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Non-isolated high-voltage gain soft-switching dc-dc converter is an ideal candidate for distributed generation system converters. This paper proposes a high-voltage gain soft switching quasi-Z-source dc-dc converter. The converter integrates a coupled inductor and switched capacitor into a quasi-Z-source network. Soft switching is achieved for all active devices in the converter by controlling the auxiliary switch Sa. By inheriting the advantages of the quasi-Z-source network and coupled-inductor/switched-capacitor, the converter has high voltage gain, high efficiency, low input current ripple, low voltage spike of main switch, and common ground. In addition, the efficiency of the converter is improved by recycling the energy of leakage inductance, resulting from an inherent active clamp of the main switch. The steady-state operation, voltage relationship, current/voltage stress, and power dissipation of each component of the converter have been analyzed and derived in detail. The properties of the proposed converter are verified by designing a 200 W prototype in the laboratory. When the input voltage is 48 V and the output voltage is 380 V, the converter efficiency reaches 96.92%, while the efficiency is 93% in a hard switching. The key waveforms of the converter obtained from the experiment agree well with the theoretical analysis results.

This paper proposes a high step-up dc-dc converter with a continuous input current which is suitable for sustainable energy systems. A three-winding coupled inductor, two power switches, three diodes, and three capacitors are utilized to perform the functions of active switched inductor and switched capacitor. By charging the two primary windings in parallel, and discharging the two primary windings in series to the intermediate capacitor and the output, the conversion ratio can be further improved with lower voltage stresses and current stresses on its power switches. In addition, the energy stored in the leakage inductance is recycled to reduce the voltage spikes of the power switches. Eventually, a laboratory prototype with an input voltage of 36 V - 48 V, and output voltage of 400 V - 600 V with a rated power of 600 W is implemented to validate the correctness and effectiveness of the theoretical analyses. The maximum efficiency and full load efficiency are 97 % and 96.2 %, respectively.

This paper presents two topologies which provide high leakage inductance in shunt-inserted integrated magnetic transformers. These differ from conventional designs by replacing the low-permeability magnetic shunt of a planar transformer with high-permeability magnetic shunt segments, separated by many small air gaps. This approach results in a shunt with the same bulk permeability as the conventional design, while using lower cost and readily available magnetic materials such as ferrite. A modelling and design approach which can estimate the leakage and magnetising inductances precisely is provided for each topology. Theoretical analysis is presented and verified using finite-element analysis and experimental implementation. AC resistance analysis for both transformer topologies is also presented. In addition, an LLC resonant converter is built to verify the performance of the proposed fully-integrated magnetic transformers in practice. It is shown that the proposed topologies can integrate all three magnetic components of an isolated LLC resonant converter in a single planar transformer, which reduces the converters volume and cost.

The leakage inductance of medium-frequency transformers (MFTs) significantly affects the operation and efficiency of isolated converters, that are one of the most important components in solid state transformers, and should be accurately controlled or be minimized. This paper proposes a general analytical model of leakage inductance based on the superposition theorem and Rogowski coefficients, taking non-ideal geometric factors, such as the different heights of the primary and secondary winding in practical implementations, into account, with only less than 4% error compared to most 3D finite element simulations and 7% to all experiments. Based on the proposed model, an optimization scheme to minimize the leakage inductance for typical winding structures through adjustment of the winding arrangement is proposed and mathematically proved, which can reduce the leakage inductance by up to over 40% compared with the traditional concentrated arrangement, also validated in experiments. In addition, the optimization method does not need to redesign other magnetic parameters, basically free to use at no cost.

A multistep predictive algorithm eliminates overshoots of the current vector outside the boundary circle while the processor identifies the next optimal switching state vector following a boundary transition. The predictions of the current vector trajectories refer to a simplified machine model consisting only of the leakage inductance. Nevertheless is good accuracy of the predictions achieved. Operation at low switching frequency minimizes both har-monic distortion and switching losses. Using higher switching frequencies does not lead to noticeable improvement over ordinary carrier modulation. Maximum fundamental output voltage is achieved by predictive overmodulation.

