ACTIVE VOLTAGE DAMPER AND VOLTAGE CONVERTER

Abstract

This active voltage damper (108) comprises: a ground terminal (BM) and an input terminal (BE1, BE2); a damping capacitor (C); a damping activation device (D1, D2) designed to connect the input terminal (BE1, BE2) to a second terminal (BC) of the damping capacitor (C) to charge the damping capacitor (C) through this second terminal (BC); a discharge switch (Q) for the damping capacitor (C); and a control circuit (110) for the discharge switch (Q) designed to close the discharge switch (Q) so that the damping capacitor (C) discharges through its second terminal (BC) via the discharge switch (Q). The control circuit (110) is electrically powered by the damping capacitor (C) by being connected to the second terminal (BC) of the damping capacitor (C) to receive current from the damping capacitor (C). Figure for the abridged version: Fig. 1

Description

Title of the invention: ACTIVE VOLTAGE DAMPER AND VOLTAGE CONVERTER Technical field of the invention

[0001] The present invention relates to an active voltage damper, a voltage converter. Technological background

[0002] The American patent published under number US 5,898,581 describes an active voltage damper of the type comprising: - a ground terminal and an input terminal designed to receive an input voltage relative to the ground terminal; - a damping capacity having a first terminal connected to the ground terminal; - a damping activation device designed to connect the terminal input to a second terminal of the damping capacitor when the input voltage at this input terminal reaches a certain threshold, to charge the damping capacitor through this second terminal; - a discharge switch of the damping capacity, this discharge switch being connected to the second terminal of the damping capacity; and - a discharge switch control circuit adapted to close the discharge switch so that the damping capacitor discharges through its second terminal through the discharge switch.

[0003] In this active damper of the prior art, the discharge switch is controlled by a control member of the converter to which the active damper belongs. It is therefore necessary to route connection links between said control member and this discharge switch, which can cause complexity in the routing of the converter connections and additional cost.

[0004] It may thus be desirable to provide an active voltage damper which makes it possible to simply control the discharge switch. Summary of the invention

[0005] There is therefore proposed an active voltage damper of the aforementioned type, characterized in that the control circuit is electrically powered by the damping capacitor, being connected to the second terminal of the damping capacitor to receive current from the damping capacitor.

[0006] Thanks to the invention, an external power supply is not necessary for the circuit of order. The latter can thus be autonomous.

[0007] Optionally, the control circuit comprises a comparator circuit configured to compare a voltage presented by the damping capacitor with at least one threshold, the control circuit being configured to control the discharge switch as a function of the comparison.

[0008] Thus, since the comparison function can be easily implemented in an analog manner, the control circuit can be implemented in a simple manner, without requiring processing by a microprocessor.

[0009] Also optionally, the at least one threshold comprises a first threshold and a second threshold, lower than the first, and the control circuit is designed to close the discharge switch when the voltage of the damping capacitor reaches the first threshold and to open the discharge switch when the voltage of the damping capacitor reaches the second threshold.

[0010] Thus, due to the hysteresis, it is possible to control the discharge switch without a fixed clock. In fact, a pseudo clock (of variable frequency) is produced by the hysteresis.

[0011] Also optionally, the control circuit comprises a power supply circuit designed to provide, from the damping capacitor, a supply voltage to the comparator circuit.

[0012] Such a supply voltage makes it possible to power the usual electrical components, such as an operational amplifier, making it possible to implement the comparison function.

[0013] Also optionally, the discharge switch has a current input terminal connected to the second terminal of the damping capacitor and the control circuit is configured to control the discharge switch by a control voltage applied between a control terminal of the discharge switch and its current input terminal.

[0014] Indeed, in US patent 5,898,581, the switch is an N-channel insulated gate field effect transistor so that it is controlled between its control terminal and its current output terminal. Thus, when the switch is open, the current output terminal is at a floating potential, so that it is necessary to use an isolated driver to control it. In this implementation of the invention, because the current input terminal has a fixed voltage, it is possible to simply control the switch without an isolated driver.

[0015] Also optionally, the at least one input terminal comprises two input terminals.

[0016] Also optionally, the damping activation device comprises, for each input terminal, a diode having an anode connected to this terminal. input and a cathode connected to the second terminal of the damping capacitor.

