Power Switching Circuits Research Articles

Envelope following method for the transient analysis of electrical circuits

An envelope following method (EFM) that allows efficient transient simulations of electrical circuits is here presented. Its mathematical and electrical bases are considered and the influence of some general properties, such as stability and truncation error of integration methods employed by EFM, are studied. Furthermore, we present a new state variable prediction algorithm that improves previously reported ones, since it better adapts to fast dynamics of the solution. A set of power switching circuits is employed as a benchmark and numerical results of our algorithm are compared to those of conventional integration and of previous EFM versions. Remarkable results are obtained in the electrothermal simulation of power converters where the efficiency gain rises up to some magnitude orders with respect to conventional integration.

Self-protected low-side power switchagainst abrupt current overload

The authors present a current limit, gate drive and 0.3 Ω low-side power switch circuit which provides fast current regulation (2 µs) to a preset current limit when an abrupt current overload occurs. This efficiency reduces excessive energy dissipation by the switch to prevent the switch from being burnt out.

Development and test of the poloidal field prototype coil POLO at the Forschungszentrum Karlsruhe

A superconducting prototype (3 m Ø and nominal current 15 kA) of a poloidal field coil was developed, constructed and tested according to the typical specification of the Tokamak magnet system in collaboration with European industry. In order to withstand fast ramping (≈2 T s −1), plasma disruption (80 T s −1, 10 ms) and plasma control (≈ ±0.05 T, 10 Hz) in the superconducting state a low loss conductor and a well developed high voltage technique at 4 K were indispensable attributes of the design. The sc cable of the conductor consists of mixed matrix strands (NbTi in Cu/CuNi) cooled by a dual cooling system (two phase forced flow helium for heat removal at constant temperature, and stagnant helium for good transient stability). The sc cable is inclosed in a thick walled stainless steel jacket. All coil components are designed and constructed according to the rules of the high voltage technique. The coil was tested in the TOSKA facility at FZK-Karlsruhe. For generating the typical positive and negative magnetic field transients a special high power switching circuit of a discharge power up to 700 MW (30 kA, 23 kV) was constructed and used. The coil was investigated considering its superconducting, electromagnetic and mechanical properties. All results were conclusive in agreement with calculations and fulfil the specifications. A highlight is that for this conductor type the stability against transient field changes is only determined by the expected stability margin or the critical current boundary no other limitations of the ramp rate were observed.

Analysis and suppression of high-frequency leakage current attributable to the parasitic capacitor of a transistor module

Recently, electromagnetic inference (EMI) and high-frequency leakage current are grave concerns for power supply authorities. Due to rapid switching of high current and high voltage, interference emission is a serious problem in many switching power circuits. However, high-frequency switching is necessary for the reduction of size and the improvement of performance of the products. Usually, EMI noise reduction is attempted using EMI filters and shielding products. But, in many cases, those trials resulted in unsatisfactory results because an analytical investigation was not performed. Recently, the analysis of high-frequency leakage current caused by the step change of common mode voltage produced by the PWM inverter was reported. But the other cause of high-frequency leakage current was not made clear. In this paper, it is clarified theoretically that the parasitic capacitors between the heat sink and the switching semiconductor devices cause high-frequency leakage current. Furthermore, this paper shows that equalization of the parasitic capacitors and increase of the impedance for grounding the heat sink at high-frequency range reduces high-frequency leakage current. Finally, those results are verified from simulation and bread board setup. © 1997 Scripta Technica, Inc. Electr Eng Jpn 119(2): 60–71, 1997

Switching time bifurcations in a thyristor controlled reactor

Thyristor controlled reactors are high power switching circuits used for static VAR control and the emerging technology of flexible AC transmission. The static VAR control circuit considered in the paper is a nonlinear periodically operated RLC circuit with a sinusoidal source and ideal thyristors with equidistant firing pulses. This paper describes new instabilities in the circuit in which thyristor turn off times jump or bifurcate as a system parameter varies slowly. The new instabilities are called switching time bifurcations and are fold bifurcations of zeros of thyristor current. The bifurcation instabilities are explained and verified by simulation and an experiment. Switching time bifurcations are special to switching systems and, surprisingly, are not conventional bifurcations. In particular, switching time bifurcations cannot be predicted by observing the eigenvalues of the system Jacobian. We justify these claims by deriving a simple formula for the Jacobian of the Poincare map of the circuit and presenting theoretical and numerical evidence that conventional bifurcations do not occur.

