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Some advantages of the SEPIC buck-boost converter makes it stand out from other configurations. It makes possible to obtain from a unipolar input voltage both unipolar and bipolar output voltage with a good symmetry between positive and negative output voltages. It also provides efficient performance as well as circuit simplicity in unipolar and bipolar topology owing to the use of a single switch which can be operated by available integrated controllers of boost converters. The article considers the topologies of a SEPIC buck-boost converter built according to the traditional scheme (with two inductors) and according to the scheme on magnetically coupled chokes. To analyze the processes and factors affecting the converter operation efficiency, a circuit simulation has been done using the Electronics Workbench. The results of the investigation of a pulsed DC converter of input voltage to unipolar or bipolar output voltage using SEPIC buck-boost topology are presented. The circuit simulation enables to specify the switching process characteristics, to estimate the ripple level of the input current and its spectral characteristics, and to develop recommendations concerning the choice of parameters of converters elements and generation of control signals. Based on the simulation results, the load, control, and noise characteristics of the converter are obtained. The level of symmetry of positive and negative output voltage is investigated for the converter on discrete and magnetically coupled chokes. The assessment of the effect of leakage inductance on converters with magnetic coupling of inductive elements is given. Examples of practical implementation of converters built according to the SEPIC topology are shown. It is found that the resistance of the choke windings, which is less than 0.5 Ohm, has practically no effect on the efficiency of the converter, retaining the factor of about 0.9 in a wide range of load currents, while the main source of conversion losses is a passive diode switch. Synchronous converter circuits of a number of manufacturers are more efficient, but require more complex controllers for active switches with elements for protection against through currents.

Medium-frequency transformer (MFT) dc bias is critical for the safe operation of dual-active-bridge (DAB) converters. To analyze the dc bias, expressions of dc bias are derived for SiC MOSFET DAB converters. It shows that the dc bias is a current source in steady state; thus, a dc bias current capacity is defined and used as a design constraint in the optimization of MFT. The dc bias current capacity is related to core materials, geometric parameters, and flux density, which is analyzed with analytical expression. Optimization equations with geometric variables are derived, which can be solved theoretically or numerically for both interleaved winding (IW) and separated winding (SW) MFT without and/or with leakage inductance design. Based on the optimization equations, different MFT designs for a 150-kW SiC MOSFET DAB converter are compared on the aspects of core materials, winding structures, and without/with leakage inductance design. The combination of IW structure MFT with auxiliary phase shift inductors is chosen, and the assembled prototype is tested with the 150-kW DAB converter. The designed dc bias capacity, temperature rise, and efficiency are verified.

High-frequency link matrix rectifier (HFLMR) is advantageous in three-phase isolated ac–dc conversion due to its elimination of dc-link components. However, the input current distortion increases in an HFLMR when it operates in discontinuous conduction mode (DCM). The modulation scheme forms the high-frequency link current shape, which directly affects the input current distortion. Space vector pulsewidth modulation (SVPWM) is a popular modulation method for the matrix-type converter for its flexibility of arranging switching vectors. In this article, a new switching scheme based on SVPWM is proposed for the HFLMR to improve the current quality in DCM without adding complexity to the control. In DCM, the resonance between diode capacitance and transformer leakage inductance becomes a source of converter harmonics and instability. The method of shorting the transformer secondary is implemented to eliminate the voltage and current ringing in the discontinuous period. A 600-W lab prototype HFLMR that converts 115Vrms, 400-Hz three-phase input voltage to 270-V dc output voltage is implemented for experimental verification of the proposed switching scheme and converter topology. With the proposed switching scheme, the input current distortion is effectively reduced. With the proposed topology, the high-frequency voltage and current ringing are eliminated.

This brief proposes a method to dynamically modeling the coupled-inductor double-boost converter operating in continuous-conduction mode. Such method has the advantage of including the leakage inductance effect on the dynamic behavior of the converter in a simple, straightforward approach. The presence of the leakage inductance is initially neglected and a traditional circuit-averaging technique is used. The averaged models are then refined by accounting the impacts of the reported inductance. Since its major impact is on the damping factor of the system, this dynamic change is modeled by equivalent resistors. Equations for describing the equivalent resistors are derived based on the analysis of the duty cycle loss caused by leakage inductance in the static gain of the converter. The effect on the averaged small-signal model is shown by a closed-form control-to-output transfer function and experimental results demonstrate its accurate performance.

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

This paper presents a new optimized winding and core design for improved performance of an induction machine. The performance improvement is attained by space harmonic reduction in the winding magnetomotive force (MMF). In the proposed design, the new conductor distribution of the winding and its slot positions are obtained by solving an optimization problem which maximizes the fundamental component of the MMF and reduces certain harmonic components in it, number of which depends on the number of slot per pole per phase. The novel formulation of the optimization results in the modified slot sizes while keeping the width of stator and rotor teeth same as that for the conventional machine. In the proposed design, for certain machine rating, when compared with conventional machine the active length of conductor and the amount of iron is unchanged. However, the winding overhang reduces which leads to copper saving ( $$\approx $$ 6.46%), less winding resistance ( $$\approx $$ 6.5%) and leakage reactance ( $$\approx $$ 7.69%) and finally resulting in decreased total copper losses ( $$\approx $$ 21.6%). Also, improvement in the steady-state torque and efficiency and decrease in the maximum flux density in core is obtained with the proposed machine design.

