Robert Louis Steigerwald

High-Frequency Resonant Transistor DC-DC Converters

Transistor dc-dc converters which employ a resonant circuit are described. A resonant circuit is driven with square waves of current or voltage, and by adjusting the frequency around the resonant point, the voltage on the resonant components can be adjusted to any practical voltage level. By rectifying the voltage across the resonant elements, a dc voltage is obtained which can be either higher or lower than the input dc voltage to the converter. Thus, the converter can operate in either the step-up or step-down mode. In addition, the switching losses in the inverter devices and rectifiers are extremely low due to the sine waves that occur from the use of a resonant circuit (as opposed to square waves in a conventional converter); also, easier EMI filtering should result. In the voltage input version, the converter is able to use the parasitic diode associated with an FET or monolithic Darlington, while in the current input version, the converter needs the inverse blocking capability which can be obtained with an IGT or GTO device. A low-power breadboard operating at 200-300 kHz has been built. Two typical application areas are switching power supplies and battery chargers. The converter circuits offer improvements over conventional circuits due to their high efficiency (low switching losses), small reactive components (high-frequency operation), and their step-up/stepdown ability.

Microcomputer Control of a Residential Photovoltaic Power Conditioning System

Microcomputer-based control of a residential photovoltaic power conditioning system is described. The microcomputer is responsible for array current feedback control, maximum power tracking control, array safe zone steering control, phase-locked reference wave synthesis, sequencing control, and some diagnostics. The control functions are implemented using Intel 8751 single-chip microcomputer-based hardware and software. The controller has been tested in the laboratory with the prototype power conditioner and shows excellent performance.

An AC-to-DC Converter with High Quality Input Waveforms

An ac-to-dc converter which draws sinusoidal and inphase current waveforms from the ac power source is described. Harmonic and power factor measurements obtained from a field- effect transistor (FET) converter operating at 45 kHz for a single- phase and a three-phase connection are presented. A stability analysis and design methodology are given.

A comparison of high power DC-to-DC soft-switched converter topologies

Many industrial and military applications are arising that require high power DC-DC conversion. These applications include shipboard, spaceborne, and transportation power systems. By employing new high voltage, high power IGBTs, along with modern soft-switching techniques, the switching frequency can be significantly higher than obtained using GTO devices, which in turn can lead to smaller, lighter weight, and potentially more cost effective equipment. The purpose of this paper is to compare the properties of several soft-switching converter topologies when used to achieve DC-DC conversion at high power and high voltage levels. As an example, a 100 kW transformer isolated converter with 700-1400 V DC input is designed with an estimated weight in the 200 pound range and an energy efficiency of 95%. >

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

The performance of the parallel resonant power converter and the combination series/parallel resonant power 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 behavior 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. >

Development of a Unipolar Converter for Variable Reluctance Motor Drives

A new converter concept for driving the switched reluctance motor has been developed. This converter has only one switching device per phase, uses a unipolar dc supply, returns all the trapped energy to the source, and does not require bifilar windings; it is called a C-dump converter because the trapped energy is dumped in a capacitor and then returned to the dc source. The topology for several different C-dump converters is presented. In addition, the design and experimental results for a C-dump converter using a chopper to recover the energy dumped on the capacitor are presented.

A comparative evaluation of new silicon carbide diodes and state-of-the-art silicon diodes for power electronic applications

Recent progress in silicon carbide (SiC) material has made it feasible to build power devices of reasonable current density. This paper presents recent results including a comparison with state-of-the-art silicon diodes. Switching losses for two silicon diodes (a fast diode, 600 V, 50 A, 60 ns Trr), an ultra-fast silicon diode (600 V, 50 A, 23 ns Trr) and a 4H-SiC diode (600 V, 50 A) are compared. The effect of diode reverse recovery on the turn-on losses of a fast WARP/sup TM/ IGBT are studied both at room temperature and at 150/spl deg/C. At room temperature, SiC diodes allow a reduction of IGBT turn-on losses by 25% compared to ultra-fast silicon diodes and by 70% compared to fast silicon diodes. At 150/spl deg/C junction temperature, SiC diodes allow a turn-on loss reduction of 35% and 85% compared to ultra-fast and fast silicon diodes respectively. The silicon and SiC diodes are used in a boost power converter with the WARP/sup TM/ IGBT to assess the overall effect of SiC diodes on the power converter characteristics. Efficiency measurements at light load (100 W) and full load (500 W) are reported. Although SiC diodes exhibit very low switching losses, their high conduction losses due to the high forward drop dominate the overall losses, hence reducing the overall efficiency. Since this is an ongoing development, it is expected that future prototypes will have improved forward characteristics.

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

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.<<ETX>>

Analysis of a Resonant Transistor DC-DC Converter with Capacitive Output Filter

Resonant dc-dc converters offer several advantages over the more conventional PWM converters. Some of these advantages include: 1) low switching losses and low transistor stresses; 2) medium speed diodes are sufficient (transistor parasitic, inverse-parallel diodes can be used, even for frequencies in the hundreds of kilohertz); and 3) ability to step the input voltage up or down. This paper presents an analysis of a resonant converter which contains a capacitive-input output filter, rather than the more conventional inductor-input output filter. The switching waveforms are derived and design curves presented along with experimental data. The results are compared to the inductor-input filter case obtained from an earlier paper.

A comparative study of central and distributed MPPT architectures for megawatt utility and large scale commercial photovoltaic plants

In this paper different distributed PV architectures are studied from an energy yield perspective. These distributed architectures are applied to massively paralleled thin film plants employing high voltage PV modules, mc-Si plants with long series strings of low voltage modules and plants with medium voltage thin film modules in order to evaluate the effectiveness of the distributed architecture in each case. The effects of partial shading, module mismatch and cable losses are quantified in order to obtain the energy yield for each of the architectures under study. The results of this trade-off study are used to quantify the benefits of a distributed architecture as well as determine the optimal location of the dc/dc converters that perform the MPPT function.