JP2019097301A - Control device for switched reluctance motor - Google Patents

Abstract

To provide a control device for a switched reluctance motor capable of suppressing heat generation of a coil even in a case where a heavy current flows to the coil.SOLUTION: The present invention relates to a control device for a switched reluctance motor including a rotor, a stator, and a coil wound around the stator, and mounted on a vehicle as a drive source for travel. The control device for the switched reluctance motor comprises a control part which performs first control for exciting the coil at a predetermined current value in a predetermined excitation interval. In a case where it is determined that the vehicle cannot be started even by performing the firs control, in the coil, the control part performs second control for reversely rotating the rotor in such a manner that a phase where inductance is a positive gradient is changed, and then exciting the coil at a current value greater than the predetermined current value in an excitation interval narrower than the predetermined excitation interval.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a control device of a switched reluctance motor mounted on a vehicle.

  A magnetic attraction force generated between the stator and the salient poles of the rotor includes a stator and a rotor each having a plurality of salient poles facing each other, and a three-phase coil wound around the salient poles of the stator. A switched reluctance motor is known which rotates a rotor.

  With respect to such a switched reluctance motor, for example, Patent Document 1 discloses that when a vehicle equipped with a switched reluctance motor can not start, a current larger than that for normal control is supplied to the three-phase coil. Techniques for improving launch performance are disclosed.

JP, 2016-134937, A

  Here, in the current control of the conventional switched reluctance motor as shown in Patent Document 1, among the three-phase coils, a coil of a phase whose inductance has a positive gradient is excited. Then, when the vehicle can not be started by the above-described normal control, although the coil of the switched reluctance motor is excited with a large current, the switched reluctance motor is not rotating, so the coil of a certain phase has a current Keep flowing That is, when the vehicle can not be started by the normal control, the coil of a certain phase may already generate heat. Therefore, when a current larger than that in the normal control is further supplied to the coil of a certain phase, the coil that is already generating heat may generate more heat. As a result, for example, it has been necessary to increase the size of a cooling device for suppressing heat generation.

  The present invention is made in view of the above, and an object of the present invention is to provide a control device of a switched reluctance motor capable of suppressing heat generation of a coil even if a large current is applied to the coil.

  In order to solve the problems described above and achieve the object, a control device of a switched reluctance motor according to the present invention includes a rotor, a stator, and a coil wound around the stator, and serves as a drive source for traveling. A controller of a switched reluctance motor mounted on the controller, the controller performing first control to excite the coil at a predetermined current value in a predetermined excitation section, the controller performing the first control When it is determined that the vehicle can not be started, the rotor reversely rotates so that the phase whose inductance has a positive gradient changes in the coil, and then the predetermined current is generated in the excitation section narrower than the predetermined excitation section. A second control is performed to excite the coil with a current value larger than the value.

  Thereby, the control device of the switched reluctance motor reversely rotates the rotor so that the phase whose inductance is a positive gradient changes before performing the second control, so that the temperature of the coil of the phase performing the second control is Lower than before the reverse rotation of the rotor.

  According to the control device of the switched reluctance motor according to the present invention, when a large current is supplied to the coil by the second control which excites the coil with an excitation interval narrower than the first control and a larger current value than the first control. Even if there is, the heat generation of the coil can be suppressed.

FIG. 1 is a view schematically showing a system configuration including a control device of a switched reluctance motor according to an embodiment of the present invention. FIG. 2 is a view schematically showing a configuration of a switched reluctance motor in a control device of a switched reluctance motor according to an embodiment of the present invention. FIG. 3 is a view schematically showing a configuration of an inverter in the control apparatus of the switched reluctance motor according to the embodiment of the present invention. FIG. 4 is a view showing applied voltage and current waveforms in the control apparatus of the switched reluctance motor according to the embodiment of the present invention. FIG. 5 is a graph showing a relationship between an excitation interval and a target current value in the first control and the second control in the controller of the switched reluctance motor according to the embodiment of the present invention. FIG. 6 is a flowchart showing a drive control method by the control device of the switched reluctance motor according to the embodiment of the present invention. FIG. 7 is a graph showing the relationship between the rotation angle of the rotor and the inductance of the coil in the controller of the switched reluctance motor according to the embodiment of the present invention. FIG. 8 is a graph showing the temperatures of the U-phase, V-phase and W-phase coils shown in FIG. FIG. 9 is a graph showing the relationship between the rotation angle of the rotor and the inductance of the coil in the controller of the switched reluctance motor according to the embodiment of the present invention. FIG. 10 is a graph showing the temperatures of the U-phase, V-phase and W-phase coils shown in FIG. FIG. 11 is a graph showing the relationship between the rotation angle of the rotor and the inductance of the coil in the controller of the switched reluctance motor according to the embodiment of the present invention. FIG. 12 is a skeleton diagram showing a vehicle to which the control device of the switched reluctance motor according to the embodiment of the present invention is applied.

