http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

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

Solid-state switch-mode rectification converters have reached a matured level for improving power quality in terms of power-factor correction (PFC), reduced total harmonic distortion at input AC mains and precisely regulated DC output in buck, boost, buck-boost and multilevel modes with unidirectional and bidirectional power flow. This paper deals with a comprehensive review of improved power quality converters (IPQCs) configurations, control approaches, design features, selection of components, other related considerations, and their suitability and selection for specific applications. It is targeted to provide a wide spectrum on the status of IPQC technology to researchers, designers and application engineers working on switched-mode AC-DC converters. A classified list of more than 450 research publications on the state of art of IPQC is also given for a quick reference.

/pdf/a-review-of-single-phase-improved-power-quality-ac-dc-2pm6h4zjxq.pdf

A review of single-phase improved power quality AC-DC converters

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. >

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

A more general averaging procedure that encompasses state-space averaging and that is potentially applicable to a much broader class of circuits and systems is presented. Examples of its application in resonant and PWM power convertors are presented. The technique is shown to be effective on a number of examples. including resonant type converters. The approach offers refinements to the theory of state-space averaging, permitting a framework for analysis and design when small ripple conditions do not hold. The method may find applications in simulation and design since it is considerably easier to simulate an averaged model than a switched model. >

/pdf/generalized-averaging-method-for-power-conversion-circuits-da237et2wc.pdf

Generalized averaging method for power conversion circuits

The purpose of a voltage controller for uninterruptible-power-supply inverters is to produce stable output voltage with low distortion under all loading conditions, particularly under nonlinear loads and load transients. Since the output impedance of the inverter is the source for tracking error caused by load current, this paper proposes a simple digital feedback controller that focuses on reducing the output impedance of inverters by a feedback of the load current. The proposed control strategy ensures high-quality steady-state and dynamic responses from the inverter system. The design of the proposed digital controller is simple and requires only a reasonably accurate knowledge of the output L-C filter parameters. In addition, only the output voltage and the load current are sensed if the dc link voltage is constant. The results of simulations and experiments show that the proposed controller can achieve very low total harmonic distortion and fast dynamic response under varied loads including nonlinear loads with low switching frequency.

A Simple Control Method for High-Performance UPS Inverters Through Output-Impedance Reduction

In this paper, a soft-switched power converter with two variations is discussed. An asymmetrical PWM control scheme is used to control the power converter under constant switching frequency operation. The modes of operation for both variations are discussed. The DC characteristics which can be used in design of the converters are also presented. Two 50 W converters were built to verify the characteristics of the converters. Due to the zero voltage switching (ZVS) operation of the switches and low device voltage and current stresses, the converters have high full load and partial load efficiencies. They are potential candidates for high efficiency, high density power supply applications. >

Soft-switched DC/DC converter with PWM control

A tri-state boost converter with an additional boost-inductor free-wheeling interval was proposed earlier to eliminate the right-half-plane (RHP) zero that occurs in the control-to-output transfer function of a classical boost converter under continuous-conduction mode of operation. A "constant-D/sub o/" control scheme, in which the "capacitor-charging" interval of the converter was kept constant, was employed. This resulted in a relatively large inductor current, especially under high line and load conditions, thereby causing high circuit losses. This paper proposes two variations of a novel dual-mode control (DMC) scheme that vary both the "boost" and the "capacitor-charging" intervals. Control analysis, design, and limitations of the proposed DMC schemes are presented. Through computer simulations and hardware experiments the performance of the tri-state boost converter with DMC schemes are compared with those of the tri-state boost converter with "constant-D/sub o/" control scheme, and the classical PI-controlled boost converter. The DMC schemes achieve a significant (about 10%) improvement in converter's efficiency for a wide load range over the "constant-D/sub o/" control scheme.

Dual-mode control of tri-state boost converter for improved performance

A comprehensive analysis of the high-frequency quasiresonant buck converter is presented using the graphical state-plane technique. The analysis has revealed, for the first time, the presence of several unfamiliar modes of operation. The voltage-conversion ratio and boundary-switching frequency for each mode are derived. The existence of various operating modes are verified experimentally.

State-Plane Analysis of Quasi-Resonant Converters

High performance UPS inverters have stringent control requirements both under steady-state and under transient conditions Many different control techniques have been applied to UPS inverters However, there are few publications reviewing the literature on these control techniques and classifying the same, particularly with regard to the more recent developments in this area In this paper, the control problem of a single-phase UPS inverter is presented and discussed Both the transfer function and the state-space models of the inverter are presented Then a review of the most popular solutions for control of UPS inverters is carried out These control techniques are classified as model-based instantaneous feedback control, feedforward learning control and nonlinear control The major advantages and disadvantages of these methods are highlighted and compared

Ramesh Oruganti

Papers

A Simple Control Method for High-Performance UPS Inverters Through Output-Impedance Reduction

Soft-switched DC/DC converter with PWM control

Dual-mode control of tri-state boost converter for improved performance

State-Plane Analysis of Quasi-Resonant Converters

Modeling and Control of Single-Phase UPS Inverters: A Survey