EP1000459A1

EP1000459A1 - Self-compensating converter

Info

Publication number: EP1000459A1
Application number: EP98940326A
Authority: EP
Inventors: Henri Courier De Mere
Original assignee: SNC Hb Industries
Current assignee: SNC Hb Industries
Priority date: 1997-07-28
Filing date: 1998-07-23
Publication date: 2000-05-17
Also published as: FR2766636A1; WO1999005775A8; FR2766636B1; CN1266548A; US6185117B1; WO1999005775A1

Abstract

The invention concerns a converter, powered by an alternating network, taking therefrom a current with a power factor close to one unit and a non-linear distortion factor close to 5 %, whereas the amplitude of the current applied at the output load (2) remains substantially constant. It comprises a bridge structure using switching means (1', 1") and capacitors (3a, 3b) whereof the reactance at the quench frequency is selected such that a portion of the converted energy, after being rectified, is added between the terminals of a capacitor (6) to the mains current rectified by a bridge (7). A buffer source (4) has a direct voltage with substantially constant amplitude, which enables to balance the potentials generated thereby eliminating all risks of destruction by uncontrollable excess voltages.

Description

SELF-COMPENSE CONVERTER

The present invention relates to so-called "self-compensated" electronic converters, which, supplied from the AC network, are capable of outputting a high frequency signal of substantially constant amplitude, while the current taken from said network remains substantially sinusoidal and in phase with the voltage thanks to the recovery carried out according to the so-called energy transfer mode (in English "energy transfer") of a suitable portion of the energy at high frequency previously converted.

The most efficient of the devices of this kind already described by the prior art is illustrated by FIG. 1, attached hereto, which represents the most interesting embodiment which has been claimed in US Patent No. 5,134,556. According to this embodiment, representative of the prior art, the output terminal B of the converter A delivers the energy converted at high frequency through the galvanic isolation capacitor C, the value of which is chosen so that the impedance that it offers at said high frequency does not substantially disturb the resonant frequency of the oscillating output circuit, which comprises the inductance D, the output load E and the phase-shifting capacitor F. Unlike the capacitor C, the capacitor F must offer this high switching frequency a suitable impedance, so that the amplitude of the alternating signal developed between its terminals reaches a chosen value. This signal, applied to one of the non-polarized input terminals of the rectifier bridge I, makes it possible to recover between the terminals of the capacitor H the envelope of a rectified signal at low frequency. The polarized outputs of the rectifier bridge I are connected in series with the polarized outputs of the sector rectification bridge J, so that the aforementioned low-frequency envelope present between the terminals of the capacitor H, is added to the rectified sector signal, which improves the power factor of the current taken from the network. By thus recovering, proportionally to the current flowing in the output load E, a portion of the energy at high frequency converted, it is only possible to obtain a very approximate compensation for the power factor of the current taken. on the network as well as an illusory reduction in the rate of the harmonic currents affecting the latter. For this reason, it is therefore necessary to have recourse to an additional circuit which will make it possible to add to the above-mentioned signal proportional to the current flowing in the output load E, a second rectified signal which will, in turn, be proportional to the voltage at high frequency present between the terminals of the output load E.

This circuit includes the capacitor G, the impedance of which, chosen as a function of the above high frequency, allows the delivery of a voltage signal of suitable amplitude on the second non-polarized input terminal of the rectifier bridge I. After erection , a new low frequency envelope is then available between the terminals of the capacitor H where it is added to the current envelope previously recovered.

Only the addition of these three envelopes will allow such a device to meet the standards concerning the current taken from the network. Despite its good energy efficiency and its apparent simplicity, such a device suffers from certain drawbacks, which are discussed below. 1 *> Need to precisely adjust the respective amplitude of the current and voltage envelopes which are thus recovered between the terminals of the capacitor H.

2 *> Need to use an additional protection device which must be able to absorb transient overvoltages which could develop between the terminals of the capacitor H, especially when the converter A is started and whose energy , in some cases, may cause immediate destruction of this half.

