Electric-motor drive device and air conditioner

Abstract

This electric-motor drive device drives an electric motor that is provided with a stator having a coil and a rotor having permanent magnets that are ferrite magnets. The electric-motor drive device is provided with an inverter that outputs voltage to the coil of the electric motor, and a control device that controls the inverter. Before starting the electric motor, the control device applies, to the coil and from the inverter, superimposed voltages that contain a DC component and a high-frequency AC component the frequency of which is higher than the operating frequency when the electric motor is spinning, thereby heating the coil without rotating the electric motor. On the basis of detected values of the current and the voltage when the superimposed voltages are being applied, the control device computes the temperature of the permanent magnets.

Description

Electric motor drive device and air conditioning device

[0001] The present disclosure relates to an electric motor drive device that drives an electric motor, and an air conditioner having an electric motor drive device.

[0002] Electric motors with ferrite magnets mounted on the rotor have been known for some time. Ferrite magnets have the property of being prone to irreversible demagnetization at low temperatures. Patent Document 1 proposes a technology for warming up the motor by passing a current through the stator coil before starting the motor.

[0003] JP 2012-186917 A (see abstract)

[0004] However, if the temperature of the ferrite magnet rises too much, the saturation magnetic flux density of the ferrite magnet will decrease, which may result in a decrease in motor efficiency.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to suppress irreversible demagnetization of ferrite magnets while avoiding a decrease in motor efficiency.

[0006] The electric motor drive device according to the present disclosure drives an electric motor having a stator with a coil and a rotor with a ferrite permanent magnet. The electric motor drive device includes an inverter that outputs a voltage to the coil of the electric motor, and a control device that controls the inverter. Before starting the electric motor, the control device applies a superimposed voltage from the inverter to the coil, the superimposed voltage including a high-frequency AC component and a DC component, the frequency of which is higher than the operating frequency of the electric motor during rotational operation, thereby causing the coil to heat up without rotating the electric motor. The control device calculates the temperature of the permanent magnet based on detected values ​​of current and voltage when the superimposed voltage is applied.

[0007] According to the above configuration, a superimposed voltage is applied to the coil of the electric motor before starting the electric motor, thereby raising the temperature of the permanent magnet, which is a ferrite magnet, and suppressing irreversible demagnetization. Furthermore, because the electric motor drive device calculates the temperature of the permanent magnet, excessive temperature rise of the permanent magnet can be suppressed, and a decrease in the efficiency of the electric motor can be avoided.

[0008] 1 is a cross-sectional view showing an electric motor according to a first embodiment; FIG. 2 is a cross-sectional view showing a rotor according to the first embodiment; FIG. 3 is a diagram for explaining the arrangement of coils in the electric motor according to the first embodiment; FIG. 4 is a longitudinal cross-sectional view showing a compressor according to the first embodiment; FIG. 5 is a diagram showing the overall configuration of an air conditioning apparatus according to the first embodiment; FIG. 6 is a diagram showing a refrigerant circuit of the air conditioning apparatus according to the first embodiment; FIG. 7 is a block diagram showing an electric motor drive device according to the first embodiment; FIG. 8 is a diagram showing a current waveform flowing in a coil of the electric motor according to the first embodiment, a diagram showing a temperature change of a permanent magnet, and a diagram showing a change in demagnetization current of the permanent magnet; FIG. 9 is a diagram showing a voltage waveform applied to a coil during preheating of the electric motor according to the first embodiment; FIG. 10 is a schematic diagram showing table data corresponding to inductance and temperature of a permanent magnet, which is stored in a storage device according to the first embodiment; FIG. 11 is a schematic diagram showing table data corresponding to temperature of a permanent magnet and control parameters, which is stored in a storage device according to the first embodiment; FIG. 12 is a flowchart showing the operation of the electric motor according to the first embodiment; FIG. 13 is a cross-sectional view showing an example of a configuration of a rotor of the electric motor according to the first embodiment; FIG. 14 is a cross-sectional view showing another example of a configuration of a rotor of the electric motor according to the first embodiment; Fig. 1 is a block diagram showing an electric motor drive device of embodiment 2. Fig. 2 is a block diagram showing an electric motor drive device of embodiment 3. Fig. 3 is a flowchart showing the operation of the electric motor of embodiment 3. Fig. 4 is a block diagram showing an electric motor drive device of embodiment 4. Fig. 5 is a schematic diagram (A) and (B) for explaining the concept of machine learning of embodiment 4. Fig. 6 is a functional block diagram showing a control device of the electric motor drive device of embodiment 4.

[0009] Embodiment 1. <Configuration of electric motor> Fig. 1 is a cross-sectional view showing an electric motor 2 according to embodiment 1. The electric motor 2 shown in Fig. 1 is an embedded permanent magnet electric motor, and is used, for example, in a compressor 5 (Fig. 4) of an air conditioner 4. The electric motor 2 is driven by an electric motor drive device 6 (Fig. 7) that includes an inverter 62.

[0010] The electric motor 2 has a rotor 1 attached to a shaft 25, which is a rotating shaft, and a stator 3 provided to surround the rotor 1. An air gap of, for example, 0.3 to 1.0 mm is formed between the stator 3 and the rotor 1. The stator 3 is incorporated inside a sealed container 51 of a compressor 5 (FIG. 4) described below.

[0011] Hereinafter, the direction of the central axis Ax, which is the central axis of rotation of the rotor 1, will be referred to as the "axial direction." The radial direction centered on the central axis Ax will be referred to as the "radial direction." The circumferential direction centered on the central axis Ax will be referred to as the "circumferential direction." A cross-sectional view taken along a plane parallel to the central axis Ax will be referred to as a "longitudinal cross-sectional view," and a cross-sectional view taken along a plane perpendicular to the central axis Ax will be referred to as a "transverse cross-sectional view."

[0012] Fig. 2 is a cross-sectional view showing the rotor 1. As shown in Fig. 2, the rotor 1 has an annular rotor core 10 centered on a central axis Ax, and permanent magnets 20 embedded in the rotor core 10. The rotor core 10 is made by laminating electromagnetic steel sheets in the axial direction and fixing them in place with crimped portions 19. The thickness of the electromagnetic steel sheets is 0.1 to 0.7 mm, and is, for example, 0.35 mm.

[0013] A center hole 15 is formed in the radial center of rotor core 10. The shaft 25 is fixed in center hole 15 of rotor core 10 by shrink fitting, press fitting, or the like. Rotor core 10 also has a circular outer periphery 10a.

[0014] A plurality of magnet insertion holes 11 are formed along the outer periphery 10a of the rotor core 10. One permanent magnet 20 is inserted into each magnet insertion hole 11. One magnet insertion hole 11 corresponds to one magnetic pole. The circumferential center of the magnet insertion hole 11 corresponds to the pole center P. An inter-pole portion M is formed between adjacent magnet insertion holes 11.

[0015] Because the rotor core 10 has six magnet insertion holes 11, the rotor 1 has six poles. However, the number of poles of the rotor 1 is not limited to six and may be two or more. The magnet insertion holes 11 extend in a direction perpendicular to a radial line passing through the pole center P, but may also extend in a V-shape, for example. Furthermore, two or more permanent magnets 20 may be arranged in each magnet insertion hole 11.

[0016] The permanent magnets 20 are flat plates that are long in the axial direction of the rotor core 10, have a width in the circumferential direction, and a thickness in the radial direction. The thickness of the permanent magnets 20 is, for example, 2.0 mm. The permanent magnets 20 are magnetized in the thickness direction. The magnetization directions of adjacent permanent magnets 20 in the circumferential direction are opposite to each other.

[0017] The permanent magnet 20 is made of a ferrite magnet. A ferrite magnet is a permanent magnet whose main component is ferrite (iron oxide). Ferrite magnets include sintered ferrite magnets made by sintering ferrite powder, and bonded ferrite magnets made by mixing ferrite powder with a binder and molding them, but either may be used.

