Speed-limiting constant-power control method for direct-current brushless motor

Abstract

The invention discloses a speed-limiting constant-power control method of a direct-current brushless motor, which is based on an existing motor vector control system and comprises the following steps of: firstly, determining a Q-axis target current Iqspd required for reaching the highest speed limit by taking the highest speed limit as a target value of constant-speed PI (Proportional Integral) control; and then the Q-axis target current Iqref is clamped below the constant-rotating-speed Q-axis target current Iqspd so as to ensure that the motor operates at the speed lower than the highest rotating speed. According to the invention, the constant power control module and the constant speed module in the FOC control logic are multiplexed, and low-cost realization of the technology is realized. And on the other hand, the method is high in control bandwidth and accurate in actual speed limit.

Description

Technical Field

[0001] The present invention relates to the technical field of motor control, and in particular to a speed-limited constant-power control method for a brushless DC motor. Background Art

[0002] The constant power control of the motor means that the input command represents the target power of the motor operation. When the input command remains unchanged, the motor operation power remains unchanged regardless of how the load changes. Since the control target of the motor in the constant power mode is power, not speed, this mode has the characteristics of high-speed operation under light load and low-speed operation under heavy load when the input command remains unchanged. However, in practical applications, a simple constant power control method sometimes cannot meet the needs, especially for applications with large load fluctuations such as fascia guns and nail grinders. Even if the command power is small, the motor speed will be too high when no-load. At this time, a constant power control method with a speed limit function is required, that is, when the speed corresponding to the command power exceeds the speed limit threshold, the motor runs at the specified maximum speed. At this time, the motor is in speed limit mode, and the actual power is lower than the command power. When the load gradually increases, the actual power of the motor increases accordingly. When the actual power reaches the command power, the motor works in constant power mode, and the actual power no longer changes with the load.

[0003] In the traditional constant power control method, the speed limit function can be approximately achieved by limiting the driving voltage of the motor. This is because the back electromotive force generated when the motor is running is proportional to the speed and cannot exceed the driving voltage of the motor. Therefore, when the driving voltage is constant, the theoretical maximum speed of the motor is also determined accordingly. However, part of the driving voltage is used to offset the back electromotive force, and the other part is used to offset the voltage drop on the resistance and inductance in the stator coil of the motor. Since the proportion of the two parts still changes with the load, limiting the driving voltage cannot accurately limit the maximum value of the back electromotive force, that is, the method of limiting the driving voltage cannot accurately achieve the speed limit function. Another constant power speed limit method is realized through the principle of closed-loop feedback, that is, the motor works in constant power mode and monitors the speed of the motor at the same time. When the motor speed exceeds the established threshold, it means that the load is too small, and the original command power needs to be gradually reduced to reduce the speed to the speed limit threshold; when the speed is lower than the established threshold, it means that the load has increased, and the original command power is slowly restored at this time. However, the bandwidth of this method is too low, and it is very easy to overshoot the speed in a short time. When the load fluctuates violently, this method may even fail.

[0004] It can be seen that a new speed-limited constant-power control method for a brushless DC motor is needed in the art, which can provide a higher control bandwidth and achieve precise speed limitation at the same time. Summary of the invention

[0005] The present invention proposes a new speed-limited constant power control method for a brushless DC motor, which is based on a vector control (FOC) method. On the one hand, the method reuses the constant power control module and the constant speed module in the FOC control logic to achieve low-cost technology. On the other hand, the method has a high control bandwidth and accurate actual speed limit.

[0006] Based on the above technical purpose, the present invention provides a speed-limited constant power control method for a brushless DC motor, the method is used for a motor vector control system, the motor vector control system comprises: a Q-axis voltage generation unit, a D-axis voltage generation unit, a three-phase voltage generation unit, a three-phase current acquisition unit and a Q-axis target current calculation unit; the Q-axis target current calculation unit comprises: a constant speed PI control unit, a constant power control unit and a current clamping logic unit;

[0007] The speed-limited constant power control method comprises:

