Motor control device

Abstract

To provide a motor control device having great versatility for easily adapting to a variety of target systems.SOLUTION: A motor control device 11 includes: an information acquisition unit 21 that acquires information about a motor driving state including a motor rotation speed RSmtr and a DC voltage value Vdc; an information storage unit 23 that stores correspondence information between the DC voltage value Vdc and an optimum carrier frequency fpwm_op for each motor rotation speed RSmtr; an optimum carrier frequency setting unit 25 that sets an optimum carrier frequency fpwm_op corresponding to the motor driving state on the basis of the motor rotation speed RSmtr and the DC voltage value Vdc obtained by the information acquisition unit 21 and the content stored in the information storage unit 23; and a PWM control unit 27 that controls an inverter on the basis of the set optimum carrier frequency fpwm_op.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a motor control device that controls an inverter that converts DC power into AC power to drive a motor. [Background technology]

[0002] A PWM (Pulse Width Modulation) controlled inverter is used as a power supply device for driving a motor. A PWM control inverter determines the width of the pulse signal (the time the pulse is on) by comparing a carrier wave (e.g., a triangular wave) with a voltage command signal, and by turning on and off a switching element (e.g., IGBT) in response to the generated pulse signal, it converts the input DC power into AC power with the frequency required to drive the motor and supplies it to the motor.

[0003] When driving a motor, it is necessary to reduce losses in the motor as well as in the inverter from the viewpoint of energy conservation, thereby achieving high efficiency in the entire motor drive system. The carrier frequency (frequency of the carrier wave) of PWM control is an important factor in reducing the aforementioned losses.

[0004] Generally, as the carrier frequency increases, motor loss decreases but inverter loss increases. Conversely, as the carrier frequency decreases, inverter loss decreases but motor loss increases. As such, it is not simple to set the carrier frequency to minimize losses in the entire system.

[0005] As an example of a technique for setting an optimal carrier frequency so as to minimize losses in the entire system, Patent Document 1 discloses that the minimum value of the optimal carrier frequency is derived in relation to the motor torque and the optimal carrier frequency that minimizes the total loss of the motor loss and the inverter loss, and the relationship between the motor torque and the carrier frequency is determined so that, in a range below the motor torque corresponding to the minimum optimal carrier frequency, the carrier frequency remains approximately the same or decreases as the motor torque increases, and that, in a range above the motor torque corresponding to the minimum optimal carrier frequency, the carrier frequency remains approximately the same or increases as the motor torque increases. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Republished Patent No. 2020 / 009062 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the technology for setting the optimal carrier frequency disclosed in Patent Document 1 derives the relationship between motor torque and the optimal carrier frequency through loss measurement and numerical analysis for each carrier frequency, and controls the carrier frequency when the motor torque fluctuates, so that loss measurement and numerical analysis for each carrier frequency are required each time the target system differs, resulting in a lack of versatility.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a motor control device that is highly versatile and can be easily adapted to various target systems. [Means for solving the problem]

