Discontinuous Capacitor Voltage Mode Research Articles

An Input-Series Output-Parallel Modular Three-Phase AC–AC Capacitive-Link Power Converter

Modular converters with stackable cells are widely used in high-power applications, where the voltages and/or currents are beyond the ratings of the commercially available switches. Majority of existing modular converter topologies are based on dc-link converters that require several electrolytic capacitors with large capacitances, which reduce the lifetime of the power converter and increase size and volume. This article proposes an input-series output-parallel modular three-phase ac-ac universal power converter, which is formed by three identical and stackable capacitive-link modules that do not require electrolytic capacitors for power conversion. Exclusion of the electrolytic capacitors is achieved by operating the modules in discontinuous capacitor voltage mode. Each module requires two film capacitors with very small capacitances for transferring the power and provides galvanic isolation through high-frequency transformers. Utilization of film capacitors with small capacitances enhances the reliability. Furthermore, the proposed stackable capacitive-link modules enable a scalable and modular design. In this article, power cells are connected in series at the input and in parallel at the output to form a modular universal power converter that can share voltage/current among the power cells in an ac-ac power conversion system. Frequency transformation and voltage step-up/-down are among the other features of the proposed converter. The details of the operation principles along with design considerations are discussed in this article. Moreover, the proposed modular power converter with two power cells is evaluated through simulations and experiments.

Soft-Switching Bridgeless Buck–Boost PFC Converter Using Single Magnetic Core

In this article, a new bridgeless single-phase buck-boost power factor correction (PFC) converter with one magnetic core is introduced. The proposed converter is designed to operate in discontinuous capacitor voltage mode (DCVM) to achieve low total harmonic distortion (THD) and continuous input current with a simple structure. The DCVM operation gives additional advantages, such as inherent PFC, low turn-off losses, and reduced complexity of the control circuitry. Unlike the buck converter, the proposed converter eliminates the dead angle of input current without adding any extra circuits. Also, by eliminating two input diodes in power flowing path, the efficiency is further improved. Due to achieved almost zero current switching at the turn-on and almost zero voltage switching at the turn-off, the switching losses are eliminated. In this article, theoretical analysis and principal operation of the converter are discussed. An experimental prototype is implemented to verify the performance of the proposed converter. Experimental results are presented for a 120-W prototype at 110-V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> input and 48-V output.

Series-Capacitor-Based Buck PFC Converter With High Power Factor and Ultrahigh Step-Down Conversion Ratio

In this paper, a series-capacitor-based interleaving buck power factor correction (PFC) converter is proposed, the intermediate energy storage capacitance of which is operated at discontinuous capacitor voltage mode (DCVM), and automatic power factor (PF) correction for this converter is obtained. Moreover, the voltage across the series capacitor of the proposed PFC converter is clamped at the input voltage, and thus peak voltage stress existed in the traditional DCVM buck PFC could be relieved. By effectively regulating the charge/discharge time for the series capacitor, ultrahigh step-down conversion ratio of the proposed converter is achieved, the conversion ratio of which is independent of the duty cycle and only related to the switching frequency and circuit parameters. Therefore, high PF can be obtained due to very narrow deadtime of the input current. Meanwhile, the proposed PFC converter can realize the soft turn- on of part power switch and soft turn- off of part power diodes. In addition, comparing with the traditional discontinuous inductor current mode PFC, the input current of the proposed PFC converter is continuous so that the peak value and root-mean-square value of input current can be reduced. The operational principle, performance analysis, and parameter design principle are given in this paper. The analysis results show that the PF and total harmonic distortion are also independent of the duty cycle. Finally, a 220-Vac input, 60 W/15 V output experimental prototype is built to verify the validity of the theoretical analysis.

Effect of intermediate capacitance on slow‐scale instability of Cuk power factor correction converter operating in discontinuous capacitor voltage mode

Due to features of near-unity power factor, soft turn-off switching and low switch current stress, Cuk power factor correction (PFC) converter operating in discontinuous capacitor voltage mode (DCVM) has attracted much attention. However, it is found that with the increase of intermediate capacitance, slow-scale instability occurs in voltage mode control (VMC) DCVM Cuk PFC converter. In this study, a simplified model for VMC DCVM Cuk PFC converter is established, upon which the effect of intermediate capacitance on the slow-scale instability and the corresponding bifurcation behaviours are studied by using harmonic balance method and Floquet theory. Furthermore, the stability boundaries in terms of the intermediate capacitance under different load resistance and input voltage are given, which is helpful for parameter design of VMC DCVM Cuk PFC converter. Finally, numerical simulations and experimental results are provided to verify the analysis results.