A high gain nonisolated dc–dc converter is proposed for the distributed generation systems. High voltage gain is achieved by integrating different methods with reduced duty ratio. Inductive voltage spikes across MOSFET s are alleviated and stress is reduced with inclusion of a passive-clamp circuit. Thus, lower voltage rating (small ${R}_{\text{ds}({\textsc {ON}})}$ ) active devices can be adopted. Using this clamp, zero-voltage switching over wide load range is achieved for both the MOSFET s. In addition, leakage energy of the coupled inductor is recycled without using auxiliary switch and thus, the gain get further improved. Zero-current switching is obtained for all the diodes using quasi $-$ resonance principle, which diminishes voltage spikes across the diode caused by the parasitic ringing between leakage inductance and diode's stray capacitance. Therefore, snubbers are not necessary to protect the diodes and to mitigate reverse-recovery losses. Overall efficiency improves because of lower switching and conduction losses of the semiconductor devices. A 600 W prototype working at 75 kHz is built in the laboratory to verify the performance. The peak efficiency is nearly 96.5% and is above 95% for wide load range.

In order to avoid the bus voltage spikes caused by leakage inductance endangering the normal operation of the inverter, based on the improved Y-source inverter, the traditional clamping structure and voltage peak absorption circuit are introduced, and a high step-up and low-voltage stress improved Y-source inverter with the capability of absorbing bus voltage spike is proposed. This topology fully utilizes the structural characteristics of the improved Y-source inverter itself, and further increases the DC-side voltage gain on the basis of ensuring the busbar voltage peak absorption capacity, while reducing the capacitor voltage stress. This paper demonstrates the superiority of the proposed topology over improved Y-source inverter topology by analyzing its working principle and voltage gain, simulation and experiment platform are constructed to perform the circuit simulation and experiment, and the correctness of the theoretical analysis of the proposed inverter and the effectiveness of the busbar voltage peak absorption capacity are verified.

In this article, we propose a novel interleaved high step-up converter. The proposed converter integrates the built-in transformer voltage multiplier cell (VMC) to the interleaved boost converter with voltage lift capacitor. The voltage gain is increased by both of the turns ratio of the built-in transformer and the voltage lift capacitor. Hence, there is no need to operate the converter around unity duty cycles to obtain high voltage gains. Meanwhile, the voltage stress across semiconductors is reduced considerably, facilitating the utilizing of mosfet s with low on -state resistance and diodes with low forward voltage drop decreasing the conduction losses. The leakage inductance of the built-in transformer not only provides zero current switching (ZCS) for mosfet s but also controls the falling current rate of the diodes alleviating the reverse current recovery problem. In addition, the energy of the leakage inductance is recycled by the clamp capacitor avoiding high spikes across switches. In comparison with the recently published converters, the proposed converter introduces all of the abovementioned advantages with a low number of components that make it an interesting solution for high efficiency and high step-up applications. Finally, a 40-V to 580-V prototype with 930 W power is fabricated to explore the merits of the proposed converter.

Model predictive control (MPC) has been recently suggested as an interesting alternative for the regulation of multiphase electric drives because it easily exploits the inherent advantages of multiphase machines. However, the standard MPC applies a single switching state during the whole sampling period, inevitably leading to an undesired $xy$ voltage production. Consequently, its performance can be highly degraded when the stator leakage inductance is low. This shortcoming has been, however, mitigated in recent work with the implementation of virtual/synthetic voltage vectors (VVs) in MPC strategies. Their implementation reduces the phase current harmonic distortion since the average $xy$ voltage production becomes null. Nevertheless, VVs have a static nature because they are generally estimated offline, and this implies that the flux/torque regulation is suboptimal. Moreover, these static VVs also present some limitations from the point of view of the dc-link voltage exploitation. Based on these previous limitations, this article proposes the implementation of dynamic virtual voltage vectors (DVVs), where VVs are created online within the MPC strategy. This new concept provides an online optimization of the output voltage production depending on the operating point, resulting in an enhanced flux/torque regulation and a better use of the dc-link voltage. Experimental results have been employed to assess the goodness of the proposed MPC based on DVVs.

