EPE Association: EPE 1987 - 32 - Dialogue Session 2.1: SIGNAL PROCESSING AND CONTROL IN POWER ELECTRONICS SYSTEMS

EPE 1987 - 32 - Dialogue Session 2.1: SIGNAL PROCESSING AND CONTROL IN POWER ELECTRONICS SYSTEMS
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 1987 - Conference > EPE 1987 - 32 - Dialogue Session 2.1: SIGNAL PROCESSING AND CONTROL IN POWER ELECTRONICS SYSTEMS

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   HIGH QUALITY THREE PHASE INVERTER
By J. Jalade; S. Senanayake [View]
[Download]

Abstract: Recent analytical studies on the functioning of static power converters and resulting new structures permit the realisation of reliable, lightweight and economic power supplies for domains as diverse as UPS, aerospace power supply, speed variable drive, instrumentation, etc. In this article, the authors present the realisation of a three phase inverter which combines the advantages of high frequency switching conversion with that of advance reversible power control. Thus, it is possible to assure the functioning of the inverter on no-load or full-Ioad conditions with good regulation and easy protection. Moreover, third harmonic techniques make it possible to obtain an o/p voltage 15 % higher than that of conventional systems. For applications related to speed variable drives for AC motors, the absence of HF and LF harmonics is equally advantageous. On this breadboard realisation, the condition U/f = const. is easily met even at low frequencies and the motor is braked regeneratively.

   LINE SIDE HARMONICS OF THREE-PHASE CURRENT CONTROLLED RECTIFIERS IN CONTINUOUS AND DISCONTINUOUS OPERATION MODE
By Manfred Grötzbach; Thomas Strasser; Leo Lorenz [View]
[Download]

Abstract: Because of the nonlinear switch function of the semiconductor valves, the line current of converters contains harmonics. These produce voltage drops across the equivalent supply impedance which must not exceed certain limits in the interest of other loads. A simple method which permits any dc ripple including discontinuous operation is provided for the pre-determination of these disturbances. The analytical calculation is based on the difference equation for the dc current and results in a piecewise description. The associated control and overlap angles are determined from the working point specified by the mean dc current value and the emf. Because of the analytical description, it is possible to carry out the evaluations on a small desk-top computer. The results show that, as dc ripple increases, the line current harmonics differ very considerably from the known values for good smoothing. The harmonics of the mains voltage also therefore change quite considerably and this affects the distortion factor correspondingly.

   INFLUENCE OF HARMONIC DISTORTION CAUSED BY CONVERTERS ON STANDARD MEASURING INSTRUMENTS
By Vladimir A. Katic; Radojle M. Radetic [View]
[Download]

Abstract: The influence of harmonic distortion caused by converters on standard measuring instruments was observed. It was concluded that harmonics diminished the accuracy of measurement. The original indirect method for determination of that influence was developed. The method consists of determination of harmonic characteristic of instrument, recording of harmonic spectrum of current and/or voltage and computer treatment of results. It gives network harmonic data, relative and class error of instrument and accurate value. The method is convenient for networks with "rich" harmonic contents as a result of multiconverter operation. Two examples of the methode procedure are presented: determination of ampermeter error and determination of induction watthour meter error. Both ampermeter and induction watthour meter show negative error as a result of the presence of harmonics in a measured value.

   ELIMINATING 5TH-AND-7TH LINE CURRENT HARMONICS IN AC/DC CONVERTERS BY HARMONIC CURRENTS INJECTION
By Jean-Paul Swan; Robert Bausiere; Guy Seguier [View]
[Download]

Abstract: Elimination of 5th-and-7th line current harmonic components in 3-phase AC-DC converters may be achieved by current injection. Injected current 5th-and-7th harmonics must have the same order, the same rms values and the same phase-angles, respectively, as these of the harmonic components to be eliminated. Analysis of the rms values and phase-angles of 5th-and-7th line current harmonics of a 6-pulse AC-DC converter shows that rms values and phase-angles of the injected currents can be deduced from those of the fundamental component I1 of the line current. The injected currents are generated by a transistor converter which switches a direct current proportional to I1.

