JP2009189181A - Motor driving system, its control method, and electric vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To protect equipment including power conversion units by controlling a switching frequency (carrier frequency) of the inverter so that the relationship between the temperature of magnets of an AC motor and the temperature of the power conversion units is optimized. <P>SOLUTION: In a motor driving system, a magnet temperature estimating part 300 calculates a motor temperature (magnet temperature) estimating value Tm#. A reference temperature setting part 320 sets a reference temperature Th according to a capacitor temperature Tc acquired by a capacitor temperature acquisition part 310, and characteristics of a capacitor withstand voltage and a motor no-load induced voltage. A carrier frequency setting part 330 sets a carrier frequency of the inverter according to a normal map 332 when Tm#≥Th is satisfied, while it sets the carrier frequency lower than that at normal time according to the normal map 332 when Tm#<Th is satisfied. As a result, an eddy current is increased to promote the motor temperature rise by increasing a ripple current of a motor current. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a motor drive system, a control method therefor, and an electric vehicle, and more particularly to a motor control technique for driving an AC electric motor by pulse width modulation (PWM) control.

  In general, for driving control of a motor (including a motor generator) used as a vehicle driving force source of an electric vehicle such as an electric vehicle or a hybrid vehicle, a power semiconductor switching element (hereinafter simply referred to as a switching element) that is controlled to be turned on / off is used. A power converter configured to include the above is used. For example, an inverter is used for AC motor driving. As a typical control method for the inverter, on / off of the power semiconductor switching element is controlled for each cycle of a carrier wave such as a triangular wave or a sawtooth wave, and a pseudo AC waveform is generated by a set of square waves for each cycle. Pulse width modulation (PWM) control is known.

  In such a power converter that performs PWM control, a configuration is known in which the frequency of a carrier wave (carrier frequency) used for PWM control is variably controlled. For example, Japanese Patent Laid-Open No. 5-115106 (Patent Document 1) describes a signal supplied to a power element by changing the carrier frequency in accordance with a change in the temperature detection value of the power element (switching element). A control device for changing the frequency (corresponding to the carrier frequency) to a low or high level is described. In this way, overheating can be suppressed by lowering the switching frequency of the power element at a high temperature of the power element, and electromagnetic noise can be suppressed by increasing the switching frequency when the temperature of the power element is low. Is possible.

  Similarly, in JP 2007-203817 (Patent Document 2), in a vehicle equipped with an internal combustion engine that is started by electric power from a power source, when starting the engine in a power source low temperature state in which the output density of the power source decreases, There is described a start control device that controls the setting of the carrier frequency so that the switching frequency of the switching elements constituting the inverter connected to the power supply is lower than that at the normal time.

Furthermore, Japanese Patent Laying-Open No. 2006-25565 (Patent Document 3) describes a configuration having a function of switching the carrier frequency of the inverter circuit according to the temperature of the switching element and the motor rotation speed. As a result, by monitoring both the temperature of the switching element and the motor speed and determining and switching the carrier frequency, it is possible to prevent damage to the switching element due to overheating regardless of the load state of the motor.
JP-A-5-115106 JP 2007-203817 A JP 2006-25565 A

  If an abnormality occurs during the control of the AC motor, it is necessary to forcibly turn off each switching element constituting the inverter, and the motor may be in an uncontrolled state. In such a case, an induced voltage (no load) corresponding to the rotational speed at that time is generated in the AC motor. In particular, in a permanent magnet motor that generates a field magnetic flux by a permanent magnet attached to a rotor, this induced voltage becomes high. Further, it is known that the magnetic flux generated by the permanent magnet has temperature dependence, and so-called demagnetization occurs at high temperatures. For this reason, the no-load induced voltage of the permanent magnet motor also has temperature dependence, and the induced voltage becomes relatively high at a low temperature of the magnet.

  On the other hand, it is known that the breakdown voltage of a smoothing capacitor or switching element connected to the DC link side, typically a component of an inverter, has the same temperature dependency. That is, the pressure resistance tends to be relatively lowered as the temperature rises.

  For this reason, at the time of occurrence of the motor non-control state as described above, depending on the relationship between the motor temperature (magnet temperature) and the inverter temperature at that time, when the no-load induced voltage by the permanent magnet motor is applied to the inverter, If the applied voltage exceeds the withstand voltage of the inverter components (inverter withstand voltage), equipment damage may occur.

