A method of motor control

Abstract

This application discloses a motor control method, including: Step A: Alignment control of the rotor, then forced commutation operation of the rotor, and back EMF zero-crossing signal; if a preset number of back EMF zero-crossing signals are continuously detected according to the predetermined commutation sequence, then Step B is executed; Step B: Speed ​​loop closed-loop control of the motor, and after the rotor speed is accelerated to a preset starting speed, back EMF zero-crossing signal is detected; then Step C is executed; Step C: Whenever a back EMF zero-crossing signal is detected, during the period from the detection time of the currently detected back EMF zero-crossing signal to the next commutation time, the drive signal for the motor is stopped, and the electrical angle corresponding to each back EMF is adjusted through the phase-locked loop until the electrical frequency output by the phase-locked loop converges to a target electrical frequency range. Then, the motor is controlled by FOC, avoiding problems such as loss of synchronism and difficulty in starting the FOC sine wave when the motor load torque is large.

Description

Technical Field

[0001] This invention relates to the technical field of motor control, and more particularly to a motor control method. Background Technology

[0002] A brushless DC motor consists of a motor body and a driver, and is an electromechanical integrated product. Existing technology can use back electromotive force to control a sensorless brushless DC motor (BLDC). For example, a six-step trapezoidal wave (120-degree commutation method) is used to energize the motor windings. When the permanent magnet motor rotor rotates, the stator windings generate a voltage, i.e., back electromotive force, the amplitude of which is proportional to the motor speed.

[0003] Field-oriented control (FOC), also known as vector control, is a technology that uses a frequency converter to control a three-phase motor. It controls the motor's output by adjusting the frequency, voltage, and angle of the frequency converter.

[0004] While sine wave FOC control of brushless DC motors offers advantages such as noiseless startup, minimal startup jitter, and smooth start-up, it typically applies a large load torque during startup. This torque is mismatched with the motor's initial speed, leading to small angular velocity fluctuations and a strong pull phenomenon with only a small electrical angle. This results in startup failure, step loss (i.e., the motor fails to follow the commanded number of steps during operation; similarly, the rotor of a synchronous motor cannot rotate synchronously with the stator's rotating magnetic field), and stall, preventing startup. Furthermore, it requires high-precision startup algorithms, necessitating the addition of Hall effect sensors to identify motor parameters and drive signals in various processes, increasing the hardware calibration cost of the sensors. Therefore, current technology cannot solve the problem of low-cost, low-speed startup of brushless DC motors. Summary of the Invention

[0005] This application discloses a motor control method, the specific technical solution of which is as follows:

[0006] A motor control method includes: Step A, aligning the rotor, then controlling the rotor to perform forced commutation so that the rotor passes through multiple sectors in a predetermined commutation sequence without pre-determining the commutation time, and detecting a back EMF zero-crossing signal during the forced commutation operation; if a preset number of back EMF zero-crossing signals are continuously detected in the predetermined commutation sequence, then Step B is executed; wherein, no position sensor is installed inside the motor, and the motor includes a rotor; the preset number is the difference between the maximum number of different sectors allowed to be passed by the rotor in one electrical cycle and the value 1; Step B, performing speed loop closed-loop control on the motor, and detecting a back EMF zero-crossing signal during the forced commutation operation. After the rotational speed is accelerated to the preset starting speed, the drive signal is activated, and the back EMF zero-crossing signal is detected so that the rotor determines the next commutation time based on the currently detected back EMF zero-crossing signal before commutation; then step C is executed; Step C: Whenever a back EMF zero-crossing signal is detected, during the period from the detection time of the currently detected back EMF zero-crossing signal to the next commutation time, the drive signal for the motor is stopped. At the same time, the electrical angles corresponding to all back EMFs of the motor are acquired. Based on the electrical angles corresponding to the back EMF zero-crossing signals, the electrical angles corresponding to each back EMF are adjusted through a phase-locked loop until the electrical frequency output by the phase-locked loop converges to a target electrical frequency range. Then, the motor is controlled by FOC.

[0007] Compared with existing technologies, this application performs rotor alignment control on the motor. Starting from a stationary rotor, after rotor alignment, a speed loop closed-loop control is initiated to increase the motor speed by repeatedly detecting back EMF zero-crossing signals. This continues until a back EMF zero-crossing signal is detected again, at which point the drive signal for the motor is stopped. Then, based on the electrical angle corresponding to the latest detected back EMF zero-crossing signal, a phase-locked loop (PLL) is used to perform electrical angle feedback detection on the rotor. Once the electrical frequency output by the PLL converges, the system switches to using FOC (Focus-Oriented Control) to control the motor, achieving high-speed FOC sine wave sensorless closed-loop control. This eliminates the need for position sensors, instead utilizing the characteristic signals of the motor itself to obtain signal parameters and angle position detection effects equivalent to those of position sensors, saving sensor design and calibration costs. It also avoids the problems of starting failure, loss of synchronization, and stalling caused by using sine wave low-speed starting (which can start the rotor from a stationary state) when the motor is under heavy load, thus reducing the difficulty of starting the motor.

[0008] Further, in step A, the method for aligning the rotor includes: setting a predetermined position before the rotor starts rotating to align the rotor to the predetermined position; then controlling the motor windings in the motor to be energized, driving the rotor to rotate from rest until the rotor rotates to the predetermined position, thus confirming the completion of the rotor alignment control; wherein, the magnetic poles of the rotor at the predetermined position are parallel to the magnetic field of the stator; the motor includes a stator, and the stator includes multi-phase motor windings; the rotor is a magnet with at least one pair of opposite magnetic poles. This determines that setting the predetermined position as the rotor's alignment position and performing a forced commutation operation from the predetermined position improves the accuracy of subsequent detection of the back EMF zero-crossing signal and prevents loss of synchronization during motor startup.

[0009] Furthermore, the rotor is a magnet with a pair of opposite magnetic poles; the stator includes three-phase motor windings to form six sectors with different magnetic field directions; wherein, the predicted position is a position at 30 degrees to a specified direction, or a position at 90 degrees to a specified direction, or a position at 150 degrees to a specified direction, or a position at 210 degrees to a specified direction, or a position at 270 degrees to a specified direction, or a position at 330 degrees to a specified direction; the arrangement order among the positions at 30 degrees to a specified direction, 90 degrees to a specified direction, 150 degrees to a specified direction, 210 degrees to a specified direction, 270 degrees to a specified direction, and 330 degrees to a specified direction is the predetermined commutation sequence; wherein, the specified direction is a coordinate axis direction of the motor stator coordinate system. During one revolution of the rotor in the predetermined commutation sequence, it successively passes positions at 30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees, and 330 degrees to the designated direction, with at least 5 commutation opportunities. This ensures that the rotor completes one revolution every 6 sectors, thus establishing the motor speed.

[0010] Further, in step A, the method of controlling the rotor to perform forced commutation operation so that the rotor passes through multiple sectors in a predetermined commutation sequence without pre-determining the commutation time, and detecting the back EMF zero-crossing signal during the forced commutation operation includes: controlling two phase motor windings of the motor to be energized, and controlling the remaining phase motor winding to be de-energized, so that the three-phase motor windings generate a magnetic field force that changes according to a predetermined commutation sequence; wherein, the stator includes three-phase motor windings; driven by the magnetic field force that changes according to the predetermined commutation sequence, the rotor starts from the predetermined position and rotates in a predetermined commutation sequence and performs commutation according to a preset forced frequency; during the rotor rotation, each time a back EMF zero-crossing signal is detected, it is counted once, and the location of the currently detected back EMF zero-crossing signal and its detection time are recorded, wherein the location of the currently detected back EMF zero-crossing signal is represented by the current electrical angle of the rotor, so that each back EMF zero-crossing signal has a corresponding electrical angle. This application uses a magnetic field force that changes according to a predetermined commutation sequence to control the rotor during commutation at a preset forced frequency. In this process, the motor speed is generated in an open-loop manner. By changing along the predetermined commutation sequence, the motor can be accelerated to a certain speed in an open-loop manner, generating excessive load torque. However, there is no feedback of the speed back to the motor; that is, the changes in motor speed and back EMF are not constrained by feedback. Sufficient back EMF is generated to achieve the level required for zero-crossing detection. This aims to detect multiple back EMF zero-crossing signals within a certain number of forced commutation cycles, improving the detection capability of the back EMF zero-crossing signal. Subsequently, step B will be executed to adjust the excessive load torque to suppress the loss of synchronism problem.

[0011] Furthermore, during the forced commutation operation, the method for detecting the back EMF zero-crossing signal includes: sampling the phase port of the unenergized motor winding to obtain the sampling terminal voltage; determining whether the sampling terminal voltage is equal to half of the bus voltage; if so, determining that a back EMF zero-crossing signal has been detected; otherwise, determining that no back EMF zero-crossing signal has been detected; wherein, the bus voltage is the supply voltage used to drive the motor; the resistance of each phase motor winding is equal, and each phase motor winding is connected to an external three-phase inverter circuit through a phase port. Therefore, when the rotor rotates to the unenergized phase motor winding, the back EMF zero-crossing signal generated by the unenergized phase can be detected by detecting the terminal voltage of the unenergized phase.

[0012] Furthermore, in step A, if a preset number of back EMF zero-crossing signals are continuously detected according to the predetermined commutation sequence, it is determined that the rotor has continuously rotated through a preset number of sectors according to the predetermined commutation sequence, and that the preset number of back EMF zero-crossing signals are generated sequentially in the corresponding sectors according to the predetermined commutation sequence. This improves the accuracy of detecting back EMF zero-crossing signals in subsequent closed-loop control processes and reduces the impact of rotor jitter and large speed fluctuations.

[0013] Furthermore, step A also includes: if no preset number of back EMF zero-crossing signals generated according to the predetermined commutation sequence are detected, then the preset forced frequency is reduced and the reduced preset forced frequency is updated to the preset forced frequency, or the duty cycle of the MOSFET used to turn on the upper arm of the three-phase inverter circuit is increased to improve the output torque of the motor; then the rotor is controlled to perform forced commutation operation again until the preset number of back EMF zero-crossing signals are continuously detected according to the predetermined commutation sequence. This overcomes the problems of unstable commutation cycle and loss of back EMF zero-crossing signals.

