JP2013208009A - Motor controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor controller capable of reducing a switching loss even when a rotational speed of a motor is slow.SOLUTION: A motor control section is equipped with an inverter circuit and a control section. The control section controls the inverter circuit. The control section calculates modulation rate α (S2). The control section sets a drive switching cycle td by using the modulation rate α calculated in S2 (S3). The control section measures upper arm continuous ON time t (S6 and S13). The control section drives a motor by a two-phase modulation method when it is not in an upper arm continuous ON section (S7:NO). The control section drives the motor by the two-phase modulation method when rotational speed of the motor is fast and the upper arm continuous ON time t does not reach the drive switching cycle td (S10:NO)(S8). The control section, when rotational speed of the motor is slow, switches from the two-phase modulation method to a three-phase modulation method every time when the upper arm continuous ON time t reaches the drive switching cycle td (S10:YES,S11) .

Description

  The present invention relates to a motor control device that controls an inverter circuit to drive a motor.

  2. Description of the Related Art Conventionally, there is a motor control device that can control an inverter circuit by a PWM (Pulse Width Modulation) method and switch a motor driving method between a two-phase modulation method and a three-phase modulation method. The inverter circuit includes a three-phase switching element, a capacitor, and a charge pump circuit. The three-phase switching element includes an upper arm switching element and a lower arm switching element. The capacitor stores an electric charge for turning on and off the upper arm switching element. The charge pump circuit charges the capacitor when the lower arm switching element is in the on state.

  The two-phase modulation method can reduce the switching loss because the switching frequency of the switching element is less than that of the three-phase modulation method. In the two-phase modulation method, the on / off state of the switching element for one phase among the three-phase switching elements is fixed, and the motor is driven by changing the on / off state of the other switching elements. The phase to be fixed is switched at regular intervals according to the rotation angle of the output shaft of the motor. As the rotation speed of the motor becomes slower, the cycle for switching the phase to be fixed becomes longer. If the cycle for switching the phase to be fixed becomes long, the charge (voltage) stored in the capacitor becomes small, and the switching element cannot be switched. Therefore, the motor cannot be driven normally. For this reason, for example, the inverter control device described in Patent Document 1 controls the motor by the two-phase modulation method when the motor rotation speed is high, and the motor by the three-phase modulation method when the motor rotation speed is low. Is controlling. The inverter control device drives the motor in a state where the rotation speed is low while charging the capacitor by the charge pump circuit by driving the motor by the three-phase modulation method.

Japanese Patent No. 4389746

  However, the inverter control device of Patent Document 1 has a large number of switching operations because the motor must be driven by a three-phase modulation method when the rotational speed of the motor is slow. For this reason, there has been a problem that the switching loss becomes large when the rotational speed of the motor is low.

  An object of the present invention is to provide a motor control device capable of reducing switching loss even when the rotational speed of the motor is slow.

  The motor control device according to the present invention includes a three-phase switching element including an upper arm switching element and a lower arm switching element, a capacitor for storing electric charges for turning on and off the upper arm switching element, and the lower arm switching element. A motor control device for driving a motor by controlling an inverter circuit having a charge pump circuit for charging the capacitor when on by a PWM method, and driving the three-phase switching element when driving the motor A modulation factor calculating means for calculating a modulation factor in the case of performing the motor driving method from the two-phase modulation method in order to secure time for the charge pump circuit to charge the capacitor by turning on the lower arm switching element. The drive switching period, which is the period for switching to the three-phase modulation method, is calculated as the modulation factor calculating unit. The upper arm continuous on-time which is the time when the upper switching element of one phase is continuously turned on when the motor is driven by the two-phase modulation method and the period setting means which is set according to the modulation factor calculated by And when the upper arm continuous on time acquired by the time acquisition means has not reached the drive switching period set by the period setting means, the inverter circuit is controlled. Each time the upper arm continuous on time acquired by the first drive control means for driving the motor by the two-phase modulation method and the time acquisition means reaches the drive switching period set by the period setting means. And second drive control means for driving the motor by temporarily switching from the two-phase modulation method to the three-phase modulation method.

