METHOD FOR ELECTRICAL PROTECTION OF A FREEWHEELING DIODE POWER CONVERTER

Abstract

The present invention relates to a method for protecting a power converter (3) of an electrified vehicle electrical system, said system comprising at least one energy storage device (1) and an electric drive machine (5) connected to the power converter (3). The method comprises the following steps: upon disconnection of the energy storage device (1) from the power converter (3) during a traction phase of the electric drive machine (5), monitoring an electrical parameter at the input and output of the power converter, including current and voltage, to detect the electrical disconnection of the storage device; and, upon detection of the disconnection of the storage device (1), closing at least one freewheeling diode switch of the power converter (3) for the duration of the disconnection detection. Figure 2.

Description

Title of the invention: METHOD FOR ELECTRICAL PROTECTION OF A FREEWHEELING DIODE POWER CONVERTER

[0001] The field of the invention relates to a method for protecting a power converter of an electrical system of an electrified vehicle.

[0002] Electrified vehicles are vehicles whose powertrain includes an electric drive unit connected to a voltage network supplied by an electrical energy storage device. In some architectures, an electrical system may include two storage devices connected to a power converter capable of managing the energy between the two storage devices and the drive unit. This type of system is used when it is necessary to manage energy between storage units operating at different voltage levels. For example, in a fuel cell vehicle, the power converter may be connected to a first storage unit on a low-voltage network of the fuel cell and to a second storage unit on a high-voltage network of the drive unit.

[0003] If it happens that the two storage units disconnect from the low voltage and high voltage network in a very short time, of about 10 to 100ms, during a phase where the driving machine is operating in traction mode with a high current which must continue to flow in one of the two voltage networks, this current generally passes through the freewheeling diodes of the power converter switches.

[0004] This situation is likely to cause heating proportional to the current that the diodes cannot withstand. Furthermore, in voltage converters with multiple boost stages, the current distribution among the different diodes is not uniform. Only one or two conduct. One solution to this situation is to add a protection component to prevent damage to the power converter.

[0005] Prior art is known from document EP-B2-2232663, which describes a power management system comprising a power supply module connected to a DC power source and an inverter connected to a power grid, where the power supply module operates in a safety mode with limited power until it receives a superimposed signal from the inverter. Furthermore, the safety mode is configured to limit the power absorbed by limiting the current flow or by limiting the voltage.

[0006] This type of protection is not suitable for protecting the power electronics when the storage devices disconnect from the power converter in a situation of operation of the electric machine in traction mode because the stator current must continue to flow through the electrical system.

[0007] There is therefore a need to address the aforementioned problems. One object of the invention is to provide a protection solution for a power converter supplying a motor electric machine in the event of disconnection of the energy storage unit(s) in traction mode.

[0008] More specifically, the invention relates to a method for protecting a power converter of an electrified vehicle electrical system, said system comprising at least one energy storage device and one electric drive machine connected to the power converter.

[0009] According to the invention, the method comprises the following steps during the disconnection of the energy storage device from the power converter during an operating phase of the electric machine in traction mode:

[0010] - monitoring an electrical parameter at the input and output of the converter power, among parameters including current and voltage, to detect electrical disconnection of the storage device.

[0011] - in the event of detection of the disconnection of the storage device, the closure of minus a freewheeling diode switch of the power converter during the disconnection detection time.

[0012] According to one variant, the closing is controlled as long as a current is detected at the output of the power converter.

[0013] According to one variant, disconnection detection is activated if the input current of the power converter is less than a first current threshold and if simultaneously the output current is greater than a second current threshold.

[0014] According to one variant, disconnection detection is activated if the input voltage and output voltage of the power converter between two successive instants is less than a voltage threshold.

[0015] According to one variant, the closure includes the closing control of at least two freewheeling diode switches, connected in parallel, of a DC-DC voltage booster circuit of the power converter.

[0016] An electrified vehicle electrical system is further provided, comprising a power converter, at least one energy storage device and an electric drive machine connected to the power converter and a control unit configured to implement any of the preceding embodiments of the protection method.

[0017] According to one variant, the power converter includes a DC-DC voltage boost circuit with a freewheeling diode switch structure.

[0018] According to one variant, the electrical system further comprises a second energy storage device including a fuel cell and electrically supplying the power converter.

[0019] An electrified vehicle comprising such an electrical system is also planned.

[0020] The main advantage of the protection method is that it avoids oversizing electronic components of the power converter supplying the electric motor. It improves the reliability of the power electronics in situations where energy storage devices might disconnect from the electrical system of an electrified vehicle.