   ANALYSIS AND MEASUREMENT OF PWM WAVEFORMS
By M. Savino; A. Trotta [View]
[Download]

Abstract: The paper presents an efficient digital method of measurement, suitable to computer-processing of pulse width modulated (PWM) waveforms. The aim is to provide a technique which can be applied both to simulated and actual PWM inverter outputs, in order to obtain precise information about their harmonic structure. The analysis is performed implementing the fast Fourier transform (FFT) algorithm to the sequence deriving from a sampling of the analog signal. Particularly, the methods to reduce the negative effects due to aliasing and spectral leakage are emphasized, namely, it is shown how the aliasing can be averted through a non-recursive realization of a suitable low-pass digital filter, having a Finite Impulse Response (FIR). Spectral leakage, caused by a non-synchronized sampling, is considerably reduced performing the convolution between the sequence returned from the FFT and the spectrum of a suitable window, in the frequency domain. Successively, simple interpolation formulas must be applied to the windowed spectral lines in order to find the frequency of the PWM signal, with a high degree of accuracy. Several test results, performed both on simulated models and on actual inverter outputs, are presented. They confirm the effectiveness of the proposed method, encouraging future applications in microprocessor-based digital instrumentations.

   A SAMPLING TECHNIQUE FOR PHASE DIFFERENCE MEASUREMENT AT POWER FREQUENCIES
By G. D. Bergman [View]
[Download]

Abstract: In microprocessor based equipment for the control and instrumentation of power systems, signal processing of waveform samples can be used to messure phase difference. In this way a reduction in equipment cost can be achieved by trading processing software for the hardware circuitry usually needed for phase measurement. This technique is described and consideration is made of its practical implementation, performance accuracy and economic implications.

   ANALOG VERSUS DIGITAL CONTROL IN POWER ELECTRONICS: A PERFORMANCE COMPARISON ON CONTROLLED AND SWITCHING CONVERTERS
By Juan Peracaula; Josep Bordonau; Xavier Soler [View]
[Download]

Abstract: The aim of this work is to provide a comparison of power converters operation with analog and digital control. It is desired to look at the respective features in equal conditions. Then the comparison is performed on the same converter, i.e., its operation is evaluated under both analog and digital control. This method provides a reasonable way to establish the convenience in choosing one or another sort of control. Moreover, further generalization of the results is shown through the application of this approach to the main converter structures: controlled converters (implemented with a full bridge thyristor rectifier) and switching converters (with a Cuk converter). The conclusion is centered on the flexibility offered by microprocessor control. The results obtained varing the same control policy implemented with digital or analog technologies on the same converter, as can be expected, are the same. Nevertheless, it is easier to change and prove new policies on a converter with digital control.

   CONTROL ALGORITHMS MINIMISING LOSSES IN DC-CHOPPER AND AC MOTOR DRIVES
By P. Gruszczynski; R. Szczesny [View]
[Download]

Abstract: A chopper-controlled DC motor drive losses can be reduced by independent control of the average output voltage and the chopper frequency. A four-quadrant thyristor DC chopper with two different control methods is considered. Eddy-current armature winding losses of separately excited DC motor are taken into account. An equation is derived permitting evaluation of the frequency minimising the total DC drive losses, given the duty cycle. Several conditions for frequency and duty cycle limits are established, including the conditions for continuous armature current flow. Theoretical results are verified using a 2.2 kW microprocessor-controlled experimental set-up. AC motor drive losses can be reduced by independently controlling the voltage and the frequency. The total losses for the minimum loss operation and the constant V/f operation for a 55 kW induction traction motor are compared. Eddy-current winding losses of a current-source inverter drive are taken into account. The suggested control method makes unnecessary application of oversize motors.

   MICROPROCESSOR CONTROL OF VARIABLE-SPEED PWM INVERTER-MACHINE DRIVE
By Young Fu-Wen [View]
[Download]

Abstract: This paper presents a new scheme of vector control of variable-speed PWM inverter-machine drive. Meanwhile, in order to decrease the sensitivity and disturbance of the drive system, Robust controller is used. Hardware end software implementation of the drive system using 1.1 KVA asynchronous machine and a Z-80 microprocessor is designed. Practical design aspects are discussed and experimental results are given.

