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In this letter, an internal electric field shielding layer for high voltage winding of medium voltage high frequency transformer used in a modular cascaded medium voltage solid state transformer is proposed. Without breaking the litz wire insulation layer, the high electric field is effectively shielded by a semiconducting layer and an unclosed copper foil spiral, which are electrically connected together. Not only the electric field in the main wall insulation is uniformed but also the peak value of the internal field is greatly reduced, which will help to achieve lower partial discharge and higher insulation reliability. With this structure, the difficulties of pouring process and electric field estimation for the litz wire winding are both avoid. Finally, a no partial discharge 100 kW medium voltage high frequency transformer prototype with 75 kV base insulation level is built and verified with the insulation tests. [ABSTRACT FROM AUTHOR]

An interturn short-circuit fault in the stator winding of an electric machine, denoted as turn fault, has been recognized as one of the most severe faults in permanent magnet machines, which require a swift and reliable detection, in order to implement appropriate mitigations. The asymmetry brought by a turn fault is widely used for fault detection. However, similar features also emerge in a less severe high-resistance connection (HRC) fault, which may lead to an incorrect fault identification. In this article, a more exclusive turn fault detection method with the ability to differentiate from the HRC fault is proposed. It injects high-frequency square-wave voltage signals and makes use of the difference in the high-frequency impedance under the two fault conditions. The sensitivity to the HRC fault is largely reduced. The proposed turn fault indicator is independent of the operating conditions and robust with respect to state transients. This method is validated in a fault-tolerant permanent magnet assisted synchronous reluctance machine drive. [ABSTRACT FROM AUTHOR]

In this paper, a novel multiphase reconfigurable and fault-tolerant drive converter topology is proposed for driver with fail-work capability, and fault-tolerant strategies are proposed for open-circuit and short-circuit faults in the single-phase windings, aiming to improve the motor drive system's fail-work ability in the high reliability applications. The drive converter topology can isolate open-circuit and short-circuit faults in power supplies, power devices, or switches. Then, it can reconfigure the drive circuit topology from independent H-bridge to star type by reconfigurable switches and power devices, according to the fault-type and the fault-tolerant truth tables. After reconfiguration, remedial operation will be utilized for open- and short-circuit faults of windings, so that the motor system has twofold fail-work capabilities in driver and windings. Finally, based on a series of experiments on a transit co-simulation model and test bench, the effectiveness and validity of fault-tolerant capability and the strategies are verified, and has twofold fail-work remedy. [ABSTRACT FROM AUTHOR]

A half-turn transformer with symmetrical magnetic flux is proposed for high-frequency-isolated dc/dc converters. The transformer structure can reduce the minimum number of turns from 1 to 0.5. By adopting a novel winding and circuit configuration, a symmetrical magnetic flux is realized to make full utilization of the ferrite core. A simple EI core, which is easily manufacture and commercially available, can be used to make the half-turn transformer. The operation principles of the transformer are analyzed and simulated. The performance of the transformer is experimentally evaluated on a 750-kHz, 380/12-V, 600-W LLC converter using gallium nitride devices with a peak efficiency of 98%. [ABSTRACT FROM AUTHOR]

This research proposes a novel low-voltage inverter-fed motor drive with variable parameters achieved through the independent armature winding for the automobile traction motor. The independent armature winding with low-voltage inverters can improve the total efficiency by reducing the converter losses. The inverters are able to change their connections to different coils groups of the armature winding in order to achieve the wide operating range. The voltage equation of each mode can be shown by using the transformation matrix when the winding connection is changed. Thus, the proposed motor is called the MATRIX motor. In this paper, the downsized model was designed to verify the principle. The principle model is able to achieve four motor parameters. It was confirmed that the principle model could extend the operating range and could achieve the high-efficiency driving in wide speed range. Furthermore, the novel winding reconfiguration method is proposed that not only avoids the surge voltage, but also compensates the torque reduction during the winding reconfigurations. [ABSTRACT FROM AUTHOR]

This paper describes an improved transformer winding tap injection distribution static synchronous compensator (WTI-DSTATCOM) for medium-voltage reactive power compensation. The cascaded multilevel converter based DSTATCOM is connected to the special-designed winding taps on the primary windings of the transformer instead of the conventional point of common coupling. The voltage stress for DSTATCOM to handle is reduced. The winding tap injection (WTI) method can make full use of the spare capacity of the transformer and obtain a flexible connection voltage for DSTATCOM. The compensation mechanism and winding current distribution after currents injection are analyzed by phasor diagrams under steady state. A nonlinear passivity-based control (PBC) algorithm is designed for inner-loop current control and a three-layer voltage balancing control strategy is applied to balance the dc capacitor voltage. The results obtained from the MATLAB/Simulink simulations and a down-scaled laboratory prototype experiment of 800 V verify the feasibility and effectiveness of the proposed WTI-DSTATCOM system with PBC algorithm in reactive power compensation. [ABSTRACT FROM PUBLISHER]

