Motor drive device, motor unit, fan unit, battery system, and mobile body

Abstract

This motor drive device comprises: a conversion unit that has a plurality of switching elements, converts input power to output power by switching on / off of the plurality of switching elements, and supplies the output power to a motor; an output unit that is connected to a control terminal of each of the plurality of switching elements and outputs a control voltage for controlling the switching on / off to the control terminal; an adjustment unit that can adjust a control current flowing between the output unit and the control terminal; and a control unit that performs switching control for controlling the output unit so that the input power is converted into the output power through the switching on / off of the plurality of switching elements, and that performs current control for controlling the adjustment unit so that the absolute value of the control current increases as the load torque of the motor decreases.

Description

Motor drive devices, motor units, fan units, battery systems, mobile objects

[0001] The present disclosure relates to a motor drive device, a motor unit, a fan unit, a battery system, and a moving object.

[0002] Patent Document 1 discloses an integrated circuit applied to a power conversion circuit including a series connection of a high-side switching element and a low-side switching element. In this integrated circuit, a signal generation unit generates a high-side drive signal that controls the on / off state of the high-side switching element and a low-side drive signal that controls the on / off state of the low-side switching element. A drive unit controls the on / off state of the high-side switching element based on the high-side drive signal and the on / off state of the low-side switching element based on the low-side drive signal.

[0003] In a circuit such as that disclosed in Patent Document 1, the output of a control voltage from an output section (a drive section in Patent Document 1) to a control terminal (e.g., a gate) of a switching element is started or stopped, thereby changing the voltage at the control terminal of the switching element and switching the switching element on or off.

[0004] In the above-described circuit, the control current flowing between the output unit and the control terminal of the switching element is constant when the output of the control voltage is started or stopped. Therefore, in the above-described circuit, in order to suppress the occurrence of voltage ringing at the control terminal of the switching element, it is conceivable to determine the absolute value (constant value) of the control current according to the maximum load torque of the motor (motor generator in Patent Document 1) driven by the power conversion circuit.

[0005] However, determining the absolute value of the control current according to the maximum load torque as described above raises the following concern: When the motor load torque is low, the time required from the start (or end) of the output of the control voltage to the state of the switching element stabilizing to the on state (or off state) (hereinafter referred to as the "switching transition time") becomes long.

[0006] Japanese Patent No. 6221930

[0007] The present disclosure aims to provide a technique that can suppress the occurrence of voltage ringing at the control terminal of a switching element while suppressing an increase in the length of switching transition time.

[0008] In order to achieve the above object, a motor drive device according to one aspect of the present disclosure includes a conversion unit having a plurality of switching elements, converting input power into output power by switching the plurality of switching elements on and off, and supplying the output power to a motor; an output unit connected to the control terminals of each of the plurality of switching elements and outputting a control voltage to the control terminal for controlling on / off of the switching elements; an adjustment unit capable of adjusting the control current flowing between the output unit and the control terminal; and a control unit that performs switching control to control the output unit so that the input power is converted into output power by switching the plurality of switching elements on and off, and current control to control the adjustment unit so that the absolute value of the control current becomes larger as the load torque of the motor becomes lower.

[0009] A motor unit according to another aspect of the present disclosure includes a motor and the motor drive device that drives the motor.

[0010] A fan unit according to another aspect of the present disclosure includes a blower having an impeller that transports air and a motor that drives the impeller to rotate, and the motor drive device that drives the motor.

[0011] A battery system according to yet another aspect of the present disclosure includes a battery and the fan unit that cools the battery by transporting air toward the battery.

[0012] A moving object according to yet another aspect of the present disclosure includes a main body and the battery system included in the main body.

[0013] According to the present disclosure, it is possible to suppress the occurrence of voltage ringing at the control terminal of a switching element while suppressing an increase in the switching transition time.

[0014] FIG. 1 is a block diagram illustrating the configuration of a motor unit according to a first embodiment. FIG. 2 is a block diagram illustrating the functional configuration of a control unit of the motor unit according to the first embodiment. FIG. 3 is a waveform diagram illustrating a high-side drive signal and a low-side drive signal. FIG. 4 is a diagram illustrating the correspondence between an index value indicating the load torque of a motor, a current value of a control current, and a dead time length. FIG. 5 is a graph illustrating the temporal changes in gate current and gate voltage when a switching element is turned on when the load torque of a motor is high. FIG. 6 is a graph illustrating the temporal changes in gate current and gate voltage when a switching element is turned off when the load torque of a motor is high. FIG. 7 is a graph illustrating the temporal changes in gate current and gate voltage when a switching element is turned on when the load torque of a motor is low. FIG. 8 is a graph illustrating the temporal changes in gate current and gate voltage when a switching element is turned off when the load torque of a motor is low. FIG. 9 is a schematic diagram illustrating a vehicle according to a second embodiment. 10 and 11 are graphs illustrating another example of the changes in gate current and gate voltage over time when the switching element is turned on and off under high motor load torque, respectively.

[0015] Hereinafter, the embodiments will be described in detail with reference to the drawings. Each of the embodiments described below represents a specific example of the present disclosure. Therefore, the numerical values, components, the arrangement and connection of the components, steps, and the order of steps shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Therefore, among the components in the following embodiments, components that are not described in the independent claims that represent the highest concept of the present disclosure will be described as optional components. Each figure is a schematic diagram and is not necessarily an exact illustration. The same or equivalent parts in the figures are designated by the same reference numerals, and their descriptions are incorporated herein by reference.

[0016] (Embodiment 1) Fig. 1 is a block diagram illustrating the configuration of a motor unit 1 according to embodiment 1. The motor unit 1 is connected to a power source 2. The motor unit 1 includes a motor 3 and a motor drive device 10. In this example, the power source 2 is a DC power source. The motor 3 is a three-phase AC brushless motor. The motor 3 drives a rotating body configured to transport a fluid by rotation. For example, the rotating body is an impeller 72 provided in a blower 71, which will be described later with reference to Fig. 9.

[0017] Motor drive device 10 is connected to a power supply 2 and a motor 3. Motor drive device 10 drives motor 3 using power supplied from power supply 2. In this example, motor drive device 10 includes a conversion unit 11, a smoothing capacitor 12, a plurality of drive units 20, a plurality of sensors 30, a storage unit 40, and a control unit 50.

[0018] [Conversion Unit] The conversion unit 11 has a plurality of switching elements SW. The conversion unit 11 converts input power into output power by switching on and off the plurality of switching elements SW, and supplies the output power to the motor 3. In this example, the input power is power supply power (DC power supply voltage) supplied from the power supply 2. The output power is three-phase AC power (AC voltage).

[0019] <Switching Element> The switching element SW has a control terminal SWa. The switching element SW switches on and off depending on the voltage at the control terminal SWa of the switching element SW. For example, when the voltage at the control terminal SWa of the switching element SW exceeds a threshold voltage, the switching element SW switches from off to on. When the voltage at the control terminal SWa of the switching element SW falls below the threshold voltage, the switching element SW switches from on to off.

[0020] In this example, the conversion unit 11 has six switching elements SW1 to SW6. Of the six switching elements SW1 to SW6, three switching elements SW1, SW3, and SW5 function as high-side switching elements, and the remaining three switching elements SW2, SW4, and SW6 function as low-side switching elements.

