Showing papers on "Converters published in 1986"

Control Strategy of Active Power Filters Using Multiple Voltage-Source PWM Converters

Abstract: The control strategy of active power filters using switching devices is proposed on the basis of the instantaneous reactive power theory. This aims at excellent compensation characteristics in transient states as well as steady states. The active power filter is developed, of which the power circuit consists of quadruple voltage-source PWM converters. As the result, interesting compensation characteristics were verified experimentally which could not be obtained by the active power filter based on the conventional reactive power theory.

Zero-voltage switching technique in DC/DC converters

Abstract: A novel resonant switch operating under the principle of zero-voltage switching is presented. In contrast to the zero-current switching, this technique eliminates the switching loss and dv/dt noise due to the discharging of MOSFET's junction capacitances and the reverse recovery of diodes, and enables the converters to operate at yet higher frequencies.

Generation, Classification and Analysis of Switched-Mode DC-to-DC Converters by the Use of Converter Cells

Abstract: A method is presented which combines generation, classification and analysis of DC-to-DC PWM converters. Fundamental blocks known as converter cells can be used to generate a plethora of converters leading to a number of useful new converter topologies. A classification of basic converters is proposed in terms of converter-cell generated families. The converter cells considered may be seen as three-terminal devices for which terminal characteristics may be easily found. DC and AC small-signal models for each converter cell can be derived obviating the need to rederive these models for each of the converters of a particular family.

Reference refreshing cyclic analog-to-digital and digital-to-analog converters

Abstract: A method of cyclic analog-to-digital (A/D) and digital-to-analog (D/A) conversion using switched-capacitor techniques is described. By periodically modifying the reference voltage to compensate for the nonideal signal-transfer-loop gain, it is possible in principle to build A/D and D/A converters whose linearity is independent of component ratios and that occupy only a small die area. These converters require two moderate-gain MOS operational amplifiers, one comparator, and a few capacitors. A test chip for A/D conversion was built and evaluated. The test data show that the A/D performs as a monotonic 13-bit converter with maximum 1-LSB differential and 2-LSB integral nonlinearity.

Sliding Mode Control of Power Converters

Abstract: Switched mode power converters are being used extensively for the purpose of efficient power conversion. Such converters are nonlinear, time variant systems. In the past such converters were being modelled using the state space averaging method. The theory of variable structure systems (VSS), and sliding mode control form a mutually complementary analysis and design tools for the control of switched mode power converters. The application of sliding mode control is presented for dc-to-dc converters and electrical motor drives in this thesis. The concept of sliding mode control is brought out through exhaustive examples of second order systems. The equivalent control, an analysis method of VSS, is applied to obtain transfer function description of dc-to-dc power converters. The sliding mode control is applied to the control problem of dc-to-dc power converters and speed controlled electrical drives to develop practical design techniques. The practical design methods are confirmed through experimental results.