[0018] 1, the stator 3 includes a stator core 30 that surrounds the rotor core 10 from the radial outside, and a coil 35 that is wound around the stator core 30. The stator core 30 is made by stacking electromagnetic steel sheets in the axial direction and fixing them in place with crimped portions 38. The thickness of the electromagnetic steel sheets is 0.1 to 0.7 mm, and is, for example, 0.35 mm.

[0019] The stator core 30 has an annular yoke 31 centered on the central axis Ax and a plurality of teeth 32 extending radially inward from the yoke 31. The teeth 32 are arranged at regular intervals in the circumferential direction. The number of teeth 32 is nine in this example. However, the number of teeth 32 is not limited to nine, and may be two or more.

[0020] Between the teeth 32 adjacent in the circumferential direction, slots 33 are formed, which are spaces for accommodating coils 35. The number of slots 33 is nine, the same as the number of teeth 32. The crimped portions 38 are formed on the yoke 31, but may also be formed on the teeth 32.

[0021] The stator core 30 is formed by combining a plurality of split cores 30A in the circumferential direction. Each split core 30A is a block including one tooth 32. The split cores 30A are joined by, for example, welding at split surfaces 31a formed on the yoke 31.

[0022] The coil 35 is made of copper wire or aluminum wire, with aluminum wire being more preferable. The coil 35 is wound around each tooth 32 in a concentrated winding manner. The wire diameter of the coil 35 is, for example, 1.0 mm. The number of turns of the coil 35 around one tooth 32 is, for example, 80 turns. The number of turns and wire diameter of the coil 35 are determined based on the required specifications such as rotation speed and torque, the supply voltage, and the cross-sectional area of ​​the slot 33.

[0023] Insulating portions 34 are provided on both axial end surfaces of the stator core 30 and on the inner surfaces of the slots 33. The insulating portions 34 are configured from an insulator made of a resin such as polybutylene terephthalate (PBT) or an insulating film made of a resin such as polyethylene terephthalate (PET).

[0024] The stator 3 is constructed by winding a coil 35 around the teeth 32 of each split core 30A via an insulating portion 34, and then assembling the split cores 30A into an annular shape and welding them together.

[0025] 3 is a diagram showing the arrangement of the coils 35 in the electric motor 2. The coils 35 include U-phase, V-phase, and W-phase coils 35U, 35V, and 35W. Three coils 35U, 35V, and 35W are provided, and the coils 35 of the same phase are connected in series.

[0026] Coils 35U, 35V, 35W, 35U, 35V, 35W, 35U, 35V, 35W are wound in this order counterclockwise around the nine teeth 32 of the stator core 30. When the electric motor 2 is driven, i.e., when it is rotating, an AC voltage is applied to the coils 35U, 35V, 35W, which causes a current to flow through the coils 35U, 35V, 35W and generates a rotating magnetic field.

[0027] On the other hand, during preheating of the electric motor 2 described below, a superimposed voltage (indicated by the symbol SV in FIG. 3) in which a DC voltage and a high-frequency AC voltage are superimposed is applied to the U-phase coil 35U and the V-phase coil 35V of the three-phase coils 35U, 35V, and 35W.

[0028] <Configuration of Compressor> Fig. 4 is a longitudinal cross-sectional view showing a compressor 5 equipped with an electric motor 2. Here, the compressor 5 is a rotary compressor, but is not limited to this and may be, for example, a scroll compressor. The compressor 5 includes a compression mechanism 50, an electric motor 2 that drives the compression mechanism 50, a shaft 25 that connects the compression mechanism 50 and the electric motor 2, and a sealed container 51 that houses these components.

[0029] The sealed container 51 is a container made of steel plate, and houses the compression mechanism 50 and the electric motor 2. The stator 3 of the electric motor 2 is assembled inside the sealed container 51 by shrink fitting, press fitting, welding, or the like.

[0030] A discharge pipe 55 for discharging the refrigerant to the outside and a terminal 54 for supplying power to the electric motor 2 are provided at the top of the sealed container 51. An accumulator 52 for storing refrigerant gas is attached to the outside of the sealed container 51. Refrigeration oil for lubricating the bearings of the compression mechanism 50 is stored at the bottom of the sealed container 51.

[0031] The compression mechanism 50 includes a cylinder 56 having a cylinder chamber 56a, a rolling piston 59 fixed to the shaft 25, a vane that divides the interior of the cylinder chamber 56a into an intake side and a compression side, and an upper frame 57a and a lower frame 57b that close both axial ends of the cylinder chamber 56a.

[0032] Both the upper frame 57a and the lower frame 57b have bearings that rotatably support the shaft 25. An upper discharge muffler 58a and a lower discharge muffler 58b are attached to the upper frame 57a and the lower frame 57b, respectively.

[0033] The cylinder chamber 56a of the cylinder 56 is cylindrical and centered on the central axis Ax. The eccentric shaft portion 25a of the shaft 25 is located inside the cylinder chamber 56a. The eccentric shaft portion 25a has a center that is eccentric with respect to the central axis Ax. A rolling piston 59 is fitted onto the outer periphery of the eccentric shaft portion 25a. When the electric motor 2 rotates, the eccentric shaft portion 25a and the rolling piston 59 rotate eccentrically within the cylinder chamber 56a.

[0034] An intake port 56b is formed in the cylinder 56 to draw refrigerant gas into the cylinder chamber 56a. An intake pipe 53 communicating with the intake port 56b is attached to the sealed container 51, and refrigerant gas is supplied from the accumulator 52 to the cylinder chamber 56a via the intake pipe 53.

[0035] The accumulator 52 receives low-pressure refrigerant gas and liquid refrigerant from the refrigerant circuit of the air conditioning device 4 (FIG. 5) via a suction pipe 52a, separates them, and supplies only the refrigerant gas to the compression mechanism 50. The refrigerant gas supplied from the accumulator 52 is supplied through a suction pipe 53 into a cylinder chamber 56a of a cylinder 56.

[0036] When the rotor 1 rotates, the shaft 25 rotates together with the rotor 1. Then, the rolling piston 59 fitted to the shaft 25 rotates eccentrically within the cylinder chamber 56a, compressing the refrigerant within the cylinder chamber 56a. The compressed refrigerant passes through the discharge mufflers 58a and 58b, and further passes through the gap between the rotor 1 and the stator 3 of the electric motor 2, rises within the sealed container 51, and is discharged from the discharge pipe 55.

[0037] <Configuration of Air Conditioner> Fig. 5 is a schematic diagram showing the entire air conditioner 4 equipped with a compressor 5. Fig. 6 is a diagram showing the refrigerant circuit of the air conditioner 4. As shown in Fig. 5, the air conditioner 4 is equipped with an outdoor unit 4A and an indoor unit 4B. The outdoor unit 4A and the indoor unit 4B are connected by a refrigerant pipe 4C.

[0038] 6, the air conditioning device 4 includes a compressor 5, a switching valve 41, an outdoor heat exchanger 42, a pressure reducing device 43, and an indoor heat exchanger 44. The compressor 5, the switching valve 41, the outdoor heat exchanger 42, the pressure reducing device 43, and the indoor heat exchanger 44 are connected by refrigerant piping 4C to form a refrigerant circuit. An outdoor blower 45 is disposed opposite the outdoor heat exchanger 42, and an indoor blower 46 is disposed opposite the indoor heat exchanger 44.

[0039] Of these, the compressor 5, the switching valve 41, the outdoor heat exchanger 42, the pressure reducing device 43, and the outdoor blower 45 are arranged in the outdoor unit 4A (FIG. 5), while the indoor heat exchanger 44 and the indoor blower 46 are arranged in the indoor unit 4B (FIG. 5).

[0040] The outdoor blower 45 has an electric motor 45a and an impeller 45b (FIG. 5) driven by the electric motor 45a. The indoor blower 46 has an electric motor 46a and an impeller 46b (FIG. 5) driven by the electric motor 46a.

[0041] The operation of the air conditioner 4 is as follows: The compressor 5 compresses the refrigerant it has drawn in and sends it out as high-temperature, high-pressure refrigerant gas. During cooling operation, the switching valve 41 causes the refrigerant sent out from the compressor 5 to flow into the outdoor heat exchanger 42, as shown by the solid line in Figure 6.

