A brushless direct current motor speed control method, device, storage medium and motor

Abstract

The application provides a brushless direct current motor rotating speed control method and device, a storage medium and a motor, and relates to the technical field of motor control. The method comprises the following steps: acquiring three-phase terminal voltage and bus voltage of the brushless direct current motor, detecting back electromotive force zero-crossing events according to the three-phase terminal voltage and the bus voltage, and generating a zero-crossing signal; calculating actual rotating speed according to the zero-crossing signal, and dynamically adjusting commutation delay time by using the difference between target rotating speed and the actual rotating speed; after detecting the zero-crossing event, performing commutation operation after the adjusted commutation delay time, and when the target rotating speed is greater than the rated rotating speed, making the commutation delay time less than the time corresponding to the reference delay phase. The application can realize accurate rotating speed closed-loop control and weak magnetic speed-up without using a Hall sensor or a current sensor, reduces hardware cost and improves system reliability.

Description

Technical Field

[0001] This invention relates to the field of motor control technology, specifically to a method, device, storage medium, and motor for controlling the speed of a brushless DC motor. Background Technology

[0002] Brushless DC motors, due to their high efficiency, high power density, and long lifespan, are widely used in new energy vehicles (such as pure electric vehicles, hybrid electric vehicles, and fuel cell vehicles), industrial drives, and home appliances. To achieve smooth operation and precise speed control, current technologies typically require real-time rotor position detection to determine commutation timing. Mainstream solutions rely on hardware sensors to acquire rotor position information, such as using Hall effect sensors to directly detect magnetic pole positions or using current sensors to collect phase current signals and combine them with mathematical models to estimate rotor angles. In these solutions, the control system calculates the commutation time interval based on sensor feedback signals and adjusts the wave generation sequence according to the target speed to drive the motor. Especially when exceeding the rated speed, the conventional approach is to calculate the current lead angle using phase information acquired by sensors, and then implement field weakening control to extend the speed range.

[0003] However, existing brushless DC motor control technologies have long suffered from system complexity and cost issues due to reliance on additional hardware sensors. The requirement to configure Hall elements or current detection circuits not only increases the motor's size and wiring complexity but also introduces potential failure points, reducing system reliability in harsh environments. Furthermore, sensor signals are susceptible to electromagnetic interference, potentially leading to position judgment errors and thus limiting the motor's stable operation at high speeds. Achieving high-precision closed-loop speed control and effective field weakening for speed enhancement without the need for dedicated position or current sensors has remained a pressing technical challenge in this field. Summary of the Invention

[0004] In view of this, embodiments of the present invention provide a method, device, storage medium and motor for controlling the speed of a brushless DC motor, so as to realize closed-loop control of the speed of a brushless DC motor and field weakening speed increase under sensorless conditions.

[0005] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0006] A method for controlling the speed of a brushless DC motor, comprising:

[0007] Obtain the three-phase terminal voltage and bus voltage of the brushless DC motor;

[0008] Based on the three-phase terminal voltage and bus voltage, the zero-crossing event of the back electromotive force in each phase winding is detected, and a zero-crossing signal is generated.

[0009] The actual speed of the brushless DC motor is calculated based on the zero-crossing signal.

[0010] The commutation delay time is dynamically adjusted based on the difference between the target speed and the actual speed, so that the actual speed of the motor reaches the target speed.

[0011] Based on the zero-crossing signal, after each zero-crossing event is detected, a commutation operation is performed with a delayed adjusted commutation delay time.

[0012] Specifically, when the target speed is greater than the rated speed, the dynamic adjustment makes the commutation delay time less than the commutation delay time corresponding to the reference delay phase.

[0013] Optionally, in the above-mentioned brushless DC motor speed control method, the zero-crossing event of the back electromotive force in each phase winding is detected based on the three-phase terminal voltage and bus voltage, and the zero-crossing signal is generated by including:

[0014] The neutral point voltage is determined based on the bus voltage, wherein the neutral point voltage is half of the bus voltage.

[0015] Based on the comparison results between the floating phase voltage and the neutral point voltage in the three-phase terminal voltage, and the comparison results between the conducting phase voltage and the bus voltage in the three-phase terminal voltage, it is determined whether a zero-crossing event of back electromotive force has occurred, and a zero-crossing signal is generated.

[0016] Optionally, in the above-mentioned brushless DC motor speed control method, the step of determining whether a zero-crossing event of back electromotive force occurs based on the comparison result of the floating phase terminal voltage and the neutral point voltage in the three-phase terminal voltage, and the comparison result of the conducting phase terminal voltage and the bus voltage in the three-phase terminal voltage includes:

[0017] Determine whether the target condition is met. If the target condition is met, determine that a zero-crossing event of the back electromotive force has occurred.

[0018] The target conditions include:

[0019] The voltage of the first conducting phase in the three-phase terminal voltage is not less than the product of the bus voltage and the first threshold.

[0020] The voltage of the second conducting phase in the three-phase terminal voltage is not greater than the product of the bus voltage and the second threshold, wherein the first threshold is greater than 0.5 and greater than the second threshold.

[0021] The difference between the floating phase voltage and the neutral point voltage in the three-phase terminal voltage is greater than the third threshold.

[0022] When the suspended phase is phase A, the first conducting phase is phase B and the second conducting phase is phase C; when the suspended phase is phase B, the first conducting phase is phase C and the second conducting phase is phase B; when the suspended phase is phase C, the first conducting phase is phase A and the second conducting phase is phase B.

[0023] Optionally, in the above brushless DC motor speed control method, calculating the actual speed of the brushless DC motor based on the zero-crossing signal includes:

[0024] The number of zero-crossings of the zero-crossing signal within a cycle is counted, and the actual rotational speed is calculated based on the number of pole pairs, carrier frequency period, and the number of zero-crossings of the brushless DC motor.

