JPH08214583A - Driving method of brushless dc motor - Google Patents

Abstract

PURPOSE: To calculate the change of a voltage with a lapse of time with high precision regardless of the revolution of a motor in accordance with induced voltage information and estimate the position of a rotor and perform the driving control with high precision. CONSTITUTION: Terminal voltages of respective windings in a period TS shown in a diagram (b) are detected and a processed waveform shown in a diagram (c) is obtained by interpolation as the efficient induced voltage information of the stator windings. The terminal voltages of the respective windings in the detected period TS are discrete. The voltages in nondetected periods are obtained in accordance with the changes of the voltages with a lapse of time by interpolation. For that purpose, the time for obtaining the change is made to be variable following the revolution of a motor and the induced voltage information is detected with high precision and the change of the voltage with a lapse of time is obtained. The times when the processed waveform shows the highest voltage value and the lowest voltage value are used as commutation timings for the rotor and as rotor positions to be detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving a brushless DC motor, and more particularly to a so-called sensorless DC brushless motor drive capable of detecting the position of a rotor without using magnetic detection means such as a Hall element. Regarding the method.

[0002]

2. Description of the Related Art Generally, drive control of a brushless DC motor must be performed by closely associating a magnetic pole position of a rotor with a position of a winding to be passed. The output torque of the motor is generated by the interaction between the magnetic flux of the magnetic pole of the rotor and the current flowing through the winding of the stator. Therefore, when driving a brushless DC motor, the maximum torque is generated by rotating the motor by passing a current through the winding of the phase existing in the vicinity of the maximum magnetic flux generated from the magnetic poles of the rotor. is necessary.

Further, the drive control of the brushless DC motor is performed by momentarily switching the phase through which the current should flow according to the rotation of the magnetic pole position of the rotor.
When the timing of commutation, which is the switching of this phase, deviates significantly from the maximum magnetic pole position, the torque generated thereby decreases, and in the worst case, the motor loses step and stops.

Therefore, the drive control of the brushless motor is
It is necessary to detect the magnetic pole position of the rotor by some means and control it accordingly.

As a conventional technique relating to a rotor magnetic pole position detection circuit of this type of sensorless brushless motor, for example, a technique proposed in Japanese Patent Application No. 5-264814 is known.

This prior art has an A / D converter that directly detects the motor terminal voltage of the non-energized phase of the motor without using a filter, and determines the rate of change of the detected voltage with time from this sampling value. Obtained and extrapolated to obtain electromotive force information, estimate the rotor position based on this electromotive force information, and from the result estimate the commutation of the motor current including the advance and delay of the commutation phase. The timing is estimated, and the inverter circuit that drives the motor is controlled based on this timing to perform commutation at an appropriate time.

[0007]

In the above prior art, the motor terminal voltage in the non-energized phase of the motor is directly sampled without using a filter, the rate of change of the detected voltage with respect to time is obtained from the sampled value, and this is excluded. Induction voltage information is obtained by interpolation, and the position of the rotor is estimated based on this induction voltage information.

However, in the above-mentioned prior art, since the change rate of the detected voltage is obtained by using the sampling values of two adjacent points, the change rate of the voltage is small in the low rotation region and the change rate calculation accuracy is high. In the worst case, the rate of change cannot be calculated, accurate commutation timing cannot be obtained, and it is difficult to perform motor speed control with high accuracy and stability. are doing.

Further, in the above-mentioned prior art, when the power generation constant varies due to the difference in the current flowing phases of the motor, or when the DC voltage applied to the switching element changes, the rotation speed of the motor becomes constant. However, there is a problem in that the amount of change in voltage with respect to time changes and accurate commutation timing cannot be obtained, and the accumulation of this effect destabilizes the speed control of the motor.

The object of the present invention is to solve the above-mentioned problems of the prior art, to accurately calculate the rate of change of the terminal voltage with time even in the low rotation range, to correctly estimate the magnetic pole position of the rotor, and to reduce the low rotation range. The object of the present invention is to provide a method for driving a brushless DC motor, which can perform commutation at an appropriate time and can perform highly accurate control.

