Showing papers on "Converters published in 1990"

Zero-voltage switching technique in DC/DC converters

Abstract: A novel resonant switch operating under the principle of zero-voltage switching is presented. The basic configurations of the voltage-mode resonant switches are presented. The circuit's operating principles are described using a voltage-mode quasi-resonant boost converter. DC analysis of the converter is carried out. A new family of voltage-mode quasi-resonant converters are derived, and several members of this family are presented. The duality relationship between the zero-current switching technique and the zero-voltage switching technique is derived. These two techniques are compared using an example showing the duality between a current-mode quasi-resonant Buck converter and a voltage-mode quasi-resonant boost converter. The similarities and differences of the voltage-mode quasi-resonant converters and the Class-E converters are discussed. A 5 MHz 50 V to 5 V flyback converter employing the zero-voltage switching technique has been implemented. Design considerations and experimental results of this circuit are presented. >

Lyapunov-based control for switched power converters

Abstract: The fundamental properties, such as passivity or incremental passivity, of the network elements making up a switched power converter are examined. The nominal open-loop operation of a broad class of such converters is shown to be stable in the large via a Lyapunov argument. The obtained Lyapunov function is then shown to be useful for designing globally stabilizing controls that include adaptive schemes for handling uncertain nominal parameters. Numerical simulations illustrate the application of this control approach in DC-DC converters. >

Phasor transformation and its application to the DC/AC analyses of frequency phase-controlled series resonant converters (SRC)

Abstract: A novel modeling technique based on phasor transformation that provides a unified model of series resonant converters (SRCs) is proposed. The approach gives explicit and simple equations that provide fruitful physical insight. When the switching frequency deviates from the resonant frequency, a first-order SRC model is obtained, and in the case of resonance a second-order model is obtained. It is shown that the frequency band of the second-order model is very narrow in practice. The time constant, small-signal gains, and system order are highly dependent on the switching frequency, load resistor, and output capacitor. >

Transformers as equivalent circuits for switches: general proofs and D-Q transformation-based analyses

Abstract: The equivalent circuits for the switches in DC-DC, DC-AC, AC-DC, and AC-AC converters are proved to be time-varying transformers. This result is used in the analyses of DC-DC converters, an eight-order current source rectifier-inverter, and a buck-boost inverter. The circuit D-Q transformation is proposed for the analyses of the AC converters such as inverters, rectifiers, and cycloconverters which include the time-varying transformers. Gyrators appear in the D-Q transformed inductors and capacitors of the AC converters. Few equational manipulations are required to determine the steady-state operating points and the small signal gains of the converters. The analysis result for the rectifier-inverter shows that the circuit has self-short-circuit protection capability and strong immunity in the parasitic inductor resistance. >

Pulse width modulation with resonant DC link converters

Abstract: A technique for realizing pulse width modulation (PWM) capability in resonant DC link converters is presented. This technique eliminates the subharmonics present in the conventional discrete pulse modulated converters without requiring any additional switching devices. Detailed design-oriented analysis enumerating the tradeoffs involved are presented. Control techniques for simultaneously accomplishing link and output control are considered. Simulation results verifying the principle of operation are presented and backed up by experiments. >

Switched snubber for high frequency switching

Abstract: A novel snubber circuit for high-frequency PWM (pulse width modulations) DC-to-DC and DC-to-AC converters is presented. The snubber is a series circuit of a capacitor and a snubber switch which is connected across the main switch. The main switch and the snubber switch are switched alternately with a short dead time. The condition of zero-voltage switching is satisfied both in the main switch and the snubber switch by applying the switched snubber. The turn-off surge due to parasitic inductance in the circuit and the recovery of the diode are eliminated by the switched snubber without increasing the voltage stress and the conduction losses in the main switch. >

Analysis and design of class-E/sup 2/ DC/DC converter

Abstract: A family of class-E/sup 2/ DC/DC power converters is introduced. Their analysis and design are presented and experimentally verified. The converters are composed of class-E inverters and class-E rectifiers. Zero-voltage switching (with low dv/dt) of the transistor and zero-current switching (with low di/dt) of the rectifier diode reduce switching losses in both stages of the converters, making them especially suitable for high-frequency operation. Because of the high loaded quality factor of the resonant circuit, the range of frequency required for output-voltage regulation is as narrow as 5.46% for load resistances from a full load of 100 Omega to an open circuit. The full-load overall efficiency is 80.36% at 1 MHz. The converters can also operate at a fixed frequency if synchronous rectifiers are applied. The reduction of class-E/sup 2/ converters to lower order converters is presented. Many multiresonant converter topologies are created in this way. The class-E/sup 2/ converters can be utilized to build highly efficient high-power-density switching power supplies. >