[0025] Optionally, in the above-mentioned brushless DC motor speed control method, the dynamic adjustment of the commutation delay time includes:

[0026] The difference between the target speed and the actual speed is input into the speed closed-loop regulator;

[0027] The speed closed-loop regulator outputs a delayed phase compensation amount based on the difference;

[0028] The commutation delay time is dynamically adjusted using the aforementioned delay phase compensation amount.

[0029] Optionally, in the above-mentioned brushless DC motor speed control method, the dynamic adjustment of the commutation delay time using the delayed phase compensation amount includes:

[0030] The commutation delay time is dynamically adjusted based on the formula t2=cnt×(fac1-fac2)×f1;

[0031] in, t2 is the adjusted commutation delay time, cnt is the number of zero-crossings of the zero-crossing signal within one cycle, and f1 is the sampling period of the terminal voltage. fac2 is the reference delay phase, and fac2 is the delay phase compensation amount.

[0032] Optionally, in the above brushless DC motor speed control method, when the target speed is less than or equal to the rated speed, the adjustment amount output by the speed closed-loop regulator is zero, so that the commutation delay time is maintained as the commutation delay time corresponding to the reference delay phase.

[0033] A control device for a brushless DC motor, comprising:

[0034] The voltage sampling unit is used to acquire the three-phase terminal voltage and bus voltage of the brushless DC motor.

[0035] The zero-crossing detection unit is used to detect the zero-crossing event of the back electromotive force in each phase winding based on the three-phase terminal voltage and the bus voltage, and generate a zero-crossing signal.

[0036] A speed estimation unit is used to calculate the actual speed of the brushless DC motor based on the zero-crossing signal.

[0037] A speed closed-loop control unit is used to dynamically adjust the commutation delay time based on the difference between the target speed and the actual speed, so that the actual speed of the motor reaches the target speed.

[0038] A commutation control unit is configured to perform a commutation operation after a delayed commutation delay time following each detection of a zero-crossing event, based on the zero-crossing signal.

[0039] Specifically, when the target speed is greater than the rated speed, the dynamic adjustment makes the commutation delay time less than the commutation delay time corresponding to the reference delay phase.

[0040] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any of the above-described brushless DC motor speed control methods.

[0041] A brushless DC motor, comprising:

[0042] At least one processor and a memory connected to the processor, wherein:

[0043] The memory is used to store computer programs;

[0044] The processor is used to execute the computer program so that the brushless DC motor can implement any of the above-described brushless DC motor speed control methods.

[0045] Based on the above technical solution, the brushless DC motor speed control provided in this embodiment of the invention acquires the three-phase terminal voltage and bus voltage of the brushless DC motor, and generates a zero-crossing signal by detecting a zero-crossing event of the back electromotive force. The actual speed is calculated based on the zero-crossing signal, and the commutation delay time is dynamically adjusted using the difference between the target speed and the actual speed. After detecting a zero-crossing event, the commutation operation is performed after a delay of the adjusted commutation delay time, and when the target speed is greater than the rated speed, the commutation delay time is made less than the time corresponding to the reference delay phase. This application can achieve accurate closed-loop speed control and field weakening acceleration without using Hall sensors or current sensors, reducing hardware costs and improving system reliability. This control scheme is particularly suitable for new energy vehicle drive systems, and can effectively meet the requirements of pure electric, hybrid, and fuel cell vehicles for high-efficiency operation of motors over a wide speed range. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0047] Figure 1 A flowchart illustrating the brushless DC motor speed control method provided in this application embodiment;

[0048] Figure 2 This is a schematic diagram of the delay angle before speed adjustment;

[0049] Figure 3 This is a schematic diagram of the delay angle after speed adjustment;

[0050] Figure 4 A flowchart illustrating a brushless DC motor speed control method according to another embodiment of this application;

[0051] Figure 5 A schematic diagram of a conduction scenario for the star winding of a brushless DC motor;

[0052] Figure 6 A schematic diagram illustrating the six-step commutation principle of a brushless DC motor;

[0053] Figure 7 This is a schematic diagram of the delay time adjustment process;

[0054] Figure 8 This is a schematic diagram of the structure of the brushless DC motor speed control device provided in the embodiments of this application. Detailed Implementation

[0055] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] like Figure 1 As shown, the brushless DC motor speed control method provided in this application embodiment includes:

[0057] Step S101: Obtain the three-phase terminal voltage and bus voltage of the brushless DC motor.

[0058] The three-phase terminal voltage and bus voltage of a brushless DC motor are acquired through a voltage sampling circuit in conjunction with an analog-to-digital converter (ADC). The three-phase terminal voltage refers to the real-time potential of the motor's A, B, and C phase windings relative to the negative terminal of the DC bus, reflecting the conduction state and back electromotive force changes of each phase winding. The bus voltage refers to the power supply voltage applied to the DC side of the motor inverter, determining the winding voltage amplitude. To reduce switching noise interference, the ADC sampling time can be aligned with the midpoint of the Pulse Width Modulation (PWM) carrier wave; that is, when the midpoint of the PWM carrier wave is detected, the three-phase terminal voltage and bus voltage of the brushless DC motor are obtained through ADC sampling. When acquiring the three-phase terminal voltage and bus voltage of the brushless DC motor, a resistor divider network can be used to condition the high-voltage signal into the ADC range, or a differential sampling circuit can be used to obtain the phase-to-phase voltage and then convert it to obtain the terminal voltage. This voltage data serves as the basis for reconstructing the internal electrical state of the motor, providing input for subsequent rotor position detection.

[0059] Step S102: Detect the zero-crossing event of the back electromotive force in each phase winding based on the three-phase terminal voltage and bus voltage, and generate a zero-crossing signal.

