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High penetration of green energy has driven conventional utility grids into smart grids to accommodate dc appliances and various types of dc equipment, increasing effectiveness, efficiency, and resilience. In a smart grid, ac is harmonized with dc, and therefore, a multi-function converter is required to transfer power between ac and dc grids. This paper presents system configuration, operational principle and control of multi-function high-power converters for smart-grid applications. Simulated and experimental results from a 350 kVA converter are used to verify the feasibility of the proposed system configuration and control.

In this paper, an improved current-doubler rectifier with coupled inductors is proposed. The proposed rectifier can extend duty ratio to reduce the peak current through the isolation transformer winding and lower output current ripple as well as voltage stress of the rectifier diodes. In this study, a 500-W prototype with a full-bridge phase-shift converter, the proposed rectifier, with input voltage of 400 V and output voltage of 12 V was built. Theoretical analysis and experimental results have verified that the proposed rectifier is attractive for high step-down voltage and high-power applications. Index Terms--Coupled inductors, current-doubler rectifier, full-bridge phase-shift converter, isolation transformer, tapped inductor.

In this paper, a multistring light-emitting diode (LED) backlight driving system for liquid crystal display (LCD) panels with color sequential display (CSD) and area control is proposed. In large-scale LCD panels, multistring LED backlights are required to provide sufficient back lighting. The most popular structure to achieve multistring current regulation is a current mirror. However, it cannot be applied to high-power LED (>100 mA) driving, and the number of LEDs in each string is highly limited. In the driving system, a multioutput flyback converter associated with a novel control IC is proposed to tightly regulate LED driving currents and to readily achieve CSD and area control. The proposed driving system for a 32-in LCD panel has been built, from which experimental measurements have verified that the proposed driving system has the following features: low power consumption, high power conversion efficiency, stable driving currents, and high reliability. Index Terms--Area control, color sequential display (CSD), light-emitting diode (LED), liquid crystal display (LCD).

Interleaving control schemes are widely used in converter applications. Merits of such control methods are in reducing input/output current or voltage ripples and volume, and increasing the processed power capacity of converters. For converters with constant frequency operation, it is easy to achieve interleaving control. However, it is difficult to realize interleaving features with variable frequency operation, such as boost-type power factor correctors (PFCs) operated in critical-mode (CM) condition. This paper proposes several interleaving phase shifters for CM boost PFCs. Analysis and design of the interleaving phase shifters are first described in detail. Moreover, simulated results of the CM boost PFCs with interleaving two-phase and four-phase shifters are introduced. Finally, experimental results of a two-phase interleaved CM boost PFC are presented to verify the discussed features. Index Terms--Critical-mode control, interleaved power factor corrector, phase shifter.

This paper first reviews the mechanism of transdermal drug delivery (TDD) and then presents the method for generating multiphase pulsed voltages (MPPVs) for TDD applications. In TDD applications, it offers many potential advantages over conventional methods, such as oral and injection treatments, and it avoids drug degradation through the gastrointestinal tract and liver. Due to the energy stored in an equivalent capacitor of human skin which is about 30% of the total energy consumption, a full-bridge type of converter is designed to recover this energy, and additionally, it is equipped with a soft-switching cell to achieve a zero-voltage switching or a zero-current switching, improving the efficiency of about 20%. The overall system needs only a set of soil-switching cells to achieve a soft-switching feature even though it can generate N sets of pulsed voltages, reducing size and cost significantly. Moreover, the MPPVs are introduced to further improve the effectiveness of drug delivery. Experimental results from the TDD application with a 150-V output voltage and a 110-W peak power have demonstrated the feasibility of the proposed generator. Index Terms--Full-bridge converter, multiphase pulsed voltages (MPPVs), transdermal drug delivery (TDD).

This paper proposes a wide pulse combined with a narrow-pulse generator for solid-food sterilization. The proposed generator is composed of a full-bridge converter in phase-shift control to generate a high dc-link voltage and a full-bridge inverter associated with an L-C network and a transformer to generate wide pulses combined with narrow pulses. These combined pulses can prevent undesired strong air arcing in free space, reduce power consumption, and save power components, while sterilizing food effectively. The converter and inverter can be operated at high frequencies and with pulsewidth-modulation control; thus, its weight and size can be reduced significantly, and its efficiency can correspondingly be improved. Experimental results obtained from a prototype with [+ or -]10-kV wide pulses combined with [+ or -]10-kV narrow pulses and with 10- to 50-kW peak output power, depending on pulsewidth of the output pulses, have demonstrated its feasibility. Index Terms--Food sterilization, full-bridge converter (FBC), phase-shift control, pulse-voltage generator (PVG).

