Switched reluctance motor and method of controlling the same

Abstract

In a switched reluctance motor (10), a motor main body (30) includes a rotor (35) having a plurality of rotor salient poles, a stator (31) having a plurality of stator salient poles, drive windings of phases wound to the stator salient poles of the respective phases, and permanent magnets (40, 41) disposed to a stator yoke. A drive circuit (20) outputs drive currents to the drive windings of the respective phases in order to rotationally drive the rotor (35). A pulse current output circuit (21) outputs a pulse current, which is shorter in application time of the drive current than the drive current, to the drive windings of the respective phases so as to overlap the drive current.

Description

Technical Field

[0001] This disclosure relates to switched reluctance motors and control methods thereof. Background Technology

[0002] In order to improve the power factor and efficiency of a switched reluctance motor, in addition to the drive windings located on the stator salient poles, permanent magnets are also placed on the stator yoke.

[0003] For example, according to the method disclosed in Patent Document 1 (Japanese Patent Application Publication No. 2018-174649), a permanent magnet functions as an excitation unit, applying magnetic force to the stator salient poles via a magnetic circuit. The stator salient poles that attract the rotor salient poles are switched by adding or subtracting the magnetic flux generated by the current in the drive winding from the magnetic flux generated by the permanent magnet.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2018-174649 Summary of the Invention

[0007] In the switched reluctance motors described in the aforementioned literature, it is generally believed that when the speed and load torque are each a fixed value, the power factor and efficiency can be improved by selecting a permanent magnet with a magnetic force corresponding to that value. However, it is unclear how to optimize the power factor and efficiency when the speed and load torque vary over a wide range.

[0008] Typically, neodymium magnets are used in motors. Neodymium magnets have high holding force, so their magnetic force hardly changes under normal operating conditions. Therefore, when neodymium magnets are used in switched reluctance motors with the aforementioned structure, the power factor and efficiency of the motor can only be optimized within a narrow operating range.

[0009] This disclosure was made in consideration of the aforementioned problems. The purpose of this disclosure is to provide a switched reluctance motor capable of operating with optimal power factor and efficiency over a wide range of speeds and a wide range of load torques.

[0010] One embodiment of a switched reluctance motor includes a motor body, a drive circuit, and a pulse current output circuit. The motor body includes a rotor with multiple rotor salient poles, a stator with multiple stator salient poles and permanent magnets, and drive windings wound around the stator salient poles of each phase. The drive circuit outputs drive current to the drive windings of each phase to rotate the drive rotor. The pulse current output circuit outputs a pulse current, shorter in duration than the application time of the drive current applied to the drive windings of each phase, to the drive winding of any one phase.

[0011] According to the above embodiments, the residual magnetic flux density of the permanent magnet can be changed by applying a pulse current, thus providing a switched reluctance motor that can operate with optimal power factor and efficiency over a wide range of speeds and a wide range of load torques. Attached Figure Description

[0012] Figure 1 This is a block diagram illustrating an example of the structure of the switched reluctance motor according to the first embodiment.

[0013] Figure 2 Cut off with symmetry plane Figure 1 A cross-sectional perspective view of the motor body.

[0014] Figure 3 This is a graph showing the B-H curves of various magnets.

[0015] Figure 4 This is a timing diagram showing the on / off timing of each semiconductor switching element and the output timing of the pulse current output circuit.

[0016] Figure 5 It is a graph showing the load torque, motor speed, applied current in each phase, and the time variation of motor torque.

[0017] Figure 6 Is Figure 5 The example shows the change in the magnetization state of a permanent magnet on a B-H diagram.

[0018] Figure 7 It is a graph showing the applied current, magnetic flux density of the permanent magnet, and time variation of motor torque in each phase in other simulation examples.

[0019] Figure 8 This is a block diagram illustrating an example of the structure of the switched reluctance motor according to the second embodiment.

[0020] Figure 9 It is shown Figure 8 The timing diagram shows the opening and closing timing of each semiconductor switching element and the output timing of the pulse current output circuit in the switched reluctance motor.

[0021] Figure 10 It is a diagram used to illustrate the magnetization of a permanent magnet located on the stator.

[0022] Figure 11 This is a graph showing the time variations of load torque, motor torque, and applied current in each phase in other embodiments.

[0023] (Symbol Explanation)

[0024] 10: Switched reluctance motor; 20: Drive circuit; 21: Pulse current output circuit; 22: DC power supply; 30: Motor body; 31: Stator; 32: Stator salient pole; 33: Stator yoke; 35: Rotor; 36: Rotor salient pole; 38: Drive winding; 38a: Phase A winding; 38b: Phase B winding; 38c: Phase C winding; 40, 41: Permanent magnets; 50: Control circuit; D1~D6: Diodes; Hc: External magnetic field; N1~N6: Connection nodes; NN: Negative side node; NP: Positive side node; S1~S6: Semiconductor switching element; SW1: Switch. Detailed Implementation

[0025] Hereinafter, various embodiments will be described in detail with reference to the accompanying drawings. The following description will use a so-called 6-4 configuration switched reluctance motor having a 6-pole stator and a 4-pole rotor as an example. However, the technology disclosed herein can also be applied to switched reluctance motors with other configurations. Furthermore, in the following description, the same or equivalent parts are sometimes given the same reference numerals, and their description will not be repeated.

[0026] <First Implementation>

[0027] [Device Structure]

[0028] Figure 1 This is a block diagram illustrating an example of the structure of the switched reluctance motor according to the first embodiment. Figure 2 Cut off with symmetry plane Figure 1 A cross-sectional perspective view of the motor body. See below for reference. Figure 1 as well as Figure 2 This section describes a structural example of the switched reluctance motor 10 in this embodiment.