[0009] In order to solve the above problems, the motor control device according to the present invention comprises: A motor control device that controls an inverter (17) that converts DC power into AC power to drive a motor (18), an information acquisition unit (21) that acquires information about the driving state of the motor (18), including a rotation speed (RSmtr) of the motor (18) and a DC voltage value (Vdc) based on the DC power; an information storage unit (23) that stores correspondence information (20) that indicates a correspondence between the DC voltage value (Vdc) and an optimal carrier frequency (fpwm_op) for each rotation speed (RSmtr) of the motor (18); a setting unit (25) that sets an optimal carrier frequency (fpwm_op) according to a driving state of the motor (18) based on the rotation speed (RSmtr) of the motor (18) and the DC voltage value (Vdc) acquired by the information acquisition unit and the stored contents of the information storage unit (23); a control unit (27) that controls the inverter (17) based on the optimal carrier frequency (fpwm_op) set by the setting unit (25). This is its most important feature. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a motor control device that is highly versatile and can be easily adapted to various target systems. Problems, configurations, and effects other than those described above will be described in detail in the following embodiments. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic configuration diagram of a motor control system including a motor control device according to an embodiment of the present invention. [Figure 2] 1 is a functional block diagram of a motor control device according to an embodiment of the present invention. FIG. [Figure 3A] 10 is a diagram showing the correspondence relationship between the DC voltage value and the optimum carrier frequency when the stick-type vacuum cleaner is in the standard operation mode. FIG. [Figure 3B]10 is a diagram showing the correspondence relationship between the DC voltage value and the optimum carrier frequency when the stick-type vacuum cleaner is in the standard operation mode. FIG. [Figure 4] FIG. 10 is a diagram showing the correspondence relationship between the optimum carrier frequency and the combination of the motor rotation speed and the DC voltage value. [Figure 5] FIG. 3 is a flowchart illustrating the operation of the motor control device according to the embodiment of the present invention. [Figure 6] FIG. 1 is an explanatory diagram showing the relationship between loss that varies in accordance with changes in the carrier frequency and the carrier frequency. [Figure 7] FIG. 10 is an explanatory diagram showing the dependence of inverter loss on carrier frequency. [Figure 8A] FIG. 10 is a motor current waveform diagram illustrating the relationship of copper loss to carrier frequency. [Figure 8B] FIG. 10 is a motor current square waveform diagram illustrating the relationship of copper loss to carrier frequency. MODE FOR CARRYING OUT THE INVENTION

[0012] A motor control device according to an embodiment of the present invention will be described in detail with reference to the appropriate drawings. In the description of the motor control device according to the embodiment of the present invention, components having common functions are given common reference numerals, and redundant description thereof will be omitted.

[0013] [Schematic configuration of motor control system 11] First, a schematic configuration of a motor control system 10 including a motor control device 11 according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram of a motor control system 10 including a motor control device 11 according to an embodiment of the present invention. In the following description, an example will be given in which the motor control system 10 is installed in a stick-type electric vacuum cleaner (not shown) equipped with a rechargeable battery.

[0014] As shown in FIG. 1, the motor control system 10 is configured to include a motor control device 11, a DC power supply 13 consisting of a rechargeable battery, a smoothing capacitor 14 that smoothes the power supply voltage (DC voltage) Vd of the DC power supply 13, a voltage sensor 15 that detects the DC voltage Vd, a shunt resistor 16 that detects the DC bus current, an inverter (inverter) 17, a motor 18, and a load 19 such as a fan.

[0015] Inverter 17 includes power semiconductor switching elements Q1 to Q6 made of IGBTs in the U-phase upper arm, U-phase lower arm, V-phase upper arm, V-phase lower arm, W-phase upper arm and W-phase lower arm, respectively.

[0016] The inverter 17 switches on and off the power semiconductor switching elements Q1 to Q6 in accordance with a switching control signal from the control circuit 11 B. As a result, the inverter 17 converts the DC voltage Vdc based on the DC power supply 13 into a three-phase AC voltage and supplies it to a stator winding (not shown) of the motor 18, thereby driving the motor 18.

[0017] The motor 18 is not particularly limited, but is, for example, a synchronous motor whose rotor (not shown) is made of a permanent magnet.

[0018] The motor control device 11 includes a microcomputer 11A and a control circuit 11B.

[0019] The microcomputer 11A is a processing unit that outputs a predetermined PWM control signal to the control circuit 11B. The functions of the microcomputer 11A will be described in detail later.

[0020] The control circuit 11B includes a gate driver, a protection circuit (neither of which are shown), and the like, and applies a switching control signal (inverter control signal) to each of the power semiconductor switching elements Q1 to Q6, which are made up of a plurality of IGBTs, provided in the inverter 17.

