JPH0642793B2 - Brushless DC motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless DC motor, and more particularly to a brushless DC motor that obtains a position detection signal from a motor terminal voltage by using a filter and a comparator. is there.

[Background of the Invention]

A conventional three-phase brushless DC motor of the back electromotive force detection type, which has a back electromotive force position detection circuit including a filter and a comparator, which creates a position detection signal from a motor terminal voltage, has been disclosed in, for example, Japanese Patent Laid-Open No. -162793, Japanese Patent Publication No. 59-36519, The Institute of Electrical Engineers of Japan, B, 105, 5
Issue (1985) "Brushless Motor without a Shaft Posit
ion Sensor "(brushless motor with position adjustment sensor).

In these conventional brushless DC motors based on the general back electromotive force position detection circuit, when the motor induced voltage E _o is considered as a reference, the position of the brushless DC motor increases as the winding current increases due to an increase in load, as is clear from the above-mentioned paper. The detection signal phase, in other words, the winding current phase of the same phase as this, leads to a decrease in motor efficiency, and further, the lead angle is about 3
If the angle is about 0 °, the position cannot be detected and the motor stops.

FIG. 5 is a voltage vector diagram of the case where the brushless DC motor is rotated in the reverse direction by the conventional general back electromotive force position detection.
It will be described below with reference to the drawings.

In the figure, the applied voltage V is equal to the vector sum of the motor induced voltage E _o , the resistance drop voltage γI _M, and the reactance drop voltage XI _M. The position PS of the position detection signal and the position of the winding current I _M on the vector diagram are in phase with the phase of the applied voltage V on the principle of the counter electromotive voltage position detection circuit.

Here, when the winding current I _M increases, the vector diagram changes from a solid line to a broken line.

That is, the control advance angle γ, which is the phase difference between the motor induced voltage E _o and the winding current I _M , increases as the winding current increases.

Further, when the control advance angle γ is about 30 ° or more as described above, the winding current increases with the increase of the control advance angle γ even with a constant load. Therefore, the control advance angle increases → Positive feedback of increase in line current → increase in control advance angle occurs, the control advance angle γ further increases, and finally the motor output torque becomes equal to or less than the load torque, and the motor stops.

[Object of the Invention]

The object of the present invention is to eliminate the drawbacks of the conventional general back electromotive force position detection circuit, to correct the phase change of the position detection signal due to the increase in load, and to prevent the position detection means from stopping the motor. Brushless DC motor,
In particular, the present invention provides a brushless DC motor equipped with a position detecting means capable of continuously correcting a phase change of a position detection signal due to an increase in load according to the magnitude of a motor current which is a load current and improving its accuracy. Especially.

[Outline of Invention]

The present invention is a brushless DC motor of a type that obtains a position detection signal from a motor terminal voltage by using a filter and a comparator. A position detection signal phase correction means for creating a phase correction amount that is substantially the same as the phase of the induced voltage by using a motor constant according to the amount related to the current flowing through the motor is provided, and the output of this phase correction means In addition to the configuration for operating the brushless DC motor based on the corrected position detection signal is, the comparator is a comparator having a hysteresis characteristic,
The position detection signal phase correction means includes a winding current detection circuit that outputs at least one set of current detection voltages having different signs from the comparator, and an analog that switches the current detection voltages having different signs according to the corrected position detection signal. And a switch, the hysteresis width of the comparator is changed by the current detection voltage, the relationship between the hysteresis width and the current detection voltage is determined based on the motor constant, and the correction phase amount is created. It is a feature.

Example of Invention

An embodiment of a brushless DC motor according to the present invention will be described with reference to the drawings.

First, FIG. 1 is a configuration diagram of a main part of a control circuit in a brushless DC motor according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a general example brushless DC motor, and FIG. 3 is FIG. FIG. 4 is a waveform chart of each part of the above, and FIG.

That is, first, in FIG. 2 relating to a format in which a position detection signal is obtained from a motor terminal voltage using a filter and a comparator, a DC voltage E _d is obtained from a rectifier circuit 2 and a smoothing capacitor 3 from an AC power source 1 shown in FIG. It is supplied to the inverter 4.