   PULSEWIDTH MODULATIONS FOR CURRENT SOURCE INVERTERS
By F. Jenni; R. Zwicky [View]
[Download]

Abstract: A new kind of pulse pattern for current-source-inverters (CSI) has been developped. It is considered for three pulse width modulation (PWM) procedures: First for the elimination of unwanted harmonics. Secondly for a new synchronous modulator (fixed number of pulses per period). The third application is an asynchronous modulator (with a variable number of pulses per period). For the second and the third of these modulation principles, good practical results are shown.

   DESIGN OF A5-kVA TRANSISTORIZED INVERTER WITH REAL-TIME IMPLEMENTATION OF THE SYMMETRICAL-PULSE PWM ON A MICROCONTROLLER
By J. Brochu; P. Viarouge [View]
[Download]

Abstract: The design of a 5-kVA transistorized PWM inverter for the variable-frequency supply of a three-phase induction motor (127 VLL, 22.7 A) is presented. A detailed description is given of various design aspects, including determination of the converter structure, development of the base drive circuits and the related auxiliary switching power supply, and real-time implementation of symmetrical-pulse PWM strategy on a 8031 microcontroller. A three-phase PWM signal from 3.1 to 64.1 Hz is computed under real-time operating conditions with a carrier frequency of 1 to 2. 5 kHz and a minimum modulation ratio of 39. The inverter performance is illustrated by experimental results.

   VARIABLE TOPOLOGY: A NEW APPROACH IN C.A.D.
By F. Boulos; C. Glaize [View]
[Download]

Abstract: This paper deals with the use of variable topology simulation of static converters which ensures a significant reduction of the order of the system to be resolved as well as the computational time allowing its use on standard micro-computers. After the presentation of the modelization of the semi-conductors, we indicate the principle of such a method of simulation. In particular, we show the methods used to simplify the initial schema of the converter. The generation of equations is automatic. To illustrate our work, we present the results obtained by simulating a chopper. We emphasize the form of the minimal topology obtained at each change of configuration by indicating the numbering of the branches with their entry and exit nodes, as well as the values of the voltage across turned off semi-conductors or conducting semi-conductors which become turned off.

   THYRISTOR CURRENT SOURCE CONTROL BY REAL TIME SIMULATION: A SUCESSFUL TEST AGAINST EXISTING TECHNICS
By J. Fernando Silva [View]
[Download]

Abstract: A new algorithm for current control, and elimination of troublesome commutation failures in a six pulse thyristor bridge is described. The algorithm, suitable for implementation in a fast digital signal microprocessor, is tested by computer simulation, and is found to have higher performances than classic methods, such as digital proportional plus integral (P. I.) controller or adaptive control. The new approach not only eliminates all the commutation failures, but also recovers the bridge to normal operation after a short zero voltage fault in the AC bus.

   Z-TRANSFORM METHOD APPLICATION TO THE LINE COMMUTATED THYRISTOR CONVERTERS ANALYSIS
By Milorad D. Gvozdenovic [View]
[Download]

Abstract: Line commutated thyristor converters are very often used in drive engineering. But, difficulties in modeling and analysis such systems, due to thyristor converter non-linearity, are also present. In most cases in practice the change of the firing angle between two consecutive thyristor pairs activation is small, we can assume that sampling instants are equidistantly spaced in time, and linearisation around working point can be done. That leads to the Z-transform method application in the analysis of automatic control systems containing thyristor converters. The thyristor converter transfer function is presented, and stability analysis in the Z-domain of realized high speed current mean value control system by line commutated thyristor converter is given. Experimental results, i.e. system response on sudden changes in reference and load are also presented.

