CH617549A5 - Electrical power converter - Google Patents

Abstract

The power converter supplies a load (22) from a supply voltage source (20). It includes power switches (55, 56, 57, 58) controlled by a control device (37, 40, 43) in such a way that two switches connected to opposite terminals of the supply voltage source and to two different output conductors (23, 24) are simultaneously conducting at moments such that the current supplying the load has at each instant a requisite polarity independent of the polarity of the supply voltage source. <IMAGE>

Description

The present invention relates to a power converter for transferring electrical energy to a load independently of the polarity of a supply voltage applied to the converter via two conductors 1 (1 of line.

Many studies have been carried out recently with regard to the use of induction machines or asynchronous machines in relation to a static tcr ^ f-rttor. It has been found that a circuit similar to that of a static converter can be connected to the output conductors of an induction machine and, when the machine is driven as a generator, the converter or inverter acts as switching device to recycle or redirect reactive energy from one phase winding to another of the induction machine.

Thus, this switching device replaces the separate machine for excitation or the bank of capacitors previously used. After this first step, it has been found that the switching frequency of the thyristors in the converter circuit can be modulated in relation to the reference frequency or synchronous frequency at which the induction machine is actuated to supply an output voltage. alternative (with a continuous component). By implementing this modulated induction generator device, it has been found that the machine is out of adjustment because, when the device is modulated, the effective alternative square wave output voltage is about half of that supplied by the machine. .

It is known that an induction machine can be driven 55 as a generator and, instead of a capacitor bank or a separate machine, a converter can be connected to the terminals of the induction generator to circulate reactive energy. Such a device is described in US Patent No. 3,829,758. Then, it was discovered that the switching frequency of the converter itself can be modulated above and below the synchronous frequency of the machine to produce an AC output voltage which is a function of the input voltage. modulating.

Figures 1 to 5 of the accompanying drawing illustrate such a device, 5 of modulated induction generator and its operating mode. The assembly represented in FIG. 1 constitutes a single-phase circuit supplied by an induction machine 20 driven by a shaft 21, for supplying electrical energy to a load 22. A bridge converter comprises conductors 23 and 24 and thyristors 25, 26, 27 and 28. Diodes 30, 31, 32 and 33 are connected as shown so as to be conductive and provide a path for reactive energy when the adjacent thyristor is cut. That is to say that, if the thyristor 25 is conductive and transmits a current to the load, following the switching of this thyristor (by a circuit not shown but well known), the reactive load current flows initially via the diode 30. Such an operation is also well known. An output filtering capacitor 34 is connected between the conductors 23 and 24; the load 22 which includes a resistive component 35 and an inductive component 36 is connected between the same conductors. A logic circuit 37 is arranged to supply separate trigger signals on these four individual output conductors to the thyristors 25 to 28, as a function of synchronization signals received via a line 38 from an oscillator circuit 40 Of course, each single output line from the logic circuit can represent two lines to apply the signal between the trigger and the cathode of each thyristor.

Other switches such as power transistors, thyratrons, ignitrons, or other switching elements can also be used. The oscillator 40 receives a modulation signal designated by the reference 41 via a line 42 coming from a modulator circuit 43. A starting circuit comprising a switch 44 and a battery 45 is provided in the cases where necessary during the start-up of the device.

The frequency of the modulating signal 41 is kept constant at a certain desired value. The modulation signal is used to modify the switching frequency of the converter, above and below a certain average frequency. The frequency of the variation is equal to that of the modulating frequency, and the amplitude of the frequency variation is proportional to the amplitude of the modulating signal. Thus, the output voltage of the generator is caused to establish and decrease as shown in FIG. 2. The output voltage across the terminals of the converter is that shown in FIG. 3. To obtain an AC voltage without DC level, the DC component must be removed by other means, usually by a high value capacitor.

Another drawback of the device described is that the use of the generator is rather ineffective. For example, FIG. 4 represents the unfiltered output voltage at the terminals of the converter when the latter is used in connection with an induction generator whose output voltage is supposed to be a square wave of amplitude E. After deletion of the DC component, the output voltage appears as shown in Figure 5. Thus, the amplitude of the square wave is reduced to E / 2. If a resistive load letting a current I was provided from a generator acting as a normal generator, then a square wave of current would flow and an output power El would result. When the generator is used in the modulating device, the output current and the generator current are identical. Thus, the current I flowing from the terminals of the generator would flow in the load but, since, as indicated in Figure 5, the output voltage is E / 2, a decrease in the AC output power by a ratio from 2 to 1 occurs. This misalignment, leading to less efficient use of the generator, is inherent when the modulation device uses a conventional converter, which must be supplied with a voltage of a single polarity.

The main object of the present invention is to provide a power converter which can be used in particular in

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connection with an induction generator, and making it possible to supply a load with a current of a desired polarity whatever the polarity of the supply voltage.

To this end, the power converter according to the invention has the characters listed in the characteristic part of claim 1.

The invention further aims to use such a converter in a device comprising a modulated induction generator, according to claim 14. In such use according to the invention, the efficiency is significantly increased, that is to say the 'a better use of the power supplied by the generator is obtained.

