Showing papers on "Converters published in 1991"

Principles of power electronics

Abstract: 1. Introduction. 2. Form and Function: An Overview. 3. Introduction to Rectifier Circuits. 4. Bridge and Polyphase Rectifier Circuits. 5. Phase-Controlled Converters. 6. High-Frequency Switching dc/dc Converters. 7. Isolated High-Frequency dc/dc Converters. 8. Variable-Frequency dc/ac Converters. 9. Resonant Converters. 10. ac/ac Converters. 11. Dynamics and Control: An Overview. 12. State-Space Models. 13. Linear and Piecewise Linear Models. 14. Feedback Control Design. 15. Components: An Overview. 16. Review of Semiconductor Devices. 17. Power Diodes. 18. Power Transistors. 19. Thyristors. 20. Magnetic Components. 21. Ancillary Issues: An Overview. 22. Gate and Base Drives. 23. Thyristor Commutation Circuits. 24. Snubber Circuits and Clamps. 25. Thermal Modeling and Heat Sinking.

A unified analysis of PWM converters in discontinuous modes

Abstract: 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. >

Analysis of a concentrated winding induction machine for adjustable speed drive applications. II. Motor design and performance

Abstract: For pt.I. see ibid, vol.6, no.4, p.679-83 (1991). The performance of multiphase machines designed for operation with static power converters is described. The winding distributions are intentionally rectangular to better accommodate the rectangular waveforms of solid-state inverters. Fourier analysis is used for investigation of the effects of different air-gap-field spatial distributions and time harmonics in the supply. The approach to analysis of such machines, derived in Part I, is implemented by means of a digital-computer simulation. Compound results indicate that when operating in conjunction with a converter supply, a specially wound five-phase machine is theoretically capable of a 10% improvement in torque per root-mean-square ampere assuming the same peak air-gap-flux density level in the air gap of the machine as in a conventionally designed induction motor of the same rating. >

Multi-loop control for quasi-resonant converters

Abstract: A multiloop control scheme for quasi-resonant converters (QRCs) is described. Like current-mode control for pulse width modulation (PWM) converters, this control offers excellent transient response and replaces the voltage-controlled oscillator (VCO) with a simple comparator. In this method, referred to as current-sense frequency modulation (CSFM), a signal proportional to the output-inductor current is compared with an error voltage signal to modulate the switching frequency. The control can be applied to either zero-voltage-switched (ZVS) or zero-current-switched (ZCS) QRCs. Computer simulation is method applied to a ZCS buck QRC. A circuit implementation is presented that allows multiloop control to be used on circuits switching up to 10 MHz. This circuit requires few components and produces clean control waveforms. Experimental results are presented for zero-current flyback and zero-voltage buck QRCs, operating at up to 7 MHz. Good small-signal characteristics have been obtained. >

Nonlinear P-I controller design for switchmode DC-to-DC power converters

Abstract: Extended linearization techniques are proposed for the design of nonlinear proportional-integral (P-I) controllers stabilizing, to a constant value, the average output voltage of pulsewidth modulation (PWM) switch-regulated DC-to-DC converters. The Ziegler-Nichols method is used for the P-I controller specification, as applied to a family of parametrized transfer function models of the linearized average converter behavior around a constant operating equilibrium point of the average PWM controlled circuit. The form in which the designed nonlinear P-I controllers are to be used in the actual discontinuous PWM feedback scheme is also indicated. The boost and the buck-boost converters are specifically treated, and the regulated performance is illustrated through computer simulation experiments. >

