Motor control device

Abstract

This effectively suppresses the deterioration of the upper and lower arms of the inverter connected to the open-winding motor. [Solution] Prior to starting an open-winding motor, the motor control device of the present disclosure sets either the upper-phase single-sided drive mode or the lower-phase single-sided drive mode as the operating mode so that the upper arm and lower arm of one of the first and second inverters with less accumulated stress are fixed to the ON position. When transitioning the operating mode from the double-sided drive mode to the upper-phase single-sided drive mode or the lower-phase single-sided drive mode, the device sets the upper-phase single-sided drive mode and the lower-phase single-sided drive mode, whichever was not set as the operating mode immediately before setting the double-sided drive mode, as the operating mode.

Description

Technical Field

[0001] The present disclosure relates to a motor control device that controls first and second inverters connected to an open winding motor.

Background Art

[0002] Conventionally, as a control device for an open winding motor, depending on the rotational speed and torque of the motor, there is known one that selectively executes either one-sided drive control in which one of two inverters connected to the open winding motor is neutralized and the other is switched, or two-sided drive control in which both of the two inverters are switched (see, for example, Patent Document 1). In this control device, in one of the two inverters to be neutralized, an upper arm on-state in which all upper arm elements are fixed on and a lower arm on-state in which all lower arm elements are fixed on are switched at a vertical switching frequency. Thereby, in the inverter to be neutralized, it is possible to switch the element through which the maximum phase current flows and disperse heat generation.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, in the inverter that has been neutralized, when the element that has been fixed on is turned off, stress caused by rapid cooling acts on the element. Further, when the element that has been fixed off is turned on, stress caused by rapid heat generation acts on the element. However, in the invention described in Patent Document 1 above, the stress acting on the element due to a rapid temperature change is not sufficiently considered, and there is a risk that deterioration of the upper arm and lower arm of the inverter cannot be suppressed.

[0005] Therefore, the primary objective of this disclosure is to effectively suppress the deterioration of the upper and lower arms of an inverter connected to an open-winding motor. [Means for solving the problem]

[0006] The motor control device of this disclosure is a motor control device that controls first and second inverters connected to an open-winding motor, and in response to a request from the open-winding motor, it controls any of the following modes: an upper-phase single-side drive mode in which the upper arm of one of the first and second inverters is turned ON and the lower arm is turned OFF, thereby controlling the other of the first and second inverters by switching; a lower-phase single-side drive mode in which the lower arm of one of the first and second inverters is turned ON and the upper arm is turned OFF, thereby controlling the other of the first and second inverters by switching; and a double-side drive mode in which both of the first and second inverters by switching. The system includes a mode setting unit for setting the operating mode, wherein, prior to starting the open-winding motor, the mode setting unit sets either the upper-phase single-sided drive mode or the lower-phase single-sided drive mode to the operating mode such that the upper arm and lower arm of one of the first and second inverters with less accumulated stress are fixed to the ON position, and when transitioning the operating mode from the double-sided drive mode to the upper-phase single-sided drive mode or the lower-phase single-sided drive mode, the unit sets the upper-phase single-sided drive mode and the lower-phase single-sided drive mode, whichever was not set to the operating mode immediately before setting the double-sided drive mode, to the operating mode.

[0007] Prior to starting the open-winding motor, the mode setting unit of the motor control device disclosed sets either the upper-phase single-sided drive mode or the lower-phase single-sided drive mode to the operating mode such that the upper arm or lower arm of one of the first and second inverters with less accumulated stress is fixed to the ON position. This suppresses the stress applied to the upper arm or lower arm of one of the first and second inverters, which has a large amount of accumulated stress, when starting the open-winding motor, and makes it possible to equalize the accumulated stress on the upper arm and lower arm of one of the first and second inverters. Furthermore, when the operating mode is changed from the double-sided drive mode to the upper-phase single-sided drive mode or the lower-phase single-sided drive mode, the mode setting unit sets the upper-phase single-sided drive mode or the lower-phase single-sided drive mode, whichever was not set to the operating mode immediately before the setting of the double-sided drive mode, to the operating mode. As a result, the upper or lower arm, which was turned on and generated heat in response to the transition from the previous upper-phase single-sided drive mode or lower-phase single-sided drive mode to the double-sided drive mode, is no longer turned off and rapidly cooled in response to the current transition from the double-sided drive mode to the upper-phase single-sided drive mode or lower-phase single-sided drive mode. This allows for the equalization of the cumulative stress on one of the upper and lower arms of the first and second inverters. Consequently, the motor control device of this disclosure makes it possible to effectively suppress the deterioration of one of the upper and lower arms of the first and second inverters connected to the open-winding motor. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram showing a vehicle including a motor control device in this disclosure. [Figure 2] This flowchart shows the routines executed by the motor control device of this disclosure. [Figure 3] This flowchart shows other routines performed by the motor control device of this disclosure. [Modes for carrying out the invention]

