FR2459568A1 - CONTROL CIRCUIT OF A NETWORK - Google Patents

Abstract

CONTROL CIRCUIT FOR UNDERVOLTAGES AND OVERVOLTAGES AS WELL AS FOR PHASE FAILURES OF AN ALTERNATIVE OR THREE-PHASE VOLTAGE NETWORK. THE PHASE OR PHASES OF THE VOLTAGE SYSTEM TO BE CONTROLLED IS CONNECTED OR ARE CONNECTED VIA A BRIDGE RECTIFIER TO THE NEGATIVE INPUT AND, RESPECTIVELY, TO THE POSITIVE INPUT OF TWO COMPARATORS 13, 14, THE OTHER INPUTS COMPARATORS 13, 14 RECEIVING REFERENCE VOLTAGES AND THE CONNECTED OUTPUTS OF THESE COMPARATORS BEING CONNECTED ON THE ONE HAND TO A VOLTAGE SOURCE AND ON THE OTHER HAND, THROUGH A SERIAL CIRCUIT OF DIODE 16 AND D 'A RESISTOR 17, A CAPACITOR 19 AS WELL AS A RESISTOR 18 WHICH THE OTHER TERMINAL IS CONNECTED TO A VOLTAGE SOURCE. APPLICATION FOR EXAMPLE TO THE ADJUSTMENT OF THE SPEED OF A DIRECT CURRENT MOTOR SUPPLIED BY A THREE-PHASE NETWORK.

Description

The invention relates to a circuit for controlling undervoltage and

  surges as well as failures

  phase of an alternating or three-phase network.

  The invention is applicable for example to adjusting the speed of a DC motor. In that case,

  a power transistor controlled by clock signals

  lodges and operating in intermittent operation

  is often used as a direct con-

  tinu of a DC motor and thus regulator of

  speed. The use of this kind of a transistor in common

  The text is described in W. Bitterlich, "The Influence Indie Elektronik" (introduction to electronics), Springer-Verlag Editions, Vienna - New York, 1967, pp.

390 to 396.

  When the motor is supplied with direct current by a three-phase network and a bridge rectifier is mounted upstream of this motor, the voltage fluctuations

  of the three-phase supply network or also the failures

  phase lances have a great influence on the control

  of the priming of the power transistor. In case of failure

  of a phase, for example, the transistor is supplied with control current that is too low, with the result that

  rise of its DC resistance in the state not-

  health. The consequences are loss peaks that can damage the transistor. The function of the regulator

  speed is no longer ensured, for example in case of

  one phase, that is to say that the regulator of

  speed must be cut off from the network.

  The subject of the invention is a circuit for controlling overvoltages, voltages or phase failures

  alternating or three-phase network, which adequately protects

  speed of the user devices in case of deviations of the mains voltage and possibly the

cutting of this network.

  According to an essential feature of the invention, the phase or phases of the voltage system to be controlled

  is connected or connected by a bridge rectifier to the

  negative and, respectively, to the positive input of two comparators whose other inputs receive reference voltages and whose combined outputs are connected on the one hand to a voltage source and, on the other hand, via a series circuit formed of a diode and a resistor, a capacitor and a resistor whose terminals are connected to the source

  Of voltage. The advantages of the invention are in particular

  link that the control circuit detects very quickly the disturbances that can occur in the network, which

  is important when user devices are sensitive

  to network voltage variations. The circuit of the invention has a structure which is not complicated, it can be realized inexpensively, it is reliable and risks little

to break down.

  According to another advantageous feature of the invention

  vention, resistors and capacitor are dimension-

  in such a way that the time constant resulting from a capacitor discharge on the series circuit formed of a diode and a resistance is small in comparison with

  that resulting from the charging of the capacitor through

  of the other resistance. This provision offers in

  particular a reliable possibility of acquisition and

  interpretation in case of failure of a phase of the circuit

whose voltage is controlled.

  According to another advantageous feature of the invention

  vention, the outputs of the comparators which are connected are

  connected to a logic circuit. The latter is advantageous-

  used for the interpretation or memorization of

  failures occurring in the network.

