METHOD FOR INSULATION CHECK OF AN ON-BOARD CHARGER FOR DETECTION OF AN INSULATION FAULT BETWEEN THE PRIMARY AND SECONDARY CIRCUITS OF A POWER CONVERSION STAGE OF THE CHARGER

Abstract

The invention relates to a method for checking the insulation between the primary and secondary circuits of a power conversion stage, implemented in a vehicle-mounted charger. The charger comprises: - a controller; - a phase, a neutral, and an earth; - an insulation checking device including a DC voltage source, a voltage divider, and a filtering stage for an AC voltage component. The insulation checking method comprises the following steps: - a step (E1) for determining a charging mode for the charger; - a step (E3) for injecting a DC electric current into the voltage divider; - a step (E4) for receiving a voltage signal supplied at the output of the filtering stage; - a step (E5) for comparing said received voltage value to a threshold voltage value. Abstract figure: Fig. 3

Description

Title of the invention: METHOD FOR TESTING THE INSULATION OF AN ON-BOARD CHARGER FOR DETECTING AN INSULATION FAULT BETWEEN THE PRIMARY AND SECONDARY CIRCUITS OF A POWER CONVERSION STAGE OF THE CHARGER

[0001] The invention relates to the field of on-board chargers for electric motor vehicles. The invention relates more particularly to insulation control in these AC chargers.

[0002] An insulation monitoring device (IMD) is generally provided in an on-board charger illustrated in [Fig. 1]. It is a hardware module that is inserted between the phase L, the neutral N and the earth PE.

[0003] This equipment communicates via digital and analog signals with a C microcontroller. The C microcontroller is configured to be able to disconnect the IMD insulation control device from the PE earth.

[0004] Insulation control between the live AC part and the protective earth conductor already exists for computer electrical installations, but these solutions are dedicated to fixed installations (for example in a home, a building).

[0005] New features such as vehicle charging are being developed for electric vehicles, and also require insulation control.

[0006] The on-board charger can operate in an electric vehicle according to several operating modes, including: - grid to vehicle (or G2V for "grid to vehicle" in English); - vehicle to grid (or V2G for "vehicle to grid" in English); - vehicle to home (or V2H for "vehicle to home" in English); - vehicle to load (or V2L for "vehicle to load" in English).

[0007] The new vehicle-to-load (V2L) functionality, which is coming soon, will require such control, but not V2G, G2V, or V2H. Indeed, the IMD insulation monitoring device can disrupt the network in certain configurations (e.g., V2G, G2V, or V2H) and not in others (e.g., V2L).

[0008] In V2L mode, the supply of alternating current (typically 230 V single-phase) is typically achieved by drawing electrical energy from the vehicle's high-voltage battery (400 V or 800 V nominal voltage battery) and converting this into alternating current (using a stage (power conversion CV present in the charger). It is then possible to connect an external electrical device to the vehicle in order to power the device with alternating current. The power conversion stage typically comprises a primary circuit PI, located on the alternating current side and connected to phase L and neutral N, and a secondary circuit P2, located on the high-voltage battery side of the vehicle.

[0009] In V2L mode, since the charger is no longer connected to the domestic electrical network, it is necessary to ensure coordinated electrical isolation between the primary PI and secondary P2 circuits (corresponding respectively to the AC and DC domains) of the CV power conversion stage. Indeed, in the event of a fault in electrical isolation between the primary PI and secondary P2 circuits of the CV power conversion stage, a current loop can form, introducing parasitic capacitance into the loop, which itself could cause an electric shock and injure a vehicle user.To this end, new standards require that the charger include either a protective separation between the primary and secondary windings in the electrical circuit, or a simple separation combined with a mechanism to detect any loss or fault in electrical insulation, and to allow the microcontroller C to disable the transfer of electrical energy from the vehicle to the load if necessary.

[0010] However, in this latter case of "simple separation", it is necessary that the separation be a galvanic isolation.

[0011] There is therefore a need to detect any insulation fault in this galvanic insulation, without introducing an insulation monitoring circuit that is not galvanically connected.