The device according to the invention makes it possible, while overcoming these drawbacks, to obtain with very simple means, a power factor of the current taken from the network close to the unit while the total harmonic distortion, called "THD" , affecting it is around SX, a value which is currently far from being respected by the most sophisticated devices built according to prior art. Figure 2, attached, illustrates a general embodiment of the device according to the present invention. This device comprises a high frequency self-oscillator using a structure known as a "capacitor half-bridge" which is supplied with direct current from the common polarized terminals 8a and 8b, which are shunted by a decoupling capacitor 8. The active branch of this bridge converter comprises the switching means 1 ′ and 1 ", which are connected in series. The free terminals of the series circuit thus formed are connected, respectively, to terminals 8a and 8b. The passive branch of this converter in bridge comprises capacitors 3a and 3b which are also connected in series. The free terminals of the series circuit thus formed are connected, respectively, to terminals 8a and 8b. Between midpoint 1 of the above-mentioned active branch and midpoint 3 of the the aforementioned passive branch is connected the output load 2 which must receive the energy at converted high frequency. Under these conditions, as soon as a continuous voltage of sufficient amplitude is applied between the terminals 8a and 8b and that the alternating cyclic conduction of the switching means 1 ′ and I "is maintained by a control device which has not been shown here, a high frequency switching current can then tr pour the load 2 to close through the capacitors 3a and 3b whose reactance at the above high frequency is calculated so that the alternating voltage developed between the midpoint 3 and any one of the terminals 8a and 8b is not null, but presents, on the contrary, an amplitude of selected value.

The high frequency alternating voltage thus developed between the midpoint 3 and one of the common polarized terminals is then applied, via the DC voltage buffer source 4, to the non-polarized input terminal 5 of the full-wave rectifier bridge comprising the Sa and Sb diodes, This is made possible by the fact that the impedance which the buffer DC voltage source 4. opposes the high frequency alternating current thus generated, is negligible, even though the DC voltage of almost constant amplitude present between the terminals 3 and 5 can be considerable.

The polarized output circuit of said doubler bridge which is shunted by the decoupling capacitor 6, after having been suitably oriented, is connected in series with the polarized output circuit of the mains rectifier bridge 7 whose non-polarized input terminals 7a and 7b are connected to the sector. As soon as the terminals 7a and 7b are energized, the rectified mains current can charge the decoupling capacitor 8 through the diodes Sa and 5b, suitably polarized.

Once the alternating cyclic conduction of the switching means 1 ′ and 1 ″ has been established, an alternating current at high frequency then flows through the output load 2.

The predetermined fraction of this current which cannot flow through the capacitors 3a and 3b due to their reactance at the above high frequency, charges, via the DC buffer source 4, the input terminal 5 of the above bridge doubler.

After this current has been rectified, a low frequency envelope whose amplitude is proportional to the high frequency current passing through the load 2 is then recovered between the terminals of the decoupling capacitor 6.

This low frequency envelope is then added, between terminals 7c and 8b, with the low frequency envelope from the rectified mains current. The value of the voltage V3 is in direct relation with that of the direct voltage V2 developed between the midpoint 1 and one of the common terminals 8a or

8b and with that of the DC voltage V4. developed between terminal S and common terminal 8b.

This value can be approximated t calculated by the relation V3 as (V2 - V-t).

To fix the ideas, we will admit, for example, that the decoupling capacitor 8 is charged at a direct voltage VI of 370V,

As VI s. 2 x V2, the voltage V2 is then substantially equal to: 370V 4- 2, i.e. 185V,

Under these conditions, the DC voltage V5 present between the terminals 7c and 8b is approximately 160V. Like V5 ≈ V4. x 2, the DC voltage developed between terminals 5 and 8b is substantially equal to 160V 4 2, or approximately 80V.

The mean DC voltage V3 which must be maintained between terminals 3 and 5 of buffer source 4 will then be: 185V - 80V, or approximately OS.

By observing this simple rule, it is possible to achieve a perfect adaptation of the device according to the invention and to obtain, without additional circuit, an almost perfect correction of the power factor and of the harmonic distortion of the current taken from the network.

