JP2000232797A - Driver for brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize sensorless detection of the rotational position of a rotor and sine wave driving. SOLUTION: A comparator 27 compares the neutral voltage Vn of a brushless motor 24 with a reference voltage Vm (=Vdc/2) to produce a comparison signal Cs. A positional signal detecting circuit 30 generates a positional signal Ps corresponding to the rotor position based on the comparison signal Cs and a sine wave signal generating circuit 31 generates a PWM controlled sine wave conduction signal Dup-Dwn having a phase corresponding to the positional signal Ps. On the other hand, a comparator 36-38 compares a terminal voltage Vu-Vw with the reference voltage Vm to detect a comparison signal Cu-Cw and a positional signal detecting circuit 40 generates, in conjunction with a rectangular wave signal generating circuit 41, a rectangular wave conduction signal Dup"-Dwn" by 120 deg. conduction system based on the comparison signal Cu-Cw. A switching circuit 42 selects the rectangular wave conduction signal Dup"-Dwn" when the brushless motor is started or operating at low speed and selects the sine wave conduction signal Dup-Dwn when the brushless motor is operating at high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor driving device for detecting a rotational position of a rotor based on an induced voltage of a winding.

[0002]

2. Description of the Related Art Compressor motors or fan motors for air conditioners and refrigerators are required to be able to operate in a wide speed range and to be able to operate efficiently. To meet this demand,
In recent years, a brushless motor driven by an inverter circuit has been used. In driving this brushless motor, the rotational position of the rotor must be accurately detected. However, when a brushless motor is used as a compressor motor, the brushless motor is placed in a high-temperature and high-pressure environment, so that a position sensor such as a rotary encoder cannot be provided to detect the rotational position of the rotor.

Therefore, a conventional brushless motor driving device detects a terminal voltage of a winding wound around a stator,
A position signal corresponding to the rotational position of the rotor is obtained based on the induced voltage included in the terminal voltage. In other words, the driving device is 120 ° with respect to each phase winding.
It is configured to perform rectangular wave drive for energizing the width, detect the terminal voltage of each phase and compare it with the reference voltage, and detect the zero cross point of the induced voltage appearing in the energization open period having a 60 ° width for each phase. I was The zero-cross point of the induced voltage has a fixed positional relationship with the rotational position of the rotor, and by using this comparison signal as a position signal, sensorless driving of the brushless motor is possible.

[0004]

However, when the brushless motor is driven by a rectangular wave, the winding current also becomes rectangular as the voltage applied to the winding becomes rectangular.
On the other hand, a brushless motor generates torque by an electromagnetic force acting between a permanent magnet provided on a rotor and a winding current of a stator. Therefore, in the rectangular wave drive in which the harmonic component is superimposed on the winding current, the generated torque pulsates, and the torque ripple generates vibration and noise.

In order to prevent such vibrations and noises, for example, it is conceivable to drive the brushless motor with a sine wave using a driving device having a PWM control circuit based on a sine wave-triangle wave comparison method. However, in such a sine wave drive, since each winding is always energized and there is no energization release period, it is necessary to detect a position signal using the same position detection method as the above-described conventional drive device. Can not. Therefore, in a usage mode of a brushless motor that requires sensorless driving, rectangular wave driving is still used.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a brushless motor driving device capable of detecting a rotational position of a rotor without a sensor and enabling sine wave driving.

[0007]

According to a first aspect of the present invention, there is provided a brushless motor driving apparatus, comprising: a stator having a plurality of phase windings capable of detecting a neutral point voltage; An inverter circuit for sequentially energizing the windings of the plurality of phases to a brushless motor having a DC power supply circuit for outputting a DC voltage to the inverter circuit; and a reference according to the DC voltage output from the DC power supply circuit. Reference voltage generating means for generating a voltage, comparing means for comparing the reference voltage with the neutral point voltage of the brushless motor, and a position signal corresponding to the rotational position of the rotor based on a comparison result of the comparing means. Position signal detection means for detecting, and a sine wave signal for generating a sine wave energization signal for the inverter circuit to output a sine wave voltage based on the position signal A generation unit, characterized in that a drive means for driving the inverter circuit in accordance with the wave energization signal.