The inverter 4 is a 120 ° conduction type inverter composed of transistors TR _{1 to} TR ₆ and free wheeling diodes D _{1 to} D _6, and its AC output voltage is a DC voltage E.
_It is assumed that the conduction period (electrical angle 120 °) of the positive potential side transistors TR _{1 to} TR ₃ of _d is controlled by the pulse width modulation and the chipper operation.

Further, the common emitter terminal of the transistor _TR 4 to Tr _6, between the common anode terminal of the freewheeling diode _D 4 to D _6, in which low resistance _{R 1} is connected.

Reference numeral 5 denotes a synchronous motor related to the brushless DC motor body, which is composed of a rotor 5-1 and an armature winding 5-2,
Winding current of 3-phase flowing in the armature winding 5-2, wherein the well flow to a low resistance R _1, the voltage drop of the low-resistance R _1, the motor current I _{L (3-phase} winding current the I _M in which the full-wave rectified current) can be detected.

The control circuit for controlling the speed of the synchronous motor 5 is
Microcomputer 7, rotor 5-1 of synchronous motor 5
The counter electromotive force position detection circuit 6 for detecting the magnetic pole position, the current control unit 8 for generating the chipper signal 10 for controlling the motor current I _L, and the base driver 9 for the transistors TR _{1 to} TR ₆ .

The microcomputer 7 is composed of the CPU 7-1, RO
It is composed of an M7-2, a RAM 7-3, a timer 7-4, etc., and is connected by an address bus, a data bus and a control bus (not shown), respectively.

The ROM 7-2 stores various processing programs necessary for driving the synchronous motor 5, for example, those related to speed control processing.

On the other hand, the position detection signals a, b and c which are the outputs of the back electromotive force position detection circuit 6 are input to the micro computer 7, and the drive signal 11 to the base driver 9 and the current to the current control unit 8 are input. The command I _LC is output.

The counter electromotive force position detection circuit 6 uses the filter circuit and the comparator based on the terminal voltages V _A , V _B , and V _C of the armature winding 5-2 to detect the position detection signal a corresponding to the rotor position. , B, c.

With respect to the brushless DC motor having the above structure, one embodiment of the brushless DC motor having the structure according to the present invention will be described below with reference to FIGS. 1, 3, and 4.

FIG. 1 shows a circuit configuration in which a position detection signal correction circuit 13 is added to the counter electromotive voltage position detection circuit 12 and is related to a main part configuration.

That is, in this embodiment, the counter electromotive voltage position detection circuit 6 of FIG. 2 is provided with the position detection signal correction circuit 13 related to the position detection signal correction means, and the entire configuration is provided. The other things are the same.

In FIG. 1, the terminal voltages V _A , V _B , and V _C , which are the outputs of the inverter 4, are input to the counter electromotive voltage position detection circuit 12, and the two capacitors C ₅ , C ₆ , and
C ₁ , C ₂ , C ₃ , C ₄ and two resistors R ₆ , R ₇ ,
A filter circuit 18 composed of R ₂ , R ₃ , R ₄ and R _5.
Filter passing voltages V _AF , V _BF and V _CF are created by passing through −3, 18-1 and 18-2.

These 3-phase filters pass voltage V _AF in, V _BF, from V _CF, using the resistor _{R 8,} R _{9, R 10} and buffer 17, to create a neutral point voltage _{V N,} the neutral point voltage _{V N} and wherein the filter pass voltage V _AF, V _BF, and V _CF, respectively compared in the comparator CP-3, CP-1, CP-2, to create the position detection signal _{a h,} b _h, the _{c h.}

The comparator CP-1~CP-3 of the each resistor _{R 11,} R _12, R _{13, R 14,} and R
_This is a comparator having a hysteresis characteristic including ₁₅ and R ₁₆ , and also serves as a part of the position detection signal correction circuit 13.

Then, the position detection signal correction circuit 13 further includes a resistor R ₁₇ and a capacitor C _7, and the motor current I _L
Is composed of a current averaging circuit 19 for averaging the voltage of the low resistance R ₁ for detection, a current amplifier 14, a sign inverter 15 and analog switches 16-1 to 16-3.

