GB2176952A - Method of determining the switch-over instants of static converters of a controlled inverter - Google Patents
Method of determining the switch-over instants of static converters of a controlled inverter Download PDFInfo
- Publication number
- GB2176952A GB2176952A GB08614916A GB8614916A GB2176952A GB 2176952 A GB2176952 A GB 2176952A GB 08614916 A GB08614916 A GB 08614916A GB 8614916 A GB8614916 A GB 8614916A GB 2176952 A GB2176952 A GB 2176952A
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- ofthe
- currents
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- over
- parallel opposition
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- 230000003068 static effect Effects 0.000 title claims abstract description 22
- 238000000034 method Methods 0.000 title claims abstract description 17
- 230000010355 oscillation Effects 0.000 claims abstract description 21
- 230000015572 biosynthetic process Effects 0.000 claims description 2
- 101100456896 Drosophila melanogaster metl gene Proteins 0.000 claims 1
- 230000000694 effects Effects 0.000 claims 1
- 238000009499 grossing Methods 0.000 abstract description 8
- 230000002123 temporal effect Effects 0.000 abstract description 4
- 238000005259 measurement Methods 0.000 abstract description 2
- 238000010586 diagram Methods 0.000 description 5
- 230000007704 transition Effects 0.000 description 5
- 239000004576 sand Substances 0.000 description 2
- 230000000903 blocking effect Effects 0.000 description 1
- 230000000295 complement effect Effects 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 238000004804 winding Methods 0.000 description 1
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
- H02M7/5387—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 bridge configuration
- H02M7/53871—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 bridge configuration with automatic control of output voltage or current
- H02M7/53873—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 bridge configuration with automatic control of output voltage or current with digital control
-
- 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
- H02M7/505—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 thyratron or thyristor type requiring extinguishing means
- H02M7/515—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 thyratron or thyristor type requiring extinguishing means using semiconductor devices only
- H02M7/525—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 thyratron or thyristor type requiring extinguishing means using semiconductor devices only with automatic control of output waveform or frequency
- H02M7/527—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 thyratron or thyristor type requiring extinguishing means using semiconductor devices only with automatic control of output waveform or frequency by pulse width modulation
- H02M7/529—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 thyratron or thyristor type requiring extinguishing means using semiconductor devices only with automatic control of output waveform or frequency by pulse width modulation using digital control
Abstract
A method of determining the switch-over instants of static converters, which are connected in parallel opposition and free of circular currents, of a multiphase controlled inverter feeding asynchronous motors at variable frequency in four-quadrant operation, serves to ensure that a correctly timed switching-over of the converters takes place without having to take into account the operating frequency during a smoothing of the current measurement value. For this purpose the Fourier transforms of the fundamental oscillation of the currents are formed in component form from the temporal courses of the individual currents of the multiphase system with the use of auxiliary magnitudes, which are of constant amplitude and free of harmonic oscillations, as multiplier function. Subsequently, the Fourier transforms of the fundamental current oscillations of all phases are added separately according to the active and the reactive components. The quotient of the temporally smoothed sum values or its arc tagent is compared with the running time angles and the switching-over of the parallel opposition circuit is initiated at each instant of the equality. <IMAGE>
Description
SPECIFICATION
Method of determining the switch-over instants of static converters of a controlled inverter
The present invention relates two a method of determining the switch-over instants of static converters of a controlled inverter. A method for such a purpose is disclosed in DE-AS 2509177.
For the feeding at variable frequency of polyphase current drives at frequencies down to about half mains frequency, a three-phase controlled inverter is particularly suitable and can be constructed particularly economically in parallel opposition connection free of circular current. If asynchronous motors are used as drive motors, particularly a group of motors for, for example, roller conveyor drives, then there is no useful report back fro the motors on either rotational speed or rotary angle. Nevertheless, a mains-like polyphase voltage system of selectable frequency and direction is to be provided, for which it can be accepted that individual motors ofthe group switch offin the case ofthe overload by excess current.Whilstthe formation of the variable control angles for the current inverters presents few difficulties, a problem exists in the generation of the switch-on and switch-off signals for the current inverters ofthe parallel opposition circuit.