[0042] The outdoor heat exchanger 42 exchanges heat between the refrigerant and the outdoor air sent by the outdoor air blower 45, condenses the refrigerant, and sends it out as a liquid refrigerant. The pressure reducing device 43 expands the liquid refrigerant sent out from the outdoor heat exchanger 42, and sends it out as a low-temperature, low-pressure liquid refrigerant.

[0043] The indoor heat exchanger 44 exchanges heat between the low-temperature, low-pressure liquid refrigerant sent from the pressure reducing device 43 and the indoor air, evaporating the refrigerant and sending it out as refrigerant gas. The air from which heat has been removed by the indoor heat exchanger 44 is supplied into the room by the indoor fan 46.

[0044] During heating operation, the switching valve 41 allows the refrigerant sent from the compressor 5 to flow into the indoor heat exchanger 44, as shown by the dashed line in Fig. 6. In this case, the indoor heat exchanger 44 functions as a condenser, and the outdoor heat exchanger 42 functions as an evaporator.

[0045] <Motor drive device> Figure 7 is a block diagram showing the motor drive device 6 that drives the motor 2. The motor drive device 6 is a drive circuit mounted on the air conditioner 4 shown in Figures 5 and 6. The motor drive device 6 can be mounted on a circuit board attached to the outdoor unit 4A (Figure 5), for example.

[0046] As shown in FIG. 7, the electric motor drive device 6 has a rectifier circuit 61 , an inverter 62 , an inverter drive circuit 65 , a control device (controller) 70 , a voltage detection circuit 66 , and current detection circuits 67 and 68 .

[0047] The rectifier circuit 61 includes bridge diodes 61a, 61b, 61c, and 61d and a smoothing capacitor 61e. The rectifier circuit 61 converts an AC voltage supplied from a commercial AC power supply into a DC voltage, and outputs the DC voltage from the buses B1 and B2.

[0048] The inverter 62 has U-phase switching elements 62a and 62b, V-phase switching elements 62c and 62d, and W-phase switching elements 62e and 62f. The switching elements 62a, 62c, and 62e form upper arms, and the switching elements 62b, 62d, and 62f form lower arms.

[0049] The switching elements 62a and 62b are connected to the coil 35U via an output line F1. The switching elements 62c and 62d are connected to the coil 35V via an output line F2. The switching elements 62e and 62f are connected to the coil 35W via an output line F1. A return rectifying element is connected in parallel to the switching elements 62a to 62f.

[0050] The inverter 62 converts the DC voltage output from the rectifier circuit 61 into AC voltage and supplies it to the coils 35U, 35V, and 35W of the electric motor 2. As a result, current flows through the coils 35U, 35V, and 35W, generating a rotating magnetic field, which causes the rotor 1 to rotate.

[0051] The inverter drive circuit 65 generates a PWM (Pulse Width Modulation) signal based on a control command value from the control device 70 and outputs the signal to the inverter 62. The inverter drive circuit 65 is also referred to as a PWM signal generation unit.

[0052] Voltage dividing resistors 63a and 63b are connected in series between the buses B1 and B2 of the rectifier circuit 61. A voltage detection circuit 66 detects the electrical signals converted to low voltage by the voltage dividing resistors 63a and 63b and outputs the detected electrical signals to the control device 70.

[0053] The current detection circuit 67 is connected to the shunt resistor 64 connected to the bus B 2 of the rectifier circuit 61 , and detects the current value of the current input to the inverter 62 .

[0054] The current detection circuit 68 is connected to output lines F1, F2, F3 from the inverter 62 to the coils 35U, 35V, 35W, and detects the current output from the inverter 62 to the coils 35U, 35V, 35W. The control device 70 detects position information of the rotor 1 based on the current value detected by the current detection circuit 68.

[0055] The control device 70 includes a microcomputer 71 and a storage device 72. The storage device 72 stores control parameters used to control the electric motor 2. The control parameters include, for example, a motor constant and a control gain. The motor constants include, for example, an induced voltage constant, a d-axis inductance, a q-axis inductance, and a winding resistance.

[0056] The microcomputer 71 of the control device 70 performs calculations necessary for controlling the rotation of the electric motor 2 based on the above control parameters, an operation instruction signal received by a signal receiving unit 69 from a remote control device (remote controller), and detection signals from the voltage detection circuit 66 and the current detection circuits 67 and 68. The control device 70 outputs a control command value to the inverter drive circuit 65 based on the calculation results.

[0057] <Preheating of the motor> The permanent magnets 20 are ferrite magnets, which are prone to irreversible demagnetization at low temperatures. Therefore, by passing a current through the coil 35 before starting the motor 2, the temperature of the motor 2 is raised and irreversible demagnetization is suppressed. This operation is called preheating of the motor 2.

[0058] When preheating the motor 2, a superimposed voltage including a DC component and a high-frequency AC component is applied to the coil 35. The frequency of the high-frequency AC component of the superimposed voltage is higher than the operating frequency range during rotational operation of the motor 2. Both the DC component and the high-frequency AC component of the superimposed voltage cause the motor to heat up, contributing to preheating of the motor 2.

[0059] Fig. 8(A) is a graph showing the waveform of the current flowing through the coil 35. As shown in Fig. 8(A), the control device 70 (Fig. 7) of the electric motor drive device 6 applies a superimposed voltage including a DC component and a high-frequency AC component to the coil 35 from time t1 to time t2 (also referred to as period A1) before the start of the electric motor 2. As a result, a superimposed current in which a DC current and a high-frequency AC current are superimposed flows through the coil 35.

[0060] The DC component of the superimposed current generates a magnetic field of constant strength and direction in the coil 35. When the coil 35 and the permanent magnet 20 are in a specific relative position, the magnetic attraction force between the coil 35 and the permanent magnet 20 becomes maximum, and the rotor 1 comes to a standstill at that relative position.

[0061] That is, the DC component of the superimposed current can stop the rotor 1. Furthermore, since the frequency of the high-frequency AC component of the superimposed current is higher than the operating frequency range during rotation, the rotor 1 will not rotate due to the influence of the high-frequency AC component.

[0062] The superposed voltage is applied between the coils 35U and 35V as indicated by the symbol SV in Fig. 3. However, this is not limiting, and it is sufficient that the superposed voltage is applied to at least one phase of the coil 35. For example, the superposed voltage may be applied to the coils 35U and 35W or the coils 35V and 35W. Alternatively, the superposed voltage may be applied to all of the coils 35U, 35V, and 35W.

[0063] Based on the control command value output from the control device 70, the inverter drive circuit 65 outputs a PWM signal to the inverter 62, and the superimposed voltage is applied from the inverter 62 to the coil 35 of the electric motor 2. The control command value output from the control device 70 includes a control command value for the magnitude of the DC component of the superimposed voltage, as well as control command values ​​for the amplitude, frequency, and phase of the high-frequency AC component.

[0064] At time t2, the control device 70 stops applying the superimposed voltage to the coil 35 of the electric motor 2. The length of the time t1 to t2 (i.e., period A1) is the duration of preheating, and is, for example, 5 seconds or more.

[0065] The period between times t2 and t3 (also referred to as period A2) is a period during which the supply of current to the coil 35 is stopped.

[0066] At time t3, the control device 70 starts applying an AC voltage to the coil 35 of the electric motor 2 to rotate the electric motor 2. In other words, it starts the electric motor 2. From time t3 onwards (also referred to as period A3) is a period during which the rotational operation of the electric motor 2 continues.

[0067] The frequency of the high-frequency AC component of the superimposed voltage applied to the coil 35 during preheating of the motor 2 may be higher than the range of the operating frequency during rotation of the motor 2. Specifically, the frequency of the high-frequency AC component of the superimposed voltage during preheating is preferably five times or more the operating frequency during rotation.

