GB2087172A

GB2087172A - Contactless alternating current relay

Info

Publication number: GB2087172A
Application number: GB8132931A
Authority: GB
Original assignee: Licentia Patent Verwaltungs GmbH; Licentia Oy
Current assignee: Licentia Patent Verwaltungs GmbH; Licentia Oy
Priority date: 1980-11-03
Filing date: 1981-11-02
Publication date: 1982-05-19
Also published as: GB2087172B; FR2493639A1; FR2493639B1; DE3041280C1

Abstract

The relay has a setting element St comprising two parallel push-pull thyristors 11,12 and a control circuit 15, said control circuit having a rectifier bridge D1-D4 in which the control paths of the thyristors 11,12 lie along the a.c. diagonal A,A' of the bridge and a control thyristor 16 which switches the control current lies along the d.c. diagonal, a transistor amplifier with a phototransistor Ph connected to the control input of thyristor 16 and also having a light generating control signal generator 19 from which the phototransistor receives light signals which are used to control the thyristor 16 and the setting element thyristors 11,12 to connect, at a zero axis crossing, an operating voltage into a load 14. The two a.c. connections A,A' of the rectifier bridge are connected to the operating voltage via the control paths of the setting element thyristors 11,12 and the control signal generator 19 is energised by a pulse generator 2, which emits continuous pulses I, which last for a whole number of full periods of the operating voltage u depending on a continuous control signal Ust. The relay may be used for single-phase operation, Figure 1, or for the three-phase operation (Figure 2 not shown) e.g. as an economising circuit. <IMAGE>

Description

SPECIFICATION Contactless alternating current relay The invention relates to a contactless alternating current relay and more particularly to a relay comprising a thyristor setting element with a parallel push-pull circuit to two thyristors series-connected with a load and an alternating voltage source, and also comprising a control circuit associated with the two thyristors.

Alternating current relays of this type are designated as "solid-state relays", which is shortened to SSR, and are also known as "electronic load relays" (ELR).

A contact-free a.c. relay designated as a solid-state relay and also comprising a thyristor setting element and its associated control circuit is known from German Auslegeschrift No. 22 52423. The known a.c. relay is in the open relay condition when the phototransistor of the control circuit does not receive a light signal from the light-producing control signal generator. A control voltage cannot then reach the control input of the control thyristor. If on the other hand a light signal is emitted by the electrically energised control signal generator to the phototransistor, then while the alternating voltage of the output source is sufficiently small - i.e. only during the zero axis crossings of the alternating voltage - a control voltage can be applied to the control input of the control thyristor.The control circuit is equipped with special means for this purpose which allow sufficiently high ignition currents to pass to the thyristors of the thyristor setting element during the zero axis crossings. The control signal generator is separated from the control circuit and the thyristor setting element in terms of potential by the optical signal transmission. The control circuit also requires in the rectifier bridge circuit the two conventional connections for the alternating voltage of the output source and current limiting means for the said ignition current.

On the other hand a single-phase thyristor setting element of the type stated at the outset is known for example from AEG-Telefunken printed document entitled: "Leistu ngsstel ler THYROTAKT THYR- OVAR", 1979 edition, No./31.15.105/0280, page 12 et seq. The thyristor setting element has a control device by means of which it is so controlled in accordance with a continuous signal from a controllervia an input network, a comparator and a control logic unit with the aid of a pulse generator that it switches and operates in accordance with the socalled principle of full oscillation beat.As a result the thyristor setting element can also be triggered during a zero-axis crossing of the alternating voltage of the output source if a control signal is fed into the control device and is kept triggered in each case for a whole number of full periods of the alternating voltage (as a function of the signal).

The control device is part of a control circuit, for example for controlling temperature. The control circuit can be further improved by adding into the control device if desired a low frequency voltage control or output control so that it is possible firstly to directly control fluctuations in the alternating voltage of the power source, whilst avoiding a slow response temperature control circuit, and secondly to directly control the produuct of the load voltage and the load current.