[0017] Thus, the damping activation device can be implemented in a simple manner using standard electrical components.

[0018] Also optionally, the active voltage damper further comprises an inductor connected to a current output terminal of the discharge switch.

[0019] Thus, due to the inductance, the discharge current can be limited.

[0020] A DC-DC voltage converter is also proposed comprising: - a voltage rectifier comprising at least one switch; and - an active voltage damper according to the invention, each switch being connected between a respective input terminal and the ground terminal of the active voltage snubber.

[0021] Optionally, the DC-DC voltage converter further comprises: - a galvanic isolation transformer; - a DC-AC converter connected to a primary of the transformer; and the rectifier is connected to a secondary of the transformer.

[0022] A motor vehicle is also proposed comprising: - first and second batteries; and - a direct-direct voltage converter according to the invention, connected between the first and second batteries. Brief description of the figures

[0023] The invention will be better understood with the aid of the following description, given solely by way of example and with reference to the appended drawings in which:

[0024] [Fig-1] [Fig.l] is a simplified electrical diagram of a first example of voltage converter according to the invention,

[0025] [Fig.2] [Fig.2] is a simplified electrical diagram of a control circuit of the voltage converter of [Fig.l],

[0026] [Fig.3] [Fig.3] groups together timing diagrams of electrical quantities of the voltage converter of [Fig.l], and

[0027] [Fig.4] [Fig.4] is a simplified electrical diagram of a second example of voltage converter according to the invention. Detailed description of the invention

[0028] With reference to [Fig.l], a first example of a voltage converter 100 according to the invention will now be described.

[0029] For example, the voltage converter 100 is an isolated DC-DC converter, such as a “flyward” type converter, described for example in detail in the French patent application published under the number FR 3 056 038 A1.

[0030] The voltage converter 100 is for example provided in a motor vehicle to connect two motor vehicle batteries with different voltages to each other. The higher voltage battery, called HT for "high voltage", is generally used to power a motor vehicle's traction system. Its nominal voltage can be between 400V and 800V. The lower voltage battery, called BT for "low voltage", is generally used to power motor vehicle accessories (headlights, radio, on-board computer, heated seats, etc.) and its nominal voltage can be between 10V and 50V, for example 12V.

[0031] The voltage converter 100 firstly comprises a galvanic isolation transformer 102.

[0032] The voltage converter 100 further comprises a direct-alternating converter 104 connected to a primary 102P of the transformer 102.

[0033] The DC-AC converter 104 comprises, for example, two controllable switches QA, QB. Preferably, each of them comprises a semiconductor switch, for example a transistor switch such as an insulated gate field effect transistor (from the English "Metal Oxide Semiconductor Field Effect Transistor", also designated by the acronym MOSFET) or an insulated gate bipolar transistor (from the English "Insulated Gate Bipolar Transistor", also designated by the acronym IGBT).

[0034] The DC-AC converter 104 further comprises, for example, a capacitor CF connected between the two controllable switches QA, QB. A DC input voltage VE is thus intended to be received at the terminals of all the switches QA, QB and the capacitor CF.

[0035] The voltage converter 100 further comprises a voltage rectifier 106 connected to a secondary 102S of the transformer 102.

[0036] The voltage rectifier 106 comprises two switches Q1, Q2. Preferably, each of them is controllable and comprises a semiconductor switch, for example a transistor switch such as a MOSFET or an IGBT. Each controllable switch Q1, Q2 is connected between a respective end of the secondary 102S of the transformer 102 and an electrical ground M. The controllable switches Q1, Q2 are thus designed to respectively have voltages V1, V2.

[0037] Alternatively, the switches Q1, Q2 could be two diodes respectively.

[0038] The voltage rectifier 106 further comprises an output capacitor CS connected between the electrical ground M and a midpoint of the secondary 102S of the transformer 102. The output capacitor CS is thus designed to have a continuous output voltage VS.

[0039] The voltage converter 100 further comprises a device 107 for controlling the switches QA, QB, Ql, Q2. In particular, the control device 107 can be designed to control the switches Ql, Q2 in opposition with a duty cycle of 50% (and with a possible dead time).

[0040] The voltage converter 100 further comprises an active voltage damper 108 designed to dampen the voltages VI, V2, i.e. to limit their value.