In multiwinding transformers, different geometry of the individual windings leads to unbalanced leakage flux paths. The unbalance affects the behavior of the power electronic converters, where these transformers are used. This paper proposes an approach to model the leakage flux path of transformer with repetitive multiwinding structure using permeance magnetic circuit. The model is composed of lumped components, it can be seamlessly integrated into system-level simulation of power electronic circuits and achieve good accuracy in time-domain simulation. Taking advantage of the repetitive structure, the model requires very limited number of parameters, which can be easily obtained from the geometry information together with only a few experimental tests. The fidelity of the model is experimentally confirmed on a multiwinding transformer prototype connected to power electronic devices. [ABSTRACT FROM PUBLISHER]

This letter presents a 20-pulse multiphase staggering autoconfigured transformer (MSAT) for power quality improvement in medium and high power applications. The proposed autoconfigured transformer is a combination of delta and zig-zag transformers. Contrary to the prior art multipulse autoconnected transformers, magnetic rating of the proposed configuration is only 40% of the load rating in addition to improved power quality indices. Moreover, the creation of a neutral point ascribed to inbuilt zig-zag windings supplements as one of the remarkable advantages of the proposed MSAT. Therefore, with this suggested configuration, the performance of zig-zag transformer is accomplished within the autoconfigured transformer. A detailed comparison of the proposed MSAT configuration with that of other multipulse autoconnected transformers in terms of magnetic rating and power quality indices are presented. Further, the feasibility and operability of the proposed MSAT are verified and validated through experimental tests on the laboratory prototype. The test results so obtained complies with the IEEE-519 and IEC 61000-3-2 standards on power quality requirements. [ABSTRACT FROM AUTHOR]

This paper presents a dc–dc boost converter topology for low input and high output voltage applications, such as photovoltaic systems, fuel cell systems, high-intensity discharge lamp, and electric vehicles. The suggested configuration consists of a three-winding coupled-inductor, a single switch and two hybrid voltage multiplier cells. Furthermore, two independent hybrid voltage multiplier cells are in parallel when the single switch S is turned on, and they are in series when the switch S is turned off. So, the advantages of the proposed converter structure are summarized as follows: 1) A coupled inductor with three windings is introduced in the presented converter structure. The two secondary windings of the coupled inductor are, respectively, used to form a hybrid multiplier cell on the one hand, on the other hand, it increases the control freedom of the voltage gain, enhances the utility rate of magnetic core and power density, and reduces the stress of power components to provide a stable constant dc output voltage. 2) The two hybrid multiplier cells can absorb synchronously the energy of stray inductance, which not only reduces the current stress of corresponding diodes, but also greatly alleviates the spike voltage of the main switch, which improves the efficiency. 3) The two hybrid multiplier cells are connected in series to supply power energy for the load, so the voltage gain is extended greatly due to this particular structure. Thus, low-voltage low-conduction-loss devices can be selected and the reverse-recovery currents within the diodes are inhibited. The operating principles and the steady state analyses of the proposed converter are discussed in detail. Finally, a test prototype has been implemented in the laboratory, and the simulated and experimental results show satisfactory agreement with the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper studies and proposes the vector space decomposition-based direct torque control (DTC) scheme for the T-type neutral-point-clamping (T-NPC) three-level inverters-fed double-stator-winding permanent magnet synchronous machine (PMSM) drive, which provides an effective solution for high-power high-reliability applications. The key is to propose a simple but effective space vector modulation (SVM) for DTC of T-NPC double-stator-winding drives-based two-step voltage vector synthesis, in such a way that good dynamic response and harmonic performance are obtained. The closed-loop controllers on harmonic subspace are incorporated to suppress the possible harmonics induced from back electromotive force and unbalanced parameters in phase windings of electrical machine. Furthermore, a hybrid current control is proposed for fault-tolerant operation of the T-NPC double-stator-winding PMSM drives under one-phase open-circuit conditions. In the hybrid current controller, the healthy winding still uses the SVM-DTC control while the faulty winding uses the closed-loop current controller to track the optimized current references. Both simulation and experimental results are presented to verify the performance of the proposed switching strategies and control schemes. [ABSTRACT FROM AUTHOR]

Dual three-phase machines are attractive due to advantages such as inherent fault tolerance. Several strategies for current reference generation have been proposed to improve the postfault performance under open-phase fault. However, for the development and analysis of these strategies, only the stator winding losses were considered, but not the converter ones. In fact, there are no studies so far evaluating the converter losses during postfault operation. Aiming to fill this gap, this letter addresses this topic. Namely, it compares the main postfault control strategies in terms of converter losses for dual three-phase machines with sinusoidally distributed windings under single open-phase fault. [ABSTRACT FROM AUTHOR]

For isolated dc–dc power converters, the interwinding parasitic capacitance of the transformer is usually one of the main paths for common-mode (CM) noise. In order to simplify the CM noise analysis, this paper proposes a two-capacitor transformer winding capacitance model. The model is derived based on general conditions so it can be applied to different isolated converter topologies. A measurement technique is also proposed to obtain the lumped capacitance for the model. The CM noise models of several isolated converter topologies are analyzed with the proposed two-capacitor transformer winding capacitance model to achieve simplicity. Finally, the proposed transformer winding capacitance model and measurement technique are verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

