Method for controlling a BLDC motor with a cascaded closed-loop control

Abstract

The invention relates to a method for controlling a BLDC motor (10) with a cascaded closed-loop control, wherein the closed-loop control comprises two or more hierarchically arranged closed-loop control systems (12, 14, 16) with one or more pairs consisting of, in each case, a superordinate closed-loop control system (14, 16) and a subordinate closed-loop control system (12, 14); the output variable of each superordinate closed-loop control system (14, 16) forms the control variable for the respective subordinate closed-loop control system (12, 14); the BLDC motor (10) is controlled using the output variable of the most subordinate closed-loop control system (12); and the output variable of the superordinate closed-loop control system (14, 16) is limited in each closed-loop control system pair, the limitation being specified by an open-loop control of the closed-loop control.

Description

[0001] R. 413291

[0002] 1

[0003] Method for controlling a BLDC motor with a cascaded control system

[0004] The invention relates to a method for controlling a BLDC motor using cascaded control. In particular, the invention relates to an extension of known control methods.

[0005] State of the art

[0006] Brushless DC motors (BLDC motors) are widely used electric drives, particularly as auxiliary units in commercial and passenger vehicles. Despite their name, BLDC motors are not true DC motors, but rather permanent magnet synchronous motors (PMSMs) operated with an inverter. This inverter converts the DC voltage of the vehicle's electrical system into a three-phase AC system.

[0007] Field-oriented control (FOC) is typically used to control BLDC motors. In this method, the physical quantities are transformed into a rotating dq coordinate system that rotates with the motor speed. The three AC voltages generated by the inverter are calculated to produce a rotating magnetic field in the stator that is synchronized with the rotor. The transformation into the dq coordinate system ensures that this rotating field maintains a constant relative position to the rotor. In this system, the d-axis corresponds to the flux distribution of the rotor's permanent magnets, while the q-axis is responsible for generating the torque.

[0008] Through appropriate control, the current in the q-axis is adjusted to generate the desired torque, while the current in the d-axis is regulated to zero or a predefined value to optimize the magnetic field. The rotational speed of the generated rotating field depends on the desired rotor speed and is determined by a higher-level speed control. The continuous adjustment of the inverter control thus enables precise regulation of the motor's mechanical speed.

[0009] Field-oriented control typically forms the innermost loop of a cascaded control structure, which also includes speed and position controls. Furthermore, the

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[0012] BLDC motors are usually controlled via interfaces such as CAN / J1939 or via internal control logic.

[0013] Common intelligent BLDC actuators currently only allow control with constant current, torque, or speed values, without the ability to adjust these values ​​via a freely definable function depending on the rotor position. This is because controlling BLDC motors, especially via CAN / J1939 interfaces, presents challenges. The CAN bus system is subject to limitations regarding message rate and latency, which can be problematic, particularly for highly dynamic or precise applications such as clutch actuators. Reducing message cycle times increases the bus load and thus decreases availability for other network participants. However, switching to an analog or digital interface would limit the control flexibility of the CAN / J1939 interface.

[0014] The object of the invention is therefore to propose a control system for a BLDC motor which reduces the bus load without compromising the precision of the control system.

[0015] The problem is solved by the subject matter of the independent claims.

[0016] Disclosure of the invention

[0017] According to a first aspect of the invention, this problem is solved by a method for controlling a BLDC motor using cascaded control. The control system comprises two or more hierarchically arranged control loops, each with one or more pairs consisting of a higher-level control loop and a lower-level control loop. An output variable of the respective higher-level control loop forms a controlled variable of the respective lower-level control loop. The BLDC motor is controlled by an output variable of a lowest-level control loop. In each pair of control loops, the output variable of the higher-level control loop is limited, with this limitation being defined by a control parameter of the system.

[0018] The control system preferably comprises three control loops, forming two control loop pairs. An innermost control loop is configured to control the BLDC motor. A middle control loop is superior to this innermost control loop, and its output is used as the input by the innermost control loop. The innermost control loop and the middle control loop thus form an inner control loop pair.

[0019] In this specific example, the third control loop is an outer control loop, which is superior to the middle control loop. The output of the outer control loop is therefore...

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[0022] an input variable of the middle control loop. The outer control loop and the middle control loop thus form an outer control loop pair. The middle control loop is therefore part of both the inner control loop pair and the outer control loop pair.

