CN1387310A - Electric machine driving device - Google Patents

Abstract

A motor drive device for controlling a three-phase np pole (np is an even number not less than 4) brushless DC motor, which includes a DC/AC conversion unit that includes a plurality of switching elements and is capable of turning on and off all switching elements in response to The switching element is turned on and off by the control signal of the switching element, the DC voltage is converted into a desired pseudo AC voltage, and the pseudo AC voltage is output to the brushless DC motor; the control signal is used to open the switching element Pulse Width Modulation (PWM) with ON and OFF; a position detection unit for detecting a rotational phase obtained from an induced voltage of a three-phase armature winding of a brushless DC motor to output rotational phase information; and a duty control unit for outputting a control signal .

Description

motor drive

technical field

The present invention relates to a motor drive for controlling the frequency of a brushless direct current (DC) motor.

Background technique

As shown in FIG. 7, a 120° excitation control (square wave excitation control) type motor driving device is known, and this device is used to control a three-phase np pole (np is an even number not less than 4) brushless DC motor. revolutions. As shown in FIG. 7, this known motor driving device includes a DC/AC converter 2 for converting a DC voltage into a pseudo AC voltage to output a pseudo AC voltage to a motor 1 and a motor for detecting the rotor position of the motor 1. Magnetic pole position detector 3. A pulse width modulation (PWM) duty controller 5' outputs an added voltage to the DC/AC converter 2 to control the number of revolutions of the motor 1, and outputs a duty signal to control the frequency and phase of the motor 1. The DC/AC converter 2 is composed of six switching elements that are turned on and off at high speed.

In the existing motor driving device described above, the DC/AC converter 2 converts the DC voltage into a pseudo AC voltage having a variable frequency and a variable phase, and outputs the pseudo AC voltage to the motor 1 . The number of revolutions of the motor 1 can be controlled by changing the frequency and phase of the pseudo AC voltage output from the DC/AC converter (hereinafter referred to as "inverter frequency"). A PWM duty controller 5' controls this inverter frequency. According to the frequency command value ωs input to the PWM duty controller 5', the PWM duty controller 5' outputs six different basic patterns to the DC/AC converter 2 to turn on the six switching elements of the DC/AC converter 2 . The inverter frequency output by the DC/AC converter 2 can be controlled by turning on and off the switching elements in the basic pattern. Here, the inversion frequency is the reciprocal value of one period of the basic pattern.

When the number of revolutions of the motor 1 changes, according to the rotation phase information corresponding to the change of the magnetic pole position detector 3 to the frequency command value ωs, the PWM duty controller 5' can change the inverter of the DC/AC converter 2 Frequency to control the number of revolutions of motor 1. Regardless of the inverter frequency (phase) or voltage magnitude output from the DC/AC converter 2, the phase detection characteristic of the magnetic pole position detector 3 can directly detect the induced voltage generated from the motor 1 and estimate and calculate the motor 1 the magnetic pole position.

Based on the rotational phase information of the magnetic pole position detector 3, the PWM duty controller 5' outputs six basic patterns to the DC/AC converter 2. The DC/AC converter 2 is provided with six switching elements in total, including an upper branch switching element and a lower branch switching element for each of the U, V, and W phases.

In the case of performing motor driving by such a known motor driving device, when the load torque applied to the motor 1 is constant, the number of revolutions of the motor 1 is always constant. Therefore, the output timing of each basic pattern PTNm (m=1 to 6) is also substantially fixed on the basis of the following reasons. That is to say, since the PWM duty width output by the PWM duty controller 5 is fixed and has nothing to do with the rotation angle, the torque output by the motor 1 is also fixed. Therefore, due to the difference between the output torque and the load torque The resulting residual torque is assumed to be always zero. As a result, when the load torque applied to the motor 1 is fixed, the motor 1 rotates at a substantially constant speed, so excellent speed control performance is obtained.

