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These days, constant on-time current mode (COTCM) control scheme is widely used in the voltage regulator (VR) controllers because it has a higher light-load efficiency and a higher BW design capability while maintaining a simpler compensation requirement. One issue plaguing the COTCM control is its slow transient response which is caused by its fixed TON operation. During the heavy-load step-up transient, the duty cycle becomes saturated and the inductor current increment becomes limited by TON and the minimum off time (TOFF$\_$ MIN) ratio, which can create a large undershoot at load step up. On the other hand, in the load step-down case, if the load step down occurs at the beginning of TON, a large overshoot can be created at the output. To solve this issue, this paper presents a method designed to increase the TON at load step up and then very quickly, decrease at load step down in order to reduce the undershoot and overshoot at output or otherwise save the output capacitor. In this proposed method, the increase or decrease of T ON is proportional to the output change which eliminates the chance of any overcorrection or ring-back problem unlike the methods presented in prior forums. This feature enables the control to work seamlessly in a high-frequency load repetitive case in VR applications. Since this TON change occurs only in the transient period when duty cycle is saturated, it does not affect the small-signal property of the COT control. Moreover, the proposed methods are very much compatible with the state-of-the-art single and multiphase COT control structures. Simulation and test results in both single and multiphase operations are also presented in the paper to verify the proposed concept. [ABSTRACT FROM PUBLISHER]

A novel soft-switching interleaved coupled-inductor boost converter is proposed in this paper. Only a single active soft-switching module is needed to simultaneously achieve the soft-switching property of the two switches in the interleaved coupled-inductor boost converter. The better efficiency is achieved with the less components and cost. The two main switches can achieve the ZVT turn-on and smaller-current turn-off simultaneously when the single active soft-switching module is active. Due to the coupling characteristic of the inductors, the voltages across the two inductors are changed at the same time; therefore, the equivalent circuit is equal to the parasitic capacitors of the two main switches in parallel to resonate with the auxiliary inductor. By coupling two input inductors, the volume and cost of the circuit can be reduced. The interleaved coupled-inductor topology can also reduce the input and output current ripples and share the input and output currents. The operating modes, analysis, and design of the proposed circuit have been discussed in this paper. Simulation and experiments are finally conducted to verify the validity of the proposed circuit. [ABSTRACT FROM PUBLISHER]

It is mandatory to keep the total harmonic distortion in the output of most inverters below the limits prescribed by different international standards. The harmonic distortions caused due to nonlinear loads may not get corrected by typical magnitude controller, like PID controller. Repetitive controller is more effective in such situations. Often, repetitive controller is used as add-on block to the conventional magnitude controller. Design of repetitive controller can be easily implemented on digital platform. Rapid change in phase and magnitude of inverter-filter's transfer function near corner frequency causes instability problems in repetitive controller. Various techniques have been proposed by researchers to overcome this problem. Most of the reported techniques rely on digital compensation. However, it is hard to find a digital compensator, which simultaneously meets the phase and gain requirements at moderate computational effort. Here, a new output voltage feedback scheme has been proposed, which simplifies the requirement of digital compensation. The proposed scheme requires an extra hardware but at negligible added cost. In spite of this extra hardware, the proposed circuit turns out to be more energy efficient in comparison to few popular schemes, reported in literature, where some resistance is introduced in the inverter's filter for better stability of controller. In addition to the proposed modification the paper presents a simplified explanation of the various factors affecting stability of repetitive controller. The paper also discusses a novel experimental method for verifying the efficacy of repetitive controller in suppressing distortion of any particular harmonic order. [ABSTRACT FROM PUBLISHER]

In this paper, a new zero voltage zero current transition (ZVZCT) boost DC–DC converter using a coupled inductor is proposed. This topology provides the main switch ZVZCT for the turn-on and zero voltage switching (ZVS) for the turn-off. Moreover, the auxiliary switch turns on at zero current switching (ZCS) and turns off at ZVS. The main diode turns on with ZVT and turns off with ZCS, and other diodes also operate under soft-switching conditions. Besides, due to the coupling effect, the proposed converter improves efficiency additionally since resonant energy in the resonance tank could be transferred to the output, and the circulating current can be limited as well. The soft-switching can be realized in almost all the load rang. In this design, there always exist energy releasing circuits to conduct magnetic flux leakage currents, such that the surge currents are eliminated and switch current stress can be accordingly reduced. All the devices resonate in a unique direction within less than half of a resonance period, so power losses with respect to the resonance can be decreased. In this paper, the converter design and operation principles of the converter are given. It also has been verified by a 1-kW experimental prototype with switching frequency of 100 kHz, and the related experimental results are presented. [ABSTRACT FROM PUBLISHER]