An object of the present invention is to create a contactless alternating current relay operating as a zero voltage switch and having a thyristor setting element and a control circuit which is without any special additional means and receives optically transmitted control signals through which the thyristor setting element can be switched by using a control device having the features indicated above in accordance with the full oscillation beat principle.

According to the present invention there is provided a contactless alternating current relay comprising a thyristor circuit, a control circuit for the thyristor circuit and optical control signal generating means, the thyristor circuit comprising an antipara llel pair of thyristors arranged to be connected in series with a load and an a.c. source and the control circuit comprising a single phase rectifying circuit, the alternating voltage connections of the rectifying circuit each being connected to the control electrode of a respective one of the thyristors, and the direct voltage connections of the rectifying circuit being interconnected by a further thyristor, the control electrode of said furtherthyristor being operatively connected to light detecting means which is arranged to receive optical control signals from said control signal generating means, the control signal generating means generating pulse signals which begin at a zero axis crossing of the alternating voltage of the source and which last for one or more whole periods of the a.c. source.

Preferably the optical control signal generating means is electrically connected to a pulse generator which is arranged to be synchronised with the a.c.

source, and/or the output of the optical control signal generating means varies with a continuously predetermined further control signal.

In a preferred embodiment a transistor amplifier is connected to the control electrode of said further thyristor, the amplifier, or a first stage thereof, comprising a phototransistor which consitutes said light detecting means.

A relay for three-phase current application may comprise two thyristor circuits and two respective control circuits, each thyristor circuit being arranged to be connected in series with a respective load phase and a respective phase of a three-phase source. In this case the two optical control signal generating means are jointly electrically energised and either are in series connection or are connected in parallel via respective matching resistors. The two optical signal generating means may be jointly electrically energized by a single pulse generator which is synchronised with a voltage of the source.A contact-free alternating current relay according to the present invention may be used as a static setting element, in an economising circuitforthree-phase current, said element comprising two thyristor setting elements and two associated control circuits which are series-connected in each case with a load phase and one phase of a three-phase voltage source, the two light-generating control signal generators of two control circuits being electrically energised jointly by means of a pulsed generator which is synchronised by a linked voltage of the source.

Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings of which: Figure 1 shows the circuit of a contact-free singlephase alternating current relay controlled by a control device for thyristor setting elements, and in accordance with a first embodiment of the preset invention; Figure 2 shows a block circuit diagram of a contact-free three-phase alternating current relay with a control device for thyristor setting elements, and in accordance with a second embodiment of the present invention; and Figure 3 shows voltage/time diagrams and a time diagram for the control signal for the alternating current relay shown in Figure 2.

Referring now to the drawings, a control device 2 is associated with the alternating current relays of Figures 1 and 2 and the thyristor setting elements St, of the alternating current relays. In the embodiment of Figure 1 the elements St comprises two parallel push-pull thyristors 11 and 12 which are controlled by the control device 2 with the aid of control signals so that they switch according to the full oscillation beat principle. This control device is known and its components and functions are described in the introduction above. In Figure 1 the control device is shown as a block circuit diagram in which an input network is designated 21, a control voltage Ust being supplied to the said input network by means of a temperature controller (not shown) and a comparator is designated 22, a control logic unit 23, and a pulse generator 24.Switching the thyristor setting element St on and off is made dependent on two conjunctively linked criteria by the control logic unit 23 with the aid of the pulse generator 24. The store of the control logic unit can only be set when the comparator provides a signal and a pulse is produced by a synchronising device 25, said pulse being emitted at the positive zero axis crossing of the alternating voltage u of the power source 13. The control device 2 also contains a supply rectifier G and two detecting elements 26,27 for the voltage at the load 14 and the load current and is also equipped in Figure 1 with a multi-vibrator 28 and a converter modulator 29 for low frequency output control.The modulator 29 carries out so-called time division modulation in which the rectified load voltage is scan modulated in dependence upon the instan taneousvalues of the rectified load current so that the current-modulated rectified value of the load voltage is proportional to the effective output at the load.

