Motor control device

Abstract

This motor control device controls a vehicle driving motor that is driven by a power converter for performing power conversion from DC power to AC power and is provided with coils of a plurality of phases. The motor control device comprises: a coil temperature acquisition unit that acquires or estimates the temperatures of the coils of the plurality of phases; a torque restriction unit that restricts the output of the motor when the temperature of the coil of at least one phase among the coils of the plurality of phases exceeds a first threshold value; and a position control unit that controls a stop position of the rotor of the motor when the temperature of the coil exceeds a second threshold value that is a threshold value lower than the first threshold value. When the temperature of the coil exceeds the second threshold value, the position control unit controls the stop position of the rotor of the motor so that the absolute value of current flowing through the phase having said coil temperature is equal to or less than a predetermined value when the vehicle stops.

Description

Motor control device

[0001] The present invention relates to a motor control device.

[0002] Regarding the motor control device of a vehicle, for example, in Patent Document 1, a control device of a vehicle having the following configuration is disclosed. First, the temperature of a multi-phase coil is estimated from the detection information of a temperature sensor that detects the temperature of a single-phase coil, and a motor protection is provided by using a current concentration counter for a specific phase. Also, for example, when the vehicle is on a steep uphill slope, the vehicle may reverse due to a decrease in the motor output by the motor temperature protection function. In this case, it is configured to detect whether the current concentration phase has switched based on the position of the rotor and determine whether to restore the motor output.

[0003] Japanese Patent Application Laid-Open No. 2008-131714

[0004] In view of the configuration of the prior art, an object of the present invention is to provide a motor control device that can prevent an unintentional motor temperature protection function from operating and having an adverse effect on vehicle start-up, and further extend the life of motor components.

[0005] A motor control device that controls a vehicle drive motor driven by a power converter that performs power conversion from direct current power to alternating current power and has a plurality of phase coils, the motor control device including a coil temperature acquisition unit that acquires or estimates the temperature of the plurality of phase coils, a torque limitation unit that limits the output of the motor when the coil temperature of at least one phase of the plurality of phase coils exceeds a first threshold value, and a position control unit that controls the stop position of the rotor of the motor when the coil temperature exceeds a second threshold value that is a threshold value lower than the first threshold value, and the position control unit controls the stop position of the rotor of the motor so that the absolute value of the current flowing through the phase of the coil temperature becomes a predetermined value or less when the vehicle stops when the coil temperature exceeds the second threshold value.

[0006] A motor control device that can achieve both prevention of the operation of an unintentional motor temperature protection function and extension of the life of motor components can be provided.

[0007] A circuit diagram illustrating a configuration related to a motor control device according to one embodiment of the present invention. A graph showing temperature thresholds and temperature ranges related to motor control according to one embodiment of the present invention. A flowchart relating to the control of a motor control device according to one embodiment of the present invention. A diagram illustrating the control of the motor rotor and related electrical angles according to one embodiment of the present invention.

[0008] Embodiments of the present invention will be described below with reference to the drawings. The following description and drawings are illustrative for illustrating the present invention, and have been omitted and simplified as appropriate for clarity of explanation. The present invention can also be carried out in various other forms. Unless otherwise specified, each component may be singular or plural.

[0009] The positions, sizes, shapes, and ranges of the components shown in the drawings may not represent their actual positions, sizes, shapes, and ranges in order to facilitate understanding of the invention. Therefore, the present invention is not necessarily limited to the positions, sizes, shapes, and ranges disclosed in the drawings.

[0010] (First Embodiment and Overall Configuration) (Figure 1) The motor 1 equipped with the motor control device 8 of the present invention is, for example, a drive device for a hybrid vehicle or an electric vehicle, and is a three-phase AC synchronous motor with magnets built into the rotor. The motor 1 consists of a stator having coils for three phases, U-phase, V-phase, and W-phase, and a rotor in which rotational force is generated by the magnetic flux that changes as current flows through the coils wound in each slot of the stator.

[0011] The inverter 2 is equipped with six transistors 2a, two of which are connected in series. This allows the inverter 2 to have an upper arm and a lower arm for the U-phase, V-phase, and W-phase, respectively. A diode is electrically connected in antiparallel between the collector and emitter of each transistor 2a. The inverter 2 is a power converter that converts DC power input from the battery 4 (described later) into AC power, and uses the converted AC power to drive the motor 1. The inverter 2 also includes a motor control device 8.

