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。     

“Dead-band” PWM switching patterns

Reference/modulating waveform continuity is not a necessary condition for the implementation of switching patterns for three-phase pulse-width modulated (PWM) converters if the load or the source are Y-connected. This is based on the fact that the converter phase-voltages do not need to be sinusoidal and switching pattern discontinuities-“dead-bands”-do not degrade the quality of output/input voltage/current waveforms by introducing low-order harmonics if certain parameters are optimized. This paper discusses general characteristics of various discontinuous switching patterns for PWM converters and shows that they can yield better performance than their continuous counterparts in some operating regions. Performance is defined as harmonic distortion normalized with respect to effective switching frequency and serves as a measure of comparison with continuous PWM techniques, The applications considered include general purpose and application specific solid-state power supplies using voltage source inverters and PWM rectifiers. Theoretical considerations are verified on an experimental unit     

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     

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     

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.     

Comparative study of pulsed DC-link voltage converters

This paper classifies the pulse pulsed dc-link voltage (PDCLV) topologies in six types, depending on both the shape of the pulsed DC-link voltage waveform and the circuit ability to synchronize, or not, with external pulse width modulation (PWM) signals. Main features are compared for a large number of topologies in which the bridge devices commutate under zero-voltage-switching (ZVS) technique. The paper also presents a comparative study of the losses produced by these converters and discusses the principles they employ causing generation such losses. An overview of the control and PWM possibilities for these converters is given and an extensive bibliography is included.     

Spectral characteristics of randomly switched PWM DC/DC convertersoperating in discontinuous conduction mode

This paper addresses a comparative study of the spectral characteristics of four random-switching schemes that apply to the basic pulsewidth-modulation (PWM) DC/DC converters operating in discontinuous conduction mode (DCM). They include randomized pulse position modulation, randomized pulsewidth modulation, and randomized carrier frequency modulation with fixed duty cycle and with fixed duty time, respectively. Mathematical models that characterize the input current and output voltage of the three basic PWM converters operating in DCM are derived. In particular, the effectiveness of spreading the dominant switching harmonics in the input current that normally exist in the standard PWM scheme and the introduction of low-frequency harmonics in the output voltage with respect to the randomness level are investigated. The validity of the models and analyses are confirmed experimentally by using a DC/DC buck converter     

A unified analysis of PWM converters in discontinuous modes

Three discontinuous operating modes of PWM (pulsewidth modulated) converters are considered: the discontinuous inductor current mode (DICM), the discontinuous capacitor voltage mode (DCVM), and a previously unidentified mode called the discontinuous quasi-resonant mode (DQRM). DC and small-signal AC analyses are applicable to all basic PWM converter topologies. Any particular topology is taken into account via its DC conversion ratio in the continuous conduction mode. The small-signal model is of the same order as the state-space averaged model for the continuous mode, and it offers improved predictions of the low-frequency dynamics of PWM converters in the discontinuous modes. It is shown that converters in discontinuous modes exhibit lossless damping similar to the effect of the current-mode programming     

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     

Output plane analysis of load-sharing in multiple-module convertersystems

This paper explores the origin of the DC current-sharing problem of parallel-converter systems and the dual problem of voltage sharing in series-converter systems. Both problems may be studied by examining the output plane (output current versus output voltage) of a particular converter. It is shown that strict current source behavior is unnecessary for good current sharing in parallel-converter systems. Furthermore, a broad class of converters whose output voltage is load-dependent, i.e., those that have a moderate value of output resistance, all exhibit good voltage- and current-sharing characteristics. Such converters are often suitable for a×b arrays of converters that can meet a large range of power-conversion requirements. The output planes of discontinuous mode PWM converters as well as conventional and clamped series resonant converters are examined in detail. A simple small-signal model of the modular converter system is developed. Experimental confirmation of load sharing and the small-signal model is given for the clamped series resonant converter and the series resonant converter for various configurations of four converters     

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     

A passive lossless snubber cell for nonisolated PWM DC/DCconverters

A passive lossless snubber cell is proposed to improve the turn-on and turnoff transients of the MOSFETs in nonisolated pulsewidth modulated (PWM) DC/DC converters. Switching losses and EMI noise are reduced by restricting di/dt of the reverse-recovery current and dv/dt of the drain-source voltage. The MOSFET operates at zero-voltage-switching (ZVS) turnoff and near zero-current-switching (ZCS) turn-on. The freewheeling diode is also commutated under ZVS. As an example, operation principles, theoretical analysis, relevant equations, and experimental results of a boost converter equipped with the proposed snubber cell are presented in detail. Efficiency of 96% has also been measured in the experimental results reported for a 1 kW 100 kHz prototype in the laboratory, Six basic nonisolated PWM DC/DC converters (buck, boost, buck-boost, Cuk, Sepic, and Zeta) equipped with the proposed general snubber cells are also shown in this paper     

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.     

