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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.

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.

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 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 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.

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]

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]

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]

This paper presents a three-phase back-to-back transformerless inverter for online uninterruptible power supply applications. The inverter consists of a three-phase three-wire input rectifier stage and a three-phase four-wire output inverter stage with their ground wires tied together. Both of the two stages are with sinusoidal pulse width modulation based division-summation (D-∑) digital control. The input stage controls the power flow between utility grid and dc link, regulates the dc-link voltage, and fulfills power factor correction. While the output stage tracks three-phase ac reference voltages. The proposed control laws derived based on the D-∑ digital approach take into account the effects of dc-link voltage fluctuation, grid-voltage distortion, and inductance variation due to different current levels. Thus, distortion of input current and output voltage, and filter inductor core size can be reduced significantly. Moreover, circulating current through their common ground can be suppressed effectively. Simulated and experimental results from a three-phase back-to-back transformerless inverter have confirmed the analysis and discussion of the proposed control approach. [ABSTRACT FROM PUBLISHER]

Pulse-width-modulated (PWM) converters have been widely applied for power processing, and they are typically the stems of other types of converters, such as quasi-resonant, Z-source, and switched-inductor hybrid converters. Development of PWM converters has been spanning over a century, starting from the buck converter. The well-known PWM converters include buck, boost, buck–boost, Ćuk, single ended primary inductive converter (SEPIC), zeta, Z-source, quasi-Z source, etc. Many attempts have been proposed to develop these converters based mostly on canonical cell concepts and by introducing extra LC filters to the cells. This paper presents an enhancement to the layer and graft schemes by introducing the ideas of dc voltage/current offsetting, capacitor/inductor component splitting, diode grafting, and inverse operation of PWM converters. The PWM converters, which can be operated in continuous conduction mode (CCM) or discontinuous conduction mode (DCM), therefore can be synthesized systematically according to decoded transfer gains. Decoding and synthesizing PWM converters uniquely bridge transfer gains to converter topologies and provide readers a comprehensive understanding of PWM-converter evolution from the original converter, the buck converter. Additionally, in this paper, the Ćuk, SEPIC, and zeta converters all with the same transfer gain of $D/(1 - D)$ are proved to be equivalent to the buck–boost converter with an extra LC filter. For further illustrating the proposed approaches, various types of Z-source converters, switched-capacitor/switched-inductor hybrid converters, and a single-stage interleaved converter are reviewed, and new PWM converters are developed. [ABSTRACT FROM AUTHOR]

This study is focused on integration and operation of a single-phase bidirectional inverter with two buck/boost maximum power point trackers (MPPTs) for dc-distribution applications. In a dc-distribution system, a bidirectional inverter is required to control the power flow between dc bus and ac grid, and to regulate the dc bus to a certain range of voltages. A droop regulation mechanism according to the inverter inductor current levels to reduce capacitor size, balance power flow, and accommodate load variation is proposed. Since the photovoltaic (PV) array voltage can vary from 0 to 600 V, especially with thin-film PV panels, the MPPT topology is formed with buck and boost converters to operate at the dc-bus voltage around 380 V, reducing the voltage stress of its followed inverter. Additionally, the controller can online check the input configuration of the two MPPTs, equally distribute the PV-array output current to the two MPPTs in parallel operation, and switch control laws to smooth out mode transition. A comparison between the conventional boost MPPT and the proposed buck/boost MPPT integrated with a PV inverter is also presented. Experimental results obtained from a 5-kW system have verified the discussion and feasibility. [ABSTRACT FROM AUTHOR]

This paper presents two-phase modulated digital control for a three-phase bidirectional inverter with wide inductance variation in dc distribution systems. The bidirectional inverter can fulfill both grid connection and rectification with power factor correction. With the proposed control, the inverter can track its sinusoidal reference currents, and it is allowed to have wide inductance variation, reducing core size significantly. The control laws based on space-vector pulsewidth modulation are first derived with either an accurate approach or an approximated one, and the gate signals were then derived based on two-phase modulation for lower switching loss and switching noise spectra. Determination of control parameters and stability analysis are also presented. In the design and implementation, the inductances corresponding to various inductor currents were measured and tabulated into a single-chip microcontroller for tuning loop gain cycle by cycle, ensuring system stability. Measured results from a 10 kVA 3φ bidirectional inverter have been presented to confirm the feasibility of the discussed control approaches. [ABSTRACT FROM AUTHOR]

This paper presents dc-bus voltage control with a three-phase bidirectional inverter for dc distribution systems. The bidirectional inverter can fulfill both grid connection and rectification modes with power factor correction. The proposed control includes two approaches, one line-cycle regulation approach (OLCRA) and one-sixth line-cycle regulation approach (OSLCRA), which take into account dc-bus capacitance and control dc-bus voltage to track a linear relationship between the dc-bus voltage and inverter inductor current. Since both of the approaches require the parameter of dc-bus capacitance, this paper first presents determination of dc-bus capacitor size and an online capacitance estimation method. With the OLCRA, the inverter tunes the dc-bus voltage every line cycle, which can reduce the frequency of operation-mode change and current distortion. The OSLCRA adjusts current command every one-sixth line cycle to adapt to abrupt dc-bus voltage variation. The two approaches together can prevent dc-bus voltage from wide variation and improve the availability of the dc distribution systems without increasing dc-bus capacitance. Experimental results measured from a three-phase bidirectional inverter have verified the feasibility of the discussed control approaches. [ABSTRACT FROM AUTHOR]

This paper presents design and implementation of a 5-kW single-phase bidirectional inverter with wide inductance variation. For dc-microgrid applications, the bidirectional inverter has to fulfill grid connection and rectification with power factor correction to regulate the dc bus to a certain range of voltages. In the inverter operation, inductor current can vary from 0 to 32 A in one line cycle. This will result in wide inductance variation, around seven times for an inductor constructed with a molybdenum permalloy powder core, and thus, high current ripple and fluctuation. In this paper, we take into account this variation while designing controller and selecting key components to ensure inverter normal operation. Additionally, to adopt a cost-effective microcontroller for the inverter, the sensitivities of the control to various parameters are investigated and presented in this paper. Experimental results measured from a 5-kW single-phase prototype have verified the feasibility of the designed inverter. [ABSTRACT FROM PUBLISHER]

Presents a study which discussed improved scenario for electronic ballast derived with synchronous switch technique. Merits of electronic ballast; Results; Conclusion.

Presents information on a study that described a robust-controlled single-stage converter (SSC) operating either in discontinuous conduction mode or in continuous conduction mode to achieve high power factor for universal line voltage. Derivation of the proposed SSC; Analysis of the SSC power stage; Design consideration and small-signal modeling; Experimental results and discussion; Conclusion.

Presents information on a study which introduced an electric dimming ballast with a lead-lag tank operation (LLTO) having the properties of high efficiency and low stress. Analysis of the proposed circuit operation scheme; Outline of the design procedure; Presentation of a design example of electronic dimming ballast with the LLTO scheme for a two-fluorescent-lamp lighting system.

Analysis the design and practical consideration of a single-stage electronic ballast with dimming feature and unity power. Details on the use of a pulse-width modulation (PWM); Reference made to the hardware measurements conducted on the ballast which showed that desired performance can be achieved feasibly; Methodology used in the analysis; Implications of the findings.