[0008] According to this configuration, the comparing means compares the reference voltage generated by the reference voltage generating means in accordance with the DC voltage with the neutral point voltage of the brushless motor. The neutral point voltage of the brushless motor in which a DC voltage is applied to the winding terminals of each phase according to the energization pattern of the inverter circuit is calculated based on a predetermined voltage corresponding to the DC voltage as a composite voltage of the induced voltage of each phase. Will change accordingly. Therefore, by setting a voltage equal to the predetermined voltage as the reference voltage to be compared with the neutral point voltage, it becomes possible to detect the induced voltage of the brushless motor.

Since the induced voltage has a fixed phase relationship with the rotational position of the rotor, the position signal detecting means determines the position corresponding to the rotational position of the rotor based on the result of comparison between the reference voltage and the neutral point voltage. The signal can be detected. According to such a detection method, since the driving device does not need to detect the terminal voltage of the brushless motor, it is possible to perform a sine wave drive in which the terminal voltage of each phase does not have a power supply open period. That is, according to the present driving device, it is possible to detect a position signal required for the energization control of the inverter circuit without using a sensor, and to perform sine wave driving with small torque fluctuation. Thereby, vibration and noise of the brushless motor during driving are reduced. In this driving device, it is preferable that the position signal detecting means and the sine wave signal generating means are constituted by a microcomputer.

According to a third aspect of the present invention, there is provided a brushless motor driving apparatus comprising an inverter circuit, a DC power supply circuit, and a reference voltage generating means having the same configuration as described above.
A first comparing means for comparing the reference voltage with a neutral point voltage of the brushless motor; and a first position signal corresponding to a rotational position of the rotor based on a comparison result of the first comparing means. A sine wave signal generation means for generating a sine wave energization signal for the inverter circuit to output a sine wave voltage based on the first position signal; Second comparing means for comparing a reference voltage with a terminal voltage of the windings of the plurality of phases;
Second position signal detecting means for detecting a second position signal corresponding to the rotational position of the rotor based on the comparison result of the second comparing means; and the inverter circuit based on the second position signal A rectangular wave signal generating means for generating a rectangular wave energizing signal for outputting a rectangular wave voltage, a selecting means for selecting one of the sine wave energizing signal and the rectangular wave energizing signal, Driving means for driving the inverter circuit according to the selected energization signal.

According to this configuration, the first comparing means, the first
The position signal detecting means and the sine wave signal generating means detect the first position signal without a sensor by comparing the reference voltage with the neutral point voltage of the brushless motor as described above, and based on the position signal. To generate a sine wave energization signal for performing sine wave driving.

On the other hand, the second comparing means compares the reference voltage with the terminal voltages of the windings of a plurality of phases. In the winding terminal of the brushless motor, an induced voltage corresponding to the rotational position of the rotor appears during the power-release period in which no voltage is applied to the winding terminal. Therefore, the second position signal detection means obtains a second position signal without a sensor based on the comparison result,
The rectangular wave signal generation unit and the driving unit drive the inverter circuit with the rectangular wave conduction signal based on the second position signal in order to secure the conduction opening period.

The selecting means and the driving means determine whether one of the sine wave energizing signal generated based on the first position signal and the rectangular wave energizing signal generated based on the second position signal is generated. By selectively driving the inverter circuit, the present driving device can use a driving method suitable for the operation state such as the rotation speed of the brushless motor. As a result, the present driving device can detect the position signal without error and can drive the brushless motor stably.

In this case, it is preferable that the selecting means be configured to select the rectangular wave energizing signal when the brushless motor is started and at low speed driving, and to select the sine wave energizing signal at high speed driving (claim 4). Since the induced voltage appearing at the neutral point of the brushless motor described above is a combined voltage of the induced voltages of the respective phases, the amplitude is smaller than the amplitude of the induced voltage appearing at the terminal voltage during the power-discharging period. Therefore, according to this configuration in which the energization signal is switched according to the speed, the driving device uses the second position signal that can detect the induced voltage in a relatively large state at the time of starting and low-speed driving when the induced voltage is 0 or small. During high-speed driving in which a sufficiently large induced voltage can be obtained, sine-wave driving with small torque ripple is performed using the first position signal.
In this case, at the time of starting at which the second position signal cannot be detected and at the time of extremely low-speed driving, driving by an open loop or the like is performed.

