VOLTAGE CONVERTER AND MOTOR VEHICLE WITH SUCH A VOLTAGE CONVERTER

Description

[0001] The present invention relates to a voltage converter and a motor vehicle comprising such a voltage converter.

[0002] The present invention can be applied in particular in the field of hybrid motor vehicles.

[0003] Publication WO 2019 / 120536 A1 describes the system detects a short circuit between the ground and internal phase points from a DC current and a DC voltage detected at the first end of the DC transmission link.

[0004] US Patent Application Publication US 2015 061 388 A1 discloses a voltage converter of the type comprising: a ground point for connection to an electrical ground; a high voltage point for presenting a high voltage relative to the electrical ground; a low voltage point for presenting a low voltage relative to the electrical ground; at least one voltage conversion cell connected to the ground, high voltage and low voltage points to perform a conversion between high voltage and low voltage; and a protection system designed to detect a short circuit between the ground and high voltage points and / or between the ground and low voltage points.

[0005] In this publication, a high voltage point current measuring device and a low voltage point current measuring device are provided.

[0006] The protection system is thus designed to detect a short circuit between the ground and high voltage points from the measurement of the high voltage current, and a short circuit between the ground and low voltage points from the measurement of the low voltage current.

[0007] It may therefore be desirable to provide a voltage converter to simplify short-circuit detection.

[0008] A voltage converter of the aforementioned type is therefore proposed, characterized in that it further comprises a device for measuring a ground current flowing between this ground point and the electrical ground, and in that the protection system is designed to detect the short circuit from the measured ground current.

[0009] Thus, thanks to the invention, a single measuring device can be used to detect both a short circuit on the high voltage side and a short circuit on the low voltage side.

[0010] Optionally, the ground current exits the voltage converter through the ground point.

[0011] Optionally, the protection system is designed, in response to detection of the short circuit, to place the voltage converter in a safe mode preventing current flow between the high voltage and low voltage points and vice versa through the cell(s).

[0012] Also optionally, in the safe mode, the low voltage point is disconnected from each cell to prevent current flow between the cell(s) and the low voltage point and vice versa.

[0013] Also optionally, the voltage converter further comprises a safety switch for each cell, placed between this cell and the low voltage point and the protection device is designed to place the voltage converter in safe mode, by opening this or these safety switches.

[0014] Also optionally, in safe mode, each cell is in a safe state in which any current input to the cell is blocked.

[0015] Also optionally, in safe mode, each cell is in a safe state in which all current flow into the cell is blocked.

[0016] Also optionally, each cell has a switching arm having a high side switch and a low side switch connected to each other at a midpoint, the switching arm being connected between the high voltage point and the ground point, while the midpoint is connected to the low voltage point, for example via an inductor.

[0017] Also optionally, the protection system is designed to place each cell in its safe state, by controlling the opening of its high and low side switches.

[0018] Also optionally, the protection system includes a comparison device designed to detect the short circuit when the ground current measurement is greater than a predefined threshold.

[0019] Optionally, the voltage converter also comprises a high voltage measuring device and the protection system is designed to detect a short circuit from the high voltage measurement, for example when the latter falls below a predefined threshold. For example, the protection system comprises a device for comparing the high voltage measurement with this predefined threshold.

[0020] Optionally, the voltage converter also comprises a low voltage measuring device and the protection system is designed to detect a short circuit from the low voltage measurement, for example when the latter falls below a predefined threshold. For example, the protection system comprises a device for comparing the low voltage measurement with this predefined threshold.

[0021] Also optionally, the voltage converter further comprises, for each cell, a device for measuring a cell current entering the cell from the low voltage point, as well as a system for validating the measured ground current from the measured cell currents.

[0022] Optionally, the validation system is also designed, in the event of non-validation, to provide a message indicating the non-validation of the measured ground current.

[0023] Also optionally, the validation system includes a ground current estimation module and a module for comparing the measured ground current with the estimated ground current to determine whether the measured and estimated ground currents are consistent with each other.

[0024] A motor vehicle comprising a voltage converter according to the invention is also provided.

[0025] 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: There [ Fig. 1 ] is an electrical functional diagram of an example of a voltage converter according to the invention, The [ Fig. 2 ] is an electrical circuit illustrating an embodiment of a voltage conversion cell of the voltage converter of the figure 1 , and The [ Fig. 3 ] is an electrical circuit illustrating an embodiment of a safety switch of the voltage converter of the figure 1 .

[0026] In reference to the figure 1 , an electrical system 100 intended to equip, for example, a motor vehicle will now be described.