[0012] AC cable 3 is a three-phase AC cable that electrically connects motor 1 and inverter 2, and conducts AC power converted from DC power in inverter 2. AC cable 3 is also a cable through which current due to the induced voltage originating from motor 1 flows, and is subject to temperature protection by motor control device 8, which will be described later.

[0013] Battery 4 is a secondary battery, such as a nickel-metal hydride battery or a lithium-ion battery, and maintains a voltage of approximately 100V to 400V. DC cable 5 is a cable that electrically connects inverter 2 and battery 4.

[0014] The current sensor 6 is built into the motor 1 and detects the current of each phase flowing through the AC cable 3. The temperature sensor 7 is built into the motor 1 and detects the temperature of the coils of each phase of the motor 1. The angle sensor 9 is built into the motor 1 and detects the rotation angle of the motor 1. A reduction gear 11 and a clutch 10 are provided between the motor 1 and an axle (not shown) of the vehicle. The clutch 10 is provided between the motor 1 and the reduction gear 11 and can disconnect the rotation axis of the motor 1 from the axle (not shown), preventing the rotation from being synchronized, thus facilitating the control of the stopping position of the rotor of the motor 1, which will be described later. The reduction gear 11 reduces the rotation of the motor 1 via multiple gears and transmits the torque obtained by reducing the rotational speed to the axle.

[0015] The motor control device 8 is installed in the inverter 2 and outputs control signals (PWM signals) to the gate terminals of the six transistors 2a of the inverter 2. By controlling each transistor 2a, the motor control device 8 controls the current supplied from the inverter 2 to the motor 1. In this way, the motor control device 8 controls the torque of the motor 1.

[0016] The motor control device 8, which is a feature of the present invention, will now be described in detail. The motor control device 8 has the function of a coil temperature acquisition unit that acquires the temperature of the coils of each phase of the motor 1, a torque limiting unit that limits the output of the motor 1 when the coil temperature of at least one of the coils of each phase exceeds a first threshold (Figure 2) described later, and a position control unit that controls the stopping position of the rotor of the motor 1 when the coil temperature of at least one of the coils of each phase exceeds a second threshold (Figure 2) described later, which is lower than the first threshold. In Figure 2, the motor control device 8 is shown to have a position control determination unit 8a and a position control command unit 8b, where the position control determination unit 8a has the functions of a coil temperature acquisition unit, a torque limiting unit, and a position control unit. Based on the determination result, the position control determination unit 8a outputs the determined information to the position control command unit 8b, and the position control command unit 8b outputs a motor control command to each transistor 2a of the inverter 2 based on the input information.

[0017] The position control determination unit 8a and the position control command unit 8b will now be described in detail. The position control determination unit 8a acquires information detected by the current sensor 6, temperature sensor 7, and angle sensor 9, and determines an appropriate stopping position for the rotor of the motor 1 based on this acquired information. The position control determination unit 8a outputs the determined rotor stopping position information to the position control command unit 8b. In addition, when determining the stopping position of the rotor of the motor 1, the position control determination unit 8a may not only make a determination based on the coil temperature acquired from the temperature sensor 7, but may also make a determination based on an estimated coil temperature. Furthermore, as will be described later, depending on the acquired coil temperature of the motor 1, the position control determination unit 8a may not only make a determination to control the stopping position of the rotor of the motor 1, but also make a determination to implement torque limiting for temperature protection of the motor 1.

[0018] (Figure 2) In the graph in Figure 2, the vertical axis represents temperature (T [°C]) and the horizontal axis represents time (t [min]). The vertical axis of the graph shows a first threshold Ttp and a second threshold Tpc, where the first threshold Ttp is a temperature threshold higher than the second threshold Tpc. The present invention is characterized by providing a motor position control region 20b, which is a temperature region lower than the motor temperature protection region 20c, for the temperature range in which the motor control device 8 determines what kind of motor control is necessary for the coil temperature acquired. A first threshold Ttp is provided at the boundary between the motor position control region 20b and the motor temperature protection region 20c, and a second threshold Tpc is provided at the boundary between the normal operation region 20a and the motor position control region 20b.