However, in case the load torque of the motor 1 is not constant with respect to the rotation angle of the motor 1, the residual torque caused by the difference between the output torque and the load torque makes the motor 1 The rotational speed of the motor 1 changes momentarily, so the speed control of the motor 1 is unstable. Therefore, the mechanical system should be made robust against noise and vibration, and the occurrence of this problem greatly increases the production cost, and the motor 1 and the mechanical system may break if measures against noise and vibration are not very useful.

Contents of the invention

Therefore, in order to eliminate the above-mentioned disadvantages of the prior art, it is an object of the present invention to provide a motor drive device in which not only the residual torque caused by the difference between the output torque and the load torque is minimized, but the mechanical system is reduced. Noise and vibration, so that the measures against these noise and vibration can be simplified without increasing the production cost of the circuit.

In order to achieve the purpose of the present invention, the present invention provides a motor drive device for controlling a three-phase np pole (np is an even number not less than 4) brushless DC motor, which includes a DC/AC conversion unit, and the conversion unit includes a plurality of Switching elements, and by turning on and off each switching element in response to a control signal, the DC voltage is converted into a required pseudo AC voltage, and the pseudo AC voltage is output to the brushless DC motor. Pulse Width Modulation (PWM) control of the OFF switching element. The motor drive device further includes a position detection unit that detects a rotational phase obtained from a three-phase armature winding of the brushless DC motor to output rotational phase information; and a duty control unit that outputs a control signal.

The duty control unit includes a reference duty determination unit for determining a reference duty value in the control signal on the basis of the frequency command value for obtaining the The rotational speed of the brushless DC motor is based on the rotational speed of a correction unit for correcting a reference duty value based on the output duty value and an output unit for outputting a control signal including the output duty value. The duty control unit includes: a part for determining the reference duty value, which is used to determine the reference duty value in the control signal according to the frequency command value; a correction part, which is used to equal np of one rotation angle of the brushless DC motor in the rotation angle interval - Obtaining the rotation speed of the brushless DC motor in the case of division, so as to correct the reference duty value into an output duty value according to the rotation speed; and an output part, used for outputting a control signal including the output duty value.

Description of drawings

Objects and features of the present invention will be made clear from the following description of the embodiments with reference to the accompanying drawings, in which:

Fig. 1 is a block diagram showing the structure of a motor drive device of an embodiment of the present invention;

2 is a schematic diagram illustrating a basic pattern of a control signal output by a PWM duty controller used in the motor drive device of FIG. 1;

Fig. 3 is a schematic diagram illustrating detection of motor speed and speed difference by the motor drive device of Fig. 1;

Fig. 4 is a flow chart showing the duty value correction process in the motor drive device of Fig. 1;

FIG. 5 is a schematic diagram illustrating the use of a nonlinear algorithm to correct the velocity difference in FIG. 3;

6A is a graph showing the relationship between the reference duty value and the output duty value in the PWM duty controller of FIG. 2; FIG. 6B is a graph showing the relationship between the output torque and the load torque of the motor in FIG. 3;

Fig. 7 is a block diagram showing the structure of a conventional motor drive device.

Before proceeding to describe the present invention, it should be noted that like reference numerals are used to designate like parts in the various drawings.

Detailed ways

An embodiment of the present invention is described below with reference to the accompanying drawings. (Structure of motor drive unit)

Fig. 1 shows the structure of a motor drive device according to a specific embodiment of the present invention. The motor drive device of FIG. 1 is arranged to be able to control the number of revolutions of three-phase np poles (np is an even number not smaller than 4) of the brushless DC motor 1 by 120° field control (square wave field control).

As shown in FIG. 1 , this motor driving device includes: a DC/AC converter 2 for converting a DC voltage into a pseudo AC voltage to output a pseudo AC voltage to the motor 1; a magnetic pole position for detecting the rotor position of the motor 1 a detector 3; a speed difference detector 4 for detecting the rotational speed of the motor 1 from the rotor position of the motor 1 measured by the magnetic pole position detector 3, and a pulse width modulation (PWM) duty controller 5 for supplying DC/ The AC converter 2 outputs a voltage applied to control the number of revolutions of the motor 1 and a PWM duty signal for controlling the frequency and phase of the motor 1 . The DC/AC converter 2 includes six switching elements 2u, 2v, 2w, 2x, 2y, 2z that are turned on and off at high speed.

