Heat recovery methods and the amount of heat that can be recovered from fuel cell exhaust gas is described. The cooling performance of an absorption refrigerator that uses fuel cell waste heat is also described. Two heat recovery methods from the exhaust gas are considered: one uses heat recovery from mixed exhaust gas from the cathode side of the cells and the reformer (mixed type); the other uses separate heat recovery from these sites (separate type). Simulation shows that the amount of heat recovered between 60 and 75 with the separate type of heat recovery is greater than with the mixed type of heat recovery. The cooling capacity of the refrigerator using the separate type heat recovery and recovering heat between 65 and 85 is about 2.5 times that of one using a generator (heat source) with a constant 85 temperature.

This paper describes configuration and operation of a high-frequency link resonant inverter using cycloconverter techniques. In this inverter, a resonant link high-frequency voltage generated in a primary resonant inverter is isolated by a high-frequency transformer, then directly converted into a resonant link low-frequency voltage in a cycloconverter. The switching losses and surge voltage levels can be reduced by making all switches in the primary inverter and the cycloconverter operate at zero voltage. The relationship between characteristic impedance of the resonant circuit and the conversion efficiency, and the distortion factor characteristics of the output voltage waveforms are discussed by comparing of analytical and experimental results.

Under conditions of order reduction, a nonlinear control of a bidirectional coupled-inductor Cuk converter suitable for large-signal applications is presented. The converter is accurately modelled as a second order bilinear system and the conditions established for local stability. The nonlinear control law which is implemented by means of one analog divider, standard operational amplifiers and a pulse-width modulator. As a result, the output variable follows proportionally the reference signal, thus allowing the obtention of different types of power waveforms in the converter output. Experimental results verify the theoretical predictions.

The effectiveness of random-switching control, by which the switching-noise spectrum is spread and its level is reduced, is briefly described through experimental results. The noise spectrum by random switching is analyzed in general approach including a noise-generation model and a switching function with random process. Taking the normal distribution as an instance, the discussion on the amount of random perturbation is made quantitatively. The validity of the analysis is confirmed experimentally by a series of pulse serving as ideal switching-noise.

A new circuit and a transformer structure is described for a high-input-voltage converter operating at a high switching frequency. The two-MOSFET forward converter is suitable for a high-input-voltage converter. To increase the switching frequency, the reset period of the transformer core flux must be reduced. There are a few methods for decreasing the reset period. Increasing the transformer flyback voltage and reducing its stray capacitance are effective in decreasing the reset period without increasing power loss. A new two-MOSFET forward converter is proposed which uset the increased flyback voltage and a transformer structure to reduce the stray capacitance. The new converter using this transformer provides the basis for a 48-V, 100-W output, 270-V input converter operating at 200kHz with high efficiency (above 95%).

The characteristics of voltage-resonant dc-dc converters have already been analyzed and described. However, in the conventional analysis, the inductance of the reactor is assumed to be infinity and the loss resistance of the power circuit is not taken into account. Also, in some cases, the averaging method is applied to analyze the resonant dc-dc converters as well as the pwm dc-dc converters. Consequently, the results from conventional analysis are not entirely in agreement with the experimental ones. This paper presents a general design-oriented analysis of the buck-boost type voltage-resonant dc-dc converter in the continuous and discontinuous modes of the reactor current. In this analysis, the loss resistance in each part of the power circuit, the inductance of the reactor, the effective value (not mean value) of the power loss, and the energy-balance among the input, output and internal-loss powers are taken into account. As a result, the behavior and characteristics of the buck-boost type voltage-resonant dc-dc converter are fully explained. It is also revealed that there is a useful mode in the discontinuous reactor current region, in which the output voltage can be regulated sufficiently for the load change from no load to full load and for the relatively large change of the input voltage, and then the change in the switching frequency can be kept relatively small.

This paper presents a new type of zero-voltage-switched (ZVS) push-pull dc-dc converter with two synchronous rectifiers in the secondary circuit. ZVS is realized using the magnetizing current of the transformer as a constant current source during the commutation. The output voltage is controlled by PWM with a constant switching frequency. The circuit operation is described using equivalent circuits. The steady-state and dynamic characteristics are analyzed and confirmed experimentally.