[0009] Next, with reference to the drawings, embodiments for carrying out the invention of this disclosure will be described.

[0010] Figure 1 is a schematic diagram showing a vehicle 1 including an electronic control unit (hereinafter referred to as "ECU") 10 as a motor control device of the present disclosure. The vehicle 1 shown in the figure is a battery electric vehicle (BEV) including a motor generator MG and a battery (energy storage device) B. In addition to the motor generator MG and battery B, the vehicle 1 includes a motor drive device 2 that exchanges power with battery B to drive the motor generator MG.

[0011] The motor-generator MG is a three-phase AC motor (synchronous generator motor) including a U-phase coil Lu, a V-phase coil Lv, and a W-phase coil Lw, each wound around a stator (stator core) (not shown), and is an open-winding motor in which the ends of the U-phase coil Lu, V-phase coil Lv, and W-phase coil Lw are not connected to each other. The motor-generator MG is connected to an output shaft, which is connected to the left and right wheels (drive wheels) W via a differential gear DF ​​and a drive shaft DS, via a reduction mechanism (not shown), and is driven by power from the battery B to output drive torque to the output shaft. In addition, the motor-generator MG outputs regenerative braking torque to the output shaft when the vehicle 1 is braked. Note that the U-phase coil Lu, V-phase coil Lv, and W-phase coil Lw may include multiple coils connected in parallel.

[0012] Battery B is, for example, a lithium-ion secondary battery or a nickel-metal hydride secondary battery having a rated output voltage of 200 to 800V. The positive terminal of battery B is connected to the positive side power line PL, and the negative terminal of battery B is connected to the negative side power line NL. The first and second inverters 3 and 4 are electrically connected in parallel to the positive side power line PL and the negative side power line NL.

[0013] The motor drive unit 2 includes a first inverter 3 and a second inverter 4. The first inverter 3 includes six transistors (e.g., insulated-gate bipolar transistors (IGBTs)) Tr1, Tr2, Tr3, Tr4, Tr5, and Tr6 as switching elements, and six diodes D1, D2, D3, D4, D5, and D6 connected in parallel in opposite directions to each of the transistors Tr1-Tr6. The transistors Tr1-Tr6 are paired up so that they act as the source and sink sides with respect to the positive power line PL and the negative power line NL. As shown in Figure 1, one end of the U-phase coil Lu of the motor generator MG is electrically connected to the connection point between the pair of transistors Tr1 and Tr2. Also, one end of the V-phase coil Lv of the motor generator MG is electrically connected to the connection point between the pair of transistors Tr3 and Tr4. Furthermore, one end of the W-phase coil Lw of the motor generator MG is electrically connected to the connection point between the pair of transistors Tr5 and Tr6. Transistors Tr1, Tr3, and Tr5 constitute the upper arm of the first inverter 3, and transistors Tr2, Tr4, and Tr6 constitute the lower arm of the first inverter 3.

[0014] The second inverter 4 includes six transistors (e.g., IGBTs) Tra, Trb, Trc, Trd, Tre, and Trb as switching elements, and six diodes Da, Db, Dc, Dd, De, and Df connected in parallel in the opposite direction to each transistor Tra-Trf. The transistors Tra-Trf are paired up so that they act as the source and sink sides with respect to the positive power line PL and the negative power line NL. As shown in Figure 1, the other end of the U-phase coil Lu of the motor generator MG is electrically connected to the connection point between the pair of transistors Tra and Trb. Also, the other end of the V-phase coil Lv of the motor generator MG is electrically connected to the connection point between the pair of transistors Trc and Trd. Furthermore, the other end of the W-phase coil Lw of the motor generator MG is electrically connected to the connection point between the pair of transistors Tre and Trb. Transistors Tra, Trc, and Tre constitute the upper arm of the second inverter 4, and transistors Trb, Trd, and Tref constitute the lower arm of the second inverter 4.

