JP2008125264A - Control method and controller of brushless dc motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control method and a controller that drives a brushless DC motor without a position sensor by sine waves stably and highly efficiently without causing out-of-synchronization (step out) even with load fluctuation. <P>SOLUTION: A current phase difference estimate section 4 estimates a current phase difference ϕ from a winding current of the brushless DC motor 1 detected by a current sensor 2. A load angle estimate section 5 estimates a load angle δ from the current phase difference ϕ, the maximum drive voltage value V<SB>m</SB>, the maximum counter electromotive voltage value E<SB>m</SB>, and a command drive angular frequency ω<SP>*</SP>. A load angle deviation circuit 7 takes deviation between the command load angle δ<SP>*</SP>and an estimated load angle δ<SP>^</SP>(δ with circumflex) and sends it out to a drive voltage control section 6. The drive voltage control section 6 adjusts and controls the drive voltage V<SB>m</SB>so as to eliminate the load angle deviation. A motor drive circuit 3 generates a sine wave voltage by the drive voltage V<SB>m</SB>and the command drive angular frequency ω<SP>*</SP>to drive the brushless DC motor 1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a control method and a control apparatus for controlling a brushless DC motor (hereinafter referred to as a BLDC motor) without a position sensor.

A BLDC motor includes a rotor having a permanent magnet and a plurality of phases of windings, and detects the position of the rotor by a position sensor such as a Hall element or an encoder (see, for example, Patent Documents 1 and 2).
The position sensor has restrictions on the installation (use) environment of the BLDC motor, and cannot be used in a high temperature environment, for example. In the case of a device using a BLDC motor, for example, a handpiece of a dental treatment grinding device, the position sensor becomes an obstacle to miniaturization of the handpiece.
Therefore, a method for estimating position information without using a position sensor, so-called position sensorless, has been proposed. For example, a method for estimating rotor position information using a voltage induced in a winding of a BLDC motor (see, for example, Patent Document 3), and a method for estimating rotor position information using a winding current (for example, Patent Document). 4)).

FIG. 4 is an example of a control device in the case where rotor position information is estimated using a conventional winding current and a three-phase BLDC motor is driven in a sine wave based on the position information.
A motor drive circuit 93 composed of an inverter or the like converts the DC voltage of the DC power supply 94 into a sine wave voltage and supplies it to the three-phase BLDC motor 91. A control circuit 95 composed of a CPU or the like estimates the position information of the rotor of the BLDC motor 91 using the winding current detected by the current sensor 92 and controls the motor drive circuit 93 based on the estimated position information. The motor drive circuit 93 generates a sine wave voltage and drives the BLDC motor 91.

JP 2000-350485 A JP 2003-23791 A JP 2003-111482 A JP 2000-350487 A

When the position information of the rotor is estimated by the conventional winding current and the BLDC motor is driven in a sine wave, when the load fluctuates excessively, the BLDC motor is out of synchronization (step-out) and the drive is unstable. In order to prevent this from happening, excessively stable ultimate power must be supplied to the BLDC motor. For this reason, the driving efficiency of the BLDC motor is reduced when the load is light.
The present invention provides a control method and a control apparatus for a BLDC motor that can solve the above-mentioned problems when a BLDC motor is driven by a sine wave without a position sensor and can stably drive the BLDC motor even when the load fluctuates. The purpose is to do.

In order to achieve the object of the present invention, the brushless DC motor control method according to claim 1 generates a sine wave voltage based on the drive voltage and controls the brushless DC motor driven by the sine wave voltage. The load angle is estimated, the load angle deviation between the estimated load angle and the command load angle is taken, and the drive voltage is controlled based on the load angle deviation so that the load angle becomes equal to the command load angle. .
The brushless DC motor control method according to claim 2, wherein the motor drive circuit generates a sine wave voltage based on the drive voltage and the drive angular frequency, and the brushless DC motor is driven by the sine wave voltage. The current phase difference (φ) is estimated based on the line current, and the current phase difference (φ), the maximum value of the drive voltage (V _m ), the maximum value of the back electromotive voltage (E _m ), and the drive angular frequency (ω) The load angle (δ) is estimated based on the load angle deviation between the estimated load angle and the command load angle, and the drive voltage is controlled based on the load angle difference so that the load angle becomes equal to the command load angle. Features.
The brushless DC motor control method according to claim 3 is the brushless DC motor control method according to claim 2, wherein the load angle (δ) is:
δ = sin ⁻¹ [{V _m tan ² φ ± (E _m ² (1 + tan ² φ) −V _m ² tan ² φ) ^1/2 } / {E _m (1 + tan ² φ)}]
It estimates by these.
The brushless DC motor control method according to claim 4 is the brushless DC motor control method according to claim 1, 2 or 3, wherein the brushless DC motor is applied to a handpiece of a dental treatment grinding apparatus. It is a brushless DC motor to be used.

