JP2014117118A - Control system of ac motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly select whether or not step-up operation in a converter for variably controlling a DC link voltage is required, in a control system in which a plurality of inverters for driving a plurality of AC motors commonly uses the DC link voltage.SOLUTION: A step-up converter 15 is operated either in a non-step-up mode setting a step-up ratio of a DC voltage VL corresponding to the output voltage of a DC power supply B to a DC voltage VH of a power line 7 as 1 or a non-step-up mode setting the step-up ratio as 1 or higher. Inverters 20 and 30 convert a common DC voltage VH to an AC voltage and output it to MG1 and MG2 respectively. When at least either one of a MG1 modulation degree and a MG2 modulation degree which are the modulation degrees of a DC/AC voltage conversion in each of the inverters 20 and 30 is higher than a step-up threshold value, a step-up mode is selected, and on the other hand, when both of the MG1 modulation degree and the MG2 modulation degree are lower than a non-step-up threshold value, the non-step-up mode is selected.

Description

  The present invention relates to an AC motor control system, and more particularly to a control system that variably controls a DC link voltage common to a plurality of inverters that drive a plurality of AC motors.

  In order to control an AC motor using a DC power source, a control system using an inverter is generally used. For example, Japanese Patent Laying-Open No. 2010-252488 (Patent Document 1) describes a configuration in which a DC link voltage of an inverter is variably controlled by a boost converter.

  In the above-mentioned Patent Document 1, in the control of an AC motor that selectively applies pulse width modulation (PWM) control and rectangular wave voltage control, the drivability performance is improved by driving the AC motor with sine wave PWM control as much as possible. Controls for improving fuel consumption without being impaired are described. Specifically, the degree of modulation is obtained from the required motor voltage calculated based on the torque command value of the AC motor and the system voltage command value, and the degree of modulation is maximum in the sinusoidal PWM control during the non-boosting operation of the converter. There is described control for requesting the converter to start a boost operation when the value is exceeded.

JP 2010-252488 A JP 2010-273512 A

  Patent Document 1 discloses control for switching the non-boosting operation / boosting operation of a boost converter in a system that controls a single AC motor. On the other hand, as described in Patent Document 2, a control system is used in which a plurality of inverters respectively driving a plurality of AC motors share a DC link voltage.

  When the control of Patent Document 1 is applied to such a control system, the degree of modulation differs depending on the AC motor, and therefore, how to select whether or not the boost operation of the converter is necessary as a whole system is a problem. It becomes. If this selection cannot be made properly, there is a concern that the boosting operation and non-boosting operation of the converter are frequently switched within a short period of time, thereby adversely affecting the control of the DC link voltage of the inverter and the control of the AC motor. .

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a converter in a control system in which a plurality of inverters driving a plurality of AC motors share a DC link voltage. In order to avoid frequent switching of the step-up operation and the non-step-up operation within a short time, the necessity of the step-up operation in the converter that variably controls the DC link voltage is appropriately selected.

  In one aspect of the present invention, an AC motor control system includes a booster configured to perform bidirectional DC power conversion between a DC power source and a power line so that the DC voltage of the power line is controlled according to a voltage command value. A converter, a plurality of inverters respectively connected between a common power line and a plurality of AC motors, and a control device are included. Each of the plurality of inverters is supplied with an AC voltage applied to the corresponding AC motor so that the output torque of the corresponding AC motor among the plurality of AC motors is controlled according to the torque command value of the AC motor. Convert to voltage. The control device has a non-boosting mode in which the boosting ratio indicated by the ratio of the DC voltage to the voltage of the DC power source is 1, and the boosting ratio according to the degree of modulation indicated by the ratio of the AC voltage to the DC voltage in each AC motor. The boost converter is operated by selectively applying the boost mode in which the voltage command value is set to be higher than 1. Further, the control device selects the non-boosting mode when the modulation degree is lower than the first threshold in all of the plurality of AC motors, while the modulation degree is the first in at least one of the plurality of AC motors. The boost converter is controlled to select the boost mode when a second threshold value higher than the second threshold value is exceeded.

  Preferably, the second threshold value is set lower when the boost mode is selected than when the non-boost mode is selected.

  Preferably, the first threshold value is output from the inverter to the AC motor by pulse width modulation control based on a comparison between a sinusoidal voltage command signal and a carrier wave signal for operating each of the plurality of AC motors according to the torque command value. Or less than the upper limit value of the modulation degree in the control mode for controlling the AC voltage to be applied.

  Preferably, the plurality of AC motors include AC motors for generating vehicle driving force of the electric vehicle.

  According to the present invention, in a control system in which a plurality of inverters that drive a plurality of AC motors share a DC link voltage, it is possible to avoid frequent switching of the boosting operation and the non-boosting operation of the converter within a short time. In addition, it is possible to appropriately select whether or not a boosting operation is required in the converter that variably controls the DC link voltage.

1 is an overall configuration diagram of an AC motor control system according to an embodiment of the present invention. FIG. It is a figure explaining the control mode for AC motor control. The conceptual diagram for demonstrating the relationship between the operating point of an AC motor and the control mode applied is shown. FIG. 6 is a transition diagram between a boosting mode and a non-boosting mode in an AC motor control system according to an embodiment of the present invention. It is a wave form diagram explaining the problem of selection of boosting mode / non-boosting mode according to a comparative example. It is a wave form diagram explaining the control operation in the step-up mode of the step-up converter. It is an operation waveform diagram of the boost converter in the boost mode with a low boost ratio. It is a flowchart explaining the control processing for selection of the pressure | voltage rise mode / non-boost mode in the control system of the AC motor according to the present embodiment. It is a flowchart explaining the modification of the control processing for the setting of the pressure | voltage rise threshold value in the control system of the alternating current motor according to this Embodiment. FIG. 10 is an operation waveform diagram when a boost threshold value is set according to the flowchart shown in FIG. 9.