In high-power traction system, the stator current of the dual three-phase permanent magnet synchronous motor (DTP-PMSM) suffers from large number of current harmonics due to the limitation of the switching frequency of the inverter. Thus, this paper proposes a novel current harmonic distortion minimization (CHM) pulse width modulation (PWM) method under low carrier ratio to suppress current harmonics for the DTP-PMSM, which takes the salient pole ratio, the leakage inductance and the load angle of DTP-PMSM into consideration. The mathematical model of current harmonics of DTP-PMSM using synchronous PWM is established under low carrier ratio. The established model demonstrates that the current harmonics of the DTP-PMSM are not only affected by the inverter output voltage, but also affected by the salient pole ratio, the leakage inductance and the load angle of DTP-PMSM. To achieve better control performance on harmonics suppression of the DTP-PMSM, an optimization problem considered characteristics of the DTP-PMSM is formulated to minimize the current harmonics by regulating the switching angles of each phase. The total harmonic distortion (THD) of stator current can be reduced effectively by solving the optimization problem. The effectiveness and robustness of the proposed method are verified and compared with three other methods under the same switching frequency.

This paper discusses electrical design optimization of a 3.3 kW, 380 V to 250-380 V, 500 kHz, dual-active-bridge dc-dc converter for on-board chargers, operated with constant-power (CP) charging. In order to operate the converter at 500 kHz without concerns on switching performance and efficiency while also improving power-density, a low-parasitics, PCB-based, wire-bondless full-bridge module featuring bare-die SiC MOSFETs and compact, electro-thermally multi-functional coolers is employed. High switching frequency operation also felicitates realization of the DAB inductor using the transformer’s leakage inductance, thereby enhancing power-density by eliminating the need for a discrete inductor. Design strategy for such magnetic integration in a planar transformer is discussed followed by a systematic design optimization of the transformer, including selection of leakage inductance value, core geometry and number of turns for achieving zero-voltage-switching (ZVS) and maximum average efficiency over the entire charging profile. Experimental validation was performed using a proof-of-concept prototype, which is operated up to 3.3 kW and has a final projected power density of 5.44 kW/L. Results demonstrate operation with ZVS over the entire charging profile with satisfactory high-frequency waveforms and a peak efficiency of 98%.

The switching action of power electronic devices causes high frequency current, magnetic field, vibration and annoying noise of induction machines fed by inverters, and these high-frequency components concentrate around the switching frequency and its multiple times. Adding auxiliary winding with capacitors is an effective way to reduce the high frequency vibration by weakening the high frequency magnetic field. In order to analyze the vibration mitigation effect of adding auxiliary winding with capacitors, this method is systematically and theoretically analyzed in the paper. The accurate equivalent circuit of induction machines with auxiliary winding is proposed considering the mutual leakage inductance between stator main winding and auxiliary winding. The transfer function of electromotive force and its frequency response are used to illustrate the effect of vibration reduction. To verify the correctness of the analysis, two induction machines with different auxiliary winding arrangements are prototyped and tested.

This article introduces a push–pull series connected (PPSC) ac–dc converter intended for high-voltage direct current applications. The proposed topology requires fewer submodules compared to a standard modular multilevel converter (MMC) to withstand the same dc voltage. Each converter phase unit is connected to its corresponding phase on the ac side via a center-tapped single-phase transformer which also provides the galvanic isolation needed in most applications. The required arm inductance can be merged into the transformer leakage inductance avoiding the need for additional inductors. In this article, both the design and operation of the converter are discussed in detail. Furthermore, a comparison of the PPSC and MMC in terms of energy storage requirements and efficiency is presented. The converter concept and the control strategy proposed is validated by computer simulations using the piecewise linear electrical circuit simulation (PLECS) simulation package as well as through experiments on a small-scale, 300-V, 2-kW laboratory prototype.

This paper presented a high-efficiency push-pull resonant converter solution for auxiliary power supply in 70 kV isolated applications. This power supply consists of a two-stage structure with a resonant push-pull inverter and a buck regulator. A series resonance is introduced in the inverter with its operation and parameter design to achieve high-efficiency voltage isolation. A buck converter with feedforward control is presented with the small-signal model and controller design to regulate the output voltage. Besides, the transformer is another challenge as a crucial part of the voltage isolation. Specifically, the optimization design of toroidal core and sector windings is presented, including the analysis of isolation, loss analysis, and leakage inductance. The paper presents comprehensive converter and transformer models, describing the proposed power supply’s design process. Furthermore, a case study is demonstrated under 70 kV isolation with 36 V-84 V input and 48 V output. A prototype of a 200 W, 1.4 L isolated power supply has been built to demonstrate the design model’s validity and process. Results convincingly indicate that the proposed converter has the highest efficiency of 93.1% and can maintain the 70 kV isolation voltage with good regulation performance.

