阅读说明：本技术 控制无刷直流电机平稳工作的方法和系统 (Method and system for controlling brushless direct current motor to work stably ) 是由 王根平 于 2021-08-04 设计创作，主要内容包括：本发明公开了一种控制无刷直流电机平稳工作的方法和系统。所述方法包括：检测电机的实际转速V,并计算与设定转速V0的速度偏差VD＝V-V0；在V>0时,计算转速的加速度B,B＝(V-V1)*f；其中,f是用于驱动电机的所述PWM波的频率,V1为比V早一个PWM周期的转速；根据所述速度偏差VD和所述加速度B,调整所述PWM波的占空比ratio。本发明方案有助于抑制电机工作过程中出现的脉动现象,能保证电机更平稳的工作,能提高电机运动的控制精度,并节省能耗。(The invention discloses a method and a system for controlling a brushless direct current motor to work stably. The method comprises the following steps: detecting the actual rotating speed V of the motor, and calculating the speed deviation VD from the set rotating speed V0 to be V-V0; when V is greater than 0, calculating the acceleration B of the rotating speed, wherein B is (V-V1) × f; wherein f is a frequency of the PWM wave for driving the motor, and V1 is a rotation speed earlier than V by one PWM period; and adjusting the duty ratio of the PWM wave according to the speed deviation VD and the acceleration B. The scheme of the invention is beneficial to inhibiting the pulsation phenomenon in the working process of the motor, can ensure the more stable work of the motor, can improve the control precision of the motor motion and save energy consumption.)

1. A method for controlling a brushless direct current motor to work stably is characterized by comprising the following steps:

detecting the actual rotating speed V of the motor, and calculating the speed deviation VD from the set rotating speed V0, wherein VD is V-V0;

when V is greater than 0, calculating the acceleration B of the rotating speed, wherein B is (V-V1) × f; where f is the frequency of the PWM wave for driving the motor, and V1 is the rotation speed one PWM cycle earlier than V;

and adjusting the duty ratio of the PWM wave according to the speed deviation VD and the acceleration B.

2. The method of claim 1, further comprising:

and when the V is 0, increasing the duty ratio, and when the duty ratio cannot be increased continuously, turning to reduce the frequency f.

3. The method according to claim 1, wherein adjusting the duty ratio of the PWM wave according to the speed deviation VD and the acceleration B comprises:

comparing the speed deviation VD with a set allowable deviation value VE;

if VD > VE and the acceleration B >0 or B ═ 0, then the duty cycle ratio is decreased;

if VD < -VE and the acceleration B <0 or B ═ 0, then the duty cycle ratio is increased.

4. The method according to claim 3, wherein adjusting the duty ratio of the PWM wave according to the speed deviation VD and the acceleration B further comprises:

if VD is larger than VE and the acceleration B is less than 0, then no adjustment is made;

if VD < -VE and the acceleration B >0, no adjustment is made.

5. The method of claim 3, further comprising:

if the duty ratio cannot be increased continuously, decreasing the frequency f;

and if the duty ratio cannot be continuously reduced, increasing the frequency f.

6. A system for controlling a brushless DC motor to work smoothly, comprising:

the detection unit is used for detecting the actual rotating speed V of the motor and calculating the speed deviation VD from the set rotating speed V0, wherein the VD is V-V0;

a calculation unit for calculating an acceleration B of the rotational speed, B ═ V1 × f, when V > 0; wherein f is a frequency of the PWM wave for driving the motor, and V1 is a rotation speed earlier than V by one PWM period;

and the adjusting unit is used for adjusting the duty ratio of the PWM wave according to the speed deviation VD and the acceleration B when V is greater than 0.

7. The system of claim 6,

the adjusting unit is further configured to increase the duty ratio when V is 0, and to decrease the frequency f when the duty ratio cannot be increased.