[0060] Based on the acquired three-phase terminal voltages and bus voltage, zero-crossing events are detected using the back electromotive force (EMF) characteristics induced in the suspended phases of the three phases. First, a virtual neutral point voltage is reconstructed based on the bus voltage; ideally, the virtual neutral point voltage is equal to half the bus voltage. Then, the difference between the suspended phase terminal voltage and the virtual neutral point voltage is compared, and a comprehensive judgment is made in conjunction with the constraints of the conducting phase terminal voltage and the preset bus voltage. When the difference between the suspended phase terminal voltage and the virtual neutral point voltage meets a preset threshold, and the conducting phase voltage state conforms to the six-step commutation logic, a back EMF zero-crossing event is determined to have occurred, and a zero-crossing signal in the form of a digital pulse is generated. This zero-crossing signal can be directly triggered by a hardware comparator or generated by a microprocessor through software algorithm calculation of a post-set flag. This step realizes the conversion from analog voltage signals to discrete position signals, establishing a time reference for speed estimation.

[0061] Step S103: Calculate the actual speed of the brushless DC motor based on the zero-crossing signal.

[0062] By utilizing the fixed correspondence between zero-crossing signals and rotor rotation angles, the zero-crossing frequency is statistically analyzed to estimate the motor speed. Within a statistical period, the number of captured zero-crossing signal pulses is accumulated; this number represents the number of electrical angle cycles the rotor has traversed. Combining this with the motor pole pair parameter, the electrical angle is converted to a mechanical angle, and the actual rotational angular velocity is calculated using the statistical duration determined by the carrier frequency period. For example, the actual speed can be expressed as the product of the number of zero-crossings and a constant factor divided by the product of the statistical time and the number of pole pairs; or, the instantaneous speed can be estimated by measuring the time interval between two consecutive zero-crossing signals and taking its reciprocal. Thus, the actual speed is obtained without relying on Hall effect sensors, serving as the feedback variable for closed-loop control.

[0063] Step S104: Based on the difference between the target speed and the actual speed, dynamically adjust the commutation delay time so that the actual speed of the motor reaches the target speed.

[0064] A closed-loop speed control circuit is constructed, dynamically adjusting the commutation delay time based on the deviation between the target speed and the actual speed. The commutation delay time refers to the time interval from detecting the zero-crossing of the back EMF to executing the commutation action of the switching transistor, corresponding to a specific commutation delay phase. The system calculates the speed deviation and inputs it to the speed closed-loop regulator (such as a proportional-integral (PI) controller, fuzzy controller, or PID controller), outputting an adjustment coefficient or compensation amount to correct the commutation delay time. When the target speed exceeds the rated speed, the regulator outputs a command to shorten the commutation delay time, making it less than the default value corresponding to the reference delay phase, achieving early commutation. At this time, the stator magnetic field generates a component on the negative half-axis of the rotor magnetic field to weaken the main magnetic field, thereby increasing the speed under the same voltage limit. This dynamic adjustment mechanism enables the motor to maintain the optimal commutation angle in the low-speed range and achieve field weakening and speed increase in the high-speed range, ensuring rapid tracking of the target speed and maintaining stable operation.

[0065] Step S105: Based on the zero-crossing signal, after each zero-crossing event is detected, perform the commutation operation after a delayed commutation delay time.

[0066] In response to a zero-crossing signal, a timer or counter is started to perform delay control, and commutation is performed after the delay ends. When a zero-crossing signal is captured, the system does not immediately commutate, but instead loads the commutation delay time dynamically adjusted in step S104 as a count value. During the delay, the current conducting phase sequence is maintained, waiting for the relative positions of the stator magnetic field and the rotor magnetic field to adjust to the optimal angle. After the timing ends, a commutation interruption or logic switch is triggered, and the current power switch is turned off and the next phase power switch is turned on according to a six-step commutation sequence or other commutation sequence, changing the direction of the stator winding current. For example, the delay count value can be loaded through a microprocessor timer capture unit, and the commutation service program can be executed after overflow; or a Complex Programmable Logic Device (CPLD) / Field Programmable Gate Array (FPGA) can be used to implement the delay and logic switching.

[0067] In one specific embodiment, due to the use of six-step commutation control, such as Figure 2 As shown, the rotor magnetomotive force Fr differs from the stator magnetomotive force Fs by 60°. When the rotor rotates 30° to the commutation point of 30°, the stator-rotor angle is 90°. At this point, the magnetic poles form the maximum tangential force with the axis of the next winding, generating the maximum torque. This application reduces the commutation delay time, thereby reducing the delay angle to [a specific value]. Figure 3 As shown in the figure, at 20°, the stator magnetic field has a component on the negative half-axis of the rotor magnetic field, which reduces the rotor magnetic field to achieve the effect of magnetic weakening and speed increase.

[0068] The aforementioned technology achieves high-precision speed control and field weakening acceleration of brushless DC motors without position sensors, making it particularly suitable for drive motor control in new energy vehicles (including pure electric vehicles, hybrid electric vehicles, and fuel cell vehicles). Specifically, by logically analyzing the voltage values ​​of the three-phase terminal voltage and the bus voltage, the rotor position is obtained by capturing the zero-crossing event of the back electromotive force. Based on the zero-crossing signal, the actual speed is statistically calculated. The speed closed-loop regulator dynamically adjusts the commutation delay time according to the speed deviation, maintaining the optimal commutation angle below the rated speed and achieving early commutation and demagnetization effects above the rated speed by shortening the delay time. This solution reduces hardware costs and system complexity, significantly improves the motor's operating performance and response speed over a wide speed range, and meets the requirements of new energy vehicles for high reliability, electromagnetic interference resistance, and low cost of the drive system. It is applicable to various power architectures such as pure electric drive, hybrid electric drive, and fuel cell drive.

[0069] One possible implementation is, such as Figure 4 The diagram shown is a flowchart of a brushless DC motor speed control method provided in this application, which detects the zero-crossing event of back electromotive force based on the three-phase terminal voltage and the bus voltage and generates a zero-crossing signal.