  An embodiment of a control apparatus for a switched reluctance motor according to the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments. In addition, constituent elements in the following embodiments include those that can be easily replaced by persons skilled in the art or those that are substantially the same.

[System configuration]
As shown in FIG. 1, the system configuration of this embodiment includes a switched reluctance motor (hereinafter referred to as “SR motor”) 1, an inverter 2, a booster 3, a battery 4 and a controller 100. It contains. The control device of the SR motor 1 according to the present embodiment is configured to include at least the inverter 2 and the control unit 100.

  The SR motor 1 is mounted on a vehicle as a driving source for traveling. The SR motor 1 is electrically connected to the battery 4 via the inverter 2 and the booster 3 as shown in FIG. Further, the SR motor 1 and the inverter 2 are electrically connected via a coil 12 (see FIG. 2). The SR motor 1 functions not only as a motor but also as a generator.

  The SR motor 1 is an electric motor that does not use a permanent magnet in a rotor, and is driven by flowing an exciting current (hereinafter referred to as “current”) through a three-phase coil 12 wound around a stator 10. As shown in FIG. 2, the SR motor 1 includes a stator 10 having a salient pole structure and a rotor 20 having a salient pole structure. Note that, in the drawing, a configuration provided with a eighteen-pole stator 10 and a twelve-pole rotor 20 as the SR motor 1 is shown as an example.

  The SR motor 1 has a U-phase composed of a pair of stator teeth 11 and a coil 12a, a V-phase composed of a pair of stator teeth 11 and a coil 12b, and a W composed of a pair of stator teeth 11 and a coil 12c. Includes the phases.

  As shown in FIG. 2, the stator 10 is provided with a plurality of stator teeth 11 as salient poles on the inner peripheral portion of the annular structure. A coil 12 connected to the inverter 2 is wound around each stator tooth 11.

  The rotor 20 is disposed radially inward of the stator 10, and is provided with a plurality of rotor teeth 21 as salient poles on the outer peripheral portion of the annular structure. The rotor 20 is configured to rotate integrally with a rotor shaft (not shown).

  As shown in FIG. 3, the inverter 2 is configured by an electric circuit (inverter circuit) including a plurality of switching elements so that a three-phase alternating current can be supplied to the coil 12. As shown in the figure, in the inverter 2, three asymmetric half bridge circuits are connected in parallel. And in inverter 2, coil 12a, 12b of each phase included in each half bridge circuit can be excited independently, respectively, and the current which flows into coil 12a of each phase, 12b and 12c is controlled independently, respectively. It is configured to be possible. That is, the SR motor 1 can be driven in a single phase, and for example, has a feature that it is difficult to generate heat even if the output is continued with high torque.

  In addition to SR motor 1, a permanent magnet field type synchronous motor (hereinafter referred to as "PM motor") is known as a motor mounted on a vehicle, but the inverter of this PM motor is a full bridge circuit. It is configured. And in the inverter of PM motor, the coil of each phase can not be excited independently, respectively, and it is impossible to control the current which flows into the coil of each phase independently, respectively. That is, the PM motor can not be driven in a single phase, and for example, when it continues to output with high torque, it becomes easy to generate heat.

  The inverter circuit constituting the inverter 2 includes a plurality of transistors and a plurality of diodes provided for each phase, and one capacitor Co. Then, the inverter 2 changes the value of the current flowing through the coil 12 by simultaneously turning on or off the plurality of transistors in each phase.