The brushless DC motor control device according to claim 5, wherein the motor drive circuit generates a sine wave voltage based on the drive voltage and the drive angular frequency and is driven by the sine wave voltage. Current phase difference estimation unit for estimating current phase difference (φ) based on line current, current phase difference (φ), maximum value of drive voltage (V _m ), maximum value of back electromotive voltage (E _m ), and drive angle Load angle estimator that estimates the load angle (δ) based on the frequency (ω), load angle deviation circuit that takes the load angle deviation of the estimated load angle from the command load angle, and the load angle is based on the load angle deviation A drive voltage control unit that controls the drive voltage so as to be equal to the corner is provided.
The brushless DC motor control device according to claim 6 is the brushless DC motor control device according to claim 5, wherein the load angle (δ) is:
δ = sin ⁻¹ [{V _m tan ² φ ± (E _m ² (1 + tan ² φ) −V _m ² tan ² φ) ^1/2 } / {E _m (1 + tan ² φ)}]
It estimates by these.
The brushless DC motor control apparatus according to claim 7 is the brushless DC motor control apparatus according to claim 5 or 6, wherein the brushless DC motor is a brushless DC motor used for a handpiece of a dental treatment grinding apparatus. It is characterized by being.

The BLDC motor control method and control device of the present invention adjusts and controls the drive voltage even when the load of the BLDC motor fluctuates, and maintains the load angle at the command load angle. Since the angle is kept constant, the BLDC motor is driven stably without causing out-of-synchronization (step-out) even if the load changes suddenly.
In addition, when the control method and the control device of the present invention are used, the BLDC motor can maintain the load angle at the command load angle even if the load fluctuates, so the load angle should be set in the vicinity of 90 degrees with the highest driving efficiency. Can do. Therefore, the BLDC motor is driven efficiently and stably when the load is large and small.
In addition, when the control method and control device of the present invention are used, the BLDC motor can be driven stably without causing out-of-synchronization (step-out) even when the load changes suddenly, and the rotation speed can be changed over a wide range. It is suitable for a motor used for a hand piece of a dental treatment grinding apparatus.

A control method and a control apparatus for a BLDC motor according to an embodiment of the present invention will be described.
The motor drive circuit generates a sine wave voltage based on the drive voltage, and drives the BLDC motor with the sine wave voltage. The load angle estimator estimates the load angle of the BLDC motor, and the load angle deviation circuit takes the deviation (load angle deviation) between the estimated load angle and the command load angle. The drive voltage control unit adjusts and controls the drive voltage based on the load angle deviation so that the load angle becomes the command load angle, that is, the load angle becomes equal to the command load angle. As described above, the BLDC motor control method and control apparatus according to the present embodiment controls the drive voltage so that the load angle becomes equal to the command load angle even when the load fluctuates, so that the load angle of the BLDC motor is always set to the command load. Hold on the corner.
Next, a BLDC motor control apparatus and control method according to an embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows a configuration of a control device when a BLDC motor according to an embodiment of the present invention is driven in a sine wave.
In the figure, 1 is a three-phase BLDC motor, 2 is a current sensor for detecting the winding current of the BLDC motor 1, 3 is a motor drive circuit comprising a PWM generator, an inverter, etc., 4 is a current phase difference φ (described later) Current phase difference estimation unit 5 for estimating the load angle δ (described later) during synchronous operation of the BLDC motor 1, and 6 a drive voltage control unit comprising a PID (proportional integral derivative) controller or the like. , 7 is a load angle deviation circuit that takes the deviation (load angle deviation) between the estimated load angle δ ^ (δ with a hat) and the command load angle δ ^* , ω ^* is the command drive angular frequency, V _m is the drive voltage, i _u Is a U-phase winding current, and _iv is a V-phase winding current.

