Motor control device and method for operating a three-phase brushless DC motor

Abstract

The invention relates to a motor control device (1) for a three-phase brushless DC motor (2). The motor control device (1) comprises a converter (3) having an electrical half-bridge (3.1, 3.2, 3.3) for each phase of the brushless DC motor (2), the electrical half-bridge having two electronic switches (H1, H2, H3, L1, L2, L3), and a dedicated integrated circuit (4) for driving the electronic switches (H1, H2, H3, L1, L2, L3) of the converter (3). The dedicated integrated circuit (4) can be controlled by a programmable control unit (9) in normal mode and has a first interface (AAD) for receiving an error signal (5) indicating the presence of a fault, and the dedicated integrated circuit is designed to place the converter (3) in a defined end-of-operation state (High_Z) independently of the programmable control unit (9) after receiving the error signal (5).

Description

Technical Field

[0001] The invention relates to a motor control device and a method for operating a three-phase brushless DC motor. Background Art

[0002] In the event of a dangerous failure, the safety-related systems must be put into a safe operating state. For example, the ISO 26262 standard specifies the safety integrity levels ASIL (=Automotive Safety Integrity Level) for safety-related systems in motor vehicles.

[0003] In some applications of brushless DC motors with electronic control devices, for example, a safe system state is achieved by actively switching the brushless DC motor to a predefined operating state (e.g., a disengaged state in the case of a transmission actuator). Alternatively, mechanical means can be used (e.g., by decoupling with the aid of a spring, or using microcontroller support) to switch the system to a safe operating state, but this partially greatly reduces the possibility of achieving an operating state with a high safety integrity level in the event of a fault in the electronic drive control system.

[0004] WO 2014 / 173792 A2 discloses a method for operating a three-phase brushless DC motor using electronic commutation controlled by pulse width modulation in the event of a fault. After indicating the presence of a fault, the rotor of the brushless DC motor rotates in a predefined motor rotation direction with a predefined maximum number of commutation steps, and the brushless DC motor is then placed in a selected end-of-operation state. Summary of the invention

[0005] The object of the present invention is to provide an improved motor control device and an improved method for safely operating a brushless DC motor in the event of a fault.

[0006] The motor control device for a three-phase brushless DC motor according to the present invention comprises a converter having an electrical half-bridge for each phase of the brushless DC motor, the electrical half-bridge having two electronic switches, and a dedicated integrated circuit for driving the electronic switches of the converter. The dedicated integrated circuit can be controlled by a programmable control unit in a normal mode, the dedicated integrated circuit has a first interface for receiving an error signal indicating the presence of a fault, and the dedicated integrated circuit is designed to place the converter into a defined end-of-operation state independently of the programmable control unit after receiving the error signal.

[0007] The motor control device according to the invention makes it possible, in the event of a safety-related fault, to actively place the brushless DC motor in a safe operating state defined by the end-of-operation state of the converter without the support of a programmable control unit, in a manner directly controlled by a dedicated integrated circuit actuating the electronic switches of the converter. This prevents in particular the situation where a safe operating state cannot be reached due to errors in the programmable control unit (e.g. undesired bit flips).

[0008] In one embodiment of the present invention, the dedicated integrated circuit has a braking position register for setting a braking position and a counting register for storing a count value, wherein the count value is a count value of the commutation (number of times) used to change the switching state of the inverter, and the dedicated integrated circuit is designed to, when an error signal is received and the braking position is set, if the count value is greater than zero, immediately place the inverter in a running termination state; if the count value is zero, place the inverter in a braking mode for a defined braking period before placing the inverter in the running termination state, thereby braking the brushless DC motor.

[0009] The above-described embodiments of the present invention enable controlled braking of the brushless DC motor before it is placed in a safe operating state, provided that braking is provided by setting the brake bit and the braking operation is not hindered by any rotation of the motor provided by the count value of the count register.

[0010] In another embodiment of the present invention, the dedicated integrated circuit has a second interface for receiving at least one sensor signal indicating the rotor position of the rotor of the brushless DC motor. The dedicated integrated circuit is designed to change the switching state of the inverter by means of at least one commutation before placing the inverter in the terminal state if the braking position is not set when an error signal is received and the count value is greater than zero, and after each commutation, check whether the commutation has changed the rotor position of the rotor, and reduce the count value by one when the rotor position changes until the count value is zero.

[0011] The above-described embodiment of the present invention enables the motor rotation provided according to the count value of the count register to be performed before the motor is placed in the safe operation state.

