EPE Association: EPE 1993 - 38 - Dialogue Session DS2.3: SYSTEM ENGINEERING: CONVERTER MODELLING, DESIGN, RFI AND EDUCATION

EPE 1993 - 38 - Dialogue Session DS2.3: SYSTEM ENGINEERING: CONVERTER MODELLING, DESIGN, RFI AND EDUCATION
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 1993 - Conference > EPE 1993 - 38 - Dialogue Session DS2.3: SYSTEM ENGINEERING: CONVERTER MODELLING, DESIGN, RFI AND EDUCATION

   [return to parent folder]

   MODELLING AND SIMULATION OF SUPPLY CURRENT INTERFERENCE IN TRACTION SYSTEMS ARISING FROM MULTI-LEVEL CONVERTERS IN HlGH-POWER LOCOMOTIVE DRIVES
By P. C. Coles; M. Fracchia; R. J. Hill; P. Pozzobon; G. Sciutto [View]
[Download]

Abstract: A railway traction system simulator intended for the study of electrical interference produced by converter-fed traction drives is described. The simulation model comprises a neutral-pont-clamped inverter drive, a 3 kV DC 12-pulse rectifier substation and a section of traction line. Time and frequency domain simulation results demonstrate the influence of the system DC current and non linear traction line impedance on the production of higher frequency harmonics in the catenary power supply circuit.

   LOW COST PROGRAM FOR SIMULATION OF POWER ELECTRONIC CONVERTERS AND SYSTEMS
By O. Mo; R. Nilssen [View]
[Download]

Abstract: This paper states that the use of simulations tools is very important, especially in order to get an increased understanding of a converters or systems behaviour. The paper presents simulation examples (controlled thyristor DC-motor drive) which requires a powerful simulation tool. The paper shows that a low cost program sold on a non- commercial basis can be used for these simulations. This should be of interest both for university and industrial people. The basic requirement to be fulfilled by a time domain simulation program is that it offers simple, ideal models of the basic components used in power electronic systems and converters. This paper focuses on a program which offers ideal component models together with possibilities of inclusion of more advanced models. The program used is KREAN [1][2] which is a special purpose program for simulation of power electronic converters and systems. The program is shown to work very wel! on the selected example. The presented results corresponds to what should be expected from an idealized circuit. The aim of this paper is not to present the simulation results themselves. The results are presented in order to illustrate the capabilities of the program and the power of simulations for illustration of circuit behaviour. Thus details such as component values, controller parameters etc. is omitted.

   DC MACHINE TEACHING EXPERIMENTS
By D. A. Staton; M. I. McGilp; T. J. E. Miller [View]
[Download]

Abstract: This paper describes a series of three undergraduate laboratory experiments developed at the University of Glasgow. The objectives are: 1. - to understand the effect that the drive has on the motor performance; 2. - to demonstrate that electric motor design encompasses the fields of electrical, magnetic, thermal and mechanical analysis; 3. - to appreciate open and closed-loop control techniques. A PC based simulation package, PC-DCM, developed for the design of DC commutator motors, is used in the first two experiments. This package is used extensively by members of the SPEED Consortium (Scottish Power Electronics and Electric Drives) in industry, but it is envisaged that it will become increasingly important as learning aid in education. In the first experiment, the student examines the effect that the drive (DC, chopper and phase control) has on the motor performance. In the second experiment, the student calculates the performance of an existing ferrite motor. He is then given the task of developing improved ferrite and rare-earth designs, in both cases maximising the torque per unit volume. In the final experiment, a dynamometer is used to study the performance of a DC commutator motor under open- and closed-loop speed control.

   SWITCHING DC / DC CONVERTERS EDUCATIONAL WORKBENCH
By F. Nuño; J. M. Alonso; J. L. González; M. Rico [View]
[Download]

Abstract: In this paper a system for the development of switching DC/DC converters tests is described. This workbench lets the analysis of converters usually called PWM, which show trapezoidal waveforms, and quasi-resonant. converters (zero voltage switched or ZVS and zero current switched or ZCS) which exhibit quasi-sinusoidal evolutions. The equipment is made in a modular way, different basic blocks can be distinguished; power stages, control circuits, drivers and closed-loop regulators. The chosen power topologies are the simplest ones: buck, boost and flyback. In the last one, the isolation transformer option is included. Another power stage topologies could be easily added to the system. Specially for the quasi-resonant converters, certain proper static points are established. Around these points, the transition between ZVS and ZCS operation modes is very simple by means of the modification and the connection of several resonant elements. Finally, some experimental practices to carry out with the system are proposed. They will be the best complement for a DC/DC converters theoretical course.