Thus constructed, the present device allows, without requiring any particular adjustment, to typically obtain for the current taken from the network, a power factor 0.995 and a total harmonic distortion rate of 7%, while the voltage present between the terminals 8a and 8b is affected only by a negligible modulation rate, The low modulation of the voltage present between the common terminals 8a and 8b results in a low rate of modulation of the envelope of the current at high frequency passing through the output load 2 as well as by the very limited amplitude of the current passing in capacitor 8.

Figure 3, appended, illustrates a practical mode of application of the present invention, which differs from the above as indicated below.

In this embodiment of the device that is the subject of the invention, use is made of a capacitor i-bridge converter having, on the one hand, the active transistors 1a and 1b, or any other semiconductor which can make office switching means, connected in series and, on the other hand, for passive branch capacitors 3a and 3b connected in series, which provide a reactance given to the above high frequency alternating current. Between the midpoints 1 and 3 of these bridge branches is connected the primary 9a which, coupled to the magnetic circuit 9, takes the place of the aforesaid output load 2. The control of the alternating cyclic conduction of the transistors a and 1b is maintained by the secondary 9b and 9c which, suitably oriented, are coupled to the magnetic circuit 9.

Said secondaries deliver, respectively, via the limiting resistors 11a and 11b, a suitable amplitude and phase signal on the control junction of the transistors a and lb, which is capable of ensuring the alternating cyclic conduction of these half er s. The high recovery AC voltage developed between terminal 3 and any of the common polarized terminals 8a or 8b is applied, via the high capacity eur capacitor S, suitably polarized, to the non-polarized input terminal 5 of the doubling rectifier bridge comprising the diodes Sa and Sb, suitably polarized. As before, the polarized output terminals 7c and Sb of said rectifier bridge are shunted by the filtering capacitor.

The high frequency current thus rectified and recovered is in the form of a low frequency envelope which, after addition, as indicated above, with the envelope corresponding to the mains current rectified by the rectifier bridge 7, allows compensation of the current taken from the sector from the non-polarized input terminals 7a and 7b. The diodes 10a and 10b, suitably polarized, connected respectively in ant i -para 11 è 1 e with the transistors la and lb, ensure the double circulation of the current between the midpoint 1 and any one of the common polarized terminals Sa or Sb . After switching on the device, the initiation of the cyclic conduction of the thus formed converter is ensured in a conventional manner by the trigger device grouping the resistor 1 .a, the capacitor 14d, the inhibition diode 14b and the device at voltage only 14c, such that the control electrode of the transistor lb is excited by a suitable signal.

Under these conditions, the winding 9d, coupled to the magnetic circuit 9, delivers the energy converted to the receiver 12 connected between its terminals, according to a voltage transfer mode, called "voltage transfer". The capacitor 13 mounted in parallel with the receiver 12 performs the following functions. Firstly, in the case where the magnetic circuit 9 is designed to have only as small an air gap as possible, the capacitor 13 will have the function of limiting the effects of the leakage inductance affecting the transformer thus formed. Secondly, in the case where the magnetic circuit S is purposely provided with a large air gap, the capacitor 13 will have the function of constituting with the secondary inductor 9d a parallel resonant circuit whose overvoltage effects may be used in the power supply of the receiver 12, In this arrangement, the energization of the high-capacity capacitor 15 which takes the place of the aforesaid buffer DC voltage source 4 is automatically obtained from the rectified mains voltage which is present between the polarized output terminals 8a and 7c of the bridge rectifier 7, ^because the charge of capacitor 15 can thus be carried out through the series circuit comprising the transistor, the primary 9a, the resistance 15a which limits the initial charge overcurrent and diode 5a which maintains the voltage present between terminals 3 and 5 at a constant value cor esponding to the above voltage V3.

Under these conditions, the DC voltage present between terminals 3 and 5 will be affected by a low frequency ripple whose rate depends essentially on the continuous charge that the capacitor 15 can accumulate.