The demand of miniaturization of power systems has accelerated the research on high-switching-frequency power converters. A flyback converter in resonant mode that features low switching losses, less transformer losses, and low switching noise at high switching frequency is investigated in this paper as an alternative to a conventional quasi-resonant (QR) flyback topology to increase power density. In order to find a compromise between magnet size, electromagnetic interference (EMI), and efficiency, the concept utilizes the resonant behavior between transformer leakage inductance and snubber capacitor to achieve near-zero-voltage switching at both turn-on and turn-off of the primary switch, low core loss due to a continuous transformer magnetizing current, and reduced EMI due to low di/dt and dv/dt values. Meanwhile, the concept uses the regenerative snubber to recycle the transformer leakage energy with two snubber diodes and one snubber capacitor. The proposed concept has been validated on a 340-kHz 65-W prototype. Compared to the conventional QR flyback converter operating at the same switching frequency, the proposed concept has 2% efficiency improvement and better EMI performance. [ABSTRACT FROM AUTHOR]

Finite element analysis is used to examine the gap losses that occur in finely laminated nanocrystalline inductor cores under high-frequency operation. The losses are seen to be concentrated in the region of the air gap and the dependence of the losses on key design parameters and operating conditions is explored. The results show that gap losses can be significant in this type of core, creating hot spots around the gap, and the losses are not accurately predicted by established design equations for low-frequency laminated cores. A modified loss equation is proposed. Validation is provided by measurements on a 300-A, 60 kHz inductor. [ABSTRACT FROM AUTHOR]

In this study, a two-switch forward converter with reset winding and an auxiliary active-clamp circuit for a wide input voltage range are proposed. The proposed converter offers simple reset scheme through reset winding, while retaining the reduced voltage stress on the switches. Hence, the operating duty ratio can be extended. Furthermore, it can also attain zero-voltage switching (ZVS) through the auxiliary active-clamp network when magnetizing inductor is properly designed. The operation principle of the proposed converter is analyzed. Analyses of the extended duty ratio and ZVS condition are then conducted in detail based on mode analysis. The performance of the proposed converter is evaluated using a 100-kHz 300-W/48-V prototype converter for an input voltage range of 200–400 V. [ABSTRACT FROM AUTHOR]

Parasitic capacitances of the high-frequency (HF) transformer used in dc–dc converter impact harmonic analysis of the transformer and interactions with the converter. Resonant frequencies of open- and short-circuit impedances characteristics (ICs) have been widely used to extract parasitic capacitances of HF transformers, but it was reported that some resonant frequencies were unobtainable as they were too high where the ICs fluctuated heavily, and parasitic capacitances remained unevaluated. In this paper, resonance features of ICs and voltage transfer characteristics (TCs) are investigated, and a new frequency of voltage TC is used for extracting parasitic capacitances. By analyzing inner links of known impedance resonant frequencies, why and which resonant frequencies are likely to be unobtainable is revealed. Furthermore, a new frequency corresponding to zero of TC, accounting for parallel resonance between leakage inductance and mutual capacitance of the two windings, is used to extract parasitic capacitances. With this new frequency mutual capacitance of the windings is evaluated, and missing equation due to unobtainable impedance resonant frequency is added. Besides, merits and limitations of extracting parasitic capacitances based on ICs and TCs are analyzed. These techniques are verified with several HF transformer prototypes in the laboratory. [ABSTRACT FROM AUTHOR]

The main challenge of medium-frequency transformers is the number of design parameters, constraints and objectives, and the difficulty of handling them on a particular design. This paper presents a novel computer-aided optimal design for MF transformers using a multiobjective genetic algorithm, in particular the nondominated sorting genetic algorithm II. The proposed methodology has the aim of reaching the best MF transformer for a given power converter topology, by optimizing transformer efficiency, weight, and also, transformer leakage and magnetizing inductances at the same time. The proposed methodology and the optimal solutions are validated with the design and the development of two 10-kVA/500-V transformers considering two different topologies. Finally, some experimental measurements are presented so as to demonstrate the proposed models and the performance of built transformers. [ABSTRACT FROM AUTHOR]

Many high-power converter systems are often connected to the medium-voltage network using a step-up transformer. In such systems, the converter-side windings of the transformer can be configured as an open end, and multilevel voltage waveforms can be achieved by feeding these open-end windings from both ends using the two-level dual converter. An $LCL$ filter with separate converter-side inductors for each of the converter is commonly used to attenuate the undesirable harmonic frequency components in the grid current. The magnetic integration of the converter-side inductors is presented in this paper, where the flux in the common part of the magnetic core is completely canceled out. As a result, the size of the magnetic component can be significantly reduced. A multiobjective design optimization is presented, where the energy loss and the volume are optimized. The optimization process takes into account the yearly load profile and the energy loss is minimized, rather than minimizing the losses at a specific operating point. The size reduction achieved by the proposed inductor is demonstrated through a comparative evaluation. Finally, the analysis is supported through simulations and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a fault-tolerant control is proposed for dual three-phase permanent-magnet synchronous machine (PMSM) drives under open-phase faults. The object of the proposed fault-tolerant control is to maximize the torque capacity while the overcurrent protection is taken into account. Hence, the proposed fault-tolerant control is named as torque mode in this paper. Another existed fault-tolerant control for dual three-phase PMSM drives under open-phase faults is loss mode, in which the system copper loss is minimized. Torque mode is compared with loss mode, and two important conclusions are given: 1) loss mode can reduce more copper loss; and 2) torque mode can output more torque. The performances of torque mode and loss mode are verified by experimental results. [ABSTRACT FROM AUTHOR]