[0029] The switched reluctance motor 10 includes a motor body 30, a drive circuit 20, and a control circuit 50. The drive circuit 20 outputs an excitation current to drive the motor body 30. The control circuit 50 controls the operation of the drive circuit 20.

[0030] (Motor body)

[0031] like Figure 1 as well as Figure 2 As shown, the motor body 30 includes a rotor 35 that rotates about a rotation axis, a stator 31 arranged to surround the rotor 35, and drive windings 38 (38a, 38b, 38c).

[0032] In the so-called 6-4 configuration, the rotor 35 has four rotor salient poles 36 protruding towards the stator 31 at 90-degree intervals. The stator 31 has an annular stator yoke 33 and six stator salient poles 32 protruding from the stator yoke 33 towards the rotor 35 at 60-degree intervals. Drive windings 38 for corresponding phases (A-phase winding 38a, B-phase winding 38b, or C-phase winding 38c) are wound on one pair of opposing stator salient poles 32.

[0033] Furthermore, the motor body 30 includes a pair of permanent magnets 40 and 41 disposed on the stator yoke 33. Figure 1 as well as Figure 2 In this case, permanent magnets 40 and 41 are positioned at a distance 90 degrees from the stator salient pole 32 for phase A, that is, at the midpoint between the adjacent stator salient poles 32 for phase B and phase C. Permanent magnets 40 and 41 are respectively arranged between the first and second portions of the stator yoke 33. Therefore, the magnetic circuit within the stator yoke 33 passes through permanent magnets 40 and 41.

[0034] As permanent magnets 40 and 41, AlNiCo magnets and iron-chromium-cobalt magnets are suitable. The residual magnetic flux density of these magnets is similar to that of neodymium magnets, but their holding force is about 1 / 10 or less of that of neodymium magnets. Therefore, the magnetic force can be easily changed by changing the external magnetic field.

[0035] Figure 3 This is a graph showing the B-H curves of various magnets. Figure 3 The horizontal axis represents the external magnetic field Hc (unit: kA / m), and the vertical axis represents the magnetic flux density Br (unit: T). Figure 3 An example of the B-H curves for neodymium (NdFeB) magnets, samarium cobalt (SmCo) magnets, and aluminum nickel cobalt (AlNiCo) magnets is shown.

[0036] like Figure 3 As shown, AlNiCo magnets possess magnetic strength comparable to that of rare-earth magnets such as neodymium and samarium cobalt magnets. The maximum magnetic flux density of AlNiCo magnets is approximately 0.5–1.2 T, similar to that of neodymium magnets. On the other hand, the holding force of AlNiCo magnets is approximately 50–150 kA / m, which is less than one-tenth of the holding force of rare-earth magnets.

[0037] Although Figure 3 Although not shown in the diagram, the maximum magnetic flux density of the iron-chromium-cobalt magnet is approximately 0.5–1.2 T, similar to that of the alnico magnet. Furthermore, the holding force of the iron-chromium-cobalt magnet is approximately 30–70 kA / m, similar to, or slightly less than, that of the alnico magnet.

[0038] In the motor body 30 of the switched reluctance motor 10 of this embodiment, cast magnets such as AlNiCo magnets and IronChromiumCo magnets are used as permanent magnets 40 and 41. As a result, it has a strong magnetic force comparable to that of rare earth magnets, and this magnetic force can be changed by applying a pulse current to the drive winding 38.

[0039] (Driver circuit)

[0040] Refer again Figure 1 as well as Figure 2 The drive circuit 20 is an asymmetric half-bridge converter. The drive circuit 20 converts the DC voltage V output from the DC power supply 22 into a three-phase pulse voltage for driving the motor body 30.

[0041] The drive circuit 20 includes self-extinguishing arc-type semiconductor switching elements S1-S6, diodes D1-D6, and switch SW1. Figure 1 In this example, insulated-gate bipolar transistors (IGBTs) are used as semiconductor switching elements S1 to S6. Their connection relationships are explained below. Regarding switch SW1, a self-extinguishing arc-type semiconductor switching element can also be used.

[0042] Semiconductor switching element S1 is connected between node N1, which is connected to one end of phase A winding 38a, and the positive node NP of DC power supply 22. Semiconductor switching element S2 is connected between node N2, which is connected to the other end of phase A winding 38a, and the negative node NN of DC power supply 22. Diode D1 is connected in reverse bias between node N2 and the positive node NP of DC power supply 22. Diode D2 is connected in reverse bias between node N1 and the negative node NN of DC power supply 22.

[0043] Similarly, semiconductor switching element S3 is connected between connection node N3, which is connected to one end of phase B winding 38b, and the positive node NP of DC power supply 22. Semiconductor switching element S4 is connected between connection node N4, which is connected to the other end of phase B winding 38b, and the negative node NN of DC power supply 22. Diode D3 is connected in reverse bias between connection node N4 and the positive node NP of DC power supply 22. Diode D4 is connected in reverse bias between connection node N3 and the negative node NN of DC power supply 22.

[0044] Similarly, semiconductor switching element S5 is connected between connection node N5, which is connected to one end of the C-phase winding 38c, and the positive node NP of the DC power supply 22. Semiconductor switching element S6 is connected between connection node N6, which is connected to the other end of the C-phase winding 38c, and the negative node NN of the DC power supply 22. Diode D5 is connected in reverse bias between connection node N6 and the positive node NP of the DC power supply 22. Diode D6 is connected in reverse bias between connection node N5 and the negative node NN of the DC power supply 22.

[0045] The drive circuit 20 also includes a pulse current output circuit 21. The pulse current output circuit 21 applies a pulse current to the windings wound around the stator 31 for a short period of time, during which the rotor 35 is not rotating, in order to change the magnetization state of the permanent magnets 40 and 41 using an external magnetic field. In this embodiment, no special winding is provided for applying the pulse current; instead, the pulse current is applied to at least one phase of the drive windings 38.