The AC output voltage can be free from the usual DC component.

The converter according to the invention also makes it possible to carry out an alternative-to-alternative power conversion.

Other advantages of the present invention will emerge from the following description of particular embodiments, given in relation to the appended drawing in which:

FIG. 6 is a simplified diagram of a circuit comprising the converter according to the invention, supplied by an alternating voltage;

FIG. 7A is a diagram partially in the form of blocks of a circuit comprising an induction generator similar to the circuit of FIG. 1 but comprising a converter according to the invention;

Figure 7B is a graphical representation useful for understanding the operation of the device of Figure 7A;

FIG. 8 is a simplified diagram of a branch of a converter according to the invention comprising thyristors mounted in anti-parallel;

FIG. 9 is a simplified schematic representation of another embodiment of the converter according to the invention using diode bridges and thyristors connected in each bridge;

FIG. 10A is a schematic representation of a power converter represented more generally in FIG. 9;

FIG. 10B is a schematic representation of a three-phase device using three induction generators;

FIG. 10C is a simplified representation of a single-phase device using a generator with a central tap winding;

FIG. 10D is a simplified representation of a three-phase device using three generators each provided with a winding with central tap;

Figure 11 is a simplified schematic representation of a conventional arrangement for returning energy from a known converter to an alternative power source;

FIG. 12 is a simplified block diagram of a device comprising a converter according to the invention for returning energy to an alternative source;

FIG. 13 is a simplified schematic representation in the form of blocks of a converter according to the invention used with an alternative source in a frequency conversion device.

FIG. 14 is a simplified representation of a three-phase converter operating from a single-phase source;

FIG. 15 is a general simplified diagram of a power conversion circuit for supplying a load with alternating energy whatever the polarity of the difference in supply potential supplied to the power conversion circuit;

FIG. 16 is a schematic representation of a branch of a power conversion circuit represented in FIG. 15, comprising a complementary switching circuit; and

FIG. 17 schematically represents a diode blocking circuit useful in the present converter.

In the present description, the term “bipolar” will be used in relation to the converter to designate an agency capable of supplying alternative output energy to a load, while it is itself supplied by continuous energy. of either polarity or by alternative input energy. A simplified arrangement of such a converter is shown in FIG. 6.

i ”In this figure, the thyristors or other switches are indicated in the form of four mechanical switches 55, 56, 57 and 58. For ease of description, the closing of any switch acts to close a path letting current flow through. the switch, whatever the polarity of the applied voltage. A load 60 includes an inductive component 61 and a resistive component 62 connected as shown. An alternating voltage source 63 is coupled to the conductors 64 and 65 to which the switches are connected. This bipolar converter arrangement 2 (i allows current to flow through the load in either direction by closing the appropriate switches, and can do so with a voltage of either polarity applied at its input terminals.

For example, assuming that current flows from a more positive potential to a less positive potential, and that the potential on conductor 64 is positive compared to that of conductor 65, if switches 55 and 58 are closed, current will flow through switch 55, load 60 and switch 58. If switches 55 and 58 are now open and switches 56 and 57 are now closed, the potential difference remaining the same, current will initially continue to flow through the same direction through the load until the inductive energy is used up. The current will then increase in the opposite direction in the load. - ■> 5 Thus, the direction of current flow through the load is controlled by the pair of switches which is closed. This is also true when the potential on conductor 65 is more positive than that on conductor 64.

There are various circuit arrangements for implementing the bipolar converter shown generally in Figure 6. For example, each of the switches 55 to 58 may be a triac or the like switch which allows current to be passed through one either direction when it is triggered by a trigger pulse. If a triac was used for each of the switches 55 to 58, each of the thyristor-diode pairs (such as 25-30 in FIG. 1) could be replaced by one of the triacs 55 to 58 to provide a single-phase device such as shown in Figure 7A. The switching circuit has been omitted, but those skilled in the art will understand how such a circuit should be connected and operate to effect triac switching. In this device, the generator is used at its full capacity, since the output voltage will be E instead of E / 2.

Figure 7A shows the use of a bipolar converter in conjunction with an induction machine to provide a frequency controlled device similar to that of Figure 1, and Figure 7B shows the output voltage of the bipolar converter device. Those skilled in the art will note that (l {, the logic circuit 37 ensures that the voltage at the terminals of the converter is a practically square wave or a pulse width modulation voltage. A phase inversion circuit 46 is shown in Figure 7A and is used to ensure continuity of operation at each zero crossing of the (, 5 waveform describing the modulated output voltage. Thus, the excitation of the machine is caused to drop at the end of each half cycle and some means should be used to re-energize the device. This circuit can typically include a small

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continuous source or a charged capacitor which is momentarily applied to the line terminals to re-energize the machine. If the charge is sufficiently inductive, the charging current will cause the device to continue operating, since the charging current continues to flow while the voltage decreases and tends to recharge the capacitor to a voltage of appropriate polarity.

