Shift method for synchronous motor for electrically driven motor vehicle and drive control device

Abstract

To improve power efficiency of a synchronous motor in a wide speed range from a low speed to a high speed.SOLUTION: In a pole-number switching method, the current value of AC current supplied to an armature is reduced at low speed by increasing the number of poles and increasing the torque multiplier of the electric motor, thereby reducing copper loss, and loss at high-speed rotation (mainly iron loss) is reduced at high speed by decreasing the number of poles and lowering the voltage and frequency of the AC current supplied to the armature. Furthermore, a further power-efficiency improvement effect is provided by connecting the circuit such that, during driving of the electric motor, inverter power-supply current of an armature winding becomes a power supply for a field winding, and such that, during regenerative braking, current generated from the armature winding is regenerated to a battery efficiently.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This paper applies vector control technology and power control technology to improve the power efficiency of synchronous motors used in electrically powered automobiles. [Background technology]

[0002] Traditionally, railcars have used series-wound DC motors with armature and field windings connected in series, controlled by variable resistance current controllers and later thyristor chopper current controllers. In recent years, advances in power semiconductor devices and the application of multivariable vector control based on modern control theory have enabled the use of induction motors in combination with VVVF inverters (abbreviated as VFDs). This has enabled high power efficiency, maintainability, and availability. However, in automotive applications, the power supply capacity is limited, necessitating strict vehicle weight reduction requirements. Furthermore, the need for a large interior space relative to the vehicle's size necessitates the need for compact and lightweight motors. Induction motors have lower power density than synchronous motors, resulting in larger size and weight for a given power output, making them unsuitable for automotive applications from a compact and lightweight perspective. Furthermore, induction motors, which accelerate and decelerate slowly using slip control at start-up, are unsuitable for vehicle operation with frequent schedules, such as waiting at traffic lights or stopping at arbitrary positions at short intervals. Due to the above operating conditions, synchronous motors are mainly used in automobiles because they are small, lightweight, and have good controllability and responsiveness. However, it has been pointed out that electric vehicles have a reduced range when driven at high speeds, and improving the power efficiency of synchronous motors at high speeds has become an urgent issue. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. JP-A-11-18382 Pole number switching rotating electric machine system [Patent Document 2] Patent Publication No. 2007-259575 Field-winding type synchronous motor and electric drive device [Patent Document 3] Patent Publication No. 2015-226425: Pole number switching induction motor driving method and pole number switching induction motor [Patent Document 4] Patent Publication No. 2014-39446 Pole number changing motor device [Patent Document 5] Patent Publication No. 2020-141493 Wound-field synchronous motor [Non-patent literature]

[0004] [Non-Patent Document 1] Motor Fan Tech, March 12, 2025 issue, "Nissan Ariya's wound field motor without permanent magnets" [Non-patent document 2] Meiden Times, Vol. 367, 2020, No. 2, Wound-field Synchronous Motor for Electric Vehicle Drive [Non-patent document 3] Transactions of the Institute of Electrical Engineers of Japan, Vol. 120, No. 11, 2000. Consideration of smooth pole change method for six-phase pole change induction motor for EV. [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 that Realize a Wide Operating Range" Summary of the Invention [Problem to be solved by the invention]

[0005] The rotational speed of synchronous motors, which are primarily used in automobiles, is determined by the frequency of the armature current. When accelerating from a standstill, where the rotational speed is low, excessive armature current increases copper loss and limits the lower limit of rotational speed, while when driving at high speeds, the frequency increases, which increases iron loss, and armature reaction reduces efficiency and limits the upper limit of rotational speed. Due to the way automobiles are used, gear ratios are set with an emphasis on maneuverability during acceleration from a standstill and low-speed driving, which has resulted in problems such as reduced range due to reduced power efficiency during high-speed driving, and reduced fuel and electricity costs. [Means for solving the problem]