[0012] In another embodiment of the invention, the ASIC has a timer / clock circuit, which is designed to start a timer after receiving the error signal and to place the converter in the end-of-operation state after a defined period of time has elapsed since the start of the timer.

[0013] The above-described embodiments of the invention make it possible to place the motor in a safe operating state at the latest after the end of a time period, in particular even when, for example, the rotor of the brushless DC motor may be blocked and cannot rotate further and therefore cannot perform the number of rotor rotations predefined by the count value of the counting register.

[0014] In another embodiment of the present invention, in the end-of-operation state of the converter, all electronic switches are turned off, which enables the rotor of the brushless DC motor to rotate freely, thereby putting the motor in a safe operating state.

[0015] In the method according to the invention for operating a three-phase brushless DC motor using a motor control device according to the invention, each phase of the brushless DC motor is connected to an electrical half-bridge of a converter, and an application-specific integrated circuit is used to drive the electronic switches of the converter, which is controlled by a programmable control unit in normal mode. After receiving an error signal, the application-specific integrated circuit puts the converter into a defined operating end state independently of the programmable control unit.

[0016] In one embodiment of the method, the dedicated integrated circuit has a braking bit register for setting a braking bit and a counting register for storing a count value, wherein the count value is a count value of the commutation (number of times) that changes the switching state of the inverter. When the braking bit is set when an error signal is received, if the count value is greater than zero, the dedicated integrated circuit immediately places the inverter in an end-of-operation state; if the count value is zero, the inverter is placed in a braking mode for a defined braking period before the inverter is placed in the end-of-operation state, thereby braking the brushless DC motor.

[0017] In another embodiment of the method, the dedicated integrated circuit has a second interface for receiving at least one sensor signal indicating the rotor position of the rotor of the brushless DC motor. If the braking position is not set when the error signal is received and the count value is greater than zero, the dedicated integrated circuit changes the switching state of the inverter by means of at least one commutation before placing the inverter in the terminal operation state, and checks after each commutation whether the commutation changes the rotor position of the rotor. When the rotor position changes, the count value is reduced by one until the count value is zero.

[0018] In another embodiment of the method, the ASIC has a timer, which is started by the ASIC after receiving the error signal and which places the converter in the final state after a defined period of time has elapsed since the start of the timer.

[0019] In a further embodiment of the method, in the final state of the converter, all electronic switches are closed.

[0020] The advantages of the method according to the invention and its embodiments correspond to the above-described advantages of the motor control device according to the invention and its above-described embodiments, and are therefore not repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Exemplary embodiments of the present invention are explained in more detail below with reference to the accompanying drawings.

[0022] In the attached picture:

[0023] Figure 1 shows a block diagram of a motor control device for a brushless DC motor,

[0024] Figure 2 A flow chart of a method for operating a brushless DC motor when an error occurs is shown. DETAILED DESCRIPTION

[0025] Figure 1 A block diagram of a motor control device 1 for a three-phase brushless DC motor 2 is shown.

[0026] The motor control device 1 comprises a converter 3 having an electrical half-bridge 3.1, 3.2, 3.3 for each phase of the brushless DC motor 2. Each half-bridge 3.1, 3.2, 3.3 has a first electronic switch H1, H2, H3, a second electronic switch L1, L2, L3 and a bridge arm / bridge branch connected to the corresponding phase of the brushless DC motor 2. The first electronic switch H1, H2, H3 is connected to the positive pole of the power supply / voltage source for the converter 3. The second electronic switch L1, L2, L3 is connected to the negative pole of the power supply for the converter 3. The electronic switches H1, H2, H3, L1, L2, L3 are each, for example, in the form of a MOSFET (metal oxide semiconductor field effect transistor) or alternatively in the form of an IGBT (insulated gate bipolar transistor).

[0027] The motor control device 1 further comprises an application specific integrated circuit 4 for driving the electronic switches H1, H2, H3, L1, L2, L3. The application specific integrated circuit 4 has a first interface AAD for receiving an error signal 5 for indicating a safety-related fault, a second interface HALLx for receiving at least one sensor signal 6 (e.g. at least one Hall sensor signal) indicating the rotor position of the rotor of the brushless DC motor 2, and at least one further interface 7 for receiving a motor control signal 8. The motor control signal 8 is generated by a programmable control unit 9, which controls the application specific integrated circuit 4 in a normal mode without errors. For example, the motor control signal 8 is a pulse width modulated signal for commutating the electronic switches H1, H2, H3, L1, L2, L3 in a pulse width modulated controlled manner.