[0014] Further, in step B, the method for detecting the back EMF zero-crossing signal includes: sampling the phase port of a non-energized phase motor winding to obtain the sampling terminal voltage; then determining whether the sampling terminal voltage is equal to half of the bus voltage; when it is determined that the sampling terminal voltage is equal to half of the bus voltage, it is determined that the back EMF zero-crossing signal is currently detected, and the current determination time is marked as the detection time of the currently detected back EMF zero-crossing signal; then, based on the latest commutation time and the detection time of the currently detected back EMF zero-crossing signal, the next commutation time is calculated, and the next commutation point is determined; wherein, the detection time of the currently detected back EMF zero-crossing signal is located at the middle of the target commutation cycle; the time period from the latest commutation time to the next commutation time is the target commutation cycle; when it is determined that the sampling terminal voltage is not equal to half of the bus voltage, it is determined that the back EMF zero-crossing signal is not currently detected, and then the rotor speed is adjusted to be equal to the preset starting speed by performing speed loop closed-loop control on the motor, so that the sampling terminal voltage is equal to half of the bus voltage.

[0015] Based on the aforementioned technical solution, this application marks the moment when the sampling terminal voltage equals half of the bus voltage as the detection moment of the current detection of the back EMF zero-crossing signal, or the detection moment of the current detection of the back EMF zero-crossing point, or the detection moment of the current detection of the zero-crossing point, as the time when the stator does not cut the magnetic field lines relative to the rotor to generate back EMF. Since the latest commutation moment and the current detection moment of the back EMF zero-crossing signal are known, half of the target commutation period can be calculated, thereby determining the next commutation moment and its corresponding electrical angle, and achieving adaptive control of the rotor to cross the back EMF zero-crossing point at the corresponding time.

[0016] Further, in step B, during the period from the latest commutation time to the detection time of the currently detected back EMF zero-crossing signal, the following occurs: The motor undergoes closed-loop speed control; when the rotor speed is accelerated to a preset starting speed, a square wave start is completed; after the square wave start, the rotor speed is adjusted back to the preset starting speed; wherein, the drive signal is a square wave; during the closed-loop speed control of the motor, two phases of the motor windings are energized, while the remaining phase winding is de-energized, to control the rotor to rotate within the stator's magnetic field. This ensures that the rotor speed is sufficient to support the detection of the back EMF zero-crossing signal, and that the rotor is not forced to commutate; instead, commutation is performed based on the actual time of the back EMF zero-crossing signal.

[0017] Further, in step C, after detecting the back EMF zero-crossing signal, from the detection time of the currently detected back EMF zero-crossing signal to the next commutation time, the three-phase motor windings of the motor are stopped from being energized so that no square wave is output to the motor. Simultaneously, the three-phase back EMFs of the motor and their corresponding electrical angles are acquired. However, the rotor continues to rotate due to the inertia accumulated between the latest commutation time and the detection time of the currently detected back EMF zero-crossing signal. The position of the currently detected back EMF zero-crossing signal is represented by the current electrical angle of the rotor, ensuring that each back EMF zero-crossing signal has a corresponding electrical angle. From the detection time of the currently detected back EMF zero-crossing signal to the next commutation time, the motor rotor is in a free-rotating state. At this time, no torque is applied to the motor rotor, and it decelerates to a stop under the torque generated by the reverse magnetic flux generated by bearing friction and induced EMF. Since there is no circuit in the three-phase motor windings and no current is generated, only back EMF is generated on the three phase lines. At this time, since the rotor of the motor is still rotating to cut the magnetic field lines, the three-phase motor windings of the motor will generate an induced electromotive force. Moreover, since the three-phase bridge arms connected to the three-phase motor windings are in a non-conductive state, the back electromotive force of each phase motor winding can be solved by constructing the voltage loop equations of each phase column.

[0018] Further, in step C, during the period from the detection time of the currently detected back EMF zero-crossing signal to the next commutation time, the following steps also exist: Step C1, generate an initial electrical frequency and obtain a reference EMF through a phase-locked loop; then execute step C2; wherein, the back EMF generated by one phase motor winding has a corresponding electrical angle; Step C2, determine whether the difference between the reference EMF and each of the currently generated back EMFs of the stator is within a preset EMF difference range, if yes, execute step C5, otherwise execute step C3; wherein, each of the currently generated back EMFs of the stator is the back EMF generated by the motor winding of the non-energized phase; Step C3, determine whether the electrical angle corresponding to one of the currently generated back EMFs of the stator is the electrical angle corresponding to the next commutation point, if yes, load the drive signal onto the motor and execute step B, otherwise obtain each of the currently generated back EMFs of the stator The dynamic force is then executed in step C4; Step C4: The phase-locked loop is controlled to integrate the initial electrical frequency to obtain the phase difference to be adjusted. Then, the sum of the electrical angle corresponding to the currently detected back EMF zero-crossing signal and the phase difference to be adjusted is input into the phase-locked loop to generate a new electrical frequency and obtain a corresponding new reference EMF. The new electrical frequency is then updated to the initial electrical frequency, and the new reference EMF is updated to the reference EMF. Then, step C2 is executed; Step C5: The electrical frequency output by the phase-locked loop is determined to converge to a target electrical frequency range. Then, the phase compensation amount is determined based on the current electrical frequency output by the phase-locked loop. Then, the absolute electrical angle of the rotor is determined according to the phase compensation amount and the electrical angle corresponding to the currently detected back EMF zero-crossing signal. The absolute electrical angle of the rotor is marked as the electrical angle estimated by the phase-locked loop. Then, the absolute electrical angle of the rotor is set as the input electrical angle of the FOC control, and the FOC is used to adjust the input electrical angle. Since the methods of square wave control and FOC control are very different and the current and voltage sampling points are inconsistent, the aforementioned steps C1 to C5 are adopted to overcome the problems of large torque load and easy loss of steps and stalling during the switching process from square wave to FOC control in step B, thereby reducing the difficulty and stability of FOC start-up.

[0019] Furthermore, the electrical angles corresponding to the zero-crossing back EMF signal are 30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees, and 330 degrees within a 360-degree range, so that the electrical angles corresponding to the predicted position and the preset number of zero-crossing back EMF signals are located in 6 sectors; wherein, the 6 sectors form a 360-degree electrical angle interval, and each sector is a 60-degree electrical angle interval; the zero-crossing back EMF signal is configured as a straight line passing through a zero-crossing point of the back EMF within a corresponding sector, and this straight line is the axis of symmetry within the corresponding sector, with the current commutation point and the next commutation point being symmetrical about this straight line within the corresponding sector; wherein, the zero-crossing point of the back EMF is used to represent the point where the polarity of the back EMF changes within the corresponding sector; the commutation point is located on the boundary between two adjacent sectors, and the commutation point forms a 30-degree electrical angle interval with respect to the zero-crossing points of the back EMF in the two adjacent sectors. Thus, as the rotor with a pair of opposite magnetic poles rotates within the magnetic field of the three-phase motor windings, it can sequentially pass through six sectors with different magnetic field directions, and detect six different back electromotive force zero-crossing signals in sequence during one rotation. Attached Figure Description

[0020] Figure 1 This is a schematic flowchart of a motor control method disclosed in one embodiment of this application. Detailed Implementation

[0021] The following description and accompanying drawings fully illustrate specific embodiments of the invention to enable those skilled in the art to practice them. Other embodiments may include structural, logical, electrical, procedural, and other changes. The embodiments represent only possible variations. Individual components and functions are optional unless explicitly required, and the order of operation may vary. Parts and features of some embodiments may be included in or replace parts and features of other embodiments. The scope of the embodiments disclosed in this application includes the entire scope of the claims and all available equivalents of the claims. These embodiments may be referred to individually or collectively by the terms "this application" or "this embodiment," which is merely for convenience and is not intended to automatically limit the scope of the application to any single invention or inventive concept if more than one inventive solution is disclosed.

[0022] This application discloses a motor control method. The execution entity can be a controller, driver, or closed-loop regulator, etc., for motor control. The control device does not have an additional position sensor; it directly uses motor parameters and drive signals to control the motor, including driving the rotor inside the motor to rotate and applying back electromotive force to the stator. The control device is used to control the motor to switch from low-speed start-up to high-speed FOC sine wave sensorless closed-loop control. Here, low-speed start-up can be achieved by starting from rest and commutating and speed adjustment at a certain frequency under the drive of a square wave. After multiple consecutive zero-crossing detections and the rotor speed being increased to a higher speed, the modulation wave is started. Then, under the drive of the modulation wave, the rotor speed is controlled by a speed loop closed-loop control, and multiple electrical angle detections are performed. When a stable electrical angle and speed are detected, the control switches to high-speed FOC sine wave sensorless closed-loop control. This avoids problems such as easy loss of steps and difficulty in starting when the FOC sine wave control motor rotates at low speeds, even when the torque load applied to the motor is large.

[0023] As one example, such as Figure 1 As shown, the motor control method includes:

[0024] Step A: Align the rotor and then force the rotor to perform a commutation operation so that the rotor crosses multiple sectors in a predetermined commutation sequence without pre-determining the commutation time. At least force the rotor to commutate at a certain frequency to a position where the correct back EMF zero-crossing signal can be detected. That is, when the torque given by the duty cycle is large enough, the rotor can be forcibly dragged into the corresponding sector within a certain time, but the commutation is not based on the actual back EMF zero-crossing signal. For example, the next commutation time is not calculated based on the actual back EMF zero-crossing signal. At this time, commutation is performed in a predetermined commutation sequence, which can control the motor to start open-loop commutation from the rotor aligned state and prevent the motor from losing synchronization due to excessive external load torque.

