JP2009011143A - Rotor position detection circuit, motor drive device and rotor position detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rotor position detection circuit that eliminates a defect from a conventional position sensorless drive method. <P>SOLUTION: A position detection circuit 23 of a motor drive device 21 outputs a first rotary position signal after a first position estimation circuit 27 compares a detection signal of phase voltage with the reference voltage (output signal of low-pass filter 10). A control part 22 produces a second rotary position signal by digitally processing the output signal of a comparator 12 in a second position estimation circuit 29 that directly compares the phase voltage with the reference voltage and compensates the rotary position indicated by the first rotary position signal with the second rotary position signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention detects a phase voltage generated in a stator coil in order to drive a brushless DC motor by a position sensorless system, and detects a rotational position of a rotor based on the detection result, a motor drive device, and a rotor position detection method About.

  When controlling the drive of a brushless DC motor, for example, as disclosed in Patent Documents 1 to 3, the phase voltage generated in the stator coil is detected when the rotor rotates without using a position sensor such as a Hall element. Thus, there is a case where a so-called position sensorless driving method for obtaining rotor position information is employed.

  FIG. 11 shows a schematic configuration when the technique (analog filter method) disclosed in Patent Document 1 is applied to, for example, a device for driving a fan motor of a radiator mounted on a vehicle. The motor drive device 1 is supplied with drive power from a vehicle battery 2, and the brushless DC motor 3 is driven via an inverter unit 4. The inverter unit 4 is configured by connecting, for example, six power MOSFETs 5a to 5f in a three-phase bridge, and each phase output terminal of the inverter unit 4 is connected to each phase stator coil 6U, 6V, 6W of the motor 3, respectively. Has been.

  The inverter unit 4 is controlled by a control unit 7 constituted by a microcomputer or a logic circuit, and a drive signal is output to the gate of each FET 5 via a gate driver 8. The rotor rotation position of the motor 3 is detected by a position detection circuit 9, and the position detection signal is given to the control unit 7. The position detection circuit 9 includes low-pass filters 10U, 10V, and 10W including capacitors C and resistors R, buffer amplifiers (voltage followers) 11U, 11V, and 11W, and an output signal from the buffer amplifier 11 as a virtual neutral point potential. Comparing comparators 12U, 12V, and 12W are used. The input terminals of the low-pass filters 10U, 10V, and 10W are connected to a common connection point of resistors R1 and R2 that divide each phase output voltage of the inverter unit 4.

FIG. 12 shows voltage waveforms (only the U phase) of each part when the motor 3 is energized via the inverter part 4. When the motor 3 is activated, the control unit 7 energizes with a predetermined pattern to activate the motor 3. When the motor 3 rotates, an induced voltage generated in the stator coils 6U, 6V, 6W appears in the terminal voltage of the coil 6 (a). Since the switching waveform by PWM control is superimposed on the terminal voltage of the coil 6, when they are removed by the low-pass filter 10, a substantially sinusoidal voltage waveform is obtained (b). Then, the comparator 12 compares the output signal of the filter 10 with the virtual neutral point potential, whereby each phase position signal having a rectangular wave shape is obtained (c).
The control unit 7 sets a PWM duty for determining the rotation speed of the motor 3 in accordance with a control signal given from an external ECU (Electronic Control Unit) (not shown). At the same time, the control unit 7 determines the commutation timing based on the position signal given from the position detection circuit 9, and outputs it to the gate driver 8 when a drive signal is generated.

FIG. 13 shows a case where the technique (reference voltage comparison method) disclosed in Patent Document 2 is applied. The motor drive device 13 is configured by removing the low-pass filter 10 from the motor drive device 1 and replacing the control unit 7 with a control unit 14. And the control part 14 detected the zero cross point by comparing the induced voltage which generate | occur | produces in the non-energization area of a 120 degree | times energization system with a reference voltage, and delayed the phase 30 degree | times using the counter etc. from the zero cross point. The energization timing is set by obtaining the time (see FIG. 14).
Further, the technique disclosed in Patent Document 3 is a so-called neutral point comparison method, in which an induced voltage 3 based on a physical neutral point of a motor, a virtual neutral point generated by a resistance circuit, and a potential difference. A second harmonic component is extracted, and a position detection signal is generated from the harmonic signal.
Japanese Patent Laid-Open No. 62-123799 JP-A-9-266690 JP-A-7-288899

  In the analog filter method of Patent Document 1, the switching noise included in the induced voltage signal is removed by the filter 10 to cause a delay in the phase of the induced voltage signal that has passed through the filter 10 (see FIG. 15B). ). In order to make this phase lag approximately 90 degrees over the entire frequency range of the passing signal, it is preferable to increase the CR time constant and lower the cut-off frequency within a range where the signal attenuation by the CR filter is allowable. However, if the CR time constant is increased, the output signal level of the filter 10 decreases accordingly (see FIG. 15A). Therefore, when the drive rotational speed range is wide, the entire rotational speed range is used. It is difficult to set the phase delay to 90 degrees.

