Motor drive device and motor

Abstract

[Problem] To provide a motor drive device capable of changing the magnetization state of a variable magnetic force magnet without using a switching element having a large current rating and without adding a switching element. [Solution] A motor 3 comprises a variable magnetic force magnet and a magnetization winding 9 for magnetizing the variable magnetic force magnet. One end of the magnetization winding 9 is electrically or magnetically connected to the connection points of upper and lower arm switching elements 18A-18F of all phases. A control device 2 for a motor drive device 1 is provided with a magnetization control unit that causes magnetization current to flow through the magnetization winding 9 by creating a period in which the upper arm switching elements 18A-18C of all phases or the lower arm switching elements 18D-18F of all phases are simultaneously turned on.

Description

Motor drive device and motor

[0001] The present invention relates to a motor drive device for driving a motor using a variable magnetic force magnet, and to a motor driven thereby.

[0002] In recent years, permanent magnet synchronous motors (PMSMs) have been adopted in electric vehicles and other applications to achieve high efficiency. These permanent magnet synchronous motors are well suited to electric vehicles that require a wide operating range, from low-speed / high-torque states to high-speed / low-torque states. However, they require flux-weakening control during high-speed rotation, which can cause a problem of reduced efficiency due to copper loss.

[0003] To solve this problem, variable magnetomotive force motors (VMFMs) have been researched. A variable magnetomotive force motor has a rotor embedded with fixed magnetomotive force magnets, which have high coercivity and a constant magnetic force / magnetization direction, and variable magnetomotive force magnets, which have low coercivity and a variable magnetic force / magnetization direction. Common methods include directly magnetizing the variable magnetomotive force magnets by passing a magnetizing current through a three-phase winding, or providing a magnetizing winding in addition to the three-phase winding and passing a magnetizing current through this magnetizing winding to change the magnetic force and magnetization direction of the variable magnetomotive force magnets (see, for example, Patent Documents 1 and 2). That is, the magnetic force of the variable magnetomotive force magnets is increased at low rotation speeds and decreased at high rotation speeds. This has led to the expectation that variable magnetomotive force motors will achieve improved efficiency and output at high rotation speeds.

[0004] Patent No. 5921244 Patent No. 5100169

[0005] However, when changing the magnetization state of the variable magnetic force magnet (magnetizing / demagnetizing) in a variable magnetic force motor, it is necessary to instantaneously pass a larger magnetizing current than when driving. For this reason, in the case of the method of direct magnetization using the three-phase winding mentioned above, a switching element made of a power semiconductor device with a large current rating is required. Furthermore, in the case of a method using a magnetizing winding, a separate switching element made of a power semiconductor device with a large current rating must be provided, and there is also the issue of a margin for the drive voltage relative to the DC voltage.

[0006] The present invention has been made to solve these conventional technical problems, and aims to provide a motor drive device that can change the magnetization state of a variable magnetic force magnet without using a switching element with a large current rating or adding an additional switching element, and a motor driven thereby.

[0007] A motor drive device of the present invention comprises an inverter circuit formed by connecting an upper arm switching element and a lower arm switching element in series for each phase between an upper arm power supply line and a lower arm power supply line, and a control device that controls the upper and lower arm switching elements of each phase of the inverter circuit, the junction of the upper and lower arm switching elements of each phase being connected to a three-phase winding of a motor to pass a three-phase current through the three-phase winding, the motor comprising a magnet with a high coercivity, two types of permanent magnets having a lower coercivity than the high coercivity magnet, and a magnetization winding for changing the magnetization state of the low coercivity magnet, one end of the magnetization winding being electrically or magnetically connected to the junction of the upper and lower arm switching elements of all phases, and the control device comprising a magnetization control section that passes a magnetization current through the magnetization winding by creating a period in which the upper arm switching elements of all phases or the lower arm switching elements of all phases are simultaneously ON.

[0008] A motor drive device of a second invention is characterized in that, in the above invention, the magnetization control unit causes a magnetizing current to flow through the magnetization winding by simultaneously turning on upper arm switching elements of all phases or lower arm switching elements of all phases.

[0009] The motor drive device of the third invention is characterized in that it comprises resonant capacitors connected between the magnetized windings and the connection points of the upper and lower arm switching elements of each phase, and the resonant circuits between these resonant capacitors and the magnetized windings prevent or suppress three-phase current from flowing through the magnetized windings.

[0010] A motor drive device of a fourth invention is characterized in that, in the above invention, it includes an interphase current interruption circuit connected between each resonant capacitor and the magnetized winding, and this interphase current interruption circuit blocks or suppresses current flowing through the magnetized winding when a phase-to-phase voltage is applied, and allows current to flow through the magnetized winding when a voltage is applied that turns on all upper arm switching elements or all lower arm switching elements.

[0011] A motor drive device of a fifth invention is characterized in that in the above invention, the interphase current interruption circuit has transformers for UVW phases, the primary and secondary sides of which have the same polarity, one end of the primary side connected to each resonant capacitor and one end of the secondary side connected to the magnetizing winding, the other end of the primary side of the U phase transformer connected to the other end of the secondary side of the W phase or V phase transformer, the other end of the primary side of the V phase transformer connected to the other end of the secondary side of the U phase or W phase transformer, and the other end of the primary side of the W phase transformer connected to the other end of the secondary side of the V phase or U phase transformer.

[0012] The motor drive device of the sixth invention is characterized in that it comprises a first neutral point capacitor and a second neutral point capacitor connected in series between the upper and lower arm power supply lines to generate a neutral point, and the other end of the magnetization winding is connected to the connection point of the first and second neutral point capacitors.

[0013] A motor of a seventh invention is driven by the motor drive device of any of the above inventions, and is characterized in that it comprises a stator on which a three-phase winding is wound, and a rotor on which magnets with high coercive force and magnets with low coercive force are provided, and the magnetized windings are wound around the teeth of the stator on which the three-phase winding is wound.

