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.

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

This paper overviews theoretical and practical design issues related to inductive power transfer systems and verifies the developed theory using a practical electric vehicle battery charger. The design focuses on the necessary approaches to ensure power transfer over the complete operating range of the system. As such, a new approach to the design of the primary resonant circuit is proposed, whereby deviations from design expectations due to phase or frequency shift are minimized. Of particular interest are systems that are neither loosely nor tightly coupled. The developed solution depends on the selected primary and secondary resonant topologies, the magnetic coupling coefficient, and the secondary quality factor.

Design considerations for a contactless electric vehicle battery charger

DC–DC converters with voltage boost capability are widely used in a large number of power conversion applications, from fraction-of-volt to tens of thousands of volts at power levels from milliwatts to megawatts. The literature has reported on various voltage-boosting techniques, in which fundamental energy storing elements (inductors and capacitors) and/or transformers in conjunction with switch(es) and diode(s) are utilized in the circuit. These techniques include switched capacitor (charge pump), voltage multiplier, switched inductor/voltage lift, magnetic coupling, and multistage/-level, and each has its own merits and demerits depending on application, in terms of cost, complexity, power density, reliability, and efficiency. To meet the growing demand for such applications, new power converter topologies that use the above voltage-boosting techniques, as well as some active and passive components, are continuously being proposed. The permutations and combinations of the various voltage-boosting techniques with additional components in a circuit allow for numerous new topologies and configurations, which are often confusing and difficult to follow. Therefore, to present a clear picture on the general law and framework of the development of next-generation step-up dc–dc converters, this paper aims to comprehensively review and classify various step-up dc–dc converters based on their characteristics and voltage-boosting techniques. In addition, the advantages and disadvantages of these voltage-boosting techniques and associated converters are discussed in detail. Finally, broad applications of dc–dc converters are presented and summarized with comparative study of different voltage-boosting techniques.

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Step-Up DC–DC Converters: A Comprehensive Review of Voltage-Boosting Techniques, Topologies, and Applications

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

A detection method for use in a primary unit of an inductive power transfer system, the primary unit being operable to transmit power wirelessly by electromagnetic induction to at least one secondary unit of the system located in proximity to the primary unit and/or to a foreign object located in said proximity, the method comprising: driving the primary unit so that in a driven state the magnitude of an electrical drive signal supplied to one or more primary coils of the primary unit changes from a first value to a second value; assessing the effect of such driving on an electrical characteristic of the primary unit; and detecting in dependence upon the assessed effect the presence of a said secondary unit and/or a foreign object located in proximity to said primary unit.

Inductive power transfer

High-frequency switching pulse modulation utility-interfaced power conditioners (HF-UPC) with a high-frequency transformer link have attracted special interest for renewable and sustainable energy utilisation. These conditioners are small and cost-effective for meeting the requirements of small-scale residential power applications. However, switching power losses due to high-frequency switching operations are unavoidable. Efforts to reduce the power losses by implementing additional snubber components can complicate the controlling methods of the system. To solve these problems, a flyback transformer linked HF-UPC is proposed. The high-frequency flyback transformer is introduced into the power conditioner system instead of the typical forward transformer to simplify the circuit configuration and related controlling methods. With the aid of the resonant snubber circuits, the high-frequency switching devices in the primary side of the proposed DC-to-AC power conditioner can be turned off with zero-voltage soft-switching (ZVS). In addition, the proposed power conditioner system takes advantage of operating the currents by the discontinuous conduction mode (DCM) to realise turn-on commutation of zero-current soft-switching schemes. The output ports of the HF-UPC treated here are directly connected to the utility grid single-phase AC power source. A prototype of the proposed soft-commutation HF-UPC has been built and tested in experiments. Its power conversion processing is verified and its output current is qualified in accordance with the guidelines of the power utility companies.

Utility AC interfaced soft-switching sinewave PWM power conditioner with two-switch flyback high-frequency transformer

Harmonic currents generated from the power electric equipment such as IH cooking heaters involve harmful influences to the other equipments connected to the utility grid. As for the IH cooking appliances, adding the PFC converter to the input stage of IH cooking heater is one of the practical solutions to suppress harmonic current influences. In this paper, two operation modes; DCM and CCM for the PFC converter are compared and tested from the view points of magnetic volume and power quality to clarify the suitable operation mode for consumer IH cooking appliance.

A comparative evaluation of DCM control and CCM control for soft-switching PFC converter

A novel prototype topology of a three-phase current-fed PWM converter with a switched capacitor type quasi-resonant snubber is proposed in the paper, which can operate under the principle of zero current switching (ZCS) commutation. However, soft switching performance is affected by output DC current in the proposed quasi-resonant snubber. In particular, PWM current is decreased in the small current region with DC current on the output side, because the charging and discharging period of a switched capacitor increases as the output DC current decreases. The operating performance in the small current region with DC current on the output side, for which performance is problematic in this converter, is investigated in the paper. Further, converter performances from the relationship between soft switching performance and the charging and discharging periods of the switched capacitor are estimated on the basis of the experimental results by a laboratory prototype of this converter.

Performance evaluations of three-phase current-fed soft switching PWM converter with switched capacitor-type quasi-resonant snubber

This paper presents a two-paralleled PWM amplifier using switch-mode power current tracking technique in order to generate a gradient magnetic field in the magnetic resonance imaging (MRI) system This circuit has 8-IGBTs at their inputs/outputs so as to realize further high-power density A digital control scheme is adopted to minimize the current ripple and improve its control response in the gradient coils (GCs) It is proved that the proposed technique will highly enlarge the diagnostic target and improve the image quality of MRI

Power conversion PWM amplifier with two paralleled four quadrant chopper for MRI gradient coil magnetic field current tracking implementation

A hybrid excitation system is presented, consisting of a capacitor bank with a small-scale active power filter (APF), to regulate the output voltage of the stand-alone induction generator (IG) by controlling its reactive current component and to filter the harmonic currents generated by a nonlinear diode rectifier load. A deadbeat current control structure for pulse-width modulation APF connected to a stand-alone IG working with variable speed and different types of loads is proposed to enhance the operating performance of the stand-alone IG. Sensorless control of the IG, meaning current vector control without voltage sensor and mechanical shaft sensor, is considered and the fixed command control for the IG line-to-line voltage is achieved with high accuracy. In the proposed system a new design of phase-locked-loop circuit is used to determine the stator voltage vector position of the IG. A 2.2 kW laboratory prototype has been built to confirm the feasibility of the proposed method. The measurement results validate the proposed power generating system with the deadbeat current controller as a good application for the IG to reduce the total system cost.

Mutsuo Nakaoka

Papers

Utility AC interfaced soft-switching sinewave PWM power conditioner with two-switch flyback high-frequency transformer

A comparative evaluation of DCM control and CCM control for soft-switching PFC converter

Performance evaluations of three-phase current-fed soft switching PWM converter with switched capacitor-type quasi-resonant snubber

Power conversion PWM amplifier with two paralleled four quadrant chopper for MRI gradient coil magnetic field current tracking implementation

Induction generator hybrid applications with active power filter