In the method described in the above-mentioned DE-AS 25 177, the actual values of the phase currents of the multiphase system are detected by way of current transformers and fed to a command stage which sends a signal to each control set ofthe respective parallelly oposed current inverter of a phase, for which of both the currentinvertersthe control pulses are to be freed each time. It must be made certain throughthecommand stage that only one current inverter of a parallel opposition connection is switched on at any time.Forthis purpose it is necessary that information concerning the correct switch-over instant from one to the other current inverter of a parallel opposition connection is obtained as rapidly as possible from the currents ofthe individual phases. The correct instant is that at which an uninterrupted flow of all currents is ensured, in which case the two halves ofthe parallel opposition connection should never conduct current at the same time.
The obtaining of information aboutthe correct switch-over instantfrom the current flows, in particularfrom their zero transitions, is only conditionally possible in view of the mode of operation of a controlled inverter, since the zero transition of the fundamental oscillation is veiled by the strong harmonic content. A smoothing of the harmonic oscillations in the current measurement value is generally connected with an error in respect ofthe required angle of lag ofthe current. Since the lowest harmonicfrequency and the secondary operating frequency are relatively close to each other, the error is in general unacceptable.
There is thus a need for a method whereby correctlytimed switching on and off of parallelly opposed current inverters of each phase may be ensured without having to have regard for the operating frequency during the smoothing of the harmonic oscillations of the currents.
According to the present invention there is provided a method of determining the instants of switch-over of static converters, which are connected in parallel opposition and free of circular currents, of a multiphase controlled inverterfeeding at least one asynchronous motor at variable frequency in four-quadrant operation, the method comprising the steps offorming the Fouriertransforms of the fundamental oscillation ofthe currents in component form from the waveforms of the individual phase currents ofthe multiphase system with the use as multiplierfunction of auxillary magnitudes which are of constant amplitude and free of harmonic oscillations, adding separately the active and the reactive components of the Fouriertransforms of the fundamental current oscillations ofall phases, comparing the quotient ofthe smoothed sum values orthe arctangentofsuch quotientwith the running time angles, and switching overthe parallel opposition curcuitat each instant of equality.
The unavoidable smoothing of the harmonic oscillations of the current isthereby independent ofthe operating frequency, so that the switch-over instant of the parallelly opposed connected current inverters is determined withoutfrequency-dependent angle errors.
An example of the method of the invention will now be more particularly described with reference to the accompanying drawings, in which: Figure lisa circuit diagram showing the setting up ofthe Fouriertransforms of the fundamental oscillations of the phase currents of a controlled inverter,
Figure 2 is a circuit diagram showing the setting up of a switch-over signal for the static converters of a controlled inverter; and
Figure 3 is a set of diagrams showing the temporal courses of signals for the setting up of the switch-over signal in the circuit of Figure 2.
Referring nowt the drawings, it is presupposed for an understanding of Figures 1 to 3 that a known three-phase controlled inverter (for example as disclosed in DE-AS 25 177, Figure 1) is present, which has threethree-phase parallel opposition circuits of static converters connected in star configuration and feed one or more asynchronous motors by way of three phases.
For the setting-up of the guide magnitudes of a downstream voltage regulator (not shown) or of the direct control magnitudes for the static converters, a presetting for the desired frequency and direction of rotation of the asynchronous motors takes place according to Figure 1 through a direct voltage + Wf.This signal issplitup according to amount and direction in functional blocks 1 and 3.
The pulse chain of a frequency proportional to amount is generated in a voltage-frequency converter 2 and is switched in dependence on sign to the forward or reverse input of a counter4. The counter-state z is passed digitally to function formers 14with sine/cosine output. The sine outputs are flattened off according to a known method in a block5 for reduction of the maximum phasevoltage and modulated proportionallyto frequency in a member 6. Serving forthis purpose is a frequency generator7, which is also acted on by the input signal + Wf. The 1 underthe root of the generator 7 stands for the ohmic resistance ofthe windings ofthe asynchronous motors.
The outputs of the members 6 can now be processed as guide magnitudes Wu of a downstream voltage regulatorforthe static converters lying in the three phases R, Sand Tofthe controlled inverter or, after inversion for the parallelly opposed group of the static inverters, be used directly as control magnitudesforthe static converters (notshown).