  The invention will be described in more detail in

  annexed drawings as an example in no way

and on which:

  FIG. 1 is a functional block diagram of

  network control circuit according to the invention.

  tion; and FIG. 2 is a graph showing the variations as a function of time of the voltages of a network

  three-phase rectified in case of undervoltage, normal voltage

  service, overvoltage and phase failure.

  FIG. 1 represents a block diagram of the control circuit of a network according to the invention. A three-phase network to be controlled and whose phases

  R, S, T are connected by resis-

  protection or series resistors 1, 2, 3 to a three-phase rectifier consisting of diodes 4, 5, 6, 7, 8, 9. The three-phase bridge rectifier is connected on the DC side to resistors 10 and 11, a diode of

  Zener 12 being in parallel on the resistor 11.

  The anode of the zener diode 12 is connected to the

  DC output of the rectifier which is

  of the "mass", while its cathode is connected to the common junction of resistances 10 and 11 which

  form a voltage divider. The negative entry of a

  paratrix 13 and the positive input of a comparator 14 are

  otherwise connected to this last common point.

  The combined outputs of the two comparators 13 and 14 are connected to a series resistor 15 and to the cathode of a diode 16. The other terminal of the series resistor 15 is connected to a voltage source U1. The anode

  of the diode 16 is connected to a resistor 17 whose

  terminal is connected on the one hand to a resistor 18 and on the other hand to a capacitor 19 connected to the potential of the mass. The resistor 18 is connected to a source of

U2 voltage.

  The positive input of the comparator 13 is connected

  at the junction point of two resistors 20 and 21, the

  resistance 20 being connected to a voltage source U3 and

  the resistance 21, to the potential of the mass. The negative entry

  The voltage of the comparator 14 is connected to the common point of two resistors 22 and 23, the resistor 22 being moreover connected to a voltage source U4 and the resistor 23 to the potential of the mass. The positive and negative inputs, respectively, of the comparators 13 and 14 therefore each receive a reference voltage, the reference voltages being adjustable as a function of the choice of the voltages U3 and U4.

  and adopted values of resistors 20 to 23.

  The supply input of the comparator 13 receives a voltage U5 and the supply input of the comparator 14 is at ground potential. The combined outputs of the comparators 13 and 14 result in a logic circuit 24. The operating mode of the control circuit of a network will be described. To this end, the variations as a function of time of the voltages of a rectified three-phase network are shown in FIG. 2, the range I illustrating the case of an "undervoltage", the range II, the case of a " normal continuous voltage of service ", the range III, the case of an" overvoltage "and the range IV, the case of a" failure

  a phase of the three-phase supply circuit ".

  The case of undervoltage of the three-phase supply network

  "is always by definition when the minimum

  my (= tension collapses) of the corrugations of

  Continuous voltage resulting from the rectified three-phase voltage just reach a predetermined voltage threshold Uu or fall below this threshold (I range). The case "overvoltage of the three-phase voltage supply network" appears by definition when the peaks of the DC voltage waves reach just a predetermined threshold of voltage U ..- or exceed this threshold (range III). The case "normal voltage of

  service of the three-phase supply network "" always appears

  days by definition when both the minima and the

  Peaks of the waves of the DC voltage are in the

  interior of the voltage band delimited by the thresholds

determined Uu and Uil (range II).

  In the case of the range IV "failure of a phase of the three-phase current", the peaks of the alternations are certainly within the voltage band, but the minima of the waves of the DC voltage fall below the voltage threshold Uu and therefore undervoltage also appears in the

beach IV.

  The control circuit of the network responds as well to the case "overvoltage" as to the case "undervoltage" or "failure

  The voltage thresholds U .. and U are

  u to kill with voltages U3 and U4 through the corresponding resistors 20/21 and 22/23. In the particular embodiment, the comparator 13 controls the overvoltages of the network and the comparator 14,

  under-voltages as well as phase failures.

  Resistors 1, 2 and 3 are intended to lower the three-phase voltage to be controlled. DC voltages appearing at the output of the bridge rectifier

  three phases (4, 5, 6, 7, 8, 9) are subdivided by the division

  10/11 and directed on the comparators 13, 14, the zener diode 12 protecting these comparators

  13, 14 against too high voltage peaks.

