PESC Record - IEEE Annual Power Electronics Specialists Conference

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ISSN 0275-9306

Publications in this journal

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    ABSTRACT: A soft-switching inverter topology (the Class Phi ) is presented which draws dc source current through a transmission line or a lumped-network approximation of a distributed line. By aligning the inverter switching frequency just below the line's lambda/4-wave resonance, the Class Phi topology enforces odd-and even-harmonic content in its drain voltage and input current, respectively. The symmetrizing action of the transmission-line dynamics results in natural square-wave operation of the switch, reducing the inverter stresses (relative to a Class E) for a given power throughput. The inverter waveforms and normalized power-output capability are analyzed in simple terms, and supported by measurements of an inverter built around a length of distributed line, and an inverter incorporating a lumped L-C ladder network. The latter implementation is constructed with air-core magnetics and inter-layer capacitances that are integrated into the thickness of a printed-circuit board. A comparison with a Class E inverter of similar size and ratings demonstrates the small passive-component values and manufacturing advantages afforded by the Class Phi topology.
    No preview · Article · May 2014 · PESC Record - IEEE Annual Power Electronics Specialists Conference
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    ABSTRACT: When Ultra-Capacitors are used for providing energy to power downstream switch mode converters used for power conversion, the significant change in their capacitance with frequency can result in significantly higher voltage ripple and current ripple in these capacitors. This results in over voltage and temperature rise in these capacitors resulting in their consequent lifetime reduction. Based on extensive measurements of these voltage ripple and current ripple at different converter switching frequencies, design considerations that can significantly reduce these voltage and current ripple is proposed in this paper.
    Preview · Conference Paper · Oct 2009
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    ABSTRACT: Based on commonly used parameters for a generic transcutaneous transformer model, a remote power supply using resonant topology for artificial heart is analyzed and designed for easy controllability and high efficiency. Primary and secondary windings of the transcutaneous transformer are positioned outside and inside human body respectively for energy transfer. The two large leakage inductances and the mutual inductance of the transformer are varying parameters of the coupling-coefficient which varies with transformer alignment and gap due to external positioning. Varying resonant-frequency resonant-tank circuits are formed using the transformer inductors and external capacitors to obtain a load insensitive frequency for the voltage transfer function at given range of coupling coefficients and loads. Previous researches usually use frequency modulation which may require a wide control frequency range well above the load insensitive frequency. In this paper, fundamental frequency study of the input-to-output voltage transfer function is carried out. Using the proposed control method, the switching frequency can be locked at just above the load insensitive frequency at heavy load for best efficiency. Specifically, above resonant operation in driving the resonant circuits when varying the coupling-coefficient is maintained using a digital-phase-lock-loop (PLL) technique to achieve zero-voltage switching of a full-bridge switches configuration which is also programmed to provide pulse-width-modulation (PWM) in controlling the output voltage. A prototype transcutaneous power regulator is built and found to have good efficiency and regulation in responding to changing alignment or gap of the transcutaneous transformer, load and input voltage dynamically. Author name used in this publication: Chi K. Tse
    No preview · Article · Jan 2009 · PESC Record - IEEE Annual Power Electronics Specialists Conference
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    ABSTRACT: In this paper, unbalanced three-phase control method is proposed to increase the fault tolerance for H-bridge multilevel inverter under the conditions of faulty power cells. It is possible to generate a balanced three-phase line-to-line voltage by phase-shifting and bypassing faulty power cells with a minimum voltage drop. In this method, the concept of voltage modulation by using offset voltage is applied to an unbalanced three-phase control method. Especially, it is possible to use the maximum output voltage of inverter by adopting the real time unbalanced control method of phase voltage irrespective of the fault location and the number of disabled power cells. Also, the feasibility of the proposed method is proved by the H-bridge multilevel inverter test composed of 7-level.
    No preview · Conference Paper · Jul 2008
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    ABSTRACT: A speed sensorless induction motor drive fed by a 3-level neutral point clamped (NPC) inverter is presented, which combines the principle of sliding mode controller (SMC), sliding mode observer (SMO), direct field oriented control (DFOC) and space vector modulation (SVM). PI is widely used in field oriented control for speed, flux and current regulation whereas the performance of drive is usually affected by the invariant parameters of PI. In this paper, SMC is introduced in stead of conventional PI to produce fast and accurate response and reject the external disturbance and motor parameters variation. Moreover, SMO is introduced to observe rotor speed and flux for the implementation of DFOC. The induction motor is driven by a 3-level NPC inverter, which provides more smooth and accurate response than conventional 2-level inverter, and the neutral point potential is well controlled using hysteresis control. By introducing sliding mode theory in both controller and observer, the system demonstrates excellent dynamic and steady-state performance, robustness to motor parameter variations and wide speed range operation, which is confirmed by simulation and experimental results.
