Multifunctional Grid-Connected Multimodule Power Converters Capable of Operating in Single-Pulse and PWM Switching Modes

Pulsewidth-modulated (PWM) techniques equip power converters with unique features such as input-output linearity and control flexibility. Nevertheless, frequent switching of semiconductor switching devices causes considerable switching loss, and therefore makes traditional two-level PWM converters inappropriate for high-power applications. Two alternatives for building modular structures, namely multipulse and multimodule PWM converters were introduced to provide not only voltage and current sharing among the semiconductor switching devices, but also a high-quality output voltage at a much lower switching frequency. While multipulse converters offer minimal switching losses, low-order harmonic neutralization, and the best utilization of the inverter, multimodule PWM converters give control flexibility and power structure simplicity. This paper combines these two, and preserves the advantages of both multipulse and multimodule PWM converters. This not only provides an additional degree of freedom for voltage control, but also enables the converter to operate in PWM mode during transient and in single-pulse mode during the steady state. For the PWM switching mode, a special space vector strategy of 3 p.u. switching frequency is presented to maximize the voltage utilization and maintain a linear transfer characteristic. The power structure and control methods are analyzed, and validated by simulation and experimentally.     

A Systematic Approach to Synthesizing Multi-Input DC–DC Converters

The objective of this paper is to propose a general approach for developing multi-input converters (MICs). The derived MICs can deliver power from all of the input sources to the load either individually or simultaneously. By analyzing the topologies of the six basic pulsewidth modulation (PWM) converters, the method for synthesizing an MIC is inspired by adding an extra pulsating voltage or current source to a PWM converter with appropriate connection. As a result, the pulsating voltage source cells (PVSCs) and the pulsating current source cells (PCSCs) are proposed for deriving MICs. According to the presented synthesizing rules, two families of MICs, including quasi-MICs and duplicated MICs, are generated by introducing the PVSCs and the PCSCs into the six basic PWM converters.      

高频软开关PWM功率变换技术的发展与现状

本文介绍了三类零电压软件开关ＰＷＭ变换器和两类零电流软件开关ＰＷＭ变换器的特点和工作原理。     

Optimal PWM Control of Switched-Capacitor DC–DC Power Converters via Model Transformation and Enhancing Control Techniques

This paper presents an efficient and effective method for an optimal pulsewidth-modulated (PWM) control of switched-capacitor dc-dc power converters. Optimal switching instants are determined based on minimizing the output ripple magnitude, the output leakage voltage and the sensitivity of the output load voltage with respect to both the input voltage and the load resistance. This optimal PWM control strategy has several advantages over conventional PWM control strategies: 1) it does not involve a linearization, so a large-signal analysis is performed; and 2) it guarantees the optimality. The problem is solved via both the model transformation and the optimal enhancing control techniques. A practical example of the PWM control of a switched-capacitor dc-dc power converter is presented.     

Engineering design of lossless passive soft switching methods for PWM converters. II. With nonminimum voltage stress circuit cells

This paper proposes the analysis and design methodology of lossless, passive soft switching methods for PWM converters. The emphasis of the design and analysis is for PWM converters that use nonminimum voltage stress (non-MVS) circuit cells to provide soft switching. PWM converters with non-MVS circuit cells have several distinct advantages over converters that use minimum voltage stress (MVS) cells. With the same relative size of the inductor and capacitor added for soft switching, the non-MVS cells have a substantially larger duty ratio range where soft switching is guaranteed. In addition, the overcurrent stress of the main switch, under most conditions, will be lower and an optimum value of inductor and capacitor added for soft switching can be used. Therefore, with proper design, the non-MVS cells provide higher efficiency. These advantages are obtained with the price of higher switching voltage stress and one additional inductor. The loss model for a MOSFET and optimum capacitor and inductor values are utilized in the design procedure. Examples of the design procedure are given for PFC and DC-DC applications. Experimental results backup the claim of higher efficiency.     

Quasi-square-wave converters: topologies and analysis

A class of converters with zero-voltage or zero-current switching characteristics is analyzed using a method originally developed for quasiresonant and PWM (pulsewidth-modulated) converters. The method relies on identifying simple three-terminal structures, called converter sections, that contain the switches and the resonant tank elements. The various zero-voltage-switched and zero-current-switched converters are obtained by permutation of these converter sections between source and sink. The method unifies the analysis of this class of converters in a single equivalent circuit model. The voltage and current waveforms in these converters are essentially squarelike except during the turn-on and turn-off switching intervals     

Advanced Control and Analysis of Cascaded Multilevel Converters Based on P-Q Compensation