There are various circuit arrangements for implementing the bipolar converter generally represented in FIG. 6 and more particularly with an induction machine in FIG. 7A. If controlled static rectifiers of the thyristor type are used instead of triacs, a circuit such as that shown in FIG. 8 can be provided. As shown, a generator 70 is connected to supply alternative energy to supply conductors 71 and 72 to a branch of the converter. This branch could be the equivalent of switches 55-56 of FIGS. 6 and 7A. In FIG. 8, the branch comprises a first pair of thyristors connected in anti-parallel 73,74, to provide a switch 75. Another pair of thyristors connected in anti-parallel 76, 77 forms another switch 78. The switches 75 and 78 are connected in series between the conductors 71 and 72. A switching circuit 80 is connected to the common terminal 81, and a load conductor 82 is also connected to this same point of the circuit. The switching circuit is used to switch off one of the thyristors before switching on another. For example, if the thyristor 73 of the switch 75 was conductive so that current from the conductor 71 flowed through the thyristor 73 and the conductor 82 to the load, the switching circuit would be allowed to cut off the thyristor 73 before the thyristor 74 or one of thyristors 76 and 77 is not made conductive.

Figure 9 depicts a separate circuit for implementing the basic switching arrangement discussed in connection with Figure 6. As shown, a pair of switching circuits 83 and 84 are connected in series between the supply conductors 71 and 72. Each of the switching circuits includes a diode bridge and a thyristor. In the upper switching circuit 83, for example, four diodes 85 to 88 are connected in a conventional bridge arrangement and a thyristor 90 which may be a silicon controlled rectifier is connected across the normal output connections of the diode bridge. In addition, a switching circuit 91 is shown, connected to the thyristor, to effect the switching of this thyristor when desired. Likewise, the lower circuit arrangement comprises four diodes 92 to

95 connected in a bridge arrangement, a thyristor 96 being arranged at the terminals of the normal output connections, and a switching circuit 97 being connected to cut off the thyristor 96 when it is actuated.

It is clear that, when the thyristor 90 is conductive, current can flow from the conductor 71 via the upper switch 83 to the load conductor 82, or from the conductor 82 via the switching circuit 83 to conductor 71. As with the arrangement in Figure 8, the upper switch 83 in Figure 9 should be turned off before the thyristor trips

96 in the lower switching arrangement 84, and of course the switch 84 should be turned off before the switching circuit 83 is triggered again. In the circuits of Figures 8 and 9, the voltage from the supply member 70 can be of either polarity, and energy can flow in either direction — to the load or from the load - with the two different polarities on the reference conductors 71 and 72. Thus, these two arrangements act to increase the efficiency of the modulated induction generator device as has been described above in relation with figure 6.

Figure 10A shows the upper switching circuit 83 of Figure 9, as well as details of the switching circuit 91. As shown, the switching inductor 98 is connected in series with the thyristor 90. All components having reference numbers 100 to 106 form part of the switching circuits 91. These components comprise a series circuit consisting of a capacitor 100, io of an inductor 101 and an auxiliary thyristor 102, this series circuit being connected in parallel with the thyristor 90. A diode 103 is connected in anti-parallel with the auxiliary thyristor 102 as shown. In addition, the switching circuit comprises a second series circuit consisting of a resistor 104, a diode 105 and an external battery or voltage source 106; this second series circuit is also connected in parallel with the thyristor 90.

In operation, it is initially assumed that the source

70 provides a potential to the conductor 71 which is positive by

20 with respect to the conductor 82 and that the thyristor 90 has not yet been triggered in the conductive state. To initially charge the capacitor 100, the auxiliary thyristor 102 is made conductive to close a current path from the conductor

71 via diode 85, inductor 98, capacitor 100, inductor 101, auxiliary thyristor

102, from diode 86 and from conductor 82 to the load. This charges the capacitor 100 at a polarity voltage indicated by the + and - signs arranged above the capacitor in the figure. An auxiliary power supply 106 can also charge the capacitor 100 and replace the load from the main source when the main source voltage is low or in the case of operation in the absence of load. After this charge, the first time the thyristor 90 is started, the capacitor 100 will discharge according to the circuit comprising the thyristor 90, the diode 103 and the inductor 101 to the other plate of the capacitor 100, supplying the terminals of the capacitor. a charge having the polarity represented by the signs - and + below this capacitor. When it is desired to cut the thyristor 90, the auxiliary thyristor 102 is triggered in the conducting state 40 and the capacitor 110 discharges according to the loop comprising the inductance 101, the auxiliary thyristor 102 and initially the reverse direction of the thyristor 90 towards the other plate of the capacitor 100. When the thyristor 90 blocks the reverse current flow, the switching pulse is transferred to the 45 path provided by the diodes 85 and 88 and the diodes 86 and 87. The capacitor 100 is then recharged according to the polarity indicated above the capacitor. During part of the time when the diodes 85 and 88 and 86 and 87 are conductive, the voltage developed at the terminals of the inductor 98 polarizes the main thyristor 90 in reverse, which is desirable to minimize the cut-off time of the device. The next time the thyristor 90 is triggered, the polarity of the charge across the capacitor 100 will be reversed again to prepare the circuit for the next switching cycle.

