GB2074390A - Ignition arrangement for thyristors, triacs or the like - Google Patents

Abstract

The ignition pulse for a thyristor (5) is produced by induction in that, at the position of a bistable magnetic element (1), a variable, reversible magnetic field is created, for example by movable permanent magnets (4) connected to a movable machine part. The field reversal causes an abrupt change in direction of magnetisation in element (1), which change induces in winding (2) a voltage pulse for said ignition. Bistable Wiegand wires and multi-layer elements are described for magnetic element (1). Variations include a movable BME or ferromagnetic object. Phase displacement may be controlled by a second DC Winding (Fig. 2, not shown) or setting magnet (3) may be made movable or its coupling controlled by a displaceable ferromagnetic tongue. Rotary as well as linearly moving permanent magnets are described and asymmetrical and symmetrical excitation of the BME considered. <IMAGE>

Description

SPECIFICATION Switching arrangement for the ignition of thyristors triacs or the like The invention relates to a switching arrangement suitable for the ignition of, for example, thyristors, triacs or like components.

The control of thyristors and triacs by way of switch contacts, such as are employed for example with machine control in the determining of conditions of movement of movable parts, requires special preparation of the control signal conveyed through the switch contacts. For this purpose, measures are required for debouncing the switch or for suppressing interference components in the control signal which are attributable to the bouncing of the switch contacts, and also the provision of leakage resistors, and means for curtailing the duration of pulses, e.g. by the employment of four-layer diodes.

In order to prevent unintentional ignition of the thyristor or triac, the gate input must be closed at a sufficiently low ohm level. The required increase in control signal output associated therewith must be provided by the control circuit.

Moreover, for the ignition of thyristors and triacs, pulse transformers have been proposed which are relatively expensive.

An object of the present invention is to provide a switching arrangement which is, in particular, controllable by mechanical movement and which is of simple construction and substantially trouble-free in operation.

According to the present invention there is provided a switching arrangement for the ignition of thyristors, triacs or like components, in which a voltage pulse is induced in an electrical winding coupled magnetically with a ferromagnetic core, which pulse is further employed as an ignition pulse, characterised in that said ferromagnetic core is a bistable magnetic element (hereinafter referred to as BME), and that means are provided for the production of a magnetic field at the position of the BME which is governed by the position of a movable member and is reversible in direction.

As bistable magnetic elements, also referred to as bistable magnetic switch cores (and hereinafter and in the claims referred to as BMEs), it is recommended in particular that so-called Wiegand wires be employed, whose structure and manufacture are described in DE-OS 2,143,326. Wiegand wires are homogeneous, ferromagnetic wires (e.g. of an alloy or iron and nickel, preferably 48% iron and 52% nickel; or of an alloy of iron and cobalt; or of an alloy of iron with cobalt and nickel; or an alloy of cobalt with iron and vanadium, preferably 52% cobalt, 38% iron and 10% vanadium) which, due to special mechanical and heat treatment, possess a soft magnetic core and a hard magnetic outer surface, i.e. the surface possesses higher coercive force than the core. Typical Wiegand wires have a length of 5mm to 50mm, preferably 20mm to 30mm.If a Wiegand wire, in which the direction of magnetisation of the soft magnetic core coincides with that of the hard magnetic surface, is introduced into an external magnetic field whose direction coincides with that of the axis of the wire, but is opposed to the direction of magnetisation of the Wiegand wire, on exceeding a field strength of approximately 1 6 A/cm, the direction of magnetisation of the soft core of the Wiegand wire is reversed. This reversal is also referred to as resetting. On further reversing of the direction of the external magnetic field, and on the external magnetic field exceeding a critical field strength, the direction of magnetisation of the core is again reversed, so that the core and the surface are again of parallel magnetisation.This reversal of the direction of magnetisation occurs very abruptly and is accompanied by a correspondingly notable change in magnetic flux per unit of time (Wiegand effect). In an induction coil, this alteration of magnetic flux may induce a short and very high voltage pulse (according to the number of turns and to the load resistance of the coil, up to approximately 1 2 v.) known as a Wiegand pulse.