[0014] The motor of the eighth invention is driven by the motor drive device of the first to sixth inventions, and is characterized in that it comprises a stator wound with a three-phase winding and a rotor provided with magnets having high coercivity and magnets having low coercivity, the magnets having low coercivity being arranged circumferentially around the rotor, and magnetized windings being provided on the stator at positions corresponding to the magnets having low coercivity.

[0015] A motor of a ninth invention is driven by a motor drive device of any one of the first to sixth inventions, and is characterized in that it comprises a stator wound with a three-phase winding, and a rotor provided with magnets having high coercive force and magnets having low coercive force, the magnetized winding being provided on the rotor in the vicinity of the magnets having low coercive force, and power being supplied by contact or non-contact.

[0016] According to the present invention, a motor drive device is provided which includes an inverter circuit formed by connecting upper arm switching elements and lower arm switching elements in series for each phase between an upper arm power supply line and a lower arm power supply line, and a control device which controls the upper and lower arm switching elements of each phase of the inverter circuit, and connects the connection points of the upper and lower arm switching elements of each phase to a three-phase winding of a motor to pass a three-phase current through the three-phase winding, the motor is provided with a magnet with a high coercive force, two types of permanent magnets with a coercive force lower than the high coercive force magnet, and a magnetization winding for changing the magnetization state of the magnet with a low coercive force, One end of the winding is electrically or magnetically connected to the connection point of the upper and lower arm switching elements of all phases, and the control device is equipped with a magnetization control unit that causes a magnetizing current to flow through the magnetized winding by creating a period in which the upper arm switching elements of all phases or the lower arm switching elements of all phases are ON simultaneously.By using this magnetization control unit to turn ON the upper arm switching elements of all phases or the lower arm switching elements of all phases simultaneously, as in the second aspect of the invention, and causing a magnetizing current to flow through the magnetized winding, the current flowing through the upper arm switching element or lower arm switching element of one phase will be one-third of the magnetizing current.

[0017] In other words, it is possible to reduce the current rating of the switching element to one-third, and it becomes possible to change the magnetization state of a magnet with low coercive force without using a switching element with a high current rating.

[0018] Furthermore, as in the third aspect of the present invention, by connecting resonant capacitors between the magnetizing windings and the connection points of the upper and lower arm switching elements of each phase, and by using a resonant circuit between these resonant capacitors and the magnetizing windings to prevent or suppress three-phase current from flowing through the magnetizing windings, normal motor operation becomes possible. Furthermore, it becomes possible to suppress the voltage required to flow the magnetizing current, and it becomes possible to relax restrictions on the power supply voltage when magnetizing magnets with low coercive force at high speed rotation.

[0019] In this case, as in the fourth aspect of the invention, by connecting an interphase current blocking circuit between each resonant capacitor and the magnetized winding, and this interphase current blocking circuit blocking or suppressing the current flowing through the magnetized winding when a phase-to-phase voltage is applied, and allowing current to flow through the magnetized winding when a voltage is applied that turns on all the upper arm switching elements or all the lower arm switching elements, it becomes possible to achieve even more normal motor drive.

[0020] This phase-to-phase current interruption circuit can be configured, for example, as in the fifth aspect of the invention, by transformers for U, V, and W phases, the primary and secondary sides of which have the same polarity, one end of the primary connected to each resonant capacitor, and one end of the secondary connected to the magnetizing winding, with the other end of the primary of the U phase transformer connected to the other end of the secondary of the W phase or V phase transformer, the other end of the primary of the V phase transformer connected to the other end of the secondary of the U phase or W phase transformer, and the other end of the primary of the W phase transformer connected to the other end of the secondary of the V phase or U phase transformer.

[0021] As a result, when a phase-to-phase voltage is applied, each transformer in the phase-to-phase current interruption circuit acts to suppress current in the same direction, and when a voltage is applied that turns on the upper arm switching elements of all phases or the lower arm switching elements of all phases, each transformer acts to pass current in the opposite direction as is.In this case, the current that passes is only the all-phase component, so it is possible to configure the circuit using a small-capacity transformer.

[0022] Furthermore, as in the sixth aspect of the present invention, by providing a first neutral point capacitor and a second neutral point capacitor that are connected in series between the upper and lower arm power supply lines to generate a neutral point, and connecting the other end of the magnetization winding to the connection point of the first and second neutral point capacitors, there is no longer a need to provide a special switching element to magnetize a magnet with low coercive force, and it is possible to reduce the number of devices.

[0023] Here, the motor driven by the motor drive device of each of the above inventions has, as in the seventh invention, a stator on which a three-phase winding is wound, and a rotor on which magnets with high coercive force and magnets with low coercive force are provided, and in this case, the magnetized winding is wound around the teeth of the stator on which the three-phase winding is wound.

[0024] Alternatively, as in the eighth aspect of the present invention, low-coercive magnets may be arranged circumferentially around the rotor, and magnetization windings may be provided on the stator at positions corresponding to the low-coercive magnets. In this case, low-coercive magnets can be magnetized over a wide circumferential range, which alleviates or eliminates restrictions on the position of the low-coercive magnets when magnetizing them.

[0025] Alternatively, as in the ninth aspect of the present invention, the magnetization winding may be provided on the rotor near the magnet with low coercivity, and power may be supplied by contact or non-contact means. In this case, there is an advantage that magnetization can be performed regardless of the position of the magnet with low coercivity.