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If the capacitor 100 was not charged at a sufficiently high value for effective switching of the initial cycle, the auxiliary source 106 would be used to supply the required level of switching energy. Thus, when the auxiliary thyris-6o tor 102 is triggered, a charge path of the capacitor 100 is closed. This path extends from the battery 106 via the diode 105, the resistor 104, the capacitor 100, the inductor 101 and the auxiliary thyristor 102 to the other side of the battery 106. This completes the initial charge 65 of the capacitor 100 as described above and, when the thyristor 90 is turned on for the first time, the charge across the capacitor will be reversed to switch in the normal direction. If the operating voltage level-

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nement across the supply conductors drops to a level too low for effective switching at any time, then the necessary charge level will be supplied from the battery 106 according to the circuit described above. At this time, the general bipolar converter arrangement described in FIG. 9 and the switching circuits represented in FIGS. 10A and 16 constitute embodiments of implementation of the present invention.

Another notable area of application of the present invention lies in the field of energy regeneration. It is often desirable to return energy from a motor or load that can instantly function as a generator to the main power source. Frequently, this main source produces an alternating voltage which is then rectified by a circuit such as a controlled thyristor bridge, filtered in an LC filter and then applied to the converter. Therefore, when it is necessary to return the reproduced energy to the source, a second thyristor bridge is added as shown in Figure 11. A conventional sine wave source 70 is connected to provide the alternative energy which is rectified by means of a first thyristor bridge comprising thyristors 110, 111, 112 and 113. The continuous energy thus supplied passes through the line conductors 114 and 115 and through a filter 116 which comprises an inductance connected in series 117 and a capacitor connected in parallel 118, to supply the conventional converter 120. When it is desired to return the regenerated energy through the conventional converter 120 and the filter 116 to the source 70, a second thyristor bridge comprising the four thyristors 121,122,123 and 124 must be added. The polarity of the voltage on line 114,115 remains the same as the polarity across the capacitor 118, but the direction of the current through the filter inductor is reversed in the regeneration process using a conventional converter.

The use of the bipolar converter to simplify the return of regenerated energy is described in FIG. 12. It will be noted that a single bridge, comprising the thyristors 110 to 113, is necessary between the line conductors and the source 70. In addition, the capacitor 118 is replaced by a bipolar capacitor 126. In this arrangement, the direction of the current always remains the same, from the source via the filter to the bipolar converter, while the voltage reverses across the terminals of the capacitor that energy is returned through this bipolar converter.

The bipolar converter can also be used in the field of frequency conversion. A general arrangement of such a converter is represented in FIG. 13, the switching circuits of the converter being represented in a simplified way as power switches 83, 84.83A and 84A and the load by a resistor 131. The source 70 provides an alternating voltage at a frequency fs. The frequency of the converter is identified by f ;. On the output conductors 71,72, before the filter 130, both the frequencies sum f; + fs and difference f; - fs of the converter and the source are present. In the example shown, the filter 130 is a low-pass filter which consequently blocks the upper frequency fj + fs. The filter 130 could be a high-pass filter and block the lower frequency f; - fs. There are also harmonic frequencies produced in such an arrangement, but the device shown is especially usable for producing a sum or difference frequency of the frequencies fj and fs. H can be used, for example, for direct-to-AC voltage conversion without requiring an intermediate DC switch to produce a frequency voltage controlled from a fixed or variable voltage source.

A circuit for producing a three-phase alternating voltage from a single-phase source is shown in Figure 14.

A three-phase bipolar converter provided with three branches 146, 147 and 148 is shown as being coupled to a single-phase source 70. Each branch comprises a pair of power switches 83,84; 83A, 84A; and 83B, 84B. If the triggering of the power switches is controlled so as to switch in the manner of a conventional quasi-square wave, then the voltage appearing at the output terminals will include both sum and difference components. If it is assumed, for example, that the sum components are eliminated by filtering, the output voltage will include three-phase voltages balanced at the difference frequency.

It will further be emphasized that the individual power switches, such as the circuits 83 shown in Figure 10A, have a utility separate from their connection in a bipolar converter circuit i5. Circuit 83 can be used as a power switch, for example between an energy source and a load.