Power electronic converters: AC-DC conversion

Abstract: 1 Introduction and Presentation.- 1.1 Types of Inverters: Principles.- 1.1.1 Voltage-Source Inverters.- 1.1.2 Current-Source Inverters.- 1.1.3 Resonant Load Inverters.- 1.2 Types of Semiconductor Devices. Supply and Load Imperfections. Filters.- 1.2.1 Types of Semiconductor Devices.- 1.2.2 DC-Supply Imperfection. Input Filter.- 1.2.3 AC-Load Imperfection. Output Filter.- 1.2.4 Remarks on Reversibility.- 1.3 Principal Applications. Consequences on the Study.- 1.3.1 Constant Frequency and Voltage Supplies.- 1.3.2 Speed Variation of AC-Current Motors.- 1.3.3 Load-Resonant Inverter Applications.- 2 Voltage-Source Inverters with One Square-Pulse per Half-Cycle.- 2.1 Single-Phase Inverter with Centre-Tapped Transformer.- 2.1.1 Principle.- 2.1.2 Characteristics.- 2.2 Single-Phase Half-Bridge Inverter.- 2.2.1 Principle.- 2.2.2 Characteristics.- 2.3 Single-Phase Full-Bridge Inverter.- 2.3.1 Principle.- 2.3.2 Characteristics.- 2.3.3 Comparison of the Three Single-Phase Voltage-Source Inverters.- 2.4 Three-Phase Full-Bridge Inverter.- 2.4.1 Balanced Mode Operation.- 2.4.2 Balanced Operation Characteristics.- 2.4.3 Delta-Connected AC Load.- 2.4.4 Operation with an Unbalanced Load.- 2.5 Input Filter.- 2.5.1 Input Current and Output Voltage Harmonics.- 2.5.2 Application to the Different Inverters.- 2.5.3 Remark Concerning the Use of the Half-Bridge Inverter Divider as an Input Filter Element.- 2.6 Output Filter.- 2.6.1 General Equations.- 2.6.2 Effects of the Filter on the Fundamental.- 2.6.3 Effects of the Filter on the Harmonics.- 2.6.4 Choosing L and C.- 2.6.5 Notes on Other Filters.- 2.6.6 Notes on Variable Frequency-Supplied Loads.- 3 Pulse-Width-Modulated Voltage-Source Inverters.- 3.1 Single-Phase Half-Bridge Inverter.- 3.1.1 "Switch" Control. Waveforms.- 3.1.2 Output Voltage.- 3.1.3 Currents.- 3.1.4 Remarks on Control Phase Lock and on Asynchronous Modulation.- 3.2 Three-Phase Full-Bridge Inverter.- 3.2.1 "Switch" Control. Waveforms.- 3.2.2 Sinusoidal Reference.- 3.2.3 Injection of Harmonic 3 into the Reference.- 3.2.4 Other Modifications of the Control Law.- 3.3 Single-Phase Full-Bridge Inverter.- 3.3.1 "Switch" Control. Waveforms.- 3.3.2 Study of the Output Voltage.- 3.3.3 Study of the Currents.- 3.3.4 Digital Reference.- 3.4 Computed Modulation.- 3.4.1 Characterising the Output Voltage.- 3.4.2 Eliminating the First Harmonics of the Output Voltage.- 3.4.3 Minimising the Weighted Harmonic Rate.- 3.4.4 Control of the Full-Bridge Inverter by Shifting the Voltage of the Two Half-Bridges.- 4 Commutations in Voltage-Source Inverters.- 4.1 Commutation of the Bipolar Transistor in Full-Wave Inverters.- 4.1.1 Commutation Process with RC Snubber.- 4.1.2 Computing the Losses.- 4.2 Commutations of the Bipolar Transistor in PWM Inverters.- 4.2.1 Commutation at Turn-On.- 4.2.2 Commutation at Turn-Off.- 4.2.3 Power Dissipated in the Resistances.- 4.2.4 Remarks on Reverse Conduction in the Transistor.- 4.3 GTO Thyristor Commutations.- 4.3.1 Commutation at Turn-On.- 4.3.2 Commutation at Turn-Off.- 4.3.3 Power Dissipated in the Resistance.- 4.4 Field Effect Transistor Commutations.- 4.4.1 ON-Commutation.- 4.4.2 OFF-Commutation.- 5 Current-Source Inverters.- 5.1 Single-Phase Inverters.- 5.1.1 Inverters with a Centre-Tapped Transformer.- 5.1.2 Full-Bridge Inverter with One Square-Wave Pulse per Alternance.- 5.1.3 PWM-Controlled Full-Bridge Inverter.- 5.1.4 Remarks on PWM Current-Source Inverters.- 5.2 Full-Bridge Three-Phase Inverter.- 5.2.1 Full-Wave Control.- 5.2.2 PWM Control with Sinusoidal Modulation.- 5.2.3 PWM Control with Computed Modulation.- 5.3 Feeding an Inductive Load.- 5.3.1 Thyristor Current-Source Inverter with Auxiliary Commutation Bridge.- 5.3.2 Self-Commuted Current-Source Inverter with Thyristors.- 5.3.3 GTO Current Inverter with Clamping Circuit.- 5.4 Notes on the Configurations with a Pulse Number Greater than 6.- 5.4.1 Configuration with Pulse Number Equal to 12.- 5.4.2 Configuration with Pulse Number Equal to 18.- 5.5 Notes on the Computation of the Current-Source Inverter Input Filter.- 6 Resonant Inverters.- 6.1 Series Resonant Inverter.- 6.1.1 Response of the Series Resonant Circuit to a Square-Wave Voltage.- 6.1.2 First Harmonic Method.- 6.1.3 Operation and Control of the Inverter.- 6.1.4 Characteristics.- 6.1.5 Starting. Protection.- 6.1.6 Variants.- 6.2 Parallel Resonant Inverter.- 6.2.1 Response of the Parallel Resonant Circuit to a Square-Wave Current.- 6.2.2 Inverter Operation and Control.- 6.2.3 Characteristics.- 6.2.4 Starting. Protection.- 6.2.5 Variants.- 6.3 Resonant Supplies.- 6.3.1 Supply with a Series Resonant Inverter.- 6.3.2 Supply with a Series-Parallel Resonant Inverter.- 6.3.3 Double Resonance Supplies.- Appendices.- Appendix A: Input Filter in Voltage-Source Inverters.- A.1 Inverters with Two "Switches" per Phase.- A.2 Full-Bridge Single-Phase Inverter.- Appendix B: "Sinusoidal" Voltage-Source Inverters.- B.1 Voltage Waveform.- B.2 Production of Optimized Waveforms.- B.3 Variation in the Output Voltage.- B.4 The most Usual Type of Configuration.- Appendix C: Forced Turn-Off of Thyristors in Voltage-Source Inverters.- C.1 Parallel Commutation by Oscillating Circuit.- C.2 Parallel Commutation by Capacitor.- C.3 Series Commutation.- Appendix D: PWM Rectifier.- D.1 The Structure.- D.2 The Converter Alone.- D.3 The Converter and its Input Filter.- D.4 The Converter with its Input and Output Filters.- Appendix E: Use of the Four-Quadrant Chopper as a PWM Rectifier.- E.1 "Switch" Control.- E.2 Current Harmonics Taken from the Supply.

