PESC Record - IEEE Annual Power Electronics Specialists Conference

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ISSN 0275-9306

Publications in this journal

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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.
    Power Electronics and Applications, 2009. EPE '09. 13th European Conference on; 10/2009
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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
    PESC Record - IEEE Annual Power Electronics Specialists Conference 01/2009; DOI:10.1109/PESC.2008.4592210
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    ABSTRACT: Power converters are known to generate spectral components in the range of interest of electromagnetic compatibility measurements. Common approaches to manipulate some selected components in these frequency ranges are shown here. These approaches add components to the input signal of the modulator to derive a slightly varied spectrum. To achieve a rectangular output signal, those modulators use a triangular or saw tooth carrier signal. A novel family of modulators is shown here, using more than one carrier signal to obtain a completely changed spectrum while maintaining the rectangular shaped waveform at the output. The multiple carriers are fed into multiple comparators and their outputs are intelligently combined by logic gates to get a single signal to drive one power stage of any type of converter. This commutation distinguishes between the four members of the novel family: the first one uses an or- gate to combine the signals; the second one utilizes therefore an and-gate. The third modulator combines the outputs of those two and switches between the or-output and the and- output after each pulse. The last described modulator is commutating one of the described outputs dependent on the state of a master clock. The nonlinear operation of all modulators is described with nonlinear algebra in conjunction with Boolean algebra. The benefits for electromagnetic compatibility of the new schemes are presented, all modulators are examined in terms of steady state operation, dynamic behavior, maximum modulation range and added distortion. Finally the implementation of one of the modulators in a switch-mode power supply is presented. Experimental results are verifying the simulation.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
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    ABSTRACT: In this paper, a method for reducing the voltage stresses on switching components and power losses in a shunt current source active power filter (CSAPF) is presented. The method is based on the series capacitor structure which is used to block the fundamental supply voltage component. The results show that the component voltage stresses and power losses are lower in the CSAPF with a series-connected capacitor than in the conventional topology.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
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    ABSTRACT: The output current of contemporary AC-DC front-end converters is steadily increasing due to higher power density requirements. The use of shunt resistors to sense the output current is becoming unacceptable due to high power losses and new techniques for current sensing need to be investigated. In this paper, we investigate the possible use of the voltage drop across the trace resistance to sense the output current. This approach promises very low cost since no dedicated shunt resistor is required, no additional power losses occur and no extra space on the printed-circuit-board (PCB) is necessary. To overcome the problems associated with the temperature drift of the copper, and variability in the trace resistance of the copper track, a digital controller can be used to calibrate the trace resistance and implement a temperature drift compensation. This form of microcontroller is readily available on todaypsilas AC-DC front-end converters. However, theoretical and practical investigations revealed that the parasitic inductance and skin effect may limit the bandwidth of this measurement principle down to several hundred Hz. To overcome this limitation, we proposed a compensation technique that has the potential to increase the bandwidth beyond ten kilohertz. Experiments with output currents of up to 240 A demonstrated that the measurement uncertainty for DC currents is less than plusmn1 A for temperatures between 25 to 60 degrees, and that the effective bandwidth can be enhanced using a compensation technique.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
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    ABSTRACT: The PMSM is inherently electronically controlled and requires rotor position information for proper drives. However, the problems of the space, cost, and reliability of rotor position sensors have motivated research in the area of position sensorless PMSM drives. Numbers of rotor position sensorless control techniques have been proposed for PMSM drives, but most rely on the estimation of the rotor flux linkage vector. The performance of this method, however, is poor at low speed region due to the voltage distortions caused by the nonlinear behavior of a pulse width-modulation (PWM) voltage source inverter (VSI). In this paper, a new online voltage distortion compensation method is employed to overcome this problem. To prove effectiveness of the voltage distortion compensation method to the improvement of the rotor position estimation, the proposed method is applied to PMSM drive system and implemented in a digital manner using a digital signal processor.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
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    ABSTRACT: This paper presents a novel isolated single stage buck-boost inverter for implementing dc-to-ac, ac-to-dc or dc-to-dc. The BBI has better performances, in terms of low cost, high efficiency and high voltage gain. Through the HEV/EV application, the circuit operation principles and characteristics have been analyzed. And then, a novel Synchro-Switching SVPWM have been presented to obtain the maximum buck-boost factor and ZVS or ZCS conditons on the main switches and to reduce the magnetizing inductance value of transformer. The experimental results have confirmed the operating principle and the analysis method.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
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    ABSTRACT: In designing a LLC resonant converter, the ratio of magnetizing inductance (L<sub>M</sub>) to resonant inductance (L<sub>M</sub>), the inductor ratio (K) is usually considered. In high power density adapter, both adapter size and efficiency are important factors. considering the size of adapter, high K design can be more attractive. But, wide frequency variation of high K design results in design difficulty of magnetic elements and decrease in efficiency. To solve these drawbacks, an adaptive link voltage variation (ALVV) control is proposed. With the proposed control method, the LLC resonant converter can be operated at the resonant frequency despite the output voltage variation. The control strategy and schematics are presented, and verified experimentally.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