[0025] In step A, during the forced commutation operation, a back EMF zero-crossing signal is detected. If a preset number of back EMF zero-crossing signals are detected consecutively according to the predetermined commutation sequence, step B is executed to switch to speed loop closed-loop control. It is determined that the current commutation cycle is stable and can correctly detect the back EMF zero-crossing point and its generation time (also understood as the detection time, because the back EMF zero-crossing signal is only generated on the corresponding phase when the rotor rotates to the back EMF zero-crossing point). If a preset number of back EMF zero-crossing signals cannot be detected consecutively according to the predetermined commutation sequence, a phase delay or loss of the back EMF zero-crossing signal may occur. In this case, based on the completed rotor alignment control, the forced commutation operation is adjusted by reducing the frequency or increasing the duty cycle, so that the rotor re-crosses multiple sectors according to the predetermined commutation sequence without pre-determining the commutation time, until a preset number of back EMF zero-crossing signals are detected consecutively according to the predetermined commutation sequence. Then, step B is executed to perform closed-loop control of the rotor speed.

[0026] In this embodiment, no position sensor is installed inside the motor; the position sensor includes a Hall sensor. Therefore, the motor control method disclosed in this embodiment is a sensorless motor control method. The motor includes a rotor. The preset number is the difference between the maximum number of different sectors allowed to be traversed by the rotor in one electrical cycle and the value 1. The motor includes three-phase motor windings, and when the number of opposite pole pairs of the rotor is one pair (i.e., only one N pole and one S pole are provided), the preset number is equal to 5.

[0027] Step B: Perform closed-loop speed control on the motor. After the rotor speed is accelerated to the preset starting speed, start the drive signal and detect the back EMF zero-crossing signal. At this time, it is determined that the drive signal has been officially started and is still under the closed-loop control of the drive signal, so that the rotor determines the next commutation time based on the currently detected back EMF zero-crossing signal before commutation. Specifically, the next commutation time is calculated based on the time of the latest commutation and the time period of the currently detected back EMF zero-crossing signal. Then, proceed to step C.

[0028] During the closed-loop speed control process, the rotor speed increases under the control of an external drive signal (such as a square wave). The high torque of the speed loop can be used to drive the rotor to a higher speed, and the back EMF zero-crossing signal is detected in real time, including multiple electrical angle measurements. Specifically, to avoid large angular velocity fluctuations and motor step loss after applying a large load torque, the back EMF zero-crossing signal is detected before each commutation in the closed-loop speed control process. The next commutation time is estimated based on the back EMF zero-crossing signal, and then commutation occurs only after a delay. This can be understood as... Stable control of externally applied load torque; during the closed-loop speed control process, the time for the motor to rotate one commutation cycle is adaptively adjusted by estimating the next commutation moment. This allows the electrical angle of the zero-crossing point leading the next commutation point to be calculated based on the electrical angle of the zero-crossing point being delayed by the previous commutation point, thereby achieving stable control of the real-time speed of the rotor or the externally applied load torque. After detecting the back EMF zero-crossing signal, the rotor is not affected by the stator magnetic field, but can continue to rotate forward by inertia until it reaches the next commutation point, i.e., the next commutation moment, and then performs a new commutation to stably cross a sector.

[0029] It should be noted that the motor disclosed in this application can be controlled as a sensorless brushless direct current motor (BLDC) using back electromotive force. To make the BLDC motor rotate continuously in a specified direction, the rotor windings are energized in a certain sequence. The switching of the motor from one energizing state to another is called "commutation," for example, changing from energizing the U phase to energizing the V phase, commutation causes the rotor to rotate to the next position. When using a six-step trapezoidal wave (120-degree commutation method) to energize the motor windings, the change occurs every 60 degrees, and six commutations are sufficient to make the motor rotate one electrical cycle. In some embodiments, when two phases of the motor are energized, controlling the rotor to rotate forward or backward to the next position is considered as one commutation.

[0030] Step C: Whenever a back EMF zero-crossing signal is detected, the electrical angle corresponding to the currently detected back EMF zero-crossing signal can be obtained. During the period from the detection time of the currently detected back EMF zero-crossing signal to the next commutation time, the drive signal is stopped from being applied to the motor, and each phase of the motor is not energized. The rotor continues to rotate by inertia. The drive signal can be a square wave. At the same time, the electrical angles corresponding to all back EMFs of the motor are obtained. Based on the electrical angles corresponding to the back EMF zero-crossing signals, the electrical angles corresponding to each back EMF are adjusted by a phase-locked loop until the electrical frequency output by the phase-locked loop converges to a target electrical frequency range. Then, the motor is controlled by FOC.

[0031] Electrical angle and electrical frequency are both rotational variables in motor vector control. The accuracy of the electrical angle is related to the decoupling of the two orthogonal components of the current vector in the motor stator coordinate system.

[0032] This embodiment obtains the electrical angle increment corresponding to each back electromotive force (EMF) by integrating the electrical frequency output by the phase-locked loop (PLL) each time. The electrical angle increment corresponding to each back EMF can include the phase difference obtained by integrating the electrical frequency generated by the PLL in real time. Then, the sum of the electrical angle increment and the electrical angle corresponding to the currently detected zero-crossing signal of the back EMF is used as a feedback quantity and input to the PLL to accelerate the convergence of the PLL. The PLL will adjust based on the difference between the reference back EMF it generates and the corresponding currently detected back EMF. Since there is a delay in the convergence of the PLL, multiple iterative detections are required until the PLL outputs the correct electrical angle. When the output frequency converges to a target frequency range, the output frequency of the phase-locked loop is equal to the actual rotation frequency formed by the rotor rotating under the magnetic field generated by the corresponding phase motor winding within the allowable error range, thus obtaining a stable rotation frequency. The actual speed of the rotor or motor is represented by the actual rotation frequency of the rotor, and then the rotor absolute electrical angle is obtained by integration. Then, the motor is controlled by FOC. In the scenario of FOC motor control, the voltage vector corresponding to the motor output is controlled by the rotor absolute electrical angle and decomposed into each phase motor winding to adjust the actual speed of the motor, thereby implementing high-speed FOC sine wave sensorless closed-loop control.

[0033] Compared with existing technologies, this application performs rotor alignment control on the motor. Starting from a stationary rotor, after rotor alignment, a speed loop closed-loop control is initiated to increase the motor speed by repeatedly detecting back EMF zero-crossing signals. This continues until a back EMF zero-crossing signal is detected again, at which point the drive signal for the motor is stopped. Then, based on the electrical angle corresponding to the latest detected back EMF zero-crossing signal, a phase-locked loop (PLL) is used to perform electrical angle feedback detection on the rotor. Once the electrical frequency output by the PLL converges, the system switches to using FOC (Focus-Oriented Control) to control the motor, achieving high-speed FOC sine wave sensorless closed-loop control. This eliminates the need for position sensors, instead utilizing the characteristic signals of the motor itself to obtain signal parameters and angle position detection effects equivalent to those of position sensors, saving sensor design and calibration costs. It also avoids the problems of starting failure, loss of synchronization, and stalling caused by using sine wave low-speed starting (which can start the rotor from a stationary state) when the motor is under heavy load, thus reducing the difficulty of starting the motor.

[0034] As one embodiment, in step A, the method for aligning the rotor includes:

[0035] Before the rotor starts rotating, a predetermined position is set, which can be set within the motor stator coordinate system. This allows the rotor to be aligned to the predetermined position and forced commutation to begin from that position. In this embodiment, the rotor is aligned with one phase of the stator winding when it is not rotating. This means that the rotor's magnetic poles at the predetermined position are parallel to the stator's magnetic field, thus aligning the rotor with the stator. Therefore, when the rotor is not rotating, the stator does not generate back electromotive force. The approximate angle range or sector of the rotor must be determined before positioning / mapping the rotor to the predetermined position. The predetermined position is preferably the N / S pole exchange region of the stator closest to the rotor's original position before rotation, ensuring that the rotor is aligned with the direction of the stator's magnetic field at the predetermined position.

[0036] It should be noted that the motor also includes a stator. Specifically, the rotor is located in the inner layer of the motor, and the stator is located in the outer layer. The stator includes multi-phase motor windings to form multiple sectors after energization. Each phase motor winding includes at least two sets of coils. The rotor is a magnet with at least one pair of opposite magnetic poles, where each pair of poles includes an N pole and a S pole. Each phase motor winding generates a voltage, i.e., a back electromotive force (EMF), the magnitude of which is proportional to the rotor speed. The number of opposite magnetic pole pairs of the rotor is negatively correlated with the electrical cycle. For example, when the rotor has one pair of magnetic poles, the rotor completes one circumference in six phase cycles of the stator; when the rotor has six pairs of magnetic poles, the rotor only completes one-sixth of the circumference. The more pairs of magnetic poles the rotor has, the lower the rotor speed at the same electrical frequency.

[0037] Then, the motor windings in the control motor are energized, driving the rotor to rotate from rest. The motor windings cut the rotor's magnetic field lines, thereby generating a back electromotive force (EMF) in the motor windings until the rotor rotates to the predetermined position, thus completing the rotor alignment control. Sufficient conduction current can be supplied to the motor externally for a sufficient time for the rotor to rotate to the corresponding angle. The energizing state for driving the rotor can be achieved by de-energizing one phase of the motor winding and energizing the other two phases, thereby driving the rotor to rotate and generating a back EMF in the motor windings. When the rotor rotates to the predetermined position, the voltage generated by the de-energized phase motor winding is set as the zero-crossing signal of the back EMF. This voltage is generated at a phase port (one lead terminal of the motor) where the de-energized phase motor winding is connected to the external three-phase inverter circuit. This determines the predetermined position as the rotor's alignment position and initiates a forced commutation operation from the predetermined position, improving the accuracy of subsequent detection of the back EMF zero-crossing signal and preventing loss of synchronization during motor startup.

[0038] Preferably, the rotor is a magnet with a pair of opposite magnetic poles; the motor includes three-phase motor windings to form six sectors with different magnetic field directions, each sector can be named a six-phase commutation sector; specifically, at least two phase motor windings are energized to form six sectors, or only two phases of the three-phase motor windings are energized but the remaining phase is not energized; a sector is the range of angles through which the rotor rotates between two adjacent commutations.

