EP0159334A1 - Pulse width modulated inverter - Google Patents

Pulse width modulated inverter

Info

Publication number
EP0159334A1
EP0159334A1 EP84903585A EP84903585A EP0159334A1 EP 0159334 A1 EP0159334 A1 EP 0159334A1 EP 84903585 A EP84903585 A EP 84903585A EP 84903585 A EP84903585 A EP 84903585A EP 0159334 A1 EP0159334 A1 EP 0159334A1
Authority
EP
European Patent Office
Prior art keywords
inverter
power supply
frequency
filter
sine wave
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP84903585A
Other languages
German (de)
French (fr)
Other versions
EP0159334A4 (en
Inventor
David J. Hucker
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Sundstrand Corp
Original Assignee
Sundstrand Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sundstrand Corp filed Critical Sundstrand Corp
Publication of EP0159334A1 publication Critical patent/EP0159334A1/en
Publication of EP0159334A4 publication Critical patent/EP0159334A4/en
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/538—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a push-pull configuration
    • H02M7/53803—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a push-pull configuration with automatic control of output voltage or current
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/4815—Resonant converters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Definitions

  • the present invention relates to a pulse v/idth modulated inverter and more particularly to a pulse width modulated inverter having an improved output filter and a circuit for providing a low impedance path for AC ripple current or regenerative current flowing to the DC power supply of the inverter.
  • a known pulse width modulated (PWM) inverter includes a center tapped power supply with positive and negative terminals, the center tap being connected to neutral or ground.
  • the positive and negative terminals are connected to a low pass output filter through res- pective switches which may be transistors or the like.
  • the inverter switches are controlled to alternately conduct current to the output filter, the switches providing a pulse width modulated waveform to the filter, which in response thereto, provides an AC output which is applied to a load.
  • a very large output filter is typically required. Where the inverter is to be used in applications where weight is critical, such as on an aircraft, the use of such large filters is extremely undesirable.
  • PWM inverters Another problem with known PWM inverters is their capacity to accept regenerative or ripple currents.
  • Single phase inverter circuits or multiphase inverter circuits with unbalanced reactive loads circulate high levels of energy into and out of the DC power supply of the inverter.
  • the DC power supply of the inverter typically includes capacitors for accepting all regenerative currents. Such capacitors, however, are typically large and bulky, increasing the weight of the inverter which is undesirable for many applications.
  • the pulse width modulated inverter of the present invention includes a low pass output filter for providing a sine wave output in response to the pulse width modulated waveform and a notch filter which is coupled to the low pass filter and tuned to the frequency of the pulse width modulated waveform to eliminate that frequency from the sine wave output.
  • the notch filter allows the size of the low pass output filter to be reduced.
  • the pulse width modulated inverter also in ⁇ cludes a series resonant circuit connected in parallel with the DC power supply of the inverter, the circuit being tuned to two times the frequency of the sine wave output of the inverter for providing a low impedance path for AC ripple current flowing to the power supply from the load when the load is reactive. Because the power supply capacitors need only support the remaining com- ponents of the current flowing to the power supply, the capacitors may be reduced in size.
  • Fig.l is a schematic diagram of one phase of the neutrally clamped PWM inverter of the present in- vention
  • I AJ.. ⁇ P ⁇ I Fig. 2 is a graph illustrating the pulse width modulated waveform output from the inverter of Fig. 1 and the output voltage and current waveforms from the in ⁇ verter output filter.
  • the inverter provides a pulse width modulated waveform at a junction 10 to an output filter generally designated 12, the filter having an AC output at a junction 16 which is applied to a load 18.
  • the inverter includes a center tapped power supply generally designated 20 having a DC source 22 connected to a terminal 24 for providing a positive DC voltage and having a DC source 26 connected to a terminal 28 to provide a negative DC voltage, the center tap 30 being connected to neutral or ground.
  • the inverter output filter and load 18 are coupled between the grounded center tap 30 and the positive and negative power supply terminals 24 and 28 through a pair of series connected transistors 32 and 34.
  • the transistors 32 and 34 are controlled by a controller 36 to provide at the junction 10 a pulse width modulated waveform 37 as illustrated in Fig. 2.