[0070] Step S401: Determine the neutral point voltage based on the bus voltage. The neutral point voltage is half of the bus voltage.

[0071] During the research and development process, the applicant verified the relationship between the neutral point voltage and the bus voltage. The specific verification process is as follows:

[0072] First, by reconstructing the virtual neutral point, such as Figure 5 Taking the conduction of phase B+A and the zero crossing of phase C as an example, the neutral point voltage u is constructed. N and the voltage at the C-phase terminal of the floating phase :

[0073]

[0074]

[0075] Since ia = ib, we get -

[0076] And because + ,

[0077] ,have to

[0078] in, Bus voltage , , The three back electromotive forces are A, B, and C. , , Let R be the phase current, B be the phase current, and C be the phase current, R be the phase winding resistance, and L be the phase winding inductance. From the above formulas, it can be deduced that the terminal voltage of the floating phase (phase C) is... This is equivalent to a fixed DC bias (0.5 × 10⁻⁶). Add a factor related to the back electromotive force. The proportional AC component (1.5×) Specifically, the above formula is first based on Kirchhoff's voltage law, establishing the terminal voltage equation under the specific commutation state of B+A being on and C phase being floating. The current term is then eliminated by simultaneously solving the equation and utilizing the symmetry of the three-phase windings. =- The neutral point voltage expression is obtained. Furthermore, the sum of the three back electromotive forces is zero. + + Based on the physical constraint of (=0), the linear relationship between the voltage at the floating phase terminal and the back electromotive force is further derived. This relationship proves that the voltage at the floating phase terminals... It is not a random physical quantity, but rather a back electromotive force. The "amplification + translation" differs from the "bus voltage" by only a fixed DC bias (0.5 times the bus voltage) and a fixed scaling factor (1.5 times). When the back electromotive force... Zero crossing (i.e.) When =0), It must equal 0.5×UDCB, which means that "the voltage at the floating phase terminal crosses half of the bus voltage" and "the back electromotive force crosses zero" are mathematically equivalent. Therefore, in engineering, it is only necessary to obtain the voltage at the floating phase terminal by sampling with an ADC and determine whether it is close to 0.5×UDCB to accurately identify the zero-crossing event, without having to directly measure the unobtainable back electromotive force.

[0079] Based on the above arguments, when executing the back EMF zero-crossing detection logic, a virtual neutral point voltage is first constructed as a reference. This neutral point voltage is not obtained through real-time measurement of the physical resistance network, but is a theoretical reference value determined based on the circuit topology characteristics of the brushless DC motor in the two-phase conduction mode. During the six-step commutation operation of the brushless DC motor, at each moment, two phase windings are connected in series and conduct (conducting phase), while the third phase winding is in a floating state (floating phase). Ignoring phase resistance voltage drop and assuming symmetrical parameters of the three-phase windings, the center potential of the conducting loop is approximately equal to half of the DC bus voltage in steady state. Based on this principle, the neutral point voltage is determined by acquiring the bus voltage and halving its value, i.e., calculated. As a reference threshold for voltage comparison, This is the bus voltage.

[0080] Bus voltage is typically acquired via a voltage divider network in conjunction with an analog-to-digital converter sampling stage. To avoid high-frequency noise interference from switching operations, the sampling time is usually configured at the midpoint of the pulse width modulation carrier cycle to obtain a relatively stable voltage value. The purpose of determining this neutral point voltage is to provide a stable benchmark for subsequently determining when the floating back electromotive force crosses zero, enabling the system to accurately capture the phase change of the back electromotive force without introducing additional hardware neutral point extraction.

[0081] Step S402: Based on the comparison results of the floating phase voltage and the neutral point voltage in the three-phase terminal voltage, and the comparison results of the conducting phase voltage and the bus voltage in the three-phase terminal voltage, determine whether a zero-crossing event of back electromotive force has occurred, and generate a zero-crossing signal.

[0082] After establishing the neutral point voltage as a reference, the real-time state of the three-phase terminal voltages is further analyzed logically to identify the zero-crossing moment of the back electromotive force. This process employs dual judgment conditions: firstly, monitoring the relative relationship between the voltage at the floating phase terminal and the neutral point voltage; and secondly, monitoring the relative relationship between the voltage at the conducting phase terminal and the bus voltage.

[0083] When a brushless DC motor is running, the three-phase windings alternately switch between conducting and floating states. For the phase winding currently in a floating state, its terminal voltage is mainly determined by the induced back electromotive force (EMF). The polarity change of the back EMF is monitored by comparing the magnitude of the floating phase terminal voltage with the neutral point voltage determined in the preceding steps in real time. When the floating phase terminal voltage crosses from above the neutral point voltage to below the neutral point voltage, or vice versa, and the difference falls within a preset error bandwidth, it is preliminarily determined that a physical event of the back EMF of that phase winding crossing zero has occurred; that is, a zero-crossing event is detected, and a zero-crossing signal is generated.

[0084] Meanwhile, to eliminate false signals caused by non-ideal factors, a verification logic for the conduction phase state is introduced. For two-phase windings currently in conduction, their terminal voltages should theoretically approximate the positive and negative potentials of the power supply, or exhibit line voltage characteristics consistent with the current conduction logic. The bus voltage is the expected voltage difference that should exist between the conduction phases under the current conduction mode. The real-time acquired terminal voltage of the conduction phase is compared with the bus voltage to determine whether the voltage state of the conduction phase conforms to the expected conduction logic. Only when the comparison result between the voltage of the floating phase and the neutral point voltage indicates that the back EMF has reversed polarity, and the comparison result between the voltage of the conduction phase and the bus voltage indicates that the current conduction state is normal, is a valid back EMF zero-crossing event finally confirmed, and a zero-crossing signal is generated and output.

