APPARATUS FOR PROVIDING MULTIPHASE CURRENT

Abstract: The invention relates to an apparatus for providing a multiphase current with desired frequency and voltage, and comprises a frequency generator (11) for sending a control voltage, i.e. a single phase, controlling, alternating current, with variable frequency, and sensing means (12) for sensing the zero passes of the control voltage. A dividing means is arranged to divide each time or angular distance between at least two zero passes into the number of parts, period parts, coresponding to the number of phases in the multiphase current. A signal means (12) transmits a plurality of signal pulses (13, 14, 15) in response to the period parts obtained in the dividing means, said signal pulses finally controlling current valves (21-22) such as thyristors, adapted for controlling a direct current with a voltage corresponding to the operating current.

Description: Apparatus for providing multiphase current The present invention relates to an apparatus for providing multiphase operating current, especially apparatus which can be fed by ordinary alternating current. By means of the apparatus, an operating current with the desired number of phases, desired frequency and voltage can be achieved. This is attained in that the apparatus includes a frequency generator transmitting a single phase, controlling, alterning voltage with variable frequency, sensing means for sensing the zero passes of the control voltage curve, andadividing means arranged to divide each time or angular distance between at least two zero passes into a plurality of parts corresponding to the number of phases in the multiphase operating current, e.g. three parts for a three- phase operating current. Signal means is adapted to transmit pulses in response to the period pulses obtained in the dividing means, e.g. one pulse for each part period, there being current valves such as thyristors controlled by the signal pulses, and arranged for controlling a direct current with a voltage corresponding to the operating current. The dividing means can be adapted for dividing the basic distance between the selected number of zero passes into three parts for providing a three-phase current. The invention will now be described in detail while referring to the drawing, on which Figure 1 is a diagram of the chief components in the apparatus, and Figure 2 illustrates an operational loading. In the illustrated and described embodiment, the apparatus is formed for providing a three-phase current. In Figure 1, a frequency generator generating a control voltage with optional, variable frequency is denoted by the numeral 11. * The control voltage is applied to a phase pulsator 12 with sensing and dividing means. The sensing means senses the number of zero passes of the control voltage and defines a bsic distance which covers a given plurality of zero passes and corresponds to a complete period length. In the described embodiment, the dividing means divides the basic distance into three period parts to obtain a three-phase current. The phase pulsator 12 also contains a signal means transmitting three start pulses to initiate three current phases. The first start pulse constitutes a basic pulse, while both the following start pulses have phase lags of 120 and 240 , respectivel in relation to the basic pulse. The phase pulsator 12 can contain an integrated circuit, known per se, for providing the pulses. The phase pulsator 12 has three outputs 13, 14 and 15 with phase angles 0 , 120 and 240 , i.e. three pulses are transmitted with an interval corresponding to 1/3 of the period length or, if so desired, with a frequency which is three times the desired operating frequency. The three-phase pulses are amplified in amplifiers 16, 17 and 18, the outputs of which are each being connected to a pair of thyristors, which it controls, said pairs of thyristors being denoted respectively by 21a, 21b, 22a, 22 and 23a, 23b. The thyristors are fed from a DC source, the terminals of which are denoted by 25 and 26, where the terminal 25 has an operating voltage of + U volts and the terminal 26 an operating voltage of - U volts. U can be 220 volts or 380 volts, for example. During one period of the operating current, the thyristor pairs 21 - 23 will thus generate three square waves on the outputs R, S and T between each thyristor pair, said waves having the operating voltage - U and being phase-shifted 120 in relation to each other, the frequency being determined by the frequency generator 11. As is apparent from above, the frequency of the operating current is in a constant relationship to the frequency of the control voltage depending on the formation of the phase pulsator 12. The outputs R, S and T between the thyristors in the thyristor pairs 21a - 21b, 22a - 22b and 23a - 23b can be connected to a three-phase load of an arbitrary kind, e.g. the stator winding of a Δ -coupled three-phase induction motor. By varying the frequency of the control voltage coming from the frequency generator 11, the revolutionary speed of an induction motor can be controlled very accurately in the mode described and with the operating voltage desired. One skilled in the art will see quite clearly that an operating current with ' an arbitrary number of phases can be provided with the aid of the invention. Thus, a 2-phase current can be provided by the phase pulsator 12 giving two start pulses on two outputs, or in an arbitrary case, give n start pulses on n outputs to provide an n-phase current. It is naturally also possible to feed each thyristor pair in one phase from an individual direct current source instead of feeding all the phases from a single direct current source. ^--^TJ E ^**-

Claims: PATENT CLAIMS 1. An apparatus for providing a multiphase current with desired frequency and voltage, characterized in that it comprises a frequency generator (11) for transmitting a single-phase controlling alternating current, - a control voltage, - with variable frequency, sensing means (12) for sensing the zero passes of the control voltage, - dividing means (12) adapted for dividing each time or angular distance between at least two zero passes into the number of parts, parts period, corresponding to the number of phases in the multiphase current, signal means (12) adapted for transmitting a plurality of signal pulses (13, 14 " , 15) depending on the period parts obtained in the dividing means and current valves (21-22) such as thyristors, controlled by the signal pulses, and adapted for controlling a direct current with a voltage corresponding to the operating current. 2. Apparatus as claimed in claim 1, characterized in that the current valves are arranged in pairs (21a-21b, 22a-22b, 23a-23b) , the arrangement being such that the firs current valves (21a, 22a, 23a) open with mutual phase shift corresponding to the number of phases in the multiphase current, while the other current valves (21b, 22b, 23b) are controlled so that they open phase shifted 180° in relation to coacting first current valves, there being an output (R, S, T) ' arranged from the connection between the current valves in each pair to serve as outputs for the multiphase current provided. 3. Apparatus as claimed in claim 1, characterized in that the signal means (12) is adapted to transmit signal pulses with a time or phase angle interval corresponding to the distance between an uneven number of zero passes. 4. Apparatus as claimed in claim 1 or 2, characterized in that the signal means (12) is adapted to transmit a signal pulse per period part such that the number of signal pulses is a multiple of the digit 3.

Inventors: NYSTROEM S
Applicants: NYSTROEM S
Application year: 1980
Main classification: H02P7
IPC codes: H02M1, H02M7