A light-emitting diode LED is energised electrically by the pulse generator 24 and constitutes a lightgenerating control signal generator 19 lying in the output current circuit of the pulse generator of the control device. A continuous pulse I is produced by the control device via the pulse generator as soon as a sufficiently large control pulse Ust is supplied to the input network 21. If there is a voltage at the load 14 the network 21 is recharged via 26. The permanent pulse and therefore the period of time during which the thyristor setting element carries current lasts at least one period of the alternating voltage u. This is the case if Ust does not remain sufficiently large within the first period of u.In this case, the pulse generator is given a switch off comman via the control logic unit, said switch off command being produced by a second synchronising device 25' at the negative zero axis crossing at the end of the first half period. If, on the other hand, Ust is only sufficiently large for the nth period of u then the permanent pulse and the period for which current is carried are a whole number n of periods (full oscillations) of the alternating voltage u.

The continuous pulse I is transmitted from the pulse generator 24 to the thyristor setting element St as a light control signal between the diode LED and the input of a control circuit which is arranged directly in front of the thyristor setting element. The control circuit comprises a Graetz rectifier bridge circuit 15 with full rectifier diode D1 to D4 and a control thyristor 16 along the d.c. diagonal. The two alternating current inputs A, A' of the bridge circuit are connected as shown to the control electrodes of the thyristors 11, 12 of the thyristor setting element and are connected to the alternating voltage u via the control paths of the thyristors.The control circuit also contains an amplifier 17 comprising two transistor stages, the output of the said amplifier 17 being connected to the control electrode of the control thyristor. The input stage of the amplifier contains a phototransistor Ph, which receives the light control signal from the control signal generator 19. The transistor T of the output stage is in parallel with the control path of the thyristor 16 and the photo transistor is in parallel with the control path of the transistor T. The amplifier circuit and its use of the signal amplifier are known per se. The control thyristor 16 is only triggered when a control signal from the control device is transmitted to the control circuit.The thyristor 16 then acts as a closed control contact by means of which the control circuit of the thyristor setting element is connected to the alternating voltage u. Thus a control current is switched on, said control current flowing out of the power source 13, through the control path of the blocking thyristor of the thyristor setting element to the control electrode of the thyristor which is under load by u in the forward direction and which switches the said thyristor on. Thyristor 12 is blocked in Figure 1 for example and thyristor 11 is switched on when the alternating current relay is biased more positively by the alternating voltage at the upper current connection than at the lower current connection.

Control signals, which being in each case at a positive zero axis crossing of the alternating voltage u, are produced by means of the control device in dependence upon the existence of a control voltage Ust. Thus the thyristor setting element of the alternating current relay is triggered as a zero voltage switch with the aid of the said control device. A two-stage amplifier with a phototransistor Ph, which receives the light control signal from the signal generator 19, serves as the control circuit of the thyristor setting element at the input side, and has the function of reconverting the light control signals into voltage signals and amplifying them for triggering the control thyristor 16.The control circuit also has the special feature mentioned above according to which its rectifier bridge circuit 16 does not require any direct connection to the alternating voltage u nor any safety resistors in the control circuits on the alternating current side.

In Figure 2 there is shown a second embodiment of the present invention in the form of a contact-free three-phase relay. This three-phase relay, assembled as an economising circuit, comprises two relays IR, IT according to Figure 1 which are in the two phase lines from R and T of a three-phase voltage/output source. The relays IR, IT are each arranged in a series connection with the phase voltage source 1 3R or 1 3T and a phase load 14R or 14T. The relays are shown in the form of two blocks. A control device 2 according to Figure 1 is associated with the two relays said control device 2 also being shown as a block, to which a control voltage U5t is fed.Two LED's are arranged in series connection as light-emitting control signal generators 19 of the control circuit of the two alternating current relays 1 R, 1T in the output circuit of the pulse generator 24 of the control device 2 and also form an economising circuit. The action and mode of switching of the three-phase current relay is apparent from diagrams c) toe) in Figure 3, in which the time curvves of the three-phase load voltages UR, US, UT are shown. A continuous pulse I and consequently a control signal s are emitted which last exactly one period, (see diagram b)). In diagram a) the time curve of the three phase voltages R, S, T of the three-phase voltage/output source 13R, 13S, 13T is shown.