[0068] For example, if the operating frequency range of the electric motor 2 during rotation is 10 Hz to 600 Hz, the frequency of the high-frequency AC component of the superimposed voltage applied to the coil 35 during preheating is 3 kHz. The operating frequency during rotation of the electric motor 2 is the frequency of the current flowing through the coil 35 during rotation of the electric motor 2.

[0069] 8(B) is a graph showing the temperature change of the permanent magnet 20. When the motor 2 is preheating (period A1), Joule heat is generated by the application of a superimposed voltage to the coil 35, and the temperature of the entire motor 2 rises. As a result, the temperature of the permanent magnet 20 also rises. During the rotational operation of the motor 2 (period A3), the rate of increase in the temperature of the permanent magnet 20 gradually decreases and converges to a constant temperature.

[0070] 8(C) is a graph showing changes in the current (referred to as the demagnetizing current) that causes irreversible demagnetization in the permanent magnet 20. Because irreversible demagnetization of the ferrite magnet that is the permanent magnet 20 is likely to occur at low temperatures, the demagnetizing current increases as the temperature of the permanent magnet 20 rises. In other words, irreversible demagnetization of the permanent magnet 20 becomes less likely to occur.

[0071] 8A and 8C also show overcurrent protection levels, which will be explained in the second embodiment.

[0072] 9A is a schematic diagram showing an example of a waveform of the superimposed voltage. In the example shown in FIG. 9A, the amplitude Vh of the high-frequency AC component of the superimposed voltage is greater than the magnitude Vd of the DC component. Such a superimposed voltage is suitable for an IPM (Interior Permanent Magnet) type electric motor 2 in which permanent magnets 20 are embedded in rotor core 10, as shown in FIG.

[0073] 9B is a schematic diagram showing another example of the waveform of the superimposed voltage. In the example shown in FIG. 9B, the amplitude Vh of the high-frequency AC component of the superimposed voltage is smaller than the magnitude Vd of the DC component. This type of superimposed voltage is suitable for an SPM (Surface Permanent Magnet) type electric motor in which permanent magnets 220 are held on the outer peripheral surface of rotor core 210, as shown in FIG. 14 (described later).

[0074] <Temperature detection of permanent magnet> While irreversible demagnetization of the permanent magnet 20 can be suppressed by preheating the electric motor 2 as described above, if the temperature of the permanent magnet 20 cannot be determined, the permanent magnet 20 may be heated more than necessary. In this case, the saturation magnetic flux density of the permanent magnet 20 may decrease, reducing the efficiency of the electric motor or wasting input energy.

[0075] Here, there is a correlation between the temperature of the permanent magnet 20 and the inductance of the electric motor 2. That is, as the temperature of the permanent magnet 20 rises, the saturation magnetic flux density of the permanent magnet 20 decreases, thereby increasing the inductance of the electric motor 2. Also, as the temperature of the permanent magnet 20 drops, the saturation magnetic flux density of the permanent magnet 20 decreases, thereby decreasing the inductance of the electric motor 2. Therefore, if the inductance of the electric motor 2 can be determined, the temperature of the permanent magnet 20 can be estimated.

[0076] Therefore, in this embodiment, when preheating the electric motor 2, the inductance is calculated using a principle similar to the well-known Dalton-Cameron method, and the temperature of the permanent magnet 20 is estimated based on the calculated inductance.

[0077] The Dalton-Cameron method is widely used in manufacturing sites as a method for measuring the inductance of electric motors. In the Dalton-Cameron method, the rotational position of the rotor is fixed using a jig, an AC voltage is applied between two of the three-phase coils of the stator, the current and voltage at that time are detected, and the inductance of the electric motor is calculated based on the detection results. Japanese Patent Application Laid-Open No. 5-137303, for example, is an example of a document related to the Dalton-Cameron method.

[0078] In this embodiment, instead of fixing the rotor 1 with a jig, the position of the rotor 1 is fixed by the DC component contained in the superimposed current during preheating of the motor 2. Then, the inductance of the motor 2 is calculated using the high-frequency AC component contained in the superimposed current, based on a principle similar to the Dalton-Cameron method.

[0079] During preheating of the motor 2, while a superimposed voltage is being applied from the inverter 62 to the coil 35 of the motor 2, the microcomputer 71 of the control device 70 detects the current using the current detection circuit 68 and detects the voltage using the voltage detection circuit 66, for example. From these detection results, the inductance of the motor 2 is calculated.

[0080] In addition to the current and voltage, power (=current x voltage) may also be detected.Furthermore, the frequency may be detected from the detected current waveform or the detected voltage waveform.

[0081] 10, table data correlating the inductance of the electric motor 2 with the temperature of the permanent magnet 20 is stored in the storage device 72 of the control device 70. This table data is stored in advance in the storage device 72, and is obtained by experimentally determining the relationship between the inductance of the electric motor 2 and the temperature of the permanent magnet 20.

[0082] The microcomputer 71 of the control device 70 estimates the temperature of the permanent magnet 20 by referring to the table data of FIG. 10 based on the inductance of the electric motor 2 calculated from the detection results of the current and voltage.

[0083] Then, when the estimated temperature of the permanent magnet 20 reaches or exceeds the reference temperature, the control device 70 starts the electric motor 2 and starts rotating the rotor 1. The reference temperature is the temperature at which the coercive force of the permanent magnet 20 increases to a level at which irreversible demagnetization does not occur.

[0084] In this way, by starting the electric motor 2 after the temperature of the permanent magnet 20 has risen sufficiently, irreversible demagnetization of the permanent magnet 20, which is a ferrite magnet, can be suppressed.

[0085] Furthermore, by estimating the temperature of the permanent magnet 20, the temperature of the permanent magnet 20 is prevented from rising more than necessary. This makes it possible to suppress a decrease in saturation magnetic flux density due to an excessive temperature rise of the permanent magnet 20 and an accompanying decrease in motor efficiency. It is also possible to suppress waste of input energy required to preheat the motor 2.

[0086] <Correction of Control Parameters> The microcomputer 71 of the control device 70 corrects the control parameters when starting the electric motor 2, based on the estimated temperature of the permanent magnet 20. The control parameters are, for example, a motor constant and a control gain. The motor constants are, for example, an induced voltage constant, an inductance, and a winding resistance. These motor constants vary relatively greatly with temperature.

[0087] For example, the higher the temperature of the permanent magnet 20, the smaller the induced voltage constant and the larger the d-axis inductance and q-axis inductance. Also, the higher the temperature of the permanent magnet 20, the higher the temperature of the coil 35 close to the permanent magnet 20, and therefore the winding resistance increases.

[0088] The memory device 72 of the control device 70 stores table data that associates the temperature of the motor 2 with the induced voltage constant, d-axis inductance, q-axis inductance, winding resistance, and control gain, as shown in Figure 11, for example.

[0089] The storage device 72 is assumed to have the following initially set control parameters: temperature T1 of the permanent magnet 20, induced voltage constant C1, d-axis inductance Id1, q-axis inductance Iq1, winding resistance R1, and control gain G1.

[0090] On the other hand, when the estimated temperature of the permanent magnet 20 is T2 (°C), the microcomputer 71 corrects the induced voltage constant C1 to C2, the d-axis inductance Id1 to Id2, the q-axis inductance Iq1 to Iq2, the winding resistance R1 to R2, and the control gain G1 to G2 based on the table data of FIG. 11.

[0091] This makes it possible to control the rotational operation of the electric motor 2 using accurate control parameters that take into account temperature changes in the magnetic properties of the electric motor 2. As a result, it is possible to suppress noise from the electric motor 2 and reduce the amount of current supplied to the coil 35.

[0092] 12 is a flowchart showing the operation of the electric motor 2 driven by the electric motor drive device 6. When the control device 70 of the electric motor drive device 6 receives a start signal at the signal receiving unit 69 (FIG. 7) (Y in step S11), it starts preloading (step S12).

[0093] Specifically, the control device 70 outputs a control command value to the inverter drive circuit 65, and applies a superimposed voltage including a DC component and a high-frequency AC component from the inverter 62 to the coil 35. The application of the superimposed voltage to the coil 35 is continued for at least the specified time, as described above.

