Multi-pole variable-speed shaft-center powered wound-field synchronous motor

Abstract

This project aims to reduce power loss in synchronous motors used in electric vehicles, and to miniaturize, lighten, and improve the efficiency of the drive system. [Solution] 1) By switching the number of poles, the number of poles is increased at low speeds to increase the torque multiplier of the motor, thereby reducing copper losses by lowering the current value of the AC current supplied to the armature, and the number of poles is decreased at high speeds to lower the voltage and frequency of the AC current supplied to the armature, thereby reducing losses (mainly iron losses) during high-speed rotation, and providing a synchronous motor and drive control device with high power efficiency over a wide speed range from low to high speeds. 2) By extending the number of poles switching mechanism, it becomes possible to change the speed of multi-pole synchronous motors with a larger number of poles than the drive control device, eliminating the need for mechanisms such as reduction gears and transmissions. Furthermore, because shaft-center power supply enables the design of short-shaft, flat, thin, high-torque variable-speed motors, this technology contributes to miniaturization and weight reduction of automobiles, as well as improved power efficiency, and provides motors that contribute to the practical application of in-wheel motor vehicles.

Description

Technical Field

[0001] Relates to improving the power efficiency of a synchronous motor used in an electric vehicle that applies vector control technology and power control technology and uses electricity as a power source.

Background Art

[0002] Conventionally, in railway vehicles, a lap-wound DC motor in which an armature winding and a field winding are connected in series, and a variable resistance current control device, and later a thyristor chopper current control device have been used as its control means. In recent years, due to the development of power semiconductor devices and the application of multivariable vector control based on modern control theory, an induction motor is used in combination with a VVVF inverter (abbreviated as VFD in English), and high power efficiency, maintainability, and availability can be achieved simultaneously. However, in automotive applications, there are restrictions on the amount of power that can be supplied, so the requirement for vehicle weight reduction is very strict. Furthermore, since a large passenger compartment space is required for the size of the vehicle, miniaturization and weight reduction of the motor are strongly demanded. An induction motor has a lower power density than a synchronous motor, so its size and weight for the same power are large, and it is not suitable for automotive applications in terms of miniaturization and weight reduction. In addition, an induction motor with gentle acceleration and deceleration due to slip control during starting is not suitable for automobiles with many operation patterns such as starting and stopping while waiting for a signal and stopping at an arbitrary position at short intervals in terms of controllability. Due to the above operating conditions, mainly small, lightweight synchronous motors with good controllability and responsiveness are used for automobiles. However, it has been pointed out that the cruising range of electric vehicles decreases during high-speed operation, and improving the power efficiency of synchronous motors during high-speed operation has become an urgent issue.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

[0004] [Non-Patent Document 1] Motor Fan Tech, March 12, 2025 issue: "Nissan Ariya's wound-field motor that does not use permanent magnets" [Non-Patent Document 2] Meiden Times, Issue No. 367, 2020, No. 2: Wound-field type synchronous motor for electric vehicle drive [Non-Patent Document 3] Transactions of the Institute of Electrical Engineers of Japan, Vol. 120, No. 11, 2000: Study on a smooth pole switching method for six-phase pole-switching induction motors for electric vehicles. [Non-Patent Document 4] Kagoshima University Faculty of Engineering Research Report No. 60 (2018) "Research on Permanent Magnet Variable Field Motors" [Non-Patent Document 5] January 11, 2024, Institute of Electrical Engineers of Japan, Tokai Branch Academic Conference: "Latest Research Trends on Variable Field Permanent Magnet Synchronous Motors for Achieving a Wide Operating Range" [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Synchronous motors, primarily used in automobiles, have their rotational speed determined by the frequency of the armature current. During low-speed acceleration, excessive armature current increases copper loss and limits the lower rotational speed. During high-speed operation, higher frequency increases iron loss, and armature reaction reduces efficiency and limits the upper rotational speed. Due to the nature of automobile operation, gear ratio settings are prioritized for dynamic performance during acceleration and low-speed driving. As a result, problems such as reduced driving range, fuel consumption, and electricity efficiency due to decreased power efficiency at high speeds have become apparent. [Means for solving the problem]