[0012] An objective of the present invention is to remedy the defects of the prior art, and in particular to propose a protection solution against electrical insulation defects that may appear between the primary and secondary circuits of the power conversion stage of a vehicle charger in the V2L mode of the latter (i.e. when the vehicle is no longer connected to the domestic electrical network), which makes it possible to meet the requirements imposed by the new standards, and in particular which makes it possible to detect an electrical insulation defect precisely and reliably and to monitor the insulation while maintaining galvanic isolation between the primary and secondary circuits.

[0013] To achieve this objective, the invention proposes, in its broadest sense, a method for controlling the insulation between the primary and secondary circuits of a power conversion stage, the method being implemented in a charger installed in a vehicle, the charger comprising: - said electrical power conversion stage; - a controller, connected to the electrical power conversion stage; - a phase, a neutral and an earth, the phase and the neutral being connected to the primary circuit of the electrical power conversion stage; - an insulation control device connected to the phase, neutral, earth and controller in an electrical circuit, and comprising a DC voltage source, a voltage divider whose input is connected to the DC voltage source and to one of the phase or neutral, and an AC voltage component filtering stage, said AC voltage component filtering stage being connected between the output of the voltage divider and an input of the controller; The insulation control procedure includes the following steps: - a first step of determining the charger's charging mode; - if the charging mode is a vehicle-to-load mode: - a step of injecting, by the DC voltage source, a DC electric current into the voltage divider, the DC electric current then flowing through the filtering stage of an AC voltage component; - a stage of reception, by the controller, of a voltage signal supplied at the output of the filtering stage of an alternating voltage component; - a step where the controller compares the received voltage value to a threshold voltage value, and - if said received voltage value is greater than the threshold voltage value over a predetermined time interval, a step of emission, by the controller, of a deactivation signal of the electrical power conversion stage.

[0014] Thus, when an electrical insulation fault between the primary and secondary circuits of the power conversion stage is detected by the controller (received voltage value exceeding the threshold voltage value over a predetermined time interval), the controller deactivates the electrical power conversion stage, thereby stopping the transfer of electrical energy and protecting the vehicle user from a potential electric shock. The voltage divider attenuates the AC and DC components of the voltage signal, thereby facilitating subsequent detection, while the AC voltage component filtering stage eliminates the AC component.When an electrical insulation fault occurs between the primary and secondary circuits, it behaves as if a parasitic capacitance appears at the input of the voltage divider (common-mode capacitance on the secondary side in parallel with the common-mode capacitance on the primary side). This causes a variation in the residual voltage measured by the controller during the predetermined time interval, thus enabling detection. When no electrical insulation fault is present between... In the primary and secondary circuits, the residual voltage measurement remains fixed and is determined by the value of the injection resistance and the measurement resistance.

[0015] Advantageously, the invention provides a protection solution against electrical insulation faults that may occur between the primary and secondary circuits of the power conversion stage of a vehicle charger in V2L mode, thus meeting the requirements of the new standards. Furthermore, the charger according to the invention allows for the precise and reliable detection of an electrical insulation fault between the primary and secondary circuits of the power conversion stage. The charger according to the invention is also advantageous in that it is inexpensive to produce and allows for monitoring the insulation while maintaining galvanic isolation between the primary and secondary circuits. In particular, the charger according to the invention does not require an additional circuit in parallel with the electrical insulation barrier: galvanic isolation is therefore maintained.

[0016] Advantageously, if the charging mode is a vehicle-to-load mode and if said received voltage value is greater than the threshold voltage value over the predetermined time interval, the method further comprises a first intermediate step of emission, by the controller, of a deactivation signal of the DC voltage source, a second intermediate step of emission, by the controller, of a reactivation signal of the DC voltage source, then a reimplementation of said steps of injection of a DC electric current, of reception of a voltage signal, and of comparison of the received voltage value to a threshold voltage value, the step of emission of a deactivation signal of the electrical power conversion stage being implemented if and only if, during said last comparison step, the received voltage value is still greater than the threshold voltage value over the predetermined time interval.

[0017] This makes it possible to confirm the presence of an electrical insulation fault between the primary and secondary circuits of the power conversion stage, and therefore to improve the reliability of the detection.