Also on returning of the core, a pulse is produced in an induction coil, which is however of much lower amplitude and of a different sign from the case of the reversal from the anti-parallel to the parallel direction of magnetisation.

If, as external magnetic field, an alternating field is selected, which is capable of reversing magnetisation firstly of the core and then also of the surface layer and of bringing these to magnetic saturation, Wiegand pulses occur, due to the reversal of the direction of magnetisation of the soft magnetic core, alternately of positive and negative polarity, which is termed symmetrical excitation of the Wiegand wire.

For this purpose, field strengths of approximately - (80 to 120 A/cm) to + (80 to 1 20 A/cm) are required. The change of magnetisation of the surface also occurs abruptly and also produces a pulse in the induction coil, which is however much smaller than the pulse induced in the reversal of the core and is generally not evaluated.

If however an external magnetic field is selected which is capable of reversing only the soft core but not the hard surface layer in direction of magnetisation, the high Wiegand pulses occur only with unchanged polarity which is referred to as asymmetrical excitation of the Wiegand wire. For this purpose, a field strength is required in one direction of at least 1 6 A/cm (for the resetting of the Wiegand wire) and in the opposite direction a field strength of approximately 80 to 1 20 A/cm.

It is characteristic of the Wiegand effect that the amplitude and width of the pulses it produces are largely independent of the speed of change of the external magnetic field and that they possess a high signal-to-noise ratio.

Also suitable for the purpose of the invention are differently constructed bistable mag netic elements which possess two zones of differing magnetic hardness (coercive force) magnetically coupled to each other, and may be employed in the same manner as Wiegand wires for producing pulses by an induced, abrupt reversal of the soft magnetic zone.

Thus, a bistable magnetic switch core in the form of a wire has previously been proposed in, for example, DE-PS 2,514,131, which comprises a hard magnetic core (e.g. of nickel-cobalt), an electrically conductive intermediate layer (e.g. of copper) deposited thereon, and a soft magnetic layer (e.g. of nickel-iron) deposited thereon. Another variant additionally employs a core of a magnetic, non-conductive metal inner conductor (e.g. of berryllium-copper), on to which the hard magnetic layer is deposited, then on this the intermediate layer, and on this the soft magnetic layer. This bistable magnetic switch core does, however, produce smaller switch pulses than a Wiegand wire.

In the arrangement of the present invention, when the BME is situated in a magnetic field, the direction of which may be changed by movement of a member at the position of the BME, this magnetic field may also change the magnetisation of the BME whereby, in the winding which is coupled with the BME (sensor winding), it can produce a characteristic pulse which may be employed for controlling a thyristor of triac.

For this purpose, of course, the BME must be so orientated that its two magnetisation directions have a component in the direction of the outer field zone and are preferably directed as far as possible parallel to this latter in order that the magnetic coupling between the two is as high as possible. Furthermore, the outer magnetic field zone at the position of the BME must at least attain the values required for asymmetrical excitation. In one direction at least the field strength HR (with Wiegand wires approximately - 1 6 A/cm) necessary for the magnetic resetting of the BME is required (pole-reversal of the soft magnetic portion of the BME from parallel orientation-with reference to the magnetisation of the hard magnetic portion-to antiparallel orientation).With reversal of the field direction, a field strength Ha is then required which is sufficient to reverse the poles of the soft magnetic portion of the BME once again into parallel orientation of the direction of magnetisation (with Wiegand wires Ha is approximatly 80 to 120 A/cm).

There are numerous possible ways of achieving the desired magnetic field geometry. For example, it is possible to construct a spatially invariable, static magnetic field which has a zero-crossing. This can be achieved, for example, by an arrangement of two magnetic pole-pairs of alternating polarity. In this mag netic field a BME connected to the movable member can be moved, which, after a zero crossing in one direction is returned and, after a zero-crossing in the other direction produces a characteristic pulse.

The sensor winding may be moved together with the BME, but it may also be located in the vicinity of that part of the magnetic field where the release of the characteristic puls.e is expected.

A further preferred embodiment of the invention employs two static magnetic fields one of which is at rest, relative to the position of the BME, and the other is movable relative to it. Both fields are opposed to each other. In this way, at the position of the BME, a magnetic field may also occur, the change of direction of which is governed by the movable member, whereby it is basically immaterial whether the BME is moved or one of the magnets.

