Monday, April 10, 2017

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Chien-an Chen
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Changwei Liang

Khai D. T. Ngo

Lei Zuo

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Abstract
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A comprehensive and accurate model is essential for reliability estimation and output power optimization. Wave energy converters (WECs) involve hydrodynamic, mechanical structure, and power electronics converter. An equivalent circuit provides a faster and reliable way to estimate the characteristic of WEC as electrical components. A general approach is shown in this paper to derive a total circuit model from mechanical–electrical subsystem i.e. from buoy to generator. Least-square approximation and Brune network synthesis method are applied to derive a RLC circuit network for a buoy-wave behavior. The Mechanical-Motion-Rectifier (MMR) set based on the mechanical disengagement is analogue to the combination of transformers and diodes. Additional with the generator circuit model, the WEC equivalent circuit is developed. Two different applications based on the equivalent circuit are demonstrated to show its capability of the reliability analysis and the output power optimization. The methodology provides electrical engineers a complete perspective of a multidisciplinary system, and an electrical controller can be developed based on the model.

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Lujie Zhang
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Andrew Ritter

Craig Nies

Suman Dwari

Ben Guo

Shashank Priya

Rolando Burgos

Khai D. T. Ngo

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Abstract
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This paper presents a Voltage Controlled Capacitor (VCC) that varies from 20% to 100% of the rated capacitance (1 μF) with a control voltage from half of the voltage rating to 0 V. Capacitance, self-resonant frequency, and equivalent series resistance (esr) were measured with respect to the control voltage. An equivalent circuit and a nonlinear model derived from relationship between permittivity and electric field were created and implemented in SPICE based on previous measurements. A buck converter with input of 12 V, output of 5 V, and switching frequency of 500 kHz was built to demonstrate the change from 85% to 40% of the rated capacitance of VCC. The error between the simulation and experiment was limited within 10%, which verifies the model.

Shuilin Tian

Jian Li

Fred C. Lee

Qiang Li

Pei-Hsin Liu

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Please note: This paper will be presented by Syed Bari (pictured), as Shuilin Tian has graduated.
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Abstract
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Multiphase constant on-time current-mode control based on pulse distribution structure is widely used in voltage regulator application for microprocessor. To minimize ripple cancellation effect, external ramp compensation is used in commercial products. However, external ramp will introduce dynamic to the system and stability margin will be suffered without considering its effect. This paper first studies the effect of external ramp by deriving small-signal transfer function based on describing function method. It is found that external ramp brings additional dynamic, with time constant related with switching period. Then, a simple equivalent circuit model based on three-terminal switch concept is proposed, which considers the effect of external ramp by adding an additional R–L branch. The equivalent circuit model can be reduced to previous unified three-terminal switch model when external ramp is zero and can be reduced to model of constant on-time voltage mode control when external ramp is much larger than inductor current ramp. The proposed three-terminal switch model is a completemodel, which can be used to examine all transfer functions and is accurate up to half of switching frequency. The analytical transfer functions are provided for easy reference. The model is verified by SIMPLIS simulation and experimental measurement.

Bo Wen

Dushan Boroyevich

Zhiyu Shen

Rolando Burgos

Paolo Mattavelli

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Please note: This paper will be presented by Zeng Liu (pictured), as Bo Wen has graduated.
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Abstract
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Islanding detection is critical to the safety of grid-tied inverters. This paper presents an impedance-based analysis of the active frequency drift (AFD) islanding detection method. To study this method, the output impedance of a grid-tied inverter is modeled. The Z_{qq} of the inverter impedance features a negative incremental resistor, whose magnitude is equal to the dc impedance magnitude of the local load defined by the test standard. With a large value of feedforward gain N in the AFD method, the phase of Z_{qq} is shown to drop below 180°. Under an islanding condition, due to a lack of phase margin, the inverter system becomes unstablewith a frequency drift away fromits steady state. The islanding condition is then identified by a frequency detection unit. Experimental results verify the analysis.

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Virginia Li
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Qiang Li

Fred C. Lee

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Abstract
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For the new-generation of server voltage regulators (VRs), companies are employing the use of 48V bus to improve system efficiency and to reduce the cost of datacenters. For 48V to 1V VR, a quasi-parallel topology, the sigma converter, is shown to have 93.4% maximum efficiency and 420W/in^{3} power-density. In order to design the sigma converter to meet the VR requirements, the large-signal performance as well as the small-signal behavior of the sigma converter must be studied. In this paper, the small-signal model of the sigma converter is examined for server application.

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Niloofar Rashidi Mehrabadi
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Rolando Burgos

Christopher Roy

Jianghui Yu

Dushan Boroyevich

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Abstract
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The deviation of real system behavior from the predictions made from modeling and simulation is inevitable due to variations in different model input parameters as well as inaccurate modeling. The potential sources of uncertainty in modular multilevel converters (MMCs) is significant in medium- and high-voltage applications where each arm consists of several power electronics building blocks (PEBBs) connected in series. Therefore, assessing the predictive proficiency of the model, in the presence of various uncertainties, is critical in gaining confidence in modeling and simulation results. This paper investigates the predictive capability of MMC simulation models when adding more PEBBs. The relationship between the total uncertainty in modeling and simulation, and the number of PEBBs in each arm is presented for different model outputs. The results reveal an interesting feature of MMC—despite the fact that the number of potential sources of uncertainty increases by adding more PEBBs in each arm, the total uncertainty in the prediction of a system response quantity remains the same or decreases, depending on the selected model output response.