[0039] A three-phase inverter circuit is located outside the motor. Each of the three motor windings is electrically connected to a bridge arm in the three-phase inverter circuit via a phase port (lead terminal). The corresponding phase winding is energized by a MOSFET in the bridge arm. Since the rotor is a permanent magnet, it rotates parallel to the stator magnetic field under the influence of the magnetic field, reaching a position parallel to one of the motor windings, thus aligning the rotor's north magnetic pole with the stator's south magnetic pole. Therefore, the rotor is rotated to the predetermined position during the alignment control process.

[0040] A three-phase inverter circuit drives the three-phase motor windings to form a rotating hexagonal magnetic field, which in turn drives the motor rotor to rotate. The rotor rotates relative to the three-phase motor windings, causing the three-phase motor windings to cut the magnetic field lines of the rotor, generating a back electromotive force (EMF) in the three-phase motor windings. In the three-phase inverter circuit, each phase motor winding can be equivalent to a series connection of a resistor, an inductor, and a back EMF.

[0041] By implementing the alignment control disclosed in the aforementioned embodiments, the rotor can be aligned to one of six angles—30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees, and 330 degrees—within one rotation of the rotor, thus achieving alignment between the rotor and the stator. The predicted position is a position at 30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees, or 330 degrees with a specified direction, where the specified direction can be a coordinate axis of the motor stator coordinate system. After energizing the corresponding phase motor winding, the predicted position aligned to the rotor changes to the predicted position corresponding to the current energized state. At this point, the predicted position can also be understood as the zero-crossing point of the back electromotive force, causing the rotor to rotate one revolution every six sectors, thus forming the motor speed.

[0042] It should be noted that the positions at 30 degrees to the specified direction and the positions at 210 degrees to the specified direction constitute the distribution position of one phase of the three-phase motor winding; the positions at 90 degrees to the specified direction and the positions at 270 degrees to the specified direction constitute the distribution position of one phase of the three-phase motor winding; and the positions at 150 degrees to the specified direction and the positions at 330 degrees to the specified direction constitute the distribution position of one phase of the three-phase motor winding. The arrangement of the positions at 30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees, and 330 degrees with respect to the specified direction is the predetermined commutation sequence, which is considered as the rotation direction of the rotor or the energizing sequence of the rotor. During the rotor's rotation in the predetermined commutation sequence, it successively passes through the positions at 30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees, and 330 degrees with respect to the specified direction, and the rotor has at least 5 opportunities for commutation.

[0043] As one embodiment, in step A, the method of controlling the rotor to perform forced commutation so that the rotor passes through multiple sectors in a predetermined commutation sequence without pre-determining the commutation time, and detecting the back EMF zero-crossing signal during the forced commutation operation, includes: controlling two phases of the motor windings to be energized and controlling the remaining phase of the motor windings to be de-energized. In this embodiment, the stator of the motor is configured as a three-phase motor winding. Therefore, after determining that the rotor alignment control is completed, it is possible to determine which switches in the three-phase inverter circuit outside the motor should be turned on next, and which two phases should be energized. Then, it is possible to continue controlling two phases of the three-phase motor windings to be energized and controlling the remaining phase to be de-energized, so that the three-phase motor windings generate a magnetic field force that changes according to the predetermined commutation sequence. Driven by the magnetic field force that changes according to a predetermined commutation sequence, the rotor rotates from the predetermined position according to the predetermined commutation sequence and generates a back electromotive force (EMF) from the stator. The rotor commutates according to a preset forced frequency. Each time a back EMF zero-crossing signal is detected, it is counted once, and the location of the currently detected back EMF zero-crossing signal and its detection time are recorded. The location of the currently detected back EMF zero-crossing signal is represented by the current electrical angle of the rotor, that is, the electrical angle of the rotor when the back EMF zero-crossing signal is detected. The generation position of the currently detected back EMF zero-crossing signal (when the rotor rotates to the generation position relative to the stator cutting the magnetic field lines) can also represent the location of the currently detected back EMF zero-crossing signal, so that each back EMF zero-crossing signal has a corresponding electrical angle and is located in different sectors.

[0044] Specifically, driven by the magnetic field force that changes according to a predetermined commutation sequence, the rotor starts from the predetermined position and rotates according to the predetermined commutation sequence, while the stator generates a back electromotive force (including a back electromotive force zero-crossing signal) for detection and statistical analysis. Since one phase of the motor winding cuts the rotor's magnetic field lines during the rotation, one phase of the motor winding generates a back electromotive force. Consequently, the rotor is controlled to rotate in a direction parallel to the stator magnetic field, thereby forcibly controlling the rotor to rotate forward or backward to the next position for the next commutation.

[0045] Furthermore, driven by the magnetic field force that changes according to a predetermined commutation sequence, the rotor is controlled to commutate at a preset forced frequency, so that the rotor is dragged from the predetermined position to the corresponding sector within a corresponding time. The corresponding time is related to the forced commutation cycle, the number of pole pairs of the rotor, and the number of phases of the motor windings of the stator. The reciprocal of the preset forced frequency is equal to the forced commutation cycle. In this embodiment, the rotor is controlled to commutate at a preset forced frequency using the magnetic field force that changes according to a predetermined commutation sequence. During this process, the corresponding motor speed is generated in an open-loop manner. By changing along the predetermined commutation sequence, the motor can be accelerated to a certain speed in an open-loop manner, which can generate excessive load torque. However, there is no feedback of the speed to the motor, that is, the change of motor speed and back EMF is not constrained by feedback. Sufficient back EMF is generated to reach the level of zero-crossing detection. In this way, multiple back EMF zero-crossing signals are detected within a certain number of forced commutation cycles, thereby improving the detection capability of back EMF zero-crossing signals. Subsequently, step B will be executed to adjust the excessive load torque to suppress the step loss problem.

[0046] Furthermore, in this embodiment, to verify the detection capability of the back EMF zero-crossing signal and accurately activate the square wave in step B to enter closed-loop control, the relevant method includes: during the process of the rotor being controlled to commutate according to a preset forced frequency, rotating according to a predetermined commutation sequence (or its pointing direction), counting once for each detected back EMF zero-crossing signal to achieve statistics on the back EMF zero-crossing signal or the back EMF zero-crossing point, and recording the location of the currently detected back EMF zero-crossing signal and its detection time. This detection time can be recorded as... The zero-crossing time of the back EMF is used to determine the zero-crossing time of the back EMF according to the predetermined commutation sequence. This allows for the determination of whether the currently detected back EMF zero-crossing signal is generated according to the predetermined commutation sequence, and reflects whether the rotor has traversed multiple sectors within the corresponding time period according to the predetermined commutation sequence. The location of the back EMF zero-crossing signal includes the electrical angle corresponding to the signal and the sector it belongs to, determining its generation sequence or magnetic field direction. This serves as the positioning result of the rotor being forced to commutate according to a preset forced frequency and predetermined commutation sequence. It is worth noting that if the rotor has not yet started rotating or the angle traversed to the predicted position is too small initially, the generated back EMF is not obvious or the back EMF zero-crossing signal has not been accurately obtained. Therefore, forced commutation is required from the completion of alignment control to improve the detection accuracy of the back EMF zero-crossing signal and avoid problems such as loss of synchronization and ineffective motor start-up during low-speed rotation under heavy load.

[0047] Preferably, the preset forced frequency is a pre-set six-phase commutation frequency, so that the rotor commutates six times for every one revolution. For a motor with one pair of magnetic poles, six phase commutations correspond to one revolution of the rotor, so each forced commutation cycle corresponds to a 60-degree rotor rotation, and half a cycle is only 30 degrees. For a motor with multiple pairs of magnetic poles, the angle range corresponding to the forced commutation cycle is even smaller.

[0048] In scenarios where a three-phase inverter bridge circuit is used to control a motor, switching on different combinations of upper and lower bridge arm MOSFETs can control the direction of current flow, generating magnetic fields in different directions, causing the rotor to rotate to a designated position. To make the motor disclosed in this embodiment rotate continuously according to the predetermined commutation sequence or a certain direction of rotation, each phase of the motor windings must be energized in a specific sequence. The switching from one energizing state to another is called "commutation," for example, changing from energizing one phase to energizing another. Commutation causes the rotor to rotate to the next position. If there are three switching transistors in each of the upper and lower bridge arms, resulting in six combinations, the rotor can complete one electrical cycle of rotation after six commutation steps, changing every 60 degrees.

[0049] In the above embodiments, the method for detecting the back EMF zero-crossing signal during the forced commutation operation includes:

[0050] The phase port of the unenergized motor winding is sampled to obtain the sampling terminal voltage. This sampling terminal voltage indicates that during the rotor's rotation in a predetermined commutation sequence, two phases of the motor winding are energized while the remaining phase winding is de-energized. The voltage signal of the phase port of the unenergized motor winding is acquired in real time, and then the voltage signal is converted from analog to digital to obtain the sampling terminal voltage. It is worth noting that this sampling terminal voltage is not equal to the back electromotive force generated by the unenergized motor winding cutting the rotor's magnetic field lines.

[0051] The system determines whether the sampling terminal voltage is equal to half of the bus voltage. If yes, it confirms that a back EMF zero-crossing signal has been detected; otherwise, it confirms that no such signal has been detected. The bus voltage is the supply voltage used to drive the motor. The impedance of each phase motor winding is equal; the impedance of one phase motor winding can be understood as the resistance of one phase line of the motor. Each phase motor winding is connected to an external three-phase inverter circuit through one phase port.