[0026] 1 is an electrical circuit diagram of a motor drive device according to an embodiment of the present invention. FIG. 2 is a block diagram of a control device according to an embodiment of the motor drive device of FIG. 1. FIG. 3 is a partial cross-sectional plan view of a motor according to an embodiment of the present invention. FIG. 4 is a diagram showing three-phase current waveforms during normal motor driving. FIG. 5 is a diagram showing current waveforms at various parts when magnetizing the variable magnetic force magnet of FIG. 3. FIG. 6 is an electrical circuit diagram of a motor drive device according to another embodiment of the present invention. FIG. 7 is a diagram showing a specific configuration of the interphase current cut-off circuit of FIG. 6 (when a phase-to-phase voltage is applied between U and W). FIG. 8 is a diagram showing a specific configuration of the interphase current cut-off circuit of FIG. 6 (when a voltage with all phases ON is applied). FIG. 9 is a partial cross-sectional plan view of a motor according to another embodiment of the present invention. FIG. 10 is a perspective view of the stator of the motor of FIG. 9. FIG. 11 is a partial longitudinal cross-sectional view of a motor according to yet another embodiment of the present invention, driven by the motor drive device of the present invention.

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0028] Figure 1 is an electrical circuit diagram of a motor drive device 1 according to one embodiment of the present invention, Figure 2 is a block diagram of a control device 2 of the motor drive device 1, and Figure 3 is a partial cross-sectional plan view of a motor 3 driven by the motor drive device 1. The motor drive device 1 of the embodiment is mounted on a so-called inverter-integrated electric compressor that drives a compression mechanism using the motor 3, and the electric compressor constitutes a refrigerant circuit of a vehicle air conditioner that conditions the interior of an electric vehicle, for example.

[0029] (1) Configuration of Motor 3 First, the structure of the motor 3 that is driven by the motor drive device 1 of the present invention will be described with reference to Fig. 3. The motor 3 in this embodiment is a permanent magnet synchronous motor (PMSM), and as shown in Fig. 3, it is made up of a stator 4 and a rotor 6 that rotates inside the stator 4. This rotor 6 is attached to the rotating shaft of the electric compressor described above, and this rotating shaft drives the compression mechanism described above.

[0030] The stator 4 of the motor 3 of the embodiment includes a stator core 7 made of laminated electromagnetic steel sheets, three-phase windings 8U, 8V, and 8W (star connection) for U, V, and W phases wound around the stator core 7, and a magnetizing winding 9. The stator core 7 has a plurality of teeth 12 (12 in the embodiment) extending radially inward from a cylindrical yoke portion 11, and a three-phase winding 8U, 8V, or 8W is wound around each tooth 12. In the embodiment, the magnetizing winding 9 is wound around the teeth 12 in a series configuration using two of the three-phase windings (a U-phase three-phase winding 8U and a V-phase three-phase winding 8V in the embodiment).

[0031] In this case, the magnetization winding 9 uses a thinner coil than the three-phase windings 8U to 8W, and has a high number of turns to save space. Although copper loss due to the magnetization current increases in the magnetization winding 9, this is considered acceptable due to the instantaneous current flow (pulse) as described below. The space ratio between the three-phase windings 8U to 8W and the magnetization winding 9 is designed to be optimal, taking into account the torque characteristics of the motor 3 and the magnetization characteristics of the variable magnetic force magnet 13 described below.

[0032] On the other hand, the rotor 6 of the motor 3 includes two types of permanent magnets: a rotor core 16, a plurality of fixed magnetic force magnets 17 (high-coercivity magnets according to the present invention) embedded radially inside the rotor core 16, and a plurality of variable magnetic force magnets 13 (low-coercivity magnets according to the present invention) embedded radially outside the fixed magnetic force magnets 17. That is, the motor 3 is a variable magnetomotive force motor (VMFM). In this case, for example, NdFeB magnets are used as the fixed magnetic force magnets 17. On the other hand, for the variable magnetic force magnets 13, permanent magnets whose magnetization state (magnitude and direction of magnetic force) can be changed by a magnetic field, such as alnico magnets, are used. The coercive force of the NdFeB magnet that constitutes the fixed magnetic force magnet 17 is 1000 kA / m, and the coercive force of the Alnico magnet that constitutes the variable magnetic force magnet 13 is 120 kA / m, so the coercive force of the variable magnetic force magnet 13 is lower than the coercive force of the fixed magnetic force magnet 17.

[0033] In the present embodiment, the fixed magnetic force magnet 17 is disposed facing the aforementioned rotation axis, and the variable magnetic force magnets 13 are disposed extending from the inside to the outside in the radial direction, spaced apart from each other, on both sides of the fixed magnetic force magnet 17. A set of the fixed magnetic force magnet 17 and two variable magnetic force magnets 13 constitutes one magnetic pole, and eight such sets are provided to constitute eight magnetic poles.

[0034] (2) Configuration of Motor Drive Device 1 Next, a description will be given of the configuration of the motor drive device 1 of the embodiment. The motor drive device 1 of the embodiment includes a three-phase inverter circuit 21, a control device 2, and the like.

[0035] (2-1) Inverter Circuit 21 The inverter circuit 21 of this embodiment is a circuit that converts the DC voltage of a DC power source (vehicle battery: for example, 300 V) 23 into a three-phase AC voltage and applies the voltage to the motor 3, thereby causing a three-phase current to flow through the motor 3. This inverter circuit 21 has a U-phase half-bridge circuit 19U, a V-phase half-bridge circuit 19V, and a W-phase half-bridge circuit 19W, and each of the half-bridge circuits 19U to 19W for each phase has upper arm switching elements 18A to 18C and lower arm switching elements 18D to 18F. Furthermore, a flywheel diode 24 is connected in anti-parallel to each of the switching elements 18A to 18F.

[0036] In this embodiment, each of the switching elements 18A to 18F is made up of an insulated gate bipolar transistor (IGBT) or the like, which is a power semiconductor device incorporating a MOS structure in the gate portion.

[0037] The upper ends of the upper arm switching elements 18A to 18C of the inverter circuit 21 are connected to an upper arm power supply line (positive bus) 26 of the DC power supply 23. On the other hand, the lower ends of the lower arm switching elements 18D to 18F of the inverter circuit 21 are connected to a lower arm power supply line (negative bus) 27 of the DC power supply 23.

