FR2530893A1 - Method and device for supplying a resistance electrical appliance with alternating current through selected alternations. - Google Patents

Abstract

Control of the supply to an electrical appliance. The device comprises: - a distribution circuit 1 supplying an appliance 3 via a switch 2; - a phase inversion transformer 4 branched to a circuit 1; - a generator 5 delivering a pulse to a circuit 6 for controlling the switch 2; - a mixer 12, a comparator amplifier 15, an integrator 17 and an "AND" gate 10 with a threshold triggering level. Application to the regulating of heating resistors for plastics moulding facilities.

Description

 The present invention relates to the technical field of controlling the AC supply of resistance devices. The invention relates, more particularly, to heating appliances for which it is necessary to control or regulate the electrical supply, either as a function of a pre-set reference value, or as a function of the result that the operation of said appliance provides.

 The invention relates, more especially but not exclusively, to the field of heating elements which are provided in machines for injecting plastics for which it is necessary to ensure the establishment of a precise regular temperature, in order to obtain a correct plasticization, without reaching the carbonization threshold.

 To control the supply of resistance electrical appliances and, more particularly, of heating elements5, it is known to implement a technique of varying the surface of the sinus of the alternations of the applied electric current, taking a portion more or less important of this surface, called variation in phase angle.

 The undeniable advantage of this technique lies in the fact that the voltage which is applied across the terminals of the heating element is proportional to the opening angle. The applied voltage therefore evolves in relation to needs, without the resistance of such an apparatus being subjected to electric and thermal shock.

Such a technique therefore has the advantage of promoting a long duration of use of the resistors.

 On the other hand, it should be noted that the abrupt establishment of the alternation, at any moment of its evolution, generates a brutal variation of tension that is to say, creates a steep front containing an important frequency spectrum.

 This results in electrical and electromagnetic radiation which generates disturbances by producing parasites for neighboring electrical or electronic devices of economic concept.

 A second solution has also been proposed which consists in using, for the supply of a resistance apparatus, the technique of the wave train. According to this technique, provision is made to supply the device with power for fractions of time by applying to it always complete sinuses, in more or less quantity, according to the power requested.

 In this type of technique, a control switch, of the thyristor or triac type, is generally used, controlled by a pulse generator each time the voltage of the supply current crosses zero. The interruption of the wave train is thus carried out automatically when the voltage goes to zero, if the static switch is not controlled to be kept in a closed state.

 The advantage of this second technique lies in the fact that the establishment and stopping of the supply current voltage is always carried out in the vicinity of zero, so that no interference emission results.

 On the other hand, the main drawback of this technique lies in the fact that the total voltage of the supply current is suddenly applied to the device which thus receives a voltage passing from zero to, for example, 220 volts, for a relatively long time. short. The resistance of such an apparatus is thereby subjected to an electric shock, as well as a thermal shock, which are responsible for a significant reduction in the life of such an element.

 In the industrial field, this second technique is generally used, because of the advantage of the absence of parasites.

 However, in the field of application of temperature control to continuously operating assemblies, it is necessary to be able to guarantee such operation for the longest possible time. However, the risk of deterioration of the heating element, as a result of repeated thermal and electrical shocks, represents in these techniques a serious subjection. Indeed, in the event of rupture, it is necessary to stop, for a long period, an entire assembly or industrial process, in order to proceed, on the one hand, to repair or change the deteriorated element and, d 'on the other hand, to the refurbishment of a device which has suffered sometimes serious deterioration due to the sudden interruption of its operation.

 This is particularly sensitive in the field of plastic injection where it is understood that the sudden stop of one or more heating resistors leads to a solidification of the plasticized material, either in the injection barrel , either in the molds. it then becomes necessary to carry out disassembly, cleaning and reassembly operations which are delicate, long and sometimes difficult to carry out in order to avoid any risk of damage to fragile machine members, such as the injection nozzles or mold impressions. complex configurations.

 The object of the invention is to propose a new method and a new device for supplying alternating current to an electrical resistance apparatus making it possible to preserve the advantages of the known methods, while eliminating the notorious disadvantages.

 Another object of the invention is to propose a new method and a new device which can be implemented in the case where the supply of a heating element must be ensured in relation to a predetermined constant reference value, adjustable or , again, by automatic regulation according to the result obtained by the operation of a heating element.

