Power control device, power control method, and motor unit

Abstract

To provide a power control device, a power control method, and a motor unit capable of simultaneously achieving reduction of noise and reduction of a switching loss while ensuring motor controllability.SOLUTION: In a motor unit 1, a power control device 10 comprises: a power conversion circuit 11 that converts DC power into AC power and supplies it to a motor; and a control unit that controls a switching frequency for a plurality of switches QUH-QWL included in the power conversion circuit. The control unit determines a frequency fluctuation width fw on the basis of the revolution speed and the torque of the motor, and causes the switching frequency to fluctuate within the frequency range of f0±fw in which a prescribed reference frequency f0 is a center frequency.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power control device, a power control method, and a motor unit. [Background technology]

[0002] Patent Document 1 discloses a technology for an inverter device that supplies a three-phase AC voltage to a three-phase motor, in which a three-phase PWM (Pulse Width Modulation) signal is generated using three types of basic voltage vectors, and switching signals that are supplied to at least six switching elements included in the inverter device are generated based on the three-phase PWM signal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3447366 Summary of the Invention [Problem to be solved by the invention]

[0004] In the inverter device described above, noise is generated due to the switching operation during PWM control. [Means for solving the problem]

[0005] One aspect of the power control device of the present invention includes a power conversion circuit that converts DC power into AC power and supplies it to a motor, and a control unit that controls the switching frequency of a plurality of switches included in the power conversion circuit, wherein the control unit determines a frequency fluctuation width fw based on the rotation speed and torque of the motor, and fluctuates the switching frequency within a frequency range of f0±fw, with a predetermined reference frequency f0 as the center frequency.

[0006] One aspect of the power control method of the present invention includes controlling the switching frequencies of a plurality of switches included in a power conversion circuit that converts DC power into AC power and supplies the AC power to a motor, and controlling the switching frequency further includes determining a frequency fluctuation width fw based on the rotation speed and torque of the motor, and fluctuating the switching frequency within a frequency range of f0±fw, with a predetermined reference frequency f0 as the center frequency.

[0007] One aspect of the motor unit of the present invention includes a motor and the power control device of the above aspect that supplies power to the motor. [Effects of the Invention]

[0008] According to the above aspects of the present invention, a power control device, a power control method, and a motor unit are provided that are capable of achieving both reduced noise and reduced switching loss while ensuring motor controllability. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a schematic diagram of the overall configuration of a motor unit according to one embodiment of the present invention. [Figure 2] FIG. 2 is a functional block diagram showing the functions of the control unit of the power control device according to one embodiment of the present invention. [Figure 3] FIG. 3 is a diagram showing an example of a frequency control table in which the rotation speed N and torque T of the motor are used as input values, and the frequency fluctuation width fw is used as an output value. [Figure 4] FIG. 4 is a timing chart showing how the control unit of the power control device generates each high-side gate signal by comparing the three-phase voltage command signal with the carrier signal. [Figure 5] FIG. 5 is a flowchart showing a switching control process executed by the control unit of the power control device according to a program. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram schematically illustrating the overall configuration of a motor unit 1 according to this embodiment. As shown in FIG. 1, the motor unit 1 includes a power control device 10 and a motor 20. The power control device 10 supplies power to the motor 20. As an example, the motor 20 is an inner rotor type three-phase brushless DC motor. The motor 20 is, for example, a drive motor (traction motor) mounted on an electric vehicle.

[0011] The motor 20 has a U-phase terminal 21u, a V-phase terminal 21v, a W-phase terminal 21w, a U-phase coil 22u, a V-phase coil 22v, a W-phase coil 22w, and a position sensor 23. Although not shown in FIG. 1 , the motor 20 also has a motor case, a rotor, and a stator housed in the motor case. The rotor is a rotating body rotatably supported by bearing components such as rotor bearings inside the motor case. The rotor has a rotor shaft that axially penetrates the radially inner side of the rotor and is coaxially joined to the rotor. The stator is fixed inside the motor case, surrounding the outer circumferential surface of the rotor, and generates the electromagnetic force required to rotate the rotor.