[0023] Advantageously, limiting the output of each higher-level control loop effectively limits the manipulated variables within the cascaded control structure. This stabilizes the control behavior and prevents undesirable overshoots or excessive dynamics in the lower-level control loops. Since each lower-level control loop operates only within the limits defined by the higher-level control loop, overdriving individual control loops is prevented, which is particularly beneficial during rapid load changes or highly dynamic operating conditions.

[0024] The limit is set by the engine control unit (ECU), i.e., within the engine's control system. Because the limit values ​​are processed directly in the ECU, they can be applied with high temporal resolution and without delays in bus communication. This enables precise and rapid adaptation of the limit curves to the engine's current operating state. At the same time, the higher-level control system is relieved of the burden, as no high-frequency updates of the limit values ​​via the bus are required. Instead of sending new setpoints or limits at short intervals, a higher-level control system can simply provide general guidelines, while the precise implementation is handled by the local control system within the engine.

[0025] This not only significantly reduces the bus load but also improves the overall dynamics of the system. Particularly during highly dynamic processes such as rapid changes in speed or torque, the control remains stable and can react immediately to changes in operating conditions without being limited by communication latencies. This results in an overall more efficient and robust control of the BLDC motor, ensuring both high precision and rapid adaptability to different load cases. This fulfills the objective of the invention.

[0026] In one embodiment, the restriction is updated at defined times.

[0027] Updating the constraint at defined times advantageously allows the control limits to be adapted to changing operating conditions without impairing the stability of the control system or unnecessarily increasing the communication load. By updating the constraint values ​​at defined times,

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[0030] This ensures that adjustments occur at a predetermined rate, thus avoiding abrupt or uncontrolled changes. This helps to keep the control behavior predictable and stable, especially in dynamic applications where sudden changes in torque or speed can occur.

[0031] In one embodiment, the limitation is updated with a higher cycle time compared to a control frequency of the BLDC motor.

[0032] Advantageously, updating the limit with a longer cycle time compared to the BLDC motor's control frequency reduces the computational and communication load without affecting the motor's control dynamics. Since the internal control loops operate at a high frequency but do not require new limit values ​​in every cycle, the limit can be updated with a longer cycle time, thus avoiding unnecessary data transmissions. This is particularly beneficial when using a CAN interface, as it reduces the load on the bus network, since the limit values ​​are updated at longer intervals. Simultaneously, the motor's control remains highly dynamic because the limit values ​​stored locally in the control unit can be applied at a high frequency. This achieves an efficient balance between communication overhead and control performance.

[0033] In one embodiment, the restriction is updated in a time interval of 0.5 s to 1.5 s, preferably 1.0 s.

[0034] In one embodiment, the lowest control loop regulates the torque for the BLDC motor.

[0035] Advantageously, the control of the BLDC motor using the lowest control loop for torque provides direct and precise control of the motor's mechanical power, enabling rapid adaptation to changing load requirements.

[0036] In one embodiment, the control loop superior to the control loop for the torque regulates a rotational speed of a rotor of the BLDC motor.

[0037] Advantageously, the higher-level control of the rotor's rotational speed ensures precise adjustment of the motor speed to the respective operating requirements, while the immediately subordinate torque control loop continues to provide dynamic load adjustment. This hierarchical structure ensures that the motor

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[0040] not only does it deliver the required torque, but it also operates within a predetermined speed limit, which in turn allows for more stable and efficient speed control.

[0041] Limiting the torque output of the speed control loop can further help optimize energy consumption, as the motor only rotates as fast as necessary to deliver the desired power. This improves the control.

[0042] In one embodiment, the restriction for the control loop for the rotational speed includes an upper limit for the torque and / or a limit for the current required to generate the torque.

[0043] Advantageously, limiting the torque and / or the current required to generate the torque in the speed control loop allows for targeted control of the motor's power output, thereby improving control efficiency. Since the torque control loop directly affects the motor's manipulated variables, excessive load can be avoided by limiting the maximum permissible torque and / or current values ​​in the higher-level speed control loop. This not only prevents thermal overloads and mechanical stresses on the drive components but also ensures smoother and more stable control, especially during rapid speed changes or load transients.

[0044] In one embodiment, a control loop superior to the control loop for the rotational speed regulates the position of the rotor of the BLDC motor.