Here, the current amplifier 14 and the sign inverter 15 are
The present invention relates to a winding current detection circuit that outputs at least one set of current detection voltages having different signs, and the analog switches 16-1 to 16-3 have the above-mentioned signs depending on the output of each comparator. The present invention relates to an analog switch that switches different current detection voltages.

That is, the analog switches 16-1 to 16-3 have the output + V _IL of the current amplifier 14 and the sign inverter 15 respectively.
Output -V _IL and the two voltages are switched, and these two voltages are switched and transmitted to the comparators CP-1 to CP-3 having the hysteresis characteristic.

However, in the figure, analog switches 16-1 to 16-
In the operation of No. 3, when the output of each comparator is at the high level, the output + V _IL of the current amplifier 14 is equal to the comparator CP-
1 to CP-3, and vice versa when it is Low level.

Next, from the terminal voltage V _B of the inverter 4, the position detection signal a
_The process of creating _h will be described below with reference to FIG.

As described above, FIG. 3 shows the waveform of each part of the counter electromotive voltage phase detection circuit 12 of FIG. 1, and from the terminal voltage V _B ,
The filter passing voltage V _BF described above which has a triangular waveform is obtained.

This filter passing voltage V _BF is the comparator CP-1.
Of the neutral point voltage V _N , the output + V _IL of the current amplifier 14 and the sign inverter 1
5 output-V _IL and comparator CP-1 created from
And the corrected position detection signal a _h is obtained by comparison with the positive terminal input voltage of.

Here, the sterisis width ΔV _IL of the comparator CP-1 shown in FIG. 3 is given by the following equation.

Further, V _IL (output of the current amplifier 14) in the above equation is given as the following equation by the motor current detecting low resistance R ₁ , the gain K of the current amplifier 14 and the average value _L of the motor current I _L.

V _IL = K · R ₁ · _L (2) As a result, when the motor current I _L increases, the hysteresis width ΔV _IL increases in proportion to the motor current I _L.

On the other hand, as the hysteresis width ΔV _IL increases, the position detection signal becomes a delay phase, and the delay angle Δθ related to the correction phase amount
If the filter passing voltage V _BF is a triangular wave and its peak value is V _TP shown in FIG. 3, the height is V _TP , the rare triangle with a base of π / 2 and the height ΔV _IL / 2, the base Is obtained as the following equation from the comparison with the same triangle of Δθ.

As described above, the comparator that configures the back electromotive force position detection circuit has a hysteresis characteristic, the hysteresis width is proportionally changed according to the motor current, and the phase of the position detection signal is delayed to increase the motor current. It is possible to correct the phase lead phenomenon of the position detection signal due to, and particularly according to the present invention, by changing the hysteresis width of the comparator in accordance with the magnitude of the motor current that is the load current, The accuracy can be improved by continuously performing the correction.

Japanese Patent Application Laid-Open No. 57-160386 discloses a technique of correcting a detected position by a motor current value in a brushless DC motor which detects a position from a terminal voltage of the motor using a filter and a comparator.

However, in the technique described in the publication, the comparator constituting the back electromotive force position detection circuit is provided with a hysteresis characteristic, and its systemic width is proportionally changed according to the motor current which is a load current, It cannot be denied that the phase correction cannot be continuously performed to improve its accuracy, and the phase correction becomes discontinuous.

Next, the relationship between the delay angle Δθ given by the above equation (3) and the motor current I _L will be described with reference to the operation explanatory diagram of FIG. This figure is a voltage vector diagram obtained when the brushless DC motor is driven by the above-mentioned corrected position detection signal.

When choosing the phase of equal winding current I _M of the correction position detection signal on the motor induced voltage E _o, the phase difference δ between the applied voltage V and the induced voltage E _o, is given as follows.

Then, by ignoring the winding resistance r and performing an approximation of tan θ = θ, the following equation is obtained.

Here, k _E is the motor power generation constant, L is the winding inductance, and the position is set so that the load angle δ given by equation (5) and the delay angle Δθ given by equation (3) are equal. On the contrary, if each constant of the detection signal correction circuit is determined, the brushless DC motor can be operated so that the voltage vector diagram of FIG. 4 is obtained.