[0008] According to the target constant power setting value Pwr, the constant power Q-axis target current I is obtained. q_pwr ; The operation process satisfies: Where V d is the D-axis control voltage, V q is the Q-axis control voltage, I d_fb is the measured current of the D axis;

[0009] Set the preset maximum speed value Spd max And the actual speed of the motor Spd act Input the constant speed PI control unit to calculate and obtain the constant speed Q axis target current I q_spd ;

[0010] Set the constant power Q-axis target current I q_pwr and constant speed Q axis target current I q_spd The current clamp logic unit outputs the constant power Q-axis target current I q_pwr and constant speed Q axis target current I q_spd The smaller value of the current clamp logic unit is used as the Q-axis target current I q_ref Input to the Q-axis voltage generation unit.

[0011] In one embodiment, the Q-axis voltage generating unit is used to generate a Q-axis control voltage V for controlling the operation of the motor. q The D-axis voltage generating unit is used to generate a D-axis control voltage V for controlling the operation of the motor. d .

[0012] In one embodiment, the three-phase voltage generating unit is used to convert the Q-axis control voltage V generated by the Q-axis voltage generating unit and the D-axis voltage generating unit into qand D-axis control voltage V d It is converted into a three-phase voltage value for controlling the operation of the motor and output to the motor to control the operation of the motor.

[0013] In one embodiment, the three-phase current acquisition unit is used to acquire the three-phase current value of the motor under the actual operation state, and convert the three-phase current value into the Q-axis measured current I q_fb And the D-axis measured current I d_fb .

[0014] In one embodiment, the PI control performed by the constant speed PI control unit includes:

[0015] Using the preset maximum speed value Spd max and actual speed Spd act Real-time calculation value err;

[0016] The difference err is amplified by Kp times through the proportional multiplier and sent to the adder;

[0017] The difference err is amplified by Ki times through the integral term multiplier and sent to the integrator, and the result of the integrator is also sent to the adder;

[0018] The current calculated by the adder is the maximum speed value Spd. max Required constant speed Q-axis target current I q_spd ; Among them, the proportional gain Kp is positively correlated with the load moment of inertia, negatively correlated with the motor pole pair number and back electromotive force constant, and the integral gain Ki is positively correlated with the constant speed PI control update cycle.

[0019] Compared with the prior art, one or more embodiments of the present invention may have the following advantages:

[0020] The present invention proposes a speed-limited constant power control method for a brushless DC motor. On the one hand, the method is based on the existing motor vector control system, firstly uses the maximum speed limit as the target value of the constant speed PI control to determine the Q-axis target current Iq_spd required to achieve the maximum speed limit, and then q_ref Clamped at constant speed Q axis target current I q_spd The following is to ensure that the motor runs below the maximum speed. This method reuses the constant power control module and constant speed module in the FOC control logic to achieve low-cost technology. On the other hand, this method has a high control bandwidth and accurate actual speed limit.

[0021] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0023] Figure 1 1 is a schematic diagram of the structure of a vector control system of a motor according to an embodiment of the present invention;

[0024] Figure 2 is a schematic diagram of the structure of a Q-axis target current calculation unit according to an embodiment of the present invention;

[0025] Figure 3 It is a schematic diagram of a constant speed PI control process according to an embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings.

[0027] It should be understood that when an element or layer is referred to as "on ...", "adjacent to ...", "connected to" or "coupled to" other elements or layers, it can be directly on, adjacent to, connected to or coupled to other elements or layers, or there can be intervening elements or layers. On the contrary, when an element is referred to as "directly on ...", "directly adjacent to ...", "directly connected to" or "directly coupled to" other elements or layers, there is no intervening element or layer. It should be understood that although the terms first, second, third, etc. can be used to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or part from another element, component, region, layer or part. Therefore, without departing from the teachings of the present invention, the first element, component, region, layer or part discussed below can be represented as the second element, component, region, layer or part. And when the second element, component, region, layer or part is discussed, it does not indicate that the present invention necessarily has the first element, component, region, layer or part.

