Control system for motor drive

Abstract

A control system for a motor drive configured to supply energy from a battery to an electric motor (1), said motor drive (22) comprising a set of power switches and configured to convert a continuous voltage (Vdc1) into an alternating voltage, the invention relates to a control system (1) for controlling a power switch (2) of a motor and further configured to supply a reverse generated first DC voltage (Vdc2) to a battery when the motor is operating as a generator, the control system comprising:-a driver unit (5) for controlling the power switch by an active short circuit (ASC) function to place phases of the motor in a short circuit configuration; and-an input of the driver unit (5) for enabling an ASC function; -an independent auxiliary inverter (71) providing a signal representative of the back electromotive force of the motor, in which the signal provided by the auxiliary inverter can be processed and linked to the input of the driver unit for activating the ASC function.

Description

[0001] The present disclosure relates to a control system for a motor drive. TECHNICAL FIELD

[0002] The present disclosure relates to the field of vehicles motorized by electric motors and recovering energy during deceleration. It relates to all types of vehicles with electric motors: two- or three-wheelers and also cars. BACKGROUND

[0003] It is known for a vehicle to have an electric motor, a battery to power the motor, and a motor drive between the battery and the motor. The motor drive serves as a converter: the motor drive delivers the direct current from the battery to the phases of the motor in an alternating manner, and when the motor works as a generator, the motor drive rectifies the back electromotive force from the motor so that it can charge the battery. The motor drive comprises power switches (for example field effect transistors) controlled by a drive unit. This drive unit comprises, in most cases, a safe operating mode which prevents damage due to high voltages. If a high back electromotive force is detected, this safe operating mode (also called active short circuit (ASC) mode) is activated by the control unit and the drive unit switches on the switches so that the phases of the motor are short-circuited.

[0004] However, if the control unit stops working for some reason, it can no longer send instructions to the power switch drive unit and the motor drive can no longer work properly. In this case, if the back electromotive force generated by the motor becomes too high, this back electromotive force can damage the components on the vehicle, since the drive unit is no longer controlled and the ASC mode or function cannot be activated. This can happen, for example, when the vehicle is driven with the engine off, especially downhill. SUMMARY

[0005] The present disclosure improves this situation. The general object of the present disclosure is to provide an auxiliary protection circuit which also works when the drive unit of the power switch is not working.

[0006] A control system for a motor drive configured to be connected on the one hand to a traction electric motor of a vehicle and on the other hand to a battery, said motor drive comprising a set of power switches, the control system comprising: - a drive unit for controlling the power switches of the motor drive by an active short circuit function to put at least one phase of the motor in a short-circuit configuration; and - an input of the drive unit for activating the active short circuit function.

[0007] According to the disclosure, the control system further comprises an independent auxiliary circuit which provides a signal representative of the back electromotive force of the motor and which signal provided by the auxiliary circuit can be processed and linked to the input of the driver unit for activating the active short-circuit function.

[0008] In this new type of control system, the implementation of an auxiliary circuit allows measuring the back electromotive force (EMF) or a signal equivalent to this back EMF in an independent manner, so that the signal provided by the auxiliary circuit can be used in all conditions and the driver unit can be controlled even when the motor control unit controlling the power switch driver unit is no longer working in "normal" mode. From another point of view, the motor is protected from an overvoltage of the back EMF, whatever the battery is connected to the motor driver. The back EMF (or equivalent) can also be measured when the battery is connected to the motor driver.

[0009] The following features can be optionally implemented alone or in combination with each other: - the auxiliary circuit is an auxiliary inverter with a low-pass filter and, in a preferred embodiment, - the independent auxiliary inverter is an inverter diode bridge linked to at least one phase of the motor and preferably to all phases of the motor, - the signal provided by the auxiliary circuit is processed by a logic circuit for activating the active short-circuit function and the logic circuit is configured so that when the signal provided by the auxiliary circuit exceeds a first threshold, the active short-circuit function is enabled, at which time the auxiliary circuit measures the back EMF voltage independently of the DC link voltage, - the logic circuit is configured so that when the signal provided by the auxiliary circuit is below a second threshold (which is lower than the first threshold), the active short-circuit function is disabled, - the logic circuit comprises a comparator with hysteresis, - the motor driver is connected to a battery, the control system being characterized in that said motor driver is capable of supplying a first direct voltage generated in reverse when the motor works as a generator to the battery and when the first direct voltage generated in reverse is below a third threshold, the active short-circuit function is disabled, - the first direct voltage generated in reverse and the signal provided by the auxiliary circuit are electronically linked by a circuit, in particular by a diode.

