FR2566208A1 - Electronic switch - Google Patents

Abstract

Electronic switch for power loads. Electronic switch including, placed in series with a load 1, a thyristor 2 and a choke 4 placed in parallel with a block 5 for forced blocking of the thyristor 2. One terminal of the choke 4 is wired to an electrode of a valve 6 and the other terminal via a second thyristor 7 is connected electrically to another electrode of the valve 6 and to one pole of a supply source 3. To a common point 9 of the valve 6 and thyristor 7 is wired an energy store 8 accumulating electrical energy and also wired to the electrode of a valve 10 and to the other pole of the source 3 connected electrically to the thyristor 2. The other electrode of the valve 10 is wired to a common point 11 of the choke 4 and thyristor 7. The triggers of the thyristors 2, 7 and the block 5 for forced blocking are wired to the outputs 17, 18, 19 of a control block 16. Application to the supply to lasers.

Description

 The invention relates to pulse and conversion techniques, and more particularly to an electronic switch intended for switching powerful loads and used essentially in power converters and in laser power sources.

 Among the devices for switching powerful loads, the most attractive are the assemblies of forced block thyristor switches of the series type, the blocking being carried out using a pulse coming from a blocking circuit applied to self series with thyristor, load and power source.

 In these arrangements, provision must be made for the elimination or reduction of excess energy which accumulates in the inductor when the charge current passes and which remains there after the thyristor is blocked. In the absence of means for evacuating energy, the voltage on the elements of the switch increases with each operating cycle, which can lead to the switch failing and the efficiency to be reduced.

There is an electronic switch (cf. for example
Juice. Zabrodin C "Forced thyristor capacitor switching assemblies". M., ed. "Energia", 1977 it p. 82, Figures 2 to 15) in which the excess energy is dissipated using a transformer connected to a choke by means of valves.

The use of a transformer only partially meets the requirements for reducing over-voltages and increasing efficiency. The use of a transformer with a high transformation ratio decreases the overvoltages but also the efficiency, and vice versa, with a low transformation ratio the efficiency increases but the overvoltages increase. In addition, the transformer must be designed in such a way as to present the dissipation inductances and the minimum stray capacitances while transmitting long and powerful pulses. This significantly complicates the organization of the transformer and the electronic switch as a whole.

 There is also an electronic switch with dissipation of excess energy without a transformer (cf., for example, Ju.S. Zabrodin Fractional switching sets with thyristor capacitor ". M., ed." Energia ", 1977.0 p. 83, Figures 2 to 16.) The electronic switch comprises, put in series with the load, a thyristor, electrically connected to a pole of the power source, and a choke, which is put in parallel with a circuit of forced blocking of the thyristor, one terminal of which is electrically connected to the thyristor, is connected to one electrode of a valve and the other terminal is electrically connected to the other electrode of the same valve and to the other pole of the source d It also includes a control block whose outputs are connected to the thyristor control electrode (trigger) and to the forced thyristor blocking circuit. This electronic switch uses as a valve a diode mounted in parallel with the self.

 When the first control pulse from the control block arrives, the thyristor becomes conductive, current begins to flow through the load and the self accumulates energy. The second control pulse received from the control block operates the forced blocking circuit, the thyristor is blocked, the current no longer flows in the load. In this case, the energy accumulated in the inductor is dissipated in the form of heat thanks to the diode dissipation circuit.

 The installation of this electronic switch is simpler than the transformer installation. Overvoltages on the choke and other mounting elements are at a minimum level due to the low voltage drops existing on a conductive diode during the dissipation of excess energy. However, it is clear that the energy dissipated on the diode cannot be used later, which means that the switch has a low efficiency.

 In addition, this electronic switch is characterized by a low frequency of working cycles at switching because the evacuation of excess energy from the inductor on the low resistance of the diode is relatively long due to a large constant of time due to the inductance of the inductor and the resistance of the diode. The increase in the frequency of the operating cycles by a reduction in the time constant obtained by the insertion of an auxiliary resistance put in series with the diode causes an overvoltage on the elements of the assembly because of the additional voltage drop in resistance, which is not acceptable and moreover does not increase the efficiency of the installation.

 The invention relates to an electronic switch provided with a circuit for dissipating the excess energy accumulated in the choke making it possible to use this excess energy to supply the load while ensuring the minimum level of over-voltage on the elements of the electronic switch.