[0052] Specifically, during rotor rotation, no current flows through the unenergized phase motor winding, and therefore no self-induced electromotive force is generated in the unenergized phase motor winding, thus eliminating the interference of self-induced electromotive force on the detection of the zero-crossing signal of the back electromotive force. When the rotor's magnetic poles rotate to be parallel to the unenergized phase motor winding, it can be determined that the rotor has rotated to the stator's NS pole exchange region (the stator's NS pole exchange region is set at a certain electrical angle in different sectors of the six-phase commutation). The motor windings do not cut the magnetic field lines, and the unenergized phase motor winding does not generate back electromotive force or self-induced electromotive force. Then, based on the common connection method between each bridge arm and the corresponding phase motor winding in the three-phase inverter circuit (for example, each phase motor winding is equivalent to a series connection of resistance, inductance, and back electromotive force, and then connected to the MOS of the corresponding bridge arm), One pole of the tube; wherein the impedance of each phase motor winding is equal), it is determined that in the three-phase motor winding, the unenergized phase motor winding is located in the middle of the energized two phase motor windings. Since no current flows through the unenergized phase, the unenergized phase motor winding does not generate self-induced electromotive force and resistance voltage drop. Therefore, the back electromotive force generated by the unenergized phase motor winding is 0. It can be calculated that the voltage at the phase port of the unenergized phase motor winding (i.e., the aforementioned sampling terminal voltage, which is also a terminal voltage) is equal to half of the bus voltage. At the same time, the moment when it is determined that the sampling terminal voltage is equal to half of the bus voltage is marked as the detection time when the back electromotive force zero-crossing signal is detected, or the detection time when the back electromotive force zero-crossing point is detected, or the detection time when the zero-crossing point is detected, which is the time when the stator does not cut the magnetic field lines relative to the rotor to generate back electromotive force. Therefore, by detecting the relationship between the port voltage of the unenergized phase and the bus voltage, the back EMF zero-crossing signal can be reconstructed. That is, when the rotor rotates to the stator N / S pole exchange point and the back EMF equals zero, the phase port voltage of the unenergized phase is equal to half of the bus voltage. The relationship between the terminal voltage required to detect / generate the back EMF zero-crossing signal and the voltage value of the back EMF zero-crossing signal, and the relationship between the terminal voltage required to detect / generate the back EMF zero-crossing signal and the electrical angle corresponding to the back EMF zero-crossing signal can be reconstructed. Thus, the relationship between the terminal voltage required to detect / generate the back EMF zero-crossing signal and the electrical angle corresponding to the back EMF zero-crossing signal can be determined. In each sector, the electrical angle corresponding to the back EMF zero-crossing signal is preset.

[0053] Schematic, in a six-phase commutation sector, the two energized motor windings are the W-phase and V-phase windings, respectively, while the U-phase winding is the de-energized winding. Each back-EMF zero-crossing signal is generated in the de-energized motor winding. For example, the current flowing through the W-phase winding is positive, the current flowing through the V-phase winding is negative, and the current flowing through the U-phase winding is zero. This indicates that current flows from the W-phase to the V-phase, and the U-phase is open-circuited. During rotor rotation within the stator magnetic field, the back-EMF zero-crossing signal or the back-EMF zero-crossing point occurs precisely in the U-phase. Since the U-phase does not generate a self-induced EMF, a mapping relationship is formed between the terminal voltage of the U-phase winding and the back-EMF generated by it. Therefore, within each sector, based on this mapping relationship, when the rotor rotates to the de-energized motor winding, the back-EMF zero-crossing signal generated in the de-energized phase can be detected by detecting the terminal voltage of the de-energized phase.

[0054] It should be noted that the point at which the back electromotive force changes from positive to negative or from negative to positive is called the zero-crossing point. Utilizing this characteristic of the back electromotive force, the zero-crossing point can be detected. Furthermore, in a scenario where a magnet with a pair of opposite magnetic poles rotates in the magnetic field generated by the windings of a three-phase motor, delaying the zero-crossing point of the back electromotive force by 30 degrees yields the next point where commutation is required.

[0055] Based on the above embodiments, in step A, if a preset number of back EMF zero-crossing signals are continuously detected according to the predetermined commutation sequence, it is determined that the rotor has continuously crossed a preset number of sectors according to the predetermined commutation sequence, and it is determined that the preset number of back EMF zero-crossing signals are generated sequentially in the corresponding sectors according to the predetermined commutation sequence. Thus, it can be determined that each back EMF zero-crossing point is distributed sequentially in the corresponding sector according to the predetermined commutation sequence. It is understood that being forced to continuously cross a preset number of sectors according to the predetermined commutation sequence from the known position, so as to rotate at least one electrical cycle from rest, may not reach the level of rotating one electrical cycle, but it can serve the purpose of calibration. This determines that the motor has entered the state of detecting a valid back EMF zero-crossing point, improves the accuracy of detecting back EMF zero-crossing signals in the subsequent closed-loop control process, and reduces the impact of rotor jitter and large speed fluctuations.

[0056] It should be noted that the preset number is the difference between the maximum number of different sectors that the rotor is allowed to traverse in one electrical cycle and the value 1. Specifically, a back EMF zero-crossing signal has an electrical angle within its corresponding sector to indicate the position of the back EMF zero-crossing point; a back EMF zero-crossing point is distributed within a sector corresponding to one electrical angle.

[0057] Based on the above embodiment, step A further includes: if no preset number of back EMF zero-crossing signals generated according to the predetermined commutation sequence are detected, at least one back EMF zero-crossing signal may have a period that is not consistent with the forced commutation period, resulting in a short and unstable commutation period, and potentially a shortened commutation period due to zero-crossing phase delay; therefore, the preset forced frequency is reduced, and the reduced preset forced frequency is updated to the preset forced frequency, so that the period of the detected back EMF zero-crossing signal is equal to the reciprocal of the preset forced frequency, and the period of the detected back EMF zero-crossing signal is equal to the forced commutation period; then, the rotor is controlled to perform forced commutation operation again until a preset number of back EMF zero-crossing signals are continuously detected according to the predetermined commutation sequence. This overcomes the problem of unstable commutation period.

[0058] If a preset number of back EMF zero-crossing signals generated according to the predetermined commutation sequence are not detected, there may be a phenomenon where the back EMF zero-crossing signals cannot be detected, which is reflected as a problem of back EMF zero-crossing signal loss. Therefore, the duty cycle of the MOSFET used to turn on the upper bridge arm of the three-phase inverter circuit is increased to improve the output torque of the motor. Specifically, in the three-phase inverter circuit, the duty cycle of the MOSFET used to turn on the upper bridge arm is increased, where the upper bridge arm is the phase line with the applied positive voltage. The current in the two-phase motor windings connected to the three-phase inverter circuit increases, that is, the current flowing through the two phase lines increases, the magnetic field generated is enhanced, the rotor speed is increased, and thus the output torque of the motor is increased, thereby enhancing the detection capability of the back EMF zero-crossing signal. Then, the rotor is controlled to repeat the aforementioned forced commutation operation until a preset number of back EMF zero-crossing signals are continuously detected according to the predetermined commutation sequence. This overcomes the problem of back EMF zero-crossing signal loss.

[0059] As one embodiment, in step B, the method for detecting the zero-crossing signal of the back electromotive force includes:

[0060] The phase terminals of the unenergized motor windings are sampled to obtain the sampling terminal voltage. The detection stage differs from that in step A above, where the back EMF zero-crossing signal is detected. In step B, the back EMF zero-crossing signal is detected during the motor's speed loop closed-loop control, with feedback adjustment of the rotor speed to prevent it from becoming too low, ensuring the detection capability of the back EMF zero-crossing signal. In step A, the back EMF zero-crossing signal is detected during forced commutation, without feedback adjustment of the rotor speed; the rotor is configured to commutate according to a specific commutation sequence and a fixed commutation frequency. Therefore, after completing step A, confirming that a preset number of back EMF zero-crossing signals are continuously detected according to the predetermined commutation sequence, and then executing step B, the accuracy of the detection results can be further improved.

[0061] The system determines whether the sampling terminal voltage is equal to half of the bus voltage. If it is, a back EMF zero-crossing signal is detected; otherwise, no such signal is detected. The bus voltage is the supply voltage used to drive the motor. The impedance of each phase motor winding is equal, and the impedance of one phase winding can be understood as the resistance of one phase line of the motor. Each phase motor winding is connected to an external three-phase inverter circuit through one phase port. In this embodiment, after the closed-loop control rotor speed reaches a speed greater than the preset starting speed, it determines whether the sampling terminal voltage is equal to half of the bus voltage. The change in rotor speed alters the back EMF generated by each phase motor winding. Based on the pre-constructed phase terminal voltage loop equations, the changed back EMF generated by each phase motor winding directly or indirectly causes a change in the sampling terminal voltage.

[0062] When it is determined that the sampling terminal voltage is equal to half of the bus voltage, the back EMF zero-crossing signal is detected, and the current determination time is marked as the detection time of the back EMF zero-crossing signal. Then, based on the latest commutation time and the detection time of the current back EMF zero-crossing signal, the next commutation time is calculated, and the next commutation point is determined. The detection time of the current back EMF zero-crossing signal is located in the middle of the target commutation cycle. The time period from the latest commutation time to the next commutation time is the target commutation cycle. The more magnetic poles the rotor has (equivalent to more pole pairs), the shorter the target commutation cycle; the fewer magnetic poles the rotor has (equivalent to fewer pole pairs), the shorter the target commutation cycle. The longer the target commutation period, the better. In this embodiment, the target commutation period is the time interval between two adjacent commutation points. It is determined by the difference between the detection time of the currently detected back EMF zero-crossing signal and the latest commutation time. Based on this difference, the time interval between the detection time of the currently detected back EMF zero-crossing signal and the next commutation time can be determined, and the next commutation time can be obtained. Based on the mapping relationship between the time interval and the phase difference, the electrical angle corresponding to the next commutation point can be calculated. For example, the preset starting speed accelerated to by the speed loop closed-loop control of the motor can be used to convert between time and electrical angle to obtain the phase difference corresponding to the time interval, so as to determine the location of the next commutation point. The relationship between the terminal voltage (the sampling terminal voltage) required for detecting the back EMF zero-crossing signal and the electrical angle corresponding to the back EMF zero-crossing signal, as well as the relationship between the detection time of the currently detected back EMF zero-crossing signal and the time interval and phase difference between the next commutation time (or the latest commutation time), are the basis of closed-loop control. In each sector, the electrical angle corresponding to the back EMF zero-crossing signal is preset, but the back EMF zero-crossing signal is determined by real-time detection and the time interval between the detection time of the currently detected back EMF zero-crossing signal and the latest commutation time, and then the next commutation time is calculated. The next commutation time is obtained by judging and calculating based on the actual detected phase port voltage (i.e., terminal voltage) of the non-energized phase motor winding.