    No preview · Conference Paper · Jul 2008
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    ABSTRACT: A general boost converter has limited voltage step-up ratio because of its parasitic resistances. Thus, it is not applicable for high step-up applications. As a solution, combining a boost converter with a series output module can be considered to supplement the insufficient step-up ratio. By applying this concept, a new integrated boost-sepic (IBS) converter, which provides additional step-up ratio with the help of an isolated sepic converter, is proposed in this paper. Since the boost converter and the sepic converter share a boost inductor and a switch, its structure is simple. Moreover, the proposed IBS converter needs no current- snubber for the diodes, since the transformer leakage inductor alleviates the reverse recovery. The operational principle and characteristics of proposed converter are presented, and verified experimentally with a 200-W, 42-V<sub>dc</sub> input, 400-V<sub>dc</sub> output converter prototype.
    No preview · Conference Paper · Jul 2008
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    ABSTRACT: Typically, electric energy is available from mains via a.c. feeders, which are usually 1-phase for power levels below several kVA due to convenience reasons. Anyway, the availability of a 3-phase supply might benefit also such class of loads, e.g. permitting to directly supply better quality induction motors. This paper proposes a converter able to generate an almost symmetrical 3-phase supply from a 1-phase feeder, featuring low complexity, full reversibility, a quasi-sinusoidal output and a pseudo-resistive or quasi-sinusoidal in-phase input. After a circuital theoretical analysis, considerations about the possible control strategies are developed and a simulation model purposely get ready is described. Finally, simulation results illustrating the proposed solution are reported and commented.
    No preview · Conference Paper · Jul 2008
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    ABSTRACT: This paper describes the control strategy of an integrated starter-alternator prototype. Control specifications include a high starting torque in the low speed range as well as a smooth transition from motor to generator operation mode at higher speed. Inverter voltage limitation has to be managed during high speed operation. An interior permanent magnet synchronous machine with a fractional-slot winding is adopted. The control strategy takes advantage of the magnetic model of the electrical machine, which is well suited for flux-weakening application with advantages for the power stage ratings. Details of the control design and experimental test results are reported.
    No preview · Conference Paper · Jul 2008
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    ABSTRACT: An N-phase sensorless current sharing digital controller algorithm and architecture for multiphase power converter is presented in this paper. It demonstrates the visibility of sensor-less current sharing implemented for buck converter with more than two- phases. The presented N-phase sensor-less current sharing controller eliminates the need for current sensing for the current sharing loops and the need for analog-to- digital converters for phase current sampling when digital controllers are used. The presented current sharing controller operation is discussed and verified with experimental results obtained from a four-phase proof of concept prototype.
    No preview · Conference Paper · Jul 2008
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    ABSTRACT: In this paper, the principle and basic structure of the thermoelectric module is introduced. The steady- state and dynamic behaviors of a single TE module are characterized. An electric model of TE modules is developed and can be embedded in the simulation software for circuit analysis and design. The issues associated with the application of the TEG models is analyzed and pointed out. Power electronic technologies provide solutions for thermoelectric generation with features such as load interfacing, maximum power point tracking, power conditioning and failed module bypassing. A maximum power point tracking algorithm is developed and implemented with a DC-DC converter and low cost microcontroller. Experimental results demonstrated that the power electronic circuit can extract the maximum electrical power from the thermoelectric modules and feed electric loads regardless of the thermoelectric module's heat flux and load impedance or conditions.
    No preview · Conference Paper · Jul 2008
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    ABSTRACT: This paper introduces a new adaptive notch filtering (ANF) approach as a powerful tool for synchronization of the single-phase converter-interfaced DG systems. The technique is simple and capable of extracting harmonics, tracking the amplitude and frequency variations, and providing the phase angle of the grid signal. The methodology is applicable for a wide range of equipment like converter- interfaced distributed generation (DG) units, e.g. wind, photovoltaic, fuel cells and micro-turbines, and also in active power filters and uninterrupted power supplies. Theoretical analysis is presented and the performance of the method is evaluated through simulation and experimental work.
    No preview · Conference Paper · Jul 2008
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    ABSTRACT: SiC semiconductor devices are becoming more common in high power applications. This is largely due to higher blocking voltages and faster switching speeds. The development of SiC devices, specifically thyristors and GTOs, is still an evolving process [1]. There is not yet a single device capable of handling the magnitude of current typically seen in transmission and distribution systems and as a result these devices must be paralleled into a single switching position. SiC thyristors were used to carry out a study on paralleled SiC bipolar devices. Si bipolar devices are much better matched than SiC devices, but they exhibit much slower turn-on times [2]. Thus, the most suitable method of inducing current sharing in these devices is through gate control. However, SiC devices exhibit fast turn-on times while being poorly matched. Using various methods of gate control for SiC bipolar devices in parallel does not significantly affect the current sharing. The best way to improve current sharing is obtained using series resistors. These resistors should be chosen so that the voltage drop and power losses are minimized. The effects of thermal runaway are observed as well. As a device rises in temperature relative to the other devices, it conducts more current due to its negative temperature coefficient of on-state resistance. In order to maintain proper heat sharing, a design for a package is presented that includes three thyristors in parallel on a common substrate.