  • the pulse width modulated waveform output from the inverter at the junction 10 may, for example, have a frequency of 10 KHz, the pulse width modulated waveform being applied to the output filter 12 to provide a sine wave output at the junction 16 having a frequency of 400 Hz.
  • the output filter 12 includes a low pass filter comprised of an inductor 38 and a capacitor 39 to provide a sine wave output at the junction 16 in response to the pulse width modulated waveform applied thereto.
  • the filter 12 also includes a notch filter 40 in shunt with the load 18, the notch filter being comprised of an inductor 42 and a series connected capacitor 44.
  • the notch filter 40 is tuned to the frequency of the pulse width modulated -waveform at the junction 10, i.e., 10 KHz to eliminate that frequency from the waveform output at the junction 16.
  • the notch filter 40 reduces the atten ⁇ uation requirement of the low pass filter so that the size of the low pass filter may be reduced.
  • the values of the inductor 42 and capacitor 44 of the notch filter may be selected to provide a product of 2.53 x 10 " so as to tune the notch filter to the pulse frequency of 10 KHz.
  • the inductor 38 and capacitor 39 of the low pass filter are tuned to attenuate noise typically .on the order of 100 KHz, the inductor 38 having a value of 52.5 microhenries and the capacitor 39 having a value of .00048 microfarads.
  • regenerative current flows from the load 18 to the DC power supply 20 during the 0°-60° and 180°-240° portions of the output waveform.
  • the regenerative current flows to the power supply 20 through a. diode 50 connected in parallel with the transistor 32.
  • the inverter transistor switch 34 is on, the regenerative current flows to the power supply from the load 18 through a diode 52.
  • a series resonant circuit generally designated 54 is connected in parallel with the power supply 20 to provide a low impedance path for the AC component of current, a pair of capacitors 54 and 56 being connected in parallel with each of the DC sources 22 and 26 to accept the remaining components of current flowing to the power supply.
  • the series resonant circuit 54 includes a first series resonant circuit 60 comprised of a capacitor 62 and an inductor 64 connected between the positive power supply terminal 24 and the center tap 30.
  • the series resonant circuit 54 also includes a second series resonant circuit 66 comprised of a capacitor 68 and an inductor 70 connected between the negative power supply terminal 28 and the center tap 30.
  • Each of the first and second series resonant circuits 60 and 66 is tuned to two times the frequency of the inverter output at the junction 16 to provide the. low impedance path for the AC component of current flowing to the power supply from the load.
  • the frequency of the inverter output at the junc ⁇ tion 16 is 400 Hz
  • —6 resonant circuit should be equal to .04 x 10 so that each of the circuits is tuned to 800 Hz or two times 400 Hz, the frequency of the sine wave output at the junction 16.
  • the values of the capacitors 56 and 58 may be 720 microfar ds.
  • the first series resonant circuit 60 provides a low impedance path for the AC component of current flowing to the power supply from the load while the transistor 32 is on.
  • the second series resonant circuit provides a low impedance path for the AC component of
  • OMPI WIPO current flowing to the power supply from the load when the transistor 34 is on because the power supply capacitors 56 and 58 need only support the remaining components of current flowing to the power supply, the size of the capacitors may be minimized.

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)
  • Dc-Dc Converters (AREA)

Abstract

L'inverseur présente un filtre de sortie amélioré (12) comprenant un filtre passe-bas (38, 39) produisant un signal sinusoïdal de sortie en réponse à une onde modulée par largeur d'impulsions, et un filtre de réjection à flancs raides (40) couplé au filtre passe-bas et accordé sur la fréquence de l'onde modulée par largeur d'impulsions afin d'éliminer cette fréquence du signal sinusoïdal de sortie. L'inverseur comprend également un circuit résonant (54) monté en série et couplé aux bornes de l'alimentation en courant continu (20) de l'inverseur et accordé sur une fréquence égale à deux fois la fréquence du signal sinusoïdal de sortie, de manière à former un chemin à basse impédance pour le courant alternatif s'écoulant vers l'alimentation.The inverter has an improved output filter (12) comprising a low-pass filter (38, 39) producing a sinusoidal output signal in response to a pulse width modulated wave, and a steep flank rejection filter ( 40) coupled to the low-pass filter and tuned to the frequency of the pulse-width modulated wave in order to eliminate this frequency from the sinusoidal output signal. The inverter also comprises a resonant circuit (54) connected in series and coupled to the terminals of the direct current supply (20) of the inverter and tuned to a frequency equal to twice the frequency of the sinusoidal output signal, of so as to form a low impedance path for the alternating current flowing to the power supply.