The BLDC motor 1 is driven by a sine wave voltage supplied from the motor drive circuit 3. Current sensor 2, 2-phase winding current, for example, the winding current i _u, detects the i _v, and sends to the current phase difference estimation unit 4. Current phase difference estimation unit 4, the winding current i _u, i _v by estimated by calculating the current phase difference φ of instantaneous values of winding current. The load angle estimator 5 estimates the load angle δ from the current phase difference φ estimated by the current phase difference estimator 4, the maximum value V _m of the drive voltage, the maximum value E _m of the counter electromotive voltage, and the command drive angular frequency ω ^*. To do. For the sake of explanation, the load angle of the BLDC motor 1 is represented by δ, and the load angle estimated by the load angle estimator 5 is represented by δ ^ (δ with a hat). The maximum value E _m of the counter electromotive voltage is obtained by E _m = K _E × ω _s (K _E : counter electromotive voltage constant, ω _s : rotational angular velocity of BLDC motor) (described later).

The load angle deviation circuit 7 takes the load angle deviation between the estimated load angle δ ^ (δ with a hat) and the command load angle δ ^* and sends it to the drive voltage control unit 6. The drive voltage control unit 6 adjusts the drive voltage V _{m in accordance} with the load angle deviation between the estimated load angle δ ^ (δ with hat) and the command load angle δ ^* , and estimates the load angle δ ^ (δ with hat). ) is adjusted by controlling the driving voltage V _m so as to command load angle [delta] ^*. The drive voltage V _m is adjusted by, for example, a power amplifier of a PID controller. The motor drive circuit 3 generates a sine wave voltage having an angular frequency ω (corresponding to the command drive angular frequency ω ^* ) based on the command drive angular frequency ω ^* and the drive voltage V _m and supplies the sine wave voltage to the BLDC motor 1.
The estimation of the current phase difference of the current phase difference estimation unit 4, the estimation of the load angle of the load angle estimation unit 5, the control of the drive voltage of the drive voltage control unit 6 and the like can also be performed by the CPU.

In this embodiment, the deviation (load angle deviation) between the estimated load angle δ ^ (δ with a hat) and the command load angle δ ^* is eliminated, that is, the estimated load angle δ ^ (δ with a hat) is the command load angle. Since the drive voltage V _m is adjusted to be equal to δ ^* , the load angle δ is held at a constant value even if the load of the BLDC motor 1 fluctuates. The BLDC motor 1 can be driven at a desired load angle δ by changing the command load angle δ ^* .
Further, in this embodiment, the load angle δ can be estimated without using a position sensor such as a Hall element or an encoder. Therefore, a device using a BLDC motor can be reduced in size, and the load angle δ can be set using a winding current. Since the estimation is performed, the load angle δ can be instantaneously estimated when a load is applied to the BLDC motor.

Next, the setting of the load angle of this embodiment will be described.
When the BLDC motor is driven in a sine wave, the torque generated by the BLDC motor increases as the load angle δ increases from 0 degree and becomes maximum when the load angle δ is 90 degrees. When the load angle δ exceeds 90 degrees, the BLDC motor stops. Accordingly, when the load angle δ is set in the vicinity of 90 degrees within a range not exceeding 90 degrees, the driving efficiency becomes the highest.

  When the device using the BLDC motor is a device with a large load fluctuation, for example, a hand piece of a dental treatment grinding device, the hand piece rotates a grindstone (grinding blade) attached to the motor shaft to grind teeth. When shifting from a state where the teeth are not ground to a state where the grindstone is brought into contact with the teeth to be ground, the load of the BLDC motor changes suddenly and a large load torque is required. In this case, the BLDC motor according to the present embodiment can maintain the load angle at the command load angle even when the load changes suddenly, and therefore, the BLDC motor can be driven stably without causing out-of-synchronization (step-out). That is, the BLDC motor of this embodiment can be driven stably even when used in an apparatus with a large load fluctuation. In addition, since the BLDC motor of the present embodiment can maintain the load angle at the command load angle even when the load fluctuates, the load angle can also be set, for example, in the vicinity of 90 degrees with the highest driving efficiency. Therefore, the BLDC motor of this embodiment is driven efficiently and stably when the load is large and small.