This paper presents the analysis and experiments of a variable inductor (VI) based LED driver for dc grid lighting applications. The proposed driver requires only a series inductor and a transformer as major components to drive the LED lamp from a half-bridge inverter. By introducing a VI as the series inductor, the LED current can be controlled independently from any other parameter, which makes it possible to drive and regulate several LED branches from the same half-bridge output. Other advantages of the proposed converter include inherent open-circuit and short-circuit protections, zero-voltage switching for the bridge transistor and zero-current switching for the output rectifier diodes, simple dynamics, possibility of analog and pulse width modulation dimming, constant switching frequency operation, and high efficiency. The converter is thoroughly analyzed and modeled for both steady-state and dynamic operation. As another novelty of this paper, the dynamic response of the VI has been studied and taken into account to obtain the complete transfer function of the VI-controlled system. In addition, some housekeeping issues that usually arise when dealing with VI, e.g., how to drive the VI bias winding, are solved in this work. Experimental results provided from a 50 W laboratory prototype demonstrate the correctness of the performed analysis and the good possibilities of the proposed converter. [ABSTRACT FROM PUBLISHER]

An extended-duty-ratio (EDR) boost converter is studied extensively in this paper for high voltage gain applications with a wide input (and/or output) voltage range. The EDR is a unique combination of an interleaved, multiphase boost converter and switched capacitor configuration that achieves high voltage gain with significantly lower switch voltage stress and switching losses compared to conventional high-gain solutions. Most of the switches in the multiphase EDR experience only a fixed fraction of the output voltage ($1/M, 2/M$ , etc., where $M$ is the number of phases). Through extensive analysis over a wide operating range, it is shown here that the EDR boost converter has inherent current sharing among the phases only in a limited range of duty ratio— $(M-1)/M \leq D \leq 1$. As the duty ratio reduces beyond this range as required in wide input voltage applications, inherent current sharing property is lost. In this paper, techniques to ensure current sharing under all operating zones without requiring current sensors are presented. Instead of having equal duty ratio for each phase, it is adjusted for each phase according to the operating region of the converter. Extensive analysis is presented to derive the required duty ratio changes for the different phases. The proposed concept is validated with experimental results from a 250 W, 3-phase EDR boost, and GaN-based hardware prototype. [ABSTRACT FROM AUTHOR]

Conventional single-phase power-factor-correction (PFC) rectifiers with active power decoupling capability typically require more than three active switches in their circuits. By exploring the concept of power-buffer cell, a new single-stage PFC rectifier with two active switches, one inductor and one small power-buffering capacitor is reported in this paper. The proposed converter can achieve high-power factor, wide output voltage range, and power decoupling function without using electrolytic capacitor. Additionally, an automatic power decoupling control scheme that is simple and easy to implement is proposed in this paper. The operating principle, control method, and design considerations of the proposed rectifier are also provided. A 100-W prototype with ac input voltage of 110 Vrms and a regulated dc output voltage ranging from 30 to 100 V has been successfully designed and practically tested. The experimental results show that with only a 15 μF power-buffering film capacitor, the proposed converter can achieve an input power factor of over 0.98, peak efficiency of 93.9%, and output voltage ripple of less than 3%, at 100-W output power. [ABSTRACT FROM PUBLISHER]

Renewable energy generations have been attracting sustained attentions in academic and industry. Current-fed-isolated-bidirectional dc/dc converters (CF-IBDCs) are widely adopted in low-voltage high-current applications such as solar photovoltaic fuel cell with energy storage. This paper gives an overview and a comprehensive comparative evaluation of CF-IBDCs. The active clamped, dual half-bridge, L-L type dual active bridge, resonant-type, naturally clamped, and other type topologies of CF-IBDCs are investigated, analyzed, and compared regarding their circuit topological structures, operation characteristics, modulation methods, and soft-switching technologies. In addition, component cost models and loss models of converters are deduced and presented. On this basis, quantitative and comprehensive performance comparison of seven typical CF-IBDC topologies selected from each type is conducted in terms of costs, losses, weight, volume, and power density for the given system specifications and design constraints. Finally, the application range of different CF-IBDCs and future trend are presented to encourage further development. [ABSTRACT FROM AUTHOR]

