Active input-voltage and load-current sharing in input-series and output-parallel connected modular DC-DC converters using dynamic input-voltage reference scheme

This paper explores a new configuration for modular DC/DC converters, namely, series connection at the input, and parallel connection at the output, such that the converters share the input voltage and load current equally. This is an important step toward realizing a truly modular power system architecture, where low-power, low-voltage, building block modules can be connected in any series/parallel combination at input or at output, to realize any given system specifications. A three-loop control scheme, consisting of a common output voltage loop, individual inner current loops, and individual input voltage loops, is proposed to achieve input voltage and load current sharing. The output voltage loop provides the basic reference for inner current loops, which is modified by the respective input voltage loops. The average of converter input voltages, which is dynamically varying, is chosen as the reference for input voltage loops. This choice of reference eliminates interaction among different control loops. The input-series and output-parallel (ISOP) configuration is analyzed using the incremental negative resistance model of DC/DC converters. Based on the analysis, design methods for input voltage controller are developed. Analysis and proposed design methods are verified through simulation, and experimentally, on an ISOP system consisting of two forward converters.     

基于开环的临界续断模式交错并联Boost PFC

文中主要研究的对象是开环控制的交错并联BOOST PFC,且工作于临界续断模式,它的从变换器与主变换器在开通时同步,且主从变换器都工作在电流模式。文章指出只有这种主从方式能提供一个稳定的开环工作点。仿真实验设计了一台输入功率为400W,宽范围输入电压,400V输出电压的实验样机,实验结果验证了理论分析的正确性。     

Isolated DC-DC converters with high-output voltage for TWTA telecommunication satellite applications

Two alternatives for the implementation of an isolated DC-DC converter operating with a high output voltage and supplied by an unregulated low input voltage are presented in this paper. The proposed topologies are especially qualified for the implementation of travelling wave tube amplifiers (TWTA) utilized in telecommunication satellite applications due to their low mass and volume and their high-efficiency. The converters studied follow different principles and the main operational aspects of each topology are analyzed. A two-stage structure composed by a regulator connected in series with a ZVS/ZCS isolated DC-DC converter is the first topology proposed. The second topology studied is an isolated single-stage converter that continues being highly efficient even with a large input voltage variation. The experimental results obtained from two prototypes, implemented following the design procedures developed, are presented, verifying experimentally the characteristics and the analysis of the proposed structures. The prototypes are developed for an application requiring an output power of 150 W, a total output voltage of 3.2 kV and an input voltage varying from 26 V to 44 V. The minimum efficiency obtained for both converters operating at the nominal output power, is equal to 93.4% for the two-stage structure and equal to 94.1% for the single-stage converter.     

Novel soft-switching DC-DC converter with full ZVS-range andreduced filter requirement. I. Regulated-output applications

A novel soft-switching topology for DC-DC converters is proposed. It is well suited for applications in the range of a few hundred watts to a few kilowatts. It is essentially a hybrid combination of an uncontrolled half-bridge section and a phase-shift controlled full-bridge section, realized with just four switches. The main features of the proposed topology are zero-voltage-switching down to no-load without serious conduction loss penalty, constant frequency operation and, near-ideal filter waveforms. The improved filter waveforms result in significant savings in the input and output filter requirement, resulting in high power-density. The new topology requires two transformers and two DC-bypass capacitors. The combined VA rating of the two transformers is more than that of the single transformer of conventional full-bridge converters, for variable-input applications. In Part I of the paper, the converter operation is analyzed for typical switch-mode power supply applications, where the input voltage varies widely but the output voltage is fixed and is well regulated. Experimental results obtained from a 100 W/200 kHz proof-of-concept prototype confirm the superior features of the proposed hybrid configuration     

Single-stage three-phase buck-boost type AC-DC converter with highpower factor

A new control process for single-stage three-phase buck-boost type AC-DC power converters with high power factor, sinusoidal input currents and adjustable output voltage is proposed. This converter allows variable power factor operation, but this work focus on achieving unity power factor. The proposed control method includes a fast and robust input current controller based on a vectorial sliding mode approach. The active nonlinear control strategy applied to this power converter, allows high quality input currents. Given the comparatively slow dynamics of the DC output voltage, a proportional integral (PI) controller is adopted to regulate the converter output voltage. The voltage controller modulates the amplitudes of the current references, which are sinusoidal and synchronous with the input source voltages. Experimental results from a laboratory prototype show the high power factor and the low harmonic distortion characteristics of the circuit     