Further, an object of the present invention is to prevent these influences from occurring even when the power generation constants of the current flowing phases of the motor vary, or when the DC voltage applied to the switching element fluctuates. It is an object of the present invention to provide a method of driving a brushless DC motor, which can correctly estimate the magnetic pole position of a rotor without receiving it, can perform commutation at an appropriate time, and can perform highly accurate control.

[0012]

SUMMARY OF THE INVENTION According to the present invention, the above object is to provide an A / D converter which directly detects a motor terminal voltage of a non-energized phase of a motor without using a filter, and an A / D converter which detects the sampling value. When calculating the rate of change of the detected voltage with time, the time interval of the sampling value used for the calculation is changed according to the number of rotations of the motor, and the calculated rate of change of the detected voltage with time is extrapolated and interpolated. The position of the rotor is estimated based on this induced voltage information, and the commutation timing of the motor current including the advance and delay of the commutation phase is estimated from the result and commutation is performed at an appropriate time. And a controller for driving the brushless DC motor.

Further, in order to suppress the influence of the variation of the power generation constant due to the difference of the conduction phases when obtaining the change rate of the detected voltage with respect to time from the above-mentioned sampling value, the above-described object is to change the plurality of detected voltages with respect to time. The average value of the ratio is calculated, and the induced voltage information is obtained by extrapolating the rate of change of the detected voltage with time.The rotor position is estimated based on this induced voltage information. This is achieved by providing a control unit that estimates the commutation timing of the motor current including advance and delay and drives the brushless DC motor so as to perform commutation at an appropriate time.

[0014]

The A / D converter samples and detects the motor terminal voltage in the non-energized phase of the motor.
The induced voltage information is calculated by extrapolating the detected voltage value based on the rate of change of the voltage value discretely taken in by the D converter with respect to time, and the commutation timing is calculated from this information. Then, the driver of the inverter that drives the motor is driven, and the motor is finally rotated. Further, the control unit has a memory function for storing the captured detected voltage value and time, a function for calculating commutation timing from the information and the rate of change of the voltage value with time,
It has a function of changing a sampling point when calculating the change rate according to the number of rotations of the motor, a function of calculating an average value of a plurality of change rates, and the like.

As described above, according to the present invention, it is possible to perform good drive control of a DC brushless motor using an inverter circuit.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for driving a brushless DC motor according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the system configuration of a brushless DC motor to which the driving method according to the present invention is applied, and FIG. 2 is a diagram showing the flow control of the motor at an ideal commutation timing so that the motor has a constant speed. Showing schematically the waveforms of the induced voltage, the detection terminal voltage and the processing voltage of the motor in the state where the motor rotates, FIG. 3 shows an enlarged view of the detection terminal voltage waveform, and FIG. 4 shows the detection terminal voltage waveform at low speed rotation. FIG. 5 is an enlarged view, FIG. 5 is a diagram showing processing voltage waveforms for explaining the advance and delay of the phase of the commutation timing, and FIG. 6 is a commutation estimated to be the optimum commutation interval when the power generation constant differs depending on the conduction phase. It is a figure which shows the difference with a flow space. In FIG. 1, 1 is a DC power supply, 2 is an inverter circuit, 3 is a selector, 4 is an A / D converter, 5 is a control unit, 6 is a driver circuit unit, 7 is a stator, 8 is a rotor, and 9 is a load. .

As shown in FIG. 1, a brushless DC motor system to which the present invention is applied includes a DC power source 1, an inverter circuit 2, and a selector 3 for selecting one non-energized phase among three-phase windings. Converts the analog value of the terminal voltage of the selected terminal into a digital value so that it can be calculated by an electronic computer A
/ D converter 4, a control unit 5 that determines the rate of change and commutation time from the detected voltage and outputs a signal to a driver that controls the inverter circuit 2, a driver circuit unit 6, U, V of the inverter circuit 2. , A W-phase winding is connected at one end to a stator 7 of a three-phase DC brushless motor, a rotor 8 having magnetic poles using permanent magnets, and a load 9 connected to the motor.