[0085] In another optional embodiment, the process of determining the zero-crossing event of back EMF based on the comparison result of the voltages of the floating phase and the conducting phase specifically includes: determining whether the target conditions are met; when the target conditions are met, determining that a zero-crossing event of back EMF has occurred; the target conditions include: the voltage of the first conducting phase in the three-phase terminal voltage is not less than the product of the bus voltage and a first threshold; the voltage of the second conducting phase in the three-phase terminal voltage is not greater than the product of the bus voltage and a second threshold, wherein the first threshold is greater than 0.5 and greater than the second threshold; the difference between the voltage of the floating phase and the neutral point voltage in the three-phase terminal voltage is greater than a third threshold; when the floating phase is phase A, the first conducting phase is phase B and the second conducting phase is phase C; when the floating phase is phase B, the first conducting phase is phase C and the second conducting phase is phase B; when the floating phase is phase C, the first conducting phase is phase A and the second conducting phase is phase B.

[0086] For example, see Figure 6Taking the zero-crossing point of phase A at 180° as an example, the specific logic for judging the zero-crossing event is as follows: (Phase B terminal voltage ≥ bus voltage × first threshold) && (Phase C terminal voltage ≤ bus voltage × second threshold) && (Phase A terminal voltage - 0.5 × bus voltage ≤ third threshold).

[0087] The above process monitors the three-phase terminal voltage status in real time and identifies the zero-crossing moment of the back electromotive force based on preset logical judgment criteria. The target condition consists of multiple sub-conditions, which are logically ANDed with each other. That is, all voltage threshold constraints must be satisfied simultaneously to be confirmed as a valid zero-crossing event, thereby effectively filtering out false triggers caused by signal noise or transient fluctuations in the circuit.

[0088] Among the above target conditions, the condition that the voltage at the first conducting phase terminal must be no less than the product of the bus voltage and the first threshold is included. The voltage at the first conducting phase terminal refers to the winding terminal voltage value currently in forward conduction or about to complete conduction. The first threshold is a pre-set proportional coefficient used to define the characteristic range of the conducting phase voltage in the steady-state or rising phase. Setting the first threshold to a value greater than 0.5 (e.g., any value between 0.8 and 0.95) ensures that only when the voltage at the first conducting phase terminal is higher than half the bus voltage and has a certain margin is the phase determined to have the expected voltage amplitude characteristics, thus eliminating the possibility that the voltage is in a critical ambiguity range.

[0089] Among the above target conditions, the condition that the voltage at the second conducting phase terminal must not exceed the product of the bus voltage and the second threshold, wherein the first threshold is greater than 0.5 and greater than the second threshold, is also included. The voltage at the second conducting phase terminal refers to the voltage value at the terminal of another phase winding that forms a loop with the first conducting phase and is currently in a freewheeling or reverse voltage state. The second threshold is also a pre-set proportional coefficient, its value being less than the first threshold and typically less than 0.5 (e.g., any value from 0.05 to 0.2). This condition aims to limit the voltage level of the second conducting phase to a relatively low level, reflecting the physical state of current freewheeling or energy release during commutation. By setting the first threshold to be greater than 0.5 and greater than the second threshold, a clear voltage window is constructed, requiring the first conducting phase voltage to be sufficiently high and the second conducting phase voltage to be sufficiently low. This significant voltage contrast characteristic is typical of a specific sector during the normal six-step commutation process of a brushless DC motor, thereby greatly improving the robustness of identification.

[0090] Among the above target conditions, the following condition must be met: the difference between the floating phase voltage and the neutral point voltage must be greater than the third threshold. The floating phase voltage refers to the voltage at the winding terminal that is currently not conducting and is in a high-impedance state, directly reflecting the change in back electromotive force. The neutral point voltage is usually obtained by voltage division of the DC bus voltage (ideally half of the bus voltage). The third threshold serves as the threshold for determining the voltage jump variable at the moment of zero crossing, and its setting is based on factors including the noise level of the signal conditioning circuit, the quantization error of the analog-to-digital conversion, and the slope of the motor's back electromotive force. For example, the third threshold can be set as a fixed value between 1% and 5% of the bus voltage, or it can be dynamically adjusted according to the rotational speed. When the floating phase voltage crosses the neutral point voltage and exceeds the third threshold, it indicates that the voltage signal has completed an actual logical flip rather than a simple jitter, thus locking in the true zero crossing point.

[0091] The voltage comparison operation described above depends on the current specific combination of conducting phases. Based on the currently detected floating phase identifier, the corresponding first and second conducting phases are automatically locked through table lookup or logical operations: when the floating phase is phase A, the first conducting phase is phase B, and the second conducting phase is phase C; when the floating phase is phase B, the first conducting phase is phase C, and the second conducting phase is phase B; when the floating phase is phase C, the first conducting phase is phase A, and the second conducting phase is phase B. This mapping relationship follows the conduction logic of a three-phase bridge inverter circuit for a brushless DC motor, ensuring that the voltage comparison operates on the correct phase.

[0092] In another optional embodiment, this application also provides a specific implementation method for calculating the actual speed of a brushless DC motor based on the zero-crossing signal. Specifically: the number of zero-crossings of the zero-crossing signal within one cycle is counted, and the actual speed is calculated based on the number of pole pairs, carrier frequency period, and number of zero-crossings of the brushless DC motor. The number of zero-crossings is a count value obtained by accumulating the zero-crossing signals generated in the aforementioned steps. Its physical meaning represents the frequency at which the back electromotive force waveform of the motor crosses the neutral point voltage within a unit statistical cycle. Since the back electromotive force of each of the three phase windings will have two zero-crossing points for each electrical angle cycle during the operation of the brushless DC motor, a total of 6 zero-crossing events are generated. Therefore, there is a definite mathematical correspondence between the number of zero-crossings and the electrical angular frequency of the motor. Within a set statistical cycle, the number of zero-crossings in integer form can be obtained by accumulating the rising or falling edges of the zero-crossing signal using an internal counter. The number of pole pairs, as an inherent structural parameter of the motor, refers to the number of permanent magnet pole pairs in the motor rotor, which determines the proportional relationship between the electrical angle and the mechanical angle of the motor. The carrier frequency period refers to the period of the pulse width modulation signal used to drive power switching devices in a motor control system. Its reciprocal is the carrier frequency, and it is also the reference time unit for the terminal voltage sampling period. In practical calculations, the carrier frequency period is used to convert the discrete statistical zero-crossing count into a continuous time quantity, thereby establishing a correlation between rotational speed and time. For example, the carrier frequency period can be a specific value such as 100 microseconds or 50 microseconds, and this parameter is determined by the hardware clock frequency of the control system and the preset PWM frequency.