As a result, the present brushless motor driving device can start sensorless driving from a lower speed region using the second position signal, and can perform position detection due to detection of a small induced voltage in a small state. Stable driving can be performed by preventing erroneous detection of signals. Further, after switching to the sine wave drive in the high-speed region, the vibration and noise of the brushless motor accompanying the drive can be suppressed.

In this driving device, the first and second position signal detecting means, the sine wave signal generating means, the rectangular wave signal generating means, and the selecting means are preferably constituted by a microcomputer. ). Further, in each case described above, the reference voltage may be set to の of the DC voltage output by the DC power supply circuit.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment A first embodiment (corresponding to claims 1, 2 and 6) of the present invention will be described below with reference to FIGS. FIG. 1 shows a schematic electrical configuration of a drive device 1 for a brushless motor. In FIG. 1, for example, both terminals of a single-phase AC power supply 2 are connected to an AC input terminal of a full-wave rectifier circuit 4 configured as a diode bridge with a power factor improving reactor 3 on one terminal side. It is connected to the. The DC output terminal of the full-wave rectifier circuit 4 is connected to a positive power supply line 5a and a negative power supply line 5b, and a smoothing capacitor 6 is connected between the power supply lines 5a and 5b. The reactor 3, the full-wave rectifier circuit 4, and the capacitor 6 constitute a DC power supply circuit 7. The DC power supply circuit 7 supplies a DC voltage Vdc to the inverter circuit 8 and the voltage dividing circuit 9 via power supply lines 5a and 5b.

The inverter circuit 8 includes a switching element 10 such as an IGBT between the power supply lines 5a and 5b.
To 15 and the reflux diodes 16 to 21 connected in parallel to each other are connected as a three-phase bridge to form a voltage-type inverter circuit. Further, the voltage dividing circuit 9 as the reference voltage generating means is configured such that resistors 22, 23 having the same resistance value are connected in series between the power supply lines 5a, 5b, and a common connection point between the resistors 22 and 23 is provided. To generate a reference voltage Vm having a voltage value of Vdc / 2.

The three-phase brushless motor 24, which is rotationally driven by the driving device 1, has a three-phase star-connected winding 25.
u, 25v, 25w wound stator (not shown)
And a rotor (not shown) provided with permanent magnets. In addition, the brushless motor 24
The neutral point voltages Vn of 5u, 25v, and 25w can be detected from outside the motor. Winding 25u,
Terminals 25v and 25w are connected to output terminals 26u, 26v and 26w of each phase of the inverter circuit 8, respectively.

The comparator 27 as a comparing means has a non-inverting input terminal connected to a neutral point of the windings 25u, 25v, 25w of the brushless motor 24 via a filter circuit 28 for removing a PWM frequency component. The inverting input terminal is connected to a common connection point between the resistors 22 and 23 in the voltage dividing circuit 9. An output terminal of the comparator 27 is connected to an input terminal of a microcomputer 29 (hereinafter, referred to as a microcomputer 29). In an actual circuit, a step-down circuit (not shown) having an appropriate step-down ratio is added so that an excessive voltage is not input to the non-inverting input terminal and the inverting input terminal of the comparator 27.

The microcomputer 29 is shown as a block diagram for each function of a position signal detecting circuit 30 as a position signal detecting means and a sine wave signal generating circuit 31 as a sine wave signal generating means. These circuits 30 and 31 are operated according to a program stored in advance (not shown). The position signal detection circuit 30 receives the comparison signal Cs from the comparator 27 and generates a position signal Ps corresponding to the rotational position of the rotor. On the other hand, the sine wave signal generation circuit 31
Is composed of a modulation signal generation circuit 32 and a PWM circuit 33. The modulation signal generation circuit 32 generates sine wave modulation signals Du, Dv, and Dw based on the position signal Ps from the position signal detection circuit 30 and the voltage command signal Dc provided from outside the microcomputer 29. . Also,
The PWM circuit 33 includes, for example, a carrier signal generation circuit that generates a carrier signal having a triangular waveform and three comparators. The PWM circuit 33 receives the modulation signals Du, Dv, and Dw and receives the sine wave energization signals Dup, Dvp, and Dwp. Dun, Dvn, and Dwn are generated.

A drive circuit 34 as a driving means electrically insulates the sine wave energization signals Dup to Dwn using a photocoupler or the like, and connects the sine wave energization signals Dup to Dwn to the respective gate terminals of the switching elements 10 to 15 constituting the inverter circuit 8. It is configured to output.