  In this case, when the rotational speed of the motor is fast and the upper arm continuous on-time does not always reach the drive switching cycle (when the upper arm continuous on-time is smaller than the drive switching cycle), the first drive control means is a two-phase modulation system. Drive the motor. Therefore, the motor control device always drives the motor by the two-phase modulation method. When the rotation speed of the motor is slow and the upper arm continuous on-time has reached the drive switching cycle (when the upper arm continuous on-time is longer than the drive switching cycle), the second drive control means temporarily changes from the two-phase modulation method. The motor is driven by switching to the three-phase modulation method. The controller 11 turns off the upper arm switching element and turns on the lower arm switching element by driving the motor using the three-phase modulation method. Therefore, the charge pump circuit charges the capacitor. As described above, the motor control device can drive the motor by the two-phase modulation method while temporarily switching to the three-phase modulation method and charging the capacitor even when the rotation speed of the motor is low. Therefore, switching loss can be reduced as compared with the case where the motor is always driven by the three-phase modulation method when the rotation speed of the motor is low.

  In the motor control device, the cycle setting unit may lengthen the drive switching cycle as the modulation rate calculated by the modulation rate calculation unit is smaller. In this case, the motor control device can reduce the number of times of switching to the three-phase modulation method when the modulation rate becomes small. Therefore, the motor control device can further reduce the switching loss as compared with the case where the switching period is calculated only by the rotation speed of the motor regardless of the modulation rate.

1 is a block diagram showing an electrical configuration of a motor control device 1. FIG. FIG. 3 is a circuit diagram showing an electrical configuration of an inverter circuit 6. The figure which shows an example of the on-off timing of the switching element 61 in the case of a three-phase modulation system. The figure which shows an example of the output voltage of the inverter circuit 6 in the case of a three-phase modulation system. The figure which shows an example of the on-off timing of the switching element 61 in case the upper arm switching element 611A turns on continuously in a two-phase modulation system. The figure which shows an example of the on-off timing of the switching element 61 in case the upper arm switching element 611C turns off continuously in a two-phase modulation system. The figure which shows an example of the output voltage of the inverter circuit 6 in the case of a two-phase modulation system. The flowchart of a main process. The figure which shows the experimental result of the change of the voltage of the capacitor | condenser 641 in an upper arm continuous ON area. The figure which shows the other experimental result of the change of the voltage of the capacitor | condenser 641 in an upper arm continuous ON area.

  Hereinafter, an embodiment embodying the present invention will be described with reference to the drawings. The outline of the motor control device 1 will be described with reference to FIG. The motor control device 1 includes a motor 10, a control unit 11, an inverter circuit 6, a detector 12, a current detector 13, and the like. The inverter circuit 6 is electrically connected to the control unit 11 and the motor 10. The control unit 11 controls the motor 10 by PWM control of the inverter circuit 6. The detector 12 detects the electrical angle, mechanical angle, etc. of the motor 10. The detector 12 is, for example, a resolver or an encoder. The current detector 13 detects the currents iu and iv generated by the U-phase and V-phase outputs from the inverter circuit 6 and inputs the currents iu and iv to a three-phase AC / dq coordinate converter 115 (described later) provided in the control unit 11.

  The control unit 11 includes a speed controller 111, current controllers 112 and 113, a non-interacting controller 114, a three-phase AC / dq coordinate converter 115, a dq / 3-phase AC coordinate converter 116, a speed / A position signal processor 117 and the like are provided. The control unit 11 is, for example, a CPU. Each device provided in the control unit 11 may be realized by a circuit or a program. The speed / position signal processor 117 outputs an electrical angle signal and a mechanical angle signal from the output value of the detector 12. The three-phase AC / dq coordinate converter 115 converts the currents iu and iv detected by the current detector 13 into currents id and iq in the dq coordinate system.