[0021] Other features and advantages of the present invention will become more apparent upon reading the following detailed description, which includes embodiments of the invention given by way of non-limiting examples and illustrated by the accompanying drawings, in which:

[0022] [Fig. 1] represents an embodiment of the protection process according to the invention.

[0023] [Fig.2] represents an embodiment of an electrical system according to the invention.

[0024] The invention applies to electrified vehicles, that is to say, vehicles comprising an electric drive machine and power electronics, with fully or partially electric motors, preferably motor vehicles, but not exclusively such as aircraft, trucks, tractors, bicycles, and ships. The invention relates, for example, to electrified vehicles comprising a battery storage device and a fuel cell storage device.

[0025] Figure 1 represents an embodiment of the protection method in the form of a block diagram. The purpose of the protection method is to protect an electrical system of an electrified vehicle in a driving situation when the energy storage device(s) supplying the electric machine disconnect for a very short time, i.e. for a duration of up to approximately 100 milliseconds, in other words, a duration less than or equal to 100 milliseconds.

[0026] In an initial first step E0 of the process, the vehicle is started and the electrical system is initialized and put into operation. At least one energy storage device supplies a motor electric machine via at least one power converter. The electric machine can be electrically connected to two different energy storage devices operating at different voltages via power converters adapted for this purpose.

[0027] For example, in the case of a fuel cell vehicle, a first fuel cell device is provided to supply energy for the main energy needs and a second energy storage device with electrochemical cells is specifically designed for the needs of transient phases in peak current or for energy recovery during regenerative braking.

[0028] In a second stage E1, the vehicle is in traction mode, meaning it is moving at a non-zero speed. The energy storage device(s) supply electrical power to the electric drive machine. A current flows in the stator of the electric drive machine. The protection method includes a step of measuring an electrical parameter at the input and output of the power converter, from among parameters including current and voltage. The measurement is implemented by sensors electrically positioned at the input and output of the power device. The sensors can be current and voltage sensors at the input and output of the power converter.

[0029] In addition, the protection method includes a third monitoring step E2 consisting of measuring the input and output current and / or voltage and comparing these values ​​with predetermined thresholds to detect an electrical disconnection of the energy storage device(s) and current and voltage characteristics requiring activation of the electrical protection.

[0030] For example, a first monitoring strategy consists of monitoring whether the input current of the power converter is below a first threshold, for example 20 amperes, and whether the output current of the power converter is above a second threshold, for example 100 amperes. This situation indicates the presence of a high current flowing in the stator inductors.

[0031] Alternatively or in addition, a second strategy consists of monitoring whether the voltage difference between two successive measurement instants, at the input of the power converter, is less than a voltage threshold, for example 50 volts and whether the voltage difference between the same two instants, at the output of the power converter, is less than a second voltage threshold, for example 50 volts.

[0032] If either of these two situations is detected in step E2, or if both situations are detected simultaneously, then the process triggers a fourth step E3, which closes at least one switch, preferably all the switches in the voltage step-up circuit of the power converter supplying the electric machine. The closing command is maintained as long as current is present at the output of the power converter. A switch closing command means that the switch is in the on position, commonly referred to as "SWITCH ON" in English terminology.

[0033] This step E3 prevents the freewheeling diodes from overheating and their characteristics from deteriorating due to the induced current flowing in the stator inductors of the electric machine when the storage devices disconnect from the electrical grid. Furthermore, closing the switches allows for control The current is distributed evenly between each switching structure. This allows the power to be distributed between the N switching structures to prevent individual heating.

[0034] The method includes a fifth step E4 for monitoring the protection deactivation condition, which consists of controlling the completion of the closing of the power converter switch(es). The deactivation condition involves measuring the current and detecting a lack of current at the power converter output and the electrical disconnection of the energy storage devices. In other words, the switch(es) will remain closed until the current is interrupted if the energy storage devices are still disconnected.

[0035] If a power outage is detected, the closing command is deactivated. The method includes step E5 of the protection strategy exit.

[0036] In [Fig. 2], an embodiment of the electrical system is schematically described by way of non-limiting example. The electrical system is an electrified vehicle power system comprising two energy storage devices 1 and 2 for the needs of an electric drive machine 5.

[0037] The electric drive machine 5 can be an electric machine operating in direct current or alternating current.

