The photovoltaic (PV) grid-connected power system in the residential applications is becoming a fast growing segment in the PV market due to the shortage of the fossil fuel energy and the great environmental pollution. A new research trend in the residential generation system is to employ the PV parallel-connected configuration rather than the series-connected configuration to satisfy the safety requirements and to make full use of the PV generated power. How to achieve high-step-up, low-cost, and high-efficiency dc/dc conversion is the major consideration due to the low PV output voltage with the parallel-connected structure. The limitations of the conventional boost converters in these applications are analyzed. Then, most of the topologies with high-step-up, low-cost, and high-efficiency performance are covered and classified into several categories. The advantages and disadvantages of these converters are discussed. Furthermore, a general conceptual circuit for high-step-up, low-cost, and high-efficiency dc/dc conversion is proposed to derive the next-generation topologies for the PV grid-connected power system. Finally, the major challenges of high-step-up, low-cost, and high-efficiency dc/dc converters are summarized. This paper would like to make a clear picture on the general law and framework for the next-generation nonisolated high-step-up dc/dc converters.

Review of Nonisolated High-Step-Up DC/DC Converters in Photovoltaic Grid-Connected Applications

Over the last few decennia, power DC/DC converters have been the subject of great interest due to its extensive increment of utilization in different applications. A thorough review on recent developed power DC/DC converters is presented in this paper. The study is focused on the topologies in different applications such as renewable energy, automobile, high-voltage and medium-voltage DC power systems, telecommunication, etc. In addition, an overview of the modulation techniques, the state-of-the-art of control strategies of well-established converters are discussed. Photovoltaic (PV) systems as the noticeable renewable energy resources generally suffer from poor conversion efficiency with instability and intermittent characteristics. Therefore, DC/DC converter with Maximum Power Point Tracking (MPPT) algorithm is essential to ensure maximum available power harnessed from the PV. Important features of DC/DC converters with MPPT are also figured with various performances. Furthermore, the design and optimization of different parameters are addressed systematically. Finally, the researcher’s future challenges and focusing trends are briefly described. For the next-generation converters design and applications, these are considered in details, and will provide useful framework and point of references.

Recent progress and development on power DC-DC converter topology, control, design and applications: A review

A new 16-phase interleaved bidirectional dc/dc converter is developed featuring smaller input/output filters, faster dynamic response and lower device stress than conventional designs, for hybrid vehicle applications. The converter is connected between the ultracapacitor (UC) pack and the battery pack in a multisource energy storage system of a hybrid vehicle. Typically, multiphase interleaved converters require a current control loop in each phase to avoid imbalanced current between phases. This increases system cost and control complexity. In this paper, in order to minimize imbalance currents and remove the current control loop in each phase, the converter is designed to operate in discontinuous conduction mode (DCM). The high current ripple associated with DCM operation is then alleviated by interleaving. The design, construction, and testing of an experimental hardware prototype is presented, with the test results included. Finally, a novel soft switch topology for DCM operation is proposed for future research, to achieve zero-voltage switching (ZVS), or zero-current switching (ZCS) in all transitions.

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High Power Current Sensorless Bidirectional 16-Phase Interleaved DC-DC Converter for Hybrid Vehicle Application

This paper focuses on a new three-phase high power current-fed DC/DC converter with an active clamp. A three-phase DC/DC converter with high efficiency and voltage boosting capability is designed for use in the interface between a low-voltage fuel-cell source and a high-voltage DC bus for inverters. Zero-voltage switching in all active switches is achieved through using a common active clamp branch, and zero current switching in the rectifier diodes is achieved through discontinuous current conduction in the secondary side. Further, the converter is capable of increased power transfer due to its three-phase power configuration, and it reduces the RMS current per phase, thus reducing conduction losses. Moreover, a delta-delta connection on the three-phase transformer provides parallel current paths and reduces conduction losses in the transformer windings. An efficiency of above 93% is achieved through both improvements in the switching and through reducing conduction losses. A high voltage ratio is achieved by combining inherent voltage boost characteristics of the current-fed converter and the transformer turns ratio. The proposed converter and three-phase PWM strategy is analyzed, simulated, and implemented in hardware. Experimental results are obtained on a 500-W prototype unit, with all of the design verified and analyzed.

A Three-Phase Current-Fed DC/DC Converter With Active Clamp for Low-DC Renewable Energy Sources

This paper presents the characteristic study of a clean hybrid power supply system combining proton exchange membrane fuel cell (PEMFC) as the main power source and ultracapacitor (UC) as the energy storage unit. Unlike the conventional fuel-cell hybrid system with power conditioning unit, the study investigated the electrical characteristic of the PEMFC and UC hybrid system without dc/dc converter. As a platform to evaluate the proposed system, the fuel-cell-based electric bicycle is implemented. The platform consists of PEMFC stack, metal hydride, thermal balance system, UC, dc motor, system control and data logging unit, as well as user interface. The test results showed that the proposed architecture is functional and leads to good results. By road testing, it was verified that the PEMFC can provide the rated power to the load and that the UC can deliver the power at system startup and the peak power if needed. The road testing results showed that the design objectives are fulfilled.

