Showing papers on "Transient (oscillation) published in 1988"

Direct self-control (DSC) of inverter-fed induction machine

Abstract: The new direct self-control (DSC) is a simple method of signal processing that gives converter-fed three-phase machines an excellent dynamic performance. To control the torque of, say, an induction motor, it is sufficient to process the measured signals of the stator currents and the total flux linkages only. In the basic version of DSC, the power semiconductors of a three-phase voltage source inverter are directly switched on and off via three Schmitt triggers, comparing the time integrals of line-to-line voltages to a reference value of desired flux, if the torque has not yet reached an upper-limit value of a two-limit torque control. Optimal performance of drive systems is accomplished in steady state as well as under transient conditions by combination of several two-limit controls. >

Surge protection device

Abstract: A surge or transient protection circuit is described which operates in an immediate fail-safe mode of failure. If an incoming transient exceeds the transient absorption capacity of the circuit, precision fast-blow fuses are immediately opened to remove current from the load to prevent damage to the equipment connected to the transient suppression circuit and to indicate to the user that the transient suppression abilities of this circuit have been damaged. The transient suppression circuit uses silicon transient voltage suppressor components to absorb the fast-rising edge of transients and also uses slower-acting MOV transient absorption devices for the bulk of the overvoltage transient power. Upon short-circuit failure of any of the suppressor components, the excessive current draw produced thereby results in blowing of the fast-blow fuses.

A Three-Dimensional Model for the Analysis of Transient Thermal and Conversion Characteristics of Monolithic Catalytic Converters

Abstract: A transient three-dimensional model has been developed to simulate the thermal and conversion charasteristics of nonadiabatic monolithic converters operating under flow maldistribution conditions The model accounts for convective heat and mass transport, gas-solid heat and mass transfer, axial and radial heat conduction, chemical reactions and the attendant heat release, and heat loss to the surroundings The model was used to analyze the transient response of an axisymmetric ceramic monolith system (catalyzed monolith, mat, and steel shell) during converter warm-up, sustained heavy load, and engine misfiring

Simulation of MOSFET lifetime under AC hot-electron stress

Abstract: A substrate current model and a quasistatic hot-electron-induced MOSFET degradation model have been implemented using the Substrate Current And Lifetime Evaluator (SCALE) package. It is shown that quasistatic simulation is valid for a class of waveforms that includes those encountered in inverter-based logic circuits. The validity and limitations of the model are illustrated with experimental results. SCALE is linked to SPICE externally in a pre- and postprocessor fashion to form an independent simulator. The preprocessor interprets the input deck and requests SPICE to output the transient node voltages of the user-selected devices. The postprocessor then calculates the transient substrate current and makes a lifetime prediction. >

Real-time analytic sensitivity method for transient security assessment and preventive control

Abstract: An analytic sensitivity method is proposed for the transient security assessment of large power systems. It is based on the recently developed ‘extended equal area criterion’, and on a related transient stability margin. It is shown that this margin leads to a simple algebraic formulation of sensitivity coefficients. Particular attention is focused on the sensitivity with respect to generation power, and possible applications to power system planning and online operation are suggested. For example, the computation of generation and load supply limits provides transient stability constraints and thence means of online transient security assessment and preventive control. Within the limits of the simplified electromotive force behind the transient reactance model, the method proves to be accurate, demanding very little with respect to computing time and fairly independent of the system size. The simulation results reported in the paper corroborate these conclusions.

Analysis of transient stability swings in large interconnected power systems by Fourier transformation

Abstract: A novel technique to analyze transient stability program swing curves is developed which uses the Fourier transformation. This approach generalizes the swing characteristics to specific frequency components over the range of time. The frequency components of the power system swings are identified in the frequency spectrum. These components can then be selected for further analysis. The mathematical process to determine the amount of damping in the respective frequency components is outlined. The damping constants can be obtained by comparing the magnitudes of the respective frequency components in different time windows. Good correlations of the results with conventional linear eigenvalue analysis have been observed. Advantages and necessary precautions in applying the method are presented. >

Capacity responsive control circuit

Abstract: A capacitive detecting circuit for detecting transient capacitive changes such as that of a person moving into proximity of a sensing element. A sensing element is coupled to a threshold level controlled amplifier supplied with relatively high frequency signals from an oscillator through a high input impedance. A detector circuit is coupled to the amplifier output to detect D.C. variations in the level control loop caused by transient capacitive changes and provide a control output signal representative of such change.

Time‐domain transient elastodynamic analysis of 3‐D solids by BEM

Abstract: The BEM algorithm developed by Banerjee and Ahmad (1985) and Banerjee et al. (1986) for the analysis of three-dimensional time-dependent elastodynamics problems is extended and refined to improve the accuracy of the internal stress predictions. A quadratic spatial shape function and a linear temporal shape function are employed, and the complete numerical implementation (as part of BEST3D) is outlined. Applications of the improved BEM to typical problems are presented graphically and briefly characterized. Included are spherical cavities subjected to sudden radial expansion, triangular or rectangular pulses of radial pressure, or ramp loading; a circular loaded area on a half space; and a flexible square plate foundation on an elastic half space.