State of the art PWM techniques: A critical evaluation

Abstract: With the introduction and wide acceptance of gate turn off power devices (e.g. Bipolars, Power Fets, GTO's, etc.), the switching behavior of converters has reached the point where further improvements in firing and switching networks bring only marginal benefits. Consequently, the research interests in the area of static converters have been shifting toward improving the process of power conversion through a combination of new circuit topologies and improved voltage and harmonic control PWM techniques. As a result several such techniques have been proposed lately.

Low Frequency Characterization of PWM Converters

Abstract: Low frequency components of states or outputs in pulse-width modulation (PWM) dc and ac converters can be characterized by differential equations called describing state-space equations. These equations are derived by inspection of converter topology and use of switching functions and duty ratios. Their steady-state and small-signal dynamic solutions show how energy-storage elements in a converter/load system shape the frequency response of conversion functions established by the switches.

Small-Signal Frequency Response Theory for piecewise-constant two-switched-network dc-to-dc converter systems

Abstract: Small-Signal Frequency Response Theory is a theory for calculating the output spectrum of ideal dc-to-dc converter systems, i.e. systems with system coefficients piecewise constant in time, for a given spectrum of the signal injected into the control-input, in the small-signal limit. This theory, unlike other methods, can be applied to both resonant and PWM converters, and gives analytic results in closed form for ideal converters. This paper discusses the special case of ideal two-switched-network converter systems in PWM, programmed, and bang-bang operation. For the examples under study, theoretical prediction and experimental results are found to differ by at most 2dB in amplitude and 10 degrees in phase at most frequencies up to three times the switching frequency. Examples are given in this paper for which the theory gives the correct prediction, while other methods fail.

A Computation Algorithm for Assessing Voltage Stability at AC/DC Interconnections

Abstract: A new method for the analysis of ac voltage stability problems at HVDC terminals, when imbeded in large networks, is presented. The method can be used to evaluate the effects of dc modes of operation, ac system operating conditions and VAr compensation schemes on the combined system voltage stability. Dynamic properties of both ac and HVDC systems are incorporated in the solution algorithm. A step-by-step technique is developed for integrating the new algorithm with available load flow programs. Examples are given to demonstrate the performance of a new control strategy for HVDC converters connected to weak ac systems and the results are compared to classical solutions.

Nonlinear control laws for switching power converters

Abstract: Nonlinear control laws for switching power converters are explored, using an up-down converter as a vehicle. A nonlinear change of variables is used to transform the usual state-space description into one that is more amenable to design of a sliding mode control. Results of numerical simulations and of a microprocessor implementation based on look-up tables are presented.

Small-Signal Dynamic Analysis of Regulated Class E DC/DC Converters

Abstract: Class E dc/dc converters can operate at high switching frequencies with very low switching power losses. Using commercially available power transistors and diodes, Class E converters can operate at switching frequencies in the low-MHz range, with efficiencies of about 85 percent. Previous papers dealt with the circuit parameter values needed to obtain high-efficiency operation and output-voltage regulation, and with the static control characteristics of the Class E dc/dc converter cell. The analysis is extended to include the dynamic control characteristics and further information about the static characteristics. The theoretical predictions are verified by experimental measurements on a 40-W 1.5-MHz converter.

Conducted interference voltage of AC-DC converters

Abstract: In this article an analytical method for calculating the conducted interference voltages of the three basic ac-dc converters buck, boost and buck-boost with sinusoidal input current and unity power factor is presented. The analysis includes a simulation of the quasi-peak measurement according to CISPR (Comite International Special des Perturbations Radioelectriques). The influence of the different circuit parameters is investigated and the validity is confirmed by experimental results.