  By the way, since the apparatus which drives the fan motor for vehicles is mounted in an engine room, operating environment temperature becomes very wide range. The CR time constant of the filter 10 is easily affected by temperature in addition to the tolerance of the element itself, resulting in a large variation. Therefore, there is a high possibility that the time constant of the filter 10 of each phase is shifted.

In the reference voltage method of Patent Document 2, when the energized phase is switched during high-speed rotation or high load, the section through which the return current flows through the flywheel diode widens, so that the zero-cross point cannot be detected (FIG. 16 ( a)). Also, the zero cross point cannot be detected when conducting lead angle energization of 30 degrees or more (see FIG. 16B). Since the length of the reflux section is roughly proportional to the electric time constant (L / R) of the motor and the motor current, it is possible to expand the rotation speed range by selecting a motor with a small time constant. However, such motors generally tend to be large when compared at the same output. Although it is possible to reduce the size by using a high-grade magnet, there is a problem that the cost increases.
The neutral point comparison method of Patent Document 3 cannot be used for a motor that employs a Δ connection or a motor that is difficult to connect to a neutral point because of its structure. There is a problem that the number of wirings increases even when a connection with a neutral point is established.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rotor position detection circuit that can eliminate the disadvantages of the conventional position sensorless drive system, a motor drive device including the position detection circuit, and a rotor position detection. It is to provide a method.

  According to the rotor position detection circuit of the first aspect, the first position estimating means outputs the first rotational position signal by comparing the output signal of the low-pass filter for low-pass filtering the phase voltage detection signal with the reference voltage. The second position estimating means digitally processes the output signal of the comparator that directly compares the phase voltage with the reference voltage to generate and output the second rotational position signal. Then, the correcting means corrects the rotational position indicated by the first rotational position signal with the second rotational position signal.

  That is, there is a high possibility that the first rotational position signal output from the first position estimating means that performs analog signal processing includes variations, but the rotational position signal is output over a wide range of motor rotational speeds. Basically, it is preferable to use the first rotational position signal because it can be output. On the other hand, the second position estimating means can output a position signal with higher accuracy, but position estimation may be impossible depending on the driving conditions of the motor. Therefore, if both are combined and the rotational position indicated by the first rotational position signal is corrected with the second rotational position signal, a highly accurate position signal can be output over a wide rotational speed range.

  According to the rotor position detection circuit of claim 2, when the rotational speed of the motor is controlled by PWM control, the correction means does not perform correction based on the second rotational position signal in a region where the rotational speed of the motor is below the lower limit. Correction is performed using a map that gives a correction position amount corresponding to the rotation speed of the motor. That is, since the pulse width of the PWM signal becomes narrow in the low speed rotation region, the position of the rotor cannot be estimated by the second position estimating means. Therefore, in such a region, the first rotational position signal can be corrected by using a map that gives the correction position amount.

  According to the rotor position detection circuit of claim 3, the correction means does not perform correction based on the second rotation position signal even in a region where the rotation speed of the motor exceeds the upper limit, and the correction position amount corresponding to the rotation speed of the motor. Correction is performed using the map that gives As described above, when the motor is driven via the inverter, the return section may be widened in the high speed rotation region depending on the load condition, and the zero cross point of the phase voltage cannot be detected. The rotor position cannot be estimated. Accordingly, even in such a region, the first rotational position signal can be corrected by using a map that gives the correction position amount.

  According to the rotor position detection circuit of claim 4, the correction means does not perform correction based on the second rotation position signal in a region where the rotational speed of the motor exceeds the upper limit, and does not perform correction based on the second rotation position signal. An approximate expression is obtained from the correction position amount obtained based on the signal, and correction is performed using the approximate expression. If comprised in this way, compared with the case where it correct | amends using a map like Claim 3, the correction | amendment adapted more to an actual drive state can be performed.

  According to the rotor position detection circuit of the fifth aspect, the correction means determines the region that can be corrected based on the second rotational position signal, based on the power supply current detected by the current detection means or the value of the current flowing through the stator coil. To decide. That is, the region that can be corrected based on the second rotational position signal is determined according to the width of the return zone, and the zone increases as the current increases. Therefore, the region that can be corrected can be appropriately determined based on the current value.

  According to the rotor position detection circuit of the sixth aspect, the second position estimation means is arranged for one phase. That is, if the second position estimation means has at least one phase for correction, assuming that the correction is performed when the motor has a certain number of poles or the rotation speed is constant, the first rotation position Signal correction can be sufficiently performed. Therefore, the circuit configuration can be simplified and the cost can be reduced.