[0006] The characteristics of a synchronous motor, such as the torque multiplier, change depending on the number of poles. Specifically, the torque multiplier Kr changes proportionally to the square root of the number of poles p. The armature voltage coefficient Kv changes proportionally to the square root of the number of poles p. The relationship between rotational speed R [rpm] and power supply frequency f [Hz] changes inversely proportional to the number of poles p (R [rpm] = 60 × f [Hz] × 2 / p). Since the torque τ of the motor is given by the product of the torque multiplier kr and the armature current Ia, increasing the number of poles p at low speeds to increase the torque multiplier seems to solve the copper loss problem. Decreasing the number of poles p at high speeds to lower the frequency f seems to solve the iron loss problem. Therefore, a solution can be considered using pole switching, which increases the number of poles at low speeds to raise the motor's torque multiplier, thereby lowering the current value of the AC current supplied to the armature and reducing copper losses. At high speeds, it is possible to reduce losses (mainly iron losses) during high-speed rotation by decreasing the number of poles to lower the voltage and frequency of the AC current supplied to the armature. By switching the number of poles, it is possible to improve the power efficiency of synchronous motors over a wide speed range from low to high speeds.

[0007] To change the poles of a synchronous motor, the number of poles in both the armature and the field windings must be changed simultaneously. Considering the driving performance of an automobile, the pole change must be performed in the shortest possible time while the vehicle is in operation, without generating large shocks or vibrations. Pole change of a synchronous motor is realized by electronically controlling the phase of the current flowing through the multiphase armature windings for the armature, and by electronically controlling the direction and magnitude of the multi-pole field current for the field.

[0008] The speed change of a synchronous motor by the method described in paragraph 0007 can be realized by the following three steps: 1) a pole number switching command step in which a pole number switching command is issued based on the magnitude of the motor's rotational speed while the vehicle is in operation; 2) an armature pole number switching step in which the number of poles of the armature is switched by electronically switching the phase of the armature current of the synchronous motor in response to the pole number switching command from the pole number switching command step; and 3) a field pole number switching step in which the number of poles of the field is switched simultaneously with the armature by electronically controlling the direction and magnitude of the current in each field winding so that the field generated by the field winding of the wound-field synchronous motor has a phase similar to the spatial vector of the magnetic field caused by the armature current described above.

[0009] To realize the speed change of the synchronous motor in the manner described in Section 0008, Figure 3 shows means to be added to or modified from the conventional synchronous motor and drive control device. These means include: 1) a wound-field synchronous motor having armature winding connection means in which the multiphase armature windings are concentrated for each phase and connected to the bridge circuit of a voltage-type PWM inverter, and field winding connection means in which each field winding is connected to the bridge circuit of a field current control means through a slider equal to the number of field windings; 2) a coordinate transformation calculation means having a function to switch the number of phases and poles of the multiphase armature current, instead of the conventional coordinate transformation calculation means that generates a three-phase AC waveform; and 3) The system consists of a bridge circuit composed of the same number of power control elements such as IGBTs as the number of positive and negative field poles of a constant current source, and a field current control means that controls the magnitude of the current in the positive or negative direction over a time period by turning the gate signals of either the positive or negative IGBT ON or OFF, and a pole number switching command means that, as a pole number switching command process, uses a microprocessor to determine from the rotational speed of the motor and issues a pole number switching command to the aforementioned coordinate transformation calculation means, field current control means, and other control means to comprehensively control the entire system.

[0010] This section describes the relationship between the number of phases in the armature current and the number of poles in the armature. For example, if there are 12 armature windings spaced 30 degrees apart for one rotation of the motor shaft, the relationship between the number of phases ph and the number of poles p is as follows: Number of phases ph × Number of poles p / 2 = 12. In other words, using a synchronous motor with 12 armature windings, it is possible to switch between three speed settings—3-phase 8-pole, 6-phase 4-pole, and 12-phase 2-pole—by switching the number of phases. The ratio of the electrical angle (phase angle of the AC waveform) θr to the mechanical angle (rotation angle of the motor shaft) θrm is θr = θrm × p / 2. The ratio of the electrical angular velocity (phase angular velocity of the AC waveform) ωr to the mechanical angular velocity (rotation angular velocity of the motor shaft) ωrm is ωr = ωrm × p / 2. Furthermore, in a synchronous motor with 24 phase armature windings (where there are 24 phase armature windings spaced 15 degrees apart for one rotation of the motor shaft), the number of phases ph × the number of poles p / 2 = 24, meaning that four speed settings are possible: 3-phase 16-pole, 6-phase 8-pole, 12-phase 4-pole, and 24-phase 2-pole.