Multimodule isolated converters incorporating excellent features of galvanic isolation, bidirectional power flow, and simple control are widely adopted in medium-voltage (MV) high-power dc–dc applications. However, the converter size and dc-link capacitor voltage balancing are significant concerns in galvanically isolated cascaded dc–dc converters. This article proposes a new design of an integrated transformer implementing toroidal cores named toroidal core multilimb transformer (TCMLT), employed in a dc–dc modular isolated bidirectional dual-active-bridge (IB-DAB) resonant converter topology. The modular design structure of the proposed transformer can be conveniently constructed and implemented for more number of participating modules conforming the compactness constraint. Moreover, an external coupling winding is implemented in the TCMLT structure to resolve the dc-link voltage balancing issue. This coupling winding method substitutes the expensive complex control circuits, which consequently results in cost reduction and reliability enhancement. Besides, the reluctance model of the proposed structure is analyzed. Based on the reluctance model, a common mode–difference mode (CM-DM) electrical circuit is realized for the proposed scheme. Furthermore, unlike the conventional approach of implementing U, UI, and EI cores for multilimb transformer (MLT) structure with separate limbs, a synthesis method of TCMLT in toroidal form is proposed. The comparative study of the proposed design with the conventional U-core MLT confirms that the proposed TCMLT offers less leakage inductance with significant size reduction. Finally, to validate the efficacy of TCMLT, a three-limb laboratory-scale prototype is employed in a 6-kW cascaded IB-DAB resonant converter topology.

Coupled inductors are used in power electronics to improve transient response and reduce component size. To further increase inductance density and reduce fringing fields, a combination of different magnetic materials was introduced to create a hetero-magnetic coupled inductor (HMCI) core. To simplify and speedup the prototyping of HMCI designs, in this study a paste-extrusion additive manufacturing platform was used to co-process a custom-developed magnetic and conductive feedstock. First, ferrite plates of each having a winding were co-printed and co-sintered. Then, the HMCI was assembled by bonding together the ferrite + winding plates using a low-temperature curable magnetic paste. The finished HMCI was characterized by measuring its dc winding resistances, leakage inductance, and coupling coefficient. The coupling coefficient of the HMCI was easily adjustable to meet various requirements for high-frequency interleaved multiphase buck converters. This work demonstrates the feasibility of applying an additive manufacturing process for rapid prototyping of an unconventional power magnetic component having an inhomogeneous magnetic core.

This paper deals with a control system and an algorithm of Lithium-ion battery fast charging. Charger structure consists of an electromagnetic filter, two parallel full-bridge DC-DC converters with low-pass filter. The parallel full-bridge DC-DC converter has two isolated transformers. Sometimes, changes are observed in the transformer ratio and the leakage inductance due to a fault caused by partial short circuit in the transformer. In addition, a transformer is rarely open circuit by a fault or out of service for maintenance. So, a control system which is based on sliding mode control is used for covering the uncertainties of transformer ratio and its leakage inductance. The transformer ratio has an important role in state-space equation of the charger circuit and has important effects on the control system in constant current and constant voltage modes. Therefore, this paper analyses the impact of the parameters of isolated transformer and the control system on the reference signal tracking and the accuracy of current sharing between two parallel DC-DC converters. The simulation results show the effectiveness of the proposed control system.

Triple active bridge (TAB) as an isolated multiport converter is a promising integrated energy system for smart grids or electric vehicles. This article aims to derive and analyze zero voltage switching (ZVS) regions of TAB, in which both switching losses are reduced, and electromagnetic interference issues are mitigated. In the proposed closed-form solution of ZVS criteria, parameters such as the parasitic capacitance of the switches, the leakage inductance of the transformer, the switching frequency, the port voltage, the phase-shift inside and between the full-bridges are all taken into account. The analysis shows how the five degrees of freedom can be used to maintain ZVS operation in various operating points. The analysis and derived closed-form ZVS criteria are experimentally verified using a laboratory prototype. The derived analytical ZVS criteria are a powerful tool to study and optimize the operation of TAB converters.

Solid-state transformers (SSTs) are a promising solution photovoltaic (PV), wind, traction, data center, battery energy storage system (BESS), and fast charging electric vehicle (EV) applications. The traditional SSTs are typically three-stage, i.e., hard-switching cascaded multilevel rectifiers and inverters with dual active bridge (DAB) converters, which leads to bulky passives, low efficiency, and high electromagnetic interference (EMI). This article proposes a new soft-switching solid-state transformer (S4T). The S4T has full-range zero-voltage switching (ZVS), electrolytic capacitor-less dc link, and controlled dv/dt , which reduces EMI. The S4T comprises two reverse-blocking current-source inverter (CSI) bridges, auxiliary branches for ZVS, and transformer magnetizing inductor as a reduced dc link with 60% ripple. Compared with the prior S4T, an effective change on the leakage inductance diode is made to reduce the number of the devices on the main power path by 20% for significant conduction loss saving and retain the same functionality of damping the resonance between the leakage and resonant capacitors and recycling trapped leakage energy. The conduction loss saving is crucial, being the dominating loss mechanism in SSTs. Importantly, the proposed single-stage SST not only holds the potential for high power density and high efficiency but also has full functionality, e.g., multiport dc loads integration, voltage regulation, and reactive power compensation, unlike the traditional single-stage matrix SST. The S4T can achieve single-stage isolated bidirectional dc–dc, ac–dc, dc–ac, or ac–ac conversion. It can also be configured input-series output-parallel (ISOP) in a modular way for medium-voltage (MV) grids. Hence, the S4T is a promising candidate for the SST. The full functionality, e.g., voltage buck–boost, multiport, etc., and the universality of the S4T for the dc–dc, dc–ac, and ac–ac conversion are verified through the simulations and experiments of two-port and three-port MV prototypes based on 3.3 kV SiC mosfet s in dc–dc, dc–ac, and ac–ac modes at 2 kV.