The speed controller 111, the current controllers 112 and 113, and the non-interacting controller 114 are inverter circuits on the dq axes using the speed command ω ^* rm, electrical angle signal and mechanical angle signal, current id, iq, and the like. 6, the voltage commands V ^* d and V ^* q for the output voltages Vd and Vq are output to the dq / 3-phase AC coordinate converter 116. Non-interference control is control that cancels out the speed electromotive force that interferes between dq coordinates in the motor 10. Non-interference control is performed to improve current controllability. The dq / 3-phase AC coordinate converter 116 outputs voltage commands V ^* u, V ^* v, V ^* w for the three-phase voltages Vu, Uv, Uw from the voltage commands V ^* d, V ^* q, etc. To do. The control unit 11 controls the inverter circuit 6 so that the inverter circuit 6 outputs the output voltages Vu, Vv, Vw based on the voltage commands V ^* u, V ^* v, V ^* w. The motor control device 1 includes a storage unit (not shown) such as a ROM, a RAM, and a flash memory. The control unit 11 reads the program stored in the storage unit and performs main processing (see FIG. 8) described later. The control unit 11 can store various temporary data and the like in the storage unit.

  The inverter circuit 6 will be described with reference to FIG. The inverter circuit 6 includes a switching element 61, diodes 621 to 626, upper arm driving circuits 631A to 631C, lower arm driving circuits 632A to 632C, a main component 64 of a charge pump circuit (hereinafter referred to as “charge pump circuit 64”). .), And a power source 65 and a power source 66. Switching element 61 includes upper arm switching elements 611A to 611C for three phases and lower arm switching elements 612A to 612C for three phases. That is, the switching element 61 has three phases. The upper arm switching element 611A and the lower arm switching element 612A are U-phase switching elements. The upper arm switching element 611B and the lower arm switching element 612B are V-phase switching elements. Upper arm switching element 611C and lower arm switching element 612C are W-phase switching elements. The switching element 61 is, for example, an insulated gate bipolar transistor.

  The diodes 621 to 626 are provided between the emitters and collectors of the six switching elements 611A to 611C and 612A to 612C. The positive terminal of the power supply 66 is connected to the collectors of the upper arm switching elements 611A to 611C. The upper arm drive circuits 631A to 631C are electrically connected to the gates of the upper arm switching elements 611A to 611C, respectively. Lower arm drive circuits 632A to 632C are electrically connected to the gates of lower arm switching elements 612A to 612C, respectively. The control unit 11 is electrically connected to the upper arm drive circuits 631A to 631C and the lower arm drive circuits 632A to 632C. The control unit 11 controls the on / off of the switching element 61 by controlling the upper arm driving circuits 631A to 631C and the lower arm driving circuits 632A to 632C. Thereby, the control unit 11 controls the inverter circuit 6 by the PWM method and drives the motor 10.

  The charge pump circuit 64 includes capacitors 641A to 641C, diodes 642A to 642C, and a resistor 643. Capacitors 641A to 641C are electrically connected to upper arm drive circuits 631A to 631C, respectively. Capacitors 641A to 641C drive upper arm drive circuits 631A to 631C and store electric charges (voltages) for turning on upper arm switching elements 611A to 611C. The cathodes of the diodes 642A to 642C are electrically connected to the capacitors 641A to 641C and the upper arm drive circuits 631A to 631C, respectively. The resistor 643 is electrically connected to the anodes of the diodes 642A to 642C and the positive terminal of the power source 65. The power source 65 is electrically connected to the lower arm drive circuits 632A to 632C. The lower arm drive circuits 632A to 632C are driven by power supplied from the power supply 65, and turn on and off the lower arm switching elements 612A to 612C. When the lower arm switching elements 612A to 612C are turned on, the power supply 65 supplies electric charges to the capacitors 641A to 641C. That is, the charge pump circuit 64 charges the capacitors 641A to 641C when the lower arm switching elements 612A to 612C are on.

  In the following description, the upper arm switching elements 611A, 611B, and 611C are collectively referred to as “upper arm switching element 611” when not specified either. When the lower arm switching elements 612A, 612B, and 612C are generically named or when any of them is not specified, the lower arm switching elements 612 are referred to as the lower arm switching elements 612. When the capacitors 641A, 641B, and 641C are generically named or when any of them is not specified, the capacitor 641A is referred to as a capacitor 641. When the upper arm drive circuits 631A, 631B, and 631C are generically named or when any of them is not specified, the upper arm drive circuit 631 is referred to. When the lower arm drive circuits 632A, 632B, and 632C are generically named or when any of them is not specified, the lower arm drive circuit 632 is referred to.