[0010] - the control system further comprises a switching device controlled by the motor control unit to inhibit the action of the independent auxiliary circuit, i.e. to disable the activation of the active short-circuit function; or the control system further comprises a switching device controlled by the motor control unit to disable the processed signal of the auxiliary circuit; - the independent auxiliary circuit and the logic circuit are implemented in hardware, - the independent auxiliary circuit further comprises a discharge resistor; In another aspect, a propulsion system for a vehicle is presented, the propulsion system comprising an electric motor and a battery, characterized in that the propulsion system further comprises a control system as described above.

[0011] In another aspect, a vehicle is presented, characterized in that the vehicle comprises a propulsion system as described above. BRIEF DESCRIPTION OF DRAWINGS

[0012] Further features, details and advantages will appear in the following detailed description and in the attached drawings, in which: Figure 1 [ Figure 1 ] is a schematic diagram of an electric motor and a control system of the motor according to an embodiment.

[0013] Figure 2 [ Figure 2 ] is a first diagram showing the variation of signals over time in a first operating mode.

[0014] Figure 3 [ Figure 3 ] is a second diagram showing the variation of signals over time in a second operating mode.

[0015] Figure 4 [ Figure 4 ] is a schematic diagram of an auxiliary inverter according to an embodiment.

[0016] Figure 5 [ Figure 5 ] is a schematic diagram of an advanced logic circuit according to an embodiment. DETAILED DESCRIPTION

[0017] Reference is now made to Figure 1 . This figure first shows an electric motor 1 having three electrical phases U, V and W. The electric motor 1 is controlled by a motor drive comprising a power module 2 and a motor control unit 3. A battery 4 with integrated battery management module supplies the electric motor 1 with energy through the motor drive.

[0018] The power module 2 comprises a set of switches forming an inverter 21 which on one side can supply each phase of the electric motor 1 with current from the battery 4 in AC when the electric motor 1 is doing work, and which on the other side can rectify the AC produced by the electric motor 1 into DC when the electric motor 1 is working as a generator, which DC can charge the battery 4. The set of switches is driven by a power switch driver unit 5 which is controlled by the motor control unit 3. In Figure 1 In the embodiment shown, the switches are MOSFET switches, but other switches are possible.

[0019] The battery 4 is connected to the power module 2 and between the battery 4 and the power module 2 there is foreseen a battery relay SW1 which is managed by a battery management system of the battery 4. A DC link capacitor Cl is installed in parallel to the inverter 21 (and to the battery 4). The battery end voltage is Vdcl and the capacitor (Cl) end DC link voltage is Vdc2.

[0020] The system is a known well functioning system. Sensors provide information to the motor control unit 3 and to the battery 4 and the switches are automatically driven whether the motor is working as an electric motor or as a generator.

[0021] To protect the power module 2, the motor control unit 3 measures the so called DC link voltage Vdc2. If this voltage exceeds a predetermined high threshold, the motor control unit 3 activates an active short circuit (ASC) function (or mode) so that the phases (preferably all phases) of the motor are short circuited. If this DC link voltage is below a predetermined low threshold, the motor control unit 3 deactivates the active short circuit (ASC) function. The system can alternate between these two states: ASC active / deactivated.

[0022] For this configuration (with only the motor control unit 3 and without other auxiliary circuits as explained below), the ASC function can only be activated (and deactivated) when the battery relay SW1 is open, i.e. when the battery 4 is disconnected. Otherwise, the DC link voltage Vdc2 remains equal to the battery voltage. In the last case (battery relay closed), if a counter electromotive force (EMF) is generated, and if this counter EMF becomes high, it will cause a current to flow from the electric motor 1 to the battery 4, while the DC link voltage Vdc2 will not rise significantly. This current will first flow through the inverter 21 and can damage the power switches, and can also damage the battery 4 due to uncontrolled battery charging. This in turn can even cause a fire.

[0023] When the battery relay SW1 is open (battery 4 is disconnected), the DC link voltage Vdc2 will vary with the back electromotive force (back EMF) or voltage and can exceed the voltage rating of the components linked to the DC link Vdc2 if the ASC function cannot be activated, for example because the motor control unit 3 is not powered (vehicle switched off). The consequences of this situation can be the destruction of components, for example the power switches of the inverter 21 and / or the damage of auxiliary devices linked to the system.

[0024] For both cases (i.e. battery relay SW1 open or closed), Figure 1 An auxiliary protection circuit 6 is proposed which allows the activation of the ASC function also when the motor control unit 3 is no longer powered.