[0063] Additionally, it's important to note that the zero-crossing point always precedes the commutation point by 30 electrical degrees. Therefore, after detecting the zero-crossing point, a 30-degree electrical angle delay is required before commutation. However, in closed-loop speed regulation or closed-loop control, the motor may not commutate according to the aforementioned preset forced frequency. Therefore, the time it takes for the motor rotor to rotate one electrical cycle may not be constant. It's impossible to predict the time required for the next 30-degree electrical angle rotation after detecting the back EMF zero-crossing point; this needs to be calculated in advance. In other words, after detecting the zero-crossing point, timing is required to predict the length of the next 30-degree electrical angle. Since the 60-degree electrical angle between two commutation points is measurable, the timer is reset at each commutation, and the timer value read at the next commutation is the length of the commutation cycle. Therefore, an approximation method is used: the time of the previous commutation cycle (60 degrees electrical angle) is halved as the delay time for the next 30-degree electrical angle.

[0064] When it is determined that the sampling terminal voltage is not equal to half of the bus voltage, it is confirmed that no back EMF zero-crossing signal has been detected. Then, the rotor speed is adjusted to equal the preset starting speed by performing speed loop closed-loop control on the motor, so that the sampling terminal voltage is equal to half of the bus voltage. The specific speed loop closed-loop control method includes changing the conduction current in the MOS transistor of the upper bridge arm by adjusting the duty cycle of the square wave. For example, if it is determined that the sampling terminal voltage is too low, the duty cycle is increased to increase the rotor speed to equal the preset starting speed. Correspondingly, the current in the motor winding of the energized phase is increased to a certain current value. The rotor speed can also be maintained within the target speed range, where the preset starting speed is the middle value of the target speed range.

[0065] It should be noted that two adjacent commutation points include the current commutation point and the next commutation point. The moment the current commutation point appears within a sector is the latest commutation moment, and the moment the next commutation point appears within a sector is the next commutation moment. The detection moment of the currently detected back EMF zero-crossing signal is located midway between the latest commutation moment and the next commutation moment. Midway between every two commutation points or two adjacent commutation points corresponds to a point where the polarity of the back EMF changes, i.e., the point where the back EMF changes from positive to negative or from negative to positive; this is called the aforementioned back EMF zero-crossing point. Utilizing this characteristic of the back EMF, as long as the back EMF zero-crossing point can be accurately detected, delaying it by a certain electrical angle (determined by the phase difference between the previous commutation point and the currently detected back EMF zero-crossing point) yields the next commutation moment. The system controls which two phases will be energized next, and then continues to detect the terminal voltage of the phase port of the currently unenergized phase. When the terminal voltage is equal to half of the bus voltage, the zero-crossing point of the back electromotive force and its generation time are determined. This process is repeated in the closed-loop control method, and the duty cycle of the square wave is continuously adjusted until a stable closed loop is established, including when the load torque applied to the rotor by the outside becomes stable.

[0066] Based on the foregoing embodiments, this application marks the moment when the sampling terminal voltage equals half of the bus voltage as the detection moment when the back EMF zero-crossing signal is detected, or the detection moment when the back EMF zero-crossing point is detected, or the detection moment when the zero-crossing point is detected, as the time when the stator does not cut the magnetic field lines relative to the rotor to generate back EMF. Since the latest commutation moment and the detection moment when the back EMF zero-crossing signal is detected are known, half of the target commutation period can be calculated, thereby determining the next commutation moment and its corresponding electrical angle, and achieving adaptive control of the rotor to cross the back EMF zero-crossing point at the corresponding time.

[0067] As one embodiment, in step B, during the period from the latest commutation time to the detection time of the currently detected back EMF zero-crossing signal, the following exists:

[0068] The motor is subjected to speed loop closed-loop control. When the rotor speed is accelerated to the preset starting speed, the square wave start is completed. After the square wave starts, the motor switches to square wave closed-loop control, and the rotor speed is adjusted back to the preset starting speed so that the rotor speed is sufficient to support the detection of the back EMF zero-crossing signal. The rotor is not controlled to perform forced commutation operation, but commutation is performed according to the actual time when the back EMF zero-crossing signal exists.

[0069] In this embodiment, the square wave is the driving signal, serving as the driving source for accelerating the rotor speed to a preset starting speed; the motor speed is represented by the rotor speed. Using a speed loop with high torque to drive the rotor to a higher speed (the specific speed depends on the actual working environment) can be considered as initiating a sensorless closed-loop control using the square wave. Specifically, from the latest commutation time to the detection time of the currently detected back EMF zero-crossing signal (the time at which the currently detected back EMF zero-crossing signal is located), the rotor speed is adjusted using a square wave. During the adjustment of the rotor speed, two phases of the motor windings are energized, while the remaining phase is de-energized. That is, in the three-phase motor windings, the energization state for both the square wave control and the square wave closed-loop control is that only two phases of the three-phase control line are energized, with one phase de-energized, to control the rotor to rotate within the stator's magnetic field. The back EMF zero-crossing signal is generated at half the target commutation cycle; the period from the latest commutation time to the detection time of the currently detected back EMF zero-crossing signal corresponds to half of the target commutation cycle.

[0070] Based on the above embodiments, in step C, after detecting the back EMF zero-crossing signal, from the detection time of the currently detected back EMF zero-crossing signal to the next commutation time, the three-phase motor windings of the motor are stopped from being energized so that no square wave is output to the motor. At this time, the three-phase motor windings of the motor change from two phases energized and one phase de-energized to three phases de-energized. Then, the three-phase back EMFs of the motor and their corresponding electrical angles are obtained, that is, the back EMFs and their corresponding electrical angles of the three de-energized phases are obtained simultaneously. In addition, the electrical angle corresponding to the currently detected back EMF zero-crossing signal has been obtained before the energization of the three-phase motor windings of the motor is stopped. However, the rotor continues to rotate due to the inertia accumulated during the period from the latest commutation time to the detection time of the currently detected back EMF zero-crossing signal. Specifically, during the first half of the target commutation cycle, two phases of the three-phase motor windings of the motor remain energized. The rotational speed can be increased through closed-loop control to make the rotor rotate faster. This is equivalent to the first half-cycle of a sector, where the rotor rotates from a commutation point towards the back EMF zero-crossing point. The motor control is enabled, allowing the rotor to accelerate under the influence of the stator magnetic field. However, once the motor reaches a sufficient speed, upon detecting the back EMF zero-crossing signal, all three-phase motor windings are opened, i.e., the square wave load on the motor is stopped. The rotor is then in an uncontrolled state, continuing to rotate by inertia from the detection time of the current back EMF zero-crossing signal to the next commutation time. In the second half-cycle of the same sector, that is, from the back EMF zero-crossing point to the next commutation point, the control of the MOS transistors in the bridge arm of the three-phase inverter circuit is turned off. At this time, the rotor is not affected by the stator magnetic field, but because the rotor still maintains speed after the acceleration in the first half-cycle, it can continue to rotate by inertia until reaching the next commutation point. Therefore, the second half-cycle of the same sector can be understood as the motor being in a free-rotating state.

[0071] It should be noted that the location of the currently detected back EMF zero-crossing signal is represented by the electrical angle of the rotor, so that each back EMF zero-crossing signal has a corresponding electrical angle.

[0072] From the moment the zero-crossing signal of the back EMF is detected until the next commutation moment, the motor rotor is in a free-rotating state. At this time, no torque is applied to the rotor. It decelerates to a stop under the torque generated by the reverse magnetic flux produced by bearing friction and induced EMF. Since there is no circuit in any of the three-phase motor windings and no current is generated, only back EMF is generated on each of the three phases. Meanwhile, because the motor rotor is still rotating to cut the magnetic field lines, induced EMF will be generated in the three-phase motor windings. Furthermore, since the three-phase bridge arms connected to the corresponding three-phase motor windings are in a non-conductive state, the back EMF of each phase winding can be solved by constructing the voltage loop equations for each phase column.

[0073] When in a free-stalling state, the motor may lose synchronism. This loss of synchronism occurs when the motor initially experiences excessive torque, causing the rotor inertia to continuously shift the operating point towards increasing electrical angle, eventually exceeding the power limit. Consequently, the motor rotor cannot rotate synchronously with the stator's rotating magnetic field. Therefore, a phase-locked loop (PLL) is needed to input the back electromotive force obtained in real time. This back electromotive force is then used to adjust the integrated electrical frequency (the number of electrical cycles the rotor completes in 1 second) until the PLL output stabilizes, preventing problems such as loss of synchronism and vibration during subsequent FOC (Free Start-up) operation.

[0074] As one embodiment, in step C, during the period from the detection time of the currently detected back EMF zero-crossing signal to the next commutation time, the following steps also exist:

[0075] Step C1: Generate an initial electrical frequency and obtain a reference electromotive force (EMF) through a phase-locked loop (PLL); then execute step C2; wherein, the back EMF generated by one phase motor winding has a corresponding electrical angle; at least after the rotor is aligned, a mapping relationship between the back EMF generated by one phase motor winding and the electrical angle to which the rotor rotates can be established. The reference EMF is used to simulate the fixed back EMF caused by the stator cutting magnetic field lines during the rotor's rotation at the preset starting speed. The initial electrical frequency is the frequency information output by the PLL based on the preset initial input and initial feedback. The initial input and initial feedback can come from the back EMF and rotational speed generated in the stator magnetic field during the period from the latest commutation moment to the detection moment of the currently detected back EMF zero-crossing signal (within the first half of the target commutation cycle) when the rotor is under closed-loop control.

[0076] Preferably, the reference electromotive force corresponds to the back electromotive force generated by a phase motor winding; in the process of generating the initial electrical frequency through the phase-locked loop, the process may include accumulating the angular velocity to obtain the electrical angle, and then setting the accumulated electrical angle as the original electrical angle.

