Ashoka K. S. Bhat

Analysis and Design of High-Frequency Isolated Dual-Bridge Series Resonant DC/DC Converter

Bidirectional dual-bridge dc/dc converter with high frequency isolation is gaining more attentions in renewable energy system due to small size and high-power density. In this paper, a dual-bridge series resonant dc/dc converter is analyzed with two simple modified ac equivalent circuit analysis methods for both voltage source load and resistive load. In both methods, only fundamental components of voltages and currents are considered. All the switches may work in either zero-voltage-switching or zero-current-switching for a wide variation of voltage gain, which is important in renewable energy generation. It is also shown in the second method that the load side circuit could be represented with an equivalent impedance. The polarity of cosine value of this equivalent impedance angle reveals the power flow direction. The analysis is verified with computer simulation results. Experimental data based on a 200 W prototype circuit is included for validation purpose.

Analysis, Design and Experimental Results of Wide Range ZVS Active-Clamped L-L Type Current-Fed DC/DC Converter for Fuel Cells to Utility Interface

A wide range zero-voltage switching (ZVS) active-clamped L-L type current-fed isolated dc-dc converter is proposed for fuel cells to utility interface application. The proposed converter maintains ZVS of all switches from full load down to very light load condition for wide input voltage variation. Detailed operation, analysis, design, simulation and experimental results for the proposed converter are presented. The auxiliary active clamping circuit absorbs the turn-off voltage spike and also assists in achieving ZVS of main switches. The ZVS of auxiliary switches and main switches is achieved by the energy stored in the boost inductors and series inductor (aided by parallel inductor), respectively. Rectifier diodes operate with zero-current switching. An experimental converter rated at 200 W has been designed, built and tested in the laboratory to verify the analysis, design and performance of the proposed converter for wide variations in input voltage and load.

Analysis and Design of a High-Frequency Resonant Converter Using LCC-Type Commutation

The modeling, analysis, and design of a high-frequency resonant converter using an LCC-type commutation circuit is presented. Constant-current model and state-space approaches are used for the analysis. Closed-form solutions are derived for the inverter under steady-state conditions. Experimental results obtained from a prototype converter under different loading conditions are compared with the theory.

Fixed-frequency PWM series-parallel resonant converter

A pulse-width-modulated (PWM) high-frequency link series-parallel resonant converter operating with fixed frequency is proposed. A simple analysis and design procedure are presented. The proposed configuration has a number of desirable features, such as high efficiency for very wide load variations with a narrow range of duty-cycle ratio control, and load short-circuit capability. Detailed experimental results obtained from a 48 V output, 500 W experimental converter are presented to verify the concept.<<ETX>>

An Output-Power-Control Strategy for a Three-Phase PWM Rectifier Under Unbalanced Supply Conditions

Instantaneous power regulation is an effective way to improve the performance of a pulsewidth-modulation rectifier operating under unbalanced supply-voltage conditions. By properly setting current commands, this approach aims to achieve performance features that are normally achievable only under ideal balanced operating conditions. This paper proposes an instantaneous power-regulation strategy called output-power-control method, in which the current commands are determined so as to appropriately distribute the input power to maintain a constant dc output voltage and sinusoidal line currents. Although the power factor is not directly controlled, it is shown that the proposed scheme results in near unity vector power factor. The current commands are given by a set of simple linear equations in which the proposed control scheme can be easily implemented. Experimental results obtained with a 1-kW laboratory prototype demonstrate that the proposed scheme fulfils all the main objectives of a high-performance rectifier.

Analysis and design of a series-parallel resonant converter

A high-frequency link series-parallel resonant power converter is analyzed using the state-space approach. Analysis is presented for both the continuous capacitor voltage mode and the discontinuous capacitor voltage mode. Steady-state solutions are derived. Design curves for the converter gain and other component stresses are obtained. A method of optimizing the converter under certain constraints is presented and a simple design procedure is illustrated by a design example. Experimental results are presented to verify the theory. >

A Comparison of Soft-Switched DC-DC Converters for Fuel Cell to Utility Interface Application

High frequency (HF) transformer isolated DC-DC converter is a part of a fuel cell inverter system for utility interface, required to translate the level of low fuel cell stack voltage to meet the peak utility line voltage and provides isolation between inverter and utility line. This paper presents a comparison of various soft-switched HF transformer isolated DC-DC converters for fuel cell to utility interface application. It is shown that due to wide variation in fuel cell voltage with load variation, none of the voltage-fed converters can maintain ZVS for the complete operating range. Active clamped two-inductor current-fed converter is able to maintain ZVS for wide load and fuel cell stack voltage variations and is suitable for the present application. Analytical and simulation results to evaluate the performance of the current-fed converter are presented.

A unified approach for the steady-state analysis of resonant converters

A generalized approach for the steady-state analysis of resonant converters is presented. Different resonant converter tank circuit configurations are combined into a single tank circuit referred to as a generalized tank circuit. The load presented to this tank circuit is represented by an AC equivalent resistance, and simple complex circuit analysis is used to analyze such a generalized tank circuit. This type of unified approach simplifies the method of analysis for different configurations and eliminates the need for analysis of different schemes separately. In addition, in a computer program, the results for a particular scheme can be obtained by opening or shorting the nonrequired tank circuit components of the generalized scheme. The effect of high-frequency transformers and other parasitics can be taken into account in the analysis. A design example is presented to illustrate the method of designing a converter, and experimental results are presented to verify the analysis. >

A generalized approach for the steady-state analysis of resonant inverters

A generalized approach is presented for the steady-state analysis of resonant inverters which leads to the selection of an optimum scheme for a particular application. Six load-commutation schemes are combined into a single commutation scheme, referred to as a generalized load-commutation circuit, and the steady-state analysis for the circuit with RL load is presented using a Fourier series approach in the continuous-current mode. The equations for different load-commutation circuits are obtained as the particular cases of the generalized configuration. This type of unified approach simplifies the method of analysis for different commutation schemes and eliminates the need for the separate analysis of different schemes. Also, in a computer program, the results for a particular configuration can be obtained simply by opening or shorting the nonrequired commutating components of the generalized scheme. The method of analysis is used to select resonant inverter schemes with resistive load, based on certain constraints. Experimental results are presented for the selected schemes to support the theory. >

A Simple Single-Input–Single-Output (SISO) Model for a Three-Phase PWM Rectifier

The challenge in controlling a three-phase pulsewidth modulation (PWM) rectifier under balanced conditions arises from the fact that the state-space averaged model reported in literature has a multi-input-multi-output nonlinear structure and furthermore exhibits a nonminimum phase feature. In this paper, a simple single-input-single-output model is constructed by separating the d -axis and the q-axis dynamics through appropriate nonlinear feedforward decoupling while maintaining nearly unity power factor operation. With the proposed model, the nonminimum phase feature inherent in an AC-to-DC rectifier becomes a simple right-half-plane zero appearing in the small-signal control-to-output transfer function. In addition, the model exhibits a close similarity to a DC-DC boost converter under both large-signal and small-signal operating conditions. This makes it possible to extend the system analysis and control design techniques of DC-DC converters to the three-phase PWM rectifier also. The validity of the proposed model has been verified experimentally in the frequency domain under open-loop operation of the PWM rectifier. The usefulness of the model is further demonstrated through closed-loop operation of the rectifier with both voltage mode and inner-current-loop-based schemes.