Motor control device

Abstract

A motor control device (11) includes: an information acquisition unit (21) that acquires information pertaining to the drive state of a motor (18), including the rotation speed (RSmtr) of the motor (18) and a DC voltage value (Vdc); an information storage unit (23) that stores correspondence relationship information between the DC voltage value (Vdc) and an optimal carrier frequency (fpwm_op) for each rotation speed (RSmtr) of the motor (18); an optimal carrier frequency setting unit that sets the optimal carrier frequency (fpwm_op) in accordance with the drive state of the motor (18) on the basis of the rotation speed (RSmtr) of the motor (18) and the DC voltage value (Vdc) acquired by the information acquisition unit (21) and the storage contents of the information storage unit (23); and a PWM control unit (27) that controls an inverter (17) on the basis of the set optimal carrier frequency (fpwm_op). As a result, it is possible to obtain a motor control device (11) having excellent versatility which makes it possible to easily cope with various target systems.

Description

Motor control device

[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.

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

[0003] When driving a motor, it is necessary to reduce losses in the motor and inverter to achieve high efficiency in the entire motor drive system from the viewpoint of energy conservation. The carrier frequency (frequency of the carrier wave) of PWM control is an important factor in reducing the 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 a technique for deriving the minimum value of the optimal carrier frequency 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 determining the relationship between the motor torque and the carrier frequency 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, 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.

[0006] Republished Patent No. 2020 / 009062

[0007] However, in the technology for setting the optimal carrier frequency disclosed in Patent Document 1, the relationship between the motor torque and the optimal carrier frequency is derived through loss measurement and numerical analysis for each carrier frequency, and the carrier frequency is controlled 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 problem of 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.

[0009] In order to solve the above problems, the motor control device of the present invention is a motor control device that controls an inverter (17) that converts DC power to AC power to drive a motor (18), and includes: an information acquisition unit (21) that acquires information on 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 optimum carrier frequency (fpwm_op) for each rotation speed (RSmtr) of the motor (18); and a setting unit (25) that sets an optimum 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 and the stored contents of the information storage unit (23). The most important feature of the present invention is that it is configured to include a control unit (27) that controls the inverter (17) based on the optimum carrier frequency (fpwm_op) set by the setting unit (25).

[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.

[0011] 1 is a schematic configuration diagram of a motor control system including a motor control device according to an embodiment of the present invention; FIG. 2 is a functional block diagram of a motor control device according to an embodiment of the present invention; FIG. 3 is a diagram showing the correspondence relationship between DC voltage values ​​and optimal carrier frequencies when the operation mode of a stick-type vacuum cleaner is a standard operation mode; FIG. 4 is a diagram showing the correspondence relationship between DC voltage values ​​and optimal carrier frequencies when the operation mode of a stick-type vacuum cleaner is a standard operation mode; FIG. 5 is a diagram showing the correspondence relationship between optimal carrier frequencies corresponding to combinations of motor rotation speeds and DC voltage values; FIG. 6 is a flowchart used to explain the operation of a motor control device according to an embodiment of the present invention; FIG. 7 is an explanatory diagram showing the relationship between loss that varies with changes in carrier frequency and carrier frequency; FIG. 8 is an explanatory diagram showing the dependency of inverter loss on carrier frequency; FIG. 9 is a motor current waveform diagram used to explain the relationship between copper loss and carrier frequency; and FIG. 10 is a motor current squared waveform diagram used to explain the relationship between copper loss and 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 assigned common reference numerals, and duplicate descriptions thereof will be omitted.

[0013] [General Configuration of Motor Control System 11] First, the general 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. 1. Fig. 1 is a schematic configuration 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 described 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 includes 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 may be, 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 Figures 2, 3A, 3B, and 4 as appropriate. Figure 2 is a functional block diagram of the microcomputer 11A. Figure 3A is a diagram showing the correspondence relationship between the DC voltage value Vdc and the optimal carrier frequency fpwm_op when the stick-type vacuum cleaner is in the standard operation mode (calculation condition: constant load torque). Figure 3B is a diagram showing the correspondence relationship between the DC voltage value Vdc and the optimal carrier frequency fpwm_op when the stick-type vacuum cleaner is in the high operation mode (calculation condition: constant load torque). Figure 4 is a diagram showing the correspondence relationship between the rotation speed RSmtr of the motor 18 and the optimal 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 / high operation mode) of the stick-type 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 FIGS. 3A, 3B, and 4) that indicates 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 speeds RSmtr of the motor 18 across multiple ranges, for example, a reference rotation speed RSmtr_std in the standard operation mode, a reference 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 electric vacuum cleaner may be appropriately adopted (see FIGS. 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 is 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 optimal carrier frequency fpwm_op corresponding to the combination of the rotational speed RSmtr of the motor 18 and the DC voltage value. The sum of the inverter loss and the motor loss [Pcar(fpwm)], which is a function of the carrier frequency fpwm, will be described in detail later.

[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 can be seen, for 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 optimum carrier frequency fpwm_op set by the optimum 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. 5. Fig. 5 is a flowchart illustrating the operation of the motor control device 11 according to the embodiment of the present invention.