[0018] The invention also relates to a charger intended to be installed in a vehicle, the charger comprising: - an electrical power conversion stage equipped with a primary circuit and a secondary circuit; - a controller, connected to the electrical power conversion stage; - a phase, a neutral and an earth, the phase and the neutral being connected to the primary circuit of the electrical power conversion stage; - an insulation testing device connected to the phase, neutral, earth and the controller in an electrical circuit, and comprising a DC voltage source, a voltage divider whose input is connected to the DC voltage source and to one of the phase or neutral, and a filtering stage for an AC voltage component, said filtering stage for an AC voltage component being connected between the output of the voltage divider and an input of the controller; the charger being configured to implement the steps of the insulation control process as described above.

[0019] According to one variant, the DC voltage source includes a boost converter and a current injection resistor connected between the boost converter and the input of the voltage divider.

[0020] This makes it possible to obtain a 20 V DC voltage source from components already present in the charger (advantageous reuse of existing components, which allows for a reduction in costs).

[0021] According to one variant, the current injection resistance has a resistance value of substantially equal to 600 kQ.

[0022] According to one variant, the voltage divider is a voltage divider bridge equipped with two resistors connected in series, the two resistors being such that the division ratio of the voltage divider bridge is between 8 and 12, preferably substantially equal to 10.

[0023] This effectively attenuates both the AC and DC components of the voltage signal present at the input of the voltage divider, allowing for better matching of the operational amplifiers in the filtering stage and thus better subsequent discrimination between the AC and DC components. The two resistors of the voltage divider bridge are connected in series in order to reduce electrical power dissipation in the event of an overvoltage applied to the AC voltage input of the charger.

[0024] According to one variant, the filtering stage of an alternating voltage component includes a current measuring resistor, the current measuring resistor having a resistance value substantially equal to 1.2 MQ.

[0025] The invention further relates to a computer program comprising program code instructions for executing the steps of the insulation control process according to the invention, when said program is running on a computer.

[0026] The invention will be further detailed by the non-limiting description of variants, and based on the accompanying figures, in which: - [Fig.l] schematically illustrates an on-board charger according to the invention, the charger comprising a controller and an insulation control device; - [Fig.2] is a detailed view of the electrical and electronic components of the insulation control device of [Fig.1]; and - [Fig.3] is a flowchart representing the insulation control process according to the invention.

[0027] The invention relates to an on-board OBC charger such as that of an electric vehicle, as well as an insulation control method implemented in such an on-board charger.

[0028] The OBC on-board charger comprises: - - an electrical power conversion stage CV; - a C controller; - a phase L, a neutral N and an earth PE (the latter being connected to the electrical ground and the chassis of the vehicle); - an IMD insulation control device.

[0029] The electrical power conversion stage CV is equipped with a primary circuit PI and a secondary circuit P2.

[0030] The controller C is connected to the electrical power conversion stage CV and to the insulation control device IMD.

[0031] The insulation monitoring device IMD is connected to phase L, neutral N, earth PE, and controller C in a circuit of the on-board charger OBC, as illustrated in [Fig. 1]. Phase L and neutral N are connected to the primary circuit PI of the electrical power conversion stage CV. One or more common-mode filtering capacitors (not shown in the figures) are present in the AC network on the secondary circuit side PI (when an external electrical device is connected to the network), such capacitors typically being in the range of 10 nF to 200 nF. One or more common-mode filtering capacitors (not shown in the figures) are also present in the DC network on the secondary circuit side P2, which are typically in the range of 1 pF to 1.5 pF.

[0032] The IMD insulation control device has the following main functions: - impedance control: a hardware and software function that must manage impedance measurement; - confirm the plausibility of the measurements: a software function that manages the plausibility of the measurements; - compare impedances: a software function that compares measurements to a calibrated threshold; - activate the safety state: a software function that puts the system into a safety state in case of insulation failure; - perform self-check: self-check must be performed before starting the energy transfer from the OBC on-board charger.

