A sensorless brushless motor starting control method

Abstract

The application discloses a kind of sensorless brushless motor starting control method in the field of motor control, comprising the following steps: S1: initial positioning to motor rotor, make rotor according to predetermined phase sequence to next phase conduction;S2: calculate the current angle of rotor, judge whether rotor meets commutation condition, if meet, enter S3, do not meet, repeat current step;S3: continuously collect bus current, calculate the trend of bus current, determine when bus current is stably at minimum, enter S4;S4: set the current angle of rotor to zero, count the starting time t1 from S1 to the current time, judge whether it meets the second set time threshold t s , if meet, starting is finished, if not meet, return S2.The application can improve the accuracy of commutation in starting process, reduce the pulsation of current, improve the fault tolerance of motor starting commutation, ensure the reliable commutation of motor, and effectively increase the adaptability of motor load.

Description

Technical Field

[0001] This invention relates to the field of motor control, specifically a sensorless brushless motor starting control method. Background Technology

[0002] Reliable starting is essential for the normal operation of sensorless motor control systems. This is achieved primarily through initial motor positioning, commutation according to a pre-planned sequence, real-time rotor position estimation, and comparison of the estimated position with the set commutation point to determine whether commutation should proceed. Then, relevant registers are cleared based on the bus current variation trend. Finally, the starting time is calculated to determine if starting is complete. This method can be widely applied to motion control systems in military fields such as aerospace, shipbuilding, weaponry, and electronics, as well as industrial motor drive control in fields such as drones, robots, electric vehicles, refrigerators, and washing machines.

[0003] The current sensorless brushless motor starting control method includes initial rotor positioning, performing the next commutation according to a specified phase sequence table after a specified time, while simultaneously increasing the duty cycle and commutation frequency of the applied stator voltage, and determining whether the motor starting time meets the predetermined time to confirm whether starting is complete. The software flow is as follows: Figure 1 As shown, this method first initializes the voltage input duty cycle D, voltage u, positioning time t0, and start-up time t1. Then, it applies power to two specified phases and counts the positioning time t0. If the positioning time meets the preset time t... a Then the positioning ends, the next phase is turned on, the duty cycle D = D + ε is increased, the commutation waiting time t2 = t2 - μ is reduced, and the start-up time t is recorded. 1, When t1>t s At that time, the motor starting process is completed.

[0004] The above-mentioned method for detecting motor speed has obvious defects, which are manifested in the following aspects:

[0005] (1) The increase in voltage input duty cycle ε and commutation waiting time μ are extremely difficult to determine;

[0006] (2) This method has weak adaptability to external loads. As the motor load changes, the input duty cycle and commutation waiting time may need to be readjusted.

[0007] (3) Poor parameter fault tolerance; slight changes in starting parameters may lead to starting failure.

[0008] (4) During the motor starting and commutation process, the current pulsation of the motor is very large, which can cause the motor to vibrate.

[0009] To address the shortcomings of the aforementioned motor starting methods, the applicant proposes a novel sensorless brushless motor starting control method. Summary of the Invention

[0010] The purpose of this invention is to provide a sensorless brushless motor starting control method to solve the problems mentioned in the background art.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] A sensorless brushless motor starting control method includes the following steps:

[0013] S1: Initially position the motor rotor so that the rotor conducts the next phase according to the predetermined phase sequence;

[0014] S2: Calculate the current angle of the rotor and determine whether the rotor meets the commutation conditions. If it does, proceed to S3; otherwise, repeat the current step.

[0015] S3: Continuously collect bus current, calculate the trend of bus current change, and enter S4 when the bus current is stable at the minimum value;

[0016] S4: Set the current angle of the rotor to zero, count the start-up time t1 from S1 to the current moment, and determine whether it meets the second set time threshold t. s If the conditions are met, the startup ends; otherwise, return to S2.

[0017] Furthermore, the initial pre-positioning of the motor rotor includes:

[0018] Preset first time threshold t a A voltage signal u with a fixed duty cycle is applied to any two phases of the motor stator;

[0019] Count the positioning time t0 of the motor rotor to the initial position, until t0 > t a If the initial pre-positioning of the motor rotor is successful, the next phase will be turned on, and the process will enter S2.

[0020] Furthermore, calculating the current angle of the rotor includes:

[0021] The current bus current i[kT] is acquired, the integral value of the bus current is calculated, and the rotor angle value θ[kT] is obtained through an iterative algorithm; where k represents the sampling step size and KT represents the sampling time.

[0022] Furthermore, determining whether the rotor meets the commutation conditions includes:

[0023] Preset commutation angle threshold θ0, angle comparison threshold δ, and first threshold N0;

[0024] Determine whether θ[kT]-θ0>δ holds true and count the number of times it holds true, N. If θ[kT]-θ0>δ and N>N0 hold true at the same time, then the commutation condition is met, and proceed to S3.