[0006] The torque multiplier and other characteristics of a synchronous motor change depending on the number of poles. Specifically, the torque multiplier Kr varies in proportion to the pole number p to the 1 / 2 power. The armature voltage coefficient Kv varies in proportion to the pole number p to the 1 / 2 power. The relationship between the rotation speed R [rpm] and the power supply frequency f [Hz] varies inversely with the pole number p. (R [rpm] = 60 × f [Hz] × 2 / p) The motor torque τ is given by the product of the torque multiplier kr and the armature current Ia. Therefore, increasing the pole number p and increasing the torque multiplier at low speeds appears to solve the copper loss problem. Reducing the pole number p and lowering the frequency f at high speeds appears to solve the iron loss problem. Figure 1 summarizes the relationship between the pole number of a wound-field synchronous motor and the armature current, voltage, frequency, and torque for each operating mode (low, medium, and high speed). The advantages and disadvantages of each pole number are compared for each operating mode. The overall evaluation results in the table in Figure 1 show that for an 8-pole motor, there are no problems with power efficiency at low and medium speeds, but at high speeds, even if the armature reaction problem is eliminated through flux-weakening control, power efficiency issues remain. Therefore, a possible solution is to use a pole-switching method: at low speeds, the number of poles is increased to raise the motor's torque multiplier, thereby lowering the value of the AC current supplied to the armature and reducing copper loss; at high speeds, the number of poles is reduced to lower the voltage and frequency of the AC current supplied to the armature, thereby reducing losses (mainly iron loss) during high-speed rotation. Pole-switching is expected to improve the power efficiency of synchronous motors over a wide range of speeds, from low to high.

[0007] To change the number of poles of a synchronous motor, the number of poles of both the armature and the field must be changed simultaneously. Considering the driving performance of an automobile, the number of poles must be changed while the automobile is in operation, in the shortest possible time, without generating large shocks or vibrations. For the armature, the number of poles of a synchronous motor with a multi-phase armature winding is changed electronically, and for the field, the number of poles of a synchronous motor with a multi-pole field magnetic pole is changed electronically.

[0008] The speed change of a synchronous motor by the method described in paragraph 0007 can be realized by the following four processes: 1) a pole number switching command process of issuing a pole number switching command depending on the magnitude of the rotation speed; 2) an armature pole number switching process of switching the number of armature poles by switching the number of phases of the armature current of the synchronous motor in response to the pole number switching command from the pole number switching command process; 3) a field pole number switching process of switching the number of field poles by controlling the direction and magnitude of the current in the field winding of the synchronous motor in response to the pole number switching command from the pole number switching command process; and 4) an armature winding and field winding connecting process of the synchronous motor in which the armature current from the armature pole number switching process and the field current from the field pole number switching process are introduced to the armature winding and field winding.

[0009] In order to realize the speed change of a synchronous motor by the method described in paragraph 0008, means to be added or changed to a conventional synchronous motor and drive control device are shown in Fig. 2. The means include, as an armature winding and field winding connecting step, 1) an armature winding connecting means in which the multi-phase armature windings are collected for each phase and connected to the armature pole number switching step, and a field winding connecting means in which each field winding is connected to the field pole number switching step through a number of sliders equal to the number of field windings plus one, and, as an armature pole number switching step, 2) a coordinate conversion calculation means having a function of switching the number of phases and the number of poles of the multi-phase armature current instead of the conventional coordinate conversion calculation means that generates a three-phase AC waveform, and a field pole number switching step. The process is 3) field current control means for controlling the direction and magnitude of the DC current in each field winding so that the field generated by the field winding of the wound-field synchronous motor is similar in phase to the space vector of the magnetic field caused by the armature current described above, and as a pole number switching command process, 4) pole number switching command means for overall control by using a microprocessor to determine the rotation speed of the motor and issue pole number switching commands to the rotation coordinate conversion calculation means, field current control means, and other control means described above.

[0010] We will now discuss the relationship between the number of armature current phases and the number of armature poles. For example, if there are 12 phases of armature winding spaced 30 degrees apart in 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 x number of poles p / 2 = 12. In other words, if a synchronous motor with a 12-phase armature winding is used, it is possible to change the speed in three stages: 3-phase 8-pole, 6-phase 4-pole, or 12-phase 2-pole by changing the number of phases. The ratio of the electrical angle (phase angle of the AC waveform) θr to the mechanical angle (rotational 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 (rotational angular velocity of the motor shaft) ωrm is ωr = ωrm × p / 2 Furthermore, a synchronous motor with a 24-phase armature winding (24-phase armature windings spaced 15 degrees apart per rotation of the motor shaft) has number of phases ph × number of poles p / 2 = 24, meaning that four speed levels are possible: 3-phase 16 poles, 6-phase 8 poles, 12-phase 4 poles, and 24-phase 2 poles.

