A control method and control system for a permanent magnet brushless motor

Abstract

This invention belongs to the field of permanent magnet brushless motor control technology, and particularly relates to a control method for a permanent magnet brushless motor, comprising: acquiring the back electromotive force (EMF) of the permanent magnet brushless motor in real time; determining whether a first preset condition for shutting off the PWM signal is met based on the back EMF and a preset voltage; when the first preset condition is met, shutting off the PWM signal; and according to commutation logic, changing the energized phase of the permanent magnet brushless motor when the back EMF crosses zero; determining whether a second preset condition for turning on the PWM signal is met based on the back EMF and a preset voltage; and when the second preset condition is met, turning on the PWM signal. This invention constrains the PWM signal by comparing the back EMF of the permanent magnet brushless motor with a preset voltage, and disconnects the PWM signal before commutation, thus preventing the PWM signal from mixing in the zero-crossing judgment region, thereby avoiding signal interference and preventing stalling, loss of synchronism, or overload.

Description

Technical Field

[0001] This invention belongs to the field of permanent magnet brushless motor control technology, and particularly relates to a control method and control system for a permanent magnet brushless motor. Background Technology

[0002] Permanent magnet brushless motors are permanent magnet motors controlled by electronic circuit commutation or current. They have two control methods: FOC vector control and six-step square wave control. When the speed of the permanent magnet brushless motor is maintained between (0.5~2)×105rpm, for applications where torque stability is not critical, either FOC vector control or a six-step square wave control strategy with less computation and lower switching frequency can be used.

[0003] Six-step square wave control is low in cost and widely used. However, during commutation, the PWM signal can cause signal interference, induce stall, loss of synchronism, or overload, which greatly reduces the reliability of the six-step square wave. To ensure reliability, most six-step square wave control schemes currently control the speed by controlling the bus voltage of the pre-DC-DC converter. However, the real-time performance is often slightly worse, and the cost of DC-DC converter is also increased. Summary of the Invention

[0004] This invention provides a control method and control system for a permanent magnet brushless motor, which solves the problem in the prior art that the PWM signal causes signal interference during commutation, inducing stall, loss of synchronism or overload.

[0005] One technical solution of the present invention is as follows: a control method for a permanent magnet brushless motor, comprising:

[0006] S10: Real-time acquisition of the back electromotive force of the permanent magnet brushless motor, and determination of whether the first preset condition for turning off the PWM signal is met based on the back electromotive force and the preset voltage.

[0007] S20: When the first preset condition is met, the PWM signal is turned off. According to the commutation logic, when the back EMF crosses zero, a commutation control signal is generated to replace the energized phase of the permanent magnet brushless motor.

[0008] S30: Determine whether the second preset condition for enabling the PWM signal is met based on the back electromotive force and the preset voltage;

[0009] S40: When the second preset condition is met, the PWM signal is turned on, and a speed control signal is generated according to the PWM signal to control the speed of the permanent magnet brushless motor.

[0010] Furthermore, the preset voltage is less than the bus voltage but greater than the zero-point voltage.

[0011] Furthermore, the preset voltage is 0.7~0.9V lower than the bus voltage.

[0012] Furthermore, the first preset condition includes:

[0013] The number of times the real-time acquired back electromotive force is less than the preset voltage reaches N, where N≥1.

[0014] Furthermore, the second preset condition includes:

[0015] The number of times the real-time acquired back electromotive force is greater than the preset voltage reaches M, where M≥1.

[0016] Another technical solution of the present invention is as follows: a control system for a permanent magnet brushless motor, used to execute any of the control methods for the permanent magnet brushless motor described above, including a data acquisition module, a comparison and judgment module, a commutation module, a PWM generation module, and a logic operation module. The output terminal of the data acquisition module is connected to the input terminal of the commutation module and the input terminal of the comparison and judgment module, respectively. The output terminal of the comparison and judgment module is connected to the PWM generation module. The output terminals of the commutation module and the PWM generation module are both connected to the input terminal of the logic operation module.

[0017] The acquisition module can acquire the back electromotive force of the permanent magnet brushless motor in real time.

[0018] The comparison and judgment module can determine whether the first preset condition for turning off the PWM signal and the second preset condition for turning on the PWM signal are met based on the back electromotive force and the preset voltage. When the first preset condition is met, a PWM turn-off signal is generated to turn off the PWM generation module. When the second preset condition is met, the PWM generation module is turned on.

[0019] The PWM generation module is capable of generating PWM signals;

[0020] The commutation module can generate a commutation logic signal when the back electromotive force crosses zero, according to the commutation logic.

[0021] The logic operation module can generate commutation control signals based on commutation logic signals and speed control signals based on PWM signals.