[0046] exist Figure 1 In this case, the pulse current output circuit 21 is connected between the connection nodes N1 and N2 for phase A. In this case, the switch SW1 is connected between connection node N1 and the cathode of diode D2, or between connection node N2 and the anode of diode D1. When the drive current used to drive the rotor 35 flows to the phase A winding 38a, the switch SW1 is controlled to be in the on state. On the other hand, when the pulse current flows from the pulse current output circuit 21 to the phase A winding 38a, the switch SW1 and the semiconductor switching elements S1 and S2 are both controlled to be in the off state.

[0047] Specifically, the pulse current output circuit 21 has an output terminal T1 connected to connection node N1 and an output terminal T2 connected to connection node N2. When the pulse current is output with output terminal T1 as the positive side and output terminal T2 as the negative side, a current flows in the A-phase winding 38a in the same direction as the drive current of the drive rotor 35. On the other hand, when the pulse current is output with output terminal T1 as the negative side and output terminal T2 as the positive side, a current flows in the A-phase winding 38a in the opposite direction to the drive current.

[0048] The magnetic force of the permanent magnets 40 and 41 can be adjusted according to the magnitude and duration of the pulse current applied from the pulse current output circuit 21. Details regarding the timing of the applied pulse current will be described later.

[0049] (Control circuit)

[0050] Control circuit 50 outputs gate control signals to control the on / off states of semiconductor switching elements S1 to S6. Control circuit 50 also controls the on / off state of switch SW1. Furthermore, control circuit 50 controls the magnitude and timing of the pulse current output from pulse current output circuit 21. Additionally, when pulse current is not output from pulse current output circuit 21, control circuit 50 controls pulse current output circuit 21 by making output terminals T1 and T2 high-impedance or open-circuit states. Alternatively, when pulse current is not output from pulse current output circuit 21, control circuit 50 may also shut off the power supply voltage to pulse current output circuit 21 or its output driver.

[0051] exist Figure 1 In this example, the control circuit 50 is based on a computer. That is, the control circuit 50 includes a CPU (Central Processing Unit) 51, a memory 52, and an interface (I / F) circuit 53. The control circuit 50 can also be based on circuits such as ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array).

[0052] Specifically, in Figure 1 In this case, the CPU 51 executes commands according to the control program, thereby controlling the semiconductor switching elements S1 to S6, the pulse current output circuit 21, and the switch SW1. The memory 52 includes RAM (Random Access Memory) and ROM (Read Only Memory) which operate as the main memory of the CPU 51, as well as non-volatile memory for storing the control program and auxiliary storage devices. The interface circuit 53 includes driver circuits, etc., which output gate control signals to the gate terminals of the semiconductor switching elements S1 to S6. Furthermore, the interface circuit 53 outputs control signals for controlling the pulse current output circuit 21 and the switch SW1.

[0053] [Action Method]

[0054] Next, the operation of the switched reluctance motor 10 with the above structure will be explained. First, the rotation drive of the rotor 35 is performed in the same way as before.

[0055] For example, when the control circuit 50 controls both semiconductor switching elements S1 and S2 for phase A to be in the conducting state, power is supplied to the phase A winding 38a to magnetize and demagnetize the stator salient pole 32 for phase A. At the same time, the magnetization state of the permanent magnets 40 and 41 also changes.

[0056] When no power is needed to supply to the A-phase winding 38a, the control circuit 50 controls either semiconductor switching element S1 or S2 to the off state. For example, when semiconductor switching element S1 is controlled to the off state, current circulates through semiconductor switching element S2 and diode D2 due to the magnetic energy stored in the A-phase winding 38a. Conversely, when semiconductor switching element S2 is controlled to the off state, current circulates through semiconductor switching element S1 and diode D1 due to the magnetic energy stored in the A-phase winding 38a. In either case, there is no power supply from the DC power supply 22.

[0057] When the control circuit 50 controls both semiconductor switching elements S1 and S2 to be in the off state, current flows through diodes D1 and D2. As a result, the magnetic energy stored in phase A winding 38a returns to the DC power supply 22. When a voltage with the opposite polarity to that supplied with power is applied to the two ends of phase A winding 38a, the winding current gradually decreases.

[0058] exist Figure 1 When the drive rotor 35 rotates counterclockwise, the control circuit 50 supplies power to the drive circuit 20 in the order of phase A winding 38a, phase B winding 38b, and phase C winding 38c. This generates an electromagnetic field whose magnetic flux direction varies every 120 degrees in electrical angle. When the drive rotor 35 rotates clockwise, the control circuit 50 supplies power to the drive circuit 20 in the order of phase A winding 38a, phase C winding 38c, and phase B winding 38b.

[0059] Specifically, in Figure 1 The diagram shows the stator salient pole 32 and rotor salient pole 36 for phase A in an aligned position. When the drive rotor 35 rotates counterclockwise, the control circuit 50 switches the power supply from phase A winding 38a to phase B winding 38b at that timing. Conversely, when the drive rotor 35 rotates clockwise, the control circuit 50 switches the power supply from phase A winding 38a to phase C winding 38c at that timing.

[0060] In addition, Figure 1The example illustrates the initial position of rotor 35 when it is rotated counterclockwise and a drive current is initially applied to phase A winding 38a. In this case, any rotor salient pole 36 of rotor 35 must be located between the stator salient pole 32 for phase A and the stator salient pole 32 for phase B as the initial position. For example, any rotor salient pole 36 of rotor 35 may be positioned at a position 40 to 45 degrees from the stator salient pole 32 for phase A. When rotor 35 is rotated clockwise and a drive current is initially applied to phase A winding 38a, any rotor salient pole 36 of rotor 35 must be located between the stator salient pole 32 for phase A and the stator salient pole 32 for phase C as the initial position.