Constant-frequency control of quasi-resonant converters

Abstract: An additional independent control needed to eliminate the undesirable variable switching frequency of quasi-resonant (QR) converters is obtained by replacing the output rectifier by an active switch. The concept is applicable to all classes of converters. Compared to QR converters with conventional switch realization, constant-frequency quasi-resonant (CF-QR) converters exhibit the same type of switching transitions and similar switch voltage and current stresses. Advantages of CF-QR converters are not restricted to the constant-frequency control. In all classes, operation at zero load is possible, so that the available load range is unlimited. The range of attainable, conversion ratios is significantly extended in the classes of zero-voltage quasi-square-wave (CF-ZV-QSW) and zero-voltage multiresonant (CF-ZV-MR) topologies. A practical design example of a 25 W CF-ZV-MR buck converter is constructed and evaluated. The converter operates at 2 MHz from zero load to full load, with a full-load efficiency of 83%. Simple duty ratio control is used to maintain the output voltage constant for all loads. The circuit is inherently immune to the short-circuit condition at the output. Disadvantages of CF-QR converters are the increased gate-drive losses and increased complexity of the power stage and the control circuitry. >

A unified analysis of resonant converters

Abstract: The general method of analysis for resonant power converters is presented. This analytical method generalizes the idea of state-space-averaging technique to overcome the limitations of the conventional state-space-averaging method. As the result, the characteristics of resonant power converters are clarified so that transfer functions and stability conditions are revealed. In addition, a computer program of analysis based on the proposed method is developed. The program can be applied to various resonant power converters, even when they have parasitic losses and higher-order resonant circuits. >

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

Abstract: The performance of the parallel resonant converter and the combination series/parallel resonant 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 behaviour 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. >

The control of switching DC-DC converters-a general LWR problem

Abstract: The control of switching DC-DC converters is reviewed. It is regarded as a general linear quadratic regulator (LQR) problem, and an innovative optimal and robust digital controller is proposed. The control strategy adopted can achieve good regulation, rejection of modest disturbances, and the ability to cater to switching converters with RHP zeros. This controller design is a general approach that is applicable to all PWM-type DC-DC converters with their circuit topologies known or unknown. Modern CAD techniques are used to reach the final control law. Application to a published Cuk converter is used as an example, and the performance is evaluated. >

A new approach to low ripple-noise switching converters on the basis of switched-capacitor converters

Abstract: A new approach to a low ripple-noise switching converter is presented. The starting circuit is a basic switched-capacitor (SC) converter cell from which several types of low ripple-noise switching converters are generated. Two generated converters are employed for switching regulators hybridized by copper thick films on alumina substrates to realize low ripple noise. As a result, the ripple noise in the output voltages is reduced to less than 5 mVpp. Finally, this approach enables design of an ideal switching converter with zero input and output current ripple. >

Small signal equivalent circuit modeling of resonant converters

Abstract: A general analytical procedure is presented for the equivalent circuit modeling of resonant converters, using the series and parallel resonant converters as examples The switched tank elements of a resonant converter are modeled by a lumped parameter equivalent circuit The tank element circuit model consists, in general, of discrete energy states, but may be approximated by a low-frequency continuous time model These equivalent circuit models completely characterize the terminal behavior of the converters and are solvable for any transfer function or impedance of interest With the approximate model it is possible to predict the lumped parameter poles and zeros, and to quickly determine the relevant DC gains of the output impedance and the control to output transfer function Closed-form solutions are given for the equivalent circuit models of both converter examples Experimental verification is presented for the control-to-output transfer functions of both series and parallel resonant converters, and good agreement between theoretical prediction and experimental measurement is obtained >

A true PWM zero-voltage switching pole, with very low additional RMS current stress

Abstract: A converter topology referred to as true pulsewidth modulated zero-voltage switching pole with very low additional RMS current stress is presented The main switches are turned on and off at zero-voltage without overvoltage stress, from non-load up to full-load It is regulated by the conventional PWM Auxiliary devices, such as diodes, transistors, inductors, and autotransformers, are employed, but rated at very low RMS current, leading to high efficiency and compactness Analysis, design, simulation, and experimental results are provided The converter is suitable for high-power and high-frequency converters, for UPS and electric drives applications >