This paper presents a semi-analytical method for calculating AC copper loss of stator form-wound windings. The proposed method is capable for simulating circulating current effect between parallel strands with torsion transposition in the end region, as well as skin and proximity effect inside the strand. The solution model of circulating current is firstly derived, and the key parameter, namely the slot leakage inductance matrix, is also obtained by analytical method. Then, with the calculated current of each strand, the current density distribution inside the strand is induced. Finally, the calculated copper loss of a permanent magnet generator is compared with the finite element result, which validates the accuracy of the proposed model.

This paper proposes an accurate impedance model of line commutated converter (LCC) in the stationary frame. The commutation overlap process caused by the transformer leakage inductance complicates the modeling for LCC. Traditional impedance models are derived in positive sequence and negative sequence frame based on the simplified commutation overlap process, which degrades the modeling accuracy and limits the description of frequency coupling. This paper systematically analyzes the effects of the commutation overlap process on the impedance model, and the impedance model with the accurate commutation overlap process is established in the dq-frame. For clearly revealing the frequency coupling phenomenon of the LCC, the complex space vector is employed to extend the impedance model in the dq-frame to the complex -frame. A closed-loop model on PSCAD/EMTDC is used to verify the proposed impedance model in the time-domain and the frequency-domain. The consistency between the simulation results and theoretical analysis effectively verifies the accuracy of the proposed model.

This article proposes a voltage-fed zero-voltage-switched topology based on the push–pull converter. The proposed converter uses the leakage inductance of the transformer to transfer power from input to output. Phase-shift modulation strategy is used to control the flow of this power. A coupled LC regenerative snubber-based energy recovery circuit reclaims the trapped energy in the leakage inductance. The snubber circuit also ensures soft-switched operation and reduces the voltage stress across the semiconductor switches. The power-flow equation is characterized and experimentally verified for the proposed converter. The gate control signals are implemented using an field-programmable gate array (FPGA). A 240-W prototype validates the steady-state behavior and snubber design equations.

In this article, a 10 MHz dc/dc converter based on three-dimensional air core transformer with zero-phase difference synchronous driving signals is designed. By using the characteristics of no leakage inductance in the inner winding of the nested toroidal air core transformer, the phase difference between the output voltage of the inverter and the input voltage of the rectifier can be regarded as zero, so that the rectifier and the inverter can use the same driving signal, which simplifies the control of the synchronous rectifier switches, and realizes the reliable and efficient synchronous rectification control at 10 MHz. The prototypes with primary and secondary compensation are proposed and the experimental results verify the feasibility of the proposed control method and numerical design method.

This article proposes a new high step-up DC-DC converter for fuel cell applications. Built-in transformers and voltage multiplier cells are integrated into the structure to step-up the voltage gain. The paper proposes a new topology with common ground. Two of them are connected using the dual boost concept. Thus, the final structure provides input current interleaved that reduces the current ripple, output-series connection that increases the voltage gain and floating ground on the output voltage, which can be a limitation for some applications. Additionally, on designing the built-in transformer with a leakage inductance value much less than the magnetizing inductance value (less than 0:5%), the proposed topology does not need a clamp circuit, which reduces the number of components and increases the efficiency. Operational steps, static gain analysis, and design guide of the new converter are described in details herein. Furthermore, a 1 kW, 48-800 V prototype was built to verify the theoretical analysis. Tests in laboratory reached 94:60% of maximum efficiency at 480 W and 93:00% of efficiency at 1.0 kW (rated power).

This article presents a novel planar-based transformer winding and core structure with controllable leakage inductance generation for integrated magnetics applications. As a result of limitations in integrated magnetics from the literature, a new approach is proposed utilizing semi-interleaved windings and controllable leakage via a leakage flux core leg featuring a horizontal air gap. The proposed transformer design is analyzed via detailed reluctance modeling to determine closed-form equations for the magnetizing and asymmetrically distributed leakage inductances. Next, a genetic-algorithm-based multiobjective design optimization problem is developed, seeking to minimize the core and winding losses of the proposed transformer subject to a set of parametric and geometric constraints in a dc–ac dual-active-bridge topology for microinverter applications. The optimization was extended to include other integrated magnetic structures from the literature, where it is determined that the proposed transformer is superior from the perspectives of efficiency, footprint area, and parasitic capacitance. Based on the results of the optimization analysis, two designs with theoretical transformer California Energy Commission (CEC) efficiency drops (i.e., CEC efficiency reduction specifically due to the transformer loss mechanisms) of 1.19% and 0.83% were fabricated and evaluated for electrical and thermal performance in the proposed 40 V, 400 W microinverter.