  With reference to FIG. 3, the operation of the switching element 61 when the motor 10 is driven by the three-phase modulation method will be described. In the three-phase modulation method, the motor 10 is controlled by turning on and off the three-phase switching element 61. The controller 11 turns on and off the switching element 61 by a known triangular wave comparison method. As shown in FIG. 3, in the case of the three-phase modulation method, the upper arm switching element 611 is switched on and off according to the change of the triangular wave carrier signal 51. When the upper arm switching element 611 is on, the lower arm switching element 612 is off. When the upper arm switching element 611 is off, the lower arm switching element 612 is on.

  Here, ON is “1” and OFF is “0”. In this case, the on / off combinations of the upper arm switching elements 611A, 611B, 611C are (0, 0, 0), (1, 0, 0), (1, 1, 0), (1, 1, 1), It changes as (1, 1, 1), (1, 1, 0), (1, 0, 0), (0, 0, 0). For example, the binary number (1, 1, 1) is “7” in decimal number. Therefore, the voltage vector at (1, 1, 1) is represented as V7. When other ON / OFF combinations are also expressed in the same manner, the voltage vector changes between V0 and V7 as shown in FIG. Specifically, the voltage vector is switched in the order of V0, V4, V6, V7, V7, V6, V4, and V0.

  The output voltage of the inverter circuit 6 in the case of the three-phase modulation method is shown in FIG. The U-phase, V-phase, and W-phase output voltages are Vu, Vv, and Vw, respectively. As shown in FIG. 4, the output voltages Vu, Vv, and Vw are sine waves that are 120 ° out of phase.

With reference to FIG. 5, the operation of the switching element 61 when the motor 10 is driven by the two-phase modulation method will be described. In the two-phase modulation method, the switching element 61 of one of the three phases is fixed on / off (continuously on or continuously off), thereby reducing the number of switching of the inverter circuit 6 and reducing the switching loss, Realize energy saving. For example, when the upper arm switching element 611A is continuously turned on, the on / off timing of the upper arm switching element 611 is as shown in FIG. As shown in FIG. 5, the output time of the upper arm switching element 611A is stopped by stopping the output of the V0 vector, that is, adding the same time (t ₀ ) as V0 when the output is stopped to V7 and outputting it. And the on-time is extended. That is, the upper arm switching element 611A is continuously turned on. Then, the on-time of the upper arm switching elements 611B and 611C is extended by the extent that the on-time of the upper arm switching element 611A is extended (see FIGS. 3 and 5). V0 and V7 are called zero voltage vectors. In the two-phase modulation, of the zero voltage vectors V0 and V7, the duty occupying the entire zero voltage vector when only the zero voltage vector V7 is output, and the duty occupying the entire zero voltage vectors V0 and V7 in the three-phase modulation. Since are not changed, the output vectors are equivalent.

For example, when the one-phase upper arm switching element 611C is continuously turned off, the on / off timing of the switching element 611 is as shown in FIG. As shown in FIG. 6, the output time of the upper arm switching element 611C is stopped by stopping the output of the V7 vector, that is, adding the same time (t ₇ ) as V7 when the output is stopped to V0 and outputting it. And the off time is extended. For this reason, the lower arm switching element 612C is continuously turned on. The off-time of the upper arm switching elements 611A and 611B is increased by the extension of the off-time of the upper arm switching element 611C (see FIGS. 3 and 6). In other words, the on-time of the lower arm switching elements 612B and 612C is extended. As shown in FIGS. 3, 5, and 6, the two-phase modulation method (see FIGS. 5 and 6) has a switching frequency of ON / OFF of the switching element 61 of 2 compared to the three-phase modulation method (see FIG. 3). / 3. Therefore, the two-phase modulation method can reduce the switching loss.