This paper presents an active-clamp push--pull converter for battery sourcing applications. A pair of auxiliary switches, resonant inductors, and clamping capacitors is added to the primary side of the transformer to clamp voltage spike and recycle the energy trapped in the leakage inductors. In the proposed active-clamp push--pull converter, since both main and auxiliary switches can be turned ON with zero-voltage switching, switching loss can be reduced and conversion efficiency therefore can be improved significantly. Furthermore, the proposed converter can eliminate potential flux-imbalance problems existing in the conventional push--pull converter. In this paper, a 1 kW active-clamp push--pull converter was implemented, from which experimental results have shown that efficiency improvement and surge suppression can be achieved effectively. It is relatively feasible for applications to battery sourcing converters. Index Terms--Active clamp, push-pull converter, zero-voltage switching (ZVS).

This paper proposes a boost converter with coupled inductors and a buck-boost type of active clamp. In the converter, the active-clamp circuit is used to eliminate the voltage spike that is induced by the trapped energy in the leakage inductor of the coupled inductors. The active switch in the converter can still sustain a proper duty ratio even under high step-up applications, reducing voltage and current stresses significantly. Moreover, since both main and auxiliary switches can be turned on with zero-voltage switching, switching loss can be reduced, and conversion efficiency therefore can be improved significantly. A 200-W prototype of the proposed boost converter was built, from which experiment results have shown that efficiency can reach as high as 92% and surge can be suppressed effectively. It is relatively feasible for low-input-voltage applications, such as fuel cell and battery power conversion. Index Terms--Active clamp, boost converter, coupled inductors, zero-voltage switching (ZVS).

This paper presents a bipolar narrow-pulse generator with energy-recovery feature for liquid-food sterilization. The generator is formed from a bidirectional flyback converter and active-clamp circuits which are further simplified to the proposed topology with the synchronous-switch technique. In the converter, the leakage inductance of the transformer will resonate with the active-clamp capacitors to recover the trapped energy and to reduce switching loss, improving efficiency by about 13%. In addition, the capacitors can reduce voltage stress significantly. Experimental results obtained from a prototype with the output of [+ or -] 6-20 kV, depending on loads, and the peak power of 1.2 MW has confirmed these discussions. Index Terms--Active-clamp circuit, bipolar narrow-pulse generator, synchronous-switch technique.

This paper presents the analysis, design, and implementation of a parallel-inverter system with failure isolation and hot-swap features. The system is controlled with a system control unit to achieve output voltage regulation, inverter synchronization, and the aforementioned features. By incorporating a current-weighting-distribution control, the system allows inverters with identical or different power ratings. The failure isolation feature is achieved with a scanning circuit, a resistor-capacitor filter, and transistors, which are also used in achieving the hot-swap one. In the proposed system, power capacity can be readily expanded, and inverter-failure disturbance can be correspondingly reduced. Experimental results that are obtained from a six-inverter system have illustrated the discussed features and significantly demonstrated its feasibility, improving system reliability, and stability. Index Terms--Failure isolation, hot-swap feature, parallel-inverter system, scanning circuit.

This paper presents a half-bridge single-phase two-wire (1[phi]2W) photovoltaic (PV) inverter system that can perform both active power filtering and real power injection. In the proposed system, it needs only two active switches, reducing cost significantly. In addition, output current of the inverter can be controlled to prevent switches from exceeding their current ratings. Thus, power rating of the inverter can be effectively used and power quality can be improved. For controlling inverter output current, an amplitude-clamping algorithm and an amplitude-scaling algorithm are proposed, which can determine inverter current command without needs of complicated calculation. Simulations and experimental results have verified the feasibility of the proposed PV inverter system and the two current control algorithms. Index Terms--Active power filtering (APF), amplitude-clamping algorithm (ACA), amplitude-scaling algorithm (ASA), half-bridge inverter, photovoltaic (PV) power injection.

In this paper, a sequential color light emitting diode (LED) backlight driving system for liquid crystal display (LCD) panels is proposed. Due to improvement on luminous efficacy, long life and wide color gamut, LED has gradually substituted for cold cathode fluorescent lamp as backlight. The proposed driving system adopts sequential color scanning scheme to improve light utilization efficiency by removing color filter. To meet display performance requirement that chromaticity variation [DELTA]uv needs to be limited below 0.002, this paper also proposes a family of output current ripple free topologies to control the average driving current precisely, which in turn can reduce chromaticity variation. In addition, an LED bypass circuit is proposed to prevent LED arrays from open-circuit, and a driving voltage resetter is introduced to eliminate current spikes, improving backlight reliability and availability significantly. A forward-type output current ripple free converter has been built to sequentially drive color LED arrays, from which experimental measurements have verified the discussed performance and feasibility of the proposed system. Index Terms--Light emitting diode (LED), liquid crystal display (LCD), ripple free, sequential color display.