According to the motor drive device arranged as described above, the DC/AC converter 2 converts the DC voltage supplied from the DC power supply VDC into a pseudo AC voltage whose frequency and phase are variable, and outputs the pseudo AC voltage to the motor 1 . The number of revolutions of the motor 1 is controlled by changing the frequency and phase of the output of the DC/AC converter 2 (hereinafter referred to as "inversion frequency"). This inverter frequency is controlled by PWM duty controller 5 . According to the frequency command value ωs input to the PWM duty controller 5, the PWM duty controller 5 outputs to the DC/AC converter 2 six different switching elements 2u to 2z for turning on or off the DC/AC converter 2. Basic pattern signal. By using these basic patterns to turn on or off the switching elements 2u to 2z, the inverter frequency output by the DC/AC converter 2 can be controlled.

According to the output signal of the magnetic pole position detector 3, the commutation switching of the respective basic pattern signals is completed. The magnetic pole position detector 3 detects the zero-crossing signal of the three-phase induced voltage of the motor 1 , and outputs its detection signal to the speed difference detector 4 . The zero-crossing signal occurs six times for the three phases in one conduction angle cycle. At the same time, (3×np) zero-crossing signals are generated during one rotation of the motor 1 . When the zero-crossing signal of the magnetic pole position detector 3 has been input into the PWM duty controller 5 through the speed difference detector 4, the PWM duty controller 5 follows the basic patterns PTN1, PTN2, ---, PTN6, PTN1, --- The sequence of each basic pattern signal is switched according to the zero-crossing signal.

At the same time, the number of revolutions of the motor 1 can be judged from the zero-crossing signal. It is assumed here that for one rotation cycle, the time constant of phase change and the time constant of torque change are not less than 2 with respect to the rotation angle of the motor 1 . (basic pattern)

The basic pattern output by the PWM duty controller 5 is described below. The basic pattern is a pulse signal for driving the switching elements 2u to 2z of the DC/AC converter 2 . In one conduction angle cycle of the output voltage of the DC/AC converter 2, the basic patterns include six basic patterns. The inversion frequency is equal to the reciprocal of one cycle of the basic pattern.

Fig. 2 shows an example of a basic pattern. As shown in FIG. 2 , the first basic pattern PTN1 electrically conducts the U-phase upper-arm switching element 2u with the V-phase lower-arm switching element 2y. The second basic pattern PTN2 electrically conducts the upper arm switching element 2u of the U-phase with the lower arm switching element 2z of the W-phase. The third basic pattern PTN3 electrically conducts the V-phase upper arm switching element 2v with the W-phase lower arm switching element 2z. The fourth basic pattern PTN4 electrically conducts the V-phase upper arm switching element 2v with the U-phase lower arm switching element 2x. The fifth basic pattern PTN5 electrically conducts the W-phase upper arm switching element 2w with the U-phase lower arm switching element 2x. The sixth basic pattern PTN6 electrically conducts the W-phase upper arm switching element 2w with the V-phase lower arm switching element 2y. (Operation of the motor drive unit)

When the load torque applied to the motor 1 is always constant, the number of revolutions of the motor 1 is also always constant. Therefore, at this time, the basic pattern PTNm' (m=1 to 6) is output every time the rotor rotates through the conduction angle of 60°, and the output period is constant for the following reason. That is to say, because the PWM duty value output by the PWM duty controller 5 is fixed and has nothing to do with the rotation angle of the motor, the output torque of the motor 1 is also fixed in essence, so that it can be assumed to be equal to the output torque and the load in essence. The residual torque of the torque difference is always zero.