Description

it 11
Pulse Width Modulated Inverter
Technical Field
The present invention relates to a pulse v/idth modulated inverter and more particularly to a pulse width modulated inverter having an improved output filter and a circuit for providing a low impedance path for AC ripple current or regenerative current flowing to the DC power supply of the inverter.
Background of the Art A known pulse width modulated (PWM) inverter includes a center tapped power supply with positive and negative terminals, the center tap being connected to neutral or ground. The positive and negative terminals are connected to a low pass output filter through res- pective switches which may be transistors or the like. The inverter switches are controlled to alternately conduct current to the output filter, the switches providing a pulse width modulated waveform to the filter, which in response thereto, provides an AC output which is applied to a load. In order to provide the desired AC output, a very large output filter is typically required. Where the inverter is to be used in applications where weight is critical, such as on an aircraft, the use of such large filters is extremely undesirable. Another problem with known PWM inverters is their capacity to accept regenerative or ripple currents. Single phase inverter circuits or multiphase inverter circuits with unbalanced reactive loads circulate high levels of energy into and out of the DC power supply of the inverter. The DC power supply of the inverter typically includes capacitors for accepting all regenerative currents. Such capacitors, however, are typically large and bulky, increasing the weight of the inverter which is undesirable for many applications.
Disclosure of the Invention in accordance with the present invention, the disadvantages of prior PWM inverters as discussed above have been overcome.
The pulse width modulated inverter of the present invention includes a low pass output filter for providing a sine wave output in response to the pulse width modulated waveform and a notch filter which is coupled to the low pass filter and tuned to the frequency of the pulse width modulated waveform to eliminate that frequency from the sine wave output. The notch filter allows the size of the low pass output filter to be reduced.
The pulse width modulated inverter also in¬ cludes a series resonant circuit connected in parallel with the DC power supply of the inverter, the circuit being tuned to two times the frequency of the sine wave output of the inverter for providing a low impedance path for AC ripple current flowing to the power supply from the load when the load is reactive. Because the power supply capacitors need only support the remaining com- ponents of the current flowing to the power supply, the capacitors may be reduced in size.
Brief Description of the Drawings
Fig.l is a schematic diagram of one phase of the neutrally clamped PWM inverter of the present in- vention;
OMPI
I AJ.. ΓPΓI Fig. 2 is a graph illustrating the pulse width modulated waveform output from the inverter of Fig. 1 and the output voltage and current waveforms from the in¬ verter output filter.
Best Mode for Carrying Out the Invention
The inverter, as shown in Fig. 1, provides a pulse width modulated waveform at a junction 10 to an output filter generally designated 12, the filter having an AC output at a junction 16 which is applied to a load 18. The inverter includes a center tapped power supply generally designated 20 having a DC source 22 connected to a terminal 24 for providing a positive DC voltage and having a DC source 26 connected to a terminal 28 to provide a negative DC voltage, the center tap 30 being connected to neutral or ground. The inverter output filter and load 18 are coupled between the grounded center tap 30 and the positive and negative power supply terminals 24 and 28 through a pair of series connected transistors 32 and 34. The transistors 32 and 34 are controlled by a controller 36 to provide at the junction 10 a pulse width modulated waveform 37 as illustrated in Fig. 2.
The pulse width modulated waveform output from the inverter at the junction 10 may, for example, have a frequency of 10 KHz, the pulse width modulated waveform being applied to the output filter 12 to provide a sine wave output at the junction 16 having a frequency of 400 Hz. The output filter 12 includes a low pass filter comprised of an inductor 38 and a capacitor 39 to provide a sine wave output at the junction 16 in response to the pulse width modulated waveform applied thereto. The filter 12 also includes a notch filter 40 in shunt with the load 18, the notch filter being comprised of an inductor 42 and a series connected capacitor 44. The notch filter 40 is tuned to the frequency of the pulse width modulated -waveform at the junction 10, i.e., 10 KHz to eliminate that frequency from the waveform output at the junction 16. The notch filter 40 reduces the atten¬ uation requirement of the low pass filter so that the size of the low pass filter may be reduced. For an inverter having an effective power rating of 30 KVA with a rated output at the junction 16 of 115 volts and a frequency of 400 Hz, the values of the inductor 42 and capacitor 44 of the notch filter may be selected to provide a product of 2.53 x 10" so as to tune the notch filter to the pulse frequency of 10 KHz. The inductor 38 and capacitor 39 of the low pass filter are tuned to attenuate noise typically .on the order of 100 KHz, the inductor 38 having a value of 52.5 microhenries and the capacitor 39 having a value of .00048 microfarads.
If the load 18 is reactive and the waveforms output from the inverter at the junction 16 are as illustrated in Fig. 2 wherein the output current 46 lags the output voltage 48 by 60°, regenerative current flows from the load 18 to the DC power supply 20 during the 0°-60° and 180°-240° portions of the output waveform. During the 0°-60° or 180°-240° periods, when the inverter switch 32 is on, providing a positive pulse at the junction 10, the regenerative current flows to the power supply 20 through a. diode 50 connected in parallel with the transistor 32. During the 0°-60° or 180°-240° period, when the inverter transistor switch 34 is on, the regenerative current flows to the power supply from the load 18 through a diode 52.
OMPt In order to accept regenerative current flowing to the power supply from the load, a series resonant circuit generally designated 54 is connected in parallel with the power supply 20 to provide a low impedance path for the AC component of current, a pair of capacitors 54 and 56 being connected in parallel with each of the DC sources 22 and 26 to accept the remaining components of current flowing to the power supply. The series resonant circuit 54 includes a first series resonant circuit 60 comprised of a capacitor 62 and an inductor 64 connected between the positive power supply terminal 24 and the center tap 30. The series resonant circuit 54 also includes a second series resonant circuit 66 comprised of a capacitor 68 and an inductor 70 connected between the negative power supply terminal 28 and the center tap 30. Each of the first and second series resonant circuits 60 and 66 is tuned to two times the frequency of the inverter output at the junction 16 to provide the. low impedance path for the AC component of current flowing to the power supply from the load. In the above example where the frequency of the inverter output at the junc¬ tion 16 is 400 Hz, the product of the inductor and capacitor values of each of the first and second series
—6 resonant circuit should be equal to .04 x 10 so that each of the circuits is tuned to 800 Hz or two times 400 Hz, the frequency of the sine wave output at the junction 16. The values of the capacitors 56 and 58 may be 720 microfar ds.
The first series resonant circuit 60 provides a low impedance path for the AC component of current flowing to the power supply from the load while the transistor 32 is on. The second series resonant circuit provides a low impedance path for the AC component of
OMPI WIPO current flowing to the power supply from the load when the transistor 34 is on. Because the power supply capacitors 56 and 58 need only support the remaining components of current flowing to the power supply, the size of the capacitors may be minimized.