High Frequency Leakage Current Caused by the Transistor Module and Its Suppression Technique.

Recently, Electro-Magnetic Interference (EMI) and high frequency leakage current are grave concern for power supply authorities. Due to rapid switching of high current and high voltage, interference emission is a serious problem in many switching power circuit. However, high frequency switching is neccesary for the reduction of size and the improvement of performance of the products. Usually, EMI noise reduction is tried to accomplish by using EMI filters and shielding products. But, in many cases, those trial resulted in unsatisfactory because the analytical investigation was not performed. Recently, the analysis of high-frequency leakage currnt caused by the step change of common mode voltage produced by the PWM inverter was reported. But the other cause of high-frequency leakage current did not being made clear.In this paper, it is clarified theoretically that the parasitic capacitor between the heat-sink and the switching semiconductor devices cause high-frequency leakage current. Furthermore, this paper shows that equalization of the parasitic capacitors and increase of the impedance for grounding the heat-sink at high-frequency range makes high-frequency leakage current reduce. Finaly, those results are verified from simulation and bread board set-up.

Algorithm to simulate periodically switchedpower circuits in the time domain

A new algorithm for efficiently and accurately simulating periodically switched power circuits in the time domain is presented. It originates from conventional algorithms for time domain analysis and from algorithms for steady state analysis. The time domain solution of the circuit is computed by means of a steady state sequence which represents the power circuit behaviour during its working cycles.

Reduction of power supply EMI emission by switching frequency modulation

Electromagnetic interference (EMI) emission is always of grave concern for power electronic circuit designers. Due to rapid switching of high current and high voltage, interference is a serious problem in switching power circuits. Here, the effect of frequency modulation on power supply EMI noise is investigated. Significant reduction of emission is possible with the proposed scheme.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Programmed pulsewidth modulated waveforms for electromagnetic interference mitigation in DC-DC converters

The regular switching action of a pulse-width-modulated (PWM) circuit generates conducted and radiated electromagnetic interference (EMI) and may also generate acoustical disturbances. Programmed pulsewidth modulation techniques have been applied using various methods to control harmonics inherent in switched power circuits. A method for generating an optimal programmed switching waveform for a DC-DC converter is presented. This switching waveform is optimized to reduce the amplitude of harmonic peaks in the EMI generated by the converter. Experimental results, a brief discussion of sensitivity, and a practical implementation of a circuit to generate the PWM waveform are given. >

Digital oscilloscope measurements in high-frequency switching power electronics

The requirements for measuring instantaneous power of a switching power circuit using a digital storage oscilloscope are discussed. The measurements are difficult to perform and involve the use of high-speed, high-resolution measurement instrumentation. Careful consideration needs to be given to overload conditions. Averaging and advanced sampling techniques are necessary to obtain a satisfactory result. Performance enhancements of instruments that will allow improvement of the quality of the measurements remain desirable. An indication of measurement accuracy is obtained by comparing the mean dissipated power to the same quantity obtained by a calorimetric test (water flow heating). The mean dissipated power is the integral of the instantaneous power divided by the switching period. The two results agree within 5%.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Gate Drive Circuits for Power Mosfets

Gate drive circuits for power mosfets Advances in recent years in the manufacture of metal oxide Field Effect Transistors (Mosfets) have paved the way for new design criteria in solid-state switching power circuits. This paper gives an insight into the knowledge gained in the design of gate drive circuits for power mosfet switching devices.

An envelope-following approach to switching power converter simulation

The implementation of an envelope-following method that is particularly efficient for open-loop switching power converters with fixed clock frequencies is described. A simple method for computing envelopes that involves solving a sequence of two-point boundary value problems is derived. The two-point boundary value problems are solved with a shooting or Newton method. The computations involved are explained and their implementation in the Nitswit program, along with results from using it to simulate several switching power circuits, is described. Results demonstrating the method's effectiveness are presented. >

A transformation method for the solution of power switching circuits based on network topological concepts

AbstractIn this paper, a general and systematic method for the analysis of varying topology power semiconductor circuits is presented. the changes of the conduction state of the semiconductor switching devices are handled by successive modifications of the tree of the circuit graph. These tree modifications are systematically reflected on a square transformation tensor. On the basis of well known network topological concepts, this generalized transformation tensor can be constructed in a relatively simple way. This tensor constitutes a flexible and powerful tool to assemble automatically the necessary on‐switch current and off‐switch voltage equations required for any conduction pattern. These manipulations are accomplished with a step‐by‐step modification procedure of the equations describing the circuit in the most previous conduction state. the basic steps of an algorithm suitable for the practical implementation of the analysis of any power switching network on a digital computer are described, and an example is used to demonstrate the effectiveness of the proposed method.