DC-DC converter: four switches V/sub pk/=V/sub in//2, capacitive turn-off snubbing, ZV turn-on

A new four-switch full-bridge dc-dc converter topology is especially well-suited for power converters operating from high input voltage: it imposes only half of the input voltage across each of the four switches. The two legs of a full-bridge converter are connected in series with each other, across the dc input source, instead of the usual topology in which each leg is connected across the dc source. The topology reduces turn-off switching losses by providing capacitive snubbing of the turn-off voltage transient, and eliminates capacitor-discharge turn-on losses by providing zero-voltage turn-on. (Switching losses are especially important in converters operating at high input voltage because turn-on losses are proportional to the square of the input voltage, and turn-off losses are proportional to the input voltage). The topology is suitable for resonant and nonresonant converters. It adds one bypass capacitor and one commutating inductor to the minimum-topology full-bridge converter (that inductor is already present in many present-day converters, to provide zero-voltage turn-on, or is associated with one or two capacitors to provide resonant operation), and contains a dc-blocking capacitor in series with the output transformer, primary winding, and some nonresonant converters (that capacitor is already present in resonant power converters). The paper gives a theoretical analysis, and experimental data on a 1.5-kW example that was built and tested: 600-Vdc input, 60-Vdc output at up to 25A, and 50-kHz switching frequency. The measured performance agreed well with the theoretical predictions. The measured efficiency was 93.6% at full load, and was a maximum of 95.15% at 44.8% load.     

Soft switching resonant converter with duty-cycle control in DC micro-grid system

Resonant converter has been widely used for the benefits of low switching losses and high circuit efficiency. However, the wide frequency variation is the main drawback of resonant converter. This paper studies a new modular resonant converter with duty-cycle control to overcome this problem and realise the advantages of low switching losses, no reverse recovery current loss, balance input split voltages and constant frequency operation for medium voltage direct currentgrid or system network. Series full-bridge (FB) converters are used in the studied circuit in order to reduce the voltage stresses and power rating on power semiconductors. Flying capacitor is used between two FB converters to balance input split voltages. Two circuit modules are paralleled on the secondary side to lessen the current rating of rectifier diodes and the size of magnetic components. The resonant tank is operated at inductive load circuit to help power switches to be turned on at zero voltage with wide load range. The pulse-width modulation scheme is used to regulate output voltage. Experimental verifications are provided to show the performance of the proposed circuit.     

Simple Unified Approach to Develop a Time-Domain Modulation Strategy for Single-Phase Multilevel Converters

Single-phase power converters are widely used in power applications as photovoltaics and fuel-cell power conditioners. In addition, multilevel converters are a well-known solution in order to achieve high-quality output waveforms in power systems. In this paper, a time-domain duty-cycle computation technique for single-phase multilevel converters named 1DM is presented. The proposed technique is based on geometrical calculations with outstanding simplicity and generality. The proposed modulation technique can be easily applied to any multilevel converter topology carrying out the necessary calculations. The most common multilevel converter topologies have been studied in this paper as examples to introduce the proposed modulation strategy. Any other multilevel converter topology could be studied, and the corresponding 1DM could be easily developed. In addition, the well-known optimized voltage balance strategy for voltage capacitor control using the redundant switching states of the system is applied working with the proposed 1DM method, showing that both techniques are compatible. Experimental and simulation results for several single-phase multilevel converters are shown to validate the proposed modulation technique.      

A performance comparison of PWM rectifiers and synchronous linkconverters

PWM AC/DC power converters have been shown to be superior to thyristor phase-controlled rectifiers in terms of power factor and input current/output voltage harmonics. This paper presents a systematic comparison of the two topologies, the current-source topology and the voltage-source topology, from the point of view of power converter and switch kVA ratings, filtering requirements, power factor, operating regions, and control aspects     

Combined deadbeat control of a series-parallel convertercombination used as a universal power filter

This paper presents the notion of combined control of a system of interconnected power electronic converters. The concept is demonstrated using a three-phase series-parallel active power filter as an example. The described active power filter consists of a series-parallel combination of two full bridge VSIs capable of arbitrarily controlling the input current and output voltage. The proposed control scheme treats the converter combination as a single unit and uses the inverse system model to generate deadbeat control response for both input current and output voltage. A full-order predictive state observer is used to reduce the number of sensors. Simulation results show better disturbance rejection characteristics of the proposed control when compared to the separately controlled converter scheme     