[0011] This section describes how to calculate the waveform of a multiphase AC current from the pole number command value pn and the electrical angle θr. The phase of the armature current for each phase is calculated using the coordinate transformation matrix below. Here, the number of pole pairs pn = number of poles p / 2, and the speed command [Vd* Vq*] is the input from the current controller in the block diagram of Figure 2. TIFF2025166268000002.tif24169The following describes the transformation matrix. TIFF2025166268000003.tif18161(i=1~12) The input / output relationship and processing contents of the coordinate transformation calculation means are shown in the block diagram of Figure 3. TIFF2025166268000005.tif9136

[0012] An example of the operation of the coordinate conversion calculation means when the number of phases of the armature current is switched will be described below. First, at the timing when the mechanical angle θrm=0, the pole pair number advance command value pn' is sent from the pole number switching command means. The coordinate transformation calculation means is a transformation matrix for the current pole pair number command value pn. TIFF2025166268000006.tif18153 Transformation matrix for pole log advance command value pn' The waveforms output by the calculation means during phase number switching operation are shown in Figure 5. Phase number switching is completed within one rotation of the motor (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 changed at the same time as the number of armature current phases are changed. The number of field poles is changed by electronically controlling the direction and magnitude of the DC current in the field winding. Details are given below. The field winding of the motor is connected to a field current control means (circuit) through a multi-pole wiper. As shown in the field current control circuit diagram in Figure 6, it is composed of a half-bridge circuit made up of two positive and negative pole constant current sources and the same number of power control elements such as IGBTs as the number of field poles. By turning on / off the gate signal of either the positive or negative IGBT, the magnitude of the current is controlled by the time width, allowing the field current to flow in either a positive or negative direction.

[0014] The calculation principle for determining the direction and magnitude of the current in the field winding is explained. Consider the rotating magnetic field caused by the armature winding current of one pole pair. As shown in Figure 7, the direction of the magnetic field (North pole) at a certain moment (t = 0) is taken as the α-axis. Suppose a sinusoidal current with angular frequency ωr is passed through the armature winding mentioned above. 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 an amount θr from the α-axis. If the number of magnetic fluxes at a position rotated an electrical angle θr from the α-axis is taken as φi, then φi = φ0 × cos(θr). (Figure 7) If the field fluxes created by the eight-pole field are each taken as Φi, and the magnetic field created by the armature at that phase angle is taken as φi, then the torque τ produced by the motor is proportional to the dot product of φi and Φi. If we define torque τ = torque coefficient Kri × [φi] · [Φi], [φi] and [Φi] as the armature magnetic field vector and field vector, respectively, then in order to increase torque τ relative to the magnitude of the field, the inner product of the armature magnetic field vector and the field vector must be maximized; in other words, the ratio of the magnitude of each element of [φi] must be equal to the ratio of the magnitude of each element of [Φi]; this is the optimization condition for increasing torque τ relative to the magnitude of the field.

[0015] In the previous section 0014, it was explained that making the ratio of the magnitude of each element of [φi] equal to the ratio of the magnitude of each element of [Φi], in other words, making the armature magnetic field vector and the field vector similar, is a condition for optimization that increases the torque τ relative to the magnitude of the field. FIG. 8 shows that the phase of the space vector of the magnetic field generated by the field current control means is similar to the phase of a 2-pole, 4-pole, or 8-pole field.

[0016] FIG. 9 shows an example of a wound-field synchronous motor having the armature winding connection means and field winding connection means shown in paragraph 0009. The eight-pole field winding is connected to the field current control means of FIG. 6 via one more slider than the number of field windings. The motor has a three-layer structure: a fixed shaft at the innermost part of the central axis, a rotor with field windings and field poles in the middle, and a stator (stator core) with an armature winding at the outermost part. Nine rows of sliders are provided between the outer surface of the innermost fixed shaft and the inner surface of the rotor. The armature has 48 teeth and is distributed-wound. The windings are grouped into one phase every 30 degrees of rotation, and are collected into 12 phase windings.

[0017] The pole number switching command means judges from the rotation speed of the motor and issues pole number switching commands to the rotation coordinate conversion calculation means, field current control means and other control means, thereby controlling the entire drive control device. ○ Speed ​​control circuit Ksp speed proportional gain (selection of characteristic value that changes depending on the number of poles) Ksi Speed ​​integral gain (same as above) Current command generator: General torque control of electric motors performed by current commands (same as above) Current controller Kcd Current proportional gain (selection of characteristic value that changes 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 effective current ○ Coordinate transformation Overall processing of multi-phase and multi-pole switching of armature ○Field current control Overall process of switching the number of poles in the field FIG. 10 is a diagrammatic representation of the processing contents of the pole number switching command means in the form of a flow chart, etc. The series of procedures for switching the number of poles is completed within the time it takes for the motor shaft to make one rotation.