Claims

Claims
1. In an inverter for providing a pulse width modulated waveform having a pulse frequency, the output of said inverter being coupled to a low pass filter to provide a sine wave output, the improvement comprising: • a second filter coupled to said low pass filter and tuned to said pulse frequency to eliminate the pulse frequency from the sine wave output.
2. The inverter of claim 1 wherein said second filter is a notch filter.
3. The inverter of claim 1 wherein said second filter includes a series combination of an inductor and a capacitor, said combination being connected across the output of said low pass filter.
4. The inverter of claim 1 wherein said low pass filter has an attenuation requirement to provide a desired sine wave output, said second filter reducing the attenuation requirement of said low pass filter.
5. In an inverter for providing a sine wave output to be applied to a load, said inverter including a DC power supply, the improvement comprising: a series resonant circuit connected in parallel with said power supply and tuned to two times the frequency of said sine wave output for providing a low impedance path for AC current flowing to the power supply from said load.
6. In an inverter for providing a sine wave output to be applied to a load, said inverter including a
DC power supply having positive and negative terminals and a center tap. connected to ground, the improvement comprising: a first resonant circuit connected between said positive power supply terminal and ground; and a second resonant circuit connected between said negative power supply terminal and ground; said first and second resonant circuits each being tuned to two times the frequency of said inverter sine wave output to provide first and second low im¬ pedance paths to ground for AC current flowing to the power supply from said load.
7. The inverter of claim 6 wherein each of said first and second resonant circuits includes an inductor connected in series with a capacitor.
8. In an inverter having a DC power supply, said inverter providing a pulse width modulated waveform to a low pass filter to provide a sine wave output to be applied to a load, said pulse width modulated waveform having a first frequency and said sine wave output having a second frequency, the improvement comprising: a notch filter coupled to said low pass filter and tuned to said first frequency to eliminate the first frequency from the sine wave output; and a series resonant circuit connected in parallel with said power supply and tuned to two times said second frequency for providing a low impedance path for AC current flowing to the power supply from said load.
EP19840903585 1983-10-07 1984-09-17 Pulse width modulated inverter. Withdrawn EP0159334A4 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US54000183A 1983-10-07 1983-10-07
US540001 2000-03-30