  The output voltage of the inverter circuit 6 in the case of the two-phase modulation method is shown in FIG. In FIG. 7, sections 80, 81, 82, and 83 are sections in which the one-phase upper arm switching element 611 is continuously turned on (hereinafter referred to as “upper arm continuous on section”). Sections 84, 85, 86, and 87 are sections where the one-phase lower arm switching element 612 is continuously turned on. As shown in FIG. 7, the control unit 11 alternately turns on the upper arm switching element 611 and turns on the lower arm switching element 612 alternately in order to equalize the load on the switching element 61 (the electric power of the motor 10). Switch every 60 degrees). Moreover, the control part 11 switches the phase which turns on continuously between U phase, V phase, and W phase.

  The capacitor 641 is charged in the sections 84, 85, 86, and 87 in which the lower arm switching element 612 is turned on. In the upper arm continuous on section 80, 81, 82, 83, the lower arm switching element 612 is not turned on. Therefore, the charge pump circuit 64 does not charge the capacitor 641 in the upper arm continuous on section 80, 81, 82, 83. In this case, the capacitor 641 turns on the upper arm switching element 611 while consuming the stored charge. However, if the upper arm switching element 611 is turned on for a long time in the upper arm continuous on sections 80, 81, 82, 83, the voltage of the capacitor 641 drives the upper arm driving circuit 631 to turn on the upper arm switching element 611. Therefore, the voltage is lower than the lower limit voltage (hereinafter referred to as “operation lower limit voltage”). Therefore, the control unit 11 cannot normally turn on the upper arm switching element 611 and cannot drive the motor 10. Therefore, in the present embodiment, the control unit 11 temporarily switches from the two-phase modulation method to the three-phase modulation method before the voltage of the capacitor 641 becomes smaller than the operation lower limit voltage (S11 in FIG. 8, which will be described later). In the three-phase modulation method, since there is a section in which the lower arm switching element 612 is turned on, the charge pump circuit 64 can charge the capacitor 641.

  Let α be the modulation factor when driving the three-phase switching element 61 when driving the motor 10. When switching from two-phase modulation to three-phase modulation, the time for turning on and charging the lower arm switching element 612 varies according to the value of the modulation factor α. For example, if the modulation factor is 0%, the duty time of the capacitor 641 is at least 50%. For this reason, the charging time can be secured. When the modulation rate becomes 100%, the duty of the charging time becomes 0%. For this reason, charging is not possible. However, since the induced voltage of the motor 10 is low at low speed, a desired torque is generated without applying a high voltage to the motor 10. That is, the motor 10 can be driven with a low modulation rate. Therefore, even if the value of the modulation factor α is limited, the charging time during the three-phase modulation operation at low speed can be secured without any problem. For example, when the modulation factor α is 50% (0.5) at the maximum, the duty of the capacitor 641 can be secured at 25% (0.25) as the minimum. Thus, the minimum duty of the charging time of the capacitor 641 is (1−α) / 2. Therefore, when the carrier frequency is fHz, the minimum charge pulse width in the three-phase modulation in one carrier section (section corresponding to one triangular wave) is (1-α) / 2f.

The current consumption of the upper arm drive circuit 631 is Ia, and the maximum charge current for the capacitor 641 when the voltage drops by ΔV from the voltage Vcc of the power supply 65 is Ib. The charge amount charged by the charge pump circuit 64 to the capacitor 641 with respect to the charge pulse width in one carrier section is considered that the capacitance of the capacitor 641 is sufficiently large with respect to the carrier frequency and is ∫Idt≈Ib · t, Assuming that the safety factor is 2 and the allowable discharge time td is half, Expression (1) is established.
td = (1−α) · Ib / (2 · 2f · Ia) (1)

  As can be seen from the equation (1), if the time t <td from the start of the upper arm continuous on section 80, 81, 82, 83, (charge charge of the capacitor 641)> (discharge charge), The arm switching element 611 can be normally turned on. Therefore, the inverter circuit 6 can continue to drive the motor 10 by the two-phase modulation method.

  Therefore, in the present embodiment, in the two-phase modulation method, when the time t after the start of the upper arm continuous on section 80, 81, 82, 83 exceeds td, the time td elapses. In addition, only the one carrier section of PWM is switched to the three-phase modulation method, and the capacitor 641 is charged (see S11 in FIG. 8, described later). That is, the time td is a cycle in which the driving method of the motor 10 is switched from the two-phase modulation method to the three-phase modulation method in order to secure the time for the charge pump circuit 64 to charge the capacitor 641 by turning on the lower arm switching element 612. In the following description, time td is referred to as “drive switching period td”.