[0061] Next, the operation of the pulse current output circuit 21 will be explained. When the stator salient pole 32 of a specific phase, determined by the arrangement of the permanent magnets 40 and 41, is aligned with any rotor salient pole 36, the pulse current output circuit 21 supplies pulse current to at least the drive winding 38 wound around the stator salient pole 32 of that specific phase.

[0062] Specifically, in Figure 1 as well as Figure 2 In the example shown, permanent magnets 40 and 41 are positioned midway between the adjacent stator salient poles 32 for phase B and phase C in the stator yoke 33. That is, the pair of permanent magnets 40 and 41 are positioned symmetrically relative to the stator salient pole 32 for phase A. In this case, when the stator salient pole 32 for phase A is aligned with any rotor salient pole 36, a pulse current is supplied to the phase A winding 38a from the pulse current output circuit 21 while the semiconductor switching elements S1 and S2 are turned off. As a result, as... Figure 1 The magnetic circuit formed by the stator salient pole 32, rotor 35, stator yoke 33 and permanent magnets 40 and 41 in phase A is shown, so that the magnetic force of permanent magnets 40 and 41 can be increased or decreased efficiently.

[0063] Here, when a pulse current is injected in the same direction as the driving current, the magnetic force of permanent magnets 40 and 41 increases; when a pulse current is injected in the opposite direction to the driving current, the magnetic force of permanent magnets 40 and 41 decreases. Specifically, in Figure 1 In the example shown, the output terminals T1 and T2 of the pulse current output circuit 21 are made to a high-impedance state or an open-circuit state, and the switch SW1 is made to be in a conducting state. When both semiconductor switching elements S1 and S2 are made to be in a conducting state in this state, thereby applying a drive current to the A-phase winding 38a, in Figure 1 The arrow indicates the direction in which magnetic flux MF is generated. In this case, as... Figure 1As shown, in each of the permanent magnets 40 and 41, the upstream side of the magnetic flux MF is magnetized into the S pole, and the downstream side of the magnetic flux MF is magnetized into the N pole.

[0064] Next, both semiconductor switching elements S1 and S2 are turned off, and switch SW1 is also turned off. When a pulse current is output from the pulse current output circuit 21 in this state with output terminal T1 as the positive side and output terminal T2 as the negative side, the pulse current flows in the same direction as the drive current. As a result, a current is generated in the same direction as... Figure 1 The same magnetic flux is applied, thus increasing the magnetization of permanent magnets 40 and 41. Conversely, when semiconductor switching elements S1 and S2, as well as switch SW1, are all turned off, and a pulse current is output from the pulse current output circuit 21 with output terminal T1 as the negative side and output terminal T2 as the positive side, the pulse current flows in the opposite direction to the driving current. As a result, a current is generated in the direction of... Figure 1 The magnetic flux is opposite to that of the permanent magnets 40 and 41, so that the magnetization of the permanent magnets 40 and 41 can be reduced.

[0065] Furthermore, when the timing of the applied pulse current differs from that described above, the generation of torque ripple may cause rotor 35 to vibrate, which may, as a result, hinder the stable operation of the motor.

[0066] In the normal driving state of rotor 35, the current magnetic field of drive winding 38 overlaps with the magnetic field based on permanent magnets 40 and 41 (magnetic force enhancement effect). As described above, by using pulsed current to change the magnetic force of permanent magnets 40 and 41, the magnetic flux MF generated by the magnetic circuit can be significantly changed. As a result, the output torque of the motor can be changed or adjusted to an appropriate value corresponding to the variation of load torque.

[0067] The application time of the current pulse from the pulse current output circuit 21 needs to be set to a short time, sufficient to prevent the rotor 35 from rotating. Therefore, the pulse application time T... p It needs to be set to the specific time constant τ e Long enough, but longer than the mechanical time constant τ m Short enough. When the pulse is applied for time T p Not comparable to the electrical time constant τ e When the time is long enough, it is impossible to inject pulse current into phase A winding 38a. Additionally, when the pulse application time T... p Not compared to the mechanical time constant τ m If the torque is short enough, it may generate large torque ripple in the motor output or cause rotor vibration, which may hinder the stable operation of the motor.

[0068] Here, regarding the electrical time constant τ eAs shown in Equation (1), the average inductance L of each phase of the motor body 30 and the resistance R of each phase drive winding 38 are given by Equation (1).

[0069] τ e =L / R…(1)

[0070] Regarding the mechanical time constant τ m The inertial torque J and braking coefficient B of rotor 35 are given by equation (2) below.

[0071] τ m =J / B…(2)

[0072] Therefore, the pulse application time T p Need to meet

[0073] τ e <<T p <<τ m …(3)

[0074] Table 1 shows the mechanical time constant τ. m and the electrical time constant τ e Specific design example. Pulse application time T p For example, it is set as the specific energy time constant τ e It is 10 times larger than the mechanical time constant τ m A value one-tenth of the original value (approximately 0.5 to 2 seconds in the examples in Table 1).

[0075] [Table 1]

[0076] constant name Numerical Example Phase resistance R 0.78Ω Phase inductance L (alignment position) Maximum: 0.5H Minimum: 0.03H Phase inductance L (unaligned position) Maximum: 0.032H Minimum: 0.0066H Phase inductance L (average value at 10A) 0.0349H Inertial torque J <![CDATA[0.00325kgm 2 ]]> Braking coefficient B 0.00156 Nms / rad <![CDATA[Electrical time constant τ e = L / R]]> 0.0349 / 0.78＝0.0447s <![CDATA[Mechanical time constant τ m = J / B]]> 0.00325 / 0.00156＝2.08s

[0077] [Specific examples of switch timing]

[0078] The following is for reference Figure 1 as well as Figure 4 This section describes a specific example of controlling the semiconductor switching elements S1 to S6 that constitute the drive circuit 20 and the pulse current output circuit 21. The polarity of the output terminal T1 of the pulse current output circuit 21 is set to positive, and the polarity of the output terminal T2 is set to negative. In this case, switch SW1 can always be in the on state.