Next, the operation of the present embodiment will be described with reference to FIG. First, the neutral point voltage Vn of the brushless motor 24 when the driving device 1 drives the brushless motor 24 by outputting a sinusoidal voltage is obtained.
The phase voltage of the brushless motor 24 is the sum of the induced voltage having a magnitude substantially proportional to the rotation speed and the voltage generated by the impedance of the winding. Since the impedance of the winding is equal for each phase, the terminal voltages and induced voltages of the U phase, V phase and W phase are respectively Vu, Vv, Vw and Eu, Ev
, Ew, the neutral point voltage Vn can be obtained by the following equation.

Vn = ((Vu-Eu) + (Vv-Ev)
+ (Vw-Ew)) / 3 Here, the terminal voltages Vu, Vv, Vw, that is, the output voltages of the inverter circuit 8 are as follows.

Vu = (Vdc / 2) .KDc.sin (θ
ps) + Vdc / 2 Vv = (Vdc / 2) KDc sin (θps + 120
°) + Vdc / 2 Vw = (Vdc / 2) · KDc · sin (θps + 240
°) + Vdc / 2 where KDc: standardized voltage command value of voltage command signal Dc 0 ≦ KDc ≦ 1 θps: angle of position signal Ps 0 ° ≦ θps ≦ 360 °

From these four equations, the neutral point voltage Vn is as follows. Vn = (Vu + Vv + Vw) / 3- (Eu + Ev + Ew) / 3 = Vdc / 2- (Eu + Ev + Ew) / 3 In contrast, the reference voltage Vm output from the voltage dividing circuit 9 is as follows. Vm = Vdc / 2

Accordingly, in the comparator 27, the neutral point voltage Vn input to the non-inverting input terminal via the filter circuit 28 and the reference voltage Vn input to the inverting input terminal are output.
The potential difference Vmn with respect to m is as follows. Vmn = Vm-Vn = (Eu + Ev + Ew) / 3

FIG. 2 shows the induced voltages Eu, Ev and Ew.
3 is a timing chart showing the waveforms of FIG. 2A shows an example of the induced voltage waveform of the brushless motor 24. FIG. In the figure, the thick solid line represents the U-phase induced voltage Eu, the thin solid line represents the V-phase induced voltage Ev, and the dashed line represents the W-phase induced voltage Ew. FIG. 2B shows a waveform of the potential difference Vmn. When the induced voltages Eu, Ev, Ew are trapezoidal waves as shown in FIG. 2A, the potential difference Vmn is the induced voltage Eu of each phase.
, Ev, and Ew result in a triangular waveform having a frequency three times that of the fundamental wave.

Accordingly, the comparator 27 is arranged as shown in FIG.
As shown in (5), a comparison signal Cs that is inverted every time the potential difference Vmn crosses 0 V is generated and output to the microcomputer 29 as a digital signal level. The angle interval at which the comparison signal Cs is inverted is an electrical angle of 60 °, and the point at which the comparison signal Cs is inverted, that is, the induced voltages Eu, Ev, Ew.
Has a certain correspondence with the rotational position of the rotor when either of them becomes 0V.

The position signal detection circuit 30 in the microcomputer 29
For example, each time the comparison signal Cs is inverted by a timer (not shown), the inversion time interval is measured, and the rotational position of the rotor during the time when the comparison signal Cs is inverted is estimated and calculated based on the measured time. Then, the position signal detection circuit 3
0 generates a position signal Ps representing the rotor position as an angle θps of 0 ° to 360 ° using the result of the estimation operation as shown in FIG. 2D. In this case, the position signal detection circuit 30 generates the induced voltages Eu, Ev, Ew and the phase currents Iu, Iw.
v, Iw are in phase with each other, and the brushless motor 24
In order to enhance the efficiency, the lead angle control for advancing the phase of the position signal Ps, which is the energizing phase, by a predetermined angle よ り from the actual rotor position is performed. The position signal detection circuit 30 calculates the number of revolutions based on the measured inversion time interval of the comparison signal Cs.