Publications (2)

Publication Number Publication Date
EP0159334A1 true EP0159334A1 (en) 1985-10-30
EP0159334A4 EP0159334A4 (en) 1986-02-20

Family

ID=24153555

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19840903585 Withdrawn EP0159334A4 (en) 1983-10-07 1984-09-17 Pulse width modulated inverter.

Country Status (7)

Country Link
EP (1) EP0159334A4 (en)
JP (1) JPS61500148A (en)
DE (1) DE3490486T1 (en)
GB (1) GB2158663A (en)
IL (1) IL72925A0 (en)
IT (1) IT1178036B (en)
WO (1) WO1985001844A1 (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4967334A (en) * 1989-09-12 1990-10-30 Sundstrand Corporation Inverter input/output filter system
US5107491A (en) * 1990-02-20 1992-04-21 Advanced Micro Devices, Inc. Collision filter
US6469919B1 (en) 1999-07-22 2002-10-22 Eni Technology, Inc. Power supplies having protection circuits
EP1272014B1 (en) * 1999-07-22 2009-09-09 MKS Instruments, Inc. Plasma power supply having a protection circuit
US7180758B2 (en) 1999-07-22 2007-02-20 Mks Instruments, Inc. Class E amplifier with inductive clamp
GB2571732A (en) * 2018-03-06 2019-09-11 Reid Acoustic Designs Ltd An apparatus
US10686376B1 (en) * 2019-05-06 2020-06-16 Hamilton Sunstrand Corporation Method and system for control of tunable passive component based power filters

Citations (1)

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US4067057A (en) * 1976-06-25 1978-01-03 Pacific Electronic Enterprises Inc. DC to AC switching converter

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US3038134A (en) * 1958-01-18 1962-06-05 Asea Ab Means for reducing the harmonic currents in a static converter plant
US3205424A (en) * 1961-05-23 1965-09-07 Gulton Ind Inc Voltage phase controller employing synchronized square wave generators
US3461372A (en) * 1965-01-22 1969-08-12 Int Standard Electric Corp D.c. to a.c. power converter
US3636430A (en) * 1970-10-26 1972-01-18 Westinghouse Electric Corp Anticipatory feedback control for inverters
US3746963A (en) * 1971-06-09 1973-07-17 Static Power Inc Polyphase inverter with d.c. supply
GB2043370B (en) * 1979-02-28 1983-03-09 Chloride Group Ltd Converters

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Publication number Priority date Publication date Assignee Title
US4067057A (en) * 1976-06-25 1978-01-03 Pacific Electronic Enterprises Inc. DC to AC switching converter

Non-Patent Citations (1)

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Title
See also references of WO8501844A1 *

Also Published As

Publication number Publication date
EP0159334A4 (en) 1986-02-20
IT8448966A1 (en) 1986-04-05
JPS61500148A (en) 1986-01-23
IL72925A0 (en) 1984-12-31
DE3490486T1 (en) 1985-12-12
GB8513694D0 (en) 1985-07-03
IT8448966A0 (en) 1984-10-05
GB2158663A (en) 1985-11-13
WO1985001844A1 (en) 1985-04-25
IT1178036B (en) 1987-09-03

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Inventor name: HUCKER, DAVID, J.