Vernier permanent magnet (VPM) machine has become a good candidate to drive the pump and fan loads, since these loads always operate at low speed and require high output torque. In these applications, the machine operates near a fixed speed and requires no speed adjustment capability. Hence, the inverter can be replaced by a line-start unit, and the machine can be connected directly to the grid, which reduces the weight, volume, and cost of the whole system. However, the novel magnetic gearing effect in the VPM machine causes two issues. First, the abundant magnetic field harmonics interact with the line-start unit and produce strong braking torque even at steady-state operation; second, large harmonic leakage inductance reduces the starting capability. Therefore, the traditional method to build a line-start machine is not suitable for the VPM machine. In this article, a line-start VPM (LSVPM) machine topology is proposed. By analyzing two issues above, the structure and pole-pair of both stator armature and rotor wound windings are carefully selected, and finally pole-changing strategy is chosen to start the machine. The performances of the proposed machine are verified by finite element analysis (FEA), which shows it has 49% higher torque density than regular line-start permanent magnet machine, and has the capability to start with the rated pump load. A prototype also has been built and tested to demonstrate the analysis and simulation.

In optimizing design of the iron core, it is essential to know the magnetic field of the coil outside the core to get the leakage inductance, because the leakage inductance in this area usually provides high contribution to the flux density in the iron core. In this paper, an analytical solution as an alternative to three-dimensional FEM (finite element method) to calculate the field outside the iron core by solving analytical equation using MathCAD is presented. The analytical method provides results that are close to result given by three-dimensional FEM, but with the great advantage of dramatically reduced computing time.

This article presents the design of a dual-mode V-band power amplifier (PA) that enhances the efficiency at power back-off (PBO) using load modulation. The PA utilizes a reconfigurable two-/four-way power combiner to enable two discrete modes of operation–full power and back-off power. The power combiner employs two techniques to further improve the PA efficiency at PBO: 1) usage of transformers with non-uniform turns ratios to reduce the difference in impedance presented to the PA cores between the two modes and 2) utilize a proposed switching scheme to eliminate the leakage inductance associated with the disabled path in back-off power mode (BPM). The two-stage PA achieves a peak gain of 21.4 dB with a fractional BW (fBW) of 22.6% (51–64 GHz). At 65 GHz, the PA has a Psat of +17.9 dBm with an OP1 dB of +13.5 dBm and a peak power added efficiency (PAE) of 26.5% in full-power mode. In BPM, the measured Psat, OP1 dB, and peak PAE are +13.8 dBm, +9.6 dBm, and 18.4%, respectively. The PAE is enhanced by 6% points at a 4.5-dB back-off. The PA is capable of amplifying a 6 Gb/s 16-QAM modulated signal with an EVMrms of −20.7 dB at an average Pout/PAE of +13 dBm/13.6%, respectively. This PA was implemented in 16-nm FinFET, occupies a core area of 0.107 mm2, and operates under a 0.95-V supply.

This article proposes a high-power density 1.8 kW auxiliary power module (APM) for electric vehicles (EVs) based on gallium nitride devices. A design procedure for the high-frequency phase-shift full-bridge with current-doubler rectifier using printed circuit board (PCB)-based planar magnetics is proposed. Leakage inductance analysis of the high-frequency pulsewidth-modulation converter is given to achieve both regulation and zero-voltage-switching turn- on . Then, the magnetics optimization procedure for the customized planar core is proposed with a magnetic figure-of-merit concept to meet the high-power density target. Technical considerations are detailed to meet the extreme temperature constraint imposed on the EVs components. Finally, the proposed APM is demonstrated with a switching frequency of 700 kHz and a power density of 8.1 kW/L (132.8 W/in3).

Nowadays the use of electronic equipment finds a progressive development in the modern world. Hence it becomes a mandate to check whether the harmonic content of line current of any electronic device which is connected to the ac supply meets the appropriate standards. This demand is satisfied by implementing the Power Factor Correction (PFC) circuit in order to make the input current to be in sinusoidal in nature and in-phase with the input voltage. Numerous solutions are available to make the line current almost sinusoidal. This paper describes an isolated power factor corrected power supply that utilizes the leakage inductance of the isolation transformer to provide boost inductor functionality. The bulk capacitor is in the isolated part of the power supply allowing for controlled startup without dedicated surge limiting components. A control method based on switch timing and input/output voltage measurements is developed to jointly achieve voltage regulation and input power factor control.