[0079] Figure 4 This is a timing diagram showing the on / off timing of each semiconductor switching element and the output timing of the pulse current output circuit. Figure 4 At time t1, the control circuit 50 switches the semiconductor switching elements S1 and S2 to the on state. As a result, a drive current is applied to the A-phase winding 38a.

[0080] At the next time t2, the control circuit 50 switches semiconductor switching elements S1 and S2 to the off state and switches semiconductor switching elements S3 and S4 to the on state. This ends the application of the drive current to phase A winding 38a and begins the application of the drive current to phase B winding 38b. At time t2, phase A winding 38a and any rotor salient pole 36 of rotor 35 are approximately aligned. During the period from time t2 to time t3 when they are in this aligned position, according to the command from the control circuit 50, the pulse current output circuit 21 outputs a pulse current to phase A winding 38a. As a result, the pulse current overlaps with the residual current of the drive current and flows to phase A winding 38a, thereby adjusting the magnetization of permanent magnets 40 and 41. Specifically, when the pulse current flows in the same direction as the residual current of the drive current, the magnetization of permanent magnets 40 and 41 increases; when the pulse current flows in the opposite direction to the residual current of the drive current, the magnetization of permanent magnets 40 and 41 decreases. Furthermore, when a pulse current is injected into the A-phase winding 38a, the control circuit 50 controls the semiconductor switching elements S1 and S2 to the off state, and also controls the switch SW to the off state. At this time, the semiconductor switching elements S3 and S4 can be controlled to either the on state or the off state.

[0081] At the next moment t4, the control circuit 50 switches semiconductor switching elements S3 and S4 to the off state and switches semiconductor switching elements S5 and S6 to the on state. Thus, the application of drive current to phase B winding 38b ends, and the application of drive current to phase C winding 38c begins.

[0082] Subsequently, similarly, at time t5, the destination of the driving current is switched from phase C winding 38c to phase A winding 38a. At time t6, the destination of the driving current is switched from phase A winding 38a to phase B winding 38b. At time t7, the destination of the driving current is switched from phase B winding 38b to phase C winding 38c. At time t8, the destination of the driving current is switched from phase C winding 38c to phase A winding 38a. At time t9, the destination of the driving current is switched from phase A winding 38a to phase B winding 38b.

[0083] During the period from time t9 to time t10, similarly to the period from time t2 to time t3, the pulse current output circuit 21 outputs a pulse current to the A-phase winding 38a according to the command of the control circuit 50. As a result, the pulse current overlaps with the residual current of the drive current and flows to the A-phase winding 38a, thereby adjusting the magnetization of the permanent magnets 40 and 41. Then, at time t11, the destination of the drive current application switches from the B-phase winding 38b to the C-phase winding 38c.

[0084] [Simulation Example 1]

[0085] The following describes the results based on numerical simulation. First, it explains the results of numerical simulation. Figure 1 The result is achieved without activating the pulse current output circuit 21 while the permanent magnets 40 and 41 are fully magnetized. AlNiCo magnets are used as permanent magnets 40 and 41.

[0086] Compared to the case without permanent magnets 40 and 41, the output at 1200 rpm increased from approximately 600 W to approximately 1200 W. Efficiency increased from approximately 80% to approximately 90%. The power factor at 1200 rpm increased from 0.35 to 0.55. It has been confirmed that by installing permanent magnets 40 and 41, output, efficiency, and power factor all increase.

[0087] [Simulation Example 2]

[0088] Next, refer to Figure 5 as well as Figure 6 The results of numerical simulations are presented, illustrating the application of a pulsed current from the pulsed current output circuit 21 to the drive winding 38. AlNiCo magnets are used as permanent magnets 40 and 41. The residual magnetic flux density of the AlNiCo magnets is set to 0 in the initial state.

[0089] Figure 5 It is a graph showing the load torque, motor speed, applied current in each phase, and the time variation of motor torque. Figure 6 Is Figure 5 The example shows the change in the magnetization state of a permanent magnet on a B-H diagram. Figure 5 In the diagram, the times t1 to t11 represent the switching timing of semiconductor switching elements S1 to S6 and the output timing of the pulse current of the pulse current output circuit 21, respectively, corresponding to... Figure 4 The time intervals t1 to t11.

[0090] like Figure 5 As shown, at times t2 and t9, the load torque increases, which correspondingly increases the average value of the motor's output torque. Therefore, during the periods from t2 to t3 and from t9 to t10, a pulse current is output from the pulse current output circuit 21 to the A-phase winding 38a. This, in turn, increases the residual magnetic flux density of the permanent magnets 40 and 41.

[0091] In addition, Figure 5 as well as Figure 6 In the example, at the same timing, the pulse current also comes from other pulse current output circuits (in... Figure 1(Not shown in the diagram) is applied to phase B winding 38b. However, the stator salient pole 32 used for phase A is aligned with any rotor salient pole 36, so the change in magnetic force of permanent magnets 40 and 41 is mainly generated by the injection of pulse current into phase A winding 38a. The current injection into phase B winding 38b is only for supporting the change in magnetic force of permanent magnets 40 and 41.

[0092] like Figure 6 As shown, through the initial pulse current injection from time t2 to time t3, the magnetization state of the permanent magnet changes in the order of states ST1, ST2, and ST3. Through the subsequent pulse current injection from time t9 to time t10, the magnetization state of the permanent magnet changes further in the order of states ST4, ST5, and ST6. Thus, the magnetic force of permanent magnets 40 and 41 can be changed by injecting pulse current into phase A winding 38a and phase B winding 38b.