  Further, if the number of turns of the stator winding is increased to reduce the motor current necessary for securing the same output in order to reduce the power loss in the motor, the no-load induced voltage for the same rotational speed increases. That is, in order to realize such a motor design, it becomes a problem to secure a margin of the inverter withstand voltage, but it is necessary to avoid an increase in the size of the apparatus for securing the withstand voltage.

  Therefore, as in Patent Documents 1 and 3, in order to suppress the temperature rise of the inverter itself (power semiconductor switching element), it is only necessary to control the number of switching frequencies (carrier frequency) of the switching element. It is difficult to efficiently and sufficiently protect the equipment.

  The present invention has been made to solve such problems, and an object of the present invention is to improve the relationship between the magnet temperature of the AC motor and the temperature of the power conversion unit. By controlling the switching frequency (carrier frequency), it is possible to efficiently and sufficiently protect the equipment of the power conversion unit.

  The motor drive system according to the present invention includes an AC motor having a rotor with a permanent magnet attached thereto, a power conversion unit that controls power supply to the AC motor, a magnet temperature estimation unit, and a carrier frequency setting unit. The power conversion unit is configured to include a plurality of power semiconductor switching elements and is connected to an inverter that performs power conversion by on / off control of the plurality of power semiconductor switching elements according to pulse width modulation control, and connected to the DC link side of the inverter Capacitor. The magnet temperature estimator calculates an estimated temperature value of the permanent magnet based on the operating state value of the AC motor. The carrier frequency setting unit is based on a comparison between the reference temperature set in consideration of the temperature of the power conversion unit and the temperature estimated value by the magnet temperature estimating unit, and in the first temperature region where the temperature estimated value is lower than the reference temperature, Compared with the second temperature region in which the estimated temperature value is higher than the reference temperature, the frequency of the carrier used for the pulse width modulation control is set relatively low.

  In the motor drive system control method according to the present invention, the motor drive system includes an AC electric motor having a rotor to which a permanent magnet is attached, and a power conversion unit that controls power supply to the AC electric motor. An inverter that performs power conversion by on / off control of a plurality of power semiconductor switching elements according to pulse width modulation control configured to include a plurality of power semiconductor switching elements, and a capacitor connected to the DC link side of the inverter Including. The control method includes a step of calculating a temperature estimation value of the permanent magnet based on the operating state value of the AC motor, and a reference temperature set in consideration of the temperature of the power conversion unit and a temperature estimation by the magnet temperature estimation unit. In the first temperature range where the estimated temperature value is lower than the reference temperature, compared with the second temperature range where the estimated temperature value is higher than the reference temperature. And setting the frequency of the carrier wave used for the pulse width modulation control to be relatively low.

  According to the motor drive system or the control method thereof, a region where the estimated temperature value of the permanent magnet is lower than the reference temperature set in consideration of the temperature of the power conversion unit, that is, the AC motor is in an uncontrolled state In the temperature range where it is feared that the withstand voltage of the power conversion unit can be secured with respect to the no-load induced voltage, the control of setting the carrier frequency of the inverter relatively low (magnet temperature rise control) causes the eddy current in the AC motor to increase. The magnet temperature can be increased. As a result, considering the temperature dependence of the no-load induced voltage of the AC motor and the breakdown voltage of the power converter unit component (power semiconductor switching element or capacitor), the relationship between the magnet temperature and the temperature of the power converter unit is appropriate. Therefore, it is possible to protect the equipment of the power conversion unit. As a result, it is possible to achieve both the avoidance of upsizing for ensuring the withstand voltage in the power conversion unit, the efficient design by increasing the number of turns of the stator winding, and the protection of the power conversion unit, thereby reducing the cost. be able to.

  Preferably, the reference temperature is a predetermined value set in advance so as to correspond to the temperature of the capacitor in a steady state in accordance with the temperature rise characteristic of the power conversion unit during operation of the motor drive system.

  In this way, it is possible to easily set the reference temperature for determining whether or not the magnet temperature increase control is necessary according to the temperature increase characteristics of the component (capacitor) of the power conversion unit, which is experimentally obtained in advance.

