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EPE 1987 - 31 - Dialogue Session 1.1: COMPONENTS AND CONVERTERS
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	A NEW METHOD FOR THE EVALUATION OF INTERNAL CAPACITANCES OF POWER MOSFET'S   By M. I. Castro Simas; M. Simoes Piedade; J. Costa Freire	[View]   [Download]
Abstract: In the last few years, MOS transistors have been developed in order to achieve high power levels. The structure of these devices is somewhat different from that of the classical low power MOSFET transistor, and as a consequence the classical models (Sah, 1964) are not suited for the new power devices. Recent modelling approaches (Latreche and others, 1985), that represent accurately the behaviour of power MOS transistors, even at high levels of commutation, are oriented to the manufacturers and need technological parameters, that usually are not known by the circuit designers. In this paper we present an experimental method for the characterization of power MOS transistors in commutation that does not need any technological parameter. The method is based on the time domain analysis of the MOS transistor performance in commutation, when constant currents are injected into its terminals. The analysis of the time domain waveforms and the knowledge of the internal structure of the MOS devices allows the evaluation of the transistor capacitances. It is then possible to introduce a simple large-signal model for power MOSFETs that is particularly suited to the analysis of circuits using the MOS transistor in commutation (e.g. in switching power converters). We also present a camparison between the results obtained experimentally and by computer simulation, that confirm the accuracy of the proposed method.
	OPTIMIZATION OF BV-Ron-Cgd OF POWER VDMOS TRANSISTORS   By M. Le Helley; J. P. Chante	[View]   [Download]
Abstract: The trade-off between the on-state resistance, the breakdown voltage and the gate-drain capacitance of power VDMOS transistors is studied by numerical methods. A new structure is proposed. A gain for the active area (27 %) and a decreasing of the gate-drain capacitance (x 0,2) without decreasing of the breakdown voltage are obtained.
	COMPARISON OF THE FOLLOWING POWER COMPONENTS: BIPOLARMOS, MOSFETS, GTO THYRISTORS AND HYBRID DARLINGTON using a 60 amp, 240 volt DC chopper   By J. Bonfante; J. P. Epiard; R. Sénée	[View]   [Download]
Abstract: The aim of the study is the comparison of these components from the practical point of view of the user: - The ease of paralleling is excellent for BIPOLARMOS, MOSFETS as well as for the transistors of the HYBRID DARLINGTON. It is well known that this is not the case with GTOs. - The residual voltage drop is, in general, of 2 or 3 volts, except for the "modified" HYBRID DARLINGTON (which can reach 0.33 V). - The MOSFETs need special radiator cooling (with water for example) to attain a reasonable residual voltage drop (2 or 3 V). - The GTOs need very carefully designed circuitry. - The MOS need a simple snubber. - The HYBRID DARLINGTON can be used without a snubber. - The latch up phenomenon of BIPOLARMOS does not occur if: the temperature is lower than 100°C, the fall time of the voltage Vds is sufficiently long (for example 10 us) and the gate pulses are sufficient (18 V for example).
	PROTECTION OF SEMI-CONDUCTORS lN VOLTAGE COMMUTATED SYSTEMS CONNECTED TO A D.C. SOURCE   By René Deshayes	[View]   [Download]
Abstract: Emphasis has been put on the particular aspect of current protection of convertors necessitating the use of fuses whose electrical characteristics and presentation of these, enables direct and rapid applications. The case of GTO's as well as rapid thyristors are considered. Some aspect of the protection of transistors is also considered.
	A SPICE2 HIGH-FREQUENCY TRANSFORMER MODEL FOR DC-DC CONVERTERS   By E. Tatakis	[View]   [Download]
Abstract: In this paper we present a SPICE2 high frequency transformer model, which can be used for the analysis and the design of dc-to-dc converters. For the evaluation of the transistor switching losses and the dimensioning of the converter components, a model of high precision is required. Furthermore, due to the transformer leakage inductance and parasitic capacitances, voltage spikes can occur across the semiconductors and noise voltages appear in the output. The general purpose circuit simulation package SPICE2 can be used as a tool to analyse dc-dc converters. Neverthenless, the built-in transformer model is inaccurate and when we use it, iteration procedure fails to converge to a solution. Therefore, the study of a more accurate model is needed. A SPICE2 model for soft-recovery power diodes is also presented. These SPICE2 models are compared with previously published experimental results, on a flyback converter and on a forward one with power MOSFETs transistors.