The stacked polyphase bridges (SPB) converter consists of several submodules that all are connected in series to a voltage source. The total dc-link voltage should split in a balanced way among the submodules. This does not always occur inherently. This paper presents an analysis of the capacitor voltage stability for the SPB converter. From the analysis, criteria for stability are derived and three alternatives of a suitable balancing controller are designed. The proposed controller alternatives and their associated stability properties are verified on an experimental setup and by simulation. [ABSTRACT FROM PUBLISHER]

A copper-loss-minimizing torque control method is considered for wound synchronous machines (WSMs) in the field-weakening region. In general, the current-minimizing solutions are often found at the intersection of the torque and voltage curves. However, those curves change depending on the rotor field current in WSM. This complicates the problem of obtaining an analytic loss-minimizing solution. In this study, a hybrid approach is suggested: analytic method, iterative computation, and curve fitting. The Ferrari's method is repeatedly applied for each field current to find intersections between the voltage limit and torque curves. Then, a loss-minimizing current set is found at the minimum of a second-order function fitted to three Ferrari's solutions. At each step, inductance changes are reflected. In the cost function, the field-winding copper loss is included along with the stator copper loss. The results show that the total loss is minimized at a point where the power factor is slightly lower than unity. Simulations and experiments were carried out for a 60-kW WSM to show the usefulness of the algorithm. [ABSTRACT FROM PUBLISHER]

Point-of-load converter at light load has low efficiency owing to the “fixed losses” such as core loss and ac winding loss. This paper focuses on two-dimensional (2-D) gapping of a ferrite core to shape inductance versus load current to reduce inductor loss at light load. Since the maximum inductance of conventional stepped gap is limited by the cross-sectional area of the thin gap, a 2-D gap is formed by joining two orthogonal gaps to gain flexibility. Higher inductance is achieved at light load compared with uniform-gap and stepped-gap geometries having the same volume and dc resistance. AC resistance is reduced at light load thanks to a magnetic path that steers ac flux away from the winding. Two C-cores with 2-D gap were fabricated and tested on a buck converter with 50% reduced total inductor loss at 10% load current. [ABSTRACT FROM AUTHOR]

The redundancy of multiphase drives provides an inherent fault-tolerant capability that is appreciated in applications with a complicated corrective maintenance or safety-critical requirements. Fault restrictions, however, force the system to be reconfigured to operate in a smooth and efficient manner. Previous works have been focused on the optimization of current waveforms to generate an undisturbed operation but still maintaining the prefault rated flux settings. This study shows that efficient controllers can improve the postfault performance in six-phase induction machines supplied by parallel-connected converters if offline optimization is used to obtain a variable reference flux. Theoretical and experimental results confirm that the proposed flux adaptation method provides higher torque/power capability, lower degree of imbalance in the current sharing between windings and efficiency improvement. [ABSTRACT FROM AUTHOR]

Newly emerged gallium nitride (GaN) devices feature ultrafast switching speed and low on-state resistance that potentially provide significant improvements for power converters. This paper investigates the benefits of GaN devices in an LLC resonant converter and quantitatively evaluates GaN devices’ capabilities to improve converter efficiency. First, the relationship of device and converter design parameters to the device loss is established based on an analytical model of LLC resonant converter operating at the resonance. Due to the low effective output capacitance of GaN devices, the GaN-based design demonstrates about 50% device loss reduction compared with the Si-based design. Second, a new perspective on the extra transformer winding loss due to the asymmetrical primary-side and secondary-side current is proposed. The device and design parameters are tied to the winding loss based on the winding loss model in the finite element analysis (FEA) simulation. Compared with the Si-based design, the winding loss is reduced by 18% in the GaN-based design. Finally, in order to verify the GaN device benefits experimentally, 400- to 12-V, 300-W, 1-MHz GaN-based and Si-based LLC resonant converter prototypes are built and tested. One percent efficiency improvement, which is 24.8% loss reduction, is achieved in the GaN-based converter. [ABSTRACT FROM AUTHOR]

The semicontrolled open-winding PMSG system has been widely investigated due to its simplified topology and easy control implementation. Nevertheless, compared with the conventional controllable converter structure, the current zero crossing phenomenon will last a longer time in the semicontrolled configuration, which is determined by the phase displacement between voltage and current. Since a long current zero crossing duration will lead to voltage pulse disturbance, serious electromagnetic interference, and output power fluctuation, it is necessary to reduce the zero crossing duration to improve the open-winding PMSG performance. This paper gives a detailed analysis on the zero crossing phenomenon of the semicontrolled open-winding PMSG system in the 3-D space vector modulation perspective. Meanwhile, a third harmonic injection method is suggested to reduce the zero crossing duration. It is also demonstrated that the torque and power pulsation are effectively improved, while the zero-sequence current amplitude does not increase. A proportional resonant controller is used to regulate the desired zero-sequence current. The proposed method is validated in a 1-kW semicontrolled open-winding PMSG experimental system with id = 0 control method. [ABSTRACT FROM AUTHOR]