[0022] Furthermore, the logic operation module performs AND logic operations;

[0023] When the first preset condition for turning off the PWM signal is met, the logic operation module performs an AND operation between the commutation logic signal output by the commutation module and the low-level signal to generate a commutation control signal.

[0024] When the second preset condition for enabling the PWM signal is met, the logic operation module performs an AND operation between the PWM signal output by the PWM generation module and the low-level signal to generate a speed control signal.

[0025] Furthermore, the commutation module includes a zero-crossing detection module and a commutation logic module, wherein the output terminal of the zero-crossing detection module is connected to the input terminal of the commutation logic module;

[0026] The zero-crossing detection module can detect whether the back electromotive force crosses zero, and generate a zero-crossing signal when the back electromotive force crosses zero.

[0027] The commutation logic module can generate commutation logic signals based on preset commutation logic and zero-crossing signals.

[0028] Furthermore, the comparison and judgment module, commutation module, PWM generation module, and logic operation module are all microcontrollers.

[0029] The beneficial effects of this invention are as follows: This invention constrains the PWM signal by comparing the back electromotive force of the permanent magnet brushless motor with a preset voltage. The PWM signal is disconnected before commutation, preventing it from mixing in the zero-crossing detection region and thus avoiding signal interference, stalling, loss of synchronism, or overload. This invention eliminates the need for a DC-DC converter for amplitude modulation and speed control, resulting in a simple, stable, and reliable structure. Attached Figure Description

[0030] Figure 1 This is a flowchart of the control method for the permanent magnet brushless motor of the present invention.

[0031] Figure 2 This is a block diagram of the control system of the permanent magnet brushless motor of the present invention.

[0032] Figure 3 This is the back electromotive force waveform diagram of the present invention. Detailed Implementation

[0033] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. The described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0034] In an embodiment of the present invention, Figure 1 This is a flowchart provided by a control method for a permanent magnet brushless motor according to the present invention, such as... Figure 1 As shown, the present invention includes:

[0035] S10: Real-time acquisition of the back electromotive force of the permanent magnet brushless motor, and determination of whether the first preset condition for turning off the PWM signal is met based on the back electromotive force and the preset voltage.

[0036] The back electromotive force (EMF) of a permanent magnet brushless motor can be detected by a three-phase inverter. Even without power, the third phase can be used to detect the back EMF. The analog signal can be converted to a digital signal using an analog-to-digital converter. The three-phase inverter is an essential component for controlling the operation of the permanent magnet brushless motor.

[0037] The real-time acquired back electromotive force (EMF) is compared with a preset voltage. The preset voltage is a threshold value that is slightly lower than the bus voltage (approximately equal to the peak value of the back EMF) and greater than the zero-point voltage. Generally, the preset voltage is 0.7~0.9V lower than the bus voltage, preferably 0.8V. The first preset condition includes: the real-time acquired back EMF is lower than the preset voltage N times, where N≥1.

[0038] S20: When the first preset condition is met, the PWM signal is turned off. According to the commutation logic, when the back EMF crosses zero, a commutation control signal is generated to replace the energized phase of the permanent magnet brushless motor.

[0039] As the speed of the permanent magnet brushless motor increases, the current increases, which in turn increases the oscillation of the PWM signal, making it difficult to determine the zero-crossing point of the back EMF and affecting the stability of the algorithm.

[0040] When the first preset condition is met, PWM signal generation stops, i.e., the PWM signal is turned off. At this point, the back EMF is about to cross zero. According to the commutation logic, a commutation control signal is generated when the back EMF crosses zero to change the energized phase of the permanent magnet brushless motor. The back EMF zero-crossing point is determined by comparing the back EMF with the zero-crossing voltage using a comparator. When the back EMF and the zero-crossing voltage are the same, the back EMF is determined to have crossed zero. Since the PWM signal is turned off when the back EMF crosses zero, interference from the PWM signal in the back EMF zero-crossing determination is avoided.

[0041] The commutation logic is based on the six-step square wave control logic, a technique well-known to those skilled in the art, and therefore will not be elaborated upon here. By shutting off the PWM signal, smooth and stable back EMF crossing at zero is ensured, and zero-crossing judgment is accurate and reliable, significantly improving the reliability of motor control.

[0042] S30: Determine whether the second preset condition for enabling the PWM signal is met based on the back electromotive force and the preset voltage.

[0043] The real-time acquired back electromotive force (EMF) is compared with a preset voltage. The second preset condition includes: the real-time acquired back EMF is greater than the preset voltage M times, where M ≥ 1 and M is a natural number. The PWM signal is then activated for PWM pulse width modulation speed control. A narrower pulse width results in less current flowing into the windings and a slower motor speed.

[0044] S40: When the second preset condition is met, the PWM signal is turned on, and a speed control signal is generated according to the PWM signal to control the speed of the permanent magnet brushless motor.

[0045] When the second preset condition is met, a PWM signal is generated. At this time, the back electromotive force crosses zero and PWM speed regulation begins.

