FR3125930A1 - METHOD FOR PROTECTION AGAINST UNDERVOLTAGE OF AN ELECTRIC MOTOR VEHICLE TRACTION MACHINE - Google Patents

Abstract

The invention relates to a method for protecting against undervoltage of an electric traction machine (11) of a motor vehicle comprising: - a step of detecting an undervoltage at the terminals of the electric traction machine (11) for a predetermined period, - a step of opening the high voltage contactors (13) to electrically isolate the traction battery (12) from the high voltage electrical network (10), - a step of stopping a regenerative braking function to prevent the electrical traction machine (11) operating in alternator mode from supplying current to the high voltage electrical network, and - a step of carrying out an active discharge of the high voltage electrical network (10) to evacuate an electric current from the high voltage electric network (10). Figure 1

Description

METHOD FOR PROTECTION AGAINST UNDERVOLTAGE OF AN ELECTRIC MOTOR VEHICLE TRACTION MACHINE

The present invention relates to a method of protecting against undervoltages of an electric motor vehicle traction machine. The invention finds a particularly advantageous, but not exclusive, application with motor vehicles of the electric or hybrid type having a rotating electrical machine operating at high voltage, that is to say a rotating electrical machine having an operating voltage greater than 300 Volts.

In a manner known per se, an electric or hybrid vehicle may comprise a high voltage electrical network to which are connected an electric traction machine as well as a high voltage electric battery, referred to as a traction battery. Other electrical loads can also be connected to the high voltage electrical network. The high voltage electrical battery is associated with contactors to selectively connect or disconnect the battery to the high voltage electrical network.

The voltage at the terminals of the electric traction machine is monitored when the electric traction battery contactors are closed. In other words, the voltage at the terminals of the electric traction machine is monitored only when the traction battery and the electric traction machine are connected via the high voltage electrical network.

The appearance of an undervoltage at the supply terminals of the electric traction machine is problematic, insofar as the traction machine is not sized to operate at this voltage level. In addition, it can lead to life safety and powertrain operation issues.

Indeed, in the case where the voltage drop at the terminals of the electrical machine is linked to a drop in current, several causes are possible:

- the traction battery may have a malfunction preventing it from supplying nominal current to the electrical network. There is then a risk of serious failure of the traction battery which could cause overheating harmful to the operation of the powertrain.

- part of the current delivered by the battery has leaked outside the electrical machine towards the vehicle. Given the high levels of voltage and current, there is then a risk of electrocution that can endanger people's lives.

- a resistance of the electric machine is damaged due to overheating of one of its components, which is likely to damage the electric machine.

The invention aims to effectively remedy the aforementioned drawbacks by proposing a method of protecting against undervoltages of an electric traction machine of a motor vehicle comprising a high voltage electric network to which said electric traction machine is connected as well as a traction battery associated with contactors for selectively connecting or disconnecting the traction battery to the high voltage electrical network, said method comprising:

- a step of detecting an undervoltage at the terminals of the electric traction machine for a predetermined period,

- a step of opening the high voltage contactors to electrically isolate the traction battery from the high voltage electrical network,

- a step of stopping a regenerative braking function to prevent the electrical traction machine operating in alternator mode from supplying a current to the high voltage electrical network, and

- A step of performing an active discharge of the high voltage electrical network to evacuate an electrical current from the high voltage electrical network.

The invention thus makes it possible to fully secure the electrical network of the vehicle to avoid any risk of electrocution for a person working on the powertrain. The invention also makes it possible to isolate the electrical network from the traction battery to avoid damaging the electrical traction machine in the event that the latter presents a malfunction.

According to one implementation of the invention, said method further comprises a step of prohibiting a computer of the traction battery from closing the high voltage contactors on its own initiative.

According to one implementation of the invention, the active discharge consists in transforming a current stored in electrical bundles of the high-voltage electrical network into heat by means of resistors.

According to one implementation of the invention, said method further comprises a step of activating a water pump of the cooling circuit of the electric machine in the event that an electric component in the electric traction machine has been damaged in due to overheating.