In this paper, a novel topology combining reconfigurability and hybridization is presented. Reconfigurability allows the proposed converter to operate in three different operating modes, yielding a wide range of step-up conversion ratios. The combination of two charge-pump cells and an inductor allows to reduce the average inductor current if compared to a standard equivalent boost converter. A prototype with integrated MOS, drivers, and logic but external passives was built. Experimental results show that with $\mathbf {f_{s} }=\text{300}\,$ kHz, $\mathbf {V_{in} = \text{6}}\,$ V, and $\mathbf {I_o = \text{70}}\,$ mA, the converter can cover conversion ratios in the range from $\text {2.5}$ to $\text {10}$ , with a maximum output voltage equal to $\text {60}\,$ V. Peak efficiency is $\text {91}$ %. When the output current is increased to $\text {100}\,$ mA peak efficiency is $\text {92.8}$ %. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of active zero vector pulsewidth modulation (AZPWM-1) and space vector pulsewidth modulation (SVPWM) on the design of passive common-mode (CM) attenuation methods to reduce CM current and shaft voltage in inverter-fed V/f-controlled induction motor drives. The passive CM attenuation methods examined here are the CM choke, the CM electromagnetic interference (EMI) filter, and the CM transformer. The attenuation requirement of AZPWM-1 and SVPWM is identified to design the passive CM choke and EMI filter. Based on the attenuation requirement, the design guidelines are revisited for SVPWM, and design rules are proposed for AZPWM-1. However, the CM transformer is designed based on the step change in magnitude of CM voltage of both the pulsewidth modulations (PWMs). The limitations in design, regarding switching frequency and component size for each case, are also established. It is shown that to have a similar attenuation in the considered two PWM cases, AZPWM-1 requires smaller passive components compared to SVPWM. The proposed design guidelines are substantiated with experimental results on a 1.1-kW induction motor drive. [ABSTRACT FROM AUTHOR]

This paper proposes a very simple analog control for quasi-square-wave zero voltage switching (QSW-ZVS) and triangular current mode bidirectional converters. The proposed circuit controls the inductance current, thanks to the use of a variable-width hysteretic current mode control. The upper and lower bounds of the hysteretic band are clamped to ensure QSW-ZVS operation with a single current command and independently from power flow direction. This enables the control to achieve a seamless transition between source and sink modes. The advantages and disadvantages of the proposed analog control are analyzed and two different power converters are built to demonstrate the validity of this solution: a 50 W, 48 to 24 V bidirectional buck converter and a 100 W, 24 to 48 V bidirectional boost converter. [ABSTRACT FROM AUTHOR]

The power efficiency and weight of present point-of-load (POL) dc–dc converters for drone applications are often compromised because they suffer from large switching losses at continuous conduction mode for heavy loads and excessive hardware overheads at discontinuous conduction mode for light loads. This paper presents a boundary conduction mode (BCM) control scheme for POL converters embodying a single operation mode. This is achieved by means of a hysteresis voltage controller to turn on/off the output power stage when necessary. The proposed BCM control scheme achieves high power efficiency (≥91.2%) over a wide load range (5 mA–1 A) by means of fully soft switching. Specifically, a hysteretic current controller is proposed to realize ZCS, and an adaptive dead time controller is proposed to realize ZVS. Further, the proposed BCM control scheme requires a small output inductor (0.82 μH) by means of designing the customizable peak inductor current. To verify the proposed BCM control scheme, we realize a BCM-based POL converter that features an input voltage range of 5–16 V, output voltage range of 2.5–8 V, switching frequency of 1.5 MHz, peak power efficiency of 96.8%, and ≤35 mV output voltage undershoot/overshoot for 1-A load step. When being benchmarked against state-of-the-art counterparts, the proposed design features the lowest voltage undershoot/overshoot, the highest switching frequency, ∼5.7× smaller inductor, and ∼11% higher power efficiency at light loads. [ABSTRACT FROM AUTHOR]

