FR3156916A1 - METHOD FOR CHECKING 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 - Google Patents

Abstract

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

Description

METHOD FOR CHECKING 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

The invention relates to the field of on-board chargers for electric motor vehicles. The invention relates more particularly to insulation control in these alternating current chargers.

An IMD (or “ Insulation Monitoring Device ” in English) is generally provided in an on-board charger illustrated in FIG. 1 . It is a hardware module that is inserted between phase L, neutral N and earth PE.

This hardware communicates via digital and analog signals with a microcontroller C. The microcontroller C is configured to be able to disconnect the IMD insulation control device from the PE ground.

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

New features such as vehicle charging are developing for electric vehicles, and also require insulation control.

The on-board charger can operate in an electric vehicle in several operating modes, including:
- network 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).

The new vehicle-to-load (V2L) functionality that is coming will require such control, but not V2G, G2V or V2H. Indeed, the IMD isolation control device can disrupt the network in some configurations (e.g. V2G, G2V or V2H) and not in others (e.g. V2L).

In V2L mode, the supply of an alternating electric current (typically 230 V single-phase) is typically achieved by taking electrical energy from the vehicle's high-voltage battery (400 V or 800 V nominal voltage battery) and converting it into alternating electric current (using a CV power conversion stage present in the charger). It is then possible to connect an external electrical device to the vehicle so as to power the device with the alternating electric current. The power conversion stage typically comprises a primary circuit P1, located on the alternating electric current side and connected to phase L and neutral N, and a secondary circuit P2, located on the vehicle's high-voltage battery side.

In V2L mode, moreover, since the charger is no longer connected to the domestic electrical network, it is necessary to guarantee coordination of the electrical insulation between the primary P1 and secondary P2 circuits (corresponding respectively to the AC and DC domains) of the CV power conversion stage. Indeed, in the event of an electrical insulation fault between the primary P1 and secondary P2 circuits of the CV power conversion stage, a current loop may form, introducing the charging of parasitic capacitances in the loop, which themselves may cause an electric shock and injure a vehicle user. To this end, new standards require the provision in the charger of either a protective separation between the primary and secondary 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 be able, if necessary, to deactivate the transfer of electrical energy from the vehicle to the load.

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

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

An objective of the present invention is to remedy the defects of the prior art, and in particular to propose a solution for protection against electrical insulation faults likely to 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 fault precisely and reliably and to monitor the insulation while maintaining the galvanic isolation between the primary and secondary circuits.

To achieve this objective, the invention proposes, in its broadest sense, a method for controlling insulation between the primary and secondary circuits of a power conversion stage, the method being implemented in a charger on board 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 monitoring device connected to the phase, neutral, earth and controller in an electrical circuit, and comprising a direct voltage source, a voltage divider whose input is connected to the direct voltage source and to one of the phase or the neutral, and a filtering stage of an alternating voltage component, said filtering stage of an alternating voltage component being connected between the output of the voltage divider and an input of the controller;
the insulation control method comprising the following steps:
- a first step of determining a charging mode for the charger;
- if the charging mode is a vehicle-to-charge mode:
- a step of injecting, by the direct voltage source, a direct electric current into the voltage divider, the direct electric current then circulating in the filtering stage of an alternating voltage component;
- a step of reception, by the controller, of a voltage signal provided at the output of the filtering stage of an alternating voltage component;
- a step of comparison, by the controller, of said received voltage value with 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 transmission, by the controller, of a signal for deactivating the electrical power conversion stage.

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 higher than the threshold voltage value over a predetermined time interval), the controller deactivates the electrical power conversion stage, thus stopping the transfer of electrical energy and protecting the vehicle user against a possible electric shock. The voltage divider makes it possible to attenuate the AC component and the DC component of the voltage signal and thus facilitate subsequent detection, while the filtering stage of an AC voltage component makes it possible to eliminate the AC component. When an electrical insulation fault appears between the primary and secondary circuits, everything happens as if a parasitic capacitance appeared at the input point of the voltage divider (common mode capacitance on the secondary side coming in parallel with the common mode capacitance on the primary side), which causes a variation in the value of the residual voltage measured by the controller during the predetermined time interval, and allows detection. When no electrical insulation fault is present between 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.