[0025] Furthermore, the aforementioned

[0026] Furthermore, the calculation of the bus current variation trend to determine that the bus current is stably at its minimum value includes:

[0027] Preset current comparison threshold γ and second threshold N1;

[0028] Continuously collect the current bus current i[kT], determine whether i[(k-2)T]-i[(k-1)T]>γ and i[kT]-i[(k-1)T]>γ are true, and count the number of times N' that both are true at the same time;

[0029] When N'>N, the bus current is determined to be stable at its minimum value, and the process proceeds to S4.

[0030] Beneficial effects: This invention enables more precise control of variable parameters, reduces current ripple, effectively increases the adaptability of the motor to load, and ensures small calculation errors. Simultaneously, this invention repeatedly judges the calculated values ​​until the set conditions are met, expanding the fault tolerance capability of the motor's starting commutation, thereby ensuring reliable commutation of the motor. Attached Figure Description

[0031] Figure 1 For existing technology process control diagrams;

[0032] Figure 2 This is the flow control diagram of the present invention. Detailed Implementation

[0033] 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.

[0034] See Figure 2 The flowchart of the present invention, a sensorless brushless motor starting control method, includes the following steps:

[0035] S1: Initial pre-positioning of the motor rotor. This step is mainly used to provide an initial position reference for subsequent rotor angle calculations, thereby ensuring the subsequent commutation threshold determination and bus current comparison. Specifically, the initial pre-positioning of the motor rotor includes:

[0036] A voltage signal u with a fixed duty cycle D is applied to any two phases of the motor stator, where:

[0037] u=D×V s

[0038]

[0039] V s R represents the bus voltage, and R represents the average phase resistance of the three phases of the motor stator. The three-phase resistance R... x x = 1, 2, 3 together determine the result, that is ω is the angular velocity of the motor, T L k is the load torque of the motor. e This represents the back electromotive force constant of the motor.

[0040] Preset first time threshold t a , t a The selected value should be long enough to ensure that the motor rotor can reach the position of its current phase sequence. The positioning time t0 of the motor rotor reaching the initial phase sequence position is recorded until t0 > t0. a If the initial pre-positioning of the motor rotor is successful, the rotor will conduct the next phase according to the predetermined phase sequence and enter S2.

[0041] The phase sequence is set according to six steps: U+V-, U+W-, V+W-, V+U-, W+U-, W+V-. For example, if the initial phase sequence is U+V-, then proceed in the sequence direction, with the next phase selected to conduct using U+W-. If the initial phase sequence is W+U-, then the next phase selected to conduct using W+V-. The sequence can also be reversed; in this case, the + and - phases in the phase sequence table are simply swapped.

[0042] S2: Calculate the current angle of the rotor, specifically including:

[0043] Acquire the current bus current i[kT] and calculate the discrete integral value of the bus current. Based on the relationship between parameters such as bus current and input voltage and the local rotor angle, the rotor angle value θ[kT] is calculated using an iterative algorithm. The iterative algorithm formula is as follows:

[0044]

[0045] In the above formula, T represents the sampling step size, L represents the phase inductance of the motor, k represents the number of times the bus current is sampled, KT represents the sampling time, and the rotor position is determined by i, T, R, L, u, and k. e It is also determined that the accuracy of the position estimation will have a serious impact on the starting commutation of the motor. If the error is too large, the motor will fail to start, and may even cause the motor to vibrate or stop. In severe cases, the drive and the motor will burn out.

[0046] To avoid excessive errors in rotor position calculation, commutation conditions are set to determine whether the commutation timing is met. Specifically, these include:

[0047] The preset commutation angle threshold θ0, angle comparison threshold δ, and first threshold N0 are defined.

[0048] Determine whether θ[kT]-θ0>δ holds true. If not, then k=k+1, return to S2 to re-collect the bus current i[kT]. If true, then count the number of times it holds true N using a counter and determine whether N>N0 holds true.

[0049] If N>N0 is not true, the counter increments by one to make N=N+1, and returns to S2 to re-collect the bus current i[kT]; until N>N0 is true, the commutation condition is met, and the next phase is turned on according to the phase sequence table, and enters S3.

[0050] In this step, preferably This angle value ensures that the stator and rotor magnetic fields of the motor are orthogonal, allowing for maximum torque during commutation and requiring less bus current, thus promoting energy savings. This step involves repeatedly checking the calculated rotor angle value by setting δ and N0 to keep the current rotor angle value as close as possible to the desired value. Minimize errors and maximize the fault tolerance of rotor position estimation to ensure reliable commutation and prevent motor start-up failure.

[0051] S3: After commutation, the counter is cleared, the bus current i[kT] is updated, and the trend of bus current change is calculated.