[0012] The U-phase terminal 21u, the V-phase terminal 21v, and the W-phase terminal 21w are metal terminals exposed from the surface of the motor case. The U-phase terminal 21u is connected to a U-phase connection terminal 13u of the power control device 10. The V-phase terminal 21v is connected to a V-phase connection terminal 13v of the power control device 10. The W-phase terminal 21w is connected to a W-phase connection terminal 13w of the power control device 10. The U-phase coil 22u, the V-phase coil 22v, and the W-phase coil 22w are excitation coils provided in the stator. As an example, the U-phase coil 22u, the V-phase coil 22v, and the W-phase coil 22w are star-connected inside the motor 20.

[0013] The U-phase coil 22u is connected between the U-phase terminal 21u and the neutral point N. The V-phase coil 22v is connected between the V-phase terminal 21v and the neutral point N. The W-phase coil 22w is connected between the W-phase terminal 21w and the neutral point N. The power control device 10 controls the energization states of the U-phase coil 22u, the V-phase coil 22v, and the W-phase coil 22w, thereby generating an electromagnetic force required to rotate the rotor. As the rotor rotates, the rotor shaft also rotates in synchronization with the rotor.

[0014] The position sensor 23 detects the rotational position θ of the rotor shaft and outputs a position detection signal indicating the detected rotational position θ to the control unit 12 of the power control device 10. The position sensor 23 is an absolute encoder, an incremental encoder, a Hall sensor, or the like.

[0015] The power control device 10 includes a power conversion circuit 11, a control unit 12, a U-phase connecting terminal 13u, a V-phase connecting terminal 13v, a W-phase connecting terminal 13w, a U-phase current sensor 14, a V-phase current sensor 15, and a W-phase current sensor 16. The power conversion circuit 11 is connected to a motor 20 and a DC power supply 50, and performs mutual conversion between DC power and three-phase AC power. For example, when the power conversion circuit 11 functions as an inverter, the power conversion circuit 11 converts DC power supplied from the DC power supply 50 into three-phase AC power and outputs it to the motor 20. As an example, the DC power supply 50 is one of multiple batteries mounted on an electric vehicle.

[0016] The power conversion circuit 11 has six switches. The power conversion circuit 11 includes a U-phase high-side switch Q UH and the V-phase high-side switch Q VH and W-phase high-side switch Q WH and U-phase low-side switch Q UL and V-phase low-side switch Q VL and W-phase low-side switch Q WL In this embodiment, each switch is, for example, an IGBT (Insulated Gate Bipolar Transistor).

[0017] U-phase high-side switch Q UH Collector terminal of V-phase high-side switch Q VH and the collector terminal of the W-phase high-side switch Q WH The collector terminals of the U-phase low-side switch Q are connected to the positive terminal of the DC power supply 50. UL emitter terminal of V-phase low-side switch Q VL and the emitter terminal of the W-phase low-side switch Q WL The emitter terminals of the transistors 11 and 12 are connected to the negative terminal of a DC power supply 50 .

[0018] U-phase high-side switch Q UH The emitter terminal of the U-phase connection terminal 13u and the U-phase low-side switch Q UL In other words, the collector terminals of the U-phase high-side switch Q UH The emitter terminal of this is connected to a U-phase terminal 21u of the motor 20 via a U-phase connecting terminal 13u.

[0019] V-phase high-side switch Q VH The emitter terminal of the V-phase connection terminal 13v and the V-phase low-side switch Q VL In other words, the V-phase high-side switch Q VH The emitter terminal of is connected to a V-phase terminal 21v of the motor 20 via a V-phase connecting terminal 13v.

[0020] W-phase high-side switch Q WH The emitter terminal of the W-phase connection terminal 13w and the W-phase low-side switch Q WL In other words, the collector terminals of the W-phase high-side switch Q WH The emitter terminal of this is connected to a W-phase terminal 21w of the motor 20 via a W-phase connecting terminal 13w.

[0021] U-phase high-side switch Q UH Gate terminal of V-phase high-side switch Q VH and the gate terminal of the W-phase high-side switch Q WHThe gate terminals of the U-phase low-side switch Q are connected to the control unit 12. UL Gate terminal of V-phase low-side switch Q VL and the gate terminal of the W-phase low-side switch Q WL The gate terminals of the transistors 11 and 12 are also connected to the control unit 12.

[0022] As described above, the power conversion circuit 11 is configured as a three-phase full-bridge circuit having three high-side switches and three low-side switches. The power conversion circuit 11 configured in this manner performs mutual conversion between DC power and three-phase AC power by controlling the switching of each switch by the control unit 12.