It has been reported that the efficiency of a low voltage power supply is improved by replacing diodes in an output-stage with synchronous rectifiers (SR). A SR consists of a bipolar junction transistor with a low-saturation voltage and a current transformer. Although the SR has low offset-voltage, its reverse recovery characteristic is usually poor. In this paper, an RCD circuit which improves the reverse recovery characteristic of the SR is proposed. This circuit is simple, and it is composed of a diode, a capacitor and a resistor. The analysis and the experimental results of the SR with the proposed RCD circuit are presented. The optimum design of the RCD to improve the reverse recovery characteristic of SR is discussed.

A newly developed planar inductor and its application to dc-dc converters are described. The planar inductor consists of a planar spiral coil and soft magnetic sheets, it has a small size (11110.8mm), 33µH inductance and a maximum quality factor of 14. The step down chopper dc-dc converter has been developed by using planar inductor, which has small size (20154mm), 5V-2W typical output and output power/volume ratio of 1.7W/cc. The switching converter can be miniaturized by using the planar inductor.

Ac resistivity and power loss values for Mn-Zn ferrite material have been investigated by electrical and magnetic measurements. The ac resistivity shows an inductive dependency on frequency for the low dc resistive samples or for highly dc resistive ones at high temperature, while a capacitive dependency on frequency was observed for the highly resistive materials at the room temperature. These phenomena were interpreted by the dependence of ac resistivity on the dc resistivity, complex permeability and complex permittivity. The dependency of the power losses on the dc resistivity, temperature and frequence were also examined with analysis of power loss term. Dividing the power loss into hysteresis loss and eddy current loss, the frequency dependence of the eddy current loss was found to vary with the magnitude of the dc resistivity as follows: The eddy current loss of low dc resistive materials depends on the dc resistivity. On the other hand, the eddy current loss for high resistive materials is determined by the ac resistivity, contributed from dielectric loss.

Rate-based congestion/flow control is a promising way to achieve high throughput in high speed packet-switching networks. We consider a rate-based congestion control to aim at obtaining high throughput and fair sharing of the communication resources. In the scheme, each intermediate node informs its congestion status to the source node. Two kinds of control packets are used for this mechanism. One (a choke packet) is to throttle the rate and another (a loosen packet) is to allow increase of the rate. The source node initiates transmission with a low rate and increases the rate slowly to avoid a rapid increase of the packet queueing at an intermediate node. When the source node receives a choke packet, it decreases the rate rapidly to relieve congestion as soon as possible. The source node upon receipt a loosen packet increases the rate slowly again. We develop a queueing model to investigate the parameter settings to provide a good performance via simulation. The increasing and decreasing parameters of the rate control function are first investigated in various load conditions. We next examine the effect of the queue-length threshold value for the indication of congestion at the intermediate node. The numerical results indicate that the threshold value should be small to obtain a good performance. We finally introduce a technique which accurately recognizes congestion and inhibits an acceptable queueing of the packets at intermediate nodes.

This paper presents a new architecture of a copy network which employs the principle of recursive generation of copy cells. The proposed architecture achieves high utilization of the links and buffers of the copy network, and preserves the cell sequence. The architecture lends itself modularity so that large multicast ATM switches can be fabricated by employing the proposed copy network. Two different modular structures - one for reduced latency of the unicast cell and the master cell from which copies are made, and the other for reduced hardware overhead - for realizing large multicast ATM switches are configured. The hardware of functional elements of the copy network are the same as those of the functional elements of a modular point-to-point switch proposed earlier, thereby resulting in the modularity of functional elements as well. Simulation studies show that the proposed copy network achieves high throughput and low cell loss probability, and the required buffer sizes are small. The delay of cells is found to be very small for traffic loads up to 90%.

Dependence of SIR-B image intensity on local incidence angles has been investigated to estimate quantitatively topographic effects in SAR imagery. Local incidence angles were computed from a digital elevation model (DEM) produced from a topographical map. Slope images representing the variation of local incidence angles of a hilly area were compared with the SIR-B images. Since the studied area is uniformly covered by shrubs and grass, the topograghic effect can be easily detected. Based on the topographic effects, backscattering coefficients (σ⁰) of the hilly area were estimated and compared with the existing σ⁰ data base.