   DESIGN OF STATIC CONVERTERS: AN EXPERT SYSTEM APPROACH
By D. Fezzani; H. Piquet; Y. Chéron; M. Metz [View]
[Download]

Abstract: In order to design the structure of static converters a new approach is presented. Required specifications are described by the waveforms of input and output voltages and currents, which are expected to be generated by the converter. These data are analysed by use of design rules and methods; it permits to identify the stresses on the commutation cells, which themselves lead to the synthesis of the switches: identification of the type (diode, thyristor, transistor or dual thyristor), description of electrical constraints and firing orders. Rules and methods are implemented on a micro computer by use of an 'expert system generator'; the actual system establishes the feasibility in the domain of the direct converters and enables the use of these tools in the education domain: deductions and used rules can be exhibited, making this software a powerful tool to help students understanding the design methods.

   MULTIMEDIA, AN APPLICATION FOR EDUCATION IN POWER ELECTRONICS
By A. Jaafari; J. P. Picard; R. Bessège [View]
[Download]

Abstract: In this paper, we present an application using the Multimedia for the teaching of power electronics. The program proposed has for object, in a first step, a recalling of basis principles. Then an inventory of essential tools for the operation of converters is drawn up. The application ends with a concrete study: the fly back converter. All the necessary elements for the elaboration of an experimental device are given. The interest of our application is that during all the development of the program the user can make an updating and check bis knowledges.

   THE USE OF A KNOWLEDGE-BASED SYSTEM IN POWER ELECTRONIC CIRCUIT FAULT DIAGNOSIS
By A. C. Renfrew; J. X. Tian [View]
[Download]

Abstract: The diagnosis of faults on electronic equipment requires the provision of monitoring outlets. To avoid expensive additions to existing circuits or to well integrated designs, monitoring of only input and output quantities is preferable. To determine the location of an internal fault, a reasoned diagnosis is required and a knowledge-based system provides an automatic method of carrying out the reasoning process. Three-phase power electronic inverters have similar configurations of switches and thus can be treated in a more standard form than can other electronic circuits. A commercial inverter has been tested under normal conditions and with specific faults created. The results have been compared with these obtained from two alternative simulation methods. From the slightly differing results, ranges of uncertainty of parameter values have been obtained and the results have been used to create a rule base for a proprietary expert system environment. The work is described at an intermediate stage in an ongoing programme.

   FREQUENCY DOMAIN MODELLING OF TRACTION PWM CONVERTERS
By J. A. Taufiq; J. Shen [View]
[Download]

Abstract: In a previous paper by one of the authors (1), a frequency domain model (FDM) was described for calculating the DC side harmonics in a traction VSI drive. In this paper, this principle has been extended to describe a FDM for an interlaced PWM converter drive system. Such a model, which can be 20-30 times faster than the corresponding time domain model, is useful for obtaining steady-state results of these drives for systems engineering. Typical results which can be produced are circuit and device waveforms, harmonic spectra and psophometric current. Such a fast simulation tool is particularly invaluable when a series of calculations are required over the entire speed range of the designed drive system. Results from an interlaced PWM converter fed inverter drive simulation are presented, including the effects of parameter asymmetry and load unbalance. A comparison is also made of the computed converter input current waveforms and those measured from a 1.5MVA test rig. Computed and measured converter input current harmonic spectra are also compared to confirm the accuracy of the FDM.

   DEVELOPMENT OF A MODULAR SIMULATION SYSTEM FOR POWER ELECTRONICS AND CONTROL APPLICATIONS
By A. Kern; U. Kunz [View]
[Download]

Abstract: Simulating complex drive systems requires software packages covering the fields of power electronics and control engineering. Our institute has developed a software package for the simulation and design of drive systems. The simulation system is easy to use and enables the engineer to transfer often used and well established methods of the fields stated above to the work on screen. The system is helpful in assessing the feasibility of a drive system at an early stage of development. Standard circuits can be defined as building blocks. It is possible to simulate and analyse fairly complex systems. The software package is equipped with a graphical user-interface.