[0094] Next, in a state where the superimposed voltage is applied to the coil 35, the control device 70 detects the current and voltage, for example, using the current detection circuit 68 and the voltage detection circuit 66 (step S13). Furthermore, the control device 70 may further detect the power or frequency.

[0095] The control device 70 calculates the inductance of the electric motor 2 based on the detection result in step S13, and estimates the temperature of the permanent magnet 20 based on the table data of FIG. 10 (step S14).

[0096] The control device 70 determines whether the temperature of the permanent magnet 20 estimated in step S14 is higher than a reference temperature (step S15). The reference temperature is set to a temperature at which irreversible demagnetization does not occur in the permanent magnet 20, which is a ferrite magnet. If the estimated temperature is equal to or higher than the reference temperature, it means that the temperature of the permanent magnet 20 has risen to a temperature at which irreversible demagnetization does not occur.

[0097] If the control device 70 determines that the estimated temperature is below the reference temperature (N in step S15), the process returns to step S12. On the other hand, if the control device 70 determines that the estimated temperature is equal to or higher than the reference temperature (Y in step S15), the control device 70 starts the electric motor 2 (step S16). Specifically, the control device 70 outputs a control command value to the inverter drive circuit 65, and applies an AC voltage from the inverter 62 to the coils 35U, 35V, and 35W of the electric motor 2 to generate a rotating magnetic field, thereby starting the rotation of the electric motor 2.

[0098] Furthermore, the control device 70 corrects the control parameters based on the table data of Fig. 11 based on the temperature of the permanent magnet 20 estimated in step S14 (step S17). This makes it possible to perform control using control parameters that reflect the estimated temperature of the permanent magnet 20.

[0099] When the control device 70 receives the operation stop signal via the signal receiving unit 69 (FIG. 7) (Y in step S18), it outputs a stop signal to the inverter drive circuit 65 and stops the supply of current from the inverter 62 to the coils 35U, 35V, and 35W, thereby ending the rotational operation of the electric motor 2 (step S19).

[0100] <Function> When a magnetic field in the opposite direction to the magnetization direction (i.e., a demagnetizing field) is applied to the permanent magnet 20, a phenomenon called demagnetization occurs, in which the magnetic force decreases. If the demagnetizing field is small, the magnetic force of the permanent magnet recovers after the application of the demagnetizing field, but if the demagnetizing field is large, the magnetic force of the permanent magnet does not recover even after the application of the demagnetizing field. This is called irreversible demagnetization.

[0101] Since the demagnetizing field is proportional to the current flowing through the coil 35, the amount of current to be passed through the coil 35 is determined taking into consideration the coercive force of the permanent magnet 20 so as not to cause irreversible demagnetization.

[0102] Irreversible demagnetization occurs when the coercive force of the permanent magnet 20 decreases. Magnets whose main component is ferrite, i.e., ferrite magnets, have the property that their coercive force decreases as the temperature decreases. When an electric motor having a ferrite magnet is used at low temperatures, irreversible demagnetization is more likely to occur as the coercive force decreases, and the amount of current that can be supplied to the coil 35 decreases.

[0103] The demagnetizing field acting on the permanent magnet 20 is inversely proportional to the thickness of the permanent magnet 20 and the number of magnetic poles of the rotor 1. Therefore, it is conceivable to suppress irreversible demagnetization of the permanent magnet 20 at low temperatures by increasing the thickness of the permanent magnet 20 or the number of magnetic poles of the rotor 1.

[0104] However, increasing the thickness of the permanent magnets 20 increases the amount of permanent magnets 20 used, raising the manufacturing cost of the electric motor 2. Increasing the number of magnetic poles of the rotor 1 also increases the operating frequency of the rotor 1 in proportion to the number of magnetic poles, resulting in increased iron loss occurring in the rotor core 10 and stator core 30 of the electric motor 2 and increased switching loss of the inverter 62, leading to a decrease in the efficiency of the electric motor.

[0105] A technique has been proposed for a motor to be warmed up by passing a current through the stator coil before starting the motor (see Patent Document 1). The warming up operation improves the coercive force of the ferrite magnet, thereby suppressing irreversible demagnetization.

[0106] However, if the temperature of the permanent magnet cannot be determined, the permanent magnet may be heated more than necessary, which may result in a decrease in the saturation magnetic flux density of the permanent magnet, reducing the efficiency of the motor and wasting input energy. While it is possible to install a temperature sensor to detect the temperature of the permanent magnet, this increases the number of parts and leads to higher manufacturing costs.

[0107] In this embodiment, as described above, a superimposed voltage including a DC component and a high-frequency AC component is applied to the coil 35 before starting the electric motor 2. Both the DC component and the high-frequency AC component of the superimposed voltage contribute to a temperature rise in the electric motor 2. Furthermore, the DC component of the superimposed voltage can bring the rotor 1 to a standstill.

[0108] Furthermore, the inductance of the motor 2 is calculated from the current and voltage detection results using the high-frequency AC component of the superimposed current, based on a principle similar to the Dalton-Cameron method. Then, the temperature of the permanent magnet 20 is estimated from the inductance of the motor 2 based on the table data shown in Fig. 10.

[0109] Then, when the estimated temperature of the permanent magnet 20 reaches or exceeds the reference temperature, the electric motor 2 is started. In this way, the electric motor 2 is started only after the temperature of the permanent magnet 20 has risen sufficiently, so that irreversible demagnetization of the permanent magnet 20, which is a ferrite magnet, can be suppressed.

[0110] Furthermore, by estimating the temperature of the permanent magnet 20, excessive temperature rise of the permanent magnet 20 is suppressed, which makes it possible to suppress a decrease in the saturation magnetic flux density of the permanent magnet 20 and an accompanying decrease in motor efficiency. Furthermore, it is possible to suppress waste of input energy required for preheating the motor 2.

[0111] Furthermore, since there is no need to provide a sensor for detecting the temperature of the permanent magnet 20, an increase in the manufacturing cost of the electric motor 2 can be suppressed.

[0112] The DC component and high-frequency AC component of the superimposed current cause iron loss in the rotor core 10 and stator core 30 of the electric motor 2, and cause copper loss in the coils 35. Both iron loss and copper loss are thermal energy, and contribute to a rise in the temperature of the electric motor 2. In particular, the DC component contributes greatly to the generation of copper loss, and the high-frequency AC component contributes greatly to the generation of iron loss.

[0113] From the viewpoint of suppressing irreversible demagnetization of the permanent magnet 20, an instantaneous upper limit is determined for the current value that can be passed through the coil 35. It is necessary to adjust the ratio of the DC component and the high-frequency AC component of the superimposed current so that this upper limit is not exceeded.

[0114] In the case of an IPM electric motor 2 (see FIG. 1), it is desirable that the amplitude Vh of the high-frequency AC component is greater than the magnitude Vd of the DC component, as shown in FIG. 9A. In the IPM electric motor 2, the permanent magnets 20 are embedded in the magnet insertion holes 11 of the rotor core 10, and therefore the high-frequency AC component generates a large amount of iron loss in the rotor core 10, thereby allowing the permanent magnets 20 to be heated efficiently.

[0115] In the case of an SPM type electric motor (see Fig. 14), it is desirable that the magnitude Vd of the DC component is larger than the amplitude Vh of the high frequency AC component, as shown in Fig. 9(B) . In an electric motor with an SPM structure, the permanent magnets 20 are arranged on the outer periphery of the rotor 1 and are close to the coils 35 of the stator 3, so that the DC component generates a lot of copper loss in the coils 35, thereby allowing the permanent magnets 20 to be heated efficiently.

[0116] The coil 35 may be made of copper wire, but it is more preferable to form it from aluminum wire. Aluminum has a higher electrical resistance than copper, which results in a relatively large copper loss occurring in the coil 35, making it possible to efficiently heat the permanent magnet 20. In particular, in an electric motor with an SPM structure in which the permanent magnet 20 and the coil 35 are close to each other, forming the coil 35 from aluminum wire is particularly effective.