[0093] In the examples above, the average torque of the motor is greater than the load torque. Specifically, as the load torque increases to 2, 5, and 8 [Nm], the average torque of the motor varies accordingly to 2.11, 6.31, and 8.43 [Nm]. Based on these results, it is clear that the motor's performance depends on whether its torque increases with increasing load torque. By applying a pulsed current, the motor torque increases by approximately 10-20% in response to the increase in load torque. Therefore, by applying a pulse width greater than a predetermined value, the motor torque is increased, thereby improving efficiency.

[0094] Furthermore, in the above-described situation, the motor speed increases due to the energy difference between the load torque and the motor's average torque. By adjusting the magnitude of the pulse current output from the pulse current output circuit 21 to match the average motor torque with the load torque, it is possible to control the motor speed in a manner that keeps it almost unchanged.

[0095] [Simulation Example 3]

[0096] Next, refer to Figure 7 This section describes the results of a numerical simulation, similar to Simulation Example 2, where a pulse current is applied from the pulse current output circuit 21 to the drive winding 38. The magnitude of the drive current for each phase is set to 10A, and the motor speed is set to 500 rpm. Furthermore, AlNiCo magnets are used as permanent magnets 40 and 41.

[0097] Figure 7 This is a graph showing the time-varying applied current, magnetic flux density of the permanent magnet, and motor torque for each phase in other simulation examples. Figure 7 In the meantime, pulse current is output from pulse current output circuit 21 near each time t20, t21, t22, and t23.

[0098] Specifically, around time t20 and time t21, the pulse current output circuit 21 applies a pulse current to the A-phase winding 38a in the same direction as the drive current. As a result, the average magnetic flux density of the permanent magnets 40 and 41 increases sequentially, and the average motor torque also increases sequentially.

[0099] Near the next moment t22, the pulse current output circuit 21 applies a pulse current to the A-phase winding 38a in the same direction as the drive current. Simultaneously, other pulse current output circuits (in...) Figure 1 (Not shown in the diagram) A pulsed current is applied to the C-phase winding 38c in the same direction as the drive current. As a result, the average magnetic flux density of permanent magnets 40 and 41 further increases, and the average motor torque also further increases.

[0100] Around time t23, the pulse current output circuit 21 applies a pulse current to the A-phase winding 38a in the opposite direction to the drive current. This reduces the average magnetic flux density of the permanent magnets 40 and 41, and consequently reduces the average motor torque. Thus, by applying a pulse current from the pulse current output circuit 21 to the drive winding 38 in the opposite direction to the drive current, the magnetic flux density of the permanent magnets 40 and 41 is reduced, resulting in a reduction in motor torque.

[0101] [Effects of the first embodiment]

[0102] As described above, in the switched reluctance motor according to the first embodiment, permanent magnets with low holding force, such as AlNiCo magnets or IronChromiumCo magnets, are disposed on the stator yoke. Furthermore, when the stator salient pole 32 of a specific phase, determined by the arrangement of the permanent magnets, is aligned with any rotor salient pole 36, a pulse current is applied to at least the drive winding 38 of that specific phase. The application time of this pulse current is shorter than the application time of the drive current for each phase, and is limited to a period during which the rotor 35 does not rotate. The magnitude of the pulse current is larger than the magnitude of the drive current. By applying this pulse current, the residual magnetic flux density of the permanent magnets is changed, thereby improving the motor's output and efficiency.

[0103] <Second Implementation Method>

[0104] The switched reluctance motor 10 of the second embodiment has the same arrangement of permanent magnets 40, 41 as the first embodiment, but differs from the first embodiment in that it applies pulse current to the drive winding 38 of phases other than phase A. Hereinafter, refer to... Figures 8-10 A detailed explanation will be provided.

[0105] [Device Structure]

[0106] Figure 8 This is a block diagram illustrating an example of the structure of the switched reluctance motor according to the second embodiment.

[0107] Figure 8 The drive circuit 20B of the switched reluctance motor 10 shown is similar in that it has a pulse current output circuit 21B and switch SW2 for phase B, and a pulse current output circuit 21C and switch SW3 for phase C, instead of the pulse current output circuit 21 and switch SW1 for phase A. Figure 8 The switched reluctance motor 10 is different. Alternatively, it can be configured to switch the output destination of the shared pulse current output circuit 21.

[0108] Specifically, the pulse current output circuit 21B for phase B has an output terminal T1B connected to connection node N3 and an output terminal T2B connected to connection node N4. Switch SW2 is connected between connection node N3 and the cathode of diode D4 or between connection node N4 and the anode of diode D3.

[0109] When switch SW2 and semiconductor switching elements S3 and S4 are both controlled to be off, pulse current output circuit 21B outputs pulse current to phase B winding 38b. When pulse current is output from pulse current output circuit 21B with output terminal T1B as positive and output terminal T2B as negative, pulse current is applied to phase B winding 38b in the same direction as the drive current. Conversely, when pulse current is output from pulse current output circuit 21B with output terminal T1B as negative and output terminal T2B as positive, pulse current is applied to phase B winding 38b in the opposite direction to the drive current.

[0110] The pulse current output circuit 21C for phase C has an output terminal T1C connected to connection node N5 and an output terminal T2C connected to connection node N6. Switch SW3 is connected between connection node N5 and the cathode of diode D6 or between connection node N6 and the anode of diode D5.