 Another object of the invention is to provide a new device that can be produced at a particularly attractive cost price and capable of providing a reliable service over time, without risk of deterioration by fatigue of its components.

 An additional object of the invention is to provide a new power supply method which makes it possible to carry out successive power supplies of less power than that of the current known methods, but of greater recurrences, thus leading to a possibility of power supply, regulated or no, finer, more precise and faster in reaction time.

To achieve the above goals, the feed method according to the invention is characterized in that
- displays a reference value consisting of
a continuous tension,
- modulates this continuous voltage by a voltage
alternative delivered in phase inversion by
report -an alternating current source so
to obtain a resulting tension,
- place between the source and a distribution circuit
tion leading to the device to be powered, an inter
static breaker with controlled closure connected to
a control circuit comprising a generator
emitting a pulse whenever the ten
alternative phase reversal pass
by zero,
- controls the control circuit by a threshold
trigger,
- draws from the distribution circuit, between the in
switch and device, a de-modu voltage
lation of the resulting voltage in order to obtain
a modulated control voltage applied to the
threshold so as to command by the latter the
closing the control circuit every time
that said modulated control voltage has,
when a pulse is issued by the
generator, a value greater than the threshold of
door release.

The invention also relates to a device for implementing the above method and characterized in that it comprises:
- a distribution circuit ensuring, by an in
static controlled switch, power supply
an electrical resistance appliance,
- a phase inversion transformer connected in
bypass on the distribution circuit,
- a generator powered by the trans output
trainer and connected to a control circuit
the switch, said generator providing a
pulse for each zero crossing of the ten
transformer output current,
- a mixer receiving a reference voltage
continuous and the AC output voltage of the
transformer
- a comparator amplifier, one of the
very connected to the mixer outlet,
- an integrator connected to the dlstri circuit
bution between the switch and the device and
providing the other amplifier input,
depending on the current consumed, a voltage on
dulante of modulation of continuous type and
variable level,
- and an "AND" door with trigger level at
threshold placed on the control circuit and bran
at the output of the comparator amplifier
Various other characteristics will emerge from the description given below with reference to the appended drawings which show, by way of nonlimiting examples, embodiments of the subject of the invention.

Figs 1 to 15 are curves illustrating different stages of implementation of the liintentionO process
Fig. 16 is a diagram illustrating the embodiment of a device for implementing the method.

Fig. 1 shows the succession of positive and negative alternations of an alternating electric current supplying a device having a resistance representing, for example, a heating element
The operation of this heating element is placed under the general dependence of a reference value which is constituted by a direct voltage, not shown, the level of which is, for example, adjustable by means of a display device. .

 According to the invention, this direct voltage is subject to modulation by means of an alternating voltage produced, from the alternating supply current C, by a phase inversion transformer.

 The resulting voltage TR, which results from the mixture of the direct voltage and the alternating voltage with reversed phase, is illustrated diagrammatically by fig. 2. Taking into account the phase inversion, the resulting voltage TR has successive waves which are in opposition to those of the voltage of the alternating current C shown in FIG. I.

 The reverse phase voltage supplied by the transformer is also used to generate a pulse I, illustrated in FIG. 3, each time this voltage passes through the zero value. Pulse I is intended for a control circuit of a static switch of the triac or thyristor type. Such a circuit is controlled by an "AND" gate which is at the triggering threshold.

Such a threshold, designated by the reference S, is shown diagrammatically in FIG. 2 in combination with the resulting voltage TR.

 According to the method of the invention, it is ensured that the passing state of the "AND" gate is influenced by the voltage TR.

Thus, each time this voltage TR exceeds the value of the threshold
S, the control circuit of the interrupter becomes passing through the door, so that the switch then receives a pulse I, each time the voltage of the supply current passes through the value zero.

 Thus, when the switch is controlled, it allows the alternating current alternating current to be applied to the resistance electrical appliance if, at the time of the following zero crossing, it does not receive another control pulse.

 According to the invention, the alternations which are delivered to the device are taken from the supply circuit and after the interrupter, so as to define a variable continuous modulation voltage TM, as illustrated in FIG. 4. This modulation voltage is applied to the resulting voltage prior to the entry of the 'AND' gate, so as to obtain a modulated control voltage TC, as illustrated in fig. 5. The modulation voltage TM is chosen so that the control voltage TC is damped and of a lower level compared to the resulting voltage TR.