  The inverter 2 includes transistors Tra1 and Tra2 and diodes Da1, Da2, Da3 and Da4 around the U-phase coil 12a. The inverter 2 also includes transistors Trb1 and Trb2 and diodes Db1, Db2, Db3 and Db4 around the V-phase coil 12b. The inverter 2 further includes transistors Trc1 and Trc2 and diodes Dc1, Dc2, Dc3 and Dc4 around the W-phase coil 12c.

  In addition, unlike the inverter of a general PM motor, since two diodes are added to each phase of the inverter 2 (diodes Da3, Da4, Db3, Db4, Dc3, Dc4), the current is caused to flow by direct current. be able to. Furthermore, since the inverter 2 does not have a neutral point like an inverter of a general PM motor, it is possible to control each phase under independent excitation conditions.

  The booster 3 is provided between the inverter 2 and the battery 4 and boosts the voltage applied to the SR motor 1. The boosting unit 3 is configured of, for example, a boosting converter, and is controlled by the control unit 100.

  The control unit 100 is an electronic control unit (ECU) that drives and controls the SR motor 1. The control unit 100 includes a CPU, a storage unit in which data such as various programs are stored, and an operation unit that performs various operations for driving and controlling the SR motor 1. Then, as a result of the calculation in the calculation unit, a command signal for controlling the inverter 2 is output from the control unit 100 to the inverter 2. As described above, the control unit 100 controls the inverter 2 to control the voltage and current applied to the SR motor 1.

  The control unit 100 is connected to the rotation speed sensor 51, the accelerator opening sensor 52, the vehicle speed sensor 53, and the temperature sensor 54. Specifically, the rotation speed sensor 51 is formed of a resolver, detects the rotation speed of the rotor 20 of the SR motor 1, and outputs the detection signal (resolver signal) to the control unit 100. Further, the accelerator opening degree sensor 52 detects the depression amount of the accelerator pedal by the driver, and outputs the detection signal to the control unit 100. The vehicle speed sensor 53 also detects the traveling speed of the vehicle, and outputs a detection signal to the control unit 100. Further, the temperature sensor 54 detects the temperature of the coil 12 and outputs the detection signal to the control unit 100.

  The control unit 100 specifies the relative positional relationship between the stator teeth 11 and the rotor teeth 21 in the rotational direction from the detection signal input from the rotational speed sensor 51 described above, and based on this positional relationship, The control of repeating switching of the coil 12 is performed for each phase. Then, in this control, the control unit 100 causes a current to flow through the coil 12 of a certain phase to excite the stator teeth 11 to attract magnetic attraction between the stator teeth 11 and the rotor teeth 21 near the stator teeth 11. To rotate the rotor 20.

As shown in FIG. 4, when a rotation angle of a certain rotor tooth 21 enters an excitation section, that is, an ON angle (excitation start angle), as shown in FIG. start. Further, when the rotation angle of the rotor tooth 21 is out of the excitation section, that is, when the rotation angle of the rotor tooth 21 is off (excitation end angle), the control unit 100 sets the current flowing to the coil 12 to be excited to zero. The “excitation section” is not the section (A ₁ + A ₂ + A ₃ ) in which the current flows in the coil 12 as shown in the figure, but the rotation angle range of the rotor 20 from the ON angle to the OFF angle That is, the section (A ₁ + A ₂ ) from the start to the end of excitation of a certain coil 12 is shown.

Control unit 100, when the rotation angle of the rotor teeth 21 is within the interval A _1, performs a positive voltage mode for applying a positive voltage to the coil 12 of the stator teeth 11 to be energized subject, target current current Control to rise to the value.

Furthermore, the control unit 100, when the rotation angle of the rotor teeth 21 is within the interval A _2, the coil 12 of the stator teeth 11 to be energized subject to perform a positive voltage mode and the reflux mode are alternately current Is controlled to have a magnitude near the target current value. The “refluxing mode” indicates a control mode in which current is circulated in the inverter 2 via the coil 12 without applying a voltage to the coil 12.

Furthermore, the control unit 100, when the rotation angle of the rotor teeth 21 is within the interval A _3, executes a negative voltage mode for applying a negative voltage to the coil 12 of the stator teeth 11 to be candidate excitation, current Control to be 0.