This paper introduces new controls for the cascaded multilevel power converter. This converter is also sometimes referred to as a ldquohybrid converterrdquo since it splits high-voltage/low-frequency and low-voltage/pulsewidth-modulation (PWM)-frequency power production between ldquobulkrdquo and ldquoconditioningrdquo converters respectively. Cascaded multilevel converters achieve higher power quality with a given switch count when compared to traditional multilevel converters. This is a particularly favorable option for high power and high performance applications such as naval ship propulsion. This paper first presents a new control method for the topology using three-level bulk and conditioning inverters connected in series through a three-phase load. This control avoids PWM frequency switching in the bulk inverter. The conditioning inverter uses a capacitor source and its control is based on compensating the real and reactive (P-Q) power difference between the bulk inverter and the load. The new control explicitly commands power into the conditioning inverter so that its capacitor voltage remains constant. A unique space vector analysis of hybrid converter modulation is introduced to quantitatively determine operating limitations. The conclusion is then generalized for all types of controls of the hybrid multilevel converters (involving three-level converter cells). The proposed control methods and analytical conclusions are verified by simulation and laboratory measurements.     

A systematic approach to developing single-stage soft switching PWMconverters

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     

Resonant link bidirectional power converter. I. Resonant circuit

This paper proposes a novel resonant circuit capable of PWM operation with zero switching losses. The resonant circuit is aimed at providing zero voltage intervals in the DC link of the PWM converter during the required converter device switching periods, and it gives minimum DC bus voltage stresses and minimum peak resonant current. It requires only two additional switches compared to a conventional PWM converter. It is observed that the resonant circuit guarantees the soft switching of all the switching power devices of converters including the switches for resonant operation. Simulation results and experimental results are presented to verify the operating principles     

Pseudo-resonant full bridge DC/DC converter

A DC-DC power converter topology that combines the ease of control and wide range of conventional DC-DC converters, with low switching losses, low dv/dt and low electromagnetic interference that is typical of zero voltage switched resonant converters is proposed. Consequently, the ratings of these components are substantially lower than for similarly rated resonant topologies. While resonant elements are used to ensure zero voltage switching of all devices, they have little or no role in the actual power transfer and can thus be reasonably sized. As the resonant elements are not involved in the primary power transfer, the converter is referred to as a pseudo-resonant converter. It is shown that the converter offers significantly higher levels of performance than either the pulse width-modulated (PWM) or typical resonant converters. Operation at very high frequencies is possible and is shown with the fabrication of a 200 W 1 MHz DC-DC converter     

Recent developments of high power converters for industry andtraction applications

The introduction of new high power devices like integrated gate commutated thyristors (IGCTs) and high voltage insulated gate bipolar transistors (IGBTs) accelerates the broad use of pulse width modulation (PWM) voltage source converters in industrial and traction applications. This paper summarizes the state-of-the-art of power semiconductors. The characteristics of IGCTs and high voltage IGBTs are described in detail. Both the design and loss simulations of a two level 1.14 MVA voltage source inverter and a 6 MVA three-level neutral point clamped voltage source converter with active front end enable a detailed comparison of both power semiconductors for high power PWM converters. The design and the characteristics of a commercially available IGCT neutral point clamped PWM voltage source converter for medium voltage drives are discussed. Recent developments and trends of traction converters at DC mains and AC mains are summarized     

Output voltage distortion characterization in multilevel PWM converters

One of the main features to consider in the development of new pulsewidth modulations (PWM) for multilevel converters is the high-frequency output-voltage distortion. In this letter, a novel per-switching-cycle figure, the harmonic distortion of order n for switching cycle k(HD/sub n,k/), is introduced to quantitatively characterize the output three-phase voltage harmonic distortion of multilevel converters around all the integer multiples of the switching frequency. This figure allows for the decomposing of the modulation design problem within an output voltage fundamental cycle into an independent set of smaller problems for every switching cycle. The expression of HD/sub n,k/ as a function of the switching states' duty-ratio is presented for the three-level three-phase neutral-point-clamped voltage source inverter and it can be easily obtained for any other multilevel converter. From the evaluation of HD/sub n,k/ over 1/6th of the output-voltage fundamental-period the value of HD/sub n/ is obtained, providing a measure of the output voltage distortion in a fundamental period. This information is obtained at a lower computational cost than conventional fast Fourier transform (FFT) analysis. The accuracy of the HD/sub n/ distortion predictions is verified by comparing it to FFT-based results obtained from simulation and experiments. The expression to compute the total harmonic distortion (THD) as a function of HD/sub n/ is also derived.     

A Single-Phase Active Filter Using an H-Bridge PWM Converter With a Sampling Frequency Quadruple of the Switching Frequency

This paper presents a digital current regulator for H-bridge pulsewidth modulation (PWM) converters, whose sampling frequency equals quadruple of the switching frequency. The current regulator detects the ac current and manipulates the voltage reference not only at the upper and lower peaks of the PWM triangle carrier but also at its zero crossings. This paper theoretically discusses the switching sequence of the H-bridge PWM converter, and reveals the amount of the voltage error and the condition where the voltage error occurs. A modified deadbeat current regulator is proposed to suppress the current oscillation induced by the voltage error, based on the theoretical analysis. Experimental results are shown to verify the control performance of the proposed current regulator. Moreover, a proposed current regulator is applied to a single-phase active power filter to demonstrate the effectiveness in harmonic compensation.     