[0021] [Internal configuration of microcomputer 11A] Next, the internal configuration of the microcomputer 11A will be described with reference to FIGS. 2, 3A, 3B, and 4 as appropriate. Fig. 2 is a functional block diagram of the microcomputer 11A. Fig. 3A is a diagram showing the correspondence relationship between the DC voltage value Vdc and the optimum carrier frequency fpwm_op when the operation mode of the stick-type vacuum cleaner is the standard operation mode (calculation condition: constant load torque). Fig. 3B is a diagram showing the correspondence relationship between the DC voltage value Vdc and the optimum carrier frequency fpwm_op when the operation mode DM of the stick-type vacuum cleaner is the strong operation mode (calculation condition: constant load torque). Fig. 4 is a diagram showing the correspondence relationship between the rotation speed RSmtr of the motor 18 and the optimum carrier frequency fpwm_op corresponding to combinations of DC voltage values. The microcomputer 11A corresponds to the "motor control device" of the present invention.

[0022] The microcomputer 11A includes an information acquisition unit 21, a table data storage unit 23, an optimum carrier frequency setting unit 25, and a PWM control unit 27.

[0023] The information acquiring unit 21 has a function of acquiring information related to the driving state of the motor 18, including rotational position data and the DC voltage value Vdc of the motor 18. The information acquiring unit 21 acquires information on the rotational speed RSmtr of the motor 18 by time differentiating the rotational position of the motor 18. The information acquiring unit 21 acquires the DC voltage value Vdc via the voltage sensor 15.

[0024] The information acquisition unit 21 also acquires information about the driving state of the motor 18, including an operation mode command related to the operation mode (standard operation mode / strong operation mode) of the stick-type electric vacuum cleaner and the motor current value. The various pieces of information acquired by the information acquisition unit 21 are sent to the optimum carrier frequency setting unit 25 and the like.

[0025] The table data storage unit 23 has a function of storing correspondence relationship information (hereinafter, sometimes referred to as "table data": see Figures 3A, 3B, and 4) that represents the correspondence relationship between the DC voltage value Vdc and the optimal carrier frequency fpwm_op for each of a plurality of rotational speeds RSmtr of the motor 18. The table data storage unit 23 corresponds to the "information storage unit" of the present invention.

[0026] As the rotation speed RSmtr of the motor 18 across multiple modes, for example, a standard rotation speed RSmtr_std in the standard operation mode, a standard rotation speed RSmtr_str in the strong operation mode, etc., corresponding to each of the operation modes (standard operation mode / strong operation mode) of the stick-type vacuum cleaner may be appropriately adopted (see Figures 3A, 3B, and 4).

[0027] The table data (correspondence information) 20 shown in FIG. 4 is set taking into consideration that the optimal carrier frequency fpwm_op corresponding to the combination of the rotational speed RSmtr of the motor 18 and the DC voltage value becomes the carrier frequency fpwm that reduces or minimizes the sum of the inverter loss and the motor loss (Pcar), which is a function of the carrier frequency. By referring to the table data 20 shown in FIG. 4, it is possible to uniquely identify the optimum carrier frequency fpwm_op corresponding to the combination of the rotation speed RSmtr of the motor 18 and the DC voltage value. The sum of inverter loss and motor loss [Pcar(fpwm)], which is a function of carrier frequency fpwm, will be described in more detail below.

[0028] For example, when the DC voltage value Vdc is 25 V in the standard operation mode shown in Fig. 3A, the optimum carrier frequency fpwm_op is approximately 148,000 Hz. When the DC voltage value Vdc is 25 V in the strong operation mode shown in Fig. 3B, the optimum carrier frequency fpwm_op is approximately 88,000 Hz. As such, it can be seen that at a common DC voltage value Vdc, the optimum carrier frequency fpwm_op in the strong operation mode is lower than the optimum carrier frequency fpwm_op in the standard operation mode.

[0029] The optimum carrier frequency setting unit 25 sets an optimum carrier frequency fpwm_op according to the driving state of the motor 18 based on the combination of the rotation speed RSmtr and DC voltage value Vdc of the motor 18 acquired by the information acquisition unit 21 and the stored contents of the information storage unit 23. The optimum carrier frequency setting unit 25 corresponds to the "setting unit" of the present invention.