  Here, the control unit 100 performs first control and second control as current control of the SR motor 1. The first control is current control performed during normal traveling, and as shown in FIG. 5, the coil 12 of three phases (specifically, excitation among three phases should be performed at a predetermined target current value in a predetermined excitation section) The control of exciting the phase coil 12) is shown. In the first control, the three-phase coil 12 is excited with a target current value to be output by the SR motor 1 in order to satisfy the driving force required during normal traveling. FIG. 5 visually shows the relationship between the excitation section of the coil 12 and the target current value, and does not show a current waveform (see FIG. 4 for the current waveform).

  The second control is current control performed when the vehicle can not start even after the first control, and as shown in FIG. 5, in the excitation section narrower than the excitation section of the first control, the current value of the first control The control of exciting the three-phase coil 12 (specifically, the coil 12 of the phase to be excited among the three phases) with a larger current value is shown. In the present embodiment, by performing the second control instead of the first control under predetermined conditions, it is possible to achieve both suppression of heat generation of the coil 12 and improvement of the vehicle's start performance. The second control can be performed not only when the vehicle can not start with full acceleration, but also when the vehicle can not start with constant acceleration. In addition, as described later, the control unit 100 reversely rotates the rotor 20 in the three-phase coil 12 so that the phase whose inductance is a positive gradient changes (see FIGS. 9 and 11). 2) Control.

  In the present embodiment, the excitation interval in the first control is referred to as a "first excitation interval", the target current value in the first control is referred to as a "first current value", and the second An excitation interval in control is defined as a "second excitation interval", and a target current value in the second control is defined as a "second current value".

  Further, target current values in the first control and the second control are described in an excitation condition map (not shown) along with the ON angle (excitation start angle) and the OFF angle (excitation end angle) in the excitation section described above. . The control unit 100 derives a required driving force based on the accelerator opening detected by the accelerator opening sensor 52 during drive control of the SR motor 1 described later, and generates an excitation condition map corresponding to the required driving force. By reading, each target current value in the first control and the second control is determined.

[Drive control method]
Hereinafter, an embodiment of a drive control method by the control device of the SR motor 1 according to the present embodiment will be described with reference to FIGS. In addition, at the time of normal driving | running | working of a vehicle, ie, the start time of FIG. 6, the control part 100 is performing 1st control.

  First, as shown in FIG. 6, the control unit 100 reads various information used for drive control of the SR motor 1 (step S1). The “various information” specifically indicates the number of rotations and the rotation angle (phase) of the rotor 20 based on the detection signal of the rotation number sensor 51. Although not shown in the figure, in this step, the control unit 100 derives the required driving force based on the accelerator opening detected by the accelerator opening sensor 52 and reads the excitation condition map.

  Subsequently, the control unit 100 reads the temperature of the three-phase coil 12 based on the detection signal of the temperature sensor 54 (step S2). Subsequently, based on the detection signal of the vehicle speed sensor 53, the control unit 100 determines whether the vehicle is moving in the traveling direction (step S3). Note that "the vehicle is not moving in the traveling direction" includes, for example, a state in which the vehicle is stopped on a slope or the like, and a state in which the vehicle is moving in the opposite direction to the traveling direction (sliding state). It is.

  When it is determined in step S3 that the vehicle is not moving in the traveling direction (Yes in step S3), the control unit 100 determines that the accelerator opening detected by the accelerator opening sensor 52 is a preset threshold (the It is determined whether or not one threshold value or more (step S4).

  When it is determined in step S4 that the accelerator opening is equal to or greater than a preset threshold (first threshold) (Yes in step S4), the control unit 100 determines that the inductance of the phase coil 12 has a positive slope. It is determined whether the temperature is less than or equal to a preset threshold (second threshold) (step S5). In the present embodiment, when the vehicle is not moving in the traveling direction (Yes in step S3), and when the accelerator opening is equal to or greater than the first threshold (Yes in step S4), "vehicle can not start" It corresponds to

  In step S5, when it is determined that the temperature of coil 12 of the phase whose inductance has a positive gradient is less than or equal to a preset threshold (second threshold) (Yes in step S5), control unit 100 determines that the inductance The second control is performed for the coil 12 of the phase having a positive gradient, and the first control is continued for the coils 12 of the remaining phases, that is, the coils 12 of the phase having a negative gradient (step S6). Do. In step S6, specifically, “a coil of a phase with a positive gradient of inductance: second control, a coil of a phase with a negative gradient of inductance: first control” until the vehicle moves in the traveling direction. After the vehicle has moved in the traveling direction, the control is switched to "coils of all phases: first control" to end the processing.