Let "To" and "Tl" denote the output torque and load torque respectively, "ω" denote the speed of the motor 1, and "Jm" denote the combined moment of inertia of the motor 1 and the load mechanical system, then satisfy the following physical laws ( 1).

     dω/dt＝(To-Tl)/Jm≈0------(1)

However, when the output torque To is basically fixed and the load torque Tl changes momentarily, there is the following relationship (2).

dω/dt＝(To-Tl)/Jm≠0------(2)

According to the relationship (2), the speed ω of the motor 1 changes momentarily, so the motor 1 does not rotate at a constant speed.

In order to fix the rotational speed ω of the motor 1 under the condition that the load torque T1 varies momentarily, equation (1) should be satisfied. If the difference between the output torque To and the load torque T1 can be significantly reduced to zero by controlling the output torque To, the variation in the rotational speed of the motor 1 will be reduced. Therefore, in the motor driving device of the present invention, the speed difference detector 4 detects the speed variation of the motor 1, and makes the duty value controlled so that the output torque To and the load torque T1 become equal to each other.

At the same time, the rotation speed of the motor 1 can be changed by controlling the duty value of the basic pattern output by the PWM duty controller 5 . That is to say, as the PWM duty value of the basic pattern increases, the rotational speed of the motor 1 increases accordingly, and as the PWM duty value of the basic pattern decreases, the rotational speed of the motor 1 decreases accordingly. When the rotational speed of the motor 1 is fixed, if the PWM duty value increases, the output torque To of the motor 1 increases. As mentioned above, the PWM duty value is closely related to the rotation speed and output torque of the motor 1 .

Therefore, in the motor drive device of the present invention, the PWM duty value determined from the frequency command value ωs to control the rotation speed of the motor 1 is called a "reference duty value", and the correction duty value limiting the rotation speed of the motor 1 is defined. By adding the reference duty value to the modified duty value, the duty value to be output can be obtained, which is called "output duty value". Using the output duty value, it is possible to make the output torque coincide with the load torque, and thus smooth motor drive can be realized. Meanwhile, the reference duty value Do is determined by the following equation (3), where "Ds" represents a predetermined duty value determined by the frequency command value ωs, while "KD" is a constant, and "ω0" represents the motor 1 average speed.

Do＝Ds+KD(ωs-ω0)-------(3)

The calculation of the corrected duty value and the corrected reference duty value by using the corrected duty value is described in detail below. (Determination of motor speed and speed change)

Due to the characteristics of the three-phase motor, the desired accuracy can be improved by obtaining the speed change value according to the zero-crossing signal of one of the three phases U, V and W. That is to say, in the case of using the zero-crossing signals of at least two phases of U, V and W to simultaneously obtain the speed change amount, the speed difference will be composed of U phase, V phase and W phase of the magnetic pole position detector 3 Due to the difference in components, and the great influence of the difference in electrical characteristics between the U phase, V phase and W phase of the motor 1 caused by the excitation balance and the rotor installation tolerance, etc., it is impossible to obtain a high-precision speed change. In this embodiment, in order to eliminate these influences as much as possible, the rotational speed and the speed variation are obtained according to the zero-crossing signal generated by the same phase.

That is to say, since the motor 1 is a three-phase motor, np zero-crossing signals are generated in a certain phase during one revolution of the rotor. Therefore, in this embodiment, at the rotation angle interval of (360°/np), the rotation speed ω _θ within the rotation angle range of (360°/np) is obtained according to the zero-crossing signal generated by a certain phase. Also, the speed difference Δω between the rotational speed ω _θ obtained at a certain point in time and the rotational speed ω _θ+360 at a conduction angle of 360° from that time point is obtained by the following equation (4).

Δω＝ω _θ+360 -ω _θ --------(4)

By using the zero-crossing signal of a certain phase, the rotational speed ω _θ and the rotational speed ω _θ+360 at the angle at which the conduction angle passes through one cycle from the instant of the rotational speed ω _θ can be obtained. That is, the speed difference (speed change value) can be detected from the zero-crossing signal based only on the induced voltage information of one phase.