New zero voltage switching DC converter with flying capacitors

A new soft switching converter is presented for medium power applications. Two full-bridge converters are connected in series at high voltage side in order to limit the voltage stress of power switches at V_in/2. Therefore, power metal–oxide–semiconductor field-effect transistors (MOSFETs) with 600 V voltage rating can be adopted for 1200 V input voltage applications. In order to balance two input split capacitor voltages in every switching cycle, two flying capacitors are connected on the AC side of two full-bridge converters. Phase-shift pulse-width modulation (PS-PWM) is adopted to regulate the output voltage. Based on the resonant behaviour by the output capacitance of MOSFETs and the resonant inductance, active MOSFETs can be turned on under zero voltage switching (ZVS) during the transition interval. Thus, the switching losses of power MOSFETs are reduced. Two full-bridge converters are used in the proposed circuit to share load current and reduce the current stress of passive and active components. The circuit analysis and design example of the prototype circuit are provided in detail and the performance of the proposed converter is verified by the experiments.     

Uniform Voltage Distribution Control for Series Connected DC–DC Converters

This paper investigates applications of current-mode, shared-bus commercial-off-the-shelf (COTS) dc-dc converters to power system architectures configured as parallel-input, series-output (PISO) and series-input, parallel-output (SIPO). By employing a PISO (or SIPO) architecture, current-mode COTS converters can transform their system input voltage to higher (or lower) system output voltage, provide ease and flexibility of power expansion, and preserve system efficiencies equal to those of standalone converters. Nonuniform output (or input) voltages still exist within a PISO (or SIPO) power system using identical converters when the system lacks proper distribution control of the series connected output (or input) voltages-and thus, system reliability suffers from thermal overstress to the converters that contribute a greater portion of the output power. Through unified approaches of voltage distribution control for the PISO and SIPO architectures, a series-connected converter power system attains robust stability and reliability. Two effective approaches to uniform voltage distribution control-the central-limit and maximum-limit voltage distribution-will be discussed. Both computer simulation and experimental prototypes validate both of the uniform voltage distribution power converter architectures.     

DC/DC Conversion Systems Consisting of Multiple Converter Modules: Stability, Control, and Experimental Verifications

This paper investigates dc/dc conversion systems constructed from connecting multiple converter modules in series and/or parallel at both the input and output sides. Control strategies aiming at achieving proper sharing of the voltage and/or current at the input or output sides are studied in detail. The relationship between sharing of input voltages/currents and that of output voltages/currents is studied. In particular, the inherent stability of control operations applied at the input side and the output side is analyzed. Based on the analysis, a general control strategy for series–parallel systems, which decouples the output voltage control loop and the sharing control loop, is proposed. Furthermore, three modularization architectures are proposed for input-series–output-parallel (ISOP), input-parallel–output-series (IPOS), and input-series–output-series (ISOS) connected systems. These architectures enjoy full advantages of modularization and no external controller is needed to coordinate the sharing control for the individual modules. Experimental prototypes are built and tested to validate the general control strategy and the proposed modularization architectures.      

A parallel-connected single phase power factor correction approach with improved efficiency

In this paper, a new parallel-connected single phase power factor correction (PFC) topology using two flyback converters is proposed to improve the output voltage regulation with simultaneous input power factor correction and control. This approach offers lower cost and higher efficiency by parallel processing of the total power. Flyback converter-I primarily regulates output voltage with fast dynamic response and processes 55% of the power. Flyback converter-II with ac/dc PFC stage regulates input current shaping and PFC, and processes the remaining 45% of the power. This paper presents a design example and circuit analysis for 200 W power supply. A parallel-connected interleaved structure offers smaller passive components, less losses even in continuous conduction inductor current mode, and reduced volt-ampere rating of dc/dc stage converter. TI-DSP, TMS320LF2407, is used for implementation. Simulation and experimental results show the performance improvement.     