According to one implementation of the invention, said method further comprises a step of sending an alert signal to the driver.

According to one implementation of the invention, said method further comprises a step of cooling the traction battery in the event that a temperature sensor associated with the traction battery returns a value greater than a temperature threshold.

According to one implementation of the invention, the predetermined duration is of the order of a few milliseconds.

According to one implementation of the invention, said method is implemented only when the motor vehicle is operating in a driving mode.

The invention also relates to a motor vehicle computer comprising a memory storing software instructions for implementing the method as defined above.

The invention further relates to a motor vehicle comprising a computer as defined above.

The invention will be better understood on reading the following description and on examining the accompanying figures. These figures are given only by way of illustration but in no way limit the invention.

There is a schematic representation of a high-voltage electrical network interfaced with an on-board network of a motor vehicle implementing the method according to the invention;

There is a diagram of the different steps of the method of protection against undervoltage of an electric traction machine of a motor vehicle.

There shows a high voltage electric network 10 of a motor vehicle to which an electric traction machine 11 is connected. A high voltage electric battery 12, called "traction battery", is associated with contactors 13 to selectively connect or disconnect the battery traction 12 to the high voltage electrical network 10. This electrical network 10 has an operating voltage greater than 300 volts. Other electrical loads 14, in particular a second electrical machine 11, can also be connected to the high voltage electrical network 10.

The electric traction machine 11 can operate in a motor mode to ensure the traction of the motor vehicle. The electric machine 11 may also implement a regenerative braking function allowing the electric machine 11 operating in alternator mode to supply electrical energy to the battery during a braking phase. Thus, during a braking phase, the electric machine 11 transforms at least part of the kinetic energy of the vehicle into electric energy used to recharge the traction battery 12. The electric machine 11 could for example be a synchronous type with permanent magnets or any other type of machine suited to the application (asynchronous machine, polyphase, with or without brushes, etc.).

The high voltage electrical network 10 is interfaced with a low voltage electrical network 16 corresponding to the on-board network via a DC/DC converter 17. Electrical consumers 18 of the vehicle of the lighting type, window or seat actuators, and engine control, are connected to the onboard network 16. The onboard network 16 is associated with a low voltage battery 20 having an operating voltage lower than that of the high voltage electrical network 10. The operating voltage of the onboard network 16 is around 12 volts.

The traction battery 12 is associated with a computer called BMS 21 for "Battery Management System" in English. The BMS computer 21 manages the traction battery 12 of the vehicle. The BMS computer 21 is able to estimate the charge level of the traction battery 12 and to send the information to the supervisor 22 of the powertrain called eVCU (for "Electric Vehicle Control Unit").

The electric traction machine 11 is associated with a computer 23 called the MCU computer (for "Motor Control Unit"). The MCU computer 23 manages the electric traction machine 11 by ensuring in particular the control of the current flowing in the phases of the electric traction machine 11 as well as the control of the temperature of the electric machine 11.

The eVCU supervisor 22 of the powertrain coordinates the computers connected to a data bus 19 of the vehicle, for example a CAN type data bus (for "Controller Area Network"). The eVCU supervisor 22 calculates in particular the remaining autonomy of the vehicle on the basis of the estimate of the charge level returned by the BMS computer 21 of the traction battery 12.

An OBCDC 24 charging module is a component composed of two parts: an OBC part (for On-Board Charger) and a DC/DC converter part. The OBC part manages an operation of the electric current charger of the vehicle. In particular, the OBC part manages the communication with the various charging stations 25 and monitors the electrical charging of the vehicle. The DC/DC converter part manages an operation of the current converter. Following certain electrical charging phases, the DC/DC converter converts 220V alternating current from a domestic electrical network into direct current that can reach 450V. Following other electrical charging phases, the DC/DC converter part does not intervene because the direct current is sent directly to the traction battery 12 via a voltage of 450 V direct. During a driving phase, the DC/DC converter converts part of the direct current of the 350V/450V high voltage traction battery 12 into a low intensity current to supply the on-board network 16 and recharge the corresponding low voltage 12V battery .