   DEVELOPMENT OF A KNOWLEDGE-BASED (EXPERT) SYSTEM (PECT) FOR POWER ELECTRONIC CIRCUIT DESIGN
By M. J. N. Cumbi; D. W. Shepherd; L. N. Hulley [View]
[Download]

Abstract: A knowledge-based (expert) system approach to power electronic circuit design is presented. The resulting system is designated PECT. It is written using Smalltalk-80 and integrates Al techniques of production rules for 'high-level' knowledge representation. PECT embraces elements of power circuitry design and contains such features as selection of circuit configuration, control facility and the best choice of power device for a given application.It is interfaced with HSPICE and a semiconductor power device library. System architecture as well as the target design realisation process are described. The criteria of development and the factors and requirements in building the PECT are also outlined.

   A MULTIMEDIA BASED TEACHING LABORATORY ON ELECTRIC DRIVES
By V. Cecconi; R. Miceli; S. Millemaci; M. Mori; C. Serporta; M. Trapanese; G. Vitale [View]
[Download]

Abstract: The course of diagnostic of electric machines, which is held at the electrical department of Palermo University by one of the authors, has been provided with a multimedia teaching laboratory on electric drives. In this work the multimedia architecture of this laboratory is described. This multimedia architecture allows to present and to use through one apparatus a theoretic section, a simulation section and the experimental section. In this work the instrumentation, the software, the hardware, which has been used, and several tests, which have been prepared, are presented. All tests describe the standard experimental investigation on the electric drive focusing the investigation on the important parts of a drive (electronic stage, power stage, etc.).

   MODELLING AND CONTROL OF AN AC/AC BOOST-BUCK CONVERTER
By N. H. M. Hofmeester; P. P. J. van den Bosch; J. B. Klaassens [View]
[Download]

Abstract: A single-phase, four-switch AC/AC power conditioner with active filtering is proposed, based on the DC/DC Boost-Buck topology. The circuit is designed as a link between a single-phase utility grid and a single-phase consumer (up to +/- 10 kVA). This converter is used in a feasibility study for a power utility company to enable peak shaving by means of grid voltage reduction, while satisfying supply conditions. This requires a simple AC / AC converter with both step-up and step-down capabilities. The proposed converter has two control inputs to control independently both the input power factor and the output voltage. This paper presents a feedback control algorithm needed for converter operation under dynamical grid disturbances and load variations. The controller uses a vector-control like approach with a discrete Fourier transformation in the control loop. The resulting digital controller can easily be integrated for mass production.

   AN OBJECTIVE FOR POWER ELECTRONICS ENGINEERS: OPTIMIZE THE LIFETIME COST
By Berthold Fuld [View]
[Download]

Abstract: In the past power electronic engineers normally tried to optimize the manufacturing costs of a product. In this paper it is demonstrated, that it is more important to optimize lifetime cost than manufacturing cost. For power electronic systems the most important after sales costs are the costs for loss energy. An estimation of the cost of loss energy is done. For the examples of a switch mode power supply and an electric locomotive it is shown, that this costs are significant high compared to the price of the product itself. Some approaches to increase efficiency are presented. An important issue is the selection of an effective system structure. Other possibilities to reduce losses are "oversizing", optimized switching frequency, optimized snubbers, intelligent modulation techniques, multi-level-inverters, low-slip-machines, conductors with reduced skin-effect related losses or avoiding noload.

   TECHNIQUES BASED ON BIPOLAR POWER TRANSISTOR ARRAYS FOR REGULATION OF AC LINE VOLTAGE
By A.D.V.N. Kularatna [View]
[Download]

Abstract: Use of a series transistor array in an AC voltage regulator could substantially reduce the weight and volume and also lower the manufacturing costs by eliminating special transformers (in ferro-resonant systems) and servo mechanisms (in servo driven auto transformers). This non-switching analogue technique has advantages over thyristor driven tap change systems too. This basic technique could be further improved to achieve higher overall efficiency, higher power ratings and to achieve a harmonic and spike free sinusoidal output. The article outlines the proposed circuit enhancements for a bipolar power transistor array technique for achieving a clean sinusoidal output with high overall efficiency.

   AC REGULATOR CONTROLLED BY L.V.I.
By I. Bonanni [View]
[Download]

Abstract: The paper describes a recently developed family of AC regulators using the LVI (Linear Variable Inductor) to control the input current. The LVI limits the input current at the minimum value requested to sustain the output voltage for any line and load condition. In such a way a good efficiency has been obtained still maintaining many advantages typical of ferroresonant regulators, like continous regulation and intrinsic short-citcuit protection. The power ranges between 2 and 5 kVA. The paper describes the operation of the regulators and reports the most important experimental results gained out from the 5 kVA prototype. The experimental results show the ability of the new regulators to supply non-linear loads, like PC and their accessories.