 The implementation of the method described above can be analyzed as follows after a start-up phase for which the reference value is preset to an extreme low level.

In this state, if the result of the operation of the apparatus supplied with alternating current supply leads to a lowering of temperature compared to the preset value, the resulting voltage TR shows, at time t, a more pronounced rising slope which, for example, makes him exceed the threshold S of the door
P. If the modulation maintained by the voltage TM is not sufficient to bring this curve below the level S, the control voltage TC applied to the gate "AND" also occurs at time t with a higher value at the trigger level or threshold S of the door.

 The comparison of figs. I to 5 shows that if this higher level occurs - at the moment of the pulse I, the power supply circuit of the device will be closed by the switch to allow the passage, towards said device, of the alternation A, as shown in fig. 6.

However, the passage of this alternation A has an influence on the modulation voltage TM which itself influences the voltage TC which undergoes a corresponding reduction;
Insofar as this voltage TC then drops below the triggering threshold S, the static switch opens -automatically during the next zero crossing of the voltage, so that the circuit of the device is open and that the latter does not receive any other alternating supply.

If, at time t1, the phenomenon of lowering of temperature occurs again, the curve TC passes again above the threshold S and authorizes the passage towards the apparatus of an alternation Ai
From the operation described above, it is understood that, if the reference value is increased, for example in the case of an increase in power, the resulting voltage TR rises. This results in a modification of the profile of the control voltage TC which is brought to authorize, through the door, the closing of the switch to deliver to the device a greater frequency of alternations A.

 It should be noted that, taking into account the voltage TR, with phase reversed with respect to the voltage of the supply current, the various waves of this voltage, - as well as those of the control voltage> have the effect of cause, through the door and the switch, the passage to the device of waves or alternations of a privileged sign and, in the case shown, negative alternations.

 Thus, as the reference value increases during an increase in power, the method of the invention allows the passage to the device of waves or alternations of the same polarity, which are either applied at variable intervals to the device, or applied successively when the control voltage authorizes the passage of each of the A waves successively of the same sign.

 It follows from the method of the invention that, in the case described above, the heater receives a voltage equal to half that of the supply current, until it reaches an operating state at 50% of its power, corresponding to the absorption of all the alternations of the same polarity, as shown in figs. 7 and 8.

 During this operating phase, the hot element ~ fant receives a peak voltage twice lower than the voltage of the supply circuit. This results in an absence of electric or thermal shock making it possible to obtain a longer service life of the resistor.

 In addition, since the application of one or more of the alternations, as well as the interruption> always takes place at the time of the zero crossing of the voltage, this results in an absence of interference.

It should be noted that in this operating phase, the method of the invention makes it possible to carry out a much more gradual rise in power of the heating element, given that the power applied to this element is significantly less than that of currently known feeding methods
Indeed, if we consider that a cold resistor receives a voltage equal to 220 volts for a time of 0.02 seconds from, corresponding to the passage of two alternations of opposite polarities, the heating element receives for an intensity by example of 22 amps, an instantaneous power in joules of around 9628.

 On the contrary, by implementing the method of the invention1 the voltage of 110 volts, corresponding to the application of alternation, leads to an application time of 0.01 seconds and to an intensity of 11 amps which produce an instantaneous power in joules of 12.1.

 By properly setting the reference value, it therefore becomes possible to gradually increase the power supplied to a heating element - from 0 to 50% by applying to it only a voltage of 110 volts relative to a voltage of power supply of 220 ett consequently, to achieve a progressive rise in power free of electric and thermal shock.

 If beyond the operating threshold at 50%, the setting of the reference value further increases the demand, the resulting voltage TR evolves notably beyond the threshold S. The modulation voltage TM is no longer able to to influence the passage of the control voltage TC below the threshold S for one passage out of two by the zero of the supply voltage.

 The door then remains open from time to time, so that the additional demand results in the application to the heating element of alternations of positive polarities (fig. 3).

This application grows with demand> until the application of all positive and negative alternations.

 From a passage of operation at 50% of its power to an operation at 100% of its power, the chaufw fant element is thus always subjected to the application of a voltage of 220 volts, but receives only gradually the additional positive half-waves according to the demand expressed from the setting of the reference value.

 The modulation voltage TM, a function of the number of alternations applied to the heating element, makes it possible to achieve, by feedback, a kind of balance between the demand formulated by the reference value and the operation resulting from the applica - tion of at least some of the alternations of the supply current to the heating appliance.