State feedback control of current type PWM AC-to-DC converters

Abstract: A control method for current-type PWM AC-to-DC converters that realizes a sinusoidal AC input current and unity power factor is discussed in detail. In such converters, an LC filter placed on the AC side may cause a resonant problem, especially in the transient condition. To overcome this problem, state feedback control is introduced, and a control strategy suitable for DC-output current control as well as AC-side current control is proposed. Circuit parameters and feedback coefficients in the AC-side current control system are optimized on the basis of an analysis in which the system is treated as a sampled-data system. A method of investigating parameters in the DC-side current control system is shown. To confirm the effectiveness of the control strategy and the validity of the analytical results, an experimental investigation of the basic characteristics of the system is made. As an example, this system is applied to controlling the current waveform in the reactor. The experimental results for this application are also included. >

Application of the time varying transfer function for exact small-signal analysis

Abstract: An analysis method for determining the control-to-output linearized describing function of time-interval-modulated switched networks using time-varying system theory was previously proposed by the author. A simplification is now presented which eases the analysis considerably. Use of the simplified approach is demonstrated in the derivation of the control-to-output frequency response of pulse-width-modulated (PWM) DC-to-DC switching power converters operating in discontinuous conduction mode (DCM) and current programmed converters operating in continuous conduction mode (CCM) as well as in DCM. Experimental results are presented which verify the modeling approach. >

Digital equalization of time interleaved analog to digital converters

Abstract: An equalization method is provided for compensating for variations in the characteristics of individual analog-to-digital converters found in a time interleaved analog-to-digital converter circuit. One of a plurality of converters is chosen as a reference converter. Individual characteristics of the remaining converters are compared with the reference converter to provide differential responses therewith. The differential responses are equalized to provide compensation for variations in gain, offset, phase/frequency response, and timing found amongst the plurality of time interleaved converters.

A three-phase resonant PWM DC-DC converter

Abstract: Two types of three-phase resonant pulsewidth-modulation (PWM) controlled DC-DC converters are presented. It is shown that the combination of resonant and PWM control methods can be used to tightly regulate the output voltage from no load to full load at constant switching frequency and with low switching losses. It is also shown that both topologies exhibit zero voltage switching in continuous conduction mode. In discontinuous mode the turn-on losses are very similar to PWM converters. Relevant input and output current waveforms and component design ratings are derived. Key predicted results are verified experimentally on a laboratory prototype unit. >

Control art of switching converters

Abstract: Switching Flow-Graph Model: The Switching Flow-Graph is a unified graphical model of large-signal, small-signal and steady-state behavior of pulse-width-modulated (PWM) switching converters. Switching branches are introduced into the flow-graph to represent the switches of the PWM switching converters. The Switching Flow-Graph model is easy to derive, and it provides a visual physical understanding of switching converter systems. The small-signal Switching Flow-Graph generates analytical transfer functions and the large-signal Switching Flow-Graph is compatible with the TUTSIM simulation program. The Switching Flow-Graphs of PWM switching converters reveal a regular pattern, and they predict right-half-plane (RHP) zeros, caused by the imbalanced effects of the duty-ratio control signal on the output of the switching converters. Criteria are found for the design of damping circuits that are capable of eliminating RHP zeros. General models are derived for current-mode controlled switching converters. In addition, the large-signal model and the small-signal model are verified by experiments. One-Cycle Control Technique: The One-Cycle Control technique is conceived to control the duty-ratio d of the switch in real time such that in each cycle the average of the chopped waveform at the switch output is exactly equal to the control reference. Implementation circuits are found for any type of switch, constant frequency, constant ON-time, constant OFF-time, and variable. One-Cycle Control fully rejects the input signal, and linearly all passes the control signal. This technique turns a nonlinear switch into a linear one. Experiments were conducted using the One-Cycle Control technique on the buck converter and the Cuk converter. One-Cycle Control was found to reject input perturbations and input filter dynamics. The diode voltage of One-Cycle Controlled converters follows the control reference instantaneously in one cycle. One-Cycle Control takes advantage of the pulsed and nonlinear nature of switching converters to achieve instantaneous control of the average value of the diode voltage. This technique is suitable for large-signal control of PWM switching converters and quasi-resonant converters.