The calculation of the velocity is correctly described below with reference to FIG. 3 . As shown in FIG. 3 , the basic patterns PTN1 to PTN6 are sequentially output. For the convenience of explanation, it is assumed here that "ω _n,m " represents the rotational speed. When the rotation angle range of one revolution of the motor 1 is divided into np parts, the subscript "n" indicates the divided part used as a starting point for obtaining the rotational speed. Meanwhile, the subscript "m" indicates the position (angle) of the starting point in each divided section. That is, when the subscript m is 0, the rotational speed is calculated by taking the initial position of each divided area as a starting point. When the subscript m is 1, the rotational speed is calculated by taking a conduction angle offset of 60° from the initial position of each divided area as a starting point. When the subscript m is 2, the rotational speed is calculated by taking the position offset by the conduction angle of 120° from the initial position as the start.

For example, the rotational speed ω _n,0 in FIG. 3 indicates that an angle of 0° is used as a starting point within a conduction angle range of 180° from the output of the basic pattern PTN1 to the output of the basic pattern PTN4. The rotational speed ω _n,0 can be obtained from the two output times given by the output time of the basic pattern PTN1 and the output time of the basic pattern PTN4 and the zero-crossing signal of the U phase.

The meaning of the rotational speed ω _n,m is described below with reference to FIG. 3 . The rotation speed ω _n,0 is the rotation speed during the period from the output of the basic pattern PTN1 to the output of the basic pattern PTN4, and can be obtained by the zero-crossing signal of the U phase. The rotation speed ω _n,1 is the rotation speed during the period from the output of the basic pattern PTN2 to the output of the basic pattern PTN5, and can be obtained by the zero-crossing signal of the W phase. The rotation speed ω _n,2 is the rotation speed during the period from the output of the basic pattern PTN3 to the output of the basic pattern PTN6, and can be obtained by the zero-crossing signal of the V phase. The rotation speed ω _n+1,0 is the rotation speed during the period from the output of the basic pattern PTN4 to the output of the basic pattern PTN1, and can be obtained by the zero-crossing signal of the U phase. The rotation speed ω _n+1,1 is the rotation speed during the period from the output of the basic pattern PTN5 to the output of the basic pattern PTN2, and can be obtained by the zero-crossing signal of the W phase. The rotation speed ω _n+1,2 is the rotation speed during the period from the output of the basic pattern PTN6 to the output of the basic pattern PTN3, and can be obtained by the zero-crossing signal of the V phase.

The rotation speed ω _n+2,0 is the rotation speed during the period from the output of the basic pattern PTN1 to the output of the basic pattern PTN4, and can be obtained by the zero-crossing signal of the U phase. The rotation speed ω _n+2,1 is the rotation speed during the period from the output of the basic pattern PTN2 to the output of the basic pattern PTN5, and can be obtained by the zero-crossing signal of the W phase. The rotation speed ω _n+2,2 is the rotation speed during the period from the output of the basic pattern PTN3 to the output of the basic pattern PTN6, and can be obtained by the zero-crossing signal of the V phase. The rotation speed ω _n+3,0 is the rotation speed during the period from the output of the basic pattern PTN4 to the output of the basic pattern PTN1, and can be obtained by the zero-crossing signal of the U phase. The rotation speed ω _n+3,1 is the rotation speed during the period from the output of the basic pattern PTN5 to the output of the basic pattern PTN2, and can be obtained by the zero-crossing signal of the W phase. The rotation speed ω _n+3,2 is the rotation speed during the period from the output of the basic pattern PTN6 to the output of the basic pattern PTN3, and can be obtained by the zero-crossing signal of the V phase. (Correction of Duty Value)

Next, the rotational speed ω _n,m of each divided part can be obtained, and the speed difference Δω _n,m can be obtained at 60° conduction angle intervals. By multiplying the speed difference Δω _n,m by a correction factor K (K>0), the corrected duty value can be obtained by the following formula (5).