EPE 1993 - 38 - Dialogue Session DS2.3: SYSTEM ENGINEERING: CONVERTER MODELLING, DESIGN, RFI AND EDUCATION
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 1993 - Conference > EPE 1993 - 38 - Dialogue Session DS2.3: SYSTEM ENGINEERING: CONVERTER MODELLING, DESIGN, RFI AND EDUCATION
	[return to parent folder]

	MODELLING AND SIMULATION OF SUPPLY CURRENT INTERFERENCE IN TRACTION SYSTEMS ARISING FROM MULTI-LEVEL CONVERTERS IN HlGH-POWER LOCOMOTIVE DRIVES By P. C. Coles; M. Fracchia; R. J. Hill; P. Pozzobon; G. Sciutto	[View] [Download]
Abstract: A railway traction system simulator intended for the study of electrical interference produced by converter-fed traction drives is described. The simulation model comprises a neutral-pont-clamped inverter drive, a 3 kV DC 12-pulse rectifier substation and a section of traction line. Time and frequency domain simulation results demonstrate the influence of the system DC current and non linear traction line impedance on the production of higher frequency harmonics in the catenary power supply circuit.

	LOW COST PROGRAM FOR SIMULATION OF POWER ELECTRONIC CONVERTERS AND SYSTEMS By O. Mo; R. Nilssen	[View] [Download]
Abstract: This paper states that the use of simulations tools is very important, especially in order to get an increased understanding of a converters or systems behaviour. The paper presents simulation examples (controlled thyristor DC-motor drive) which requires a powerful simulation tool. The paper shows that a low cost program sold on a non- commercial basis can be used for these simulations. This should be of interest both for university and industrial people. The basic requirement to be fulfilled by a time domain simulation program is that it offers simple, ideal models of the basic components used in power electronic systems and converters. This paper focuses on a program which offers ideal component models together with possibilities of inclusion of more advanced models. The program used is KREAN [1][2] which is a special purpose program for simulation of power electronic converters and systems. The program is shown to work very wel! on the selected example. The presented results corresponds to what should be expected from an idealized circuit. The aim of this paper is not to present the simulation results themselves. The results are presented in order to illustrate the capabilities of the program and the power of simulations for illustration of circuit behaviour. Thus details such as component values, controller parameters etc. is omitted.

	DC MACHINE TEACHING EXPERIMENTS By D. A. Staton; M. I. McGilp; T. J. E. Miller	[View] [Download]
Abstract: This paper describes a series of three undergraduate laboratory experiments developed at the University of Glasgow. The objectives are: 1. - to understand the effect that the drive has on the motor performance; 2. - to demonstrate that electric motor design encompasses the fields of electrical, magnetic, thermal and mechanical analysis; 3. - to appreciate open and closed-loop control techniques. A PC based simulation package, PC-DCM, developed for the design of DC commutator motors, is used in the first two experiments. This package is used extensively by members of the SPEED Consortium (Scottish Power Electronics and Electric Drives) in industry, but it is envisaged that it will become increasingly important as learning aid in education. In the first experiment, the student examines the effect that the drive (DC, chopper and phase control) has on the motor performance. In the second experiment, the student calculates the performance of an existing ferrite motor. He is then given the task of developing improved ferrite and rare-earth designs, in both cases maximising the torque per unit volume. In the final experiment, a dynamometer is used to study the performance of a DC commutator motor under open- and closed-loop speed control.

	SWITCHING DC / DC CONVERTERS EDUCATIONAL WORKBENCH By F. Nuño; J. M. Alonso; J. L. González; M. Rico	[View] [Download]
Abstract: In this paper a system for the development of switching DC/DC converters tests is described. This workbench lets the analysis of converters usually called PWM, which show trapezoidal waveforms, and quasi-resonant. converters (zero voltage switched or ZVS and zero current switched or ZCS) which exhibit quasi-sinusoidal evolutions. The equipment is made in a modular way, different basic blocks can be distinguished; power stages, control circuits, drivers and closed-loop regulators. The chosen power topologies are the simplest ones: buck, boost and flyback. In the last one, the isolation transformer option is included. Another power stage topologies could be easily added to the system. Specially for the quasi-resonant converters, certain proper static points are established. Around these points, the transition between ZVS and ZCS operation modes is very simple by means of the modification and the connection of several resonant elements. Finally, some experimental practices to carry out with the system are proposed. They will be the best complement for a DC/DC converters theoretical course.