A current-weighting-distribution-control, (CWDC) strategy for multi-inverter systems to achieve current sharing is presented in this paper. With a CWDC strategy, the inverters connected in parallel are allowed to have different power ratings and can achieve a weighted output current distribution by adding only simple circuits to each inverter. In such systems, each inverter has an outer voltage loop controller to govern system stability, an inner current loop controller to expedite dynamic response, and a weighting current controller to achieve current distribution and to reduce possible interactive effects among inverters. Experimental results from a two-inverter system and a three-inverter system have demonstrated the feasibility of the proposed strategy in weighting current distribution and fast regulation during a step-load change or hot-swap operation. Index Terms--Current sharing, current-weighting-distribution-control, fault-tolerance, hot-swap operation, multi-inverter systems.

This paper proposes a single-phase two-wire inverter system for photovoltaic (PV) power injection and active power filtering (APF) with nonlinear inductor consideration. The proposed system can fully or partially perform APF, process PV power, eliminate harmonic currents, improve power factor, and take into account the nonlinear effect of its output filter inductor. In the system, even though only the utility current is sensed, both APF and maximum power point tracking features can be still achieved, reducing the number of current sensors and cost significantly. To prevent output current from exceeding switch ratings, inverter current is properly controlled through a current estimator and a defined limit circle. A self-learning algorithm is also proposed to determine nonlinear inductance, which can increase the accuracy of the estimated current. Simulations and experimental results have verified the feasibility of the proposed PV inverter system and the algorithm. Index Terms--Current estimator, nonlinear inductor consideration, photovoltaic (PV) power injection, self-learning algorithm, single-phase two-wire (1 [empty set] 2W) inverter system.

This paper presents single-stage regulators with power-factor correction (PFC) based on an asymmetrical half-bridge topology. The proposed regulator is formed from a boost converter with two coupled inductors and an asymmetrical half-bridge converter with the synchronous switch technique, and it is controlled with pulsewidth modulation to achieve zero-voltage switching (ZVS). The boost converter is operated in discontinues conduction mode to achieve PFC. With the coupled inductors, input current ripple and power factor can be improved significantly. The proposed regulator has the features of constant-frequency operation, ZVS, and low voltage stress imposed on the active switches. Moreover, the regulator can achieve high power factor, high power density, high efficiency, low switching loss, and low component count, which makes its applications at medium-power levels feasible. Experimental results have verified the discussed features of the proposed regulator. Index Terms--Asymmetrical half-bridge converter, power-factor correction, zero-voltage switching (ZVS).

This paper presents design and implementation of a single-phase three-wire (1[empty set]3W) inverter with grid connection and active power filtering which is based on nonlinear programming and fast-zero-phase detection (FZPD) algorithm. The proposed inverter system can transmit photovoltaic power, compensate harmonic currents, supply reactive power, and balance power at source side even when the line voltages are highly distorted. Simulated and experimental results have verified the FZPD algorithm and demonstrated that when the voltage sources are highly distorted, the proposed inverter system can yield better power quality over that with conventional zero-crossing-detection algorithm. Index Terms--Active power filter, fast-zero-phase detection (FZPD), grid connection, inverter, nonlinear programming, photovoltaic arrays.

This paper presents three improved plasma display panel (PDP) sustainers for reducing current stress and nonlinear effect due to parasitic and distributed components. In the paper, a useful cell equivalent circuit model is first introduced to describe the behavior of PDP cell operation, and a widely used sustainer is then reviewed, on which three improved ones are proposed. The proposed sustainers can reduce currents through the switches and nonlinear effect due to parasitic and distributed components along the energy-recovery circuit paths. Derivation and operating principle of the proposed sustainers are addressed in detail. In addition, their related gaseous discharge mechanism in PDP cells is also presented. Hardware measurements have verified the feasibility of the proposed sustainers. Index Terms--Plasma display panel (PDP) sustainers.

This paper first reviews viable microbe processing mechanism and then presents generation of pulsed electric fields for processing microbes. Microbe processing includes food sterilization, waste treatment, pollution control, and medical diagnostics and treatment. To generate pulsed electric fields for achieving sterilization, a generated high dc output voltage is chopped into pulsed waveforms, in which their pulse-width varies from tens of nanoseconds to hundreds of microseconds, period changes from 0.1 to 1 ms, and electric field intensity is from tens to hundreds of kV/cm. In this study, we propose wide pulses stacked with narrow pulses to prevent undesired air breakdown and reduce power consumption. Modified half-bridge series resonant converters are used to generate high dc voltages. They are operated at high frequency, in discontinuous conduction mode and with a PWM control; therefore, its weight and size can be reduced significantly and its efficiency can be correspondingly improved. Index Terms--Half-bridge series resonant converter, microbe processing, pulsed electric fields, wide pulses stacked with narrow pulses.

This paper proposes interleaved buck converters with a single-capacitor snubber to smooth ant switch turn-off transition, The single-capacitor snubber is used to limit rising rate of drain-source voltage of the metal-oxide-semiconductor field-effect transistor (MOSFET) switch in the converters to reduce turn-off loss. In addition, the converters are operated at the boundary of continuous and discontinuous conduction modes (CCM), (DCM) to reduce turn-on loss, and in an interleaving fashion to reduce output current ripple. As compared with the counterparts of conventional converter topologies, the proposed converters have the merits of less component count, higher efficiency over a certain load range, smaller size, and they are easier to implement. Hardware measurements obtained from experimental prototypes have verified these merits.