In order to deal with the challenges in establishing a high input voltage high step-down auxiliary power supply (APS) for modular converters, a flyback converter utilizing series-connected silicon carbide (SiC) MOSFETs is proposed in this article. With the aid of a novel snubber circuit structure, the used series-connected SiC MOSFETs can switch with nearly perfect dynamic voltage sharing. Besides, the snubber circuit acts as voltage clamping circuit for the flyback converter, so voltage overshoot caused by transformer leakage inductance can be effectively controlled. Furthermore, the snubber circuit helps to power the control, gate driver, and startup circuits of the APS, leading to a reduction in system complexity and improvement in efficiency. Detailed circuit analysis and design considerations of the APS are presented. Finally, hardware of a 4 kV/120 W APS is established and experimentally verified.

Leakage inductance is a critical design element of a transformer in a galvanically isolated power converter. For multi-objective optimization-based designs of power converters, analytical leakage inductance models that are computationally efficient and accurate are preferred over the finite element methods (FEMs). In this article, three new analytical models are proposed—triple-2-D, double-2-D, and single-2-D—that are formulated using the magnetic image method. These 2-D models are used to calculate the leakage inductance of a partially filled shell-type transformer having a circular center leg, and the resulting errors are less than 1.25% for each model when compared to the 3-D FEM simulated value of the leakage inductance. Additionally, three different conductor models are considered, and their relative accuracies and computational efficiencies are investigated. Furthermore, a variable inductance transformer (VIT) is designed, whose leakage inductance can be modified by moving one of the windings vertically along the central core leg. The analytically evaluated variable leakage inductances of the VIT are in good agreement with the 3-D FEM simulated and experimentally measured values.

Current-fed dual active bridge dc–dc converters are suited for renewable energy systems such as solar photovoltaic and fuel cells, due to the advantages of small input current ripple and wide input voltage range. In this article, a current-fed dual active bridge dc–dc converter based on pulse width modulation plus phase shift control is studied. The working principle and zero-voltage switching (ZVS) conditions of the converter are analyzed in depth, and it is proved mathematically for the first time that all switches can naturally achieve ZVS independently of dc inductance and leakage inductance under a wide input voltage range within full load range. Based on maximum power transfer, peak current, and root mean square (RMS) current analysis, optimal dc inductance and leakage inductance design to obtain low inductor RMS current is proposed. In addition, the detailed loss breakdown was implemented by comparing it with the nonoptimized case. The effectiveness of the theoretical analysis and design method has been verified by experimental results.

In this article, a reduced-component-count centralized equalization system based on a novel integrated cascade equalization topology is proposed to achieve the equalizing of series-connected battery packs. The proposed converter topology is the integration of the polarity switches and the bidirectional converter in traditional centralized battery equalization systems, and can also be regarded as a cascade structure composed of a bidirectional buck-boost converter and a bidirectional flyback converter. Compared with existing centralized equalizers, the number of components applied in the proposed scheme is significantly reduced, which obtains higher cost performance and reliability, and is more suitable for the equalization of large-capacity battery packs. Meanwhile, this integrated cascade structure enables the proposed topology to achieve an ultra-high voltage conversion ratio, hence the efficiency can be significantly enhanced by employing a transformer with a smaller turns ratio and reduced leakage inductance. Furthermore, the operating principles, design considerations and comparative analysis are presented in detail. Finally, an experimental prototype based on a 13-cell lithium-ion battery pack is established to verify the superior performance of the proposed equalization system.