Analysis of HVDC converters connected to weak AC systems

Abstract: A method of analysis is presented and applied to a model system which is well established and extensively used in studies of HVDC converters connected to weak AC systems. The method is based on fundamental frequency quantities. A variety of phenomena and interactions of the AC/DC system can be analyzed, and basic understanding of the mechanisms can be gained. Some important properties of the system, such as voltage/power stability in different control modes and stability of tap changer action, are analyzed. Furthermore, they dynamics of a system consisting of a static VAr compensator (SVC) and DC converters are analyzed, and the requirements for stable operation are derived within the framework of the method of analysis presented. These results are verified by time simulation done by a transient stability program. >

Sinusoidal line current rectification at unity power factor with boost quasi-resonant converters

Abstract: A sinusoidal line current rectifier is considered at unity power factor, where the conventional boost converter, usually utilized between the diode rectifier bridge and the DC bus capacitor, is replaced with a boost zero-current switching quasi-resonant converter (boost ZCS-QRC). The zero-current switching quasi-resonant rectifier (ZCS-QRR) is analyzed theoretically. Normalized curves are plotted, and equations that allow high flexibility in design are developed. A design example is proposed, and experimental results are presented to demonstrate the operating principle, the feasibility of the technique, and the validity of the theoretical analysis. >

A 500 kHz multi-output converter with zero voltage switching

Abstract: A detailed analysis of topological modes of the converter and its relation to the design, development, and performance of a multioutput prototype converter are given. The implemented topology is found to be a good solution for eliminating converter switching losses at high frequencies. The breadboarded converter demonstrates the zero voltage switching very clearly, resulting in improved efficiency. The implementation of the circuit was relatively simple and was not susceptible to noise problems associated with high-frequency converters. >

A fast time-domain algorithm for the simulation of switching power converters

Abstract: An efficient algorithm for the simulation of switched-mode power converters is developed. A Chebyshev series expansion is used to effectively solve the differential equations describing the system in each topology. The power of the new simulation technique lies both in the simple, but accurate, polynomial approximation for the state transition matrices and in the ability to explicitly obtain the instants at which the switching of the circuit topology takes place. The simulation technique is illustrated with reference to a simple Buck converter operating at a constant frequency. The derivation of the new algorithm is presented and its performance is analyzed. The case of a rapidly varying input forcing function is analyzed. Examples illustrating the generality and the computational efficiency of the algorithm are presented. >

Synthesis of averaged circuit models for switched power converters

Abstract: Averaged circuit models for switching converters are developed using a direct circuit averaging method. The method proceeds in a systematic fashion by determining appropriate averaged circuit elements that are consistent with the averaged circuit waveforms. The averaged circuit models that are obtained are synthesis of the state-space averaged models for the underlying switched circuits. An important feature of the method is that it is applicable to switched circuits whose nonswitch elements may be nonlinear. The results obtained using this method are compared with the results on averaged circuit models available in the literature. >

Comparison of performance of single-loop and current-injection-control for PWM converters which operate in both continuous and discontinuous modes of operation

Abstract: A comparison of single-loop and current-mode controlled power converters operating in the continuous and discontinuous modes is performed using the PWM (pulse width modulation) switch model and a new, continuous-time model of current injection control (CIC). The theoretical and experimental results show a significant performance improvement that can be realized when CIC is employed in converters which operate over a wide load range. Except for the single-loop, continuous mode transient response time, all the CIC figures are equal to or better than the single-loop figures. The transient response time of CIC can be improved to be equal to or better than single-loop control by placing the compensation zero at a higher frequency. The penalty is that the system loop gain will be conditionally stable. This may not be significant, though, since the system loop gain crossover frequency is governed by the current loop. The current loop is determined by the external ramp slope. >

Elimination of the positive zero in fixed frequency boost and flyback converters

Abstract: It is shown how a fixed-frequency, leading-edge modulated pulse width modulation can eliminate the undesirable positive zero in practical boost and flyback converters. This allows a substantial improvement in the closed-loop characteristics. Several techniques are employed to predict this result. The design procedure for elimination of the positive zero is presented. Experimental verification is provided. By providing an effective feedforward of the load current, this technique ensures excellent load transient response and low output impedance. There are several advantages to this technique. Measurement of the control-to-output transfer function cannot be easily performed. Also, the positive zero elimination is dependent on the capacitor ESR value. This technique can be susceptible to noise since the output voltage switching ripple is not filtered in the compensation network. >