The main process will be described with reference to FIG. The controller 11 calculates the output voltages Vd and Vq of the inverter circuit 6 on the dq axes from the speed command ω ^* rm (S1). The output voltages Vd and Vq of the inverter circuit 6 on the dq axis correspond to the output voltage commands V ^* d and V ^* q input to the dq / 3-phase AC coordinate converter 116 (see FIG. 1). The speed command ω ^* rm is a command for the number of revolutions for rotating the motor 10, and is generated by the control unit corresponding to the speed set on the panel by the operator or the amount of depression of the operation pedal of the sewing machine. As shown in FIG. 1, the control unit 11 controls the output voltages Vd and Vq by a feedback control system using a speed command ω ^* rm as an input.

The control unit 11 calculates the modulation factor α using the output voltages Vd and Vq calculated in S1 (S2). The modulation factor α is expressed by the following equation (2) when the DC bus (DC power supply) voltage Vbus (voltage of the power supply 66) and the output voltages Vd and Vq are used.
α = √ (Vd ² + Vq ² ) / Vbus (2)

The controller 11 sets the drive switching period td according to the modulation factor α calculated in S2 (S3). In S2, the control unit 11 calculates the maximum charge current Ib at the operation lower limit voltage, and calculates the drive switching period td using the maximum charge current Ib. In detail, it calculates as follows. A voltage drop from the voltage Vb when the capacitor 641 is fully charged is represented by ΔV. The resistance value of the resistor 643 is R1. The maximum charge current Ib at the operation lower limit voltage is expressed by the following formula (3).
Ib = ΔV / R1 (3)

  And the control part 11 calculates the drive switching period td from the above-mentioned Formula (3) and Formula (1). For example, it is assumed that Vcc = 15V, ΔV = 1V, R1 = 10Ω, capacitance C1 of the capacitor 641 = 10 μF, Ia = 0.55 mA, f = 10 kHz, α = 0.5 (50%). In this case, the control unit 11 calculates Ib = 100 mA and Td = 2.27 ms from the equations (3) and (1). As a result, the control unit 11 sets the drive switching period td. The control unit 11 stores the drive switching period td in a RAM (not shown).

  The control unit 11 refers to the electrical angle signal output from the speed / position signal processor 117, and determines whether it is time to newly start the upper arm continuous on section (S4). In the example shown in FIG. 7, if the electrical angle is 60 °, 180 °, 300 ° 420 ° (= 60 °), which is the timing at which the upper arm continuous on section 80 to 83 is started, the control unit 11 is the upper arm continuous. It is determined that the ON section is newly started.

  If it is not time to newly start the upper arm continuous on section (S4: NO), the control unit 11 performs the process of S7 described later. When it is time to newly start the upper arm continuous on section (S4: YES), the control unit 11 sets the time t to “0” (S5). The control unit 11 starts measuring time t (S6). Time t indicates the time when the upper arm switching element 611 is continuously turned on. In the following description, time t is referred to as “upper arm continuous on time t”.

  The controller 11 refers to the electrical angle signal output from the speed / position signal processor 117, and determines whether or not the upper arm is continuously on (S7). For example, if it is other than the upper arm continuous on section 80 to 83 shown in FIG. 7, the control unit 11 determines that it is not the upper arm continuous on section (S7: NO), and drives the motor 10 by two-phase modulation (S8). . The process returns to S1. For example, if it is upper arm continuous on section 80-83 (refer to Drawing 7) (S7: NO), control part 11 will acquire upper arm continuous on time t (S9). Next, the controller 11 determines whether or not the upper arm continuous on time t acquired in S9 has reached the drive switching period td set in S3 (S10). That is, the control unit 11 determines whether or not the upper arm continuous on time t is equal to or longer than the drive switching period td.