It will therefore be advantageous to give the capacitor 15 a capacity as high as possible, This capacitor must transmit, without attenuating it, the rectified envelope of the sector.

Concerning current low power applications, by giving the capacitor 15 a value of several tens of microfarads, the ripple rate of the DC voltage V3 present between the terminals 3 and 5 remains practically negligible. Conc omm i tammen t, the impedance offered by a capacitor of this value to the current recovered at high frequency which passes from terminal 1 to terminal 5 also remains negligible.

The high capacity capacitor 15 then behaves as a buffer continuous voltage source whose amplitude, almost constant, allows the adaptation of the different potentials developed in such a device.

Under these conditions, the capacitor 15 then perfectly fulfills the function which is assigned to the aforesaid buffer continuous voltage source 4. Thus constructed the device according to the invention per and to obtain excellent compensation for the power factor of the current taken from the network and an extremely reduced level of the rate of harmonic currents affecting the latter. In addition, the low frequency ripple affecting the DC voltage present between the common terminals Sa and Sb occurs at a very low level which ultimately results in a low ripple rate of the envelope of the current to high frequency applied to the receiver 12 as well as by a small excursion in the amplitude of the low frequency ripple current passing through the capacitor 8,

FIG. 4, attached hereto, illustrates another practical embodiment of the device which is the subject of the invention, This latter mode, in accordance with what has been described above, differs from the previous one by the points indicated below. Firstly, the inductance of the primary 9a constitutes with the capacitor 16 which is connected to it in series a series oscillating circuit whose resonance occurs at a frequency close to that at which the alternating cyclic conduction maintained by the transistors is maintained. la and 1 b.

In this device, the extraction of energy converted at high frequency is obtained from the so-called "energy transfer" mode. Indeed, here, the receiver 12 which is directly connected between the terminals of the capacitor 16, is subjected to the alternating potential at high frequency developed between the terminals of the latter. Thus connected, this receiver derives a suitable portion of the high frequency current flowing between terminal 1 and terminal 3.

The portion of converted energy thus applied to the receiver 12, the impedance of which is known, will then be limited to a suitable value which is determined by the impedance of the primary 9a and the reactance of the capacitor 16.

By a judicious choice of the values affecting these two components, one will easily obtain a precise adjustment of the amplitude of this current, The resistor 17, connected in parallel with the receiver 12 and the capacitor 16, has the function of ensuring the passage of the direct current required by the charge of the capacitor 15, in the event that said receiver includes a dielectric barrier. In this case, the resistor 17 could also be connected between the terminal 8a and the terminal 3, which would allow, as before, the continuous charging of the capacitor 15. This resistor could still be replaced by the bridge of the resistors 17a and 17b which is established between the common terminals 8a and 8b and whose midpoint is common with the terminal 3. In this way, could also be obtained the DC voltage charge, at a substantially constant amplitude, of the capacitor 15 acting as a source continuous buffer 4.

The diode 18, suitably polarized, connected in parallel with the capacitor 15 has the optional role of improving the transmission of the alternating current at high frequency passing between the terminals 3 and 5.

In fact, this diode allows the capacitor 15 to be crossed only by a single half-wave of said current recovered at high frequency.

Figure 5, attached, illustrates another embodiment of the device object of the invention. This embodiment differs from the previous ones by the fact that an additional inductor 19 is connected in series with the capacitor 16 to form with the latter a series oscillating circuit. In this case, the impedance of the primary 9a no longer plays a significant role in the resonance frequency of said oscillating circuit because, this primary, associated with the secondary 9b and 9c, has no other function than to constitute an independent transformer. which ensures the control of the alternating cyclic conduction of the transistors la and lb. In this embodiment, the capacitors 3a and 3b are replaced by a single capacitor 3c whose own capacity is double the unit capacity of each of the first two, thus, at said high frequency, the reactance of this single capacitor remains substantially identical to the result of the other two capacitors, which makes it possible to obtain similar performances while achieving the economy of a component. Here, as indicated above, the resistor 17 makes it possible to charge from the terminals 8a and 7c the voltage reservoir capacitor 15 while overcoming the galvanic isolation or the non-linear characteristics which the output receiver 12 could have.