 So that this state of equilibrium can be established under the best conditions, the method of the invention provides that the different alternations applied are taken into account by means of an integrator capable of providing an average value which represents the voltage. modulation. In addition, according to the method of the invention, it is also intended to give such an integrator a relatively short charging time for each alternation taken, for example of the order of a quarter of alternation of the alternating current of power supply, and a relatively long discharge time, which can be equal, for example, to about one hundred half-waves at least n periods. In addition, it is planned to take the alternations applied to the electrical appliance, by means of 'A rectifier bridge, so as to obtain, in all cases, a variable DC modulation voltage which is applied to the resulting voltage to dampen and lower the latter. This makes it possible to obtain a control voltage TC having the particularity of being of digital or logic type, taking into account its periodic fluctuations coming from the alternating voltage with reverse phase, while being, at the same time, of analog type by the amplitude variations conferred on it by the modulation voltage.

 The method of the invention can be implemented when it is also a question of ensuring the regulated supply of a heating element. Indeed, in such a case, the reference value. no longer corresponds to a preset DC voltage, but to a DC voltage varying according to the comparison of an effective voltage representative of the operation of the heating element with an adjustable level setpoint voltage. In such a case, the effective voltage may be produced by a thermocouple measuring a temperature which is the result of the operation of the heating element.

 In order to better show the operating characteristics of the object of the invention, FIGS. 11 to 15 show comparative curves corresponding respectively to the modulation voltage TM before its influence on the voltage TR, to the output signal of the amplifier 15 and to the output voltage applied to the device 3.

 The comparison of these figures clearly shows the relative evolution of the curves for examples of operation at less than 10%, at less than 50 2, at 50 X, at more than 50 X and at more than 90% of the voltage. output in relation to the supply voltage.

 Fig. 16 shows an apparatus for implementing the method. This device comprises a distribution circuit 1 leading, by a static switch 2, to a consumption device 3.

Switch 2 is of the triac type. The distribution circuit I supplies a phase inversion transformer 4 in parallel, the output of which leads to a generator 5 emitting a short pulse each time the inverted phase voltage goes through zero. The generator 5 is placed on a control circuit 6 comprising an amplifier 7 and an isolation transformer 8 from which the trigger 9 of the triac 2 is controlled. The circuit 6 is controlled by a gate 10, of the "AND" type, whose trigger threshold is placed under the dependence of input 11.

 The reverse phase alternating voltage produced by the transformer 4 is applied to a mixer 12 which also receives on its input 13 a reference DC voltage produced by an apparatus 14. The output of the mixer 12 is connected to one of the inputs a comparator amplifier 15, the other input of which is connected by a modulation loop 16 to the kind of an integrator 17, also assuming an isolation function. The integrator 17 is connected by a rectifier bridge 18 to the circuit 1, in the part of the latter between the triac 2 and the element 3 to be supplied.

 The device 14 may be of the type delivering a DC voltage of adjustable level or, alternatively, be made up, as illustrated in the drawings, by a differential amplifier 19 whose output is connected to input 13 and whose inputs are connected to a setpoint potentiometer 20 and to a thermocouple 21 assessing the operation of the device 3. In such a case, the differential amplifier 19 emits, after taking into account the two pieces of information that it receives, a variable direct voltage which is modulated at the level of the mixer 12 to constitute the resulting voltage TR. This voltage is modulated and damped by the voltage TM at the level of the amplifier-comparator 15 which produces the control voltage TC applied to the input 11 for triggering the door 10.

 As is apparent from the above, the method of the invention makes it possible to supply a resistance device with selected alternations, first of the same polarity, then, then, of double polarity by offering the possibility of modu-ling the number of alternations directed to the device to be supplied, according to the needs resulting from the operation of said device relative to a reference or comparison value.

 Given the means used to authorize the application of one or more half-waves, the implementation of the method makes it possible to establish or interrupt the supply for each zero crossing of the voltage of the supply current, so that it does not result in the creation of any parasite capable of disturbing the operation of neighboring electrical devices, even of poorly developed technical qualities.

 In addition, the possibility of being able to supply the power to a device, with a voltage equal to half of the nominal value, makes it possible to avoid any electric and thermal shock and therefore to give such a device a duration particularly long service.