	A TEST AND LOSS MEASUREMENT CIRCUIT FOR DC-REACTORS   By J. Ch. Bendien; H. Van Der Broeck; H.-Ch. Skudelny	[View]   [Download]
Abstract: A test circuit for DC-reactors is described and discussed. The circuit is suited for high power chokes, but requires only the losses of the circuit components and of the choke to be taken from the supply. Furthermore, the circuit is particularly suited for medium frequency loss measurements, especially eddy-current losses. Results of measurements are presented.
	MATHEMATICAL MODEL OF H.R.C. FUSE DESIGNED FOR CONVERTERS SIMULATION   By B. Grzesik	[View]   [Download]
Abstract: The paper presents a mathematical model of H.R.C. fuse used for protection of diodes and thyristors. The model is designed for simulation purposes of power electronic converters. It reflects all principal features of the fuse such as prearcing, arc building and arcing processes. Its complexity is not higher than complexity of other compenents of converters.The parameters of the model were obtained on the basis of laboratory measurements and checked using catalogue data. The work proves that designing protection measures with the use of fuses can be considerably simplified when using models of the fuse and simulation.
	OVERCURRENT PROTECTION FOR GTO-THYRISTORS   By G. Fregien	[View]   [Download]
Abstract: The application of GTO-thyristors requires special short-circuit protection equipment. A simple method based on the proportionality of turn-off current and storage-time of a GTO is shown to protect GTO-thyristors against turn-off failure. This method can be employed for overload protection, failure diagnosis and current measurement.
	IMPROVEMENT ON A THREE PHASE GTO CONVERTER WITH PWM BY AN ASYMMETRICAL PULSE PATTERN   By G. D. Marques	[View]   [Download]
Abstract: The practical problems resulting from the introduction of the PWM technique to the three phase controlled rectifiers are analysed. In practice, the pulse pattern known in the literature produces additional impulses on the output waveforms. This paper describes a method to solve this problem by using a different and asymmetric pulse pattern that reduces the number of the GTO commutations (from 28 to 24) and maintains output characteristics expected in the theory.
	THE ANALYSIS TO THE POWER SYSTEM WITH BOTH TRYRISTOR CONVERTER AND CAPACITOR BANKS BY DIGITAL COMPUTER SIMULATION   By Ting-xin Lu; Li Zhang	[View]   [Download]
Abstract: The existence of capacitors has some influence on the harmonics injected into the a.c power system by thyristor converters. This paper presents the analysis of the relation between them by digital computer simulation and arrives at the conclusion that if neglect the capacitors in the a.c. system, the commutating angles of a thyristor converter and harmonic current flowing into the power system would cause some errors in the calculating results. It also discusses the errors and gives some corresponding results.
	CURRENT-MODE CONTROL IN COUPLED-INDUCTOR STEP-DOWN SWITCHING DC-DC CONVERTER   By A. Pietkiewicz; D. Tollik	[View]   [Download]
Abstract: In the paper the small-signal low-frequency model of the coupled-inductor step-down switching converter operated in current-programmed mode is derived using the unified topological modelling method. From the model the two essential open-loop transfer functions are found: the input-to-output transmittance predicting complete rejection of the line voltage variations and the control-to-output transmittance having the extremely simple one-pole form, which drastically simplifies the loop-gain compensation design. These advantages combined with integration of both inductors into one magnetic element prove the usefulness of the structure for voltage step-down applications without dc isolation.
	INTRODUCTION OF THE TRANSIENT PHENOMENA IN THE DIRECT VOLTAGE CHARACTERISTIC OF THE RECTIFIER CIRCUIT   By E. Lambin	[View]   [Download]
Abstract: The voltage characteristic gives only the steady state values of the current from zero to short circuit in accordance with the reactance of the AC side only. The graphical method proposed here gives the possibility to calculate both the values, steady state and transient of the current and individual influence on these values of each parameter, resistance or reactance of the AC or DC side taken separately. A comparison with the traditionnal computer method and tests on laboratory gives an error of a few percent.