[0045] Advantageously, the higher-level control of the rotor position ensures that the motor's rotational speed is precisely adjusted to a desired positioning requirement, thus enabling highly precise motion sequences. Since the output of the position control loop is the motor's rotational speed, the motor's speed can be controlled so that it reaches the exact required position without generating unwanted overshoot or positional errors.

[0046] In one embodiment, the restriction for the control loop for the position of the BLDC motor rotor includes an upper limit for the rotational speed of the BLDC motor rotor.

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[0049] Advantageously, limiting the rotor's rotational speed in the position control loop ensures stable and precise motor positioning by preventing the rotational speed from exceeding a defined level. Since the rotational speed serves as the output of the position control loop, targeted limitation ensures that the motor moves to the desired position in a controlled manner, without excessively sudden speed changes or accelerations leading to mechanical stress or control instabilities.

[0050] In one embodiment, the control system includes a CAN interface, in particular a CAN / J1939 interface, wherein the restriction is received via the CAN interface.

[0051] In one embodiment, the limitation depends on the position of the rotor of the BLDC motor.

[0052] Advantageously, the dependence of the BLDC motor's rotor position on the speed limit enables targeted and optimized adaptation of the control variables to the current operating state, thus allowing for more precise control and improved drive dynamics. Since the motor's behavior can change depending on the rotor position, for example, due to varying torque requirements or different load conditions, position-dependent limiting allows for finely tuned control that adapts flexibly to these circumstances. This can lead to a reduction in unwanted fluctuations, prevent excessive loads, and improve the overall efficiency of the motor.Particularly in highly dynamic applications or cyclic motion sequences, such as those found in positioning or switching actuators, position-dependent limitation can help to ensure smooth transitions between different operating states and to minimize the mechanical stress on the components.

[0053] In one embodiment, the restriction is processed locally.

[0054] Advantageously, local processing of the constraint significantly reduces communication latency and enables faster control response to changes in operating conditions. Since the constraint values ​​are processed directly in the BLDC motor's control unit, there is no need to transmit new constraint values ​​via the CAN interface at short intervals, thus reducing bus load and improving system efficiency. This allows for highly dynamic adjustment of the controlled variables without delays caused by external signal transmissions, thereby

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[0057] Particularly in applications with rapid load changes or precise motion requirements, the reliability and stability of the control system can be improved. Furthermore, the higher-level control system is relieved of this burden, as it can concentrate on overarching specifications, while the detailed implementation of the constraint takes place directly in the motor controller in real time.

[0058] In another aspect, the invention relates to a computer program with program code for executing a method as described above when the computer program is executed on a computer.

[0059] In another aspect, the invention relates to a computer-readable data carrier containing program code of a computer program for carrying out a method as described above when the computer program is executed on a computer.

[0060] In another aspect, the invention relates to a control system for controlling a BLDC motor, wherein the control system is configured to perform a method as described above.

[0061] In summary, the present invention provides a method for controlling a BLDC motor, a computer program, a computer-readable data carrier, and a control system.

[0062] The described configurations and training programs can be combined in any way desired.

[0063] Further possible embodiments, developments and implementations of the invention also include combinations of features of the invention described previously or subsequently with regard to the exemplary embodiments that are not explicitly mentioned.

[0064] Brief description of the drawing

[0065] The accompanying drawing is intended to provide a further understanding of the embodiments of the invention. It illustrates embodiments and, in conjunction with the description, serves to explain the principles and concepts of the invention.

[0066] Other embodiments and many of the aforementioned advantages become apparent with reference to the drawing. The elements shown in the drawing are not necessarily drawn to scale.

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[0069] It shows:

[0070] Fig. 1 schematically shows a control system for a BLDC motor according to one embodiment.

[0071] In the figure of the drawing, identical reference numerals denote identical or functionally equivalent elements, parts or components, unless otherwise specified.

[0072] Fig. 1 shows an exemplary cascaded control system for a BLDC motor 10. The cascaded control system comprises an innermost control loop 12, a middle control loop 14 and an outer control loop 16.

[0073] The innermost control loop controls the torque of the BLDC motor 10. The output value of the innermost control loop can therefore be the torque itself or a current used in the BLDC motor 10 to generate the torque. In the illustrated embodiment, the innermost control loop 12 includes a module 18 to determine the parameters for the rotating dq coordinate system. This is preceded by a module 20, which specifies the target value of the torque or the current required for it.