This paper proposes a dual-space vector control scheme for the open-end winding permanent magnet synchronous motor (OEW-PMSM) drive fed by the dual inverter with a single dc supply. Potential zero-sequence current in the open-end winding drive system has to be considered since it causes circulating current in the winding and leads to high current stress of power semiconductor devices and high losses. Zero-sequence current in open-end winding ac motor drives is usually caused by the zero-sequence voltage, and therefore switching combinations which do not produce zero-sequence voltage are used to synthesize the reference voltage in existing methods. But even so, the zero-sequence voltage can also be produced by the dead time of the inverter. In order to suppress zero-sequence current in the OEW-PMSM drive, a dual-space vector control scheme is proposed and a novel dual-inverter space vector pulse width modulation (PWM) with the zero-sequence voltage reference is employed to regulate system zero-sequence voltage in this paper. Compared with existing dual inverter PWM strategies, the novel algorithm build a regulation mechanism for the zero-sequence voltage. The proposed method is compared with the conventional vector control by simulations and experiments, and the results shown that the proposed scheme can suppress zero-sequence current effectively. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of three transformer winding configurations, i.e., the Y–Y, the Y– $\Delta$, and the $\Delta$– $\Delta$ configuration, on the performance of a three-phase dual active bridge (DAB) dc–dc converter. For each configuration, equations for the phase currents, power flow, and zero-voltage switching (ZVS) boundaries are derived for all possible switching modes of the three-phase DAB. Thereafter, a comparison is made of the stress on the switches, the transformer, and the filter capacitors for the selected winding configurations. The comparison reveals that the Y–Y and $\Delta$ –$\Delta$ configuration perform equally regarding above aspects, with the only difference of a lower winding current for the $\Delta$– $\Delta$ configuration. The Y– $\Delta$ configuration shows a constant commutation current for phase-shifts from 0 to 30 degrees. Therefore, this configuration features a wider ZVS region for low output powers. Overall, the Y–$\Delta$ configuration performs best for power levels between 50% and 80%, regarding the stress on the switches, the transformer, and the filter capacitors. The theoretical analysis is supported with measurements obtained from a high-power experimental setup. [ABSTRACT FROM AUTHOR]

This paper proposes a high-precision primary-side regulation constant voltage (CV) and constant current (CC) ac–dc converter. CV output is achieved by adjusting the switching frequency and primary peak voltage simultaneously, for better dynamic adjustment ability. In order to improve CV precision, a cable compensation module is adopted to inject current to pull-down resistor of auxiliary winding divider, compensating the cable voltage loss caused by the output cable resistance. On the other hand, CC output is acquired by maintaining the ratio of switching frequency and output voltage constant. The inductance compensation module regulates further to keep the product of demagnetization time and switching frequency fixed, equalizing the inconsistent output current result from the big tolerance of the transformer primary-side inductance in the same batch. Moreover, an improved demagnetization time detector is proposed, which is beneficial to raise CC precision. The control chip is implemented based on TSMC 0.35-μm 5-V/40-V BCD process, and a 12 V/1 A prototype has been built to prove the proposed control method. In CV mode, the deviation of the output voltage is within ±1.5%, while that of output current is within ±3% in CC mode. [ABSTRACT FROM AUTHOR]

With the widespread growth of slim portable electronics, research into planar spiral windings for wireless power transfer (WPT) battery charging systems has gained a lot of attention due to their low profile, reproducibility, and manufacturability. The major design goal for windings in WPT systems is high-quality factor (Q) for a given inductance. This study presents a new method to improve Q by using a nonunity track-width-ratio (TWR) geometrical arrangement in conjunction with increasing the inner radius of winding to make an improved hollow planar spiral winding. The inductance regulation of this technique combined with its exceptional improvements in Q make it a superior choice for resonant WPT systems. Inductance and resistance models are provided in order to assess the Q improvement. A 5-W, 110–200-kHz WPT system was built and tested based on the wireless power consortium Qi standard to confirm the advantages of the improved windings on the transmission efficiency of the system. An increase from 70% to 90% are observed from employing the proposed winding technique designed using the provided models. [ABSTRACT FROM AUTHOR]

This paper studies the rotor-speed stability improvement of dual stator-windings induction generator (DWIG)-based wind farms under power system fault conditions. The characteristics of the DWIG-based wind turbines are described. The factors affecting the rotor-speed stability are analyzed, and a novel control-winding voltage oriented drive together with braking resistor (BR) is proposed to control both the active and the reactive power of DWIG during the fault. The proposed control method provides additional supplementary control loop to conventional control-winding voltage oriented drive. The supplementary control loop devoted to adjust the BR value in such a way that the whole kinetic energy of generator and turbine is absorbed by BR. Additionally, the orientation of control winding voltage forces the slip of DWIG to be approximately constant; thereby, limiting the reactive power consumption during the fault. The simulation and experimental works from the prototype of 1.2-kW three/three-phase DWIG wind power system demonstrate the effectiveness of the control scheme as also the significant influence of BR for improving the rotor-speed stability of DWIGs. [ABSTRACT FROM AUTHOR]