The magnetic field which is spatially connected firmly to the BME may be produced either by a current-carrying winding on or near the BME, or else by a permanent magnet, e.g. by a bar-magnet parallel to the BME.

The magnetic field governed by the moved able object is also preferably produced by permanent magnets whereby it is immaterial whether these permanent magnets coincide with the movable member or are connected thereto, or whether stationary permanent magnets are influenced by a movable ferromagnetic object, whereby the strength of the field created thereby fluctuates at the position of the BME.

In any case, it is of advantage if the magnetic field moved with the BME is the weaker, serving only for the resetting of the BME. In this case, as the stronger magnetic field governed by the moved object is brought into the vicinity of the BME, a characteristic pulse is released as soon as it falls short of a critical threshold distance, whilst on removal of this moved magnetic field, resetting of the BME is effected. This can be employed very effectively in machine control.

In addition to asymmetrical excitation, symmetrical excitation is also possible if the field strengths at the position of the BME can attain sufficiently high values in both directions (approximately Hs = + (80 to 120) A/cm for Wiegand wires), although this does not offer any advantage over asymmetrical excitation. Due to the high signal yield, a Wiegand wire is preferably employed as BME, around which the sensor winding is placed.

The employment of a BME to produce ignition pulses has the advantage that-the pulse width and height are almost independent of form and frequency of the exciter alternating current. In addition, ambient influences, especially temperature, have no noticeable effect on the production of pulses. When employing Wiegand wires as BMEs, the half-value width of the pulses is 20 ys.

In most cases therefore, the pulse produced by the reversal of the direction of magnetisation of the soft magnetic portion from the antiparallel direction to the parallel direction can be employed directly, without further preparation, for control purposes. With asymmetrical excitation of the BME, the pulse produced by the reversal of magnetisation of the soft magnetic portion to anti-parallel orientation, is notably smaller than that produced by the reversal to parallel orientation. With symmetrical excitation of the BME, the pulse produced by the reversal of the hard magnetic portion to parallel orientation, is notably smaller than the pulse occurring during reversal of the soft magnetic portion to anti-parallel orentation.

The smaller pulse in each case can, if necessary, be suppressed by a simple discriminator circuit. In addition, circuitry measures to adapt the gate-cathode resistance in the thyristor are no longer necessary, whilst bouncefilters and the like, which are normally required, can be dispensed with.

The pulse transformer according to the invention is also eminently suitable for changing of the phase position of the pulses produced, which is of essential importance in the directing of thyristors and triacs. In the known systems for controlling thyristors and triacs, phase displacement of the pulses is effected for example by the employment of a phase bridge or rotary transformer in conjunction with a pulse transformer. This type of phase displacement of pulses is expensive and is also not suitable for control through progression of movement. A further possibility consists in the employment of an electrical pulsedelay circuit.

The invention offers an ingenious solution to phase displacement whereby, as second winding, a D.C. winding is provided which is coupled magnetically with the BME. Said second winding produces a magnetic direct field which is super-imposed upon the movable magnetic field at the position of the BME, which, because of its movement at the place of the BME, fluctuates in strength (pulsates).

Since the field strengths, which are necessary for symmetrical or asymmetrical excitation of the BME for pulse production, have a predetermined value, the phase position of the pulses produced in the BME is displaced within each period of fluctuation of the field strength of the movable magnetic field by the addition or substraction of a static (in relation to the duration of the fluctuation period of the magnetic field pulsating at the position of the BME) or quasi-static magnetic direct field, whereby the relation between the phase position and the strength of the direct current supplied to the second winding is linear, if the movable magnetic field at the position of the BME follows a linear course in time.However, in the case also of the employment of a magnetic field which fluctuates sinusoidally at the position of the BME, which can be achieved for example by the use of a rotating permanent magnet, the relation between the phase position of the pulses and the strength of the direct current in the second winding is still simple.

In order to obtain a firm coupling between the BME and the second winding, said winding is also preferably placed around the BME.