	THE SIMULATION, ANALYSIS AND FILTERING OF CYCLOCONVERTERS   By R. N. Tunçay; I. Alan; P. J. Brown	[View]   [Download]
Abstract: In this study, the simulation and analysis of a three-phase cycloconverter is achieved by employing two modelling techniques. In the first method the SCR is represented by a L,R,Uo model. In the second, a simple switch model is used. For both techniques, the non-sinusoidal load current is considered and, performance values are computed for various output frequencies and lagging load angles. Later, the analysis is extended covering the non-sinusoidal input voltage case and, performance values are compared with those of sinusoidal input voltages. Input power filter is added into the model and the same analysis technique is employed. The effect of the filter is evaluated by computing and comparing the input current harmonics.
	A NEW METHOD FOR SIMULATING 3-PHASE THYRISTOR BRIDGE CIRCUITS   By Huang Shaogang	[View]   [Download]
Abstract: This paper describes a new method for dealing efficiently with the time-varying topology of 3-phase thyristor bridge circuits during digital simulation.The method is to separate the whole system into three subsystems, i.e. thyristor bridge circuits, a.c. network and d.c. network, and respectively to establish their state equations and interface equations. During the digital simulation, the unknown interface variables can be easily calculated through the interface equations of the three subsystems, it is not necessary to assemble the state equations at each change of the topology of the bridge. The method can be used in simulating various types of system connected to the bridge in normal operating and abnormal operating conditions.
	PWM VOLTAGE CONVERTER CELLS AS D.C. TRANSFORMERS   By P. Maranesi; V. Varoli	[View]   [Download]
Abstract: The complete dynamic characterization of a PWM DC/DC converter under the assumption of piecewise linearity implies the definition of four transfer functions; a suitable set is: input admittance, audio-susceptibility, output impedance and input-to-output current ratio. It is shown here how to get the D.C. values of these f'unctions starting from an open-loop analysis. Experimental confirmations of the formulae are reported.
	CURRENT SOURCE MEDIUM FREQUENCY TRANSISTOR INVERTER   By I. Nagy; T. Ruzsányi; Cs. Bacsányi	[View]   [Download]
Abstract: Medium frequency thyristor inverters are widely used for induction heating. They cover the frequency range from network frequency to (10-20)kHz. Vacuum tube inverters have served above 100kHz. There was a gap from 20 to 100kHz. No suitable power supply has been available although it is of particular interest for hardening processes. Inverters applying power transistors seem to be capable of filling the gap. The MOSFETs can even replace the vacuum tubes above 100kHz. This paper reports on the computer results of a 10kW, 20kHz current source inverter. The discussion of three current source inverters and their comparison are included. Two start-up procedure, design principles, control solutions are treated.
	FAST SWITCH WITH HIGH OVERLOAD   By A. Jaafari; A. Goy	[View]   [Download]
Abstract: The purpose is to build a power switch to use it in converters which supply variable load engines. This switch is made of the parallel association of a thyristor and a power transistor, which works only to turn off the thyristor. The interest of this solution is to reduce the switch's weight and volume, by removing components used to turn off the thyristor. Furthermore, the thyristor can be used at higher frequency : 20 to 30 KHz.
	NONLINEAR CONTROL CHARACTERISTICS OF PWM FOUR-QUADRANT CHOPPERS IN CURRENT CONTROL LOOPS   By Rolf-Dieter Klug	[View]   [Download]
Abstract: This paper describes the effects of the switching dead times - protecting the power switches by avoiding a bridge leg short circuit in PWM amplifiers - on the control characteristic first generally for one bridge leg (2-quadrant d.c. chopper), then for circuits with two (4-quadrant d.c. chopper) and three (3-phase inverter) bridge legs at resistive-inductive-active load operation. The effect of the resulting ambiguous and non-linear control characteristic on the current control loop is shown exemplary for the 4-quadrant d.c. chopper. A signal processing correction circuit for the PWM control signal is presented to get a definite and linear behaviour of the mentioned bridge amplifiers. The results are shown at a 4-quadrant d.c. chopper.