  According to a motor drive device of a seventh aspect, the rotor position detection circuit according to any one of the first to sixth aspects is provided, and energization timing in the drive circuit is determined based on a rotational position signal obtained by the circuit. Since the brushless DC motor is driven, the motor can be driven with low vibration and low noise, and the driving efficiency can be improved.

  According to the motor driving apparatus of the eighth aspect, the first and second position estimating means configured similarly to the first aspect are provided, and the phase shift amount calculating means is configured to output the first rotational position signal and the second rotational position signal. When the phase shift amount is calculated, the energization timing determining means starts from the level change edge indicated by the first rotational position signal, and is based on the phase shift amount or a phase amount equivalent to n times the electrical angle of 60 degrees. To determine the energization timing. Therefore, the same effect as in the first aspect can be obtained, and for example, when it is necessary to perform advance angle energization, the necessary advance angle amount is given from the time when the phase amount equivalent to n times the electrical angle of 60 degrees is added. This can be easily realized.

  According to the motor drive device of claim 9, when the rotational speed of the motor is controlled by PWM control, the energization timing determining means is a correction position amount corresponding to the rotational speed of the motor in a region where the rotational speed of the motor is below the lower limit. Since the energization timing is determined based on the correction amount obtained from the map to which is applied, or by adding a phase amount equivalent to n times the electrical angle of 60 degrees to the correction amount, the same effect as in claim 2 can be obtained.

  According to the motor drive device of claim 10, the energization timing determining means is based on a correction amount obtained from a map that gives a correction position amount corresponding to the motor rotation speed in a region where the rotation speed of the motor exceeds the upper limit. Alternatively, since the energization timing is determined by adding a phase amount corresponding to n times the electrical angle of 60 degrees to the correction amount, the same effect as in the third aspect can be obtained.

  According to the motor drive device of the eleventh aspect, in the region where the rotational speed of the motor exceeds the upper limit, the energization timing determining means has the phase of the second rotational position signal and the first rotational position signal obtained in the region below the upper limit. The approximate expression is obtained from the deviation amount, and the energization timing is determined by the correction amount obtained using the approximate expression or by adding a phase amount equivalent to n times the electrical angle of 60 degrees to the correction amount. The same effect can be obtained.

  According to the motor drive device of the twelfth aspect, the energization timing deciding means determines the current flowing through the power line or the stator coil detected by the current detecting means in the region that can be corrected based on the second rotational position signal. Since the determination is based on the value, the same effect as in the fourth aspect can be obtained.

  According to the motor drive device of the thirteenth aspect, the motor load is a fan mounted on the vehicle. That is, when the load is a fan, the torque increases in proportion to the square of the rotational speed, and the current supplied to the motor through the drive circuit increases, so that the detection position shift generated in the first rotational position signal The amount tends to increase. Therefore, the present invention can be applied effectively.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. Note that the same parts as those in FIG. 11 are denoted by the same reference numerals, description thereof will be omitted, and different parts will be described. The motor drive device 21 of this embodiment includes a control unit 7 and a position detection circuit 9 in the motor drive device 1, a control unit (second position estimation unit, correction unit, phase shift amount calculation unit, energization timing determination unit) 22 and The position detection circuit 23 is replaced. Further, a shunt resistor 24 is inserted between the sources of the lower arm side FETs 5d to 5f in the inverter unit 4 and the ground. The terminal voltage of the shunt resistor (current detection means) 24 is detected by a current detection circuit (current detection means) 25, and the detection output is given to the control unit 22. The voltage dividing resistors R1 and R2 are not shown.

The position detection circuit 23 uses a low-pass filter 10, a buffer amplifier 11, and a comparator 12 as a first position estimation circuit (first position estimation means) 27, and a second position estimation circuit (second position estimation) including comparators 28U, 28V, and 28W. Means) 29. Unlike the first position estimation circuit 27, the comparators 28U, 28V, and 28W directly compare the U, V, and W phase voltages of the motor 3 with the virtual neutral point voltage without using a low-pass filter. Then, the control unit 22 receives the output signals of the comparators 28U, 28V, and 28W, performs digital processing therein, and generates a (second rotation) position signal.
The load of the motor 3 is a fan 41. The fan 41 blows air to a radiator (heat exchanger) 42 and a condenser (condenser) 43 of an air conditioner mounted on the vehicle.

  Details of the digital processing performed by the control unit 22 will be described with reference to FIG. The phase voltage waveform input to the comparator 28 is a waveform switched by the PWM signal as shown in FIG. 2A, and the comparator 28 indicates the input phase voltage by a broken line in the figure. Compared with the reference voltage (virtual neutral point voltage), the section in which the return current flows through the diode of the FET 5 constituting the inverter unit 4 is not subject to comparison, so the output signal of the comparator 28 must be masked. (See FIG. 2 (b)).