[0023] U-phase current sensor 14 detects the current flowing through the U phase of motor 20 as a U-phase current Iu, and outputs a U-phase current detection signal indicating the detected U-phase current Iu to control unit 12. V-phase current sensor 15 detects the current flowing through the V phase of motor 20 as a V-phase current Iv, and outputs a V-phase current detection signal indicating the detected V-phase current Iv to control unit 12. W-phase current sensor 16 detects the current flowing through the W phase of motor 20 as a W-phase current Iw, and outputs a W-phase current detection signal indicating the detected W-phase current Iw to control unit 12.

[0024] The control unit 12 is a processor incorporating a memory (not shown). As an example, the control unit 12 is an MCU (Microcontroller Unit). The control unit 12 controls the power conversion circuit 11 according to a program pre-stored in the memory. The control unit 12 receives a U-phase current detection signal output from a U-phase current sensor 14, a V-phase current detection signal output from a V-phase current sensor 15, a W-phase current detection signal output from a W-phase current sensor 16, and a position detection signal output from a position sensor 23. Based on these input signals, the control unit 12 acquires a U-phase current Iu, a V-phase current Iv, a W-phase current Iw, and a rotational position θ.

[0025] As will be described in detail later, the control unit 12 generates gate signals that control the switching timing of each switch included in the power conversion circuit 11 based on the torque command value Tref, the U-phase current Iu, the V-phase current Iv, the W-phase current Iw, and the rotational position θ to rotate the motor 20 with the torque specified by the torque command value Tref. The switching timing refers to the timing at which the switch switches from an OFF state to an ON state and from an ON state to an OFF state. The gate signals are, for example, pulse-width-modulated rectangular wave signals.

[0026] The control unit 12 controls the U-phase high-side switch Q UH and supplies the generated U-phase high-side gate signal G1 to the U-phase high-side switch Q UH The control unit 12 outputs the voltage to the gate terminal of the U-phase low-side switch Q UL and generates a U-phase low-side gate signal G2 that controls the switching timing of the U-phase low-side switch Q. UL The U-phase low-side gate signal G2 is a complementary signal of the U-phase high-side gate signal G1.

[0027] The control unit 12 controls the V-phase high-side switch Q VH and supplies the V-phase high-side gate signal G3 to the V-phase high-side switch Q VH The control unit 12 outputs the voltage to the gate terminal of the V-phase low-side switch Q VL and generates a V-phase low-side gate signal G4 that controls the switching timing of the V-phase low-side switch Q. VL The V-phase low-side gate signal G4 is a complementary signal of the V-phase high-side gate signal G3.

[0028] The control unit 12 controls the W-phase high-side switch Q WHand supplies the generated W-phase high-side gate signal G5 to the W-phase high-side switch Q WH The control unit 12 outputs the signal to the gate terminal of the W-phase low-side switch Q WL and generates a W-phase low-side gate signal G6 that controls the switching timing of the W-phase low-side switch Q. WL The W-phase low-side gate signal G6 is a complementary signal of the W-phase high-side gate signal G5. A dead time is inserted into each gate signal to prevent the high-side switch and the low-side switch of the same phase from being switched on at the same time.

[0029] 2 is a functional block diagram showing each function of the control unit 12. Each function of the control unit 12 may be a function realized by hardware including digital circuits and analog circuits, or may be a function realized by software, that is, a function realized by the control unit 12 executing a program.

[0030] As shown in FIG. 2, the control unit 12 includes a current command generation unit 30, a first coordinate conversion unit 31, a first subtraction unit 32, a second subtraction unit 33, a voltage command generation unit 34, a second coordinate conversion unit 35, a frequency fluctuation width determination unit 36, a random number generation unit 37, a multiplication unit 38, an addition unit 39, a carrier generation unit 40, and a PWM modulation unit 41.

[0031] The current command generating unit 30 generates a d-axis current command value Idref and a q-axis current command value Iqref based on a torque command value Tref input from a higher-level control device. For example, the higher-level control device is one of a plurality of ECUs (Electronic Control Units) mounted on the electric vehicle. A current command table indicating the d-axis current command value Idref and the q-axis current command value Iqref corresponding to the torque command value Tref is stored in advance in the memory of the control unit 12. The current command generating unit 30 reads the d-axis current command value Idref and the q-axis current command value Iqref corresponding to the input torque command value Tref from the current command table stored in the memory.