A behavioral model of A/D converters using a mixed-mode simulator

Abstract: A mixed-mode behavioral model of analog-to-digital (A/D) converters is described. A generalized model structure is introduced. The basic function of an A/D converter is to convert an analog voltage into a digital code, for example, a binary number. Three conversion methods (successive approximation, flash, and dual integration) which are commonly used in A/D converters are modeled and can be selected simply by specifying a parameter of the model. For brevity, only the successive-approximation method is described. The modeling considerations of various parts in the A/D converter, including the input amplifier, D/A converter, comparator, and the synchronization problem, are described. The model has been implemented in the Saber mixed-mode simulator. Simulation results are given. >

Two stage a/d converter utilizing dual multiplexed converters with a common converter

Abstract: A converter including an even and an odd digital-to-analog converter for converting digital signals from a successive approximation circuit and controlling the odd and even converters and the analog-to-digital converter device to alternate conversion by the even and odd converters. The odd and even converters operate in oppostie phases such that while one is in an acquisition phase the other is in a conversion phase. Each of the odd and even converters includes a separate coarse digital-to-analog converter and a common fine digital-to-analog converter. The control circuit resets the fine digital-to-analog converter during an initial portion of the conversion phase of each of the coarse digital-to-analog converters. In a two stage flash converter, the first stage includes a single analog-to-digital converter and the second stage includes a single digital-to-analog converter and alternatingly operating even and odd analog-to-digital converters.

Practical switch based state-space modeling of DC-DC converters with all parasitics

Abstract: All parasitics such as switch conduction voltages, conduction resistances, switching times, and ESRs of capacitors are counted in a proposed DC-DC power convertor state-space modeling based method on nonideal switching functions. An equivalent simplified model is derived from the complex circuit with parasitics. The modeling procedure is shown for the buck-boost converter as the general converter among the buck, boost, and buck-boost converters. The pole frequency, DC voltage gain, and efficiency are analyzed and verified by experiments that show good agreement with theory. The procedures for determining the gain margin of the controller, the turn ratio of an isolation transformer, the optimum duty factor, and the switching frequency are given for an example flyback converter. >

A SPICE model for current mode PWM converters operating under continuous inductor current conditions

Abstract: A SPICE simulation model of current-mode pulse-width modulation (PWM) converters operating in the continuous mode is described and tested against analytical expressions and experimental data for buck and boost converters. The simulation model is also used to compare an earlier average model to a recently suggested modification and to examine the effect of the gain factor in the current feedback path. >

Dynamic current distribution controls of a parallel connected converter system

Abstract: Based on the central-limit control algorithm for the parallel connected converter system, two improved dynamic current distribution control methods are introduced: the programmable current distribution control (PCDC) and the maximum current limit control (MCLC). In PCDC, the ratio of the output current of each converter to the total output current can be programmed according to the desired application objective while the output voltage remains regulated. In the MCLC, all converters in the system may not be turned on at the same time depending on the load conditions. The steady-state analyses and design consideration of the PCDC controlled converter system are presented. The steady-state current distribution error (CDE) between the output current of converters is used as a criterion to evaluate the system performance. The design consideration of choosing proper loop compensators, and scaling factors to reduce the CDE is also introduced. These two schemes can be combined to achieve better system performance, which increase the life-time, reliability, and efficiency of the overall converter system. >

Reliability improvement in parallel connected converter systems

Abstract: The authors present methods and analyses for improving the reliability of a parallel-connected converter system under master-slave control with maximum current limit. The proposed schemes can identify the defective converters and take appropriate action to ensure the normal operation of the system. In addition, the control techniques used are able to determine the necessary number of active converters for any load condition. Consequently, the degree of redundancy increases significantly and the overall system reliability and performance are improved. >

A new combined system of series active and shunt passive filters aiming at harmonic compensation for large capacity thyristor converters