 The electronic switch according to the invention comprises a power source, a load, a thyristor and a choke with which a thyristor blocking circuit is put in parallel and one terminal of which, electrically connected to the thyristor, is connected to an electrode d a valve, the other terminal of this choke being electrically connected to the other electrode of this valve and to the other pole of the power source; a control block, the outputs of which are connected respectively to the thyristor control electrode (trigger) and to the thyristor forced blocking circuit; an auxiliary thyristor interposed between the power source and that of the points common to the choke and blockage which is closest to the power source; an auxiliary valve, an electrode of which is connected to the point common to the auxiliary thyristor and to the choke; and an electrical energy storage connected to the other electrode of the auxiliary valve, to the point common to the main valve and to the auxiliary thyristor and to the pole of the power source electrically connected to the main thyristor.

 It is useful to insert at least one controlled valve in the electrical switch, connected by its control electrode to another additional, auxiliary output of the control block.

 The electronic switch proposed has a high efficiency because the evacuation of excess energy from the inductor is done through the valves in the electrical energy storage device from where it is, simultaneously with the energy of the source. applied to the load during the following switching cycles. The electronic switch ensures a low level of overvoltages on its elements because, during the elimination of excess energy from the inductor, the conducting valves prevent an increase in the voltage on said inductor greater than the value necessary for the operation of the device. In addition, the electronic switch is characterized by a high switching rate because the duration of the evacuation of energy from the inductor in the storage is done quickly.

 The electronic switch can use both a power source of the "current source" type and a voltage source (in the case where the valves are made in the form of thyristors).

The invention will emerge from the description which follows of concrete examples of its execution shown diagrammatically in the appended drawings, in which:
- Figure 1 shows an electrical circuit diagram of the electronic switch according to the invention;
- Figure 2 shows the same diagram as in Figure 1, but with thyristors playing the role of valves.

 The electronic switch comprises, placed in series with a load 1 (FIG. 1), a thyristor 2 electrically connected to a pole of a power source 3 and to a choke 4. In the variant described, the thyristor 2 is directly connected by its cathode on a terminal of the choke 4 and is electrically connected through the load 1 to the pole (+) of the source 3.

 The inductor 4 is put in parallel with a block 5 for forced blocking of the thyristor 2. The terminal of the inductor 4 connected to the cathode of the thyristor 2 is connected to an electrode of a valve 6, (in the following: on the cathode of diode 6), and the other terminal of inductor 4 is connected to a cathode of a thyristor 7, (in the variant described on its anode). The cathode of thyristor 7 is connected to the pole (-) of the power source 3. The anode of diode 6 is connected to the cathode of thyristor 7.

 The electronic switch also includes a storage means 8 for electrical energy, the pole (-) of which is connected to a point 9 common to the diode 6 and to the thyristor 7. The pole (+) of the energy storage 8 is connected to an electrode of a second valve (in the following on the cathode of a diode 10) and on the pole (+) of the power source 3. The anode of the diode 10 is connected to the common point 11 at the anode of the thyristor 7 and at the inductor 4. As energy storage 8, it is possible to use a capacitor or a battery of capacitors.

 One of the alternative embodiments of the forced blocking block 5 shown in FIG. 1 comprises a capacitor 12, one of the armatures of which is connected to the anode of a thyristor 13 and to the cathode of a diode 14. The cathode of the thyristor 13 is connected to the anode of the diode 14 and to the terminal of the inductor 4 connected to the cathode of the thyristor 2. The other armature of the capacitor 12 is connected to the point 11 common to the anode of the thyristor 7 and the self 4.

 The initial charge of the capacitor 12 is done from the power source 30, having terminals (+) and (-) through a choke 15.

 The electronic switch also includes a control block 16, a first output 17 of which is connected to the control electrode (trigger) of thyristor 2, a second output 18, to the control electrode (trigger) of thyristor 7 and a third output 19, on the control electrode (trigger) of the thyristor 13 of the block 5 of forced blocking. The outputs 17, 18 are outputs of a pulse generator 20, another output of which is connected to the input of a delay circuit 21.

 The described connection of thyristors 2, 7 and diodes 6, 10 corresponds to the arrangement of the poles of the power source 3. The change in the polarity of this source 3 causes the corresponding change in the connection of these thyristors and diodes.

