J.L. Russi

Coupled-Filter-Inductor Soft-Switching Techniques: Principles and Topologies

Pulsewidth-modulation inverters and rectifiers are required in widespread applications such as energy-storage power plants, telecommunication systems, and electric-vehicle propulsion systems. Some of the stringent requirements of these applications can be achieved by high switching frequency. On the other hand, the use of high switching frequency may degrade the overall system efficiency, which can be alleviated by the utilization of soft-switching techniques. In this paper, a generic soft-switching diagram that can generate topologies for turn-on snubber, zero- voltage transition, zero-current-zero-voltage transition inverters with coupled filter inductor is proposed. This approach facilitates the understanding of these techniques by both newcomers and senior engineers, making the advantages and disadvantages of each soft-switching technique much clearer.

Novel design methodology and comparative analysis for ZVT PWM converters with resonant auxiliary circuit

The zero-voltage transition (ZVT) pulsewidth-modulation (PWM) converters with resonant auxiliary circuit (RAC) are gathered and analyzed by means of a common topology derived in this paper. Its operation modes are identified and analyzed. Moreover, a similarity transformation is applied to the three-state-variable system in such a way that the whole system dynamics can be represented in a two-dimensional state space. With this representation, the soft-switching conditions are easily defined. In addition to the unified analysis of the ZVT PWM converters with RAC, a theoretical comparative analysis addresses the converter current and voltage stresses, as well as the time-delay intervals taken during the main-switch turn-on process. By means of this analysis, the main characteristics and constraints of the converters are identified. Moreover, a novel design methodology is presented. It is based on the soft-switching-condition abacus obtained from the analytical description of the common ZVT-RAC topology. Besides the soft-switching conditions, a set of performance parameters is also plotted into the soft-switching-condition abacus, making it a simple and useful tool for the proper design of a ZVT-RAC converter. An experimental efficiency comparison is also carried out among three ZVT-RAC boost converters. The experimental results have been obtained from ZVT PWM boost prototypes operating at 1 kW and 100 kHz.

A unified design criterion for ZVT DC-DC PWM converters with constant auxiliary Voltage source

This paper proposes a design criterion for calculating the resonant auxiliary elements of zero-voltage transition dc-dc pulsewidth-modulated (PWM) converters that use a dc auxiliary voltage source. The proposed criterion is based on stored energy in resonant auxiliary elements and takes into account the influence of the auxiliary voltage source value. Using this criterion, the reactive energy can be kept at a minimum level and a reduction of the auxiliary elements current ratings is achieved, which leads to lower conduction losses and improved converter efficiency. In addition, a reduction in size of auxiliary magnetic elements can be accomplished. To illustrate the usefulness of the proposed design criterion, the paper compares results obtained from the True-PWM Zero-Voltage Switching pole boost converter designed according to the proposed criterion, and from the original design guidelines. Experimental results show an efficiency gain of about 1% for a wide load range and 1.5% at full load. In addition, a reduction of about 52% in the auxiliary transformer volume for the implemented prototype was achieved, ensuring a reduction in overall converter size. Experimental results were obtained using a 1-kW 100-kHz laboratory prototype.

Synthesis Methodology for Multipole ZVT Converters

This paper proposes a novel synthesis methodology to generate integrated zero-voltage-transition (ZVT) topologies, as well as to systematize the topologies that are already known. An approach is presented to classify single-pole ZVT converters. This approach can be expanded to multipole systems, such as polyphase inverters and rectifiers, uninterruptible power supplies, and variable-speed drives. The connections among several presented topologies are easily seen by means of the general diagrams that are shown in this paper. Analysis and understanding of the advantages, disadvantages, merits, and limitations of each converter are made easier since these converters are obtained from a common approach that is presented in this paper

DC-DC converters in a multi-string configuration for stand-alone photovoltaic systems

As an alternative to centralized autonomous photovoltaic systems, this paper proposes a modular configuration that utilizes a distributed input energy processing, maximum power point tracking and a bidirectional converter to control the battery bank power flow. Preliminary experimental results demonstrate that the proposed system presented an increase of 16% on the generated energy at the DC bus, for the solar irradiation levels analyzed, in which one or more photovoltaic panels are shaded, damaged or aged.