[0027] The system 100 firstly comprises an electrical ground M, a direct voltage source 102 (such as a battery) designed to provide a high voltage HT (for example 48 V) relative to the electrical ground M and a load 104 designed to be electrically powered by a low voltage LV (for example 12 V) relative to the electrical ground M. Generally speaking, the high voltage HT is greater than or equal to the low voltage LV.

[0028] In order to obtain the low voltage LV from the high voltage HV, the system 100 further comprises a voltage converter 106.

[0029] The voltage converter 106 firstly comprises a ground point PM intended to be connected to the electrical ground M, a high voltage point P HT connected to the direct voltage source 102 in order to present the high voltage HT with respect to the electrical ground M and a low voltage point P BT connected to the load 104 in order to present the low voltage BT with respect to the electrical ground M. A high voltage current I HT is intended to output from the voltage converter 106 via the high voltage point P HT and a low voltage current I BT is intended to enter the voltage converter 106 via the low voltage point P BT.

[0030] The voltage converter 106 further comprises at least one voltage conversion cell connected to the ground points PM, high voltage P HT and low voltage P BT to carry out a conversion between the high voltage HT and the low voltage BT.

[0031] In the example described, three cells 108 1-3 are provided in parallel.

[0032] Still in the example described, each cell 108 1-3 is a switching cell.

[0033] In reference to the figure 2 , we will now describe these cells.

[0034] Each cell 108 1-3 comprises for example a switching arm comprising a high side switch 202 and a low side switch 204 connected to each other at a midpoint 206. The switching arm is connected between the high voltage point P HT and the ground point PM to receive the high voltage HT. Each cell 108 1-3 further comprises an inductor 208 connecting the midpoint 206 to the low voltage point P BT and a capacitor 210 connecting the low voltage point P BT to the electrical ground M, for example directly or, as illustrated, by being connected to the ground point PM . Each cell 108 1-3 further comprises for example a resistor 212 in series with the inductor 208. Alternatively, the cells 108 1-3 do not comprise a resistor 212 in series with the inductor 208.

[0035] The switches 202, 204 are for example transistor switches such as FET (Field-Effect Transistor) type transistors or insulated gate bipolar transistors, generally designated by the acronym IGBT (Insulated Gate Bipolar Transistor) or even high electron mobility transistors designated by the acronym HEMT (High-Electron-Mobility Transistor).

[0036] For example, FET type transistors are silicon MOSFETs (Si-MOSFETs) or silicon carbide MOSFETs (SiC-MOSFETs) or are gallium nitride FETs (GaN-FETs).

[0037] For example, HEMT type transistors are gallium nitride HEMT transistors (GaN-HEMT).

[0038] Back to the figure 1 , we will now explain how switches 202, 204 are controlled.

[0039] Each cell 108 1-3 is designed to be controlled in normal operation by CC 1-3 commands to alternately open and close the high side 202 and low side 204 switches, in opposition to each other. Furthermore, as will be explained later, CC 1-3 commands can open both switches 202, 204 at the same time.

[0040] The voltage converter 106 further comprises a device 110 for measuring a ground current IM flowing between this ground point PM and the electrical ground M. In other words, in the example described, the ground current IM leaves the voltage converter 106 via the ground point PM.

[0041] The voltage converter 106 further comprises a device 112 for measuring the high voltage HT and a device 114 for measuring the low voltage LV. The respective measurements of these devices 112, 114 will be referred to hereinafter as MHT and MBT.

[0042] The voltage converter 106 further comprises, for each cell 108 1-3 , a device 116 1-3 for measuring a cell current I 1-3 entering the cell 108 1-3 from the low voltage point P BT .

[0043] Each of the current measuring devices 110 and 116 1-3 may for example comprise a shunt, i.e. a resistor through which the current to be measured passes and the voltage at its terminals of which is measured.

[0044] The voltage converter 106 further comprises a protection system 118 designed to detect a short circuit between the ground points PM and high voltage points P HT (hereinafter called high voltage short circuit) and / or between the ground points PM and low voltage points P BT (hereinafter called low voltage short circuit). More specifically, the protection system 118 is designed to detect the short circuit from the ground current MI M measured by the measuring device 110, and preferably independently of the high voltage MHT and low voltage MBT measurements.

[0045] For this, in the example described, the protection system 118 firstly comprises a comparison device 120 designed to detect the short circuit when the measurement of ground current MI M is greater than a predefined threshold. Indeed, when a high voltage or low voltage short circuit occurs, a high short circuit current flows to ground M so that the ground current IM becomes high in both cases. Thus, with the single measuring device 110, it is possible to detect both types of short circuit.

