GB1585666A - Variable frequency electrical inverters - Google Patents

Variable frequency electrical inverters Download PDF

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Publication number
GB1585666A
GB1585666A GB35773/77A GB3577377A GB1585666A GB 1585666 A GB1585666 A GB 1585666A GB 35773/77 A GB35773/77 A GB 35773/77A GB 3577377 A GB3577377 A GB 3577377A GB 1585666 A GB1585666 A GB 1585666A
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United Kingdom
Prior art keywords
inverter
counter
store
pulse
frequency
Prior art date
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Expired
Application number
GB35773/77A
Inventor
Boleslaw Kaczmareck
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ACEC
Original Assignee
ACEC
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Publication of GB1585666A publication Critical patent/GB1585666A/en
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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
    • H02M7/505—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
    • 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
    • H02M7/5152—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 separate extinguishing means
    • H02M7/5155—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 separate extinguishing means wherein each commutation element has its own extinguishing means
    • 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

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)
  • Control Of Multiple Motors (AREA)

Description

(54) IMPROVEMENTS IN VARIABLE FREQUENCY ELECTRICAL INVERTERS (71) We, ATELIERS DE CONSTRUC TIONS ELECTRIQUES DE CHARLEROI (ACEC) of 54 Chaussee de Charleroi, Saint Gillies, Brussels, Belgium, a body corporate organized according to the laws of Belgium, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to electrical inverters and in particular to a variable frequency electrical inverter which has a plurality of thyristors provided with control electrodes and is controlled by a control chain supplying a command signal for the frequency of the invertor.
It is an object of the invention to provide an inverter, and in particular its logical control system which, for any frequency in a very wide range of operating frequencies, supplies throughout that range of frequencies a voltage of determined form in relation to the electrical angles and having either a minimum of harmonic components or a complete lack of certain particularly troublesome harmonic components.
According to the present invention there is provided a variable frequency electrical inverter having a plurality of thyristors provided with control electrodes, which is controlled by a control chain supplying a command signal to a pulse generator of variable frequency establishing the frequency of the inverter, the pulses supplied by the pulse generator having a frequency higher than the desired frequency of the inverter, said inverter including: a counter receiving the output pulses from the pulse generator, said counter being reset to zero after every n pulses wherein n is a preselected positive integar at least equal to 12; and a read-only store, the stages of the counter acting as addresses for the store, whereby in succession and in cyclic order during each period of the operating frequency of the inverter, n groups of predetermined control signals are fed from the read-only store to the control electrode of the thyristors of the inverter in the same cyclic order.
The present invention will now be described in greater detail by way of example with reference to the accompanying drawing, wherein: Figure 1 is a block diagram of one preferred form of an electrical inverter and its logical control system; Figure 2 is a waveform showing the evolution of a control voltage during one period of the operating frequency.
Referring to Figure 1, a three-phase electrical inverter comprises six main thyristors 1 to 6, each having a diode associated therewith, and, eight thyristors 7 to 14 constituting an extinction circuit. The number of thyristors in the extinction circuit is not critcal and may be reduced to three if desired. From a D.C. voltage network +U, -U this inverter feeds three busbars R,S and T of an A.C. voltage network, which may, for example, be used to drive an asynchronous motor M. The speed of this motor M is controlled by a control chain (not shown) supplying an analogue speed instructio between two terminals 15. The two terminals 15 are the input terminals of an analogue-todigital converter 16. The converter 16 has a plurality of outputs at which appear the primary states of a number corresponding to the digital value of the analogue signal applied to the input 15. The outputs of the converter 16 are applied to the input of an address selector of a read-only store 17. In the store 17 are stored a whole series of closely spaced values of times corresponding to the different times between two fronts of successive pulses supplied by a pulse generator 18, thus making it possible to produce pulses at a whole series of different rates of closely values. These times are for example a series of 3800 values between 200 and 4000 microseconds, the differences between two neighbouring times of the series being one microsecond. In this case the rates ol the pulse generator vary between 5000 Hz and 250 Hz, and they correspond to a series of 3800 frequency between 13.8 Hz and 0.694 Hz multiplied by a number n (=360), from which the converter 16 may select the suitable value for a frequency instruction supplied through the address selector of the store 17.