  The voltages U1 and U2 and the resistors 17 and 18 are adopted so that in the presence of a

  normal service voltage in the three-phase network (that is,

  that is, when the comparators 13 and 14 have not responded and are in the blocking state), no flow of current passes through the diode 16 (i.e.

  diode 16 also blocks). In case of appearance of a person

  turbation in the network, that is to say a surge,

  undervoltage or phase failure, the

  corresponding parator 13 or 14 switches. When the waves of the DC voltage reach or exceed the threshold U, the comparator 13 switches and when the waves of the DC voltage reach or fall below the threshold Uu, the comparator 14 switches. In both cases, the capacitor

  19 that was charged by the U2 voltage source through the

  resistance 18 discharges through resistance

  17 and the diode 16 which is passing on the output correspon-

  comparator 13 or 14 which has switched, and more particularly

  with a time constant T1 = C19. R17, C19 corresponding to the capacitance of the capacitor 19 and R17 'to

the value of the resistance 17.

  In the case of "overvoltage" or "undervoltage", the corresponding comparator 13 or 14 switches when the maximum or minimum instantaneous value of the rectified voltage of the network just reaches the threshold U .. or U u. The periodic signaling that appears then is transformed by the components 17, 18, 16 and 19 into constant signaling. In the case of "phase failure", the value of the DC voltage wave fluctuates continuously at the rate of the period of the network between a peak within the normal band of the operating voltage and a minimum which is below the voltage threshold U. The comparator 14 switches in this case at the rhythm of the period of the network permanently between the blocking state and

  the passing state and vice versa. Capacitor 19 goes off

  load on the resistor 17 during the conduction period of the comparator 14, as previously described. While the comparator 14 is in the blocking state, the capacitor

  19 recharges via resistor 18.

  The value R18 of the resistor 18 is adopted so that it is large enough for the time constant T2 of the charging process T2 = C9. R 18 is large in comparison with the time constant T1 of the discharge process, that is T2 must be larger

  that a period of the period of the system in three-phase voltage.

  Thus, a "phase failure" warning signal remains permanently established and does not appear in the

  period of the three-phase network and then dis-

  appear. The logic circuit 24 acquires and interprets the warning signals "phase failure"

  as well as "undervoltage" or "overvoltage". The logic circuit

  24 interprets the voltage levels appearing at the connected outputs of the comparators 13 and 14, that is to say that, in the simplest case, the logic circuit 24 can distinguish between the voltages appearing when the comparator 13 or the comparator 14 has switched and the voltage

  appearing when comparators 13 and 14 are on the

  blocked state and can emit impulses cor-

  respondantes. The logic circuit 24 crosses the network

  user organization that is sensitive to variations in

  the voltage of this network snacks of occurrence of a disturbance

  in the latter. It simultaneously memorizes the presence

  a failure in the network and the poster.

  It is not intended that the user equipment cut off from the network is reconnected automatically at the end of a disturbance of the network. This reconnection on the network is only possible by manual actuation of a pushbutton (not shown). It is thus certain that a disturbance of the supply network is communicated to the

  staff. It is of course possible, however,

  if necessary to provide automatic reconnection of the equipment cut off from the network when the disturbance

disappeared in the latter.

Claims (3)

R E V E N D I C A T IO N S   1. Undervoltage and overvoltage control circuit   and phase failure of an alternating or three-phase voltage network, characterized in that the phase or phases of the voltage control system is connected or connected via a rectifier.   bridge at the negative or positive entry respectively   two comparators (13, 14), the other inputs of the comparators (13, 14) receiving reference voltages and the connected outputs of the comparators (13, 14) being connected on the one hand to a voltage source and another part through a series circuit of a diode (16) and a resistor (17), a capacitor (19) and a resistor (18) whose other terminal is connected to a source of tension.   2. Circuit according to claim 1, characterized in that said resistors (17, 18) and the capacitor (19) are dimensioned so that the time constant of a discharge of the capacitor (19) via the series circuit of the diode (16) and the resistance (17)   is small compared to the time constant of a char-   of this capacitor (19) via the other resistance (18).   3. Circuit according to one of claims 1 and 2,   characterized in that the connected outputs of the comparators   (13, 14) are connected to a logic circuit (24).