A Novel Control for a Cascaded Buck–Boost PFC Converter Operating in Discontinuous Capacitor Voltage Mode

This paper presents a new dual-switch control structure for an ac/dc noninverting cascaded buck–boost power factor correction converter. The proposed converter operates at a discontinuous capacitor voltage mode providing an inherent high-power factor and a zero voltage turn-off switching. Additionally, the proposed control structure enables for a nondistorted sinusoidal current for a wide range of output voltage levels. Unlike the conventional methods, a mode detector is not required and consequently there is no hard transition between buck and boost modes. Although both converter switches are controlled, only one feedback control loop is required to obtain the desired power flow at a unity power factor. The principle of operation, theoretical analysis, simulation, and experimental results of a 1.6-kW prototype grid-connected converter are presented. The results confirmed the validity of the proposed system under various operating conditions.

Low‐power single‐stage power factor rectifier based on discontinuous capacitor voltage mode double‐ended forward converter

A double-ended forward converter with an input inductor-capacitor (LC) filter operating in discontinuous capacitor voltage mode is proposed in this study. The most important advantage of the proposed topology is that the operations of the proposed converter make the switches bear only a portion of the peak capacitor voltage without any extra control and auxiliary winding, which result in a relatively low switches voltage stress. This study presents a detailed analysis of the switch voltage stress. The experimental results for a 36 Vdc/100 W are presented.

Power Factor Correction With a Modified Sheppard–Taylor Topology Operating in Discontinuous Capacitor Voltage Mode and Low Output Voltage

In this paper, a modified Sheppard-Taylor converter operating in continuous inductor current mode and discontinuous capacitor voltage mode (CICM/DCVM) is studied and implemented. The operation sequences are described and the averaged model of the converter over a switching cycle is developed. With the obtained, the dc characteristics of the converter were derived, and design criteria for components selection to ensure DCVM operation were reported. The converter is then used for power factor correction in a single-phase rectifier with a front-end diode-bridge. This mode of operation provides the converter some desirable features: zero-voltage turnoff switching and natural purely resistive behavior at low dc output voltage level. This can be achieved by simply using an open-loop control, which offers better reliability than the CICM/CCVM previously reported in the literature, where feedback control is required. The theoretical study of the converter is presented and validated through experimental measurements carried out on a 500 W laboratory prototype. It is shown that this rectifier exhibits an input power factor higher than 99.7% and a source current distortion lower than 6% at small output voltage level.

Small‐signal model analysis and control design of a double‐ended forward converter in discontinuous‐capacitor‐voltage mode

A double-ended forward converter with an input inductor–capacitor filter has inherent power factor correction (PFC) properties and continuous input current when operating in discontinuous-capacitor-voltage mode (DCVM). In this study, the minimum separable switching configuration modelling is applied to the proposed converter operating in DCVM to obtain a small-signal model of the converter. The impact of the circuit parameters on the small-signal characteristic are discussed in details. The difference between the small-signal behaviour of the converter when operating as a DC/DC converter and a PFC converter is investigated. The modelling methodology is intended for the design of controllers in closed-loop operation. A 100 W prototype is implemented to demonstrate the feature of the small-signal behaviour.

Bridgeless High-Power-Factor Buck-Converter Operating in Discontinuous Capacitor Voltage Mode

In this paper, a new bridgeless single-phase ac-dc power factor correction (PFC) rectifier based on buck topology operating in discontinuous capacitor voltage mode (DCVM) is proposed. The bridgeless topology and the presence of only one or two semiconductor switches in the current flowing path during each interval of the switching cycle result in lower conduction losses compared with the conventional DCVM buck PFC rectifier. The DCVM operation offers additional advantages such as zero-voltage turn-off in the power switches, zero-voltage turn-on in the output diode, and continuous input current. Hence, the electromagnetic interference noise emission is minimized. The converter achieves high power factor naturally with low total harmonic distortion in the input current. Theoretical analysis and experimental results for 100 W/48 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</sub> at 100 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> line voltage are provided to evaluate the performance of the proposed scheme. The measured conversion efficiency reached 96.3%.