Analysis of half-wavelength transmission lines with simulation of corona losses

Abstract: The growing interest in very-long-distance transmission (2-3000 km) and the state of the art of half-wavelength transmission lines are briefly discussed. A model for the numerical simulation of corona losses at high electric gradients is proposed. Then an analysis is made of the steady-state and transient operation of an 800 kV, 60 Hz, 2500 km double circuit line. Results show that corona losses drastically limit the sustained overvoltages, but also place a limit on transmissible power and can affect transient stability. Possible schemes for interconnection of two half-wavelength lines at intermediate switching stations are also examined in order to attain acceptable system reliability. >

Transient finite element modeling of solenoid actuators: the coupled power electronics, mechanical, and magnetic field problem

Abstract: A transient 2-D finite element model for fast-acting pulse-width-modulated (PWM) solenoid actuators is presented. The unique feature of this model is that it couples the electrical, mechanical, and magnetic systems of these devices. Transient calculations taking into account the nonlinearity of the magnetic materials, eddy currents, and motion are compared with dynamic test results for a ball-type solenoid. Flexibility of the software allows one to apply it to any type of PWM solenoid actuator and any desired excitation profile. >

Dynamic performance of a DC shunt motor connected to a photovoltaic array

Abstract: The dynamic performance of a DC shunt motor directly connected to a photovoltaic array is studied. The motor is represented by the dynamic equations of its electrical and mechanical systems. The photovoltaic array is represented by an equivalent circuit whose parameters are computed using experimentally determined voltage-current characteristics. Simultaneous solution of both the motor and array equations is obtained using a Range-Kutta computer program. This enabled the transient performance of the motor to be determined during the starting period under different conditions of solar intensity and shaft load. Simulation results as well as those obtained from experiments on a 1 hp, DC shunt motor connected to a 4 kW photovoltaic array confirm that the dynamic performance of a DC shunt motor connected to a photovoltaic array differs from its performance when it is operated from a constant-voltage source. >

An envelope-following method for the efficient transient simulation of switching power and filter circuits

Abstract: The transient behavior of circuits like switching power converters and switched capacitor filters are expensive to simulate because they are clocked at a frequency whose period is orders of magnitude smaller than the time interval of interest to the designer. It is possible to reduce the simulation time without compromising accuracy by exploiting the fact that the behavior of such a circuit in a given high-frequency clock cycle is similar, but not identical, to its behavior in the preceding and following cycles. In particular, the envelope of the high-frequency clock can be followed by accurately computing the circuit behavior over occasional cycles. The authors describe the implementation of an envelope-following method that is particularly efficient for switching power and filter circuits, and they present results demonstrating the method's effectiveness. >

An envelope-following method for the efficient transient simulation of switching power and filter circuits

Abstract: The transient behavior of circuits like switching power converters and switched capacitor filters are expensive to simulate because they are clocked at a frequency whose period is orders of magnitude smaller than the time interval of interest to the designer. It is possible to reduce the simulation time without compromising accuracy by exploiting the fact that the behavior of such a circuit in a given high-frequency clock cycle is similar, but not identical, to its behavior in the preceding and following cycles. In particular, the envelope of the high-frequency clock can be followed by accurately computing the circuit behavior over occasional cycles. The authors describe the implementation of an envelope-following method that is particularly efficient for switching power and filter circuits, and they present results demonstrating the method's effectiveness. >

Temperature, voltage, and process compensated output driver

Abstract: An output driver for high performance integrated circuits. The driver dynamically compensates for variations in temperature, voltage and process. To perform the compensation, the driver is divided into two parts: static and transient. The static part is used to maintain the DC level. The transient part is active only during logic 0 to 1 and 1 to 0 transitions and is used only to assist the static part during such transitions. A closed loop feedback technique is used to compensate the driver for temperature, process, and voltage variations; specifically, a scaled down version of an output driver is used to monitor speed variations due to temperature, process, and voltage, the output of which is fed back to the output driver which then performs the necessary compensation.