A family of modulation schemes based on mathematical construction for the multimodular matrix converter (MC) with ordinary multiwindings transformer is proposed in this paper. The key to the schemes are the calculation of offset signals. A geometric method is introduced to determine the range of the offset signals. The modulation schemes could be divided in two categories based on the geometric positions of the offset signals: continuous modulation (Method I) and discontinuous modulation (Method II). The former has the advantages of ease of use and good power quality. While the later has the advantage in power losses. Additionally, both methods can achieve the maximum linear voltage transfer ratio. To obtain better output current quality, a switching pattern with specific sequence is provided. Finally, a scaled-down prototype is built to verify the correctness and effectiveness of the proposed modulation strategies. [ABSTRACT FROM AUTHOR]

Transformer parasitics such as leakage inductance and self-capacitance are rarely calculated in advance during the design phase, because of the complexity and huge analytical error margins caused by practical winding implementation issues. Thus, choosing one transformer architecture over another for a given design is usually based on experience or a trial and error approach. This paper presents analytical expressions for calculating leakage inductance, self-capacitance, and ac resistance in transformer winding architectures (TWAs), ranging from the common noninterleaved primary/secondary winding architecture, to an interleaved, sectionalized, and bank winded architecture. The calculated results are evaluated experimentally, and through finite-element simulations, for an RM8 transformer with a turns ratio of 10. The four TWAs such as, noninterleaved and nonsectioned, noninterleaved and sectioned, interleaved and nonsectioned, and interleaved and sectioned, for an EF25 transformer with a turns ratio of 20, are investigated and practically implemented. The best TWA for an RM8 transformer in a high-voltage bidirectional flyback converter, used to drive an electro active polymer based incremental actuator, is identified based on the losses caused by the transformer parasitics. For an EF25 transformer, the best TWA is chosen according to whether electromagnetic interference due to the transformer interwinding capacitance, is a major problem or not. [ABSTRACT FROM AUTHOR]

The bidirectional cell-to-cell equalization methods perform well to prevent the series-connected batteries from overcharging and undercharging. However, it remains a challenge to achieve fast equalization and high equalization efficiency with low complexity. To address the issue, we propose a new bidirectional cell-to-cell active equalization method using a multiwinding transformer. The new method allows the energy to transfer directly from the highest voltage cell to the lowest one by fly-back operation or forward operation which gives a short balancing path and guarantees a fast equalization speed. We adopt the bidirectional switches of low conduction loss for high equalization efficiency. Since the bidirectional switches are turned on or off simultaneously, a common driving circuit for the bidirectional switch has been designed to reduce the number of the driving circuits by half. The experiments with a six 50-Ah Lithium-ion battery strings are conducted and the results have demonstrated that our new approach has achieved a good overall performance of equalization in terms of speed, efficiency, and complexity of the circuit. [ABSTRACT FROM AUTHOR]

The current imbalance between stator phase windings could shorten the motor life and affect the drive performance, whereas in case of multiphase drive applications, there is not a general current balance control strategy that can apply to symmetrical inverters with any phase number m. Based on the generalized symmetrical component theory, this letter analyzed the values of relative symmetrical components of the multiphase systems in balanced and unbalanced cases. Then, developed from the conventional rotor-flux oriented control (RFOC), the current-balance RFOC is proposed to compensate the current imbalance for symmetrical m-phase inverters. Finally, the experimental results from the five-phase and nine-phase drive systems confirm the validity of the control strategy in eliminating current imbalance. [ABSTRACT FROM AUTHOR]

The structure and control strategy of a novel two-phase brushless main exciter (ME) are proposed in this paper to solve the excitation problem of the main generator (MG) when the aircraft brushless wound-rotor synchronous starter/generator start up as a motor. Two-phase symmetrical winding is adopted as the field winding of the ME and is supplied with two-phase ac by a two-phase inverter in the starting mode and dc by the traditional generator control unit in the generation mode. In order to make the field current of the MG remain constant during the start-up process, the excitation control method for the two-phase ME in the starting mode is proposed, which contains the feedback control for the two-phase field currents and speed reference control for the excitation frequency. The proposed two-phase ME and excitation control method have the advantages of capability for higher and constant field current for the MG in the starting mode and unchanged structure and control methods in the generation mode. A two-phase ME prototype, based on an original single-phase ME, is designed, manufactured, and tested. Finite-element analysis (FEA)-based simulation and experimental results verify the feasibility and advantages of the novel two-phase brushless ME and excitation control method. [ABSTRACT FROM AUTHOR]