[0032] The first coordinate transformation unit 31 calculates two-phase currents Iα and Iβ in a fixed coordinate system by performing a Clarke transformation on the U-phase current Iu obtained from the U-phase current sensor 14, the V-phase current Iv obtained from the V-phase current sensor 15, and the W-phase current Iw obtained from the W-phase current sensor 16.

[0033] Furthermore, the first coordinate transformation unit 31 transforms the two-phase currents Iα and Iβ in the fixed coordinate system into a d-axis current Id and a q-axis current Iq in the rotating coordinate system by Park transformation based on equations (1) and (2). That is, the first coordinate transformation unit 31 calculates the d-axis current Id and the q-axis current Iq by substituting the two-phase currents Iα and Iβ calculated as described above and the rotational position θ acquired from the position sensor 23 into equations (1) and (2). Id=Iα·cosθ+Iβ·sinθ …(1) Iq=-Iα·sinθ+Iβ·cosθ …(2)

[0034] The first subtraction unit 32 calculates the d-axis current deviation ΔId by subtracting the d-axis current Id from the d-axis current command value Idref. The second subtraction unit 33 calculates the q-axis current deviation ΔIq by subtracting the q-axis current Iq from the q-axis current command value Iqref.

[0035] The voltage command generator 34 calculates, by PI calculation, the d-axis voltage command value Vdref at which the d-axis current deviation ΔId becomes zero, and also calculates, by PI calculation, the q-axis voltage command value Vqref at which the q-axis current deviation ΔIq becomes zero.

[0036] The second coordinate transformation unit 35 inversely transforms the d-axis voltage command value Vdref and the q-axis voltage command value Vqref in the rotating coordinate system into two-phase voltages Vα and Vβ in the fixed coordinate system by inverse Park transformation based on equations (3) and (4). That is, the second coordinate transformation unit 35 calculates the two-phase voltages Vα and Vβ by substituting the rotational position θ, the d-axis voltage command value Vdref, and the q-axis voltage command value Vqref into equations (3) and (4). Furthermore, the second coordinate transformation unit 35 transforms the two-phase voltages Vα and Vβ into three-phase voltage command signals by space vector transformation. The second coordinate transformation unit 35 generates a U-phase voltage command signal Vu, a V-phase voltage command signal Vv, and a W-phase voltage command signal Vw as the three-phase voltage command signals. Vα=Vdref·cosθ−Vqref·sinθ…(3) Vβ=Vdref·sinθ+Vqref·cosθ…(4)

[0037] The frequency fluctuation range determination unit 36 ​​determines the frequency fluctuation range fw based on the rotation speed N and torque T of the motor 20. The memory of the control unit 12 pre-stores a table in which the rotation speed N and torque T of the motor 20 are used as input values ​​and the frequency fluctuation range fw is used as an output value. In the following description, this table may be referred to as a frequency control table.

[0038] Fig. 3 is a diagram showing an example of a frequency control table. As shown in Fig. 3, the frequency control table is two-dimensional map data with the rotation speed N (rpm) on the horizontal axis and the torque T (Nm) on the vertical axis. The frequency control table includes a first region W1 in which a first frequency fluctuation range fw1 is defined as the output value of the frequency fluctuation range fw, a second region W2 in which a second frequency fluctuation range fw2 smaller than the first frequency fluctuation range fw1 is defined as the output value of the frequency fluctuation range fw, and a third region W3 provided between the first region W1 and the second region W2. In Fig. 3, Tmax is the upper limit of the torque T, and Tmin is the lower limit of the torque T.

[0039] The output value of the frequency fluctuation range fw determined in the third region W3 changes continuously or stepwise from the first frequency fluctuation range fw1 to the second frequency fluctuation range fw2 as it moves from the first region W1 to the second region W2. As an example, the first frequency fluctuation range fw1 is 500 [Hz], and the second frequency fluctuation range fw2 is 0 [Hz].

[0040] The frequency fluctuation range determination unit 36 ​​calculates the rotation speed N and torque T based on the U-phase current Iu, V-phase current Iv, W-phase current Iw, and rotational position θ obtained from each sensor. The frequency fluctuation range determination unit 36 ​​determines the output value obtained from the frequency control table when the calculated rotation speed N and torque T are input into the frequency control table as the frequency fluctuation range fw.