The resistor 15a for limiting the inrush current caused by the charging of the voltage reservoir capacitor 15 when the mains input terminals 7a and 7b are energized is, here, connected in series with the transistors la and lb constituting the above-mentioned active bridge branch.

Figure 6, attached, illustrates a final embodiment of the device 1 according to the invention. This embodiment differs from the embodiment previously illustrated in FIG. 2, appended hereto, in that the voltage reservoir capacitor IS, acting as a buffer continuous source 4, is no longer mounted between terminals 3 and 5 , but between terminals 1 and 3, in series with the output load 2.

In this case, terminal 3 and terminal 5 are connected together, - 15 -

- 1 6 -

Thus, because the high-value reservoir capacitor 15 has only a very low impedance at the low frequency of the rectified sector, the converted high frequency alternating current which passes through it is practically free from any modulation at 100 or 120 Hz of the

This characteristic essentially differentiates the function of the capacitor 15, used as a non-modulable DC voltage buffer, from the function occupied by the capacitor C of FIG. 1, attached, which has only a barrier role. galvanic between the terminals of which the converted high frequency current undergoes a modulation at 100 or 120Hz whose amplitude can equal that of the rectified mains voltage available between the output terminals of the diode bridge J.

As just described, the device according to the invention makes it possible to correct the power factor as well as the harmonic distortion rate affecting the current taken on the 1st sector almost completely.

This result is obtained by adding to the aforesaid envelope of rectified mains current only a single envelope at low frequency originating from the rectification of a given portion of energy at high frequency converted, unlike the devices according to prior art which, to achieve a lower result, require the addition of two separate low frequency envelopes which respectively result from the rectification of a current signal and a voltage signal, both taken from the frequency energy high conversion. In addition, unlike the device illustrated in Figure 1, attached hereto, the device according to the invention makes it possible to eliminate, between the terminals of the capacitors 8 and 6, the dangerous overvoltages which the capacitors H and K bear, the main cause of which is is to be sought in a very excessive overmodulation at 100 or 120Hz of the converted current.

The device according to the invention, which is simple to construct and does not require any tedious adjustment, makes it possible to correct the drawbacks presented by the devices according to the prior art.

The device according to the invention can be advantageously used in all inexpensive applications which must meet the standards relating to the current taken from the network, such as mains supplies, electronic transformers, electronic ballasts, compact fluorescent lamps, etc ...

As is obvious, and as it follows from the above, the invention in no way limits the modes of application and embodiments which have been more particularly envisaged, it embraces, on the contrary, all variants.

Claims

1. Device supplied by the AC sector comprising a bridge converter, the active branch of which comprises switching means (! ') And (1 ") and the passive branch of which comprises capacitors (3a) and (3b), this half-bridge delivering on an output load (2) an alternating current at high frequency of substantially constant amplitude while the current taken from the network remains substantially sinusoidal and in phase with the voltage thanks to the recovery carried out according to the mode of energy transfer. of a portion of the high frequency energy developing between the midpoint (3) of said passive branch and polarized common terminals (8a) and (8b) due to the reactance opposed by said passive branch, this allowing , after rectification of this portion of energy by a full-wave rectifier bridge comprising diodes (5a) and (5b), to obtain, between the terminals of a decoupling capacitor (6), a low-frequency envelope nce, the addition of which to the signal of the rectified mains current present between a polarized output terminal (7c) of a mains rectifier bridge (7) and one of the common polarized terminals (8a) makes it possible to compensate for the effects of the low impedance d '' a decoupling capacitor (8), this resulting in a low residual ripple rate between the common polarized terminals (8a) and (8b) as well as by an almost perfect compensation of the power factor and of the harmonic distortion of the current taken from the network, characterized in that a buffer source of continuous voltage (4) of substantially constant amplitude forms with the load output (2) a series circuit which is connected between the midpoint of the active branch (1) and an unpolarized input terminal (5) of the full-wave rectifier bridge (5a, 5b), this voltage source ( 4) having only a negligible impedance when passing the aforementioned high frequency alternating current.

