A Cost-Effective, Single-Phase Line-Interactive UPS System that Eliminates Inrush Current Phenomenon for Transformer-Coupled Loads

Syed Sabir Hussain Bukhari,Shahid Atiq,Thomas A. Lipo,Byung-il Kwon 대한전기학회 2016 Journal of Electrical Engineering & Technology Vol.11 No.3

Sudden voltage drops and outages frequently disturb the operation of sensitive loads for domestic, commercial, and industrial use. In some cases, these events may even impair the functioning of relevant equipment. To maintain power under such conditions, a UPS system is usually installed. Once a disturbance happens at the grid side, the line-interactive UPS system takes over the load to prevent an interruption. But, due to magnetic saturation of the transformer, a significant inrush current may occur for the transformer-coupled loads during this transition. The generation of such transient currents may in turn decrease the line voltage and activates over-current protecting devices of the system. In this work, a cost-effective, line-interactive UPS system is proposed that eliminates the inrush current phenomenon associated with transformer-coupled loads. The strategy was implemented by connecting a standard current-regulated voltage source inverter (CRVSI) to the secondary winding of the load transformer. During any transient condition at the grid side, the load current is monitored and regulated to achieve either seamless compensation of the load current or complete transferal of load from grid to the inverter. Experimental results were obtained for a prototype under all possible operating conditions so as to validate the performance of the proposed topology.

A Novel Dual-Rotor, Axial Field, Fault-Tolerant Flux-Switching Permanent Magnet Machine With High-Torque Performance

Zhao, Wenliang,Lipo, Thomas A.,Kwon, Byung-Il IEEE 2015 IEEE transactions on magnetics Vol.51 No.11

<P>This paper proposes a novel dual-rotor, axial field, fault-tolerant flux-switching permanent magnet machine (FSPMM) with high-torque performance for direct-drive applications, in which the phase-group concentrated-coil windings and the unaligned arrangement of the two rotors are used. The adoption of the phase-group concentrated-coil windings is made to obtain a unity displacement winding factor, and to enhance the flux-focusing effects together with the use of a spoke-type PM configuration. The unaligned arrangement of the two rotors will help to achieve increased flux magnification and also to suppress the cogging torque and the torque ripple. In particular, the proposed configuration for FSPMMs exhibits the advantage of fault tolerance, benefiting from the electromagnetic isolation of phases and a dual three-phase channel of supply. The operating principle and the design criteria of the proposed FSPMM are discussed in detail. To highlight the advantages of the proposed FSPMM, two conventional FSPMMs are adopted for comparison under the same operating conditions based on a 3-D finite-element method. As a result, it is demonstrated that the proposed FSPMM exhibits significantly improved performance with not only higher torque (power) density but also lower cogging torque and torque ripple, compared with the conventional FSPMMs.</P>

A Cost-Effective, Single-Phase Line-Interactive UPS System that Eliminates Inrush Current Phenomenon for Transformer-Coupled Loads

Bukhari, Syed Sabir Hussain,Atiq, Shahid,Lipo, Thomas A.,Kwon, Byung-il The Korean Institute of Electrical Engineers 2016 Journal of Electrical Engineering & Technology Vol.11 No.3

Sudden voltage drops and outages frequently disturb the operation of sensitive loads for domestic, commercial, and industrial use. In some cases, these events may even impair the functioning of relevant equipment. To maintain power under such conditions, a UPS system is usually installed. Once a disturbance happens at the grid side, the line-interactive UPS system takes over the load to prevent an interruption. But, due to magnetic saturation of the transformer, a significant inrush current may occur for the transformer-coupled loads during this transition. The generation of such transient currents may in turn decrease the line voltage and activates over-current protecting devices of the system. In this work, a cost-effective, line-interactive UPS system is proposed that eliminates the inrush current phenomenon associated with transformer-coupled loads. The strategy was implemented by connecting a standard current-regulated voltage source inverter (CRVSI) to the secondary winding of the load transformer. During any transient condition at the grid side, the load current is monitored and regulated to achieve either seamless compensation of the load current or complete transferal of load from grid to the inverter. Experimental results were obtained for a prototype under all possible operating conditions so as to validate the performance of the proposed topology.