Advantageously, the invention provides a solution for protecting against electrical insulation faults 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, which makes it possible to meet the requirements imposed by the new standards. In addition, the charger according to the invention makes it possible to accurately and reliably detect 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 in that it makes it possible to monitor the insulation while maintaining the 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 isolation barrier: the galvanic isolation is therefore maintained.

Advantageously, if the charging mode is a vehicle-to-charging 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 transmission, by the controller, of a signal for deactivating the DC voltage source, a second intermediate step of transmission, by the controller, of a signal for reactivating the DC voltage source, then a re-implementation of said steps of injecting a DC electric current, receiving a voltage signal, and comparing the received voltage value with a threshold voltage value, the step of transmission of a signal for deactivating 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.

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 detection.

The invention also relates to a charger intended to be mounted 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 monitoring device connected to the phase, neutral, earth and controller in an electrical circuit, and comprising a direct voltage source, a voltage divider whose input is connected to the direct voltage source and to one of the phase or the neutral, and a filtering stage of an alternating voltage component, said filtering stage of an alternating 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 method as described above.

According to one variant, the direct voltage source comprises a boost converter and a current injection resistor connected between the boost converter and the input of the voltage divider.

This allows a 20V DC voltage source to be obtained from components already present in the charger (advantageous reuse of components already present, which allows for cost reduction).

According to one variant, the current injection resistor has a resistance value substantially equal to 600 kΩ.

According to one variant, the voltage divider is a voltage divider bridge provided 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.

This effectively attenuates both the AC and DC components of the voltage signal present at the input of the voltage divider, allowing better adaptation to the operational amplifiers of the filter stage and therefore 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.

According to a variant, the filtering stage of an alternating voltage component comprises a current measuring resistor, the current measuring resistor having a resistance value substantially equal to 1.2 MΩ.

The invention further relates to a computer program comprising program code instructions for executing the steps of the insulation control method according to the invention, when said program operates on a computer.

The invention will be further detailed by the non-limiting description of variants, and on the basis of the appended figures, in which:
- FIG. 1 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 monitoring device of the FIG. 1 ; And
- FIG. 3 is a flowchart representing the insulation control method according to the invention.

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

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

The CV electric power conversion stage is equipped with a primary circuit P1 and a secondary circuit P2.

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

The IMD insulation monitoring device is connected to phase L, neutral N, ground PE and controller C in an OBC on-board charger circuit, as shown in FIG. 1 . Phase L and neutral N are connected to the primary circuit P1 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 side of the secondary circuit P1 (when an external electrical device is connected to the network), such capacitors being typically of the order 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 side of the secondary circuit P2, which are typically of the order of 1 µF to 1.5 µF.

The main functions of the IMD insulation control device are:
- impedance control: a hardware and software function that must manage the impedance measurement;
- confirm the plausibility of measurements: a software function that manages the plausibility of measurements;
- compare impedances: a software function that compares measurements to a calibrated threshold;
- activate safety state: a software function that puts the system in a safety state in the event of an insulation fault;
- perform self-verification: self-verification must be performed before starting the energy transfer from the OBC on-board charger.

In addition, the OBC on-board charger carries out 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 IMD insulation control device: in case of deactivated state, the corresponding IMD control device must be completely seen in open circuit (as if there was no circuit in said IMD device), in order to avoid unexpected interaction with the external protection mechanism for certain load configurations (e.g., a differential circuit breaker in case of V2G, G2V mode in TN or TT neutral regime);
- 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 ASIL functional safety level (for “Automotive Safety Integrity Level” in English - for example ASIL B);
- the status of the IMD insulation control device: information indicating whether the insulation is within the calibrated range or not (according to the threshold defined by the country's legislation), or whether there is a fault in the IMD control device (plausibility status);
- the error status of the IMD control device: information on insulation monitoring, manageable by an external system.

In V2L mode, the supply of alternating current is typically achieved by taking electrical energy from the vehicle's high-voltage battery (400 V or 800 V nominal voltage battery – not shown in the figures) and converting it into alternating electric current (using the CV power conversion stage present in the charger, the secondary circuit P2 of the CV power conversion stage being connected to the battery). Concerning the activation function of the safe state implemented by the OBC on-board charger, this function must be capable, in V2L charging mode, of putting the system in a safe state in the event of an insulation fault, in particular in the event of an insulation fault between the primary circuit P1 and the secondary circuit P2 of the CV power conversion stage.