[0041] The random number generation unit 37 randomly extracts a value α from a range of values ​​from -1 to +1. In the following description, the value α randomly extracted from the range of values ​​from -1 to +1 may be referred to as a random coefficient. The multiplication unit 38 calculates a random frequency fr by multiplying the frequency fluctuation range fw determined by the frequency fluctuation range determination unit 36 ​​by the random coefficient α obtained from the random number generation unit 37. For example, the random coefficient α is the value of a pseudorandom bit sequence (Pseudo Random Bit Sequence) having a predetermined period, such as an M-sequence (Maximum Length Sequence). In other words, the random number generation unit 37 generates a pseudorandom signal consisting of a series of values ​​falling within the range of values ​​from -1 to +1. The period of the pseudorandom signal is set to a value equal to or greater than a predetermined threshold. As an example, the predetermined threshold is the acceleration time required for the vehicle to reach a speed of 100 km / h.

[0042] The adder 39 calculates the switching frequency fs by adding the random frequency fr calculated by the multiplier 38 to a predetermined reference frequency f0. The memory of the control unit 12 pre-stores the reference frequency f0. The reference frequency f0 is a fixed value. As an example, the reference frequency f0 is 8000 Hz. The adder 39 reads the reference frequency f0 from the memory and determines the frequency obtained by adding the read reference frequency f0 and the random frequency fr as the switching frequency fs.

[0043] The carrier generator 40 generates a carrier signal CS having a carrier frequency that coincides with the switching frequency fs calculated by the adder 39. As an example, the carrier signal CS is a triangular wave signal. The switching frequency fs randomly varies within a frequency range of f0±fw, with the reference frequency f0 as the center frequency. Therefore, the carrier frequency of the carrier signal CS also randomly varies within a frequency range of f0±fw, with the reference frequency f0 as the center frequency.

[0044] The PWM modulator 41 generates each gate signal by comparing the three-phase voltage command signals generated by the second coordinate converter 35 with the carrier signal CS generated by the carrier generator 40. Specifically, as shown in FIG. 4, the PWM modulator 41 sets the V-phase high-side gate signal G3 to a high level when the V-phase voltage command signal Vv is greater than the carrier signal CS. The PWM modulator 41 also sets the W-phase high-side gate signal G5 to a high level when the W-phase voltage command signal Vw is greater than the carrier signal CS. Although not shown in FIG. 4, the PWM modulator 41 also sets the U-phase high-side gate signal G1 to a high level when the U-phase voltage command signal Vu is greater than the carrier signal CS.

[0045] 4, the PWM modulator 41 sets the U-phase low-side gate signal G2 to a low level when the U-phase voltage command signal Vu is greater than the carrier signal CS. Similarly, the PWM modulator 41 sets the V-phase low-side gate signal G4 to a low level when the V-phase voltage command signal Vv is greater than the carrier signal CS. Similarly, the PWM modulator 41 sets the W-phase low-side gate signal G6 to a low level when the W-phase voltage command signal Vw is greater than the carrier signal CS. A dead time is inserted in each gate signal to prevent the high-side switch and low-side switch of the same phase from being switched on simultaneously.

[0046] The gate signals generated by the above-described functions of the control unit 12 are output from the control unit 12 to the power conversion circuit 11, thereby controlling the switching timing of each switch included in the power conversion circuit 11. As a result, three-phase AC power that rotates the motor 20 with the torque specified by the torque command value Tref is supplied from the power conversion circuit 11 to the motor 20.

[0047] As can be understood from the above description, the control unit 12 has a function of controlling the switching frequency fs (i.e., carrier frequency) of the multiple switches included in the power conversion circuit 11. More specifically, the control unit 12 has a function of determining a frequency fluctuation width fw based on the rotation speed N and torque T of the motor 20, and randomly fluctuating the switching frequency fs within a frequency range of f0±fw with a predetermined reference frequency f0 as the center frequency.

[0048] The control unit 12 also has a function of calculating a random frequency fr by multiplying the frequency fluctuation range fw by a numerical value α (random coefficient) randomly extracted from a numerical range from -1 to +1, and determining the frequency obtained by adding the random frequency fr and a reference frequency f0 as the switching frequency fs. Furthermore, the control unit 12 has a function of storing in advance a table (frequency control table) in which the rotation speed N and torque T are input values ​​and the frequency fluctuation range fw is output value, and determining the output value obtained from the frequency control table when the rotation speed N and torque T are input into the table as the frequency fluctuation range fw.