Purpose Despite its well-founded criticism and lack of proper justification under core saturation conditions, the T-equivalent transformer model (Steinmetz scheme) is obviously championing in the literature. This educational paper aims to explain in a simple manner the limitations of the T-model of a low-frequency transformer and critically analyses some attempts to improve it. Design/methodology/approach Using a simplified examination of magnetic fluxes in the core and windings and using the modeling in ATPDraw, it is shown that transient transformer models with the indivisible leakage inductance allow circumventing the drawbacks of the T-model. Findings The authors show the absence of valid grounds for subdividing the leakage inductance of a transformer between its primary and secondary windings. The connection between the use of individual leakage inductances and inaccurate prediction of inrush current peaks is outlined as an important example. Practical implications The presented models can be used either as independent tools or serve as a reference for subsequent developments. Social implications Over generations, the habitual transformer T-equivalent is widely used by engineers and Electromagnetic Transients Program experts with no attention to its inadequacy under core saturation conditions. Having studied typical winding configurations, the authors have shown that neither of them has any relation to the T-equivalent. Originality/value This educational paper will contribute to the correct understanding of the transients occurring in a transformer under abnormal conditions such as inrush current or ferroresonance events, as well as during an out-of-phase synchronization of step-up generator transformers.

An isolated high step-up converter, which is derived from the reverse structure of a regular LLC resonant converter, is proposed in this article. The proposed converter consists of an inverter stage, a secondary-side resonant tank, and an active voltage-doubler rectifier. An additional input diode is introduced into the regular push–pull inverter so as to make the magnetizing inductance free from being always clamped by the input voltage and make up new voltage gain features. The leakage inductance, which always shows a significant value when reflected to the secondary side in a high step-up transformer, can be used to make up the resonant tank. Under a simple pulse-frequency-modulation control with 0.5 duty ratios for both the primary-side and secondary-side switches, a high step-up function can be easily realized by the converter with good load regulation ability. Meanwhile, synchronous rectification (SR) can be naturally achieved by the secondary-side switches. The additional input diode can be replaced by a MOSFET with an analog SR chip to further improve the efficiency, without changing the original control scheme. The validity of the study is confirmed by a 500-W prototype with 36–42 V input and 380-V output. The peak efficiency can reach 96.9%.

Model predictive control (MPC) has been recently in the limelight within the field of multiphase machines and drives because it can naturally exploit some of their inherent advantages. Unfortunately, the phase current quality provided by standard MPC is unacceptable when the values of the stator resistance and leakage inductance are low. Aiming to overcome this disadvantage, different MPC strategies using synthetic/virtual voltage vectors (VVs) have been developed. Nevertheless, static VVs are created offline, and consequently, they cannot be adapted to the operating point. This limitation has been recently mitigated with the creation of dynamic virtual voltage vectors (DVVs), where VVs are generated online combining two different switching states per sampling time. Despite the current quality improvement using DVVs, the refinement of the voltage output is still limited, and consequently, the solution is suboptimal. This article suggests the use of smart voltage vectors (SVVs) that are obtained by composing the three best voltage vectors in a smart proportion during the sampling period. The calculation of the duties is performed with an online smart search that allows the real-time implementation of this MPC version. The capability of the proposed SVV-MPC to enhance the current quality indices is validated with experimental results.

A current-fed dual-inductor resonant full-bridge dc–dc isolated boost converter is proposed. The converter is most suitable for applications that demand wide input voltage and load ranges. It can be used as a front-end dc–dc converter that can boost variable low voltage from a power source [battery (home/industrial inverter/industrial UPS application), fuel-cell, or solar-PV] and interface it to a high-voltage dc-link, which typically feeds an inverter. It removes all major drawbacks of conventional current-fed isolated dc–dc converters, namely high-voltage spikes across the switches due to transformer leakage inductance, need for additional start-up circuit, and difficulty in converter tripping in case of faults. Soft-switching of rectifier didoes and clamping power switches is load independent leading to good efficiency over entire load range. Converter can be operated with D < 0.5, making it suitable for wide input voltage range applications. A detailed comparative analysis with state-of-the-art converters for wide input voltage range applications considering the major important factors, such as power device utilization, transformer utilization, inductive energy requirement, and dc capacitors utilization, confirms the superiority of the proposed converter. Experimental results for a 2.5 kVA inverter application with an input dc voltage range of 90–160 V and output ac voltage of 230 V are provided.