A motor driving method according to an embodiment of the present invention in the following description is a 120-degree energization type driving capable of obtaining a high output torque, and a motor controlling method is a DC voltage conduction ratio. This is a so-called PWM control for controlling, and the switching element for chopping is connected to the positive voltage side of the DC power supply 1.

The switching element for chopping may be connected to the negative voltage side of the DC power supply 1,
Further, although the inverter circuit 2 is omitted in the figure,
Three sets of switching elements are provided so as to correspond to the windings of each phase.

In general, in a DC motor which is full-wave driven by the inverter circuit 2, the effective induced voltage information from the winding is obtained from the winding of one phase which is not always energized among the windings of three phases. Only the voltage, and the induced voltage information during the period in which the chopping by the inverter circuit is not performed is effective. Therefore, the selector 3 has a switching function of switching the terminals of the detected phases in accordance with the current flow mode, and the A / D converter 4 converts the analog voltage value into a digital value in synchronization with the PWM control signal. It has a so-called A / D conversion function.

The control unit 5 receives the detected value of the induced voltage described above as an input, and calculates the rate of change of the voltage with time, that is, the slope of the voltage based on the detected value, and the time from the slope to the target voltage value. And a driver circuit section 6 for controlling the switching element of the inverter circuit 2
It is constituted by a microcomputer having a function of outputting a signal for controlling the above, and a function of storing the above-mentioned detected value and inclination.

Further, the driver circuit section 6 has a function of driving a switching element forming the inverter circuit 2 in response to a signal from the control section 5.

In the above-described embodiment of the present invention, the control section 5 and the driver circuit section 6 of the switching element of the inverter circuit 2 are constituted by different circuits. However, these functions are combined into one. Alternatively, a microcomputer may be used as the control unit.

The stator 7 constituting the motor is composed of three-phase windings U, V, W which are magnetically poled by passing an electric current, and one ends of these windings are connected to each other. . The rotor 8 is a permanent magnet having a magnetic pole, and rotates in accordance with the change in the proper magnetic pole position of the stator described above.

Next, in the brushless DC motor configured as described above, the respective windings of the stator 7 are controlled to flow at an ideal commutation timing, and the motor is assumed to be rotating at a constant speed. The state will be described with reference to FIG.

FIG. 2 (a) shows the induced voltage waveform of each phase which occurs as a physical phenomenon in this state, and FIG. 2 (b) shows the terminal voltage waveform of the winding of each phase detected in full-wave drive. Two
In the present invention, (c) is a signal waveform that can be obtained by detecting the terminal voltage waveform in synchronization with the PWM signal and extrapolating and interpolating the undetectable point from the change amount of the detected value with respect to time.

As shown in FIG. 2, when the motor commutates at an ideal commutation timing and rotates at a constant speed, a voltage as shown in FIG. Induced. This induced voltage is induced by the magnetic poles of the rotor, its Peak To Peak value is proportional to the rotation speed of the motor, and the transient value is determined by the correlation with the magnetic pole position of the rotor. Usually, the commutation timing of the motor can be determined based on this induced voltage information.

That is, the ideal commutation timing (maximum output can be obtained) of the motor is represented by the points tp1 and tp shown in the drawing where the induced voltages of the adjacent phases intersect.
In the embodiment of the present invention, the voltage at this time is the maximum value e (tp1) of the voltage which is the upward convex inflection point, and the minimum value e of the voltage which is the downward convex inflection point. It is obtained as (tp2).
When the motor is rotating at a constant speed, the maximum value and the minimum value of the voltage at that time are substantially equal in any adjacent phases.

On the other hand, what can be detected as an actual system is the terminal voltage of the stator winding of the motor, which has a waveform as shown in FIG. 2 (b). This detected waveform shows the voltage between the negative side of the DC power supply and the terminal of each phase winding, and is a mixture of the drive voltage and the induced voltage applied to rotate the motor. Then, in the 120-degree energization type drive of the motor, the effective induced voltage information is the period Ts shown in FIG. 2B, and only one of the three phases is always present.