[0015] Furthermore, as shown in Figure 1, the motor drive unit 2 includes a drive mode selector switch 5 provided on the positive-side power line PL and the negative-side power line NL, and a switch 6 provided on the positive-side power line PL. The drive mode selector switch 5 includes a switching element 5p that connects the positive-side power line PL, i.e., the positive terminal of battery B, to the second inverter 4 and also disconnects the connection between them, and a switching element 5n that connects the negative-side power line NL, i.e., the negative terminal of battery B, to the second inverter 4 and also disconnects the connection between them, thereby enabling the electrical connection between battery B and the second inverter 4 to be disconnected. The switch 6 also connects the positive-side power line PL, i.e., the positive terminal of battery B, to the second inverter 4 and also disconnects the connection between them.

[0016] The ECU10 includes a microcomputer with a CPU, ROM, RAM, input / output interface, etc. (not shown). The ECU10 acquires the accelerator opening from an accelerator pedal position sensor (not shown), the vehicle speed from a vehicle speed sensor (not shown), the detection value of a resolver (not shown) that detects the rotational position of the rotor of the motor generator MG, the detection values ​​of various voltage sensors, the detection values ​​of various current sensors, the temperature TTa of transistor Tra of the second inverter 4 detected by the temperature sensor 7, and the temperature TTb of transistor Trb of the second inverter 4 detected by the temperature sensor 8. The ECU10 also calculates the rotational speed Nm of the motor generator MG based on the detection value of the resolver. Furthermore, the ECU10 sets the required torque required for the vehicle 1 to run based on the accelerator opening and vehicle speed, and sets the torque command value Tm* to the motor generator MG based on the set required torque. In addition, the ECU10 controls the opening and closing of the drive mode selector switch 5 and switch 6.

[0017] The ECU 10 controls the first and second inverters 3 and 4 of the motor drive unit 2 based on the rotational speed Nm and torque command value Tm* when the vehicle 1 is running. More specifically, while the vehicle 1 is running, the ECU 10 functions as a mode setting unit that sets one of the following operating modes for the first and second inverters 3 and 4: upper-phase single-sided drive mode (hereinafter referred to as "upper-phase Y drive mode"), lower-phase single-sided drive mode (hereinafter referred to as "lower-phase Y drive mode"), or both-sided drive mode (hereinafter referred to as "H (full-bridge) drive mode"), in response to the rotational speed Nm and torque command value Tm*, i.e., the requests to the motor generator MG, and controls the first and second inverters 3 and 4 in a manner corresponding to the set operating mode.

[0018] When the operating mode is the upper-phase Y drive mode, the ECU 10 opens the drive mode selector switch 5 (switching elements 5p and 5n) and closes switch 6, thereby turning on the upper arm of the second inverter 4 (one of the first and second inverters 3 and 4), namely transistors Tra, Trc and Tre, and turning off the lower arm, namely transistors Trb, Trd and Tref. As a result, a neutral point (neutral potential) is formed by the turned-on transistors Tra, Trc and Tre, and the other ends of the U-phase coil Lu, V-phase coil Lv and W-phase coil Lw of the motor generator MG are connected in a Y connection. Furthermore, the ECU 10 switches transistors Tr1-Tr6 of the first inverter 3 (the other of the first and second inverters 3 and 4) based on the torque command value Tm*. This allows the motor generator MG to be driven efficiently by a single first inverter 3.