[0111] When switch SW3 and semiconductor switching elements S5 and S6 are both controlled to be off, the pulse current output circuit 21C outputs a pulse current to the C-phase winding 38c. When the pulse current is output from the pulse current output circuit 21C with output terminal T1C as the positive side and output terminal T2C as the negative side, the pulse current is applied to the C-phase winding 38c in the same direction as the drive current. Conversely, when the pulse current is output from the pulse current output circuit 21C with output terminal T1C as the negative side and output terminal T2C as the positive side, the pulse current is applied to the C-phase winding 38c in the opposite direction to the drive current.

[0112] The control circuit 50 outputs control signals for controlling semiconductor switching elements S1 to S6, the aforementioned switches SW2 and SW3, and pulse current output circuits 21B and 21C. Figure 8 Other points and Figure 1 Since the situation is the same, the same reference symbols will be added to the same or equivalent parts, and the description will not be repeated. Furthermore, regarding the magnetic flux MF shown on the motor body 30, reference will be made to... Figure 10 To be described later.

[0113] [The switching timing of each semiconductor switching element and the output timing of the pulse current]

[0114] Figure 9 It is shown Figure 8 The timing diagram shows the opening and closing timing of each semiconductor switching element and the output timing of the pulse current output circuit in the switched reluctance motor.

[0115] exist Figure 9 In the timing diagram, the timing of the application of the drive current is related to... Figure 4 The timing diagram is the same. That is, during the period from time t30 to time t31, semiconductor switching elements S1 and S2 are controlled to be in the conducting state, thereby applying a drive current to the A-phase winding 38a. During the following period from time t31 to time t32, semiconductor switching elements S3 and S4 are controlled to be in the conducting state, thereby applying a drive current to the B-phase winding 38b. During the following period from time t32 to time t34, semiconductor switching elements S5 and S6 are controlled to be in the conducting state, thereby applying a drive current to the C-phase winding 38c. Similarly, during the period from time t34 to time t40, the phases of the drive winding 38 to which drive current is applied are switched sequentially in the order of A-phase, B-phase, and C-phase.

[0116] The pulse current output circuit 21B applies a pulse current to the B-phase winding 38b during the periods t32 to t33 and t40 to t41 when the B-phase winding 38b and any rotor salient pole 36 of the rotor 35 are approximately aligned. When the pulse current is applied to the B-phase winding 38b, switch SW2 and semiconductor switching elements S3 and S4 are controlled to be in the off state. Figure 9 In the process, the pulse current is applied to the B-phase winding 38b in the same direction as the drive current.

[0117] During the period from time t34 to time t35, when the C-phase winding 38c and any rotor salient pole 36 of the rotor 35 are approximately aligned, the pulse current output circuit 21C applies a pulse current to the C-phase winding 38c. When the pulse current is applied to the C-phase winding 38c, switch SW3 and semiconductor switching elements S5 and S6 are controlled to be in the off state. Figure 9In the process, the pulse current is output to the C-phase winding 38c in the same direction as the drive current.

[0118] like Figure 9 As shown, to improve the uniformity of magnetization of permanent magnets 40 and 41, after applying a pulsed current to phase B winding 38b, it is preferable to apply a pulsed current of the same value to phase C winding 38c. With any applied pulsed current, the direction of the magnetic flux MF generated in permanent magnets 40 and 41 is the same. Furthermore, when the drive current is applied in the order of phase A, phase C, and phase B, after applying a pulsed current to phase C winding 38c, a pulsed current is then applied to phase B winding 38b with the same value.

[0119] [Regarding magnetization of permanent magnets]

[0120] Figure 10 It is a diagram used to illustrate the magnetization of a permanent magnet located on the stator. Figure 10 Figure (A) is shown as a reference diagram, illustrating the magnetic flux distribution in the case of the first embodiment. Figure 10 (B) shows Figure 9 The magnetic flux distribution between time t32 and time t33. Figure 10 (C) shows Figure 9 The magnetic flux distribution between time t34 and time t35.

[0121] like Figure 10 As shown in (A), in the first embodiment, a pulsed current is applied to the A-phase winding 38a when the A-phase winding 38a and any rotor salient pole of the rotor 35 are approximately aligned. In this case, a detour path of magnetic flux MF through the stator salient pole for phase B, the rotor salient pole, and the stator salient pole for phase C may be generated, parallel to the path of magnetic flux MF through the permanent magnets 40 and 41. When the rotor salient pole is designed with a wide width, the proportion of magnetic flux MF through the detour path increases, resulting in a problem where the magnetization efficiency to the permanent magnets 40 and 41 decreases.

[0122] like Figure 10 As shown in (B), a pulsed current is applied to the B-phase winding 38b when the B-phase winding 38b and any rotor salient pole of the rotor 35 are approximately aligned. In this case, the path of the magnetic flux MF through the permanent magnets 40 and 41 is not parallel to the circuitous path of the magnetic flux MF through the rotor salient pole. Similarly, as Figure 10 As shown in (C), a pulsed current is applied to the C-phase winding 38c when the C-phase winding 38c is approximately aligned with any rotor salient pole of the rotor 35. In this case, the path of the magnetic flux MF through the permanent magnets 40 and 41 is not parallel to the detour path of the magnetic flux MF through the rotor salient pole.

[0123] Therefore, when permanent magnets 40 and 41 are provided between the stator salient poles for phase B and phase C, applying a pulse current to either phase B winding 38b or phase C winding 38c will not cause a decrease in magnetization efficiency due to the detour of the magnetic flux MF. It is also possible to apply a pulse current to only one of phase B winding 38b and phase C winding 38c, but to improve the uniformity of magnetization, it is best to apply a pulse current to one of phase B winding 38b and phase C winding 38c, and then apply a pulse current to the other drive winding 38 with the same current value and the same polarity as generating magnetic flux MF in the same direction in the permanent magnets 40 and 41.