[0077] Step C2: Determine whether the difference between the reference electromotive force and the current opposite electromotive forces generated by the stator is within the preset electromotive force difference range. If yes, execute step C5 to determine that the phase-locked loop output has converged; otherwise, execute step C3 to determine that the phase-locked loop output has not converged. The current opposite electromotive forces generated by the stator are all back electromotive forces generated by the motor windings of the non-energized phases. Because step C is executed from the detection time of the zero-crossing signal of the currently detected back electromotive force to the next commutation time, the three-phase motor windings of the motor have been stopped from being energized during this period. The three-phase bridge arms in the corresponding three-phase inverter circuit are all in a non-conducting state. However, since the rotor is still rotating, the stator can cut the magnetic field lines generated by the rotor, so the terminal voltages of the three-phase motor windings can all be non-zero.

[0078] Step C3: Determine if the electrical angle corresponding to one of the current back EMFs generated by the stator is the same as the electrical angle corresponding to the next commutation point. If yes, load the drive signal onto the motor and execute step B to perform commutation via the drive signal; otherwise, acquire the current back EMFs generated by the stator and execute step C4. Therefore, if it is determined in step C2 that the phase-locked loop output has not converged, then if commutation is required, reload the square wave to enter the square wave speed closed-loop control, and continue executing steps B and C within the new target commutation cycle. If commutation is not required, calculate the three back EMFs and acquire the corresponding electrical angles, thereby achieving multiple electrical angle detections of the rotor.

[0079] When the rotor is a magnet with a pair of opposite magnetic poles and the stator has three-phase motor windings, the calculation of the three-phase back electromotive force includes:

[0080] The three-phase motor windings are U-phase, V-phase, and W-phase windings. The terminal voltages of the three-phase motor windings are: U-phase terminal voltage VW. u Phase V terminal voltage V v and the voltage V at the W phase terminal w All of these can be obtained in real time. Specifically, the voltage loop equations for each phase column and the three-phase balance system are constructed based on the loop formed by the three-phase inverter circuit and the three-phase motor windings. Then, the voltages are obtained by calculating the voltages on the inductors, resistors, back EMFs, and MOSFETs in the bridge arms. The voltages of two phase terminals can be obtained by constructing the voltage loop equations for the corresponding phase column using the inductors, resistors, back EMFs, and MOSFETs in the bridge arms. Then, the three-phase balance system is obtained by combining the three back EMFs using the three-phase balance principle (i.e., adding the three back EMFs to get 0). Based on this, the voltage of one phase terminal in the three-phase motor windings, excluding the voltages of two phase terminals, can be calculated.

[0081] During the rotor's rotation in the stator magnetic field, the back electromotive force generated by the U-phase motor windings is represented as e. uThe back electromotive force generated by the V-phase motor winding is represented as e v The back electromotive force generated by the W-phase motor winding is represented as e. w It should be noted that each back electromotive force corresponds to an electrical angle, which is the electrical angle at which the rotor rotates to the corresponding sector. Specifically, the correspondence between the back electromotive force zero-crossing signal and the electrical angle is preset, for example, including positions at 30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees, or 330 degrees with respect to a specified direction; where the specified direction is a coordinate axis direction of the motor stator coordinate system.

[0082] For example, from the formula for the voltage at the non-conducting phase terminals of the motor (obtained by combining the voltage loop equations of each phase series and the three-phase balance system), it can be seen that the voltage at the U-phase terminals is... This is denoted as Formula 1; where the voltage used to drive the motor is the bus voltage V. dc Bus voltage V dc Half of it is the neutral point voltage V n neutral point voltage V n This represents the voltage at the common connection node of the three-phase motor windings.

[0083] Since neither the W-phase motor winding nor the V-phase motor winding is energized during step C, the V-phase winding is set to... dc =V v +V w This is denoted as Formula 2.

[0084] Then, by combining Formula 1 and Formula 2, we can obtain:

[0085] The back electromotive force generated by the U-phase motor windings Similarly, the back electromotive force generated by the V-phase motor windings can be obtained as follows: The back electromotive force generated by the W-phase motor winding

[0086] Step C4: The phase-locked loop (PLL) integrates the initial electrical frequency to obtain the phase difference to be adjusted. This phase difference can be understood as the electrical angle increment corresponding to each back electromotive force (EMF). At this point, a Hall sensor is not used for angular velocity detection, reducing design costs. The sum of the electrical angle corresponding to the currently detected zero-crossing back EMF signal and the phase difference to be adjusted is then input into the PLL to accelerate PLL convergence, generating a new electrical frequency and obtaining a corresponding new reference EMF. This new electrical frequency is then updated to the initial electrical frequency, achieving feedback adjustment of the initial electrical frequency. The new reference EMF is also updated to the reference EMF, achieving adjustment of the reference EMF using the electrical frequency. Then, step C2 is executed to determine whether the difference between the updated reference EMF and each of the currently generated back EMFs of the stator is within the preset EMF difference range, performing a new round of convergence detection. This overcomes the delay problem in PLL convergence.

[0087] Step C5: Determine that the electrical frequency output by the phase-locked loop converges to a target electrical frequency range. That is, when the phase-locked loop determines that the difference between the reference electromotive force and the opposite electromotive forces currently generated by the stator are all within the preset electromotive force difference range, the electrical frequency output by the phase-locked loop enters a target electrical frequency range, or even locks to a fixed electrical frequency. In this way, combined with the aforementioned steps, the phase synchronization characteristics of the phase-locked loop are used to control the rotor speed to tend to stabilize, reducing the step loss problem that exists when the rotor is started by the FOC sine wave.

[0088] Preferably, the electrical frequency is the number of electrical cycles the motor rotor completes in one second. Therefore, multiplying the electrical frequency by 60 and then dividing by the number of magnetic pole pairs of the rotor yields the motor speed.

[0089] Then, the phase compensation amount is determined based on the current output frequency of the phase-locked loop (PLL). This can be obtained by integration to obtain a phase difference, or it can be directly used as the electrical angle rotated within 1 second. Next, the absolute electrical angle of the rotor is determined based on the electrical angle corresponding to the phase compensation amount and the currently detected back EMF zero-crossing signal. Generally, the phase compensation amount is added to the electrical angle corresponding to the currently detected back EMF zero-crossing signal, and the sum is taken as the absolute electrical angle of the rotor. This absolute electrical angle of the rotor is then marked as the electrical angle estimated by the PLL. Finally, the absolute electrical angle of the rotor is set as the input electrical angle for FOC control, and FOC is used to adjust this input electrical angle. Since the methods of square wave control and FOC control differ significantly, and the current and voltage sampling points are inconsistent, steps C1 to C5 are used to overcome the problems of large torque load and easy loss of steps or stalling during the switching process from square wave control to FOC control in step B, thus reducing the difficulty and stability of FOC startup.

[0090] By employing the steps disclosed in the aforementioned embodiments, this application fully utilizes the characteristics of fast closed-loop convergence and large starting torque of square wave start-up to start the motor. After the rotor reaches a high speed in the first half of the target commutation cycle, this application does not apply a drive signal to the motor in the second half of the cycle. Then, between the zero-crossing point of the currently detected back EMF and the next commutation point, while the square wave is stopped, the phase-locked loop adjusts the real-time detected back EMF and its corresponding electrical angle until the output tends to stabilize. Based on the electrical angle corresponding to the zero-crossing signal of the back EMF, the phase-locked loop adjusts the electrical angle corresponding to each back EMF until the electrical frequency output by the phase-locked loop converges to a target electrical frequency range. Before commutation, the phase-locked loop's phase synchronization characteristics are used to perform multiple electrical angle detections on the rotor until a stable electrical frequency is identified. Then, it can directly switch to FOC sine wave control, using the electrical angle obtained by the phase-locked loop convergence for motor FOC control, thereby starting the sensorless closed-loop control of the FOC sine wave. The motor control method described above results in fewer sudden changes in electrical angle, less step loss, and strong real-time tracking. It can also converge phase differences, overcoming the problem that the sensorless FOC algorithm used in the prior art is easily affected by changes in external load torque when starting the motor.

[0091] Preferably, the electrical angles corresponding to the zero-crossing back EMF signal are 30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees, and 330 degrees within a 360-degree range, so that the predicted position and the electrical angles corresponding to the preset number of zero-crossing back EMF signals are located in 6 sectors; the preset number is the difference between the maximum number of different sectors allowed to be crossed by the rotor in one electrical cycle and the value 1; correspondingly, the premise of setting the electrical angles corresponding to the 6 zero-crossing back EMF signals of 30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees, and 330 degrees within a 360-degree range is that the rotor in the motor is a magnet with a pair of opposite magnetic poles (i.e., the rotor only has one N pole and one S pole), and the stator is equipped with three-phase motor windings, and the preset number is equal to 5.

[0092] The system comprises six sectors forming a 360-degree electrical angle interval, with each sector being a 60-degree electrical angle interval. A back-EMF zero-crossing signal is configured as a straight line passing through a back-EMF zero-crossing point within a corresponding sector. This straight line is the axis of symmetry within the corresponding sector, and the current commutation point and the next commutation point are symmetrical about this line within the corresponding sector. The back-EMF zero-crossing point represents the point where the polarity of the back-EMF changes within a corresponding sector; specifically, the point where the back-EMF changes from positive to negative or from negative to positive is called the aforementioned back-EMF zero-crossing point. A commutation point is located on the boundary between two adjacent sectors, and a commutation point forms a 30-degree electrical angle interval relative to the back-EMF zero-crossing points in the two adjacent sectors. Thus, during the rotation of a rotor with a pair of opposite magnetic poles within the magnetic field of the three-phase motor windings, it can sequentially traverse six sectors with different magnetic field directions, and detect six different back-EMF zero-crossing signals sequentially during one rotation.