The static or quasi-static magnetic direct field at the position of the BME might also be produced by a permanent magnet, in which case the change in strength of the direct field at the position of the BME can be effected by moving the permanent magnet closer or further away or, where the permanent magnet is stationary, by moving a ferromagnetic object closer or further away, which deforms the field of the permanent magnet.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 shows a switching arrangement with a Wiegand wire in the control circuit of a thyristor; Figure 2 shows an arrangement similar to that of Fig. 1, but with a second winding of the Wiegand wire for phase displacement; Figure 3 is a diagram to illustrate phase displacement of the pulses of a Wiegand wire, with the field following a sinusoidally fluctuating course; and Figure 4 is a diagram corresponding to that of Fig. 3, with movable magnetic field following a linear course.

In Fig. 1 a thyristor 5 is shown, having a resistance RL in its load circuit. A gate 6 and cathode 7 of the thyristor 5 are connected to a sensor winding 2 which encloses a Wiegand wire 1. Parallel to the Wiegand wire 1 is a bar-magnet 3 serving as a resetting magnet.

On the opposite side of the Wiegand wire 1 is a further, stronger bar magnet 4 which is also arranged parallel to the Wiegand wire 1 but is of opposite magnetisation from the resetting magnet 3. The bar-magnet 4 is mounted on the rod of a piston 8 which is displaceable in direction of the arrow 9. The piston 8 can be operated, for example, by a movable machine part.

On moving the magnet 4 towards the Wiegand wire as far as a predetermined threshold value, there is produced in the sensor winding 2 a Wiegand pulse which ignites the thyristor 5. When the magnet 4 is withdrawn, the Wiegand wire is returned by the resetting magnet 3 and is then ready for further release of an ignition pulse.

The embodiment of Fig. 2 coincides with that of Fig. 1, except that a D.C. winding 11 is also provided which is connected to an adjustable D.C. source 1 2 and produces at the position of the Wiegand wire 1 a static or quasi-static magnetic field which is superimposea upon the field of the magnet 4. Additionally, the resetting magnet 3 is no longer present, since its function has been taken over by the D.C. winding 11. Alternatively, it would be quite possible to transfer the function of the D.C. winding 11 to the resetting magnet 3, for which purpose said magnet 3 would require to be able to alter its position relative to the Wiegand wire 1, or its coupling with the Wiegand wire 1 would have to be adjustable by means of a movable ferromagnetic tongue or the like.

Figs. 3 and 4 illustrate the process of phase displacement of Wiegand pulses 10 from an example of asymmetrical excitation of the Wiegand wire 1.

In Fig. 3 it is assumed that the strength of the magnetic field produced by the magnet 4 fluctuates sinusoidally at the position of the Wiegand wire 1, e.g. as a result of a crank drive acting on the piston 8 in direction of the arrow 9 which moves the piston sinusoidally to-and-fro according to the formula: (I) S = SO . sin xt, where S is the displacement of the piston 8 around a central position, SO is the amplitude of this displacement, U is the cycle frequency of the crank drive and t is time.In order to obtain fluctuation of the magnetic field of the magnet 4 at the place of the Wiegand wire 1 with the said frequency according to: (II) H = Who . sinxt where H is the field strength of the magnet 4 at the place of the Wiegand wire 1, and Ho is the amplitude of this field strength, the magnetic field of the magnet 4 must possess a constant gradient of field strength in the direction of the Wiegand wire 1 (direction of the arrow 9), that is to say, must be spatially linear. Means for linerarisation of the course of field strength belong to the prior state of the art and do not require to be further discussed here.

The static magnetic field of the D.C. winding 11 is superimposed upon the field H and possesses at the position of the Wiegand wire 1 the strength H=, whilst being oppositely directed to the magnetic field of the magnet 4. The resulting magnetic field at the position of the Wiegand wire 1 is then: (111) H = H0. sinwt - H ~ The production of a Wiegand pulse occurs invariably with field strength: (IV) H=Hz, which is referred to hereinafter also as actuation field strength Hz.The corresponding phase position a'tz = (pz of the Wiegand pulse 10 is obtained by combining (III) and (IV), to give:

In place of a magnet 4, movable in linear fashion, for producing the pulsating magnetic field, in many cases, a rotating magnet can be employed with advantage, which is moved periodically towards the Wiegand wire 1 as a result of the rotation.