Generalized techniques of selective harmonic elimination andcurrent control in current source inverters/converters

This paper presents generalized techniques for realizing PWM patterns which provide selective harmonic elimination and current magnitude modulation (SHEM) for current source inverters/power converters (CSI/C). A combination of chops and short circuit pulses are positioned in such a way that lower order harmonics are eliminated selectively besides current magnitude modulation with minimum switching frequency. Generalized equations and tables which show the relationship of various PWM-SHEM parameters to the position of short circuit pulses and the number of chops per 30° are provided and discussed in detail     

Zero-voltage-switching half-bridge DC-DC converter with modified PWM control method

Asymmetric control scheme is an approach to achieve zero-voltage switching (ZVS) for half-bridge isolated dc-dc converters. However, it is not suited for wide range of input voltage due to the uneven voltage and current components stresses. This paper presents a novel "duty-cycle-shifted pulse-width modulated" (DCS PWM) control scheme for half-bridge isolated dc-dc converters to achieve ZVS operation for one of the two switches without causing the asymmetric penalties in the asymmetric control and without adding additional components. Based on the DCS PWM control scheme, an active-clamp branch comprising an auxiliary switch and a diode is added across the isolation transformer primary winding in the half-bridge converter to achieve ZVS for the other main switch by utilizing energy stored in the transformer leakage inductance. Moreover, the auxiliary switch also operates at ZVS and zero-current switching (ZCS) conditions. Furthermore, during the off-time period, the ringing resulted from the oscillation between the transformer leakage inductance and the junction capacitance of two switches is eliminated owing to the active-clamp branch and DCS PWM control scheme. Hence, switching losses and leakage-inductance-related losses are significantly reduced, which provides the converter with the potential to operate at higher efficiencies and higher switching frequencies. The principle of operation and key features of the proposed DCS PWM control scheme and two ZVS half-bridge topologies are illustrated and experimentally verified.     

Novel zero-voltage-transition PWM converters

To date, soft-switching techniques applied to the PWM converters, with the exception of a few isolated cases, are subjected to either high switch voltage stresses or high switch current stresses, or both. A new class of zero-voltage-transition PWM converters is proposed, where both the transistor and the rectifier operate with zero-voltage switching and are subjected to minimum voltage and current stresses. Breadboarded converters are constructed to verify the novelty of the proposed new family of converters     

单周期控制三相电压型PWM整流器

文章对基于单周期控制的三相PWM高功率因数整流器进行了研究,推导了单周期控制三相电压型PWM整流器的控制规律。它不需要乘法器更不需要对输入电压进行检测,其控制逻辑简单并且以恒定频率工作,可以在每个开关周期控制输入电流跟踪正弦参考量,从而实现低电流谐波畸变和高功率因数。基于Multisim2001软件平台,建立了基于单周期控制的三相电压型PWM整流器的仿真模型,完成了6kW三相PWM整流器的设计和实验研究,仿真和试验结果都验证了理论分析的正确性。     

调速传动用四象限级联中压变频器(上)

由于性能优良,H桥级联变频器在中压调速传动中得到最广泛应用。通常这类变频器H桥中的交-直变换都采用二极管整流,使之不能四象限工作。把二极管整流改为PWM整流(AFE),变频器就可以四象限工作,但需在整流输入端增加电感和电容,控制也复杂。本文建议改用I GBT整流/回馈单元,器件按同步开关模式工作,使变频器成为具有与常规H桥级联变频器同样性能的四象限变频器,且不必像AFE那样增加电感和电容,控制也特别简单。矩阵变换器MC是一类性能优良的PWM交-交直接变频器。通过三相/单相MC桥的级联可以实现四象限中压变频。文中介绍了安川公司的MC桥级联中压变频器,并把它和基于整流/回馈单元的H桥级联中压变频器进行比较。     

调速传动用四象限级联中压变频器（下）

由于性能优良,H桥级联变频器在中压调速传动中得到最广泛应用。通常这类变频器H桥中的交一直变换都采用二极管整流,使之不能四象限工作。把二极管整流改为PWM整流（AFE）,变频器就可以四象限工作,但需在整流输入端增加电感和电容,控制也复杂。本文建议改用IGBT整流／回馈单元,器件按同步开关模式工作．使变频器成为具有与常规H桥级联变频器同样性能的四象限变频器,且不必像AFE那样增加电感和电容．控制也特别简单。矩阵变换器Mc是一类性能优良的PWM交一交直接变频器。通过三相／单相MC桥的级联可以实现四象限中压变频。文中介绍了安川公司的Mc桥级联中压变频器,并把它和基于整流／回馈单元的H桥级联中压变频器进行比较。