Showing papers on "Converters published in 1999"

Multilevel converters for large electric drives

Abstract: This paper presents transformerless multilevel power converters as an application for high-power and/or high-voltage electric motor drives. Multilevel converters: (1) can generate near-sinusoidal voltages with only fundamental frequency switching; (2) have almost no electromagnetic interference or common-mode voltage; and (3) are suitable for large voltampere-rated motor drives and high voltages. The cascade inverter is a natural fit for large automotive all-electric drives because it uses several levels of DC voltage sources, which would be available from batteries or fuel cells. The back-to-back diode-clamped converter is ideal where a source of AC voltage is available, such as in a hybrid electric vehicle. Simulation and experimental results show the superiority of these two converters over two-level pulsewidth-modulation-based drives.

A fast space vector modulation algorithm for multilevel three-phase converters

Abstract: This paper introduces a general space vector modulation algorithm for n-level three-phase power converters. This algorithm is computationally extremely efficient and is independent of the number of levels of the power converter. At the same time, it provides excellent insight into the operation of multilevel power converters.

Multifrequency averaging of DC/DC converters

Abstract: This paper presents some of the issues involved in applying frequency-selective averaging to modeling the dynamic behavior of pulsewidth-modulated (PWM) DC-DC converters. We use the boost converter as an example to show the details involved in deriving some novel extended averaged models, and we use simulations to highlight the accuracy of the models even when traditional small-ripple conditions are not satisfied.

Positive output Luo converters: voltage lift technique

Abstract: The voltage lift technique is a popular method that is widely applied in electronic circuit design. Because of the effect of parasitic elements, the output voltage and power transfer efficiency of DC-DC power converters are limited. The voltage lift technique opens a good way to improve circuit characteristics. After long-term research, this technique has been successfully applied for DC-DC power converters. Positive output Luo converters are a series of new DC-DC step-up (boost) converters, which were developed from prototypes using the voltage lift technique. These converters perform positive to positive DC-DC voltage increasing conversion with high power density, high efficiency and cheap topology in simple structure. They are different from other existing DC-DC step-up power converters and possess many advantages including a high output voltage with small ripples. Therefore, these converters will be widely used in computer peripheral equipment and industrial applications, especially for high output voltage projects.

Performance characteristics of a cascaded two-level converter

Abstract: A cascaded two-level power converter is proposed which utilizes two six-transistor inverters and is capable of producing voltages which are identical to those of three-level and four-level converters. Since the machine voltages are the same, the converter performance is the same as is verified through laboratory tests. The advantages and disadvantages of the proposed cascaded converter are explored. The proposed converter is simpler to construct and offers more nonredundant switching states per number of active semiconductors than standard multi-level converters.

Digital controller design for switchmode power converters

Abstract: A thorough and systematic evaluation of different digital control design approaches is presented. The performance of the approaches is compared in terms of both the bandwidth and the phase margin of the control loop, as well as the output transient response subject to line and load step change. Furthermore, the difference of these design approaches under a lower sampling rate is studied. Best digital design approach for power converter applications is identified based on the comparison results.

Integrated high-quality rectifier-regulators

Abstract: A new family of AC-DC converters is derived which integrate the functions of low-harmonic rectification, low-frequency energy storage, and wide-bandwidth output voltage control into a single converter containing one, two, or four active switches. These converters utilize a discontinuous conduction mode input inductor, an internal energy storage capacitor, and transformer secondary circuits which resemble the bridge, forward, flyback, or Cuk DC-DC converters. A large-signal equivalent circuit model for this family is presented, which uses the "loss-free resistor" concept. Design strategies and experimental results are given. High-performance regulation with satisfactory line-current harmonics is demonstrated with conventional duty-ratio control. Further improvements in line current are possible by simultaneous duty-ratio and switching-frequency control.

A control system for HVDC transmission by voltage sourced converters

Abstract: A national technical project is under way in Japan to develop a high-power voltage sourced converter and its control system for the future DC interconnection between AC systems. Three developed prototype 53 MVA GTO-based converters were manufactured and went into operation. As for the control system, the voltage margin method for two terminal, and the 2-stage DC voltage control method for multi-terminal DC link were developed. Field testing is being carried out at Shin-Shinano Substation of Tokyo Electric Power Company. Satisfactory results verify the superiority of the DC link with voltage sourced converters.