[0021] One high-side switching element and one low-side switching element are connected in series between a positive electrode line L1 and a negative electrode line L2 to form one pair (leg). In this example, the positive electrode line L1 is connected to the positive electrode of the power supply 2. The negative electrode line L2 is connected to the negative electrode of the power supply 2. In this way, the multiple switching elements SW include a high-side switching element and a low-side switching element connected in series.

[0022] In this example, switching elements SW1 and SW2 are connected in series between a positive electrode line L1 and a negative electrode line L2 to form a "leg corresponding to the U phase." The connection point between switching elements SW1 and SW2 is connected to an output line LOu that is connected to a U-phase input terminal of the motor 3. Switching elements SW3 and SW4 are connected in series between a positive electrode line L1 and a negative electrode line L2 to form a "leg corresponding to the V phase." The connection point between switching elements SW3 and SW4 is connected to an output line LOv that is connected to a V-phase input terminal of the motor 3. Switching elements SW5 and SW6 are connected in series between a positive electrode line L1 and a negative electrode line L2 to form a "leg corresponding to the W phase." The connection point between switching elements SW5 and SW6 is connected to an output line LOW that is connected to a W-phase input terminal of the motor 3.

[0023] <Freewheeling Diodes> The conversion unit 11 has a plurality of (six in this example) freewheeling diodes DF. The plurality of freewheeling diodes DF are connected in parallel to the plurality of switching elements SW. The freewheeling diodes DF may be parasitic diodes that are parasitic on the switching elements SW, or may be diode elements configured separately from the switching elements SW.

[0024] The free wheel diode DF connected in parallel to the high-side switching element (e.g., switching element SW1) has a forward direction (direction in which current flows easily) that is from the output line (e.g., output line LOu) to the positive electrode line L1. The free wheel diode DF connected in parallel to the low-side switching element (e.g., switching element SW2) has a forward direction that is from the negative electrode line L2 to the output line (e.g., output line LOu).

[0025] [Smoothing Capacitor] The smoothing capacitor 12 is connected between the positive electrode line L1 and the negative electrode line L2. The smoothing capacitor 12 smoothes the power supply power (DC power supply voltage) applied between the positive electrode line L1 and the negative electrode line L2. Specifically, the smoothing capacitor 12 reduces ripples in the power supply power and absorbs surge voltages. For example, the smoothing capacitor 12 is formed by an electrolytic capacitor.

[0026] [Driver Unit] The multiple drivers 20 correspond to the multiple switching elements SW, respectively. In this example, six drivers 20 are provided corresponding to the six switching elements SW, respectively. Each of the multiple drivers 20 has an output unit 21 and an adjustment unit 22.

[0027] [Output Unit] The output unit 21 included in the drive unit 20 is connected to the control terminal SWa of the switching element SW corresponding to that drive unit 20. The output unit 21 included in the drive unit 20 is configured to output a control voltage to the control terminal SWa of the switching element SW. The control voltage is a voltage for controlling the on / off of the switching element SW. In this example, each of the six output units 21 constitutes "an output unit 25 connected to the control terminal SWa of one switching element SW and outputting a control voltage to the control terminal SWa of that switching element SW for controlling the on / off of that switching element SW."

[0028] Hereinafter, the output unit 21 included in the drive unit 20 corresponding to the high-side switching element (e.g., switching element SW1) will be referred to as the "high-side output unit 21." The output unit 21 included in the drive unit 20 corresponding to the low-side switching element (e.g., switching element SW2) will be referred to as the "low-side output unit 21."

[0029] The high-side output unit 21 has a positive terminal and a negative terminal. In response to control by the control unit 50, the high-side output unit 21 connects one of the positive and negative terminals to the control terminal SWa of the high-side switching element. A voltage for turning on the high-side switching element is applied to the positive terminal of the high-side output unit 21. A voltage for turning off the high-side switching element (a voltage serving as a reference potential) is applied to the negative terminal of the high-side output unit 21. For example, the positive terminal of the high-side output unit 21 is connected to a power supply (not shown) that supplies the voltage for turning on the high-side switching element. The negative terminal of the high-side output unit 21 is connected to the negative line L2.

[0030] In this example, when the positive terminal of the high-side output unit 21 is connected to the control terminal SWa of the high-side switching element, the output of a control voltage from the high-side output unit 21 to the control terminal SWa of the high-side switching element begins, and the high-side switching element switches from off to on. When the negative terminal of the high-side output unit 21 is connected to the control terminal SWa of the high-side switching element, the output of the control voltage from the high-side output unit 21 to the control terminal SWa of the high-side switching element ends, and the high-side switching element switches from on to off.

[0031] The low-side output unit 21 has a positive terminal and a negative terminal. In response to control by the control unit 50, the low-side output unit 21 connects one of the positive and negative terminals to the control terminal SWa of the low-side switching element. A voltage for turning on the low-side switching element is applied to the positive terminal of the low-side output unit 21. A voltage for turning off the low-side switching element (a voltage serving as a reference potential) is applied to the negative terminal of the low-side output unit 21. For example, the positive terminal of the low-side output unit 21 is connected to a power supply (not shown) that supplies the voltage for turning on the low-side switching element, and the negative terminal of the low-side output unit 21 is connected to the negative line L2.

[0032] In this example, connecting the positive terminal of the low-side output unit 21 to the control terminal SWa of the low-side switching element starts outputting a control voltage from the low-side output unit 21 to the control terminal SWa of the low-side switching element, and switches the low-side switching element from off to on. Connecting the negative terminal of the low-side output unit 21 to the control terminal SWa of the low-side switching element stops outputting the control voltage from the low-side output unit 21 to the control terminal SWa of the low-side switching element, and switches the low-side switching element from on to off.

[0033] The power supply that supplies the voltage for turning on the low-side switching element may be the same as the power supply that supplies the voltage for turning on the high-side switching element.

[0034] In the following description, switching a switching element from off to on will be referred to as "turning on," and switching a switching element from on to off will be referred to as "turning off."

[0035] The adjustment units 22 included in the drive unit 20 are configured to be able to adjust the control current flowing between the output unit 21 included in the drive unit 20 and the control terminal SWa of the switching element SW corresponding to the drive unit 20. In this example, each of the six adjustment units 22 constitutes an "adjustment unit 26 capable of adjusting the control current flowing between one output unit 25 and the control terminal SWa of one switching element SW."

[0036] For example, the adjustment unit 22 included in the drive unit 20 is a variable resistor provided in a current path (specifically, a wiring through which a control current flows) from the output unit 21 included in the drive unit 20 to the control terminal SWa of the switching element SW corresponding to the drive unit 20. The variable resistor changes its resistance value in response to control by the control unit 50. When the resistance value of the variable resistor is increased, the absolute value of the control current decreases.

[0037] [Sensors] The multiple sensors 30 detect various types of information used for control in the motor drive device 10. The information detected by the multiple sensors 30 is transmitted to the control unit 50. In this example, the multiple sensors 30 include a U-phase current sensor 31u, a V-phase current sensor 31v, a W-phase current sensor 31w, and the like.