[0032] 5, the information acquisition unit 21 belonging to the motor control device 11 acquires a target value for the rotation speed RSmtr of the motor 18 through the operation mode of the stick vacuum cleaner. More specifically, when the operation mode DM of the stick vacuum cleaner is the standard operation mode, the rotation speed RSmtr_std that serves as a reference 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 vacuum cleaner is the strong operation mode, the rotation speed RSmtr_str that serves as a reference 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 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 reaches the target value. Immediately after starting the motor 18, before the current rotation speed RSmtr of the motor 18 has reached the target value, the motor control device 11 generates a predetermined PWM control signal that takes into account the early arrival of the motor 18 in a steady operating state, and controls the 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 in 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 a case where the target value of the rotation speed RSmtr of the motor 18 is the rotation speed RSmtr_std that 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] Furthermore, for example, in a case where the target value of the rotation speed RSmtr of the motor 18 is the reference rotation speed RSmtr_str 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 of 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 is in operation.

[0042] [Basic Concept for Determining Optimal Carrier Frequency fpwm_op] Next, the basic concept for determining the optimal carrier frequency fpwm_op will be described with reference to Figures 6, 7, 8A, and 8B as appropriate. Figure 6 is an explanatory diagram showing the relationship between the carrier frequency fpwm and losses that vary with changes in the carrier frequency fpwm. Figure 7 is an explanatory diagram showing the dependency of inverter losses on the carrier frequency fpwm. Figure 8A is a motor current waveform diagram used to explain the relationship between copper loss and the carrier frequency fpwm. Figure 8B is a motor current squared waveform diagram used to explain the relationship between copper loss and the 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 the motor control system 10 are roughly divided into inverter losses, which are losses occurring in the inverter 17, and motor losses, which are losses occurring in the motor 18.

[0045] As shown in Figure 7, inverter losses are roughly divided into switching losses Pinv_sw and conduction losses Pinv_cond. On the other hand, motor losses are roughly 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 varies 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). In (Equation 1), Pinv_sw [W] is the switching loss, Vdc [V] is the DC voltage value, Iload [Arms] is the motor current effective value, ton is the rise delay time [s], toff is the fall delay time [s], and fpwm [Hz] is the carrier frequency. Note that various parameters in (Equation 1), including the DC voltage value Vdc, the motor current effective value Iload, the rise delay time ton, and the fall delay time toff, can be obtained as appropriate from the datasheet or specifications of the DC power supply 13, which is a rechargeable battery, and the datasheets or specifications of the power semiconductor switching elements Q1 to Q6 used in the inverter 17.

[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). In (Equation 2), ΔPmtr_cop [W] is the copper loss associated with the motor, Rm [Ω] is the motor winding resistance value (for one phase), Vdc [V] is the DC voltage value, KhV1 [-] is the modulation factor, fpwm [Hz] is the carrier frequency, and Lm is the motor inductance [H]. Note that various parameters in (Equation 2), including the motor winding resistance value (for one phase) Rm, the DC voltage value Vdc, the modulation factor KhV1, and the motor inductance Lm, may be obtained as appropriate from the data sheet or specifications of the DC power supply 13, which is a rechargeable battery, the data sheet or specifications of the motor 18 to be used, etc.

[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). From the above, if the carrier frequency fpwm that minimizes the loss Pcar is found, it becomes the optimum carrier frequency fpwm_op.

[0051] [Procedure for Deriving Copper Loss Pmtr_cop] Here, the procedure for deriving the copper loss Pmtr_cop will be described with reference to Fig. 8A and Fig. 8B. Fig. 8A is a motor current waveform diagram used to explain the relationship between the copper loss Pmtr_cop and the carrier frequency fpwm. Fig. 8B is a motor current squared waveform diagram used to explain the relationship between the copper loss Pmtr_cop and the carrier frequency fpwm.

[0052] The copper loss Pmtr_cop can be expressed by (Equation 4). Here, Rm [Ω] is the motor winding resistance (for one phase), and Iload [Arms] is the motor current effective value. Note that 3Rm (motor winding resistance for three phases) is an invariable fixed value. (Iload) ２ It is difficult to directly calculate using the carrier frequency fpwm.

[0053] The procedure for deriving the copper loss Pmtr_cop is as follows. Here, Im(t) [A] is the motor current, and T [s] is the rotation period of the motor 18.

[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] Here, Lm [H] is the motor inductance, duty [-] is the duty ratio (duty = KhV1 / √2), V1 [V] is the phase voltage peak value, and KhV1 [-] is the modulation factor (V1 / (Vdc / 2)).

[0056] [Configuration, operation and effect of motor control device 11 according to the present invention] A motor control device 11 according to a first aspect is a motor control device 11 that controls an inverter 17 that converts DC power into AC power to drive a motor 18, and includes: an information acquisition unit 21 that acquires information on 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 relationship information that indicates a correspondence relationship between the DC voltage value Vdc and an optimal carrier frequency fpwm_op for each rotation speed RSmtr of the motor 18; and an optimal carrier frequency setting unit (setting unit) 25 that sets an optimal carrier frequency fpwm_op in accordance with the driving state of the motor 18, based on 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. 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] The motor control device 11 based on the first aspect can provide a highly versatile motor control device that can be easily adapted to a variety of target systems. Furthermore, even when fluctuations in the DC voltage value Vdc occur, the optimal carrier frequency fpwm_op is set in accordance with the driving state of the motor 18, including the fluctuations, so that a highly flexible motor control device can be provided that can adapt to load fluctuations.