[0093] It should be noted that the electrical angle is an important variable in motor vector control, as it affects the decoupling of the two orthogonal components of the current vector in the motor stator coordinate system. The current vector in the motor stator coordinate system originates from the phase voltages output to the motor by the three-phase inverter circuit. These phase voltages also reflect the motor's rotation angle, thus enabling the control of the rotational magnetic field within the motor by converting it into the motion trajectory of a voltage vector.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A motor control method, characterized in that, The motor control method includes: Step A: Align the rotor, then force the rotor to perform a commutation operation so that the rotor passes through multiple sectors in a predetermined commutation sequence without pre-determining the commutation time, and detects the back EMF zero-crossing signal during the forced commutation operation; if a preset number of the back EMF zero-crossing signals are detected consecutively in the predetermined commutation sequence, then proceed to Step B; wherein, no position sensor is installed inside the motor, and the motor includes a rotor; the preset number is the difference between the maximum number of different sectors that the rotor is allowed to pass through in one electrical cycle and the value 1; Step B: Perform closed-loop speed control on the motor, and after the rotor speed is accelerated to the preset starting speed, start the drive signal and detect the back EMF zero-crossing signal so that the rotor can determine the next commutation time based on the currently detected back EMF zero-crossing signal before commutation; then execute step C. Step C: Whenever a back EMF zero-crossing signal is detected, during the period from the detection time of the current back EMF zero-crossing signal to the next commutation time, stop applying the drive signal to the motor. At the same time, acquire the electrical angles corresponding to all back EMFs of the motor. Based on the electrical angles corresponding to the back EMF zero-crossing signals, adjust the electrical angles corresponding to each back EMF through a phase-locked loop until the electrical frequency output by the phase-locked loop converges to a target electrical frequency range. Then, use FOC to control the motor.

2. The motor control method according to claim 1, characterized in that, In step A, the method for aligning the rotor includes: Before the rotor starts rotating, a predetermined position is set to align the rotor to the predetermined position; Then, the motor windings in the motor are energized to drive the rotor to rotate from rest until the rotor rotates to the predetermined position, thus completing the alignment control of the rotor. In this motor, the magnetic poles of the rotor at a predetermined position are parallel to the magnetic field of the stator; the motor includes a stator, which includes multiphase motor windings; and the rotor is a magnet with at least one pair of opposite magnetic poles.

3. The motor control method according to claim 2, characterized in that, The rotor is a magnet with a pair of opposite magnetic poles; the stator includes three-phase motor windings to form six sectors with different magnetic field directions. The predicted position is a position at 30 degrees to the specified direction, or a position at 90 degrees to the specified direction, or a position at 150 degrees to the specified direction, or a position at 210 degrees to the specified direction, or a position at 270 degrees to the specified direction, or a position at 330 degrees to the specified direction. The arrangement order among the positions at 30 degrees to the specified direction, 90 degrees to the specified direction, 150 degrees to the specified direction, 210 degrees to the specified direction, 270 degrees to the specified direction, and 330 degrees to the specified direction is the predetermined commutation order; The specified direction is the direction of one coordinate axis in the motor stator coordinate system.

4. The motor control method according to claim 2, characterized in that, In step A, the method for controlling the rotor to perform forced commutation so that the rotor passes through multiple sectors in a predetermined commutation sequence without pre-determining the commutation time, and for detecting the back EMF zero-crossing signal during the forced commutation operation, includes: By energizing two phases of the motor windings and de-energizing the remaining phase of the motor windings, the three-phase motor windings generate a magnetic field force that changes according to a predetermined commutation sequence; wherein, the stator includes three-phase motor windings. Driven by the magnetic field force that changes according to a predetermined commutation sequence, the rotor starts from the predetermined position and rotates according to the predetermined commutation sequence and commutates at a preset forced frequency. During the rotation of the rotor, each time a back EMF zero-crossing signal is detected, it is counted once, and the location of the currently detected back EMF zero-crossing signal and its detection time are recorded. The location of the currently detected back EMF zero-crossing signal is represented by the current electrical angle of the rotor, so that each back EMF zero-crossing signal has a corresponding electrical angle.

5. The motor control method according to claim 4, characterized in that, The method for detecting the zero-crossing signal of the back electromotive force during forced commutation includes: The phase port of a non-energized motor winding is sampled to obtain the sampling terminal voltage. Determine whether the sampling terminal voltage is equal to half of the bus voltage. If yes, it is determined that a back EMF zero-crossing signal has been detected. Otherwise, it is determined that the back EMF zero-crossing signal has not been detected. Among them, the bus voltage is the power supply voltage used to drive the motor; the resistance of each phase motor winding is equal, and each phase motor winding is connected to an external three-phase inverter circuit through a phase port.

6. The motor control method according to claim 5, characterized in that, In step A, if a preset number of back EMF zero-crossing signals are continuously detected according to the predetermined commutation sequence, it is determined that the rotor has continuously rotated through a preset number of sectors according to the predetermined commutation sequence, and it is determined that the preset number of back EMF zero-crossing signals are generated sequentially in the corresponding sectors according to the predetermined commutation sequence.

7. The motor control method according to claim 6, characterized in that, Step A further includes: If no preset number of back EMF zero-crossing signals are detected according to the predetermined commutation sequence, the preset forced frequency is reduced and the reduced preset forced frequency is updated to the preset forced frequency, or the duty cycle of the MOS transistor used to turn on in the upper arm of the three-phase inverter circuit is increased to improve the output torque of the motor. Then, the rotor is controlled to perform a forced commutation operation again until a preset number of back EMF zero-crossing signals are continuously detected according to the predetermined commutation sequence.

8. The motor control method according to claim 2, characterized in that, In step B, the method for detecting the zero-crossing signal of the back electromotive force includes: The phase port of a non-energized motor winding is sampled to obtain the sampling terminal voltage. Then determine whether the sampling terminal voltage is equal to half of the bus voltage; When it is determined that the sampling terminal voltage is equal to half of the bus voltage, it is determined that the back EMF zero-crossing signal has been detected, and the current determination time is marked as the detection time of the back EMF zero-crossing signal. Then, based on the latest commutation time and the detection time of the current back EMF zero-crossing signal, the next commutation time is calculated, and the next commutation point is determined. The detection time of the current back EMF zero-crossing signal is located at the middle of the target commutation cycle; the time period from the latest commutation time to the next commutation time is the target commutation cycle. When it is determined that the sampling terminal voltage is not equal to half of the bus voltage, it is confirmed that no back EMF zero-crossing signal has been detected. Then, the rotor speed is adjusted to equal the preset starting speed by performing closed-loop speed control on the motor, so that the sampling terminal voltage is equal to half of the bus voltage.

9. The motor control method according to claim 8, characterized in that, In step B, during the period from the latest commutation time to the detection time of the currently detected back EMF zero-crossing signal, the following exists: The motor is subjected to closed-loop speed control. When the rotor speed is accelerated to the preset starting speed, square wave start is completed. After the square wave is started, the rotor speed is adjusted back to the preset starting speed; wherein, the drive signal is a square wave; During the closed-loop speed control of the motor, two phases of the motor windings are energized while the remaining phase of the motor windings is de-energized, in order to control the rotor to rotate within the magnetic field of the stator.

10. The motor control method according to claim 9, characterized in that, In step C, after detecting the back EMF zero-crossing signal, from the detection time of the currently detected back EMF zero-crossing signal to the next commutation time, the three-phase motor windings of the motor are stopped from being energized so that no square wave is output to the motor. At the same time, the three-phase back EMFs of the motor and their corresponding electrical angles are obtained. However, the rotor continues to rotate due to the inertial influence accumulated during the period from the latest commutation time to the detection time of the currently detected back EMF zero-crossing signal. The location of the currently detected back EMF zero-crossing signal is represented by the electrical angle of the rotor, so that each back EMF zero-crossing signal has a corresponding electrical angle.

11. The motor control method according to claim 10, characterized in that, In step C, during the period from the detection time of the currently detected back EMF zero-crossing signal to the next commutation time, the following steps also exist: Step C1: Generate an initial electrical frequency and obtain a reference electromotive force through a phase-locked loop; then execute step C2; wherein, the back electromotive force generated by one phase motor winding has a corresponding electrical angle; Step C2: Determine whether the difference between the reference electromotive force and the current opposite electromotive forces generated by the stator are all within the preset electromotive force difference range. If yes, proceed to step C5; otherwise, proceed to step C3. Herein, the current opposite electromotive forces generated by the stator are all back electromotive forces generated by the motor windings of the non-energized phase. Step C3: Determine whether the electrical angle corresponding to one of the current opposite electromotive forces generated by the stator is the electrical angle corresponding to the next commutation point. If yes, load the drive signal onto the motor and execute step B. Otherwise, obtain each of the current opposite electromotive forces generated by the stator and execute step C4. Step C4: Control the phase-locked loop to integrate the initial electrical frequency to obtain the phase difference to be adjusted, and then input the sum of the electrical angle corresponding to the currently detected back EMF zero-crossing signal and the phase difference to be adjusted into the phase-locked loop to generate a new electrical frequency and obtain a corresponding new reference EMF. Then update the new electrical frequency to the initial electrical frequency and update the new reference EMF to the reference EMF, and then execute step C2. Step C5: Determine that the electrical frequency output by the phase-locked loop converges to a target electrical frequency range. Then, determine the phase compensation amount based on the current electrical frequency output by the phase-locked loop. Next, determine the absolute electrical angle of the rotor based on the electrical angle corresponding to the phase compensation amount and the currently detected zero-crossing back EMF signal. Mark the absolute electrical angle of the rotor as the electrical angle estimated by the phase-locked loop. Then, set the absolute electrical angle of the rotor as the input electrical angle of the FOC control and use the FOC to adjust the input electrical angle.

12. The motor control method according to claim 10, characterized in that, The electrical angles corresponding to the zero-crossing back EMF signals are 30 degrees, 90 degrees, 150 degrees, 210 degrees, 270 degrees and 330 degrees within a 360-degree range, so that the known position and the electrical angles corresponding to the preset number of zero-crossing back EMF signals are located in 6 sectors. The six sectors form a 360-degree electrical angle interval, with each sector being a 60-degree electrical angle interval. The back EMF zero-crossing signal is configured as a straight line passing through a back EMF zero-crossing point within a corresponding sector. This straight line is the axis of symmetry within the corresponding sector, and the current commutation point and the next commutation point are symmetrical about this straight line within the corresponding sector. Among them, the zero-crossing point of the back EMF is used to indicate the point where the polarity of the back EMF changes within a sector; the commutation point is located on the boundary between two adjacent sectors, and the commutation point forms an electrical angle interval of 30 degrees with respect to the zero-crossing point of the back EMF in the two adjacent sectors.

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