[0038] The U-phase current sensor 31u detects a U-phase current value iu, which is the current value of the current flowing through the U-phase of the motor 3. The V-phase current sensor 31v detects a V-phase current value iv, which is the current value of the current flowing through the V-phase of the motor 3. The W-phase current sensor 31w detects a W-phase current value iw, which is the current value of the current flowing through the W-phase of the motor 3.

[0039] [Storage Unit] The storage unit 40 stores various types of information used for control in the motor drive device 10. The information stored in the storage unit 40 will be described in detail later.

[0040] [Control Unit] The control unit 50 is connected to each unit of the motor drive device 10 so as to be able to transmit signals. The control unit 50 controls each unit of the motor drive device 10 based on information obtained by the sensor 30, information stored in the storage unit 40, information provided from the outside, and the like. For example, the control unit 50 has a processor and a memory that stores various programs for operating the processor. The various functions of the control unit 50 are realized by the processor executing the various programs stored in the memory. Control by the control unit 50 will be described in detail later.

[0041] [Characteristics of Switching Elements] In this example, each of the multiple switching elements SW is configured by a transistor. The control terminal SWa of the switching element SW corresponds to the gate of the transistor. Examples of transistors that configure the switching elements SW include field-effect transistors (FETs) such as metal-oxide-semiconductor field-effect transistors (MOSFETs), and insulated gate bipolar transistors (IGBTs). The switching elements SW configured by the above-described transistors have the following characteristics.

[0042] 5 is a graph illustrating the temporal changes in gate current and gate voltage when the switching element SW is turned on when the load torque of the motor 3 is high. As shown in FIG. 5, when the switching element SW is switched from off to on by starting to output a control voltage to the control terminal SWa of the switching element SW, the voltage (gate voltage) at the control terminal SWa of the switching element SW gradually increases during a first period P1, remains constant during a second period P2 following the first period P1, and gradually increases during a third period P3 following the second period P2. The third period P3 is the period during which the gate voltage reaches a predetermined voltage from the gate voltage during the second period P2.

[0043] The specified voltage is set to the gate voltage at which the transistor constituting the switching element can be considered stable in the "on" state. The above "specified voltage" is an example of a transistor characteristic.

[0044] 6 is a graph illustrating the temporal changes in gate current and gate voltage when the switching element SW is turned off when the load torque of the motor 3 is high. As shown in FIG. 6, when the output of the control voltage to the control terminal SWa of the switching element SW is terminated to switch the switching element SW from on to off, the voltage (gate voltage) at the control terminal SWa of the switching element SW gradually decreases during a fourth period P4, remains constant during a fifth period P5 following the fourth period P4, and gradually decreases during a sixth period P6 following the fifth period P5. The fourth period P4 is the period during which the gate voltage reaches the gate voltage in the fifth period P5 from a predetermined specified voltage.

[0045] The gate voltage (voltage at the control terminal SWa of the switching element SW) in the fifth period P5 is the same as the gate voltage in the second period P2. The threshold voltage of the transistor constituting the switching element SW is, for example, slightly lower than the gate voltage in the second period P2. The above "gate voltage in the second period P2," "gate voltage in the fifth period P5," and "threshold voltage" are examples of the characteristics of the transistor constituting the switching element.

[0046] [Length of each of the first to sixth periods] The length of each of the first to sixth periods P1 to P6 can be determined based on the absolute value of the gate current flowing between the gate of the transistor constituting the switching element SW and the output section 21 and the characteristics of the transistor constituting the switching element SW.

[0047] The length of the first period P1 depends on the rate of rise of the gate voltage during the first period P1 (the amount of rise per unit time) and the difference between the reference potential voltage (zero in the example of FIG. 5 ) and the gate voltage during the second period P2. For example, the faster the rate of rise of the gate voltage during the first period P1, the shorter the length of the first period P1. The smaller the difference between the reference potential voltage and the gate voltage during the second period P2, the shorter the length of the first period P1.

[0048] The rate at which the gate voltage rises during the first period P1 depends on the absolute value of the gate current during the first period P1 and the characteristics of the transistor that constitutes the switching element SW. For example, the greater the absolute value of the gate current during the first period P1, the faster the rate at which the gate voltage rises during the first period P1. The smaller the parasitic capacitance (e.g., parasitic capacitance between the gate and source) of the transistor that constitutes the switching element SW, the faster the rate at which the gate voltage rises during the first period P1.

[0049] The length of the second period P2 depends on the absolute value of the gate current during the second period P2 and the characteristics of the transistor that constitutes the switching element SW. For example, the greater the absolute value of the gate current during the second period P2, the shorter the length of the second period P2. The smaller the parasitic capacitance (e.g., parasitic capacitance between the gate and source) of the transistor that constitutes the switching element SW, the shorter the length of the second period P2.

[0050] The length of the third period P3 depends on the rate of rise of the gate voltage during the third period P3 (the amount of rise per unit time) and the difference between the gate voltage during the second period P2 and the specified voltage. For example, the faster the rate of rise of the gate voltage during the third period P3, the shorter the length of the third period P3. The smaller the difference between the gate voltage during the second period P2 and the specified voltage, the shorter the length of the third period P3. Like the rate of rise of the gate voltage during the first period P1, the rate of rise of the gate voltage during the third period P3 depends on the absolute value of the gate current during the third period P3 and the characteristics of the transistor that constitutes the switching element SW.

[0051] The length of the fourth period P4 depends on the rate of decline of the gate voltage during the fourth period P4 (amount of decline per unit time) and the difference between the specified voltage and the gate voltage during the fifth period P5. For example, the faster the rate of decline of the gate voltage during the fourth period P4, the shorter the length of the fourth period P4. The smaller the difference between the specified voltage and the gate voltage during the fifth period P5, the shorter the length of the fourth period P4.

[0052] The rate at which the gate voltage falls during the fourth period P4 depends on the absolute value of the gate current during the fourth period P4 and the characteristics of the transistor that constitutes the switching element SW. For example, the greater the absolute value of the gate current during the fourth period P4, the faster the rate at which the gate voltage falls during the fourth period P4. The smaller the parasitic capacitance (e.g., parasitic capacitance between the gate and source) of the transistor that constitutes the switching element SW, the faster the rate at which the gate voltage falls during the fourth period P4.

[0053] The length of the fifth period P5 depends on the absolute value of the gate current during the fifth period P5 and the characteristics of the transistor that constitutes the switching element SW. For example, the greater the absolute value of the gate current during the fifth period P5, the shorter the length of the fifth period P5. The smaller the parasitic capacitance (e.g., parasitic capacitance between the gate and source) of the transistor that constitutes the switching element SW, the shorter the length of the fifth period P5.

[0054] The length of the sixth period P6 depends on the rate of decline of the gate voltage during the sixth period P6 (amount of decline per unit time) and the difference between the gate voltage during the fifth period P5 and the voltage serving as the reference potential (zero in the example of FIG. 6 ). For example, the higher the rate of rise of the gate voltage during the sixth period P6, the shorter the length of the sixth period P6. The smaller the difference between the gate voltage during the sixth period P6 and the voltage serving as the reference potential, the shorter the length of the sixth period P6. The rate of decline of the gate voltage during the sixth period P6, like the rate of decline of the gate voltage during the fourth period P4, depends on the absolute value of the gate current during the sixth period P6 and the characteristics of the transistor constituting the switching element SW.