[0025] The proposed auxiliary protection circuit 6 comprises an auxiliary inverter 7 and a triggering system 8.

[0026] The auxiliary inverter 7 is configured to measure directly the back electromotive force. In the proposed embodiment, the auxiliary inverter comprises an auxiliary inverter 71 and an RC filter 72.

[0027] The auxiliary inverter 71 proposed here is a diode bridge with three pairs of diodes (one pair of diodes per phase of the electric motor 1). In a simplified embodiment, the inverter can have only one pair (or two pairs) of diodes. The RC filter 72 is in parallel with the auxiliary inverter 71 and forms with it a peak inverter which provides a signal V BEMF representative of the back electromotive force generated by the electric motor 1. Figure 1

[0028] The proposed auxiliary inverter 7 is completely passive. No power supply is needed: the signal V BEMF is provided under all conditions. This signal is provided to the triggering system 8.

[0029] Figure 1 An example of a triggering system 8 is provided together with Figure 4 The system comprises as a core element a comparator 81 with hysteresis. The signal V BEMF is divided by two resistors and a new signal V ASC_TRIG is obtained, which is also representative of the back electromotive force of the electric motor 1. This new signal is compared inside the comparator 81 with a reference signal V 12 provided by an independent voltage generator (not shown). The comparator 81 provides an ASC signal (0 or 1) which is intended to enable or disable the active short-circuit function in the power switch driver unit 5. The ASC signal is therefore linked to the input of this driver unit 5.

[0030] ​The proposed auxiliary system operates both when battery 4 is connected (battery relay SW1 is closed) and disconnected (battery relay SW1 is open).

[0031] The improved embodiment anticipates a disable function controlled by the motor control unit 3, which disables the auxiliary protection circuit 6. Under predetermined conditions, i.e., when the motor control unit 3 operates (turns on the ignition switch), the unit can transmit an INHIBIT (disable) signal. In this case, the motor control unit 3 directly controls the power switch driver unit 5 ( Figure 1 (COMM line). Figure 4 An example of an electrical component designed to disable auxiliary protection circuit 6 is shown. When an "active" INHIBIT signal is sent ( Figure 4 When ), signal V ASC_TRIG It is forcibly triggered, causing the comparator's output signal (ASC signal) to remain at 0.

[0032] Figure 5 Further improvements to the system described above are proposed. Figure 5 An example of implementing the following approach is provided: When auxiliary protection circuit 6 is active, the ASC function is based on the signal (V) transmitted by auxiliary inverter 7. BEMF or V ASC_TRIG It is enabled, but the ASC function is disabled based on the DC link voltage (Vdc2). Figure 5 The components shown are merely a proposed solution for implementing this idea, but those skilled in the art are aware of other ways to implement this working mode. Figure 5 The components can be easily implemented in hardware, and are therefore an advantageous embodiment among the many implementations.

[0033] What is clear to those skilled in the art is that Figure 5 Electronic components in V BEMF The ASC function is enabled when the threshold is exceeded, and in V DC (=Vdc2) Disables ASC function when it is below a lower threshold.

[0034] Figure 2 It shows that when only V is considered BEMF Enabling and disabling the ASC function triggers the operation of System 8, and Figure 3 It shows that when based on V BEMF and Vdc2 ( Figure 5 Enabling and disabling the ASC function triggers the operation of System 8.

[0035] exist Figure 2 (corresponding to) Figure 1Vdc1 is the terminal voltage of battery 4. Two thresholds, VTh1 and VTh2, are defined such that Vdc1 > VTh1 > VTh2. The higher threshold VTh1 needs to be lower than the minimum possible battery voltage. When electric motor 1 operates as a generator, V... BEMF It can be increased and can reach VTh1 (depending on the motor speed). In this case, the ASC function is enabled, and V BEMF It will automatically decrease until VTh2. Then, the ASC function will be disabled. If electric motor 1 is still operating as a generator, then if the motor speed is still high enough, V... BEMF This will increase again. In this example, the ASC function will be enabled and disabled as long as electric motor 1 operates as a generator at a high speed (sufficient to reach VTh1).

[0036] exist Figure 3 (combined) Figure 5 Under the same conditions, such as when the vehicle is driving downhill, there are fewer switchings between enabling and disabling the ASC function. For increased back electromotive force, V BEMF Measured directly by auxiliary inverter 7. When the upper threshold (e.g., with) Figure 2 When the same signal (i.e., VTh1) is passed from below, the ASC function is activated. As a result, the back electromotive force begins to decrease (and VTh1...). BEMF It also decreases). In order to reduce V BEMF The DC link voltage Vdc2 is measured. The ASC function is disabled when the lower threshold (VTh3, which may or may not be equal to VTh2) is crossed from above. The back EMF then begins to rise. There is also a cyclical operation between the higher and lower thresholds.