[0038] In this case, the upper arm switching element 18A and the lower arm switching element 18D of the U-phase half-bridge circuit 19U are connected in series, the upper arm switching element 18B and the lower arm switching element 18E of the V-phase half-bridge circuit 19V are connected in series, and the upper arm switching element 18C and the lower arm switching element 18F of the W-phase half-bridge circuit 19W are connected in series.

[0039] The connection point between the upper arm switching element 18A and the lower arm switching element 18D of the U-phase half-bridge circuit 19U is connected to the U-phase three-phase winding 8U of the motor 3, the connection point between the upper arm switching element 18B and the lower arm switching element 18E of the V-phase half-bridge circuit 19V is connected to the V-phase three-phase winding 8V of the motor 3, and the connection point between the upper arm switching element 18C and the lower arm switching element 18F of the W-phase half-bridge circuit 19W is connected to the W-phase three-phase winding 8W of the motor 3.

[0040] In this embodiment, one end of a U-phase resonant capacitor 28U is electrically connected to the connection point between the upper arm switching element 18A and the lower arm switching element 18D of the U-phase half-bridge circuit 19U, one end of a V-phase resonant capacitor 28V is electrically connected to the connection point between the upper arm switching element 18B and the lower arm switching element 18E of the V-phase half-bridge circuit 19V, and one end of a W-phase resonant capacitor 28W is electrically connected to the connection point between the upper arm switching element 18C and the lower arm switching element 18F of the W-phase half-bridge circuit 19W.

[0041] (2-2) Resonance circuit 31 The other ends of the resonant capacitors 28U to 28W for each of the U, V and W phases are connected to one end of the magnetized winding 9. That is, the resonant capacitors 28U to 28W for each of the U, V and W phases are electrically connected between the magnetized winding 9 and the connection point of the upper and lower arm switching elements 18A and 18D, the connection point of the upper and lower arm switches 18B and 18E, and the connection point of the upper and lower arm switches 18C and 18F, respectively. As a result, the magnetized winding 9 is electrically connected to the connection point of the upper and lower arm switching elements 18A and 18D, the connection point of the upper and lower arm switches 18B and 18E, and the connection point of the upper and lower arm switches 18C and 18F via the resonant capacitors 28U to 28W.

[0042] Each of the resonant capacitors 28U to 28W, together with the magnetizing winding 9, constitutes a resonant circuit 31 (LC resonant circuit). The resonance point of this resonant circuit 31 is set to be at or near the frequency of a magnetizing voltage, which will be described later, and to a value that is away from the frequencies of the three-phase voltages (U-phase voltage Vu, V-phase voltage Vv, and W-phase voltage Vw, which will be described later). Therefore, the resonant circuit 31 has a low impedance with respect to the magnetizing voltage, allowing a magnetizing current to flow through the magnetizing winding 9, and a high impedance with respect to the three-phase voltage, preventing or suppressing the flow of three-phase current through the magnetizing winding 9.

[0043] A series circuit of a first neutral point capacitor 32 and a second neutral point capacitor 33 is connected between the upper arm power supply line 26 and the lower arm power supply line 27 of the DC power supply 23. The first neutral point capacitor 32 and the second neutral point capacitor 33 have the same capacitance, and their junction point is at the potential of the neutral point of the motor 3 (the neutral point potential of the star-connected three-phase windings 8U to 8W). The other end of the magnetization winding 9 is connected to the junction point of the first and second neutral point capacitors 32, 33.

[0044] (2-3) Control Device 2 Next, the configuration of the control device 2 will be described with reference to Fig. 2. In this embodiment, the control device 2 is composed of a microcomputer having a processor, and receives operation commands and rotation speed commands from the vehicle ECU 34, and receives motor current (phase current) from the motor 3, and controls the ON / OFF state (switching) of each of the switching elements 18A to 18F of the inverter circuit 21 based on these commands. Specifically, it controls the gate voltage applied to the gate terminal of each of the switching elements 18A to 18F.

[0045] The control device 2 of the embodiment has a motor control unit 35, a PWM signal generation unit 36, a gate driver 37, a magnetization control unit 38, and a magnetization PWM signal generation unit 39. The control device 2 also has current sensors (not shown) for measuring U-phase current Iu, V-phase current Iv, and W-phase current Iw, which are motor currents of each phase (phase currents) required to detect the magnetic pole position of the rotor 6 of the motor 3, and this information is input to the motor control unit 35.

[0046] The motor control unit 35 calculates and generates three-phase modulated voltage command values ​​Vu' (hereinafter referred to as U-phase voltage command value Vu'), Vv' (hereinafter referred to as V-phase voltage command value Vv'), and Vw' (hereinafter referred to as W-phase voltage command value Vw') for generating three-phase voltages of U-phase voltage Vu, V-phase voltage Vv, and W-phase voltage Vw to be applied to each of the three-phase windings 8U to 8W of the motor 3, by vector control based on the electrical angle of the motor 3, the current command value, and the d-axis current and q-axis current obtained from the phase currents.

[0047] The PWM signal generating unit 36 ​​receives the three-phase modulation voltage command values ​​Vu', Vv', Vw' calculated by the motor control unit 35, and compares the magnitude of these three-phase modulation voltage command values ​​Vu', Vv', Vw' with that of a carrier signal (e.g., a sawtooth wave carrier), thereby generating and outputting PWM signals that serve as drive command signals for the U-phase half-bridge circuit 19U, the V-phase half-bridge circuit 19V, and the W-phase half-bridge circuit 19W of the inverter circuit 21.

[0048] The magnetization control unit 38 receives a magnetization command and position information of the rotor 6 from the motor control unit 35, and when a magnetization command is received from the magnetization control unit 38, it generates magnetization voltage command values ​​Vum', Vvm', Vwm' for generating a magnetization voltage Vm for passing a pulsed magnetization current Im to the magnetization winding 9 to change (magnetize / demagnetize) the magnetized state of the variable magnetic force magnet 13. In this case, based on the position information of the rotor 6, the magnetization control unit 38 generates the magnetization voltage command values ​​Vum', Vvm', Vwm' at the timing when the variable magnetic force magnet 13 reaches a position corresponding to the magnetization winding 9.