The modulation signal generation circuit 32 outputs a voltage command signal D
has an amplitude corresponding to c and an angle θps indicated by the position signal Ps.
, And sine wave modulated signals Dv and Dw having a phase difference of 120 ° and 240 ° with respect to the sine wave modulated signal Du (see FIG. 2E).
Then, the PWM circuit 33 compares the triangular wave signal generated by the carrier signal generation circuit with the sine wave modulated signals Du, Dv, and Dw by three comparators provided for each phase, and outputs a pulse width modulated sine wave. Wave energization signals Dup, Dvp, D
Generate wp, Dun, Dvn, Dwn.

The sine wave energizing signals Dup to Dwn are supplied to the switching elements 10 to 1 through the drive circuit 34, respectively.
5, the inverter circuit 8 outputs a sine-wave three-phase AC voltage from the output terminals 26u, 26v, 26w, and the brushless motor 24 is driven to rotate.

As described above, according to the present embodiment, the drive unit 1 compares the neutral point voltage Vn of the brushless motor 24 with the reference voltage Vm having a voltage value of (Vdc / 2) to determine the position. The signal Ps is detected. According to this configuration for detecting the induced voltage appearing at the neutral point voltage Vn in this manner, the terminal voltages Vu, Vv, V
Since it is not necessary to detect the induced voltages Eu, Ev, and Ew from w, the driving device 1 can perform sensorless driving and employ sine-wave driving in which the terminal voltages Vu, Vv, and Vw do not have a power supply open period. Becomes possible.

When the sine-wave drive is adopted, a sine-wave voltage is applied to each winding terminal of the brushless motor 24, so that the currents Iu, Iv, and Iw flowing through the respective windings also become substantially sine waves. Therefore, the pulsation of the torque generated by the electromagnetic force acting between the permanent magnets disposed on the rotor and the winding currents Iu, Iv, Iw is reduced, and the vibration and noise of the brushless motor 24 can be reduced. it can. Therefore, by applying the present driving device 1 to, for example, a compressor motor or a fan motor of an air conditioner or a refrigerator, it is possible to reduce vibration and noise as compared with a case where a driving device having a conventional configuration performing rectangular wave driving is used. Further, the effect that the reliability of the compressor and the fan is improved with the lower vibration can be expected.

In this embodiment, since the advance angle control is performed, as shown in FIGS. 2A and 2F, the phases of the induced voltages Eu, Ev, Ew and the currents Iu, Iv, Iw are changed. And the motor efficiency can be increased.

(Second Embodiment) Next, a second embodiment of the present invention (corresponding to claims 3 to 6) will be described with reference to FIGS. Here, in FIG. 3, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. Hereinafter, portions different from the first embodiment will be described.

FIG. 3 shows a driving device 35 for a brushless motor.
1 shows a schematic electrical configuration of the first embodiment. In FIG. 3, the comparator 27 corresponds to the first comparing means, the position signal detecting circuit 30 corresponds to the first position signal detecting means, and the position signal Ps corresponds to the first position signal. The comparators 36, 37, and 38 as the second comparing means have inverting input terminals connected to a common connection point between the resistors 22 and 23 in the voltage dividing circuit 9, and non-inverting input terminals respectively correspond to the inverter circuit 8
Are connected to the output terminals 26u, 26v, 26w.
Each output terminal of the comparators 36, 37, and 38 is connected to an input terminal of a microcomputer 39 (hereinafter, referred to as a microcomputer 39). In an actual circuit, a step-down circuit (not shown) having an appropriate step-down ratio is added so that an excessive voltage is not input to the non-inverting input terminals and the inverting input terminals of the comparators 36, 37, and 38. I have.

The microcomputer 39 includes, in addition to the position signal detecting circuit 30 and the sine wave signal generating circuit 31, a position signal detecting circuit 40 as second position signal detecting means, and a rectangular wave signal generating circuit 41 as rectangular wave signal generating means. , A switching circuit 42 as a selection means, and a switching signal generation circuit 43. The position signal detection circuit 40 includes the comparator 3
6, 37, and 38, and receives position signals Pu, Pv, and Cv corresponding to the rotational position of the rotor.
Pw is generated. Further, the position signal detection circuit 40 detects the number of rotations by calculation and outputs it to the switching signal generation circuit 43.