[0011] This section describes a coordinate transformation calculation method for calculating the waveform of a multiphase AC system from the pole number command value pn and the electrical angle θr. The phase of the armature current of each phase is calculated using the following coordinate transformation matrix. The number of pole pairs pn = number of poles p / 2, and the speed command [Vd*Vq*] is from the current controller in the block diagram of Figure 3. The transformation matrix is ​​described below in TIFF2026123300000002.tif25170. TIFF2026123300000003.tif17160(i=1~12) The input / output relationship and processing details of the coordinate transformation calculation means are shown in the block diagram in Figure 4. TIFF2026123300000005.tif11136

[0012] An example of the operation of the coordinate transformation calculation means when the phase number of the armature current is switched will be described. First, at the timing when the mechanical angle θrm = 0, the pole number switching command means sends a pole pair number advance command value pn'. The coordinate transformation calculation means provides a transformation matrix for the current pole logarithm command value pn. TIFF2026123300000006.tif17151 Transformation matrix for pole logarithmic leading command value pn' Figure 6 shows the waveform output by the calculation unit during phase switching operation. Phase switching is completed within one motor rotation (when switching from 2 poles to 4 poles) or half a rotation (when switching from 4 poles to 8 poles).

[0013] In the case of a synchronous motor, the number of field poles must be switched simultaneously with the phase switching of the armature current. The switching of the number of field poles is performed by electronically controlling the direction and magnitude of the direct current in the field winding. Details are described below. The field winding of the motor is connected to the bridge circuit of the field current control means through a multi-pole commutator. As shown in the field current control circuit diagram of Fig. 7, it is composed of a half-bridge circuit formed by positive and negative constant current sources with two poles and power control elements such as IGBTs having the same number as the number of field poles. By turning on / off the gate signal of either the positive or negative IGBT, a field current in a positive or negative direction, whose magnitude is controlled by the time width, flows.

[0014] Explain the calculation principle for determining the direction and magnitude of the current in the field winding. Consider the rotating magnetic field generated by the armature winding current of one pole pair. Taking the direction of the magnetic field (N pole) at a certain moment (t = 0) as shown in Fig. 8 as the α-axis. Assume that a sinusoidal current with an angular frequency ωr flows through the aforementioned armature winding. Let the number of magnetic fluxes in the α-axis direction at a certain moment (t = 0) be φ0. Consider the position where the rotor has rotated by θr from the α-axis. Let the number of magnetic fluxes at the position rotated by an electrical angle θr from the α-axis be φi, then φi = φ0 × cos(θr). Let each field magnetic flux generated by the 8-pole field be Φi and the magnetic field generated by the armature be φi at its phase angle. Then, the torque τ generated by the motor is proportional to the inner product of φi and Φi. Torque τ = Torque coefficient Kri × [φi]·[Φi] If [φi] and [Φi] are defined as the armature magnetic field vector and the field magnetic vector respectively, to increase the torque τ with respect to the magnitude of the field, it is the optimization condition to maximize the inner product of the armature magnetic field vector and the field magnetic vector, that is, to make the ratio of the magnitudes of each element of [φi] equal to the ratio of the magnitudes of each element of [Φi].

[0015] ​​In the previous section 0014, it was explained that making the ratio of the magnitudes of the elements in [φi] equal to the ratio of the magnitudes of the elements in [Φi], that is, making the armature magnetic field vector and the field vector similar, is an optimization condition for increasing the torque τ with respect to the field magnitude. Figure 9 shows that the phase of the spatial vector of the magnetic field generated by the field current control means is similar to the phase of the 2-pole, 4-pole, or 8-pole field. Figure 10 shows the overall circuit diagram including the armature.

[0016] The pole number switching command means determines the rotational speed of the motor and issues pole number switching commands to the aforementioned rotational coordinate transformation calculation means, field current control means, and other control means, thereby comprehensively controlling the entire drive control device. The objects of control are as follows: ○ Speed ​​control circuit Ksp speed-proportional gain (selection of characteristic value that changes depending on the number of poles) Ksi velocity integral gain (same as above) ○Current command value generator: General torque control of electric motors performed by current commands (same as above) ○Current controller Kcd Current proportional gain (selection of characteristic value which varies depending on the number of poles) Tcd Integral time constant (same as above) Ld: Armature inductance equivalent to reactive current Lq: Armature inductance equivalent to the active current. ○ Coordinate transformation: The entire process of multi-phase / multi-pole switching of an armature. ○Field Current Control: The entire process of switching the number of poles in the field. The entire process of switching the number of poles is completed within the time it takes for the motor's rotating shaft to complete one rotation.