In this article, we present a new type of Z -source inverter (ZSI) that replaces two inductors in the original quasi-ZSI with two transformers. It can produce a very high output voltage with the high value of the modulation index. Moreover, it enables both to provide a better power quality of output and to reduce the switching loss. In particular, the proposed quasi-clamped ZSI with two transformers give a unique solution to obtain high gain by reducing the turns ratio, rather than increasing it. Also, the leakage inductance of the transformer might cause huge voltage spikes across the inverter bridge. To deal with this problem, an effective clamping technique is proposed. As a result, this increases the overall efficiency of the system by utilizing the low-power switching devices. The characteristics of the proposed quasi-clamped ZSI with two transformers are comprehensively discussed with the detailed theoretical analysis. Thereafter, its performances are evaluated by both simulation and experimental tests.

The conventional method to model a dc–dc converter is by averaging its state variable over a switching period. However, due to the dc–ac–dc structure of the dual active bridge converter (DABC), the average value of the inductor current over a switching cycle is zero. Therefore, the conventional methodology cannot be applied to the DABC. The time-scale discrete-time modeling of the DABC is proposed to mitigate the zero average state variable problem. The time-scale methodology simplifies the analysis of the DABC by segregating the fast state variable inductor current and slow state variable output voltage. The proposed model has the advantage of the explicit large signal in terms of the circuit parameter, like the average value model. The explicit steady-state circuit expression from the large-signal model helps in the study of the soft-switching range of the DABC. Moreover, the small-signal model from the proposed method results in an explicit small-signal model. The model incorporates semiconductor on -resistance, inductor equivalent series resistance, transformer resistance, and leakage inductance. The effect of the converter net equivalent resistance on the small-signal model is thoroughly studied. Finally, the model accuracy in the steady-state, open-loop, and the small-signal are verified in both the switching simulation model and experimental setup.

A critical factor deciding the controllability of a doubly-fed induction generator (DFIG) in a wind power system is the ratio of its leakage reactance to resistance. If this ratio is high then the DFIG has two uncontrollable slow resonant modes. The emergence of these modes, often referred to as parametric resonance, can cause the wind farm to exhibit poorly damped transient behavior, irrespective of any control action. In this letter we resolve this problem by presenting a new series compensation strategy in the stator line of the DFIG that prevents this uncontrollability. By tuning the compensation and the controller gains of the DFIG, the controllability of the wind farm is shown to be improved drastically, and accordingly the inter-area oscillations on the grid side to be damped significantly. We illustrate various implementation aspects of the proposed approach via numerical simulations of the IEEE 68-bus power system model with one wind farm.

A segmented three-phase interior permanent magnet synchronous motor (IPMSM) can bring a significant advantage in the development of electric vehicles (EVs) since it can be used as a simple inductor filter for an integrated battery charger without torque production during charging/vehicle-to-gird (V2G) mode. However, unlike an induction machine, majority of IPMSMs have low value of stator inductance, possibly below the minimum limit of the pulsewidth modulation rectifier requirement; therefore, the integrated battery chargers based on these types of IPMSMs may have difficulty dealing with grid current harmonics during charging/V2G mode. This article presents the method to design a suitable segmented three-phase IPMSM with nine windings (S3-IPMSM-9W) for integrated battery chargers. The optimization of stator winding inductance is proposed in order to get a large stator inductance capable of achieving acceptable ripple during charging and does not degrade the traction mode performance. Therefore, an optimized inductance, which is eight times greater than the nonoptimized stator inductance value was obtained. 96% of the efficiency of the optimized machine was achieved during the motoring mode. Moreover, with the help of optimized leakage inductance acting as a grid-side filter, the total harmonic distortion below 5% is reached during charging. Simulation and experimental results are provided to validate the theoretical analysis.

In this article, a vector control strategy based on indirect rotor field-oriented control (IRFOC) for star-connected three-phase induction motor (SCTPIM) drives under open-phase fault (OPF) using balanced and unbalanced transformation matrices (TMs) is proposed. Most of the current works studying SCTPIM drives under this type of fault are based on using two unbalanced TMs and ignore the leakage inductance in the FOC equations. This article studies a novel control strategy, considering the leakage inductance in the FOC equations of an SCTPIM drive under OPF. It is shown that using an unbalanced TM for stator current components and the conventional balanced TM for stator voltage components, it is possible to control an SCTPIM under OPF using a modified IRFOC system. The proposed vector control scheme is simulated and implemented using MATLAB/M-File software and DSP/TMS320F28335 controller board for a 0.75 kW SCTPIM drive system. Results show that the introduced IRFOC technique can satisfactorily control the SCTPIM under OPF condition.