Before considering a so-called complementary switching circuit, the general type bipolar converter circuit shown in FIG. 15 will be examined. The potential source 20 ′ must be an alternative source in such a device, but this source 20 ′ is shown more generally because the power conversion circuit provided with a switching circuit, complementary, can be used for other arrangements than to AC-AC power conversion circuits. As shown, a potential difference from source 20 'is applied on line conductors 21' and 22 'to a power conversion arrangement comprising four power switches 23', 24 ', 25' and 26 '. The two power switches 23 'and 26' are connected together to a common terminal or load connection 27 '. Likewise, the other two power switches 25 'and 24' are connected together to a common terminal 28 'which provides another load connection. An induction motor 30 'receives energy via conductors 31' and 32 'from connections 27' and 28 'of the power conversion circuit. If the power switches 23 'and 26' are real switches in the sense that they can let energy pass in 0 in another direction, it is obvious that the alternating voltage from the source 20 'can be switched by these power switches to provide alternating voltage. When the induction motor is supplied, the source 20 'supplying an alternating voltage at the first frequency, 45 of the power switches 23' to 26 'being switched to a different frequency, the voltage in the windings of the induction machine present the sum and difference frequencies in addition to the fundamental frequencies. Since the difference frequency is very small, the induction machine can be driven as a motor from the energy at this lower frequency, and the energy at the relatively higher frequencies will have little effect on the operation of the machine. The switching of the power switches is regulated by pulses applied from an oscillating and logic circuit 55 'as will be readily understood by those skilled in the art. The oscillator and logic circuit 33 'is shown generally to designate a means for applying trigger pulses to the individual power switches 23' to 26 '. If power switches are to be connected in a truly symmetrical arrangement, the power switches themselves must be able to carry current in either direction, to block a voltage from one or the other. other polarity, and to be made conductive or cut under any of these conditions. In the agency described in FIG. 15, it is assumed that, when the power switch 23 'is conductive, then the switch 26' of the same branch of the circuit is not and vice versa. This saves power components and simplifies

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in addition, the logic circuit 33 'if the power switch 23' can be automatically cut when the other switch 26 'in the same branch is made conductive.

In this presentation, the power conversion circuit comprising the power switches 23 'to 26' can be considered to have two branches, such as the branch 23 ', 26' and the branch 25 ', 24'. Those skilled in the art will note that another branch can still be provided and that another charge conductor can be added to ensure three-phase operation from a single source 20 ′. i (1

FIG. 16 represents a branch of the power conversion circuit comprising the power switches 23 'to 26' represented in FIG. 15. FIG. 16 represents these switches connected between the line conductors 21 'and 22'. Between the power switches is the load connection 27 'to which one of the load conductors 31' is connected. An inductor 34 'is shown connected to the line conductor 21'. Inductance 34 'is not essential for the implementation and operation of the invention.

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The first power switch 23 'is connected between the line conductor 21' and the load connection 27 '. A part of the power switch comprises a diode bridge or a rectifier bridge provided with a pair of charging terminals 35 'and 36' and a pair of switching terminals 37 '25 and 38'. The power switch 23 'further comprises four diodes 40' to 43 'connected as shown to conduct current between the charging terminals 35' and 36 'each time a continuous circuit is closed between the switching terminals 37 'and 38'. This first power switch 30 also includes a thyristor 44 'coupled between the switching terminals 37' and 38 'to close such a continuous circuit when the thyristor 44' is triggered.

Similarly, the second power switch 26 'is inductors 60' and 62 'appear as connected in the power switches, it will be noted that these inductors are in fact part of the complementary switching circuit. In addition, although a third inductor 65 'is described and

5 presently used in this particular embodiment of the present invention for the protection of tripping in di / dt, it is not necessary according to the constitution and the fundamental implementation of the present invention to provide such an inductor 65 ′.

"It is initially assumed that the power conversion circuit has been supplied and that the source 20 'provides a potential difference which is positive on the line conductor 21' compared to the line conductor 22 '. In practice, it is simple ensure, via the logic arrangement circuit 33 ', that the thyristor 44' in the upper power switch is initially triggered to charge the capacitor 64 '. When the thyristor 44' is started, current flows from the line conductor 21 'via the diode 40', the thyristor 44, the inductor 65 ', the capacitor 64', the inductance 62 'and the diode 51' towards the conductor 22. This charges the capacitor 64 ′ positively on its upper plate adjacent to the inductor 65 ′ with respect to the potential on the other plate. It will be noted that, even if the thyristor 44 ′ was not initially triggered to charge the capacitor , when thyristor 44 'is initially triggered hey to conduct the charging current from the line to the diode 40 ', the thyristor 44', the inductance 60 ', the diode 41' and the charging connection 27 'to the charging conductor, the path previously described for charging the capacitor 64 ′ is also closed and that it will be charged as described. There is no charge path for the capacitor 66 'at this time.

The second thyristor 54 'in the second switch connected between the load connection 27' and the other conductor 35 power 26 can now be triggered, by a line pulse 22 '. The power switch 26 'includes a pair of charging terminals 45' and 46 'and a pair of switching terminals 47' and 48 '. Four diodes 50 'to 53' are connected in the power switch 26 'to conduct the current between the charging terminals 45' and 46 'when a continuous circuit is closed between the switching terminals 47' and 48 '. For this purpose, a second thyristor 54 'is connected as shown between the switching terminals 47' and 48 'to close such a continuous path when the thyristor 54' is triggered. Of course, in practice, there may not exist such “physical” terminals such as load terminals 45 ′ and 46 ′ and switching terminals 47 ′ and 48 ′ if the rectifier bridge is constituted according to a single integrated circuit or another arrangement, but such terminology is useful for the description of the present invention.