[0093] Based on the above parameters, the calculation logic for the rotational speed is as follows: First, combining the statistically obtained zero-crossing count and the known carrier frequency period, the actual operating time of the current electrical cycle is calculated; then, the electrical angular velocity is converted into mechanical angular velocity using the number of pole pairs, and finally, the mechanical rotational speed of the motor, i.e., the actual rotational speed, is calculated. This calculation process can be formally expressed as the following rotational speed calculation formula:

[0094]

[0095] In the formula, This represents the calculated actual speed of the brushless DC motor, in revolutions per minute (r / min). It represents the carrier frequency, which is the reciprocal of the carrier frequency period, and its unit is Hertz; This indicates the number of pole pairs in a brushless DC motor. This represents the number of zero-crossings counted within a statistical period.

[0096] Using the above formula, the actual motor speed can be accurately calculated using only the back EMF zero-crossing signal, without the need for additional Hall sensors or resolvers. The calculated actual speed is then fed back to the speed closed-loop control system and compared with the set target speed to dynamically adjust the commutation delay time, thereby achieving precise control of the motor speed.

[0097] In another embodiment, this application also provides a process for determining the reference commutation delay time corresponding to the reference delay phase. This process includes: acquiring the reference delay phase, and determining the commutation delay time corresponding to the reference delay phase based on the reference delay phase and the sampling period of the terminal voltage. The reference delay phase characterizes the electrical angle value by which the desired commutation moment lags behind the zero-crossing point of the back electromotive force during the operation of a brushless DC motor. This value directly determines the relative positional relationship between the stator magnetic field and the rotor magnetic field, thereby affecting the motor's output torque and operating efficiency. The setting of this parameter is typically based on the number of pole pairs of the motor, the desired electromagnetic characteristics, and a predefined commutation strategy. For example, in a conventional six-step commutation logic, the reference delay phase can be set to 30 electrical degrees to ensure that the stator magnetomotive force and the rotor magnetomotive force maintain a specific phase difference at the moment of commutation. The specific calculation formula is: t1 = cnt × fac1 × f1. Where t1 is the reference commutation delay time, and cnt is the number of zero-crossings of the zero-crossing signal within one cycle. The reference delay phase is, for example, 30°, and f1 is the sampling period of the terminal voltage. That is, when there is no target speed input, or when the target speed is less than the rated speed, a commutation operation can be performed after a reference commutation delay time is delayed each time a zero-crossing event is detected, based on the zero-crossing signal.

[0098] In yet another embodiment, see Figure 7 The specific process of dynamically adjusting the commutation delay time provided in this application embodiment includes:

[0099] Step S701: Input the difference between the target speed and the actual speed into the speed closed-loop regulator.

[0100] Based on the target speed and actual speed of the brushless DC motor obtained from the aforementioned steps, the difference between the two is calculated to obtain the speed error reflecting the deviation between the current operating state and the desired state. This speed error is sent as an input signal to the speed closed-loop regulator. As the core algorithm module for achieving precise speed control, the speed closed-loop regulator can essentially employ a proportional-integral-derivative controller or its variants, such as a proportional-integral (PI) control strategy.

[0101] Step S702: The speed closed-loop regulator outputs a delayed phase compensation amount based on the difference.

[0102] After receiving the aforementioned speed error, the speed closed-loop regulator performs calculations according to a preset control algorithm and outputs a delay phase compensation amount to correct the reference commutation delay time. In this process, the speed closed-loop regulator first calculates the speed error. ,in This is the current actual speed. The target speed is then set. Subsequently, the speed closed-loop regulator calculates the delay phase compensation amount based on this error. , To prevent the system from going out of control, the calculated... Limited to 0 to between.

[0103] Step S703: Dynamically adjust the commutation delay time using the delay phase compensation amount.

[0104] Specifically, the commutation delay time is dynamically adjusted based on the formula t2=cnt×(fac1-fac2)×f1;

[0105] in, t2 is the adjusted commutation delay time, cnt is the number of zero-crossings of the zero-crossing signal within one cycle, and f1 is the sampling period of the terminal voltage. fac2 is the reference delay phase, and fac2 is the delay phase compensation amount.

[0106] The formula above is used to calculate This is the delay time ultimately used to trigger the commutation operation. When the target speed is greater than the rated speed, the delay phase compensation amount output by the speed closed-loop regulator prompts... Less than the reference commutation delay time This allows for early commutation. This early commutation causes the stator magnetic field vector to lead the rotor magnetic field vector, producing a demagnetizing effect and achieving field weakening speed control. This enables the motor to exceed the rated speed limit under the same bus voltage and reach a higher target speed.