  Embodiments of the present invention will be described below in detail with reference to the drawings. In the following description, the same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated in principle.

(System configuration)
FIG. 1 is an overall configuration diagram of an AC motor control system according to an embodiment of the present invention. FIG. 1 shows a configuration of a hybrid vehicle 1 on which an AC motor control system according to an embodiment of the present invention is mounted.

  Referring to FIG. 1, hybrid vehicle 1 includes an AC motor control system 100 (hereinafter simply referred to as control system 100), an engine 110, a power split mechanism 120, and a motor generator MG1 (hereinafter simply referred to as MG1). A motor generator MG2 (hereinafter simply referred to as MG2), a speed reducer 130, a drive shaft 140, and a drive wheel 150. The outputs of MG1 and MG2 are controlled by the control system 100.

  Control system 100 includes a DC power supply B, smoothing capacitors C0 and C1, a boost converter 15, inverters 20 and 30, and a control device 50.

  The engine 110 is constituted by, for example, an internal combustion engine such as a gasoline engine or a diesel engine. The engine 110 is provided with a cooling water temperature sensor 112 that detects the temperature of the cooling water. The output of the cooling water temperature sensor 112 is sent to the control device 50.

  Power split device 120 is configured to be able to split the power generated by engine 110 into a route to drive shaft 140 and a route to MG1. As the power split mechanism 120, a planetary gear mechanism having three rotation shafts of a sun gear, a planetary gear, and a ring gear can be used. For example, the engine 110 and MG1 and MG2 can be mechanically connected to the power split mechanism 120 by making the rotor of MG1 hollow and passing the crankshaft of engine 110 through the center thereof. Specifically, the rotor of MG1 is connected to the sun gear, the output shaft of engine 110 is connected to the planetary gear, and output shaft 125 is connected to the ring gear. The output shaft 125 that is also connected to the rotation shaft of the MG 2 is connected to a drive shaft 140 for rotationally driving the drive wheels 150 via the speed reducer 130. A reduction gear for the rotation shaft of MG2 may be further incorporated.

  MG1 operates as a generator driven by engine 110 and operates as an electric motor that starts engine 110, and is configured to have both functions of an electric motor and a generator.

  Similarly, MG 2 is incorporated into hybrid vehicle 1 for generating vehicle driving force whose output is transmitted to drive shaft 140 via output shaft 125 and speed reducer 130. Furthermore, MG2 is configured to have a function for the electric motor and the generator so as to perform regenerative power generation by generating an output torque in a direction opposite to the rotation direction of drive wheel 150. MG1 and MG2 correspond to the “plurality of AC motors” in the present invention. That is, the “AC motor” to which the present invention is applied includes an AC drive motor, a generator, and a motor generator (motor generator).

Next, the configuration of the control system 100 will be described.
The DC power supply B is typically constituted by a rechargeable power storage device such as a secondary battery such as nickel metal hydride or lithium ion or an electric double layer capacitor. The DC power source B is provided with a monitoring sensor 10. Thereby, the output voltage Vb, the output current Ib, and the temperature Tb of the DC power supply B are detected. A value detected by the monitoring sensor 10 is input to the control device 50.

  Smoothing capacitor C1 is connected between power lines 5 and 6. The power line 5 is connected to the negative terminal of the DC power supply B, and the power line 6 is connected to the positive terminal of the DC power supply B.

  A smoothing capacitor C1 is connected between the power lines 5 and 6. In power lines 5 and 6, a relay (not shown) that is turned on when the vehicle is driven and turned off when the vehicle is stopped is interposed between DC power supply B and smoothing capacitor C1.

  The voltage between the terminals of the smoothing capacitor C1, that is, the DC voltage VL of the power line 6 is detected by the voltage sensor 11. The detected value of the DC voltage VL is input to the control device 50. The DC voltage VL corresponds to the output voltage of the DC power supply B.

  Boost converter 15 includes a reactor L1 and power semiconductor switching elements Q1, Q2. Power semiconductor switching elements Q 1 and Q 2 are connected in series between power line 7 and power line 5. On / off of power semiconductor switching elements Q 1 and Q 2 is controlled by switching control signals S 1 and S 2 from control device 50.

  In this embodiment, power semiconductor switching elements (hereinafter simply referred to as “switching elements”) include IGBTs (Insulated Gate Bipolar Transistors), power MOS (Metal Oxide Semiconductor) transistors, or power bipolar transistors. Can be used. Anti-parallel diodes D1, D2 are arranged for switching elements Q1, Q2. Reactor L1 is connected between a connection node of switching elements Q1 and Q2 and power line 6. Further, the smoothing capacitor C0 is connected between the power line 7 and the power line 5.

  Smoothing capacitor C0 is connected between power lines 5 and 7 to smooth the DC voltage on power line 7. The voltage sensor 13 detects the voltage across the smoothing capacitor C0, that is, the DC voltage VH on the power line 7. The detected value of the DC voltage VH by the voltage sensor 13 is input to the control device 50.

  The DC voltage side of inverters 20 and 30 is connected to boost converter 15 via common power lines 5 and 7. That is, the power line 7 corresponds to the “power line” in the present invention. Hereinafter, DC voltage VH corresponding to the DC link voltage common to inverters 20 and 30 is also referred to as “system voltage VH”. With the arrangement of boost converter 15, system voltage VH can be variably controlled without being fixed to the output voltage of DC power supply B. As a result, the amplitude of the AC voltage applied to MG1 and MG2 is variably controlled to enable highly efficient motor control.

