Three DC/DC converter topologies suitable for high-power-density high-power applications are presented. All three circuits operate in a soft-switched manner, making possible a reduction in device switching losses and an increase in switching frequency. The three-phase dual-bridge converter proposed is shown to have the most favorable characteristics. This converter consists of two three-phase inverter stages operating in a high-frequency six-step mode. In contrast to existing single-phase AC-link DC/DC converters, lower turn-off peak currents in the power devices and lower RMS current ratings for both the input and output filter capacitors are obtained. This is in addition to smaller filter element values due to the higher-frequency content of the input and output waveforms. Furthermore, the use of a three-phase symmetrical transformer instead of single-phase transformers and a better utilization of the available apparent power of the transformer (as a consequence of the controlled output inverter) significantly increase the power density attainable. >

A three-phase soft-switched high power density DC/DC converter for high power applications

The half-bridge series-resonant, parallel-resonant, and combination series-parallel resonant converters are compared for use in low-output-voltage power supply applications. It is shown that the combination series-parallel converter, which takes on the desirable characteristics of the pure series and the pure parallel converter, avoids the main disadvantages of each of them. Analyses and breadboard results show that the combination converter can run over a large input voltage range and a large load range (no load to full load) while maintaining excellent efficiency. A useful analysis technique based on classical AC complex analysis is introduced. >

A comparison of half-bridge resonant converter topologies

A surgical instrument including a handle assembly, a first endoscopic portion, a motor, and a first end effector is disclosed. The first endoscopic portion is selectively connectable to a distal portion of the handle assembly and defines a longitudinal axis. The first endoscopic portion includes a housing adjacent its proximal portion and includes an actuation member. The motor is disposed in mechanical cooperation with the housing of the first endoscopic portion and is operatively connected to the actuation member for moving the actuation member substantially along the longitudinal axis. The first end effector is selectively connectable to a distal portion of the first endoscopic portion and is configured to perform a first stapling function.

Powered surgical instrument

Maximum power point tracking (MPPT) is used in photovoltaic (PV) systems to maximize the photovoltaic array output power, irrespective of the temperature and irradiation conditions and of the load electrical characteristics. A new MPPT system has been developed, consisting of a buck-type DC/DC converter, which is controlled by a microcontroller-based unit. The main difference between the method used in the proposed MPPT system and other techniques used in the past is that the PV array output power is used to directly control the DC/DC converter, thus reducing the complexity of the system. The resulting system has high-efficiency, lower-cost and can be easily modified to handle more energy sources (e.g., wind-generators). The experimental results show that the use of the proposed MPPT control increases the PV output power by as much as 15% compared to the case where the DC/DC converter duty cycle is set such that the PV array produces the maximum power at 1 kW/m/sup 2/ and 25/spl deg/C.

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Development of a microcontroller-based, photovoltaic maximum power point tracking control system

DC–DC converters with voltage boost capability are widely used in a large number of power conversion applications, from fraction-of-volt to tens of thousands of volts at power levels from milliwatts to megawatts. The literature has reported on various voltage-boosting techniques, in which fundamental energy storing elements (inductors and capacitors) and/or transformers in conjunction with switch(es) and diode(s) are utilized in the circuit. These techniques include switched capacitor (charge pump), voltage multiplier, switched inductor/voltage lift, magnetic coupling, and multistage/-level, and each has its own merits and demerits depending on application, in terms of cost, complexity, power density, reliability, and efficiency. To meet the growing demand for such applications, new power converter topologies that use the above voltage-boosting techniques, as well as some active and passive components, are continuously being proposed. The permutations and combinations of the various voltage-boosting techniques with additional components in a circuit allow for numerous new topologies and configurations, which are often confusing and difficult to follow. Therefore, to present a clear picture on the general law and framework of the development of next-generation step-up dc–dc converters, this paper aims to comprehensively review and classify various step-up dc–dc converters based on their characteristics and voltage-boosting techniques. In addition, the advantages and disadvantages of these voltage-boosting techniques and associated converters are discussed in detail. Finally, broad applications of dc–dc converters are presented and summarized with comparative study of different voltage-boosting techniques.

/pdf/step-up-dc-dc-converters-a-comprehensive-review-of-voltage-6dlytctzg2.pdf

Step-Up DC–DC Converters: A Comprehensive Review of Voltage-Boosting Techniques, Topologies, and Applications

A synchronous rectifier is able to operate at higher frequencies and provides an output having lower noise than prior art FET synchronous rectifier system by using field effect switching devices which contain only one conductivity type of semiconductor material and connecting a high speed, low charge storage diode in parallel. Schottky diodes are preferred whereby there is no junction diode in the structure. Conventional FETs may be used when paralleled with a Schottky diode which prevents the FET's parasitic internal diode from becoming conductive.

Low noise, high frequency synchronous rectifier

The performance of the parallel resonant converter and the combination series/parallel resonant converter (LCC converter) when operated above resonance in a high power factor mode are determined and compared for single-phase applications. When the DC voltage applied to the input of these converters is obtained from a single-phase rectifier with a small DC link capacitor, a relatively high power factor inherently results, even with no active control of the input line current. This behaviour is due to the pulsating nature of the DC link and the inherent capability of the converters to boost voltage during the valleys of the input AC wave. With no active control of the input line current, the power factor depends on the ratio of operating frequency to tank resonant frequency. With active control of the input line current, near unity power factor and low input harmonic currents can be obtained. >

Characteristics of load resonant converters operated in a high power factor mode

A single phase, high frequency, transistor or gate turnoff thyristor chopper ballast circuit especially suited for mercury vapor lamps preferably operates on a unfiltered full wave rectified line voltage and electronically shapes the lamp current and therefore the line current to obtain a high power factor. The ballast circuit is lightweight with low volume due to elimination of large low frequency energy storage, filtering, and transformer components. The forced, high frequency ripple lamp current waveshape, achieved by comparison of the sensed current with an appropriate reference signal, provides for good regulation, an initially high starting current to eliminate glow-to-arc mode, automatic sweeping of the chopping frequency to avoid acoustic resonance effects, and a minimum current in the valley regions of the supply voltage for improved reignition characteristics.

Solid state chopper ballast for gaseous discharge lamps

57 A control for a voltage fed series resonant inverter includes controllable switch means (83, 85) which supplies square wave voltage signals to a resonant series circuit (95; 97). The output of the inverter is coupled to a rectifier (99) to provide dc power to a load. The control comprises summer means (58) for comparing a commanded dc voltage (Eo) to an actual dc output voltage and providing an error signal. An oscillator (64) responsive to the error signal generates a frequency signal that is coupled to the controllable switch means (83, 85) to vary the frequency of the square wave voltage supplied to the resonant circuit. The duty cycle of the frequency signal is adjusted so that the frequency signal is provided in bursts during low load conditions thereby minimizing circulating currents while maintaining the output voltage with dosed loop frequency control.

Full load to no-load control for a voltage fed resonant inverter

A resonant dc-dc converter employing power transistors as the switching elements generates a high dc output voltage (150 kilovolts) to drive an X-ray tube. The converter is configured such that the resonating circuit elements can be realized using the transformer parasitic elements. Voltage step up is achieved due to the transformer turns ratio as well as the resonant rise of voltage across the energy storage elements of a series resonant circuit.

Robert Louis Steigerwald

Papers

Low noise, high frequency synchronous rectifier

Characteristics of load resonant converters operated in a high power factor mode

Solid state chopper ballast for gaseous discharge lamps

Full load to no-load control for a voltage fed resonant inverter

Regulated dc-dc converter using a resonating transformer