This paper presents analysis, design, and practical considerations for 500 W boost power factor correctors (PFCs). The boost PFCs with three active soft-switching cells, which are boost, forward and flyback, and a passive soft-switching cell are first discussed. The operating principle and performance characteristics of the PFCs are then presented in detail, from which the boost with a flyback soft-switching cell and that with a passive soft-switching cell are designed and implemented. Performance comparison among these PFCs is also presented. Hardware measurements are used to verify the theoretical discussion. The presented information can provide designers a good application reference.

An averaged current-sharing strategy (ACSS) for paralleled multi-inverter systems with digital signal processor (DSP)-based robust controls is presented. With an ACSS, the inverters are in parallel operation and each inverter has a voltage robust controller to achieve system stability and robustness, and a current robust controller to track the averaged inductor current of the inverters to achieve equal current distribution. In the proposed system, the current-sharing control loop is independent of the voltage control loop. Therefore, equal current distribution among the inverters, fast response, and tight regulation can be achieved. Additionally, the ACSS in each inverter can be readily implemented with two operational amplifiers. Simulation results and hardware measurements of a single-inverter system and a two-inverter system, and simulation results of a three-inverter system with linear and nonlinear loads have demonstrated the feasibility of the proposed control scheme in equal current distribution and fast regulation.

This paper presents a single-phase three-wire (1[phi] 3W) grid-connection photovoltaic (PV) power inverter with a feature of partial active power filter (PAPF), which can not only deal with PV power but filter current harmonics and improve power factor. Once the processed power exceeds the switch ratings, the inverter can reduce its output reactive power and harmonic power, while still supplying the maximum real power generated by the PV arrays. In derivation of control laws, a limit circle is defined to confine the output power of the inverter. To determine the power that the inverter can process, instantaneous reactive power of a 1[phi] 3W system is defined and used to calculate reactive power, which can avoid complex detections of phase angle and magnitude of the fundamental component of a nonlinear load current. Simulation results and experimental measurements have verified the proposed algorithm and the feasibility of the inverter.

In this paper, a new soft-switching Zeta converter with an asymmetrical pulsewidth modulation (PWM) control is proposed. The proposed Zeta converter has the features of constant frequency operation, zero voltage switching (ZVS), and low voltage stress on the active switches. Moreover, it can achieve high power density, high efficiency, low switching loss, and low component count, which make converter operation at low to medium power level feasible. Operational principle of the Zeta converter is presented in detail, and a specific example is designed and implemented to verify its feasibility.

This paper presents design and development of driving waveforms to improve efficacy, contrast, and resolution for ac plasma display panels (PDPs). In the paper, the conventional driving waveforms are first reviewed, and the proposed driving waveforms are then discussed. The driving of PDPs in each subframe is divided into three periods: the reset period, scan period, and sustain period. During the reset period, the proposed ramp-like reset waveforms can enhance the contrast and resolution, and can lower the scan voltage while still sustaining a reliable wail-charge control. Additionally, a square sustain waveform stacked with the ramp-like waveform can induce self-erasing discharges which will improve efficacy during the sustain period. Operation of a PDP and comparison among various driving waveforms are also presented. Experimental results measured from a 46-in PDP system have verified the feasibility of the proposed driving waveforms. Index Terms--AC plasma display panel (PDP), high-definition television (HDTV), linear-ramp waveform, self-erasing discharge.

This paper presents a switch-mode approach to efficiently and flexibly generating reset waveforms for ac plasma display panels (PDPs). In the paper, the existing reset waveforms and circuits are first reviewed, and the proposed reset circuits for generating reset waveforms are then discussed. The proposed reset circuits are based on a flyback converter topology, which can generate reset waveforms more efficiently and can have more degrees of freedom in programming the waveforms. With the proposed approach, high-contrast ratio and resolution can still be sustained. Moreover, power conversion efficiency can be improved significantly, and components for generating various voltage levels can be reduced. Hardware implementation and measurements from a 46-in PDP system have verified the theoretical discussions. Index Terms--AC plasma display panel (PDP), high-definition TV, linear-ramp waveform, self-erasing discharge.

This paper presents a structural approach to synthesizing soft switching PWM converters based on the concept of basic converter units (BCUs). With a proper reconfiguration, several families of passive and active soft switching PWM converters can be synthesized from either buck BCU or boost BCU plus certain linear networks. These typical soft switching converters include the well known topologies of buck, buck-boost, Zeta, boost, `Cuk and Sepic. It has been shown that analysis of the converters can be conveniently performed from the derived general configurations, reducing the complexity significantly. Therefore, using the structural approach not only can explore more physical insights into the converters in a family, but can reveal more relationships among these soft switching converters over conventional approaches. These merits have made the proposed approach become uniquely valuable. Index Terms--Basic converter unit, PWM converter.

