Bulk Capacitor Research Articles

Origin of defects in CuIn 1 − xGa xSe 2 solar cells with varied Ga content

A series of CuIn 1 − x Ga x Se 2 solar cells with varied Ga content (0 ≤ x ≤ 1) was prepared using a three-stage co-evaporation process. The grain sizes of these devices vary with gallium content, exhibiting a maximum for approximately x = 0.2, which does not coincide with the maximum of the solar conversion efficiency observed between 0.34 < x < 0.37 for these devices. Admittance spectroscopy and drive-level capacitance profiling measurements were performed yielding a defect level with an activation energy of E a = 0.1 eV which is independent of the amount of Ga and the grain size respectively. This defect closely resembles the N1 defect level reported in the literature. Only for relatively high Ga contents ( x > 0.7) an additional defect appears. An equivalent circuit model describing a parallel connection of bulk and grain boundary capacitors allows us to conclude that the detected shallow defect is not predominantly located at the grain boundaries.

Integrated Buck-Flyback Converter as a High-Power-Factor Off-Line Power Supply

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper investigates the integrated buck-flyback converter (IBFC) as a good solution for implementing low-cost high-power-factor ac–dc converters with fast output regulation. It will be shown that, when both buck and flyback semistages are operated in discontinuous conduction mode, the voltage across the bulk capacitor, which is used to store energy at low frequency, is independent of the output power. This makes it possible to maintain the bulk capacitor voltage at a low value within the whole line voltage range. The off-line operating modes of the IBFC are also investigated to demonstrate that the control switch of the proposed converter handles lower root-mean-square currents than those in similar integrated converters. The off-line operation of the IBFC is analyzed to obtain the design characteristics of the bulk capacitor voltage. Finally, the design and experimental results of a universal input 48 V-output 100 W ac–dc converter operating at 100 kHz is presented. Experiments show that the IEC-61000-3-2 input current harmonic limits are well satisfied and efficiency can be as high as 82%. </para>

Analysis and design of a single-phase hybrid mode power factor correction converter

Two-stage power factor correction (PFC) configuration usually suffers from low conversion efficiency due to twice power processing. Detailed analysis and operations of a hybrid mode PFC pre-regulator which employs both active and passive PFC techniques at different time slots are presented. The approach can achieve high power conversion efficiency, as well as low output voltage stresses on switch and bulk capacitor. Furthermore, analyses of PF and losses of components with the circuit inductance are also discussed. Experiments were performed to verify the effectiveness of the approach.

A novel single‐stage parallel high power factor correction AC/DC flyback converter: Dynamics and control

Based on the structure of parallel power factor correction, a novel single‐stage parallel high power factor correction AC/DC flyback converter is proposed in this paper. By use of a transformer with a tertiary winding, the novel converter inherently possesses a high power factor. It has low voltage stress across the bulk capacitor at light loads. In this paper, the operation principle of the proposed converter is analyzed, and then the ac small‐signal mathematical model is derived by averaging method. PI and sliding mode controllers are designed to achieve output voltage regulation on the basis of the derived model. The experimental measurements are provided to verify the accuracy of the theoretical analysis. It is shown that both controllers can regulate the output voltage under line and load variations. The inherent capacity for high power factor correction of the overall system is still maintained.

Predicting state of charge of lead-acid batteries for hybrid electric vehicles by extended Kalman filter

This paper describes and introduces a new nonlinear predictor and a novel battery model for estimating the state of charge (SoC) of lead-acid batteries for hybrid electric vehicles (HEV). Many problems occur for a traditional SoC indicator, such as offset, drift and long term state divergence, therefore this paper proposes a technique based on the extended Kalman filter (EKF) in order to overcome these problems. The underlying dynamic behavior of each cell is modeled using two capacitors (bulk and surface) and three resistors (terminal, surface and end). The SoC is determined from the voltage present on the bulk capacitor. In this new model, the value of the surface capacitor is constant, whereas the value of the bulk capacitor is not. Although the structure of the model, with two constant capacitors, has been previously reported for lithium-ion cells, this model can also be valid and reliable for lead-acid cells when used in conjunction with an EKF to estimate SoC (with a little variation). Measurements using real-time road data are used to compare the performance of conventional internal resistance ( R int) based methods for estimating SoC with those predicted from the proposed state estimation schemes. The results show that the proposed method is superior to the more traditional techniques, with accuracy in estimating the SoC within 3%.