Switched-capacitor DC-DC converters for low-power on-chip applications

Abstract: The paper describes switched-capacitor DC-DC power converters (charge pumps) suitable for on-chip, low-power applications. The proposed configurations are based on connecting two identical but opposite-phase SC converters in parallel, thus eliminating the need for separate bootstrap gate drivers. The authors focus on emerging very low-power VLSI applications such as battery-powered or self-powered signal processors where high power conversion efficiency is important and where power levels are in the milliwatt range. Conduction and switching losses are considered to allow design optimization in terms of switching frequency and component sizes. Open-loop and closed-loop operation of an experimental, fully integrated, 10 MHz voltage doubler is described. The doubler has 2 V or 3 V input and generates 3.3 V or 5 V output at up to 5 mW load. The converter circuit fabricated in a standard 1.2 /spl mu/ CMOS technology takes 0.7 mm/sup 2/ of the chip area.

Interleaved converters operation based on CMC

Abstract: A new family of low-ripple DC-to-DC switching converters based on a parallel connection of N-identical boost converters with current-mode control (CMC) is presented. The CMC strategy ensures that all the converters operate at the same duty cycle, sharing an equal amount of input current and forcing the output voltage to be an integer multiple (N) of the input voltage. As a result, the total input current and output voltage ripples are extremely low. The generation of control signals from inductor currents feedback without using external triangular or sawtooth signals is another characteristic of the new converter family.

Novel zero-voltage and zero-current-switching full-bridge PWM converter using a simple auxiliary circuit

Abstract: A novel zero-voltage and zero-current-switching (ZVZCS) full-bridge pulsewidth modulation converter is presented to simplify the circuits of the previously presented ZVSCS converters. A simple auxiliary circuit, which consists of one small capacitor and two small diodes, is added in the secondary to provide ZVZCS conditions to primary switches, as well as to clamp secondary rectifier voltage. The additional clamp circuit for the secondary rectifier is not necessary. The auxiliary circuit includes neither lossy components nor additional active switches, which makes the proposed converter efficient and cost effective. The principle of operation, features, and design considerations are illustrated and verified on a 2.5 kW 100 kHz insulated-gate-bipolar-transistor-based experimental circuit.

Properties and synthesis of passive lossless soft-switching PWM converters

Abstract: This paper derives general topological and electrical properties common to all lossless passive soft-switching power converters with defined characteristics, and proposes a synthesis procedure for the creation of new power converters. The synthesis procedure uses the properties to determine all possible locations for the resonant inductors and capacitors added to achieve soft switching. A set of circuit cells is then used to recover the energy stored in these resonant elements. This paper also explains the operation of the circuit cells and the many new passive lossless soft-switching power converters. A family of soft-switching boost converters is given as an example of the synthesis procedure. Experimental waveforms are also shown for a new soft-switching Cuk converter.

An RC load model of parallel and series-parallel resonant DC-DC converters with capacitive output filter

Abstract: A novel analytical methodology is proposed and applied to investigate the steady-state processes in voltage-fed parallel and series-parallel resonant DC-DC power converters with a capacitive output filter. In this methodology, the rectifier, output capacitor and load are replaced by an equivalent circuit which includes a capacitor and resistor connected in parallel. Excellent agreement was obtained when comparing numerical values calculated by the proposed model to cycle-by-cycle SPICE simulation and to the numerical results of earlier studies.

Dynamics and control of DC-to-DC converters driving other converters downstream

Abstract: This paper reveals that the dynamics of a converter loaded with other converters downstream are markedly different from those of a standalone converter and conventional design techniques developed for converters with a resistive load could destabilize the control loop of converters combined with other converters. Based on comprehensive small-signal analyses, this paper presents the proper way of designing the control loop of converters driving other converters downstream. The analysis and design results are verified by both time- and frequency-domain simulations.