[0046] The above control method is for the high-speed range of permanent magnet brushless motors. In the low-speed range of permanent magnet brushless motors, due to the low frequency, small current, and little interference of the PWM signal, the interference of the PWM signal on the zero-crossing judgment is small. At this time, it is not necessary to turn off the PWM signal. During the zero-crossing judgment, the signal generated according to the commutation logic and the signal output by the PWM module are ANDed to generate a low-speed commutation signal to control the motor commutation. This control method can be applied to the entire low-speed range.

[0047] When the motor is running at full speed, the duty cycle of the PWM signal is adjusted to 100%, which is equivalent to the case without chopping. Figure 3 As shown, the PWM signal will not affect the zero-crossing judgment of the back EMF at this time, thus realizing the non-bus amplitude modulation type full speed domain six-step square wave control.

[0048] The specific speed ranges for low speed, high speed, and full speed can be determined by those skilled in the art based on actual conditions, and therefore are not limited here.

[0049] It should be noted that the above methods can be implemented in the form of software programs in the MCU, or they can be implemented in the form of hardware circuits.

[0050] Another technical solution of the present invention provides a control system for a permanent magnet brushless motor, which is capable of executing any of the control methods described above. Figure 2 This is a structural block diagram provided based on the specific structure of the control system of the permanent magnet brushless motor. In the figure, reference numeral 7 represents the permanent magnet brushless motor.

[0051] like Figure 2As shown, the technical solution adopted by the present invention is as follows: it includes a data acquisition module 1, a comparison and judgment module 2, a commutation module 4, a PWM generation module 3, and a logic operation module 5. The output terminal of the data acquisition module 1 is connected to the input terminal of the commutation module 4 and the input terminal of the comparison and judgment module 2, respectively. The output terminal of the comparison and judgment module 2 is connected to the PWM generation module 3. The output terminals of the commutation module 4 and the PWM generation module 3 are both connected to the input terminal of the logic operation module 5.

[0052] The acquisition module 1 can acquire the back electromotive force (EMF) of the permanent magnet brushless motor in real time. The acquisition module 1 is a physical module and can be implemented using an analog-to-digital converter (ADC) to convert the analog signal of the back EMF into an electrical signal for transmission to subsequent modules for data processing. Specifically, when using an ADC as the acquisition module 1, the acquisition module 1 is enabled when the back EMF is high, ensuring that the voltage when the switch in the three-phase inverter 6 is turned on is read.

[0053] The comparison and judgment module 2 can determine whether a first preset condition for turning off the PWM signal and a second preset condition for turning on the PWM signal are met based on the back electromotive force (EMF) and a preset voltage. When the first preset condition is met, a PWM turn-off signal is generated to turn off the PWM generation module 3; when the second preset condition is met, the PWM generation module 3 is turned on. The comparison and judgment module 2 can be implemented using a comparator circuit and an MCU chip. Specifically, comparing the back EMF and the preset voltage can be implemented using a comparator circuit. The condition that the number of times the real-time acquired back EMF is less than the preset voltage reaches N can be implemented in the MCU program. It should be noted that the comparison process can also be implemented in the form of a program using the MCU chip, in which case the comparator circuit can be omitted.

[0054] The PWM generation module 3 can generate PWM signals. The PWM can be generated by a PWM generation chip or an MCU, so there is no limitation here.

[0055] The commutation module 4 generates a commutation logic signal when the back electromotive force (EMF) crosses zero, based on the commutation logic. Specifically, the commutation module 4 includes a zero-crossing detection module and a commutation logic module, with the output of the zero-crossing detection module connected to the input of the commutation logic module. The zero-crossing detection module detects whether the back EMF crosses zero. When the back EMF crosses zero, it generates a zero-crossing signal by comparing the back EMF with the zero-crossing voltage. If they are equal, the back EMF is determined to have crossed zero. This determination can be implemented using a comparator circuit or by the MCU program. When the back EMF crosses zero, a zero-crossing signal is sent to the commutation logic module.

[0056] The commutation logic module can generate a commutation logic signal based on a preset commutation logic and a zero-crossing signal. Specifically, when a zero-crossing signal is received, the commutation logic module executes the corresponding program based on the preset commutation logic to generate the commutation logic signal.

[0057] The commutation logic is the same as that in the control method described above.

[0058] The logic operation module 5 can generate a commutation control signal based on the commutation logic signal and a speed control signal based on the PWM signal. Specifically, the logic operation module 5 performs AND logic operations. The logic operation module 5 can be implemented by multiple AND gate chips. If an MCU chip is used, the AND operation logic program runs within the chip.