Design and Analysis of a Novel Brushless Wound Rotor Synchronous Machine

Ali, Qasim,Lipo, Thomas A.,Kwon, Byung-Il IEEE 2015 IEEE transactions on magnetics Vol.51 No.11

<P>This paper presents a new concept for brushless excitation of a wound rotor synchronous machine (WRSM) based on the generation and utilization of a subharmonic component of the stator magnetomotive force (MMF). In this method, a dual inverter topology for the stator winding is proposed. The idea is to generate and utilize an additional subharmonic stator MMF component along with the fundamental component. The rotor carries two different windings: 1) excitation winding and 2) field winding. The subharmonic component induces voltage in the excitation winding and feeds the field winding through a rotating rectifier on the rotor. A 2-D finite-element analysis was performed to analyze and verify the proposed brushless WRSM.</P>

Optimal Design of a Novel Asymmetrical Rotor Structure to Obtain Torque and Efficiency Improvement in Surface Inset PM Motors

Wenliang Zhao,Lipo, Thomas A.,Byung-Il Kwon IEEE 2015 IEEE transactions on magnetics Vol.51 No.3

<P>This paper proposes an optimal design of a novel asymmetrical rotor structure for surface inset permanent magnet (PM) motors to obtain torque and efficiency improvement. Different from the conventional approach, the proposed design of asymmetrical rotor structures is employed to improve the torque production by creating rotor asymmetry to allow the reluctance torque and the magnetic torque to reach a maximum at the same current phase angle. To evaluate the contribution, the frozen permeability method is utilized to segregate the torque into its reluctance and magnetic torque components. For demonstrating the design concept and obtaining a criterion for improving torque by making full use of torque components, an optimal design by iterative computation is first to be performed utilizing the finite-element method. Based on the obtained criterion, the optimal design by algorithms, such as the Kriging method and genetic algorithm, is applied to further improve the torque and efficiency. As a result, the performance of the proposed surface inset PM motor by two-step optimization is dramatically improved compared with that of the conventional surface inset PM motor. Furthermore, a comparison between the optimized surface inset PM motor and a conventional surface-mounted PM (SPM) motor is also performed under the same operating condition, which demonstrates that the optimized surface inset PM motor can significantly save the magnet amount compared with the conventional SPM motor for producing the same output torque.</P>

PM Assisted, Brushless Wound Rotor Synchronous Machine

Qasim Ali,Shahid Atiq,Thomas A. Lipo,Byung-il Kwon 한국자기학회 2016 Journal of Magnetics Vol.21 No.3

This paper presents a new permanent magnet (PM) assisted topology for a recently introduced brushless wound rotor synchronous machine (BL-WRSM). The BL-WRSM had a dual-inverter configuration for generating a composite magneto motive force (MMF) with a fundamental component and a subharmonic component. The subharmonic component of the MMF is used for brushless excitation of the rotor. In this paper, additional PMs were introduced on the rotor of the BL-WRSM, making it a hybrid BL-WRSM. We also discussed the flux weakening operation for the hybrid BL-WRSM. The hybrid BL-WRSM offered advantages for starting the machine and provided better performance under full-load conditions. The finite element method (FEM) was used to analyze the performance of the hybrid BL-WRSM, and we compared its performance with BL-WRSM. Finally, prototypes were built with and without the PM-assistance, and experiments were conducted to demonstrate their performance.