A 2-degree-of-freedom (2DoF) induction machine realizes rotary, linear, and helical motions, exhibiting the merits of integrated structure and high material utilization. Compared with traditional electric machines, one of the special factors affecting the electromagnetic performances is the helical motion coupling effect (HMCE). This article systematically investigates its production mechanism based on the proposed HMCE model first. Then, a comprehensive comparison of the torque performances between the rotary and linear motion parts is conducted to evaluate the HMCE in two motion parts, and then the results are verified by 3-D finite element model. Besides, resistant torque and force ratios are proposed and calculated to assess the extent of the HMCE. It can be concluded that the torque performances of the rotary motion component are weakened more than those of the linear motion component by the HMCE. Further, two methods to suppress the coupling effect, namely adjustment of linear motion slip ratio and change of linear motion frequency, are discussed. Experimental results have validated the analytical results and effectiveness of the suppression strategies. [ABSTRACT FROM AUTHOR]

This paper presents the analysis and design of an isolated single-stage converter achieving high-power-factor correction and fast regulation. By using the technique suggested by Wu et al., a buck-boost converter and a flyback converter can be integrated to form the discussed converter. The buck-boost semistage working in the discontinuous conduction mode (DCM) functions as a power-factor corrector, and the flyback semistage operating in the DCM is a voltage regulator which is controlled, theoretically, to be independent of load variation. An approximated small-signal model of the converter operating in the DCM is developed. Design of a peak-current feedback loop with an optimal proportional integral controller is also presented. A prototype is implemented to verify that the analysis and design are effective and feasible. Index Terms - Fast regulation, power-factor correction, single-stage converter.

This paper presents an approach to systematically model single-stage dc/dc converters operated in discontinuous conduction mode (DCM) based on the graft scheme. With the graft scheme, the active switches which are with a common node and operating in unison can be integrated to form a single-stage converter (SSC). The small-signal models of the SSC can, therefore, be derived by combining those of its originally separate converters. Using the proposed approach can help yield highly related dynamic models of the converters in a family and, in addition, physical insights between the converters can be readily identified. Moreover, the expressions of the small-signal models for the SSC's operated in DCM can be extended to those in continuous-conduction-mode operation. These have made the proposed modeling method valuable and viable. Experimental measurements have demonstrated that the small-signal model of an SSC derived with the proposed approach is relatively accurate. Index Terms - Power factor correction, single-stage converter, small-signal model.

An electronic dimming ballast with a lead-lag tank operation (LLTO) having the properties of high efficiency and low stress is introduced in this paper. The ballast is configured with a voltage-fed half-bridge series-resonant parallel-loaded inverter (SRPLI) acting as a !amp driver. It is loaded with resonant tanks which are designed and operated to be capacitive and inductive to theoretically achieve both zero-voltage switching (ZVS) and zero-current switching (ZCS) and to eliminate the reactive current circulating through the switches, resulting in low switching and conduction losses. Moreover, the merit of a successive lamp ignition can be attained with the proposed operation scheme so that current stress imposed on the switches can be reduced. With the plasma model of fluorescent lamps, the analysis, operating principle, and dimming control strategy of the electronic ballast are described in detail. On the other hand, the limitations of the proposed scheme are pointed out. Computer simulation results and experimental measurements are used to verify the theoretical prediction and analytical discussion. Index Terms - Dimming ballast, lead-lag tank operation.

Based on the comparisons of several inverter configurations in the aspects of efficiency, response, volume, current distortion, and price, in this article, we present a feasible three-phase four-wire (3Φ4W) grid-connected hybrid-frequency parallel inverter system (HbFPIS) with ripple compensation to achieve low current distortion and fast response. An HbFPIS consists of a low-frequency-high-power inverter (LFHPI) and a high-frequency-low-power inverter (HFLPI) connected in parallel. An LFHPI design results in higher power output with lower frequency (LF) switching devices, such as insulated gate bipolar transistors (IGBTs) being more cost-effective. An HFLPI design can reduce switching loss by lowering the power requirement of high-frequency (HF) switching devices while increasing dynamic response. With the direct digital control and ripple compensation, LF current ripples are attenuated by the HFLPI to a smaller level, remaining mainly HF current ripples and, thus, resulting in smaller filter size and weight. The design of an HbFPIS ensures that the system has high power output with cost-effective devices, fast response, and smaller output filters. Ripple attenuation, current tracking capability, and inverter stability are analyzed in the article. Low current distortion and fast current tracking performance are validated by the 300-kW simulated and the 10-kW experimental results of a 3Φ4W HbFPIS in grid-connected and active power filter modes. [ABSTRACT FROM AUTHOR]

Analysis, design, practical consideration, and implementation of a microprocessor-based toggle-control lighting system are presented. The system is primarily configured with a power factor corrector (PFC), a square-wave voltage generator, a manually controlled toggle switch, and two relays. Toggling the toggle switch can select a different number of lamps in operation, resulting in a mutual dimming feature. A lighting system with this specific ballast gains the merits of lower system cost and more flexibilities in lighting fixture design, as compared to conventional systems. Index Terms - Ballast, fluorescent lamp.