This article presents a novel flux-cancellation-based modular multilevel converter (MMC) with power decoupling capability. Conventional MMC suffers from low-frequency (fundamental and second-order) ripple power in the submodule (SM) capacitors. The low-frequency ripple power makes the SM capacitors bulky, responsible for a significant portion of the volume and weight of the whole system. The ripple power on the SM capacitor of the three-phase module is phase-shifted by $2\pi $ /3 rad from each other. The proposed flux cancellation is based on directing the low-frequency ripple power to a common core of a three-winding transformer to cancel out. A three-port bidirectional isolated dual half-bridge is introduced for flux cancellation. For this scheme, the main problem is the presence of leakage inductances of the transformer, and another one is three-port isolated bidirectional converter modeling as it has only input ports. The average model is proposed for the flux cancellation circuit. It provides a practically simple model for the complex circuit. Second, a virtual-capacitance-based power decoupling controller is proposed to overcome the leakage inductance problem by the benefits of simple current estimation and of no need for the current sensor. The proposed power decoupling method reduces the system size significantly and enables the MMC to operate with a nonelectrolytic SM capacitance of few microfarads. The operating principle and control design of the proposed MMC are presented. The proposed MMC is validated by simulation and experimentation.

This article presents the analysis and design considerations of a phase shift full-bridge converter with a new simple and reliable passive auxiliary circuit for zero-voltage switching (ZVS) operation. The steady-state behavior of the converter is analyzed in detail. The contribution of the energy stored to both auxiliary circuit and leakage inductance is considered in the analysis of ZVS condition, the auxiliary current adjustment ability and the rms circulating current of the auxiliary circuit are described, and the impacts of narrow frequency variation on the converter are analyzed. The design procedures based on analytical models considering phase shift angle and input voltage variation are presented, which gives basic parameter configurations for the converter operating at a fixed frequency. The function model between the switching frequency and phase shift angle is established, which is helpful to design and optimize the converter operating at an adaptive frequency to reduce circulating current. In the proposed converter, the auxiliary current is adaptively controlled and has a sharp peak current, so the circulating current and conduction loss are greatly reduced. An experimental prototype is implemented to confirm the predicted results.

Dielectric barrier discharge (DBD)-based plasma reactor and lamp are widely used for the growing areas of medical science, bacterial disinfection, pollution control, surface treatment, and so on. In this article, a simplified high-frequency, high-voltage short-pulse power modulator (HV-SPPM) is proposed for DBD plasma sources that are effectively capacitive loads. An energy discharge circuit (EDC) has been devised in the HV-SPPM to terminate the high-voltage pulses increase indefinitely for a capacitive load, which causes damage to the pulse power modulator. The HV-SPPM is using a wide bandgap (WBG) device without having a dissipative snubber circuit on primary side and magnetic compression circuit. The performance of the HV-SPPM has been validated experimentally by using a suitable DBD plasma-UV load. In the proposed HV-SPPM, a series diode with resistor has been introduced across the DBD plasma-UV lamp to damp out the sinusoidal oscillations between DBD capacitance and leakage inductance of the transformer. The HV-SPPM is capable to generate negative voltage pulses up to 6 kV and pulse width 800 ns with frequency variation up to 50 kHz. The proposed arrangement makes the HV-SPPM more compact, lightweight, simple, and highly efficient with very short rise and fall times voltage pulses suitable for the DBD plasma applications.

A novel hybrid cascaded dc–dc converter is proposed for high voltage gain applications in this article, which is characterized by the hybrid series-parallel connection based on coupled inductors and voltage multiplier cells. The input current ripple is decreased due to the interleaved operation and the voltage stress of the switches is only 1/6 of the output voltage when the turn ratio is 1. So the high-performance MOSFETs with low ON-state resistance can be used to reduce the conduction losses. The reverse-recovery problem of the output diode can be suppressed by the leakage inductance of the coupled inductors. The leakage inductance energy of the coupled inductors is absorbed and recycled to the output, which can largely improve the efficiency of the proposed converter. The working principle and steady-state characteristics of the converter are analyzed in detail. Finally, the correctness of the theoretical analysis is verified through experimental results of a 400-W laboratory prototype.

Soft switching based on resonant operation, through mitigating switching loss and alleviating electromagnetic interference, is essential to high-frequency operation to achieve high power density. To overcome the obstacles of high switch voltage stress and ease the contradiction between voltage stress and conduction loss for traditional single-switch resonant converters, a family of zero-voltage-switched (ZVS) isolated resonant converters is proposed which utilizes a novel resonant switch. The converters enable parasitic components, including transformer leakage inductance, switch output capacitance, and diode junction capacitance to act as a part of resonant components, which facilitates ZVS and zero-current-switching operation and pushes up switching frequency. The specific derivation of the topologies is expounded, and one of the proposed converters is taken for example to perform in-depth analysis, whose mode analysis, operation principles, and parameter design method are minutely presented. Synchronous rectification is employed to further improve efficiency. A prototype was built in the laboratory and the experimental results validate the theoretical analysis well.