In orderthat of the six static converters of the controlled inverter always only one static converter carries current in each parallel opposition connection and during operation a correctly timed switching-overtothe respective other static converter ofthe parallel opposition connection takes place, the zero transition necessary for determination of the switching-over instant - of the currents in the three phases is to be determined. Since, as explained above, the currents are strong in content of harmonics so that an error-free indication ofthe true instant of the zero transition is not possible by direct detection of the temporal current courses, the Fouriertransform ofthe fundamental oscillation is employed for determination of the zero transition.
As is known, the Fouriercoefficients av and bv of a function f(t) can be calculated by theformulae
According to Figure 1, the products of the measured phase currents 1R, is and iT and the outputs ofthe function formers are calculated in multipliers 8. These products are added and smoothed in amplifiers 9 separately for sine and cosine components. Through the addition of the three products, the harmonic oscillations of twice the operating frequency drop out in the individual products. The outputs of the amplifiers 9 representthe active and the reactive components ofthefundamental current oscillation as directvoltages.
The unavoidable smoothing ofthe harmonic oscillations of about six times the mains frequency is no longer limited by the operating frequency. At constant load, the smoothing of the Fourier coefficents, by contrastto the smoothing of thetemporal courses, could be as high as desired without causing an angle error. Atvariable load, the smoothing ofthe Fourier coefficents is limited merely by the frequency content ofthe load/time course. Because of the mass inertia ofthe motors and the dependence ofthe load on slip, this spectrum ends at least a power often below the operating frequency.
It is expedientforthe structuring ofthe circuit to replace the angle of lag (phase angle) thus the lag ofthe current relative to the voltage caused in consequence of the reactive component, by its complement to 7r/2: = r/2 - . -cp. This angle lies between about + 60"(cos = + 0.87) forasychronous machines of normal mode of construction.
The tangent is calculated in a divider 10 by division ofthe active and reactive components ofthe current, theangleRin an arctangentformer 11 and its inverse - Pin an inverter12.
These values ## must now be compared with the running time angle counter state z is converted according to Figure 2 in a function former 13 into an analog signal f(z), (see Figure 3, middle diagram).The signal f(z) is a linear image ofthetime angle tinthe limits ofthe possible value ofW, i.e. about t 60'. According to Figure 3, the calculated values + arecomparnd in comparators 14.1 and 14.2 with the time angles 9tseparatelyfor righthand and lefthand rotation and separately for the three phases.The outputs ofthe comparators 14.1 and 14.2 are fed, according to direction of rotation either straight or crosse over, to pulse formers 15.1 and 15.2. Aswitch-oversignal for a bistable trigger stage 16 is derived from output signals K1 and K2 of the pulse formers 15.1 and 15.2. The trigger stage 16 respectively associated with each phase R, Sand Delivers a blocking signal to the control stage of one of the parallelly opposed connected static converters Bri, whilstthe control stage of the previously blocked other static converter Br2 receives a clearing signal.
The comparison ofthevalues + with the running time angle o)tcan, however, take place in otherways,for example on a digital base.
The output signal of the trigger stage 16, before passing-on of a signal for clearing one ofthe parallelly opposed connected static inverters, is subject to the known tests for admissibility, i.e. that the currentthrough the static converterto be switched off is 0, that the release time ofthe static converter valves has been observed and that no new ignition pulse has been delivered during this time.
The temporal course of the output signals K1 and K2 ofthe pulse formers 15,1 and 15.2 is illustrated separatelyfor righthand and lefthand rotation in Figure 3. According to direction of rotation, i.e. sign ofthe frequency, the abscissa Z ~ xt is traversed from left to right or conversely. The not-bracketed designations apply for positive + and the bracketed designations for negative + (see Figure 3, middle diagram).
To initiate the operation of the controlled inverter, i.e. before any currents, B, is and have been measured and consequently before outputs ofthe amplifiers 9 deliver any signals, the approximately known reactive current according to a voltage U5 iS simulated in every case by means of contacts "start" according to Figure 1 and the correct switch-on instant is thereby preset for a pure reactive current. Moreover, it can be expedient according to magnitude and direction ofthe expected torque to additionally simulate a certain active current through addition of a voltage Uwand thereby reduce the initial error. As soon as a measurable currentflows, these starting aids are switched off.
