K.M. Smedley

University of California, Irvine, Irvine, California, United States

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Publications (157)288.4 Total impact

  • Wensheng Song, Xiaoyun Feng, Keyue Ma Smedley
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    ABSTRACT: Single-phase three-level neutral point clamped (NPC) converters are widely applied in high-speed railway electrical traction drive systems. A significant problem related to the single-phase three-level NPC converters is the fluctuation of the neutral-point voltage. In this paper, a capacitor voltage balancing technique is proposed that injects an offset voltage into the sinusoidal modulating signals of the conventional carrier-based pulsewidth modulation (CBPWM) method. Furthermore, when the injected offset voltage is maximized, it cannot only balance the dc-link capacitors voltages, but also reduce switching losses. Theoretical analysis has shown that both methods can control the neutral point voltage effectively, but the neutral point voltage controller in the CBPWM with maximum offset voltage injection (CBPWM-MOVI) has a faster dynamic response. It was observed that the high-order harmonics frequencies of the line current are centered around the twice switching frequency in the CBPWM with the offset voltage injection (CBPWM-OVI) but are centered around the switching frequency in the CBPWM-MOVI. And also, the CBPWM-MOVI has switching commutations number at least 25% below that of the CBPWM-OVI in one modulating signal period. The performances of the two strategies were verified by simulation and experimental tests.
    IEEE Transactions on Power Electronics 03/2013; 28(3):1083-1095. · 5.73 Impact Factor
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    ABSTRACT: The flyback converter is a popular topology for implementing low power and multiple output power supplies. However, the high leakage inductance of the flyback transformer causes high voltage spikes that can damage the main transistor when the switch is turned OFF. Therefore, a turn-off snubber is needed to limit the peak voltage stress. This paper presents the analysis of an energy regenerative snubber using the graphical state-plane technique. The undertaken approach yields a clear-cut design procedure for minimum switch voltage stress. Experimental evaluation of the energy regenerative snubber in comparison with other common snubbers shows that under the same voltage stress the efficiency of energy regenerative snubber has 8% improvement on average over an RCD snubber and 2% improvement over the nondissipative LC snubber.
    IEEE Transactions on Power Electronics 01/2013; 28(11):5323-5332. · 5.73 Impact Factor
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    ABSTRACT: The fault current limiter is considered a viable solution for reducing the fault current in the power line. In the U.S., great effort has been reported in academia and industry in developing such devices. However, demonstrating a fault current limiter in the live power grid is challenging not only technologically but regulatory. This paper reports a joint effort of academia, industry, and utility on prototyping and testing of saturable core high temperature superconductive fault current limiters (HTS FCLs). This device is the first fully operational HTS FCL installed on the commercial medium voltage distribution grid in the U.S.
    IEEE Transactions on Power Delivery 01/2013; 28(3):1271-1279. · 1.52 Impact Factor
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    ABSTRACT: This study is concerned with application of the universal one-cycle control (OCC) technique to implement a three-phase AC electronic load. The proposed AC electronic load is able to emulate complex load behaviour. The study describes the principles of operation and the digital implementation of AC electronics load. To validate the approach, the start-up transient of an induction motor was successfully emulated. Both the simulation and experimental results are reported.
    IET Power Electronics 01/2012; 5(6):827-832. · 1.52 Impact Factor
  • A. Abramovitz, K.M. Smedley
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    ABSTRACT: This paper presents a comparative survey of research activities and emerging technologies of solid-state fault current limiters for power distribution systems.
    IEEE Transactions on Power Electronics 01/2012; 27(6):2770-2782. · 5.73 Impact Factor
  • M.N. Slepchenkov, K.M. Smedley, Jun Wen
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    ABSTRACT: This paper studies the effectiveness of reactive power compensation using a multilevel, hexagram-converter-based STATic COMpensator (STATCOM) with one-cycle control (OCC) for a wind farm with fixed-speed turbines, and the interaction with the power system network. Comparison is made with several common types of multilevel voltage source converters used for STATCOM applications. A new voltage control method based on OCC principles for hexagram-based STATCOMs is proposed and proven by a wind farm power system simulation showing the improvement of voltage variations caused by wind speed changes. The experimental results from tests of a small-scale hexagram converter prototype have verified the proposed converter and control method.
    IEEE Transactions on Industrial Electronics 05/2011; · 6.50 Impact Factor
