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Being an integral part of many high-power converters, it is imperative to estimate the natural resonance frequencies of a medium/high-frequency (MF/HF) transformer. Experiment/measurement based methods reported in literature determine the resonance frequencies based on the input impedance measurements. However, their applications are limited if these resonance frequencies are to be estimated prior to the transformer prototyping. To ameliorate the drawback, this article provides a comprehensive modeling procedure for the winding capacitances of a two-winding transformer and its resonance frequency estimation. By integrating the prior capacitance modeling techniques, this article establishes an electrostatic energy based transformation model, which directly translates the static winding capacitances into equivalent model based capacitances. These derived capacitances are further utilized to represent a reduced ${\pi }$ -model of a two-winding transformer, compute its frequency responses and estimate the resonance frequencies. The proposed model based approach is simple and easily executable, and helps avoiding any infeasible transformer design during the preprototyping stage. Experimental results derived from MF transformer prototypes, constructed of solid round, foil, and litz wires, are used to corroborate the theoretical analysis and feasibility of the proposed model based approach. [ABSTRACT FROM AUTHOR]

A split dc-link dual-active-bridge (SDLDAB)-based multiport converter (MPC) is proposed in this article. The intended application of the SDLDAB converter is to interface two solar photovoltaic (PV) modules and a battery bank with a dc microgrid. Depending upon the prevailing atmospheric condition, these two solar PV modules can be operated at their maximum power points. This is achieved by maintaining appropriate voltages at the input terminals of the two PV modules. A high-frequency transformer is employed to provide high voltage gain between the dc microgrid and PV as well as battery ports. A direct power flow path is established between the solar PV modules and the battery without involving the transformer. The transformer current is minimized by appropriately modulating the switching sequence of the SDLDAB. Detailed simulation studies are carried out to predict the performance of the system. A laboratory prototype of the SDLDAB having 1-kW power rating is fabricated. The performance of the MPC is validated by carrying out detailed experimental studies on the developed prototype. [ABSTRACT FROM AUTHOR]

An optimized configuration of bidirectional Z-source circuit breaker using a coupled inductor is introduced for the fault isolation in low-voltage dc microgrid. The proposed circuit breaker is designed to operate with a single coupled inductor for bidirectional power flow. Use of the single coupled inductor for the power flow in both the directions reduces the component count. In this article, the operating principle of the breaker is explained for a short-circuit fault condition and breaker design criteria are derived. The performance of the circuit breaker is evaluated by carrying out a MATLAB simulation study. The functional prototype is developed to validate the breaker capabilities. Experimental results show that the fault is cleared within few microseconds. Additionally, the breaker is tested under the step load change condition for a current five times the steady-state rated current of the breaker and results are satisfactory. [ABSTRACT FROM AUTHOR]

Gearless and small motors operating at speeds above 10 000 rpm are finding many applications nowadays. Axial flux permanent magnet (AFPM) motors are compact and lightweight compared to radial flux motors and hence, are considered for various high-speed applications. Eliminating the stator core minimizes the associated high-frequency losses, and hence, coreless AFPM motor can be an option for high-speed applications. Furthermore, the coreless AFPM motor design minimizes the cogging torque and the axial attraction force between the stator core and the rotor magnets. However, the reduction of flux linkage in the stator windings is a challenge in coreless AFPM motor. In this article, the advantages and disadvantages of the printed circuit board (PCB)-based AFPM motor for high-speed, low-power applications are investigated. A detailed performance comparison of the PCB-based coreless AFPM motor and the AFPM motor with the laminated stator core is made. Finite-element analysis is carried out for the electromagnetic, mechanical, and thermal comparison of the two motors and the simulation results are presented. Finally, motor prototypes are fabricated and are tested to ascertain the simulation results. [ABSTRACT FROM AUTHOR]

This paper discusses the analysis and experimental validation of bidirectional Z-source breaker and bidirectional Z-source breaker using coupled inductor for low-voltage dc microgrid application. The proposed topologies use an SCR as a switch to isolate the fault from the system, and LC network to generate required commutation conditions for the SCR under fault conditions. Thus, both topologies are able to isolate the fault naturally within a few microseconds without any fault detection and sensing circuit. In this paper, the breaker operating principle is discussed during fault condition and breaker design criteria are derived. When the breaker is connected in series with power electronic converter, Z-source components offer filtering characteristic. The filtering characteristic offered by the breaker components is analyzed. Functional prototypes are developed for both configurations to validate the breaker performance and experimental results are presented. [ABSTRACT FROM AUTHOR]