This paper presents the analysis, design, and practical consideration of a single-stage electronic dimming ballast with unity power factor. The power stage of the ballast is derived from combining a buck-boost converter and a half-bridge series-resonant parallel-loaded inverter (SRPLI). With the plasma model of the lamp, the analysis of the ballast is carried out, from which the key equations used for dimming control are derived. Starting performance and dimming consideration are also addressed in the paper. In this dimming ballast, both pulsewidth modulation (PWM) and variable-frequency control strategies are employed. The discussed ballast with the controls can save a controller and a switch driver, reduce size and cost, and possibly increase system reliability over conventional two-stage systems in the applications with moderate power level. Simulated and experimental results of the ballast for an OSRAM T8 32-W lamp are used to verify the discussion. Index Terms - Electronic ballast, power factor correction, single stage.

Analysis, design, and practical consideration of a single-stage electronic ballast with dimming feature and unity power factor are presented in this paper. The proposed single-stage ballast is the combination of a boost converter and a half-bridge series-resonant parallel-loaded inverter. The boost semistage working in the discontinuous conduction mode functions as a power factor corrector and the inverter semistage operated above resonance are employed to ballast the lamp. Replacing the lamp with the plasma model, analysis of the ballast is fulfilled. The dimming feature is carried out by pulse-width modulation (PWM) and variable-frequency controls simultaneously. The proposed single-stage ballast is suitable for applications with moderate power level and low-line voltage while requiring a high-output voltage. It can save a controller, an active switch and its driver, reduce size, and possibly increase system reliability while requiring two additional diodes over a conventional two-stage system. A prototype was implemented to verify the theoretical discussion. The hardware measurements have shown that the desired performance can be achieved feasibly. Index Terms - Electronic dimming ballast, plasma model, power factor corrector.

A systematic and unified approach to modeling pulsewidth modulated (PWM) dc/dc converters based on the graft scheme is presented in this paper. With the graft scheme, the typical PWM switch-mode converters, such as buck-boost, boost-buck (Cuk), Sepic, and dual Sepic, can be generated from the two basic converters, buck and boost. The small signal models of these converters can, therefore, be derived by properly combining those of the buck and boost. Using the proposed approach can help to yield highly related dynamic models of the converters in a family and, in addition, physical insights into the converters can be readily identified. This has made the proposed modeling method valuable and viable. Index Terms - Graft scheme, single-stage converter, small signal model.

A unified approach to developing single-stage power converters which can fulfill multiple functions is presented. Four synchronous switches corresponding to the four common node types of two active switches are introduced. The approach is then to replace the active switches in multistage converters (in cascade or cascade connection) with one or several of the synchronous switches and their degenerated versions to form a single-stage converter. Illustrations of using these switches to develop single-stage converters are presented. These are started with the development of the well-known single-stage switch-mode converters (SMCs), buck-boost, Cuk, sepic, and Zeta (also named dual sepic), from the basic converters, buck and boost. Then, synthesis and applications of other single-stage converters are addressed. Due to increased component stresses, the developed single-stage converters are primarily suitable for applications with moderate power levels.

Off-line applications with single-stage converters (SSC's) are presented in the paper. The approach used in synthesizing the SSC's is first described, and their applications are then introduced. In addition, viable control strategies for the SSC's are addressed. The developed SSC's can fulfill multifunctions, such as input power factor correction, fast output regulation and lamp ballasting, and possess the merits of compact size, simple driver design and high reliability. Prototypes of SSC's applied to an electronic dimming ballast and a dc regulator are built, which show high feasibility in such moderate power applications. Index Terms - Electronic ballast, off-line application, single-stage converter, synchronous switch.

A simple, but accurate, PSpice circuit model simulating the electrical characteristics of low-pressure gaseous discharge lamp operating at high frequency is proposed. The model is constructed from a two-parameter equation and is suitable for computer simulation and analytic derivation in a preliminary design of electronic dimming ballasts. Simulated and measured results are used to verify the theoretical discussion. Index Terms - Electronic dimming ballasts, low-pressure gaseous discharge lamps, PSpice circuit model.