[0049] The magnetization PWM signal generation unit 39 of the embodiment receives the magnetization voltage command values ​​Vum', Vvm', Vwm' output by the magnetization control unit 38 as input, and generates and outputs magnetization PWM signals that also serve as drive command signals for the U-phase half-bridge circuit 19U, the V-phase half-bridge circuit 19V, and the W-phase half-bridge circuit 19W of the inverter circuit 21. The magnetization PWM signal in the case of the embodiment is a signal that simultaneously turns ON the upper arm switching element 18A of the U-phase half-bridge circuit 19U, the upper arm switching element 18B of the V-phase half-bridge circuit 19V, and the upper arm switching element 18C of the W-phase half-bridge circuit 19W (i.e., the upper arm switching elements of all phases) (the lower arm switching elements 18D to 18F of all phases are OFF).

[0050] The magnetization PWM signal is not limited to the above, and may be a signal that simultaneously turns on the lower arm switching element 18D of the U-phase half-bridge circuit 19U, the lower arm switching element 18E of the V-phase half-bridge circuit 19V, and the lower arm switching element 18F of the W-phase half-bridge circuit 19W (i.e., the lower arm switching elements of all phases) (in this case, the upper arm switching elements 18A to 18C of all phases are OFF).

[0051] The magnetization PWM signal output by the magnetization PWM signal generation unit 39 is superimposed on the PWM signals output by these PWM signal generation units 36 and input to the gate driver 37. Based on the PWM signal on which the magnetization PWM signal is superimposed, the gate driver 37 generates gate voltages for the upper arm switching element 18A and the lower arm switching element 18D of the U-phase half-bridge circuit 19U, gate voltages for the upper arm switching element 18B and the lower arm switching element 18E of the V-phase half-bridge circuit 19V, and gate voltages for the upper arm switching element 18C and the lower arm switching element 18F of the W-phase half-bridge circuit 19W.

[0052] Each of the switching elements 18A to 18F of the inverter circuit 28 is driven to turn on and off based on the gate voltage output from a gate driver 37. That is, when the gate voltage is in the ON state (a predetermined voltage value), the switching element operates to turn on, and when the gate voltage is in the OFF state (zero), the switching element operates to turn off. When the switching elements 18A to 18F are the IGBTs described above, the gate driver 37 is a circuit for applying the gate voltage to the IGBTs based on a PWM signal, and is composed of a photocoupler, a logic IC, a transistor, etc.

[0053] The voltage at the connection point between the upper arm switching element 18A and the lower arm switching element 18D of the U-phase half-bridge circuit 19U is applied (output) as a U-phase voltage Vu (three-phase voltage) to the U-phase three-phase winding 8U of the motor 3, the voltage at the connection point between the upper arm switching element 18B and the lower arm switching element 18E of the V-phase half-bridge circuit 19V is applied (output) as a V-phase voltage Vv (three-phase voltage) to the V-phase three-phase winding 8V of the motor 3, and the voltage at the connection point between the upper arm switching element 18C and the lower arm switching element 18F of the W-phase half-bridge circuit 19W is applied (output) as a W-phase voltage Vw (three-phase voltage) to the W-phase three-phase winding 8W of the motor 3.

[0054] Furthermore, the voltage at the connection point between the upper arm switching element 18A and the lower arm switching element 18D of the U-phase half-bridge circuit 19U, the voltage at the connection point between the upper arm switching element 18B and the lower arm switching element 18E of the V-phase half-bridge circuit 19V, and the voltage at the connection point between the upper arm switching element 18C and the lower arm switching element 18F of the W-phase half-bridge circuit 19W are applied (output) to the magnetized winding 9 of the motor 3 via resonant capacitors 28U to 28W, respectively.

[0055] (3) Operation of the control device 2 (3-1) During normal motor driving Next, the actual control operation of the control device 2 will be described with reference to Figures 4 and 5. Figure 4 shows the waveforms of three-phase currents Iu, Iv, and Iw during normal motor driving, in which three-phase voltages (phase voltages for each of the U, V, and W phases) generated by the PWM signals output by the PWM signal generating unit 36 ​​are applied to the three-phase windings 8U to 8W of the motor 3. During normal motor driving, a phase-to-phase voltage is applied between the phases, causing sinusoidal three-phase currents Iu, Iv, and Iw that are shifted in phase by 120° to flow through the windings 8U to 8W of the motor 3.

[0056] 4 also shows the magnetizing current Im at this time. The voltage at the connection point between the upper arm switching element 18A and the lower arm switching element 18D of the U-phase half-bridge circuit 19U, the voltage at the connection point between the upper arm switching element 18B and the lower arm switching element 18E of the V-phase half-bridge circuit 19V, and the voltage at the connection point between the upper arm switching element 18C and the lower arm switching element 18F of the W-phase half-bridge circuit 19W, i.e., the three-phase voltages (U-phase voltage Vu, V-phase voltage Vv, and W-phase voltage Vw) in this case, are also applied to the magnetizing winding 9 of the motor 3 via the resonant capacitors 28U to 28W. However, as described above, the resonance point of the resonant circuit 31 formed by the resonant capacitors 28U to 28W and the magnetizing winding 9 is set to a value that is far from the frequency of the three-phase voltages (U-phase voltage Vu, V-phase voltage Vv, and W-phase voltage Vw), so the impedance with respect to the three-phase voltages is high. Therefore, no or almost no magnetizing current Im flows through the magnetizing winding 9. As a result, the motor 3 is driven normally.

