M.H. Kheraluwala

Bio: M.H. Kheraluwala is an academic researcher from University of Wisconsin-Madison. The author has contributed to research in topics: Delta modulation & Pulse-width modulation. The author has an hindex of 4, co-authored 4 publications receiving 310 citations.

Delta modulation strategies for resonant link inverters

Abstract: The suitability of delta modulation strategies for resonant link inverters is explored in detail. The control and spectral characteristics of various delta modulators are examined in an effort to develop a model for the same. The more fundamental question of comparing delta modulation systems with conventional pulse-width-modulated (PWM) systems, given similar devices, is addressed, and it shown that the former provides a viable high-performance alternative. As the resonant DC link topology allows at least an order of magnitude increase in the switching frequency, Sigma Delta M systems using a given family of devices are capable of better spectral response than a conventional PWM inverter. >

Delta modulation strategies for resonant link inverters

Abstract: This paper explores in detail the suitability of delta modulation strategies for resonant link inverters. The control and spectral characteristics of various delta modulators are examined in an effort to develop a model for the same. The more fundamental question of comparing delta modulation systems with conventional pwm systems, given similar devices, is addressed and it is shown that the former provides a viable high performance alternative.

Design considerations for high power high frequency transformers

Abstract: Various design considerations for high-power (multikilowatt), high-frequency transformers for DC-DC power converters are investigated Although Ferrite (PC40) is lossier than Permalloy80 (05 mil) at the frequencies of interest (25-50 kHz) the use of the former is justified on the basis of cost, weight, and wide ranges of shapes The influence of the leakage flux distribution in the window region on the copper losses has been demonstrated for various conventional winding arrangements However, it is seen that in conventionally wound transformers a considerable amount of leakage flux enters the core, resulting in localized core saturation and hot-spots This becomes a very critical issue for high-power, high-frequency transformers Coaxially wound transformers are seen to be a viable alternative, in that the leakage flux is contained with the interwinding space, with very little or none of it permeating the core Such transformers can also realize multiple benefits of a low distributed and controllable leakage inductance, robust construction, low electromechanical forces, and low core and copper losses Test results on two coaxially wound transformers with different tube geometries, designed for 50 kW, 50 kHz, primary voltage of 200 V, and secondary voltage of 1000 V (two windings), are presented Finally the concept of coaxial winding technique for three-phase transformers is also presented >

Optimal discrete pulse modulation waveforms for resonant link inverters

Abstract: The advent of zero-voltage-switching resonant link inverters has raised the question of modulation strategies that satisfy the regular sampling constraints of such systems. An easy and elegant approach to the synthesis of optimal discrete pulse modulation waveforms is presented. Utilizing the finiteness of the set of possible waveforms, an exhaustive search algorithm is deployed to derive a set of optimum waveforms simultaneously satisfying specified fundamental voltage constraints and cost functions. For frequency ratios of up to around 80, the technique is tractable and gives excellent results. For aerospace applications with 400 Hz outputs, which result in frequency ratios of 50 for 20 kHz link frequency, the strategy results in substantially higher levels of performance. For larger frequency ratios of 100-2000, typical of industrial resonant link inverter drive systems, this technique requires unworkably high computation times. A suboptimal limited search technique is proposed with reasonable performance characteristics is proposed for this case. >

Current control techniques for three-phase voltage-source PWM converters: a survey

Abstract: The aim of this paper is to present a review of current control techniques for three-phase voltage-source pulsewidth modulated converters. Various techniques, different in concept, have been described in two main groups: linear and nonlinear. The first includes proportional integral (stationary and synchronous) and state feedback controllers, and predictive techniques with constant switching frequency. The second comprises bang-bang (hysteresis, delta modulation) controllers and predictive controllers with on-line optimization. New trends in current control-neural networks and fuzzy-logic-based controllers-are discussed, as well. Selected oscillograms accompany the presentation in order to illustrate properties of the described controller groups.

Performance characterization of a high-power dual active bridge DC-to-DC converter

Abstract: The performance of a high-power, high-power-density DC-to-DC converter based on the single-phase dual active bridge (DAB) topology is described. The dual active bridge converter has been shown to have very attractive features in terms of low device and component stresses, small filter components, low switching losses, high power density and high efficiency, bidirectional power flow, buck-boost operation, and low sensitivity to system parasitics. For high output voltages, on the order of kilovolts, a cascaded output structure is considered. The effects of snubber capacitance and magnetizing inductance on the soft switching region of control are discussed. Various control schemes are outlined. Coaxial transformer design techniques have been utilized to carefully control leakage inductance. The layout and experimental performance of a prototype 50 kW 50 kHz unit operating with an input voltage of 200 V DC and an output voltage of 1600 V DC are presented. >

Hybrid multilevel power conversion system: a competitive solution for high power applications

Abstract: Use of multilevel inverters is becoming popular in recent years for high power applications. Various topologies and modulation strategies have been investigated for utility and drive applications in literature. Trends in power semiconductor technology indicate a trade-off in the selection of power devices in terms of switching frequency and voltage sustaining capability. New power converter topologies permit modular realization of multilevel inverters using a hybrid approach involving integrated gate commutated thyristors (IGCT) and insulated gate bipolar transistors (IGBT) operating in synergism. This paper is devoted to the investigation of a hybrid multilevel power conversion system typically suitable for high performance, high power applications. This system designed for 4.16 kV, /spl ges/100 hp load comprises of a hybrid seven-level inverter, a diode bridge rectifier and an IGBT rectifier per phase. The IGBT rectifier is used on the utility side as a real power flow regulator to the low voltage converter and as a harmonic compensator for the high voltage converter. The hybrid seven-level inverter on the load side consists of a high voltage, slow switching IGCT inverter and a low voltage, fast switching IGBT inverter. By employing different devices under different operating conditions, it is shown that one can optimize the power conversion capability of entire system. A detailed analysis of a novel hybrid modulation technique for the inverter, which incorporates stepped synthesis in conjunction with variable pulse width of the consecutive steps is included. In addition, performance of a multilevel current regulated delta modulator as applied to the single phase full bridge IGBT rectifier is discussed. Detailed computer simulations accompanied with experimental verification are presented in the paper.

Zero-switching-loss inverters for high-power applications

Abstract: The development of zero switching loss inverters has attracted much interest for industrial applications. Two topologies for realizing zero switching losses in high-power converters are proposed. The actively clamped resonant DC link inverter uses the concept of a lossless active clamp to restrict voltage stresses to only 1.3-1.5 supply voltage. For applications demanding substantially better spectral performance, the resonant pole inverter (RPI), also called the quasi-resonant current mode inverter, is proposed as a viable topology. Using only six devices rated at supply voltage, this circuit transfers the resonant components to the AC side of each phase and thus requires additional inductor and capacitor (LC) components. On the other hand, the RPI is capable of true pulsewidth modulation (PWM) operation at high frequency as opposed to discrete pulse modulation operation found in resonant DC link invertors. >