[0055] [Control by Control Unit] The control unit 50 performs various types of control. In this example, the control unit 50 performs switching control, current control, and dead time control.

[0056] <Switching Control> In switching control, the control unit 50 controls the output unit 25 (in this example, the output unit 21 included in the multiple drive units 20) so that input power is converted into output power by switching multiple switching elements SW on and off.

[0057] The control unit 50 performs switching control such that one of the high-side and low-side switching elements (e.g., switching element SW1 and switching element SW2) that make up a leg is turned off and then the other switching element is turned on after a dead time has elapsed. The dead time is the time during which both the high-side and low-side switching elements that make up a leg are off.

[0058] In this example, the control unit 50 performs switching control so that the rotation speed of the motor 3 becomes a target rotation speed. The target rotation speed is an example of an externally applied command.

[0059] <Current Control> In current control, the control unit 50 controls the adjustment unit 26 (in this example, the adjustment unit 22 included in each of the multiple drive units 20) so that the absolute value of the control current flowing between the output unit 25 (in this example, the output unit 21 included in each of the multiple drive units 20) and the corresponding switching element SW increases as the load torque of the motor 3 decreases. In this example, the control unit 50 performs current control based on an index value corresponding to the load torque of the motor 3. The index value will be described in detail later.

[0060] In this example, the control unit 50 controls the adjustment unit 26 so that, in current control, the control current in the first period P1 is maintained at a positive first initial current value, the control current in the second period P2 and the third period P3 becomes a positive current value whose absolute value is smaller than the first initial current value according to the load torque of the motor 3, the control current in the fourth period P4 is maintained at a negative second initial current value, and the control current in the fifth period P5 and the sixth period P6 becomes a negative current value whose absolute value is smaller than the second initial current value according to the load torque of the motor 3.

[0061] Here, the control current flowing from the output section 21 toward the control terminal SWa of the switching element SW is referred to as the "positive control current," and the gate current flowing from the control terminal SWa of the switching element SW toward the output section 21 is referred to as the "negative control current."

[0062] <Dead Time Control> In the dead time control, the control unit 50 adjusts the dead time in the switching control so that the dead time in the switching control becomes longer as the load torque of the motor 3 decreases. In this example, the control unit 50 performs the dead time control based on an index value corresponding to the load torque of the motor 3. The control unit 50 performs the switching control based on the dead time adjusted by the dead time control.

[0063] In other words, the control unit 50 performs switching control so that the lower the load torque of the motor 3, the shorter the dead time, which is the time from when one of the high-side and low-side switching elements connected in series is turned from on to off to when the other switching element is turned from off to on.

[0064] 2 is a block diagram illustrating the functional configuration of the control unit 50 of the motor unit 1 of embodiment 1. The control unit 50 has a three-phase to two-phase conversion unit 51, a deviation calculation unit 52, a speed control unit 53, a current control unit 54, a two-phase to three-phase conversion unit 55, a rotation estimation unit 56, a switching control unit 57, and an adjustment control unit 58.

[0065] The three-phase to two-phase converter 51 performs predetermined calculations (specifically, Clarke transformation and Park transformation) on the three-phase current values ​​(U-phase current value iu, V-phase current value iv, and W-phase current value iw) detected by the U-phase current sensor 31u, V-phase current sensor 31v, and W-phase current sensor 31w, thereby deriving the d-axis current value id and the q-axis current value iq. The predetermined calculations by the three-phase to two-phase converter 51 use the rotation angle θ of the motor 3 estimated by a rotation estimator 56, which will be described later.

[0066] The deviation calculation unit 52 derives the deviation between the rotation speed R of the motor 3 estimated by the rotation estimation unit 56 (described later) and the target rotation speed R*. The speed control unit 53 derives a d-axis current command value id* and a q-axis current command value iq* in accordance with the deviation between the rotation speed R of the motor 3 derived by the deviation calculation unit 52 and the target rotation speed R*. For example, the greater the deviation between the rotation speed R of the motor 3 and the target rotation speed R*, the greater the q-axis current command value iq*.

[0067] The current control unit 54 derives a d-axis voltage command value Vd* and a q-axis voltage command value Vq* based on the d-axis current command value id* and the q-axis current command value iq* derived by the speed control unit 53 and the d-axis current value id and the q-axis current value iq derived by the three-phase to two-phase conversion unit 51. Specifically, the current control unit 54 derives the d-axis voltage command value Vd* and the q-axis voltage command value Vq* so that the d-axis current value id and the q-axis current value iq approach the d-axis current command value id* and the q-axis current command value iq*.

[0068] The two-phase to three-phase converter 55 derives three-phase voltage command values ​​(U-phase voltage command value Vu*, V-phase voltage command value Vv*, and W-phase voltage command value Vw*) by performing a predetermined inverse calculation (specifically, an inverse Park transform and an inverse Clarke transform) on the d-axis voltage command value Vd* and the q-axis voltage command value Vq* derived by the current controller 54. The predetermined inverse calculation by the two-phase to three-phase converter 55 uses the rotation angle θ of the motor 3 estimated by a rotation estimator 56, which will be described later.

[0069] The rotation estimator 56 estimates the rotation angle θ and the rotation speed R of the motor 3 based on the d-axis current value id and the q-axis current value iq derived by the three-phase to two-phase converter 51 and the d-axis voltage command value Vd* and the q-axis voltage command value Vq* derived by the current controller 54. Well-known estimation techniques can be used for the rotation estimator 56 to estimate the rotation angle θ and the rotation speed R.

[0070] The switching control unit 57 generates drive signals to be supplied to each of the plurality of output units 21 constituting the output unit 25 (specifically, the output units 21 included in the plurality of drive units 20 corresponding to the plurality of switching elements SW) based on the three-phase voltage command values ​​(U-phase voltage command value Vu*, V-phase voltage command value Vv*, and W-phase voltage command value Vw*) obtained by the two-phase to three-phase conversion unit 55 and a preset dead time (specifically, the delay time corresponding to the dead time adjusted by the adjustment control unit 58). The drive signals are signals for controlling the operation of the output units 21 (start and end of output of the control voltage). The drive signals include a high-side drive signal SH and a low-side drive signal SL. The processing by the switching control unit will be described in detail later.

[0071] The adjustment control unit 58 controls each of the multiple adjustment units 22 that make up the adjustment unit 26 (specifically, the adjustment units 22 included in the multiple drive units 20 that respectively correspond to the multiple switching elements SW) based on an index value corresponding to the load torque of the motor 3, and adjusts the dead time (specifically, the delay time corresponding to the dead time) used in the switching control unit 57.

[0072] In this example, the adjustment control unit 58 combines the d-axis current value id and the q-axis current value iq obtained by the three-phase to two-phase conversion unit 51 to derive a "composite current value idq," which is an example of an index value corresponding to the load torque of the motor 3. For example, the composite current value idq is the square root of the sum of the squares of the d-axis current value id and the q-axis current value iq, and is expressed as √(id ２ +iq ２ ) The higher the load torque of the motor 3, the larger the composite current value idq. The adjustment control unit 58 controls the adjustment unit 26 and adjusts the dead time based on the composite current value idq. The processing by the adjustment control unit 58 will be described in detail later.