Purpose. The purpose of the article is to show the inadequacy of the traditional T-shaped equivalent circuit for modeling transformer operations with saturated core. The aim is to point out the unreasonableness of the separation of the transformer leakage inductance into components. The aim is also to explain the need to apply the П-shaped transformer equivalent circuits to transformers with two and three windings with finite radial thickness. Methodology. Analysis of magnetic fields in the transformer window and simulation of transient processes in equivalent circuits of the transformer using a preprocessor ATPDraw to the program ATP. Findings. The unfoundedness of the well-known T-shaped transformer equivalent circuit is shown. Differences in the processes in the core legs and yokes when transformer is connected to the network and during short circuits of the windings are noted. Equivalent circuits of a transformer with two and three windings of finite thickness are proposed, reproducing these differences. Originality. The absence of physical meaning in dividing the transformer leakage inductance into components is stated. The advantages of the П-shaped equivalent circuit are shown when calculating inrush currents accompanying the transformer switching to the network on its inner and outer windings. Practical value. We show theoretical insolvency and practical unsuitability of the Т-shaped equivalent circuit for studying transformer operations accompanied by saturation of the magnetic circuit. Advantages of the П-shaped equivalent circuit are clarified.

Three-level isolated DC-DC converter is an attractive topology in high input voltage applications, which can provide the voltage stress of the power devices to only a half of the dc voltage and also reduce the size of dc filter requirement. But major limitations in the existing three level ZVS converter topologies are brought out with an increased inductance in the primary side and it required to provide complete ZVS of all primary devices down to light loads. By employing an external inductance in the primary of the transformer, total leakage inductance of the transformer increases which is required for realization of soft switching of the converter switches but there are some disadvantages of connecting external inductance in the primary of the transformer. To overcome all these drawbacks, the three-phase three-level isolated DC-DC soft switching converter has been proposed in order to reduce voltage and current stresses. This converter topology requires less number of control switches and operates with an asymmetrical duty cycle control. The proposed three level DC-DC converters provide two- level voltage waveform before dc output filter, which significantly reduce the size of dc output filter. The proposed work has been implemented using MATLAB/SIMULINK and the performance of the proposed converter is verified through simulation results.

High-temperature superconducting (HTS) transformers with multi-segment windings have been proposed in earlier literatures for the hysteresis loss reduction and short circuit electromagnetic force mitigation. The optimum distributive ratios for these multi-segment windings have been determined in earlier literatures. Asymmetrical seven segment winding with its optimum distributive ratio (k = 1/12) results in minimization of short circuit electromagnetic forces under normal tap and any adjusted tap. However, insulation design and leakage inductance calculation for the multi-segment winding of an HTS transformer have not been addressed in past literatures. Insulation design is one of the most crucial aspects in the transformer design, especially for high voltage power transformers. The analysis and optimization of the electric field distribution over the winding’s segments insulation in these HTS transformers provide the required dimensions for precise determination of the leakage inductances. In this paper, for the first time, winding insulation design and leakage inductance calculation of a 200 MVA, 230/20 kV HTS transformer with asymmetrical seven segment winding (and k of 1/12), are carried out. The analytical method besides a two-dimensional (2D) finite element method (FEM), through COMSOL Multiphysics software, is utilized for insulation design and calculation of leakage inductances of this transformer.

Compared to Si FETs, when the main GaN FET is in full zero voltage switching condition, maximum switching loss reduction can be achieved. Therefore, in this article, an active clamp flyback converter with GaN devices that implements fast ZVS by using the proposed dynamic resonant period control (DRPC) technique can reduce large transformer leakage inductance energy loss on the active resonant circuit. As the loading changes, the DRPC technique can dynamically adjust the on -time in auxiliary switch to prevent large voltage stress on the components in the primary side. In full load condition, the leakage energy loss can be reduced, thereby transferring more energy to the secondary side with maximum efficiency up to 94%.

Parameter mismatches in a control scheme would cause the additional harmonic components and torque ripples in permanent magnet synchronous machines (PMSMs). Moreover, there is an additional leakage inductance mismatch in dual three-phase PMSM when comparing with its three-phase counterparts. In this article, a robust model predictive current control (MPCC) scheme is proposed in order to release the parameter dependence of model predictive control (MPC) in application of dual three-phase PMSM. First, the parameter sensitivity of conventional MPC in dual three-phase PMSM is discussed. Then, an incremental predictive model is applied to reject the influence of flux mismatch. Additionally, the concept of virtual vectors is introduced to deal with the influence of leakage inductance. In this case, the predictive errors are the result of inductance mismatches. Therefore, the inductance information could be obtained through the predictive errors. Finally, a discrete inductance compensation system is applied to update inductance. Comparative simulation and experimental results both verify that the proposed robust MPCC scheme could estimate the inductance information and eliminate the influence of parameter mismatches.

For the LCL -type grid-connected inverter, grid voltage full feedforward scheme is an effective method to improve the quality of the injected grid current. However, in the applications where a step-up transformer is adopted and its leakage inductance serves as the grid-side inductor, it is difficult to directly measure the grid voltage. For this case, the capacitor voltage full feedback scheme is proposed in this article to suppress the injected grid current distortion due to the grid voltage harmonics, and the full feedback function includes proportional, derivative, and second-derivative components. It is found that the derivative component counteracts the capacitor current feedback active damping, and both of them can be removed. Thus, the current sensor for sensing the capacitor current is saved. Instead, the LCL filter resonance is damped by the proportional and second-derivative feedback components, and a low-pass filter is added to the second-derivative component for ensuring a positive equivalent resistance within the full controllable frequency range. Experimental results from a 6-kW single-phase grid-connected inverter are provided to verify the effectiveness of the proposed method.