[0052] The commutation method in this application processes the entire electrical cycle in six partial steps. Therefore, between the completion of the first commutation step and the start of the next commutation step, the angle calculation needs to be reset to zero to provide a new starting point for the next commutation step. This step is achieved by selecting a reference point and detecting the minimum value of the bus current. Specifically, it includes:

[0053] Preset current comparison threshold γ and second threshold N1;

[0054] Compare the bus current i[(k-1)T] collected in the previous period with the bus current i[(k-2)T] collected in the period before that, and determine whether i[(k-2)T]-i[(k-1)T]>γ holds true.

[0055] If not true, execute k = k + 1 and return to S3 to update the bus current; if true, further compare the currently acquired bus current i[kT] with the previously acquired bus current i[(k-1)T] to determine whether i[kT] - i[(k-1)T] > γ is true.

[0056] If not true, execute k = k + 1 and return to S3 to update the collected bus current. If true, count the number of times true N' is true and determine whether N' > N1 is true.

[0057] If not true, execute N' = N' + 1 and return to S3 to update the collected bus current. If true, it means that the bus current is continuously detected to be in a state of first decreasing and then increasing. It can be considered that the bus current is stable at the minimum value, and the motor can continue to start, and enter S4.

[0058] It should be noted that N' is merely a symbol used for easy distinction in expression; it has no specific meaning and is equivalent to the symbol used when the counter is reset to zero. Figure 2 N in the context.

[0059] S4: Reset the counter to zero, set the current rotor angle θ[kT] = 0, count the start-up time t1 from S1 to the current moment, and determine whether the second time threshold t is met. s If the condition is not met, execute k=0 and return to S2; if the condition is met, the process ends.

[0060] This invention uses a fixed duty cycle, with the commutation waiting time determined by the sampling period and frequency of the bus current. This makes the variable parameters more accurate and easier to control, reduces current ripple, effectively increases the motor's load adaptability, and ensures small calculation errors. Furthermore, this invention sets a first time threshold, a second time threshold, and a number of thresholds to repeatedly judge the calculated value until the set conditions are met, expanding the fault tolerance of the motor's starting commutation and thus ensuring reliable commutation.

[0061] Although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0062] Therefore, the above description is only a preferred embodiment of this application and is not intended to limit the scope of this application; that is, all equivalent modifications made in accordance with the scope of the claims of this application shall be within the protection scope of the claims of this application.

Claims

1. A sensorless brushless motor starting control method, characterized in that, Including the following steps: S1: Initially position the motor rotor so that the rotor conducts the next phase according to the predetermined phase sequence; S2: Calculate the current angle of the rotor and determine whether the rotor meets the commutation conditions. If it does, proceed to S3; otherwise, repeat the current step. The calculation of the rotor's current angle includes: acquiring the current bus current i[kT], calculating the integral value of the bus current, and obtaining the rotor's angle value through an iterative algorithm. The iterative algorithm formula is as follows: In the above formula, T represents the sampling step size, L represents the phase inductance of the motor, k represents the number of times the bus current is sampled, and kT represents the sampling time. This represents the average phase resistance of the three phases of the motor stator. The back electromotive force constant of the motor is represented by u, and the voltage signal is represented by u. The determination of whether the rotor meets the commutation conditions includes: a preset commutation angle threshold θ0, an angle comparison threshold δ, and a first threshold. ;judge Does θ0 > δ hold true, and count the number of times it holds true, N? θ0>δ and If both conditions are met, then the commutation condition is satisfied; S3: Continuously collect bus current, calculate the trend of bus current change, and enter S4 when the bus current is stable at the minimum value; S4: Set the current angle of the rotor to zero, count the start-up time t1 from S1 to the current moment, and determine whether it meets the second set time threshold t. s If the conditions are met, the startup ends; otherwise, return to S2.

2. The sensorless brushless motor starting control method according to claim 1, characterized in that, The initial pre-positioning of the motor rotor includes: Preset first time threshold t a A voltage signal u with a fixed duty cycle is applied to any two phases of the motor stator; The positioning time t0 from the initial position of the motor rotor is recorded until... If the initial pre-positioning of the motor rotor is successful, the next phase will be turned on, and the process will enter S2.

3. The sensorless brushless motor starting control method according to claim 1, characterized in that, The θ0= .

4. The sensorless brushless motor starting control method according to claim 3, characterized in that, The calculation of the bus current variation trend to determine that the bus current is stably at its minimum value includes: Preset current comparison threshold γ and second threshold ; Continuously collect and obtain the current bus current i[kT], and determine and Determine if the condition is true and count the number of times N' is true simultaneously; When N' When N1 is reached, the bus current is determined to be stable at its minimum value, and then the process proceeds to S4.

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