[0073] With the above-described functional configuration, the control unit 50 performs switching control so that the d-axis current value id and the q-axis current value iq of the motor 3 approach the d-axis current command value id* and the q-axis current command value iq* that correspond to the difference between a predetermined target rotation speed R* and the rotation speed R of the motor 3. Through this control, the rotation speed R of the motor 3 is maintained at the target rotation speed R*.

[0074] [Processing by Switching Control Unit] Next, processing by the switching control unit 57 will be described. The switching control unit 57 supplies a high-side drive signal SH to a high-side output unit 21 (an output unit 21 included in the drive unit 20 corresponding to a high-side switching element), and supplies a low-side drive signal SL to a low-side output unit 21 (an output unit 21 included in the drive unit 20 corresponding to a low-side switching element). In this example, the switching control unit 57 supplies three high-side drive signals to the three high-side output units 21, respectively, and supplies three low-side drive signals to the three low-side output units 21, respectively.

[0075] Specifically, the switching control unit 57 generates three PWM signals (pulse width modulation signals) corresponding to the three phases of the motor 3, based on the three-phase voltage command values ​​(U-phase voltage command value Vu*, V-phase voltage command value Vv*, and W-phase voltage command value Vw*). The PWM signals are pulse signals, and the duty ratio, which indicates the ratio of the pulse width (the length of time during which the signal level is high) to the pulse period (the length of time of one cycle), is adjusted. Next, the switching control unit 57 performs the following processing on each of the three PWM signals.

[0076] FIG. 3 is a waveform diagram illustrating an example of a high-side drive signal and a low-side drive signal. As shown in FIG. 3, the switching control unit 57 generates a delay signal S2 by delaying the PWM signal S1 by a delay time T1 adjusted by the adjustment control unit 58. The delay time T1 corresponds to the dead time DT. Next, the switching control unit 57 generates a high-side drive signal SH by calculating the logical product (AND) of the PWM signal S1 and the delay signal S2. The switching control unit 57 generates a low-side drive signal SL by calculating the negative logical sum (NOR) of the PWM signal S1 and the delay signal S2. In FIG. 3, the horizontal axis represents time, and the vertical axis represents the amplitude (signal level) of various signals.

[0077] [Processing by Adjustment Control Unit] Next, processing by adjustment control unit 58 will be described. Fig. 4 is a diagram illustrating an example of the correspondence between an index value indicating the load torque of motor 3, the current value of the control current, and the time length of the dead time. Based on the information table illustrated in Fig. 4, adjustment control unit 58 controls each of the multiple adjustment units 22 constituting adjustment unit 26 (specifically, adjustment units 22 included in the multiple drive units 20 corresponding to the multiple switching elements SW, respectively), and adjusts the dead time used in switching control unit 57 (specifically, delay time T1 corresponding to the dead time).

[0078] The information table shows the correspondence between "index value," "current value (target value) of control current," and "length of dead time (delay time)." The information table is an example of correspondence information showing the above correspondence. In the example of FIG. 4, "composite current value idq" is shown as an example of an index value, and "gate current" is shown as an example of a control current. The information table is stored in the memory unit 40. In the information table, the larger the index value, the smaller the absolute value of the control current corresponding to that index value. In the information table, the larger the index value, the longer the length of dead time corresponding to that index value.

[0079] 4, the information table registers the current values ​​(target values) of the control current in each of the first to sixth periods P1 to P6 as "current values ​​(target values) of the control current." For example, when the combined current value idq, which is an example of an index value, is 20 A, the current values ​​(target values) of the gate current, which is an example of the control current, are 300 mA, 300 mA, and 200 mA in the first period P1, the second period P2, and the third period P3, respectively, and are −300 mA, −300 mA, and −200 mA in the fourth period P4, the fifth period P5, and the sixth period P6, respectively.

[0080] The information table stores the duration (not shown) of each of the first to sixth periods P1 to P6. For example, the duration of each of the first to sixth periods P1 to P6 is determined based on the current value of the control current in each of the first to sixth periods P1 to P6 and the characteristics of the switching element SW.

[0081] To summarize the above, the information table shows the correspondence between the "index value," the "current value (target value) of the control current in each of the first period P1 to the sixth period P6," the "duration of each of the first period P1 to the sixth period P6," and the "duration of the dead time (delay time)."

[0082] The adjustment control unit 58 selects, from the information table stored in the memory unit 40, the "current value of the control current in each of the first period P1 to the sixth period P6," the "duration of each of the first period P1 to the sixth period P6," and the "duration of the dead time (delay time)" that correspond to the input index value (composite current value idq).

[0083] Next, the adjustment control unit 58 controls each of the multiple adjustment units 22 that make up the adjustment unit 26 so that the "current value of the control current in each of the first period P1 to the sixth period P6" and the "duration of each of the first period P1 to the sixth period P6" become the "current value of the control current in each of the first period P1 to the sixth period P6" and the "duration of each of the first period P1 to the sixth period P6" selected from the information table.

[0084] The adjustment control unit 58 adjusts the dead time (specifically, delay time T1) used in the switching control unit 57 so that the dead time (specifically, delay time T1) used in the switching control unit 57 becomes the "length of dead time (delay time)" selected from the information table.

[0085] The "index value" registered in the information table is a discrete value. Therefore, if an index value that exactly matches the "input index value" is not registered in the information table, the adjustment control unit 58 performs the following process.

[0086] First, the adjustment control unit 58 selects from the information table a set of two control values ​​(specifically, a set of "current value of the control current in each of the first period P1 to the sixth period P6," "time length of each of the first period P1 to the sixth period P6," and "time length of the dead time (delay time)") corresponding to two index values ​​(for example, a composite current value idq indicating "10 A" and a composite current value idq indicating "20 A") sandwiching the input index value (for example, a composite current value idq indicating "15 A").

[0087] Next, the adjustment control unit 58 interpolates "a set of control values ​​corresponding to the input index values" from the set of two control values ​​corresponding to the two index values ​​selected from the information table, and performs the above-mentioned processing based on the set of control values ​​obtained by interpolation. Examples of this interpolation include spline interpolation and linear interpolation.

[0088] [Ringing and Switching Transient Time] The following describes ringing of the voltage (e.g., gate voltage) at the control terminal SWa of the switching element SW and the switching transient time. The switching transient time is the time required from the start (or end) of output of the control voltage by the output unit 25 until the state of the switching element SW stabilizes in the on state (or off state).

[0089] The higher the load torque of the motor 3, the more likely it is that voltage ringing will occur at the control terminal SWa of the switching element SW. The smaller the absolute value of the control current (e.g., gate current) flowing between the output unit 25 and the control terminal SWa of the switching element SW, the more gradual the change in voltage over time at the control terminal SWa of the switching element SW. As a result, it is possible to make it less likely that voltage ringing will occur at the control terminal SWa of the switching element SW.

[0090] Therefore, in order to suppress the occurrence of voltage ringing at the control terminal SWa of the switching element SW, a control (comparison example) can be considered in which the absolute value (constant value) of the control current flowing between the output section 25 and the control terminal SWa of the switching element SW is determined based on the maximum load torque of the motor 3 (the maximum value of the expected load torque).