[0017] As a power source for automobiles, multi-pole electric motors with high torque at low speeds are highly useful. Approximately 16 to 48 poles are effective. By using such multi-pole motors and eliminating the reduction gear, the motor's rotation shaft can be directly connected to the input shaft of the differential gear or the axles of the left and right drive wheels, thereby reducing or eliminating the number of reduction gear stages. This can lead to reduced mechanical losses, miniaturization, weight reduction, and improved dynamic performance. Furthermore, in applications of in-wheel motor vehicles, it becomes possible to provide thin and compact multi-pole motors essential for practical use. However, in such applications, because reduction gears and transmissions are not used, the frequency of the armature current becomes too high during high-speed operation, leading to increased iron loss and a serious problem of reduced power efficiency and motor overheating. These problems (reduced power efficiency during high-speed operation, motor overheating, and conflicting requirements for miniaturization and weight reduction) can be solved by using the synchronous motor speed control method described in section 0016. However, this requires field winding connection means for each field pole to switch the number of poles, leading to problems such as larger motors and drive control devices, and increased costs. If it were possible to switch the number of poles of a multi-pole (approximately 16 to 48 poles) synchronous motor using a drive control device that can handle around 8 poles (extension of pole switching), these problems associated with multi-pole motors would be resolved.

[0018] The following explains the method for extending the number of poles switching, using an example with an 8-pole drive control device. First, starting from the mechanical angle θm=0, the total number of armature windings is divided into pole groups equal to the quotient obtained by dividing the total number of armature windings by 12. Similarly, the number of field windings is divided into the same number of pole groups as the armature. For example, in the case of a wound-field synchronous motor with 36 armature windings and 24 field windings, the number of pole groups m is 3, the number of armature windings per pole group is 12, and the number of field windings per pole group is 8. If the armature and field of each pole group are driven simultaneously by an 8-pole drive control device, the motor will rotate 1 / 1 of the number of pole groups (m) with a signal from the drive control device equivalent to one rotation of the motor. The ratio of the electrical angle (phase angle of the AC waveform) θr to the mechanical angle (rotation angle of the motor shaft) θrm is θr = θrm × p / 2 × number of pole groups m. In other words, the number of poles is expanded to a multiple of the number of pole groups m. As mentioned above, in the case of a wound-field synchronous motor with 36 armature windings and 24 field windings, the number of pole groups m is 3. When the drive control device operates in 2-pole mode, the number of poles p = 2 × number of pole groups m (= 3) = 6 poles. When the drive control device operates in 4-pole mode, the number of poles p = 4 × number of pole groups m (= 3) = 12 poles. When the drive control device operates in 8-pole mode, the number of poles p = 8 × number of pole groups m (= 3) = 24 poles.

[0019] In the pole group of the armature winding and field winding of a synchronous motor in the extension of pole number switching described in the previous section 0019, the armature winding numbers of each pole group are numbered in ascending order from Φ1 to Φ1, starting from the mechanical angle θm=0. TIFF2026123300000008.tif10170 explained that if the fields are driven simultaneously in the same phase and with the same number of poles p, the total number of poles in the synchronous motor will be m times the number of pole groups. Driving the armature and field of each pole group simultaneously in the same phase and with the same number of poles p means that the i-th armature windings Φi of each pole group are connected by the i-th inverter of the drive control device. This is done by connecting to the j-th bridge circuit of the field current control means.

[0020] The method for connecting the armature winding and field winding of a multi-pole synchronous motor, as explained in the preceding section 0019, can be applied to the connection means for a wound-type synchronous motor as described in section 0009 of the specification, as follows. A multi-pole synchronous motor having a number of poles that is an integer multiple of the number of poles of the drive control device, comprising: an armature winding connection means in which multi-phase armature windings are concentrated for each phase and connected to each other for each pole group divided into units of the number of poles of the drive control device, and a field winding connection means in which field windings of the same number are connected to each other for each of the aforementioned pole groups, and connected to a bridge circuit of a field current control means through the sliders of the number of poles of the drive control device, wherein the multi-pole wound-field synchronous motor has Figure 11 shows an example of an armature winding connection means, and Figure 12 shows an example of a field winding connection means. In these embodiments, the armature windings are connected in series to increase impedance in order to reduce copper loss, and the field windings are connected in parallel to decrease impedance in order to reduce copper loss.