Electrical Characteristic Study of a Hybrid PEMFC and Ultracapacitor System

This paper describes a simple dc-dc step-up converter topology for switch-mode dc power supplies. The proposed configuration is well suited for high-power applications with battery supply. In the automotive framework, the push-pull architecture is the most widespread. However, as power increases, the use of a full-bridge architecture is mandatory. This paper presents a full-bridge architecture where the traditional single-phase transformer is replaced by a three-phase transformer. A prototype was realized and tested for the power supply of automotive devices. In this environment, one of the most important requirements is the ability to provide a burst of power during short-duration events, together with high-efficiency and high-quality output voltage. The latter constraints can be achieved by only using closed-loop switch-mode dc-dc converters at high switching frequency, thus reducing converter efficiency and creating electromagnetic-compatibility (EMC) problems. In this paper, the aforementioned issues were tackled relying on an open-loop topology. Open-loop converters are feasible if the output resistance of the converter is as low as possible, and a possible solution is the minimization of power losses. The solution is the use of a three-phase transformer with a delta-wye connection within a full-bridge converter topology. The configuration will be referred to as 3boost power supply. The three-phase transformer replaces the common single-phase transformer, and it is driven by a three-phase full-bridge inverter operating in six-step modulation. At secondary, a three-phase full wave diode rectifier is used to obtain the output dc voltage level. Therefore, a unitary transformer utilization factor is achieved. A simple theoretical comparison between the three types of converters-push-pull, conventional full bridge, and 3boost is shown. A low-power version of the converter was realized. Experiments confirm that this topology allows to achieve a high efficiency, a lower ripple factor, and a good EMC behavior.

3boost: A High-Power Three-Phase Step-Up Full-Bridge Converter for Automotive Applications

This paper presents a simple and original DC/DC step-up converter topology for switch-mode DC power supplies. The proposed architecture is well suited for high power applications with battery supply. A prototype was realized and tested for the power supply of automotive devices. In this environment signals are characterized by high dynamic variations, thus they can be operated only relying on power supplies with high dynamic capabilities. The latter constraint can be achieved only using closed-loop switch-mode DC/DC converters at high switching frequency. So doing converter efficiency is reduced, and EMC problems arise. In summary power supply efficiency and supply voltage quality are key features of the converter design. In this paper the above mentioned issued were tackled relying on an open loop topology. The original solution is the adoption of a three-phase transformer with delta-wye connection within a full-bridge converter topology. The proposed architecture will be referred to as 3boost power supply. The three-phase transformer replaces the common single-phase transformer and it is supplied at primary by three square waves, produced by a three-phase full bridge inverter. At secondary a three-phase full wave diode rectifier is used to obtain the output DC voltage level. Experimental results confirm that this topology, with respect to a single-phase push-pull converter, allows to achieve higher efficiency, a lower ripple factor, and a unitary transformer utilization factor. The proposed architecture is patent pending.

3boost a high power three-phase step-up full-bridge converter for automotive applications

Motor current signature analysis (MCSA) is used for non-invasive diagnosis of incipient or actual faults of grid supplied induction machine stator defects, being the negative sequence component of current space vector the diagnostic index most widely used. Supply unbalance and load influence of the machine however affect the negative component and they may cause the failure of the diagnostic procedure. Recently, deceleration test that may remove some drawbacks of MCSA has been proposed for rotor and stator fault diagnosis. In this paper it is shown that the residual voltage signature analysis (RVSA) obtained by the deceleration test provides, once removed the intrinsic manufacturing asymmetry, a diagnostic index directly related to the percentage of shorted turns. The main advantage of RVSA is that any influence caused by the supply unbalance and load is masked. Therefore a new diagnostic index is presented that is the residual voltage negative sequence component. The novel index performances have been proofed thanks to a simplified model of the faulted machine and experimentally validated by a special test motor that allows the introduction of different short circuits. This novel index can be used to confirm the MCSA-based diagnostic procedure developed by the same authors.

http://ieeexplore.ieee.org/iel5/9792/30878/01431777.pdf

M. Cavatorta

Papers

3boost: A High-Power Three-Phase Step-Up Full-Bridge Converter for Automotive Applications

3boost a high power three-phase step-up full-bridge converter for automotive applications

Experimental validation of a robust diagnostic index for induction motors stator faults