[0091] However, in this control (comparison example), when the load torque of the motor 3 is low, the change in the voltage at the control terminal SWa of the switching element SW becomes slower than necessary. This results in a longer switching transition time. Furthermore, the longer the switching transition time, the longer the dead time. As a result, the driving noise (electromagnetic noise) caused by the dead time is generated noticeably.

[0092] [Specific Example of Control by the Control Unit] Control (switching control and current control) by the control unit 50 will be described in detail with reference to FIGS. 5 to 8 . FIG. 7 is a graph illustrating the temporal changes in gate current and gate voltage when the switching element SW is turned on when the load torque of the motor 3 is low. FIG. 8 is a graph illustrating the temporal changes in gate current and gate voltage when the switching element SW is turned off when the load torque of the motor 3 is low. The following describes an example in which the switching element SW is configured as a "transistor," the control terminal SWa of the switching element SW is the "gate," the control current flowing between the output unit 21 and the control terminal SWa of the switching element SW is the "gate current iG," and the voltage at the control terminal SWa of the switching element SW is the "gate voltage VG." In each of FIGS. 5 to 8 , the horizontal axis represents time, and the vertical axis represents the current value of the gate current iG or the voltage value of the gate voltage VG.

[0093] 5 and 6 illustrate control when the load torque of the motor 3 is relatively high (for example, when the composite current value, which is an example of an index value, is "20 A"), while FIGS. 7 and 8 illustrate control when the load torque of the motor 3 is relatively low (for example, when the composite current value, which is an example of an index value, is "10 A").

[0094] As shown in FIGS. 5 and 6 , when the load torque of the motor 3 is relatively high, the control unit 50 controls the adjustment unit 26 so that the absolute value of the gate current iG becomes relatively small. In the example of FIG. 5 , the control unit 50 controls the adjustment unit 26 so that the absolute value of the gate current iG in the third period P3 becomes smaller than the absolute value of the gate current iG in the first period P1 and the second period P2 (the absolute value of the first initial current value). When the third period P3 ends, the control unit 50 controls the adjustment unit 26 so that the gate current iG becomes zero. In the example of FIG. 6 , the control unit 50 controls the adjustment unit 26 so that the absolute value of the gate current iG in the sixth period P6 becomes smaller than the absolute value of the gate current iG in the fourth period P4 and the fifth period P5 (the absolute value of the second initial current value). When the sixth period P6 ends, the control unit 50 controls the adjustment unit 26 so that the gate current iG becomes zero.

[0095] By the control described above, the change over time of the gate voltage VG when the load torque of the motor 3 is relatively high (specifically, the change over time in the third period P3 and the sixth period P6) becomes more gradual than the change over time of the gate voltage VG when the load torque of the motor 3 is relatively low. This makes it possible to sufficiently suppress the occurrence of ringing in the gate voltage VG. In this way, by suppressing the occurrence of ringing in the gate voltage VG, it is possible to suppress electromagnetic interference (EMI).

[0096] As shown in FIGS. 7 and 8 , when the load torque of the motor 3 is relatively low, the control unit 50 controls the adjustment unit 26 so that the absolute value of the gate current iG becomes relatively large. In the example of FIG. 7 , the control unit 50 controls the adjustment unit 26 so that the absolute value of the gate current iG in the third period P3 remains the same as the absolute value of the gate current iG in the first period P1 and the second period P2 (the absolute value of the first initial current value). When the third period P3 ends, the control unit 50 controls the adjustment unit 26 so that the gate current iG becomes zero. In the example of FIG. 8 , the control unit 50 controls the adjustment unit 26 so that the absolute value of the gate current iG in the sixth period P6 remains the same as the absolute value of the gate current iG in the fourth period P4 and the fifth period P5 (the absolute value of the second initial current value). When the sixth period P6 ends, the control unit 50 controls the adjustment unit 26 so that the gate current iG becomes zero.

[0097] By the control described above, the change in the gate voltage VG over time when the load torque of the motor 3 is relatively low (specifically, the change in the gate voltage VG over time in the third period P3 and the sixth period P6) becomes steeper than the change in the gate voltage VG over time when the load torque of the motor 3 is relatively high. This makes it possible to shorten the switching transition time TSW. In this way, by shortening the switching transition time TSW, it becomes possible to shorten the length of the dead time.

[0098] Effects of First Embodiment As described above, in the first embodiment, the control unit 50 controls the adjustment unit 26 in current control so that the absolute value of the control current (the control current flowing between the output unit 25 and the control terminal SWa of the switching element SW) increases as the load torque of the motor 3 decreases. This control makes it possible to suppress the occurrence of ringing in the voltage at the control terminal SWa of the switching element SW when the load torque of the motor 3 is relatively high. It is also possible to suppress the lengthening of the switching transition time when the load torque of the motor 3 is relatively low.

[0099] In the first embodiment, the control unit 50 controls the output unit 25 in the switching control so that the dead time becomes shorter as the load torque of the motor 3 decreases. By such control, the dead time can be made relatively short when the load torque of the motor 3 is relatively low. Therefore, the generation of drive noise (electromagnetic noise) caused by the dead time can be suppressed.

[0100] In embodiment 1, the control unit 50 controls the adjustment unit 26 so that, in current control, the control current in the first period P1 is maintained at a positive first initial current value, the control current in the second period P2 and the third period P3 becomes a positive current value whose absolute value is smaller than the first initial current value according to the load torque of the motor 3, the control current in the fourth period P4 is maintained at a negative second initial current value, and the control current in the fifth period P5 and the sixth period P6 becomes a negative current value whose absolute value is smaller than the second initial current value according to the load torque of the motor 3.

[0101] By maintaining the control current in the first period P1 at a positive first initial current value (positive maximum current value), it is possible to prevent the first period P1 from becoming long. This makes it possible to prevent the switching transition time from becoming long. The first period P1 is a period in which ringing (ringing of the voltage at the control terminal SWa of the switching element SW), which affects the stability of the state of the switching element SW, does not occur. Therefore, it is possible to prevent the switching transition time from becoming long while avoiding the occurrence of such ringing.

[0102] Similarly, by maintaining the control current in the fourth period P4 at the negative second initial current value (negative maximum current value), it is possible to prevent ringing (ringing of the voltage at the control terminal SWa of the switching element SW) that affects the stability of the state of the switching element SW while suppressing the lengthening of the switching transition time.

[0103] [Index Value] Next, the index value according to the load torque of the motor 3 will be described.

[0104] Examples of the index value include a composite current value idq obtained by combining the d-axis current value id and the q-axis current value iq, a composite current command value idq* obtained by combining the d-axis current command value id* and the q-axis current command value iq*, a q-axis current value iq, and a q-axis current command value iq*. For example, the composite current command value idq* is the square root of the sum of the squares of the d-axis current command value id* and the q-axis current command value iq*, and is expressed as √(id* ２ +iq* ２ ) As the load torque of the motor 3 increases, the q-axis current value iq increases, and the combined current value idq increases. As the load torque of the motor 3 increases, the q-axis current command value iq* increases, and the combined current command value idq* increases.