[0041] For this, the active voltage damper 108 firstly comprises two input terminals BEI, BE2, for example connected respectively between the ends of the secondary 102S of the transformer 102 and the controllable switches Q1, Q2, to receive the voltages VI, V2 respectively. The active voltage damper 108 further comprises a ground terminal BM connected to the ground M of the voltage converter 100 and an output terminal BS connected to the output capacitor CS.

[0042] The active voltage damper 108 further comprises a damping capacitor C having a first terminal connected to the ground terminal BM. This damping capacitor C is designed to have a capacitance voltage VC.

[0043] The active voltage damper 108 further comprises a damping activation device designed to connect a second terminal BC of the damping capacitor C to the input terminal BEI, respectively BE2, when the voltage VI, respectively V2, reaches a certain threshold.

[0044] The damping activation device may for example comprise two diodes D1, D2 each having an anode connected to the respective input terminal BE1, BE2 and a cathode connected to the second terminal BC of the damping capacitor C. Thus, assuming the diodes D1, D2 to be ideal, the diode D1, respectively D2, becomes conductive when the voltage VI, respectively V2, reaches the capacitor voltage VC. The damping capacitor C is then charged through this diode D1, respectively D2.

[0045] The active voltage damper 108 further comprises a switch Q for discharging the damping capacitor C. The discharge switch Q is controllable and designed to allow, when closed, a discharge of the damping capacitor C, in particular in the output capacitor CS. Preferably, the discharge switch Q is a semiconductor switch, for example a transistor switch such as a MOSFET or an IGBT.

[0046] The discharge switch Q has a current input terminal S connected to the second terminal BC of the damping capacitor C, a current output terminal D and a control terminal G. The discharge switch Q is designed to be controlled by a control voltage VGs applied between its control terminal G and its current input terminal S.

[0047] For example, the discharge switch Q comprises a P-channel MOSFET. Thus, terminals S, D, G respectively comprise a source, a drain and a gate of this MOSFET. In addition, still for example, the discharge switch Q is open when the voltage VGs is substantially zero and closed when the voltage VGs is negative, for example less than - 4 V.

[0048] The active voltage damper 108 further comprises a component connected between the current output terminal D of the discharge switch Q and the output terminal BS. Thus, when the discharge switch Q is closed, the damping capacitor C discharges to the output terminal BS through this component. The presence of this component thus makes it possible to connect the damping capacitor C to the capacitor CS while the voltage VC can be higher, in practice up to three times higher, than the voltage VS. Preferably, this component is an inductance L which has the advantage of making it possible to limit the current flowing from the damping capacitor C to the output terminal BS. Indeed, as will be explained later, when the discharge switch Q is closed, the inductance is traversed by a substantially linearly increasing current.

[0049] The active voltage damper 108 further comprises a freewheel diode D' having an anode connected to the ground terminal BM and a cathode connected between the controllable switch and the inductance L. This freewheel diode D' is designed to allow the current to continue to pass through the inductance L when the discharge switch Q is open.

[0050] The discharge switch Q, the inductance L and the freewheeling diode D' can thus be considered as a DC-DC converter which converts the voltage VC of the damping capacitor C into the output voltage VS.

[0051] The active voltage damper 108 further comprises a circuit 110 for controlling the discharge switch Q. The control circuit 110 is connected to the control terminal G and to the current input terminal S of the discharge switch Q in order to provide the control voltage VGS. The control circuit 110 can further be connected to the output terminal BS, as illustrated in [Fig.2].

[0052] Since the current input terminal S of the discharge switch Q and the terminal BC of the damping capacitor C are connected to each other, the control circuit 110 is also connected to the terminal BC of the damping capacitor C. As will be explained in more detail later, the control circuit 110 receives current from the damping capacitor C through the terminal BC, in order to be electrically powered by the damping capacitor C. This allows the control circuit 110 to be autonomous, i.e. not to require an external power supply.

[0053] With reference to [Fig.2], an exemplary control circuit 110 will now be described in more detail.

[0054] The control circuit 110 firstly comprises a power supply circuit 202 designed to provide a continuous supply voltage Vaiim. This supply voltage Vaiim can for example be obtained from a voltage present between the capacitance terminal BC and the output terminal BS. In the example described, the supply voltage Vaiim is provided between the capacitance terminal BC and a floating RF reference terminal of the supply circuit 202.