The traction battery 12 powers the electric traction machine 11 and the DC/DC converter. The voltage of the traction battery 12 depends on its state of charge. Thus the voltage of the traction battery 12 can vary between 350V when the state of charge of this traction battery 12 is less than 5% and 450V when the state of charge of this traction battery 12 is at 100%. Of course, this voltage range varies according to the power of the electric machine 11 installed in the powertrain of the vehicle and the characteristics of the traction battery 12.

We describe below, with reference to the , the different steps of the method for protecting the electric machine 11 against undervoltage at the terminals of the electric traction machine 11. One or more computers of the vehicle includes a memory storing software instructions for the implementation of this method.

The method is triggered when the MCU computer 23 detects, during a step 100, an undervoltage at the terminals of the electric traction machine 11 for a predetermined duration. It is considered that the electric machine 11 undergoes an undervoltage when the voltage of the electric machine 11 falls below a voltage threshold, for example of the order of 220 V for the predetermined duration. Of course, this voltage threshold can be configured according to the electric traction machine 11 on board the vehicle.

As long as the voltage of the electric machine 11 remains above the voltage threshold, the MCU computer 23 does not report any fault to the supervisor of the motor vehicle. As soon as the voltage at the terminals of the electric traction machine 11 falls below the voltage threshold for the predetermined duration, the MCU computer 23 reports a fault to the eVCU supervisor 22. The predetermined duration is advantageously of the order of a few milliseconds, for example 19ms. The predetermined duration can of course be calibrated according to the characteristics of the powertrain.

Even if the voltage at the terminals of the electric machine 11 rises beyond the predetermined duration, the MCU computer 23 sends the fault back to the eVCU supervisor 22. The protection function detailed below will be launched without the possibility of restoration on the cycle road on which the fault was detected.

It should be noted that the voltage at the terminals of the electric traction machine 11 is monitored only when the vehicle is operating in a driving mode. When the vehicle is stationary in a charging phase at an electric charging station, the voltage at the terminals of the electrical machine 11 is not monitored. In other words, the voltage at the terminals of the electric traction machine 11 is only monitored once the contactors 13 of the traction battery 12 are closed, that is to say that the voltage at the terminals of the machine electric traction 11 is only monitored once the traction battery 12 and the electric traction machine 11 are connected via the high voltage electrical network 10.

During a driving phase, when the MCU computer 23 sends an alert to the eVCU supervisor 22 via the CAN data bus 19, the eVCU supervisor 22 commands, in a step 101, the opening of the high voltage contactors 13. This makes it possible to electrically isolate the traction battery 12 from the high voltage electrical network 10.

The traction battery 12 can then no longer supply current to the high voltage electrical network 10 in the event that the high voltage electrical network 10 is short-circuited with the structure of the vehicle. In a step 102, the eVCU supervisor prohibits the BMS computer 21 from closing the contactors 13 on its own initiative.

In addition, the eVCU supervisor 22 stops, in a step 103, the regenerative braking function to prevent the electrical machine 11 operating in alternator mode from supplying a current to the high voltage electrical network, in particular in the case where the high voltage electrical network 10 would be short-circuited with the structure of the vehicle.

When the contactors 13 are open, the eVCU supervisor 22 requests the MCU computer 23 and/or the OBCDC charging module computer 24 to perform, in a step 104, an active discharge aimed at evacuating the electric current still present in the electrical network. high voltage 10 of the vehicle.

Active discharge consists of transforming a current stored in electrical bundles of the high voltage electrical network into heat by means of resistors. Indeed, it is possible that the current from the traction battery 12 which was supplied to the powertrain before the opening of the contactors 13 has not yet been consumed. The active discharge therefore makes it possible to drain the high-intensity current from the electrical harnesses of the powertrain when the contactors 13 are open.

The electric circuit of the OBCDC charging module 24 and the electric circuit of the electric traction machine 11 include resistors enabling this active discharge function to be performed. The active discharge can be carried out independently by the electronics of the electric traction machine 11 or the electronics of the OBCDC charging module 24. The high voltage electrical network 10 is then safe for the operators who do not risk being electrocuted during an operation.