VR Transient Improvement at High Slew Rate Load—Active Transient Voltage Compensator

To meet the stringent transient response requirements of a voltage regulator (VR) at high slew rate load current while keeping high VR efficiency, this paper proposes a new topology: active transient voltage compensator (ATVC). ATVC only engages in transient periods operating at several MHZ to handle ac current and main VR operates at low switching frequency for better efficiency mainly providing dc current. ATVC injects a very high slew rate current in step up load and recovers energy in step down load. With introduction of a transformer, ATVC significantly reduces its conduction and switching losses due to the reduced current. Also, the new topology reduces the number of VR bulk capacitors while keeping the same output impedance. A built prototype and detailed experimental results verify the theoretical analysis.

Three-phase three-level voltage source inverter with low switching frequency based on the two-level inverter topology

A new configuration of the three-phase three-level voltage source inverter has been presented. The proposed inverter is based on the two-level inverter. The inverter is built of one two-level conventional inverter, an auxiliary circuit which comprises of three bidirectional switches, and two bulk capacitor banks. A selected harmonic elimination control scheme is employed to achieve lower harmonic contents in the inverter output waveforms. Two-level inverter switches operate at the line power frequency (50 Hz) whereas the auxiliary circuit switches operate at twice line power frequency (100 Hz). To validate the proposed inverter, a low power prototype inverter has been designed and implemented; analytical, simulation and experimental results have been provided.

Analysis and Design for a Novel Single-Stage High Power Factor Correction Diagonal Half-Bridge Forward AC&amp;#8211;DC Converter

By means of components placement, the buck-boost and diagonal half-bridge forward converters are combined to create a novel single-stage high power factor correction (HPFC) diagonal half-bridge forward converter. When both the PFC cell and dc–dc cell operate in DCM, the proposed converter can achieve HPFC and lower voltage stress of the bulk capacitor. The circuit analysis of the proposed converter operating in <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$ DCM+ DCM$</tex> mode is presented. In order to design controllers for the output voltage regulation, the ac small-signal model of the proposed converter is derived by the averaging method. Based on the derived model, the proportional integral (PI) controller and minor-loop controller are then designed. The simulation and experimental results show that the proposed converter with the minor-loop controller has faster output voltage regulation than that with the PI controller despite the variations of line voltage and load. Finally, a 100-W prototype of the proposed ac–dc converter is implemented and the theoretical result is experimentally verified.

Synthesis and analysis for a novel single-stage isolated high power factor correction converter

A novel single-stage isolated high power factor correction (HPFC) converter operating in the discontinuous conduction mode is proposed in this paper. It is an integration of a buck-boost converter with a flyback converter by means of components placement and synchronous switching technology. It can achieve HPFC, tight output voltage regulation and lower voltage stress of the bulk capacitor, which is independent of the loads. The small-signal mathematical model for the proposed converter is derived separately by the averaging method and the current injected equivalent circuit approach. The IsSpice simulations and experimental results successfully verify the dynamics and performances of the proposed converter.

Nonlinear Observers for Predicting State-of-Charge and State-of-Health of Lead-Acid Batteries for Hybrid-Electric Vehicles

This paper describes the application of state-estimation techniques for the real-time prediction of the state-of-charge (SoC) and state-of-health (SoH) of lead-acid cells. Specifically, approaches based on the well-known Kalman Filter (KF) and Extended Kalman Filter (EKF), are presented, using a generic cell model, to provide correction for offset, drift, and long-term state divergence-an unfortunate feature of more traditional coulomb-counting techniques. The underlying dynamic behavior of each cell is modeled using two capacitors (bulk and surface) and three resistors (terminal, surface, and end), from which the SoC is determined from the voltage present on the bulk capacitor. Although the structure of the model has been previously reported for describing the characteristics of lithium-ion cells, here it is shown to also provide an alternative to commonly employed models of lead-acid cells when used in conjunction with a KF to estimate SoC and an EKF to predict state-of-health (SoH). Measurements using real-time road data are used to compare the performance of conventional integration-based methods for estimating SoC with those predicted from the presented state estimation schemes. Results show that the proposed methodologies are superior to more traditional techniques, with accuracy in determining the SoC within 2% being demonstrated. Moreover, by accounting for the nonlinearities present within the dynamic cell model, the application of an EKF is shown to provide verifiable indications of SoH of the cell pack.