Dynamic Model Development and Variable Switching-Frequency Control for DCVM Cúk Converters in PFC Applications

A Cuk converter operating in discontinuous capacitor voltage mode (DCVM) is an inherent power factor correction converter. A reduced-order switch-network model of a Cuk converter in DCVM is developed, which is valid for both dc-dc and ac-dc applications. The model can be used for controller analysis and design. Moreover, a fast dynamic response controller is proposed, which is an integration of a switching-frequency control unit and a proportional-integral (PI) controller. The PI controller is in charge of duty ratio adjustment. In the proposed controller, unlike conventional PI controllers, switching frequency is no longer fixed and varies as load changes. The switching-frequency control unit reacts much faster than the PI controller and instantly compensates for the output voltage in case of drastic load change, thus significantly improving the transient response. Furthermore, the proposed control scheme keeps the switch voltage stress constant, which eases switch selection and improves converter reliability.

DICM and DCVM of a PFC-based SEPIC-fed PMBLDCM Drive

This paper deals with two different discontinuous conduction modes of a Power Factor Corrected (PFC) Single Ended Primary Inductor Converter (SEPIC) -fed Permanent Magnet Brushless DC Motor (PMBLDCM) Drive. A novel scheme of speed control of PFC-based SEPIC-fed PMBLDCM drive is proposed using a single voltage sensor. The SEPIC is operated in a Discontinuous Inductor Current Mode (DICM) and Discontinuous Capacitor Voltage Mode (DCVM) feeding PMBLDCM Drive. A Diode Bridge Rectifier (DBR) fed from a single-phase AC supply followed by a SEPIC DC-DC converter is used for power factor correction. A three-phase Voltage Source Inverter (VSI) is used for the electronic commutation of the PMBLDC motor. The speed control is achieved by controlling the DC link voltage of the VSI. A voltage follower approach is used to control the DC link voltage of the front-end SEPIC converter. The developed model of the system is used to simulate the performance of the drive system to achieve improved power quality at AC mains with a wide range of speed control.

Single‐stage single‐switch power factor correction converter based on discontinuous capacitor voltage mode buck and flyback converters

A new single-switch, single-stage power factor correction (PFC) converter based on discontinuous capacitor voltage mode (DCVM) is presented in this study. The conventional single-stage PFC converters have high voltage across their bulk capacitor which imposes high voltage stress on the switch and also the bulk capacitor voltage stress increases at light load condition. The most important advantage of the proposed topology is that the voltage across the bulk capacitor is low and the input current is continuous. Furthermore, this topology does not have high voltage stress across the bulk capacitor at light loads. The proposed topology is derived from a DCVM buck converter integrated with a flyback converter. The proposed PFC topology contains low number of passive components and employs only one switch, resulting in reduced complexity and cost. The presented simulation and experimental results of the proposed converter justify the theoretical analysis.

Fuzzy Controlled Individual Cell Equalizers for Lithium-Ion Batteries

A fuzzy logic control battery equalizing controller (FLCBEC) is adopted to control the cell voltage balancing process for a series connected Li-ion battery string. The proposed individual cell equalizer (ICE) is based on the bidirectional Cuk converter operated in the discontinuous capacitor voltage mode (DCVM) to reduce the switching loss and improve equalization efficiency. The ICE with the proposed FLCBEC can reduce the equalizing time, maintain safe operations during the charge/discharge state and increase the battery string capacity.

A High-Quality Rectifier Based on Sheppard–Taylor Converter Operating in Discontinuous Capacitor Voltage Mode

This paper presents a single-phase soft-switched high power factor (PF) Sheppard-Taylor rectifier suitable for applications requiring low-voltage and high-current output. The proposed rectifier is designed to operate at discontinuous capacitor voltage mode. The Sheppard-Taylor converter in this mode of operation provides zero-voltage turnoff switching, as well as natural input PF correction over a wide range of input voltage, which makes the converter suitable for universal input applications. Due to its simplified control circuitry and reduced switch current stress, this converter presents better efficiency and higher reliability. In addition, the presented converter features continuous input-output currents, which result in low electromagnetic interference emission. Principle of operation, theoretical analysis, and experimental results from a laboratory prototype rated at 45 W/10 Vdc output voltage are presented. The measured efficiency and total harmonic distortion of the input line current were 85% and 3.2%, respectively. The input current harmonics meet the EN61000-3-2 Class D requirements.

Averaged-Switch Modeling of Fourth-Order PWM DC–DC Converters Considering Conduction Losses in Discontinuous Mode

This manuscript addresses dynamic average-value modeling for fourth-order pulse-width modulation (PWM) DC-DC converters in discontinuous capacitor-voltage mode. Although significant literature is devoted to analysis of the inductor-based switching stage of second-order DC-DC converters in discontinuous current mode, much less has been published regarding the discontinuous voltage mode in the capacitor-based switching stage in fourth-order converters. Accurate average-value models are further complicated by the presence of non-ideality in the switching stage components. This manuscript presents a full-order average-value model for the capacitor-based switching stage, taking into account conduction losses according to the energy conservation principle. The proposed model is validated with a hardware prototype and detailed simulation and is shown to accurately predict large-signal time-domain transients as well as small-signal frequency-domain characteristics.

