Showing papers in "IEEE Transactions on Power Electronics in 1992"

Modeling of chaotic DC-DC converters by iterated nonlinear mappings

Abstract: In parameter ranges where conventional methods break down, DC-DC converters may be described by iterated mappings, a nonlinear discrete modeling technique. The underlying principles are explained and are applied to the example of a PWM-controlled buck converter. Stable behavior and bifurcations to chaos are predicted by numerical evaluation of the governing mapping and are confirmed by experiment. >

Small-signal analysis of the phase-shifted PWM converter

Abstract: The specific circuit effects in the phase-shifted PWM (PS-PWM) converter and their impact on the converter dynamics are analyzed. The small-signal model is derived incorporating the effects of phase-shift control and the utilization of transformer leakage inductance and power FET junction capacitances to achieve zero-voltage resonant switching. The differences in the dynamic characteristics of the PS-PWM converter and its PWM counterpart are explained. Model predictions are confirmed by experimental measurements. >

Topologies for three-element resonant converters

Abstract: Many of the limitations of two-element resonant topologies can be overcome by adding a third reactive element. However, using three elements greatly increases the number of possible topologies, making it very difficult to explore this class of circuits on a trial-and-error basis. An orderly search procedure that exposes a large number of new topologies, many of which are resonant and have useful properties, is presented. >

Recent advances in power electronics

Abstract: Recent advances in several key areas of power electronics technology, such as power semiconductor devices, power converter circuits, and control of power electronics, are discussed. The structure and characteristics of IGBT, SIT, SITH, and MCT devices are reviewed. The principal converter types and their recent trends are described. A brief review of power integrated circuits is included. The features of microcomputer and VLSI control are described, and recent advances in microcomputers are highlighted. The principles of expert systems, fuzzy control, and neural networks are presented. >

Harmonic transfer through converters and HVDC links

Abstract: Power converters are known to be generators of harmonics on both their AC and DC sides. They also transfer existing harmonics from one side to the other side with an associated change of frequency. Analysis techniques that can be used to calculate these transferred harmonics using amplitude modulation (AM) theory are proposed. The authors also show how, in a high-voltage direct-current (HVDC) link, the converters can intercouple the AC and DC systems and can thus act as a transfer medium for harmonics. Examples that show how to calculate these harmonics are given and comparisons are made with a computer-aided design (CAD) model as a check on the accuracy of the method. >

Switching frequency optimal PWM control of a three-level inverter

Abstract: A pulse-width-modulation (PWM) method for the control of a three-level inverter is described. The switching frequency optimal-PWM method (SFO-PWM) works with a constant carrier frequency not synchronized with fundamental stator frequency. SFO-PWM gives an optimal utilization of the mean thyristor switching frequency permitted; therefore, PWM carrier frequency may be chosen to a value of two times the permitted mean thyristor switching frequency. The signal processing structure is simple. Many applications of three-level inverter work with a DC-link neutral point not stabilized from the power input converter. A neutral-point potential control is described, which is capable of stabilizing potential by varying the switching sequences of the three-level inverter itself. Results from computer simulation and practical experience show the good performance of SFO-PWM. >

A balanced commutator for switched reluctance motors to reduce torque ripple

Abstract: A method of computing the reference currents for current tracking feedback control, called a balanced commutator, is presented. For a given motor, this commutator reduces the peaks and the rates of change of the reference currents. Although primarily intended for lower-speed direct-drive applications, the commutator design allows accurate current tracking, and therefore reduced torque ripple, over a reasonably wide range of operating speeds. Three motor models, (analytical, numerical, and measured) are considered. Issues relating commutation schemes to amplifier requirements are addressed by simulating simple analytical models of the electrical dynamics. To reveal the interplay between motor design and commutator output, torque models produced by numerical field calculations are considered. To demonstrate the practical benefits and limitations of the method, a balanced commutator based on measured motor data is implemented, and torque ripple reduction is quantified in a laboratory experiment. >

Canonical modeling of power processing circuits based on the POPI concept

Abstract: The fundamental power-processing properties of switching converter circuits are modeled using generalized power-conservative (POPI) networks. Depending on the application, it may be most appropriate to model the first-order converter properties as those of an ideal transformer, gyrator, loss-free resistor, or other POPI network. These basic functions can be obtained either through selection of a topology that naturally possesses the desired characteristics or by addition of a suitable control network. Some well-known converter topologies are shown to behave naturally as gyrators, loss-free resistors, and constant power networks. The application of the gyrator to network two voltage sources and the use of the loss-free resistor as a unity power factor rectifier are described. >