8. The system according to claim 6, wherein the adjusting unit is specifically configured to:

comparing the speed deviation VD with a set allowable deviation value VE;

if VD > VE and the acceleration B >0 or B ═ 0, then the duty cycle ratio is decreased;

if VD < -VE and the acceleration B <0 or B ═ 0, then the duty cycle ratio is increased.

9. The system according to claim 8, wherein the adjusting unit is further configured to:

if VD is larger than VE and the acceleration B is less than 0, then no adjustment is made;

if VD < -VE and the acceleration B >0, no adjustment is made.

10. A brushless DC motor system, comprising a motor body, a controller, a driver, an inverter circuit and a sensor, wherein the controller is operated to realize the method for controlling the smooth operation of the brushless DC motor according to any one of claims 1 to 5.

Technical Field

The invention relates to the technical field of motor control, in particular to a method and a system for controlling a brushless direct current motor to work stably.

Background

Brushless dc motors are increasingly used. However, the dynamic performance of the brushless dc motor is affected due to the existence of the pulsation problem during the operation of the brushless dc motor, which limits the application of the brushless dc motor in the field of high-precision control.

The most important disadvantage of the brushless direct current motor is that pulsation occurs in the working process, which affects the running precision and causes great energy waste. Therefore, a stable and effective method for reducing the pulsation is found, and the method is very significant for improving the working performance of the brushless direct current motor, expanding the application space of the brushless direct current motor and reducing the working energy consumption of the brushless direct current motor.

Disclosure of Invention

The invention mainly aims to provide a method and a system for controlling a brushless direct current motor to work stably, which are used for inhibiting the pulsation phenomenon of the brushless direct current motor in the working process, so that the motor works more stably, the control precision is higher, and the energy consumption is saved more.

In order to achieve the above purpose, the technical scheme adopted by the invention is as follows.

In a first aspect of the present invention, a method for controlling a brushless dc motor to work smoothly is provided, the method comprising the steps of: detecting the actual rotating speed V of the motor, and calculating the speed deviation VD from the set rotating speed V0, wherein VD is V-V0; when V is greater than 0, calculating the acceleration B of the rotating speed, wherein B is (V-V1) × f; where f is the frequency of the PWM wave for driving the motor, and V1 is the rotation speed one PWM cycle earlier than V; and adjusting the duty ratio of the PWM wave according to the speed deviation VD and the acceleration B.

In a possible implementation, the method further includes: and when the V is 0, increasing the duty ratio, and when the duty ratio cannot be increased continuously, turning to reduce the frequency f.

In one possible implementation, adjusting the duty ratio of the PWM wave according to the speed deviation VD and the acceleration B includes: comparing the speed deviation VD with a set allowable deviation value VE; if VD > VE and the acceleration B >0 or B ═ 0, then the duty cycle ratio is decreased; if VD < -VE and the acceleration B <0 or B ═ 0, then the duty cycle ratio is increased.

In one possible implementation manner, adjusting the duty ratio of the PWM wave according to the speed deviation VD and the acceleration B further includes: if VD is larger than VE and the acceleration B is less than 0, then no adjustment is made; if VD < -VE and the acceleration B >0, no adjustment is made.

In a possible implementation, the method further includes: if the duty ratio cannot be increased continuously, decreasing the frequency f; and if the duty ratio cannot be continuously reduced, increasing the frequency f.

In a second aspect of the present invention, there is provided a system for controlling a brushless dc motor to operate smoothly, the system comprising: the detection unit is used for detecting the actual rotating speed V of the motor and calculating the speed deviation VD from the set rotating speed V0, wherein the VD is V-V0; a calculation unit for calculating an acceleration B of the rotational speed, B ═ V1 × f, when V > 0; wherein f is a frequency of the PWM wave for driving the motor, and V1 is a rotation speed earlier than V by one PWM period; and the adjusting unit is used for adjusting the duty ratio of the PWM wave according to the speed deviation VD and the acceleration B when V is greater than 0.

In one possible implementation, the adjusting unit is further configured to increase the duty ratio when V is equal to 0, and to decrease the frequency f when the duty ratio cannot be increased.

In a possible implementation manner, the adjusting unit is specifically configured to: comparing the speed deviation VD with a set allowable deviation value VE; if VD > VE and the acceleration B >0 or B ═ 0, then the duty cycle ratio is decreased; if VD < -VE and the acceleration B <0 or B ═ 0, then the duty cycle ratio is increased.

In a possible implementation manner, the adjusting unit is further specifically configured to: if VD is larger than VE and the acceleration B is less than 0, then no adjustment is made; if VD < -VE and the acceleration B >0, no adjustment is made.

In a third aspect of the present invention, a brushless dc motor system is provided, which includes a motor body, a controller, a driver, an inverter circuit, and a sensor, and is characterized in that when the controller operates, the method for controlling the brushless dc motor to work smoothly as described in the first aspect is implemented.

According to the technical scheme, the embodiment of the invention has the following advantages:

the invention adjusts the duty ratio (pulse width) of the PWM wave according to the rotating speed of the motor and in combination with the variation of the speed, namely the acceleration variation of the rotating speed, realizes the adjustment of the power of the PWM wave, and thus inhibits the pulsation phenomenon of the motor. The actual acceleration is determined by the torque, and the invention actually achieves the purpose of adjusting power according to the torque so as to inhibit the pulsation phenomenon.

Compared with the technology of adjusting duty ratio (pulse width) suppression pulse only according to the speed in the prior art, the scheme of the invention further considers acceleration change on the basis of speed factors, improves the fineness and accuracy of power adjustment, enables the motor to work more stably, has higher control accuracy and saves energy consumption. Therefore, it is substantially different from the prior art that the duty ratio (pulse width) is adjusted only according to the speed.

In general, the scheme of the invention is beneficial to inhibiting the pulsation phenomenon in the working process of the motor, further is beneficial to preventing the motor from being blocked in the running process, can ensure the motor to work more stably, can improve the control precision of the motor motion, and saves energy consumption.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the embodiments and the drawings used in the description of the prior art, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.

FIG. 1 is a schematic diagram of a brushless DC motor operating system;

FIG. 2 is a schematic view of a stator field rotation control state of the brushless DC motor;

fig. 3 is a flowchart of a method for controlling smooth operation of a brushless dc motor according to an embodiment of the present invention;

FIG. 4 is a flow chart of one embodiment of a method of an embodiment of the present invention;

fig. 5 is a structural diagram of a system for controlling smooth operation of a brushless dc motor according to an embodiment of the present invention.

Detailed Description

In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The terms "first," "second," "third," and the like in the description and in the claims, and in the above-described drawings, are used for distinguishing between different objects and not for describing a particular order. Furthermore, the terms "include" and "have," as well as any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those steps or elements listed, but may alternatively include other steps or elements not listed, or inherent to such process, method, article, or apparatus.

The following will explain details by way of specific examples.

For the convenience of understanding, the structure and the working mode of the brushless direct current motor system are firstly introduced, then theoretical analysis is carried out, a related principle formula is deduced to be used as a theoretical basis of the invention, and finally, specific contents of the technical scheme of the invention are proposed and described under the guidance of the theoretical basis.

Introduction of brushless DC motor system

Fig. 1 is a schematic diagram of a practical brushless dc motor driving circuit. The whole brushless direct current motor is composed of five parts as can be seen from the schematic diagram: the controller part, the drive circuit (driver) part, the inverter circuit part, the motor body part and the motor rotation position detection (sensor) part.

As can be seen from the system composition of the dc motor, the dc motor is a synchronous motor. The field rotation of the rotor is synchronized with the excitation field of the stator. Since the magnetic field rotation frequency of the stator is determined by the frequency of the power source to be excited, the rotation frequency of the rotor is also determined by the power source frequency of the stator.

The working process of the motor is to generate a controllable rotating magnetic field by the stator so as to drive the rotor carrying the load to rotate. In a brushless direct current motor, a stator adopts an excitation winding and basically adopts a star connection method; the rotor is pasted with permanent magnetic material, the number of magnetic pole pairs of the rotor has influence on the rotating speed of the motor, and the number of the magnetic pole pairs is generally assumed to be P.

Fig. 2 is a schematic diagram of a state in which a stator coil generates a rotating magnetic field under the control of a drive circuit, A, B, C is a winding coil on the stator, and N-S indicate permanent magnets on the rotor. A. B, C are connected to respective fet switch controlled output ports A, B, C of the driver circuit. The three coils are controlled by a driving circuit to generate a rotating magnetic field. A rotation process essentially consists of six basic control states, commonly referred to as six-beat mode of operation. The six-beat operation of the stator coil controlled by the drive circuit is shown in the six steps shown in (1) to (6) of fig. 2, as described below.

Step (1): the driving circuit controls the connection A with the power supply, the connection B is suspended, the connection C is grounded, and at the moment, a rotating shaft of the motor with the permanent magnet N-S is fixed at the position of the rotating shaft.

Step (2): on the basis of the step (1), the driving circuit controls the connection A to be connected with a power supply, the connection B to be grounded and the connection C to be suspended, and at the moment, a rotating shaft of the motor with the permanent magnet N-S rotates for an angle on the basis of the step (1) to reach a position II.

And (3): and (3) on the basis of the step (2), controlling the connection C with the power supply, grounding the connection B and suspending the connection A, wherein the rotating shaft of the motor with the permanent magnet N-S rotates by an angle on the basis of the step (2) to reach the position of the step (C) at the moment corresponding to the step (C).

And (4): and (4) on the basis of the step (3), controlling the connection of the power supply C, the grounding of the power supply A and the suspension of the power supply B by the driving circuit, wherein the rotating shaft of the motor with the permanent magnet N-S rotates by an angle on the basis of the step (3) to reach the position of the power supply B.

And (5): on the basis of step (4), the drive circuit controls the connection of B with the power supply, the connection of A with the ground and the suspension of C, at this time, the rotating shaft of the motor with the permanent magnet N-S rotates an angle on the basis of step (4) to reach the position of step (C).

And (6): on the basis of the step (5), the driving circuit controls the connection B to be connected with the power supply, the connection C to be grounded and the connection A to be suspended, and at the moment, a rotating shaft of the motor with the permanent magnet N-S rotates by an angle on the basis of the step (5) to reach a position of (C).

In the steps (1) - (6), the driving circuit generates a basic rotating magnetic field by controlling A, B, C three coils to be connected with a power supply, grounded and suspended; and (4) returning to the step (1) to continue circulation, and the motor also continues to rotate.

In the six-beat phase sequence control process of the steps (1) - (6), the driving circuit needs to know which state position the motor rotor is in at any time, and then the driving circuit can determine to switch to the next working state. The position of the rotor is checked by detecting the magnetic pole position of the rotor by a position sensor such as a hall sensor, or by detecting the back electromotive force of the stator coil.

The brushless dc motor is mainly used to control the speed and power of the moving system and various dynamic performances of the brushless dc motor, except for the reason of the motor manufacturing process itself, and the controller is used to control the driver to output a PWM (Pulse Width Modulation) wave to control the rotating magnetic field of the stator.

As can be seen from the above-mentioned structure and operation principle of the brushless dc motor, the total rotation speed of the brushless dc motor is determined by the frequency of the PWM wave. But the power of the PWM wave directly affects the instantaneous speed of the motor. Therefore, under the condition that the total speed is inconsistent with the instantaneous speed, the motor inevitably generates the conditions of rapid acceleration and rapid deceleration, which is the pulsation phenomenon existing in the brushless direct current motor. Due to the existence of the pulsation phenomenon, the control precision of the brushless direct current motor is deteriorated, and unnecessary energy consumption loss is also caused.

(II) power calculation analysis of driving motor rotation

Without loss of generality, the voltage of the DC power supply of the driving circuit is set to be U_sThe duty ratio of the output PWM wave is ratio, and the frequency is f. Then f is 1/T, and T is the signal period of the PWM wave.

Let T be T_H+T_L，T_HAnd T_LHigh level time and low level time in one period of PWM wave, obviously having high level u_H＝U_sLow level u_L＝0。

Thus, there are: t is_H＝ratio*T (1)

Assuming that the effective voltage of the entire PWM wave is u, there are:

the following formulae (1) and (2) give: u ═ ratio u ═ u-_H (3)

Without loss of generality, if three winding coils of the brushless dc motor, i.e. A, B, C coil inductances are all L, and an effective current flowing through the coil is i, then:

in the formula (4), the angular frequency ω is 2 pi f, and f is the frequency of the PWM wave. (4) The inductance in the denominator includes any two of the coils A, B, C, and thus the total inductance is 2L. And R is coil resistance. j is the imaginary flag parameter of the complex number.

Since the resistance of the coil is much smaller than the impedance value of the inductor, i.e., R < j ω L, it can be simplified from equation (4):

further simplified by the formula (5):

in the above equations (5) and (6), k is a constant value, f is the frequency of the PWM wave, and L is the inductance value of the stator coil winding.

By the expressions (3) and (6), the power value output to the motor by the driving power supply can be calculated as follows:

as can be seen from equation (7), the power output from the drive circuit to the motor is proportional to the product of the square of the power supply voltage value Us and the square of the duty ratio of the PWM wave, and inversely proportional to the product of the inductance L of the coil and the frequency f of the PWM wave. (7) The result of the formula is very important, and the design of the driving circuit and the control parameters of the motor and the adjustment of the working state of the motor have very important guiding significance.

Relation between power output by driving circuit to motor and motor rotation state

Assume that the rotational speed of the motor is N revolutions per minute. Considering that the resistance of the coil is small, it can be ignored in practical application. Let the torque that the motor obtains from the drive circuit be TM, then there are:

P＝TM*Ω＝0.105*TM*N (8)

in equation (8), P is the power output by the driving circuit, Ω is the angular speed of the motor, N is the number of revolutions per minute (rotational speed) of the motor, and Ω is 2 × pi × N/60 is 0.105N.

The two formulas (7) and (8) can obtain:

wherein c is a constant.

Assuming that the motor can maintain the required torque of uniform rotation of N0 revolutions per minute under a certain load (or no load), which is TM0, there are:

TM＝TM0+(1/2)*J*β (10)

wherein J is the inertia of the motor, and J-mr²M is the mass of the motor rotating system, r is the rotating radius of the motor rotating system, and beta is the acceleration of the motor rotation.

In addition, by analyzing the characteristics of the brushless dc motor principle, i.e., the rotor driven by the stator magnetic field of the brushless dc motor, it can be known that the total rotation speed of the motor is determined by the frequency f of the PWM wave, and there is a relation:

N＝60*f/P (11)

in (11), N is the number of revolutions per minute of the motor, and P is the number of magnetic pole pairs on the rotor of the motor.

From (9) (11), it is possible to obtain:

in (12), C is a constant,

as above, equations (10), (11) and (12) are basic equations for restricting the operation of the motor. Based on the equations (10), (11) and (12), the characteristic conditions of the working states of the motor and how to adjust the PWM parameters of the working states of the motor can be analyzed, so that the motor keeps high-quality operation.

Parameter setting and control principle and method for suppressing brushless direct current motor pulsation

According to the above two analysis, the pulsation phenomenon of the brushless dc motor has a great relationship with the power thereof.

(1) When the power is large enough

The motor can normally rotate, and TM is larger than or equal to TM 0. As can be seen from equation (11), the rotational speed of the motor is determined by the frequency f of the power supply PWM wave.

If the number of revolutions per minute of the motor is set to be N0 according to actual production conditions, N0 is 60 f₀/P, where PWM is required to set the power supply frequency to f₀The required torque is TM 0. If the TM port TM0 is used, the motor rotation will pulsate dramatically.

When TM □ TM0, the acceleration β of the angular velocity of the motor rotation is >0, and the angular velocity will increase. However, the total rotational speed N0 of the motor is defined by f₀And if so, repeatedly accelerating and decelerating the motor in the rotating process. When the rotor position is consistent with the stator magnetic field direction (see the rotor position state of the motor of figure 2) (-sixth), the motor rotates violently and accelerates; when the rotor continues to rotate and deviates from the direction of the magnetic field of the stator (in figure 2, the position of the rotor of the motor deviates from the state of (i) -sixth, and the rotor enters the gap between two adjacent positions), the rotation of the motor is decelerated violently. Electric machineThis is so that the pulsation occurs continuously throughout the rotation. The whole process speed N0 is still formed by f₀The decision is not changed.

The motor works with violent pulsation, the operation is not stable, and the working quality characteristic is poor. In order to reduce the pulsation during the operation of the motor, the operation load of the motor may be increased, i.e., TM0 is lifted so that TM is TM 0; if the rotation speed N0 is to be kept constant without changing the load, the adjustment can be made according to equation (12). As can be seen from equation (12), since N0 is set, f is also set; us is the supply voltage, and the value is also set after the system is designed; c is constant and therefore to let TM fall, it is the duty cycle of the PWM wave of the power supply signal that can be adjusted, i.e. the value of ratio is gradually reduced until TM becomes TM 0.

(2) When power may be insufficient

Obviously, at this time TM < TM0, and thus β <0, the angular velocity of the motor is reduced. But according to formula (9)When N is gradually reduced, TM is rapidly increased, beta is larger than 0 at the moment, and the rotating speed of the motor is increased. However, the power of the motor is insufficient to drive the load to rotate, so that once the motor has the rotating speed, the speed is rapidly reduced. Therefore, in this case, the motor exhibits a vibration state, and is not activated by a user, and continuously generates vibration noise, thereby causing a seizure.

If the motor drives the load to work normally, the power of the motor, namely TM, must be increased.

In the debugging process of increasing TM, it is known from equation (12) that if it is desired to increase TM, the duty ratio of the power supply PWM wave can be increased, and the frequency f of the PWM wave can be decreased. When the rotation speed of the motor is set, f is determined by considering the formula (11) N-60 × f/P. Therefore, if the motor is required to run at the desired set speed, the remaining method only increases the duty ratio of the power supply PWM wave, and finally enables TM to be larger than or equal to TM0, so that the motor can be ensured to run normally at the set speed.

However, because the duty ratio of the PWM wave is constantly less than, i.e. ratio is less than or equal to 1, if the duty ratio is increased to the maximum extent and TM is not less than or equal to TM0, under the condition that the motor cannot work normally, as shown in equation (12), it is necessary to consider to reduce the set rotation speed N0 of the motor, i.e. reduce the frequency f of the PWM wave of the motor, and finally the motor can drive the load to rotate normally, and at this time, TM is greater than or equal to TM 0.

The details of the parameter setting and control principle and method for suppressing the brushless dc motor pulsation according to the embodiment of the present invention are described above, and the theoretical basis is the formulas (10), (11) and (12), especially the formula (12), obtained by theoretical analysis and calculation.

(V) implementation process of method for suppressing brushless direct current motor pulsation

As can be seen from the above reasoning in the third section, in order to suppress the ripple phenomenon very well, the duty ratio or frequency of the PWM wave of the power signal should be adjusted according to the torque of the motor. For this reason, how to obtain the torque of the motor is first solved. As can be seen from equation (10), the torque of the motor is positively correlated with the acceleration of the motor rotation. Therefore, we can adjust the power according to the acceleration of the motor rotation. Based on the above thought, the embodiment of the invention provides a method for controlling a brushless direct current motor to work stably by suppressing the pulsation of the brushless direct current motor.

Referring to fig. 3, a method for controlling a brushless dc motor to work smoothly according to an embodiment of the present invention includes:

s1, detecting the actual rotating speed V of the motor, and calculating the speed deviation VD from the set rotating speed V0, wherein VD is V-V0;

s2, when V is 0, increasing the duty ratio, and when the duty ratio cannot be increased, decreasing the frequency f.

S3, when V is greater than 0, calculating the acceleration B of the rotating speed, wherein B is (V-V1) × f; where f is the frequency of the PWM wave for driving the motor, and V1 is the rotation speed one PWM cycle earlier than V; and adjusting the duty ratio of the PWM wave according to the speed deviation VD and the acceleration B.

Referring to fig. 4, in an embodiment of a specific application scenario, a specific implementation process of the method according to an embodiment of the present invention includes the following steps:

(0) setting a desired motor speed, namely a set speed to be V0; setting a deviation value of the rotating speed of the allowable motor, namely an allowable deviation value VE; setting an initial value ratio of a PWM wave duty ratio of a driving motor, and adjusting a duty ratio step length delta ratio; setting the frequency of a PWM wave as f0 and setting the frequency adjustment step delta f of the PWM wave so as to enable the rotating speed of the motor to be V0;

(1) detecting the actual rotating speed (instantaneous rotating speed) of the motor, recording as V, and calculating the speed deviation as VD-V0;

the method for detecting the instantaneous rotational speed V of the motor can be implemented according to the prior art. For example, the instantaneous rotational speed can be detected by a hall sensor. In the driving scheme of the brushless direct current motor, hall sensors are often used for detecting the position of a rotor, three phases of the motor correspond to three hall sensors, each hall sensor has two state outputs in each period, a complete period can be divided into six sectors, for example, and the average rotating speed of each sector can be easily calculated. In some embodiments, if the demand for the instantaneous rotational speed is not very high, the average speed of the sector in which it is located may be used as the current actual rotational speed (instantaneous rotational speed).

(2) Determine if the motor is stuck, i.e. V? If V is 0, entering the step (3); if V >0, entering step (4);

(3) if V is 0, increasing the duty ratio, and making ratio + delta ratio; determine if there is a ratio > 1? If not, adjusting the PWM wave according to the increased duty ratio; if the duty ratio cannot be increased continuously, the frequency is adjusted, f is made to be f-delta f, and the PWM wave is adjusted according to the reduced frequency f;

then returning to the judging step (2);

(4) calculating the acceleration B of the rotating speed, wherein B is (V2-V1) f; wherein V2 is the current rotation speed, i.e. the actual rotation speed V detected in step (1), and V1 is the rotation speed one PWM period earlier than V2, i.e. the time interval between V1 and V2 is the PWM period T. Since the frequency f is 1/T, the acceleration formula can also be written as B (V2-V1)/T.

In the step, the duty ratio of the PWM wave is adjusted according to the speed deviation VD and the acceleration B.

If VD is larger than VE, the pulsation occurs and the current speed is too high, and whether the acceleration B is larger than 0 is further judged; if B is less than 0, the speed is reduced, no adjustment is needed at present, and the rotating speed is waited to be reduced; if B >0, the operation of reducing the torque is required while the acceleration is still being continued, the duty ratio is adjusted to be reduced, and the ratio is made to be ratio- Δ ratio; if B is 0, the operation can be performed with reference to B > 0;

if VD < -VE indicates that pulsation occurs and the current speed is too low, further judging whether the acceleration B is less than 0; if B is greater than 0, the acceleration is already performed, the adjustment is not needed at present, and the rotating speed is increased; if B <0, the operation of increasing the torque is required while continuing the deceleration, the duty ratio is adjusted to be increased, and ratio + Δ ratio is set; if B is 0, the operation can be performed with reference to B < 0;

and if the adjusted duty ratio is between 0 and 1, adjusting the PWM wave according to the adjusted duty ratio.