2. Device according to claim 1, characterized in that the amplitude (V3) of the DC voltage developed between the midpoint of the passive branch (3) and the non-polarized input terminal (5) of the full-wave rectifier bridge (5a , 5b), which constitute the terminals of the buffer source (4), is approximately equal to the difference existing between the amplitude (V2) of the voltage developed between the midpoint of the active branch (1) and one of the polarized common terminals (8a, 8b) and the amplitude (V4) of the voltage between the non-polarized input terminal (5) and one of said polarized common terminals, this allowing a good adaptation of the different potentials brought into play by the above device.

3. Device according to claims 1 and 2, characterized in that the DC voltage buffer source (4) is constituted by a high capacity reservoir capacitor (15) whose charging is carried out from one of the common polarized terminals (8a) and the polarized output terminal (7c) of the mains rectifier bridge (7).

4. Device according to claims 1, 2 and 3, characterized in that a low value resistor (15a) is mounted in series with the charging circuit of the reservoir capacitor (15) in order to limit the current call caused by the latter when this device is switched on.

5. Device according to claims 1, 2, 3 and 4, characterized in that a resistor (17) of high value or a bridge of resistors of high value (17a) and ⁽ 17b ⁾ derive part of the potential corresponding to the sector rectified present between the polarized terminals (8a) or ⁽ 7c ⁾ and the terminals of the reservoir capacitor (15) so that the leakage current affecting this capacitor is permanently compensated and that the DC voltage present between the terminals of the latter remains substantially constant.

6. Device according to claims i, 2, 3, 4 and 5, characterized in that the reservoir capacitor (15 ⁾ , or the DC voltage buffer source (4), form with the output load (2) a series circuit which is connected between the midpoint of the active branch (1) and the midpoint of the passive branch (3).

7. Device according to claims 1, 2, 3, 4, 5 and 6, characterized in that the capacitors (3a ⁾ and ⁽ 3b ⁾ constituting the aforementioned passive bridge branch are reduced to a single capacitor (3c) whose capacity clean is substantially double the unit capacity of the first two.

8. Device according to claims 1, 2, 3, 4, 5, 6 and 7, characterized in that the switching means

(1 ') and (1 ") are semiconductors of any type suitable for use in switching.

9. Device according to claims 1, 2, 3, 4, 5, 6, 7 and 8, characterized in that the load (2) consists of the primary (9a) of a transformer whose secondary (9b) and (9c) control the alternating cyclic conduction of switching means (la) and (lb) and whose secondary (9d) ensures the evacuation of energy converted at high frequency on an output receiver (12), depending on the voltage transfer mode.

10. Device according to claim 9, characterized in that a capacitor (13), connected between the terminals of the secondary (9d), constitutes with the latter a parallel oscillating circuit resonating on the above high frequency.

11. Device according to claims 1, 2, 3, 4, 5, 6, 7 and 8, characterized in that the inductance of the primary (9a) and the capacitance of a capacitor (16), connected in series, constitute a series oscillating circuit resonating on the above high frequency, from which, according to the energy transfer mode, the converted energy is taken, which is applied to the output receiver (12), connected between the terminals of the capacitor (16 ), while the secondary (9b) and (9c), coupled to the primary (9a) by means of a magnetic circuit (9), ensure the control of the alternating cyclic conduction of the switching means (la) and (lb) .

12. Device according to claim 11, characterized in that the magnetic circuit (9) no longer constitutes, with the primary (9a) and the secondary (9b) and (9c), a transformer capable of ensuring only the control of the alternating cyclic conduction of the switching means (la) and (lb), an independent inductor (19) being responsible for constituting with the capacitor (16) the aforesaid series oscillating circuit resonating on the above high frequency.

13. Device according to claim 3, characterized in that a diode (18), suitably polarized, is connected between the terminals of the reservoir capacitor (15).

14. Device according to claim 3, characterized in that the reservoir capacitor (15) is of a type called electrolytic.