To do this, and as illustrated in the FIG. 2 , the IMD insulation control device comprises a direct voltage source 12, a voltage divider 14, and a stage 16 for filtering an alternating voltage component.

The DC voltage source 12 delivers, for example, a DC output voltage V _inj substantially equal to 20 V. In the particular embodiment shown in the FIG. 2 , the DC voltage source 12 comprises a step-up converter 22 and a current injection resistor R _{inj_L} connected between the step-up converter 22 and the input 14A of the voltage divider 14. The step-up converter 22 is for example connected to an electronic card (not visible in the figures) which has for example a nominal voltage of 5V and which is arranged on the low voltage side of the OBC charger. The current injection resistor R _{inj_L} typically has a resistance value substantially equal to 600 kΩ.

The input 14A of the voltage divider 14 is connected both to the DC voltage source 12 and to one of phase L or neutral N (phase L in the particular embodiment of the FIG. 2 ). The output 14B of the voltage divider 14 is connected to the input of the stage 16 for filtering an alternating voltage component. In the particular embodiment shown in the FIG. 2 , the voltage divider 14 is a voltage divider bridge provided with two resistors R1, 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 which is not connected to the midpoint 14B is connected to the ground GND. The two resistors R1, R2 are advantageously chosen such that the division ratio of the voltage divider bridge 14 is between 8 and 12, preferably substantially equal to 10.

The stage 16 for filtering an alternating voltage component is connected between the output 14B of the voltage divider 14 and a first input CO1 of the controller C. As illustrated in the FIG. 2 , the stage 16 for filtering an alternating voltage component typically comprises 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 topology filter type. As seen in the FIG. 2 , the stage 16 for filtering an alternating voltage component also comprises an amplifier 30 connected to the output of the fourth-order low-pass filter 26, 28, and a follower circuit 32 connected to the output of the amplifier 30.

A first second-order low-pass filter 26 comprises two resistors R3, R4, two capacitors C1, C2, and an operational amplifier A1. The resistors R3, R4 and the capacitors C1, C2 are, for example, chosen such that the first second-order low-pass filter 26 has, for example, a cut-off frequency substantially equal to 7 Hz.

The two resistors R3, R4 are connected in series at a midpoint 34, a first resistor R3 being connected to the midpoint 34, a second resistor R4 being connected to the non-inverting input of the operational amplifier A1. A first capacitor C1 is connected between the ground GND and the non-inverting input of the operational amplifier A1. A second capacitor C2 is connected between the midpoint 34 and the output of the operational amplifier A1. The inverting input of the operational amplifier A1 is connected to the output of the operational amplifier A1. The resistor R3 is a current measuring resistor, the resistance value of which is for example substantially equal to 1.2 MΩ.

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, for example, chosen such that the second second-order low-pass filter 28 has, for example, a cut-off frequency substantially equal to 7 Hz.

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

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

The follower circuit 32 typically consists of an operational amplifier A3 connected as a follower (inverting input of operational amplifier A3 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 input CO1 of controller C via a resistor R9. A capacitor C5 is connected between ground GND and the first input CO1 of controller C.

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.

In reference to the FIG. 3 , the insulation control method includes the following steps.

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

If the charging mode is a vehicle-to-V2L charging mode, then a third step E3 occurs, and it consists of the DC voltage source 12 injecting a DC electric current into the voltage divider 14, the DC electric current then circulating in the stage 16 for filtering an AC voltage component.

During a following step E4, the controller C receives a voltage signal V1 (visible on the FIG. 2 ) which is supplied at the output of stage 16 for filtering an alternating voltage component.

During a following step E5, the controller C compares the received voltage value V1 with a threshold voltage value (value indicative of an electrical insulation fault between the primary and secondary circuits P1, P2 of the power conversion stage CV).

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 signal to deactivate the DC voltage source 12. The occurrence of this sixth step E6 indicates that the insulation monitoring device IMD has detected, a priori, an electrical insulation fault between the primary P1 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 re-implemented.

In order to confirm the detection of the fault, during a following step E7, the controller C emits a signal to reactivate the direct voltage source 12. Steps E3, E4 and E5 are then re-implemented.

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, and it consists of the controller C emitting a signal to deactivate the electrical power conversion stage CV. The occurrence of this eighth step E8 indicates that the insulation monitoring device IMD has definitely detected an electrical insulation fault between the primary P1 and secondary P2 circuits of the power conversion stage CV. 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 implemented again.