  Inverter 20 includes a U-phase arm 22, a V-phase arm 24, and a W-phase arm 26 provided in parallel between power lines 5 and 7. Each phase arm is composed of switching elements connected in series between power lines 5 and 7. For example, U-phase arm 22 includes switching elements Q11 and Q12, V-phase arm 24 includes switching elements Q13 and Q14, and W-phase arm 26 includes switching elements Q15 and Q16. Further, antiparallel diodes D11 to D16 are connected to switching elements Q11 to Q16, respectively. Switching elements Q11 to Q16 are turned on and off by switching control signals S11 to S16 from control device 50.

  MG1 includes a U-phase coil winding U1, a V-phase coil winding V1 and a W-phase coil winding W1 provided on the stator, and a rotor (not shown). One ends of the U-phase coil winding U1, the V-phase coil winding V1, and the W-phase coil winding W1 are connected to each other at a neutral point N1, and the other ends are connected to the U-phase arm 22, the V-phase arm 24, and the inverter 20 Each is connected to W-phase arm 26. The inverter 20 switches between DC power on the power line 7 and AC power input / output to / from the MG1 by on / off control (switching control) of the switching elements Q11 to Q16 in response to the switching control signals S11 to S16 from the control device 50. Bidirectional power conversion is performed.

  Specifically, inverter 20 can convert the DC voltage on power line 7 into a three-phase AC voltage and output the converted three-phase AC voltage to MG 1 according to switching control by control device 50. Thereby, MG1 is driven to generate a designated torque. Inverter 20 can also convert the three-phase AC voltage generated by MG 1 in response to the output of engine 110 into a DC voltage according to switching control by control device 50, and output the converted DC voltage to power line 7.

  Inverter 30 is configured similarly to inverter 20 and includes switching elements Q21 to Q26 that are on / off controlled by switching control signals S21 to S26 and antiparallel diodes D21 to D26.

  MG2 is configured similarly to MG1, and includes a U-phase coil winding U2, a V-phase coil winding V2 and a W-phase coil winding W2 provided on the stator, and a rotor (not shown). Similar to MG1, one ends of the U-phase coil winding U2, the V-phase coil winding V2, and the W-phase coil winding W2 are connected to each other at a neutral point N2, and the other end is connected to the U-phase arm 32 of the inverter 30, Connected to V-phase arm 34 and W-phase arm 36, respectively.

  Inverter 30 is configured to switch between DC power on power line 7 and AC power input / output to / from MG2 by on / off control (switching control) of switching elements Q21 to Q26 in response to switching control signals S21 to S26 from control device 50. Bidirectional power conversion is performed.

  Specifically, inverter 30 can convert the DC voltage received from power line 7 into a three-phase AC voltage according to switching control by control device 50, and output the converted three-phase AC voltage to MG2. Thereby, MG2 is driven to generate a designated torque. Further, the inverter 30 converts the three-phase AC voltage generated by the MG 2 in response to the rotational force from the driving wheel 150 during regenerative braking of the vehicle into a DC voltage according to the switching control by the control device 50, and the converted DC voltage is converted into the DC voltage. The power can be output to the power line 7.

  Here, regenerative braking refers to braking involving regenerative power generation when the driver driving the hybrid vehicle 1 performs a foot brake operation or turning off the accelerator pedal while traveling, although the foot brake is not operated. This includes decelerating (or stopping acceleration) the vehicle while generating regenerative power.

  Each of MG 1 and MG 2 is provided with a current sensor 27 and a rotation angle sensor (resolver) 28. Since the sum of instantaneous values of the three-phase currents flowing through MG1 and MG2 is zero, current sensor 27 detects motor currents for two phases (for example, V-phase current iv and W-phase current iw) as shown in FIG. It is enough to arrange it to do. The rotation angle sensor 28 detects the rotation angle θ of the rotor (not shown) of the MG 1 and MG 2 and sends the detected rotation angle θ to the control device 50. The control device 50 can calculate the rotational speeds (rotational angular speeds ω) of the MG1 and MG2 based on the rotational angle θ.

  The motor current MCRT (1) and rotor rotation angle θ (1) of MG1 and the motor current MCRT (2) and rotor rotation angle θ (2) of MG2 detected by these sensors are input to the controller 50. The Further, control device 50 receives torque command value Tqcom (1) of MG1 and torque command value Tqcom (2) of MG2 as motor commands.

A control device 50 including an electronic control unit (ECU) includes a microcomputer (not shown), a RAM (Random Access Memory) 51, and a ROM (Read Only Memory) 52.
including. Control device 50 includes boost converter 15 and an inverter so that MG1 and MG2 operate according to a motor command (typically torque command value) input from a host electronic control unit (ECU) according to a predetermined program process. Switching control signals S1 and S2 (step-up converter 15), S11 to S16 (inverter 20), and S21 to S26 (inverter 30) for switching control of 20, 30 are generated.

  The control device 50 has a function for managing a charge rate (SOC: State of Charge) and charge / discharge restrictions regarding the DC power supply B. For example, control device 50 has a function of limiting power consumption and generated power (regenerative power) in MG1 and MG2 as necessary so that overcharge or overdischarge of DC power supply B does not occur.

  Next, operations of boost converter 15 and inverters 20 and 30 in the control of MG1 and MG2 will be described.

  Boost converter 15 operates in either the non-boosting mode or the boosting mode. In step-up mode, step-up converter 15 is controlled such that switching elements Q1 and Q2 are complementarily and alternately turned on and off according to PWM control. Boost converter 15 can control the boost ratio (VH / VL) by controlling the ON period ratio (duty ratio) of switching elements Q1, Q2. Therefore, on / off of switching elements Q1, Q2 is controlled according to the duty ratio calculated according to the detected values of DC voltages VL, VH and voltage command value VHr. Thus, in the boost mode, VHr> VL is set, and boost converter 15 controls system voltage VH by on / off control of switching elements Q1 and Q2.