[0019] The first threshold Ttp is a threshold used by the motor control device 8 to determine whether the temperature is within the range required to protect the motor 1, based on the coil temperature information acquired by the motor control device 8. When the coil temperature of at least one of the coils of each phase of the motor 1, acquired or estimated from the temperature sensor 7, is within the motor temperature protection region 20c, that is, when the acquired coil temperature exceeds the first threshold Ttp, the motor control device 8 outputs a control command for motor temperature protection to each transistor 2a of the inverter 2. This executes torque limiting of the motor 1. The motor temperature protection region 20c is a temperature range that has been conventionally used for motor temperature protection in motor control.

[0020] The second threshold Tpc is a threshold that the motor control device 8 uses to determine whether the temperature is within the range for controlling the stopping position of the motor 1's rotor, based on the coil temperature information it has acquired. When the coil temperature of at least one of the coils of each phase of the motor 1, acquired or estimated from the temperature sensor 7, is within the motor position control region 20b, that is, when the acquired coil temperature exceeds the second threshold Tpc, the motor control device 8 outputs a control command to each transistor 2a of the inverter 2 regarding the stopping position of the motor 1's rotor. With this configuration, the stopping position of the motor 1's rotor is actively controlled before the coil temperature of the motor 1 enters the motor temperature protection region 20c, thereby preventing unintended temperature protection processing of the motor 1 that would result in torque limitation during starting.

[0021] Furthermore, if the motor control device 8 determines that the coil temperatures of two phases of the motor 1 exceed the second threshold Tpc and the motor 1 is subject to control, the motor control device 8 may compare the coil temperatures of those two phases and control the stopping position of the motor 1 rotor based on the temperature of the phase with the higher temperature. In addition, even if the coil temperature of the motor 1 determined by the motor control device 8 is within the motor temperature protection region 20c, the control of the stopping position of the motor 1 rotor may be continued.

[0022] (Figure 3) The control decisions of the motor control device 8 described in Figures 1 and 2 will be explained using a flowchart. It is assumed that after the motor 1 and inverter 2 are started, the motor control device 8 constantly monitors the coil temperature of the motor 1 and the current flowing through the coil of the motor 1.

[0023] In step S01, it is determined whether the coil temperature of the motor 1, obtained or estimated from the temperature sensor 7, exceeds the second threshold Tpc (Figure 2) when the driver is operating normally. The coil temperature of the motor 1 is the temperature of at least one of the U-phase, V-phase, and W-phase coils that has the highest temperature. If it is determined that the coil temperature exceeds the second threshold Tpc (YES), in step S02, a motor position control flag is set for the phase whose coil temperature exceeds the second threshold Tpc. The phase with the flag set will be referred to as the flag phase below. If the coil temperature does not exceed the second threshold Tpc (NO), the flowchart returns to the beginning.

[0024] Next, in step S03, the flow branches depending on whether the driver is performing an operation to continue normal driving or an operation to decelerate. If the driver is performing an operation to decelerate (NO), the rotational speed of motor 1 is low due to the deceleration of the vehicle, and at this time, motor 1 is rotating at a speed close to the point of stopping (motor lock) (extremely low rotation) (step S04). The flow when the driver continues normal driving (YES) will be described later.

[0025] In step S05, it is determined whether the coil temperature of the flag phase has fallen below the second threshold Tpc due to the vehicle's deceleration. If it is determined that the coil temperature of the flag phase has fallen below the second threshold Tpc (YES), the flag of the flag phase is cleared and the flowchart returns to the beginning. If the coil temperature of the flag phase has not fallen below the second threshold Tpc (NO), in step S06, the motor control device 8 outputs a control command to each transistor 2a of the inverter 2 to set the electrical angle to the permitted angle band B shown in Figure 4 (details are described later in Figure 4) to control the stopping position of the motor 1 rotor. In this way, the intended stopping position of the motor 1 rotor is controlled and the motor 1 rotor is stopped (step S07). By doing this, current does not concentrate in the high-temperature phase (flag phase) when starting, preventing unintended activation of the motor 1's temperature protection function. In addition, because current can be uniformly distributed to the coils of each phase without concentrating current in the flag phase, the lifespan of the motor components can be extended.