[0049] The switching operation during PWM control as described above causes noise and switching loss in the power conversion circuit 11. The higher the switching frequency fs, the lower the noise but the higher the switching loss. On the other hand, the lower the switching frequency fs, the lower the switching loss but the higher the noise. As such, it is known that there is a trade-off between the noise and switching loss that are generated depending on the switching frequency fs.

[0050] In this embodiment, the control unit 12 determines the frequency fluctuation width fw based on the operating state of the motor 20 (the rotation speed N and the torque T), and randomly fluctuates the switching frequency fs within a frequency range of f0±fw, with a reference frequency f0 as the center frequency. This prevents the switching frequency fs from being biased toward either a low-frequency range where noise is high and switching loss is low, or a high-frequency range where noise is low and switching loss is high, during the control period of the motor 20. This allows the switching frequency fs to be evenly distributed within an appropriate frequency range according to the operating state of the motor 20. As a result, the noise and switching loss generated during the control period of the motor 20 are averaged within an appropriate frequency range according to the operating state of the motor 20, making it possible to achieve both reduced noise and reduced switching loss while maintaining controllability of the motor 20.

[0051] Fig. 5 is a flowchart showing a switching control process executed by the control unit 12 according to a program. The control unit 12 repeatedly executes the switching control process shown in Fig. 5 at a predetermined cycle. The power control method of this embodiment is realized by the control unit 12 executing the switching control process shown in Fig. 5.

[0052] 5, the control unit 12 determines the frequency fluctuation range fw based on the rotation speed N and torque T of the motor 20 (step S1). Specifically, the control unit 12 calculates the rotation speed N and torque T based on the U-phase current Iu, V-phase current Iv, and W-phase current Iw, and the rotational position θ, which are obtained from the respective sensors. Then, the control unit 12 determines, as the frequency fluctuation range fw, the output value obtained from the frequency control table when the calculated rotation speed N and torque T are input into the frequency control table.

[0053] Next, the control unit 12 calculates the random frequency fr (step S2). Specifically, the control unit 12 calculates the random frequency fr by multiplying the frequency fluctuation width fw determined in step S1 by a numerical value α (i.e., a random coefficient) randomly extracted from a numerical range from −1 to +1.

[0054] Next, the control unit 12 calculates the switching frequency fs by adding the random frequency fr calculated in step S2 to a predetermined reference frequency f0 (step S3). Specifically, the control unit 12 reads the reference frequency f0 from the memory, and determines the frequency obtained by adding the read reference frequency f0 and the random frequency fr as the switching frequency fs.

[0055] Next, the control unit 12 generates a carrier signal CS having a carrier frequency that matches the switching frequency fs calculated in step S3 (step S4). Since the switching frequency fs varies randomly within a frequency range of f0±fw with the reference frequency f0 as the center frequency, the carrier frequency of the carrier signal CS also varies randomly within a frequency range of f0±fw with the reference frequency f0 as the center frequency.

[0056] The control unit 12 generates a U-phase voltage command signal Vu, a V-phase voltage command signal Vv, and a W-phase voltage command signal Vw as three-phase voltage command signals based on the torque command value Tref input from the higher-level control device and the U-phase current Iu, V-phase current Iv, W-phase current Iw, and rotational position θ obtained from the respective sensors (step S5). The method of generating the three-phase voltage command signals is as already described.

[0057] The control unit 12 generates each gate signal by comparing the three-phase voltage command signal generated in step S5 with the carrier signal CS generated in step S4 (step S6). The method of generating the gate signals is as already described.

[0058] The control unit 12 repeatedly executes the above switching control process at a predetermined cycle to generate gate signals, which are output from the control unit 12 to the power conversion circuit 11, thereby controlling the switching timing of each switch included in the power conversion circuit 11. As a result, three-phase AC power that rotates the motor 20 with a torque indicated by the torque command value Tref is supplied to the motor 20 from the power conversion circuit 11.

[0059] As can be understood from the above description, the power control method of this embodiment includes controlling the switching frequency fs (steps S1 to S6) of a plurality of switches included in the power conversion circuit 11, which converts DC power into AC power and supplies the AC power to the motor 20. Controlling the switching frequency fs further includes determining a frequency fluctuation width fw based on the rotation speed N and torque T of the motor 20 (step S1), and fluctuating the switching frequency fw within a frequency range of f0±fw, with a predetermined reference frequency f0 as the center frequency (steps S2 and S3).