In addition, even when the actual phase voltage is lower than the reference voltage, the reference voltage may be temporarily exceeded due to overshoot that occurs at the rising edge of the waveform. Therefore, it is necessary to mask the period related to the rising edge of the waveform. (See FIG. 2 (b)). Therefore, the control unit 22 masks the reflux period, the switching OFF period, and the rising period during which the transition is made from OFF to ON in synchronization with the logic of the PWM signal (see FIG. 2C). Note that FIG. 2D is an enlarged view of a part of FIG.
At this time, when the motor 3 is operated in a low speed region, the duty of the PWM signal becomes small and the on-pulse width becomes narrow, so that all the pulses are masked and detection (position estimation) becomes impossible. For example, if the carrier frequency is 20 kHz and the mask time is 5 μs, the detectable duty is in the range of more than 10%.

On the other hand, when the motor 3 is operated in a high speed region, the interval between the zero cross points of the induced voltage (in the case of 120 ° energization, the electrical angle 60 ° section) becomes short, and detection is difficult. When the load is a fan 41, for example, the load becomes heavier and the power supply current is increased as the rotational speed is increased. Therefore, the return section is extended, and as a result, the zero cross point is masked. For example, if 120 degrees energization is performed at a lead angle of 0 degrees, the zero cross point is located at the center of the electrical angle 60 degree section, and therefore, if the reflux section exceeds 30 electrical angles, it is masked.
From the above, there are a lower limit and an upper limit in the rotation region in which position estimation by the second position estimation circuit 29 is possible.

  Next, the phase shift included in the position estimation performed by the first position estimation circuit 27 will be described with reference to FIG. FIG. 3 shows the phase shift characteristic according to the change in the rotational speed of the motor 3 in the case of no load and the case of using a fan as a load for the analog filter method adopted by the first position estimation circuit 27. . In the case of no load, a curve in which the phase shift approaches 90 degrees as the rotational speed increases is shown based solely on the characteristics of the low-pass filter 10 itself. Then, when the phase shift has just reached 90 degrees, it coincides with the energization timing of the advance angle of 0 degrees.

On the other hand, when the fan is a load, the energization current increases as the rotational speed increases, so the section through which the reflux current flows is extended, and the capacitor of the low-pass filter 10 is charged more quickly. As a result, the phase shift amount starts to decrease from the middle.
Therefore, in this embodiment, the first position estimation circuit 27 and the second position estimation circuit 28 are used in combination, and the first rotational position signal output by the former is based on the second rotational position signal output by the latter. to correct. However, as described above, the position estimation by the second position estimation circuit 28 is effective when the rotational speed is within the predetermined range. Therefore, the characteristics (fans) shown in FIG. Correction is performed using a data table (referred to as a correction map) in which is mapped.

  Next, the operation of the present embodiment will be described with reference to FIGS. FIG. 5 is a flowchart showing the processing contents of the control unit 22 when the energization signal is generated based on the rising edge of the U-phase rotational position signal. When detecting the rising edge of the masked signal for the U-phase second rotational position signal output from the second position estimation circuit 28 (step S1), the control unit 22 starts the counter Au (step S2). . The outline of the mask process is shown in FIGS. 6A to 6C. As a result of performing the process as shown in FIG. 2, the rising and falling edges are induced as shown in FIG. 6C. A rectangular wave signal matching the zero cross point of the voltage is obtained. Moreover, the process of said step S1, S2 is performed independently of the process demonstrated below.

When detecting the rising edge of the U-phase first rotational position signal output from the first position estimating circuit 27 (see step S3, FIG. 6 (e)), the control unit 22 stops the counter Au, The counter B for detecting the edge interval is stopped (step S4). The counter Au is a counter for detecting the rising edge interval of the first and second rotational position signals. The counter B is stopped when any edge of the U, V, and W phases is detected.
Subsequently, the control unit 22 calculates a section length corresponding to an electrical angle of 60 degrees and the rotational speed of the motor 3 from the value of the counter B, and resets and starts the counter B (step S5), the value of the counter Au and the motor The phase shift amount of the first rotation position signal is calculated from the rotation number of 3, and the counter Au is reset (step S6).

  Next, the control unit 22 determines whether the rotational speed is in a range of 500 rpm to 2000 rpm (step S7), whether the duty of the PWM signal output from the inverter unit 4 is 10% or more (step S8), step It is determined whether or not the phase shift amount calculated in S6 is within a range of 50 degrees to 90 degrees (step S9). That is, in step S7, it is determined whether or not the position estimation by the second position estimation circuit 28 is in an effective rotation speed range, and step S8 also determines whether or not the lower limit of the effective rotation speed range is below. In step S9, it is determined whether or not the phase shift amount of the first rotational position signal is detected within a normal range.