One of the modular multilevel converter (MMC) applications with scalability is renewable energy generation. Nowadays, renewable energy is especially the source of momentum, which stimulates the energy transition and reduction of greenhouse gas emissions. However, its existing control schemes may not precisely reveal the inherent mannerism of MMCs. The aim of this article is to optimize the cell voltage, arm current, and circulating current of converter arms in MMCs based on the Lagrange multiplier of an energy cost function and arm current tracking control law. Meanwhile, determination of the capacitors and switch ratings in each cell still has a big challenge, and it can result in cell-voltage fluctuations under unbalanced grid-connection conditions. This article presents unique approaches to derive cell-voltage expression in terms of arm currents, which reduces cell-voltage fluctuations by injecting zero-mean current, and the duty-ratio control laws. Moreover, tradeoff between cell voltage and circulating current can be also conducted. Experimental and simulated results from a 3-kW single-phase MMC have verified the functionality of the proposed control method, analysis, and comprehensive discussion. [ABSTRACT FROM AUTHOR]

This paper presents bidirectional grid-connected modular multilevel converters (MMC) with direct digital control and division-summation processes to achieve power-injection and rectification functions. A direct digital control is developed to track current references, regulate dc-bus voltage and cell voltage, and balance the upper and lower dc-bus voltages. It can accommodate wide filter-inductance variation and take care of source voltage harmonics to achieve tight current tracking and low distortion output current. Based on the power-balance principle, the commands of arm currents can be determined directly. In this paper, the MMC configuration is introduced first, and then the control laws for current tracking and voltage regulation are derived in detail. Experimental and simulated results obtained from two 50 kW MMCs operated in power-injection and rectification modes have verified the analysis and discussion. [ABSTRACT FROM AUTHOR]

This paper presents a sinusoidal pulsewidth modulation (SPWM) based direct digital control with average-voltage model (AVM) and division–summation process for paralleled three-phase three-wire (3φ3W) grid-connected converters to reduce circulating currents. With the direct digital control, plant of each single-phase converter can be derived directly, and a controller is then designed to cover the variation effects of filter inductance and grid voltage. Based on SPWM and AVM over a switching cycle, each 3φ3W converter can be decomposed into three single-phase converters and each converter is controlled individually to track its sinusoidal reference current tightly, reducing circulating currents significantly. Equal current sharing is therefore also achieved. The control laws for achieving grid connection are derived in detail. In the design and implementation, the inductances corresponding to various inductor currents are measured offline and stored in the controller for scheduling loop gain cycle by cycle. Experimental and simulated results from a three-converter system confirm the analysis and discussion of the proposed control approaches. [ABSTRACT FROM AUTHOR]

Soft magnetic powder cores with their high saturation flux density and low core loss are excellent alternatives for filter inductors in inverter-based applications. However, their nonlinear current-dependent inductance characteristics pose a challenge for control of grid-connected inverter with LCL filter. In this paper, the variable inductance conundrum is discussed and a modified direct digital control method based on a variable-structure inductance estimation model that takes into consideration wide nonlinear variation in both inverter- and grid-side inductances is proposed. The proposed method is shown to have better grid-voltage harmonic rejection and improved stability margins. However, investigation of stability which is conventionally based on nominal values of filter inductors cannot predict instabilities over the entire range of inductance variation. Hence, a parametric approach to conventional stability methods with a parameter space defined by variation in actual and estimated inductance is explored in this paper. The effect of line impedance on stability is also investigated with impedance-based stability criterion by considering line inductance as an additional dimension in the parameter space. A pattern in stability margins is observed due to inductance variation, with inductance at its minimum being most vulnerable to instability. Experimental results measured from a 5 kW single-phase grid-connected inverter with various LCL filters have verified the feasibility of the proposed control method. The experimental results also match the analytical results with reasonable accuracy. [ABSTRACT FROM AUTHOR]

A systematic approach to developing soft switching PWM converters based on the synchronous switch scheme is presented in this paper. With the approach, several families of passive and active soft switching PWM converters, such as buck-boost, Zeta, Cuk, and Sepic, can be generated from the two basic converters, buck and boost. Also, the approach is used to integrate multiple converters to form a single-stage soft switching PWM converter. It has been shown that analysis of the converters can be conveniently performed from the derived general configurations, reducing the complexity significantly. Therefore, employing the technique can not only explore more physical insights into the converters in a family but reveal more relationships among the soft switching converters over conventional approaches. Measured results from a prototype have verified the feasibility of the derived single-stage converters. Index Terms--Single-stage converter, soft switching.

This paper presents the analysis and design of a series-resonant parallel-loaded inverter applied to electronic dimming ballasts with bifrequency and fuzzy logic control. The analysis of the ballast is carried out in conjunction with the fluorescent lamp represented in a plasma model. The component values of the power stage, as well as two switching frequencies, according to the desired maximum and minimum power levels are, therefore, determined. The power levels in between are controlled by varying the ratio between two time intervals for which the two frequencies last, respectively. This mechanism is achieved by using a fuzzy logic controller (FLC). A ballast prototype with the FLC which is implemented on an 8-bit microprocessor with a reduced instruction set computer architecture has been built. Experimental measurements have shown the feasibility of the ballast with the proposed control strategy. Index Terms--Ballast, fuzzy control.

