Showing papers on "Converters published in 1978"

Modelling, analyses and design of switching converters

Abstract: A state-space averaging method for modelling switching dc-to-dc converters for both continuous and discontinuous conduction mode is developed. In each case the starting point is the unified state-space representation, and the end result is a complete linear circuit model, for each conduction mode, which correctly represents all essential features, namely, the input, output, and transfer properties (static dc as well as dynamic ac small-signal). While the method is generally applicable to any switching converter, it is extensively illustrated for the three common power stages (buck, boost, and buck-boost). The results for these converters are then easily tabulated owing to the fixed equivalent circuit topology of their canonical circuit model. The insights that emerge from the general state-space modelling approach lead to the design of new converter topologies through the study of generic properties of the cascade connection of basic buck and boost converters.

Push-pull switching power amplifier

Abstract: A true push-pull switching power amplifier is disclosed utilizing two dc-to-dc converters. Each converter is comprised of two inductances, one inductance in series with a DC source and the other inductor in series with the output load, and an electrical energy transferring device with storage capability, namely storage capacitance, with suitable switching means between the inductances to obtain DC level conversion, where the switching means allows bidirectional current (and power) flow, and the switching means of one dc-to-dc converter is driven by the complement of a square-wave switching signal for the other dc-to-dc converter for true push-pull operation. For reduction of current ripple, the inductances in each of the two converters may be coupled, and with proper design of the coupling, the ripple can be reduced to zero at either the input or the output, but preferably the output.

A State-Trajectory Control Law for DC-to-DC Converters

Abstract: Mathematical representations of a state-plane switching boundary employed in a state-trajectory control law for dc-to-dc converters are derived. Several levels of approximation to the switching boundary equations are presented, together with an evaluation of the effects of nonideal operating characteristics of converter power stage components on the shape and location of the boundary and the behavior of a system controlled by it. Digital computer simulations ions of d-to-dc converters operating in conjunction with each of these levels of control are presented and evaluated with respect to changes in transient and steady-state performance.

Testing digital/analog and analog/digital converters

Abstract: This paper describes several D/A and A/D converter test circuits which range from simple and low-cost to fully automatic and expensive. Methods are presented to measure the more important specifications of offset, gain, full scale, linearity, and differential linearity errors. The discussions focus on, but are not limited to, testing 12-bit converters. Guidelines are given for determining the required accuracy of the measurement standard and for using proper circuit layout and wiring. Part of the test circuits are static and use a DVM as a reference. Other testers are dynamic and use a fast-settling D/A converter as a reference. Many of the circuits are manually operated, but others are automated using a computing controller. The unique characteristics of converters such as the symmetrical error patterns and the dynamic errors are discussed in light of how they relate to the techniques chosen to measure the errors. Part of the test methods assume that the weight of each bit in a converter is completely independent of the on/off state of the other bits (low superposition errors). When superposition errors are not small, they must be considered before choosing a test method. In general, the intent of this paper is to lay enough ground work so that the user of converter products can implement a test system that is both economical and sufficient to produce the desired results.

Three phase ac to dc voltage converter with power line harmonic current reduction

Abstract: A three phase AC to DC voltage converter includes separate single phase AC to DC converters for each phase of a three phase source with the DC voltage output of the three converters paralleled and controlled to provide necessary regulation Each of the single phase AC to DC converters includes a full-wave bridge rectifier feeding a substantially resistive load including an inverter and a second single phase full-wave bridge rectifier To the extent that each inverter and second single phase full-wave bridge rectifier approximate a resistive load, the source current harmonics are reduced Additionally, the triplen harmonics produced in the three phase source lines by each of the three AC to DC converters are cancelled by the triplen harmonics produced in the three phase source lines by the remaining two AC to DC converters

A new battery charger/discharger converter

Abstract: a new optimum topology dc-todc switching converter is extended to provide bidirectional current flow. The resulting two-quadrant converter can be employed to eliminate the discontinuous curent mode in normal unidirectional applications, but is especially suited for spacecraft battery conditioning as a charge-discharge regulator in place of the conventional separate converters. Implementation of the control features and the battery charge current and voltage limits are discussed.