[0074] In this embodiment, the innermost control loop 12 uses two input variables for control. Firstly, the current I 22 currently measured in the BLDC motor 10 is used. Secondly, a target current specified by the middle control loop 14 serves as the target variable for control.

[0075] The middle control loop 14 comprises a module 24 for limiting the setpoint current and a module 26 for controlling the rotational speed w. The middle control loop receives the current rotational speed 28 as an actual value and a rotational speed specified by the outer control loop 16 as a setpoint. From these values, a setpoint for the current is generated in module 26, which is intended to generate the torque for the rotor of the BLDC motor 10. The setpoint for the current determined in the middle control loop 14 is limited in module 24. For this purpose, a control unit of the controller specifies an upper limit for the current I 22, which depends on the position x of the rotor. This means that the setpoint for the inner control loop 12 is limited. The position x refers to a specific rotor orientation between 0° and 360°.

[0076] The inner control loop 12 and the middle control loop 14 form a control loop pair, in which the middle control loop 14 is superior to the inner control loop 12. The same principle applies.

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[0079] applicable to the outer control loop 16 and the middle control loop 14. That is, the outer control loop 16 is superior to the middle control loop 14.

[0080] The outer control loop 16 receives the current rotor position 30 as an input value and actual value. A module 32 determines the desired rotor position from the current position. Alternatively, the target value for the rotor position can be specified by an external control unit. The output is a target value for the rotational speed w. However, the rotational speed w is limited. This limitation of the rotational speed w is handled by another module 34.

[0081] Modules 24 and 34 receive the restriction at predefined time intervals as limit values ​​for the rotor positions from 0° to 360°. In this way, the control system can regulate the current in the BLDC motor 10 without overloading the bus due to a high data rate.

[0082] In one embodiment, a position-dependent restriction to an angular range exceeding 360°, particularly to 1200°, can be implemented. For this purpose, a function can be stored in the actuator, for example, that sums the angles, thereby allowing the restriction to be parameterized to larger angular ranges than 360°.

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Claims

R. 413291 10 Claims 1. Method for controlling a BLDC motor (10) with a cascaded control system, wherein the control system comprises two or more hierarchically arranged control loops (12, 14, 16) with one or more pairs of each higher-level control loop (14, 16) and lower-level control loop (12, 14), wherein an output variable of the respective higher-level control loop (14, 16) forms a controlled variable of the respective lower-level control loop (12, 14), wherein the BLDC motor (10) is controlled by an output variable of a lowest-level control loop (12), wherein in each control loop pair the output variable of the higher-level control loop (14, 16) is limited, wherein a limitation is specified by a control of the control system.

2. The method of claim 1, wherein the restriction is updated at defined times.

3. Method according to one of the preceding claims, wherein the restriction is updated with a cycle time higher compared to a control frequency of the BLDC motor (10).

4. Method according to one of claims 2 or 3, wherein the restriction is updated in a time interval of 0.5 s to 1.5 s, preferably 1.0 s.

5. Method according to any of the preceding claims, wherein the lowest control loop controls the torque for the BLDC motor (10).

6. Method according to claim 5, wherein the control loop (14) superior to the control loop (12) for the torque controls a rotational speed of a rotor of the BLDC motor (10).

7. Method according to claim 6, wherein the restriction for the control loop (14) for the rotational speed comprises an upper limit for the torque and / or an upper limit for the current required to generate the torque.

8. Method according to claim 7, wherein a control loop (16) superior to the control loop (14) for the rotational speed controls the position of the rotor of the BLDC motor. Page 10 of 12R. 413291 11 9. Method according to claim 8, wherein the restriction for the control loop (16) for the position of the rotor of the BLDC motor comprises an upper limit for the rotational speed of the rotor of the BLDC motor.

10. Method according to one of the preceding claims, wherein the regulation comprises a CAN interface, in particular a CAN / J1939 interface, wherein the restriction is received via the CAN interface.

11. Method according to one of the preceding claims, wherein the limitation depends on the position of the rotor of the BLDC motor.

12. Method according to any of the preceding claims, wherein the restriction is processed locally.

13. Computer program with program code for executing a method according to any of the preceding claims when the computer program is executed on a computer.

14. Computer-readable data carrier containing program code of a computer program for executing a method according to any one of claims 1 to 12 when the computer program is executed on a computer.

15. Control system for controlling a BLDC motor (10), wherein the control system is configured to perform a method according to any one of claims 1 to 12. Page 11 of 12

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