Next, the load angle, drive voltage, and winding current measured for the control device of FIG. 1 will be described with reference to FIG.
FIG. 2 shows measured values of load angle, drive voltage, and winding current when the load is changed.
According to FIG. 2, it can be seen that the load angle is kept substantially constant even when the load fluctuates, and the drive voltage and winding current at that time increase in proportion to the load. That is, as the load increases, the drive voltage and winding current also increase, but the load angle is kept substantially constant. Therefore, FIG. 2 shows that the control apparatus of FIG. 1 is appropriately controlling.

Next, how to obtain (estimate) the current phase difference φ and the load angle δ will be described with reference to FIG.
FIG. 3 shows the relationship between the supply voltage, back electromotive voltage, and current of the BLDC motor.
When the BLDC motor is operated synchronously, the line voltages V _uv , V _vw , V _wu supplied to the BLDC motor are equal, and the voltage and current are both balanced. Also, the electrical characteristics of each winding of the BLDC motor are equal, and the inductances L _u , L _v , L _w and resistances R _u , R _v , R _w of each winding can be expressed as follows.
L _u = L _v = L _w = L (1)
R _u = R _v = R _w = R (2)

ここで、
φ＝φ₁＋φ₂
φ₁：巻線インダクタンスＬと巻線抵抗Ｒによる電流位相の遅れ
φ₂：逆起電圧（逆起電力）の影響による電流位相の遅れ（負荷角δの影響に
よる遅れ）
φ₁＝ｔａｎ^-1（ωＬ／Ｒ） When each phase current is balanced, the winding current of the U phase i _u, the winding current of the V-phase i _v, using the maximum value I _m of the current can be expressed as follows.

here,
φ = φ ₁ + φ ₂
φ ₁ : Current phase delay due to winding inductance L and winding resistance R
φ ₂ : Current phase delay due to back electromotive force (back electromotive force)
Delay)
φ ₁ = tan ⁻¹ (ωL / R)

Using equations (3) and (4), the maximum current value _Im is obtained.

When three-phase currents are balanced, because the same maximum value I _m of each phase current, equation (5), we obtain the following equation (6).

The following equation is obtained from equation (7).

When φ is obtained from equation (9), the following equation is obtained.

ここで、
Ｖ_m：Ｕ相の駆動電圧の最大値
Ｅ_m：Ｕ相の逆起電圧の最大値
Ｅ_m＝Ｋ_E×ω_s
Ｋ_E：逆起電圧定数
ω_s：ＢＬＤＣモータの回転角速度
ω_s＝ω^*／ｐ
ω^*：指令駆動角周波数
ｐ：ＢＬＤＣモータの極対数 The U-phase terminal voltage v _u and the counter electromotive voltage _eu are expressed by the following equations, respectively.

here,
V _m : Maximum value of U-phase drive voltage E _m : Maximum value of U-phase back electromotive force E _m = K _E × ω _s
K _E : Back electromotive force constant ω _s : Rotational angular velocity of BLDC motor ω _s = ω ^* / p
ω ^* : Command drive angular frequency p: Number of pole pairs of BLDC motor

The estimated current i _u ^ (hat i _u ) of the U-phase winding of the Y connection shown in FIG. 3 indicates the U-phase drive voltage, counter electromotive voltage, and winding resistance when the winding inductance L _u can be ignored. It can be obtained using.

であるので、βを求めると次式になる。

here,

Therefore, when β is obtained, the following equation is obtained.

The phase of the U-phase winding current i _u (actually flowing through the BLDC motor winding) expressed by the equation (3) and the estimated winding current i _u ^ (hatted i _u ) estimated by calculation are equal in phase. Therefore, equation (10) and equation (14) are equal.

Equation (15) is modified to obtain the following equation.
V _m tan (φ) = E _m tan (φ) sin (δ) + E _m cos (δ) (16)
Here, when sin (δ) is solved using a relational expression of sin ² (δ) + cos ² (δ) = 1, the following expression is obtained.

Solving equation (17) with sin (δ) gives the following equation.

同様に式（１６）をｓｉｎ²（δ）＋ｃｏｓ²（δ）＝１の関係式を利用してｃｏｎ（δ）について解くと次式になる。

From this, the load angle δ is obtained by the following equation.