[0057] (3-2) Magnetizing the Variable Coercive Force Magnet 13 Next, the magnetization control unit 38 outputs magnetization voltage command values ​​Vum, Vvm, and Vwm to magnetize the variable coercive force magnet 13, and the magnetization PWM signal control unit 39 outputs a magnetization PWM signal based on these values, and the current waveforms of each unit when this is done are shown in Fig. 5. As described above, the magnetization control unit 38 passes a pulse-like magnetization current Im of a predetermined width through the magnetization winding 9 at the timing when the variable coercive force magnet 13 comes to a position corresponding to the magnetization winding 9, based on the position information of the rotor 6, thereby magnetizing the variable coercive force magnet 13. At this time, in this embodiment, as described above, the upper arm switching element 18A of the U-phase half-bridge circuit 19U, the upper arm switching element 18B of the V-phase half-bridge circuit 19V, and the upper arm switching element 18C of the W-phase half-bridge circuit 19W (i.e., the upper arm switching elements of all phases) are turned ON simultaneously. At this time, the lower arm switching elements 18D to 18F of all phases are turned OFF.

[0058] At this time, if the U-phase upper arm current flowing through the upper arm switching element 18A is Ipu, the V-phase upper arm current flowing through the upper arm switching element 18B is Ipv, and the W-phase upper arm current flowing through the upper arm switching element 18C is Ipw, then as described above, the resonance point of the resonant circuit 31 consisting of each of the resonant capacitors 28U to 28W and the magnetization winding 9 is set at or near the frequency of the magnetization voltage Vm, and therefore the impedance of the resonant circuit 31 with respect to the magnetization voltage Vm is extremely small or extremely low, and the magnetization current Im flows through the magnetization winding 9.

[0059] Furthermore, the magnetizing current Im at this time is the sum of the U-phase upper arm current Ipu, the V-phase upper arm current Ipv, and the W-phase upper arm current Ipw, i.e., three times their value (Im = Ipu + Ipv + Ipw). This large pulse-like magnetizing current Im (see FIG. 5) accurately changes the magnetized state of the variable magnetic force magnet 13.

[0060] As described above, the motor drive device 1 of the present invention drives a motor 3 that is equipped with a variable magnetic force magnet 13 and a magnetization winding 9 for magnetizing this variable magnetic force magnet 13, and one end of the magnetization winding 9 is connected to the connection point of the upper and lower arm switching elements 18A to 18F of all phases, and the control device 2 is equipped with a magnetization control unit 38 that causes a magnetization current Im to flow through the magnetization winding 9 by simultaneously turning on the upper arm switching elements 18A to 18C of all phases or the lower arm switching elements 18D to 18F of all phases. By using this magnetization control unit 38 to simultaneously turn on the upper arm switching elements 18A to 18C of all phases or the lower arm switching elements 18D to 18F of all phases and causing the magnetization current Im to flow through the magnetization winding 9, the current (Ipu, Ipv, Ipw) flowing through the upper arm switching elements 18A to 18C or lower arm switching elements 18D to 18F of one phase becomes one-third of the magnetization current Im.

[0061] In other words, the current rating of the switching elements 18A to 18F can be reduced to one third, and the magnetization state of the variable magnetic force magnet 13 can be changed without using switching elements with a large current rating.

[0062] In addition, in this embodiment, resonant capacitors 28U to 28W are connected between the connection point of the magnetization winding 9 and the upper and lower arm switching elements 18A to 18F of each phase, and a resonant circuit 31 between these resonant capacitors 28U to 28W and the magnetization winding 9 prevents or suppresses the three-phase currents Iu, Iv, and Iw from flowing through the magnetization winding 9, enabling normal motor drive. Also, it becomes possible to suppress the voltage required to flow the magnetization current Im, and it becomes possible to alleviate restrictions on the power supply voltage when magnetizing the variable magnetic force magnet 13 during high-speed rotation.

[0063] In addition, in the embodiment, a first neutral point capacitor 32 and a second neutral point capacitor 33 are provided which are connected in series between the upper and lower arm power supply lines 26, 27 to generate a neutral point, and the other end of the magnetized winding 9 is connected to the connection point of the first and second neutral point capacitors 32, 33.

[0064] Here, when the upper arm switching elements 18A to 18C of all phases are turned ON simultaneously as in the embodiment, if the other end of the magnetization winding 9 is not connected to the connection point of the neutral point capacitors 32, 33 as in the embodiment, it becomes necessary to provide a special switching element between this other end and the lower arm power supply line 27. However, by connecting the other end of the magnetization winding 9 to the connection point of the neutral point capacitors 32, 33 as in the embodiment, it becomes unnecessary to provide a special switching element related to magnetizing the variable magnetic force magnet 13, and it becomes possible to reduce the number of devices.

[0065] Next, Figure 6 shows an electrical circuit diagram of a motor drive device 1 according to another embodiment of the present invention. In this figure, the same reference numerals as in Figures 1 to 5 denote the same components, and their explanations will be omitted. In this embodiment, an interphase current interruption circuit 41 is provided between each of the resonant capacitors 28U to 28W and the magnetization winding 9.

[0066] In the embodiment described above, the resonant circuit 31 is configured by connecting the resonant capacitors 28U to 28W in series with the magnetized winding 9, but there is a risk that some three-phase current may flow due to the balance of each part. The interphase current cut-off circuit 41 is provided to eliminate or suppress this risk.

[0067] This phase-to-phase current cut-off circuit 41 is a circuit that blocks or suppresses the current flowing through the magnetized winding 9 when a phase-to-phase voltage is applied, and that allows current to flow through the magnetized winding 9 when a voltage that turns on all of the upper arm switching elements 18A to 18C or all of the lower arm switching elements 18D to 18F is applied, and its specific configuration is shown in FIG. 7.

[0068] The interphase current interruption circuit 41 of the embodiment is composed of three transformers 46 to 48 for the U, V, and W phases. The primary side 46P and secondary side 46S of the U-phase transformer 46 have the same polarity, the primary side 47P and secondary side 47S of the V-phase transformer 47 also have the same polarity, and the primary side 48P and secondary side 48S of the W-phase transformer 48 also have the same polarity.