  In addition, by switching on and off the switching element Q1 in a complementary manner with the switching element Q2, it is possible to cope with both charging and discharging of the DC power source B without switching the control according to the current direction of the reactor L1. In other words, through control of system voltage VH according to voltage command value VHr, boost converter 15 can cope with both regeneration and power running.

  At the time of low output of MG1 and MG2, MG1 and MG2 can be controlled in a state of VH = VL (boost ratio = 1.0) without boosting by boosting converter 15. In this case, the non-boosting mode is selected, and switching elements Q1 and Q2 are fixed to on and off, respectively. As a result, in the non-boosting mode, power loss in boosting converter 15 is reduced.

  The inverter 30 outputs torque according to the torque command value Tqcom (2) by the on / off operation (switching operation) of the switching elements Q21 to Q26 in response to the switching control signals S21 to S26 from the control device 50. MG2 is driven. The torque command value Tqcom (2) is a positive value (Tqcom (2)> 0), zero (Tqcom (2) = 0), or negative according to the output (torque × rotational speed) request to the MG2 according to the driving situation. The value (Tqcom (2) <0) is appropriately set.

  In particular, during regenerative braking of the hybrid vehicle 1, the torque command value of MG2 is set to a negative value (Tqcom (2) <0). In this case, the inverter 30 converts the AC voltage generated by the MG2 into a DC voltage by a switching operation in response to the switching control signals S21 to S26, and the converted DC voltage (system voltage) is passed through the smoothing capacitor C0. To the boost converter 15.

  Further, similarly to the operation of inverter 30 described above, inverter 20 is operated so that MG1 operates according to the command value by on / off control of switching elements Q11-Q16 according to switching control signals S11-S16 from control device 50. Perform the conversion.

  As described above, the control device 50 controls the driving of the MG1 and MG2 according to the torque command values Tqcom (1) and Tqcom (2), whereby the hybrid vehicle 1 generates the vehicle driving force due to the power consumption in the MG2, and the MG1 The generation of the charging power of the DC power source B or the power consumption of the MG2 by the generation of power and the generation of the charging power of the DC power source B by the regenerative power generation in the MG2 can be appropriately executed according to the driving state of the vehicle.

(Control mode in motor control)
Next, AC motor control for MG1 and MG2 by inverters 20 and 30 will be described in detail. In the following, when an item common to each of MG1 and MG2 is described, it is referred to as “MG” for comprehensive description without distinguishing between the two.

FIG. 2 is a diagram for explaining a control mode for AC motor control.
As shown in FIG. 2, in the control system for an AC motor according to the embodiment of the present invention, three control modes are switched and used for AC motor control by an inverter.

  The sine wave PWM control is used as a general PWM control, and controls on / off of the switching element in each phase arm according to a voltage comparison between a sine wave voltage command and a carrier wave (typically, a triangular wave). . The voltage command indicates an AC voltage to be output from the inverter to the MG, which is calculated by a control calculation for controlling the output torque of the MG according to the torque command value.

  With the PWM control, the fundamental wave component of a set of a high level period corresponding to the on period of the upper arm element and a low level period corresponding to the on period of the lower arm element is a sine wave within a certain period. The duty ratio is controlled.

  Hereinafter, in this specification, the ratio of the AC voltage (effective value of the line voltage) output to MG1 and MG2 to the DC link voltage (system voltage VH) in the DC / AC voltage conversion by the inverter is referred to as “modulation degree”. Define. The application of the sine wave PWM control is basically limited to a state where the AC voltage amplitude (phase voltage) of each phase becomes equal to the system voltage VH. That is, in the sine wave PWM control, the modulation degree can be increased only to about 0.61 times. Note that by superimposing the 3n-order harmonic on the sinusoidal voltage command, the maximum modulation degree in the sinusoidal PWM control can be increased to 0.70.

  The overmodulation PWM control is to perform the same PWM control as the above sine wave PWM control after expanding the amplitude of an AC voltage (sine wave shape) larger than the amplitude of the carrier wave. As a result, the modulation factor can be increased to a range of 0.61 (0.7) to 0.78 by distorting the fundamental wave component. As a result, the PWM control can be applied to a part of the region where the sine wave PWM control cannot be applied.

  In the sine wave PWM control and overmodulation PWM control, the voltage command is calculated by feedback control of the motor current flowing through the MG. Specifically, the PWM control is performed so that the d-axis current and the q-axis current obtained by dq conversion of the three-phase motor current are controlled to the d-axis current command value and the q-axis current command value set according to the torque command value. A voltage command for control is calculated. Hereinafter, when both sine wave PWM control and overmodulation PWM control are included, they are also simply referred to as PWM control.

  On the other hand, in the rectangular wave voltage control, the inverter outputs one pulse of the rectangular wave whose ratio between the high level period and the low level period is 1: 1 within the period corresponding to the electrical angle of 360 degrees of the electric motor. Thereby, the modulation degree is increased to 0.78. In the rectangular wave voltage control, the modulation degree is fixed at 0.78.

  In the control system for an AC motor according to the present embodiment, sine wave PWM control, overmodulation PWM control, and rectangular wave voltage control described above are selectively applied to each of MG1 and MG2 in accordance with the state. That is, for each of MG1 and MG2, the modulation mode changes when the system voltage VH changes even for the same output, so the applied control mode also changes.

  FIG. 3 is a conceptual diagram for explaining the relationship between the operating point of each AC motor (MG1, MG2) and the applied control mode. The horizontal axis in FIG. 3 indicates the rotation speed of the MG, and the vertical axis in FIG. 3 indicates the output torque of the MG.