  Here, current control independent of each phase as shown in step S6 is control that can be performed only because the SR motor 1 can be driven in a single phase, for example, PM that can not be driven in a single phase. This control can not be performed with a motor.

  In steps S5 and S6 described above, for example, as shown in FIGS. 7 and 8, when the temperature of V-phase coil 12 whose inductance has a positive gradient is lower than or equal to the second threshold value, as shown in FIGS. The second control is performed for the gradient V-phase coil 12 and the first control is continued for the remaining U-phase and W-phase coils 12. Note that “slope” means the inclination of the inductance with respect to the rotation angle θ of the rotor 20, as shown in FIG.

  If it is determined in step S3 that the vehicle is moving in the direction of travel (No in step S3), and in step S4, the accelerator opening is less than a preset threshold (first threshold) When it is determined that (step S4: No), the control unit 100 continues the first control for the coils 12 of all phases (step S7), and ends the process.

  In step S5 described above, when it is determined that the temperature of the coil 12 of the phase in which the inductance has a positive gradient exceeds the preset threshold (second threshold) (No in step S5), the control unit 100 The coil 12 of the phase is not excited (step S8). Subsequently, the control unit 100 determines whether the rotation angle of the rotor 20 has not changed for a predetermined time or more, that is, whether the rotor 20 has stopped for a predetermined time or more (step S9).

  When it is determined in step S9 that the rotation angle of the rotor 20 has not changed for a predetermined time or more (Yes in step S9), the control unit 100 excites the coils 12 of all phases so that the rotor 20 reversely rotates. (Step S10). Subsequently, the control unit 100 performs the second control for the coil 12 of the phase whose temperature is equal to or lower than a preset threshold (second threshold) and whose inductance has a positive gradient, and for the coil 12 of the remaining phases, One control is continued (step S11), and the process is ended. In step S11, specifically, until the vehicle moves in the traveling direction, the coil of the phase whose temperature is below the second threshold and whose inductance has a positive gradient: second control, coil of the remaining phase: first control After the vehicle moves in the traveling direction, the control is switched to "coils of all phases: first control" and the processing is ended.

  In steps S5 and S8 to S11 described above, for example, as shown in FIGS. 9 and 10, when the temperature of the V-phase coil 12 whose inductance has a positive slope exceeds the second threshold, as shown in FIGS. As shown in FIGS. 9 and 11, the rotor 20 is reversely rotated so that the phase whose inductance is positive slope changes from the V phase to the W phase. Then, the control unit 100 performs the second control on the W-phase coil 12 whose inductance has a positive gradient, and continues the first control on the remaining U-phase and V-phase coils 12.

  In step S9, when it is determined that the rotation angle of the rotor 20 is changing (No in step S9), the control unit 100 determines whether the rotor 20 is reversely rotating based on the detection signal of the rotation speed sensor 51 It is determined whether or not it is (step S12). When it is determined in step S12 that the rotor 20 is reversely rotating (Yes in step S12), the process proceeds to step S11. On the other hand, when it is determined in step S12 that the rotor 20 is not reversely rotating (No in step S12), the process proceeds to step S7.

  As described above, the control device of the SR motor 1 according to the present embodiment performs the second control by reversely rotating the rotor 20 so that the phase whose inductance is a positive gradient changes before performing the second control. The temperature of the phase coil 12 is lower than before the reverse rotation of the rotor 20. Thereby, even if a large current is supplied to the coil 12 by the second control which excites the coil 12 with an excitation interval narrower than the first control and a current value larger than the first control, the heat generation of the coil 12 is suppressed can do. In addition, in the control device of the SR motor 1, for example, it is not necessary to enlarge the cooling device in order to suppress heat generation.

[Example of application]
Hereinafter, a vehicle to which the control device for the SR motor 1 according to the present embodiment is applied will be described with reference to FIG. A vehicle 200 shown in the figure includes an engine 201, wheels 202, a transmission (T / M) 203, a differential gear 204, a drive shaft 205, and an SR motor (SRM) 1 as a power source for traveling. And. Vehicle 200 is a four-wheel drive vehicle, engine 201 drives left and right front wheels 202FL and 202FR, and SR motor 1 as a rear motor drives left and right rear wheels 202RL and 202RR.