DC to DC voltage converter

Abstract: The DC to DC voltage converter consists of two single ended pulse width modulated converters with a single voltage control loop, a power balancing control loop and overload protection circuitry. The converters which share the same input and output filters are staggered in time so as to reduce the pulse current in the input filter capacitor and the ripple current in the output filter capacitor thereby permitting a reduction in the size of the input and output filters.

Dynamic testing of high-speed A/D converters

Abstract: The proposed digital techniques determine the transfer characteristics of A/D converters under dynamic operating conditions. Characteristic parameters are derived from the digital outputs of converters. Measurements show the discrepancy between static and dynamic performances.

Dynamic Modelling of Single Generators Connected to HVDC Convertors

Abstract: The transient behaviour of 'unit-type' schemes consisting of HVDC convertors connected to isolated synchronous generators is analysed using state space theory and a numerical solution suitable for digital computation is described. Examples of computed results are illustrated including normal and disturbed operating conditions. These show that 'unit-type' schemes can operate satisfactorily with or without A. C. harmonic filters.

A New Concept for Improving the Performance of Phase-Controlled Converters

Abstract: High-power phase-controlled converters suffer from several fundamental disadvantages. They inject current hannonics into the input ac mains due to their nonlinear characteristics, thereby distort the supply voltage waveform, and demand ractive power from the associated ac power systems at retarded firing angles; also the output voltage is not smooth dc but contains superimposed harmonic ripples. A novel sequential control technique is suggested, which, when applied to more than one converter in cascade, substantially overcomes these disadvantages. The method consists of specifying the proportions of the maximum power to be handled by the individual converters and incorporating a sequence controller, the function of which is to ensure that at any output voltage the converter supplying the minimum power operates over the ful range of thyristor firing angles. The firing angles of other converters are restricted to values corresponding to their ratings. A generalized method of optimizing the performance of sequentially controlled cascaded converters is presented, and the economic viability of the proposed scheme is examined. It is shown that the effective ratings of thyristors in the proposed scheme are greatly reduced. The method should offer improved converter performance in variable speed dc drives, solid-state slip-energy recovery systems, or high-voltage dc transmission systems.

All-MOS analog digital conversion techniques

Abstract: MOS LSl technologies have recently shown their potential for use in precision analog-to-digital (A/D) and digital-to-analog (D/A) converters. Serial A/D converters with 11-bit accuracy and 100-ms conversion time, and successive approximation A/D converters with 10-bit accuracy and 25- \mu s conversion time have been demonstrated.

Control system for commutatorless motor driven through frequency converter

Abstract: A control system for a commutatorless motor comprises a frequency converter which includes two graetz-connected thyristor converters and D.C. lines interconnecting the converters, between an A.C. motor and an A.C. power supply. Motoring operation and regenerating operation are selectively effected between the motor and the power supply. In switching the operation mode, one of the converters which has been operated in a recitifier operation mode is first switched to an inverter operation mode, and after it has been confirmed that a control voltage to determine a firing angle of the one converter has been shifted to an inverter region, the other convertor is switched to the rectifier operation mode.

Parallel Connection of Convertors for HVDC Transmission

Abstract: Subdivision of the total transmission capacity of an HVDC convertor station into smaller parts then one convertor per pole can be done either by series or parallel connection of convertors. Parallel connection which is the subject of this paper, is particularly advantageous when a transmission is built in stages or when the system consists of more than two convertor stations.

D/A and A/D converters

Abstract: If a continuous signal is to be processed using digital methods, the analog variable at the input must be converted to the equivalent number. This is the purpose of an analog-to-digital converter (A/D converter, ADC). For the reconversion of the digital number to a proportional analog voltage or current, a digital-to-analog converter is used (D/A converter, DAC). The following sections deal with the most important principles of D/A and A/D conversion.