Individual Cell Equalization for Series Connected Lithium-Ion Batteries

A systematic approach to the analysis and design of a bi-directional Cuk converter for the cell voltage balancing control of a series-connected lithium-ion battery string is presented in this paper. The proposed individual cell equalizers (ICE) are designed to operate at discontinuous-capacitor-voltage mode (DCVM) to achieve the zero-voltage switching (ZVS) for reducing the switching loss of the bi-directional DC/DC converters. Simulation and experimental results show that the proposed battery equalization scheme can not only enhance the bi-directional battery equalization performance, but also can reduce the switching loss during the equalization period. Two designed examples are demonstrated, the switch power losses are significantly reduced by 52.8% from the MOSFETs and the equalization efficiency can be improved by 68-86.9% using the proposed DCVM ZVS battery equalizer under the specified cell equalization process. The charged/discharged capacity of the lithium-ion battery string is increased by using the proposed ICEs equipped in the battery string.

Application of duality principle to synthesis of single‐stage power‐factor‐correction voltage regulators

AbstractThe duality principle is applied to derive new single‐stage power‐factor‐correction (PFC) voltage regulators. This paper begins with an application of duality transformation to conventional discontinuous‐conduction‐mode buck, buck‐boost and boost converters. The resulting dual converters operate in the discontinuous capacitor voltage mode. These new converters provide the same PFC property, but in the dual manner. It is proved that in the practical case of the input being a voltage source, the mandatory insertion of inductance between the voltage input and the ‘dual PFC converter’ does not affect the power‐factor‐correcting property. A new single‐stage PFC regulator is derived by taking the dual of a well‐known circuit based on a cascade of conventional boost and buck converters. Analytical design expressions are derived, illustrating the relation between current stress and component values. Experiments are performed to confirm the operation of the circuit and its power‐factor‐correcting capability. Copyright © 2003 John Wiley &amp; Sons, Ltd.

A novel maximum power point tracking technique for solar panels using a SEPIC or Cuk converter

A novel technique for efficiently extracting the maximum output power from a solar panel under varying meteorological conditions is presented. The methodology is based on connecting a pulse-width-modulated (PWM) DC/DC SEPIC or Cuk converter between a solar panel and a load or battery bus. The converter operates in discontinuous capacitor voltage mode whilst its input current is continuous. By modulating a small-signal sinusoidal perturbation into the duty cycle of the main switch and comparing the maximum variation in the input voltage and the voltage stress of the main switch, the maximum power point (MPP) of the panel can be located. The nominal duty cycle of the main switch in the converter is adjusted to a value, so that the input resistance of the converter is equal to the equivalent output resistance of the solar panel at the MPP. This approach ensures maximum power transfer under all conditions without using microprocessors for calculation. Detailed mathematical derivations of the MPP tracking technique are included. The tracking capability of the proposed technique has been verified experimentally with a 10-W solar panel at different insolation (incident solar radiation) levels and under large-signal insolation level changes.

High power factor rectifier based on buck converter operating in discontinuous capacitor voltage mode

The buck converter with LC input filter operating in discontinuous capacitor voltage mode has inherent power factor correction properties and continuous input current. The paper presents a detailed analysis of the converter operating in this mode, leading to design criteria. Finally, experimental results for a 48 V/sub dc//100 W converter are presented.

A comparison of parallel resonant converters operating in lagging power factor mode

Three different parallel resonant converter (PRC) configurations are compared for their performance. The discontinuous capacitor voltage mode is emphasized in the comparison and is shown not to exist in the case of PRC with the resonating capacitor on the primary side of the high-frequency (HF) transformer. It is further shown that the condition for discontinuous capacitor voltage (DCV) mode in the case of a PRC with the assumption of an ideal HF transformer and a PRC with secondary-side resonance differ only in the ratio M/(M+L+L/sub p/), which is equal to 1.0 for PRCs with the assumption of an ideal HF transformer. The comparison study shows that the PRC with the resonating capacitor on the primary side of a nonideal HF transformer is more appropriate for low-voltage high-current applications, while the PRC with resonating capacitor on the secondary side of a nonideal HF transformer is better suited to supply large-voltage medium- and low-current loads. Experimental results obtained from prototype units designed and built are presented to support the theory. >