Claims (1)
1. A method of determining the instants of switch-over of static converters, which are connected in parallel opposition and free of circular currents, of a multiphase controlled inverterfeeding at least one asynchronous motor atvariable frequency in four-quadrant operation, the method comprising the steps of forming the Fouriertransforms of the fundamental oscillation of the currents in component form from the waveforms of the individual phase currents ofthe multiphase system with the use as multiplier function of auxiliary magnitudes which are of constant amplitude and free of harmonic oscillations, adding separately the active and the reactive components of the Fouriertransforms of the fundamental current oscillations of all phases, comparing the quotient of the smoothed sum values ofthe are tangent of such quotient with the runningtime angles, and switching over the parallel opposition circuit at each instant of equality.
2. A method as claimed in claim 1, wherein the at least approximately known reactive currentvalue, orthis value and additionallythe active currentvalueto be expected, is or are used as substitute magnitudefor formation ofthe quotient until measurable phase currents have arisen.
3. A method as claimed in either claim 1 orclaim 2, wherein forformation ofthe quotientthecomplement to /2 ofthe angle of lag ç between feed voltage and the phase currents is determined and the step of comparing comprises comparing the time angle with the angle 7r/2 -9.
4. A metl.od as claimed in claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.
Amendments to the claims have been filed, and have the following effect: (a) Claim 1 above has been deleted ortextually amended.
(b) New ortextually amended claims have been filed asfollows:
1. A method of controlling static converters, which are connected in parallel opposition and free ofcir- cularcurrents, of a multiphase controlled inverterfeeding at least one asynchronous motor at variable frequency in four-quadrant operation, the method comprising the steps of detecting each ofthe phase currents of the multiphase system, forming the Fourier transforms of the fundamental oscillation of the phase currents in component form from the waveforms of the phase currents with the use as multiplier function of auxiliary magnitudes which are present in the component form and free of harmonic oscillations, adding separately the active and the reactive components ofthe Fouriertransforms of the fundamental current oscillations of all phases, comparing the quotient ofthe smoothed sum values orthe arctangent of such quotientwith the running time angles, and switching over, at each instant of equality, from the static converter previously conducting phase current to the converter connected in parallel opposition thereto.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19853523659 DE3523659A1 (en) | 1985-06-28 | 1985-06-28 | METHOD FOR DETERMINING THE SWITCHING TIMES OF CIRCUIT-FREE ANTI-PARALLEL-SWITCHED CONVERTERS OF A CONTROL CONVERTER |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8614916D0 GB8614916D0 (en) | 1986-07-23 |
| GB2176952A true GB2176952A (en) | 1987-01-07 |
| GB2176952B GB2176952B (en) | 1989-07-12 |
Family
ID=6274764
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8614916A Expired GB2176952B (en) | 1985-06-28 | 1986-06-19 | Method of determining the switch-over instants of static converters of a controlled inverter |
Country Status (5)
| Country | Link |
|---|---|
| AT (1) | ATA173386A (en) |
| DE (1) | DE3523659A1 (en) |
| GB (1) | GB2176952B (en) |
| IT (1) | IT1204408B (en) |
| SE (1) | SE8602200L (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3710899C1 (en) * | 1987-04-01 | 1988-10-27 | Licentia Gmbh | Process for producing the torque-controlled variable of an asynchronous machine supplied power via a pulse rectifier |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2509177C3 (en) * | 1975-03-03 | 1978-12-14 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Circuit arrangement with three converters with single-phase AC voltage output |
-
1985
- 1985-06-28 DE DE19853523659 patent/DE3523659A1/en active Granted
-
1986
- 1986-05-14 SE SE8602200A patent/SE8602200L/en not_active Application Discontinuation
- 1986-06-19 GB GB8614916A patent/GB2176952B/en not_active Expired
- 1986-06-24 IT IT20895/86A patent/IT1204408B/en active
- 1986-06-25 AT AT861733A patent/ATA173386A/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| DE3523659A1 (en) | 1987-01-08 |
| SE8602200L (en) | 1986-12-29 |
| IT1204408B (en) | 1989-03-01 |
| GB2176952B (en) | 1989-07-12 |
| SE8602200D0 (en) | 1986-05-14 |
| IT8620895A0 (en) | 1986-06-24 |
| DE3523659C2 (en) | 1987-09-24 |
| ATA173386A (en) | 1989-03-15 |
| GB8614916D0 (en) | 1986-07-23 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |