Control method and control device of brushless DC motor

Abstract

The present invention provides a control method and control device for a brushless DC motor. The control method comprises: calculating a delay time based on a delay angle between a stator magnetomotive force and a rotor position when switching devices in a switch array of the brushless DC motor are switched; and controlling the state transition of the switching devices within each position interval of a Hall sensor based on the delay time, so that when a change in rotor position is detected by the Hall sensor, the switching devices are controlled to delay switching by the delay time.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a modeling and control method and a control device for a brushless DC motor. Background Art

[0002] Existing brushless DC motor control technologies include pulse width modulation (PWM) control and vector control. Brushless DC motor control generally consists of an outer speed loop and an inner current loop. PWM control uses the signal fed back by the Hall effect sensor to determine the region in which the motor rotor is located. This region determines the bridge arm that performs the on / off operation. Two bridge arms in the switch array simultaneously perform the switching operation. The duty cycle of the switch is determined by the inner current loop. Vector control requires first locking the rotor flux angle. For controllers equipped with a speed sensor, the flux angle is obtained by integrating the speed sensor. For controllers without a speed sensor, the current rotor flux angle is derived from the rotor's three-phase current and the three-phase voltage output by the bridge arm. The rotor flux angle and output voltage are used to control the three-phase current of the brushless DC motor.

[0003] Brushless DC motor control requires current sampling, which also plays a role in control. To maintain torque stability, the switching devices must operate at a switching frequency greater than six times the motor speed, resulting in high losses. Furthermore, the two control loops require a high computational load. Summary of the Invention

[0004] The present invention aims to at least partially overcome the deficiencies of existing brushless motor control schemes and to provide a modeling and control method for a brushless DC motor, which reduces the number of components required and improves efficiency compared to conventional vector control or PWM control.

[0005] A method for controlling a brushless DC motor includes: calculating a delay time based on a delay angle between a stator magnetomotive force and a rotor position when switching devices in a switch array connected to the brushless DC motor are switched; and controlling the state transition of the switching devices within each position interval of a Hall sensor used to detect the rotor position of the brushless DC motor based on the delay time, so as to control the switching devices to be switched with the delay time when a change in the rotor position is detected by the Hall sensor.

[0006] In the control method of the brushless DC motor, the delay angle can be obtained by the following steps: calculating the air gap length between the stator and the rotor based on the angle between the rotor position of the brushless DC motor and the synthetic magnetomotive force of the winding current; calculating the magnetic potential energy of the rotor relative to the stator based on the calculated air gap length; and calculating the delay angle based on the calculated magnetic potential energy.

[0007] In the control method of the brushless DC motor, when the control method uses proportional integral control, the proportional coefficient can be Kp=5Jw Z / 36K G , the integral coefficient can be Ki=Jw Z 2 / 36K G , where K G 6K x / J,K x is the coefficient of the transfer function from delay angle to work, J is the moment of inertia of the DC brushless motor rotor, and w Z To control bandwidth.

[0008] In the control method of the brushless DC motor, the state conversion sequence of the switching device corresponding to the position change of the Hall sensor during the rotation of the rotor can be: when 0 < calculated delay angle ≤ π / 3, relative to π / 3 < calculated delay angle ≤ π / 2, the switching state of the switching device is switched in the rotation order with an advance of π / 3 electrical angle.

[0009] In the control method of the brushless DC motor, the state conversion sequence of the switching device corresponding to the position change of the Hall sensor during the rotation of the rotor can be: when -π / 6<the calculated delay angle ≤0, relative to 0<the calculated delay angle ≤π / 3, the switching state of the switching device is switched in the rotation order with a lag of π / 3 electrical angle.

[0010] In the control method of the brushless DC motor, the switching frequency of each of the switching devices is the same as the electrical rotation speed frequency.

[0011] A computer-readable storage medium storing a computer program, which implements the above-mentioned control method for a brushless DC motor when the computer program is executed by a processor.

[0012] A computer device comprises: a processor; and a memory storing a computer program. When the computer program is executed by the processor, the control method of the brushless DC motor is implemented.

[0013] A control device for a brushless DC motor includes: a switch array connected to the three-phase windings of the brushless DC motor; a Hall sensor for detecting the rotor position of the brushless DC motor; and a controller. The controller is configured to calculate a delay time based on a delay angle between the stator magnetomotive force and the rotor position when switching devices in the switch array of the brushless DC motor are switched; and control the state transition of the switching devices within each Hall sensor position interval based on the delay time, so that when a change in rotor position is detected by the Hall sensor, the switching devices are controlled to switch with the delay time.

[0014] The controller obtains the delay angle through the following steps: calculating the air gap length between the stator and the rotor based on the angle between the rotor position of the brushless DC motor and the synthetic magnetomotive force of the winding current; calculating the magnetic potential energy of the rotor relative to the stator based on the calculated air gap length; and calculating the delay angle based on the calculated magnetic potential energy.

[0015] When the controller uses proportional integral control, the proportional coefficient Kp=5Jw Z / 36K G , integral coefficient Ki=Jw Z 2 / 36K G , where K G 6K x / J,K x is the coefficient of the transfer function from the delay angle to work, J is the moment of inertia of the rotor of the brushless DC motor, and w Z To control bandwidth.

[0016] The controller configures the state conversion sequence of the switching device corresponding to the position change of the Hall sensor during the rotation of the rotor as follows: when 0<calculated delay angle ≤π / 3, relative to π / 3<calculated delay angle ≤π / 2, the switching state of the switching device is switched in the rotation order with an advance of π / 3 electrical angle.

[0017] The controller configures the state conversion sequence of the switching device corresponding to the position change of the Hall sensor during the rotation of the rotor as follows: when -π / 6<the calculated delay angle ≤0, relative to 0<the calculated delay angle ≤π / 3, the switching state of the switching device is switched in a rotational order with a lag of π / 3 electrical angle.

[0018] The switching frequency of each of the switching devices is the same as the electrical speed frequency.

[0019] The brushless DC motor modeling and control method provided by this invention offers the following advantages: It can control the motor's speed with a reduced number of switching cycles, without requiring current parameter sampling and control. By analyzing and modeling the motor, a brushless DC motor control method is designed, simplifying the computational complexity of the control loop. The switching frequency of each switching device is equal to the electrical speed frequency, reducing switching device losses. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a block diagram of a method for controlling a brushless DC motor according to an embodiment of the present invention;

[0021] Figure 2 is a schematic diagram of a switch array of a brushless DC motor according to an embodiment of the present invention;

[0022] Figure 3 is a schematic diagram of the positional relationship between the motor winding and the rotor according to an embodiment of the present invention;

[0023] Figure 4 is a schematic diagram of the overlapping position of the air gap between the stator and the rotor of a motor according to an embodiment of the present invention;

[0024] Figure 5 is a schematic diagram of an example of the relationship between the rotor position and the Hall sensor state according to an embodiment of the present invention;

[0025] Figure 6 is a flow chart of a method for controlling a brushless DC motor according to an embodiment of the present invention;

[0026] Figure 7 FIG. 1 is a diagram of a control device for a brushless DC motor according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the present invention, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0028] Figure 1 is a block diagram of a method for controlling a brushless DC motor according to the present invention. Figure 1 Where Gc(s) is the digital controller transfer function (in the embodiment of the present disclosure, the controller may include but is not limited to a proportional-integral controller, a proportional resonant controller, an adaptive controller, and a fuzzy controller), and Go(s) is the controlled object. m is the actual speed of the motor, ω m * is the target speed of the motor, and θin is the angle between the stator magnetomotive force and the rotor position when the switch devices in the switch array of the brushless DC motor are switched.

[0029] Figure 2 FIG. 1 is a schematic diagram of a switch array of a brushless DC motor according to an embodiment of the present invention. Figure 2As shown, the switch array is connected between a DC power supply and three-phase motor windings Ua, Ub, and Uc. Taking a star connection as an example, each phase of the three-phase motor winding is connected to a corresponding phase of the three-phase output of the switch array at one end, while the other ends of the three-phase motor windings are connected to a neutral point (not shown) of the star connection. When the switch devices Q1 and Q5 in the switch array (six switch devices Q1 to Q6) are turned on and the other switch devices are turned off, the switch array state is called PNO (that is, the first upper switch device Q1 is connected to the positive pole of the power supply (P), the second lower switch device Q5 is connected to the negative pole of the power supply or ground (N), and the third upper switch device Q3 and the third lower switch device Q6 are turned off (O), collectively referred to as PNO, and so on); when the switch devices Q1 and Q6 are turned on and the other switch devices are turned off, the switch array state is called PON; when the switch devices Q2 and Q6 are turned on and the other switch devices are turned off, the switch array state is called OPN; when the switch devices Q2 and Q4 are turned on and the other switch devices are turned off, the switch array state is called NPO; when the switch devices Q3 and Q4 are turned on and the other switch devices are turned off, the switch array state is called NOP; when the switch devices Q3 and Q5 are turned on and the other switch devices are turned off, the switch array state is called ONP.

[0030] Figure 3 Schematic diagram of the relationship between the motor winding and the rotor position according to an embodiment of the present invention. Figure 3 When the state of the switch array is PNO, the direction of the synthetic magnetomotive force PNO generated by the current of phase a and phase b is taken as the reference, and the angle between the rotor position (the center axis of the SN magnetic pole) and the direction of the synthetic magnetomotive force PNO of the winding current is set as θ ψ . Air gap length l air Including the length between the rotor S pole and the b-phase winding and the length between the rotor N pole and the a-phase winding, when θ ψ In the interval (π / 6, π / 2), as θ ψ Increase the air gap length l air for:

[0031]

[0032] (where R is the rotor radius), when θ ψ In the interval (-π / 6, π / 6), as θ ψ As the length of the rotor S pole and the b-phase winding increases, the length between the rotor N pole and the a-phase winding decreases, and the length between the rotor N pole and the a-phase winding increases, so the air gap length l air is a constant value:

[0033]

[0034] Since the magnetic resistance in the magnetic circuit is mainly caused by the air gap, only when θψ The magnetomotive force changes only in the range of (π / 6, π / 2).

[0035] Figure 4 FIG. 1 is a schematic diagram of the overlap position of the air gap between the stator and the rotor of a motor according to an embodiment of the present invention. Generally, the area where the air gap overlaps between the stator and the rotor of a motor is wider. Figure 4 When the rotor rotates a certain angle relative to the stator, the overlap area is small. However, assuming that the entire magnetic circuit area S remains unchanged, the above method can still be used to calculate l air .

[0036] The total magnetic flux Φ complies with:

[0037]

[0038] The stator magnetomotive force F s for:

[0039] F s =ni (4),

[0040] n is the total number of coil turns of the two-phase winding, i is the stator phase current; the magnetomotive force F of the permanent magnet rotor r For example, the working magnetic flux satisfies:

[0041]

[0042] Where, k is the linear fitting coefficient of the demagnetization curve and its value is greater than zero, l c is the length of the permanent magnet and its value is approximately equal to 2R, B r is the residual magnetic flux of the permanent magnet, and S is the cross-sectional area of ​​the magnetic circuit. Assuming that the cross-sectional area of ​​the magnetic circuit remains unchanged at the air gap, we have:

[0043]

[0044] μ a is the air gap magnetic permeability. In summary, the magnetic flux-current relationship conforms to the following formula:

[0045] when When the magnetic link

[0046] When θ ψ In the interval (π / 6, π / 2), the magnetic potential energy W of the rotor relative to the stator m (i,θ ψ )for:

[0047]

[0048] Substitute ψ(i, θ ψ ) formula, we can get:

[0049]

[0050]

[0051]

[0052] Because, assuming that the current remains unchanged, when the cut-in angle θ in When it is greater than π / 6 and less than π / 2, from θ in The change in magnetic potential energy to π / 6 is:

[0053]

[0054] Similarly, if θ in Between -π / 6 and π / 6, from the current θ in The air gap length at -π / 6 angle remains unchanged, so let θ out is the cut-out angle of the control current, then θ out =θ in -π / 3, this value is consistent with the above in The change in magnetic potential energy from π / 6 to π / 6 is equal, so the change in magnetic potential energy at this stage is:

[0055]

[0056] For Wm(i, θ ψ ) do about θ ψ Taylor series expansion of , retaining the first-order link, can be obtained from the delay angle θ ψ The transfer function to work is:

[0057]

[0058] Therefore, the transfer function of the controlled object from the delay angle to the motor speed ω can be obtained as:

[0059]

[0060] Among them, K G is the coefficient of the controlled object transfer function from the delay angle to the motor speed ω, J is the moment of inertia of the motor shaft, and the cut-in angle θ in formula (15) in Can be obtained by in accomplish.

[0061] Design the control link parameters according to the above formula. Set the control bandwidth as w z For example, if the digital controller transfer function Gc(s) uses proportional integral (PI) control (for example, using a PI controller), the parameters can be: proportional coefficient Kp = 5Jw Z / (36KG ); Integral coefficient Ki = Jw Z 2 / (36K G ).

[0062] The Hall sensor has six feedback states within one rotor rotation cycle. These six states can be used to divide the rotor rotation cycle into six regions. When the rotor enters a new region along the rotation direction, the Hall sensor feedback state will change.

[0063] Figure 5 : is a diagram showing an example of the relationship between the rotor position and the Hall sensor position state (Hall position) according to an embodiment of the present invention. Figure 5 For example, when the rotor moves counterclockwise into the shadowed area, the state of the Hall sensor switches to 100 (i.e., Figure 5 The rotor position shown in FIG corresponds to the sensor state Hall_100). At this time, according to the aforementioned calculated θ in (t in ) Delay the corresponding time t in The corresponding relationship between the representation of the position of the Hall sensor and its actual position on the circumference of the motor is not limited to the above example.

[0064] Table 1 below is θ in Switching table when greater than 0 and less than or equal to π / 3. θ calculated by the controller in , when θ in Greater than 0 and less than or equal to π / 3 and the motor speed is ω m When the delay time t in =(π / 3-θ in ) / ω m When the Hall sensor signal changes, the controller in the system will in Then the state of the switch device is switched. For example, Figure 5 When the Hall signal becomes 100, the controller can in Thereafter, the state of the switching device is switched to PON, and as the motor rotor rotates circumferentially, the switching device may switch in sequence according to the corresponding states shown in Table 1.

[0065] Table 1

[0066] Hall position 101 100 110 010 011 001 Switch status PNO PON OPN NPO NOP ONP

[0067] Table 2 below is θ in Switching table when greater than π / 3 and less than or equal to π / 2. θ calculated by the controller in , when θ inGreater than π / 3 and less than or equal to π / 2 and when the motor speed is ω m When the delay time t in =(2π / 3-θ in ) / ω m , the switching device relative to θ in If the value is greater than 0 and less than or equal to π / 3, the switch will be advanced by π / 3 electrical angle. The delay time t based on the Hall sensor position in =(2π / 3-θ in ) / ω m , and the switching devices can be switched in the order shown in Table 2.

[0068] Table 2

[0069] Hall position 101 100 110 010 011 001 Switch status PON OPN NPO NOP ONP PNO

[0070] Table 3 below is θ in Switching table when greater than -π / 6 and less than or equal to 0. θ calculated by the controller in , when θ in Greater than -π / 6 and less than or equal to 0 and the motor speed is ω m When the delay time t in =(-θ in ) / ω m , the switching device relative to θ in If the value is greater than 0 and less than or equal to π / 3, the switch will be advanced by π / 3 electrical angle. The delay time t based on the Hall sensor position in =(-θ in ) / ω m , and the switching devices can be switched in the order shown in Table 3.