[0105] As described above, the index value may be a value corresponding to at least one of the combined current value idq obtained by combining the d-axis current value id and the q-axis current value iq, the combined current command value idq* obtained by combining the d-axis current command value id* and the q-axis current command value iq*, the q-axis current value iq, and the q-axis current command value iq*. By using such a value as the index value, it is possible to appropriately control the current according to the load torque of the motor 3.

[0106] The index value may be a value corresponding to the larger of the composite current value idq and the composite current command value idq*, or a value corresponding to the larger of the q-axis current value iq and the q-axis current command value iq*. By using such a value as the index value, it is possible to perform current control such that suppression of ringing (ringing of the voltage at the control terminal SWa of the switching element SW) takes precedence over lengthening of the switching transition time.

[0107] When the motor 3 is a "motor that rotationally drives a rotating body configured to transport a fluid by rotation," the load torque of the motor 3 depends on the rotation speed of the motor 3. For example, the higher the rotation speed of the motor 3, the higher the load torque of the motor 3. In this case, the index value may be a value corresponding to at least one of the rotation speed R and the target rotation speed R* of the motor 3. By using such a value as the index value, it is possible to appropriately control the current according to the load torque of the motor 3.

[0108] The index value may be a value corresponding to the higher of the rotation speed R and the target rotation speed R* of the motor 3. By using such a value as the index value, it is possible to perform current control such that suppression of ringing (ringing of the voltage at the control terminal SWa of the switching element SW) is given priority over lengthening of the switching transition time.

[0109] (Embodiment 2) Fig. 9 is a schematic diagram illustrating the configuration of an automobile 5 according to embodiment 2. The automobile 5 is a four-wheeled automobile (vehicle). The automobile 5 includes a main body 6 and a battery system 60 included in the main body 6. Examples of the automobile 5 include a hybrid automobile equipped with an engine and a drive battery, and an electric automobile equipped with only a drive battery. The automobile 5 is an example of a mobile body that can be driven by a battery.

[0110] The battery system 60 includes a battery 61 and a fan unit 70. The battery 61 supplies power to a drive motor (not shown) for propelling the automobile 5, etc. Examples of the battery 61 include a lithium-ion battery and a nickel-metal hydride battery. The battery 61 is an example of a power source 2. The fan unit 70 includes a blower 71 and a motor drive device 10. The blower 71 has an impeller 72 and a motor 3. The impeller 72 transports air. The motor 3 drives the impeller 72 to rotate. The battery system 60 includes a control device (not shown) that controls the supply of power from the battery 61 to the motor drive device 10 and the drive motor, etc.

[0111] In the second embodiment, the blower 71 cools the battery 61 by blowing air toward the battery 61. This makes it possible to suppress a rise in the temperature of the battery 61.

[0112] In the description of the second embodiment, a four-wheeled automobile is given as an example of a mobile body that can be driven by a battery. However, this is not limiting. Other examples of the mobile body include other vehicles such as two-wheeled automobiles and three-wheeled automobiles.

[0113] The battery 61 has been given as an example of an object (object to be cooled) to which air is delivered by the blower 71 included in the fan unit 70. However, this is not a limitation. The blower 71 may deliver air toward other components other than a battery. The case in which the fan unit 70 is included in the battery system 60 has been given as an example. However, this is not a limitation. The fan unit 70 may be included in a system other than a battery system.

[0114] (Other Embodiments) In the above description, "power supplied from the power supply 2, which is a DC power supply" has been given as an example of input power. However, this is not limiting. For example, the input power may be DC power (DC voltage) obtained by rectifying AC power supplied from the power supply 2, which is an AC power supply, using a converter.

[0115] In the above description, the impeller 72 of the blower 71 has been given as an example of a rotating body that is rotationally driven by the motor 3. However, this is not limiting. For example, the rotating body may be an impeller of a turbo machine such as a pump.

[0116] In the above description, a motor that rotates and drives the impeller 72 of the blower 71 has been given as an example of the motor 3. However, the present invention is not limited to this. For example, the motor 3 may be a drive motor that rotates and drives the drive wheels of the automobile 5, or a motor that rotates and drives other rotation mechanisms.

[0117] In the above description, the control unit 50 may be configured with a single processor or multiple processors. Similarly, the storage unit 40 may be configured with a single memory or multiple memories.

[0118] In the above description, an example has been given in which the rotation estimator 56 estimates the "rotation speed R of the motor 3" and the "rotation angle θ of the motor 3." However, this is not limiting. The sensor 30 of the motor drive device 10 may include a rotation speed sensor that detects the rotation speed R of the motor 3 and a rotation angle sensor that detects the rotation angle θ of the motor 3. The controller 50 may perform various processes based on the rotation speed R of the motor 3 detected by the rotation speed sensor and the rotation angle θ of the motor 3 detected by the rotation angle sensor.

[0119] In the above description, a case has been described in which the control current during the first period P1 is maintained at a positive first initial current value in the current control by the control unit 50. However, this is not limiting. For example, the control unit 50 may control the adjustment unit 26 so that the control current during the first period P1 becomes a positive current value whose absolute value is smaller than the first initial current value in accordance with the load torque of the motor 3.

[0120] In the above description, the control unit 50 has been described as maintaining the control current at the negative second initial current value during the fourth period P4. However, this is not limiting. For example, the control unit 50 may control the adjustment unit 26 so that the control current during the fourth period P4 becomes a negative current value whose absolute value is smaller than the second initial current value, depending on the load torque of the motor 3.

[0121] In the above description, an example was given in which the information table associates one current value (target value) of the control current with each of the first period P1 to the sixth period P6. However, this is not limiting. For example, the information table may be configured such that the first period P1 is divided into two or more periods, and a "current value (target value) of the control current" and a "duration length" are associated with each of the two or more periods constituting the first period P1. The adjustment control unit 58 may control the adjustment unit 26 so that the "current value of the control current in each of the two or more periods constituting the first period P1" and the "duration length of each of the two or more periods constituting the first period P1" are the "current value of the control current in each of the two or more periods constituting the first period P1" and the "duration length of each of the two or more periods constituting the first period P1" selected from the information table. The same applies to each of the second period P2 to the sixth period P6.

[0122] In the above description, the information table has been described as registering a "fixed value indicating that the current value remains constant from the start to the end of the period" as the current value (target value) of the control current for each of the first period P1 to the sixth period P6. However, this is not limiting. For example, the information table may register a "variable value indicating that the current value gradually decreases (or increases) from the start value to the end value as the period progresses" as the current value (target value) of the control current for each of the first period P1 to the sixth period P6. For example, the adjustment control unit 58 may control the adjustment unit 26 so that the "current value of the control current for the first period P1" gradually decreases from the start value to the end value indicated by the "current value (variable value) of the control current for the first period P1" selected from the information table. The same applies to each of the second period P2 to the sixth period P6.

[0123] 10 is a graph illustrating another example of temporal changes in the gate current and gate voltage when the switching element SW is turned on when the load torque of the motor 3 is high. For example, as shown in FIG. 10, the control unit 50 may control the adjustment unit 26 so that the absolute value of the gate current iG in the third period P3 gradually becomes smaller than the absolute value of the gate current iG in the first period P1 and the second period P2 (the absolute value of the first initial current value). FIG. 11 is a graph illustrating another example of temporal changes in the gate current and gate voltage when the switching element SW is turned off when the load torque of the motor 3 is high. As shown in FIG. 11, the control unit 50 may control the adjustment unit 26 so that the absolute value of the gate current iG in the sixth period P6 gradually becomes smaller than the absolute value of the gate current iG in the fourth period P4 and the fifth period P5 (the absolute value of the second initial current value).