[0030] The PWM control unit 27 generates a PWM control signal for reducing or minimizing inverter loss and motor loss based on the optimal carrier frequency fpwm_op set by the optimal carrier frequency setting unit 25, and controls the inverter 17 using this signal. The PWM control unit 27 corresponds to the "control unit" of the present invention.

[0031] [Operation of the motor control device 11 according to the embodiment of the present invention] Next, the operation of the motor control device 11 according to the embodiment of the present invention will be described with reference to FIG. FIG. 5 is a flowchart illustrating the operation of motor control device 11 according to the embodiment of the present invention.

[0032] In step S11 shown in FIG. 5, the information acquisition unit 21 belonging to the motor control device 11 acquires the target value of the rotation speed RSmtr of the motor 18 through the operation mode of the stick-type electric vacuum cleaner. More specifically, when the operation mode DM of the stick type vacuum cleaner is the standard operation mode, the rotation speed RSmtr_std that is the norm for the standard operation mode is acquired as the target value for the rotation speed RSmtr of the motor 18, and when the operation mode DM of the stick type vacuum cleaner is the strong operation mode, the rotation speed RSmtr_str that is the norm for the strong operation mode is acquired as the target value for the rotation speed RSmtr of the motor 18.

[0033] In step S12, the motor control device 11 determines whether or not the current rotation speed RSmtr of the motor 18 has reached the target value. The determination in step S12 is repeated until the current rotation speed RSmtr of the motor 18 has reached the target value. Immediately after starting motor 18, before the current rotation speed RSmtr of motor 18 reaches the target value, motor control device 11 generates a predetermined PWM control signal that takes into account the fact that motor 18 will quickly reach a steady operating state, and controls inverter 17 using this signal.

[0034] If it is determined in step S12 that the current rotation speed RSmtr of the motor 18 has reached the target value (Yes in step S12), the motor control device 11 advances the process to the next step S13.

[0035] In step S13, the information acquisition unit 21 belonging to the motor control device 11 acquires the current DC voltage value Vdc via the voltage sensor 15.

[0036] In step S14, the motor control device 11 extracts, by table lookup, the optimum carrier frequency fpwm_op corresponding to the combination of the target value of the rotation speed RSmtr of the motor 18 and the DC voltage value obtained in step S11.

[0037] For example, in the case where the target value of the rotation speed RSmtr of the motor 18 is the rotation speed RSmtr_std, which is the norm in the standard operation mode, and the DC voltage value Vdc is Va (Vdc=Va), fpwm_Va1 (see FIG. 4) is extracted as the optimal carrier frequency fpwm_op corresponding to this combination.

[0038] Also, for example, in a case where the target value of the rotation speed RSmtr of the motor 18 is the rotation speed RSmtr_str that is the norm in the strong operation mode and the DC voltage value Vdc is Vb (Vdc=Vb), fpwm_Vb2 (see FIG. 4) is extracted as the optimal carrier frequency fpwm_op corresponding to this combination.

[0039] In step S15, the optimum carrier frequency setting unit 25 belonging to the motor control device 11 sets the carrier frequency fpwm extracted in step S14 as the optimum carrier frequency fpwm_op according to the driving state of the motor 18.

[0040] In response to this, the PWM control unit 27 generates a PWM control signal for reducing or minimizing inverter loss and motor loss based on the optimal carrier frequency fpwm_op set by the optimal carrier frequency setting unit 25, and controls the inverter 17 using this signal.

[0041] The processes of steps S13 to S15 are repeated as long as the stick vacuum cleaner continues to operate.