  • Pengju Sun, Luowei Zhou, Keyue Ma Smedley
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    ABSTRACT: This paper presents a reconfigurable structure dc-dc converter with wide output range and constant peak power (RS- WOCP). This converter is an extension of the traditional isolated dc-dc converter with two output channels by adding an active switch and two diodes. Theoretical analysis indicates that the pro- posed RS-WOCP converter is able to smoothly reconfigure the output channels in parallel or series to realize wide output voltage range. With this approach, the output voltage is shared equally in the series operating mode and so is the output current in the parallel operating mode. Therefore, the power rating of devices is significantly reduced and the output rectifiers and filters can distribute power losses and thermal stresses. Operating principle, control strategy, modeling, and stability analysis are illustrated in this paper. An experimental prototype of a 200-W DSP-based RS- WOCP converter was built. The experimental results have verified the steady-state performance and fast dynamic response in the whole output voltage range. Comparisons with two close relatives of wide output converters show that the proposed RS-WOCP con- verter is advantageous for wide output range constant peak power applications.
    IEEE Transactions on Power Electronics 01/2011; 26(10):2925-2935. · 5.73 Impact Factor
  • Wensheng Song, Keyue Smedley, Xiaoyun Feng
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    ABSTRACT: The configuration of a single-phase AC-DC converter plus a three-phase DC-AC inverter traction system has been widely applied in high speed railway electrical drive systems. If the LC filter is not adopted in the DC-link, the DC-link voltage fluctuation may beat with the motor electric frequency, which could cause an increase in power loss, torque pulsation and audible noise. This paper aims to reduce the beat effect of DC-link voltage fluctuation in the traction drive system, Firstly, the harmonic spectra and beat phenomena are analyzed when square wave modulation is adopted in the high speed region. Secondly, a new extension of One-cycle Control (OCC) is proposed for the inverter-motor drive system in high speed region, which is used for square wave modulation, and the adopted OCC method is designed and analyzed in detail in the paper. Finally, the comparison between the performance of the adopted OCC scheme and the traditional square wave modulation is made, and the effectiveness and advantages of the OCC scheme are confirmed by simulation test.
    01/2011;
  • Wensheng Song, Xiaoyun Feng, Keyue Smedley
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    ABSTRACT: The configuration of a single-phase three-level neutral point clamped (NPC) converter has been widely applied in high-speed railway electrical traction drive systems. This paper proposes a control and modulation scheme for the single-phase three-level NPC converter. Firstly, an active and reactive current decoupled control scheme in d-q synchronous frame is presented for single-phase three-level NPC converter to reduce the influence between the traction power supply fluctuating voltage and the traction drive system. Secondly, a new space vector PWM (SVPWM) scheme is provided to restrict the voltage step of the input port voltage within half of DC-link voltage. The proposed SVPWM algorithm is designed and analyzed in detail, including sector and basic voltage vector definition, sector identification, basic vector selection, the duty-time calculation and basic vector sequence design. Finally, the effectiveness and advantages of the proposed SVPWM scheme are confirmed by simulation and prototype experimental test.
    01/2011;
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    ABSTRACT: Variable linear or nonlinear loads are necessary for testing medium voltage (MV) high power AC power supplies. Generally, those AC power supplies require performance validation, burn-in, and/or life-time testing under different load conditions, defined by the end-user or standards for the given applications. For this purpose, this paper presents a multilevel converter-based AC regenerative electronic load with One-Cycle Control (OCC), which is based on a five-level diode-clamped multilevel converter and can emulate any impedance load, whether linear or nonlinear, steady or dynamic. Simulation and experimental results are presented to verify the performance of the proposed multilevel AC regenerative load. I. INTRODUCTION
    01/2011;
  • Jun Wen, Liang Zhou, Keyue Smedley
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    ABSTRACT: The hexagram inverter is composed of six voltage source inverter (VSI) modules interconnected to form a circle via the inductors, which are required to suppress the possible circulating current in the circle. However, the design of the inductors could be challenging, where the inductance should be large enough to suppress the circulating current and small enough to minimize the effect on the output voltage. This paper proposes the utilization of coupled inductors in between any two connected VSI modules instead of stand-alone ones to optimize the hexagram inverter performance. On the basis of this structure, the circulating current can be maximally suppressed by the magnetizing inductance of the coupled inductor, while in the meantime, the output voltage is minimally affected by the leakage inductance. By sharing the magnetic core, the cost and size of the inductors are also reduced. Simulation and a small-scale experiment have been conducted to verify the proposed hexagram inverter structure with the six-winding coupled inductors.