[0019] Furthermore, when the operating mode is the lower-phase Y drive mode, the ECU 10 opens the drive mode selector switch 5 (switching elements 5p and 5n) and closes switch 6, thereby turning on the lower arm of the second inverter 4, i.e., transistors Trb, Trd and Tref, and turning off the upper arm, i.e., transistors Tra, Trc and Tre. As a result, a neutral point (neutral potential) is formed by the turned-on transistors Trb, Trd and Tref, and the other ends of the U-phase coil Lu, V-phase coil Lv, and W-phase coil Lw of the motor generator MG are connected in a Y connection. In this case as well, the ECU 10 switches and controls the transistors Tr1-Tr6 of the first inverter 3 based on the torque command value Tm*. This makes it possible to efficiently drive the motor generator MG with a single first inverter 3.

[0020] Furthermore, when the operation mode is the H driving mode, the ECU 10 closes the driving mode switching switch 5 (switching elements 5p and 5n) and the switch 6, and performs switching control on the transistors Tr1-Tr6 of the first inverter 3 and the transistors Tra-Trf of the second inverter 4 in opposite phases. Thereby, when setting the H driving mode, the phase voltage can be increased to approximately twice that in the case of setting the upper-phase Y driving mode and the lower-phase Y driving mode, and higher torque can be output to the motor generator MG.

[0021] Also, in the vehicle 1, with the switching elements 5p of the driving mode switching switch 5 and the switch 6 open, the external power source 9 is connected to the second inverter 4 via a charger (not shown) as needed (refer to the dashed two-dot line in FIG. 1), and the second inverter 4 forms a neutral point and performs switching control on the first inverter 3 to charge the battery B. That is, in the vehicle 1, the power supplied from the external power source 9 to the second inverter 4 is boosted by the motor generator MG and the first inverter 3 as a multiphase boost converter, and the battery B can be charged with the boosted power. Furthermore, when charging the battery B with the power from the external power source 9, by performing complementary switching control on the transistors Tr1 and Tr2 of the first inverter 3 with the switch 6 open, a triangular wave current with an average current of zero amperes can be made to flow through the battery B to warm up the battery B.

[0022] Subsequently, referring to FIGS. 2 and 3, the operation mode setting procedure of the first and second inverters 3 and 4 by the ECU 10 as the mode setting unit will be described.

[0023] FIG. 2 is a flowchart showing a first mode setting routine executed by the ECU 1 prior to starting the motor generator MG after the vehicle 1 is system-started. When the execution timing of the first mode setting routine arrives, the ECU 1 obtains an upper-phase cumulative stress Su indicating the cumulative value of the thermal stress applied to the upper arm of the second inverter 4, that is, the transistors Tra, Trc, and Tre, and a lower-phase cumulative stress Sl indicating the cumulative value of the thermal stress applied to the lower arm of the second inverter 4, that is, the transistors Trb, Trd, and Trf (step S100).

[0024] The upper-phase cumulative stress Su is counted using the rainflow method according to the following equation (1) during system startup of the vehicle 1. In equation (1), "Ti" is the temperature corresponding to the total amplitude of the reverse cycle in the rainflow method obtained based on the temperature TTa of the transistor Tra obtained at a sampling period approximately the same as the thermal time constant of the transistor Tra representing the upper arm of the second inverter 4, "Tn" is the maximum operating temperature of the transistor Tra, "Ni" is the number of times the temperature of the transistor Tra has changed by the temperature Ti, and "m" is a constant value specific to the second inverter 4. Also, the lower-phase cumulative stress Sl is counted using the rainflow method according to the following equation (2) during system startup of the vehicle 1. In equation (2), "Tj" is the temperature corresponding to the total amplitude of the reverse cycle in the rainflow method obtained based on the temperature TTb of the transistor Trb obtained at a sampling period approximately the same as the thermal time constant of the transistor Trb representing the lower arm of the second inverter 4, "Tn" is the maximum operating temperature of the transistor Trb, "Nj" is the number of times the temperature of the transistor Trb has changed by the temperature Tj, and "m" is a constant value specific to the second inverter 4.