[0042] [Basic idea for finding the optimal carrier frequency fpwm_op] Next, the basic concept for determining the optimum carrier frequency fpwm_op will be described with reference to FIGS. 6, 7, 8A, and 8B as appropriate. Fig. 6 is an explanatory diagram showing the relationship between carrier frequency fpwm and loss that varies in response to changes in carrier frequency fpwm. Fig. 7 is an explanatory diagram showing the dependency of inverter loss on carrier frequency fpwm. Fig. 8A is a motor current waveform diagram used to explain the relationship between copper loss and carrier frequency fpwm. Fig. 8B is a motor current squared waveform diagram used to explain the relationship between copper loss and carrier frequency fpwm.

[0043] In the motor control system 10 including the motor control device 11, the main sources of loss are the inverter 17 and the motor 18.

[0044] As shown in FIG. 6, losses occurring in motor control system 10 are roughly divided into inverter losses, which are losses occurring in inverter 17, and motor losses, which are losses occurring in motor 18.

[0045] As shown in Figure 7, inverter losses are broadly divided into switching losses Pinv_sw and conduction losses Pinv_cond. Meanwhile, motor losses are broadly divided into copper losses Pmtr_cop, iron losses, mechanical losses, etc. Switching losses Pinv_sw are losses that occur when semiconductor switching elements are turned on and off. Copper losses Pmtr_cop are losses that occur due to conductor resistance.

[0046] Of the inverter losses, the switching loss Pinv_sw varies in response to changes in the carrier frequency fpwm, while the conduction loss Pinv_cond is almost independent of the carrier frequency fpwm.

[0047] Of the motor losses, only the copper loss Pmtr_cop fluctuates in response to changes in the carrier frequency fpwm, while iron loss, mechanical loss, and the like are almost independent of the carrier frequency fpwm.

[0048] As shown in FIGS. 6 and 7, the relationship between the switching loss Pinv_sw and the carrier frequency fpwm can be expressed by (Equation 1).

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[0049] On the other hand, as shown in FIG. 6, the relationship between the copper loss Pmtr_cop and the carrier frequency fpwm can be expressed by (Equation 2).

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[0050] According to the above (Equation 1) and (Equation 2), the loss Pcar that depends on the carrier frequency fpwm can be expressed by (Equation 3).

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[0051] [Procedure for deriving copper loss Pmtr_cop] Here, the procedure for deriving the copper loss Pmtr_cop will be described with reference to FIGS. 8A and 8B. 8A and 8B are motor current waveform diagrams for explaining the relationship between copper loss Pmtr_cop and carrier frequency fpwm, respectively.

[0052] The copper loss Pmtr_cop can be expressed by (Equation 4).

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[0053] The procedure for deriving copper loss Pmtr_cop is as follows:

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[0054] 3. The motor current waveforms with and without ripples (high frequency components) are shown in Figure 8A. The motor current squared waveforms with and without ripples are shown in Figure 8B.

[0055]

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[0056] [Configuration, Functions, and Effects of the Motor Control Device 11 According to the Present Invention] A motor control device 11 according to a first aspect includes: A motor control device (11) that controls an inverter (17) that converts DC power into AC power to drive a motor (18), an information acquisition unit 21 that acquires information about the driving state of the motor 18, including the rotation speed RSmtr of the motor 18 and the DC voltage value Vdc based on the DC power; an information storage unit 23 that stores correspondence relationship information that indicates a correspondence relationship between the DC voltage value Vdc and the optimum carrier frequency fpwm_op for each rotation speed RSmtr of the motor 18; an optimal carrier frequency setting unit (setting unit) 25 that sets an optimal carrier frequency fpwm_op according to the driving state of the motor 18, based on the rotation speed RSmtr and the DC voltage value Vdc of the motor 18 acquired by the information acquisition unit 21 and the stored contents of the information storage unit 23; and a PWM control unit (control unit) 27 that controls the inverter 17 based on the optimum carrier frequency fpwm_op set by the setting unit 25.