In order to solve the problem of limited frequency selection range and simplify calculations on the grounded capacitance measurement for the ungrounded distribution system, a high-frequency injecting method for the capacitive current measurement is proposed in the paper. The injecting frequency can be high enough to ignore capacitive reactance and leakage resistance comparing with leakage inductance. The leakage inductance value is obtained directly on the base of simplified calculation. Then the resonant frequency of the power system needs to be obtained by the traditional resonant method. Finally, the grounded capacitance can be calculated through the equivalent circuit and the simultaneous equations. The simulation and experiments verify the feasibility of the high-frequency method. The experiment results prove that this method not only solves the problem of frequency selection, but also has advantages of convenience and high precision (the relative error is less than 5%), which is also suitable for the larger grounded capacitance system.

Wound-core transformers are characterized by their economical and efficient design and are therefore widely used in power distribution systems; for this reason it is of paramount importance to determine their electrical characteristics. One of the most important parameters in these transformers is leakage reactance, since this is what largely determines short-circuit currents and voltage regulation. And yet the authors have found a conspicuous gap in the scientific literature concerning analytical formulations for the calculation of leakage reactance in wound-core transformers. In order to fill this gap, the authors propose a formula in terms of leakage areas and the Rogowski’s height of the windings. A geometric model of the active part of the transformer is proposed which allows for the exact calculation of the leakage areas. The results of the proposed formula are compared with simulations with the finite element method in 3D (FEM3D) and with measurements in eight real case studies. It is concluded that although the FEM3D calculates the closest results to measurements, the proposed formula reported sufficiently accurate results for transformer design purposes.

This paper discusses an isolated switching mode power supply (SMPS) with an AC 30 kVrms insulation capability for application to the solid-state transformers (SSTs) in railway vehicles. The insulation capability of the SMPS should be higher than AC 25 kVrms for application at the SSTs in railway vehicles. The proposed highly isolated SMPS is superior to commercial isolated power supplies with low insulation capability, which is normally less than 20 kV. The input side of the proposed isolated SMPS is physically separated from its output side by a specially designed miniature high-frequency (HF) transformer to obtain high insulation capability. The core of the miniature HF transformer is separated by insulation material. The primary and secondary coils are wound around each separated core. A CLLC resonant converter that consists of a primary resonant capacitor (C), two inductors (LL), and a secondary resonant capacitor (C) is applied as the proposed isolated SMPS topology to improve the output voltage regulation performance, which varies due to a large leakage inductance derived from the airgap of the proposed miniature HF transformer. Experiments are carried out to verify the CLLC resonant converter of the proposed isolated SMPS. Electrostatic finite element method (FEM) simulations and high potential (HiPot) tests are carried out to verify the AC 30 kVrms insulation capability of the proposed isolated SMPS. The electrostatic FEM simulations demonstrate the DC 42.43 kV insulation capability, and the HiPot tests verify the insulation capability from AC 5 kVrms to AC 30 kVrms.

Two-stage power conversion of class-D amplifier with front-end switching mode power supply affects the power conversion efficiency of audio amplifier system. Single-stage inverter (SSI) developed from cycloconverter can be used as audio amplifier to improve efficiency. However, current commutation of cycloconverter switches challenges for high efficiency and low total harmonic distortion (THD). In this article, a bipolar phase shift modulation (BPSM) SSI is proposed for high efficiency low distortion audio amplification. Full bridge active clamp (FBAC) circuit is used to clamp the voltage across cycloconverter switches and recycle the energy of filter inductor and leakage inductance. By using active clamp, utilization of magnetizing inductance current and optimization of driving sequence of clamp switches, zero voltage switching of the proposed BPSM FBAC-SSI is achieved over wide range. With BPSM and voltage clamp across cycloconverter switches, low THD of output voltage is also achieved. A 200 kHz prototype with 250 W output power is presented to verify the analysis results of the proposed BPSM FBAC-SSI.

Based on a hybrid technique of coupled inductor (CL) and switched capacitor, a high step-up dc–dc converter is developed in this article. It consists of one active switch, one CL, four diodes, and four capacitors. The active switch withstands low voltage stress and all diodes’ voltage stresses do not exceed half of the output voltage. Simple structure and low-voltage-rated switches contribute to high efficiency of the proposed converter. The converter provides the ideal voltage gain of ( $2 + 2\,\,n) /(1 - d)$ , here $n$ represents the turns’ ratio of the CL and $d$ is the duty ratio. Its circuit configuration and operation principle are introduced. Effects of leakage inductance of the CL and parasitic resistance of components are analyzed in detail. The experimental results demonstrate the effectiveness of the proposed converter and the maximum efficiency is above 97%.