Corrected duty value = -K·Δω _{n, m} ------(5)

The speed difference Δω _n,m and the obtained corrected duty value are stored in the speed storage area and the corrected duty storage area of the PWM duty controller 5, respectively. For example, in Fig. 3, the rotational speed ω _{n obtained by using the zero-crossing signal of the U phase and the output moment of the previous basic pattern PTN4 earlier than the above-mentioned basic pattern PTN4 360° conduction angle, 0} obtained rotational speed ω _{n+ 2,0} Calculate the corrected duty value and store it in the corrected duty storage area.

As described below, the modified duty value stored at this time is used to obtain the duty value to be used when passing through the conduction angle of {180°×(np-2)}. The purpose is to output the corrected duty value of the rotation speed ω _n,0 when the motor rotation angle again becomes consistent with the mechanical rotation angle corresponding to the portion of the basic pattern PTN4 leading by 360°. By using the modified duty value, the output torque of the motor 1 can be controlled at 60° conduction angle intervals. (Control flowchart of motor drive unit)

Fig. 4 is a flow chart showing the control of the motor drive unit in the above operation. As shown in FIG. 4, when the basic pattern PTNm' is output at step S11, the rotational speed at a time point changed from a time to a time point 180° conduction angle prior to the time is obtained at step S12. Then in step S13, the speed difference Δω _n,m is calculated by the difference between the rotational speed ω _n, m and the rotational speed ω _n+2,m obtained at the time point of 360° conduction angle after the time point of this rotational speed ω _n,m . At this time, since the speed difference Δω _n,m includes the detection error and calculation error of the magnetic pole detector 3 to be considered, the corrected speed difference Δω _n,m is obtained by correcting the speed difference Δω _n,m in step S14 , to minimize the effects of these errors.

Specifically, the correction is performed by the nonlinear arithmetic operation shown in FIG. 5 . The processing method shown in FIG. 5 satisfies the following equation (6), in which Δω' represents a speed difference, and α (α>0) represents a constant obtained through experiments.

Next, in step S15, a corrected duty value ΔD _n,m for correcting the reference duty value Do is obtained by multiplying the corrected speed difference Δω n _,m ′ by a correction factor K. Then, in step S16, this corrected duty value ΔD _n,m is stored in the corrected duty storage area of the PWM duty controller 5 . After that, the reference duty value Do is input to the PWM duty controller 5 at step S17. In step S18, the corrected duty value ΔD _{n-(np -2), m} . Then at step S19, the output duty value D' is obtained from the corrected duty value _{ΔDn-(np-2),m} and the reference duty value Do using the following equation (7).

D'＝Do+ΔD _{n-(np-2), m} ------(7)

In step S20 , PWM duty controller 5 outputs the output duty value D′ to DC/AC converter 2 .

FIG. 6A shows the above obtained output duty value, the relationship between the reference duty value and the corrected duty value. As shown in FIG. 6A, in the motor drive device of this embodiment, the output duty value is obtained by correcting the reference duty value determined by the frequency command value ωs by the corrected duty value, and by using the output duty value value to control the operation of each switching element of the DC/AC converter 2. Therefore, as shown in FIG. 6B, since the output torque of the motor 1 corresponding to the load torque can be generated, the motor 1 can be operated stably. That is to say, as shown in FIG. 6B, since the output torque changes so as to be substantially consistent with the load torque, the residual torque in equation (1) is reduced, so the change value of the motor 1 rotational speed ω with time decrease.

Meanwhile, in the above description, a three-phase brushless DC motor has been described. However, the present invention can also be used in a motor with a number of phases other than 3, in which the speed of the motor and the range of the speed difference can be set to the speed obtained from the zero-crossing information of the armature winding of the same phase and speed difference.

Same as the description of the motor driving device of the present invention, the motor speed is obtained according to the zero-crossing information of the same phase, and the reference duty value is controlled according to the speed. Therefore, since the influence of the dissipation of each constituent element of the position detector has been eliminated as much as possible, and the armature winding difference in each phase is also eliminated, the rotation speed can be detected very accurately so that a high Resolution corrects the reference duty value to the output duty value. Therefore, in the motor drive device, since the residual torque generated by the difference between the output torque of the motor and the load torque of the mechanical system can be further limited by using the output duty value that has been accurately corrected, the mechanical system is reduced. Noise and vibration, thereby simplifying the measures against noise and vibration. Furthermore, the production cost of the circuit is reduced.