A Simple Approach to Detect ZVT and Determine Its Time of Occurrence for PWM Converters

This paper provides a mathematical expression to determine the occurrence of soft-switching for a general topology of zero voltage transition (ZVT) converters with auxiliary resonant voltage source. This expression is used to help the designer in choosing appropriately the values of inductance and capacitance for the auxiliary resonant branch ensuring ZVT. The main advantage of the proposed methodology is to point out suitable sets of circuit parameters without relying only on time consuming numerical simulations of the entire converter. Additionally, numerical methods to compute the time of occurrence of ZVT for these power converters are provided. The proposed methods are given by second-order approximations of a nonlinear function which describes the voltage on the ZVT snubber capacitor during the zero voltage resonant stage. The results can be seen as applications of second-order Taylor series and of quadratic interpolation. However, different from simply finding the root of a given nonlinear equation, the conditions given here provide analytical expressions to compute the time of occurrence of ZVT based on the converter parameters. Then, the proposed conditions become useful for analysis and design, allowing evaluating operation sequence, total commutation time, resistive losses, and other important parameters to describe the converter performance. Experimental results support the analysis presented.

Low Reactive Energy ZCZVT PWM Converters: Synthesis, Analysis and Comparison

In this paper a novel methodology to synthesize zero-current zero-voltage transition (ZCZVT) topologies is presented. The proposed methodology is based on the auxiliary voltage source (AVS) concept, which permits to generate not only a new topology but an entire class of converters. As the AVS concept is derived from the Resonant Transition mechanism, the new class of ZCZVT converters resembles some of the well-known zero-voltage transition (ZVT) converters, holding their characteristics, as simplicity, low reactive energy and high performance. The experimental results have been obtained from three boost converter laboratory prototypes rated to 1 kW, 50 kHz, and confirm the novel synthesis concept and also the high performance of the new ZCZVT converters at both: efficiency and, di/dt and dv/dt control

A design criterion to ZVT DC-DC PWM converters with constant auxiliary voltage source

This paper proposes a design criterion to calculate the resonant auxiliary elements of ZVT DC-DC PWM converters that use a DC auxiliary voltage source. The proposed criterion is based on stored energy in resonant auxiliary elements and takes into account the influence of the auxiliary voltage source value. By means of this criterion the reactive energy can be kept at a minimum level and a reduction of the auxiliary elements current ratings is achieved, which leads to lower conduction losses and improved converter efficiency. In addition, a reduction in auxiliary magnetic elements size can be accomplished. To illustrate the usefulness of the design criterion proposed, comparative results obtained from the true pulse-width modulated (PWM) zero-voltage switching (ZVS) pole boost converter designed by proposed criterion and its original design guidelines are presented. Experimental results show an efficiency gain of about 1% for a wide range and 1.5% at full load. In addition, a reduction of about 52% in the auxiliary transformer volume for the implemented prototype was achieved, ensuring a reduction in overall converter size. Experimental results were obtained from 1 kW, 100 kHz laboratory prototype.

Synthesis Methodology for Multi-Pole ZVT Converters

This paper proposes a novel synthesis methodology to generate integrated ZVT topologies, as well to systematize the topologies already known. It is presented an approach to classify the single pole ZVT converters. This approach can be expanded to multi-pole systems, such as poly-phase inverters and rectifiers. Uninterruptible Power Supplies and Variable-Speed Drives. The connections among several topologies presented so far are easily seen by means of the general diagrams shown in this paper. The analysis and understanding of advantages, disadvantages, merits and limitations of each converter is made easier since these converters are obtained from a common approach presented in this paper.

Novel Resonant Transition PWM Inverters: Synthesis and Analysis

This paper presents a generalized concept concerning the Resonant Transition technique. It is based on the Resonant Transition mechanism requirements, i.e, on the auxiliary circuit functionality. The proposed Resonant Transition Concept permits to newcomers to perceive the Resonant Transition techniques as a whole instead of dissimilar soft-switching techniques. Furthermore, by means of this concept a unique methodology to analyze and synthesize the Resonant Transition converters is developed. The easy assessment of the Resonant Transition needs makes possible the development of novel Resonant Transition topologies with improved characteristics. The paper focuses on Zero-Current Transition (ZCT) and Zero-Current-Zero-Voltage Transition (ZCZVT) Inverters, which are suitable for medium and high power applications where minority carrier devices are predominant. Theoretical analysis is verified by means of experimental results obtained from laboratory prototypes rated at 1kW, 40kHz.