[0069] One end of a primary side 46P of the U-phase transformer 46 is connected to the resonant capacitor 28U, one end of a primary side 47P of the V-phase transformer 47 is connected to the resonant capacitor 28V, and one end of a primary side 48P of the W-phase transformer 48 is connected to the resonant capacitor 28W. In addition, one end of a secondary side 46S of the U-phase transformer 46, one end of a secondary side 47S of the V-phase transformer 47, and one end of a secondary side 48S of the W-phase transformer 48 are connected to the magnetization winding 9.

[0070] Furthermore, the other end of the primary side 46P of the transformer 46 for the U phase is connected to the other end of the secondary side 48S of the transformer 48 for the W phase, the other end of the primary side 47P of the transformer 47 for the V phase is connected to the other end of the secondary side 46S of the transformer 46 for the U phase, and the other end of the primary side 48P of the transformer 48 for the W phase is connected to the other end of the secondary side 47S of the transformer 47 for the V phase.

[0071] With the above configuration, the operation of the interphase current interruption circuit 41 of the embodiment will now be described with reference to Figures 7 and 8. For example, when the upper arm switching element 18A of the U-phase half-bridge circuit 19U is ON and the lower arm switching element 18F of the W-phase half-bridge circuit 19W is ON and an interphase voltage is applied to the interphase current interruption circuit 41, current will try to flow from the U-phase to the W-phase as shown by the dashed arrows in Figure 7, but at this time, the transformers 46 to 48 work to suppress current in the same direction, so no current flows through the magnetized winding 9 and the current entering from the U-phase to the W-phase (dashed arrow in Figure 7) is also suppressed.

[0072] On the other hand, when a voltage that turns on all upper-arm switching elements 18A to 18C of all phases simultaneously is applied to interphase current interruption circuit 41, current flows as shown by the dashed arrows in Figure 8. At this time, each transformer 46 to 48 acts to pass current in the reverse direction as is, so current of all phases flows through magnetized winding 9. At this time, the current that passes is only the component of all phases, so interphase current interruption circuit 41 can be configured with small-capacity transformers 46 to 47. The same applies when a voltage that turns on all lower-arm switching elements 18D to 18F of all phases simultaneously is applied.

[0073] Incidentally, instead of the above connection example, the other end of the primary side 46P of the U-phase transformer 46 may be connected to the other end of the secondary side 47S of the V-phase transformer 47, the other end of the primary side 47P of the V-phase transformer 47 may be connected to the other end of the secondary side 48S of the W-phase transformer 48, and the other end of the primary side 48P of the W-phase transformer 48 may be connected to the other end of the secondary side 46S of the U-phase transformer 46, which will produce the same results.

[0074] In this way, by connecting an interphase current interruption circuit 41 between each of the resonant capacitors 28U to 28W and the magnetized winding 9, and this interphase current interruption circuit 41 blocking or suppressing the current flowing to the magnetized winding 9 when a phase-to-phase voltage is applied, and allowing current to flow to the magnetized winding 9 when a voltage that turns on all of the upper arm switching elements 18A to 18C or all of the lower arm switching elements 18D to 18F is applied, it becomes possible to achieve even more normal motor drive.

[0075] Next, another embodiment of the motor 3 driven by the motor drive device 1 of the present invention will be described with reference to Figures 9 and 10. In each figure, the same reference numerals as in Figure 3 denote the same or similar functions. Each figure also shows the three-phase windings 8U-8W cut at the end surfaces of the teeth 12. Figure 9 also shows a cut surface of the fixed magnetic force magnet 17, the magnetized winding 9, and the variable magnetic force magnet 13.

[0076] In this embodiment, the fixed magnetic force magnets 17 are arranged radially outside the rotor core 16, at both axial ends of the rotor core 16 (only one end is shown in FIG. 9 ). The variable magnetic force magnets 13 are arranged circumferentially inside the rotor core 16. The fixed magnetic force magnets 17 and the variable magnetic force magnets 13 form magnetic poles, as described above.

[0077] Furthermore, in this embodiment, slots 51 are formed in the circumferential direction at positions corresponding to the variable magnetic force magnets 13 on the inner peripheral surface of the stator core 7, and magnetizing windings 9 are arranged in these slots 51. In this embodiment, the magnetizing windings 9 are arranged around the entire circumference of the inner peripheral surface of the stator core 7. With this configuration, the variable magnetic force magnets 13 can be magnetized by the magnetizing windings 9 over a wide range in the circumferential direction in the form of a three-dimensional magnetic path. This makes it possible to alleviate or eliminate restrictions on the magnetic pole positions of the rotor 6 when magnetizing the variable magnetic force magnets 13, i.e., on the positions of the variable magnetic force magnets 13 on the rotating rotor 6.

[0078] Next, another embodiment of the motor 3 driven by the motor drive device 1 of the present invention will be described with reference to Figure 11. In each figure, the same reference numerals as in Figures 3, 9 and 10 denote the same or similar functions.

[0079] In this embodiment, the variable magnetic force magnet 13 is disposed facing the aforementioned rotation axis, and the fixed magnetic force magnets 17 are disposed extending from the inside to the outside in the radial direction while being spaced apart from each other on both sides of the variable magnetic force magnet 13. A set of such a variable magnetic force magnet 13 and two fixed magnetic force magnets 17 constitutes one magnetic pole, and eight such sets are provided to constitute eight magnetic poles.

[0080] Furthermore, the magnetization windings 9 are not provided on the stator core 7, but on the rotor core 16 around each variable magnetic force magnet 13. Note that in Figure 11 the magnetization windings 9 are cut at the end face of the rotor core 16 to show the end face of the variable magnetic force magnet 13. By providing the magnetization windings 9 on the rotor core 16 in this way, magnetization can be achieved without being limited by the magnetic pole position of the rotor 6, i.e., the position of the rotating variable magnetic force magnet 13.

[0081] In this case, however, power is supplied to the magnetized winding 9 by a slip ring or brush (contact), or by a rotary transformer in a non-contact manner.