Further, even during the period Ts of the effective induced voltage information, the potential is fixed to the positive or negative value of the DC voltage in the section where the current flows through the freewheeling diode during commutation, and the inverter circuit Since chopping is performed during PWM control,
It does not become continuous as shown in FIG. Therefore, it is necessary to detect the induced voltage by some method and determine the commutation timing by performing arithmetic processing based on the information.

Therefore, in one embodiment of the present invention, the effective induced voltage information is such that, in the 120-degree conduction type drive as described above, only one of the three phases is always in the period Ts shown in FIG. Selector 3 because it can only be obtained from
In this way, one of the three phase windings of the motor, which is not energized, is switched and selected according to the conduction mode, and as shown in the enlarged view of the detected waveform shown in FIG. Current is not flowing through the freewheeling diode at, and the terminal voltages e (t1) and e (t
2), e (t (n-1)), e (tn), etc. are sampled so that the induced voltage information is directly picked up from the terminal voltage although it is discrete.

Further, in one embodiment of the present invention, the control unit 5
Then, the rate of change Δv / Δt of the voltage with respect to time is calculated from the discretely obtained induced voltage information, and the induced voltage between discrete values (the broken line portion in the figure) is obtained by extrapolation, and this is calculated for three phases. By continuously connecting, a processed waveform having a triangular wave signal waveform as shown in FIG. 2C is obtained.

As described with reference to FIG. 2, in a state where the flow of current to the windings of each phase is controlled at the ideal commutation timing and the motor is rotating at a constant speed, as shown in FIG. 2 (c). In each adjacent phase, the voltage at the point where the induced voltages of the adjacent phases intersect (the maximum value of the voltage that is the upward convex inflection point, the minimum value that is the downward convex inflection point) is Also becomes almost constant, and emax and emin of the processed waveform can be obtained from the voltage value at each inflection point of this signal at this time. From this, to find the optimum commutation timing, the induced voltage in each phase is detected, and the induced voltage obtained from the rate of change with respect to time at that time is emax and
All we have to do is find the time that becomes emin.

Further, when the phase of the commutation timing generated before the update of emax and emin is delayed or advanced, FIG.
As shown in (b) and FIG. 5 (c), the voltage values e (t'51) and e (t'5) at the previous rotational flow point depending on the current rate of change of the induced voltage.
2) and the voltage values e (t51) and e (t52) at the time of the previous rotation, and the voltage value e at the time t51 and t52 at the time of the previous commutation is calculated based on the current or previous change rate information of the induced voltage. By estimating and comparing the optimum value of (tpb), the previous commutation time delay and advance time Δtbd are estimated, and correction is performed at the next commutation point without accumulating commutation time errors.

In one embodiment of the present invention, the commutation timing can be finally brought close to the optimum commutation time by repeating the above-mentioned correction. In addition, since the induced voltage information depends on the rotational speed and the magnetic pole position of the rotor, the one embodiment of the present invention makes the induced voltage due to the rotational pulsation even when the rotational pulsation occurs in the motor by the above correction. Since it changes, the proper commutation timing can always be estimated.

The above-mentioned processing for obtaining the commutation time will be described in more detail below.

Now, it is assumed that the load 9 on the motor is a constant load having no periodic load fluctuation, and the motor is rotated at a constant speed. In this case, as the induced voltage,
A voltage waveform as shown in FIG. 3 is detected. Sampling for obtaining the induced voltage information from this voltage waveform validates the data only during the period when the PWM output of the inverter circuit 2 is ON and the current does not flow through the freewheeling diode during commutation. Done.

The data of the invalid period is calculated from the detected voltage value and time by extrapolation using the change rate Δv / Δt. In this way, by obtaining the voltage value in the ineffective period by extrapolation interpolation, it is possible to continuously estimate the rotor position for each conduction period from the time or voltage obtained as a result.