[0028] Spatially relative terms such as "under", "beneath", "below", "under", "above", "above", etc., may be used here for convenience of description to describe the relationship between an element or feature shown in the figure and other elements or features. It should be understood that in addition to the orientation shown in the figure, the spatial relationship terms are intended to also include different orientations of the device in use and operation. For example, if the device in the accompanying drawings is turned over, then the elements or features described as "under other elements" or "under it" or "under it" will be oriented as "on" other elements or features. Therefore, the exemplary terms "under" and "under" may include both upper and lower orientations. The device can be oriented otherwise (rotated 90 degrees or other orientations) and the spatial descriptors used herein are interpreted accordingly.

[0029] The purpose of the terms used herein is only to describe specific embodiments and is not intended to be limiting of the present invention. When used herein, the singular forms "one", "an" and "said / the" are also intended to include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "consisting of" and / or "comprising", when used in this specification, determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0030] Example 1

[0031] The motor speed limiting constant power control system based on the vector control (FOC) method of this embodiment is as follows Figure 1 As shown, the motor speed-limited constant power control system based on the vector control (FOC) method includes: a Q-axis voltage generation unit 100, a D-axis voltage generation unit 200, a three-phase voltage generation unit 300, a three-phase current acquisition unit 400 and a Q-axis target current calculation unit 500. The Q-axis voltage generation unit 100 is used to generate a Q-axis control voltage V for controlling the operation of the motor. q The D-axis voltage generating unit 200 is used to generate a D-axis control voltage V for controlling the operation of the motor. d The three-phase voltage generating unit 300 is used to generate the Q-axis control voltage V generated by the Q-axis voltage generating unit 100 and the D-axis voltage generating unit 200. q and D-axis control voltage V d The three-phase current acquisition unit 400 is used to collect the three-phase current value of the motor under the actual operation state, and convert the three-phase current value into the Q-axis measured current I q_fb And the D-axis measured current I d_fbThe Q-axis target current calculation unit 500 is used to generate the Q-axis target current I according to the input power command and speed command. q_ref The Q-axis target current I q_ref Used to control the Q-axis voltage generating unit 100 to generate the Q-axis control voltage V q .

[0032] In the above system, the motor rotor is used as the reference to establish a DQ orthogonal coordinate system. Among them, the D axis is parallel to the magnetic field direction of the rotor, and the Q axis is perpendicular to the magnetic field direction of the rotor. Since only the current on the Q axis can provide effective torque to make the motor rotate, whether it is a constant power mode or a constant speed mode, the control outputs the corresponding Q axis target current I according to the input power command or speed command. q_ref Then according to the target D axis I d_ref and Q axis current I q_ref Generate D-axis control voltage V through closed-loop control d and Q-axis control voltage V q Finally, the system converts the voltage V d and V q It is applied to the U, V, and W phases of the motor in the form of PWM.

[0033] like Figure 2 As shown, the Q-axis target current calculation unit 500 of this embodiment includes a constant speed PI control unit 501, a constant power control unit 502 and a current clamp logic unit 503. The speed-limited constant power control method of the present invention includes:

[0034] First, the constant power Q-axis target current I is obtained according to the target constant power setting value Pwr. q_pwr ; The operation process satisfies: Where V d is the D-axis control voltage, V q is the Q-axis control voltage, I d_fb is the actual measured current of the D axis.

[0035] Then, the preset maximum speed value Spd max And the actual speed of the motor Spd act Input constant speed PI control unit 501 to calculate and obtain constant speed Q axis target current I q_spd Specifically: The PI control performed by the constant speed PI control unit is as follows: Figure 3 As shown, the preset maximum speed value Spd max is the target value in PI control, the actual speed Spd actThe constant speed PI control module uses adder 1 to calculate the difference err between the target value and the feedback value in real time. Then, on the one hand, the difference err is amplified by Kp times through the proportional multiplier and sent to one input of adder 2; on the other hand, the difference err is amplified by Ki times through the integral multiplier and sent to the integrator. The result of the integrator is sent to the other input of adder 2. The current finally generated by adder 2 is the current required to reach the preset maximum speed value Spd. max Required constant speed Q-axis target current I q_spd Here, the proportional gain Kp is positively correlated with the load moment of inertia, negatively correlated with the motor pole pair number and the back electromotive force constant, and the integral gain Ki is positively correlated with the constant speed PI control update cycle.