This paper proposes a ripple injection method in a two-stage intermediate bus architecture to overcome the incremental negative-impedance effect in the intermediate bus converter (IBC) induced by the constant power load, which is essentially a tightly regulated point of load (PoL) converter. The proposed method uses the voltage ripple of the intermediate bus in the feedback path for the closed-loop PoL converter while operating the IBC in open loop. The small-signal model is derived and verified using SIMPLIS simulation. The voltage ripple is shown to carry the inductor current information of the PoL converter. Thus, the proposed scheme is expected to retain the superior line regulation of current mode control for the PoL converter even without sensing the inductor current. Load current feed forward can improve the transient response for the PoL converter. Moreover, the load current information is also used to generate the appropriate duty ratio for the IBC during transient recovery. A simple PI controller is used for the PoL converter, which reduces the design complexity using the proposed control scheme. A hardware prototype is made, and the superior performance using the proposed control scheme is experimentally verified. [ABSTRACT FROM AUTHOR]

This paper presents a new single-phase ac–dc–ac three-level three-leg converter composed of three coupled-inductors and six active switches. The system model, operation principles, and a control strategy are presented and discussed. Additionally, a space-vector pulsewidth modulation technique is developed to double the effective frequency of the grid and load voltages and to reduce the switching losses. The proposed converter is compared to other similar converters in terms of switch count, harmonic distortion, and power losses. The results show that the proposed topology has improved power quality and uses fewer switches and gate drive circuits. These characteristics can potentially reduce the costs and the complexity of the system. In addition, the proposed converter eliminates the requirement for dead time to prevent short circuit of the dc-link. In order to validate the theoretical analysis, simulated and experimental results are presented and discussed. [ABSTRACT FROM AUTHOR]

With the conventional secondary phase-shifted (PS) control, a semidual-active-bridge (S-DAB) dc–dc converter suffers from low efficiency at light load in buck mode due to hard switching and high tank current. In order to avoid this phenomenon and extend soft-switching range, a hybrid control including the primary pulsewidth modulation plus secondary phase-shifted (PWM+PS) is proposed in this paper. Under the proposed hybrid control, all steady-state operation modes with distinctive features are identified and analyzed. Based on the operation range, power characteristics and switching behaviors in each mode, a minimum peak current control route is developed, which can enable the converter to work with low tank current and soft switching over the whole load range. A lab-scale S-DAB converter is implemented to validate the theoretical analysis, and experimental results reveal that the higher efficiency can be achieved using the proposed control route. [ABSTRACT FROM AUTHOR]

This paper proposes a high-efficiency three-level (TL) dc–dc converter with reduced circulating current and rectifier voltage stress by using coupled inductor in the rectifier circuit. Because of decreased circulating current, the conduction loss in the primary circuit is reduced. In addition, since the rectifier diodes with low forward voltage drop can be employed due to the small voltage stress, the conduction loss of rectifier diodes can be reduced. Therefore, the efficiency can be increased due to the reduction of the conduction losses in the primary circuit and rectifier diodes. The characteristics of the proposed converter are analyzed and compared with other TL converters. The validity of the proposed converter is verified by the experimental results of the prototype with 540–600 VDC input and 750 W (48 V/15.625 A) output. [ABSTRACT FROM AUTHOR]

This paper presents a pulsed power modulator with a new structure that utilizes the reverse recovery characteristics of diodes to achieve an effective pull-down circuit configuration. The proposed configuration for active pull-down applicable to negative pulsed power applications with a high-voltage direct switching method is implemented by adding a diode to the pulse discharging path of the modulator, instead of using a pull-down resistor. The diode is forward-biased while an output pulse voltage is applied to the load. When the pulse voltage applied to the load is removed, the residual energy in the load is quickly discharged through the reverse recovery path of the diode so that the pull-down function of the pulsed power supply system is efficiently performed. The operating principle of the proposed system is described, and each operating mode is analyzed in detail. In addition, the feasibility of the proposed system configuration is examined through various simulation results. Finally, it is proven that the proposed system can be used effectively in pulsed power application fields through a practical experiment in plasma source ion implantation applications. [ABSTRACT FROM AUTHOR]