Contribution to the development of wind energy systems using static power electronic converters

Abstract: A wind energy system, using a squirrel cage induction machine and a static power electronic conversion equipment, incorporating a novel and economical pulse frequency modulated three phase auxiliary impulse commutated inverter, is described. A complete description of the proposed power as well as control schemes is given, with special reference to its possible application in variable speed wind power conversion scheme. Experimental results obtained on a laboratory breadboard of the power electronic conversion equipment for a 2 KVA,208 V, 60 Hz, 3 phase squirrel cage, inverter fed induction machine in self excited mode of operation with a 3 to 1 speed range, are reported.

Discrete time domain modelling and analysis of dc-dc converters with continuous and discontinuous inductor current

Abstract: Using discrete time state variable representation, a generalized computer-aided modelling and analysis of DC-DC converters is presented. The methodology provides exact modelling and is applicable to all types of power stages and duty-cycle control, including continuous and discontinuous inductor current operation. Converter stability, transient behavior and audio susceptibility can be analytically evaluated and predicted. The generalized theory of the proposed approach to converter modelling and analysis is presented first, followed by a demonstrative example applying the theory to a constant frequency buck converter operating in continuous and discontinuous inductor current mode. Excellent agreement with laboratory test data has been observed.

Reactive-power compensating circuit for polyphase load - automatically adjusts output amplitudes and phases of static converters

Abstract: The reactive-power compensating circuit, for polyphase loads e.g. an arc furnace, has each of the static converters (11-13) coupled to the phase lines (1-3) designed to be self-commutating and with its thyristors (A-D) connected as a single-phase bridge. A transformer (14-16) is connected between the a.c. outputs of each converter and the a.c. supply (4). The converters are coupled in d.c. series with one another. A constant d.c. source (20) is coupled to the terminals (17, 18) of the series circuit. A control circuit (31-33) assigned to each converter sets the amplitude and phase of the output of that converter.

Multiport converters and inverters

Abstract: Two-port immittance converters and inverters are well known active-network ‘components’. In this paper the concepts of conversion and inversion are generalized so as to apply to multiports. A definition of multiport hybrid converter is proposed, and the necessary and sufficient conditions that the matrix description of this multiport must satisfy are derived from the definition. Multiport admittance and impedance converters and inverters are introduced as special cases of hybrid converters, and it is pointed out that, whereas 2-port admittance converters or inverters are always also impedance converters or inverters, and vice-versa, this is not generally true for the multiport converters or inverters proposed here. Multiwinding transformers, multiport gyrators, and most of the circuits that can be used for the simulation of floating inductors are shown to be special cases of multiport converters or inverters. It is believed that the theory of multiport conversion and inversion presented here provides a better understanding of these special cases and is also useful as a contribution to multiport theory in general.

Pulse ratio modulation : an interesting technique to implement dc/dc conversion

Abstract: DC/DC converters may be considered as pulse modulators; the modulation laws usually implemented are those related to pulse frequency (PFM) and pulse width modulation (PWM) techniques. The pulse ratio modulation (PRM) technique, providing several advantages over conventional pulse modulation methods, has been developed for applications in a space vehicle attitude control system. Capable of operation with a high degree of precision and overcoming certain bandwidth problems associated with other modulation techniques, the modulator appears to hold excellent possibilities for applications in a broad range of control systems, such as DC and AC drives. In order to investigate the dynamical properties presented by a feedback control system employing this modulation technique, in the paper a mathematical model is presented, characterizing the PRM in terms of input output relationships. By using the state variables approach, the system is described through a vector recurrence equation and linear bounds on the state characterizing the adopted modulation law. On the basis of this model both the steady state behaviour and the transient response are evaluated. As far as stability properties are concerned, the linearized model is developed in order to determine the local behaviour in correspondence with the steady state solutions, and a comparison is made with an equivalent PWM control system. Moreover a procedure, based on the use of projection operators in vector spaces, is presented to analyse the asymptotic stability in the large.