    No preview · Conference Paper · Jul 2008
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    ABSTRACT: This paper presents a new and simple finite-states model predictive control strategy for a four-level three-phase diode-clamped inverter. This strategy allows for fast load current control while keeping the balance of the dc-link capacitor voltages. A discrete-time model of the load and of the dc-link capacitors is used to predict the behavior of the load current and the capacitor voltages for each possible switching state. A cost function that considers the load current error and the capacitor voltages error is used to evaluate each prediction. The switching state that minimizes the cost function is selected and applied during a whole sampling period. Simulation results are shown verifying the good performance of the proposed predictive controller.
    No preview · Conference Paper · Jul 2008
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    ABSTRACT: Several inverter configurations have been proposed in literature to achieve fuel-cell power conversion at significantly lower cost, which is one of the most critical constrains to make such alternative energy systems viable. A single-stage isolated dc/ac Cuk inverter would potentially be a better alternative with reduced system complexity, costs, improved reliability, and high efficiency because it achieves direct dc/ac power conversion using only four main switches. Simple drive circuit (owing to all low-side power devices), possibility for integrated magnetics, and less turns ratio requirement for transformer lead to a low-cost, high-power-density energy-conversion system. This paper investigates the possibility of using and performance of this inverter for low power (< 3 kW) fuel-cell applications. The operational principle for isolated dc/ac Cuk inverter, which has not appeared in the literature, is presented. Key design issues of a 1 kW prototype for the application are addressed. In order to achieve higher efficiency, the turns ratio of the transformer needs to be selected to achieve a trade off between output voltage distortion and duty ratio range. Switching losses due to the leakage of the transformer and high reverse current during device turn off can be reduced by implementing active lossless clamp circuit, which has been presented in this paper.
    No preview · Conference Paper · Jul 2008
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    ABSTRACT: Available for a decade for portable electronic applications, lithium-ion battery technology encountered a swift rise, and now it represents broadly 60 % of the market on this segment. From a specific energy and power point of view, lithium-ion accumulators offer performances far more superior to other accumulator technologies. This paper deals with investigations on an accurate 6.8 Ah lithium-ion battery energetical modelling. All electrochemical devices are characterised by an electrical behaviour, which depends on temperature, state of charge and current. In the case of lithium-ion accumulators, the energetical behaviour is moreover deeply marked by line effects, due to the porosity of both electrodes. This paper shows in particular that electrode porosity can be taken into account by means of a diffusion impedance represented by a capacitive transmission line. An energetical model, which couples this line with a current independent capacitance, is proposed and characterised at constant temperature (20degC) over different states of charge intervals (5 %) and for different currents. Reactant diffusion within the electrolyte and relaxation period after discharge are investigated as well. Validation tests carried out on a 6.8 Ah lithium-ion element are conclusive.
    No preview · Conference Paper · Jul 2008
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    ABSTRACT: Switching mode power supply (SMPS) behavior depends entirely upon known component values and often unknown load impedances. Load change produces voltage over- and undershoots and a design-point shift. In most cases, the controller is blind to these shifts. However, load knowledge is an essential design parameter and should precede optimal and adaptive control techniques. System identification algorithms implemented on digital processors open new opportunities in control and system performance. Typical studies in SMPS identification are based on offline steady-state measurements that form nonparametric frequency-domain models. This paper investigates real-time system identification algorithms that generate parametric models - a practical form for pole-placement and root-locus design. Two key metrics are introduced: parameter error and convergence time to describe algorithm accuracy and speed, respectively, after abrupt parameter changes - a common SMPS load scenario. Hardware and simulation results will show that an algorithm called recursive least squares, in its most basic form, could reasonable approximate the input-to-inductor current plant for static loads during startup, but not for abrupt load steps.
    No preview · Conference Paper · Jul 2008
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    ABSTRACT: The measurement accuracy of GMR Current sensors suffers under the influence of hysteresis. For solving this problem, a hysteresis model has been implemented to keep track in real time of the sensor output signal. The model is a simplified version of the T(x) hysteresis model. Very good results have been achieved in comparing the software simulations and the real sensor characteristics. The model has been further implemented on a fixed-point Digital Signal Controller (DSC), connected to the sensor output. The linear output of the DSC confirmed the functioning of the model in the hardware implementation. An algorithm for eliminating error propagation during the measurements has been also developed.
    No preview · Conference Paper · Jul 2008