The rectangular signal generation circuit 41 comprises an energization signal generation circuit 44 and a PWM circuit 45. The energization signal generation circuit 44 generates a rectangular wave energization signal Dup ', based on the position signals Pu, Pv, Pw from the position signal detection circuit 40.
Dvp ', Dwp', Dun ', Dvn', Dwn 'are generated. In addition, the PWM circuit 45 supplies these energization signals Dup ', Dvp', Dwp ', Dun', Dvn ', Dwn'
, And based on a voltage command signal Dc ′ given from outside the microcomputer 39, the rectangular wave energization signals Dup ″, Dvp ″,
Dwp '', Dun '', Dvn '', and Dwn '' are generated.

The switching circuit 42 receives the sine wave energizing signals Dup to Dup based on the selection signal Ss from the switching signal generation circuit 43.
wn and one of the square wave energization signals Dup '' to Dwn '' is selected, and the selected energization signal is output to each gate terminal of the switching elements 10 to 15 via the drive circuit 34. ing.

Next, the operation of the present embodiment will be described with reference to FIG. First, the operation in the case where the driving device 35 selects the square wave energization signals Dup ″ to Dwn ″ and drives the brushless motor 24 with the square wave will be described.

FIG. 4 shows a driving device 35 for rectangular wave driving.
3 shows the waveforms of the respective parts. Figure 4
(A) to (c) show examples of the U-phase, V-phase, and W-phase terminal voltage waveforms of the brushless motor 24, respectively. However, in these figures, the terminal voltages Vu, Vv
, Vw are omitted. In these figures, the terminal voltages Vu, Vv, Vw are Vdc and 0.
The period of 60 ° width that changes between V and V is an energization release period, and the terminal voltages Vu, Vv, and Vw include induced voltages Eu, E
A voltage corresponding to v and Ew appears.

The comparators 36, 37 and 38 compare the terminal voltages Vu, Vv and Vw with a reference voltage Vm having a voltage value of Vdc / 2, respectively, and
The comparison signals Cu, Cv, and Cw that are inverted during the power release period as shown in FIG. These comparison signals Cu
, Cv, and Cw have a fixed relationship with the phases of the induced voltages Eu, Ev, and Ew, and have a fixed correspondence with the rotational position of the rotor.

The position signal detection circuit 40 in the microcomputer 39
Generates position signals Pu, Pv, Pw (see FIG. 3) by delaying the phases of these comparison signals Cu, Cv, Cw by 30 °, and outputs them to the energization signal generation circuit 44. Also,
The position signal detection circuit 40 measures the inversion time interval each time one of the comparison signals Cu, Cv, Cw is inverted by, for example, a timer (not shown), and detects the number of revolutions based on the measured time.

The energization signal generation circuit 44 generates the position signals Pu,
A logical operation is performed based on Pv and Pw, and FIG.
As shown in (l), rectangular wave energization signals Dup ', Dvp', Dwp ', Dun', Dvn ', and Dwn' that generate 120-degree energization are generated. Then, the PWM circuit 33 outputs the square wave energization signals Dup ', Dvp', Dwp ', Dun', Dvn ', Dwn'
Among them, the energization signals Dun ', D given to the lower arm elements (switching elements 13, 14, 15) of the inverter circuit 8
vn 'and Dwn' are directly used as square wave energization signals Dun '', Dv
n '' and Dwn ''. The PWM circuit 45 includes an upper arm element of the inverter circuit 8 (the switching elements 10 and 1).
Square wave energization signals Dup ', Dvp', D
wp 'has a carrier frequency and a voltage command signal D
PWM control for ON / OFF control at a duty ratio according to c ′ is performed to generate rectangular wave energization signals Dup ″, Dvp ″, Dwp ″.

Now, in the driving device 35 having both the configuration for the rectangular wave drive described above and the configuration for the sine wave drive described in the first embodiment, the switching signal generation circuit 43
Compares the rotation speed detection value obtained from the position signal detection circuit 40 with a preset threshold value. When the motor is started and at a low speed where the rotation speed detection value is smaller than the threshold value, the rectangular wave energization is performed. Selection signal Ss for selecting signals Dup "to Dwn"
(E.g., L level), and at high speed when the rotation speed detection value is equal to or higher than the threshold value, the sine wave energization signals Dup to D
A selection signal Ss (for example, H level) for selecting wn is output. Upon receiving the selection signal Ss, the switching circuit 42 receives the rectangular wave energizing signals Dup "to Dwn" or the sine wave energizing signal D
up to Dwn are selected and applied to the gate terminals of the switching elements 10 to 15. As a result, a three-phase AC voltage is output from the inverter circuit 8, and the brushless motor 24 is driven to rotate.