[0026] In step S03 described above, if the driver continues normal driving while the flag phase is present (YES), then motor 1 is rotating normally (step S11). In step S12, it is determined whether the coil temperature of the flag phase exceeds the first threshold Ttp (Figure 2). If the coil temperature of the flag phase exceeds the first threshold Ttp (YES), then in step S13, torque output is limited to protect motor 1 from temperature. If the coil temperature of the flag phase does not exceed the first threshold Ttp, the process returns to step S02.

[0027] In step S14, after implementing temperature protection for motor 1, the flow branches depending on whether the driver is continuing normal driving operations or performing deceleration operations. If the driver is continuing normal driving operations (YES), the process returns to step S12, and the determination of whether the coil temperature of the flag phase exceeds the first threshold Ttp is repeated. If the driver is performing deceleration operations (NO), motor 1 is rotating at a rotational speed close to the point of motor lock (extremely low rotation) (step S15). In step S06, the stopping position of the rotor of motor 1 is controlled, and in step S07, the rotation of motor 1 is stopped.

[0028] (Figure 4) Figure 4 shows the three-phase sine waves of the U-phase, V-phase, and W-phase in motor 1. In the figure, the solid line represents the current of the U-phase, the dotted line represents the current of the V-phase, and the dashed line represents the current of the W-phase. The vertical axis of the figure represents the current value flowing through the coils of each phase (U-phase, V-phase, and W-phase), and the horizontal axis represents the electrical angle. The threshold T1 is a dashed line parallel to the horizontal axis and represents the current value of 20% of the maximum current flowing through each phase (U-phase, V-phase, and W-phase). The threshold T1 may be arbitrarily changed depending on the specifications of motor 1, etc. Angle ranges where the current value is higher than the two thresholds T1 are designated as prohibited angle range A, which is unsuitable as the stopping position of the rotor of motor 1. Angle ranges where the current value flowing through the coils of each phase is lower than the two thresholds T1 are designated as permitted angle range B, which is appropriate for controlling the stopping position of the rotor of motor 1.

[0029] The motor control device 8 needs to stop the rotor of the motor 1 at an appropriate position so that the electrical angle of the target phase falls within the permitted angle band B shown in Figure 4. For example, if the flag phase in step S02 of Figure 3 is the U phase, then, as shown in Figure 4, the motor control device 8 actively stops the rotor of the motor 1 at electrical angles within the permitted angle band B, which includes electrical angles of 0 to 12 degrees, 168 to 192 degrees, and 348 to 360 degrees, and controls the stopping position of the rotor. Thus, in the present invention, when the coil temperature of the flag phase in Figure 2 exceeds the second threshold Tpc (Figure 2), the motor control device 8 controls the stopping position of the rotor of the motor 1 so that the absolute value of the current flowing through the flag phase is less than or equal to a predetermined value when the vehicle is stopped. This allows the vehicle to start with a low current value in the flag phase coil, preventing current from concentrating in the flag phase during starting and unintentionally triggering the temperature protection process of the motor 1.

[0030] Furthermore, the number of pole pairs of motor 1 may be increased to four or more. This increases the number of times the flag phase passes through the permitted angle band B relative to a rotation angle of 360 degrees, making it even easier to control motor 1.

[0031] The configuration of the present invention as described above provides the following effects. Conventionally, when a coil in any phase of a motor became hot, the torque output was suppressed to protect the motor from overheating, rendering the vehicle unable to move. When restarting the vehicle from this state, the output torque is limited, so for example, if the vehicle is stopped on a steep incline, it may not be able to output the torque necessary to start. This could have the adverse effect of causing the vehicle to roll backward when starting. Furthermore, passive motor control that waits for the coil of the phase in which current is concentrated to switch naturally when the vehicle rolls backward when a coil in any phase becomes hot has the problem of not being able to reliably prevent the unintended activation of the motor's temperature protection function (torque output suppression).