Cascaded multicell converter (CMC) is one of the effective solutions for medium-voltage high-power drives. The inability to regenerate power back to the source is one of the limitations of this converter. The regeneration capability is obtained by using a pulsewidth-modulated active rectifier instead of a conventional three-phase passive rectifier in each cell. However, due to their two-level voltage operation at the input side, an inductor is required for each cell to filter out the switching frequency components from the input current. This paper proposes a new configuration of regenerative CMC based on coupled inductor to achieve multilevel voltage at the transformer secondary terminals. This allows us to operate the rectifier devices at reduced switching frequency. The coupled inductor reduces the total harmonic distortion (THD) of the transformer secondary current and thus the transformer size. The size of the filter inductor and the transformer ratings are compared. The operating principle and the detailed analysis are presented. A technique to bypass a faulty module is proposed. The working of the converter is verified through simulation and experimental studies. [ABSTRACT FROM AUTHOR]

In recent years, modular multilevel converter (MMC) is considered for medium-voltage variable speed drives (VSD) due to its modularity and higher reliability. However, the major drawback of the MMC-based VSD is the higher capacitor ripple voltage at lower operating speeds. In literature, this ripple voltage is reduced by injecting a high-frequency circulating current into each arm. This additional circulating current increases the overall current rating of the devices, inductors, and capacitors. Alternatively, the capacitor ripple voltage can be reduced at the lower output frequency by reducing the dc-bus voltage. This paper proposes a new configuration using a multipulse diode-bridge rectifier to reduce the dc-bus voltage when the drive is operated at lower speeds. Therefore, the capacitor ripple voltage decreases without injecting any circulating current. In addition, a new technique is proposed to maintain the peak-to-peak value of the submodule capacitor ripple voltage constant at near-zero speed. The proposed converter with 24-pulse rectifier configuration is simulated in MATLAB/Simulink, and the experimental validation is carried out on a prototype with 12-pulse rectifier. [ABSTRACT FROM AUTHOR]

A single-stage, bidirectional, current-source converter (CSC) topology to interface a dc microgrid with an ac grid is reported in the literature. In this topology, under a balanced grid voltage condition, the dc-link inductor current can be regulated over a wide range—from zero to rated value—while the ac-side current has low harmonic distortion. However, unbalanced grid voltages result in second-harmonic pulsation in the current and power on the dc side of the converter. In addition, the ac-side currents will be unbalanced due to the presence of a negative-sequence component. This would result in undesired tripping of the converter if one of the phase currents exceeded its rated value. Various control loop structures for the operation of voltage-source converter under unbalanced grid voltage conditions are reported in the literature. However, use of similar control loop structures for CSC may lead to unstable operation. Therefore, a control scheme to inject balanced three-phase currents into the ac grid under an unbalanced grid voltage condition is proposed in this paper. The stability of the proposed control scheme is studied using a small-signal model of the converter. Performance of the proposed control scheme is studied using MATLAB/Simulink and is experimentally validated. [ABSTRACT FROM AUTHOR]

A paralleled multilevel inverter topology consists of n three-phase three-level current-fed inverters (CFIs) connected in parallel on ac side. AC currents with (2n+1) levels can be generated utilizing redundant switching states when all three-level inverters have equal dc-link currents. However, the multilevel space vector diagram gets modified, redundancy in the switching states is lost and the multilevel current pattern changes when the dc-link current of all inverters is not the same. This introduces low-frequency harmonics in output current, thereby deteriorating total harmonic distortion (THD). The presence of low-frequency components in the output current could be avoided by selecting suitable switching state vectors and ensuring proper time sharing among these vectors. Two methods to select such switching state vectors are proposed in this paper. In the first method, a reference current space vector is realized using the nearest switching state vectors. However, this method results in low-frequency pulsation in dc-link voltage of each inverter. In the second method, the switching state vectors are chosen to eliminate this low-frequency pulsation. Effectiveness of these methods is experimentally validated for a five-level CFI. Further, performance of these methods is compared based on efficiency, THD, and dc-link voltage ripple for various inequality ratios in dc-link currents. [ABSTRACT FROM AUTHOR]

Axial flux-segmented rotor-switched reluctance motor (SSRM) topology could be a potential candidate for in-wheel electric vehicle application. This topology has the advantage of the increased active surface area for the torque production as compared to the radial flux SSRM for a given volume. To improve the performance of axial flux SSRM (AFSSRM), various stator slot/rotor segment combinations and winding polarities are studied. It is observed that the torque ripple is high for the designed three-phase, 12/8 pole AFSSRM. Therefore, the influence of the stator pole and rotor segment arc angles on the average torque and the torque ripple is studied. In addition, the adjacent rotor segments are displaced with respect to the stator, to reduce the torque dips in the phase commutation region. The proposed arrangement is analyzed using the quasi-3-D finite-element method-based simulation study and it is found that the torque ripple can be reduced by 38%. Furthermore, the low-frequency harmonic content in the torque output is analyzed and compared. The variation of the axial electromagnetic attractive force with displaced rotor segments is discussed. The effectiveness of the proposed technique is verified experimentally. [ABSTRACT FROM PUBLISHER]