[0021] Sections 0017 to 0020 explained the high usefulness of multi-pole electric motors with high torque at low speeds as power sources for automobiles. In designing such electric motors, a large diameter and short shaft length are required, resulting in a flat and thin structure with numerous magnetic pole teeth and slots arranged circumferentially around the armature core. When mounting such a high-torque electric motor on a vehicle, the arrangement of multiple rows of sliders and slip rings on the rotating shaft outside the motor for switching the number of field poles poses a major obstacle to the layout design of the automobile's drive system. Therefore, it is conceivable to provide slip rings and sliders that supply DC current to the field windings on the rotor shaft inside the flat and thin electric motor, so that they do not protrude outside the motor.

[0022] However, placing slip rings and sliders inside the electric motor necessitates disassembling the motor for inspection and maintenance, posing a significant obstacle to motor maintenance. Therefore, a shaft-centered power supply unit was designed, which integrates the slip rings and sliders, the bearings before and after the slip rings, the wires and conduits from the slip rings to the wiring box, and the wires from the sliders to the field windings. This unit is then detachably mounted to the shaft of the hollow rotor of a flat, thin-type electric motor. Figure 1 shows the structure of the electric motor with the shaft-centered power supply unit mounted on the hollow rotor. The procedure for assembling the axial power supply unit to the hollow rotor is as follows. Note that the motor and axial power supply unit are assumed to be pre-assembled separately. The armature core and windings of the synchronous motor, stator frame, front and rear bearing brackets, armature winding wiring and wiring box, front and rear rotor bearings, field core and windings, hollow rotor, and field winding wiring are already installed. The rotor remains hollow and the rotor rear cover is not yet attached. 1) Insert the fully assembled axial power supply unit so that the key provided on the inner surface of the front end of the hollow rotor aligns with the keyway on the outer ring of the front end of the axial power supply unit. The outer ring of the axial power supply unit and the rotor are fixed in the direction of rotation. 2) Connect the wires from the slider to the field windings and the field winding wiring. 3) Attach the rotor rear cover to the rear bearing bracket so that the key position aligns with the keyway on the conduit of the axial power supply unit. The conduit of the axial power supply unit is fixed in the rotational direction. Note that there is a small radial gap between the rotor rear cover and the conduit so that the bearings before and after the slip ring are not subjected to load due to eccentricity tolerance. 4) Attach the field wiring box to the rotor rear cover and connect the wires from the slip ring of the axial power supply unit to the wiring box. To remove the axial power supply unit, follow steps 1) through 4) in reverse order.

[0023] Figure 2 shows the structure of the axial power supply unit. This axial power supply unit consists of the number of poles of wiring connecting the field wiring box and the slip ring, a conduit housing the aforementioned wiring, slip rings mounted on the outer surface of the conduit in the number of poles and connected to the aforementioned wiring, two bearings, front and rear, whose inner rings fit the aforementioned conduit, two bearing housings, front and rear, that fit the outer rings of the bearings, a slider housing whose outer surface is connected to the bearing housing with the same outer diameter as the bearing housing and on which sliders and elastic supports are attached, several sliders that slide against the outer surface of the slip ring, an elastic support that supports the sliders on the inner surface of the slider housing and presses them against the slip ring with a constant pressure, field winding wiring connected to the sliders and connected to the field winding, an outer ring rotation prevention means provided by a keyway at the front end of the front bearing housing, and a conduit rotation prevention means provided by a keyway at the rear end of the conduit. With this structure, no load is placed on the inner conduit, so the diameter of the conduit only needs to accommodate the internal wiring. As a result of the small diameter slip ring, the peripheral speed is low (about 1 / 20 to 1 / 40 of the vehicle speed), and no load is placed on the bearing. Therefore, it is considered that the slip ring, slider, and bearings will not need to be replaced for the vehicle's lifespan (10 years, 500,000 km). [Effects of the Invention]

[0024] By adding or modifying the means described in paragraphs 0008 to 0017 of the specification and drawings 3 to 10 to the synchronous motor and its drive control device, a kind of electrical speed control function is provided to the synchronous motor and its drive control device. At low speeds, the number of poles is increased to raise the torque multiplier of the motor, thereby lowering the current value of the AC current supplied to the armature and reducing copper losses. At high speeds, the number of poles is decreased to lower the voltage and frequency of the AC current supplied to the armature, thereby reducing losses (mainly iron losses) during high-speed rotation. This makes it possible to provide a synchronous motor and drive control device with high power efficiency over a wide speed range from low to high speeds.