And if it is judged as (YES) in all these steps S7-S9, a correction amount will be calculated according to the phase shift amount calculated at step S6 (step S10). On the other hand, if it is determined as (NO) in any one of steps S7 to S9, it is determined that the correction performed using the second rotational position signal is invalid, the phase shift amount is acquired from the correction map, and the correction amount is determined. Calculate (step S11). here,
(Correction amount) = 90 degrees- (Phase shift amount)
(See FIG. 6F).

After the execution of steps S10 and S11, the energization timing is corrected in step S12. That is, the timing when the correction amount is added to the electrical angle of 60 degrees (or n times the electrical angle of 60 degrees (n is a natural number)) starting from the rising edge of the first rotational position signal is the OFF of the U-phase upper arm. The timing is the ON timing of the V-phase upper arm (see FIG. 6G). When conducting the advance angle energization, as shown in FIG. 6G, the advance angle may be subtracted from the corrected timing.
A timing chart corresponding to the above case is shown in FIG. 7B corresponds to FIG. 6C, and FIG. 7C corresponds to FIG.

Further, in the case of the 120-degree energization method, the energization timing corrected when each edge is used as a reference corresponds as follows (when advance-angle energization is performed).
U phase: Rise → U phase upper arm OFF, V phase upper arm ON
: Falling → V-phase lower arm ON, U-phase lower arm OFF
V phase: Rise → W phase upper arm ON, V phase upper arm OFF
: Falling → W-phase lower arm ON, V-phase lower arm OFF
W phase: Rise → W phase upper arm OFF, U phase upper arm ON
: Falling → W-phase lower arm OFF, U-phase lower arm ON

  Further, when the correction amount obtained in step S11 is positive, the value is equal to or shorter than the calculation time until the correction amount is calculated, and advance angle energization is not performed, an electrical angle of 60 degrees is set in the process of step S12. There is no need to add. That is, the energization signal shown in FIG. At this time, the timing when the correction amount is added with the rising edge of the first rotational position signal as a base point is the ON timing of the W-phase lower arm and the OFF timing of the V-phase lower arm. Normally, a phase shift due to an increase in current or the like is on the leading side with respect to an electrical angle of 90 degrees. Therefore, when the advance angle energization is not performed, the control can be performed without adding an electrical angle of 60 degrees. And in this case, it can energize more accurately.

When advance angle energization is not performed, the energization timing corrected when each edge is used as a reference corresponds as follows.
U phase: Rise → W phase lower arm ON, V phase lower arm OFF
: Falling → W-phase upper arm ON, V-phase upper arm OFF
V phase: Rise → U phase lower arm ON, W phase lower arm OFF
: Falling → U-phase upper arm ON, W-phase upper arm OFF
W phase: Rise → V phase lower arm ON, U phase lower arm OFF
: Falling → V-phase upper arm ON, U-phase upper arm OFF
Further, even when the electrical angle of 60 degrees is not applied, it is possible to control to the advance side by energizing at a timing obtained by subtracting the advance amount and the computation time from the correction amount in consideration of the computation time. . Further, it may be determined whether or not to perform control to add an electrical angle of 60 degrees according to the result of considering the advance angle amount in the phase shift amount.

  As described above, according to the present embodiment, when the motor 3 is PWM-controlled by the position sensorless system, the position detection circuit 23 of the motor drive device 21 uses the first position estimation circuit 27 to output the phase voltage detection signal as the low-pass filter 10. The control unit 22 digitally outputs the output signal of the comparator 12 in the second position estimation circuit 29 that directly compares the phase voltage with the reference voltage. The second rotational position signal is generated by processing, and the rotational position indicated by the first rotational position signal is corrected by the second rotational position signal.

  That is, there is a high possibility that the first rotational position signal output from the first position estimation circuit 27 that performs analog signal processing includes variations, and the phase shift amount changes according to the rotational speed. The rotational position signal can be output over a wide range of motor rotation speeds. On the other hand, the second position estimation circuit 29 and the control unit 22 can obtain a more accurate position signal, but position estimation may be impossible depending on the driving conditions of the motor 3. Therefore, if both are combined and the rotational position indicated by the first rotational position signal is corrected by the second rotational position signal, a highly accurate position signal can be output over a wide rotational speed range.

Further, the control unit 22 does not perform correction based on the second rotational position signal in a region where the rotation speed of the motor 3 is below the lower limit and a region where the rotation speed exceeds the upper limit, and uses a correction map corresponding to the rotation speed of the motor 3. Therefore, even if it is difficult to estimate the position of the rotor by the second position estimation circuit 29 in a low-speed rotation region where the pulse width of the PWM signal is narrowed or in a high-speed rotation region where the reflux section is widened depending on the load condition, The map can be used to correct the first rotational position signal.
Furthermore, since the control unit 22 determines a region that can be corrected based on the second rotational position signal based on the power supply current value detected by the current detection circuit 25, the control unit 22 reflects the width of the reflux section in the inverter unit 4. Based on the power supply current, it is possible to appropriately determine an area that can be corrected.