[0060] As described above, the power control device of this embodiment includes a power conversion circuit 11 that converts DC power into AC power and supplies it to the motor 20, and a control unit 12 that controls the switching frequency of a plurality of switches included in the power conversion circuit 11. The control unit 12 determines the frequency fluctuation width fw based on the rotation speed N and torque T of the motor 20, and fluctuates the switching frequency fs within the frequency range of f0±fw, with a predetermined reference frequency f0 as the center frequency. This makes it possible to distribute the switching frequency fs within an appropriate frequency range according to the operating state of the motor 20, while preventing the switching frequency fs from being biased toward either a low frequency range where noise is high and switching loss is low, or a high frequency range where noise is low and switching loss is high, during the control period of the motor 20. As a result, the noise and switching loss generated during the control period of the motor 20 are averaged within an appropriate frequency range according to the operating state of the motor 20, making it possible to achieve both reduced noise and reduced switching loss while ensuring the controllability of the motor 20.

[0061] In this embodiment, the control unit 12 randomly varies the switching frequency fs within the above frequency range of f0±fw. This allows the switching frequency fs to be evenly distributed within an appropriate frequency range according to the operating state of the motor 20. As a result, the noise and switching loss generated during the control period of the motor 20 are more evenly averaged within an appropriate frequency range according to the operating state of the motor 20, which increases the effect of achieving both reduced noise and reduced switching loss while ensuring the controllability of the motor 20.

[0062] In this embodiment, the control unit 12 calculates the random frequency fr by multiplying the frequency fluctuation range fw by a numerical value α (random coefficient) randomly extracted from a numerical range from -1 to +1, and determines the frequency obtained by adding the random frequency fr and the reference frequency f0 as the switching frequency fs. This allows the control unit 12 to easily randomly determine the switching frequency fs within the frequency range of f0±fw, thereby reducing the processing load on the control unit 12 and allowing an inexpensive MCU to be used as the control unit 12.

[0063] In this embodiment, the random coefficient α is a value of a pseudo-random signal having a predetermined period. In this way, by using the value of a pseudo-random signal as the random coefficient α, it is possible to easily obtain a random coefficient α with higher irregularity.

[0064] In this embodiment, the control unit 12 stores in advance a table (frequency control table) in which the rotation speed N and torque T are input values ​​and the frequency fluctuation range fw is an output value, and determines the output value obtained from the frequency control table when the rotation speed N and torque T are input to the table as the frequency fluctuation range fw. In this way, the control unit 12 determines the frequency fluctuation width fw using the frequency control table, which reduces the processing load on the control unit 12, and therefore an inexpensive MCU can be used as the control unit 12.

[0065] In this embodiment, the frequency control table includes a first region W1 in which a first frequency fluctuation range fw1 is defined as the output value of the frequency fluctuation range fw, a second region W2 in which a second frequency fluctuation range fw2 smaller than the first frequency fluctuation range fw1 is defined as the output value of the frequency fluctuation range fw, and a third region W3 provided between the first region W1 and the second region W2, and the output value of the frequency fluctuation range fw defined in the third region W3 changes continuously or stepwise from the first frequency fluctuation range fw1 to the second frequency fluctuation range fw2 as it moves from the first region W1 to the second region W2, and the second frequency fluctuation range fw2 is zero. By using such a frequency control table, the frequency fluctuation width fw according to the operating state of the motor 20 can be determined more precisely.

[0066] The power control method of this embodiment includes controlling the switching frequency fs of a plurality of switches included in a power conversion circuit 11 that converts DC power into AC power and supplies the AC power to a motor 20, and controlling the switching frequency fs further includes determining a frequency fluctuation width fw based on the rotation speed N and torque T of the motor 20, and fluctuating the switching frequency fw within a frequency range of f0±fw with a predetermined reference frequency f0 as the center frequency. According to this power control method, the noise and switching loss generated during the control period of the motor 20 are averaged within an appropriate frequency range according to the operating state of the motor 20, so it is possible to achieve both a reduction in noise and a reduction in switching loss while ensuring the controllability of the motor 20.

