JP4435635B2 - Brushless motor control device - Google Patents

Description

  The present invention relates to a control device for a brushless motor used in a refrigerator, a compressor of an air conditioner, and the like.

  Conventionally, in the drive control of a three-phase brushless motor, it is necessary to energize the stator windings of each phase in accordance with (synchronizing with) the rotating rotor position. In the rotor position detection, in a compressor used in an air conditioner, a refrigerator, or the like, the inside becomes a high temperature state, and it is difficult to provide a sensor for detecting the rotor position such as a Hall IC. Therefore, a position detection method that detects the induced voltage of the stator winding and uses it as rotor position information is generally used. This position detection method energizes the two phases of the three-phase winding and uses the remaining one-phase non-energized winding to detect the induced voltage generated by the rotation of the rotor-side magnet, thereby determining the rotor position. Next, the energized phases are sequentially switched.

  As a brushless motor control device using this position detection method, for example, a configuration as shown in FIG. The brushless motor control device switches the DC power source 1 by the inverter unit 2 to supply the brushless motor 3 as a three-phase AC. Further, the terminal voltages (induced voltages) U, V, W of the armature winding of the brushless motor 3 are compared with the reference voltage for comparison by the comparators 4u, 4v, 4w, respectively, and the position detection signal as the comparison result is obtained. Input to the microcomputer 5.

  The microcomputer 5 detects a change point (position detection point) of the position detection signal in order to control the rotor 3a of the brushless motor 3, and based on this detection point, a switching element comprising a transistor of the inverter unit 2 2u, 2v, 2w, 2x, 2y, 2z are driven, and a signal for chopping the drive period is output to the control circuit 6. The reference voltage for comparison is obtained by dividing the bus voltage Vcc of the inverter unit 2 by 1/2 with the resistor circuit 7. The resistance values of the two resistors constituting the resistance circuit 7 are the same.

  When the brushless motor 3 is operating, for example, the terminal voltage U of the stator winding has the form shown in FIG. 9A, and this terminal voltage U is input to the comparator 4u. The terminal voltages V and W of the other stator windings have similar voltage waveforms, and the input voltages having these voltage waveforms are input to the comparators 4v and 4w.

  Then, the comparator 4u compares the input voltage with the reference voltage for comparison, and outputs a position detection signal shown in FIG. The comparators 4v and 4w also output similar position detection signals.

  The microcomputer 5 calculates the energization switching timing of the stator winding based on the change in the position detection signal. Also, the PWM duty ratio (on / off ratio) is calculated based on the current rotation speed and the target rotation speed of the brushless motor 3.

  The control circuit 6 outputs a signal for driving the transistor of the inverter unit 2 as shown in FIG. 9C based on the energization switching timing calculated by the microcomputer 5 and the chopping information of the predetermined duty ratio.

  In the control of the brushless motor 3, when the ON time of the duty ratio of the PWM signal is increased, the rotation speed of the brushless motor 3 increases. When the ON time of the duty ratio is shortened, the rotation speed of the brushless motor 3 decreases. By changing the ON time of the duty ratio in this way, the rotation speed of the brushless motor 3 can be set to the target rotation speed. In such a brushless motor 3, the use of the embedded magnet type rotor 3a has an advantage that the reluctance torque can be effectively used by performing the field weakening control.

  However, when this embedded magnet type rotor 3a is used, as shown in FIG. 10, the waveform of the induced voltage has a flat portion Ft that is flat in the vicinity of the zero cross point Zp that crosses the reference voltage. . If the position detection is performed in the flat portion Ft, the position detection is delayed or accelerated, which causes a disadvantage that the position detection becomes unstable. Then, the position detection accuracy is deteriorated, and the operation of the brushless motor 3 becomes unstable. As a result, noise and vibration increase and motor efficiency also deteriorates.

A technique for improving the position detection accuracy of the rotor 3a is disclosed in Patent Document 2. That is, as shown in FIG. 11, in the resistor circuit 7 for dividing the bus voltage Vcc, a plurality of resistors 7c and 7d are added in addition to the two resistors 7a and 7b. By switching on and off the switching elements 8a and 8b by a control signal from the microcomputer 5 and alternately shorting the intermediate points of the added resistors 7c and 7d, a reference voltage for comparison higher than the virtual neutral point voltage can be obtained. An up-and-down fluctuation type virtual neutral point voltage in which a low reference voltage for comparison is alternately switched is generated. Each of the comparators 4u, 4v, and 4w detects and compares the intersection between the up-and-down variation type virtual neutral point voltage and the induced voltage at the time of rising or the intersection point between the virtual neutral point voltage and the induced voltage at the time of falling. As a result, the zero cross point Zp can be shifted to a position outside the flat portion Ft, the position detection can be stabilized, and the brushless motor 3 can be stably operated.
JP-A-8-182378 Japanese Patent Laid-Open No. 11-14685