[0058] The motor control device 11 based on the second aspect may be the motor control device 11 based on the first aspect, and may employ a configuration in which the correspondence information 20 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 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 taking into consideration that it 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. 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] The motor control device 11 based on the third aspect may be the motor control device 11 based on the second aspect, and may be configured such that the inverter loss is a switching loss (Pinv_sw) associated with a switching element used in the inverter 17, and the motor loss is a 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 the copper loss ΔPmtr_cop as losses that depend on the carrier frequency fpwm, and therefore the effect of suppressing the 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] The motor control device 11 according to the fourth aspect is the motor control device 11 according to the third aspect, and may employ a configuration in which the switching elements are IGBTs.

[0063] The 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 the 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, wherein the relational expression of the switching loss (P inv_sw) with the carrier frequency (f pwm) is expressed by (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 carrier frequency (fpwm) associated with the motor is expressed by (Equation 2). In (Equation 2), the following configuration may be adopted: 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].

[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 realizing the present invention. Therefore, the technical scope of the present invention should not be interpreted as being limited by these embodiments. This is because the present invention can be embodied in various forms without departing from the spirit or main characteristics thereof.

[0067] Furthermore, it is possible to replace part of the configuration of the embodiments described herein with the configuration of other embodiments, and furthermore, it is possible to add the configuration of one embodiment to the configuration of another embodiment. It is also possible to add, delete, or replace part of the configuration of each embodiment with other configurations. Furthermore, the control lines and information lines shown are those considered necessary for the explanation, and not all control lines and information lines are necessarily shown in the product. In reality, it can be assumed that almost all of the configurations 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 a function of storing table data (correspondence information) 20 indicating 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. However, the present invention is not limited to this example. It is also possible to adopt a configuration in which the rotational speed RSmtr and the DC voltage value Vdc of the motor 18 each have a predetermined tolerance range, and the table data storage unit 23 stores the optimal carrier frequency fpwm_op in correspondence with a combination of the rotational speed RSmtr and the DC voltage value Vdc of the motor 18 that has the predetermined tolerance range.

[0069] With this configuration, even if there is some fluctuation in the rotation speed RSmtr and DC voltage value Vdc of the motor 18, the effect on the setting of the optimal carrier frequency fpwm_op is suppressed, and as a result, it is possible to expect the effect of obtaining a motor control device 11 with excellent control stability.

[0070] In addition, in the description of motor control device 11 according to the embodiment of the present invention, inverter 17 has been described with an example configuration in which power semiconductor switching elements Q1 to Q6 made up of IGBTs are provided 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 also be used as power semiconductor switching elements Q1 to Q6.

[0071] Furthermore, in the explanation of the motor control device 11 according to the embodiment of the present invention, the rotational position data of the motor 18 is used as the basic data for obtaining the rotational speed RSmtr of the motor 18. However, the present invention is not limited to this example. An induced voltage or a motor line signal may also be used as the basic data for obtaining the rotational speed RSmtr of the motor 18.

[0072] Finally, although the motor control system 10 including the motor control device 11 according to the embodiment of the present invention has been described as being installed in a stick-type electric 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 also be installed in a washing machine, a refrigerator, an air conditioner, etc.

[0073] REFERENCE SIGNS LIST 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 unit 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 Optimum carrier frequency RSmtr Motor rotation speed Vdc DC voltage value

Claims

1. A motor control device that controls an inverter that converts DC power to AC power to drive a motor, comprising: an information acquisition unit that acquires information on the driving state of the motor, including the rotation speed of the motor and a DC voltage value based on the DC power; an information storage unit that stores correspondence information that indicates the correspondence 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 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.

2. A motor control device according to claim 1, wherein the correspondence information is set taking into consideration that the optimum carrier frequency corresponding to the combination of the motor rotation speed and the DC voltage value is the carrier frequency that reduces or minimizes the sum of inverter loss and motor loss (Pcar), which is a function of carrier frequency.

3. A motor control device according to claim 2, wherein the inverter loss is a switching loss (Pinv_sw) associated with a switching element used in the inverter, and the motor loss is a copper loss (ΔPmtr_cop) associated with the motor.

4. A motor control device according to claim 3, wherein the switching element is an IGBT.

5. A motor control device according to claim 4, wherein the relational expression of the switching loss (Pinv_sw) with the carrier frequency (fpwm) is expressed by (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 carrier frequency (fpwm) associated with the motor is expressed by (Equation 2). A motor control device characterized in that, in (Equation 2), ΔPmtr_cop [W]: copper loss associated with the motor, Rm [Ω]: motor winding resistance value (for one phase), Vdc [V]: DC voltage value, KhV1 [-]: modulation factor, fpwm [Hz]: carrier frequency, and Lm: motor inductance [H].

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