  Referring to FIG. 3, in control system 100, when boost converter 15 is operated in the non-boosting mode, the output voltage of DC power supply B (that is, DC voltage VL) becomes system voltage VH as it is (VH = VL). At the time of low output of MG, MG can be driven and controlled by any one of the above three control methods.

  The non-boosting maximum torque line 200 shown in FIG. 3 is a set of maximum output torques that the MG can output at each rotation speed when the boost converter 15 is in the non-boosting mode. The substantially trapezoidal region inside the non-boosting maximum torque line 200 is distinguished into a sine wave PWM control region A1, an overmodulation PWM control region A2, and a rectangular wave voltage control region A3 according to the modulation degree described above. become.

  The boundary line 210 between the sine wave PWM control region A1 and the overmodulation PWM control region A2 is 0.61 (or 0) in which the modulation degree is the maximum modulation degree value in general sine wave PWM control at each rotation speed. .7) shows the set of output torques.

  Further, the boundary line 220 between the overmodulation PWM control region A2 and the rectangular wave voltage control region A3 indicates the output torque when the modulation degree becomes 0.78 that is the modulation degree in the rectangular wave voltage control at each rotational speed. A set of

  The boosting maximum torque line 250 indicated by a broken line in FIG. 3 is rotated when the boosting converter 15 boosts the output voltage of the DC power supply B to the upper limit voltage and sets the system voltage VH to the maximum value (for example, 600 V). It is a set of maximum output torques that MG can output at speed.

  As described above, since the switching loss in the boost converter 15 is reduced in the non-boosting mode, the efficiency of the entire system is improved. For this reason, it is advantageous in terms of efficiency to expand application of the non-boosting mode. On the other hand, when the operating point (rotational speed and torque) of MG is located on the right side of non-boosting maximum torque line 200, if boost converter 15 does not operate in the boost mode, torque according to the torque command value Cannot be generated.

  In the present embodiment, as in Patent Document 1, the boost mode of boost converter 15 is not based on the position of the operating point of MG in FIG. 3 but based on the comparison between the actual modulation degree and the determination threshold. / The application of the non-boosting mode is expanded by selecting the non-boosting mode.

  FIG. 4 shows a transition diagram between the step-up mode and the non-step-up mode in the control system for the AC motor according to the embodiment of the present invention.

  Referring to FIG. 4, when modulation degree Kmd becomes higher than boost threshold value tKmd as the output of MG increases in the non-boost mode, boost converter 15 transitions from the non-boost mode to the boost mode. The boost threshold tKmd can be arbitrarily set within a range up to 0.78. For example, when the system voltage VH is set so that the sine wave PWM control is continuously applied as in Patent Document 1, the boost threshold value tKmd is 0.61 which is the maximum modulation degree in the sine wave PWM control. (Or 0.70).

  In the boost mode, when modulation degree Kmd becomes lower than non-boosting threshold value tKmd # as the output of MG decreases, boost converter 15 transitions from boosting mode to non-boosting mode.

  By providing a hysteresis between the boost threshold tKmd and the non-boost threshold tKmd # (tKmd> tKmd #), it is possible to prevent so-called hunting that frequently switches between the non-boost mode and the boost mode.

(Description of a comparative example when a plurality of AC motors are controlled)
Here, it is considered that the selection of the boosting mode / non-boosting mode shown in FIG. 4 is applied to the control system 100 (FIG. 1) that controls a plurality of MG1 and MG2. MG1 and MG2 are set with independent torque command values Tqcom (1) and Tqcom (2), respectively, while system voltage VH is common. For this reason, the modulation degree Kmd1 of MG1 and the modulation degree Kmd2 of MG2 are different.

  For example, for each of MG1 and MG2, the necessity of boosting can be determined according to the transition diagram of FIG. Specifically, the presence or absence of a boost request by MG1 can be determined based on whether the boost mode or the non-boost mode is selected based on modulation degree Kmd1, and the boost mode and non-boost mode are determined based on modulation degree Kmd2. It can be determined whether or not there is a boost request by MG2 depending on which one is selected.

  As a most basic mode, a control for selecting the boosting mode / non-boosting mode of the boosting converter 15 by taking the logical sum of the boosting requests of MG1 and MG2 is used as a comparative example. According to this comparative example, when boosting is required for at least one of MG1 and MG2, boost converter 15 is set to the boosting mode, while boosting is not required for both MG1 and MG2. The boost converter 15 is set to the non-boost mode.

  However, in the selection of the boosting mode / non-boosting mode according to the comparative example, hunting may occur as illustrated in FIG.

  Referring to FIG. 5, motor voltage Vr1 indicating the AC voltage (effective value of line voltage) output from inverter 20 to MG1 is used to output torque according to torque command value Tqcom (1) of MG1. Change. Similarly, motor voltage Vr2 indicating the AC voltage (effective value of the line voltage) output from inverter 30 to MG2 changes in order to output torque according to torque command value Tqcom (2) of MG2. MG1 modulation degree Kmd1 = Vr1 / VH, and MG2 modulation degree Kmd2 = Vr2 / VH.

  The boost flag Fvup is turned off when the boost converter 15 is operated in the non-boost mode, and is turned on when the boost converter 15 is operated in the boost mode.

  The example of FIG. 5 shows an operation in the case where the output of MG1 increases relatively slowly, and then starts decreasing after the output of MG1 increases relatively rapidly.

  Prior to time t1, the boost flag Fvup is off and the non-boost mode is set. Therefore, the system voltage VH = VL is a constant value. Therefore, when Vr1 of MG1 and Vr2 of MG2 are increased, the modulation degrees Kmd1 and Kmd2 are increased. Since the rising speed of Vr1 is faster, the modulation degree Kmd1 reaches the boosting threshold value tKmd1 of MG1 at time t1. As a result, the boost request for MG1 is turned on, and the boost flag Fvup is turned on at time t1.