A Novel Forward AC/DC Converter With Input Current Shaping and Fast Output Voltage Regulation Via Reset Winding

This work presents a novel simple forward AC/DC converter with harmonic current correction and fast output voltage regulation. In the proposed AC/DC converter, a transformer incorporating reset winding provides two main advantages. First, the bulk inductor used in the conventional boost-based power-factor-correction cell is omitted in the proposed converter, allowing significant volume and weight of magnetic material to be saved. Second, the voltage across the bulk capacitor can be held under 450 V by adjusting the transformer winding ratio, despite the converter operating in a wide range of input voltages (90/spl sim/265 V/AC). This new converter complies with IEC 61000-3-2 under a load range of 200 W and has fast output voltage regulation.

Improved Hybrid-Parallel Single Stage PFC Converter

This paper proposes an improved type of the Hybrid-Parallel Power-Factor-Correction (HP-PFC) converter. It has the advantage of a higher efficiency and improved input current waveform. This advantage achieved through changing new charging path of the bulk capacitor and balancing the power flow from the two transformers to the output. This new circuit has been analyzed using MATLAB/Simulink and confirmed with experiment. As a conclusion, it is confirmed that this improved HP-PFC converter complies with the severe regulation of IEC61000-3-2 Class D. Moreover, a high efficiency of 90% is achieved for 15 V/6 A output power under the worldwide line voltage conditions.

Flexible and Low Cost Design for a Flyback AC/DC Converter With Harmonic Current Correction

This study presents a new simple flyback ac/dc converter with harmonic current correction and fast output voltage regulation. In the proposed ac/dc converter, an extra winding wound in the transformer provides two key advantages. The size of the bulk inductor used in the conventional boost-based power factor correction cell can be significantly reduced in the proposed converter. The voltage across bulk capacitor can be held under 450V by tuning the transformer winding ratio even though the converter operates in a wide range of input voltages (90 V/spl sim/265V/ac). This new converter complies with IEC 61000-3-2 under the load range of 200 W, and can achieve fast output voltage regulation.

Dynamics analysis of a single-stage isolated high power factor converter with a magnetic switch

The dynamics analysis of a single-stage isolated high power factor correction (PFC) converter is presented. In the single-stage PFC converter, the boost converter is operating in discontinuous conduction mode to exhibit an inherent gift of high power factor. It is integrated with a flyback converter that is operating in continuous conduction mode to achieve tight output voltage regulation. In addition, a magnetic switch is added to effectively reduce the high stress voltage across the bulk capacitor. Based on the averaging method, a nonlinear state-variable description of the converter is established. The small-signal model linearised around the operating point is then derived. The average power balance method, IsSpice simulation and experimental results successfully verify the dynamics and performances of the converter.

Flyboost Power Factor Correction Cell and a New Family of Single-Stage AC/DC Converters

A novel power factor correction (PFC) cell, called flyboost, is presented. The proposed PFC cell combines power conversion characteristics of conventional flyback and boost converters. Based on the flyboost PFC cell, a new family of single-stage (S/sup 2/) ac/dc converters can be derived. Prominent features of newly derived S/sup 2/ converters include: three power conversions, i.e., boost, flyback, and another isolated dc/dc power conversions are simultaneously realized that typically uses only one power switch and one simple controller; part of the power delivered to the load is processed only once; bulk capacitor voltage can be clamped to the desired level; and capable of operating under continuous current mode. Experimental results on example converters verify that while still achieving high power factor and tight output regulation, the flyboost PFC cell substantially improve the efficiency of the converter.