   REPRESENTATION OF FAULTS IN MATHEMATICAL MODEL OF CONVERTOR SET
By Ewa Napierulska-Juszczak [View]
[Download]

Abstract: Diode faults in network commutated convertors provide unidirectional currents strongly submagnetizing the convertor transformer. After a few periods very high saturation of the core appears. If the fuses are wrong the transformer windings undergo very peculiar dynamic strains, generally more dangereous than during usual S.C. To obtain proper wave shapes of all currents, voltages, main, leakage and so called yoke fluxes enabling the analysis of transient phenomena, the design of adequate equivalent circuit and formation of mathematical model are necessary. It has to consider the magnetic non-linearity and non-symmetry of the core, saturation of smoothing reactor, properties of diodes and SCR. This paper presents an equivalent circuit for three phase bridge with 20 nonlinear equations forming the mathematical model. It allowes the analysis of transients during all possible faults, changes of load, EMF, or impulsing angle, disconnections, blowing of fuses etc for rectifier and invertor operation. Following phenomena are analyzed as instances:
a/ short circuit of one diode in a 6 D set;
b/ short circuit on DC terminals in 6 T bridge with only a nonlinear smoothing reactor; stoping impulses when IDC > 5 In;
c/ same as "a" but in 6T set.
The results are computed and compared with experiments with good agreement.

   MODELLING AND SIMULATION OF CONVERTER SYSTEMS
By R. Szczesny; P. Gruszczynski [View]
[Download]

Abstract: Three fundamental problems of converter modelling are discussed: valve model, calculation method with properly chosen numerical integration algorithm and fast determination of the steady state solution in time domain. The developed concept of models of different valves allows application models whose degree of complication depend on particular requirements and the object of simulation. Following a discussion of numerical stability of different numerical integration algorithms the application of absolutely stable methods is recommended. A special procedure is presented intended for fast computation of the steady state response. The simulation waveforms for an example converter system are given.

   REDUCED SCALE MAINS NETWORK EXPERIMENT CARRIED OUT BY INSA AND LAAS OF TOULOUSE
By J. P. Berry; J. C. Joubert; A. Benhamou; X. Roboam; J. Fantin; G. Garcia [View]
[Download]

Abstract: Utilizing recent power electronics techniques, LAAS and INSA have set up jointly a mains supply experiment (20 KVA power) which is described in this paper. Research is applied to the dc - ac conversion in order to improve the power factor:
- simulation and realization of an inverter with a dual structure to that of the regular controlled rectifiers (thyristors)
- implementation of an artificial switch device the so-called dualistor.
Such an experiment induces and / or allows us to review more fundamental research work in the field of automatics ,i.e. motor alternator group control strategy, hierarchy and / or auto-adaptive control, stability.

EPE 1987 - 32 - Dialogue Session 2.1: SIGNAL PROCESSING AND CONTROL IN POWER ELECTRONICS SYSTEMS
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 1987 - Conference > EPE 1987 - 32 - Dialogue Session 2.1: SIGNAL PROCESSING AND CONTROL IN POWER ELECTRONICS SYSTEMS
	[return to parent folder]

	HIGH QUALITY THREE PHASE INVERTER By J. Jalade; S. Senanayake	[View] [Download]
Abstract: Recent analytical studies on the functioning of static power converters and resulting new structures permit the realisation of reliable, lightweight and economic power supplies for domains as diverse as UPS, aerospace power supply, speed variable drive, instrumentation, etc. In this article, the authors present the realisation of a three phase inverter which combines the advantages of high frequency switching conversion with that of advance reversible power control. Thus, it is possible to assure the functioning of the inverter on no-load or full-Ioad conditions with good regulation and easy protection. Moreover, third harmonic techniques make it possible to obtain an o/p voltage 15 % higher than that of conventional systems. For applications related to speed variable drives for AC motors, the absence of HF and LF harmonics is equally advantageous. On this breadboard realisation, the condition U/f = const. is easily met even at low frequencies and the motor is braked regeneratively.

	LINE SIDE HARMONICS OF THREE-PHASE CURRENT CONTROLLED RECTIFIERS IN CONTINUOUS AND DISCONTINUOUS OPERATION MODE By Manfred Grötzbach; Thomas Strasser; Leo Lorenz	[View] [Download]
Abstract: Because of the nonlinear switch function of the semiconductor valves, the line current of converters contains harmonics. These produce voltage drops across the equivalent supply impedance which must not exceed certain limits in the interest of other loads. A simple method which permits any dc ripple including discontinuous operation is provided for the pre-determination of these disturbances. The analytical calculation is based on the difference equation for the dc current and results in a piecewise description. The associated control and overlap angles are determined from the working point specified by the mean dc current value and the emf. Because of the analytical description, it is possible to carry out the evaluations on a small desk-top computer. The results show that, as dc ripple increases, the line current harmonics differ very considerably from the known values for good smoothing. The harmonics of the mains voltage also therefore change quite considerably and this affects the distortion factor correspondingly.