[0046] The protection system 118 is further designed, in the example described, to detect a high voltage short circuit from the high voltage measurement MHT carried out by the measuring device 112, preferably independently of the ground current measurement MI M . For example, the protection system 118 comprises a comparison device 122 designed to detect the high voltage short circuit when the high voltage measurement MHT is below a predefined threshold.

[0047] The protection system 118 is further designed, in the example described, to detect a low voltage short circuit from the low voltage measurement MBT carried out by the measuring device 114, preferably independently of the ground current measurement MI M . For example, the protection system 118 comprises a comparison device 124 designed to detect the low voltage short circuit when the low voltage measurement MBT is lower than a predefined threshold.

[0048] Thus, for both types of short circuit, there is detection redundancy. In this way, it is possible to achieve a high level of detection safety. For example, for each type of short circuit, current and voltage detection can each be of ASIL B (Automotive Safety Integrity Level) safety level, and their combination can achieve the higher ASIL C level.

[0049] The protection system 118 is designed, in response to the detection of a short circuit, to place the voltage converter 106 in a safe mode preventing a flow of current between the high voltage P HT and low voltage P BT points through the cell(s) 108 1-3 . Thus, the high voltage network and the low voltage network can be isolated from each other in order to prevent the propagation of the fault on the other network.

[0050] For example, the protection system 118 is designed to place the voltage converter 106 in safe mode, by disconnecting the low voltage point P BT of each cell 108 1-3 . Thus, this prevents a flow of current between the cell(s) 108 1-3 and the low voltage point P BT . For example, the voltage converter 106 comprises a safety switch 126 1-3 for each cell 108 1-3 . This safety switch 126 1-3 is placed for example between this cell 108 1-3 and the low voltage point P BT .

[0051] In reference to the figure 3 , we will now describe a safety switch.

[0052] Each safety switch 126 1-3 comprises, for example, two transistor switches 302, 304 connected in series and in opposition to each other. Thus, when they are both open, the flow of current is prevented in both directions of flow. In particular, the flow of current through the reverse diode of one is then prevented by the other.

[0053] In the example described in figure 3 , the two transistor switches 302, 304 are N-Type MOSFET transistors connected by their source. Alternatively, the two transistor switches 302, 304 may be FET or HEMT transistors connected by their source.

[0054] Back to the figure 1 , we will now explain how safety switches work.

[0055] Each of the safety switches 126 1-3 is closed during normal operation and is designed to receive a protection signal CS 1-3 from the protection device 118.

[0056] In the example described, the protection system 118 is designed to provide this protection signal in the event of detection of a short circuit (by at least one of the devices 120, 122, 124). In the example described, the “+” block of the figure 1 indicates the logical OR function.

[0057] In other embodiments, safety switches similar to safety switches 126 1-3 may be provided on the high voltage side, in addition to or instead of safety switches 126 1-3 .

[0058] In other embodiments, a single safety switch may be provided on the branch common to the cells 108 1-3 , connected to the high voltage point P HT or to the low voltage point P BT . A safety switch per cell has advantages, in particular when the converter comprises a device for detecting the cell where a failure occurs. Indeed, in certain operating modes of the voltage converter 106, not all the cells 108 1-3 need to be used at the same time. Thus, it is possible to disconnect only the defective cell via the associated safety switch, whether the latter is placed on the high voltage side or on the low voltage side. Such a mode is for example the precharge mode, in which capacitors (such as the capacitors 210) are charged from the low voltage BT, before connecting the voltage source 102 to the voltage converter 106.Another mode where the cells 108 1-3 do not all need to be used may be a degraded operating mode in which the faulty cell is isolated by opening the associated safety switch 126 1-3, but where the other cells continue to be used to perform the voltage conversion by keeping the associated safety switches closed.

[0059] Furthermore, the protection system 118 is designed to place the voltage converter 106 in a safe mode, by placing each cell 108 1-3 in a safe state. In this safe state, any current input into the cell 108 1-3 is blocked. In the example described, the protection system 118 is designed to control the opening of the high and low side switches of the cell 108 1-3 . For example, the voltage converter 106 has a driver stage 128 (from the English "driver stage") of the high and low side switches and the protection system 118 is designed to send the protection signal to the driver stage 128, so that the latter ignores the CMD commands normally received to carry out the voltage conversion and instead opens, in each cell 108 1-3 , the two high 202 and low 204 side switches.

[0060] If the failure actually occurs on one of the switches 202, 204 of the cells 108 1-3, these commands to open the control stage 128 may be ineffective. Indeed, the faulty switch may behave as a short-circuit independently of the command it receives. However, opening the safety switches 126 1-3 still makes it possible to place the voltage converter 106 in safe mode.