[0038] The electrical system includes a first power converter 3 connecting a first high-voltage voltage bus 6 to the electric drive machine 5. The first voltage bus 6 is supplied by the first storage device 1.

[0039] The electrical system further comprises a second power converter 4 connecting a second low-voltage voltage bus 7 to the first voltage bus 6. The second voltage bus 7 is supplied by the second storage device 2. The second power converter 4 also supplies the first voltage bus 6.

[0040] The first storage device 1 is a battery system 1 with electrochemical cells intended primarily for the needs of transient current phases or for energy recovery phases of the vehicle. An electrochemical cell is a storage element having two electrical connection terminals and a voltage of a few volts, most often between approximately 2.3V and 4.2V. The cells can be of the Lithium-ion type (lithiumized Nickel Manganese Cobalt oxide (NMC) or lithium iron phosphate (LFP) can be cited as examples of active materials for the positive electrode), Nickel Cadmium (Ni-Cd), Nickel Metal Hydride (Ni-MH), or Sodium-ion, for example. More specifically, a Lithium-ion cell is mainly composed of a porous positive electrode, a porous negative electrode, a separator, and an electrolyte (which can be liquid, polymeric, or solid). The operating principle of a Lithium-ion cell It is based on the reversible exchange of lithium ions between the two porous electrodes. The storage device 1 can be a supercapacitor device.

[0041] The second storage device 2 is a fuel cell, for example of the PEM type (“Proton Exchange Membrane” in English).

[0042] If the electric drive machine 5 is a DC machine, the first power converter 3 comprises a DC-DC step-up voltage circuit with a freewheeling diode switch structure 3. As is known to those skilled in the art, the switch structure of the first power converter 3 includes at least one or at least two step-up voltage structures. It may include N step-up structures connected in parallel, where N is an integer between 2 and 20, for example.

[0043] Alternatively, if the electric drive machine 5 is an alternating current machine, the first power converter 3 can be a DC-AC circuit comprising a freewheeling diode switch arm circuit.

[0044] More specifically, a switch is of the semiconductor type which may include one or more semiconductor devices, for example a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), or an IGBT (Insulated-Gate Bipolar Transistor), or any other suitable technology sufficiently robust to withstand the voltages and currents of the electrical machine 5 and the storage devices 1 and 2, and resist transient peaks.

[0045] Furthermore, the power converter 3 includes sensors 31 and 32 at its input and output respectively. The sensors can be current and voltage sensors suitable for implementing the monitoring function of the protection process.

[0046] The invention is described above by way of example. It is understood that a person skilled in the art is able to carry out different variant embodiments of the invention by combining, for example, the different features above taken alone or in combination, without departing from the scope of the invention.

Claims

Demands

1. A method for protecting a power converter (3) of an electrified vehicle electrical system, said system comprising at least one energy storage device (1) and an electric drive machine (5) connected to the power converter (3), the method being characterized in that it comprises the following steps when the energy storage device (1) is disconnected from the power converter (3) during a phase of operation of the electric machine (5) in traction mode: - monitoring (E2) an electrical parameter at the input and output of the power converter from among parameters including current and voltage to detect the electrical disconnection of the storage device, - in the event of detection of the disconnection of the storage device, closing (E3) at least one freewheeling diode switch of the power converter (3) during the duration of the disconnection detection.

2. Method according to claim 1, wherein the closure (E3) is controlled as long as a current is detected at the output of the power converter (3).

3. A method according to claim 1 or 2 wherein disconnection detection is activated if the input current of the power converter (3) is less than a first current threshold and if simultaneously the output current is greater than a second current threshold.

4. A method according to any one of claims 1 to 3 wherein disconnection detection is activated if the input voltage and output voltage of the power converter (3) between two successive instants is less than a voltage threshold.

5. A method according to any one of claims 1 to 4, wherein the closure (E3) comprises the closing control of at least two parallel-connected freewheeling diode switches of a DC-DC voltage booster circuit of the power converter (3).

6. An electrified vehicle electrical system comprising a power converter (3), at least one first energy storage device (1) and an electric drive machine (5) connected

7.

8.

9. to the power converter (3) and a control unit configured to implement the protection method according to any one of claims 1 to 5. Electrical system according to claim 6 in which the power converter comprises a DC-DC voltage boost circuit with a freewheeling diode switch structure 3. Electrical system according to claim 6 or 7 further comprising a second energy storage device (2) comprising a fuel cell and electrically supplying the power converter (3). Electrified vehicle comprising an electrical system according to any one of claims 6 to 8.

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