[0124] In the above description, an example has been given in which the adjustment control unit 58 controls the adjustment unit 26 and adjusts the dead time based on an information table. However, this is not limiting. For example, the storage unit 40 may store an arithmetic expression for calculating a set of control values ​​(specifically, a set of "current values ​​of the control current in each of the first period P1 to the sixth period P6," "durations of each of the first period P1 to the sixth period P6," and "durations of the dead time (delay time)") based on an index value corresponding to the load torque of the motor 3. The adjustment control unit 58 may be configured to calculate a set of control values ​​by substituting an input index value into the arithmetic expression, and to control the adjustment unit 26 and adjust the dead time based on the calculated set of control values.

[0125] In the above description, the sensor 30 of the motor drive device 10 may include a control current sensor that detects the control current. For example, six control current sensors may be provided corresponding to the six switching elements SW1 to SW6, respectively. The control unit 50 may control the adjustment unit 26 so that the control current detected by the control current sensor becomes the target value of the control current for each of the first period P1 to sixth period P6.

[0126] In the above description, the sensor 30 of the motor drive device 10 may include a control terminal voltage sensor that detects the voltage at the control terminal SWa of the switching element SW. For example, six control terminal voltage sensors may be provided corresponding to the six switching elements SW. The control unit 50 may be configured to determine the end of each of the first period P1 to the sixth period P6 based on the voltage at the control terminal SWa of the switching element SW detected by the control terminal voltage sensor, and to control the control current (control the adjustment unit 26) during each of the first period P1 to the sixth period P6 based on the result of this determination.

[0127] For example, when the voltage detected by the control terminal voltage sensor reaches the "voltage at the control terminal SWa of the switching element SW in the second period P2 (a voltage determined by the characteristics of the transistor)," the control unit 50 may determine that the first period P1 has ended, and control the adjustment unit 26 so that the control current becomes the "target value of the control current in the second period P2."

[0128] When the voltage detected by the control terminal voltage sensor reaches a voltage that is a predetermined amount higher than the voltage at the control terminal SWa of the switching element SW in the second period P2 (a voltage that can be considered to indicate that the third period P3 has started), the control unit 50 may determine that the second period P2 has ended and control the adjustment unit 26 so that the control current becomes the target value of the control current in the third period P3.

[0129] The above-described embodiments and modifications may be combined as appropriate. The above-described embodiments and modifications are essentially preferred examples and are not intended to limit the scope of the technology disclosed herein, its applications, or its uses.

[0130] As described above, the technology disclosed herein is useful as a motor drive device, and as a motor unit, a fan unit, a battery system, and a mobile object that include the motor drive device.

[0131] REFERENCE SIGNS LIST 1 motor unit 2 power supply 3 motor 5 automobile (mobile body) 6 main body 10 motor drive device 11 conversion unit 12 smoothing capacitor 20 drive unit 21, 25 output unit 22, 26 adjustment unit 30 sensor 40 memory unit 50 control unit 51 three-phase to two-phase conversion unit 52 deviation calculation unit 53 speed control unit 54 current control unit 55 two-phase to three-phase conversion unit 56 rotation estimation unit 57 switching control unit 58 adjustment control unit 60 battery system 61 battery (power supply) 70 fan unit 71 blower 72 impeller (rotating body) SW, SW1, SW2, SW3, SW4, SW5, SW6 switching element SWa control terminal

Claims

1. A motor drive device for driving a motor, comprising: a conversion unit having a plurality of switching elements, converting input power into output power by switching the plurality of switching elements on and off, and supplying the output power to the motor; an output unit connected to the control terminals of each of the plurality of switching elements and outputting a control voltage to the control terminal for controlling the on / off states of the switching elements; an adjustment unit capable of adjusting a control current flowing between the output unit and the control terminal; and a control unit that performs switching control for controlling the output unit so that the input power is converted into the output power by switching the plurality of switching elements on and off, and current control for controlling the adjustment unit so that the absolute value of the control current becomes larger as the load torque of the motor becomes lower.

2. A motor drive device according to claim 1, wherein the plurality of switching elements include a high-side switching element and a low-side switching element connected in series, and the control unit performs the switching control so that the lower the load torque of the motor, the shorter the dead time, which is the time from when one of the high-side switching element and the low-side switching element connected in series is changed from on to off to when the other switching element is changed from off to on.

3. A motor drive device according to claim 1, wherein the control unit performs the switching control so that a d-axis current value and a q-axis current value of the motor approach a d-axis current command value and a q-axis current command value corresponding to a difference between a predetermined target rotation speed and the rotation speed of the motor, and performs the current control based on an index value corresponding to a load torque of the motor, the index value being a value corresponding to at least one of a composite current value obtained by combining the d-axis current value and the q-axis current value, a composite current command value obtained by combining the d-axis current command value and the q-axis current command value, the q-axis current value, and the q-axis current command value.

4. A motor drive device according to claim 3, wherein the index value is a value corresponding to the larger of the composite current value and the composite current command value, or a value corresponding to the larger of the q-axis current value and the q-axis current command value.

5. A motor drive device according to claim 1, wherein the motor drives a rotating body configured to transport a fluid by rotation, and the control unit performs the switching control so that the rotational speed of the motor approaches a predetermined target rotational speed, and performs the current control based on an index value corresponding to a load torque of the motor, the index value being a value corresponding to at least one of the rotational speed of the motor and the target rotational speed.

6. A motor drive device according to claim 5, wherein the index value is a value corresponding to the higher of the rotation speed of the motor and the target rotation speed.

7. A motor drive device according to claim 1, wherein each of said plurality of switching elements is constituted by a transistor, and when the switching element is switched from off to on by starting the output of the control voltage to the control terminal of said switching element, the voltage at the control terminal of said switching element rises in a first period, becomes constant in a second period following the first period, and rises in a third period following the second period, and when the switching element is switched from on to off by terminating the output of the control voltage to said control terminal, the voltage at said control terminal falls in a fourth period, becomes constant in a fifth period following the fourth period, and falls in a sixth period following the fifth period, The control unit controls the adjustment unit so that, in the current control, the control current in the first period is maintained at a positive first initial current value, the control current in the second period and the third period becomes a positive current value having an absolute value smaller than the first initial current value in accordance with a load torque of the motor, the control current in the fourth period is maintained at a negative second initial current value, and the control current in the fifth period and the sixth period becomes a negative current value having an absolute value smaller than the second initial current value in accordance with a load torque of the motor.

8. A motor unit comprising: a motor; and a motor drive device according to any one of claims 1 to 7 that drives the motor.

9. A fan unit comprising: a blower having an impeller for transporting air and a motor for driving and rotating the impeller; and a motor drive device according to any one of claims 1 to 7 for driving the motor.

10. A battery system comprising: a battery; and a fan unit according to claim 9 included in the blower for cooling the battery by blowing air toward the battery.

11. A mobile object comprising: a main body; and the battery system of claim 10 contained in the main body.

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