The power conversion branch may include a complementary switching circuit. The switching circuit comprises a first inductor 60 ′, shown connected between the switching terminal 37 ′ and the cathode of from the logic circuit 33 ′, to make this power switch conductive and, by means of the complementary switching circuit , cut the first thyristor 44 '. When the thyristor 54 'is made conductive, it closes a path 40 for discharging the capacitor 64'. Initially, the discharge current from the capacitor 64 'begins to increase and discharges this capacitor via the inductor 65', from the reverse direction of the thyristor 44 ', the capacitor 66' and the thyristor 54 'towards l 'other plate of condenser 45' 64 '. When the amplitude of the discharge current from the capacitor 64 'rises to the level of the charge current flowing when the thyristor 54' is conductive, the thyristor 44 'is cut, and the discharge path of the capacitor 64' passes through inductance 65 ', inductance 60', diode 41 ', 50 diode 50' and thyristor 54 'to the other plate of capacitor 64'. In practice, the inductance 65 'has a low value and thus the increase in the discharge current is rapid. The conductive thyristor 54 'also closes a charge path for the capacitor 66' from the line conductor 21 'via the

first thyristor 44 'in the first power switch 55 medial of the diode 40', of the capacitor 66 ', of the thyristor 54',

23 '. There is a common connection 61 'between the inductor 60' and the thyristor 44 '. Similarly, a second inductor 62 'of the complementary switching circuit is connected in series with the second thyristor 54' between the switching terminals 47 'and 48' of a second power switch, a common connection 63 'being provided between the 'inductance 62' and thyristor cathode 54 '. The switching circuit includes a first capacitor 64 'connected in series with a third inductor 65' between connections 61 'and 63' in the respective power switches. A second capacitor 66 'is connected between the switching terminal 38' of the first power switch and the corresponding switching terminal 48 'of the second power switch. Although the inductance 62 'and diode 51' to the other line conductor 22 '. The capacitor 66 'begins to charge at the line voltage. Thus, ignoring the relatively low inductance value 65 ', the cut-off voltage of the thyris-60 tor 44' is substantially equal to the difference between the voltages across the terminals of capacitors 64 'and 66'. Consequently, the cut-off time of the thyristor 44 'ends at the moment when the voltages at the terminals of these two capacitors are equal.

65 When the voltage across the capacitor 66 'has reached the line voltage, this capacitor does not continue to charge. If there is an excess of energy trapped in the inductor 62 'due to the charge current previously flowing at

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through this inductance, this excess will flow through the diodes 51 'and 52' and the thyristor 54 'until it dissipates. However, in the inductor 60 ', there is still a certain charge current flowing even when the potential across the capacitor 64' has been reversed. Consequently, this excess energy will be transferred to the capacitor 64 'as an overload. After this switching cycle, the load current will then flow from the load through the conductor 31 ', the diode 50', the thyristor 54 ', the inductor 62' and the diode 51 'to the line conductor 22' . The capacitor 64 'is charged at a positive potential on its lower plate relative to that of its upper plate and the capacitor 66' has a positive potential on its upper plate relative to that of its lower plate.

The thyristor 54 'now being conductive, it is assumed that one wishes to cut the thyristor 54' and make the thyristor 44 'conductive. To achieve this, a trigger pulse is applied to the thyristor 44 'from the logic circuit 33'. This closes a discharge path for current flow from the upper plate of the capacitor 66 'via the thyristor 44', the inductor 65 ', the capacitor 20 64' and the reverse direction of the thyristor 54 'to the other capacitor plate 66'. As soon as the level of this discharge current rises to the level of the charge current, the thyristor 54 ′ is cut off. The discharge current from the capacitor 66 'continues to flow through the thyristor 44', the inductor 60 'and the diodes 41' and 50 'to the other plate of the capacitor 66'

until this capacitor is discharged at zero voltage. The capacitor 66 'is locked at zero voltage and it cannot charge in the opposite direction; thus, this capacitor oscillates only between the line voltage and zero volts during the 30 switching cycles. While the capacitor 66 'is discharged, the capacitor 64' is also discharged by a circuit going from the line conductor 21 by the diode 40 ', the thyristor 44', the inductance 65 ', the capacitor 64', the inductance 62 'and the diode 51 to the conductor 22. The capacitor 64' is then recharged by the same circuit at a voltage of opposite polarity, namely positive on its upper plate with respect to its lower plate. Thus, the circuit is again in its initial state; the capacitor 64 ′ is positively charged on its upper plate relative to its lower plate, the capacitor 40 ′ is at zero voltage, and the charging current flows from the conductor 21 ′ by the diode 40 ′, the thyristor 44 ', inductance 60', diode 41 ', load connection 27' and load conductor 31 'to the load.

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An inductor 34 can be placed in series with a branch of the line in a practical application. This has the effect of slowing down the charging speed of the capacitor 66 ′,

thus ensuring a longer cut-off time for the thyristor 44 ', a lower amount of trapped energy in the inductor 62' when the capacitor 66 'is charged at the line voltage, and a lower overload on the capacitor 64 'at the end of the thyristor 54' switching interval. If the inductor 34 'has an inductance of the order of 10 times the value of the inductor 60' or 62 ', then the switching process for cutting the thyristor 54' is different from that which has been described previously. When the thyristor 54 'is cut, the inductor 34' absorbs the line voltage, so that the effective voltage between the line conductors is zero. This causes the discharge path of the capacitor 64 ', during the switching off of the thyristor 54', to be modified as follows.