[0055] The power supply circuit 202 may further comprise a Zener diode ZI and a capacitor Cl connected in parallel with each other. These two components Zl, Cl are for example connected between the capacitor terminal BC and the floating reference terminal RF. The power supply circuit 202 may further comprise a resistor RI connected between the floating reference terminal RF and the output terminal BS. The Zener diode Zl has a reverse voltage, to which the supply voltage Vaiim is substantially equal and smoothed by the capacitor CL

[0056] The control circuit 110 further comprises a circuit 204 for measuring the capacitance voltage VC.

[0057] In the example described, the measuring circuit 204 comprises a resistor R2 and a Zener diode Z2 connected one after the other between the capacitance terminal BC and the output terminal BS. Thus, the resistor R2 and the Zener diode Z2 are connected to each other at a midpoint having, with respect to the floating reference RF, a voltage MVC equal to: [Math.l] MVC = Valim - VC 4- VS - Uz where Uz is a reverse voltage of Zener diode Z2.

[0058] Thus, as the supply voltage Vaiim, the output voltage VS and the reverse voltage of the Zener diode Z2 are substantially constant, the voltage MVC is indeed representative of the voltage VC and therefore constitutes a measurement of this voltage VC.

[0059] The control circuit 110 further comprises a comparator circuit 206 designed to receive the measurement MVC and, from the latter, compare the voltage VC of the damping capacitor C with at least one threshold. The comparator circuit 206 is further designed to provide a control signal S of the discharge switch Q as a function of the comparison.

[0060] Preferably, the comparator circuit 206 is hysteresis. In this case, it can be designed to provide the control signal S at a closing value of the discharge switch Q when the voltage VC of the damping capacitor C reaches, by increasing, a first threshold S1 and to provide the control signal S at an opening value of the discharge switch Q when the voltage VC of the damping capacitor C reaches, by decreasing, a second threshold S2, lower than the first threshold SL

[0061] For example, the closing value of the discharge switch Q corresponds to the voltage Vaiim relative to the floating RF reference terminal, while the opening value of the discharge switch Q corresponds to 0 V relative to the floating RF reference terminal.

[0062] Thus, due to the hysteresis, it is possible to control the discharge switch Q without a fixed clock. In fact, a pseudo clock (of variable frequency) is produced by the hysteresis. With the fact that the discharge switch Q is controlled between the terminals G, S, the absence of a clock makes it possible to produce the control circuit 110 in a very simple manner.

[0063] To achieve the hysteresis, the comparator circuit 206 comprises for example a simple comparator circuit 207 (for example an integrated analog circuit such as an operational amplifier) ​​connected between the terminals BC and RF to be powered by the supply voltage Vaiim. The simple comparator circuit 207 has two inputs el, e2 and an output s designed to present the control signal S. The control signal is defined as a function of the comparison between the voltages on the inputs el, e2. To apply a reference REF to the input e2, the comparator circuit 206 may comprise two resistors R5, R6 one after the other between the capacitance terminal BC and the floating reference terminal RF in order to form a voltage divider at their midpoint which is connected to the input e2.The comparator circuit 206 may further comprise two resistors R3, R4 one after the other between, on the one hand, a midpoint between the resistor R2 and the Zener diode Z2 and, on the other hand, the output s. These resistors R3, R4 thus form a voltage divider at their midpoint which is connected to the input el. Thus, the voltage at the input el depends both on the MVC measurement and on the control signal S, which makes it possible to create the hysteresis.

[0064] The control circuit 110 further comprises a current amplifier circuit 208 connected between the output s of the comparator circuit 206 and the control terminal G of the discharge switch Q.

[0065] In the example described, the current amplifier circuit 208 comprises two bipolar transistors TB1, TB2, respectively of NPN and PNP type, connected one after the other between the capacitance terminal BC and the floating reference terminal RF. The bipolar transistors TB1, TB2 have respective bases both connected to the output s of the comparator circuit to receive the control signal S. The current amplifier circuit 208 further comprises a resistor R8 connected between a midpoint of the bipolar transistors TB1, TB2 and the control terminal G of the discharge switch Q.

[0066] With reference to [Fig.3], an example of operation of the active voltage damper 108 will now be described.