  As described in Patent Document 2, the problem that the position detection becomes unstable can be solved by changing the virtual neutral point that is the reference voltage for comparison for position detection. However, in order to realize this, it is necessary to provide a switching element for generating a virtual neutral point and to perform drive control thereof. By newly providing a switching element, the number of components increases, and the timing for driving the switching element must be matched with the switching timing of the inverter unit, which complicates drive control.

  Therefore, in view of the above, an object of the present invention is to provide a brushless motor control device capable of improving the reliability of position detection and realizing stable operation with a simple configuration without increasing the number of components.

  According to the present invention, a DC power source is switched by an inverter unit and applied to a stator winding of a brushless motor, and a position of the rotor of the brushless motor is detected from an induced voltage generated in the stator winding, and based on this position detection information. A control device for a brushless motor that switches the energization of the stator winding by driving the inverter unit, and halves the induced voltage and the bus voltage of the inverter unit when the induced voltage rises or falls. A means for detecting a position by comparing with a reference voltage obtained by shifting by a predetermined amount, a means for calculating a time corresponding to the electrical angle R based on a position detection signal based on the comparison result, and a calculation based on the calculated time. Means for setting a switching time for switching energization of the stator winding, and from the time of performing the position detection to the switching time And it has a means for performing the energization switching after the elapse.

  The reference voltage is determined by dividing the bus voltage by two resistors having different resistance values. As a result, the reference voltage is shifted up and down by a predetermined amount from the value obtained by halving the bus voltage, and becomes a lower voltage or higher voltage than the value obtained by halving the bus voltage. That is, the reference voltage is a voltage that avoids a flat portion generated in the induced voltage, and position detection can be performed accurately, and position detection can be prevented from becoming unstable. Alternatively, position detection may be performed by comparing a voltage obtained by dividing the induced voltage with the same voltage division ratio as that of the reference voltage with the reference voltage.

  When the rotational speed of the brushless motor is controlled by the pulse width modulation method, the upper phase switching element of the inverter unit is PWM-switched. At this time, the position detection timing is when the induced voltage rises, and the reference voltage is shifted by a predetermined amount to a lower voltage side than a value obtained by halving the bus voltage. When PWM switching is performed on the lower phase switching element of the inverter unit, the position detection timing is when the induced voltage falls, and the reference voltage is a predetermined amount higher than the value obtained by halving the bus voltage. Shift. Note that the amount of voltage shift is determined by the resistance voltage dividing ratio.

  A position detection signal is output when the induced voltage and the reference voltage are compared and the zero cross point is detected. Based on this position detection signal, the time from the previous position detection to the current position detection is counted, and this time is set as the time corresponding to the electrical angle R. Based on this time, the first switching time and the second switching time are determined. Set the time. The electrical angle R is set to (360 / n) degrees, such as 120 degrees, 180 degrees, 90 degrees, etc., depending on the energization method such as a rectangular wave or a sine wave. n is a natural number. The interval from the first switching time to the second switching time is a time corresponding to the electrical angle R / 2. For example, in the case of an electrical angle of 120 degrees, the interval from the first switching time to the second switching time is a time corresponding to an electrical angle of 60 degrees.

  As another energization switching time setting, when the number of phases of the brushless motor is M and the number of poles is p poles (p is an even number), the time from the position detection before M / 2 × p times to the current position detection The time is set as a time corresponding to the electrical angle R × M / 2 × p, and the first switching time and the second switching time are set based on this time. For example, in the case of a three-phase brushless motor, the time from the position detection 3/2 × p times before the current position detection is counted, and this time is set as the time corresponding to the electrical angle R × 3/2 × p. A first switching time and a second switching time are set based on the time.

  According to the present invention, when detecting the position of the rotor, a switching element for switching a reference voltage to be compared with a conventional induced voltage is not required, and control for driving the embedded magnet is not required. Position detection can be performed in a portion that avoids a flat portion of the induced voltage generated by a mold rotor or the like. Therefore, a highly reliable brushless motor control device can be provided with a simple configuration.

  An outline of a control device for driving the three-phase brushless motor of the present embodiment is shown in FIG. This control apparatus has substantially the same configuration as the conventional one shown in FIG. 8, and includes a position detection unit and a control unit, and drives and controls a known inverter unit 2 including a switching element and a diode.