High-power isolated bidirectional dc–dc converters with wide voltage range are attracting increasing attention in many applications. The bidirectional three-phase current-fed dc–dc converters are known to be suitable for wide voltage range applications compared to dual active bridge based converters, having advantages of reduced device current ratings and prevention of transformer saturation due to high impedance nature. However, when the duty cycle becomes lower than 0.33 or higher than 0.66, power transfer capability is limited, and the efficiency is significantly reduced due to increased circulating current, which has rarely been discussed so far. In this article, a hybrid dual-asymmetrical pulsewidth modulation (DAPWM) and pulsewidth modulation plus phase-shift (PPS) switching method is proposed for efficiency improvement of the bidirectional three-phase push–pull converter with very wide voltage range. A seamless mode change method between PPS and DAPWM is also proposed for minimizing the transient state. Further, through current waveform and power flow analysis, the leakage inductance along with transformer turn ratio are designed to minimize the root mean square (rms) current of devices, while having the capability of transferring the desired power and limiting the slew rate of transformer winding current under wide voltage range operation. Experimental results from a 22-kW prototype are provided to validate the proposed concept.

Single-phase, outer-rotor squirrel cage induction motors are widely used in ceiling fan applications. Furthermore, they can be employed for pumps, and in-wheel hub drives. In this article, an analytical model based on magnetic equivalent circuit is proposed to evaluate the performance of the motor. The influence of rotor slots’ skewing, stator end windings, slots’ leakage inductance, and core saturation are included in the model. Furthermore, the windings’ copper losses and the core's iron losses are calculated using the proposed model. The results of the presented model are compared with those of time variant finite element analysis (TVFEA) and experimental measurements close agreement between the results confirms the success of the proposed model from accuracy point of view. Furthermore, the computation time required for the proposed model considering the linear and nonlinear cores are 1 min and 11 min., respectively. However, those of TVFEA considering 64 000 mesh elements for linear and nonlinear cores are 21 h and 28 h, respectively.

In this article, a new single-input multioutput high step-up dc–dc converter is proposed, which is suitable for sustainable energy applications. Basically, the presented converter consists of an interleaved and a modified single-ended primary inductor converter, which uses coupled-inductor and switched-capacitor-voltage-multiplier techniques. Each stage generates a different output voltage using only one input voltage source and one duty ratio. The output voltage gains are effectively increased at low duty ratios by employing coupled-inductors and voltage multiplier cells. Moreover, because of using low voltage rated MOSFETs, the voltage stresses on power switches are very low. Therefore, the conduction losses are reduced and the conversion efficiency will be improved. In order to lighten the reverse recovery problems of the output diodes, the leakage inductance of the coupled inductors can be beneficial. The maximum efficiency that is achieved by the proposed converter is 97.5% and 96.2%, respectively, for both output loads. The operating principles and steady-state analysis are discussed in detail. Finally, experimental results for a prototype of the proposed topology that is implemented under 24 V for input voltage source, 286 and 390 V, respectively, for both output ports are presented to assess the effectiveness of the proposed converter.

Motor drive system generates harmful differential mode (DM) and common mode (CM) electromagnetic interference (EMI) when it is working. To solve this problem, the integrated EMI filter scheme for paralleled inverter using zero-CM pulsewidth modulation (PWM) algorithm is proposed in this article. The zero-CM PWM algorithm and the coupled inductor constitute a holistic solution for the ac side EMI suppression. By using the zero-CM PWM algorithm, the CM leakage current of the system can be suppressed without adding additional CM EMI filter and only DM EMI needs to be considered. In addition, the DM inductor is naturally integrated in the coupled inductor, leakage inductance of the coupled inductor instead of the discrete DM inductor is used as the DM inductor which has less restrictions on the inductor material. The DM EMI filter can be constructed by just adding DM capacitors. Thus, using the integrated EMI filter scheme has advantageous over traditional scheme since the CM EMI filter is omitted and only DM capacitor is added which can simplify and reduce the size of EMI filter in the ac side and has the potential to increase the power density of the system since other solutions require both the DM and CM EMI filter.

This paper presents an accurate analytical method for calculating the leakage inductance of shell-type E-core transformers with rectangular windings. For this purpose, first, an expression for calculating the leakage inductance per unit length inside the core window considering the core walls as the flux-normal boundary condition is derived. Then, a new accurate method for determining the Mean Length of Turns (MLT) based on the total stored energy is presented. The MLT is needed for the leakage inductance calculation using 2-D methods. By dividing the MLT into three partial lengths and calculating the corresponding leakage inductances using three different core window arrangements, the effect of core structure on the total leakage inductance is considered. The method is verified by 3-D FEM simulations as well as the leakage inductance measurements on two different fabricated transformer prototypes. The superiority of the method is also confirmed by comparisons with the previous analytical approaches. The proposed method enables the leakage inductance calculation with an error less than 1%, compared to the 3-D FEM results. Using the presented method, the leakage inductance calculations can be performed rapidly and accurately in the design stage without the need for time-consuming 3-D FEM simulations.