[0107] In an optional embodiment, this application also provides a control strategy whereby the adjustment amount output by the speed closed-loop regulator is zero or constant when the target speed is less than or equal to the rated speed, so that the commutation delay time is maintained at the commutation delay time corresponding to the reference delay phase. After obtaining the actual speed of the brushless DC motor and the set target speed, the current operating speed range is first determined. By comparing the target speed with the rated speed in real time, if it is determined that the target speed is less than or equal to the rated speed, the control system enters the standard commutation mode. In this mode, the delay phase compensation amount output by the speed closed-loop regulator is configured to zero. At this time, the calculated commutation delay time will be strictly maintained at the standard value t1 corresponding to the reference delay phase. This reference delay phase is usually set to the angle that can generate maximum torque, such as 30° electrical angle. Accordingly, in the operating range from low speed to rated speed, the stator magnetic field vector and the rotor magnetic field vector maintain the optimal relative position relationship, thereby ensuring that the motor outputs maximum torque. This control logic effectively avoids the problem of increased non-ideal current components and reduced efficiency caused by premature commutation. By clearly distinguishing between the constant torque operating range below the rated speed and the field weakening acceleration range above the rated speed, it achieves performance optimization of the motor across the entire speed range.

[0108] In summary, the above-mentioned solution provided in this application obtains the three-phase terminal voltage and bus voltage of the brushless DC motor, uses the comparison logic of the reconstructed virtual neutral point voltage with the voltages of the floating and conducting phases to detect the zero-crossing event of the back electromotive force and generate a zero-crossing signal, and then estimates the actual speed based on the number of zero-crossings within the statistical period of the zero-crossing signal; on this basis, a speed closed-loop regulation mechanism is introduced, the difference between the target speed and the actual speed is input into the regulator output delay phase compensation amount, dynamically corrects the commutation delay time, and performs the commutation operation after the adjusted time after each zero-crossing event. In particular, when the target speed is higher than the rated speed, the commutation delay time is dynamically adjusted to be less than the time corresponding to the reference delay phase, thereby commutating earlier and generating a demagnetizing component. The synergistic effect of these technical features enables the system to accurately acquire rotor position information and achieve precise closed-loop speed control without relying on Hall sensors or current sensors. This effectively solves the system complexity and cost problems caused by the long-standing reliance on additional hardware sensors in existing brushless DC motor control technologies, avoids control failures or performance degradation due to the lack of hardware sensors, and significantly improves the integration, anti-interference ability, and stability and reliability of the motor control system in a wide speed range.

[0109] Further reference Figure 8 The present application illustrates a control device for a brushless DC motor, the device comprising:

[0110] The voltage sampling unit 801 is used to acquire the three-phase terminal voltage and bus voltage of the brushless DC motor.

[0111] The zero-crossing detection unit 802 is used to detect the zero-crossing event of the back electromotive force in each phase winding based on the three-phase terminal voltage and the bus voltage, and generate a zero-crossing signal.

[0112] The speed estimation unit 803 is used to calculate the actual speed of the brushless DC motor based on the zero-crossing signal.

[0113] The speed closed-loop regulation unit 804 is used to dynamically adjust the commutation delay time according to the difference between the target speed and the actual speed, so that the actual speed of the motor reaches the target speed.

[0114] The commutation control unit 805 is used to perform a commutation operation after a regulated commutation delay time following each zero-crossing event. Specifically, when the target speed is greater than the rated speed, the commutation delay time is dynamically adjusted to be less than the commutation delay time corresponding to the reference delay phase.

[0115] The specific functions of each unit module in the above-mentioned brushless DC motor control device can be found in the detailed description of the above method embodiments. These unit modules can be implemented entirely or partially through software, hardware, or a combination thereof. Each module can be embedded in or independent of the processor in a computer device in hardware form, or stored in the memory of a computer device in software form, so that the processor can call and execute the operations corresponding to each module.

[0116] In yet another optional embodiment, this application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the brushless DC motor speed control method described in the above embodiments. The computer-readable storage medium can be a non-volatile memory, such as read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or flash memory. Alternatively, the computer-readable storage medium can be a volatile memory, such as random access memory (RAM), which can be used as an external cache. The computer-readable storage medium in this embodiment allows the brushless DC motor speed control method described in the above embodiments to be solidified in the form of computer program code. This enables the control method to be loaded and executed on general-purpose computing hardware (such as microcontroller units (MCUs), digital signal processors (DSPs), etc.), thereby realizing closed-loop speed control and field weakening speed-up functions based on back EMF zero-crossing detection in the motor controller. This software-based implementation facilitates the upgrading and maintenance of the control algorithm, makes it easy to port and deploy in different models or application scenarios of motor drive devices, reduces hardware development costs, and improves the system's flexibility and scalability.

[0117] This embodiment provides a brushless DC motor. The brushless DC motor includes at least one processor and a memory connected to the processor. The memory stores a computer program; the processor executes the computer program to enable the brushless DC motor to implement the brushless DC motor speed control method as described in any of the above embodiments.

[0118] Specifically, the processor, as the core control unit of the brushless DC motor, is responsible for coordinating and processing various data and instructions during motor operation. The memory, electrically connected to the processor, provides data storage space and a program execution environment. The memory pre-stores computer program code for executing the brushless DC motor speed control method. This code includes a set of instructions for logical steps such as acquiring voltage signals, detecting back EMF zero-crossing events, calculating the actual speed, dynamically adjusting the commutation delay time, and executing commutation operations. During actual operation, the processor calls and executes the computer program in memory. By executing the instructions in the program, the processor can acquire the three-phase terminal voltage and bus voltage of the brushless DC motor; detect zero-crossing events of the back EMF in each phase winding based on the three-phase terminal voltage and bus voltage, generating zero-crossing signals; calculate the actual speed of the brushless DC motor based on the zero-crossing signals; dynamically adjust the commutation delay time based on the difference between the target speed and the actual speed to ensure the actual speed of the motor reaches the target speed; and execute the commutation operation after a delayed commutation delay time each time a zero-crossing event is detected, based on the zero-crossing signals.