In Fig. 4 it is assumed that the magnetic field of the permanent magnet 4 is changed at the place of the Wiegand wire 1 in timelinear fashion, at least within a certain framework. This can be achieved if the spatial course of the magnetic field is linearised in the area between the magnet 4 and the Wiegand wire 1, and the magnet 4 is moved uniformly at least over part of its path. In this linearised area between the phases wt, and cot2 (Fig. 4) the field of the magnet 4 possesses at the place of the Wiegand wire 1 a time course according to:

where HLO and H, are constant.

By superimposing with the magnetic direct field of strength H=, which is produced by the D.C. winding 11 and is oppositely directed to the field of the magnet 4, the resulting magnetic field in the area between the phase angles (Pi = w.t, and 92= = co.t2 becomes:

The production of a Wiegand pulse 10 occurs following (IV) constantly with H = so that, for the corresponding phase position: = = .tz the linear expression

is obtained. The alteration of the phase position of the Wiegand pulses 10 is therefore, in the area between zp, and zP2, proportional to the field strength H= of the static magnetic field and thus proportional to the current strength of the direct current exciting the winding 11.

Instead of producing the direct field H= by a winding 4, it is also possible to produce it by the permanent magnet 3 (Fig. 1) and to change its strength by moving it more or less close to the Wiegand wire 1.

Accruing to the invention therefore, by means of a compact, robust and inexpensive structural unit, it is possible to achieve the production and also the phase displacement of pulses which are immediately suitable for the ignition of thyristors and the like. A notable advantage in the case of the invention is that not only the production of pulses but also the phase displacement is carried out without any electrical voltage source.

Claims (11)

1. A switching arrangement for the ignition of thyristors, triacs or like components, in which a voltage pulse is induced in an electrical winding coupled magnetically with a ferromagnetic core, which pulse is further employed as an ignition pulse, characterised in that said ferromagnetic core is a bistable magnetic element (hereinafter referred to as BME), and that means are provided for the production of a magnetic field at the position of the BME which is governed by the position of a movable member and is reversible in direction.

2. A switching arrangement according to Claim 1 in which the BME is placed in a magnetic field with a spatial zero-crossing and is displaceable relative to the magnetic field in the direction of the field strength gradient.

3. A switching arrangement according to Claim 1, in which the BME is placed in a magnetic field which is created by superimposition of a stationary (in relation to the particular position of the BME) magnetic field and of a movable magnetic field which is directed opposite to the stationary field.

4. A switching arrangement according to Claim 3, in which the stationary magnetic field is the field of a current-carrying winding which co-operates with the BME.

5. A switching arrangement according to Claim 4, in which the current-carrying winding is placed around the BME.

6. A switching arrangement according to Claim 3, in which the stationary magnetic field is the field of a permanent magnet arranged near the BME.

7. A switching arrangement according to any one of the foregoing claims, in which the magnetic field governed by the movable member is provided by a permanent magnet or an arrangement of permanent magnets.

8. A switching arrangement according to Claim 7, in which the movable member is a permanent magnet or an arrangement of permanent magnets.

9. A switching arrangement according to Claim 7, in which the movable member is of ferromagnetic material and is moved within the magnetic field created by one or more stationary permanent magnets.

10. A switching arrangement according to any one of the foregoing claims, in which the BME is a Wiegand wire.

11. A switching arrangement according to any one of the foregoing claims, in which a sensor winding surrounds the BME.

1 2. A switching arrangement according to Claim 4, in which the current-carrying winding is connected to a variable D.C. source.

1 3. A switching arrangement according to Claim 1, in which the means for creating the magnetic field are two permanent magnets or arrangements of permanent magnets, which are displaceable independently of each other relative to the BME or can be influenced by ferromagnetic objects which are displaceable independently of each other.

1 4. A switching arrangement according to Claim 1 2 or 13, in which the magnetic field at the position of the BME is formed by superimposing the magnetic fields of a rotating permanent magnet and a permanent magnet moved in linear fashion.

1 5. A switching arrangement for the ignition of thyristors, triacs and like components, substantially as hereinbefore described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.