Simulation and Experimental Study of a Reactively Loaded PWM Converter as a Fast Source of Reactive Power

Abstract: The question of eliminating distorted current waveforms from power networks by active power filters is investigated. If the active current is subtracted from the distorted current, the compensating equipment must be capable of generating the inverse of this difference. Addition of this compensating current to the distorted current then eliminates the distortion. This requires the capability to generate these currents with response times many times less than the fundamental power frequency cycle. This capability is presented by reactively loaded PWM converters. A system configuration with three single-phase PWM converters building a three-phase unit is investigated. The single-phase converter with PWM operation, inductive reactance as load, low-pass input filter, and representative system losses is simulated by state-space techniques. An experimental system of 1 kVA is also constructed for verification. Good correspondence between the simulation and experiment s shown. Starting up the system, compensating the system losses from the supply, and the influence of the control system on the compensating capabilities are investigated. It is concluded that a PWM converter with a reactive load can be used as a fast distortion compensator and that the present state of the art and future development of PWM converter technology will make this technique applicable at least up to 1 Mvar.

Switched-capacitor algorithmic digital-to-analog converters

Abstract: Novel switched-capacitor circuits for algorithmic digital-to-analog conversion are described. The conversion process is insensitive both to the offset voltages of op-amps and to parasitic capacitances. The capacitance mismatch errors are also minimized because only a small number of unit capacitors are used. An error analysis is presented that shows an accuracy greater than 10-bits can be obtained using present MOS technologies. Besides being very accurate, the new converters possess the important feature of being integrable using only a minimal amount of chip area.

Unified Modeling of Rectifier-Controlled DC-Power Supplies

Abstract: The known analysis of dc-dc converters in discontinuous operation mode and with voltage commutation based on a piecewise-linear description is extended to the analysis of line-commutated converters. With the latter as system-dependent pulsewidths the overlap angles appear, which can be computed in a manner analogous to the current-flow duration and the reloading time, respectively. This leads to a unified state-space modeling of dc-dc and ac-dc converters by which the steady-state and the dynamic small-signal behavior can be evaluated directly. If the piecewise-defined system equations are integrated numerically, a rather generalized analysis of power converters is found if the structure of switched systems is taken into account. As an illustrative example, a voltage-commutated dc-dc converter with a nonlinear dc inductance is studied.

Frequency stabilization and synchronization of free-running current-mode-controlled converters

Abstract: Power converters with free-running current-mode control (hysteretic, constant-“off”- time, or constant-“on”-time) can be frequency-stabilized or can be synchronized to a reference frequency. Those can by accomplished by feedforward, feedback, or phase-locking techniques. With hysteretic control, the frequency is controlled by varying the current hysteresis. With constant-“off”-time or constant-“on”-time control, the frequency is controlled by varying the “off” time or the “on” time, respectively. We consider all possible methods of frequency stabilization and synchronization for the three types of free-running current-mode control, used with the three basic types of power converters (buck, boost, and buck-boost). We give analyses and practical design information for the most-important combinations, and experimental data for a buck converter with constant-“off”-time control and feed-forward frequency stabilization.

Sliding mode control of DC-AC converters

Abstract: Switching converters are nonlinear dynamic systems of variable structure. The control of output variables is accomplished by the proper choice of sequence and time duration of OFF and ON states of the switches. The theory of VSS (Variable Structure Systems) and deliberate introduction of sliding modes makes possible realization of rather simple and yet quite efficient control schemes for various types of converters (DC-DC, AC-AC, DC-AC). This paper presents a method for control system synthesis of DC-AC converters in the class of VSS systems.

Control system for an electric locomotive having ac to dc converters

Abstract: An electric locomotive has two AC-DC converters which are connected in cascade, and a power factor controller is connected to one of the converters. Two automatic pulse phase shifters are provided for the two converters and controlled by a signal responding to a difference signal between a current flowing in the converters and a reference signal. One of the input signals of the automatic pulse phase shifter is regulated by a bias signal. The output from each of the automatic pulse phase shifters to each of the converters is switched when the measured speed of the locomotive exceeds a predetermined reference speed signal.

DC to DC Converters with High-Frequency AC Link

Abstract: The properties of a dual thyristor are advantageously used for the development of very high-efficiency dc-dc converters. A new device named ``dual thyristor'' having static and dynamic characteristics dual to that of a thyristor has been recently reported. The development aspects of a dual thyristor based high-efficiency dc-dc converter with an intermediate ac link using a high-frequency inverter is described. The output voltage is regulated by varying the frequency of operation of the inverter. In spite of the relatively high-frequency operating range of this device between 30 kHz and 100 kHz, high efficiency of operation of the converter is obtained due to the use of lossless snubbers. Further, the selfprotective nature of the device against overcurrents enables a high reliability of operation of the dc-dc converter.