[0071] Table 3

[0072] Hall position 101 100 110 010 011 001 Switch status ONP PNO PON OPN NPO NOP

[0073] In practical applications, the motor rotor rotates π / 3 electrical degrees, and the switch state switching and the Hall sensor state switching are not completed at the same time. The switch state switching is delayed by the delay time t calculated above relative to the Hall sensor state switching. in .

[0074] The following describes a control method for a brushless DC motor according to the present invention. Figure 6 is a flow chart of a method for controlling a brushless DC motor according to an embodiment of the present invention.

[0075] Reference Figure 6 In step 610, the delay angle θ between the stator magnetomotive force and the rotor position when the switch devices in the switch array of the brushless DC motor are switched is calculated.in , to calculate the delay time t in .

[0076] Specifically, the delay angle θ can be obtained by the following steps: in : The angle θ between the rotor position of the brushless DC motor and the synthetic magnetomotive force of the winding current ψ To calculate the air gap length l between the stator and rotor air ; Based on the calculated air gap length l air Calculate the magnetic potential energy Wm(i, θ) of the rotor relative to the stator ψ ); Based on the calculated magnetic potential energy Wm(i, θ ψ ) Calculate the delay angle θ in .

[0077] In step 620, based on the delay time t calculated in step 610, in To control the state transition of the switch device within the position range of the Hall sensor used to detect the rotor position of the DC brushless motor, so as to achieve delayed switching of the switch state of the switch device relative to the time point when the Hall sensor state changes. That is, after the calculated delay time t in Then, the state transition of the corresponding switch device in each position interval of the Hall sensor is performed (that is, in each position interval of the Hall sensor, after the calculated delay time t in Afterwards, the corresponding switching devices are turned on / off, as shown in Tables 1 to 3 above).

[0078] Figure 7 FIG. 1 is a diagram illustrating a control device for a brushless DC motor according to an embodiment of the present invention.

[0079] Reference Figure 7 A control device for a brushless DC motor includes: a switch array connected to a three-phase winding of the brushless DC motor; a Hall sensor for detecting the rotor position of the brushless DC motor; and a controller. The controller is configured to calculate a delay time based on a delay angle between a stator magnetomotive force and a rotor position when switching devices in the switch array of the brushless DC motor are switched; and control the state transition of the switching devices within a position range of the Hall sensor based on the delay time, so that when a change in rotor position is detected by the Hall sensor, the switching devices are controlled to switch with the delay time.

[0080] The brushless DC motor modeling and control method provided by this invention offers the following advantages: It can control the motor's speed with a reduced number of switching cycles, without requiring current parameter sampling and control. By analyzing and modeling the motor, a brushless DC motor control method is designed, simplifying the computational complexity of the control loop. The switching frequency of each switching device is the same as the electrical speed frequency, reducing switching device losses.

[0081] According to an exemplary embodiment of the present invention, a computer-readable storage medium storing a computer program is further provided. The computer-readable storage medium stores a computer program that, when executed by a processor, causes the processor to perform the control method of a brushless DC motor according to the present invention. The computer-readable recording medium is any data storage device that can store data read by a computer system. Examples of computer-readable recording media include: read-only memory, random access memory, read-only optical disc, magnetic tape, floppy disk, optical data storage device, and carrier wave (such as data transmission via the Internet via a wired or wireless transmission path).

[0082] According to an exemplary embodiment of the present invention, a computer device is further provided. The computer device includes a processor and a memory. The memory is configured to store a computer program. The computer program is executed by the processor so that the processor executes the control method for a brushless DC motor according to the present invention.

[0083] The above describes in detail the specific embodiments of the present invention. Although some embodiments have been shown and described, those skilled in the art should understand that these embodiments may be modified and varied without departing from the principles and spirit of the present invention, the scope of which is defined by the claims and their equivalents. These modifications and variations should also be within the scope of protection of the claims of the present invention.