Analysis of the Power Delivery Path From the 12-V VR to the Microprocessor

This paper offers a thorough analysis of the power delivery path. Based on the power delivery path model, the current slew rate of each loop is derived. The relationship between the inductor current slew rate of the voltage regulator (VR) and the bandwidth is also derived. Then, the level of the voltage spike across the capacitors of each loop is determined, after which the relationship between the bandwidth and the capacitance can be plotted. We find that for today's power delivery structure, the bulk capacitors can be eliminated as long as the bandwidth is pushed beyond 350 kHz. The experimental results of a 2-MHz two-stage 12-V VR verify this analysis.

Single-Switch Parallel Power Factor Correction AC–DC Converters With Inherent Load Current Feedback

Single-stage power factor correction (PFC) ac-dc converters usually suffer from high bulk capacitor voltage stress and extra switch current stress. Bulk capacitor voltage feedback with a coupled-winding structure can dramatically alleviate the stresses. However, this type of feedback is indirect because the feedback only occurs after the bulk capacitor voltage increases. This paper presents a family of single-switch single-stage parallel PFC ac-dc converters with inherent load current feedback. Unlike the bulk capacitor voltage feedback, which utilizes the decreased duty ratio and the increased bulk capacitor voltage to reduce the input power at light load, the load current feedback can reduce the input power automatically at light load while maintaining an unchanged duty ratio. The proposed converters combine the advantages of simple topology, low bulk capacitor voltage, and no extra current stress across the switch. The concept is verified using an ac-dc converter with universal-line input and 5-V, 60-W output power. The input current harmonics meet IEC1000-3-2 Class D requirements.

EVALUATION OF THE CLASS E AMPLIFIER WITH TWO CURRENT SOURCES USED AS A HIGH-POWER-FACTOR ELECTRONIC BALLAST FOR COMPACT FLUORESCENT LAMPS

In this paper a novel class E amplifier with two current sources used to implement high-power-factor electronic ballast for fluorescent lamps is presented and evaluated. The circuit is based on the class E amplifier with two current sources, one of them was implemented using the main input voltage and the other by means of a bulk capacitor charged from the resonant tank of the class E amplifier. This topology presents a high power factor and low current crest factor and only uses one switch with zero voltage switching. Design guidelines are presented and a 300-kHz electronic ballast for a 32-W compact fluorescent lamp was designed and tested.

Design and experimental results of an input-current-shaper based electronic ballast

This paper presents some design issues and experimental results regarding the use of the input current shaper (ICS) technique to implement high power factor electronic ballasts. The ICS is placed between main rectifier and bulk capacitor to increase the conduction angle of the main rectifier diodes up to a minimum value to obtain low current harmonics injected to the mains. Two possibilities to implement ICS-based ballast are considered in this paper: the forward-based ICS and the flyback-based ICS. Experimental results obtained from two 40-W fluorescent lamp ballasts are also presented.

Voltage and current stress reduction in single-stage power factor correction AC/DC converters with bulk capacitor voltage feedback

Single-stage power factor correction (PFC) AC/DC converters integrate a boost-derived input current shaper (ICS) with a flyback or forward DC/DC converter in one single stage. The ICS can be operated in either discontinuous current mode (DCM) or continuous current mode (CCM), while the flyback or forward DC/DC converter is operated in CCM. Almost all single-stage PFC AC/DC converters suffer from high bulk capacitor voltage stress and extra switch current stress. The bulk capacitor voltage feedback with a coupled winding structure is widely used to reduce both the voltage and current stresses in practical single-stage PFC AC/DC converters. This paper presents a detailed analysis of the bulk capacitor voltage feedback, including the relationship between bulk capacitor voltage, input current harmonics, voltage feedback ratio, and load condition. The maximum bulk capacitor voltage appears when the DC/DC converter operates at the boundary between CCM and DCM. This paper also reveals that only the voltage feedback ratio determines the input current harmonics under DCM ICS and CCM DC/DC operation. The theoretical prediction of the bulk capacitor voltage as well as the predicted input harmonic contents is verified experimentally on a 60 W AC/DC converter with universal-line input.