This paper presents improved start-up scenario for single-stage electronic ballast derived with synchronous switch technique (SST). Based on the SST, the derivation of a single-stage inverter (SSI) used for realizing the ballast is then addressed. The SSI can achieve both high power factor and ballasting function. During lamp start-up transition, power imbalance may exist between the power factor correction semi-stage and the ballast semi-stage, and filament preheating is an important issue. Power imbalance usually results in a high dc-link voltage which, in turn, imposes high stress on the switching devices. Investigation of the ballast operation is conducted, from which control strategies for reducing component stresses and hot resistance detection circuits for minimizing electrode sputtering are therefore proposed. Hardware measurements have verified that on-off tests are higher than 18 000 times without significant sputtering. Index Terms--Single-stage electronic ballast.

This paper presents a fuzzy-logic-controlled single-stage converter (SSC) for photovoltaic (PV)-powered lighting system applications. The SSC is the integration of a bidirectional buck-boost charger/discharger and a class-D series resonant parallel loaded inverter. The designed fuzzy logic controller (FLC) can control both the charging and discharging current, and can improve its dynamic and steady-state performance. Furthermore, a maximum power point tracker (MPPT) based on a perturb-and-observe method is also realized to effectively draw power from PV arrays. Both the FLC and the MPPT are implemented on a single-chip microprocessor. Simulated and experimental results obtained from the proposed circuit with an FLC have verified the adaptivity, robustness, and feasibility. Index Terms--Fuzzy logic controller, photovoltaic, single-stage converter.

A circular chain control (3C) strategy for inverters in parallel operation is presented in the paper. In the proposed inverter system, all the modules have the same circuit configuration, and each module includes an inner current loop and an outer voltage loop control. A proportional-integral controller is adopted as the inner current loop controller to expedite the dynamic response, while an [H.sup.[infinity]] robust controller is adopted to reach the robustness of the multimodule inverter system and to reduce possible interactive effects among inverters. With the 3C strategy, the modules are in circular chain connection and each module has an inner current loop control to track the inductor current of its previous module, achieving an equal current distribution. Simulation results of two-module and a three-module inverter systems with different kinds of loads and with modular discrepancy have demonstrated the feasibility of the proposed control scheme. Hardware measurements are also presented to verify the theoretical discussion. Index Terms--Circular chain control, equal current distribution, multimodule inverter.

This paper presents a robust-controlled single-stage converter (SSC) operating either in discontinuous conduction mode (DCM) or in continuous conduction mode (CCM) to achieve high power factor for universal line voltage range from 90 to 264 [V.sub.rms]. At light load, the proposed system is operated in the DCM, while at heavy load the system is operated in the CCM, thus, the dc-link voltage can be properly controlled within a certain voltage range and the efficiency can be improved as well. The overall system is with a robust controller and is operated in a fixed frequency. In the design, the load variation and line voltage variation are treated as plant uncertainty and control disturbance, respectively. The [H.sup.[infinity]] robust control method is adopted to design a proper robust controller to achieve robust stability and robust performance. The measured results from a prototype have confirmed the effectiveness and feasibility of the proposed system. Index Terms--Robust control, single-stage converter.

Single-stage converters (SSCs) are proposed for applications of photovoltaic powered lighting system (PPLS). The synchronous switch technique [6] is employed to develop the SSCs which can fulfill maximum power point tracking (MPPT), battery charging, discharging, and lamp ballasting features. Several typical SSCs are discussed. One of the proposed SSCs, which is the integration of a buck-boost charger/discharger and a class-D series resonant parallel loaded inverter, is analyzed and designed into a PPLS. Both pulsewidth modulation (PWM) and variable-frequency controls are used to govern the system operation. The controller is implemented on a single-chip microprocessor. Simulated and experimental results of the proposed system for driving up to sixteen GE TBX 26W fluorescent lamps are used to verify the theoretical prediction and feasibility. The proposed system has a simple configuration, as well as a zero voltage switching (ZVS) feature, and can achieve the same functions as those in conventional systems when abrupt insolation changes do not occur frequently. These result in the inherent merits of lower cost, more compact size and possibly achieving higher reliability over conventional systems.

Current-fed bidirectional dc–dc converters have attracted much attention in battery energy storage system applications due to their zero-voltage-switching performances and greater degree of control freedom. However, high efficiency cannot be achieved for both light and heavy load ranges with the present modulation schemes for a current-fed bidirectional dc–dc converter, especially with low battery voltages. A new modulation scheme is proposed to improve the conversion efficiency over a wide load range and with variations in the battery voltage. The relationship between the duty cycle of the secondary full bridge and the phase-shift angle was investigated to lower the power losses with the wide load variations. Based on the operation mode analysis, the control loop with the proposed pulse wide modulation plus phase-shift modulation scheme was developed. Comparisons of the switch conduction loss and the core loss in the series inductor for the previous modulation schemes and the proposed modulation scheme were carried out. The results show that lower power losses occur with the proposed scheme. The experimental results verify the theoretical analysis and effectiveness of the proposed modulation scheme on loss reduction. [ABSTRACT FROM PUBLISHER]