[0036] Finally, the constant power Q-axis target current I q_pwr and constant speed Q axis target current I q_spd The current clamping logic unit 503 outputs the constant power Q-axis target current I q_pwr and constant speed Q axis target current I q_spd The smaller value of the current clamp logic unit 503 outputs the result as the Q-axis target current I q_ref Input to the Q-axis voltage generating unit 100 .

[0037] The method proposed in the present invention can have both constant power and speed limit functions. The principle is as follows: when the motor load is low, the constant speed Q-axis target current I output by the constant speed PI control is q_spd Lower than the constant power Q-axis target current I q_pwr At this time, the Q-axis target current I output by the current clamp logic q_spd , the motor speed is the target value of constant speed PI control, that is, the maximum speed limit Spd max , so the motor works in speed limit mode. As the motor load increases, in order to reach the preset maximum speed value Spd max Required constant speed Q-axis target current I q_spd The Q-axis target current I q_spd The amplitude exceeds the constant power Q-axis target current I q_pwr At this time, the Q-axis target current output by the current clamp logic becomes the constant power Q-axis target current I q_pwr , that is, the motor is in constant power control mode, and the power of the motor is equal to the input target constant power setting value Pwr.

[0038] The present invention may be a system, method and / or computer program product at any possible level of integrated technical detail. The computer program product may include a computer-readable storage medium (or multiple media) having computer-readable program instructions thereon for causing a processor to perform various aspects of the present invention.

[0039] A computer readable storage medium may be a tangible device that can retain and store instructions used by an instruction execution device. The computer readable storage medium may be, for example, but not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of computer readable storage media includes the following: a portable computer floppy disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device such as a punch card or a raised structure in a groove on which instructions are recorded, and any suitable combination of the above. A computer readable storage medium, as used herein, should not be interpreted as a transient signal itself, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through a fiber optic cable), or an electrical signal transmitted by a wire.

[0040] The computer-readable program instructions described herein may be downloaded from a computer-readable storage medium to a corresponding computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network may include copper transmission cables, optical transmission fibers, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions to be stored in a computer-readable storage medium within the corresponding computing / processing device.

[0041] The computer-readable program instructions for performing the operation of the present invention may be assembler instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state setting data, configuration data for integrated circuits, or source code or object code written in any combination of one or more programming languages ​​and process programming languages. The computer-readable program instructions may be executed entirely on the user's computer, partially on the user's computer, as an independent software package, partially on the user's computer, partially on a remote computer, or entirely on a remote computer or server. In the latter case, the remote computer may be connected to the user's computer by any type of network including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., by using the Internet of an Internet service provider). In certain embodiments, the electronic circuit including, for example, a programmable logic circuit, a field programmable gate array (FPGA) or a programmable logic array (PLA) may execute the computer-readable program instructions by utilizing the state information of the computer-readable program instructions to personalize the electronic circuit, thereby performing aspects of the present invention.

[0042] Various aspects of the present invention are described herein with reference to flowcharts and / or block diagrams of methods, devices (systems) and computer program products according to embodiments of the present invention. It is understood that each block of the flowchart illustration and / or block diagram, and the combination of blocks in the flowchart illustration and / or block diagram, can be implemented by computer-readable program instructions.

[0043] These computer-readable program instructions may be provided to a processor of a computer or other programmable data processing device to produce a machine so that the instructions executed by the processor of the computer or other programmable data processing device create instructions for implementing the flowcharts and / or block diagrams. Figure 1 These computer-readable program instructions may also be stored in a computer-readable storage medium capable of booting a computer, a programmable data processing device and / or other device that operates in a specific manner, so that the computer-readable storage medium having the instructions stored therein includes a manufactured product that includes instructions that implement aspects of the functions / actions specified in the flowchart and / or block diagram blocks.

[0044] Computer readable program instructions may also be loaded into a computer, other programmable data processing device, or other device to cause a series of operating steps to be performed on the computer, other programmable devices or other devices for producing a computer-implemented process, so that the instructions executed on the computer, other programmable device or other device implement the functions / actions specified in the flowchart and / or block diagram blocks.