Characteristics of load resonant converters operated in a high-power factor mode

Abstract: The performance of the parallel resonant power converter and the combination series/parallel resonant power converter (LCC converter) when operated above resonance in a high power factor mode are determined and compared for single phase applications. When the DC voltage applied to the input of these converters is obtained from a single phase rectifier with a small DC link capacitor, a relatively high power factor inherently results, even with no active control of the input line current. This behavior is due to the pulsating nature of the DC link and the inherent capability of the converters to boost voltage during the valleys of the input AC wave. With no active control of the input line current, the power factor depends on the ratio of operating frequency to tank resonant frequency. With active control of the input line current, near-unity power factor and low-input harmonic currents can be obtained. >

Physical origins of input filter oscillations in current programmed converters

Abstract: Addition of an input filter to a current-programmed converter can cause the controller to oscillate. Two instability mechanisms can typically occur: (1) the current programmed controller effective current feedback loop may become unstable, or (2) the controller effective input voltage feedforward loop, which becomes a positive feedback loop when an input filter is added, may oscillate. Three design criteria for preventing oscillations are derived and interpreted. When all three criteria are well satisfied, then the output voltage regulation loop gain is unchanged. Hence, input filters of current programmed converters can be designed in essentially the same manner as for duty-ratio programmed converters. Results are summarized in tabular form for the basic buck, boost, and buck-boost converters. Experimental measurements for a buck converter with different input filters support the theoretical predictions. >

Coaxially wound transformers for high-power high-frequency applications

Abstract: Design considerations for transformers utilized in high-power high-frequency DC/DC converters are addressed. Major areas of concern are core-material selection, minimization of copper losses due to skin and proximity effects, and the realization of controlled leakage inductances. Coreless characteristics for various high-frequency materials are presented, and the influence of various conventional winding arrangements on the copper losses and leakage field is also demonstrated. Coaxial winding techniques (used commonly in high-frequency transformers) are investigated next as a feasible solution for containing the leakage flux within the interwinding space, thus preventing it from permeating the core and resulting in lower core losses and the avoidance of localized heating. Added benefits of this technique are reduced forces within the transformer, lower copper losses, and robust construction. The performances of two experimental single-phase 50 kW, 50 kHz units are reported. A three-phase version of coaxially wound transformers is also presented. >

Input filter design criteria for current-programmed regulators

Abstract: The design of input filters for switched-mode regulators is discussed, and it is shown that the filter's effect on the power system depends on the control method used in the regulator's DC-DC converter. Design inequalities are reviewed for duty-ratio programmed converters, and specific expressions are presented for current-programmed converters. Examples of application to practical regulator circuits are given where current-programmed criteria, computer-driven measurement tools, and numerical evaluations of analytic expressions are used to design input filters. >

Optimum control of N-input K-output matrix converters

Abstract: Significant developments of the general optimum control theory presented in a previous paper by the authors (1988) are discussed for the specific case of multiphase matrix converters. Results hold, regardless of system configuration, input and output voltage waveforms, and loads. Applications to the most practical converter structures are illustrated, and implementation criteria of the optimum control method are derived. Simulated results confirm the flexibility and effectiveness of the approach. >

Optimal feed-forward compensation for PWM DC/DC converters with 'linear' and 'quadratic' conversion ratio

Abstract: An analytical procedure to optimize the feedforward compensation for any PWM DC/DC power converters is described. Achieving zero DC audiosusceptibility was found to be possible for the buck, buck-boost, Cuk, and SEPIC cells; for the boost converter, however, only nonoptimal compensation is feasible. Rules for the design of PWM controllers and procedures for the evaluation of the hardware-introduced errors are discussed. A PWM controller implementing the optimal feedforward compensation for buck-boost, Cuk, and SEPIC cells is described and fully experimentally characterized. >

Spectra of delta-sigma modulated inverters: an analytical treatment

Abstract: Analytic expressions for the output voltage spectrum of an asynchronous delta (or delta-sigma) modulated inverter are reported and supported by experimental data The analysis yields three functions that give the frequency, phase, and amplitude of each component of the spectrum These functions are in terms of the sinusoidal reference waveform and the properties of the modulator The method provides greater accuracy and computational efficiency than the numerical methods reported to date The spectral components form pairs of sidebands around multiples of the average switching frequency The functions detail the relationship between the number of significant sideband components and the depth of modulation and illustrate the spread-spectrum nature of delta modulation Extensions to nonsinusoidal reference waveforms and to hysteresis current controllers are considered >

Frequency-domain analysis of series resonant converter for continuous conduction mode