The difference between two neighbouring times of the above series of times can be determined by the time between the fronts of two or more successive pulses of master quartz oscillator 19. The pulses leaving this master oscillator 19 are applied to the input of a counter 20. The states of the different stages of this counter 20 are applied to one of the two series of inputs of a comparator 21, the other series of inputs of this comparator 21 being connected by means of a locking device 22 to the outputs of the read-only store 17 deter mining the rate of the pulse generator 18. The locking device 22 makes it possible to fix the state of the inputs of the comparator 21 at a predetermined moment for effecting the com parison between the two series of inputs of the comparator 21. When the counter 20 reaches the number determined by the inputs locked by the device 22 the comparator supplies a pulse to a monostable circuit 23, which also forms a part of the generator 18. At the out put of the monostable circuit 23 a pulse then appears which is of sufficiently long duration to permit the unlocking of the device 22 and the application of the state of the output stages of the store 17 to the input of the comparator 21. This same pulse passing from the monostable circuit 23 resets the counter 20 to zero and constitutes the output pulse of the pulse generator 18. As already stated, the rate of the output pulse amounts to n times the frequencyfof the inverter. The number n is preferably selected to be equal to 360, but obviously may be much greater if accuracy has to be increased, for example n = 3600. On the other hand, whenn = 12 or smaller the desired effect can no longer be achieved.
The output signal of the generator 18 is applied to a cyclic switch having n positions, n being in this instance equal to 360. This switch is composed of a nine-stage binary counter 24 associated with a detector 25 for the number 260, which acts as zeroizing signal transmitter for the counter 24. This counter 24 counts the n equal angular subdivisions of each period of each operating frequency of the inverter. The stages of the counter 24 serve as an address for a read-only store 26 and, in succession and in a cyclic order which is passed through completely during each period of each operating frequency, select the n sets of instructions preestablished for the different thyristors 1 to 14 of the inverter and stored in the store 26 for transmission, by way of suitable amplifiers (not shown), to the gates of the thyristors 1 to 14.
The selection of the instructions preestablished for the different thyristors is identical, except for constant phase displacement, for all the main thyristors 1 to 6 and is effected, not in dependence on time, but in depend ence on the electrical degrees of a period of unspecified length, corresponding to a frequency taken from the range of operating frequencies. This selection is made in accordance with the well known Fourier analysis method in order to eliminate or minimize one or more harmonic components. Because these instructions are established in dependence on electrical degrees, if a certain shape of the control wave, such as the control wave shown in Figure 2, minimizes certain harmonic components for an operating frequency of the range, it also minimizes these harmonic components for all the other operating frequencies.
If for the different frequencies in the range of operating frequencies the most troublesome harmonic components are not always the same, it is possible to provide two or more stores 26, counters 24, and detectors 25 each eliminating a different set of harmonic components. In this case, the switching of the output pulse of the generator 18 to a first set or to a second, third, etc. set can then be effected by means of a switch arranged at the output of the monostable circuit 23 and operated by one or more frequency instruction detectors 28 connected to the outputs of the store 17.
If the above described inverter is used with a motor whose slots are not parallel to the axis of the rotor, but offset by a certain angle in relation to the direction of the axis, it is possible to select this angle of offset at a value such as to make it possible to eliminate a pair of harmonics which are not eliminated by the selection of the control wave. Conversely, if the selection of the offset angle of the slots makes it possible to eliminate a certain pair of harmonics, it is possible to select a control wave shape permitting the addition or elimination of other harmonics.
In the above example the rate of the pulse generator 18 is controlled by a digital instruction. There are obviously other simpler pulse generators, but these do not have the stability of a quartz oscillator whose rate is controlled directly by an analogue input voltage. These generators are known under the name VCO (voltage control oscillator); they do not need a converter 16 and the inputs 15 then constitutes directly the input of the pulse generator. The output of a VCO pulse generator is treated in the same manner as the output of the generator 18 and is applied to a cyclic detector 24 of the read-only memory 26.
WHAT WE CLAIM IS: 1. A variable frequency electrical inverter having a plurality of thyristors provided with control electrodes, which is controlled by a control chain supplying a command signal to a pulse generator of variable frequency establishing the frequency of the inverter, the pulses supplied by the pulse generator having a frequency higher than the desired frequency of the inverter, said inverter including: a counter receiving the output pulses from the pulse generator, said counter being reset to zero after every n pulses wherein n is a preselected positive integer at least equal to 12; and a readonly store, the stages of the counter acting as addresses for the store, whereby in succession and in cyclic order during each period of the operating frequency of the inverter, n groups
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