In addition, since the load of the motor 3 is the fan 41 mounted on the vehicle, the load on the motor 3 increases as the rotational speed increases, and the current supplied to the motor 3 through the inverter unit 4 increases. Thus, the present invention can be effectively applied when the amount of detection position deviation generated in the first rotational position signal is large.
Further, the control unit 22 uses the level change edge indicated by the first rotational position signal as a starting point to set the phase deviation amount according to the phase deviation amount between the first rotational position signal and the second rotational position signal, or as necessary. Since the energization timing is determined by adding a phase amount equivalent to n times the electrical angle of 60 degrees, it is necessary from the time when the phase amount equivalent to n times the electrical angle of 60 degrees is added when it is necessary to carry out advance energization. This can be easily realized by giving a large advance amount.

(Second embodiment)
FIG. 8 shows a second embodiment of the present invention, and only parts different from the first embodiment will be described. In step S7 of the flowchart shown in FIG. 5 of the first embodiment, the upper limit of the rotation speed range is fixed at 2000 rpm, but in the second embodiment, rotation is performed according to the power supply current value detected by the current detection circuit 25. A case where the upper limit (Nmax) of the number is changed will be described.

FIG. 8 illustrates the above principle. When the number of poles of the three-phase motor 3 is “10” and the mask time of the reflux section is tmask, the upper limit rotational speed Nmax is determined as follows.
Nmax = (60 / tmask) × (2/10) × (30 degrees / 360 degrees)
And as shown to Fig.8 (a), a recirculation | reflux area expands substantially proportional to a power supply current value. In this case, if the mask time tmask is constant, the upper limit rotational speed Nmax is also constant (see FIG. 8B).

On the other hand, as shown in FIG. 8C, when the mask time tmask is changed in accordance with the increase of the power supply current value (the reflux section is extended), the upper limit rotational speed Nmax is reduced according to the above equation. As a result, a higher value can be set (see FIG. 8D).
From the above, if the control unit 22 sets the upper limit rotation speed Nmax in step S7 according to the current value detected by the current detection circuit 25 based on the curve shown in FIG. The number range can be set wider.

(Third embodiment)
FIG. 9 shows a third embodiment of the present invention. FIG. 9 is a view corresponding to FIG. 5 of the first embodiment. The configuration of the third embodiment is the same as that of the first embodiment, and the processing content in the control unit 22 is different. Step S7 in FIG. 5 is divided into two steps, step S7L for determining whether the rotational speed range is 500 rpm or more, and step S7H for determining whether the rotational speed range is 2000 rpm or less. In the same manner as in the first embodiment, steps S8 to S12 are executed. In addition, when it is determined as NO in any of steps S7L, S8, and S9, steps S11 and S12 are executed in the same manner as in the first embodiment.

  And after execution of step S10, the process of step S13-S16 is performed in parallel. Note that these processes may be executed until step S12 is executed. First, it is determined whether or not the rotational speed of the motor 3 is within the range of 900 rpm to 1000 rpm (step S13). If it is within the above range (YES), the rotational speed and the correction amount are set as N1 and R1, respectively. Store (step S14).

  On the other hand, if (NO) is determined in step S13, it is determined whether or not the rotational speed is within the range of 1800 rpm to 2000 rpm (step S15). If it is within the above range (YES), the rotational speed and the correction amount are determined. Are stored as N2 and R2, respectively (step S16). If (NO) is determined in any of steps S13 and S16, the rotational speed and the correction amount are not stored.

If it is determined in step S7H that the rotational speed exceeds the upper limit of 2000 rpm (NO), the rotational speed and correction amount data N1, R1, N, and R2 stored in steps S14 and S16 are already stored at that time. It is determined whether or not the data is stored (step S17). If the data is not complete (NO), the process proceeds to step S11, and correction using the map is performed as in the first embodiment.
On the other hand, if (YES) is determined in step S17, the control unit 22 calculates a linear equation when the data N1, R1, N, and R2 are mapped on the two-dimensional coordinates (step S18). Then, when the amount of correction is approximately calculated using the linear equation when the rotational speed exceeds 2000 rpm (step S19), the process proceeds to step S12.

  As described above, according to the third embodiment, the control unit 22 does not perform the correction based on the second rotational position signal in the region where the rotational speed of the motor 3 exceeds the upper limit, and the second rotational position in the region below the upper limit. Since a linear approximation formula is obtained from the correction position quantity obtained based on the signal and correction is performed using the approximation formula, as compared with the case where correction is performed using the correction map as in the first embodiment. Thus, it is possible to perform correction more suitable for the actual driving state. This approximate expression is not limited to linear approximation, but may be corrected using an approximate expression of a curve depending on the load, motor characteristics, and the like.