[0119] Through the above technical solution, this application integrates the aforementioned brushless DC motor speed control method into the internal hardware system of the brushless DC motor, enabling the brushless DC motor to possess intelligent control capabilities of self-sensing, self-decision-making, and self-execution. This integrated design eliminates the need for an external independent controller, simplifying the overall circuit structure of the system, reducing hardware costs and wiring complexity, while also improving the system's anti-interference capability and operational reliability. Furthermore, through the cooperation of the processor and memory, the control algorithm can be flexibly updated and upgraded, allowing the motor to adapt to different application scenarios and performance requirements, which is conducive to promoting the development of motor products towards modularity and intelligence.

[0120] For ease of description, the above system is described by dividing it into various modules based on their functions. Of course, in implementing this invention, the functions of each module can be implemented in one or more software and / or hardware components.

[0121] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for system or system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and relevant parts can be referred to the descriptions in the method embodiments. The systems and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0122] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0123] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented directly by hardware, a software module executed by a processor, or a combination of both. The software module can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0124] It should also be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0125] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling the speed of a brushless DC motor, characterized in that, include: Obtain the three-phase terminal voltage and bus voltage of the brushless DC motor; Based on the three-phase terminal voltage and bus voltage, the zero-crossing event of the back electromotive force in each phase winding is detected, and a zero-crossing signal is generated. The actual speed of the brushless DC motor is calculated based on the zero-crossing signal. The commutation delay time is dynamically adjusted based on the difference between the target speed and the actual speed, so that the actual speed of the motor reaches the target speed. Based on the zero-crossing signal, after each zero-crossing event is detected, a commutation operation is performed with a delayed adjusted commutation delay time. Specifically, when the target speed is greater than the rated speed, the dynamic adjustment makes the commutation delay time less than the commutation delay time corresponding to the reference delay phase.

2. The brushless DC motor speed control method according to claim 1, characterized in that, Based on the three-phase terminal voltage and bus voltage, the zero-crossing event of the back electromotive force in each phase winding is detected, and the zero-crossing signal is generated including: The neutral point voltage is determined based on the bus voltage, wherein the neutral point voltage is half of the bus voltage. Based on the comparison results between the floating phase voltage and the neutral point voltage in the three-phase terminal voltage, and the comparison results between the conducting phase voltage and the bus voltage in the three-phase terminal voltage, it is determined whether a zero-crossing event of back electromotive force has occurred, and a zero-crossing signal is generated.

3. The method according to claim 2, characterized in that, The determination of whether a zero-crossing event of back electromotive force has occurred based on the comparison results of the floating phase terminal voltage and the neutral point voltage in the three-phase terminal voltage, and the comparison results of the conducting phase terminal voltage and the bus voltage in the three-phase terminal voltage includes: Determine whether the target condition is met. If the target condition is met, determine that a zero-crossing event of the back electromotive force has occurred. The target conditions include: The voltage of the first conducting phase in the three-phase terminal voltage is not less than the product of the bus voltage and the first threshold. The voltage of the second conducting phase in the three-phase terminal voltage is not greater than the product of the bus voltage and the second threshold, wherein the first threshold is greater than 0.5 and greater than the second threshold. The difference between the floating phase voltage and the neutral point voltage in the three-phase terminal voltage is greater than the third threshold. When the suspended phase is phase A, the first conducting phase is phase B and the second conducting phase is phase C; when the suspended phase is phase B, the first conducting phase is phase C and the second conducting phase is phase B; when the suspended phase is phase C, the first conducting phase is phase A and the second conducting phase is phase B.

4. The method according to claim 1, characterized in that, Calculating the actual speed of the brushless DC motor based on the zero-crossing signal includes: The number of zero-crossings of the zero-crossing signal within a cycle is counted, and the actual rotational speed is calculated based on the number of pole pairs, carrier frequency period, and the number of zero-crossings of the brushless DC motor.

5. The method according to claim 1, characterized in that, The dynamic adjustment of the commutation delay time includes: The difference between the target speed and the actual speed is input into the speed closed-loop regulator; The speed closed-loop regulator outputs a delayed phase compensation amount based on the difference; The commutation delay time is dynamically adjusted using the aforementioned delay phase compensation amount.

6. The method according to claim 5, characterized in that, Dynamically adjusting the commutation delay time using the aforementioned delay phase compensation amount includes: The commutation delay time is dynamically adjusted based on the formula t2=cnt×(fac1-fac2)×f1; in, t2 is the adjusted commutation delay time, cnt is the number of zero-crossings of the zero-crossing signal within one cycle, and f1 is the sampling period of the terminal voltage. fac2 is the reference delay phase, and fac2 is the delay phase compensation amount.

7. The method according to claim 5, characterized in that, When the target speed is less than or equal to the rated speed, the adjustment amount output by the speed closed-loop regulator is zero, so that the commutation delay time is maintained as the commutation delay time corresponding to the reference delay phase.

8. A control device for a brushless DC motor, characterized in that, include: The voltage sampling unit is used to acquire the three-phase terminal voltage and bus voltage of the brushless DC motor. The zero-crossing detection unit is used to detect the zero-crossing event of the back electromotive force in each phase winding based on the three-phase terminal voltage and the bus voltage, and generate a zero-crossing signal. A speed estimation unit is used to calculate the actual speed of the brushless DC motor based on the zero-crossing signal. A speed closed-loop control unit is used to dynamically adjust the commutation delay time based on the difference between the target speed and the actual speed, so that the actual speed of the motor reaches the target speed. A commutation control unit is configured to perform a commutation operation after a delayed commutation delay time following each detection of a zero-crossing event, based on the zero-crossing signal. Specifically, when the target speed is greater than the rated speed, the dynamic adjustment makes the commutation delay time less than the commutation delay time corresponding to the reference delay phase.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps of the brushless DC motor speed control method as described in any one of claims 1 to 7.

10. A brushless DC motor, characterized in that, include: At least one processor and a memory connected to the processor, wherein: The memory is used to store computer programs; The processor is used to execute the computer program so that the brushless DC motor can implement the brushless DC motor speed control method as described in any one of claims 1 to 7.

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