  After time t1, boost converter 15 operates in the boost mode, and system voltage VH increases. By raising the system voltage VH according to the rise of the motor voltage Vr1, the rise of the modulation degree Kmd1 is suppressed to a certain level. Then, as Vr1 starts to decrease in accordance with the decrease in the output of MG1, the modulation degree Kmd1 starts to decrease. At time t2, modulation degree Kmd1 decreases to non-boosting threshold tKmd1 # of MG1. Therefore, the request for boosting MG1 is turned off at time t2.

  On the other hand, the output of MG2 (that is, Vr2) rises moderately also between times t1 and t2. However, at time t2, the modulation degree Kmd2 of MG2 has not reached the boost threshold tKmd2 of MG2. As a result, at time t2, the boost request is turned off for both MG1 and MG2. As a result, boost flag Fvup is turned off, and boost converter 15 operates in the non-boost mode.

  However, since the output of MG2 increases after time t2, the modulation factor Kmd2 of MG2 rises to the boost threshold tKmd2 of MG2 at time t3. As a result, at time t3 immediately after time t2, the boost flag Fvup is turned on again. As a result, hunting in which the boosting mode and the non-boosting mode are switched in a short time occurs.

  As shown in FIG. 5, system voltage VH changes discontinuously when switching between the boosting mode and the non-boosting mode. This discontinuous voltage change tends to promote the above hunting.

  The reason why the discontinuous voltage change occurs when the boost mode and the non-boost mode are switched will be described with reference to FIGS. 6 and 7.

  FIG. 6 shows a waveform diagram for explaining a control operation in the boost mode of the boost converter.

  Referring to FIG. 6, on / off of switching elements Q <b> 1 and Q <b> 2 of boost converter 15 is controlled according to a voltage comparison between duty command value Vdt and carrier wave 300. For example, the duty command value Vdt is obtained by feedback control based on the deviation between the detected value of the system voltage VH and the voltage command value VHr and / or feedforward control based on the voltage ratio between the DC voltage VL and the voltage command value VHr. .

  When duty command value Vdt is higher than the voltage of carrier wave 300, PWM command voltage Vpwm * is set to a high level. On the other hand, when duty command value Vdt is lower than the voltage of carrier wave 300, PWM command voltage Vpwm * is set to a low level. During the high level period of Vpwm *, the switching element Q1 that is the upper arm element is turned on, while the switching element Q2 that is the lower arm element is turned off. On the other hand, during the low level period of Vpwm *, the switching element Q2 that is the lower arm element is turned on, while the switching element Q1 that is the upper arm element is turned off.

  When the ratio of the high level period Th of Vpwm * to the carrier period Tc of the carrier wave 300 is Dh, the boost ratio in the boost converter 15 is expressed by the following equation (1).

VH = (1 / Dh) · VL (1)
As the duty command value Vdt increases, Th decreases and the boost ratio increases. On the other hand, in the non-boosting mode, the upper arm element (switching element Q1) is fixed on and Dh = 1.0, so VH = VL.

  When boost converter 15 is actually operated, in order to prevent one turn-off of switching elements Q1 and Q2 and the other turn-on from overlapping to form a short circuit path between power lines 7 and 5, Dead time is provided. For this reason, the boost ratio cannot be continuously reduced to 1.0 in the boost mode. That is, there is a lower limit for the step-up ratio that can be actually realized.

  FIG. 7 shows an operation waveform diagram of boost converter 15 in the non-boost mode in which the boost ratio is low.

  Referring to FIG. 7, when the voltage of carrier wave 300 becomes higher than duty command value Vdt at time t1, Vpwm * changes from the low level to the high level. Accordingly, the switching control signal S2 changes from the high level to the low level in order to turn off the switching element S2. On the other hand, the switching control signal S1 changes from the low level to the high level at the time t2 when the dead time DT has elapsed from the time t1 in order to turn on the switching element S1.

  Similarly, when the voltage of the carrier wave 300 becomes lower than the duty command value Vdt at time t3, Vpwm * changes from the high level to the low level. In response to this, the switching control signal S1 changes from the high level to the low level in order to turn off the switching element S1. On the other hand, the switching control signal S2 changes from the low level to the high level at the time t4 when the dead time DT has elapsed from the time t3 in order to turn on the switching element S2.

  Thus, in the boost mode, it is necessary to ensure the dead time DT every time the switching elements Q1, Q2 are switched on and off. That is, the duty command value Vdt shown in FIG. 7 is a lower limit value of the settable duty command. At this time, the actual PWM voltage Vpwm is a pulse voltage having a low level period corresponding to one dead time. Therefore, the actual step-up ratio (VH / VL) at the lower limit value of duty command value Vdt is expressed by the following equation (2).

(VH / VL) = 1 / (1-DT / Tc) (2)
As a result, in a region where the boost ratio is close to 1.0, there is a dead zone in which the boost ratio of the boost converter 15 cannot be changed continuously. At the time of switching between the non-boosting mode and the boosting mode, the boosting ratio by boosting converter 15 passes through this dead zone, so that system voltage VH changes discontinuously.

  As shown in FIG. 5, when the system voltage VH changes discontinuously, the degree of modulation also changes greatly. For this reason, in a scene where the modulation degree of one of MG1 and MG2 increases and the modulation degree of the other decreases, when either modulation degree reaches the boosting threshold value or the non-boosting threshold value, the boost request of each MG There is a possibility that the presence or absence may be switched, and as a result, there is a concern that hunting occurs between the non-boosting mode and the boosting mode.

(Selection of boosting mode / non-boosting mode according to this embodiment)
FIG. 8 is a flowchart illustrating a control process for selecting a boosting mode / non-boosting mode in the control system for an AC motor according to the present embodiment. The control process shown in FIG. 8 is executed by the control device 50 at a predetermined cycle.