[0037] If the battery relay SW1 remains closed (and battery 4 is connected), the ASC function remains enabled until, for example, when the system (motor control unit 3) sets the INHIBIT signal the next time the vehicle is started.

[0038] Industrial applications The technical solution presented here can also be used to protect the motor drive of an electric motor when the motor is being driven and the inverter of the motor drive is not controlled in a defined manner (e.g., when the corresponding vehicle is being driven with the engine off). The proposed solution works both when the battery is connected and when the battery is disconnected. Therefore, the protection is effective in all situations.

[0039] This disclosure presents an auxiliary inverter that measures back EMF in all cases with passive components, enabling active short-circuit functionality even when the control system is not powered.

[0040] In an advanced embodiment, the control system, upon activation, can transmit a disable signal so that the motor drive is controlled by the control system in a normal manner and the auxiliary protection system is not disabled in limp-home mode (e.g. the motor is driven in the event of an engine stall).

[0041] Another advanced embodiment (which is independent of the previous one) relates to triggering the active short-circuit function. In a preferred embodiment, the control system employs an asymmetric way to activate and deactivate the ASC function (or mode). Advantageously, the ASC function is activated when the back electromotive force (i.e. the voltage measured by the auxiliary inverter) exceeds a higher threshold and deactivated when the DC-link voltage, which is the voltage measured at the terminals of a capacitor in parallel with the "main" inverter (i.e. the inverter of the electric motor), is below a lower threshold.

[0042] The present disclosure is not limited to the embodiments described above and the alternatives described herein, which are merely examples. The present invention encompasses every alternative that would occur to those skilled in the art upon reading the present text.

Claims

1. Control system for a motor drive (2) configured to be connected on the one hand to a traction electric motor (1) of a vehicle and on the other hand to a battery, said motor drive (2) comprising a set of power switches, the control system comprising: - a drive unit (5) for controlling the power switches of the motor drive (2) by an active short-circuit function to put at least one phase of the motor in a short-circuit configuration, and - an input of the drive unit (5) for enabling the active short-circuit function, characterized in that, the control system further comprises an independent auxiliary circuit (71, 72) providing a signal representative of the back electromotive force of the motor (1), and The signal (V BEMF ) provided by the auxiliary circuit (71, 72) can be processed and linked to the input of the driver unit (5) for activating the active short-circuit function.

2. The control system of claim 1, wherein, the auxiliary circuit is an auxiliary inverter (71) with a low-pass filter (72).

3. The control system of claims 1-2, wherein, The independent auxiliary inverter is an inverter diode bridge linked to at least one phase of the motor and preferably to all phases of the motor.

4. The control system of claims 1 to 3, wherein, The logic circuit for activating the active short-circuit function processes the signal provided by the auxiliary circuit, and the logic circuit is configured such that the active short-circuit function is enabled when the signal (V BEMF ) provided by the auxiliary circuit (71, 72) exceeds a first threshold value (Vth1).

5. The control system of claims 1 to 4, wherein, The logic circuit is configured such that the active short-circuit function is deactivated when the signal (V BEMF ) provided by the auxiliary circuit (71, 72) is below a second threshold value (Vth2), wherein the second threshold value is lower than the first threshold value (Vth1).

6. The control system according to one of claims 1 to 5, characterized in that Said logic circuit comprises a comparator with hysteresis.

7. The control system of one of claims 1 to 6, wherein, The motor drive (2) is connected to a battery (4), the control system being characterized in that said motor drive (2) is able to supply a first direct voltage (Vdc2) generated in reverse to the battery (4) when the motor works as a generator, and that the active short-circuit function is deactivated when the first direct voltage (Vdc2) generated in reverse is lower than a third threshold (Vth3).

8. The control system of claim 7, wherein, The first direct voltage (Vdc2) generated in reverse and the signal (V BEMF ) supplied by the auxiliary circuit (71, 72) are electronically linked by means of a circuit, in particular by means of a diode.

9. The control system according to one of claims 1 to 7, characterized in that The control system further comprises a switching device controlled by the motor control unit to inhibit the action of the independent auxiliary circuit (71, 72).

10. A propulsion system for a vehicle, the propulsion system comprising an electric motor and a battery, characterized in that, The propulsion system further comprises a control system according to one of claims 1 to 9.

11. A vehicle characterized by comprising: The vehicle comprises a propulsion system according to claim 10.

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