The thyristor 54 'being conductive, it is assumed that one wishes to cut it and make the thyristor 44' conductive. Just before, a trigger pulse is applied to the thyristor 44 'from the logic circuit 33'. This closes a discharge path 65 for the current from the upper plate of the capacitor 66 'via the thyristor 44', the inductor 65 ', the capacitor 64' and the opposite direction from the thyristor 54 'to the other side of capacitor 66 '. As soon as the level of this discharge current rises in the load, the thyristor 54 'is cut and current flows through the inductor 62' and the diodes 51 'and 52' instead of the thyristor 54 '. The discharge current of the capacitor 66 'continues to flow until the capacitor 66' is discharged at zero voltage. The capacitor 66 'is locked at zero voltage and cannot charge in the opposite direction and thus this capacitor oscillates only between the line voltage and the zero voltage during the switching cycle. After the switch 66 'has been locked, the current from the capacitor 64' continues to flow from its lower plate through the inductor 62 ', the diode 53', the diode 42 ', the thyristor 44' and the inductance 65 'to its other plate, while it recharges with the opposite polarity, namely a positive voltage on its upper plate relative to its lower plate. Consequently, the circuit is again in its initial state; the capacitor 64 'is positively charged on its upper plate with respect to its lower plate, the capacitor 66' is at zero voltage, and the charging current flows from the conductor 21 'via the diode 40', of the thyristor 44 ', inductor 60', diode 41 ', load connection 27' and load conductor 31 'to the load.

Consequently, with an inductance 34 'in the line, the source must not add energy to the capacitor 64' during the switching interval. There is a small amount of energy stored in the inductor 34 'during this process, this energy ending in the form of an overload on the capacitor 64'. However, there is a clear reduction in the overload since the duration during which the inductor 34 'is actually at the line terminals is minimal.

The addition of the inductor 34 'also tends to overload the capacitor 66' during the switching of the thyristor 44 '. However, this does not significantly affect the operation of the circuit and the advantages obtained by the inductor 34 'exceed these drawbacks.

FIG. 17 represents a blocking circuit 70 'connected to the switching terminals 37' and 38 'of the power switch 23'. A similar blocking circuit is coupled to the switching terminals of the power switch 26, to prevent the occurrence of transient currents at the terminals of the diodes in the power switches at the end of the switching time. The blocking circuit 70 'comprises a diode 71' connected in series to a capacitor 72 'and a resistor 73' connected in parallel to the capacitor 72 '.

Various circuit configurations are possible using the bipolar converter. For example, a three-phase machine can be used with a bipolar converter to produce a single-phase output voltage with very low ripple content. A capacitor may not be necessary in this case.

A three-phase output voltage can be obtained by connecting three single-phase devices as shown generally in Figure 10B. Three isolated generators are required and connections are made as shown. A three-phase modulator signal is applied to each converter control circuit.

Using a center tap generator 140 can eliminate some of the power switches, as shown in the single phase device in Figure 10C. FIG. 10D shows a device for producing a three-phase output voltage using three single-phase machines with insulated central outlet 140, 141 and 142. Various other configurations will be clear to those skilled in the art.

Unlike independent or auxiliary switching circuits, the described switching circuit has advantages by reducing the number of power components required and by simplifying the logic circuit or the communication circuit.

9

617,549

doorway. Air inductors can be used as inductors 60, 62,65 reducing the cost and the physical dimension of the circuit. The circuit can be used as shown in Figure 15 to power an induction generator, or, when this element is operated as a motor, energy can be regenerated through the branches of the power conversion circuit. Another branch can be added to the circuit of FIG. 15, in a manner obvious to those skilled in the art, to supply three-phase alternative energy 5 from a single-phase source 20 '.

VS

3 sheets of drawings

Claims (16)