Abstract: Most previous analyses of a series resonant DC-DC power converter (SRC) have been performed in the time domain. A comprehensive frequency-domain analysis of the SRC for steady-state operation, along with experimental results is presented. Simple analytical design equations are derived for the basic performance parameters of the converter operating in the continuous conduction mode (CCM) using Fourier series techniques and a high-Q/sub L/ assumption. Three types of class-D current-driven rectifiers are considered. The diode threshold voltage and forward resistance as well as the ESR of the output filter capacitor are taken into account. Experimental results were in good agreement with theoretical predictions. >

Energy-storage pulsed-power capacitor technology

Abstract: Fundamentals of dielectric capacitor technology and multifactor stress aging of all classes of insulating media that form elements of this technology are addressed. The goal is the delineation of failure processes in highly stressed compact capacitors. Factors affecting the complex aging processes such as thermal, electromechanical, and partial discharges are discussed. Diagnostic measurement techniques available and those being developed to determine material degradation affecting available life and failure probability of capacitors are presented. >

Synthesis of zero-impedance converter

Abstract: A method for synthesizing a system that converts a finite value of an impedance to zero, with an associated finite current and zero voltage, is presented. The synthesis method comprises positive current feedback of an exactly specified nature and value of its transfer function. The stability and dynamics of the system are controlled by an additional voltage loop. The zero-impedance converter is used to synthesize load-independent systems including (switch-mode) power converters and electric motor drive systems incorporating any kind of motor. >

Low switching frequency and high dynamic pulsewidth modulation based on field-orientation for high-power inverter drive

Abstract: In megawatt-rated inverter-fed induction motor drive systems, the gate-turn-off switching losses account for a considerable amount of the total losses, hence, the switching frequency in such systems must be kept at a low value of only a few hundred hertz. To avoid undesired torque harmonics under such operating conditions, the pulse control of the inverter is made dependent on the orientation of the rotor flux of the drive machine. This method transfers a major portion of the unavoidable current distortions into the field axis where they have no influence on the machine torque. An optimal trajectory-oriented control is presented that achieves low switching frequency at low torque and current harmonics and exhibits a very fast dynamic response. The performance of this method is demonstrated by measured results from a 30-kW model drive. >

Small-signal circuit modeling in the frequency-domain by computer-aided time-domain simulation

Abstract: The possibility of obtaining the frequency-domain dynamic model of a circuit from transient analysis data provided by a circuit simulator is shown. The computer-aided design (CAD) program FREDOMSIM, which governs the simulations, processes the output data, and supplies the results in a well suited manner for design optimization, is introduced. Feedback circuits are modeled with all their feedback loops open, so that the designer can optimize systems by proper a posteriori loop closures. The characterization with the loops closed is also given. >

A discretized current control technique with delayed input voltage feedback for a voltage-fed PWM inverter

Abstract: A current control technique for a voltage-fed PWM inverter is presented. The discretized state equation of an inverter and a load independent of operating conditions with the delayed input voltage feedback has been derived using the averaging concept. The discretized current controller is proposed to reduce the current error as fast as possible using the deadbeat control strategy and to stabilize the closed loop system asymptotically when the variations of load parameters are given in the predetermined stabilized region. This proposed control scheme is realized by the symmetrical uniform sampling method and is easily implemented using a microprocessor-based system. Computer simulation for the proposed controller has been carried out and the results show good static and dynamic performances. >

A new approach to the modeling of converters for SPICE simulation

Abstract: An approach to the modeling of DC-DC converters for SPICE simulation is developed in which the average current in the energy-storage inductor is first simulated in a SPICE subcircuit for both the continuous and discontinuous modes of operation. The inductor current is then weighted and redistributed to related branches of the circuit to simulate the average input and output currents of the converter. Based on this technique, various converter models, including that of the Cuk converter with coupled inductors, which are valid for both continuous and discontinuous modes of operation, are developed. >

Quasi-linear modeling and control of DC-DC converters

Abstract: A quasi-linear approach is proposed for modeling and control of DC-DC power converters. The method presented is derived by perturbing an approximate large signal equation around a varying operating point in a reduced variable space. This differs from the usual practice of applying the perturbation technique around a fixed operating condition. In the proposed algorithm, the control equation and the control parameter are constantly adjusted according to environmental changes to meet the specified dynamical requirement. >

Digital control of induction motor current with deadbeat response using predictive state observer