Abstract: A novel combined system of a series active and shunt passive filter is proposed. This system, in which the required rating of the series active filter is only 0.4% as compared with the capacity of a harmonic-producing load, can suppress harmonics in power systems. Compensation characteristics are investigated in detail, and it is clarified theoretically that the compensation characteristics are equivalent to those of the already proposed combined system. Excellent practicability and validity in connection with compensating for harmonics produced by large-capacity thyristor power converters are verified experimentally. >

Computer-aided modeling of quasi-resonant converters in the presence of parasitic losses by using the MISSCO concept

Abstract: The DC and small-signal models of quasi-resonant converters, operating in both half-wave and full-wave modes, are developed in a suitable form for computer simulation. The starting step is the extraction of a minimum separable switching configuration (MISSCO) containing all power switches but a minimum number of other components (resonant ones). By using the step-response analysis and average technique, and by perturbing and separating the DC and AC components in the resulting equations, the equivalent models of MISSCO are derived. They are introduced in the converter structure to replace the circuit initially extracted. Models of different quasi-resonant converters can be obtained by this general approach. The analysis takes into account the conduction losses of the switching devices and reactive elements, which improves considerably the model accuracy. Model-based computer simulation agrees with the experimental results. >

A new state feedback control of resonant converters

Abstract: A state feedback control that can be easily implemented is proposed to improve the stability and dynamic characteristics of resonant power converters. An important characteristic of the system with the proposed control is the reduction of order in the discrete time domain. The design parameters of the control are reduced by one, compared with those of the conventional linear state feedback control, and the design procedure is similar to that of a variable structure system (VSS) control. The proposed control is illustrated by its application to a series resonant power converter. The experimental results confirm the validity of the proposed control. >

Analysis of high-performance counter-type A/D converters using RSFQ logic/memory elements

Abstract: A new family of counter-type Josephson-junction A/D converters using ultrafast rapid single-flux quantum (RSFQ) logic/memory elements is proposed. The converters are built in two main blocks: a low-bit differential-code A/D converter running with subterahertz clock speed and a RSFQ-logic-based digital processing unit providing digital low-pass filtering and sample rate reduction. It is shown that such converters can be treated as digital SQUIDs possessing an extremely high slew rate (up to 10/sup 11/ phi /sub 0//s) combined with flux resolution close to that of analog DC SQUIDs (up to 10/sup -6/ phi /sub 0/Hz/sup -1/2/). Several ways of implementing both main blocks to make it possible to tradeoff these parameters against converter complexity are presented and discussed.

A new family of isolated zero-voltage-switched converters

Abstract: A family of isolated, zero-voltage-switched converters which utilizes the magnetizing inductance of the transformer to achieve zero voltage turn-on of the primary switches is proposed. In addition, by employing saturable inductors on the secondary side, soft turn-off of the output rectifiers is obtained with a minimum circulating energy flowing through the converter. The proposed converters can operate either with a variable or constant switching frequency. A complete DC analysis and design guidelines for the half-bridge topology are described, and the performance of a 100 W experimental converter is presented. >

Practical switch based state-space modeling of DC-DC converters with all parasitics

Abstract: All parasitics such as switch conduction voltages, conduction resistances, switching times and ESR's of capacitors are counted in the new state-space modeling based on non-ideal switching functions. An equivalent simplified model is derived from the complex circuit with parasitics. Hence the results are very simple. The pole frequency, dc voltage gain and efficiency of the general converter, the buck-boost converter are analyzed and verified by experiments with good agreements with the theories. The procedure for determining the gain margin of controller, the turn-ratio of isolation transformer, the optimum duty factor and the switching frequency is given for an example fly-back converter

Economic single phase to three phase converter topologies for fixed frequency output

Abstract: Several component-minimized circuit topologies for single-phase to three-phase conversion are proposed. The proposed topologies employ fewer semiconductors devices and generate high-quality output voltages. A suitable modification to achieve an active input current shaping feature is illustrated in detail. Analysis and simulation of the proposed schemes are carried out to show the high-performance features. Suitable guidelines for the selection of filter components and to facilitate circuit design are presented. Selected results are verified experimentally on laboratory prototype converters. >