	DESIGN OF STATIC CONVERTERS: AN EXPERT SYSTEM APPROACH By D. Fezzani; H. Piquet; Y. Chéron; M. Metz	[View] [Download]
Abstract: In order to design the structure of static converters a new approach is presented. Required specifications are described by the waveforms of input and output voltages and currents, which are expected to be generated by the converter. These data are analysed by use of design rules and methods; it permits to identify the stresses on the commutation cells, which themselves lead to the synthesis of the switches: identification of the type (diode, thyristor, transistor or dual thyristor), description of electrical constraints and firing orders. Rules and methods are implemented on a micro computer by use of an 'expert system generator'; the actual system establishes the feasibility in the domain of the direct converters and enables the use of these tools in the education domain: deductions and used rules can be exhibited, making this software a powerful tool to help students understanding the design methods.

	MULTIMEDIA, AN APPLICATION FOR EDUCATION IN POWER ELECTRONICS By A. Jaafari; J. P. Picard; R. Bessège	[View] [Download]
Abstract: In this paper, we present an application using the Multimedia for the teaching of power electronics. The program proposed has for object, in a first step, a recalling of basis principles. Then an inventory of essential tools for the operation of converters is drawn up. The application ends with a concrete study: the fly back converter. All the necessary elements for the elaboration of an experimental device are given. The interest of our application is that during all the development of the program the user can make an updating and check bis knowledges.

	THE USE OF A KNOWLEDGE-BASED SYSTEM IN POWER ELECTRONIC CIRCUIT FAULT DIAGNOSIS By A. C. Renfrew; J. X. Tian	[View] [Download]
Abstract: The diagnosis of faults on electronic equipment requires the provision of monitoring outlets. To avoid expensive additions to existing circuits or to well integrated designs, monitoring of only input and output quantities is preferable. To determine the location of an internal fault, a reasoned diagnosis is required and a knowledge-based system provides an automatic method of carrying out the reasoning process. Three-phase power electronic inverters have similar configurations of switches and thus can be treated in a more standard form than can other electronic circuits. A commercial inverter has been tested under normal conditions and with specific faults created. The results have been compared with these obtained from two alternative simulation methods. From the slightly differing results, ranges of uncertainty of parameter values have been obtained and the results have been used to create a rule base for a proprietary expert system environment. The work is described at an intermediate stage in an ongoing programme.

	FREQUENCY DOMAIN MODELLING OF TRACTION PWM CONVERTERS By J. A. Taufiq; J. Shen	[View] [Download]
Abstract: In a previous paper by one of the authors (1), a frequency domain model (FDM) was described for calculating the DC side harmonics in a traction VSI drive. In this paper, this principle has been extended to describe a FDM for an interlaced PWM converter drive system. Such a model, which can be 20-30 times faster than the corresponding time domain model, is useful for obtaining steady-state results of these drives for systems engineering. Typical results which can be produced are circuit and device waveforms, harmonic spectra and psophometric current. Such a fast simulation tool is particularly invaluable when a series of calculations are required over the entire speed range of the designed drive system. Results from an interlaced PWM converter fed inverter drive simulation are presented, including the effects of parameter asymmetry and load unbalance. A comparison is also made of the computed converter input current waveforms and those measured from a 1.5MVA test rig. Computed and measured converter input current harmonic spectra are also compared to confirm the accuracy of the FDM.

	DEVELOPMENT OF A MODULAR SIMULATION SYSTEM FOR POWER ELECTRONICS AND CONTROL APPLICATIONS By A. Kern; U. Kunz	[View] [Download]
Abstract: Simulating complex drive systems requires software packages covering the fields of power electronics and control engineering. Our institute has developed a software package for the simulation and design of drive systems. The simulation system is easy to use and enables the engineer to transfer often used and well established methods of the fields stated above to the work on screen. The system is helpful in assessing the feasibility of a drive system at an early stage of development. Standard circuits can be defined as building blocks. It is possible to simulate and analyse fairly complex systems. The software package is equipped with a graphical user-interface.