 Another alternative embodiment of the electronic switch, similar to that described above, is possible.

The difference lies in the fact that in the mounting of the electronic switch are used respectively, instead of diodes 6 and 10, thyristors 22 (FIG. 2) and 23. The control electrodes (trigger) of thyristors 22, 23 are connected to outputs 24, 25 of the control unit 16. The outputs 24, 25 are outputs of a delay circuit 26, analogous to circuit 21 and connected to an output of this circuit 21.

 In addition, in the variant in question, the thyristor 2 is directly connected by its anode to the pole (+) of the source 3, which does not practically affect the operation of the switch.

 The electronic switch operates as follows.

 In the initial state, the thyristors 2 (FIG. 1), 7, 13 and the diodes 6, 10, 14 are not conductive, the energy storage 8 is loaded from the power source 3 to a voltage U1 with the polarity indicated without parentheses in Figure 1; the capacitor 12 is charged with the polarity indicated in FIG. 1 up to a voltage U2 which, in general, is not necessarily equal to U 1 ', the charge being made from the current source via the inductor 15.

 The pulses emitted on the outputs 17, 18 of the control block 16, which are produced simultaneously by the pulse generator 20, attack the control electrodes (trigger) of the thyristors 2, 7. At the same time, the generator 20 activates the delay circuit 21 operates. The thyristors 2 and 7 begin to drive and the load 1 receives energy from the power source 3 and from the energy storage 8. In this case, the current flows through the circuit: power source 3 (and energy storage 8) - load 1 - thyristor 2 - self 4 thyristor 7 - power source 3 (and energy storage 8). As the power source 3 has a decreasing characteristic (not rigid) due to its internal resistance (as a rule, reactive) and the energy storage has a limited capacity, the voltage across their terminals decreases.

 When this voltage becomes lower than the voltage across the capacitor 12, at time t1, the output 19 of the control block 16 emits a pulse produced by the delay circuit 21. This pulse attacks the thyristor control electrode 13 and unlocks it. Through the thyristor 13, the voltage U2 of the capacitor 12 is applied to the inductor 4 (the polarity of the latter is indicated in FIG. 1). As the voltage U2 is greater than the voltage across the power source 3 (and of the accumulator 8) and that it is applied according to the opposite polarity to the thyristors 7 and 2, the latter are blocked; therefore the flow of current through load 1 ceases.

 When the thyristor 13 becomes conductive (at the moment) the capacitor 12 and the inductor 4 form an oscillating circuit. In this oscillating circuit, the capacitor 12 first discharges to zero (the current in the oscillating circuit is, at this time, maximum), then begins to recharge, but the voltage on its armatures has reverse polarity (in brackets in Figure 1).

The value of the voltage across the capacitor 12 then tends to considerably exceed the initial voltage
U2. This is explained by the fact that the initial energy accumulated in the capacitor 12 before the unlocking of the thyristor 13 is increased by the energy accumulated in the inductor 4 during the passage of the current from the load 1. This additional energy is superabundant if it is not dissipated, it causes overvoltages on the inductor 4, the capacitor 12 and on other elements. It must be kept in mind that the accumulation effect increases from cycle to cycle of operation of the electronic switch and this has harmful consequences.

 In the electronic switch described, the accumulation effect does not exist because the excess energy is evacuated in the energy storage 8. This is done as follows. As already said, the voltage across the capacitor 12 tends to exceed the initial value U2, but at the time when the voltage across the capacitor 12 tends to exceed the voltage across the energy storage 8, it remains at this level because diodes 6 and 10 become conductive. The thyristor 13 in this case is blocked because the current leaves the circuit where it is mounted and moves towards the circuit of the diodes 6 and 10.

 Through the diodes 6 and 10 which have become conductive, all the residual energy in the inductor 4 passes into the storage of energy 8, after which the diodes 6 and 10 are blocked and the capacitor 12 is discharged through the diode 14 which becomes conductive at this moment. During the oscillatory process, the capacitor 12 is recharged through the diode 14 and the inductor 4, the polarities at the terminals of the capacitor 12 returning to their initial directions indicated without parentheses in FIG. 1. At the end of the recharging of the capacitor 12, the diode 14 is blocked.