  The position detection unit compares the induced voltage generated in the stator winding of the brushless motor 3 with the reference voltage for comparison, and detects the position of the rotor 3a. The position detection unit divides the bus voltage of the inverter unit 2 for reference. The reference voltage resistor circuit 10 for generating a voltage and three comparators 4u, 4v, 4w for comparing the induced voltage and the reference voltage are configured. The resistance circuit 10 includes two resistors 10x and 10y, and the respective resistance values are set to be different from each other.

  The control unit includes a microcomputer 5 that controls the switching elements 2u, 2v, 2w, 2x, 2y, and 2z of the inverter unit 2 based on the position detection signals input from the comparators 4u, 4v, and 4w, and the microcomputer 5 And a control circuit 6 that drives the inverter unit 2 by outputting a drive signal to the switching elements 2u, 2v, 2w, 2x, 2y, and 2z on the basis of a command from.

  Here, if the resistance value of the resistor 10x of the resistor circuit 10 is X and the resistance value of the resistor 10y is Y, X> Y. At this time, the reference voltage is a value obtained by multiplying the bus voltage Vcc of the inverter unit 2 by Y / (X + Y), and is lower than the conventional reference voltage obtained by halving the bus voltage as shown in FIG. That is, the reference voltage is shifted to a lower voltage side by a predetermined amount than the voltage obtained by halving the bus voltage Vcc, and the reference voltage is lower than the voltage corresponding to the flat portion Ft of the induced voltage. Thereby, the zero cross point Zp can be shifted to a position outside the flat portion Ft, and an unstable factor at the time of position detection can be eliminated.

  At this time, the zero cross point at the rise of the induced voltage shifts forward, and the zero cross point at the fall of the induced voltage shifts backward. In this state, the position detection interval varies. Therefore, zero cross point detection is not performed when the induced voltage falls, and zero cross point detection is performed only when the induced voltage rises. The control unit detects the position of the rotor 3a based on the position detection signal output from the position detection unit when the induced voltage rises.

  In the case of the prior art shown in FIG. 8, the zero crossing point detection of the induced voltage is performed by “U phase rise” → “W phase fall” → “V phase rise” → “U phase fall” → “W phase rise” → It is repeatedly performed in the order of “V-phase falling” → “U-phase rising”. The position detection interval is a time corresponding to an electrical angle of 60 degrees. On the other hand, in this embodiment, since the zero cross point is detected only when the induced voltage rises, it is repeated in the order of “U-phase rise” → “V-phase rise” → “W-phase rise” → “U-phase rise”. The position detection interval is a time corresponding to an electrical angle of 120 degrees.

  Next, the operation when the position of the rotor 3a is detected and the brushless motor 3 is driven will be described with reference to FIG. When the position detection timing at the “U-phase rising” occurs (timing t1), the time corresponding to the electrical angle of 120 degrees, which is the position detection interval from the previous position detection at the “W-phase rising” to the current position detection. Is measured. This time measurement is performed by using the timer counter function of the microcomputer 5. The microcomputer 5 measures the time from when the position detection signal at the previous zero cross point detection is input to when the position detection signal at the current zero cross point detection is input. This time measured is equivalent to an electrical angle of 120 degrees.

  The microcomputer 5 sets a switching time for switching the energization of the stator winding based on a time corresponding to an electrical angle of 120 degrees. Switching of energization is performed in two stages, and a first switching time and a second switching time are set. The first switching time is a time corresponding to an electrical angle of 30 degrees. The second switching time is a time after the first switching, and is a time corresponding to an electrical angle of 60 degrees.

  After the setting of the switching time, when the time corresponding to 30 electrical degrees has elapsed from the time of position detection (timing t1), the first energization switching is performed (timing t2). The second energization switching is performed after the passage of time corresponding to 60 degrees electrical angle after switching the energization (after the time corresponding to 90 degrees electrical angle from the time of position detection) (timing t3). Thereafter, a time corresponding to an electrical angle of 120 degrees elapses from the position detection, and the position detection timing at the “V-phase rising” comes (timing t4). Thereafter, the drive control of the brushless motor 3 is repeated in the same manner.