Further, the commutation time is estimated from the rate of change in induced voltage Δv / Δt obtained with reference to the current time, which is the maximum value which is the upwardly convex inflection point obtained at the time of one rotation last time, or The time required to reach the minimum voltage, which is a downward convex inflection point, is calculated as the reference time tbm, and further, until emax and emin are updated, the commutation phase This is performed by estimating the advance / delay time tbd, and correcting the reference time tbm described above with respect to the advance / delay of the previous commutation time with the time tbd.

In practice, the voltage value in the detectable area is treated as being represented by an approximate expression of a linear function with respect to time, and the rate of change K = Δv / Δt with respect to time is the voltage value sampled as shown in FIG. e (t1), e (t2), e (t (n-
1)), e (tn), etc. are obtained by the equation (1).

K = Δv / Δt = {e (tn) -e (t (n-1))} / {tn-t (n-1)} (1) This rate of change K has a constant sampling period. When
As described above, the induced voltage V depends on the magnitude of the induced voltage.
Is proportional to the number of revolutions N, the relationship between the induced voltage V and the number of revolutions N is expressed by equation (2).

V∝A · N (2) Here, A in the equation (2) is a constant peculiar to the motor.

From this equation (2), it can be seen that ΔV becomes small as shown in FIG. 4 when the rotation speed of the motor is low. At this time, when the induced voltage waveform is approximated by a sine wave, the amount of voltage change ΔV at the PWM cycle Tpwm interval at the point of good linearity can be approximately expressed as shown in equation (3). Note that ω in the equation (3) is a value proportional to the rotation speed N.

ΔV = V√ (2) sin (ωTpwm) (3) That is, in the low rotation speed region, the change rate of the voltage with respect to time is calculated at the same time intervals as in the high rotation speed region. Since the absolute value of the induced voltage V becomes small, the amount of change in voltage also becomes small, and the calculation accuracy of the change rate becomes low. In the present invention, in order to prevent this, the rate of change K depending on the rotational speed
By changing the interval of the data used for the calculation of Δt to increase Δt, the change rate K can be calculated accurately even in the low rotation range.

The calculation of the change rate K in this case will be described below. Now, assuming that the number of rotations of the motor is N, the number of motor poles is P, and the PWM cycle is Tpwm, the number S at which the induced voltage can be sampled within one conduction period is expressed by the equation (4).

S = 60 · Tpwm / 3 · P · N (4) From this equation (4), the number of data intervals for calculating the change rate is sampled within one flow period according to the rotation speed of the motor. Determine within the number S of possible data. The number of intervals m at that time can be expressed by Expression (5).

M = S / 2 (5) m in Expression (5) is an integer, and when a decimal point occurs, it is truncated. If the above equation (1) is rewritten so as to change the point for calculating the rate of change K according to the number of rotations of the motor, it can be expressed as shown in equation (6). Can be calculated.

K = Δv / Δt = {e (tn) -e (t (nm))} / {tn-t (nm)} (6) In the above-described embodiment of the present invention, the number of sampling intervals is m.
Was calculated by the equation (5), the sampling interval number m may be set so as to be substantially in inverse proportion to the rotation speed of the motor, and similarly, the change rate K can be calculated accurately in the low rotation range. .

Next, the next rotational flow reference time tbm, which is the time required to reach the maximum voltage which is an upwardly convex inflection point obtained at the time of one revolution the previous time based on the current time tn, is changed. Rate K
And the voltage value e (tn) at the current time, it is obtained by the equation (7). At this time, it is desirable that e (tn) be a voltage value at a position of 1/5 to 4/5 where the most linear approximation is effective in the time width from emax to emin.

In the equation (7), the maximum value is described, but the same applies to the minimum value. Then, as shown in FIG. 5 (a), the phase of the commutation timing advances, and if there is no delay, the voltage values of adjacent phases match at the commutation time, and the rotor position is continuously determined based on the above-mentioned change rate K. And the commutation timing can be determined.