[0124] [Effects of the second implementation method]

[0125] As described above, the switched reluctance motor according to the second embodiment, in addition to the effects of the first embodiment, can also prevent the decrease in magnetization efficiency of the permanent magnet caused by the detour path of the magnetic flux.

[0126] <Other Implementation Methods>

[0127] The following is for reference Figure 11 This illustrates other control examples for switched reluctance motors. Figure 11 This is a graph showing the time variations of load torque, motor torque, and applied current in each phase in other embodiments.

[0128] like Figure 11 As shown in (A), the load torque is constant at 10 [Nm]. To make this load torque consistent with... Figure 11 (B) shows a method where the motor torque is consistent, controlled by torque control. Figure 11 The currents in each phase are shown in (C). Figure 11 As shown in (B), no large torque ripple is generated in the motor output.

[0129] <Variations on each implementation method>

[0130] Alternatively, instead of the motor body with the 6-4 configuration described above, a so-called 12-8 configuration motor body consisting of a 12-pole stator and an 8-pole rotor can be used. In this case, each permanent magnet is also provided in the stator yoke 33 at the midpoint between the adjacent stator salient poles 32 for phase B and phase C. In this case, a total of 4 permanent magnets are provided. The timing of the pulse current output from the pulse current output circuit 21 is the same as in the 6-4 configuration described in the first and second embodiments. More generally, by increasing the number of stator salient poles and rotor salient poles, the permanent magnets can be arranged in positions opposite each other in the diameter direction of the annular stator yoke within the stator yoke, which allows for magnetic flux flow in one direction. As long as the total number is even, they can be arranged in any position.

[0131] The embodiments disclosed herein should be considered illustrative in all respects and not restrictive. The scope of the invention is not shown by the foregoing description but by the claims, and is intended to include all modifications within the meaning and scope of the claims.

Claims

1. A switched reluctance motor, comprising: The motor body includes a rotor having multiple rotor salient poles, a stator having multiple stator salient poles, a drive winding of each phase of the stator salient poles wound in the multiple stator salient poles, and a permanent magnet disposed on the stator yoke and whose magnetization state changes due to the current magnetic field. A drive circuit that outputs drive current to the drive windings of each phase in order to rotate the rotor; as well as The pulse current output circuit superimposes a pulse current, shorter than the application time of the drive current applied to the drive windings of each phase, onto the drive current and outputs it. This causes the drive windings of each phase to generate magnetic flux through the magnetic circuits of the rotor, the stator, and the permanent magnets, and changes the magnetization state of the permanent magnets. in, The permanent magnet is positioned between the stator salient poles of the first phase and the second phase, which are adjacent to each other. The pulse current output circuit outputs the pulse current to the drive winding of the first phase when the stator salient pole of the first phase is aligned with any rotor salient pole.

2. The switched reluctance motor according to claim 1, wherein, The permanent magnet is positioned between the stator salient poles of the first phase and the second phase, which are adjacent to each other. When the stator salient pole of the third phase is aligned with any rotor salient pole, the pulse current output circuit outputs the pulse current to the drive winding of the third phase.

3. The switched reluctance motor according to claim 1, wherein, The drive circuit outputs the drive current in the order of the drive winding for the first phase, the drive winding for the second phase, and the drive winding for the third phase. After outputting the pulse current to the drive winding for the first phase, the pulse current output circuit outputs the pulse current to the drive winding for the second phase when the stator salient pole for the second phase is aligned with any rotor salient pole.

4. The switched reluctance motor according to any one of claims 1 to 3, wherein, The application time of the pulse current is greater than the electrical time constant and smaller than the mechanical time constant. The electrical time constant is obtained by dividing the average inductance of each phase of the motor body by the resistance value of the drive winding of each phase. The mechanical time constant is obtained by dividing the rotor's inertial torque by the rotor's braking coefficient.

5. The switched reluctance motor according to any one of claims 1 to 3, wherein, The permanent magnet is an AlNiCo magnet or an IronChromiumCo magnet.

6. A control method for a switched reluctance motor, the switched reluctance motor comprising a rotor having multiple rotor salient poles, a stator having multiple stator salient poles, drive windings of each phase of the stator salient poles wound around the multiple stator salient poles, and permanent magnets disposed on the stator yoke, wherein, The control method comprises: The step of outputting drive current to the drive windings of each phase in order to rotate the rotor; as well as When the stator salient pole of the first phase is aligned with any rotor salient pole, a pulse current with a duration shorter than the application time of the drive current applied to the drive windings of each phase is output to the drive winding of the first phase, thereby generating magnetic flux in the magnetic circuit of the rotor, the stator, and the permanent magnet in each phase drive winding and changing the magnetization state of the permanent magnet. in, The permanent magnet is positioned between the stator salient poles of the first phase and the stator salient poles of the second phase, which are adjacent to each other.

7. The control method according to claim 6, wherein, The permanent magnet is positioned between the stator salient poles of the second phase and the stator salient poles of the third phase, which are adjacent to each other.

8. The control method according to claim 6, wherein, The drive current is output in the order of the drive winding for the first phase, the drive winding for the second phase, and the drive winding for the third phase. In the control method, after the pulse current is output to the drive winding for the first phase, the pulse current is output to the drive winding for the second phase when the stator salient pole for the second phase is aligned with any rotor salient pole.

9. The control method according to any one of claims 6 to 8, wherein, The application time of the pulse current is greater than the electrical time constant and smaller than the mechanical time constant. The electrical time constant is obtained by dividing the average inductance of each phase of the switched reluctance motor by the resistance value of the drive winding of each phase. The mechanical time constant is obtained by dividing the rotor's inertial torque by the rotor's braking coefficient.

10. The control method according to any one of claims 6 to 8, wherein, The permanent magnet is an AlNiCo magnet or an IronChromiumCo magnet.

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