This paper develops an analytical model for describing the behaviors of the interturn short fault in the permanent magnet synchronous motors (PMSMs) with multistrands windings. An analysis of the fault modes resulted from the deterioration of insulation in multistrands windings are first carried out. According to the possible fault influences, a consistent expressions of interturn short-circuit current, phase voltages, and electromagnetic torque for modeling the different modes of interturn short faults are then derived. The proposed model allows studying the postfault performances of these motors under transient and steady state, including fault resistance, quadrature- and direct-axis current, or speed variations. Both finite-element analysis and experimental results demonstrate the effectiveness of the developed model for predicting the interturn short-circuit behaviors in the PMSMs with multistrands windings. [ABSTRACT FROM PUBLISHER]

In circuits where there is an inherent phase shift angle between coupled winding currents such as in coupled inductors, it is important to accurately calculate the ac winding loss at the correct phase shift and frequency. Phase shift between winding currents can cause the ac winding loss to vary significantly due to changes in the magnetic field distribution. This paper presents an analysis of winding loss for the general case of coupled windings with arbitrary phase-shifted currents and its effect in a number of practical devices. A detailed approach to analytically calculate ac winding loss in microfabricated-coupled stripline inductors is presented along with a derivation of the resistance matrix for the device. The analysis and methodology are then validated using finite element analysis and experimental results. [ABSTRACT FROM AUTHOR]

In order to obtain a high step-up voltage gain, high-efficiency converter, this paper proposed a dual switches dc/dc converter with three-winding-coupled inductor and charge pump. The proposed converter composed of dual switches structure, three-winding-coupled inductor, and charge pump. This combination facilitates realization of high step-up voltage gain with a low voltage/current stress on the power switches. Meanwhile, the voltage across the diodes is low and the diode reverse-recovery problem is alleviated by the leakage inductance of the three-winding-coupled inductor. Taking all these into consideration, the efficiency can be high. This paper illustrated the operation principle of the proposed converter; discussed the effect of leakage inductance on voltage gain; the conditions of zero current shutting off of the diodes are illustrated; the voltage and current stress of the power devices are shown; a comparison between the performance of the proposed converter and previous high step-up converters was conducted. Finally, a prototype rated at 500 W has been established, and the experimental results verify the correctness of the analysis. [ABSTRACT FROM AUTHOR]

The open winding permanent magnet synchronous generator (PMSG) fed by semicontrolled converter takes the advantages of lower expense, simplified driving circuit, and reliable control realization. With a single dc supply, the implementation of open winding configuration in practical application could be much convenient. However, the common dc bus supplied configuration provides a zero-sequence current circuit unavoidably. In order to reduce the harmonic distortion, a zero-sequence current suppression scheme is proposed. The space vector pulse width modulation (SVPWM) technique is adopted to modulate the desired voltage reference in the three-dimensional (3-D) coordinate system by distributing duty cycles for active and zero vectors. With a comprehensive investigation on the semicontrolled configuration, the achievable modulation region for αβ0 voltage vector reference is analyzed. Finally, the zero-sequence current suppression method with 3-D-SVPWM technique is implemented in a 1 kW open winding PMSG experimental system. [ABSTRACT FROM AUTHOR]

Family of single-phase single-stage bridgeless power factor correctors based on tapped-inductor buck-boost converters is introduced. The converters’ family has the merits of reduced component count and alleviated losses in the conduction path. The feasibility of the proposed topologies was verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this letter, a new topology called “quasi-Y-source dc–dc converter” is presented. It inherits all the advantages of the original Y-source converter. In addition, the new topology draws a continuous current from the source, which is definitely more appropriate for most renewable sources. It also has dc-current-blocking capacitors, which will definitely help to prevent the coupled inductor core from saturation. Experimental testing has proven the validity of the proposed network and its application as a high boost dc–dc converter. [ABSTRACT FROM AUTHOR]

This paper proposes a stacked common-mode (CM) inductor for electromagnetic interference (EMI) attenuation. The proposed stacked CM inductor consists of two CM inductors with identical cores and the same number of winding turns but with opposite winding directions. The proposed stacked CM inductor has three advantages. First, it is much less susceptible to external magnetic field interference than conventional CM inductors. This suppresses the EMI due to the near-magnetic-field coupling to the CM inductor. Second, the proposed winding structure effectively increases the leakage inductance of the CM inductor, which enhances its ability to suppress differential-mode (DM) noise. Third, the magnetic field generated by the DM current in the stacked CM inductor is partially canceled outside of the inductor. As a result, the stacked CM inductor has lower magnetic field emission than that of a conventional CM inductor. Simulation and experimental results validate the advantages of the proposed CM inductor, which show the proposed technique greatly improves the performance of CM inductors. [ABSTRACT FROM AUTHOR]