DC-to-DC power supplies are critical components for processors in high performance computing and datacenter servers. Conversion from an intermediate bus voltage (e.g., 12 or 48 V) to the core voltage (∼0.9 V) of processors must be efficient, compact, and cost effective. This paper proposes two versions of active-clamp forward converter (ACFC) power blocks to supply core voltage from either 12 or 48 V intermediate bus voltage. The ACFC power block can be individually tested prior to assembly and vertically soldered onto the motherboard to fit in a standard 1U server. A low loss, compact planar transformer is designed into the ACFC power block printed circuit board (PCB). A custom, standing slab inductor not only provides high inductance and high saturation current but also helps to mechanically support the power block. A one-piece copper winding connects the transformer to the inductor, thereby reducing the dc loss in the current path. Thorough analysis is performed to model the conversion loss of the proposed power block. Experimental results show a peak efficiency of 90.4% (12 V input) and 89.5% (48 V input) with 0.9-V output. [ABSTRACT FROM AUTHOR]

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]

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 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 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 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]

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]

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]

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]

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]

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 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]

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]

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]

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]

With the increasing demand for flat displays, slim telecom/IT power supplies, and portable devices, the use of planar transformers (PTs) is becoming mandatory to achieve slim, compact converter designs. In particular, PTs present a significant opportunity to replace tall and bulky wire-wound transformers in industry standard LLC converters. However, the common-mode (CM) noise generated by PTs remains a significant obstacle to make LLCs effective. The CM noise issues are originated by large capacitances in overlapping primary and secondary layers of PTs, leading to serious electromagnetic interference issues. This paper develops a new winding method to overcome CM noise in LLC PTs. By minimizing noise, the proposed method prevents the use of bulky CM chokes, helping to keep a slim/flat form factor for LLC converters with high-power density. As well, the proposed winding method maintains low ac resistance and leakage inductance, two desirable features in high-efficiency transformers. The paper explains the root cause of CM noise in LLC PTs and develops a comprehensive method that targets all sources of CM noise in the transformer and is applicable to any type of PTs. The proposed winding method successfully shields problematic turns with high $dv/dt$ and overlaps the turns with the same $dv/dt$. As a result, circulating currents between primary and secondary (which are known as CM noise) are prevented, which leads to significant reduction of the converter's noise. Experimental results show that the proposed PT generates 11–20 dBμV less CM noise than a traditional PT with the same parasitic capacitance, which is the result of using the proposed winding method. [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]

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]

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 right-half-plane (RHP) zero in a continuous conduction mode boost converter results in a significantly restricted closed-loop bandwidth (BW) for higher voltage gain and/or load current conditions. A compensating ramp is used for current-mode control (CMC), and a higher ramp slope degrades the BW. Variable-frequency digital CMC offers inherent current-loop stability and real-time tuning scope for higher closed-loop BW. However, the challenges are to select the sampling frequency and sampling instant of the output voltage with discontinuous ripple due to the effective series resistance of the output capacitor, and its impact on stability. This paper shows that an event-based current-mode constant off-time digital modulator achieves superior stability and performance in a boost converter along with the reduced RHP zero effect over other digital CMC techniques. Using a discrete-time framework, the fast-scale stability conditions and small-signal models are analytically derived for various digital CMC techniques, which are validated using SIMPLIS simulation. A boost converter prototype is tested, and the analytical predictions are verified experimentally. Further, the analysis is extended to a non-inverting buck–boost converter. [ABSTRACT FROM AUTHOR]

This paper presents a method that overcomes the problem of the confusion during fast irradiance change in the classical maximum power point tracking (MPPT) as well as in model predictive control (MPC)-based MPPTs available in the literature. The previously introduced MPC-based MPPTs take into account the model of the converter only, which make them prone to the drift during fast environmental conditions. Therefore, the model of the photovoltaic (PV) array is also considered in the proposed algorithm, which allows it to be prompt during rapid environmental condition changes. It takes into account multiple previous samples of power, and based on that is able to take the correct tracking decision when the predicted and measured power differ (in case of drift issue). After the tracking decision is taken, it will be sent to a second part of the algorithm as a reference. The second part is used for following the reference provided by the first part, where the pulses are sent directly to the converter, without a modulator or a linear controller. The proposed technique is validated experimentally by using a buck converter, fed by a PV simulator. The tracking efficiency is evaluated according to EN50530 standard in static and dynamic conditions. The experimental results show that the proposed MPC-MPPT is a quick and accurate tracker under very fast changing irradiance, while maintaining high tracking efficiency even under very low irradiance. [ABSTRACT FROM AUTHOR]