[0082] In the embodiment, when the magnetizing current Im is passed through the magnetizing winding 9, the upper arm switching elements 18A to 18C of all phases or the lower arm switching elements 18D to 18F of all phases are turned ON simultaneously, but the instantaneous timing of switching ON or OFF may be shifted. In other words, the effect of the present application can be achieved by creating a period in which the upper arm switching elements 18A to 18C of all phases or the lower arm switching elements 18D to 18F of all phases are turned ON and passing the magnetizing current Im through the magnetizing winding 9 by the upper arm switching elements 18A to 18C of all phases or the lower arm switching elements 18D to 18F of all phases. However, it is preferable to turn them ON simultaneously as in the embodiment.

[0083] Furthermore, in the embodiment, the magnetized winding 9 is electrically connected (via the resonant capacitors 28U to 28W) to the connection points of the upper and lower arm switching elements 18A to 18F of all phases, but this is not limiting. Alternatively, a contactless power supply device may be used to magnetically connect the magnetized winding 9 to the connection points of the upper and lower arm switching elements 18A to 18F of all phases, and the magnetizing current Im may be passed through the magnetized winding 9 in a contactless manner by the upper arm switching elements 18A to 18C of all phases or the lower arm switching elements 18D to 18F of all phases.

[0084] Furthermore, in the embodiment, the present invention is applied to a motor drive device that controls the drive of an electric compressor, but is not limited to this and the present invention is effective for controlling the drive of motors in various devices that have variable magnetic force magnets.

[0085] REFERENCE SIGNS LIST 1 Motor drive device 2 Control device 3 Motor 4 Stator 6 Rotor 7 Stator core 8U to 8W Three-phase winding 9 Magnetization winding 13 Variable coercivity magnet (magnet with low coercivity) 16 Rotor core 17 Fixed coercivity magnet (magnet with high coercivity) 18A to 18F Upper and lower arm switching elements 21 Inverter circuit 26 Upper arm power supply line 27 Lower arm power supply line 28U to 28W Resonant capacitor 31 Resonant circuit 32, 33 First and second neutral point capacitors 35 Motor control unit 36 ​​PWM signal generation unit 37 Gate driver 38 Magnetization control unit 39 Magnetization PWM signal generation unit 41 Interphase current interruption circuit 46 U-phase transformer 47 V-phase transformer 48 W-phase transformer

Claims

1. A motor drive device comprising an inverter circuit formed by connecting upper-arm switching elements and lower-arm switching elements in series for each phase between an upper-arm power line and a lower-arm power line, and a control device for controlling the upper and lower arm switching elements of the inverter circuit for each phase, the junctions of the upper and lower arm switching elements of each phase being connected to a three-phase winding of a motor to pass a three-phase current through the three-phase winding, wherein the motor comprises a magnet with a high coercive force and two types of permanent magnets each with a lower coercive force than the high coercive force magnet, and a magnetization winding for changing the magnetization state of the low coercive force magnet, one end of the magnetization winding being electrically or magnetically connected to the junctions of the upper and lower arm switching elements of all phases, and the control device comprising a magnetization control section for passing a magnetization current through the magnetization winding by creating a period in which the upper-arm switching elements or the lower-arm switching elements of all phases are ON.

2. The motor drive device according to claim 1, characterized in that the magnetization control unit causes a magnetization current to flow through the magnetization winding by simultaneously turning on the upper arm switching elements of all phases or the lower arm switching elements of all phases.

3. The motor drive device according to claim 1, further comprising resonant capacitors connected between the magnetized windings and the connection points of the upper and lower arm switching elements of each phase, and wherein the resonant circuits between these resonant capacitors and the magnetized windings prevent or suppress the three-phase current from flowing through the magnetized windings.

4. A motor drive device according to claim 3, further comprising an interphase current interruption circuit connected between each of the resonant capacitors and the magnetized winding, wherein the interphase current interruption circuit blocks or suppresses current flowing through the magnetized winding when a phase-to-phase voltage is applied, and allows current to flow through the magnetized winding when a voltage is applied that turns on the upper arm switching elements of all phases or the lower arm switching elements of all phases.

5. The motor drive device according to claim 4, wherein the interphase current interruption circuit has transformers for UVW phases, the primary and secondary sides of which have the same polarity, one end of the primary connected to each of the resonant capacitors and one end of the secondary connected to the magnetized winding, the other end of the primary of the U phase transformer connected to the other end of the secondary of the W phase or V phase transformer, the other end of the primary of the V phase transformer connected to the other end of the secondary of the U phase or W phase transformer, and the other end of the primary of the W phase transformer connected to the other end of the secondary of the V phase or U phase transformer.

6. The motor drive device according to claim 1, further comprising a first neutral point capacitor and a second neutral point capacitor connected in series between the upper and lower arm power supply lines to generate a neutral point, and the other end of the magnetization winding is connected to the connection point of the first and second neutral point capacitors.

7. A motor driven by a motor drive device according to any one of claims 1 to 6, characterized in that the motor comprises a stator around which the three-phase winding is wound, and a rotor provided with the high coercive force magnets and the low coercive force magnets, and the magnetized windings are wound around the teeth of the stator around which the three-phase windings are wound.

8. A motor driven by a motor drive device according to any one of claims 1 to 6, characterized in that the motor comprises a stator around which the three-phase winding is wound, and a rotor provided with magnets having high coercive force and magnets having low coercive force, the magnets having low coercive force being arranged circumferentially around the rotor, and the magnetized windings being provided on the stator at positions corresponding to the magnets having low coercive force.

9. A motor driven by a motor drive device according to any one of claims 1 to 6, characterized in that the motor comprises a stator wound with the three-phase winding and a rotor provided with the high coercive force magnet and the low coercive force magnet, the magnetized winding being provided on the rotor in the vicinity of the low coercive force magnet and power being supplied by contact or non-contact.

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