[0033] Furthermore, the OBC on-board charger performs the following functional information exchanges: - charging modes: G2V, V2G, V2H, V2L, information is received by the OBC on-board charger from an external system; - phase-to-earth activations or deactivations at the level of the IMD insulation control device: in the case of a deactivated state, the corresponding IMD control device must be seen to be completely open circuit (as if there were no circuit in said IMD device), in order to avoid unexpected interaction with the external protection mechanism for certain load configurations (for example, a residual current circuit breaker in the case of V2G, G2V mode in TN or TT neutral system); - impedance control: the analog value which represents the impedance measured between phase L and earth PE or neutral N and earth PE; - the plausibility status of the impedance measurement (which may be necessary to achieve a certain level of functional safety ASIL (for "Automotive Safety Integrity Level" in English - for example ASIL B); - the status of the IMD insulation control device: information which indicates whether the insulation is within the calibrated range or not (according to the threshold defined by the legislation of the country), or whether there is a defect in the IMD control device (plausibility status); - the error status of the IMD control device: information on insulation monitoring, manageable by an external system.

[0034] In V2L mode, the alternating current supply is typically achieved by drawing electrical energy from the vehicle's high-voltage battery (400 V or 800 V nominal voltage battery - not shown in the figures) and converting this energy into alternating current (using the CV power conversion stage in the charger, with the secondary circuit P2 of the CV power conversion stage connected to the battery). Regarding the safety state activation function implemented by the on-board charger (OBC), this function must be capable, in V2L charging mode, of putting the system into a safety state in the event of an insulation fault, particularly in the event of an insulation fault between the primary circuit PI and the secondary circuit P2 of the CV power conversion stage.

[0035] To do this, and as illustrated in [Fig.2], the IMD isolation control device comprises a DC voltage source 12, a voltage divider 14, and a filtering stage 16 for an AC voltage component.

[0036] The DC voltage source 12 delivers, for example, a DC output voltage Vinj approximately equal to 20 V. In the particular embodiment shown in [Fig. 2], the DC voltage source 12 comprises a boost converter 22 and a current injection resistor Rinj_L connected between the boost converter 22 and the 14A input of the voltage divider 14. The boost converter 22 is, for example, connected to an electronic board (not visible in the figures) which has, for example, a nominal voltage of 5V and is located on the low-voltage side of the OBC charger. The current injection resistor Rinj_L typically has a resistance value of approximately 600 kΩ.

[0037] The input 14A of the voltage divider 14 is connected to both the DC voltage source 12 and to either phase L or neutral N (phase L in the particular embodiment shown in [Fig. 2]). The output 14B of the voltage divider 14 is connected to the input of the filtering stage 16 of an AC voltage component. In the particular embodiment shown in [Fig. 2], the voltage divider 14 is a voltage divider bridge with two resistors RI, R2 connected in series at a midpoint 14B, which is also the output of the voltage divider 14. The terminal of the second resistor R2 that is not connected to the midpoint 14B is connected to ground GND. The two resistances RI, R2 are advantageously chosen so that the division ratio of the voltage divider bridge 14 is between 8 and 12, preferably approximately equal to 10.

[0038] The AC voltage component filtering stage 16 is connected between the output 14B of the voltage divider 14 and a first COI input of the controller C. As illustrated in [Fig. 2], the AC voltage component filtering stage 16 typically includes a fourth-order low-pass filter, which is in the form of two second-order low-pass filters 26, 28 connected in series, preferably two second-order low-pass filters of the Sallen-Key type. As seen in [Fig. 2], the AC voltage component filtering stage 16 also includes an amplifier 30 connected to the output of the fourth-order low-pass filter 26, 28, and a voltage follower circuit 32 connected to the output of the amplifier 30.

[0039] A first second-order low-pass filter 26 comprises two resistors R3, R4, two capacitors Cl, C2, and an operational amplifier AL. The resistors R3, R4 and the capacitors Cl, C2 are chosen, for example, such that the first second-order low-pass filter 26 has, for example, a cutoff frequency substantially equal to 7 Hz.

[0040] The two resistors R3 and R4 are connected in series at a midpoint 34, with the first resistor R3 connected to the midpoint 34 and the second resistor R4 connected to the non-inverting input of operational amplifier AL. A first capacitor C1 is connected between ground (GND) and the non-inverting input of operational amplifier AL. A second capacitor C2 is connected between the midpoint 34 and the output of operational amplifier AL. The inverting input of operational amplifier AL is connected to the output of operational amplifier AL. The resistor R3 is a current measuring resistor, whose resistance value is, for example, approximately equal to 1.2 MQ.