  In step S100, control device 50 compares MG1 modulation degree Kmd1 and non-boosting threshold tKmd1 #, and also compares MG2 modulation degree Kmd2 and non-boosting threshold tKmd2 #. Then, when the modulation degree is lower than the non-boosting threshold value in both MG1 and MG2, that is, when Kmd1 <tKmd1 # and Kmd2 <tKmd2 # (when YES is determined in S100), control device 50 performs the process of step S120. To advance the boosting flag Fvup.

  On the other hand, when at least one of MG1 and MG2 has a modulation degree equal to or greater than the non-boosting threshold value (when NO is determined in S100), control device 50 advances the process to step S110. In step S110, control device 50 compares MG1 modulation degree Kmd1 and boost threshold tKmd1, and also compares MG2 modulation degree Kmd2 and boost threshold tKmd2.

  When at least one of MG1 and MG2 has a modulation degree higher than the boost threshold value, that is, when at least one of Kmd1> tKmd1 or Kmd2 <tKmd2 is satisfied (when YES is determined in S110), 50, the process proceeds to step S130, and the boost flag Fvup is turned on.

  On the other hand, when the degree of modulation is not more than the boost threshold value in both MG1 and MG2 (when NO is determined in S110), control device 50 proceeds to step S140 and maintains boost flag Fvup in the current state. . That is, Fvup is kept off in the non-boosting mode, and Fvup is kept on in the boosting mode.

  As described above, in the present embodiment, instead of determining whether or not there is a boost request for each of MG1 and MG2 as in the comparative example, boosting is performed until the modulation degree is lower than the non-boosting threshold value in both MG1 and MG2. Transition from mode to non-boosting mode is prohibited.

  Referring to FIG. 5 again, when the selection of the boosting mode / non-boosting mode according to the present embodiment is applied, the modulation factor Kmd1 of MG1 reaches the boosting threshold value tKmd1 at time t1, so that boosting is performed as in the comparative example. The flag Fvup is turned on.

  However, after time t1, a state in which the degree of modulation is lower than the non-boosting threshold does not occur in both MG1 and MG2. In particular, in the comparative example, even at time t2 when the boost flag Fvup is turned off, the degree of modulation Kmd2 does not reach the boost threshold tKmd2, but is higher than the non-boost threshold tKmd. Therefore, in the flowchart of FIG. It is said. Therefore, the boost flag Fvup is kept on.

  As a result, in the boost mode / non-boost mode selection according to the present embodiment, the boost mode is maintained without hunting occurring between times t2 and t3 in the comparative example.

  As described above, in the control system for an AC motor according to the present embodiment, in a configuration in which a plurality of inverters controlling a plurality of AC motors (motor generators) share a DC link voltage (system voltage), based on the actual modulation degree. When selecting whether or not the boost operation of the boost converter is necessary, the boost converter 15 shifts to the boost mode in the non-boost mode when the modulation degree in any of the AC motors (motor generators) becomes higher than the boost threshold. . Furthermore, once boosting mode is selected, boosting converter 15 is maintained in boosting mode until the degree of modulation in all AC motors (motor generators) falls below the non-boosting threshold.

  Therefore, the necessity of the boosting operation of the boosting converter shared by the plurality of AC motors (motor generators) can be appropriately selected by preventing the occurrence of hunting between the boosting mode and the non-boosting mode. As a result, the behavior of the system becomes unstable due to, for example, an overcurrent generated in the boost converter 15 due to hunting, and the torque fluctuation (vehicle vibration) due to the deterioration of the motor controllability due to the fluctuation of the system voltage VH is prevented. it can.

  Note that the boost threshold tKmd1 of MG1 and the boost threshold tKmd2 of MG2 may be a common value or different values. Similarly, the non-boosting threshold value tKmd1 # of MG1 and the non-boosting threshold value tKmd2 # of MG2 may be a common value or different values. The non-boosting threshold values tKmd1 # and tKmd2 # correspond to the “first threshold value” in the present invention, and the boosting threshold values tKmd1 and tKmd2 correspond to the “second threshold value” in the present invention.

(Modification)
In the control system for an AC motor according to the present embodiment, boost thresholds tKmd1 and tKmd2 can be variably set so as to further enhance the hunting prevention effect.

  FIG. 9 is a flowchart illustrating a modification of the control process for setting the boost threshold value in the control system for an AC motor according to the present embodiment. The control process shown in FIG. 9 is executed by the control device 50 in a predetermined cycle together with the control process shown in FIG.

  Referring to FIG. 9, control device 50 determines in step S200 whether boosting flag Fvup is turned on. When boosting flag Fvup is turned on, that is, when boosting mode is selected (YES in S200), control device 50 proceeds to step S210 to set boosting threshold tKmd1 to L1 and boost boosting threshold. tKmd2 is set to L2. L1 and L2 can be a common value or different values.

  When boosting flag Fvup is off, that is, when non-boosting mode is selected (NO in S200), control device 50 proceeds to step S220 and sets boosting threshold value tKmd1 to R1 (R1> L1). At the same time, the boost threshold tKmd2 is set to R2 (R2> L2). R1 and R2 can be a common value or different values.

  FIG. 10 shows an operation waveform diagram when the boost threshold is set according to the flowchart shown in FIG. The behavior of the voltages Vr1 and Vr2 in FIG. 10 is the same as that in FIG.

  Referring to FIG. 10, the selection of the boosting mode and the non-boosting mode is performed according to the flowchart shown in FIG.