Similarly, when equation (16) is solved for con (δ) using a relational expression of sin ² (δ) + cos ² (δ) = 1, the following equation is obtained.

一方、式（１８）と式（２０）を用いてδを求めると次式になる。

Therefore, when δ is obtained using equation (20), the following equation is obtained.

On the other hand, when δ is obtained using equations (18) and (20), the following equation is obtained.

となる。 From this, δ is

It becomes.

The load angle δ can be obtained using any of the equations (19), (21), and (23). The calculation can speed up the control cycle by using a method with a small calculation amount, and can improve the control performance. Of the formulas (19), (21), and (23), the formula (19) has the smallest amount of calculation, so that the calculation is easy. Moreover, since Formula (23) is a formula combining Formula (19) and Formula (21), the calculation accuracy may be lower than Formula (19) and Formula (21).
As described above, the current phase difference φ and the load angle δ can be obtained based on the winding currents i _u and i _v , the maximum value V _m of the drive voltage, and the maximum value E _m of the back electromotive voltage. The current phase difference φ can be estimated by the current phase difference estimation unit 4 in FIG. 1 as described above, and the load angle δ can be estimated by the load angle estimation unit 5 using the estimated current phase difference φ. .

The structure of the control apparatus in the case of carrying out the sine wave drive of the BLDC motor which concerns on the Example of this invention is shown. The load angle, drive voltage, and winding current which were measured about the control apparatus of FIG. 1 are shown. The relationship between the supply voltage of the BLDC motor, the back electromotive force, the winding current, etc. is shown. The structure of the control apparatus in the case of driving a conventional BLDC motor with a sine wave is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 BLDC motor 2 Current sensor 3 Motor drive circuit 4 Current phase difference estimation part 5 Load angle estimation part 6 Drive voltage control part 7 Load angle deviation circuit

Claims (7)

  In a control method of a brushless DC motor that generates a sine wave voltage based on a drive voltage and drives with the sine wave voltage, a load angle is estimated, and a load angle deviation between the estimated load angle and a command load angle is obtained. A control method for a brushless DC motor, wherein the drive voltage is controlled based on the deviation so that the load angle becomes equal to the command load angle. The motor drive circuit generates a sine wave voltage based on the drive voltage and the drive angular frequency, and estimates the current phase difference (φ) based on the winding current in the control method of the brushless DC motor driven by the sine wave voltage. The load angle (δ) is estimated based on the current phase difference (φ), the maximum value of the drive voltage (V _m ), the maximum value of the back electromotive force (E _m ), and the drive angular frequency (ω), and the command load angle A control method for a brushless DC motor, wherein the drive voltage is controlled so that the load angle becomes equal to the command load angle based on the load angle difference. In the control method of the brushless DC motor according to claim 2, the load angle (δ) is:
δ = sin ⁻¹ [{V _m tan ² φ ± (E _m ² (1 + tan ² φ) −V _m ² tan ² φ) ^1/2 } / {E _m (1 + tan ² φ)}]
A control method for a brushless DC motor, characterized in that   4. The brushless DC motor according to claim 1, wherein the brushless DC motor is a brushless DC motor used for a handpiece of a dental treatment grinding apparatus. Control method. The motor drive circuit generates a sine wave voltage based on the drive voltage and the drive angular frequency, and estimates the current phase difference (φ) based on the winding current in the control device of the brushless DC motor driven by the sine wave voltage. Estimate load angle (δ) based on current phase difference estimator, current phase difference (φ), maximum drive voltage (V _m ), maximum back electromotive force (E _m ), and drive angular frequency (ω) Load angle estimator, load angle deviation circuit that takes the load angle deviation of the estimated load angle from the command load angle, drive voltage control that controls the drive voltage so that the load angle becomes equal to the command load angle based on the load angle deviation A controller for a brushless DC motor, characterized by comprising a section. In the control device for a brushless DC motor according to claim 5, the load angle (δ) is:
δ = sin ⁻¹ [{V _m tan ² φ ± (E _m ² (1 + tan ² φ) −V _m ² tan ² φ) ^1/2 } / {E _m (1 + tan ² φ)}]
The control apparatus of a brushless DC motor characterized by estimating by these.   7. The brushless DC motor control apparatus according to claim 5, wherein the brushless DC motor is a brushless DC motor used for a hand piece of a dental treatment grinding apparatus.

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