[0025] In addition to the effects described in paragraph 0024 of the specification, by adding the means described in paragraphs 0018 to 0023 of the specification and in drawings 1, 2, 11, and 12, it becomes possible to change the speed of a multi-pole synchronous motor with a larger number of poles than a drive control device, and mechanisms such as reduction gears and transmissions can be omitted. Furthermore, because shaft-center power supply enables the design of a short-shaft, flat, thin, high-torque variable-speed motor, this technology can contribute to miniaturization and weight reduction of automobiles and improvement of power efficiency, as well as providing a motor that can contribute to the practical application of in-wheel motor vehicles. [Brief explanation of the drawing]

[0026] [Figure 1] Structure of a multi-pole variable-speed shaft-center powered wound-field synchronous motor [Figure 2] Structure of the axial power supply unit [Figure 3] Drive control device for variable speed synchronous motor [Figure 4] Input / Output Relationship Diagram of Coordinate Transformation Calculation Mechanism [Figure 5] Waveform of a multiphase AC generated by a coordinate transformation calculation means [Figure 6] Current waveforms of each phase when the armature current phase number switching of the coordinate transformation calculation means [Figure 7] Field current control means: field current drive circuit (bridge circuit) [Figure 8] Field current calculation method for field current control means [Figure 9] The current value calculated by the field current control means and the spatial phase of the generated magnetic field [Figure 10] Circuit diagram showing the connection between the armature winding and the field winding. [Figure 11] Armature winding connection method for a multi-pole synchronous motor (connection diagram) [Figure 12] Field winding connection method for a multi-pole synchronous motor (connection diagram) [Modes for carrying out the invention]

[0027] This project will be implemented by adding and modifying several means to an existing wound-field synchronous motor and its drive control device. The newly added elements are the number of sliders for the field windings and the field current control means, while the remaining modifications involve increasing the number of phases, poles, and modes of the current drive control device. The resulting gear shifting function and the resulting improvement in power efficiency can also be obtained using mechanical transmissions used in automobiles powered by internal combustion engines. However, adding a mechanical transmission would increase the vehicle's weight and reduce space efficiency, which would be counterproductive to the goals of electrification. Furthermore, during vehicle operation, gear shifting can be performed within the time it takes for the motor shaft to complete one rotation without generating shocks or vibrations, which is more preferable in terms of vehicle handling. [Industrial applicability]

[0028] This invention provides a fundamental technical concept, but applying this concept industrially requires the design and development of equipment, circuits, and software. Considerable difficulties are anticipated. The thermal design of the electric motor must be properly executed, the sliders and slip rings must have sufficient durability, and the servo characteristics of the speed controller, current command generator, current controller, or non-interference control must be properly matched for each pole number during pole switching. Furthermore, while sensorless vector control of the rotation sensor is possible, it requires greater precision than conventional methods to properly perform pole switching. Although this invention has high industrial applicability, industrial use requires deep knowledge and expertise in electric motors, power circuits, and software, as well as greater accuracy in vector control and power control technology than before.

Claims

1. A multi-pole synchronous motor having a number of poles that is an integer multiple of the number of poles of the drive control device, comprising: an armature winding connecting means for each pole group, divided into units corresponding to the number of poles of the drive control device, in which multi-phase armature windings are concentrated for each phase and connected to each other and connected to the bridge circuit of a voltage-type PWM inverter; and a field winding connecting means for each of the aforementioned pole groups, in which field windings of the same number are connected to each other and connected to the bridge circuit of a field current control means through the sliders corresponding to the number of poles of the drive control device, wherein the multi-pole variable-speed wound-field synchronous motor has

2. A wiring system comprising: wiring for the number of poles connecting the field wiring box and the slip ring; a conduit housing the aforementioned wiring; slip rings mounted on the outer surface of the conduit in the number of poles and connected to the aforementioned wiring; two bearings, front and rear, whose inner rings engage with the aforementioned conduit; two bearing housings, front and rear, which engage with the outer rings of the bearings; a slider housing, whose outer surface is connected to the bearing housing with the same outer diameter and on which sliders and elastic supports are attached; and several sliders that rub against the outer surface of the slip ring. A axial-powered wound-field synchronous motor is characterized by having an axial-powered power supply unit, which includes an elastic support that supports the slider on the inner surface of the slider housing and presses it against the slip ring with constant pressure, field winding wiring connected to the slider and connected to the field winding, an outer ring rotation prevention means provided by a keyway at the front end of the front bearing housing, and a conduit rotation prevention means provided by a keyway at the rear end of the conduit, fitted onto a hollow rotor, and supplying DC current to the field winding at the axial center.

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