	INFLUENCE OF HARMONIC DISTORTION CAUSED BY CONVERTERS ON STANDARD MEASURING INSTRUMENTS By Vladimir A. Katic; Radojle M. Radetic	[View] [Download]
Abstract: The influence of harmonic distortion caused by converters on standard measuring instruments was observed. It was concluded that harmonics diminished the accuracy of measurement. The original indirect method for determination of that influence was developed. The method consists of determination of harmonic characteristic of instrument, recording of harmonic spectrum of current and/or voltage and computer treatment of results. It gives network harmonic data, relative and class error of instrument and accurate value. The method is convenient for networks with "rich" harmonic contents as a result of multiconverter operation. Two examples of the methode procedure are presented: determination of ampermeter error and determination of induction watthour meter error. Both ampermeter and induction watthour meter show negative error as a result of the presence of harmonics in a measured value.

	ELIMINATING 5TH-AND-7TH LINE CURRENT HARMONICS IN AC/DC CONVERTERS BY HARMONIC CURRENTS INJECTION By Jean-Paul Swan; Robert Bausiere; Guy Seguier	[View] [Download]
Abstract: Elimination of 5th-and-7th line current harmonic components in 3-phase AC-DC converters may be achieved by current injection. Injected current 5th-and-7th harmonics must have the same order, the same rms values and the same phase-angles, respectively, as these of the harmonic components to be eliminated. Analysis of the rms values and phase-angles of 5th-and-7th line current harmonics of a 6-pulse AC-DC converter shows that rms values and phase-angles of the injected currents can be deduced from those of the fundamental component I1 of the line current. The injected currents are generated by a transistor converter which switches a direct current proportional to I1.

	ANALYSIS AND MEASUREMENT OF PWM WAVEFORMS By M. Savino; A. Trotta	[View] [Download]
Abstract: The paper presents an efficient digital method of measurement, suitable to computer-processing of pulse width modulated (PWM) waveforms. The aim is to provide a technique which can be applied both to simulated and actual PWM inverter outputs, in order to obtain precise information about their harmonic structure. The analysis is performed implementing the fast Fourier transform (FFT) algorithm to the sequence deriving from a sampling of the analog signal. Particularly, the methods to reduce the negative effects due to aliasing and spectral leakage are emphasized, namely, it is shown how the aliasing can be averted through a non-recursive realization of a suitable low-pass digital filter, having a Finite Impulse Response (FIR). Spectral leakage, caused by a non-synchronized sampling, is considerably reduced performing the convolution between the sequence returned from the FFT and the spectrum of a suitable window, in the frequency domain. Successively, simple interpolation formulas must be applied to the windowed spectral lines in order to find the frequency of the PWM signal, with a high degree of accuracy. Several test results, performed both on simulated models and on actual inverter outputs, are presented. They confirm the effectiveness of the proposed method, encouraging future applications in microprocessor-based digital instrumentations.

	A SAMPLING TECHNIQUE FOR PHASE DIFFERENCE MEASUREMENT AT POWER FREQUENCIES By G. D. Bergman	[View] [Download]
Abstract: In microprocessor based equipment for the control and instrumentation of power systems, signal processing of waveform samples can be used to messure phase difference. In this way a reduction in equipment cost can be achieved by trading processing software for the hardware circuitry usually needed for phase measurement. This technique is described and consideration is made of its practical implementation, performance accuracy and economic implications.

	ANALOG VERSUS DIGITAL CONTROL IN POWER ELECTRONICS: A PERFORMANCE COMPARISON ON CONTROLLED AND SWITCHING CONVERTERS By Juan Peracaula; Josep Bordonau; Xavier Soler	[View] [Download]
Abstract: The aim of this work is to provide a comparison of power converters operation with analog and digital control. It is desired to look at the respective features in equal conditions. Then the comparison is performed on the same converter, i.e., its operation is evaluated under both analog and digital control. This method provides a reasonable way to establish the convenience in choosing one or another sort of control. Moreover, further generalization of the results is shown through the application of this approach to the main converter structures: controlled converters (implemented with a full bridge thyristor rectifier) and switching converters (with a Cuk converter). The conclusion is centered on the flexibility offered by microprocessor control. The results obtained varing the same control policy implemented with digital or analog technologies on the same converter, as can be expected, are the same. Nevertheless, it is easier to change and prove new policies on a converter with digital control.