Voltage-source active power filter based on multilevel converter and ultracapacitor DC link

A new topology for active power filters (APF) using an 81-level converter is analyzed. Each phase of the converter is composed of four three-state converters, all of them connected to the same capacitor dc link voltage and their output connected in series through output transformers. The main advantages of this kind of converter are the negligible harmonic distortion obtained and the very low switching frequency operation. The single-phase equivalent circuit is analyzed and their governing equations derived. The dc link voltage control, based on manipulating the converter's voltage phase, is analyzed together with the circuit's characteristics that determine the capability to draw or deliver active and reactive current. Simulation results for this application are compared with conventional pulsewidth-modulated (PWM) converters, showing that this filter can compensate load current harmonics, keeping better-quality sinusoidal currents from the source. The simulated configuration uses a 1-F ultracapacitor in the dc link, making it possible to store energy and deliver it during short voltage dips. This is achieved by applying a modulation control to maintain a stable ac voltage during dc voltage drops. A prototype of the filter was implemented and tested, and the obtained current waveforms showed to be as good as expected.     

Single-phase Z-source PWM AC-AC converters

The letter proposes a new family of simple topologies of single-phase PWM ac-ac converters with a minimal number of switches: voltage-fed Z-source converter and current-fed Z-source converter. By PWM duty-ratio control, they become "solid-state transformers" with a continuously variable turns ratio. All the proposed ac-ac converters in this paper employ only two switches. Compared to the existing PWM ac-ac converter circuits, they have unique features: providing a larger range of output ac voltage with buck-boost, reversing or maintaining phase angle, reducing in-rush and harmonic current, and improving reliability. The operating principle and control method of the proposed topologies are presented. Analysis, simulation, and experimental results are given using the voltage-fed Z-source ac-ac converter as an example. The analysis can be easily extended to other converters of the proposed family. The proposed converters could be used in voltage regulation, power regulation, and so on.     

软开关PWM变换器发展综述

软开关技术已从基本谐振变换器,准谐振变换器和谐振直流环节变换器发展到软开关ＰＷＭ变换器。软开关ＰＷＭ变换器综合了软开关技术和ＰＷＭ技术各自的优点,构成新一类目前发展和应用前景的变换器。本文系统地综述了谐振直流环变换器,零电压和零电流开关ＰＷＭ变换器,零电压转换ＰＷＭ变换器和零电流转换ＰＷＭ变换器的工作原理和特点。     

Novel zero-current-transition PWM converters

A new family of zero-current-transition (ZCT) pulsewidth-modulated (PWM) converters is proposed. The new family of converters implements zero-current turn-off for power transistor(s) without increasing voltage/current stresses and operates at a fixed frequency. The proposed converters are deemed most suitable for high-power applications where the minority-carrier semiconductor devices (such as IGBTs, BJTs, and MCTs) are predominantly used as the power switches. Theoretical analysis is verified on a 100 kHz, 1 kW ZCT-PWM boost converter using an IGBT     

Behavior of PWM Active Front Ends in the Presence of Parallel Thyristor Converters

This paper investigates the effects of grid voltage distortions caused by thyristor converters on the steady-state performance of a pulsewidth modulation (PWM) rectifier with dc voltage link for low-voltage applications. The disturbance transfer function of the current control loop is used to analyze the effects of grid distortions. Influences of the current controller, the phase-locked loop parameters, and the filter inductance on the generated current harmonics are presented. For existing grid voltage harmonics, the amplitude of the corresponding current harmonics are determined and compared to measured current harmonics using a 400-V 40-kW test bench consisting of a PWM rectifier with voltage dc link parallel to a 40-kW thyristor converter.     

Simple topologies of PWM AC-AC converters

This letter proposes a new family of simple topologies of PWM AC-AC converters with minimal switches. With extension from the basic DC-DC converters, a series of AC-AC converters such as buck, boost, buck-boost, Cuk, and isolated converters are obtained. By PWM duty ratio control, they become a "solid-state transformer" with a continuously variable turns ratio. All the proposed AC-AC converters in this paper employ only two switches. Compared to the existing circuits that use six switches or more, they can reduce cost and improve reliability. The operating principle and control method of the proposed topologies are presented. Analysis and simulation results are given using the Cuk AC-AC converter as an example. The analysis can be easily extended to other converters of the proposed family.