It should be noted that the sixth and seventh steps E6, E7 may be optional. In the case where these steps E6, E7 are not implemented, the method proceeds directly from the fifth step E5 to the eighth step E8.

Claims (8)

Method for controlling insulation between the primary (P1) and secondary (P2) circuits of a power conversion stage (CV), the method being implemented in a charger (OBC) on board a vehicle, the charger (OBC) comprising:
- said electrical power conversion stage (CV);
- 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 (P1) of the electrical power conversion stage (CV);
- an insulation monitoring device (IMD) connected to the phase (L), the neutral (N), the earth (PE) and the controller (C) in an electrical circuit, and comprising a direct voltage source (12), a voltage divider (14) whose input (14A) is connected to the direct voltage source (12) and to one of the phase (L) or the neutral (N), and a stage (16) for filtering an alternating voltage component, said stage (16) for filtering an alternating voltage component being connected between the output (14B) of the voltage divider (14) and an input (CO1) of the controller (C);
the insulation control method comprising the following steps:
- a first step of determining (E1) a charger charging mode (OBC);
- if the charging mode is a vehicle-to-charge (V2L) mode:

• a step (E3) of injecting, by the direct voltage source (12), a direct electric current into the voltage divider (14), the direct electric current then circulating in the stage (16) for filtering an alternating voltage component;
• a step of reception (E4), by the controller (C), of a voltage signal (V1) provided at the output of the stage (16) for filtering an alternating voltage component;
• a comparison step (E5), by the controller (C), of said received voltage value (V1) with a threshold voltage value, and,
• if said received voltage value (V1) is greater than the threshold voltage value over a predetermined time interval, a step of transmission (E8), by the controller (C), of a signal for deactivating the electrical power conversion stage (CV).

Insulation control method according to claim 1, characterized in that, if the charging mode is a vehicle-to-charge mode (V2L) and if said received voltage value (V1) is greater than the threshold voltage value over the predetermined time interval, the method further comprises a first intermediate step of transmission (E6), by the controller (C), of a signal for deactivating the DC voltage source (12), a second intermediate step of transmission (E7), by the controller (C), of a signal for reactivating the DC voltage source (12), then a re-implementation of said steps of injection (E3) of a DC electric current, of reception (E4) of a voltage signal, and of comparison (E5) of the received voltage value (V1) with a threshold voltage value, the step of transmission (E8) of a signal for deactivating the electrical power conversion stage (CV) being implemented if and only if, during said last comparison step (E5), the received voltage value (V1) is always higher than the threshold voltage value over the predetermined time interval. Charger (OBC) intended to be embedded in a vehicle, the charger comprising:
- an electrical power conversion stage (CV) provided with a primary circuit (P1) 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 (P1) of the electrical power conversion stage (CV);
- an insulation monitoring device (IMD) connected to the phase (L), the neutral (N), the earth (PE) and the controller (C) in an electrical circuit, and comprising a direct voltage source (12), a voltage divider (14) whose input (14A) is connected to the direct voltage source (12) and to one of the phase (L) or the neutral (N), and a stage (16) for filtering an alternating voltage component, said stage (16) for filtering an alternating voltage component being connected between the output (14B) of the voltage divider (14) and an input (CO1) of the controller (C);
characterized in that the charger (OBC) is configured to implement the steps of the insulation control method according to claim 1 or 2. Charger (OBC) according to claim 3, characterized in that the direct voltage source (12) comprises a step-up converter (22) and a current injection resistor (R _{inj_L} ) connected between the step-up converter (22) and the input (14A) of the voltage divider (14). Charger (OBC) according to claim 4, characterized in that the current injection resistor (R _{inj_L} ) has a resistance value substantially equal to 600 kΩ. Charger (OBC) according to any one of claims 3 to 5, characterized in that the voltage divider (14) is a voltage divider bridge provided with two resistors (R1, R2) connected in series, the two resistors (R1, R2) being such that the division ratio of the voltage divider bridge (14) is between 8 and 12, preferably substantially equal to 10. Charger (OBC) according to any one of claims 3 to 6, characterized in that the stage (16) for filtering an alternating voltage component comprises a current measuring resistor (R3), the current measuring resistor (R3) having a resistance value substantially equal to 1.2 MΩ. A computer program comprising program code instructions for carrying out the steps of the insulation testing method according to claim 1 or 2, when said program is running on a computer.