The control signals begins at the point in time to 30O el. The alternating current relay 1 R is switched on (closed) first of all at the point in time to - 30 el and the (linked) voltage between R and S has a positive zero axis crossing. Then the relay 1T is connected up as the second and last at the point in time to + 60 el, in which the phase voltage of T has a negative zero axis crossing and the potential of the centre point M (star connection point) is approximately 0. After the end of the control signal sat time (to + 3300 el) the relay 1 R is first switched off (opened) at the point in time to + 360" el when the phase voltage R has the next zero axis crossing.At the point in time to + 450" el, the relay 1T, is switched off and the (linked) voltage between T and S becomes zero for the first time after the end offs. In the example taken here (see diagram c) to e) of Figure 3 the three-phase load voltages are passed in each case for only approximately a full period to the phase load with the aid of the three-phase current relay and therefore the phase load voltages are not exactly sinusoidal. The deviation from a sinusoidal shape can be seen by the sinusoidal curve indicated in non-contunuous lines in the relevant diagrams for each phase load voltage.

Thus the above described arrangements each provide a combination of a contact-free alternating current relay of known type, but a different control circuit, and with a control device which is also known in which the two functions mentioned are provided unrestrictedly in combination and advantageously cooperate.

Claims

1. A contactless alternating current relay comprising a thyristor circuit, a control circuit for a thyristor circuit and optical control signal generating means, the thyristor circuit comprising an antipara llel pair of thyristors arranged to be connected in series with a load and an a.c. source and the control circuit comprising a single phase rectifying circuit, the alternating voltage connections of the rectifying circuit each being connected to the control electrode of a respective one of the thyristors, and the direct voltage connections of the rectifying circuit being interconnected by a further thyristor, the control electrode of said further thyristor being operatively connected to light detecting means which is arranged to receive optical control signals from said control signal generating means, the control signal generating meanns generating pulse signals which begin at a zero axis crossing of the alternating voltage of the source and which last for one or more whole periods of the a.c. source.

2. A relay according to claim 1 wherein the optical control signal generating means is electrically connected to a pulse generator which is arranged to be synchronised with the a.c. source.

3. A relay according to claim 1 or 2, wherein the output of the optical control signal generating means varies with a continuously predetermined further control signal.

4. A relay according to any preceding claim, wherein a transistor amplifier is connected to the control electrode of said further thyristor, the amplifier, or a first stage thereof, comprising a phototran sistorwhich constitutes said light detecting means.

5. A relay according to any preceding claim for three-phase current application, comprising two said thyristors circuits and two respective said control circuits, each thyristor circuit being arranged to be connected in series with a respective load phase and a respective phase of a three-phase source, wherein the two optical control signal generating means are in series connection and are jointly electrically energised.

6. A relay according to any of claims 1 to 4 for three-phase current application, comprising two said thyristor circuits and two respective said control circuits, each thyristor circuit being arranged to be connected in series with a respective load phase and a respective phase of a three-phase source, wherein the two optical control signal generating means are jointly electrically energised and are connected in parallel via respective matching resistors.

7. A relay according to claim 5 or 6, wherein the two optical control signal generating means are jointly electrically energised by a single pulse generator which is synchronised with a voltage of the source.

8. An economising circuit comprising a static setting element constituted by a three-phase current relay according to any of claims 5 to 7.

9. A contactless alternating current relay substantially as herein described with reference to Figure 1 or Figures 2 and 3 of the accompanying drawings.