  Prior to time ta, the boost flag Fvup is turned off and the non-boost mode is selected. Therefore, the boost threshold tKmd1 is set to R1, and the boost threshold tKmd2 is set to R2. R1 and R2 are equivalent to the boost threshold values tKmd1 and tKmd2 shown in FIG.

  When modulation degree Kmd1 of MG1 becomes higher than boost threshold tKmd1 (L1) at time ta, boost flag Fvup is turned on and boost converter 15 transitions from the non-boost mode to the boost mode. Accordingly, by the process according to the flowchart shown in FIG. 9, the boost threshold tKmd1 decreases from R1 to L1, and the boost threshold tKmd2 decreases from R2 to L2.

  As a result, at time tb, the modulation degree Kmd2 of MG2 becomes higher than the boost threshold tKmd2. As a result, step S110 in FIG. 8 is YES, and the boost mode is selected. Therefore, after time tb, the boosting mode is selected at least until modulation degree Kmd2 is lower than non-boosting threshold tKmd2 #. As a result, the boost mode is reliably maintained at time tc corresponding to time t2 in FIG.

  Thus, according to the modification of FIG. 9, when the boost mode is selected by increasing the output of any AC motor (motor generator), even if the output of the AC motor (motor generator) decreases, The boosting mode can be easily requested reflecting the output increase of the AC motor (motor generator). Thereby, the occurrence of hunting between the boosting mode and the non-boosting mode can be more reliably prevented.

  In the present embodiment, the configuration in which boost converter 15 is shared by two AC motors (motor generators) MG1 and MG2 is illustrated, but the application of the present invention is not limited to such a configuration. In addition, the present invention can be applied to a configuration in which the boost converter 15 is shared by an arbitrary plurality of AC motors (motor generators). Specifically, in step S100 in FIG. 8, the boost flag Fvup is turned off when the modulation degree is lower than the non-boosting threshold in all AC motors, and in step S110 in FIG. 8, at least one AC motor is used. If the boost flag Fvup is turned on when the degree of modulation is higher than the boost threshold, the present invention can be applied to a configuration in which there are a plurality of AC motors.

  Moreover, if the control system of the AC motor according to the present embodiment has a configuration in which a plurality of AC motors are controlled by a plurality of inverters having a common DC link voltage (system voltage VH) variably controlled by a converter, The present invention can also be applied to an electric vehicle having a power train configuration different from that shown in FIG. 1 or an arbitrary load other than the electric vehicle.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 Hybrid vehicle, 5, 6, 7 Power line, 10 Monitoring sensor, 11, 13 Voltage sensor, 15 Boost converter, 20, 30 Inverter, 22, 24, 26, 32, 34, 36 Arm, 27 Current sensor, 28 Rotation Angle sensor, 50 control device, 100 control system, 110 engine, 112 cooling water temperature sensor, 120 power split mechanism, 125 output shaft, 130 reducer, 140 drive shaft, 150 drive wheel, 200 non-boosting maximum torque line, 210, 220 boundary line, 250 maximum torque line at boost, 300 carrier wave, A1 sine wave PWM control area, A2 overmodulation PWM control area, A3 rectangular wave voltage control area, B DC power supply, C0, C1 smoothing capacitor, D1, D2, D11 ~ D16, D21 ~ D26 Anti-parallel diode, DT dead data Im, Fvup boost flag, Kmd, Kmd1, Kmd2 Modulation, L1 reactor, MCRT (1), MCRT (2) Motor current, MG1, MG2 Motor generator, N1, N2 Neutral point, Q1, Q2, Q11-Q16, Q21 to Q26 Power semiconductor switching element, S1, S2, S11 to S16, S21 to S26 Switching control signal, Tb temperature (DC power supply), Tc carrier cycle, Tqcom (1), Tqcom (2) Torque command value, U1, U2, V1, V2, W1, W2 Coil winding, VH DC voltage (system voltage), VHr voltage command value, Vb output voltage (DC power supply), Vdt duty command value, Vpwm command voltage, Vpwm voltage, Vr1, Vr2 motor Voltage, tKmd, tKmd1, tKmd2 boost threshold, t Kmd #, tKmd1 #, tKmd2 # Non-boosting threshold.

Claims (4)

A boost converter configured to perform bidirectional DC power conversion between a DC power source and the power line such that a DC voltage of the power line is controlled according to a voltage command value;
A plurality of inverters respectively connected between the common power line and a plurality of AC motors,
Each of the plurality of inverters applies a DC voltage on the power line to the corresponding AC motor so as to control an output torque of the corresponding AC motor among the plurality of AC motors according to a torque command value of the AC motor. Converted into an applied AC voltage,
A non-boosting mode in which the boosting ratio indicated by the ratio of the DC voltage to the voltage of the DC power supply is 1 according to the degree of modulation indicated by the ratio of the AC voltage to the DC voltage in each AC motor; A control device for operating the boost converter by selectively applying a boost mode for setting the voltage command value so that the ratio is higher than 1.
The control device selects the non-boosting mode when the modulation degree is lower than a first threshold in all of the plurality of AC motors, while the modulation in at least one of the plurality of AC motors. An AC motor control system that controls the boost converter so as to select the boost mode when a degree exceeds a second threshold that is higher than the first threshold.   The control system for an AC motor according to claim 1, wherein the second threshold value is set lower when the boost mode is selected than when the non-boost mode is selected.   The first threshold value is output from the inverter to the AC motor by pulse width modulation control based on a comparison between a sinusoidal voltage command signal and a carrier wave signal for operating each of the plurality of AC motors according to a torque command value. The control system for an AC motor according to claim 1, wherein the control system is set to be equal to or lower than an upper limit value of the modulation degree in a control mode for controlling the AC voltage.   The control system for an AC motor according to any one of claims 1 to 3, wherein the plurality of AC motors include an AC motor for generating a vehicle driving force of the electric vehicle.

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