	VARIABLE VOLTAGE BOOSTING AND BUCKING USING THYRISTOR CONTROLLED TRANSFORMERS   By A. S. Abdel-Karim; A. I. Taalab; A. E. Lashine	[View]   [Download]
Abstract: In this paper, two interconnected transformers are thyristor controlled to obtain variable voltage boosting and bucking for load voltage regulation. Thyristor switches are used with secondary coils which can be designed to suit the available thyristor ratings. The device action is based on flux control in the two transformer cores. The proposed approach gives very fast response with no distortion or phase shift in the voltage waveform, which, in its overall action, is equivalent to the procedure of on-load tap-changing. Thyristor switches are naturally commutated and the device is rated for only the range of variation required. Firing control and commutation process of the thyristor switches are considered. The proposed circuit arrangement is analysed considering the action of flux control and mathematical expression relating the circuit voltages and currents. The device performance is computed and theoretical results are compared with these obtained experimentally using a single-phase prototype.
	CIRCULAR CURRENT ANALYSIS IN A MEDIUM FREQUENCY PARALLEL OPERATING CONVERTER SYSTEM   By Iuliu Szekely; Vasile Szentgyörgyi	[View]   [Download]
Abstract: Medium frequency induction heating plants often employ large powers (a few MW). The paper investigates the parallel connection on medium frequency bars of parallel oscillating inverter converters with random loads. In view of developing the control strategy, the first step is an analysis of the circular currents occurring due to shape and control angle differences in the rectified voltages, as well as to internal control differences in the inverters. The analytical and computer analysis of the three phenomena have yielded some design formulae and diagrams which can prove useful in developing the control system of the converter system. Reference is made to a system of three converters having an overall power of 1.1 MW at 2500Hz, feeding a random number of heating inductors. The development of the system has been based on data furnished by the present study.
	INVESTIGATIONS ON A DUAL CONVERTOR DRIVE WITH AN EXTINCTION ANGLE CONTROLLER   By V. Jagannathan; Yash Pal Singh	[View]   [Download]
Abstract: An Extinction Angle Controller (EAC) reduces the flow of lagging VAR in a Dual Convertor Drive by forced commutation of the rectifier convertor. A state space model of an experimental drive is validated through a comparison of the results of digital simulation with the experimental results. The simulation makes use of a logic module for determining the successive modes of operation of the system and predicts the 'Main ' as well as 'Transition' modes introduced by the EAC. Digital simulation also yields substantial information about the performance of the drive in respect of line power factor, displacement factor, harmonic content in the input current and other parameters of interest to the system designer like power dissipation in the diodes and thyristors in the main circuits as well as in the auxiliary EAC module.
	IMPROVEMENT OF "BANG-BANG" CONTROLLERS FOR DC-AC CONVERTERS   By G. A. Capolino; O. Hazsnaoui; D. Lafore	[View]   [Download]
Abstract: The purpose of this paper is related to modelling, simulation and implementation of two control algorithms in single-phase DC AC converter with current hysteresis controller. Both constant hysteresis mod (CHM) and proportionnal hysteresis mode (PHM) are presented and they are evaluated in terms of performance index and harmonic spectra.
	THREE-PHASE AC/AC CONVERTER REDUCTION OF THE EFFECTS OF AN UNBALANCED LOAD   By P. Goerger; C. Rombaut	[View]   [Download]
Abstract: Several AC/AC converter configurations are possible in order to regulate the power provided by a three-phase supply to an unbalanced resistive load. While certain configurations transmit the unbalance directly, others transmit an unbalance reduced to supply line. ln symmetrical control, grouping together the three single-phase AC/AC converters with common return conductor brings no reduction in unbalance. With the same control mode, delta-connected grouping of three single-phase AC/AC converters brings no reduction in the current of the three load phases, but the line supply currents are less unbalanced as homopolar component is not transmitted with these two assemblies, as each phase is separately controlled, an adapted control strategy enables the unbalance to be reduced on either the load or the source side. Even using a symmetrical control, the three-phase AC/AC converter reduces the unbalance. This converter, its operation and its characteristics will provide the subject of the paper.