[0061] Furthermore, the voltage converter 106 comprises a system 130 for validating the measured ground current MI M from the measured cell currents MI 1-3 by the measuring devices 116 1-3 .

[0062] More specifically, in the example described, the validation system 130 comprises a module 132 for estimating the ground current IM from the measured cell currents MI 1-3 , for example from their sum. In the example described, the estimation is further carried out from the high voltage MHT and low voltage MBT measurements, for example from a ratio of these two measurements. For example, the estimation takes into account the fact that the power on the high voltage side is equal to the power on the low voltage side, using a conversion efficiency factor depending on the operating mode of the voltage converter 106.

[0063] For example, when the voltage converter operates in buck mode from the source side to the load side, the estimate can be: I ^ M = ∑ I k ⋅ 1 − 1 / 0 , 9507 ⋅ MBT / MHT with k = 1...3 in the example described.

[0064] Still for example, when the voltage converter operates in voltage amplification mode (from the English "boost") from the load side to the source side, for example to recharge the DC voltage source 102, the estimate can be: I ^ M = ∑ I k ⋅ 1 − 1 / 0 , 9412 ⋅ MBT / MHT

[0065] Still for example, in other cases (neither buck nor boost), for example, when the measured high voltage MHT or the measured low voltage MBT is substantially zero, the estimate can be: I ^ M = ∑ I k ⋅ 1 − 1 ⋅ MBT / MHT

[0066] The validation system 130 further comprises a module 134 for comparing the measured ground current MI M with the estimated ground current Î M . When the measured ground currents MI M and estimated Î M are consistent with each other, the measured ground current MI M is validated. The comparison module 134 uses for this a consistency criterion which is for example that the difference between the measured ground currents MI M and estimated Î M is less than a predefined threshold.

[0067] Preferably, the modules 132, 134 are independent of each other.

[0068] In the example described, the validation system 130 comprises a computer system 136 (such as a microcontroller) comprising a data processing unit (such as a microprocessor) and a main memory (such as a RAM memory, from the English “Random Access Memory”) accessible by the processing unit. A computer program containing instructions for the processing unit is intended to be loaded into the main memory, so that the processing unit executes its instructions. Thus, in the example described, the modules 132, 134 are software modules of the computer program. To achieve the independence of the modules 132, 134, it is for example possible to share the computer system 136 (where appropriate, the microcontroller) into several independent partitions with different access authorizations (reading and writing in particular) and preferably with different protection levels.For example, module 134 has a higher level of protection than module 132.

[0069] Alternatively, all or part of these modules 132, 134 could be implemented in the form of hardware modules, that is to say in the form of an electronic circuit, for example micro-wired, not involving a computer program.

[0070] The validation system 130 is further designed to provide an estimate Î BT of the low voltage current I BT and an estimate Î HT of the high voltage current I HT . For example, one of these estimates is obtained from the measurement of the ground current MI M or from its estimate Î M . For example, the estimate Î BT of the low voltage current I BT is taken equal to the sum of the measurements of the incoming currents I 1-3 in the cells 108 1-3 , while the estimate Î HT of the high voltage current I HT is taken equal to the sum of the measurements of the incoming currents I 1-3 in the cells, less the ground current, measured MI M or estimated Î M : I ^ BT = ∑ MI k I ^ HT = ∑ MI k − MI M ou bien I ^ HT = ∑ MI k − I ^ M

[0071] Since the Î BT estimate is used when estimating the ground current Î M whose consistency is confirmed by measuring the ground current MI M , this Î BT estimate can reach ASIL B level. It follows that the Î HT estimate which is carried out on the basis of the estimated current Î BT and the ground current can also reach ASIL B level.

[0072] In the example described, these estimates Î HT and Î BT are established by the computer system 136, for example in the module 132. The computer system 136 can be connected to an electronic control unit 138, generally designated by the acronym ECU (from the English “Electronic Control Unit”) of the motor vehicle, to send these estimates Î HT and Î BT to it, at least when the measured ground current MI M has been validated.

[0073] The validation system 130 (for example, the computer system 136) can furthermore be designed, in the event of non-validation of the measured ground current MI M , to provide in addition to or instead of the estimates Î HT , Î BT , a message indicating this non-validation.

[0074] Furthermore, in the example described, the protection system 130 is designed to provide a message indicating the placement of the voltage converter 106 in safe mode, for example to the electronic control unit 138. For example, the protection signal provided by at least one of the comparison devices 120, 122, 124 can also be provided to the computer system 136, which, in response to this signal, sends the safe mode placement message to the electronic control unit 138.