If necessary, the eVCU supervisor 22 activates, in a step 105, the water pump of a cooling circuit of the electric machine 11 in the event that an electric component in the electric traction machine 11 has been damaged in due to overheating.

The eVCU supervisor 22 will be able to command, in a step 106, an emission of an alert signal intended for the driver. The warning signal may for example be an audible or visual signal, such as for example the display of a red stop light on the dashboard inviting the driver to stop the vehicle and contact the after-sales service.

The cooling of the traction battery 12 is not triggered automatically by the eVCU supervisor 22 because the temperature of the traction battery 12 is monitored by a dedicated temperature sensor. Indeed, as long as the temperature of the traction battery 12 is lower than a temperature threshold, the cooling procedure of the traction battery 12 is not triggered. It is only when the temperature sensor returns a value exceeding the temperature threshold that the cooling procedure for the traction battery 12 is triggered in a step 107.

The strategy for restarting the motor vehicle is described below. Changing from a vehicle powered up (key on state) to a vehicle off (key off state) and then back to a vehicle powered up (key on state) is not not sufficient to inhibit the alert from the MCU 23 computer to the eVCU 22 supervisor.

In fact, it is necessary to wait for the computers MCU 23, BMS 21, eVCU 22 to fall asleep completely in order to then wake them up by powering up the vehicle (“key on” state).

Following this power-up, the MCU computer 23 controls the voltage at the terminals of the electric traction machine 11. If the voltage at the terminals of the electric machine 11 goes back above the minimum voltage criterion, the electric machine 11 will be able to regain normal operation. On the other hand, if the voltage at the terminals of the electrical machine 11 remains or returns below the minimum voltage criterion, the securing process is repeated with the opening of the high voltage contactors 13, the stopping of the regenerative braking function, and the realization of an active discharge of the electrical network.

During a repair of the vehicle, a check of the faults of the traction battery 12, of the electric machine 11, and of the high voltage electric network 10 is carried out to determine the cause of the problem and remedy it by replacing the faulty system.

Claims (10)

Method for protecting against undervoltage an electric traction machine (11) of a motor vehicle comprising a high voltage electric network (10) to which said electric traction machine (11) is connected as well as a traction battery (12) associated with contactors (13) for selectively connecting or disconnecting the traction battery (12) to the high voltage electrical network (10), characterized in that said method comprises:
- a step of detecting an undervoltage at the terminals of the electric traction machine (11) for a predetermined period,
- a step of opening the high voltage contactors (13) to electrically isolate the traction battery (12) from the high voltage electrical network (10),
- a step of stopping a regenerative braking function to prevent the electrical traction machine (11) operating in alternator mode from supplying a current to the high voltage electrical network, and
- a step of carrying out an active discharge of the high voltage electrical network (10) to evacuate the electrical current still present in the high voltage electrical network (10). Method according to claim 1, characterized in that it further comprises a step of prohibiting a computer of the traction battery (12) from closing the high voltage contactors (13) on its own initiative. Method according to Claim 1 or 2, characterized in that the active discharge consists in transforming a current stored in electrical bundles of the high-voltage electrical network into heat by means of resistors. Method according to any one of Claims 1 to 3, characterized in that it also comprises a step of activating a water pump of the cooling circuit of the electric traction machine (11) in the event that a component electric in the electric traction machine (11) would have been damaged due to overheating. Method according to any one of Claims 1 to 4, characterized in that it also comprises a step of sending an alert signal to the driver. Method according to any one of Claims 1 to 5, characterized in that it also comprises a step of cooling the traction battery (12) in the case where a temperature sensor associated with the traction battery (12) returns a value greater than a temperature threshold. Method according to any one of Claims 1 to 6, characterized in that the predetermined duration is of the order of a few milliseconds. Method according to any one of Claims 1 to 7, characterized in that it is implemented only when the motor vehicle is operating in driving mode. Motor vehicle computer comprising a memory storing software instructions for implementing the method as defined according to any one of the preceding claims. Motor vehicle comprising a computer according to claim 9.