The reason for switching between the rectangular wave drive and the sine wave drive in accordance with the speed is as follows. That is, the windings 25u, 25v, 25
The induced voltages appearing at the neutral point voltage Vn of the w, as shown by the equations in the first embodiment, are the induced voltages Eu and E of the respective phases.
It is 1/3 of the combined voltage obtained by adding v and Ew. On the other hand, during the period in which the terminal voltages Vu, Vv, Vw are turned off, the induced voltage E
u, Ev, and Ew appear as they are. That is, the terminal voltage V
When u, Vv, and Vw are detected, the induced voltage can be detected in a larger state, and erroneous detection due to noise or the like can be prevented. Therefore, when the induced voltage is low and at low speed, rectangular wave driving is performed using the position signals Pu, Pv, and Pw,
At a high speed when the rotation speed becomes equal to or higher than the threshold value and the induced voltage becomes sufficiently large with respect to the noise component, the sine wave driving is performed using the position signal Ps.

In the case of start-up and at a very low rotational speed, the position signals Pu, Pv, Pw cannot be detected normally, so that the open-loop rectangle without the position signals Pu, Pv, Pw is used. Wave drive is performed.

As described above, according to the present embodiment, the driving device 35 performs sensorless rectangular wave driving based on the position signals Pu to Pw obtained by comparing the terminal voltages Vu to Vw with the reference voltage Vm. Configuration, neutral point voltage Vn and reference voltage V
and a sensorless sine-wave drive based on the position signal Ps obtained by comparing m and m, and a square-wave drive at startup and low speed and a sine-wave drive at high speed. Have.

Therefore, according to the present driving device 35, at the time of high speed, similarly to the first embodiment, the brushless motor 2
4 can be suppressed, and at low speed, the induced voltage is detected in a relatively large state, thereby preventing erroneous detection of a position signal and performing stable sensorless driving.

(Other Embodiments) The present invention is not limited to the embodiments described above and shown in the drawings, and the following expansions or modifications are possible. PWM
The carrier signal of the circuit 33 may be a sawtooth wave.

In each embodiment, the voltage command signals Dc, D
Although c ′ is configured to be supplied from outside the microcomputers 29 and 39, a configuration may be adopted in which a speed feedback control circuit is added inside the microcomputers 29 and 39 and a speed command signal is supplied from outside the microcomputers 29 and 39. In this case, the voltage command signals Dc and Dc 'are generated based on the speed command value and the rotation speed (speed) detected by the position signal detection circuits 30 and 40.

In the case where the position signal Ps is obtained, the case where the induced voltages Eu, Ev, and Ew of the brushless motor 24 include a trapezoidal wave, that is, a third-order harmonic component has been described. In general, the induced voltages Eu, Ev, and Ew are 3n. Next (n =
1, 3, 5,...). In this case, the rotation position of the rotor can be detected at (2 × 3n) points in one cycle of the comparison signal Cs. Therefore, the larger the value of n, the higher the resolution of rotor position detection, and the higher the angular accuracy of the position signal Ps.

In the second embodiment, the switching signal generation circuit 43 determines the selection signal Ss according to the number of revolutions. However, according to the values of the voltage command signals Dc and Dc ', or the time elapsed from the start, the switching signal generation circuit 43 determines the selection signal Ss. May be determined.

[0055]

Since the present invention is as described above,
The following effects are obtained. According to the brushless motor driving device of the present invention, the position signal is detected based on the comparison result between the reference voltage corresponding to the DC voltage and the neutral point voltage of the brushless motor, so that the sine wave energization signal is supplied to the inverter circuit. And vibration and noise during driving of the brushless motor can be reduced.

According to the third aspect of the present invention, a sine wave energizing signal is generated based on a comparison result between a reference voltage corresponding to a DC voltage and a neutral point voltage of the brushless motor, and A rectangular wave energizing signal is generated based on the comparison result of the voltage and the terminal voltage, and one of these energizing signals can be selected by the selection means, so that an energizing method suitable for the operation state of the brushless motor can be used. It becomes possible to drive stably.