[0041] A second second-order low-pass filter 28 comprises two resistors R5, R6, two capacitors C3, C4, and an operational amplifier A2. The resistors R5, R6 and the capacitors C3, C4 are chosen, for example, such that the second second-order low-pass filter 28 has, for example, a cutoff frequency substantially equal to 7 Hz.

[0042] The two resistors R5 and R6 are connected in series at a midpoint 36, with the first resistor R5 connected to the output of operational amplifier A1, and the second resistor R6 connected to the non-inverting input of operational amplifier A2. A first capacitor C3 is connected between ground (GND) and the non-inverting input of operational amplifier A2. A second capacitor C4 is connected between the midpoint 36 and the output of operational amplifier A2.

[0043] The amplifier 30 typically comprises two resistors R7 and R8 connected in series at a midpoint 38, which is itself connected to the inverting input of the operational amplifier A2. The terminal of the first resistor R7 that is not connected to the midpoint 38 is connected to ground (GND). The terminal of the second resistor R8 that is not connected to the midpoint 38 is connected to the output of the operational amplifier A2. The two resistors R7 and R8 are advantageously chosen such that the gain of the amplifier 30 is between 1.5 and 3, preferably equal to 2.

[0044] The follower circuit 32 typically consists of an operational amplifier A3 configured as a follower (the inverting input of operational amplifier A3 is connected to the output of operational amplifier A3). The non-inverting input of operational amplifier A3 is connected to the output of operational amplifier A2. The output of operational amplifier A3 is connected to the first COI input of controller C via a resistor R9. A capacitor C5 is connected between ground (GND) and the first COI input of controller C.

[0045] The insulation control method according to the invention is implemented by means of an IMD insulation control device provided in the electrical architecture of the OBC on-board charger, as can be seen in Figures 1 and 2.

[0046] With reference to [Fig.3], the insulation control process comprises the following steps.

[0047] A first step E1 consists of determining the charging mode of the on-board OBC charger. A second step E2 consists of determining whether the charging mode is a vehicle-to-charge (V2L) mode.

[0048] If the charging mode is a vehicle-to-charge V2L mode, then a third step E3 occurs, and it consists of the DC voltage source 12 injecting a direct electric current within the voltage divider 14, the direct electric current then flowing in the filtering stage 16 of an alternating voltage component.

[0049] During a subsequent step E4, the controller C receives a voltage signal VI (visible in [Fig.2]) which is supplied at the output of the filtering stage 16 of an alternating voltage component.

[0050] During a subsequent step E5, the controller C compares the received voltage value VI to a threshold voltage value (indicative value of an electrical insulation fault between the primary and secondary circuits PI, P2 of the power conversion stage CV).

[0051] Preferably, if the received voltage value V1 is greater than the threshold voltage value over a predetermined time interval, then a sixth step E6 occurs, and it consists of the controller C emitting a deactivation signal for the DC voltage source 12. The occurrence of this sixth step E6 indicates that the insulation control device IMD has detected, a priori, an electrical insulation fault between the primary PI and secondary P2 circuits of the power conversion stage CV (detection which requires confirmation). If the received voltage value V1 is less than or equal to the threshold voltage value over the predetermined time interval, then the fifth step E5 is reimplemented.

[0052] In order to confirm the detection of the fault, during a subsequent step E7, the controller C emits a reactivation signal from the DC voltage source 12. Steps E3, E4 and E5 are then reimplemented.

[0053] If, during the comparison step E5, the received voltage value V1 is still greater than the threshold voltage value over the predetermined time interval, then an eighth step E8 occurs, in which the controller C sends a deactivation signal to the electrical power conversion stage CV. The occurrence of this eighth step E8 indicates that the insulation monitoring device IMD has definitively detected an electrical insulation fault between the primary PI and secondary P2 circuits of the power conversion stage CV. If the received voltage value VI is less than or equal to the threshold voltage value over the predetermined time interval, then the fifth step E5 is repeated.

[0054] It should be noted that steps six and seven, E6 and E7, may be optional. If steps E6 and E7 are not carried out, the process proceeds directly from step five, E5, to step eight, E8.