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    ABSTRACT: A new half bridge converter for the personal computer (PC) power supply is proposed in this paper. Generally, PC power supply has two unique input/output specifications which are wide input voltage range and long hold up time. Therefore, it has to be operated with a small duty ratio. That makes it difficult to apply ZVS PWM topology to the PC power supply. The proposed ZVS half bridge converter controls the primary current which flows through blocking capacitor with an auxiliary switch of the secondary side. As a result, it can ensure zero DC offset of the magnetizing current even if it is operated with a small duty ratio. Moreover, ZVS conditions are maintained by reflected load current without disturbance due to the DC offset of the magnetizing current. Therefore, it shows a high efficiency and a low EMI at the PC power specifications. The operational principle, analysis and design of the proposed converter will be presented. Experimental results demonstrate that the proposed converter can achieve a significant efficiency improvement in a 280 W (12 V, 23.3 A) prototype converter.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
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    ABSTRACT: This paper investigates the loss characteristics of several commercial rf magnetic materials forpower conversion applications in the 10 MHz to 100 MHz range. A measurement method is proposed that provides a direct measurement of inductor quality factor Q<sub>L</sub> as a function of inductor current at rf frequencies, and enables indirect calculation of core loss as a function of flux density. Possible sources of error in measurement and calculation are evaluated and addressed. The proposed method is used to identify loss characteristics of different commercial rf magnetic core materials. The loss characteristics of these materials, which have not previously been available, are illustrated and compared in tables and figures. The results of this paper are thus useful for design of magnetic components for very high frequency applications.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
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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.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
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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.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
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    ABSTRACT: With an aim of optimizing the operation points of the proton exchange membrane fuel cell (PEMFC), it is better to understand the working procedure with the physical effects and to seek a prediction of its behaviour according to its operating conditions. By applying the diffusion equations of Maxwell-Stefan and the phenomenological model (developed by Springer), this approach presents a steady state ID model of the PEMFC. The fuel cell performances are also conditioned by the hydration of the membrane. In this work, we use an iterative procedure to compute the coupled diffusion equations of the reactants and the water transport in the membrane. That way, the membrane resistance behavior can be predicted for various relative humidity of the inlet gas. The water transport is always a balance between at least two competing diffusion mechanisms One is due to the proton displacement from anode to cathode that drag some water molecules with them, this phenomenon is called electro-osmotic drag. The other mechanism is back diffusion of water from cathode to anode. This water flux results from the water concentration gradient created in the membrane by the electro-osmotic drag and the water produced by the redox reaction at the cathode. In the literature, the electro-osmotic drag coefficient is mostly depending on the water content. We will study if this governing equation can be used for any membrane. The numerical results are then compared to the experimental ones. The experiments are led on a 500 W PEMFC test bench fed by dry hydrogen and humidified air, the type membrane of the stack is Gorereg.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
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    ABSTRACT: The present paper investigates the control of interleaved DC-DC converters. It proposes an alternative solution to balance the currents between the legs without using current transducer, relying instead on a feedback loop based on the measurement of the capacitor voltage ripple. The appropriate measurement circuit is proposed. The voltage control uses a model predictive control scheme, which assumes the average model of a single leg converter, the unbalance being compensated separately. The controller intrinsically limits the current during transients, achieving protection of the semiconductor devices and avoiding coil saturation. The proposed control and balance methods are validated experimentally on a two-leg interleaved converter.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
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    ABSTRACT: Usually, PWM operation is selected to drive High Brightness LEDs, because the dimming behavior is more linear than in DC operation. Nevertheless, to obtain an enhanced operation of the device (full output light control), the luminous flux should be measured. This paper proposes a control method based on an estimator of the luminous flux emitted by the LED. Firstly, the LEDs are characterized. Based on these characterization, an estimator of the flux emitted by the LED is defined. The estimator provides this flux value from only two temperature values (the case temperature and the ambient temperature). The estimator is defined and validated in steady state as well as in the transient stage. The flux estimator is then validated with actual measurements. Once the estimator is defined and validated, the electronic driver to supply the LEDs as well as the digital control scheme are presented. Finally, a built prototype is presented, and the experimental results are shown. Conclusions of this work show that with the presented estimator, both the steady state and the transient luminous flux can be accurately estimated. Thus, the output light control of the LEDs can be accomplished by sensing temperature rather than luminous flux. The final output characteristic of the system shows linearity between the output flux and the reference value, with a DC operation of the LEDs.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
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    ABSTRACT: Digitally group-asymmetrical PWM (DGAPWM) ballast for a dimmable fluorescent lamp is explored. The proposed DGAPWM can adaptively provide suitable duty-ratio in group pulse train for generating proper odd as well as even harmonics over whole spectrum of the lamp current so as to eliminate striation and thermostat effect. The DGAPWM activates during low luminance under 3,000 Cd/m<sup>2</sup> and operates the ballast working in continuous conduction mode (CCM), which achieves zero-voltage-switching (ZVS) to gain high efficiency over 90%. The proposed DGAPWM for the fluorescent lamp can increase lighting efficiency better over 20% than traditional one and provide wide dimmable range between 100% and 0%.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008