[0067] Initially, at a time t0, the two switches Ql, Q2 are closed, so that the voltages VI, V2 are zero. The diodes Dl, D2 are blocked and the current IL is substantially zero.

[0068] At a time t1, the control device 107 opens the switch Q2. The voltage V2 then increases towards a final value. The diodes D1, D2 being blocked, the damping capacitor C is not charged so that the voltage V2 increases rapidly. Due to the presence of parasitic capacitors and / or inductance, this sudden increase causes the appearance of oscillations around the final value.

[0069] At a time t2, while the voltage V2 is in the rising part of the first oscillation, the voltage V2 reaches the capacitance voltage VC and the diode D2 becomes conductive to charge the damping capacitance C, which limits the increase in the voltage V2. The voltage VC then increases with the voltage V2.

[0070] At a time t3, the control device 110 detects that the voltage VC reaches the first threshold SI and, in response, closes the discharge switch Q. The damping capacitor C then discharges through the inductance L, which causes the appearance of an increasing current IL. The current IL increases substantially linearly because the voltage VC and the output voltage VS are substantially constant, so that the voltage across the inductance L is substantially constant.

[0071] The voltage V2 is then in the falling part of the first oscillation and therefore becomes lower than the voltage VC so that the diode D2 becomes blocked again. The following oscillations are for example of lower amplitude than the first oscillation so that the voltage V2 remains lower than the voltage VC.

[0072] At time t4, the control device 110 detects that the voltage VC reaches the second threshold S2 and, in response, opens the discharge switch Q. The damping capacitor C then stops discharging, so that its voltage VC remains constant at the threshold S2. Furthermore, the inductance L is connected to the electrical ground M through the diode D' which becomes conductive. The current IL is supplied through the diode D' and decreases.

[0073] At a time t5, the control device 107 closes the switch Q2, so that the voltage V2 decreases to zero.

[0074] At a time t6, the control device 107 opens the switch Q1. The voltage VI then increases towards a final value. The diodes D1, D2 being blocked, the damping capacitor C is not charged so that the voltage VI increases rapidly. Due to the presence of parasitic capacitors and / or inductance, this sudden increase causes the appearance of oscillations around the final value.

[0075] At a time t7, while the voltage VI is in the rising part of the first oscillation, the voltage VI reaches the capacitance voltage VC and the diode D1 becomes conductive to charge the damping capacitance C, which limits the increase in the voltage VL. The voltage VC then increases with the voltage VI, until it reaches the falling part of the first oscillation. The voltage VI then becomes lower than the voltage VC so that the diode DI becomes blocked again. The following oscillations are, in the example described, of lower amplitude than the first oscillation so that the voltage VI remains lower than the voltage VC. Thus, in general, the SI threshold is not necessarily reached at each switching. This may take several switchings. In the example described, the SI threshold is reached every two switchings (one switching of Q1 and one switching of Q2).

[0076] At time t8, the inductance current IL becomes zero.

[0077] At a time t9, the control device 107 closes the switch Ql, so that the voltage VI decreases to zero.

[0078] The active voltage damper 108 is then returned to a state identical to the initial state t0 and the steps described previously are repeated.

[0079] With reference to [Fig.4], another example of a voltage converter 400 according to the invention will now be described.

[0080] In [Fig.4], the DC-AC converter connected to the primary 102P of the trans trainer 102 is not shown. It could be like the one in [Fig.l], or different.

[0081] The switches Ql, Q2 are this time diodes. Thus, the switches Ql, Q2 are not controllable, but switch according to the state of the voltage converter.

[0082] The rectifier, designated by the reference 402, further comprises an output inductance LS connected between the switches Q1, Q2 and the output capacitor CS.

[0083] Furthermore, the active voltage damper, designated by the reference 404, is similar to that of [Fig.l], except that it comprises a single input terminal BE connected to the two switches Ql, Q2 and that the damper activation device comprises a single diode D having an anode connected to the input terminal BE and a cathode connected to the damper capacitor C.

[0084] Furthermore, the ground terminal BM is connected to the midpoint of the secondary 102S of the transformer 102.

[0085] Thus, an input voltage V is present between the input terminal BE and the ground terminal BM, and the active voltage damper 404 makes it possible to dampen it, thereby protecting the diodes Q1, Q2.

[0086] It is clear that an active voltage damper such as that described above makes it possible to simplify the control of the active voltage damper switch.