Optimal Design of a Novel V-Type Interior Permanent Magnet Motor with Assisted Barriers for the Improvement of Torque Characteristics

Wenliang Zhao,Fei Zhao,Lipo, Thomas A.,Byung-Il Kwon IEEE 2014 IEEE transactions on magnetics Vol.50 No.11

<P>This paper performs a study on the optimal design of V-type interior permanent magnet motors (VIPMMs), in which the rotor is equipped with assisted barriers for the improvement of average torque and torque ripple. The approach differs from the conventional interior permanent magnet motors, in which the reluctance torque due to saliency reaches a maximum value at a current phase angle located 45 electrical degrees with respect to the maximum value obtained from the magnetic torque produced by the rotor magnets. The adoption of assisted barriers is employed to improve the torque production by creating rotor asymmetry to allow the reluctance torque and the magnetic torque reach a maximum value near or at the same current phase angle. To evaluate the contribution, the frozen permeability method is utilized to segregate the torque into its reluctance and magnetic torque components. First, an iterative optimization is performed on a concept design of a 6/4 VIPMM for demonstrating the design principle based on finite element method. Then, the VIPMM is further optimized by algorithms, such as the kriging method and genetic algorithm for improving the torque characteristics and efficiency. As a result, the optimal VIPMM with assisted barriers shows the substantially improved performance compared with a conventional design.</P>

Novel Brushless Wound Rotor Synchronous Machine With Zero-Sequence Third-Harmonic Field Excitation

Jawad, Ghulam,Ali, Qasim,Lipo, Thomas A.,Kwon, Byung-Il IEEE 2016 IEEE transactions on magnetics Vol.52 No.7

<P>This paper introduces a novel topology for generating a spatial third-harmonic current component to excite the rotor field winding of a wound rotor synchronous machine to achieve brushless operation. In this topology, each of the three-phase windings on the stator is connected with a switch in parallel. In particular, two antiparallel thyristors are used to switch during positive and negative half cycles. Two windings are mounted on the rotor of the machine: 1) the harmonic winding and 2) the field winding. Zero-sequence currents are generated, when the switches are closed near zero crossing for a short time interval. Consecutive operation of the switches creates an additional spatial third-harmonic current pulsating in the stator winding. The number of poles of the stator winding and the field winding is the same (four-poles in this case) to intercept the torque generation component of the air-gap flux, whereas, the number of poles of the harmonic windings is adjusted (12-poles in this case) to intercept the harmonic component of the air-gap flux and develop voltage across the harmonic windings. Harmonic voltage is rectified through a rotating rectifier to feed dc current to the field windings. Results verify the proposed topology simulated by a 2-D finite-element method.</P>

A Novel Dual-Stator Axial-Flux Spoke-Type Permanent Magnet Vernier Machine for Direct-Drive Applications

Fei Zhao,Lipo, Thomas A.,Byung-Il Kwon IEEE 2014 IEEE transactions on magnetics Vol.50 No.11

<P>This paper proposes a novel double-stator axial-flux spoke-type permanent magnet vernier machine, which has a high torque density feature as well as a high-power factor at low speed for direct-drive systems. The operation principle and basic design procedure of the proposed machine are presented and discussed. The 3-D finite element method (3-D-FEM) is utilized to analyze its magnetic field and transient output performance. Furthermore, the analytical method and a simplified 2-D-FEM are also developed for the machine basic design and performance evaluation, which can effectively reduce the modeling and simulation time of the 3-D-FEM and achieve an adequate accuracy.</P>

A Novel Grid-connected to Rotor Type Doubly Fed Induction Generator for Wind Turbine Systems

Yong-min You,Thomas A. Lipo,Byung-il Kwon 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

This paper proposes a grid-connected to rotor type doubly fed induction generator (DFIG) in which the rotor winding is connected to the grid instead of the stator winding. The stator size and weight of the proposed grid-connected to rotor type DFIG can be reduced because the proposed type can use rotor core more efficiently compared to the stator type DFIG. In order to verify the size and weight reduction of the proposed type, the loading distribution method (LDM) is utilized. As a design result, the stator outer diameter and weight of the proposed type were decreased. The equivalent circuit analysis and FEM analysis also performed to verify the design results and to analyze characteristics of the novel DFIG.