  The SR motor 1 is a so-called in-wheel motor, and one SR motor 1 is provided on each of the left and right rear wheels 202RL and 202RR. In the rear drive unit of the vehicle 200, the left rear SR motor 1RL is connected to the left rear wheel 202RL, and the right rear SR motor 1RR is connected to the right rear wheel 202RR. The left and right rear wheels 202RL and 202RR are rotatable independently of each other.

  The left rear wheel 202RL is driven by the output torque (motor torque) of the left rear SR motor 1RL. The right rear wheel 202RR is driven by the output torque (motor torque) of the right rear SR motor 1RR.

  The left rear SR motor 1RL and the right rear SR motor 1RR are connected to a battery (B) 4 via an inverter 2. Also, the left rear SR motor 1RL and the right rear SR motor 1RR function as an electric motor by the power supplied from the battery 4 and as a generator that converts torque (external force) transmitted from the rear wheels 202RL and 202RR into electric power. Function. The inverter 2 includes an electric circuit for the left rear SR motor 1RL and an electric circuit for the right rear SR motor 1RR.

  The control unit 100 controls the rear left SR motor 1RL and the rear right SR motor 1RR, and the engine 201. For example, the control unit 100 includes an SR motor control unit (SR motor ECU) and an engine control unit (engine ECU). In this case, the engine ECU executes engine torque control to adjust the output torque of the engine 201 to a target torque value by intake control, fuel injection control, ignition control, and the like. Further, the SR motor ECU executes motor control on the left rear SR motor 1RL and the right rear SR motor 1RR based on the resolver signal input from the rotation speed sensor 51. The rotation number sensor 51 includes a left rear rotation number sensor 51RL that detects the rotation number of the left rear SR motor 1RL, and a right rear rotation number sensor 51RR that detects the rotation number of the right rear SR motor 1RR.

  As mentioned above, although the control device for the switched reluctance motor according to the present invention has been specifically described by the embodiments for carrying out the invention, the gist of the present invention is not limited to these descriptions, and claims It should be widely interpreted based on the description of Further, it is needless to say that various changes, modifications and the like based on these descriptions are included in the spirit of the present invention.

  For example, in the control device for the SR motor 1 according to the present embodiment, a step-down unit (step-down converter) that steps down the voltage applied to the SR motor 1 may be provided instead of the booster 3 (see FIG. 1).

  Moreover, the application example of the control apparatus of the SR motor 1 which concerns on embodiment is not limited to what was shown in FIG. 12 (henceforth "the application example 1"). For example, unlike the application example 1, the application example of the control device of the SR motor 1 may have a configuration in which the SR motor 1 is provided on all the wheels 202 (application example 2). Further, unlike the application example 1, a rear wheel drive vehicle without the front side drive device may be used (application example 3).

  The application example of the control device for the SR motor 1 may be different from the first to third applications, in which the traveling power source of the vehicle 200 is only the SR motor 1 as the in-wheel motor (application example 4) . Further, unlike the application example 4, the SR motor 1 may not be an in-wheel motor (application example 5).

  The application example of the control device of the SR motor 1 may be different from the application example 5, and the configuration of the application example 1 may be mounted as a front side drive apparatus (application example 6). Moreover, unlike the application example 3, the rear side drive apparatus may not be provided, or unlike the application example 4, the arrangement of the drive apparatus may be reversed in the front and back direction (application example 7).

1 Switched reluctance motor (SR motor)
Reference Signs List 2 inverter 3 booster 4 battery 10 stator 11 stator tooth 12 coil 20 rotor 21 rotor tooth 51 rotational speed sensor 52 accelerator opening sensor 53 vehicle speed sensor 54 temperature sensor 100 control unit

Claims (1)

In a control device of a switched reluctance motor having a rotor, a stator and a coil wound around the stator and mounted on a vehicle as a drive source for traveling,
A control unit that performs first control to excite the coil at a predetermined current value in a predetermined excitation section;
When the control unit determines that the vehicle can not start even after the first control, the control unit reversely rotates the rotor so that a phase whose inductance is a positive slope changes in the coil, and then the predetermined A control apparatus for a switched reluctance motor, comprising performing a second control of exciting the coil with a current value larger than the predetermined current value in an excitation section narrower than the excitation section.

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