[0087] It will also be noted that the invention is not limited to the embodiments described above. It will indeed appear to those skilled in the art that various modifications can be made to the embodiments described above, in light of the teaching which has just been disclosed to them.

[0088] In the detailed presentation of the invention which is made above, the terms used must not be interpreted as limiting the invention to the embodiments set out in the present description, but must be interpreted to include all equivalents whose prediction is within the reach of those skilled in the art by applying their general knowledge to the implementation of the teaching which has just been disclosed to them.

Claims

Claims

1. Active voltage damper (108; 404) comprising: - a ground terminal (BM) and an input terminal (BEI, BE2; BE) adapted to receive an input voltage (VI, V2; V) relative to the ground terminal (BM); - a damping capacitor (C) having a first terminal connected to the ground terminal (BM); - a damping activation device (Dl, D2; D) adapted to connect the input terminal (BEI, BE2; BE) to a second terminal (BC) of the damping capacitor (C) when the input voltage (VI, V2; V) at this input terminal (BEI, BE2; BE) reaches a certain threshold (VC), to charge the damping capacitor (C) via this second terminal (BC); - a switch (Q) for discharging the damping capacity (C), this discharge switch (Q) being connected to the second terminal (BC) of the damping capacity (C);and - a circuit (110) for controlling the discharge switch (Q) designed to close the discharge switch (Q) so that the damping capacitor (C) discharges via its second terminal (BC) through the discharge switch (Q); characterized in that the control circuit (110) is electrically powered by the damping capacitor (C) by being connected to the second terminal (BC) of the damping capacitor (C) to receive current from the damping capacitor (C).;

2. An active voltage damper (108; 404) according to claim 1, wherein the control circuit (110) comprises a comparator circuit (206) adapted to compare a voltage (VC) presented by the damping capacitor (C) with at least one threshold (SI, S2), the control circuit (110) being adapted to control the discharge switch (Q) depending on the comparison.

3. Active voltage damper (108; 404) according to claim 2, wherein the at least one threshold (SI, S2) comprises a first threshold (SI) and a second threshold (S2), lower than the first (SI), and wherein the control circuit (110) is designed to close the switch discharge (Q) when the voltage (VC) of the damping capacitor (C) reaches the first threshold (SI) and to open the discharge switch (Q) when the voltage (VC) of the damping capacitor (C) reaches the second threshold (S2).

4. Active voltage snubber (108; 404) according to claim 3, wherein the control circuit (110) comprises a supply circuit (202) adapted to provide, from the snubber capacitor (C), a supply voltage (Vaiim) to the comparator circuit (206).

5. An active voltage damper (108; 404) according to any one of claims 1 to 4, wherein the discharge switch (Q) has a current input terminal (S) connected to the second terminal (BC) of the damping capacitor (C) and wherein the control circuit (110) is adapted to control the discharge switch (Q) by a control voltage (VGs) applied between a control terminal (G) of the discharge switch (Q) and its current input terminal (S).

6. An active voltage snubber (108) according to any one of claims 1 to 5, wherein the at least one input terminal comprises two input terminals (BEI, BE2).

7. Active voltage damper (108; 404) according to any one of claims 1 to 6, wherein the damping activation device (D1, D2; D) comprises, for each input terminal (BEI, BE2; BE), a diode (D1, D2; D) having an anode connected to this input terminal (BEI, BE2; BE) and a cathode connected to the second terminal (BC) of the damping capacitor (C).

8. An active voltage damper (108; 404) according to any one of claims 1 to 7, further comprising an inductor (L) connected to a current output terminal (D) of the discharge switch (Q).

9. DC-DC voltage converter (100; 400) comprising: - a voltage rectifier (106) comprising at least one switch (Ql, Q2); and - an active voltage damper (108; 404) according to any one of claims 1 to 8, each switch (Ql, Q2) being connected between a respective input terminal (BEI, BE2; BE) and the ground terminal (BM) of the active voltage damper (108; 404).

10. A DC-DC voltage converter (100; 400) according to claim 9, further comprising: - a galvanic isolation transformer (102); - a direct-alternating converter (104) connected to a primary (102P) of the transformer (102); and wherein the rectifier (106; 402) is connected to a secondary (102S) of the transformer (102).

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