Self-sustained oscillating resonant converters operating above the resonant frequency

Abstract: This paper presents a new control technique for resonant converters. Unlike conventional variable frequency control which externally imposes the switching frequency, the proposed scheme is based on controlling the displacement angle between one of the resonant circuit variables, typically the current through the resonant inductor, and the voltage at the output of the inverter. As a result, zero-voltage switching (ZVS) can be ensured over a wide operating range. The proposed control technique cam be applied for series, parallel, and series-parallel resonant converters. As an example, the static characteristics and dynamic model of a series-parallel resonant converter with the proposed controller are derived and the system behaviour is investigated in detail. Experimental results are given to demonstrate the operation of resonant converters with the proposed controller and to validate the analysis.

Modeling of CMOS digital-to-analog converters for telecommunication

Abstract: This paper gives an overview of some of the effects caused by circuit mismatch and parasitics in binary weighted digital-to-analog converters (DACs), and, as a special case, a current-steering CMOS converter. Matlab is used as a behavior-level simulator. In telecommunications applications, the frequency-domain parameters are of the greatest importance. Therefore, the characterization of the device and its performance is determined by frequency parameters such as the signal-to-noise ratio, spurious-free dynamic range, multitone power ratio, etc. In this paper, we show how these frequency-domain parameters are affected when mismatch errors and finite output impedance are applied to a current-steering CMOS DAC. We discuss how static performance is affected when changing the size of the errors and fundamental circuit parameters. The impact of dynamic errors such as glitches, slewing, and bit skew is discussed. Measurement results from 14-bit DACs are also shown to illustrate the correlation with the modeling.

Shared-bus current sharing parallel connected current-mode DC to DC converters

Abstract: A power system consisting of parallel connected current-mode power converters combined with a voltage error signal on a shared-bus used in common for controlling all of the power stages for improved consistency, reliability, and performance in both transient and steady states. Near uniform current sharing is achievable without sacrificing the voltage regulation performance. The improved system offers faster settling time under step loads, consistent small signal characteristics and large signal responses regardless of mismatches of components values such as reference voltages, and reduced output impedance variations in magnitude and phase even during various modes of operation.

Integrated planar inductor scheme for multi-module interleaved quasi-square-wave (QSW) DC/DC converter

Abstract: Compact, high-efficiency, low-voltage and large-current DC/DC power converters with a fast transient slew rate are needed for future generation microprocessors. The interleaved quasi-square-wave (QSW) topology is a good candidate to improve their transient response significantly. Inductors are critical components in these converters. An integrated planar inductor scheme for multi-module interleaved QSW power converters is proposed. This integrated inductor utilizes the phase relationships of the currents in each module to integrate all the separate inductors for each module into one core, resulting in great reductions in the size and power losses of the inductor.

Analysis and experimental study of the buck, boost and buck-boost inverters

Abstract: In this paper, the analysis and experimental study of three kinds of inverters are presented, beginning with the traditional full bridge buck inverter, followed by two different inverter approaches, the boost and buck boost ones. This last two converters have the property of produce an output voltage higher or lower than the input voltage additionally to its inversion capability, which is a desired characteristic to some applications. The paper includes a semiconductor device stress study of the different inverter approaches additionally to the analysis and experimental results of the converters. The control strategy used for all the converters is the sliding mode control in order to introduce a good dynamic response for the closed loop system.

Switching technique for current-controlled AC-to-AC converters

Abstract: The AC-to-AC converter called the matrix converter is very simple in structure and has powerful controllability. However, there are few practical applications, particularly in power electronics fields. The major reasons largely lie in the commutation problem and complexity of the control circuit. This paper proposes a novel commutation technique which is very simple to implement. This commutation scheme allows the deadtime to avoid current spikes of nonideal switches and, at the same time, establishes a current path of the inductive load to avoid voltage spikes. A switching technique of the matrix converter using a space-vector-modulation (SVM) based hysteresis current controller (HCC) is also proposed. The switching technique is implemented without any computational burden and is controlled with a simple control circuit. This technique utilizes advantages of the HCC and SVM technique. Simulation and experimental results obtained on a 5 kW single-phase AC chopper and an 11 kW three-phase to three-phase matrix converter are discussed.