  1. **WARNING** start of CLMS field may overlap end of DESC **.
    oscillator 19 are applied to the input of a counter 20. The states of the different stages of this counter 20 are applied to one of the two series of inputs of a comparator 21, the other series of inputs of this comparator 21 being connected by means of a locking device 22 to the outputs of the read-only store 17 deter mining the rate of the pulse generator 18. The locking device 22 makes it possible to fix the state of the inputs of the comparator 21 at a predetermined moment for effecting the com parison between the two series of inputs of the comparator 21. When the counter 20 reaches the number determined by the inputs locked by the device 22 the comparator supplies a pulse to a monostable circuit 23, which also forms a part of the generator 18. At the out put of the monostable circuit 23 a pulse then appears which is of sufficiently long duration to permit the unlocking of the device 22 and the application of the state of the output stages of the store 17 to the input of the comparator 21. This same pulse passing from the monostable circuit 23 resets the counter
    20 to zero and constitutes the output pulse of the pulse generator 18. As already stated, the rate of the output pulse amounts to n times the frequencyfof the inverter. The number n is preferably selected to be equal to 360, but obviously may be much greater if accuracy has to be increased, for example n = 3600. On the other hand, whenn = 12 or smaller the desired effect can no longer be achieved.
    The output signal of the generator 18 is applied to a cyclic switch having n positions, n being in this instance equal to 360. This switch is composed of a nine-stage binary counter 24 associated with a detector 25 for the number 260, which acts as zeroizing signal transmitter for the counter 24. This counter
    24 counts the n equal angular subdivisions of each period of each operating frequency of the inverter. The stages of the counter 24 serve as an address for a read-only store 26 and, in succession and in a cyclic order which is passed through completely during each period of each operating frequency, select the n sets of instructions preestablished for the different thyristors 1 to 14 of the inverter and stored in the store 26 for transmission, by way of suitable amplifiers (not shown), to the gates of the thyristors 1 to 14.
    The selection of the instructions preestablished for the different thyristors is identical, except for constant phase displacement, for all the main thyristors 1 to 6 and is effected, not in dependence on time, but in depend ence on the electrical degrees of a period of unspecified length, corresponding to a frequency taken from the range of operating frequencies. This selection is made in accordance with the well known Fourier analysis method in order to eliminate or minimize one or more harmonic components. Because these instructions are established in dependence on electrical degrees, if a certain shape of the control wave, such as the control wave shown in Figure 2, minimizes certain harmonic components for an operating frequency of the range, it also minimizes these harmonic components for all the other operating frequencies.
    If for the different frequencies in the range of operating frequencies the most troublesome harmonic components are not always the same, it is possible to provide two or more stores 26, counters 24, and detectors 25 each eliminating a different set of harmonic components. In this case, the switching of the output pulse of the generator 18 to a first set or to a second, third, etc. set can then be effected by means of a switch arranged at the output of the monostable circuit 23 and operated by one or more frequency instruction detectors 28 connected to the outputs of the store 17.
    If the above described inverter is used with a motor whose slots are not parallel to the axis of the rotor, but offset by a certain angle in relation to the direction of the axis, it is possible to select this angle of offset at a value such as to make it possible to eliminate a pair of harmonics which are not eliminated by the selection of the control wave. Conversely, if the selection of the offset angle of the slots makes it possible to eliminate a certain pair of harmonics, it is possible to select a control wave shape permitting the addition or elimination of other harmonics.
    In the above example the rate of the pulse generator 18 is controlled by a digital instruction. There are obviously other simpler pulse generators, but these do not have the stability of a quartz oscillator whose rate is controlled directly by an analogue input voltage. These generators are known under the name VCO (voltage control oscillator); they do not need a converter 16 and the inputs 15 then constitutes directly the input of the pulse generator. The output of a VCO pulse generator is treated in the same manner as the output of the generator 18 and is applied to a cyclic detector 24 of the read-only memory 26.
    WHAT WE CLAIM IS: 1. A variable frequency electrical inverter having a plurality of thyristors provided with control electrodes, which is controlled by a control chain supplying a command signal to a pulse generator of variable frequency establishing the frequency of the inverter, the pulses supplied by the pulse generator having a frequency higher than the desired frequency of the inverter, said inverter including: a counter receiving the output pulses from the pulse generator, said counter being reset to zero after every n pulses wherein n is a preselected positive integer at least equal to 12; and a readonly store, the stages of the counter acting as addresses for the store, whereby in succession and in cyclic order during each period of the operating frequency of the inverter, n groups
    of predetermined control signals are fed from the read-only store to the control electrodes of the thyristors of the inverter in the same cyclic order.
  2. 2. An inverter according to claim 1, wherein values pre-established in the read-only store are selected in order to eliminate harmonic components which are not eliminated by angular offsetting, in relation to the direction of the axis of the rotor, of the slots of an asynchronous motor supplied by the inverter.
  3. 3. A variable frequency electrical inverter constructed substantially as herein described with reference to and as illustrated in the accompanying drawing.
GB35773/77A 1976-08-27 1977-08-25 Variable frequency electrical inverters Expired GB1585666A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
BE1007589A BE845644A (en) 1976-08-27 1976-08-27 INVERTER

Publications (1)

Publication Number Publication Date
GB1585666A true GB1585666A (en) 1981-03-11

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GB35773/77A Expired GB1585666A (en) 1976-08-27 1977-08-25 Variable frequency electrical inverters

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BE (1) BE845644A (en)
DE (1) DE2738645A1 (en)
FR (1) FR2363222A1 (en)
GB (1) GB1585666A (en)
IT (1) IT1079946B (en)
NL (1) NL7709439A (en)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4245290A (en) * 1978-12-18 1981-01-13 United Technologies Corporation Sliding notch pulse width modulation (PWM)
DE3006924A1 (en) * 1980-02-25 1981-09-10 Walter Dittel GmbH, 8910 Landsberg Lightweight three=phase inverter - has transformer with three chopper stages with flip=flops controlling reference and delay flip=flops
US4348734A (en) * 1980-07-10 1982-09-07 Reliance Electric Company Converter by stored switching pattern

Also Published As

Publication number Publication date
FR2363222B1 (en) 1981-12-04
DE2738645A1 (en) 1978-03-02
BE845644A (en) 1977-02-28
IT1079946B (en) 1985-05-13
NL7709439A (en) 1978-03-01
FR2363222A1 (en) 1978-03-24

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