In this paper, a two-stage transformerless multiple-output converter is proposed for applications requiring a high voltage step-down ratio. The proposed circuit transfers power via a current interface and the use of current-source-mode (CSM) converters, resulting in low voltage stress and drastically simplified control. The first stage of this configuration is regulated to provide a constant current to the second stage. The second stage consists of series-connected CSM boost converters. The high step-down ratio of the proposed configuration reduces the voltage stress in the switches of the second stage. The series-connected CSM converters are inherently independent of each other, leading to a very simple control scheme without the need for decoupling of the input voltage of the interconnected converters. Input voltage variation to the system will not affect the input voltage of the second stage. Load variation in one output will not affect the other outputs. If one or more CSM converters are shorted, there is no impact on other converters. These advantages enable a high scalability. Besides, the first stage of the proposed configuration can operate both in continuous conduction mode (CCM) and discontinuous conduction mode (DCM) with the same control strategy. This feature leads to a low control complexity and elimination of inductors. The performance of the proposed converter is illustrated with a laboratory prototype driving light emitting diodes (LEDs). [ABSTRACT FROM AUTHOR]

This paper introduces a novel modeling approach that allows to obtain fast simulations of pulsewidth-modulated dc–dc switched-mode power supplies (SMPS). The proposed methodology combines the use of precise switched models during transient evolutions and averaged models during steady-state or slowly varying conditions. In that way, the resulting mixed modeling approach enables to obtain the detailed switching behavior of SMPS in the context of long-term simulations. The commutation between models is automatically performed in runtime by an algorithm that detects the transient or slowly varying condition according to the evolution of some model variables. When the precise switched model is used, the mentioned algorithm also adjusts the averaged model parameters so that its results are accurate irrespective of the operating point. This paper also describes the implementation of the methodology in the Modelica language and reports simulation experiments showing that the results are as accurate as those obtained using precise switched models, but several times faster. [ABSTRACT FROM AUTHOR]

This paper presents a multi-period frame transient switching control (MP-TSC) scheme for buck converter with a controlled coupled inductor, aiming at improving the load transient response. The proposed buck converter utilizes a controlled coupled inductor as the output inductor. During a load transient, the coupled inductor is controlled as a small equivalent inductance so as to achieve fast transient regulation. While in the steady state, the coupled inductor behaves as a large inductance to reduce the output current ripple. Furthermore, on the basis of the proposed variable inductance circuit, an MP-TSC control scheme is proposed and implemented in a digital form. With the proposed control scheme, the load transient event is divided into n + 1 sub-periods, and in each sub-period, the capacitor-charge balance principle is used to determine the switching time sequence. Moreover, the control principle design and transient response index analysis are provided. Furthermore, its feasibility is validated in simulation and experiment with a 12–3.3V low-voltage high-current synchronous buck converter. Experimental results demonstrate that the voltage deviation of the proposed MP-TSC scheme (coupled coefficient of the controlled coupled inductor is 0.52) has improved by more than 79% compared to that with the auxiliary circuit disabled. [ABSTRACT FROM AUTHOR]

This paper contains a comparison between three topologies of a three-phase two-level inverter: A quasi-Z-source inverter (qZSI), a voltage-source inverter with a boost converter and a voltage-source inverter with an interleaved boost converter. experimental results obtained from laboratory tests of equivalent 6-kW 100-kHz inverters based on SiC mosfets and Schottky diodes are provided. The following parameters are compared: Quality of input inductor current and output phase voltage as well as total power losses in the inverters. The results for these parameters are obtained for input voltage ranging from 325 V to almost 600 V (where feasible), for two sets of equivalent modulation methods (two regular methods and two reduced-loss methods), for a couple of characteristic values of deadtime and for the operation both at the maximum value of modulation index and at equal values of voltage across the inverter bridge. Results of the experiments show that the qZSI topology may, at certain conditions, surpass the traditional two-stage inverter topologies in the areas of input inductor current quality, output voltage quality and also power losses (at high values of input voltage). What is needed to obtain that is a careful examination of operating conditions, applied modulation method and deadtime value. [ABSTRACT FROM AUTHOR]