At the same time, in the motor drive device, since the armature winding generates a zero-crossing signal of the induced voltage, the motor speed can be obtained, that is, at intervals of 60° conduction angle, the residual torque can be more accurately controlled, and can be controlled through constraints Noise and vibration for higher motor performance.

At the same time, in the motor drive device, since the speed difference between the rotation speeds can be detected, the residual torque can be roughly estimated, and thus, the speed control performance can be stabilized. At this time, the obtained speed difference can be corrected by non-linear algorithm calculation to further improve the control stability, and obtain a motor drive device with high operational stability that practically eliminates the swing or out of step of the motor.

Also, in the motor drive unit, since the output duty value can be updated at 60° conduction angle intervals, the output duty value can be precisely controlled at 60° conduction angle intervals, so that higher motor performance can be obtained by restraining noise and vibration .

In addition, in the motor drive device, since the conduction angle of {180°×(np-2)} passes from the time point when the output duty value is obtained, the phase of the output torque of the motor and the phase of the load torque can be made to coincide, so that Minimizing residual torque, therefore, results in higher performance motors and more stable mechanical systems by limiting noise and vibration.

In addition, in the motor drive device, since the correction duty value used to control the speed difference is added to the reference duty value used to control the motor speed, the speed control system of the motor can respond well to the speed difference or the load difference. , so that a motor drive suitable for speed servo operation can be obtained.

Claims (8)

1. A motor drive device for controlling a three-phase np pole brushless DC motor, wherein np is an even number not less than 4, said device comprising: a DC/AC converting unit, which includes a plurality of switching elements, and is capable of converting a DC voltage into a desired pseudo AC voltage by turning on and off the switching elements in response to a control signal for turning on and off the switching elements, and supplying The brushed DC motor outputs the pseudo AC voltage; the control signal is used for pulse width modulation (PWM) of switching elements on and off; a position detection unit for detecting a rotational phase obtained from an induced voltage of a three-phase armature winding of the brushless DC motor to output rotational phase information; a duty control unit for outputting a control signal; It is characterized in that the duty control unit includes: a reference duty determination part, which is used to determine the reference duty value in the control signal according to the frequency command value; The rotation speed of the brushless DC motor is obtained by one-half of the angle interval, so that the reference duty value is corrected to the output duty value according to the rotation speed; and an output part is used for outputting an output control signal including the output duty value. 2. The motor drive device according to claim 1, wherein the correction part of the duty control unit has the same phase as the zero-crossing moment when the induced voltage of the armature winding is generated and the zero-crossing time is generated. Subsequent zero-crossing generation time, and the rotational speed of the brushless DC motor is obtained from the moment when the zero-crossing passes through the conduction angle of 180°. 3 . The motor drive device according to claim 1 , wherein the correction part of the duty control unit obtains the rotation speed at each zero crossing generated in the induced voltage of each phase of the armature winding. 4 . 4. The motor drive device according to claim 1, further comprising: A speed difference detection unit is used to detect the difference between a rotational speed and a subsequent rotational speed generated from the rotational speed through a 360° conduction angle; Wherein, the correction part of the duty control unit corrects the reference duty value according to the difference. 5 . The motor drive device according to claim 4 , wherein, after the speed difference detection unit detects the difference, the speed difference detection unit also corrects the difference through a nonlinear algorithm. 6 . 6 . The motor drive device according to claim 1 , wherein the duty control unit updates the output duty value every time the brushless DC motor rotates through a conduction angle of 60°. 7. The motor drive device according to claim 1, characterized in that, the output part of the duty control unit outputs an output duty value according to the rotational speed, as a process from the output duty value through {180°×( np-2)} The subsequent output duty value of the conduction angle. 8. The motor drive device according to claim 4, wherein the correction part of the duty control unit determines a modified duty value according to the difference, and adds the modified duty value to the reference duty value. NULL gets the output duty value.

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