Claims

1. A method for controlling a brushless DC motor, wherein: The method comprises: Calculating an air gap length between a stator and a rotor based on an angle between a resultant magnetomotive force of a winding current and a rotor position when switching devices in a switch array connected to the brushless DC motor are switched; calculating the magnetic potential energy of the rotor relative to the stator based on the calculated air gap length; Calculating a delay angle based on the calculated magnetic potential energy; calculating a delay time based on the delay angle; The state transition of the switching device in each position interval of the Hall sensor is controlled based on the delay time, so that when the rotor position change is detected by the Hall sensor, the switching device is controlled to be switched with the delay time.

2. The control method of the brushless DC motor according to claim 1, wherein: When the control method uses proportional-integral control, the proportional coefficient Kp =5 Jw Z / (36 K G ), integral coefficient Ki = Jw Z 2 / (36 K G ), in, K G 6 K x / J , K x are the coefficients of the transfer function from the delay angle to work, J is the moment of inertia of the brushless DC motor rotor, w Z To control bandwidth.

3. The control method of a brushless DC motor according to claim 1, wherein: The state transition sequence of the switching device corresponding to the position change of the Hall sensor during the rotation of the rotor is: When 0<the calculated delay angle≤π / 3, relative to π / 3<the calculated delay angle≤π / 2, the switching states of the switching devices are switched in rotational order with an advance of π / 3 electrical angles.

4. The method for controlling a brushless DC motor according to claim 1, wherein: The state transition sequence of the switching device corresponding to the position change of the Hall sensor during the rotation of the rotor is: When -π / 6<the calculated delay angle ≤ 0, relative to 0<the calculated delay angle ≤ π / 3, the switching states of the switching devices are switched in a rotational order with a hysteresis of π / 3 electrical angle.

5. The control method of a brushless DC motor according to claim 1, wherein: The switching frequency of each of the switching devices is the same as the electrical speed frequency.

6. A control device for a brushless DC motor, wherein: The control device comprises: a switch array connected to the three-phase windings of the brushless DC motor; Hall sensors for detecting the rotor position of brushless DC motors; and The controller is configured to: calculate the air gap length between the stator and the rotor based on the angle between the synthetic magnetomotive force of the winding current and the rotor position when the switching devices in the switch array of the direct current brushless motor are switched; calculate the magnetic potential energy of the rotor relative to the stator based on the calculated air gap length; calculate the delay angle based on the calculated magnetic potential energy; calculate the delay time based on the delay angle; and control the state transition of the switching device within the position range of the Hall sensor based on the delay time, so as to control the switching device to be delayed by the delay time when the rotor position change is detected by the Hall sensor.

7. The control device for a brushless DC motor according to claim 6, wherein: When the controller uses proportional-integral control, the proportional coefficient Kp =5 Jw Z / 36 K G , integral coefficient Ki = Jw Z 2 / 36 K G ,in, K G 6 K x / J , K x are the coefficients of the transfer function from the delay angle to work, J is the moment of inertia of the brushless DC motor rotor, w Z To control bandwidth.

8. The control device for a brushless DC motor according to claim 6, wherein: The controller configures the state transition sequence of the switching device corresponding to the position change of the Hall sensor during the rotation of the rotor as follows: When 0<the calculated delay angle≤π / 3, relative to π / 3<the calculated delay angle≤π / 2, the switching states of the switching devices are switched in rotational order with an advance of π / 3 electrical angles.

9. The control device for a brushless DC motor according to claim 6, wherein: The controller configures the state transition sequence of the switching device corresponding to the position change of the Hall sensor during the rotation of the rotor as follows: When -π / 6<the calculated delay angle ≤ 0, relative to 0<the calculated delay angle ≤ π / 3, the switching states of the switching devices are switched in a rotational order with a hysteresis of π / 3 electrical angle.

10. The control device for a brushless DC motor according to claim 6, wherein: The switching frequency of each of the switching devices is the same as the electrical rotational speed frequency.

11. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the control method of the brushless DC motor according to any one of claims 1 to 5 is implemented.

12. A computer device, characterized in that: The computer device comprises: processor; The memory stores a computer program, and when the computer program is executed by the processor, the control method of the brushless DC motor according to any one of claims 1 to 5 is implemented.

Images