[0117] <Configuration example of rotor> A configuration example of the rotor according to the first embodiment will be described. Fig. 13 is a cross-sectional view showing a rotor 100 according to one configuration example of the first embodiment. The rotor 100 shown in Fig. 13 has an annular rotor core 110 centered on a central axis Ax, and permanent magnets 120 embedded in the rotor core 110. The rotor core 110 is formed by laminating electromagnetic steel sheets in the axial direction and fixing them in place by crimping portions 113 and 114.

[0118] A plurality of magnet insertion holes 111 are formed along the outer periphery of the rotor core 110. Each magnet insertion hole 111 is formed in an arc shape that convex toward the central axis Ax. One permanent magnet 120 is inserted into each magnet insertion hole 111. Like the magnet insertion holes, each permanent magnet 120 has an arc shape that convex toward the central axis Ax.

[0119] Here, the number of magnet insertion holes 111 is 10. Therefore, the number of poles of the rotor 1 is 10. However, the number of poles of the rotor 1 is not limited to 10, as long as it is 2 or more. The magnet insertion holes 111 shown in Figure 13 extend in an arc shape, but they may also extend in a V-shape or a straight line, for example.

[0120] The permanent magnets 120 are made of ferrite magnets, and may be either sintered ferrite magnets or bonded ferrite magnets. Each permanent magnet 20 is magnetized in the thickness direction.

[0121] A resin portion 130 is provided between rotor core 110 and shaft 25. A protrusion 115 for preventing rotation that engages with the outer periphery of resin portion 130 may be formed on the inner periphery of rotor core 110. Note that shaft 25 may be fitted into the center hole of rotor core 110 without providing resin portion 130.

[0122] The rotor core 110 is divided into a plurality of split cores 116 in the circumferential direction. Each split core 116 has one magnet insertion hole 111. A dividing surface 112 is formed between adjacent split cores 116. The adjacent split cores 116 are fixed to each other at the dividing surface 112 by welding or by fitting concave and convex portions. Note that the rotor core 110 does not necessarily have to be divided into a plurality of split cores 116.

[0123] Fig. 14 is a cross-sectional view showing a rotor 200 according to another configuration example of embodiment 1. Rotor 200 shown in Fig. 14 has an annular rotor core 210 centered on central axis Ax, and permanent magnets 220 arranged on the outer peripheral surface of rotor core 210. Rotor core 110 is formed by stacking electromagnetic steel plates in the axial direction and fixing them with crimped portions (not shown).

[0124] The permanent magnet 220 is formed in an annular shape so as to cover the outer periphery of the rotor core 210. The permanent magnet 220 is made of a ferrite magnet, and may be either a sintered ferrite magnet or a bonded ferrite magnet. The permanent magnet 220 is magnetized in the thickness direction and has multiple magnetic poles in the circumferential direction.

[0125] The rotors 1, 100, and 200 shown in FIGS. 13 and 14 are merely examples, and the electric motor 2 of the first embodiment may be any motor that includes a rotor having a ferrite magnet.

[0126] <Hardware Configuration> Fig. 15 is a diagram showing an example of the hardware configuration of the control device 70. Each function of the control device 70 is realized by using a computer system such as a personal computer or a general-purpose computer.

[0127] The control device 70 includes a processor 91, a memory 92, an external storage device 93, an input device 94, and a display device 95. The processor 91, the memory 92, the external storage device 93, the input device 94, and the display device 95 are connected by a bus 96.

[0128] The processor 91 is, for example, a CPU (Central Processing Unit). The functions of the control device 70 are realized by the processor 91, software, firmware, or a combination of software and firmware. The software or firmware is written as a program and stored in the external storage device 93. The processor 91 reads the software or firmware stored in the external storage device 93 into the memory 92 and executes it.

[0129] The memory 92 is a random access memory (RAM), a read-only memory (ROM), a flash memory, or the like. The external storage device 93 is a hard disk drive (HDD), a solid state drive (SSD), or a cloud server. The input device 94 is, for example, a keyboard, a mouse, or a touch panel. The display device 95 is, for example, a display.

[0130] 7 can be realized by a processor 91 and a memory 92. In addition to the processor 91 and the memory 92, an input device 94 and a display device 95 may be used. The function of the storage device 72 can be realized by an external storage device 93.

[0131] <Effects of the Embodiment> As described above, the electric motor drive device 6 of the first embodiment drives the electric motor 2 including the stator 3 having the coil 35 and the rotor 1 having the permanent magnet 20 which is a ferrite magnet. The electric motor drive device 6 includes an inverter 62 that outputs a voltage to the coil 35 of the electric motor 2, and a control device 70 that controls the inverter 62. Before starting the electric motor 2, the control device 70 applies a superimposed voltage including a high-frequency AC component and a DC component, the frequency of which is higher than the operating frequency of the electric motor 2 during rotational operation, from the inverter 62 to the coil 35, thereby causing the coil 35 to generate heat without rotating the electric motor 2. The control device 70 also calculates the temperature of the permanent magnet 20 based on the detected values ​​of the current and voltage when the superimposed current is applied.

[0132] This configuration makes it possible to raise the temperature of the permanent magnets 20 before starting the electric motor 2 and suppress irreversible demagnetization of the ferrite magnets 20. Furthermore, because the temperature of the permanent magnets 20 is calculated based on the detected values ​​of the current and voltage when the superimposed current is applied, it is possible to prevent the permanent magnets 20 from overheating, and suppress a decrease in motor efficiency due to a decrease in saturation magnetic flux density and waste of input energy.

[0133] In addition, the control device 70 continues to apply the superimposed voltage to the coil 35 for more than the specified time, thereby allowing the permanent magnet 20 to be sufficiently heated, thereby enhancing the effect of suppressing irreversible demagnetization of the permanent magnet 20.

[0134] Furthermore, the control device 70 starts the electric motor 2 only after the calculated temperature of the permanent magnet 20 (i.e., the estimated temperature) reaches or exceeds the reference temperature, thereby suppressing irreversible demagnetization of the permanent magnet 20, preventing excessive heating of the permanent magnet 20, and suppressing a decrease in the efficiency of the electric motor.

[0135] The control device 70 corrects the control parameters when starting the electric motor 2 based on the calculated temperature of the permanent magnet 20, so that the rotational operation of the electric motor 2 can be controlled using accurate control parameters that reflect the temperature changes in the magnetic characteristics of the electric motor 2, thereby suppressing noise from the electric motor 2.

[0136] Furthermore, if the electric motor 2 is an IPM type in which the permanent magnets 20 are embedded inside the rotor 1, the temperature of the permanent magnets 20 can be increased by utilizing the heat generated by iron loss in the rotor core 10 by making the amplitude of the high-frequency AC component of the superimposed voltage larger than the magnitude of the DC component.

[0137] Furthermore, if the electric motor 2 is an SPM type having permanent magnets 20 on the surface of the rotor 1, the temperature of the permanent magnets 20 can be increased by utilizing heat generated by copper loss in the coil 35 by making the magnitude of the DC component of the superimposed voltage larger than the amplitude of the high-frequency AC component.

[0138] In addition, the control device 70 calculates the inductance of the electric motor 2 based on the detected values ​​of current and voltage when a superimposed voltage is applied to the coil 35, and calculates the temperature of the permanent magnet 20 based on the calculated inductance, so that temperature information of the permanent magnet 20 can be obtained without using a temperature sensor or the like.

[0139] The control device 70 has a memory device 72 that stores table data that corresponds the inductance of the electric motor 2 to the temperature of the permanent magnet 20, and therefore the temperature of the permanent magnet 20 can be calculated from the table data based on the inductance of the electric motor 2.

[0140] Furthermore, the coil 35 is made of aluminum wire, which has a higher electrical resistance than copper wire, so that the heat generated in the coil 35 can efficiently increase the temperature of the permanent magnet 20 .

[0141] 16 is a block diagram showing an electric motor drive device 6A according to embodiment 2. The electric motor drive device 6A according to embodiment 2 differs from the electric motor drive device 6 according to embodiment 1 in that a control device 70A includes an overcurrent protection circuit 73 and a protection level setting unit 74.