This paper discussed an active-bridge-active-clamp (ABAC) topology that is suitable for highpower more-electric-aircraft applications. Though conventional modulation techniques can be applied to ABAC converters, they present drawbacks, such as increased low-voltage (LV) current ripple and limited power transfer capability. To address these problems, a phase-shift-modulation (PSM) scheme is proposed to provide clean dc terminal current at the LV side while maintaining high power transfer capability and efficiency in a wide operating range. The proposed PSM has a complete switching harmonics cancellation on the LV terminals independent of the operating conditions. This results in high quality power without any ac components, thus minimizing passive filtering. In addition, when terminal voltages vary from their nominal values, the proposed PSM can improve the maximum power transfer capability of the ABAC converter compared to the conventional approach. The theoretical claims are validated by both simulation and experimental results on a 10-kW 270-V/28-V ABAC converter. [ABSTRACT FROM AUTHOR]

This paper proposes a new class of topologies of single-stage high-frequency ac-link power converters, which is capable of providing both voltage step up/down within a wide frequency and voltage ranges. The proposed family, which supports bidirectional power flow, can interface various single/multi-port dc and/or single/multi-phase ac systems to provide dc–dc, dc–ac, ac–dc, or ac–ac power conversion. In this family of converter, which offers a very modular structure, a small inductor that forms the link exchanges power entirely or partially between the source and load. The proposed family can function in buck, boost, and/or buck–boost modes of operation, and a combination of these modes of operation is also feasible. In comparison to the parallel inductive four-quadrant link converters, the proposed family features a significantly reduced link peak current, reduced switch ratings, and reduced total number of power switches. These features enhance the efficiency, reduce the total cost, and increase the power density of the system. In order to further improve the overall efficiency of the system, minimize the current/voltage stress over all utilized semiconductor devices, and lower electromagnetic interference (EMI), a small capacitor is placed in parallel with the link inductor to realize soft-switching operation for the proposed configurations. Moreover, the proposed converters have the potential to incorporate a lightweight single-phase high-frequency transformer for electrical isolation. The proposed circuit topologies prevent reverse recovery issues and eliminate losses corresponding to body diodes of power switching devices via utilizing power switches in conjunction with external fast recovery diodes. The proposed family offers a very high level of reliability owing to its immunity from short circuit of input and output terminals and open circuit of the link inductor, which may occur in other power converters due to commutation problem resulting from a short deadtime or an overlap time between switches, unwanted control command, delay in electronic circuits, or EMI noise's misgating on or off, in addition to the absence of electrolytic capacitors in the power circuit. A control approach is also developed to regulate input and output currents in one stage of power conversion. A detailed theoretical analysis, operation, design methodology, and control strategy of the proposed family are provided in this paper, and the effectiveness and performance of the proposed converter family are verified via simulation results and experimentally. [ABSTRACT FROM AUTHOR]

In the applications such as mixed-color light emitting diode (LED) lighting system, LED drivers are always required to provide constant current for each LED string and each current should be controlled independently. For this purpose, a single-stage series-type LED driver with independent control of N-channel output currents is proposed in this paper. The function of power factor correction can be realized inherently to obtain high power factor. N active output units, each one made up of a power switch, a diode, and an output filter capacitor, are series-connected to form the series-type N-channel outputs structure. According to different current reference values, N-channel output currents can be independently regulated just by sampling each output current to adjust the duty cycle of each secondary output-switch automatically. The operating principle and independent closed-loop control strategy of the proposed LED driver with N = 3 are analyzed as an example in detail. Finally, the quantitative parameter design method for a 120 W prototype is elaborated. And, the experimental results are presented to verify the effectiveness of the LED driver and the correctness of parameter design method. [ABSTRACT FROM AUTHOR]

Toroidal transformers are commonly used in power electronics applications when the volume or weight of a component is at a premium. There are many applications that require toroidal transformers with a specific leakage inductance value. A transformer with a large (or tuned) leakage inductance can be used to eliminate a (series) filter inductor. In this paper, a procedure to control the leakage inductance of toroidal transformers by leaving unwound sectors in the winding is presented. Also, a simple formula is obtained in this paper that can be used to design transformers with a specific leakage inductance value. The leakage inductance formula is expressed as a function of the number of turns, the geometrical dimensions of the toroidal transformer, such as core internal diameter, external diameter, and height, and the angle of the unwound sector. The formula proposed in this paper has been obtained and validated from laboratory experiments and hundreds of three-dimensional finite element simulations. The techniques described in this paper will find applications in the design of transformers that in addition of providing voltage boosting need to double as filters. [ABSTRACT FROM AUTHOR]