[0025] Su = Σ(Ni × Tn / Ti)^m …(1) Sl = Σ(Nj × Tn / Tj)^m …(2)

[0026] After obtaining the upper phase cumulative stress Su and lower phase cumulative stress Sl in step S100, the ECU 10 determines whether the upper phase cumulative stress Su is greater than the lower phase cumulative stress Sl (step S110). If the upper phase cumulative stress Su is greater than the lower phase cumulative stress Sl (step S110: YES), the ECU 10 sets the lower phase Y drive mode to the operating mode (step S120) and terminates the first operating mode setting routine. If the upper phase cumulative stress Su is less than or equal to the lower phase cumulative stress Sl (step S110: NO), the ECU 10 sets the upper phase Y drive mode to the operating mode (step S130) and terminates the first operating mode setting routine. Note that if the upper phase cumulative stress Su and the lower phase cumulative stress Sl are the same, instead of uniformly setting the upper phase Y drive mode to the operating mode as shown in Figure 2, the upper phase Y drive mode and the lower phase Y drive mode may be set to the operating mode alternately.

[0027] Figure 3 is a flowchart showing a second operating mode setting routine that is repeatedly executed by the ECU 10 at predetermined time intervals (small time intervals) while the motor generator MG is started and the vehicle 1 is running. When it is time to execute the second operating mode setting routine, the ECU 10 obtains the rotational speed Nm of the motor generator MG, which has been calculated separately, and the torque command value Tm*, which has been set separately (step S200). Next, the ECU 10 determines whether the current operating mode is the upper-phase Y drive mode or the lower-phase Y drive mode (step S210).

[0028] If the current operating mode is the upper-phase Y drive mode or the lower-phase Y drive mode (step S210: YES), the ECU 10 determines whether or not to switch the operating mode from the upper-phase Y drive mode or the lower-phase Y drive mode to the H drive mode based on the rotational speed Nm and torque command value Tm* acquired in step S200 (step S220). In this embodiment, an operating mode setting map (not shown) is provided in advance, which divides the drive region defined with rotational speed Nm on the horizontal axis and torque command value Tm* on the vertical axis into a Y drive region where the upper-phase Y drive mode or the lower-phase Y drive mode should be set as the operating mode, and an H drive region where the H drive mode should be set as the operating mode. Then, in step S220, the ECU 10 determines whether or not the rotational speed Nm and torque command value Tm* acquired in step S200 are included in the H drive region of the operating mode setting map.

[0029] In step S220, if it is determined that there is no need to change the operating mode from the upper-phase Y drive mode or the lower-phase Y drive mode to the H drive mode (step S220: NO), the ECU 10 terminates the second operating mode setting routine without executing any further processing in order to maintain the operating mode in the upper-phase Y drive mode or the lower-phase Y drive mode. If it is determined that the operating mode should be changed from the upper-phase Y drive mode or the lower-phase Y drive mode to the H drive mode (step S220: YES), the ECU 10 stores the current operating mode, i.e., either the upper-phase Y drive mode or the lower-phase Y drive mode, in a predetermined memory area as the previous Y drive mode (step S230). Furthermore, the ECU 10 sets the H drive mode as the operating mode (step S240) and terminates the second operating mode setting routine.

[0030] On the other hand, if the current operating mode is H drive mode (step S210: NO), the ECU 10 determines whether or not to switch the operating mode from H drive mode to upper-phase Y drive mode or lower-phase Y drive mode based on the rotational speed Nm and torque command value Tm* acquired in step S200 (step S250). In step S250, the ECU 10 determines whether or not the rotational speed Nm and torque command value Tm* acquired in step S200 are included in the Y drive region of the operating mode setting map. In step S250, if it is determined that there is no need to switch the operating mode from H drive mode to upper-phase Y drive mode or lower-phase Y drive mode (step S250: NO), the ECU 10 terminates the second operating mode setting routine without executing any further processing in order to maintain the operating mode in H drive mode. Furthermore, if it is determined that the operating mode should be changed from H drive mode to upper-phase Y drive mode or lower-phase Y drive mode (step S250: YES), the ECU 10 retrieves the previous Y drive mode stored in step S230 (step S260), sets one of the upper-phase Y drive mode and lower-phase Y drive mode, which is different from the retrieved previous Y drive mode, that is, the one of the upper-phase Y drive mode and lower-phase Y drive mode that was not set as the operating mode immediately before setting the H drive mode (step S270), and then terminates the second operating mode setting routine.