Tbm = {emax-e (tn)} / K (7) Further, as shown in FIGS. 5B and 5C, the commutation phase generated at the previous commutation is delayed, If there is a lead, the correction time tbd is the time at which the voltage value at the previous rotational flow point is estimated from the current change rate K and the change rate Kb obtained from the previous rotational flow time, and the voltage values match. That is, first, the voltage e (t'51) at the previous commutation time during which the current is flowing through the freewheeling diode is estimated by the equation (8).

E (t'51) = e (tn) − (tn-t51) · K (8) Furthermore, the pre-rotational flow previously obtained from the change rate Kb used in the previous commutation time calculation. The difference from the estimated voltage e (t51) at the time is taken, and the half point is assumed to be the voltage e (tpb) when the commutation is performed optimally, and the voltage value and the current rate of change K are From the voltage e (t'51) obtained from the previous phase delay time t'bd (n)
Is calculated by the equation (9).

T'bd (n) = {e (t'51) -e (tpb)} / K (9) Then, the final correction time tbd (n) is as shown in equation (10). Can be obtained by adding the previous phase correction time tbd (n-1) and setting the result as the phase delay time at the previous rotational flow point. The correction time tbd (n) at this time is t'bd
A method of weighting (n) and tbd (n-1) and gradually correcting is also effective. The voltage value e (tpb) assumed at this time is the voltage value at the ideal commutation timing, emax and
It is reflected when the voltage value of emin is updated.

Tbd (n) = t'bd (n) + tbd (n-1) (10) Finally, the time tb until the next rotational flow time is the phase delay time of the next rotational flow reference time tbm. It is the time corrected by equation (11) with tbd.

Tb = tbm + tbd (n) (11) The above description is for the commutation phase delay shown in FIG. 5B, but changes for the phase lead as shown in FIG. 5C. The same applies when the rate is negative. Also, this phase correction time tb
d (n) is cleared when updating the values of emax and emin.

In the above description, the commutation time is obtained from the detected change rate of the induced voltage of the motor, and the commutation is performed by managing the time at that time. However, the change rate of the induced voltage of the motor is Since it has voltage and time information, it compares the detected voltage or extrapolated voltage with the voltage value estimated to be the commutation timing, and when it matches or exceeds that voltage. It is also effective to control the drive of the motor by controlling with a voltage that causes commutation.

That is, the rate of change Δv of the voltage with respect to time
By using / Δt, since information on both voltage and time is stored, the rotor position and commutation timing can be managed by both voltage and time. Further, by changing the point for calculating the rate of change Δv / Δt according to the rotation speed, the change amount of the voltage with respect to time can be accurately calculated from the low rotation speed region to the high rotation speed region, and the change speed can be calculated accurately in a wide range of the motor rotation speed. The motor can be controlled.

In the above, the method of performing the control in the low rotation region of the motor with high accuracy has been described. Next, when the power generation constant differs due to the difference of the flow phases, the influence of the variation of the power generation constant is reduced. A method of performing stable motor speed control will be described.

As described above, the rate of change K of the phase voltage with respect to time for estimating the commutation timing for controlling the motor can be obtained as shown in the equation (1). When the power generation constant is different due to the difference between the two, or when the DC voltage applied to the switching element fluctuates, the induced voltage of each phase will vary from phase to phase as shown in FIG. 6 (a). As shown in FIG. 6B, the true commutation interval Tt is estimated as shown by Tf, which causes a difference. As a result, the output torque of the motor fluctuates, the speed fluctuates accordingly, and emax and emin fluctuate, and the control becomes unstable.

In order to prevent such control instability, one embodiment of the present invention uses the average value Kav of the change rate during one rotation of the motor as the change rate necessary for calculating the commutation timing. And The average value Kav of this rate of change is expressed by the formula (1
Required by 2).

Kav = (ΣK) / u (12) u in the equation (12) is a value represented by the equation (13) by the pole number P of the three-phase motor.