According to the brushless motor driving device of the present invention, the rectangular wave energizing signal is selected at the time of starting and low speed driving of the brushless motor, and the sine wave energizing signal is selected at the time of high speed driving, so that the induced voltage is small. It is possible to prevent erroneous detection of a position signal due to detection in a state, and to perform stable driving. Further, after switching to the sine wave drive in the high-speed region, the vibration and noise of the brushless motor accompanying the drive can be suppressed.

[Brief description of the drawings]

FIG. 1 is an electrical configuration diagram schematically showing a brushless motor driving device according to a first embodiment of the present invention;

FIG. 2 is a timing chart showing an induced voltage waveform and a waveform of each part of a driving device.

FIG. 3 is a view corresponding to FIG. 1, showing a second embodiment of the present invention;

FIG. 4 is a timing chart showing schematic terminal voltage waveforms and waveforms of various parts of the driving device.

[Explanation of symbols]

Reference numerals 1 and 35 denote drive devices, 7 a DC power supply circuit, 8 an inverter circuit, 9 a voltage divider circuit (reference voltage generation means), 24 a brushless motor, 27 a comparator ((first) comparison means), 29, 39 is a microcomputer, 30 is a position signal detecting circuit ((first) position signal detecting means), 31
Is a sine wave signal generation circuit (sine wave signal generation means), 34 is a drive circuit (drive means), 36 to 38 are comparators (second comparison means), and 40 is a position signal detection circuit (second position signal detection means) ) And 41 are rectangular wave signal generation circuits (rectangular wave signal generation means), and 42 is a switching circuit (selection means).

Claims (6)

[Claims] 1. An inverter circuit for sequentially energizing a plurality of windings of a brushless motor including a stator and a rotor having a plurality of windings configured to be capable of detecting a neutral point voltage; A DC power supply circuit that outputs a DC voltage to the inverter circuit; a reference voltage generating unit that generates a reference voltage corresponding to the DC voltage output by the DC power supply circuit; and a neutral point voltage of the brushless motor and the reference voltage. Comparing means for comparing; a position signal detecting means for detecting a position signal corresponding to the rotational position of the rotor based on a comparison result of the comparing means; and the inverter circuit detecting a sine-wave voltage based on the position signal. A sine wave signal generating means for generating a sine wave energizing signal for output; and a driving means for driving the inverter circuit according to the sine wave energizing signal. A brushless motor driving device. 2. The brushless motor driving device according to claim 1, wherein the position signal detecting means and the sine wave signal generating means are constituted by a microcomputer. 3. An inverter circuit for sequentially energizing a plurality of phase windings to a brushless motor including a stator and a rotor having a plurality of phase windings configured to be able to detect a neutral point voltage; A DC power supply circuit that outputs a DC voltage to the inverter circuit; a reference voltage generating unit that generates a reference voltage corresponding to the DC voltage output by the DC power supply circuit; and a neutral point voltage of the brushless motor and the reference voltage. First comparing means for comparing; first position signal detecting means for detecting a first position signal corresponding to the rotational position of the rotor based on a result of the comparison by the first comparing means; A sine wave signal generating means for generating a sine wave energization signal for the inverter circuit to output a sine wave voltage based on the position signal; and the reference voltage and a terminal voltage of the multi-phase winding. A second position signal detector that detects a second position signal corresponding to the rotational position of the rotor based on a comparison result of the second comparator. A rectangular-wave signal generating means for generating a rectangular-wave energizing signal for the inverter circuit to output a rectangular-wave-shaped voltage based on the position signal of (2); and one of the sine-wave energizing signal and the rectangular-wave energizing signal And a drive unit for driving the inverter circuit according to the energization signal selected by the selection unit. 4. The brushless motor according to claim 3, wherein a rectangular wave energization signal is selected when the brushless motor is started and when the brushless motor is driven at a low speed, and a sine wave energization signal is selected when the brushless motor is driven at a high speed. A driving device for the brushless motor according to the above. 5. The apparatus according to claim 3, wherein the first and second position signal detecting means, the sine wave signal generating means, the rectangular wave signal generating means, and the selecting means are constituted by a microcomputer. Drive device for brushless motor. 6. The brushless motor driving device according to claim 1, wherein the reference voltage is set to a half of the DC voltage output from the DC power supply circuit.