[0067] The motor unit 1 of this embodiment includes a motor 20 and a power control device 10 of this embodiment that supplies power to the motor 20. According to this embodiment, it is possible to provide a motor unit 1 that can achieve both reduced noise and reduced switching loss while ensuring the controllability of the motor 20.

[0068] The present invention is not limited to the above-described embodiment, and the configurations described in this specification can be combined as appropriate within a range that does not contradict each other. For example, in the above embodiment, the power control device 10 supplies power to the motor 20, which is a three-phase motor, but the motor to be controlled is not limited to a three-phase motor, and may be an n-phase motor (n is an integer equal to or greater than 3). In the above embodiment, IGBTs are used as the arm switches included in the power conversion circuit 11, but the arm switches may be high-power switching elements other than IGBTs, such as MOS-FETs. [Explanation of symbols]

[0069] 1...motor unit, 10...power control device, 11...power conversion circuit, 12...control unit, 20...motor, 30...current command generation unit, 31...first coordinate conversion unit, 32...first subtraction unit, 33...second subtraction unit, 34...voltage command generation unit, 35...second coordinate conversion unit, 36...frequency fluctuation width determination unit, 37...random number generation unit, 38...multiplication unit, 39...addition unit, 40...carrier generation unit, 41...PWM modulation unit, 50...DC power supply, Q UH …U-phase high-side switch, Q VH …V-phase high-side switch, Q WH …W-phase high-side switch, Q UL …U-phase low-side switch, Q VL …V-phase low-side switch, Q WL …W-phase low-side switch

Claims

1. a power conversion circuit that converts DC power into AC power and supplies the AC power to the motor; a control unit that controls switching frequencies of a plurality of switches included in the power conversion circuit; Equipped with the control unit determines a frequency fluctuation width fw based on the rotation speed and torque of the motor, and fluctuates the switching frequency within a frequency range of f0±fw with a predetermined reference frequency f0 as a center frequency; the control unit stores in advance a table in which the rotation speed and the torque are input values ​​and the frequency fluctuation range fw is an output value, and determines the output value obtained from the table when the rotation speed and the torque are input into the table as the frequency fluctuation range fw; the table includes a first region in which a first frequency fluctuation range fw1 is determined as an output value of the frequency fluctuation range fw, a second region in which a second frequency fluctuation range fw2 smaller than the first frequency fluctuation range fw1 is determined as an output value of the frequency fluctuation range fw, and a third region provided between the first region and the second region, the output value of the frequency fluctuation range fw determined in the third region changes continuously or stepwise from the first frequency fluctuation range fw1 to the second frequency fluctuation range fw2 as the output value moves from the first region to the second region, A power control device, wherein the second frequency fluctuation width fw2 is zero.

2. The power control device according to claim 1 , wherein the control unit randomly varies the switching frequency within the frequency range.

3. 3. The power control device according to claim 2, wherein the control unit calculates a random frequency by multiplying the frequency fluctuation range fw by a numerical value α randomly extracted from a numerical range from -1 to +1, and determines the frequency obtained by adding the random frequency and the reference frequency f0 as the switching frequency.

4. 4. The power control device according to claim 3, wherein the value α is a value of a pseudo-random signal having a predetermined period.

5. Controlling the switching frequency of a plurality of switches included in a power conversion circuit that converts DC power into AC power and supplies the AC power to the motor; Including, Controlling the switching frequency determining a frequency fluctuation width fw based on the rotation speed and torque of the motor; Varying the switching frequency within a frequency range of f0±fw with a predetermined reference frequency f0 as a center frequency; further comprising determining the frequency fluctuation range fw includes determining, as the frequency fluctuation range fw, an output value obtained from the table when the rotation speed and the torque are input into the table; the table includes a first region in which a first frequency fluctuation range fw1 is determined as an output value of the frequency fluctuation range fw, a second region in which a second frequency fluctuation range fw2 smaller than the first frequency fluctuation range fw1 is determined as an output value of the frequency fluctuation range fw, and a third region provided between the first region and the second region, the output value of the frequency fluctuation range fw determined in the third region changes continuously or stepwise from the first frequency fluctuation range fw1 to the second frequency fluctuation range fw2 as the output value moves from the first region to the second region, A power control method, wherein the second frequency fluctuation width fw2 is zero.

6. A motor; a power control device according to any one of claims 1 to 4, which supplies power to the motor; A motor unit comprising:

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