[0018] When comparing wound-field synchronous motors with permanent magnet synchronous motors, the power loss associated with the DC supplied to the field winding is a disadvantage in terms of power efficiency. However, if the strength of the field can be controlled with current, for example, if the armature reaction during high-speed rotation can be controlled, this can be an advantage in improving motor efficiency. Therefore, as shown in Figure 11, if the DC current supplied from the DC power supply to the armature winding inverter bridge is connected so that it flows to the field current control circuit, it not only reduces the power loss associated with the DC constant current power supply supplied to the field winding, but also automatically reduces the field current during high-speed, light-load rotation when a strong field is not required, thereby reducing armature reaction, thereby providing an effective effect in improving power efficiency. The specific circuit configuration is as follows: the batteries, armature windings, and inverter bridges are divided into two groups with equal load currents. The positive poles of the batteries in one group are connected to the positive poles of all the inverter bridges in that group, the negative poles of all the inverter bridges in that group are connected to the positive poles of all the half-bridges in the field current control circuit, the negative poles of all the half-bridges in the field current control circuit are connected to the positive poles of all the inverter bridges in the other group, and the negative poles of all the inverter bridges in the other group are connected to the negative poles of the batteries in the other group. The negative poles of the batteries in the first group are connected to the positive pole of the batteries in the other group, and this is called the neutral point (GN). The common wire of all the field windings is connected to the neutral point GN.

[0019] In the power supply method for the field current control circuit shown in the previous section 0018 and FIG. 11, the direction of the regenerative current is opposite to the direction of the current in the field current control circuit during braking, so no current can flow. As shown in Figure 12, a diode bridge circuit is connected in parallel to the armature inverter bridge, and all positive poles of the diode bridges connected to one inverter bridge are connected to the positive input terminal of the charging circuit, and all negative poles of the aforementioned diode bridges are connected to the neutral point GN. All negative poles of the diode bridges connected to the other group of inverter bridges are connected to the negative input terminal of the charging circuit, and all positive poles of the diode bridges are connected to the neutral point GN. In addition, the two variable constant current circuits that supply DC current to the field current control circuit during regenerative braking are configured so that their current values ​​are controlled by the brake current command from the current command value generator. By connecting in this manner, regenerative current is efficiently regenerated to the battery during regenerative braking, and a current is supplied to the field winding that generates a field magnet of a strength corresponding to the regenerative braking torque.This not only improves power efficiency when the motor is driven, but also provides excellent braking characteristics: when the motor is rotating at high speed and regenerative braking is applied, the number of poles is switched to a small number, so regeneration is applied with moderate strength without generating high-voltage regenerative current, and at low speeds the number of poles is switched to a large number, so regenerative current of sufficient voltage is generated and regeneration is applied with sufficient strength. [Effects of the Invention]

[0020] By adding or modifying the four means described in paragraphs 0008 to 0017 of the specification and drawings 2 to 10 to the synchronous motor and its drive control device, the synchronous motor and its drive control device are provided with a type of electrical speed change function, and 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 loss, and at high speeds, the number of poles is reduced to lower the voltage and frequency of the AC current supplied to the armature, thereby reducing loss (mainly iron loss) during high-speed rotation, making it possible to provide a synchronous motor and drive control device that has high power efficiency over a wide speed range from low to high.

[0021] In addition to the four means described in paragraph 0020 above, by incorporating the "field current drive control circuit with improved torque conversion efficiency" and the "regenerative current flow path of the field current drive control circuit" described in paragraphs 0018 and 0019 of the specification and drawings 11 and 12 into a synchronous motor and its drive control device, it is possible to reduce power loss associated with the DC constant current power supply supplied to the field winding, control the field current to control armature reaction during high-speed rotation and thereby improve motor efficiency, and efficiently regenerate regenerative current to the battery during regenerative braking. Furthermore, it is possible to provide a drive control device with excellent braking characteristics, in which when the motor is rotating at high speed and regenerative braking is applied, the number of poles is switched to a small number, so regeneration is performed with moderate strength without generating high-voltage regenerative current, and at low speeds the number of poles is switched to a large number, so regenerative current of sufficient voltage is generated and regeneration is performed with sufficient strength. [Brief explanation of the drawings]