The brushless excitation structure characteristics of the aviation wound-rotor synchronous starter/generator (WRSSG) put forward the requirement on the brushless exciter (BE) model that both the stator and rotor windings can be interfaced with the external circuit directly. In this paper, a double-side variable-parameter voltage-behind-reactance (DS-VP-VBR) model of the BE considering magnetic saturation was established firstly to realize the direct connection between the stator and rotor windings with external circuits. Then, a double-side constant-parameter VBR (DS-CP-VBR) model with completely decoupled RL circuit was developed through the algebraic transformation and numerical approximation from the DS-VP-VBR model. In order to further improve the model accuracy, the leakage inductance variation of the stator and rotor windings were also considered. Computer studies under steady-state and transient operating conditions verified the validity and accuracy of the proposed BE DS-VBR models.

This article presents a design and optimization methodology for a 200-kW medium-frequency transformer (MFT) based on low-loss magnetic core (FINEMET FT-3TL). The proposed optimal design methodology consists of predesign, preliminary design, and optimal design. In the preliminary design, the parallel-concentric winding structure is selected to increase the current carrying capability and reduce the leakage inductance. Based on the parallel-concentric winding concept, a novel cooing and insulation structure with 3-D printed bobbins are proposed. The optimal designed MFT prototype achieves a power density higher than 19.23 kW/L. The electrical insulation system is tested at 12 kV ac peak voltage. In addition, the partial discharge (PD) test is conducted at 7.5 kV ac peak voltage to ensure the PD-free design. The high-frequency bipolar pulsewidth modulation voltage insulation (PD) test is the first time applied in MFT design and test process. Finally, the transformer is applied in a dual-active-bridge (DAB) converter with 200 kW rated power. The peak efficiency of the DAB converter is 99.53%, and the efficiency at 200 kW is 98.85%. The peak efficiency of MFT is 99.844%, and the efficiency at 200 kW is 99.842%.

Bidirectional dc–dc converters with storage devices and high-voltage conversion ratio are widely utilized in renewable energy systems in order to manage power flow between renewable sources, storage devices, and load. One of the most important parameters in these converters, which affects the lifetime of storage devices, is the pulsating current flowing through them. This article presents a bidirectional buck/boost converter that employs a coupled inductors technique to increase the voltage conversion ratio while the current in low-side voltage source is continuous. Furthermore, only an active clamp circuit, including a clamp capacitor and an auxiliary active switch, is utilized to create soft-switching conditions for the main switches and absorb the leakage inductance energy of coupled inductors for both high step-up/step-down operating states. In this converter, the soft-switching condition is provided for all switches without any extra element in the power flow direction. Also, all diodes turn off at the ZCS condition, which removes the reverse recovery problem. A low number of elements and fully soft-switching condition for all semiconductor devices have contributed to the converter efficiency. Theoretical analysis of the proposed converter in both operating states is presented in detail, and a 500-W prototype circuit is implemented to verify the validity of the theoretical analysis and converter performance.

Sub/Super-synchronous oscillations have occurred in wind farms consisting of doubly-fed induction generators (DFIGs) or permanent magnet synchronous generators (PMSGs). This paper investigates the impact of synchronous condenser (SC) on sub/super-synchronous oscillations in wind farms with different types of generator and compares it with STATCOM. Impedance model is adopted in this paper to explain the mechanism of oscillations in wind farms and its mitigation using SC. Compared to STATCOM, SC is more effective in oscillation mitigations of the two types of wind farms. Eigenvalue analysis and time domain simulations in PSCAD/EMTDC are used to check the influence on sub/super-synchronous oscillations from different parameters of SC, such as its capacity, leakage reactance and inertia constant. The results indicate that SC would improve the system stability while a larger capacity will induce a greater improvement. A smaller leakage reactance of SC also benefits the mitigation of oscillations while its inertia constant can hardly influence system stability.

Galvanically isolated photovoltaic (PV) microinverters based on single-stage flyback topology have advantages: simplicity, better reliability, and low cost. But isolated flyback topology comes with voltage stresses on semiconductor switches caused by transformer leakage inductance. An improved regenerative snubber has been proposed to meet the ever-growing demand for higher efficiency of PV microinverters. The proposed topology is the inductor-capacitor-diode (LCD) snubber with flying capacitor modified to reduce circulating currents. Theoretical analysis reveals a number of advantages. Experimental results are presented to verify the performance.

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.