[0031] As explained above, the ECU 10, as a motor control device including a mode setting unit, sets either the upper-phase Y drive mode or the lower-phase Y drive mode to an operating mode before starting the motor generator MG, such that the upper arm (transistors Tra, Trc, and Tre) and lower arm (transistors Trb, Trd, and Tref) of the second inverter 4 (one of the first and second inverters 3 and 4) with less accumulated stress is fixed to the ON position (steps S100-S130). This suppresses the stress applied to the upper or lower arm of the second inverter 4, which has more accumulated stress, by fixing it to the ON position when starting the motor generator MG, and makes it possible to equalize the accumulated stress of the upper and lower arms of the second inverter 4. Furthermore, when the ECU 10 transitions the operating mode from the H drive mode to the upper-phase Y drive mode or the lower-phase Y drive mode, it sets the upper-phase Y drive mode or the lower-phase Y drive mode, whichever was not set to an operating mode immediately before setting the H drive mode, to an operating mode (steps S250: YES, S260-S270). As a result, the upper or lower arm of the second inverter 4, which was turned on and generated heat in response to the previous transition from the upper-phase Y drive mode or lower-phase Y drive mode to the H drive mode, is no longer turned off and rapidly cooled in response to the current transition from the H drive mode to the upper-phase Y drive mode or lower-phase Y drive mode. This equalizes the cumulative stress on the upper and lower arms of the second inverter 4. Consequently, it becomes possible to effectively suppress the deterioration of the upper and lower arms of the second inverter 4, which is connected to the motor generator MG, an open-winding motor.

[0032] Furthermore, when the operating mode is the upper-phase Y drive mode or the lower-phase Y drive mode, instead of fixing the inverter that forms the neutral point to the second inverter 4 as described above, the first inverter 3 may form the neutral point and the second inverter 4 may be switched control. Also, in the motor drive device 2, a mode in which the second inverter 4 forms the neutral point and the first inverter 3 is switched control, and a mode in which the first inverter 3 forms the neutral point and the second inverter 4 is switched control may be periodically switched. Moreover, the vehicle 1, which includes the ECU 10 as a motor control device, is not limited to a battery electric vehicle (BEV). That is, the vehicle 1 may be a two-motor hybrid vehicle (series-parallel type) with planetary gears for power distribution, a one-motor hybrid vehicle, a series hybrid vehicle, or a parallel hybrid vehicle. [Industrial applicability]

[0033] The invention disclosed herein can be used in industries such as the manufacturing of motor control devices. [Explanation of Symbols]

[0034] 1 Vehicle, 2 Motor drive unit, 3 First inverter, 4 Second inverter, 5 Drive mode selector switch, 6 Switch, 7,8 Temperature sensor, 9 External power supply, 10 Electronic control unit (ECU), B Battery, D1, D2, D3, D4, D5, D6, Da, Db, Dc, Dd, De, Df Diodes, Lu U-phase coil, Lv V-phase coil, Lw W-phase coil, MG Motor generator MG, NL Negative power line, PL Positive power line, Tr1, Tr2, Tr3, Tr4, Tr5, Tr6, Tra, Trb, Trc, Trd, Tre, Tref Transistors.

Claims

[Claim 1] A motor control device that controls first and second inverters connected to an open-winding motor, The system includes a mode setting unit that sets one of the following as the operating mode: an upper-phase single-side drive mode in which the upper arm of one of the first and second inverters is fixed ON and the lower arm is fixed OFF, thereby switching control of the other of the first and second inverters; a lower-phase single-side drive mode in which the lower arm of one of the first and second inverters is fixed ON and the upper arm is fixed OFF, thereby switching control of the other of the first and second inverters; and a double-side drive mode in which both of the first and second inverters are switched control. The mode setting unit sets either the upper-phase single-sided drive mode or the lower-phase single-sided drive mode to the operating mode before starting the open-winding motor, such that the upper arm and the lower arm of one of the first and second inverters with less accumulated stress are fixed in the ON position, and when transitioning the operating mode from the double-sided drive mode to the upper-phase single-sided drive mode or the lower-phase single-sided drive mode, the motor control device sets the upper-phase single-sided drive mode and the lower-phase single-sided drive mode, whichever was not set to the operating mode immediately before setting the double-sided drive mode, to the operating mode.

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