A hybrid structure using phase-controlled rectifiers andhigh-frequency converters for magnet-load power supplies

Thyristor rectifiers are still the preferred choice for large magnet power supplies. However, large harmonic voltages, resulting in large current ripple, and slow dynamic response are major drawbacks of these converters. This paper presents a topology and a control technique for hybrid large-power high-precision magnet power supplies. The system consists of a phase controlled rectifier connected in series with a high-frequency PWM converter. The rectifier is designed to handle the main output power and the PWM converter is used only for harmonics cancellation and error compensation. A feedforward control scheme is proposed to ensure that the desired power sharing is maintained during both the steady state and transient operations. The operating principles of the proposed structure are discussed in the paper, and the results from a 1 kVA experimental setup are provided to validate the proposed topology     

Feed-Forward Space Vector Modulation for Single-Phase Multilevel Cascaded Converters With Any DC Voltage Ratio

Modulation techniques for multilevel converters can create distorted output voltages and currents if the dc-link voltages are unbalanced. This situation can be avoided if the instantaneous dc voltage error is not taken into account in the modulation process. This paper proposes a feed-forward space vector modulation method for a single-phase multilevel cascade converter. Using this modulation technique, the modulated output voltage of the power converter always generates the reference determined by the controller, even in worst case voltage unbalance conditions. In addition, the possibility of optimizing the dc voltage ratio between the H-bridges of the power converter is introduced. Experimental results from a 5-kVA prototype are presented in order to validate the proposed modulation technique.      

Cyclic-averaging for high-speed analysis of resonant converters

The paper describes the development and application of a cyclic-averaging technique for the rapid analysis of high-order resonant power converters. To provide a focus to the paper, particular emphasis is given to a 3rd-order LCC voltage output converter topology. The proposed methodology predicts steady-state voltages and currents throughout the circuit, and provides estimates of the stresses on the resonant circuit components. State-space simulations and experimental results from a 350 V-input/150 V-output converter are used to demonstrate a prediction accuracy comparable with time-domain integration-based techniques is achievable, while requiring only 1/10,000th of the computation time. In addition, a comparison with Spice simulation results shows that cyclic averaging provides commensurate predictions of voltage and current stresses on the resonant circuit components. Issues arising from the stray capacitance associated with the resonant inductor, and the corresponding sensitivity of the predicted output voltage, are also considered.     

Control of Single-Phase-to-Three-Phase AC/DC/AC PWM Converters for Induction Motor Drives

This paper proposes a novel control scheme of single-phase-to-three-phase pulsewidth-modulation (PWM) converters for low-power three-phase induction motor drives, where a single-phase half-bridge PWM rectifier and a two-leg inverter are used. With this converter topology, the number of switching devices is reduced to six from ten in the case of full-bridge rectifier and three-leg inverter systems. In addition, the source voltage sensor is eliminated with a state observer, which controls the deviation between the model current and the system current to be zero. A simple scalar voltage modulation method is used for a two-leg inverter, and a new technique to eliminate the effect of the dc-link voltage ripple on the inverter output current is proposed. Although the converter topology itself is of lower cost than the conventional one, it retains the same functions such as sinusoidal input current, unity power factor, dc-link voltage control, bidirectional power flow, and variable-voltage and variable-frequency output voltage. The experimental results for the V/f control of 3-hp induction motor drives controlled by a digital signal processor TMS320C31 chip have verified the effectiveness of the proposed scheme     

Digital Control of Three-Phase Series-Parallel Uninterruptible Power Supply Systems

In this paper, a new digital deadbeat controller is designed, implemented, and applied to a three-phase series-parallel line-interactive uninterruptible power supply (UPS). This kind of UPS system provides input power factor correction, output voltage conditioning, and high efficiency. The objective of the controller is to achieve deadbeat dynamic response for the parallel and series converters. The proposed controller adjusts the current of the parallel converter and voltage of the series converter with two and four sampling periods, respectively. A reduced-parts topology is also introduced that has less number of power electronics components as well as switching functions. The power flow of the system in the presence of current and voltage harmonics is discussed. Simulation and experimental results are presented, which show the viability of the proposed controller for this topology.     

一种改进的二极管箝位型多电平变换器拓扑

多电平电路在高压大功率领域的拓展受到其复杂电路拓扑的制约,因此近年来不断有新型多电平电路结构被提出。本文在传统多电平逆变器拓扑结构的基础上,提出了一种新型单相七电平电压源逆变器拓扑。新型电路拓扑是在传统的单相全桥五电平箝位二极管电路基础上,增加了两个开关器件,利用10个开关器件以及4个箝位二极管产生了7种不同的电平输出。详细分析了该逆变器的拓扑结构,给出了PWM控制策略。最后通过仿真实验验证了这种拓扑的可行性。该逆变器对传统箝位二极管逆变器在结构上做出了优化。