	DEVELOPMENT OF A KNOWLEDGE-BASED (EXPERT) SYSTEM (PECT) FOR POWER ELECTRONIC CIRCUIT DESIGN By M. J. N. Cumbi; D. W. Shepherd; L. N. Hulley	[View] [Download]
Abstract: A knowledge-based (expert) system approach to power electronic circuit design is presented. The resulting system is designated PECT. It is written using Smalltalk-80 and integrates Al techniques of production rules for 'high-level' knowledge representation. PECT embraces elements of power circuitry design and contains such features as selection of circuit configuration, control facility and the best choice of power device for a given application.It is interfaced with HSPICE and a semiconductor power device library. System architecture as well as the target design realisation process are described. The criteria of development and the factors and requirements in building the PECT are also outlined.

	A MULTIMEDIA BASED TEACHING LABORATORY ON ELECTRIC DRIVES By V. Cecconi; R. Miceli; S. Millemaci; M. Mori; C. Serporta; M. Trapanese; G. Vitale	[View] [Download]
Abstract: The course of diagnostic of electric machines, which is held at the electrical department of Palermo University by one of the authors, has been provided with a multimedia teaching laboratory on electric drives. In this work the multimedia architecture of this laboratory is described. This multimedia architecture allows to present and to use through one apparatus a theoretic section, a simulation section and the experimental section. In this work the instrumentation, the software, the hardware, which has been used, and several tests, which have been prepared, are presented. All tests describe the standard experimental investigation on the electric drive focusing the investigation on the important parts of a drive (electronic stage, power stage, etc.).

	MODELLING AND CONTROL OF AN AC/AC BOOST-BUCK CONVERTER By N. H. M. Hofmeester; P. P. J. van den Bosch; J. B. Klaassens	[View] [Download]
Abstract: A single-phase, four-switch AC/AC power conditioner with active filtering is proposed, based on the DC/DC Boost-Buck topology. The circuit is designed as a link between a single-phase utility grid and a single-phase consumer (up to +/- 10 kVA). This converter is used in a feasibility study for a power utility company to enable peak shaving by means of grid voltage reduction, while satisfying supply conditions. This requires a simple AC / AC converter with both step-up and step-down capabilities. The proposed converter has two control inputs to control independently both the input power factor and the output voltage. This paper presents a feedback control algorithm needed for converter operation under dynamical grid disturbances and load variations. The controller uses a vector-control like approach with a discrete Fourier transformation in the control loop. The resulting digital controller can easily be integrated for mass production.

	AN OBJECTIVE FOR POWER ELECTRONICS ENGINEERS: OPTIMIZE THE LIFETIME COST By Berthold Fuld	[View] [Download]
Abstract: In the past power electronic engineers normally tried to optimize the manufacturing costs of a product. In this paper it is demonstrated, that it is more important to optimize lifetime cost than manufacturing cost. For power electronic systems the most important after sales costs are the costs for loss energy. An estimation of the cost of loss energy is done. For the examples of a switch mode power supply and an electric locomotive it is shown, that this costs are significant high compared to the price of the product itself. Some approaches to increase efficiency are presented. An important issue is the selection of an effective system structure. Other possibilities to reduce losses are "oversizing", optimized switching frequency, optimized snubbers, intelligent modulation techniques, multi-level-inverters, low-slip-machines, conductors with reduced skin-effect related losses or avoiding noload.

	TECHNIQUES BASED ON BIPOLAR POWER TRANSISTOR ARRAYS FOR REGULATION OF AC LINE VOLTAGE By A.D.V.N. Kularatna	[View] [Download]
Abstract: Use of a series transistor array in an AC voltage regulator could substantially reduce the weight and volume and also lower the manufacturing costs by eliminating special transformers (in ferro-resonant systems) and servo mechanisms (in servo driven auto transformers). This non-switching analogue technique has advantages over thyristor driven tap change systems too. This basic technique could be further improved to achieve higher overall efficiency, higher power ratings and to achieve a harmonic and spike free sinusoidal output. The article outlines the proposed circuit enhancements for a bipolar power transistor array technique for achieving a clean sinusoidal output with high overall efficiency.

	AC REGULATOR CONTROLLED BY L.V.I. By I. Bonanni	[View] [Download]
Abstract: The paper describes a recently developed family of AC regulators using the LVI (Linear Variable Inductor) to control the input current. The LVI limits the input current at the minimum value requested to sustain the output voltage for any line and load condition. In such a way a good efficiency has been obtained still maintaining many advantages typical of ferroresonant regulators, like continous regulation and intrinsic short-citcuit protection. The power ranges between 2 and 5 kVA. The paper describes the operation of the regulators and reports the most important experimental results gained out from the 5 kVA prototype. The experimental results show the ability of the new regulators to supply non-linear loads, like PC and their accessories.