    IEEE Transactions on Industrial Electronics 01/2011; 58(8):3421-3430. · 6.50 Impact Factor
  • M.A.S. Masoum, P.S. Moses, K.M. Smedley
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    ABSTRACT: The performance of distribution transformers serving several residential networks with multiple Plug-In Electric Vehicle (PEV) charging activity is studied in this paper. Distribution transformers are the weakest link in distribution systems that could soon be subjected to increasing stresses from PEV charging activity. This could significantly impact the reliability, security, efficiency and economy of newly developing smart grids due to possible overloads, additional losses and poor voltage regulation in transformers. In order to accurately investigate these problems, a detailed model is implemented for all distribution transformers in a smart grid system. The model implements a full equivalent circuit representation of the transformer considering winding and core losses as well as leakage flux and magnetizing reactances. A detailed 1200 node test system topology consisting of a radial high voltage (23 kV) distribution feeder with several low voltage residential networks populated with PEVs is implemented for this study.
    Innovative Smart Grid Technologies (ISGT), 2011 IEEE PES; 01/2011
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    ABSTRACT: This paper suggests application of the universal One-Cycle Control (OCC) technique to dynamically control a Three-Phase Load Emulator (TPLE). The paper offers a model of the OCC controlled current loop and derives the relationships between the controlled variables. Based on the analysis the required programming equations are derived. To validate the approach, a case study was conducted to experimentally emulate the start-up transient of a realistic Induction Motor. Experimental results are reported.
    01/2011;
  • A. Abramovitz, K.M. Smedley
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    ABSTRACT: This paper presents a single-phase power factor corrector based on a tapped-inductor buck-boost converter. This paper suggests simplified models of the power stage under current-mode control and derives small-signal transfer functions of both the current and voltage control loops. Design rules for implementation of the proposed power factor corrector (PFC) are also suggested. The proposed PFC features low dc bus voltage, arbitrary lower than the peak line voltage. The proposed PFC is suitable for applications in computers and communications, where dc isolation can be provided by the downstream dc/dc converters. Simulation and experimental results are also reported and stand in good agreement with theoretical expectations.
    IEEE Transactions on Power Electronics 01/2011; 26(9):2637-2649. · 5.73 Impact Factor
  • P.S. Moses, M.A.S. Masoum, K.M. Smedley
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    ABSTRACT: This paper investigates the impacts of Plug-In Electric Vehicle (PEV) charging stations on the performance of three-phase three-leg distribution transformers. PEV charging stations are sizeable nonlinear loads because of their large rating ac-dc power conversion electronics. The resulting current harmonics can cause abnormal operation in transformers such as additional losses, reduced efficiency, temperature rise as well as premature insulation and windings failure. This could significantly impact the reliability, security, efficiency and economy of newly developing smart grids due to possible transformer outages and loss of transformer life. In order to accurately investigate these problems, a highly detailed nonlinear three-phase three-leg transformer model is implemented for this study. The model considers core nonlinearities such as saturation, hysteresis and eddy current effects as well core flux interactions and couplings in asymmetric multi-leg core structures. The impact of diode rectifier based charging stations on losses (fundamental and harmonics) and waveform distortions in power transformers is studied.
    Innovative Smart Grid Technologies (ISGT), 2011 IEEE PES; 01/2011
  • Pengju Sun, Luowei Zhou, K. Smedley
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    ABSTRACT: The paper presents a new wide output range reconfigurable structure (WOR-RS) dc-dc converter, which is an extension of the full bridge isolated dc-dc converter with two output channels by adding an active switch and two diodes. The proposed WOR-RS is able to smoothly reconfigure the two output channels in parallel or series to realize wide output range. With this approach, the output voltage is shared equally in the series operating mode and so is the output current in the parallel operating mode. Therefore, the power rating of devices is significantly reduced compared to traditional isolated full bridge converter and the output rectifiers and filters can distribute power losses and thermal stresses. Operating principle, control strategy, modeling, and stability analysis are illustrated in the paper. An experimental prototype of a 200W DSP-based WOR-RS full-bridge dc-dc converter was built. The experimental results show the steady-state performance and fast dynamic response in the whole output voltage range, and verify the validity and applicability of this converter.