(5) Furthermore, since the duty ratio is a number between 0 and 1, if the adjusted (calculated) duty ratio > is 1, which indicates that the duty ratio cannot be increased, the frequency should be decreased according to the formula (12), and f is made to be f- Δ f; if the adjusted (calculated) duty ratio is less than 0, which means that the duty ratio cannot be decreased, the frequency should be increased according to equation (12), and f is made to be f + Δ f.

Then, the procedure returns to step (2).

As described above, the method according to the embodiment of the present invention adjusts the duty ratio (pulse width) according to the rotation speed and the acceleration change of the rotation speed, so as to adjust the power. And the actual acceleration is determined by the magnitude of the torque. The method further considers the acceleration change on the basis of considering the speed change, improves the fineness and the accuracy of power adjustment, and is substantially different from the prior art that the duty ratio (pulse width) is adjusted only according to the speed.

(VI) System for controlling brushless DC motor to work stably

Referring to fig. 5, an embodiment of the present invention further provides a system for controlling a brushless dc motor to work smoothly, the system including:

a detection unit 51 for detecting an actual rotation speed V of the motor and calculating a speed deviation VD from a set rotation speed V0, where VD is V-V0;

a calculation unit 52 for calculating an acceleration B of the rotation speed when V >0, B ═ V1 × f; wherein f is a frequency of the PWM wave for driving the motor, and V1 is a rotation speed earlier than V by one PWM period;

and an adjusting unit 53, configured to adjust a duty ratio of the PWM wave according to the speed deviation VD and the acceleration B when V > 0.

Optionally, the adjusting unit 53 is further configured to increase the duty ratio when V is equal to 0, and decrease the frequency f when the duty ratio cannot be increased.

Optionally, the adjusting unit 53 is specifically configured to:

comparing the speed deviation VD with a set allowable deviation value VE;

if VD > VE and the acceleration B >0 or B ═ 0, then the duty cycle ratio is decreased;

if VD < -VE and the acceleration B <0 or B ═ 0, then the duty cycle ratio is increased.

Optionally, the adjusting unit 53 is further specifically configured to:

if VD is larger than VE and the acceleration B is less than 0, then no adjustment is made;

if VD < -VE and the acceleration B >0, no adjustment is made.

Optionally, the adjusting unit 53 is further specifically configured to:

if the duty ratio cannot be increased continuously, decreasing the frequency f;

and if the duty ratio cannot be continuously reduced, increasing the frequency f.

In the above, the system of the embodiment of the present invention is explained, and for a more detailed description of each functional unit implementing the system, reference may be made to the contents of the foregoing method embodiment.

(seventh) the invention has the advantages:

the invention adjusts the duty ratio (pulse width) of the PWM wave according to the rotating speed of the motor and in combination with the variation of the speed, namely the acceleration variation of the rotating speed, realizes the adjustment of the power of the PWM wave, and thus inhibits the pulsation phenomenon of the motor. The actual acceleration is determined by the torque, and the invention actually achieves the purpose of adjusting power according to the torque so as to inhibit the pulsation phenomenon.

Compared with the technology of adjusting duty ratio (pulse width) suppression pulse only according to the speed in the prior art, the scheme of the invention further considers acceleration change on the basis of speed factors, improves the fineness and accuracy of power adjustment, enables the motor to work more stably, has higher control accuracy and saves energy consumption. Therefore, it is substantially different from the prior art that the duty ratio (pulse width) is adjusted only according to the speed.

In general, the scheme of the invention is beneficial to inhibiting the pulsation phenomenon in the working process of the motor, preventing the motor from being blocked in the running process, ensuring the more stable work of the motor, improving the control precision of the motor motion and saving the energy consumption.

The technical solution of the present invention is explained in detail by the specific embodiments above. In the above embodiments, the descriptions of the respective embodiments have respective emphasis, and for parts that are not described in detail in a certain embodiment, reference may be made to the related descriptions of other embodiments.

It should be understood that the above embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same; the technical solutions described in the above embodiments can be modified or part of the technical features can be equivalently replaced by those skilled in the art; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the spirit and the scope of the technical solutions of the embodiments of the present invention.