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Igor Cvetkovic
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Zeng Liu

Dushan Boroyevich

Rolando Burgos

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Abstract
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New electronic power distribution systems built for airplanes, ships, electric vehicles, data-centers and modern homes, dominantly comprise a variety of power electronics converters with very different dynamic characteristics. If their behavior is not examined carefully before system is integrated, instability becomes one of the major concerns. This paper addresses low-frequency terminal-behavioral modeling of three-phase converters which dynamics can be captured on-line, in a non-intrusive way, and later decoupled from the source and load in order to get un-terminated model of a particular converter (or a system). Experimental results of the modeling methodology applied to the voltage source inverter, and active rectifier are given at the end to verify modeling and decoupling procedure.

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Zeng Liu
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Jinjun Liu

Dushan Boroyevich

Rolando Burgos

Teng Liu

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Abstract
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Droop-controlled inverters are widely employed as power sources in three-phase AC power electronics system, such as distributed generation, while the interaction between the source and the load may lead overall system to be unstable. Terminal-characteristics based stability criteria are very attractive for analyzing the stability of three-phase AC power electronics system. However, the systems, composed by droopcontrolled inverters, exhibit the dynamical variation of fundamental angular frequency, and existing stability analysis approaches are just suitable for systems with constant fundamental angular frequency. To overcome this problem, this paper proposes small-signal terminal-characteristics model of the three-phase droop-controlled inverter covering the dynamic of fundamental angular frequency, and both current mode operation and voltage mode operation are taken into account. Finally, the proposed model is verified in frequency domain.

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Zeng Liu
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Jinjun Liu

Dushan Boroyevich

Rolando Burgos

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Abstract
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Droop-controlled parallel inverters are widely adopted in micro-grids due to its high reliability and low cost. However, the interaction among the inverters will cause whole system to be unstable even though each individual inverter can operate stably in stand-alone mode. A lot of work has been done for analyzing the stability of parallel inverters with droop control through state-space approach originally used in conventional electrical power system. For this existing approach it is necessary to have the knowledge of inside parameters of each individual inverter in advance, while in practical applications it is not so convenient to obtain the internal structure and parameters. To overcome this problem, this paper proposes a stability analysis approach for the droopcontrolled parallel inverters based on the terminal-characteristics of individual inverters. At beginning, the terminal-characteristics of individual inverter with droop control are defined in system synchronous reference frame (SRF), which can be represented by the transfer function between output current and output voltage, and the transfer function between output current and fundamental angular frequency. Then the terminal-characteristics of the whole parallel system are derived out with the ones of each individual inverter. Furthermore, a stability criterion is proposed for the parallel inverters based on the terminal-characteristics of each individual inverter according to the Generalized Nyquist Criterion. Finally, the proposed terminal-characteristics and stable criterion for droop-controlled parallel inverters are verified in frequency domain.

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Yi-Hsun Hsieh
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Fred C. Lee

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Abstract
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The modular multilevel converter (MMC), is widely adopted in high voltage applications because of its simplicity and modularity. However, the current and power flow is very complicated. As a result, methods proposed for capacitor reduction, which is required to stored line frequency related circulating energy, all went through complicated mathematical derivation. C. Li proposed a state plane analysis to visually illustrate the convoluted current and power flow. The circulating energy related to source and load as well as the circulating energy swapping between capacitors was explained for the first time. Based on the state plane analysis, this paper proposed a decoupled αβ model of MMC, which clearly identifies input and output relationship. In addition, the power flow and the causes for each component of circulating energy are well explained with the proposed model. Therefore, the proposed model paves a good way for an advanced control and a systematically understanding of MMC.

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Video Nugget
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Xiaolong Yue

Dushan Boroyevich

Rolando Burgos

Fang Zhuo

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Please note: This paper will be presented by Chi Li (pictured), as Xiaolong Yue has graduated.
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Abstract
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Impedance is very important for power electronic systems because of the close relationship between impedance and system stability. The line-frequency rectifiers are commonly used ac-dc interfaces in electrical power systems. For line-frequency rectifier, with a sinusoidal voltage perturbation excitation at input terminal, input current contains not only perturbation frequency, but also multiple additional frequency components. Therefore, input characteristics of line-frequency rectifiers are actually single input multiple output (SIMO) in frequency domain. However, in tradition, input current perturbation is simplified into a sinusoidal signal at perturbation frequency by ignoring other additional frequency components and the obtained impedance models mainly focus on frequency regions below line frequency. To describe the SIMO input characteristics of line-frequency rectifiers and to develop an impedance model that could be applied beyond switching frequency, this paper proposes a new model by using harmonic balance method. Detailed analysis indicates that input admittance of line frequency rectifier in high frequency regions acts like a resistor rather than inductor. The simulations validatethe accuracy and effectiveness of the proposed model.

Yingyi Yan

Fred C. Lee

Paolo Mattavelli

Shuilin Tian

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Please note: This paper will be presented by Syed Bari (pictured), as Yingyi Yan has graduated.
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Abstract
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In *V ^{2}* control, the direct feedback contains the in- formation of the inductor current, the capacitor voltage, and the load current. In this paper, by separating the current feedbacks and the capacitor voltage feedback, an equivalent circuit of

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Ashrarul Haq Sifat
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Jun Wang

Dushan Boroyevich

Rolando Burgos

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There is no paper associated with this session number. Click below to view the poster.
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Luxing Wang
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Syed Bari

Qiang Li

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There is no paper associated with this session number. Click below to view the poster.
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