The energization switching time may be calculated based on the time for one rotation of the brushless motor 3. The time for one rotation of the brushless motor 3 is calculated from the following equation.
(Time equivalent to an electrical angle of 120 degrees) x M / 2 x p
p: Number of poles of brushless motor (even number)
M is the number of phases of the brushless motor, and here, M = 3. For example, when the number of poles of the brushless motor 3 is 4, the time from the position detection six times before one rotation of the brushless motor 3 to the current position detection corresponds to the electrical angle of 120 degrees measured as described above. Obtained from the time. That is, the time for one rotation is equivalent to an electrical angle of 120 degrees × 6 = 720 degrees. Based on the calculated time for one rotation of the brushless motor 3, the first switching time and the second switching time are set. Instead of measuring the time corresponding to the electrical angle of 120 degrees, the time corresponding to the electrical angle R × n, for example, R = 120 degrees, the time corresponding to the electrical angle of 360 degrees or 720 degrees may be measured. Further, the number of poles of the brushless motor 3 may be six or more.

  In addition, the first switching time is the time corresponding to an electrical angle of 30 degrees, and the second switching time is the time corresponding to an electrical angle of 60 degrees after the first energization switching, but is not limited thereto. For example, if the first switching time at which the efficiency of the brushless motor 3 is optimized is a value corresponding to an electrical angle of 15 degrees, the first switching time may be a time corresponding to an electrical angle of 15 degrees. Similarly, the second switching time is a time corresponding to an electrical angle of 60 degrees after the first energization switching.

  In the above embodiment, the relationship between the resistance values of the resistors 10x and 10y of the resistor circuit 10 is X> Y, but X <Y may be satisfied. In this case, as shown in FIG. 4, the reference voltage is higher than the conventional reference voltage obtained by halving the bus voltage of the inverter unit 2. That is, the reference voltage is shifted to a higher voltage side by a predetermined amount than the voltage obtained by halving the bus voltage Vcc, and the reference voltage has a value higher than the voltage corresponding to the flat portion Ft of the induced voltage. Thereby, the zero cross point Zp can be shifted to a position outside the flat portion Ft, and an unstable factor at the time of position detection can be eliminated.

  At this time, the zero cross point at the rising of the induced voltage shifts backward, and the zero cross point at the falling of the induced voltage shifts forward. In this state, the position detection interval varies. Therefore, zero cross point detection is not performed when the induced voltage rises, and zero cross point detection is performed only when the induced voltage falls. The control unit detects the position of the rotor 3a based on the position detection signal output from the position detection unit when the induced voltage falls. The control of the brushless motor 3 based on the position detection of the rotor 3a is the same as described above.

  By the way, in this control apparatus, when the rotational speed of the brushless motor 3 is controlled by the pulse width modulation method, the upper-phase switching elements 2u, 2v, and 2w are PWM-switched as shown in FIG. In this case, the diode recirculation time generated at the time of energization switching differs between the upper phase commutation and the lower phase commutation. This is because DC current regeneration occurs during lower phase commutation, so that the motor winding current falls earlier and the diode recirculation time becomes shorter than that during upper phase commutation. Since the induced voltage cannot be detected while the diode is circulating, it is desirable that the diode reflux time be as short as possible. Therefore, when the upper-phase switching elements 2u, 2v, and 2w are PWM-switched, the zero-crossing point detection is not performed at the time of upper-phase commutation in which the diode recirculation time is long, that is, when the induced voltage falls, and the diode recirculation time is short. The zero cross point is detected only at the lower phase commutation, that is, when the induced voltage rises. Thereby, the reliability of position detection can be improved.

  Further, when the rotational speed of the brushless motor 3 is controlled by the pulse width modulation method, as shown in FIG. 6, when the lower-phase switching elements 2x, 2y, and 2z are PWM-switched, a DC current is applied during the upper-phase commutation. Therefore, the fall of the motor winding current is accelerated, and the diode recirculation time is correspondingly shortened as compared with the lower phase commutation. Therefore, when PWM switching is performed on the lower-phase switching elements 2x, 2y, and 2z, the zero-point detection is not performed at the time of lower-phase commutation in which the diode recirculation time is long, that is, at the rise of the induced voltage, and the diode recirculation time is shortened. Zero cross point detection is performed only during upper phase commutation, that is, when the induced voltage falls. Thereby, the reliability of position detection can be improved.

  Furthermore, a voltage obtained by dividing the induced voltage and the reference voltage by the same ratio may be used as an input signal to the comparators 4u, 4v, 4w. As shown in FIG. 7, a resistance circuit 11 for dividing the induced voltage of each phase is provided. There are three resistance circuits 11 corresponding to each phase, and the induced voltage of each phase is divided at the same voltage dividing ratio. The resistor circuit 11 includes two resistors 11 u 1, 11 u 2, 11 v 1, 11 v 2, 11 w 1, 11 w 2, and the resistance value is set so that the voltage dividing ratio in the resistors 11 u 1, 11 u 2 is the same as the voltage dividing ratio in the reference voltage resistor circuit 10. Is set. The same applies to the other resistors 11v1, 11v2, 11w1, and 11w2. Other configurations are the same as those of the above embodiment shown in FIG.