Time reversal duality and the synthesis of a double class E DC-DC converter

Abstract: The principle of time reversal duality is introduced and applied to DC-DC power converters. Elementary inverters and rectifiers are time reversal duals of each other. When coupled together by a reactive matching network, a DC-DC converter whose properties are determined largely by the matching network is formed. This approach has application in the analysis and syntheses of PWM (pulse width modulation), resonant, quasi-resonant, and multiresonant converters. It is used here to synthesize a Cuk converter, and a double class E DC-DC power converter in which the switch and diode both operate in class E. The converter is ideally lossless for any DC load including open and short circuits. >

Current distribution control of converters connected in parallel

Abstract: Two schemes of current distribution control in a system of power converters connected in parallel, master-slave and central-limit controls, are analyzed from system block diagrams to determine steady-state distribution errors The performance characteristics of distributive power systems using these two control techniques are presented The comparison between the system performances with and without these distribution controls is discussed The results of a FORTRAN program written to simulate the responses of two buck converters connected in parallel are described It is shown that the master-slave technique provides good current distribution but no control in the output current overshoots that occur in the output of the master converter The central-limit current distribution control is shown to provide tight control to all currents in the converters towards the central-limit reference signal that is the weighted average of the total current to the shared load Therefore the central-limit technique is regarded as superior to the master-slave technique >

Plural delta-sigma converters operating in parallel with independent dither generators

Abstract: The invention is structured to add each output signal of a plurality of signal converters connected in parallel, after a common signal is inputted to and quantized in the above plurality of signal converters, having a noise generators which input noise generated utilizing random variables unrelated to each other to respective quantizers within the above plurality of signal converters, so that quantization noise, Q, or the like can be effectively averaged, and a highly reliable signal conversion device, which can ensure an enough dynamic range across a wide frequency region, can be provided. Also, the invention is structured to add each output signal of a plurality of signal converters connected in parallel, after a common input signal is inputted to and quantized in the above plurality of signal converters, so that a highly reliable signal conversion device similar to the above can be provided.

Using AC-fed PWM converters as instantaneous reactive power compensators

Abstract: A general control method that fully utilizes the inherent capability of AC-fed PWM (pulse-width-modulated) converters to compensate for reactive and harmonic currents absorbed by other loads is presented. Suitable definitions of instantaneous active and reactive current and power terms are introduced. Optimum modulation laws are then derived according to a general control theory valid for PWM multiconverter systems, which also results maximum system efficiency. Simulated results demonstrate the capabilities of the proposed compensation method. This method can also be implemented in existing systems, since only modifications of the control section are needed. >

Constant-frequency zero-voltage-switched multi-resonant converters: analysis, design, and experimental results

Abstract: The multi-resonant-switch concept is modified to provide constant-frequency operation Complete DC analysis and designs of the constant frequency forward and half-bridge multi-resonant converters are presented Different implementations for the half-bridge topology are discussed The performances of a 50 W forward converter and a 100 W, offline, half-bridge converter are also presented A significant constant improvement of the performance of the constant-frequency zero-voltage-switched multi-resonant converter is expected from the development of MOSFETs with very low on-resistance (synchronous rectifiers) >

Resonant converter controlled by variable capacitance devices

Abstract: A new device called the variable capacitance device is proposed, and its application to the output voltage regulation of resonant converters is discussed. The new device has an independent input terminal for controlling its capacitance. The converters used are the well-known Schwarz circuit and the buck-type current-resonant converter with a resonant switch. By applying the devices to the capacitors in LC resonant tanks, the resonant converters can be regulated with the switching frequency fixed. >

Design of P-I controllers for DC-to-DC power supplies via extended linearization

Abstract: In this article, the method of ‘extended linearization’ is used for designing stabilizing non-linear proportional-integral (P-I) controllers which regulate to a constant value either the average output voltage or the average input current of PWM controlled DC-to-DC power converters such as the boost, the buck-boost and the Cuk converters, The design is carried out on the basis of the Ziegler-Nichols P-I controller design method applied to a family of linearized transfer function models of converters parametrized by constant operating equilibrium points of the average PWM controlled circuit.

Analogue to digital converters

Abstract: Oversampled delta-sigma converters are used to provide high resolution and large dynamic range in zero-IF analogue to digital converters, and narrow-band filters within the delta-sigma loops are used to force quantisation noise away from frequencies of interest.