[0057] According to the motor control device 11 based on the first aspect, it is possible to provide a motor control device that is highly versatile and can be easily adapted to a variety of target systems. Furthermore, even if fluctuations in the DC voltage value Vdc occur, the optimum carrier frequency fpwm_op is set according to the driving state of the motor 18, including the fluctuations, so it is possible to provide a motor control device that is highly flexible and can respond to load fluctuations.

[0058] A motor control device 11 according to a second aspect is the motor control device 11 according to the first aspect, The correspondence information 20 may be configured to be set in consideration of the fact that the optimal carrier frequency fpwm_op corresponding to the combination of the rotational speed RSmtr of the motor 18 and the DC voltage value Vdc is the carrier frequency fpwm that reduces or minimizes the sum of the inverter loss and the motor loss [Pcar(fpwm)], which is a function of the carrier frequency fpwm.

[0059] According to the motor control device 11 based on the second aspect, the optimal carrier frequency fpwm_op corresponding to the combination of the rotational speed RSmtr and DC voltage value Vdc of the motor 18 is set in consideration of the carrier frequency fpwm that reduces or minimizes the sum of the inverter loss and the motor loss [Pcar(fpwm)], which is a function of the carrier frequency fpwm. Therefore, in addition to the effects of the motor control device 11 based on the first aspect, it is possible to enhance the effect of suppressing the inverter loss and the motor loss.

[0060] A motor control device 11 according to a third aspect is the motor control device 11 according to the second aspect, The inverter loss is a switching loss (Pinv_sw) associated with a switching element used in the inverter 17, The motor loss may be copper loss (ΔPmtr_cop) associated with the motor 18.

[0061] According to the motor control device 11 based on the third aspect, of the inverter loss and motor loss, attention is focused on the switching loss Pinv_sw and copper loss ΔPmtr_cop as losses that depend on the carrier frequency fpwm, and therefore the effect of suppressing inverter loss and motor loss can be further enhanced compared to the action and effect of the motor control device 11 based on the second aspect.

[0062] A motor control device 11 according to a fourth aspect is the motor control device 11 according to the third aspect, The switching element may be an IGBT.

[0063] Motor control device 11 based on the fourth aspect can further enhance the effect of suppressing switching loss Pinv_sw, which is suitable for IGBTs among inverter losses, compared to the effect of motor control device 11 based on the third aspect.

[0064] A motor control device 11 according to a fifth aspect is the motor control device 11 according to the fourth aspect, The relationship between the switching loss (Pinv_sw) and the carrier frequency (fpwm) is expressed by (Equation 1):

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[0065] The motor control device 11 based on the fifth aspect can further enhance the effect of suppressing switching loss Pinv_sw and copper loss ΔPmtr_cop associated with the motor 18 compared to the effect of the motor control device 11 based on the fourth aspect.

[0066] Other Embodiments The above-described embodiments are merely examples of the present invention, and therefore the technical scope of the present invention should not be construed as being limited by them, as the present invention can be embodied in various forms without departing from the spirit or main characteristics thereof.

[0067] It is also possible to replace part of the configuration of one embodiment described here with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment.It is also possible to add, delete, or replace part of the configuration of each embodiment with another configuration. Furthermore, the control lines and information lines shown are those that are considered necessary for the explanation, and do not necessarily show all the control lines and information lines in the product. In reality, it can be assumed that almost all components are interconnected.

[0068] For example, in the description of the motor control device 11 according to an embodiment of the present invention, an example has been given in which the table data storage unit 23 has the function of storing table data (correspondence information) 20 representing the correspondence between the DC voltage value Vdc and the optimal carrier frequency fpwm_op for each of a plurality of rotational speeds RSmtr of the motor 18, but the present invention is not limited to this example. A table data storage unit 23 may be configured to store the optimum carrier frequency fpwm_op in association with a combination of the rotation speed RSmtr of the motor 18 and the DC voltage value Vdc, each of which has a predetermined tolerance range.

[0069] With this configuration, even if there is some fluctuation in the rotation speed RSmtr and the DC voltage value Vdc of the motor 18, the effect on the setting of the optimal carrier frequency fpwm_op is suppressed, and it is expected that the motor control device 11 will have excellent control stability.