[0028] The ASIC 4 is designed to place the converter 3 into a defined end-of-operation state High_Z independently of the programmable control unit 9 after receiving the error signal 5, in which all electronic switches H1, H2, H3, L1, L2, L3 are closed and a free-wheeling state of the brushless DC motor 2 is caused. To this end, the ASIC 4 has an error processor 10, which is activated when the error signal 5 is received and the operating method of the error processor is based on Figure 2 This is described in more detail below. The ASIC 4 also has a count register 11 for storing a count value AAD_Step_cnt, which counts the number of commutations for changing the switching state of the converter 3, a brake bit register 12 for setting a brake bit AAD_Brake, and a timer 13.

[0029] Figure 2 A flow chart of a method for operating brushless DC motor 2 after receiving error signal 5 is shown with method steps S1 to S9 .

[0030] In a first method step S1, the error handler 10 is activated and the processing of the motor control signal 8 generated by the programmable control unit 9 is suspended. The subsequent method steps S2 to S9 are controlled by the error handler 10 independently of the programmable control unit 9. After the first method step S1, the second method step S2 and the ninth method step S9 are performed.

[0031] In a second method step S2 , the brake bit register 12 is read. If the brake bit AAD_Brake is set, ie if AAD_Brake=1, the method continues with a third method step S3 . Otherwise, ie if AAD_Brake=0, the method continues with a fourth method step S4 .

[0032] A third method step S3 checks whether the count value AAD_Step_cnt is zero. If this is the case, the method continues with a fifth method step S5. Otherwise, the method continues with a sixth method step S6.

[0033] In a fifth method step S5, the converter 3 is placed in a braking mode for a defined braking time period to brake the brushless DC motor 2. In the braking mode, under normal circumstances, all second electronic switches L1, L2, L3 are opened and all first electronic switches H1, H2, H3 are closed; and except for a short circuit between the first electronic switches H1, H2, H3 and the phases of the brushless DC motor 2, all first electronic switches H1, H2, H3 are opened and all second electronic switches L1, L2, L3 are closed. A sixth method step S6 is performed after the fifth method step S5.

[0034] In a sixth method step S6 , the converter is placed in the end-of-operation state High_Z.

[0035] The fourth method step S4 likewise checks whether the count value AAD_Step_cnt is zero. If this is the case, the method continues with a sixth method step S6. Otherwise, the method continues with a seventh method step S7.

[0036] In a seventh method step S7, the switching state of the converter 3 is changed by means of commutation and after the commutation a check is performed to determine whether the commutation has changed the rotor position of the rotor. An eighth method step S8 is performed when the rotor position has changed.

[0037] In the eighth method step S8 , the count value AAD_Step_cnt is decremented by 1. After the eighth method step S8 , the seventh method step S7 is performed again.

[0038] In the ninth method step S9, the timer 12 is started. When the defined time period has elapsed since the start of the timer 12, the sixth method step S6 is executed, that is, after the end of the time period, the converter 3 is placed in the end-of-operation state High_Z, provided that the converter is not already in the end-of-operation state High_Z. This means that the converter 3 is placed in the end-of-operation state High_Z at the latest after the end of the time period, in particular even if the eighth method step S8 is not executed, for example, because the rotor of the brushless DC motor 2 may be blocked and cannot rotate further.

[0039] The above exemplary embodiment of the present invention can be modified and supplemented in various ways. In particular, it can be modified to control a brushless DC motor 2 with a different number of phases in a manner that is obvious to a person skilled in the art.