Abstract: For a high-power induction motor drive, the switching frequency of the inverter cannot become higher than one kilohertz, and such a switching frequency produces a large current ripple, which then produces torque ripple. To minimize the current ripple, a method based on deadbeat control theory for current regulation is proposed. The pulsewidth modulation (PWM) pattern is determined at every sampling instant based on stator current measurements, motor speed, current references, and rotor flux vector, which is predicted by a state observer with variable poles selection, so that the stator currents are controlled to be exactly equal to the reference currents at every sampling instant. The proposed method consists of two parts: (1) derivation of a deadbeat control and (2) construction of a state observer that predicts the rotor flux and the stator currents in the next sampling instant. This paper describes a theoretical analysis, computer simulations and experimental results. >

Design issues for the transformer in a low-voltage power supply with high efficiency and high power density

Abstract: Circuit model, design feasibility, and design tradeoffs are investigated for the transformer in 1.5-5 V power supplies with high efficiency and high power density. The transformer is constructed from a single or a matrix of pot cores and from interleaved planar windings. It has been determined theoretically and verified experimentally that such a transformer is realizable as long as the loss constraint is not severe (e.g. less than 0.5 W transformer loss per 100 W output). The primary source of loss is the winding, not the core, in 1.5 V/turn design. Measures to reduce the transformer height tend to increase transformer loss or volume. >

A circuit model for the class E resonant DC-DC converter regulated at a fixed switching frequency

Abstract: An averaging circuit model is developed for the class E resonant DC-DC converter regulated at a fixed switching frequency. The regulation is achieved by use of an auxiliary switch. The model is obtained based on the circuit analysis using the Fourier series expansion. Steady-state and small-signal dynamic analysis is presented, which reveals that the DC output is well controlled by the control angle of the auxiliary switch and that there exists a right-half-plane zero in the control-to-output transfer function. The analysis results are verified by the experiments. >

Series resonant converter with third-order commutation network

Abstract: To compensate for the poor output voltage regulation of the series resonant converter (SCR), a converter is derived by adding an inductor in parallel with the resonant capacitor of the conventional SCR. The resulting converter is called the LLC-SRC. This converter is analyzed via a two-dimensional state-plane diagram through a proper transformation of its state variables. Based on the analysis results, a set of characteristic curves is derived showing that the control characteristics and component stresses of the new converter are improved compared with those of a conventional SRC. Based on these curves, the design procedure for the LLC-SRC is formulated. The experimental results from the breadboard model were used to verify the theoretical work. >

Input filter design criteria for switching regulators using current-mode programming

Abstract: Design criteria are developed for a constant-frequency current-programmed switching DC-to-DC converter with an input filter to ensure stability and prevent performance degradation. The criteria are given in terms of the filter voltage transfer function H/sub S/, output admittance Y/sub s/, and the y-parameter model of the switching converter. The criteria are listed as four inequalities and illustrated graphically. The criteria may be summarized as follows: assuming a converter that satisfies its loop gain T, line-to-output transfer function A/sub gf/, and output impedance Z/sub of/ requirement is given, an input filter with H/sub s/ and Y/sub s/ can be used to attenuate the noise emissions from the converter without adversely affecting the converter if H/sub s/ >

A pulse frequency modulated PWM inverter for induction motor drives

Abstract: A PWM pulse pattern optimization method using pulse frequency modulation (PFM) is described. In conventional PWMs the pulse frequency is kept constant. In the proposed PFM, however, the pulse frequency is adjusted. The PFM technique is intended to not only reduce the magnetic acoustic noises of driven motors but also to improve the performance of sinusoidal inverters. The PWM pulse patterns are basically controlled so that the time-integral function of the voltage vectors in the space vector notation may draw a circular locus. In addition to this, the pulse frequency, of PWM is also controlled so that the performance index (PI), which represents the degree of achieved objectives, may be minimized. Two PIs, one for minimizing the distortion of output currents and the other for minimizing the torque pulsation of driven motors, are employed. The method is implemented using a single-chip microprocessor, and the experimental results demonstrate its validity. >

A unity power factor current-regulated SPWM rectifier with a notch feedback for stabilization and active filtering

Abstract: A stand-alone, unity power factor, current-regulated sinusoidal pulsewidth modulated (SPWM) rectifier is described. The topology is based on the series connection of three four-valve single-phase bridges, which allows the conventional two-stage logic SPWM strategy to be used without interphase interference. The problems of stability and low harmonic waveform distortion are identified. Solutions are found by using a simple local notch filter feedback circuit that fulfils the dual function of stabilizing and active filtering. From the clarification given by this more expensive but less constrained topology, the stage is set for the next step in incorporating the lessons learned to the more economical topology based on the six-valve, three phase parallel bridge, which requires a tristate logic for PWM control when operating in the current-source configuration. >