[0022] [Figure 1] Issues with synchronous motors during high-speed operation and speed change methods for resolving these issues [Figure 2] Four steps and methods for adding or modifying a conventional synchronous motor drive control device [Figure 3] Coordinate transformation calculation means for switching the number of phases of the armature current [Figure 4] Polyphase AC waveform generated by coordinate transformation calculation means [Figure 5] Current waveform of each phase when the number of armature current phases of the coordinate conversion calculation means is changed [Figure 6] Field current drive control circuit of field current control means [Figure 7] Field current calculation method for field current control means [Figure 8] The current value calculated by the field current control means and the spatial phase of the generated magnetic field [Figure 9] Example of a wound field synchronous motor in this patent case [Figure 10] An embodiment including a flowchart of the pole number switching command means [Figure 11]Power supply circuit for field current control means with improved torque conversion efficiency [Figure 12] Regenerative current flow path and field current flow path of the power supply circuit of the field current control means DETAILED DESCRIPTION OF THE INVENTION

[0023] The embodiment of this patent is realized by adding or modifying four means to an existing wound-field synchronous motor and its drive control device. The new additions are a wiper and field current control device (one more than the number of field windings), while the remaining modifications are to make the current drive control device multi-phase, multi-polar, and multi-mode. The speed change function and the resulting improved power efficiency provided by this patent can also be achieved with mechanical transmissions used in automobiles powered by internal combustion engines. However, adding a mechanical transmission increases vehicle weight and reduces space efficiency, which goes against the goals of electrification. Furthermore, the electrical speed change achieved by this patent occurs within one rotation of the motor shaft while the automobile is in operation, without generating shock or vibration, resulting in improved driving performance. The embodiment of this patent is an evolutionary extension of current electric vehicle technology and can be said to bring significant benefits. [Industrial Applicability]

[0024] This patent provides a complete, fundamental technical concept. Applying this concept industrially requires the design and development of devices, circuits, and software. This design and development process is expected to pose significant challenges, including: The motor's thermal design must be properly implemented; the rotors and slip rings must be sufficiently durable; and the servo characteristics of the speed controller, current command generator, current controller, and decoupling control must be properly tailored for each pole number when switching between poles. Furthermore, while sensorless vector control using a rotation sensor is possible, more precision than ever is required to properly switch between poles. While this patent has high industrial applicability, its industrial application requires in-depth knowledge and expertise in motors, power circuits, and software, as well as greater precision in vector control and power control technology than ever before.

Claims

1. A speed change method for a synchronous motor for an electric vehicle, comprising all of the following steps: a pole number switching command step of issuing a pole number switching command in accordance with the magnitude of the rotational speed; an armature pole number switching step of switching the number of armature poles by switching the number of phases of the armature current of the synchronous motor in response to the pole number switching command from the pole number switching command step; a field pole number switching step of switching the number of field poles by controlling the direction and magnitude of the current in the field winding of the synchronous motor in response to the pole number switching command from the pole number switching command step; and an armature winding and field winding connecting step of the synchronous motor of guiding the armature current from the armature pole number switching step and the field current from the field pole number switching step to the armature winding and field winding.

2. 2. A speed change method for a synchronous motor for an electric vehicle according to claim 1, characterized in that the drive control device for a synchronous motor for an electric vehicle comprises all of the following means: armature winding connection means in which polyphase armature windings are collected for each phase and connected to an armature pole number switching process; field winding connection means in which each field winding is connected to the field pole number switching process through a number of sliders equal to the number of field windings plus one; coordinate conversion calculation means having a function of switching the number of phases and the number of poles of polyphase armature currents instead of the conventional coordinate conversion calculation means for generating a three-phase AC waveform; field current control means for controlling the direction and magnitude of DC current in each field winding so that the field generated by the field winding of the wound-field synchronous motor is similar in phase to the space vector of the magnetic field generated by the armature current; and pole number switching command means for overall control by using a microprocessor to judge from the rotational speed of the motor and issue a pole number switching command to the rotational coordinate conversion calculation means, field current control means and other control means.

3. 3. A drive control device for a synchronous motor according to claim 2, wherein the battery, armature winding and inverter bridge circuit are divided into two groups having equal load currents, and the DC current supplied from the battery to the inverter bridge circuit of the armature winding is connected to flow to the field current control circuit, and the rectified current of the diode bridge circuit that rectifies the regenerative current of the armature winding is connected to flow directly to the charging circuit without passing through the field current control circuit, and a brake current command from a current command value generator is connected to two variable constant current circuits that supply DC current to the field current control circuit, so that the value of the current supplied to the field current control circuit during regenerative braking is controlled.

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