	A SYNTHESIS OF A CURRENT-FED DC CONVERTER REGULATION LOOP COMPENSATION   By Zelimir Ivanovic	[View]   [Download]
Abstract: The current-fed dc converter is very convenient in cases of wide-range power-source voltage variations.The closing of regulation loop is connected with instability of the system. The paper deals with feedback compensation at a 19-62V/24V-10A dc converter. The cannonical model of the converter has been developed, and the compensation chosen in accordance with the required static error and system stability properties. The results obtained on implemented converter are presented.
	CASCADE SYSTEM WITH VARIABLE INVERTERS STRUCTURE OF THE TYPE CVI-DC FOR HIGH POWER DRIVES   By W. Koczara; L. Grzesiak; H. Drechsler	[View]   [Download]
Abstract: In the paper the cascade system with variable inverters structure of the type CVI-DC is shown. Cascade systems with slip-ring induction motor are most frequently applied to high power drives of pumps and funs. To reduce the disadvantagageous reaction on supplying network these drives are build with 12-pulse inverters. Additional application of system with variable structure of inverters switched in function of angular speed of the motor to serial or parallel action enables reduction of reactive power absorbed from the grid. Furthermore, rated power of inverters and transformers is smaller. In the paper decomposition method for analysis of CVI-DC system is proposed Mathematical models of individual block in decomposed system (i.e. motor, inverter, transformer) are presented. Equations of multi-port networks are derived and original method for transients calculations in decomposed system is proposed which takes advantage of solutions distribution on to free and forced components and introduces the notion of instantaneous transmission coefficients.
	TEST CIRCUITS FOR HIGH POWER CHOPPERS   By H. Van Der Broeck; J. Ch. Bendien; H.-Ch. Skudelny	[View]   [Download]
Abstract: Testing high power choppers is a problem as both a high power supply and a corresponding load are needed. Two new test circuits are presented. These circuits enable tests at full voltage and full current but do not require high power laboratory equipment.
	SERIES RESONANT CONVERTER: REGULATION   By J. P. Lavieville; J. Roudet; E. Toutain	[View]   [Download]
Abstract: In this paper we studied a output voltage control of a series resonant converter. We recall the static characteristics of the three DC to DC converters which can be envisaged ; the dynamic measurements show that for control the choice of a simple P.I. corrector is suitable.
	REVIEW OF STATE OF ART HIGH FREQUENCY PWM SWITCHED-MODE POWER CONVERSION TECHNIQUES   By S. Manias; P. D. Ziogas, G. Olivier; A. R. Prasad	[View]   [Download]
Abstract: The present state or art high frequency Switched Mode Power Converters (SMPCs) tor Power Supply applications are reviewed in this paper. Different power circuit topologies and their advantages and disadvantages are discussed to provide design guidelines tor the power electronics engineer. Finally, a large number of references are provided to facilitate further access to details regarding power circuits, control schemes and other design details.
	AN IMPROVED HIGH FREQUENCY BI-MOS SWITCH APLICATION TO 300 kHz SWITCH MODE POWER SUPPLY   By C. M. Penalver; J. Farina	[View]   [Download]
Abstract: An experimental switch mode power supply with high overcurrent capability, low switches losses, high speed switching and gain has been implemented using a transistor emitter-open turn-off scheme, by a BIpolar transistor and MOSfet combination.
	THYRISTOR POWER CONTROL WITHOUT HARMONICS FOR ELECTRIC FURNACE OF STEEL HEAT TREATMENT   By G. Fekete; L. Szentirmai	[View]   [Download]
Abstract: There has been control electronics for a microcomputer-aided electric furnace of 700 kilowatts developed and put into practice recently by the Department above. Electric resistors are distributed into three symmetric heating zones and thyristors, switching elements, sensing devices, instrumentation are incorporated in two phases only due to the new thyristor control strategy. (a) Thyristor control ensures 3-phase power-input for symmetric high-powered furnace without harmonics, (b) it provides transient state-less operation, (c) tempersture control can be specified by heat treatment technology concerned, (d) thyristors are controlled in 16 portions by cycle, thus average power-input can be adjusted to industrial requirements, (e) error coding and memory circuit provides monitoring thyristor fault and electric asymmetry as well. Thyristor control has new main circuit and new electronic circuits and devices, too.