U = 3 · P (13) Since one embodiment of the present invention calculates the average value Kav of the change rate during one rotation of the motor at the same time as updating emax and emin,
The average value Kav of the rate of change is calculated for each revolution of the motor, but this calculation is not affected by the variation in the flow period even if it is not the average value during one revolution. Just ask.

Next, the next commutation reference time tbm, which is the time until the maximum voltage, which is the convex inflection point obtained at the time of the previous one rotation, is obtained based on the current time tn is obtained. Based on the average value Kav of the changed rates and the voltage value e (tn) at the current time, it is obtained by the equation (14). At this time, the voltage value e (tn)
Is preferably a voltage at a position of 1/5 to 4/5 where the most linear approximation is effective in the time width from emax to emin.

The equation (14) shows the case where the inflection point has the maximum value, but the same applies when the inflection point has the minimum value. Then, as shown in FIG. 5A, the phase of the commutation timing advances, and if there is no delay, the voltage values of adjacent phases match at the commutation time, and the rotor position is continuously determined based on the change rate Kab described above. And the commutation timing can be determined.

Tbm = {emax-e (tn)} / K (14) Further, as shown in FIGS. 5B and 5C, the commutation phase generated during the previous commutation is delayed, If there is a lead, the correction time tbd is the time at which the voltage value at the previous rotational flow point is estimated from the current change rate Kav and the change rate Kb obtained from the previous rotational flow time, and the voltage values match. That is, first, the voltage e (t'51) at the previous commutation time during which the current is flowing through the freewheeling diode.
Is estimated by the equation (15).

E (t'51) = e (tn) − (tn-t51) · Kav (15) Further, the pre-rotational flow previously obtained from the change rate Kb used in the previous commutation time calculation. Estimated voltage at time e (t51)
And the half of the point is assumed to be the voltage e (tpb) when the commutation is performed optimally, and the voltage value and the current rate of change K
From the voltage e (t'51) obtained from av and the previous phase delay time t'b
d (n) is calculated by the equation (16).

T'bd (n) = {e (t'51) -e (tpb)} / Kav (16) Then, the final correction time tbd (n) is as shown in Expression (17). Can be obtained by adding the previous phase correction time tbd (n-1) and setting the result as the phase delay time at the previous rotational flow point. The correction time tbd (n) at this time is t'bd
A method of weighting (n) and tbd (n-1) and gradually correcting is also effective. The voltage value e (tpb) assumed at this time is the voltage value at the ideal commutation timing, emax and
It is reflected when the voltage value of emin is updated.

Tbd (n) = t'bd (n) + tbd (n-1) (17) Finally, the time tb until the next rotational flow time is the phase delay time of the next rotational flow reference time tbm. It is the time corrected by equation (18) with tbd.

Tb = tbm + tbd (n) (18) The above description is for the case of commutation phase delay shown in FIG. 5B, but changes for the case of phase advance as shown in FIG. 5C. The same applies when the rate is negative.

In the above description, the commutation time is obtained from the detected change rate of the induced voltage of the motor, and the commutation is performed by managing the time at that time. However, the change rate of the induced voltage of the motor is Since it has voltage and time information, it compares the detected voltage or extrapolated voltage with the voltage value estimated to be the commutation timing, and when it matches or exceeds that voltage. It is also effective to control the drive of the motor by controlling with a voltage that causes commutation.

That is, the rate of change Δv of the voltage with respect to time
When the average value of / Δt is used, the average value is the voltage even when the power generation constant varies due to the difference in the current flowing phases of the motor or when the DC voltage applied to the switching element changes. , Since it has both time information, it is possible to manage the rotor position and commutation timing with high accuracy in both voltage and time. further,
By changing the point where the rate of change Δv / Δt is calculated according to the number of rotations of the motor, the amount of change in voltage with time can be calculated accurately from the low rotation range to the high rotation range, and it can be calculated accurately over a wide range of motor rotation speeds. The motor can be controlled.

[0073]

As described above, according to the present invention, since the rate of change of the terminal voltage with respect to time can be calculated accurately even when the rotation speed of the motor is low, the rotor position can be accurately estimated. Therefore, the motor can be controlled accurately from the low rotation range to the high rotation range.