617,549 1. Power converter for transferring electrical energy to a load regardless of the polarity of a supply voltage applied to the converter via two line conductors, characterized in that it comprises (FIG. 6 , Figure 7A) a first (55) and a second (57 or 56) switching devices, each having two connection terminals and at least one control connection, each of the first and second switching devices having one of its connection terminals connected to a first line conductor (64 ), a third (56 or 57) and a fourth (58) switching device, each having two connection terminals and at least one control connection, each of the third and fourth switching devices having one of its connection terminals connected to a second line conductor (65), the second connection terminals of the first and third switching devices being connected to each other and to a first output conductor (23), and the second connection terminals of the second and fourth devices switching devices being connected between: o and a second output conductor (24), the load (60,22) being connected between the output conductors, said control connections being connected to a control device (37,40,43) arranged to control the switching devices so as to supply the load (60,22) with an is current of a given polarity regardless of the polarity of the voltage food. 2. Converter according to claim 1, characterized in that each switching device comprises two thyristors (73,74) connected in anti-parallel (fig. 8). m 3. Converter according to claim 1, characterized in that each switching device comprises a diode bridge formed by four diodes (85,86,87,88) connected in the manner of a full wave rectifier between a line conductor and an output conductor, a thyristor (90) being connected between the connections of the diode bridge not connected to the line and output conductors so as to ensure the conduction or non-conduction of the diode bridge in one or the other direction depending on the conduction or non-conduction of the thyristor, a control device (91) being connected • "> to the thyristor to control the conduction state of the latter (fig- 9). 4. Converter according to claim 1, characterized in that it comprises (fig. 14) at least a fifth and a sixth switching devices each having two connection terminals and at least one control connection, a connection terminal connection of these fifth and sixth switching devices being connected respectively to the first and second line conductors and the other two connection terminals being connected to each other and to a third output conductor, the load being connected between the three output conductors of the converter and the control connections being connected to a control device arranged to control the switching devices so as to supply the load with polyphase alternating current. 55 5. Converter according to claim 1, characterized in that the first switching device (23 '), comprising two connection terminals (35', 36 ') and two switching terminals (37', 38 '), comprises four diodes (40 'to 43') connected (i1) to conduct the current between the connection terminals when a circuit is closed between the switching terminals, and a first thyristor (44 ') arranged to close said circuit when it is triggered, the third switching device (26 '), comprising two connection terminals (45', 46 ') and two switching terminals (47', 48 '), comprises four diodes (50' to 53 ') connected to conduct the current between the connection terminals when a circuit is closed between the switching terminals, and a second thyristor (54 ') arranged to close said circuit when it is triggered, and a switching circuit (60' to 66 ') comprising a first inductor (60 '), connected in series with the first thyristor (44') between the switching terminals d in the first switching device, a second inductor (62 ') connected in series with the second thyristor (54') in the third switching device, a first capacitor (64 ') of which an electrode is connected to the common connection (61 ') between the first thyristor and the first inductor and the other electrode of which is connected to the common connection (63') between the second thyristor and the second inductor, and a second capacitor (66 ') connected between a switching terminal ( 38 ') of the first switching device and a switching terminal (48') of the third switching device, this complementary switching circuit acting to block that of the first and second thyristors which is conductive when the other is triggered (fig. 16). 6. Converter according to claim 5, characterized in that it comprises a third inductor (65 ') mounted in series with the first capacitor (64') between said common connections (61 ', 63'). 7. Converter according to claim 5, characterized in that it comprises two blocking circuits (70 ') each connected to the switching terminals of a switching device, each blocking circuit comprising a series circuit formed by a diode ( 71 ') and a capacitor (72') and a resistor (73 ') mounted in parallel with the capacitor. 8. Converter according to claim 5, characterized in that it comprises a fourth inductor (34 ') connected in series with one of the input conductors. 9. Converter according to claim 3, characterized in that it comprises a switching circuit (100—102) mounted in parallel with the thyristor (90) to effect selective cutting of the thyristor interrupting the current flow through the device switching. 10. Converter according to claim 9, characterized in that the switching circuit comprises the series connection of a capacitor (100), an inductor (101) and a second thyristor (102), and a diode ( 103) coupled in anti-parallel to the second thyristor. 11. Converter according to claim 10, characterized in that the switching circuit comprises a second series circuit connected in parallel to the first series circuit and comprising a resistor (104), a second diode (105) and means (106) for supplying continuous tension. 12. Converter according to claim 1, characterized in that the output conductors of the converter (114—115) are connected to a filter (116) comprising an inductor (117) connected in series on one of the output conductors and a capacitor (126) mounted between the two output conductors and capable of being charged in one or the other direction, the load being connected in parallel to said capacitor, the converter making it possible on the one hand to transfer an alternative energy to the load and, on the other hand, to transfer energy returned by the load to the voltage source (fig. 12). 13. Converter according to claim 1, for transferring electrical energy from an alternating supply voltage source (70) of frequency fs to a load (131), the converter (83.83A, 84.84A) being controlled so as to have a switching frequency fj, characterized in that it comprises a filter circuit (130) connected in series with the load to allow one of the sum frequencies f, + fs or difference f to pass; - fs towards the load and block the other of these frequencies. 14. Use of the converter according to claim 1, in a circuit for supplying a load from an induction generator, the converter control device. 3 617,549 comprising a logic circuit (37) for applying control signals to the converter control inputs in response to synchronization signals from an oscillator circuit (40), and a modulator (43) connected to the oscillator circuit for modulating the signals synchronization applied to the logic circuit 5, so as to supply the load with a desired alternating current, characterized in that the induction generator (20) has an input shaft (21) for receiving mechanical input energy and two electrical output connections, the power converter being connected, by its line conductors m, to the electrical connections of the induction generator, and a capacitor (34) being mounted between the output conductors of the converter in parallel with the load ( 22) (fig. 7A). 15. Use according to claim 14, characterized in that a phase inversion circuit (46) is connected between the is modulator and the input conductors of the converter to ensure the operation of the induction machine after each passage to zero of the alternating voltage across the load. 16. Use according to claim 14 for supplying a load with polyphase alternating current, characterized in that each phase circuit comprises a supply circuit comprising an induction generator and a converter.