[0075] It is clear that a voltage converter such as the one described above allows short circuit detection in a simple and economical manner.

[0076] 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.

[0077] In the detailed presentation of the invention given above, the terms used should not be interpreted as limiting the invention to the embodiments set forth in this description, but should 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 just disclosed to them.

Claims

1. Voltage converter (106) comprising: - a ground point (PM) intended to be connected to an electrical ground (M); - a high-voltage point (PHT) intended to have a high voltage (HT) relative to the electrical ground (M); - a low-voltage point (PBT) intended to have a low voltage (BT) relative to the electrical ground (M); - at least one voltage conversion cell (1081, 1082, 1083) connected to the ground (PM), high-voltage (PHT) and low-voltage (PBT) points in order to perform a conversion between the high voltage (HT) and the low voltage (BT); and - a protection system (118) designed to detect a short circuit between the ground (PM) and high-voltage (PHT) points and / or between the ground (PM) and low-voltage (PBT) points; characterized in that it further comprises a device (110) for measuring a ground current (IM) flowing between this ground point (PM) and the electrical ground (M), and in that the protection system (118) is designed to detect the short circuit from the measured ground current (MIM).

2. Voltage converter (106) according to Claim 1, wherein the protection system (118) is designed, in response to detecting the short circuit, to place the voltage converter (106) in a safe mode preventing a flow of current between the high-voltage (PHT) and low-voltage (PBT) points and vice versa through the one or more cells (1081, 1082, 1083).

3. Voltage converter (106) according to Claim 2, wherein, in the safe mode, the low-voltage point (PBT) is disconnected from each cell (1081, 1082, 1083) in order to prevent a flow of current between the one or more cells (1081, 1082, 1083) and the low-voltage point (PBT) and vice versa.

4. Voltage converter (106) according to Claim 3, further comprising a safety switch (1261, 1262, 1263) for each cell (1081, 1082, 1083), placed between this cell (1081, 1082, 1083) and the low-voltage point (PBT) and wherein the protection device (118) is designed to place the voltage converter (106) in a safe mode by opening this or these safety switches (1261, 1262, 1263).

5. Voltage converter (106) according to any one of Claims 2 to 4, wherein, in the safe mode, each cell (1081, 1082, 1083) is in a safe state in which any passage of current through the cell (1081, 1082, 1083) is blocked.

6. Voltage converter (106) according to any one of Claims 1 to 5, wherein each cell (1081, 1082, 1083) comprises a switching arm comprising a high-side switch (202) and a low-side switch (204) connected to each other at a midpoint (206), with the switching arm being connected between the high-voltage point (PHT) and the ground point (PM), while the midpoint (206) is connected to the low-voltage point (PBT), for example by means of an inductor (208).

7. Voltage converter (106) according to Claims 5 and 6 taken together, wherein the protection system (118) is designed to place each cell (1081, 1082, 1083) in its safe state by controlling the opening of its high-side (202) and low-side (204) switches.

8. Voltage converter (106) according to any one of Claims 1 to 7, wherein the protection system (118) comprises a comparison device (120) designed to detect the short circuit when the ground current measurement (MIM) is greater than a predefined threshold.

9. Voltage converter (106) according to any one of Claims 1 to 8, further comprising a device (112) for measuring the high voltage (HT) and wherein the protection system (118) is designed to detect a short circuit from the high-voltage measurement (MHT), for example when said measurement drops below a predefined threshold.

10. Voltage converter (106) according to any one of Claims 1 to 9, further comprising a device (114) for measuring the low voltage (BT) and wherein the protection system (118) is designed to detect a short circuit from the low-voltage measurement (MBT), for example when said measurement drops below a predefined threshold.

11. Voltage converter (106) according to any one of Claims 1 to 10, further comprising, for each cell (1081, 1082, 1083), a device (1161, 1162, 1163) for measuring a cell current (I1, I2, I3) entering the cell (1081, 1082, 1083) from the low-voltage point (PBT), and a system (130) for validating the measured ground current (MIM) from the measured cell currents (MI1, MI2, MI3).

12. Voltage converter (106) according to Claim 11, wherein the validation system (130) is further designed, in the event of non-validation, to provide a message indicating the non-validation of the measured ground current (MIM).

13. Voltage converter (106) according to Claim 11 or 12, wherein the validation system (130) comprises a module (132) for estimating the ground current (IM) and a module (134) for comparing the measured ground current (MIM) with the estimated ground current (ÎM) for determining whether the measured (MIM) and estimated (ÎM) ground currents are consistent with each other.

14. Motor vehicle comprising a voltage converter (106) according to any one of Claims 1 to 13.