  The induced voltage of the U phase is divided by the resistors 11u1 and 11u2 of the resistor circuit 11 and input to the comparator 4u. Similarly, the V phase and the W phase are divided by the resistors 11v1, 11v2, and the resistors 11w1, 11w2, and input to the comparators 4v, 4w. Further, the reference voltage resistor circuit 10 halves the bus voltage of the inverter unit 2, further shifts it by a predetermined amount, and divides the voltage by the same voltage dividing ratio as that of the resistor circuit 11. , 4w. In this way, by dividing the induced voltage and the reference voltage at the same voltage dividing ratio, the divided voltage input to the comparators 4u, 4v, 4w is kept within the operation range of the comparators 4u, 4v, 4w. Can do.

  In addition, this invention is not limited to the said embodiment, Of course, many corrections and changes can be added to the said embodiment within the scope of the present invention. Although this embodiment is applied to a three-phase brushless motor, it may be applied to a two-phase, four-phase brushless motor. Further, the electrical angle may be applied to 90 degrees and 180 degrees other than 120 degrees.

The figure which shows schematic structure of the control apparatus of the brushless motor of one Embodiment of this invention. Diagram showing signal waveform of induced voltage and zero cross point of reference voltage The figure which shows the relationship between the timing of rotor position detection and the energization switching timing of the stator winding The figure which shows the signal waveform of the induced voltage in another embodiment, and the zero crossing point of a reference voltage Time chart for PWM switching of the upper phase switching element of the inverter Time chart for PWM switching of the lower phase switching element of the inverter The figure which shows schematic structure of the control apparatus of the brushless motor of other embodiment. The figure which shows schematic structure of the control apparatus of the conventional brushless motor The figure which shows the operation signal waveform of each part of a brushless motor Figure showing the signal waveform of the conventional induced voltage and the zero-cross point of the reference voltage The figure which shows schematic structure of the control apparatus of another conventional brushless motor

Explanation of symbols

2 Inverter section
3 Brushless motor
3a Rotor 4u, 4v, 4w Comparator
5 Microcomputer
6 Control circuit
10 resistance circuit 10x, 10y resistance

Claims (5)

A DC power source is switched by the inverter unit and applied to the stator winding of the brushless motor, the position of the rotor of the brushless motor is detected from the induced voltage generated in the stator winding, and the inverter unit is based on the position detection information Is a brushless motor control device that switches the energization of the stator winding by driving the stator winding, and is obtained by shifting the induced voltage and the bus voltage of the inverter unit by a predetermined amount by 1/2 when the induced voltage rises. A means for performing position detection by comparing with a reference voltage, and a time from the previous position detection to the current position detection based on the position detection signal based on the comparison result , and this time is regarded as a time corresponding to the electrical angle R. means for the electrical angle R / 2 considerable time as the interval from first switching time to the second switching time, energization of the stator winding Switching means for setting a first switching time and a second switching time, the control device for a brushless motor, characterized in that it comprises a means for performing the energization switching from the time of performing the position detection in after the switching time. 2. The brushless motor control device according to claim 1, wherein when the rotational speed of the brushless motor is controlled by a pulse width modulation method, the switching element of the upper phase of the inverter unit is PWM-switched. A DC power source is switched by the inverter unit and applied to the stator winding of the brushless motor, the position of the rotor of the brushless motor is detected from the induced voltage generated in the stator winding, and the inverter unit is based on the position detection information Is a brushless motor control device that switches the energization of the stator windings by driving the induced voltage, and when the induced voltage falls, the induced voltage and the bus voltage of the inverter unit are halved and shifted by a predetermined amount. The means for detecting the position by comparing the obtained reference voltage and the time from the previous position detection to the current position detection based on the position detection signal based on the comparison result , and this time is equivalent to the electrical angle R. means for a time, as the interval of electrical angle R / 2 considerable time from the first switching time to the second switching time, of the stator winding Control of the brushless motor, characterized in that it comprises means for setting a first switching time and a second switching time for switching the electric, and means for performing energization switching after the elapse the switching time from the time of performing the position detection apparatus. 4. The brushless motor control device according to claim 3, wherein when the rotation speed of the brushless motor is controlled by a pulse width modulation method, the lower phase switching element of the inverter unit is PWM-switched. 5. The brushless motor control device according to claim 1, wherein the reference voltage is determined by dividing the bus voltage by two resistors having different resistance values.

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