[0142] The current value detected by the current detection circuit 68, i.e., the current value of the current flowing through the coils 35U, 35V, and 35W, is input to the overcurrent protection circuit 73. When the current value of the current flowing through at least one of the coils 35U, 35V, and 35W exceeds an overcurrent protection level, the overcurrent protection circuit 73 outputs an abnormality signal to the control device 70A. The overcurrent protection level is also referred to as an overcurrent threshold or a cutoff value.

[0143] When the control device 70A receives an abnormality signal from the overcurrent protection circuit 73 while the electric motor 2 is rotating, it sends a stop signal to the inverter drive circuit 65. This causes the inverter drive circuit 65 to stop applying voltage from the inverter 62 to the coils 35U, 35V, and 35W.

[0144] The microcomputer 71 of the control device 70 has a protection level setting unit 74 that sets the overcurrent protection level in the overcurrent protection circuit 73. The protection level setting unit 74 can be configured as part of the microcomputer 71, but can also be realized by the processor 91 and memory 92 shown in FIG.

[0145] As shown in Figures 8(A) and (C), the protection level setting unit 74 sets the overcurrent protection level during preheating of the motor 2 (i.e., period A1) to be lower than the overcurrent protection level during rotational operation of the motor 2 (i.e., period A3).

[0146] When preheating the motor 2, irreversible demagnetization is likely to occur because the temperature of the permanent magnet 20 has not yet risen sufficiently. Therefore, to prevent irreversible demagnetization of the permanent magnet 20, the overcurrent protection level is set relatively small.

[0147] In contrast, when the motor 2 is rotating, the temperature of the permanent magnet 20 is sufficiently elevated, making irreversible demagnetization unlikely to occur. Therefore, by raising the overcurrent protection level, the startability of the motor 2 is improved and the range of the output torque or rotation speed of the motor 2 can be expanded.

[0148] Except for the points described above, the electric motor drive device 6A of the second embodiment is configured similarly to the electric motor drive device 6 of the first embodiment. Moreover, the electric motor 2, the compressor 5, and the air conditioner 4 of the second embodiment are configured similarly to those of the first embodiment.

[0149] As described above, in the second embodiment, the control device 70A has a protection level setting unit 74 that sets the overcurrent protection level, and the overcurrent protection level during preheating of the electric motor 2 is set lower than the overcurrent protection level during rotational operation of the electric motor 2. Therefore, irreversible demagnetization of the permanent magnets 20 is reliably suppressed during preheating of the electric motor 2, and the overcurrent protection level is raised during rotational operation of the electric motor 2, thereby achieving effects such as improved startability.

[0150] 17 is a block diagram showing an electric motor drive device 6B according to embodiment 3. The electric motor drive device 6B according to embodiment 3 differs from the electric motor drive device 6 according to embodiment 1 in that a control device 70B includes a history information management unit 75.

[0151] The history information management unit 75 acquires the usage history information of the electric motor 2 and stores it in the storage device 72. The usage history information of the electric motor 2 is, for example, the start time of use of the electric motor 2, i.e., the start time. In addition, the usage date and time of the electric motor 2, or the end time of use, etc. may be included.

[0152] The history information management unit 75 can be configured as a part of the microcomputer 71, but can also be realized by the processor 91 and memory 92 shown in Fig. 15. The history information management unit 75 and the storage device 72 correspond to a history information storage unit.

[0153] The microcomputer 71 of the control device 70 of the motor drive device 6B calculates the start-up time of the motor 2 based on the usage history information of the motor 2 stored in the storage device 72, and then calculates a time (referred to as a specified time) that is calculated by counting back the start-up time by the time required for preheating. When the specified time is reached, preheating of the motor 2 begins.

[0154] 18 is a flowchart showing the operation of the electric motor 2 driven by the electric motor drive device 6B of embodiment 3. The control device 70B calculates the start-up time of the electric motor 2 based on the usage history information of the electric motor 2 stored in the storage device 72, and determines whether a specified time before the start-up time has elapsed (step S20).

[0155] When the specified time has elapsed (Y in step S20), the control device 70B applies a superimposed voltage from the inverter 62 to the coil 35 to preheat the motor 2 (step S12). The application of the superimposed voltage is as described in the first embodiment.

[0156] Thereafter, as described in embodiment 1, the control device 70B detects the current and voltage (step S13) and estimates the temperature of the permanent magnet 20 (step S14), and when the estimated temperature of the permanent magnet 20 reaches the reference temperature (Y in step S15), it waits for reception of an activation signal (step S20).

[0157] Thereafter, when the control device 70B receives the start signal at the signal receiving unit 69 (Y in step S20), it starts the electric motor 2 (step S16). The subsequent steps S17 to S19 are the same as those described in the first embodiment.

[0158] In the first embodiment, the motor 2 is preheated after receiving the start signal, and then the motor 2 is started, so there is a time lag before the air conditioning device 4 starts operating. In the third embodiment, the control device 70B starts preheating the motor 2 before the start of use (i.e., the start time of the motor 2) based on the usage history information of the motor 2. Therefore, the motor 2 starts up immediately upon receiving the start signal, and the air conditioning device 4 starts operating. This can improve user comfort.

[0159] Except for the points mentioned above, the electric motor drive device 6B of the third embodiment is configured similarly to the electric motor drive device 6 of the first embodiment. In addition, the overcurrent protection circuit 73 and the protection level setting unit 74 of the second embodiment may be added. The electric motor 2, the compressor 5, and the air conditioner 4 of the third embodiment are configured similarly to those of the first embodiment.

[0160] As described above, in the third embodiment, the control device 70B has a history information management unit (history information management unit 75 and storage device 72) that stores usage history information of the electric motor 2, and starts applying a superimposed voltage to the coil 35 before the usage start time of the electric motor 2 that is determined from the usage history information. Therefore, upon receiving a start signal, the electric motor 2 can be started and the air conditioning device 4 can start operating, improving user comfort.

[0161] 19 is a block diagram showing an electric motor drive device 6C according to embodiment 4. The electric motor drive device 6C according to embodiment 4 differs from the electric motor drive device 6 according to embodiment 1 in that a control device 70C includes a learning unit 80.

[0162] 20A and 20B are schematic diagrams for explaining the concept of machine learning according to embodiment 4. As shown in Fig. 20A, the learning unit 80 of the control device 70C performs machine learning using, as training data, the operating state of the electric motor 2 during preheating and the control command value when applying a superimposed voltage to the coil 35 (hereinafter referred to as the control command value when the superimposed voltage is applied), and generates a trained model.

[0163] The operating state of the electric motor 2 is, for example, at least one of: (1) the detected value of the current, the detected value of the voltage, the detected value of the power, and the detected value of the frequency supplied to the coil 35 when the electric motor 2 is preheated; (2) the estimated temperature of the permanent magnet 20 described in the first embodiment; (3) the outside air temperature detected by a temperature sensor provided in the outdoor unit 4A of the air conditioning device 4; and (4) the cumulative application time of the superimposed voltage to the coil 35.

[0164] The control command value when the superimposed voltage is applied is, for example, at least one of: (1) a control command value for the magnitude of the DC component of the superimposed voltage applied to the coil 35; (2) a control command value for the amplitude of the high-frequency AC component; (3) a control command value for the frequency of the high-frequency AC component; and (4) a control command value for the phase of the high-frequency AC component.

[0165] As shown in Figure 20 (B), when the control device 70C receives a start signal at the signal receiving unit 69, it acquires the operating state of the electric motor 2, inputs the acquired operating state of the electric motor 2 into the learned model, and determines the control command value when the superimposed voltage is applied.

[0166] 21 is a functional block diagram showing a control device 70C. As shown in FIG. 21, a learning unit 80 provided in a microcomputer 71 of the control device 70C has a data acquisition unit 81 that acquires learning data including the operating state of the electric motor 2 and a control command value when a superimposed voltage is applied, and a model generation unit 82 that generates a trained model based on the acquired learning data. The storage device 72 of the control device 70C stores the trained model generated by the model generation unit 82.