(Fourth embodiment)
FIG. 10 shows a fourth embodiment of the present invention. The motor drive device 31 of the fourth embodiment is obtained by replacing the position detection circuit 23 with a position detection circuit 32. In the position detection circuit 32, the second position estimation circuit (second position estimation means) 33 has the comparator 28 only for one phase of 28U corresponding to the U phase. Then, the control unit 22a generates a second rotational position signal from the output signal of the comparator 28U and performs correction.

  That is, if there is at least one phase for correction, the second position estimation circuit 33 assumes that the correction is performed when the number of poles of the motor 3 is large to some extent or when the rotation speed is constant. The rotational position signal can be sufficiently corrected. Therefore, according to the fourth embodiment configured as described above, the circuit configuration can be simplified and the cost can be reduced.

The present invention is not limited to the embodiments described above and shown in the drawings, and the following modifications or expansions are possible.
Steps S8 and S9 may delete at least one according to individual design.
An example of the energization process shown in step S12 corresponds to the 120-degree energization method, and when the energization angle is widened, it may be changed as appropriate.
In the current detection, a current flowing through the stator coil 6 of the motor 3 may be detected using a current sensor such as a current transformer.
The present invention is not limited to a three-phase motor, and may be applied to a multiphase motor having four or more phases.
The buffer amplifier 11 may be deleted.
The virtual neutral point voltage that is the comparison reference voltage of the second rotational position estimation circuit 29 may be replaced with ½ of the power supply voltage.
The motor load is not limited to the fan 41.

FIG. 1 is a diagram illustrating a configuration of a motor drive device according to a first embodiment of the present invention. The figure explaining the detail of the digital processing which a control part performs The figure which shows the phase shift characteristic according to the number of rotations of the motor about the case of no load and the case of using a fan as a load about the analog filter The figure which shows the rotation speed area | region which correct | amends phase shift, when using a fan as a load The flowchart which shows the processing content in the case of producing | generating an energization signal based on the rising edge of the rotation position signal of U phase The figure which shows the outline | summary of the mask process for producing | generating a 2nd rotation position signal, and calculation of a correction amount Timing chart corresponding to the processing of FIG. The second embodiment of the present invention is a diagram for explaining a case where the upper limit (Nmax) of the rotational speed is varied according to the power supply current value detected by the current detection circuit. FIG. 5 equivalent diagram showing a third embodiment of the present invention. FIG. 1 equivalent view showing a fourth embodiment of the present invention. FIG. 1 equivalent diagram showing the prior art (part 1) The figure which shows the voltage waveform (only U phase) of each part FIG. 1 equivalent diagram showing the prior art (part 2) Figure equivalent to FIG. The figure explaining the problem of the structure of FIG. The figure explaining the problem of the structure of FIG.

Explanation of symbols

  In the drawing, 3 is a brushless DC motor, 10 is a low-pass filter, 21 is a motor drive device, 22 is a control unit (second position estimation means, correction means, phase shift amount calculation means, energization timing determination means, rotor position detection circuit). , 23 is a position detection circuit (rotor position detection circuit), 24 is a shunt resistor (current detection means), 25 is a current detection circuit (current detection means), 27 is a first position estimation circuit (first position estimation means), 29 Is a second position estimation circuit (second position estimation means), 31 is a motor drive device, 32 is a position detection circuit (rotor position detection circuit), 33 is a second position estimation circuit (second position estimation means), and 41 is a fan. Indicates.

Claims (18)

