. The power density of the converter can be increased with smaller magnetics; however, this requires an increase in the switching frequency. Therefore, it is necessary to provide soft-switching conditions to minimize the switching losses. In this paper, a new resonant step-up converter and the associated analysis are presented. The proposed interleaved LC resonant boost converter provides soft switching for all of the semiconductor elements even under light loading conditions. Small inductors with discontinuous conduction mode (DCM) currents can be used because the interleaving behavior ensures a continuous input current with low ripples. The interleaving also reduces the output capacitor ripple current. Burst mode operation has been applied to improve the efficiency of the converter during light loading conditions. Detailed design methodology and the control strategies are provided. To show the validity of the theoretical analysis, experimental results are provided for a 400-W prototype, and are compared to a benchmark conventional interleaved boost converter with the same components. Substantial efficiency improvements are achieved for different loads and voltage gains, particularly under light loading conditions. [ABSTRACT FROM AUTHOR]

The development and application of gallium nitride–heterojunction field-effect transistor (GaN–HFET) has been actively researched. Because GaN–HFETs have advantages in high-frequency operation, it is possible to downsize power converters by increasing the switching frequency. As the switching frequency rises, the switching loss increases in proportion to the frequency; therefore, application of a soft-switching method is needed to decrease the losses and heat generation. The resonant power conversion circuits represented by the class Phi-2 inverter have soft-switching feature; therefore, these circuits realize low-switching-loss operation even in high-frequency regions. However, the operation of these resonant circuits depends on the load conditions, generally. Thus, it is important to investigate the characteristics of the inverter for various load conditions. In this paper, we investigate the characteristics of the non-isolated and isolated class Phi-2 inverters by changing the load resistance and the duty ratio of the boost circuit connecting after the class Phi-2 circuit, which is operated at 13.56 MHz. We also developed a protection system during abnormal operations such as an open circuit. From experimental results, the class Phi-2 inverter has superior characteristics under various load conditions and changes. Moreover, we confirmed the effectiveness of the abnormal operation stop system. [ABSTRACT FROM AUTHOR]

This paper describes a theory to synthesize nonisolated dc–dc converters. It uses the fundamental flux balance equation across the inductors of a converter as a starting point in this synthesis process. The flux balance equations are the linear equations of the input voltage, capacitor voltages, and duty cycle (D). The coefficients of these linear equations can be selected from a finite set of choices. These choices define the converter topologies that are subsequently used to synthesize a converter. The synthesis procedure applies to a converter of multiple order. All the possible converters are identified for a first-order topology. In the case of second-order converters, all the choices of the flux balance equation are defined. Based on these choices, three new quadratic topologies are derived and verified to demonstrate the effectiveness of the theory. The procedure to synthesize a converter from a given voltage conversion ratio is also outlined. [ABSTRACT FROM AUTHOR]

High step-up boost converters with coupled inductor have attracted much attention in the fuel cell or photovoltaic grid-connected generation system, however, there are few literatures elaborated on the construction ideas and derivation methods of them. Accordingly, in order to obtain a clear roadmap on the derivation and inner connection of these converters, a comprehensive review and analysis are presented in this paper. First, the basic boost converter with coupled inductor is regarded as the basic topology, and its merits and demerits are analyzed in detail. Then, in order to address these demerits, various step-up techniques are introduced, such as the rectifier circuit, the active-clamped circuit, the multi-winding coupled inductor, and the voltage doubler rectifier; and numerous new topologies are continuously proposed by combinations and equivalent simplifications. In addition to a detailed synthesis of each topology, a comparative and quantitative analysis among some important converters is presented, and the optimal one is chosen to build a 250 W prototype. Finally, based on comparisons and analysis, the main characteristics and inner connections of these high step-up boost converters with coupled inductor are identified and clarified. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) systems in dynamical applications, such as roadway-powered electrical vehicles, require dynamical models for the analysis and control. Conventional modeling methods for WPT systems lead to high-order models as each resonant voltage or current is described by two slowly varying real-valued variables. Other modeling methods may reduce the order but suffer from disadvantages, such as the lack of analytical expressions, loss of generality, and incomplete modeling. This paper develops a systematic and intuitive modeling approach using time-domain dynamic phasors and proposes reduced-order models by applying appropriate s-domain approximations to the linear parts of the system. A dual-side pulse-density-modulation WPT system is completely modeled as an example. Both the equivalent circuits and the mathematical descriptions are presented. The derived models are verified by large-signal step responses and small-signal frequency responses measured during experiments. As compared with the full-order models, the proposed reduced-order models have much more concise formulae while retaining high accuracy. [ABSTRACT FROM AUTHOR]

The LLC resonant converter is popular but needs a discrete series resonant inductor and a capacitor. In order to cut down component count, a novel multilayer flexible printed circuitry (FPC) planar transformer with integrated series capacitance and inductance is proposed in this paper. This planar transformer consists of two sets of multilayer open-ended windings coupled with each other to produce the integrated resonant capacitor. The equivalent resonant capacitance can be controlled by the number of the layers without changing the number of primary winding turns or pattern. The proposed transformer successfully integrates the resonant capacitor and the resonant inductor, into a single component. A model is established to accurately predict the equivalent series resonant capacitance of the transformer from the physical structure. Several multilayer FPC planar transformers are built to test the model. Practical measurements and theoretical results show good agreement and validate the proposed model. Finally, an LLC power converter with 94% efficiency is built to demonstrate the proper functioning of the proposed multilayer FPC planar transformer. [ABSTRACT FROM AUTHOR]

In this paper, an integrated step-up inverter without transformer is investigated for photovoltaic (PV) power generation. The proposed topology can be derived by combining a traditional boost converter with a single-phase full bridge dc–ac converter. The main features of the integrated inverter are: First, the leakage current caused by the solar cell array-to-ground parasitic capacitance can be theoretically reduced to zero due to the characteristics of the converter configuration, which can improve the efficiency and the reliability of the PV generation system; second, the output ac voltage of the proposed inverter can be higher than the input dc voltage, which is capable of connecting low voltage PV panels to the grid; third, only five active switches are used in the presented inverter, and those switching devices can be synchronously driven by various sinusoidal pulsewidth modulation methods based on the carrier; therefore, the proposed inverter is compact and with curtailed cost. The working principle and analysis of the proposed integrated inverter are elaborated. Finally, simulation and experimental results are obtained in a lab prototype, which agree well with the theoretical analysis. [ABSTRACT FROM AUTHOR]

A novel high step-down dc–dc converter with voltage demultiplier cell is proposed in this paper, which is widely used in the high step-down applications such as electric vehicle and digital circuits. The combination of switched-capacitor and coupled-inductor is employed to build extended voltage demultiplier in the proposed converter, which makes a quite higher voltage conversion ratio than that of the existing counterparts. Thus, the proposed converter can achieve extremely low output voltage with an appropriate duty ratio, and the extreme duty cycle is avoided. Accordingly, voltage stress on power switches is greatly reduced. Then, mosfets with low conduction resistance could be utilized to reduce conduction loss. Importantly, zero-voltage switching could be achieved for the main switch, which promotes the conversion efficiency further. In addition, the coupled inductor operates not only as a filter inductor, but also as a transformer when the main switch is in the off state, which reduces the volume of the magnetic core and improves the power density of the converter. The operation principle, performance analysis, design considerations of the proposed converter and performance comparison with recent counterparts are discussed in detail, and finally, an experimental prototype is built to verify the theoretical analysis and performance of the proposed converter. [ABSTRACT FROM AUTHOR]