  When the upper arm continuous on-time t has not reached the drive switching period td (S10: NO), the controller 11 drives the motor 10 by the two-phase modulation method. When the upper arm continuous on-time t has reached the drive switching period td (S10: YES), the control unit 11 drives the motor 10 by one carrier section (one triangle wave section) and the three-phase modulation method (S11). . That is, the controller 11 drives the motor 10 by temporarily switching from the two-phase modulation method to the three-phase modulation method. Therefore, the lower arm switching element 612 is turned on (the upper arm switching element 611 is turned off), and the charge pump circuit 64 charges the capacitor 641. The controller 11 sets the upper arm continuous on time t to “0” (S12). The control unit 11 resumes the measurement of the upper arm continuous on time t (S13). The process returns to S1.

  As described above, the control unit 11 executes the main process. For example, it is assumed that the drive switching period td is “2.27 ms”. It is assumed that the driving speed of the motor 10 is fast and passes through each of the upper arm continuous on sections 80 to 83 (see FIG. 7) in a time shorter than 2.27 ms. In this case, the control unit 11 drives the motor by two-phase modulation when it is a section 84 to 87 (see FIG. 7) that is not the upper arm continuous on section (S7: NO) (S8). When the upper arm continuous on section 80-83 is in effect (S7: YES), the control unit 11 always drives the motor with two-phase modulation because the upper arm continuous on time t is shorter than the drive switching period td (S10: NO). (S8). That is, the control unit 11 always drives the motor 10 by the two-phase modulation method.

  It is assumed that the driving speed of the motor 10 is slow and passes through each of the upper arm continuous on sections 80 to 83 (see FIG. 7) in a time of 2.27 ms or more. In this case, in the sections 84 to 87 (see FIG. 7) that are not the upper arm continuous on section, the control unit 11 drives the motor by two-phase modulation (S7: NO, S8). When the control unit 11 is in the upper arm continuous on section 80 to 83 (S7: YES), the motor 10 is driven by the two-phase modulation method (S10: NO, S8), and the upper arm continuous on time t is drive-switched. Every time the period td is reached, the motor 10 is temporarily driven by the three-phase modulation method (S10: YES, S11). That is, before the voltage of the capacitor 641 becomes smaller than the drive lower limit voltage, the upper arm switching element 611 is turned off and the lower arm switching element 612 is turned on by changing to the three-phase modulation method. For this reason, the charge pump circuit 64 charges the capacitor 641. As described above, even when the rotation speed of the motor 10 is slow, the control unit 11 temporarily switches to the three-phase modulation method and charges the capacitor 641 (S11), and drives the motor 10 by the two-phase modulation method. (S8). Therefore, switching loss can be reduced as compared with the case where the motor is always driven by the three-phase modulation method when the rotation speed of the motor 10 is low. Since the switching loss can be reduced, the motor can be driven efficiently. Therefore, the operating cost of the motor 10 can be reduced.

  Further, since the number of times of switching is reduced in the two-phase modulation method compared to the case of the three-phase modulation method, heat generation of the switching element 61 can be reduced. Therefore, components can be mounted with high density, and the control unit 11 can be downsized.

  As an example, FIG. 9 shows an experimental result of a change in the voltage of the capacitor 641 in the upper arm continuous ON period when the modulation factor α = 0.5 (50%). FIG. 9 shows the results of an experiment using a circuit simulator. In order to show that the operation lower limit voltage is not lower than 14V, the start voltage is set to around 14V (the same applies to FIG. 10). In FIG. 9, a section 91 in which the voltage of the capacitor 641 gradually decreases is a section in which the upper arm switching element 611 is continuously turned on and the motor 10 is driven by the two-phase modulation method. The timing 92 at which the voltage of the capacitor 641 rises is the timing at which the control unit 11 switches from the two-phase modulation method to the three-phase modulation method to drive the motor 10 and perform charging. When α = 0.5, since the drive switching period td is 2.27 ms, the control unit 11 switches to the three-phase modulation method every 2.27 ms to charge the capacitor 641. The operating lower limit voltage is 14V. As shown in FIG. 9, the voltage of the capacitor 641 does not become smaller than the operating lower limit voltage 14V. Therefore, the motor 10 can be driven stably.