In order to drive the brushless DC motor by the position sensorless method, in the circuit that detects the phase voltage generated in the stator coil and detects the rotational position of the rotor based on the detection result,
A first position estimating means comprising: a low-pass filter for low-pass filtering the phase voltage detection signal; and a comparator for comparing the output signal of the low-pass filter with a reference voltage and outputting a first rotational position signal;
A second position estimating means comprising a comparator for directly comparing the phase voltage with a reference voltage, and generating and outputting a second rotational position signal by digitally processing the output signal of the comparator;
A rotor position detection circuit comprising: correction means for correcting the rotational position indicated by the first rotational position signal by the second rotational position signal. When the rotational speed of the motor is controlled by PWM (Pulse Width Modulation) control,
The correction means does not perform correction based on the second rotational position signal in a region where the rotational speed of the motor is below a lower limit, and corrects using a map that gives a correction position amount corresponding to the rotational speed of the motor. The rotor position detection circuit according to claim 1, wherein:   The correction means does not perform correction based on the second rotation position signal in a region where the rotation speed of the motor exceeds the upper limit, and corrects using a map that gives a correction position amount corresponding to the rotation speed of the motor. The rotor position detection circuit according to claim 1, wherein:   The correction means does not perform correction based on the second rotational position signal in a region where the rotation speed of the motor exceeds the upper limit, and a correction position obtained based on the second rotational position signal in a region equal to or lower than the upper limit. The rotor position detection circuit according to claim 1, wherein an approximate expression is obtained from the quantity, and correction is performed using the approximate expression. A current detection means for detecting a current flowing in the power line or the stator coil;
5. The rotor position detection circuit according to claim 2, wherein the correction unit determines an area that can be corrected based on the second rotational position signal based on a current value detected by the current detection unit. .   6. The rotor position detecting circuit according to claim 1, wherein the second position estimating means is arranged for one phase. A drive circuit for driving a brushless DC motor by a position sensorless method;
A rotor position detection circuit according to any one of claims 1 to 6,
A motor drive device characterized in that energization timing in the drive circuit is determined based on a rotational position signal obtained by the rotor position detection circuit. In order to drive a brushless DC motor by a position sensorless system, a motor drive device including a rotor position detection circuit that detects a phase voltage generated in a stator coil and detects a rotational position of a rotor based on the detection result.
The rotor position detection circuit is
A first position estimating means comprising: a low-pass filter for low-pass filtering the phase voltage detection signal; and a comparator for comparing the output signal of the low-pass filter with a reference voltage and outputting a first rotational position signal;
A second position estimating means comprising a comparator for directly comparing the phase voltage with a reference voltage, and generating and outputting a second rotational position signal by digitally processing the output signal of the comparator;
A phase shift amount calculating means for calculating a phase shift amount between the first rotational position signal and the second rotational position signal;
Starting from the level change edge indicated by the first rotational position signal, the energization timing is determined by the phase shift amount or by adding a phase amount equivalent to n times the electrical angle of 60 degrees (n is a natural number) to the phase shift amount. A motor drive device comprising: an energization timing determining means for performing the operation. When the rotational speed of the motor is controlled by PWM (Pulse Width Modulation) control,
In the region where the rotational speed of the motor is below the lower limit, the energization timing determining means is based on a correction amount obtained from a map that gives a correction position amount corresponding to the rotational speed of the motor, or an electrical angle of 60 degrees to the correction amount. The motor drive device according to claim 8, wherein the energization timing is determined by adding a phase amount equivalent to n times.   The energization timing determining means, in a region where the rotational speed of the motor exceeds the upper limit, is based on a correction amount obtained from a map that gives a correction position amount corresponding to the rotational speed of the motor, or an electrical angle of 60 degrees to the correction amount. The motor drive device according to claim 8 or 9, wherein the energization timing is determined by adding a phase amount equivalent to n times.   The energization timing determining means obtains an approximate expression from the amount of phase shift between the second rotational position signal and the first rotational position signal obtained in the region below the upper limit in the region where the rotational speed of the motor exceeds the upper limit, 10. The motor according to claim 8, wherein the energization timing is determined by a correction amount obtained using the approximate expression or by adding a phase amount equivalent to n times an electrical angle of 60 degrees to the correction amount. Drive device. The rotor position detection circuit includes a current detection means for detecting a current flowing in a power line or the stator coil,
The motor drive according to any one of claims 9 to 11, wherein the energization timing determination unit determines a region that can be corrected based on the second rotational position signal based on a current value detected by the current detection unit. apparatus.   The motor driving apparatus according to claim 7, wherein the load of the motor is a fan mounted on a vehicle. In order to drive a brushless DC motor by a position sensorless method, in the method of detecting the phase voltage generated in the stator coil and detecting the rotational position of the rotor based on the detection result,
A low-pass filter for low-pass filtering the phase voltage detection signal, and outputting a first rotational position signal by comparing the output signal of the low-pass filter with a reference voltage;
A comparator for directly comparing the phase voltage with a reference voltage, and generating and outputting a second rotational position signal by digitally processing the output signal of the comparator;
A rotor position detecting method, wherein a rotational position indicated by the first rotational position signal is corrected by the second rotational position signal.   When the motor is driven by PWM (Pulse Width Modulation) control, correction based on the second rotational position signal is not performed in a region where the rotational speed of the motor is below the lower limit, and a correction position corresponding to the rotational speed of the motor The rotor position detection method according to claim 14, wherein correction is performed using a map to which an amount is given.   In a region where the rotational speed of the motor exceeds the upper limit, correction based on the second rotational position signal is not performed, and correction is performed using a map that gives a correction position amount corresponding to the rotational speed of the motor. The rotor position detecting method according to claim 14 or 15.   In the region where the rotational speed of the motor exceeds the upper limit, correction based on the second rotational position signal is not performed, and an approximate expression is obtained from the corrected position amount obtained based on the second rotational position signal in the region below the upper limit. The rotor position detection method according to claim 14 or 15, wherein the correction is performed using the approximate expression.   18. The rotor position detection method according to claim 15, wherein an area that can be corrected based on the second rotational position signal is determined based on a current flowing in a power supply line or the stator coil.

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