On reflection from a suddenly created plasma half-space: transient solution

Abstract: The reflection by a suddenly created plasma half-space of a time-harmonic plane electromagnetic wave propagating in free space is considered. The problem involves a temporal discontinuity, a spatial discontinuity, and a dispersive medium. The steady-state solution is obtained by considering the basic features of the scattering processes due to each of the discontinuities in terms of analogous transmission-line models. The electric field of the reflected wave consists of two components. One component (called component A) is of the same frequency as the incident wave frequency and is due to the spatial discontinuity. The other component (called component B) is of a different frequency and arises because of the temporal discontinuity. The B component is damped out even if the plasma is only slightly lossy. The damping rate of the B component is calculated. The transient solution is obtained through the use of Laplace transforms. The solution is given in terms of Bessel-like functions. The limiting value of this solution is shown to agree with the steady-state solution. Numerical results illustrating the transient effects are for two typical cases. >

Frequency-dependent AC system equivalents for harmonic studies and transient convertor simulation

Abstract: A technique for the the generalization of the impedance loci is described. This technique is capable of displaying the complete frequency response of any given power system including multiphase-related effects such as phase asymmetries and mutual couplings. This information is used to derive frequency-dependent equivalent circuits suitable for integration in the time-domain solutions of power-system waveforms. Direct and optimization techniques are used in the derivation of the equivalent circuits. Their effects on impedance frequency matching and computational efficiency are compared. >

A closed-loop quasi-optical dynamic braking resistor and shunt reactor control strategy for transient stability (of synchronous generators)

Abstract: A control strategy for dynamic braking resistor and shunt reactor is proposed for stabilization of electric generators subjected to large disturbances. The time optimal control is derived as a function of synchronous machine power, its rotor angular position, and speed deviation. The response for a single-machine system with the proposed control has been obtained using the steepest-descent method. The strategy has also been tested on two multimachine systems. Results indicate that the proposed strategy provides a simple and effective method of stabilization under transient emergency conditions. It is found that the strategy is very effective in controlling first swing instability. >

Voltage forced coils for 3D finite-element electromagnetic models

Abstract: A method for modeling 3D voltage forced coils is described The magnetic vector potential A is used within the coil with an additional equation to ensure EMF balance at the terminals This approach is useful for nonlinear or transient problems when the terminal voltage is specified The coil model has been incorporated into the general 3D electromagnetics program MEGA A simple voltage-forced coil has been simulated on the computer and compared with experimental results >

A novel approach to the generation and optimization of three-level PWM wave forms

Abstract: The application of three-level pulsewidth modulation (PWM) to voltage source inverters feeding three-phase induction motors is considered. A subharmonic modulation method using two modulating waves is introduced. It is particularly well adapted to the elimination of specific harmonic bands. Systematic optimization of precalculated wave forms with respect to loss factor shows that three-level PWM is very well suited to harmonic reduction. Transient behavior is discussed. It is concluded that three-level PWM yields significant improvements compared with two-level PWM, especially in high-power (gate-turn-off) GTO applications where the high DC link voltage requires a series connection of the switches.

Mechanisms leading to single event upset

Abstract: SRAM cell recovery time following a 140 MeV Krypton strike on a Sandia SRAM is modelled using a two-dimensional transient numerical simulator and circuit code. Strikes at both n- and p-channel "off" drains are investigated. Four principle results are obtained. The recovery time after a strike is strongly dependent on the drive of the restoring transistor. A struck "off" p-channel drain-to-gate capacitive coupling has a significant effect on recovery in SRAM with feedback resistors. Recovery time is approximately linear with LET over LET in the range to 0.4 pC/?. Finally, an experimental n-channel SEU has been observed in a Sandia SRAM without feedback resistors.

A novel approach to the generation and optimization of three-level PWM wave forms for induction motor inverters

Abstract: The application of three-level pulsewidth modulation (PWM) to voltage source inverters feeding three-phase induction motors is considered. A subharmonic modulation method using two modulating waves is introduced. It is particularly well adapted to the elimination of specific harmonic bands. Systematic optimization of precalculated waveforms with respect to loss factor, shows that three-level PWM is very well suited to harmonic reduction. Transient behavior is discussed. It is concluded that three-level PWM yields significant improvements compared with two-level PWM, especially in high-power (gate-turn-off) GTO applications where the high DC link voltage requires a series connection of the switches. >

Current-voltage characteristics of a high-current pulsed discharge in air

Abstract: The time-dependent arc voltage and resistance of a high-current pulsed discharge in air are obtained accurately by solving the circuit equation using the measured values of the current and breakdown voltage. Unipolar critically damped or overdamped pulsed discharges, with rise times of about 0.7 mu and peak currents in excess of 20 kA, are investigated. These discharges are characterized by four phases: initial phase, quasistationary phase, transient phase, and relaxation phase. The quasistationary phase occurs between the time of the current maximum and twice this time. The transient phase, which occurs after the quasistationary phase, corresponds to a negative slope of the V-I characteristic. The variable parameters were electrode separation, and gas pressure. The minimum arc resistance, at peak current, was about 50 m Omega . >

A new approach to dynamic analysis of AC networks incorporating detailed modeling of DC systems. II. Application to interaction of DC and weak AC systems

Abstract: For pt.I see ibid., vol.3, no.4, p.2005-11 (1988). A digital simulation concept which combines the detailed capability of the Electromagnetic Transients Program with the large system dynamic capability of a transient stability program is applied to the study of the interaction of a DC system with weak AC systems. The interface locations between the two simulations are extended to strategic points within the AC network. Greater predictability and authenticity of the response to disturbances have been achieved than was previously possible. >