 The method of the invention has the additional advantage of being able to be implemented using only an apparatus or a device of relatively low cost of operating on and reliable over time.

 The invention is not limited to the examples described and shown, since various modifications can be made without departing from its scope.

Claims (11)

CLAIMS:  1 - Method of supplying alternating current by selected alternations of an electrical resistance device, ca ractérisé in that  - displays a reference value consisting of  a continuous tension,  - m odulates this continuous tension by a tension  alternative delivered in phase inversion by  report to an ac source so  to obtain a resulting tension,  - place, between the source and a distribution circuit  bution leading to the device to be powered, an in  static switch with controlled closing connected  to a control circuit comprising a general  tor emitting a pulse whenever the  alternating phase reverse voltage  by zero,  - controls the control circuit by a threshold of  trigger,  - draws from the distribution circuit, between the in  switch and device, a module voltage  tion of the resulting voltage in order to obtain  a modulated control voltage applied to the  threshold so as to control, by the latter, the  closing the control circuit whenever  said modulated control voltage has, at  moment of the impulse emitted by the ge  nerator, a value greater than the threshold of  door release.  2 - Method according to claim 1, characterized in that a modulation voltage of the continuous type, but of variable level, representing an average value of the alternations applied to the device, is taken in order to obtain a modulated control voltage favoring , when applied to the door during an increase in power, passage through the static switch and towards the appliance  - first of all at least some of the alter  nances of a polarity determines the voltage of the  alternating supply current,  - then, of all the alternations of the same polarity  representing the application to the device of a  voltage equal to half that of current  feed,  - then, in the event of an additional request,  some at least. alternating signs  contrary to the previous ones,  - and finally, if applicable, of all alter  nances until then applying to said device  a tension equal to that of al-tension  mentation.  3 - Method according to claim B or 2, characterized in that a modulation voltage is taken formed from successive waves each having, with respect to the alternation of the supply voltage, a slope of rapid rise and a low descent slope.  4 - Method according to claim 1R 2 ouzo characterized sd in that it displays a reference value consisting of a DC voltage of adjustable constant level.  5 - Method according to claim 1, 2 or 3, characterized in that it displays a reference value constituted by a DC voltage of variable level resulting from the comparison between a reference voltage and an effective voltage representative of the operation of the powered device.  6 - Device for supplying alternating current by selected half-periods of an electrical resistance device, characterized in that it comprises  - a distribution circuit (1) ensuring, by  a controlled static switch (2), the  mention of an electrical device (3) with resis  tance,  - a phase inversion transformer (4)  connected in bypass to the distribution circuit  bution,  - a generator (5) supplied by the output of the  transformer and connected to a circuit (6) of  switch control, said generator  providing a pulse for each pass to  zero of trans output current voltage  former,  - a mixer (12) receiving a reference voltage  continuous rence and the AC output voltage  tie of the transformer,  - a comparator amplifier (15), one of the  inputs is connected to the mixer output,  - an integrator (17) connected to the circuit  distribution between switch and device  and providing, at the other entrance of the amplifica  tor, depending on the output voltage, a  undulating modulation voltage of continuous type  and of variable level,  - and an "AND" door (10) with trigger level  with threshold placed on the control circuit and  connected to the output of the compa amplifier  rator.  7 - Device according to claim 6, characterized in that it comprises a mixer (12) receiving a reference DC voltage, of determined polarity, of constant level, delivered by a display device (14) with voltage adjustment.  8 - Device according to claim 6, characterized in that it comprises a mixer (12) receiving a continuous reference voltage of determined polarity, of variable level, delivered by a differential amplifier (19) receiving a reference voltage (20) and a variable effective voltage (21) representative of the operation of the electric appliance supplied.  9 - Device according to one of claims 6 to 8, characterized in that it comprises an integrator (17) connected to the distribution circuit (1) by a bridge (18) phase rectifier and designed to have a charging time fast of the order of a quarter of the alternation of the alternating supply current and a slow discharge time equal to n alternations.  10 - Device according to one of claims 6 to 99 characterized in that it comprises a door (10) "AND", the trigger control input of which is connected to the output of the comparator amplifier (15) and the other input of which and the output are interposed on the control circuit (6) of the switch  11 - Device according to one of claims 6 to 10 characterized in that it comprises a static switch (2) consisting of a triac of which. the trigger (9) is connected to the control circuit (6) by an isolation transformer (8) and a power amplifier (7).