[0032] Based on this, the present invention actively controls the motor 1 by utilizing the temperature protection range of a conventional motor while also providing a temperature range for controlling the stopping position of the motor 1's rotor. This prevents the repeated flow of large currents to the high-temperature coils during vehicle startup, thus preventing unintended activation of the motor 1's temperature protection function. Furthermore, by controlling the stopping position of the motor 1's rotor at a predetermined electrical angle in each phase to minimize the temperature difference between the coils of each phase, the lifespan of components of the motor 1, such as insulators, is extended, and the motor 1 is expected to fail. In addition, the margin for temperature protection of the motor 1 can be improved without changing the hardware of the motor 1.

[0033] According to the embodiments of the present invention described above, the following effects and advantages are achieved.

[0034] (1) A motor control device 8 for controlling a vehicle drive motor that is driven by a power converter that converts DC power to AC power and has multiple phase coils, comprising: a coil temperature acquisition unit that acquires or estimates the temperature of the multiple phase coils; a torque limiting unit that limits the output of the motor 1 when the coil temperature of at least one of the multiple phase coils exceeds a first threshold Ttp; and a position control unit that controls the stopping position of the rotor of the motor 1 when the coil temperature exceeds a second threshold Tpc which is a threshold lower than the first threshold Ttp, wherein the position control unit controls the stopping position of the rotor of the motor 1 when the vehicle is stopped so that the absolute value of the current flowing through the coil temperature phase is less than or equal to a predetermined value. In this way, a motor control device 8 can be provided that prevents unintended activation of the temperature protection function of the motor 1 and extends the lifespan of the motor components.

[0035] (2) If the coil temperature of two of the multi-phase coils exceeds the second threshold Tpc, the two coil temperatures are compared with each other, and the stopping position of the rotor of the motor 1 is controlled based on the coil temperature of the phase with the higher temperature. This makes it possible to more effectively prevent unintended activation of the temperature protection function of the motor 1.

[0036] (3) Between the motor 1 and the axle of the vehicle, a reduction gear 11 is provided to transmit the rotation of the motor 1's rotating shaft to the axle, and a clutch 10 is provided to disconnect the rotating shaft from the axle. The clutch 10 is provided between the motor 1 and the reduction gear 11. This makes it easy to control the stopping position of the motor 1's rotor.

[0037] (4) In motor 1, the number of pole pairs is four or more. This makes it easier to control the stopping position of the rotor of motor 1.

[0038] It should be noted that the present invention is not limited to the embodiments described above, and various modifications and combinations of other configurations can be made without departing from the spirit of the invention. Furthermore, the present invention is not limited to having all the configurations described in the embodiments described above, and may also include configurations in which some of those configurations are omitted.

[0039] 1. Motor 2. Inverter 2a. Transistor 3. AC cable 4. Battery 5. DC cable 6. Seismic intensity sensor 7. Temperature sensor 8. Motor control device 8a. Position control judgment unit 8b. Position control command unit 9. Angle sensor 10. Clutch 11. Reducer 20a. Normal operation area 20b. Motor position control area 20c. Motor temperature protection area

Claims

1. A motor control device for controlling a vehicle drive motor that is driven by a power converter that converts DC power to AC power and has multiple phase coils, comprising: a coil temperature acquisition unit that acquires or estimates the temperatures of the multiple phase coils; a torque limiting unit that limits the output of the motor when the coil temperature of at least one of the multiple phase coils exceeds a first threshold; and a position control unit that controls the stopping position of the motor rotor when the coil temperature exceeds a second threshold which is lower than the first threshold, wherein the position control unit controls the stopping position of the motor rotor when the vehicle is stopped so that the absolute value of the current flowing through the coil temperature phase is less than or equal to a predetermined value.

2. The motor control device according to claim 1, wherein if the coil temperature of two of the multiple phase coils exceeds the second threshold, the motor control device compares the coil temperatures of the two phases and controls the stopping position of the motor rotor based on the coil temperature of the phase with the higher temperature.

3. The motor control device according to claim 1, wherein a reduction gear for transmitting the rotation of the motor's rotating shaft to the axle and a clutch for separating the rotating shaft from the axle are provided between the motor and the axle of the vehicle, and the clutch is provided between the motor and the reduction gear.

4. The motor control device according to claim 1, wherein the motor has four or more pole pairs.

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