[0059] When the first preset condition for turning off the PWM signal is met, the PWM generation module 3 is turned off. The input terminal of the logic operation module 5 is equivalent to the input of the commutation logic signal output by the commutation module 4 and a set of low-level signals. At this time, the logic operation module 5 performs an AND operation on the commutation logic signal output by the commutation module 4 and the low-level signals to generate a commutation control signal.

[0060] When the second preset condition for enabling the PWM signal is met, the PWM generation module 3 is enabled. However, the back EMF has not yet crossed zero, and the commutation module 4 does not output a commutation logic signal. This is equivalent to the operation module inputting a set of low-level signals. At this time, the logic operation module 5 performs an AND operation between the PWM signal output by the PWM generation module 3 and the low-level signals to generate a speed control signal.

[0061] This invention proposes a control method to avoid chopping in the zero-crossing judgment region. By comparing the back electromotive force with a preset voltage slightly lower than the bus voltage, the PWM signal is constrained, preventing it from entering the zero-crossing region and avoiding confusion. This completely replaces DC-DC speed control via voltage regulation, while maintaining the PWM signal in other regions of the algorithm. Thus, it achieves reliable six-step square wave control with only the three-phase inverter 6 under wide speed range conditions, enabling reliable commutation and speed control.

[0062] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A control method for a permanent magnet brushless motor, characterized in that, include: S10: Real-time acquisition of the back electromotive force of the permanent magnet brushless motor, and determination of whether the first preset condition for turning off the PWM signal is met based on the back electromotive force and the preset voltage. S20: When the first preset condition is met, the PWM signal is turned off. According to the commutation logic, when the back electromotive force crosses zero, a commutation control signal is generated to replace the energized phase of the permanent magnet brushless motor. S30: Determine whether the second preset condition for enabling the PWM signal is met based on the back electromotive force and the preset voltage; S40: When the second preset condition is met, the PWM signal is turned on, and a speed control signal is generated according to the PWM signal to control the speed of the permanent magnet brushless motor.

2. The control method for a permanent magnet brushless motor as described in claim 1, characterized in that, The preset voltage is less than the bus voltage but greater than the zero-point voltage.

3. The control method for a permanent magnet brushless motor as described in claim 2, characterized in that, The preset voltage is 0.7~0.9V lower than the bus voltage.

4. The control method for a permanent magnet brushless motor as described in claim 1, characterized in that, The first preset conditions include: The number of times the real-time acquired back electromotive force is less than the preset voltage reaches N, where N≥1.

5. The control method for a permanent magnet brushless motor as described in claim 1, characterized in that, The second preset condition includes: The number of times the real-time acquired back electromotive force is greater than the preset voltage reaches M, where M≥1.

6. A control system for a permanent magnet brushless motor, characterized in that, The control method for executing the permanent magnet brushless motor according to any one of claims 1-5 includes a data acquisition module, a comparison and judgment module, a commutation module, a PWM generation module, and a logic operation module. The output terminal of the data acquisition module is connected to the input terminal of the commutation module and the input terminal of the comparison and judgment module, respectively. The output terminal of the comparison and judgment module is connected to the PWM generation module. The output terminals of the commutation module and the PWM generation module are both connected to the input terminal of the logic operation module. The acquisition module can acquire the back electromotive force of the permanent magnet brushless motor in real time. The comparison and judgment module can determine whether the first preset condition for turning off the PWM signal and the second preset condition for turning on the PWM signal are met based on the back electromotive force and the preset voltage. When the first preset condition is met, a PWM turn-off signal is generated to turn off the PWM generation module. When the second preset condition is met, the PWM generation module is turned on. The PWM generation module is capable of generating PWM signals; The commutation module can generate a commutation logic signal when the back electromotive force crosses zero, according to the commutation logic. The logic operation module can generate commutation control signals based on commutation logic signals and speed control signals based on PWM signals.

7. The control system for the permanent magnet brushless motor as described in claim 6, characterized in that, The logic operation module performs AND logic operations; When the first preset condition for turning off the PWM signal is met, the logic operation module performs an AND operation between the commutation logic signal output by the commutation module and the low-level signal to generate a commutation control signal. When the second preset condition for enabling the PWM signal is met, the logic operation module performs an AND operation between the PWM signal output by the PWM generation module and the low-level signal to generate a speed control signal.

8. The control system for the permanent magnet brushless motor as described in claim 6, characterized in that, The commutation module includes a zero-crossing detection module and a commutation logic module, wherein the output terminal of the zero-crossing detection module is connected to the input terminal of the commutation logic module; The zero-crossing detection module can detect whether the back electromotive force crosses zero, and generate a zero-crossing signal when the back electromotive force crosses zero. The commutation logic module can generate commutation logic signals based on preset commutation logic and zero-crossing signals.

9. The control system for the permanent magnet brushless motor as described in claim 6, characterized in that, The comparison and judgment module, commutation module, PWM generation module, and logic operation module all include MCU chips.

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