Input filter interaction in three phase AC-DC converters

Abstract: It is well known that the addition of an input filter preceding a switched mode regulator poses a problem of performance degradation and potential instability due to its negative input impedance at low frequencies. Three phase converters are essentially multivariable systems. The objective of this paper is to analyze the problem of input filter interaction in three phase AC-DC converters from a multivariable perspective and to establish criteria that guarantee stability and satisfactory performance of the converter with an input filter. The dq average model of a three phase boost rectifier is used for the analysis. The minor loop, the stability of which has to be guaranteed is identified. A sufficient condition for stability, based on the singular values of the filter output impedance and converter input admittance matrices is derived. Simulation results are presented to illustrate the results.

Control strategy of an interleaved boost power factor correction converter

Abstract: Power factor correction interleaved boost converters provide a reduction of the inductor volume and weight when compared with the conventional PFC boost converter. However, to achieve these benefits, proper current sharing and current ripple minimization must be ensured. This paper proposes a controller based on the Lyapunov-likelihood control technique for interleaved boost converters (IBC) that ensures output voltage regulation and proper current share for each boost cell. In addition, a switching logic scheme for the IBC is developed to guarantee the input current ripple minimization. Extensive simulations are presented to demonstrate the performance of the proposed control and switching logic scheme.

Switching-ripple-based current sharing for paralleled power converters

Abstract: This paper presents the implementation and experimental evaluation of a new current-sharing technique for paralleled power converters. This technique uses information naturally encoded in the switching ripple to achieve current sharing and requires no intercell connections for communicating this information. Practical implementation of the approach is addressed and an experimental evaluation, based on a three-cell prototype system, is also presented. It is shown that accurate and stable load sharing is obtained over a wide load range. Finally, an alternate implementation of this current-sharing technique is described and evaluated.

Output ripple analysis of multiphase DC-DC converters

Abstract: This paper presents an output ripple analysis of multiphase DC-DC power converters having an output LC filter. Analytical expressions for the output voltage ripple of two- and three-phase DC-DC power converters are derived. Influence of the coupling coefficient of the output filter inductor on the output ripple is investigated. Because the unique parameters of the LC filter cannot be determined solely based on the specified maximum output ripple, an additional criterion based on minimum energy storage is introduced. A comparative evaluation of single-phase, two-phase, and three-phase DC-DC power converters is presented. The validity of the proposed analysis method is verified by experimental results.

Modeling and control of unbalanced three-phase systems containing PWM converters

Abstract: This paper proposes two complex vector models to characterize unbalanced three-phase four-wire systems that contain pulsewidth-modulated voltage-source converters (PWM-VSCs). In the first case, the three-phase system is decomposed in orthogonal odq components. A complex vector model is then built from the dq and o components. In the second case, a complex vector model is introduced by decomposing the system in three single-phase systems. In both cases, an orthogonal, fictitious circuit is introduced to handle a single-phase system, such as the homopolar system or each one of the three single-phase systems that compose a three-phase four-wire system. From the vector models, two digital controllers, which employ two different reference frames, are proposed. Also, the use of the same gains for both controllers simplifies the equations of the controller in the stationary reference frame. As an example, current control in a PWM-VSC system is presented.

Single wire current sharing control technique for parallel/redundant operation of a plurality of PWM converters

Abstract: A modular power supply system includes DC—DC converters connected n parallel and functioning in a PWM mode. The modular power supply system controls current sharing among the DC—DC converters using a single wire current sharing control bus that drives in parallel the inputs of all the DC—DC converters. The output of each DC—DC converter is applied to a logic OR circuit. Each converter has an identical logic circuit between its output and the single wire current sharing control bus.

Bandwidth considerations for multilevel converters

Abstract: Multilevel converters can achieve an overall effective switch frequency multiplication and consequent ripple reduction through the cancellation of the lowest order switch frequency terms. This paper investigates the harmonic content and the frequency response of these multimodulator converters. It is shown that the transfer function of uniformly sampled modulators is a bessel function associated with the inherent sampling process. Naturally sampled modulators have a flat transfer function, but multiple switchings per switch cycle will occur unless the input is slew-rate limited. Lower sideband harmonics of the effective carrier frequency and, in uniform converters, harmonics of the input signal also limit the useful bandwidth. Observations about the effect of the number of converters, their type (naturally or uniformly sampled), and the ratio of modulating frequency and switch frequency are made.