[0040] List of Reference Numerals

[0041] 1 Motor control equipment

[0042] 2 Brushless DC Motor

[0043] 3 Converter

[0044] 3.1, 3.2, 3.3 Half Bridge

[0045] 4 Control unit

[0046] 5 Error signal

[0047] 6 Sensor signal

[0048] 7, AAD, HALLx interface

[0049] 8 Motor control signal

[0050] 9 Control unit

[0051] 10 Error Handler

[0052] 11 Count register

[0053] 12 Brake bit register

[0054] 13. Timer

[0055] AAD_Brake Brake position

[0056] AAD_Step_cnt count value

[0057] High_Z Operation end status

[0058] H1, H2, H3 first electronic switch

[0059] L1, L2, L3 Second electronic switch

[0060] S1 to S9 Method Steps

Claims

1. A motor control device (1) for a three-phase brushless DC motor (2), the motor control device (1) comprising: - a converter (3) having, for each phase of the brushless DC motor (2), an electrical half-bridge (3.1, 3.2, 3.3) having two electronic switches (H1, H2, H3, L1, L2, L3), and - an application specific integrated circuit (4) for driving the electronic switches (H1, H2, H3, L1, L2, L3) of the converter (3), wherein: - an application specific integrated circuit (4) which can be controlled by a programmable control unit (9) in normal mode, the application specific integrated circuit having a first interface (AAD) for receiving an error signal (5) indicating the presence of a fault, the application specific integrated circuit being designed to place the converter (3) into a defined end-of-operation state (High_Z) independently of the programmable control unit (9) after receiving the error signal (5), The dedicated integrated circuit (4) has a brake bit register (12) for setting a brake bit (AAD_Brake) and a count register (11) for storing a count value (AAD_Step_cnt), wherein the count value is a count value of a commutation for changing a switching state of the converter (3), and the dedicated integrated circuit is designed to, when an error signal (5) is received and the brake bit (AAD_Brake) is set, immediately place the converter (3) in an operation termination state (High_Z) if the count value (AAD_Step_cnt) is greater than zero; and if the count value (AAD_Step_cnt) is zero, place the converter (3) in a braking mode for a defined braking period before placing the converter (3) in the operation termination state (High_Z), thereby braking the brushless DC motor (2).

2. The motor control device (1) according to claim 1, wherein: The application-specific integrated circuit (4) has a second interface (HALLx) for receiving at least one sensor signal (6) indicating the rotor position of the rotor of the brushless DC motor (2). The application-specific integrated circuit is designed to change the switching state of the converter (3) by means of at least one commutation before placing the converter (3) in the end-of-operation state (High_Z) if the brake position (AAD_Brake) is not set and the count value (AAD_Step_cnt) is greater than zero when the error signal (5) is received, and after each commutation, check whether the commutation has changed the rotor position of the rotor, and reduce the count value (AAD_Step_cnt) by one when the rotor position has changed until the count value (AAD_Step_cnt) is zero.

3. The motor control device (1) according to claim 1, wherein: The ASIC (4) has a timer (13) which is designed to start the timer (13) after receiving the error signal (5) and to place the converter (3) in an end-of-operation state (High_Z) after a defined period of time has elapsed since the start of the timer (13).

4. The motor control device (1) according to claim 1, wherein: In the operation end state (High_Z) of the converter (3), all electronic switches (H1, H2, H3, L1, L2, L3) are disconnected.

5. A method for operating a three-phase brushless DC motor (2), wherein: - each phase of the brushless DC motor (2) is connected to an electrical half-bridge (3.1, 3.2, 3.3) of the converter (3), - using a dedicated integrated circuit (4) to drive the electronic switches (H1, H2, H3, L1, L2, L3) of the converter (3), - the ASIC (4) is controlled in normal mode by a programmable control unit (9), and - after receiving the error signal (5), independently of the programmable control unit (9), the converter (3) is placed in a defined end-of-operation state (High_Z) by the dedicated integrated circuit (4), The dedicated integrated circuit (4) has a brake bit register (12) for setting a brake bit (AAD_Brake) and a count register (11) for storing a count value (AAD_Step_cnt), wherein the count value is a count value of a commutation for changing a switching state of the converter (3). When the brake bit (AAD_Brake) is set upon receiving an error signal (5), if the count value (AAD_Step_cnt) is greater than zero, the dedicated integrated circuit (4) immediately places the converter (3) in an operation termination state (High_Z); if the count value (AAD_Step_cnt) is zero, the converter (3) is placed in a braking mode for a defined braking period before placing the converter (3) in the operation termination state (High_Z), thereby braking the brushless DC motor (2).

6. The method of claim 5, wherein: The dedicated integrated circuit (4) has a second interface (HALLx) for receiving at least one sensor signal (6) indicating the rotor position of the rotor of the brushless DC motor (2). If the brake position (AAD_Brake) is not set when the error signal (5) is received and the count value (AAD_Step_cnt) is greater than zero, the dedicated integrated circuit (4) changes the switching state of the converter (3) by means of at least one commutation before placing the converter (3) in the end-of-operation state (High_Z), and checks after each commutation whether the commutation changes the rotor position of the rotor. When the rotor position changes, the count value (AAD_Step_cnt) is reduced by one until the count value (AAD_Step_cnt) is zero.

7. The method of claim 5, wherein: The ASIC (4) has a timer (13). After receiving the error signal (5), the ASIC (4) starts the timer (13). After a defined period of time has passed since the start of the timer (13), the converter (3) is placed in an end-of-operation state (High_Z).

8. The method of claim 5, wherein: In the operational end state (High_Z) of the converter (3), all electronic switches (H1, H2, H3, L1, L2, L3) are disconnected.

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