	CONTROL ALGORITHMS MINIMISING LOSSES IN DC-CHOPPER AND AC MOTOR DRIVES By P. Gruszczynski; R. Szczesny	[View] [Download]
Abstract: A chopper-controlled DC motor drive losses can be reduced by independent control of the average output voltage and the chopper frequency. A four-quadrant thyristor DC chopper with two different control methods is considered. Eddy-current armature winding losses of separately excited DC motor are taken into account. An equation is derived permitting evaluation of the frequency minimising the total DC drive losses, given the duty cycle. Several conditions for frequency and duty cycle limits are established, including the conditions for continuous armature current flow. Theoretical results are verified using a 2.2 kW microprocessor-controlled experimental set-up. AC motor drive losses can be reduced by independently controlling the voltage and the frequency. The total losses for the minimum loss operation and the constant V/f operation for a 55 kW induction traction motor are compared. Eddy-current winding losses of a current-source inverter drive are taken into account. The suggested control method makes unnecessary application of oversize motors.

	MICROPROCESSOR CONTROL OF VARIABLE-SPEED PWM INVERTER-MACHINE DRIVE By Young Fu-Wen	[View] [Download]
Abstract: This paper presents a new scheme of vector control of variable-speed PWM inverter-machine drive. Meanwhile, in order to decrease the sensitivity and disturbance of the drive system, Robust controller is used. Hardware end software implementation of the drive system using 1.1 KVA asynchronous machine and a Z-80 microprocessor is designed. Practical design aspects are discussed and experimental results are given.

	PULSEWIDTH MODULATIONS FOR CURRENT SOURCE INVERTERS By F. Jenni; R. Zwicky	[View] [Download]
Abstract: A new kind of pulse pattern for current-source-inverters (CSI) has been developped. It is considered for three pulse width modulation (PWM) procedures: First for the elimination of unwanted harmonics. Secondly for a new synchronous modulator (fixed number of pulses per period). The third application is an asynchronous modulator (with a variable number of pulses per period). For the second and the third of these modulation principles, good practical results are shown.

	DESIGN OF A5-kVA TRANSISTORIZED INVERTER WITH REAL-TIME IMPLEMENTATION OF THE SYMMETRICAL-PULSE PWM ON A MICROCONTROLLER By J. Brochu; P. Viarouge	[View] [Download]
Abstract: The design of a 5-kVA transistorized PWM inverter for the variable-frequency supply of a three-phase induction motor (127 VLL, 22.7 A) is presented. A detailed description is given of various design aspects, including determination of the converter structure, development of the base drive circuits and the related auxiliary switching power supply, and real-time implementation of symmetrical-pulse PWM strategy on a 8031 microcontroller. A three-phase PWM signal from 3.1 to 64.1 Hz is computed under real-time operating conditions with a carrier frequency of 1 to 2. 5 kHz and a minimum modulation ratio of 39. The inverter performance is illustrated by experimental results.

	VARIABLE TOPOLOGY: A NEW APPROACH IN C.A.D. By F. Boulos; C. Glaize	[View] [Download]
Abstract: This paper deals with the use of variable topology simulation of static converters which ensures a significant reduction of the order of the system to be resolved as well as the computational time allowing its use on standard micro-computers. After the presentation of the modelization of the semi-conductors, we indicate the principle of such a method of simulation. In particular, we show the methods used to simplify the initial schema of the converter. The generation of equations is automatic. To illustrate our work, we present the results obtained by simulating a chopper. We emphasize the form of the minimal topology obtained at each change of configuration by indicating the numbering of the branches with their entry and exit nodes, as well as the values of the voltage across turned off semi-conductors or conducting semi-conductors which become turned off.