Open loop characterization of pulse width modulated DC/DC converters by sequential linear analysis

Abstract: Pulse width modulated (PWM) DC/DC converters, as typified by the transistor switching regulated (TSR) power supply treated in this paper, can be simulated by modeling each diode and/or switching transistor as a two-valued resistance. In this way, the power supply is represented as a sequence of strictly linear circuits, each having the same topology but with its two-valued resistances determined by the corresponding on-off states of its diodes and transistors. We can compute the startup behavior and periodic response of such power supplies in terms of the eigenvalues and eigenvectors of each of these linear circuits in sequence. What is more, we can also obtain directly the overall state transition matrix from which, in turn, we can predict the open loop characteristics of the entire power supply. This information is vital to the design of feedback networks that provide stable regulation.

Direct-energy converters: efficiency and cost estimates for two electrostatic concepts

Abstract: This study is concerned with two specific types of electrostatic direct energy converters for direct recovery of a large fraction of the plasma ion energy from magnetic-mirror-type fusion reactors. Simplified equations are presented for each of the important loss mechanisms in both single-stage direct converters and multistage venetian blind-type direct converters. These equations can be used to estimate the efficiency and electric power output of the direct converter subsystem. Scaling relations for the cost of each major component in the direct converter subsystem are also given; these include the vacuum tank, direct converter (DC) modules, the DC power conditioning equipment, cryogenic vacuum pumping system, and the thermal bottoming plant. Examples of cost-effectiveness studies for two specific reference direct converter designs are presented in terms of the specific capital costs (i.e., the capital cost per unit of electric power produced) for the direct converter subsubsystem. These examples show that relaxation of the requirement for small charge exchange losses can significantly reduce the specific capital costs of the direct converter subsystem.

Ad conversion system

Abstract: PURPOSE:To obtain an A/D conversion system which is able to operate at a high speed, by combining a plural number of A/D converters of the same characteristics and sample holding (SH) circuits and by enabling an electronic method to switch them as time passes.

Predicting performance of power converters operating with switching frequencies in the vicinity of 100 kHz

Abstract: Predicting the current, voltage and power stresses in high-power high-frequency converters using available component specifications and device models presents a formidable challenge. Switching phenomena and circuit layout influences that are negligible at lower switching frequencies become first-order concerns as power and frequency increase. These effects are examined for three different converter configurations.

Electromagnetic Processes in AC/DC Power Converters: Part II---Symmetrical Transient Processes in Power Converters

Abstract: The following problems are discussed in the article: 1) equivalent diagram of the converter; 2) symmetrical transient processes (short circuits in ac and dc systems, inversion of dc voltage).

Monolithic charge-transfer A/D converter

Abstract: The growing utilization of microprocessors and digital LSI circuits In solid-state control systems is currently generating a considerable interest in the development of low-cost technology-compatible analog-to-digital converters. In this paper, the design and operation of a monolithic charge-transfer analog-to-digital converter is reviewed, and its application in a digital control system where It has been used for voltage, resistance, and capacitance measurement is described. Experimental results showing better than l-mV resolution capability (equivalent to 10-12 bits) are reported.

Loading equaliser for parallel converters - derives control signals by comparing sawtooth voltage with voltage proportional to load currents

Abstract: The loading equaliser, for parallel converters, has all converters sharing the same regulator. The separate control voltages for each converter current regulating element (e.g a transistor) are derived by comparing a sawtooth voltage with a voltage dependent on a converter load current. Each converter may have its own sawtooth generator synchronised with the other sawtooth generator synchronised with the other sawtooth generators by a shared clock. The advantage lies in the equaliser making use of circuits already present in the converter system.

Non-Magnetic DC to DC Converter Circuits

Abstract: Applications and implementations of small nonmagnetic dc-to-dc converter circuits realizable as hybrid integrated circuits are reviewed. In low power applications these converters offer smaller size, lower cost, and less complexity than more traditional converters using magnetic energy storage elements. In addition, when used as on-board power units, these converters can be turned on and off in response to system power needs, resulting in significant energy savings.

Protective relay system

Abstract: PURPOSE:To improve the noise-proof property and prevent effects of harmonics by providing first and second input converters, phase shifter circuits, multipliers and an adding circuit for making the sum of the outputs of the individual multipliers.