    IECON 2010 - 36th Annual Conference on IEEE Industrial Electronics Society; 12/2010
  • Jun Wen, Liang Zhou, K. Smedley
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    ABSTRACT: This paper introduced Hexagram converter - a new type of multilevel converter for reactive power compensation and harmonics elimination at Medium-Voltage (MV) grids to improve the power quality. The Hexagram converter is composed of six three-phase two-level Voltage Source Converters (VSCs) interconnected through the inductors, and has the advantages of modular structure with easy construction, even and much reduced voltage stress, and easy control. A four-dimensional control method which is composed of three two-level One-Cycle Controllers (OCC) is proposed for the Hexagram converter system. The reactive power compensation and harmonics elimination function has been verified with both simulation model and experimental prototype.
    Energy Conversion Congress and Exposition (ECCE), 2010 IEEE; 10/2010
  • Liang Zhou, K.M. Smedley
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    ABSTRACT: This paper discusses the fault tolerance ability of the hexagram inverter motor drive. Due to its unique interconnecting nature, the hexagram inverter can tolerate one leg failure without modifying the power circuit topology. In the event of one leg failure, the control circuit can reconfigure the trigger signals to maintain a smooth torque operation at a reduced power level. When a leg fails within the inner interconnecting loop, no special postfault strategy is needed; the hexagram inverter can still work properly. When a leg fails outside of the interconnecting loop, a new postfault control strategy is initiated, which controls the two remaining phase currents to maintain an operation with smooth torque. The simulation and experimental results have shown that the hexagram inverter can maintain its operation with smooth torque after a fault.
    IEEE Transactions on Industrial Electronics 09/2010; · 6.50 Impact Factor
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    ABSTRACT: While the integration of base-load fuel cells into the built environment is expected to provide numerous benefits to the user, the steady-state and dynamic behavior of these stationary fuel cell systems can produce an undesirable impact on the grid distribution circuit at the point of connection. In the present paper, a load-following active power filter (LFAPF) is proposed to mitigate the grid impact of such systems and instead improve overall local power quality. To evaluate the strategy, the LFAPF is integrated into a SOFC system inverter with one-cycle control (OCC) to provide the fundamental benefits of a traditional active power filter (APF) while also damping out short-term line current transients. The LFAPF benefit is illustrated through simulation of an SOFC interconnected with the utility electric distribution system and a building electricity demand that is modeled as a dynamic non-linear load. Three installation cases are examined: (1) a load-following SOFC, (2) a base-loaded SOFC, and (3) an offline SOFC. Without LFAPF, the load-following SOFC causes load transients due to the finite SOFC response time, and the base-loaded SOFC case has transients that appear more severe because they represent a larger overall percentage of the grid-provided load. The integration of an LFAPF improves the steady-state behavior over the base case and mitigates voltage sags and step changes. Thus integrating an LFAPF can, by providing useful services to both the utility and the end-user, facilitate the integration of an SOFC into the distribution system.
    Journal of Power Sources 04/2010; · 5.26 Impact Factor
  • A. Abramovitz, Tang Cheng, K. Smedley
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    ABSTRACT: An energy regenerating snubber for a forward converter is presented. The proposed snubber uses a tertiary transformer winding and beneficially exploits transformers' leakage inductances. The proposed snubber is capable of resetting the transformer, as well as eliminating leakage inductance voltage spike across the power switch. The proposed snubber recycles the recovered energy partially to the load and partially back to the source. This paper presents theoretical analysis, simulation and experimental results.
    IEEE Transactions on Power Electronics 04/2010; · 5.73 Impact Factor

Publication Stats

2k Citations
288.40 Total Impact Points

Institutions

  • 1994–2009
    • University of California, Irvine
      • • Department of Mechanical and Aerospace Engineering
      • • Department of Electrical Engineering and Computer Science
      Irvine, California, United States
  • 2008
    • University of California, Davis
      Davis, California, United States
  • 2007
    • Shamoon College of Engineering
      Ukreir, Southern District, Israel
  • 1992
    • California Institute of Technology
      Pasadena, California, United States