[0045] The flowcharts and block diagrams in the accompanying drawings illustrate the possible implementation architecture, functions and operations of the system, method and computer program product according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagram may represent a module, segment or portion of an instruction, which includes one or more executable instructions for implementing a specified logical function. In some optional implementations, the functions indicated in the block may occur outside the order indicated in the figure. For example, in fact, two blocks shown in succession can be completed as a step, and depending on the functions involved, they can be executed concurrently, substantially concurrently, in a partially or fully time-overlapping manner, or sometimes these blocks can be executed in reverse order. It will also be noted that each block of the block diagram and / or flowchart illustration, as well as the combination of blocks in the block diagram and / or flowchart illustration, can be implemented by a dedicated hardware-based system that performs a specified function or action or performs a combination of dedicated hardware and computer instructions.

[0046] The embodiments of the present application are described with reference to the flowcharts and / or block diagrams of the methods, apparatuses (devices) and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0047] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0048] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

Claims

1. A speed-limited constant power control method for a brushless DC motor, the method being used in a motor vector control system, the motor vector control system comprising: Q-axis voltage generating unit, D-axis voltage generating unit, three-phase voltage generating unit, three-phase current collecting unit and Q-axis target current calculating unit; The Q-axis target current calculation unit includes: a constant speed PI control unit, a constant power control unit and a current clamping logic unit; The speed-limited constant power control method comprises: The constant power Q-axis target current I is obtained by calculating the target constant power setting value Pwr. q_pwr ; The operation process satisfies: Where V d is the D-axis control voltage, V q is the Q-axis control voltage, I d_fb is the measured current of the D axis; Set the preset maximum speed value Spd max And the actual speed of the motor Spd act Input the constant speed PI control unit to calculate and obtain the constant speed Q axis target current I q_spd ; Set the constant power Q-axis target current I q_pwr and constant speed Q axis target current I q_spd The current clamp logic unit outputs the constant power Q-axis target current I q_pwr and constant speed Q axis target current I q_spd The smaller value of the current clamp logic unit is used as the Q-axis target current I q_ref Input to the Q-axis voltage generation unit.

2. The speed-limited constant power control method according to claim 1, characterized in that: The Q-axis voltage generating unit is used to generate a Q-axis control voltage V to control the operation of the motor. q The D-axis voltage generating unit is used to generate a D-axis control voltage V for controlling the operation of the motor. d .

3. The speed-limited constant power control method according to claim 1, characterized in that: The three-phase voltage generating unit is used to generate the Q-axis control voltage V generated by the Q-axis voltage generating unit and the D-axis voltage generating unit. q and D-axis control voltage V d It is converted into a three-phase voltage value for controlling the operation of the motor and output to the motor to control the operation of the motor.

4. The speed-limited constant power control method according to claim 1, characterized in that: The three-phase current acquisition unit is used to collect the three-phase current value of the motor under the actual operation state, and convert the three-phase current value into the Q-axis measured current I q_fb And the D-axis measured current I d_fb .

5. The speed-limited constant power control method according to claim 1, characterized in that: The PI control performed by the constant speed PI control unit includes: Using the preset maximum speed value Spd max and actual speed Spd act Real-time calculation value err; The difference err is amplified by Kp times through the proportional multiplier and sent to the adder; The difference err is amplified by Ki times through the integral term multiplier and sent to the integrator, and the result of the integrator is also sent to the adder; The current calculated by the adder is the maximum speed value Spd. max Required constant speed Q-axis target current I q_spd ; Among them, the proportional gain Kp is positively correlated with the load moment of inertia, negatively correlated with the motor pole pair number and back electromotive force constant, and the integral gain Ki is positively correlated with the constant speed PI control update cycle.

6. A computer-readable storage medium having computer instructions stored thereon, wherein: When the computer instructions are executed by a processor, the steps of the method according to any one of claims 1 to 5 are implemented.

7. A motor vector control system, characterized in that: The motor vector control system executes the method described in any one of claims 1-5 to perform speed-limited constant power control on the motor operation.

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