  As another example, FIG. 10 shows an experimental result of a change in the voltage of the capacitor 641 in the upper arm continuous on period when the modulation factor α = 0.75 (75%). In FIG. 10, as in the case of FIG. 9, the voltage of the capacitor 641 does not become smaller than the operating lower limit voltage 14V. Therefore, the motor 10 can be driven stably.

  In Expression (1), the smaller the value of the modulation factor α, the longer (larger) the drive switching period td. Therefore, as shown in FIGS. 9 and 10, the drive switching cycle of FIG. 9 where the value of the modulation factor α is small is longer than the drive switching cycle of FIG. 10. As described above, the smaller the value of the modulation factor α, the longer the drive switching period td. Therefore, when the modulation factor α decreases, the number of times of switching to the three-phase modulation method can be reduced. Therefore, the control unit 11 can further reduce the switching loss as compared with the case where the switching period is calculated only by the rotation speed of the motor 10 regardless of the modulation rate.

  In the above embodiment, the control unit 11 that performs the process of S2 corresponds to the “modulation rate calculation means” of the present invention. The control unit 11 that performs the process of S3 corresponds to the “cycle setting unit” of the present invention. The control unit 11 that performs the processes of S6, S9, and S13 corresponds to the “time acquisition unit” of the present invention. The control unit 11 that performs the process of S8 corresponds to the “first drive control means” of the present invention. The control unit 11 that performs the process of S11 corresponds to the “second drive control unit” of the present invention.

  In addition, this invention is not limited to said embodiment, A various change is possible. For example, the control unit 11 switches to the three-phase modulation method and drives the motor 10 in one carrier section, but is not limited to this. It is sufficient that the control unit 11 switches to the three-phase modulation method to drive the motor 10, and may be, for example, a 5-carrier section.

  The control unit 11 uses the expression (1) to make the drive switching cycle td longer as the value of the modulation factor α is smaller, but is not limited to this. For example, the control unit 11 does not calculate the modulation rate α using the equation (1), but refers to data in which the modulation rate α stored in the storage unit in advance is associated with the drive switching period td, and the drive switching is performed. The period td may be set. Moreover, the control part 11 may lengthen the drive switching period td in steps, if the value of the modulation factor (alpha) becomes small. Further, the controller 11 does not always need to lengthen the drive switching period td as the value of the modulation factor α is smaller. For example, the control unit 11 may shorten the drive switching period td in a part of the range where the modulation rate α is small.

DESCRIPTION OF SYMBOLS 1 Motor controller 6 Inverter circuit 10 Motor 11 Control part 61 Switching element 64 Charge pump circuit 80,81,82,83 Upper arm continuous ON section 611 Upper arm switching element 612 Lower arm switching element 631 Upper arm drive circuit 632 Lower arm drive Circuit 641 capacitor

Claims (2)

A three-phase switching element including an upper arm switching element and a lower arm switching element, a capacitor for storing charges for turning on and off the upper arm switching element, and charging the capacitor when the lower arm switching element is on A motor control device for driving a motor by controlling an inverter circuit including a charge pump circuit by a PWM method,
A modulation factor calculating means for calculating a modulation factor when driving the three-phase switching element when driving the motor;
A drive switching period, which is a period for switching the motor drive system from a two-phase modulation system to a time when the lower arm switching element is turned on to ensure time for the charge pump circuit to charge the capacitor, A period setting means for setting according to the modulation rate calculated by the modulation rate calculation means;
Time acquisition means for acquiring an upper arm continuous on time, which is a time during which the upper switching element of one phase is continuously turned on when the motor is driven by the two-phase modulation method;
When the upper arm continuous on-time acquired by the time acquisition means does not reach the drive switching period set by the period setting means, the inverter circuit is controlled to control the motor to the two-phase modulation method. First drive control means for driving with,
Each time the upper arm continuous on-time acquired by the time acquisition means reaches the drive switching period set by the period setting means, the two-phase modulation method is temporarily switched to the three-phase modulation method. A motor control apparatus comprising: second drive control means for driving the motor.   The motor control device according to claim 1, wherein the cycle setting unit lengthens the drive switching cycle as the modulation rate calculated by the modulation rate calculation unit decreases.

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