Further, according to the present invention, when the power generation constant varies due to the difference in the current flowing phases of the motor, or when the DC voltage applied to the switching element varies, the terminal voltage Since the rotor position can be estimated with good stability from the rate of change with respect to time, the motor can be accurately controlled from the low rotation range to the high rotation range.

[Brief description of drawings]

FIG. 1 is a block diagram showing a system configuration of a brushless DC motor to which a driving method according to the present invention is applied.

FIG. 2 schematically shows waveforms of an induced voltage, a detection terminal voltage, and a processing voltage of the motor in a state where the commutation is controlled at an ideal commutation timing with respect to the motor and the motor is rotating at a constant speed. It is a figure.

FIG. 3 is an enlarged view of a detection terminal voltage waveform.

FIG. 4 is an enlarged view of a detection terminal voltage waveform at low speed rotation.

FIG. 5 is a diagram showing processing voltage waveforms for explaining the advance and delay of the phase of commutation timing.

FIG. 6 is a diagram showing a difference between an optimum commutation interval and an estimated commutation interval when a power generation constant varies depending on a flowing phase.

[Explanation of symbols]

 1 DC power supply 2 Inverter circuit 3 Selector 4 A / D converter 5 Control part 6 Driver circuit part 7 Stator 8 Rotor 9 Load

Front page continued (72) Inventor Yasuo Notohara 7-1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory

Claims (9)

[Claims] 1. A terminal voltage of a non-energized phase of a brushless DC motor, which has a permanent magnet and an armature coil, and one end of each phase of the armature coil is commonly connected, is detected and detected. In the method of driving a brushless DC motor that determines commutation timing based on the rate of change of the terminal voltage with respect to time, when calculating the rate of change of the detected terminal voltage with time, the data interval as the terminal voltage used, A method for driving a brushless DC motor, which is characterized in that it is changed according to the number of rotations of the motor. 2. A terminal voltage of a non-energized phase of a brushless DC motor, which has a permanent magnet and an armature coil, and one end of each phase of the armature coil is commonly connected, is detected and detected. In a method of driving a brushless DC motor that determines commutation timing based on a rate of change of a terminal voltage with time, as a rate of change of the detected terminal voltage with respect to time, an average value of a plurality of rates of change is used. Brushless DC motor driving method. 3. The brushless DC motor is driven by using an inverter circuit.
Alternatively, the method of driving the brushless DC motor according to the item 2. 4. The detection of the terminal voltage is performed in synchronization with a PWM signal for controlling an inverter circuit, and extrapolation interpolation is performed based on a rate of change of the detected voltage with respect to time, so that the rotor position when detection is impossible is continuously performed. The method for driving a brushless DC motor according to claim 3, wherein the method is a method for estimating the brushless DC motor. 5. The method for driving a brushless DC motor according to claim 4, wherein the commutation timing is determined with a point at which the interpolated value with respect to the detected value of the terminal voltage of each adjacent phase intersects as commutation time. 6. The output torque of the motor is controlled so that the maximum value and the minimum value of the voltage value at the intersection of the voltage interpolation values of the adjacent phases calculated based on the rate of change of the terminal voltage with respect to time become constant. The method for driving a brushless DC motor according to claim 4 or 5, wherein. 7. The method for driving a brushless DC motor according to claim 4, wherein the drive rate of the motor is controlled by handling the rate of change of the interpolation value with respect to time as continuous motor speed change information. 8. The voltage value at the intersection of the voltage interpolation values calculated from the voltage value at the commutation timing estimated based on the interpolation value is reflected in the maximum value and the minimum value voltage at the intersection of the voltage interpolation values at the next rotation. 8. The method according to claim 4, wherein
A method for driving a brushless DC motor according to any one of the above. 9. The method for driving a brushless DC motor according to claim 4, wherein the extrapolation is performed based on a rate of change of a portion of the detected voltage having good linearity.