Claims

1. Demands Method for checking insulation between the primary (PI) and secondary (P2) circuits of a power conversion (CV) stage, the method being implemented in an on-board charger (OBC) installed in a vehicle, the charger (OBC) comprising: - said electrical power conversion (CV) stage; - a controller (C), connected to the electrical power conversion stage (CV); - a phase (L), a neutral (N) and an earth (PE), the phase (L) and the neutral (N) being connected to the primary circuit (PI) of the electrical power conversion stage (CV); - an insulation control device (IMD) connected to phase (L), neutral (N), earth (PE) and the controller (C) in an electrical circuit, and comprising a DC voltage source (12), a voltage divider (14) whose input (14A) is connected to the DC voltage source (12) and to one of the phase (L) or neutral (N), and an AC voltage component filtering stage (16), said AC voltage component filtering stage (16) being connected between the output (14B) of the voltage divider (14) and an input (COI) of the controller (C); the insulation control process comprising the following steps: - a first step of determination (El) of a charger charging mode (OBC); - if the charging method is a vehicle-to-charge (V2L) method: • an injection step (E3), by the DC voltage source (12), of a DC electric current into the voltage divider (14), the DC electric current then flowing in the filtering stage (16) of an AC voltage component; • a reception step (E4), by the controller (C), of a voltage signal (VI) supplied at the output of the filtering stage (16) of an alternating voltage component; • a comparison step (E5), by the controller (C), of said received voltage value (VI) to a threshold voltage value, and, • if said received voltage value (VI) is greater than the threshold voltage value over a time interval

2.

3. predetermined, an emission step (E8), by the controller (C), of a deactivation signal for the electrical power conversion stage (CV). An insulation control method according to claim 1, characterized in that, if the charging mode is a vehicle-to-charge (V2L) mode and if said received voltage value (VI) is greater than the threshold voltage value over the predetermined time interval, the method further comprises a first intermediate step of emission (E6), by the controller (C), of a deactivation signal for the DC voltage source (12), a second intermediate step of emission (E7), by the controller (C), of a reactivation signal for the DC voltage source (12), then a re-implementation of said steps of injection (E3) of a DC electric current, reception (E4) of a voltage signal, and comparison (E5) of the received voltage value (VI) to a threshold voltage value, the step of emission (E8) of a deactivation signal for the electrical power conversion (CV) stage being implemented if and only if,During the last comparison step (E5), the received voltage value (VI) is always greater than the threshold voltage value over the predetermined time interval. Charger (OBC) intended to be installed in a vehicle, the charger comprising: - an electrical power conversion (CV) stage equipped with a primary circuit (PI) and a secondary circuit (P2); - a controller (C), connected to the electrical power conversion stage (CV); - a phase (L), a neutral (N) and an earth (PE), the phase (L) and the neutral (N) being connected to the primary circuit (PI) of the electrical power conversion stage (CV); - an insulation monitoring device (IMD) connected to the phase (L), neutral (N), earth (PE) and the controller (C) in an electrical circuit, and comprising a DC voltage source (12), a voltage divider (14) whose input (14A) is connected to the DC voltage source (12) and to one of the phase (L) or neutral (N), and a filtering stage (16) for an AC voltage component, said filtering stage (16) for an AC voltage component being connected between the output (14B) of the voltage divider (14) and an input (COI) of the controller (C); characterized in that the charger (OBC) is configured to implement the steps of the insulation control process according to claim 1 or 2.

4. Charger (OBC) according to claim 3, characterized in that the DC voltage source (12) comprises a boost converter (22) and a current injection resistor (Rinj_L) connected between the boost converter (22) and the input (14A) of the voltage divider (14).

5. Charger (OBC) according to claim 4, characterized in that the current injection resistance (R;nj_L) has a resistance value substantially equal to 600 kQ.

6. Charger (OBC) according to any one of claims 3 to 5, characterized in that the voltage divider (14) is a voltage divider bridge equipped with two resistors (RI, R2) connected in series, the two resistors (RI, R2) being such that the division ratio of the voltage divider bridge (14) is between 8 and 12, preferably substantially equal to 10.

7. Charger (OBC) according to any one of claims 3 to 6, characterized in that the filtering stage (16) of an alternating voltage component comprises a current measuring resistor (R3), the current measuring resistor (R3) having a resistance value substantially equal to 1.2 MQ.

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