[0167] The learning unit 80 (i.e., the data acquisition unit 81 and the model generation unit 82) can be configured as part of the microcomputer 71, but can also be realized by the processor 91 and memory 92 shown in Fig. 15. The learning unit 80 is also called an inference device.

[0168] As in the first embodiment, the microcomputer 71 of the control device 70C estimates the temperature of the permanent magnet 20 using table data (see FIG. 10 ) that associates the inductance of the electric motor 2 with the temperature of the permanent magnet 20. However, due to individual differences in the permanent magnet 20, the temperature of the permanent magnet 20 may not be the same even if the inductance of the electric motor 2 is the same, and an error may occur in the estimated temperature. Therefore, even if the estimated temperature of the permanent magnet 20 reaches the reference temperature, the actual temperature of the permanent magnet 20 may not reach the reference temperature or may exceed the reference temperature.

[0169] In the third embodiment, not only is the temperature of the permanent magnet 20 estimated by the microcomputer 71 of the control device 70C, but various operating states of the motor 2 are reflected in the control command value when the superimposed voltage is applied, using a learning model generated by the learning unit 80. Therefore, it becomes possible to more accurately reflect the actual temperature of the permanent magnet 20 in the superimposed voltage applied to the coil 35 when the motor 2 is preheated.

[0170] Except for the points mentioned above, the electric motor drive device 6C of the fourth embodiment is configured similarly to the electric motor drive device 6 of the first embodiment. In addition, the overcurrent protection circuit 73 and the protection level setting unit 74 of the second embodiment may be added, and the history information management unit 75 of the third embodiment may be added. The electric motor 2, the compressor 5, and the air conditioner 4 of the fourth embodiment are configured similarly to those of the first embodiment.

[0171] As described above, in the fourth embodiment, the control device 70C includes a learning unit 80 that generates a trained model that associates the operating state of the electric motor 2 with the control command value when the superimposed voltage is applied. The control device 70C also acquires the operating state of the electric motor 2 and calculates the control command value when the superimposed voltage is applied using the trained model generated by the learning unit 80. This enables control that more accurately reflects the actual temperature of the permanent magnets 20 when preheating the electric motor 2.

[0172] In the above-described first to fourth embodiments, an example has been described in which the electric motor 2 is incorporated into the compressor 5, but the electric motor 2 may be used as the electric motor 45a of the outdoor blower 45 or as the electric motor 46a of the indoor blower 46. In other words, the electric motor 2 may be used in at least one of the compressor 5, the outdoor blower 45, and the indoor blower 46.

[0173] Although the preferred embodiments have been specifically described above, the present disclosure is not limited to the above-described embodiments, and various improvements and modifications can be made.

[0174] REFERENCE SIGNS LIST 1 rotor, 2 electric motor, 3 stator, 4 air conditioner, 4A outdoor unit, 4B indoor unit, 5 compressor, 6, 6A, 6B, 6C electric motor drive device, 10 rotor core, 11 magnet insertion hole, 20 permanent magnet, 25 shaft, 30 stator core, 31 yoke, 32 teeth, 35, 35U, 35V, 35W coil, 42 outdoor heat exchanger, 43 pressure reducing device, 44 indoor heat exchanger, 45 outdoor blower, 46 indoor blower, 50 compression mechanism, 51 sealed container, 61 rectifier circuit, 62 inverter, 65 inverter drive circuit (PWM signal generating section), 66 voltage detection circuit, 67 current detection circuit, 68 current detection circuit 70, 70A, 70B, 70C Control device, 71 Microcomputer, 72 Storage device, 73 Overcurrent protection circuit, 74 Protection level setting unit, 75 History information management unit, 80 Learning unit, 81 Data acquisition unit, 82 Model generation unit, 83 Model generation unit.

Claims

1. An electric motor drive device for driving an electric motor having a stator with a coil and a rotor with a permanent magnet that is a ferrite magnet, comprising: an inverter that outputs a voltage to the coil of the electric motor; and a control device that controls the inverter, wherein before starting the electric motor, the control device applies to the coil from the inverter a superimposed voltage that includes high-frequency AC components and DC components at a frequency higher than the operating frequency of the electric motor when it is rotating, thereby causing the coil to heat up without rotating the electric motor, and the control device calculates the temperature of the permanent magnet based on the detected values of current and voltage when the superimposed voltage is applied.

2. The electric motor drive device according to claim 1, wherein the control device continues to apply the superimposed voltage to the coil for a specified time or longer.

3. The electric motor drive device according to claim 1 or 2, wherein the control device starts the electric motor when the calculated temperature of the permanent magnet becomes equal to or higher than a reference temperature.

4. The electric motor drive device according to any one of claims 1 to 3, wherein the control device corrects a control parameter when starting the electric motor based on the calculated temperature of the permanent magnet.

5. An electric motor drive device according to any one of claims 1 to 4, wherein the electric motor is an IPM type in which the permanent magnet is embedded inside the rotor, and the amplitude of the high frequency AC component contained in the superimposed voltage is greater than the magnitude of the DC component.

6. An electric motor drive device according to any one of claims 1 to 4, wherein the electric motor is an SPM type in which the permanent magnets are held on the surface of the rotor, and the magnitude of the DC component contained in the superimposed voltage is greater than the amplitude of the high-frequency AC component.

7. An electric motor drive device according to any one of claims 1 to 6, wherein the control device calculates the inductance of the electric motor based on the detected values of current and voltage when the superimposed voltage is applied to the coil, and calculates the temperature of the permanent magnet based on the inductance.

8. The electric motor drive device according to claim 7, wherein the control device has a memory unit that stores table data that associates the inductance of the electric motor with the temperature of the permanent magnet, and calculates the temperature of the permanent magnet from the table data based on the inductance of the electric motor.

9. The electric motor drive device according to any one of claims 1 to 8, further comprising a PWM signal generation unit that outputs a PWM signal to the inverter based on a control command value output from the control device, and the control device applies the superimposed voltage from the inverter to the coil via the PWM signal generation unit.

10. An electric motor drive device according to any one of claims 1 to 9, wherein the coil is made of aluminum wire.

11. An electric motor drive device according to any one of claims 1 to 10, wherein the control device has a protection level setting unit that sets an overcurrent protection level, and the overcurrent protection level when the superimposed voltage is applied to the coil is set lower than the overcurrent protection level during rotational operation of the electric motor.

12. An electric motor drive device as described in any one of claims 1 to 11, wherein the control device has a history information storage unit that stores usage history information of the electric motor, and starts applying the superimposed voltage to the coil at a specified time before the start time of use of the electric motor, which is determined from the usage history information stored in the history information storage unit.

13. An electric motor drive device according to any one of claims 1 to 12, wherein the control device generates a trained model that associates the operating state of the electric motor with a control command value when the superimposed voltage is applied, acquires the operating state of the electric motor, and calculates the control command value when the superimposed voltage is applied from the operating state using the trained model.

14. The electric motor drive device according to claim 13, wherein the control device has: a data acquisition unit that acquires learning data including the operating state of the electric motor and a control command value when the superimposed voltage is applied; and a model generation unit that uses the learning data to generate a trained model for inferring the control command value when the superimposed voltage is applied from the operating state of the electric motor.

15. An electric motor drive device according to claim 13 or 14, wherein the operating state of the electric motor includes at least one of the current, voltage, power and frequency when the superimposed voltage is applied, the temperature of the permanent magnet calculated by the control device, the outside air temperature and at least one of the cumulative application time of the superimposed voltage, and the control command value when the superimposed voltage is applied includes at least one of the control command value of the magnitude of the DC component when the superimposed voltage is applied, and the amplitude, frequency and phase of the high frequency AC component.

16. An air conditioning system comprising an electric motor drive device according to any one of claims 1 to 15, an indoor unit having an indoor heat exchanger and an indoor blower, and an outdoor unit having an outdoor heat exchanger, a compressor and an outdoor blower, wherein at least one of the compressor, the indoor blower and the outdoor blower has an electric motor driven by the electric motor drive device.

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