Commutated relay switching system

A basic electronic control scheme which allows relays to be utilized at fast switching rates with long lifetimes and is applicable with standard microprocessor-based systems is described. The basic power-switching circuit consists of a commutating diode connected in parallel with the contacts of a single master relay, and this combination connected in series with a parallel combination of slave switching relays and associated loads. Timing and control is provided in such a way that the relays are switched at a high frequency but never with current flowing through the contacts. An actual range application with multiple loads is described, along with the necessary circuitry and logic. In addition, a diagnostic scheme is described which takes advantage of the commutated system to determine component failures in the power switching loads. >

Gallium arsenide Schottky power rectifiers

This paper discusses the development of high-performance gallium arsenide Schottky rectifiers for power switching applications. These diodes are shown to exhibit superior turn-on and turn-off dynamic switching characteristics when compared with silicon p-i-n rectifiers. The theoretical analysis presented in the paper indicates that the gallium arsenide Schottky power rectifier will be attractive for high-frequency power switching circuits operating at 1.00-300 V.

Power Reduction Techniques for LSI Memory

Power reduction techniques are described for both LSI memory components and systems. These techniques have been verified experimentally for both read-only and random access read/write components using power switching circuits external to the chips. A number of ways to apply on-chip power switching are described. The power switching concept is also described for memory cards and systems that can be organized into blocks.

A Versatile Fail-Safe Trip Circuit for Reactor Safety Systems

A transistorized trip circuit is described which employs a simple self-testing technique to achieve a high degree of fail-safeness with a minimum number of components. It operates with d-c input currents in the range from 10 to 100 microamperes and can control up to 100 watts of load power. The trip differential for a load change from full power to zero power is less than 0.1 microampere; and the temperature stability of the trip point is better than 0.02 a/°C. This trip circuit may be used with either relay or solid-state logic and power switching circuits.

Silicon-controlled-switch — Saturable-transformer current limit

THE INCREASING use of semiconductors in power circuits requires fast-responding and accurate current-limit circuits (CLs) with high efficiency and with a control circuit insulated from the power circuits. Inverter, converter, time-ratio-control (TRC), and power-switching circuits need CLs that can turn off the power semiconductor within a few microseconds (μsec) after over current occurs. The desire for small overload in semiconductors necessitates accurate CLs (1% to 5%). The current-sensing device should require very little expenditure of power; therefore, the power-wasting current-measuring shunts ought to be avoided.

A Reactor Safety System Using Transistors and Silicon Controlled Rectifiers

An all-semiconductor reactor safety system is described which consists of a dc amplifier, an adjustable trip level bistable circuit, a diode logic circuit, and a power switching circuit. The dc amplifier is a simple emitter follower transistor stage. Three transistors are used in the bistable circuit, two in a Schmitt-trigger arrangement and one as an output drive. The diode logic circuit uses a combination of OR and AND gates to give 2-out-of-3 coincidence of the bistable circuit outputs. A unijunction transistor and two silicon controlled rectifiers are the active elements in the power switching circuit. These components are particularly well suited for the on-off control needed in reactors and the circuitry is reasonably fail-safe.

Transistor circuits and applications

Junction-transistor circuits are reviewed, and new concepts and trends in design are discussed. Improvements in transistor ratings are described, but special transistor types such as tetrodes, p-n-p-n and unipolar devices are not considered.Basic applications surveyed include low-level and power amplifiers, square-wave and sinusoidal oscillators, power convertors and regulators, waveform-shaping and computing circuits, and low-level and power-switching circuits. Numerous references are given.Transistors are capable of supplanting thermionic circuits in all except high-frequency applications (above 10 Mc/s with currently-available units). High temperatures will continue to present limitations in military applications, until silicon transistors become widely available. In more general applications, such as the entertainments field, cost is at present an important limiting consideration.