[0070] Furthermore, in the description of the motor control device 11 according to the embodiment of the present invention, an example configuration has been given in which inverter 17 has power semiconductor switching elements Q1 to Q6 made up of IGBTs in the U-phase upper arm, U-phase lower arm, V-phase upper arm, V-phase lower arm, W-phase upper arm, and W-phase lower arm, but the present invention is not limited to this example. Power MOSFETs and bipolar power transistors may be used as the power semiconductor switching elements Q1 to Q6.

[0071] Furthermore, in the description of the motor control device 11 according to the embodiment of the present invention, the rotational position data of the motor 18 was used as an example of basic data for acquiring the rotational speed RSmtr of the motor 18, but the present invention is not limited to this example. As basic data for obtaining the rotation speed RSmtr of the motor 18, an induced voltage or a motor line signal may be used.

[0072] Finally, although an example has been described in which the motor control system 10 including the motor control device 11 according to an embodiment of the present invention is installed in a stick-type vacuum cleaner equipped with a rechargeable battery, the present invention is not limited to this example. It goes without saying that the motor control system 10 including the motor control device 11 according to the embodiment of the present invention may be installed in a washing machine, a refrigerator, an air conditioner, or the like. [Explanation of symbols]

[0073] 10 Motor Control System 11 Motor control device 11A Microcomputer (Motor Control Device) 11B Control circuit (motor control device) 13 DC power supply 17 Inverter 18 Motor 19 Load 21 Information Acquisition Department 23 Table data storage unit (information storage unit) 25 Optimum carrier frequency setting unit (setting unit) 27 PWM control unit (control unit) fpwm carrier frequency fpwm_op Optimal carrier frequency RSmtr Motor rotation speed Vdc DC voltage value

Claims

1. A motor control device that controls an inverter that converts DC power into AC power to drive a motor, an information acquisition unit that acquires information about a driving state of the motor, including a rotation speed of the motor and a DC voltage value based on the DC power; an information storage unit that stores correspondence information representing a correspondence relationship between the DC voltage value and an optimal carrier frequency for each rotation speed of the motor; a setting unit that sets an optimal carrier frequency according to the driving state of the motor based on the rotation speed and the DC voltage value of the motor acquired by the information acquisition unit and the stored contents of the information storage unit; and a control unit that controls the inverter based on the optimal carrier frequency set by the setting unit. A motor control device characterized by:

2. 2. The motor control device according to claim 1, The correspondence information is set in consideration of the fact that the optimal carrier frequency corresponding to the combination of the motor rotation speed and the DC voltage value is a carrier frequency that reduces or minimizes the sum of inverter loss and motor loss (Pcar), which is a function of carrier frequency. A motor control device characterized by:

3. 3. The motor control device according to claim 2, The inverter loss is a switching loss (P inv_sw ) associated with a switching element used in the inverter, The motor loss is the copper loss (ΔPmtr_cop) associated with the motor. A motor control device characterized by:

4. 4. The motor control device according to claim 3, The switching element is an IGBT. A motor control device characterized by:

5. 5. The motor control device according to claim 4, The relationship between the switching loss (Pinv_sw) and the carrier frequency (fpwm) is expressed by (Equation 1): [Equation 1] In (Equation 1), Pinv_sw (W): switching loss, Vdc (V): DC voltage value, Iload (Arms): motor current effective value, ton: rise delay time (s), toff: fall delay time (s), fpwm (Hz): carrier frequency The relationship between the copper loss (Pmtr_cop) and the carrier frequency (fpwm) of the motor is expressed by (Equation 2). [Equation 2] In (Equation 2), ΔPmtr_cop [W]: copper loss related to the motor, Rm [Ω]: motor winding resistance value (for one phase), Vdc [V]: DC voltage value, KhV1 [-]: modulation factor, fpwm [Hz]: carrier frequency, Lm: motor inductance [H]

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