Fe-based nanocrystalline (FE-N) cores are widely used in power electronics and pulsed power applications. In pulsed power applications, it always requires high excitation current (up to tens of kiloampere) to excite large-volume cores (up to hundreds of cubic centimeter) with fewer number of winding turns, and it is hard to use the traditional test scheme to obtain the pulse magnetic properties in this case. The principles and scopes for the application of pulse magnetic properties measurement circuits, including the single-winding test circuit and double-winding test circuit, are analyzed and presented. Although the double-winding test circuit is classical to test the hysteresis loop, the single-winding test circuit is not totally useless in some cases. Based on the double-winding test circuit, the initial magnetization curves and maximum hysteresis loops of toroidal FE-N cores with high and low remanence are obtained under a relative constant magnetization rate with the order of 0.7–7 T/μs, and an equivalent frequency from 49 to 650 kHz. The unsaturated permeability is calculated based on the experimental results and fitted with the magnetization rate. The loss densities and permeability are fitted and compared. A design procedure of the saturable pulse transformer is illustrated for the application of the testing results. It is proved that the initial energy loss and unsaturated permeability are used for the design of the pulse transformer, and the traditional core loss is suitable for the estimation of power loss under the repetitive operation condition. [ABSTRACT FROM AUTHOR]

A narrow-width power-invariant inductive power transfer system (IPTS) along the driving direction is newly proposed in this paper. The conventional I-type power supply rail for on-line electric vehicles (OLEVs) has a very narrow power supply rail with 10-cm width and exposes pedestrians to a very low electromagnetic field due to its alternatively arranged magnetic poles along the driving direction of electric vehicles; however, it has a major drawback: Sinusoidal variation of the induced pick-up voltage depending on pick-up positions on the power supply rail along driving direction. To overcome this disadvantage, a dq-power supply rail fed by two high-frequency ac currents of the d-phase and q-phase is introduced in this paper. The d -phase and q-phase magnetic poles are alternatively arranged in a line; hence, the induced voltage of a pickup becomes spatially uniform. The power invariant characteristic of the proposed IPTS for OLEV has been verified by analysis, simulations, and experiments. A practical winding method is suggested as well. [ABSTRACT FROM AUTHOR]

Frequency-dependent leakage inductance is often observed. The high-frequency eddy current effects cause a reduction in leakage inductance. The proximity effect between adjacent layers is responsible for the reduction of leakage inductance. This paper gives a detailed analysis of high-frequency leakage inductance and proposes an accurate prediction methodology. High-frequency leakage inductances in several interleaved winding configurations are also discussed. Interleaved winding configurations actually give a smaller degree of reduction of leakage induction at high frequency. Finite-element analysis simulation and measurement validate the models. [ABSTRACT FROM AUTHOR]

This paper presents an efficiency optimization approach for a high-voltage bidirectional flyback dc–dc converter. The main goal is to optimize the converter for driving a capacitive actuator, which must be charged and discharged from 0 V to 2.5 kV dc and vice versa, supplied from a 24 V dc supply. The energy efficiency is optimized using a proposed new automatic winding layout (AWL) technique and a comprehensive loss model. The AWL technique generates a large number of transformer winding layouts. The transformer parasitics, such as dc resistance, leakage inductance, and self-capacitance are calculated for each winding layout. An optimization technique is formulated to minimize the sum of energy losses during charge and discharge operations. The efficiency and energy loss distribution results from the optimization routine provide a deep insight into the high-voltage transformer design and its impact on the total converter efficiency. The proposed efficiency optimization approach is experimentally verified on a 25 W (average charging power) with a 100 W (peak power) flyback dc–dc prototype. [ABSTRACT FROM AUTHOR]

It is sometimes unavoidable to use loosely coupled coils in applications, like biomedical devices, for transferring electric energy wirelessly. However, coil misalignment causes degradation of the power transfer efficiency. It is well known that the power transfer efficiency of classical parallel coils is primarily determined by the quality factors of the coils and the coupling coefficient between the coils, and is maximized by choosing an optimal turns-ratio between the coils. Changing the number of turns of the coils cannot effectively overcome such misalignment effect. This paper presents a structure that comprises two orthogonally placed windings for lessening the variation of the coupling coefficient due to the coil misalignment. An output current summing technique that keeps the windings concurrently energized and combines the output currents of the windings will be studied. A canonical model will also be derived to describe the interactions between the coils. An experimental prototype has been built and evaluated on a test bed, which allows different degrees of lateral and angular misalignments. Results reveal that the proposed structure can effectively increase the minimum efficiency zone, allowing more lateral and angular misalignments. These investigations lay the foundation for future understanding more complex loosely coupled winding structures. [ABSTRACT FROM AUTHOR]

Foil conductors and primary and secondary interleaving are normally used to minimize winding losses in high-frequency (HF) transformers used for high-current power applications. However, winding interleaving complicates the transformer assembly, since taps are required to connect the winding sections, and also complicates the transformer design, since it introduces a new tradeoff between minimizing losses and reducing the construction difficulty. This paper presents a novel interleaving technique, named maximum interleaving, that makes it possible to minimize the winding losses as well as the construction difficulty. An analytical design methodology is also proposed in order to obtain free-cooled transformers with a high efficiency, low volume, and, therefore, a high power density. For the purpose of evaluating the advantages of the proposed maximum interleaving technique, the methodology is applied to design a transformer positioned in the 5 kW–50 kHz intermediate HF resonant stage of a commercial PV inverter. The proposed design achieves a transformer power density of 28 W/cm3 with an efficiency of 99.8%. Finally, a prototype of the maximum-interleaved transformer is assembled and validated satisfactorily through experimental tests. [ABSTRACT FROM AUTHOR]