Random and programmed pulse-width modulation techniques for DC-DC converters

Abstract: An approach for minimizing worst-case spectral components of certain circuit waveforms in DC-DC converters is developed The approach is based on a programmed pulse-width-modulation (PWM) method for harmonic reduction It is demonstrated that it is possible to precompute an optimal sequence of subperiods to minimize worst-case spectral components These spectral components can also be effectively reduced by the introduction of high-index random frequency modulation

Multilevel simulation tools for power converters

Abstract: Various methods for simulating the large signal behavior of power converters are discussed. Multilevel simulation is the most efficient approach, combining the speed of behavioral circuit description with the accuracy of device models. Results for control optimization and converter loss reduction demonstrate this. Widespread use of the tools and the methodology discussed, however, depends on the availability of proper models for the various circuit components. The problem of accurate device modeling versus simulation speed is addressed, and an example of an efficient design analysis is shown. >

High voltage direct current transmission system based on voltage source converters

Abstract: It is pointed out that one application of PWM (pulse width modulation) converters is in the DC transmission grid where the voltage source (boost) type converters can be connected in parallel, each converter being capable of reversing the roles of rectification/inversion on command It is shown that the fairly large transformer leakage inductances of HVDC stations are sufficient for the proper operation of the voltage source converters Fairly low carrier frequency can be used, assuring low switching losses >

Input filter design 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 from laboratory data or from specified black box parameters. >

High-frequency multi-resonant converter technology and its applications

Abstract: Employing the resonant-switch concept, a family of zero-voltage-switched multi-resonant converters (ZVS-MRCs) is derived from the conventional pulse-width-modulated (PWM) converters. By absorbing all essential circuit parasitics into the resonant network, the ZVS-MRCS are capable of operating in megahertz range, with high efficiency and power density. Characteristics of MRCs are reviewed, and their merits and limitations are assessed. Several applications and designs using the MRC technique are presented. A 50 W forward converter is designed for single and multiple-output on-board applications. The converter is fabricated using thick-film hybrid technique and attains a power density of 50 W/in/sup 3/. A 100 W offline half-bridge converter is designed for a computer distributed power system with 150-350 V input. A full-bridge converter is used for a pulse-load application with 1.5 kW peak power.< >

Sliding mode-a new way to control series resonant converters

Abstract: The application of the theory of variable structure control systems for the control of resonant DC-DC converters is illustrated. The full-bridge configuration of series-resonant converters (SRCs) is used. The converter is operated at resonant frequency to obtain both output-to-input voltage characteristics similar to those of the buck converter and high efficiency. To arrive at an exact mathematical model, the SRC is viewed as a piecewise linear system. However, under some approximations and a suitably selected set of state variables, the SRC is characterized by a linear continuous-time model which allows determination of the equivalent control via the sliding mode control (SMC) theory. To obtain a sliding regime, the appropriate sliding surface is selected by assigning poles. This control law constitutes a new approach to the control of resonant DC-DC converters. >

The effect of dielectric relaxation on charge-redistribution A/D converters

Abstract: The authors examine the extent to which dielectric relaxation in typical monolithic capacitors degrades the performance of charge-redistribution analog-to-digital (A/D) converters. They present experimental device data from a monolithic capacitor test circuit, describe an empirical capacitor model fit to the measurements, and compare simulated A/D system errors with those observed in a monolithic, 10-b, 3.3-ms A/D converter. It is believed that these techniques for modeling and predicting A/D converter errors will play an important role in making appropriate technology decisions and in guiding system and circuit design of high-precision monolithic converters of the future

Discrete time integral sliding mode control for discrete pulse modulated converters

Abstract: Sliding mode control for resonant link converters is introduced in a formal manner through a specific example of a buck resonant link DC-DC converter. The use of variable structure systems theory as a valuable tool to characterize the dynamic behavior of discrete pulse modulated systems in demonstrated. The suboptimal steady-state behavior of discrete pulse modulated converters under conventional control methods is brought out. The discrete time integral sliding mode control as an alternative control method with better performance attributes is proposed. It is demonstrated that the sliding mode control methods developed for the control of a PWM (pulse width modulation) power converter can be extended to the resonant link converter operating under discrete pulse modulation, and the performance can be improved by adding the integral-error term to the sliding surface. The conditions for sliding mode to exist under integral sliding control are obtained. All the results are verified by simulation, and experimental results confirming the concepts are presented. >