In the embodiment described above, the delay angle Δθ increases with the increasing motor current I _L , so that the winding current I _M always exists in the same phase as the motor induced voltage E _o or in the vicinity thereof.

〔The invention's effect〕

According to the present invention, the drawbacks of the conventional general back electromotive force position detection circuit are eliminated, the phase change of the position detection signal due to the increase of the load is corrected, and the position detection means does not stop the position detection and the motor does not stop. Brushless DC motor,
In particular, the comparator that constitutes the back electromotive force position detection circuit has hysteresis characteristics, and the hysteresis width is proportionally changed according to the motor current, which is the load current, to continuously perform phase correction and improve its accuracy. It is possible to provide a brushless DC motor including a position detecting means that can be increased, and it can be said that the invention has an excellent effect.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a main part of a control circuit in a brushless DC motor according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a general example brushless DC motor, and FIG. 3 is shown in FIG. Waveform diagram of each part of the thing, FIG. 4 is the same operation explanatory diagram,
FIG. 5 is a voltage vector diagram when the brushless DC motor is reversed by conventional back electromotive force position detection. 1 ... AC power supply, 2 ... rectifier circuit, 3 ... smoothing capacitor, 4
... Inverter, 5 ... Synchronous motor, 6, 12 ... Back electromotive force position detection circuit, 7 ... Microcomputer, 7-1 ... CP
U, 7-2 ... ROM, 7-3 ... RAM, 7-4 ... Timer, 8 ... Current control section, 9 ... Base driver, 10 ... Chip signal, 11 ... Drive signal, 13 ... Position detection signal correction circuit, 14 ... current amplifier, 15 ... sign inverter, 16
-1 to 16-3 ... analog switch, 17 ... buffer,
18-1 to 18-3 ... Filter circuit, 19 ... Current averaging circuit, CP- _{1 to} CP-3 ... Comparator, TR _{1 to} T
R ₆ ... Transistor, D _{1 to} D ₆ ... Reflux diode, R
₁ ... low _resistance, R 2 to R _{17 ... resistors, C} 1 -C 7 _... capacitor, E 0 _... motor induced voltage, V ... applied voltage, rI _M ...
Resistance drop voltage, xI _M ... Reactance drop voltage, PS ...
Position detection signal phase, I _M ... Winding current, γ ... Control lead angle,
Ed ... DC voltage, I L _... motor current, a, b, c ... position detection _{signal, a h, b h, c} h ... corrected position detection _{signal, V} A ~V C _... terminal _{voltage, V} AF, V _BF , V _CF ...
Filter pass voltage, V N _... neutral point voltage, the + V _{IL ...} current amplifier output, the output of -V _{IL ...} sign inverter, [Delta] V _IL
... Hysteresis width, δ ... Load angle, Δθ ... Delay angle.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Fumio Tajima 4026 Kujicho, Hitachi City, Ibaraki Prefecture, Hitachi Research Institute, Ltd. In Tochigi Plant (72) Inventor Toru Inoue 800 Tomita, Ohira-cho, Shimotsuga-gun, Tochigi Prefecture Tochigi Plant, Hitachi Ltd. (56) Reference JP-A-57-160386 (JP, A)

Claims (1)

[Claims] 1. A brushless DC motor of a type that obtains a position detection signal from a motor terminal voltage by using a filter and a comparator, wherein a phase of a fundamental wave component of a motor current is a motor winding with respect to a phase of the position detection signal. The phase correction amount that makes the phase substantially the same as the phase of the voltage induced in the motor is created by using the motor constant according to the amount related to the current flowing in the motor. In addition to the configuration for operating the brushless DC motor based on the corrected position detection signal which is the output, the comparator is a comparator having a hysteresis characteristic, the position detection signal phase correction means, the sign of the comparator and different from each other,
A winding current detection circuit that outputs at least one set of current detection voltages, and an analog switch that switches the current detection voltages having different signs according to the corrected position detection signal, and the hysteresis width of the comparator is set to the current detection voltage. The brushless DC motor is characterized in that the correction phase amount is created by determining the relationship between the hysteresis width and the current detection voltage based on the motor constant.