The charge of capacitor 12 to the initial level
U2 is done from the current source through the inductor 15. The rise in the voltage level to the initial value U1 across the power source 3 is done when charging storage 8 to from this source 3. In general, the storage charge 8 can take place immediately after the blocking of the thyristors 2 and 7.

 Thus, the electronic switch returns to the initial state. The next cycle of operation of the switch begins when the next pulse is sent to outputs 17 and 18 of control block 16. Then, the processes are repeated in the same manner already described.

 As can be seen from the description of the operation of the electronic switch, the excess energy accumulated in the inductor 4 after the blocking of the thyristors 2 and 7 is evacuated in the energy storage 8 and participates jointly with the energy originating from the source 3 to the energy supply of load 1 in the following work cycles. This ensures high energy efficiency of the electronic switch. it follows from the operating processes examined that the value of the voltage on the capacitor 12, the inductor 4 and on other elements connected to it does not exceed the initial value, which means that the harmful effect of the accumulation of l excess energy is absent and therefore overvoltages on the switch mounting elements are suppressed.

 In addition, it is clear that the energy is removed from the inductor 4 towards the energy storage 8, the terminal voltage of which differs from zero, which is why the time of the evacuation process is not not big. Hence the possibility of operating the electronic switch at a high rate.

 The operation of the electronic switch, according to the variant represented in FIG. 2, is identical to that described above. The difference lies in the fact that the accumulated energy is evacuated from the inductor 4 (FIG. 2) in the storage 8 after the unlocking of the thyristors 22, 23. The unlocking is done by means of the signals transmitted simultaneously on the outputs 24, 25 of the control block 16. These signals are delayed by the delay circuit 26 relative to the signal transmitted by the output 19 on the block 5 forced blocking.

 The value of the delay introduced by the circuit 26 is determined by the time necessary for the voltage at the shapes of the capacitor 12, with polarity indicated in FIG. 2 in brackets to reach a value exceeding the value of the voltage across the terminals by a prefixed quantity energy storage 8 (and power source 3).

For the rest, the operation of the switch is similar to that described above.

 In the variant of the electronic switch shown in FIG. 2, the voltage U2 across the terminals of the capacitor 12 can be chosen different, if necessary, by varying the delay controlled by the circuit 26.

In particular, the voltage U2 can be chosen such that it exceeds the voltage U1 at the terminals of the energy storage 8 and of the power source 3. In this case, the electronic switch fulfills its functions if as a power source 3 a source with a rigid characteristic, with low internal resistance is used, that is to say when a voltage source is used.

 it should also be noted that in the variant of the electronic switch shown in FIG. 2, the recharging of the capacitor 12 at each cycle is not compulsory because the voltage across the terminals of the capacitor 12 is a function of the moment when the thyristors 22, 23 become conductors, that is to say that it is adjustable and can be adjusted to a determined level which remains unchanged in the following cycles of operation.

Claims (2)

 1. Electronic switch which comprises, put in series with a load (1), a thyristor (2) electrically connected to a pole of a power source (3) and a choke (4) put in parallel with a block ( 5) forced blocking of the thyristor (2) and one terminal of which is electrically connected to the thyristor (2), is connected to an electrode of a valve (6) and the other terminal is electrically connected to the other electrode of. this valve (6) and to the other pole of the power source (3), said electronic switch being provided with a control block (16) whose outputs (17, 19) are respectively connected to the electrode control (trigger) ai thyristor (2) and on the block (5) for forced blocking of the thyristor (2) characterized in that it comprises on the one hand an auxiliary thyristor (7) connected by an electrode to the terminal of the choke (4) electrically connected to the pole of the power source (3), by the other electrode on this pole of the power source (3) and by the control electrode (trigger), on a auxiliary part (18) of the control unit (16), on the other hand an auxiliary valve (10) of which an electrode is connected to a common point (11) of the connection between the auxiliary thyristor (7) and the choke (4 ) finally an energy storage (8), accumulating electrical energy, connected to the other electrode of the auxiliary valve (10), on a point (9) common to the main valve (6 ) and the auxiliary thyristor (7) and on the pole of the power source (3) electrically connected to the main thyristor (2).  2. Electronic switch according to claim 1 characterized in that at least one of the valves (6, 10) is a thyristor (22, 23) whose control electrode (trigger) is connected to another auxiliary output (24, 25) of the control block (16) whose pulses received by the trigger can be delayed to adjust the value of the voltage across the energy storage terminals (8),