High-reliability fiber optic repeater

Abstract: In a fiber-optic network having a first fiber and a second fiber, a T-connection repeater provides connection to a plurality of terminal devices. The T-connection fiber-optical repeater has converters for generating optical signals to be distributed to terminal devices connected the repeater, and redundant optical-to-electrical converters for receiving optical signals from the terminal devices. Reliability is markedly increased by including one or two mixing stars in the fiber system between the converter and the repeaters. The number of converters and supporting circuitry can be reduced by coupling more than one fiber from the star or stars to each converter. Monitoring optical-to-electrical converters can be coupled to the stars in order to detect failure of electrical-to-optical converters connected to the stars.

Static device for control of energy-exchange between electrical generating and/or receiving systems

Abstract: A device for regulating the exchange of energy between at least two generating and/or receiving, DC and/or AC electrical systems, (S0 . . . Sn) for controlling the powers delivered or absorbed by said systems, these electrical systems being Y-connected to an oscillating circuit (OSC) by means of static switches (Cp, Ca1 . . . Cn), a controllable phase-shifting circuit (D) for driving the converters for producing at their outputs electrical values with a common frequency and with constrained phases; the oscillating circuits (OSC) oscillating at the above stated frequency for assuring temporary energy storage, and control means (MC) for feeding control signals as a function of the desired energy exchanges to the phase shifting circuits (D).

New topologies of fully regulated two-output dc-to-dc converters with small frequency variation range

Abstract: This paper offers a new solution to the design of two-output dc-to-dc converters having one sole power transistor. The combination of a resonant converter and a tapped-inductor converter is the basis of this new approach which represents an improvement on previous studies. The fact that the dc voltage gain of the resonant converter is a function of the switching frequency but not of the load nor of the duty cycle and the fact that the tapped-inductor converter is a function of the duty cycle but not of the frequency nor of the load, enables the two outputs to be regulated with only small switching frequency variations and with only slight interaction between the two outputs. A prototype of this converter has been built and the results are discussed.

Two Integrated Progressive Scan Converters

Abstract: Before explaining the application and implementation of the two scan converters in detail, a brief description will be given of the digital environment in which these converters can be applied. Some general aspects of progressive scan and its impact on vertical bandwidth will also be discussed.

Resonant converters : topologies, dynamic modeling and control

Abstract: The author hereby grants to MIT permission to reproduce and distribute copies of this thesis document in whole or in part.

An improved parallel control circuit for saturable reactor output regulators in high-frequency switched-mode converters

Abstract: An improved version of the parallelcontrol circuit for saturable-core output regulators is described, and the circuit's operation is investigated in a 500 KHz forward converter. Experimental results include in-circuit B-H loop waveforms and comparisons of three practical core materials in the saturable reactor.

A systematic method for the stability analysis of multiple-output converters

Abstract: This paper deals with the dynamics of multiple-output DC-DC converters. A multi-input-multi-output (MIMO) feedback system model incorporating effects of the output fluctuation is derived for the converter. Based on system theoretic tools, a set of stability conditions is obtained for the MIMO model; the result is used to formulate a stable margin. A practical five-output converter was selected for illustration of the proposed analytic tool. Effects of the input filter and coupled inductor on system stability margin are investigated.

Control of switched-mode converter harmonic-free terminal waveforms through internal energy storage

Abstract: It is shown that internal low-frequency energy storage can be used to achieve harmonic-free operation and controllable power factors in converters whose desired operations require unequal instantaneous input and output powers, such as in single-phase rectifiers, inverters, cycloconverters, and reactive power generators. A systematic synthesis and analysis technique is developed for such converters. This technique can be used to find all converters which can be obtained from a given set of network elements. Since this technique includes converter dynamics, it leads to a systematic procedure for the design of these converters for given specifications with minimum component size.

Test results of an automatic calibration system for AC-DC thermal voltage converters and AC voltage sources

Abstract: An automatic calibration system has been developed for testing ac-dc thermal voltage converters (TYC's) and ac voltage sources. Precision, repeatability, and systematic errors are investigated using the data gathered from 100 mV to 1000 V over a frequency range of 10 Hz to 1 MHz. The ac-dc difference of a TVC is determined by the least-square fit to the characteristic equation E = k(V∗) with ac and dc inputs. A mathematical formalism incorporating the systematic errors and the ac-dc difference, or deviation, caused by the ac input source is developed for data analysis.