	THYRISTOR CURRENT SOURCE CONTROL BY REAL TIME SIMULATION: A SUCESSFUL TEST AGAINST EXISTING TECHNICS By J. Fernando Silva	[View] [Download]
Abstract: A new algorithm for current control, and elimination of troublesome commutation failures in a six pulse thyristor bridge is described. The algorithm, suitable for implementation in a fast digital signal microprocessor, is tested by computer simulation, and is found to have higher performances than classic methods, such as digital proportional plus integral (P. I.) controller or adaptive control. The new approach not only eliminates all the commutation failures, but also recovers the bridge to normal operation after a short zero voltage fault in the AC bus.

	Z-TRANSFORM METHOD APPLICATION TO THE LINE COMMUTATED THYRISTOR CONVERTERS ANALYSIS By Milorad D. Gvozdenovic	[View] [Download]
Abstract: Line commutated thyristor converters are very often used in drive engineering. But, difficulties in modeling and analysis such systems, due to thyristor converter non-linearity, are also present. In most cases in practice the change of the firing angle between two consecutive thyristor pairs activation is small, we can assume that sampling instants are equidistantly spaced in time, and linearisation around working point can be done. That leads to the Z-transform method application in the analysis of automatic control systems containing thyristor converters. The thyristor converter transfer function is presented, and stability analysis in the Z-domain of realized high speed current mean value control system by line commutated thyristor converter is given. Experimental results, i.e. system response on sudden changes in reference and load are also presented.

	REPRESENTATION OF FAULTS IN MATHEMATICAL MODEL OF CONVERTOR SET By Ewa Napierulska-Juszczak	[View] [Download]
Abstract: Diode faults in network commutated convertors provide unidirectional currents strongly submagnetizing the convertor transformer. After a few periods very high saturation of the core appears. If the fuses are wrong the transformer windings undergo very peculiar dynamic strains, generally more dangereous than during usual S.C. To obtain proper wave shapes of all currents, voltages, main, leakage and so called yoke fluxes enabling the analysis of transient phenomena, the design of adequate equivalent circuit and formation of mathematical model are necessary. It has to consider the magnetic non-linearity and non-symmetry of the core, saturation of smoothing reactor, properties of diodes and SCR. This paper presents an equivalent circuit for three phase bridge with 20 nonlinear equations forming the mathematical model. It allowes the analysis of transients during all possible faults, changes of load, EMF, or impulsing angle, disconnections, blowing of fuses etc for rectifier and invertor operation. Following phenomena are analyzed as instances: a/ short circuit of one diode in a 6 D set; b/ short circuit on DC terminals in 6 T bridge with only a nonlinear smoothing reactor; stoping impulses when IDC > 5 In; c/ same as "a" but in 6T set. The results are computed and compared with experiments with good agreement.

	MODELLING AND SIMULATION OF CONVERTER SYSTEMS By R. Szczesny; P. Gruszczynski	[View] [Download]
Abstract: Three fundamental problems of converter modelling are discussed: valve model, calculation method with properly chosen numerical integration algorithm and fast determination of the steady state solution in time domain. The developed concept of models of different valves allows application models whose degree of complication depend on particular requirements and the object of simulation. Following a discussion of numerical stability of different numerical integration algorithms the application of absolutely stable methods is recommended. A special procedure is presented intended for fast computation of the steady state response. The simulation waveforms for an example converter system are given.

	REDUCED SCALE MAINS NETWORK EXPERIMENT CARRIED OUT BY INSA AND LAAS OF TOULOUSE By J. P. Berry; J. C. Joubert; A. Benhamou; X. Roboam; J. Fantin; G. Garcia	[View] [Download]
Abstract: Utilizing recent power electronics techniques, LAAS and INSA have set up jointly a mains supply experiment (20 KVA power) which is described in this paper. Research is applied to the dc - ac conversion in order to improve the power factor: - simulation and realization of an inverter with a dual structure to that of the regular controlled rectifiers (thyristors) - implementation of an artificial switch device the so-called dualistor. Such an experiment induces and / or allows us to review more fundamental research work in the field of automatics ,i.e. motor alternator group control strategy, hierarchy and / or auto-adaptive control, stability.