	SWITCHED-MODE TECHNIQUES WITH INDUCTIVE AND CAPACITIVE LOADS   By J. K. Goodfellow; B. W. Williams	[View]   [Download]
Abstract: A two-point current feeding technique has been developed to control single or multi-phase switched-mode amplifiers. The control technique uses an adaptive and optimised strategy that can be applied to capacitive, inductive or resistive loads. Load current is a reproduction of a reference input signal which may be a variable frequency, variable magnitude sinusoid or a random waveform. The technique does not require load voltage measurement, and has been applied in single phase form up to power levels of 10 kVA. Total harmonic distortion levels lower than 0.2% have been achieved over the operating range of 2 Hz to 10 kHz and 0A to 80A rms using a modulation frequency of 100 kHz. System efficiency has been measured at greater than 92% at full rated output.
	PLL METHOD APPLICATION IN UNINTERRUPTIBLE STATIC POWER SUPPLY SYSTEMS   By Milorad D. Gvozdenovic; Borislav I. Jeftenic	[View]   [Download]
Abstract: This paper deals with Real time integration phase locked loop (RTI- PLL) method for Inverter and Mains voltage frequency and phase matching in Uninterruptible static power supply systems. By applying this method, using a quick fault detection in the system and by an appropriate filter element selection it is possible to avoid parallel load supplying (from inverter and mains) and save middle tap choke in a static switch. In this way, a small response time of the system on disturbances and a very small increasing of the harmonic content in inverter output voltage is reached.
	QUICK DETECTION OF DISTURBANCES IN THE UNINTERRUPTIBLE STATIC POWER SUPPLIES   By Borislav I. Jeftenic; Milorad D. Gvozdenovic	[View]   [Download]
Abstract: The paper presents the possibility of quick detection of the fault, voltage disturbance (increase or decrease), in the system for uninterruptible AC power supplies. In order to ensure the uninterruptible load current, in the majority of practical cases, it is indispensable to detect the disturbance of the voltage in the time shorter than one pertod (T). We have analysed the possibilities of the correct functioning verification of the system for uninterruptible supply in the intervals from T/2 and T/4. The manner of the system realization for the fault detection is presented. The results realised are displayed at the end.
	A MICROPROCESSOR BASED UPS CONTROL UNIT   By Stefano Pirani; Roberto Spazzoli	[View]   [Download]
Abstract: The paper describes a microprocessor based Uninterruptible Power Supply Control Unit which employes two microprocessors: one generates the Pulse Width Modulation control signal and the other one executes diagnostic and supervision functions. The most interesting characteristic of the control unit is the great adaptability which allows the use of this circuit for the best control of many power units: the control unit is able to drive power circuits made up with different kinds of semiconductor devices as SCRs, GTOs, Power Transistors and MOSFETs. The microprocessor based control unit may also be used for the control of an additional input circuit of the converter which modifies the rated voltage of the battery systems in order to employ different kind of storage cells.
	THE RELIABILITY OF UNINTERRUPTIBLE POWER SUPPLIES   By P. Leyten	[View]   [Download]
Abstract: The reliability of Uninterruptible Power Supplies (UPS) is discussed. A comparison is made of parallel and series UPS. The main components which influence the reliability of UPSs are discussed . The general formula is deduced for the Mean Time Between Failures (MTBF) of a parallel connected UPSs of which k are redundant. Conclusions are reached with respect to the optimum reliability of the various configurations.
	THE REDUCTION OF TRANSISTOR SWITCHING LOSSES IN NONDISSIPATlVE WAY   By Neven Cobanov	[View]   [Download]
Abstract: In d .c. converters the snubbers are used to reduce switching losses and/or to assure the operation of the switch within SOAR. While the dissipative snubber reduces transistor losses, the losses in the very snubber are increased. Therefore, the total switching losses have a limited minimum. The nondissipative snubber decreases transistor losses in a similar way, with negligible dissipation in the snubber. However, the minimum switching losses are again limited and these limitations have been derived from the permissible current and voltage stress of the transistor switch and from the converter circuit parameters as output power, input and output voltage and working frequency. A nondissipative snubber design procedure which enables the minimisation of transistor turn-off losses is shown. The measuring results obtained on a realized converter are presented.