  Preferably, the motor drive system further includes a capacitor temperature acquisition unit and a reference temperature setting unit. The capacitor temperature acquisition unit acquires the temperature of the capacitor based on at least one capacitor temperature acquisition unit of the estimation calculation based on the operation state value of the inverter and the measurement value by the temperature sensor, and the method. The reference temperature setting unit sets the reference temperature according to the capacitor temperature acquired by the capacitor temperature acquisition unit. Alternatively, the control method further includes a step of acquiring the temperature of the capacitor based on at least one of the estimation calculation based on the operation state value of the inverter and the measured value by the temperature sensor, and setting the reference temperature according to the acquired capacitor temperature. .

  If it does in this way, while estimating the temperature of the component (condenser) of an electric motor, based on this estimated temperature, it becomes possible to set appropriately the temperature area | region where magnet temperature rise control is required.

  Alternatively, an electric vehicle according to the present invention includes any one of the motor drive systems described above, and the AC electric motor is configured to generate a vehicle drive force.

  According to the electric vehicle described above, in the drive control system for an AC motor for generating vehicle driving force, the components of the power conversion unit are prevented from being damaged by the no-load induced voltage when the motor is not controlled when an abnormality occurs. In addition, it is possible to perform magnet temperature rise control by lowering the switching frequency of the inverter. As a result, the components of the power conversion unit can be efficiently protected.

  According to this invention, by controlling the switching frequency (carrier frequency) of the inverter so as to optimize the relationship between the magnet temperature of the AC motor and the temperature of the power conversion unit, it is possible to efficiently protect the equipment of the power conversion unit. Can be planned.

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

  FIG. 1 is a block diagram illustrating a configuration of a hybrid vehicle 100 shown as an example of an electric vehicle mounted with a motor drive control system according to an embodiment of the present invention.

  Referring to FIG. 1, hybrid vehicle 100 includes a power distribution mechanism 3, an engine 4, motor generators MG <b> 1 and MG <b> 2 shown as typical examples of an electric motor, a drive shaft 60 and wheels (drive wheels) 65. Hybrid vehicle 100 further includes a DC voltage generation unit 10 #, a smoothing capacitor C0, inverters 20 and 30, and a control device 50.

  A smoothing capacitor C0 and inverters 20 and 30 connected between DC voltage generator 10 # and motor generators MG1 and MG2 constitute a power conversion unit (PCU) that controls power supply to motor generators MG1 and MG2. The

  Power distribution mechanism 3 is coupled to engine 4 and motor generators MG1 and MG2 to distribute power between them. For example, as the power distribution mechanism 3, a planetary gear mechanism having three rotation shafts of a sun gear, a planetary carrier, and a ring gear can be used. These three rotating shafts are connected to the rotating shafts of engine 4 and motor generators MG1, MG2, respectively. For example, the engine 4 and the motor generators MG1 and MG2 can be mechanically connected to the power distribution mechanism 3 by making the rotor of the motor generator MG1 hollow and passing the crankshaft of the engine 4 through the center thereof. Specifically, the rotor of motor generator MG1 is connected to the sun gear, the output shaft of engine 4 is connected to the planetary carrier, and drive shaft 60 is connected to the ring gear.

  The rotation shaft of motor generator MG2 is coupled to drive shaft 60 by a reduction gear and an operation gear (not shown). Further, a reduction gear for the rotation shaft of motor generator MG2 may be further incorporated in power distribution mechanism 3.

  The motor generator MG1 operates as a generator driven by the engine 4 and operates as an electric motor that can start the engine 4, and is configured to have both functions of the electric motor and the generator.

  Similarly, motor generator MG2 is incorporated in hybrid vehicle 100 as an electric motor that drives wheels (drive wheels) 65. Further, motor generator MG2 is configured to have a function for the 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 65 (the rotation direction of 65).

  DC voltage generation unit 10 # includes a DC power supply B, a smoothing capacitor C1, and a step-up / down converter 12.

  As the DC power source B, a secondary battery such as nickel hydride or lithium ion, or a power storage device such as an electric double layer capacitor can be applied. The DC voltage Vb output from the DC power source B is detected by the voltage sensor 10. Voltage sensor 10 outputs detected DC voltage Vb to control device 50.

  A relay (not shown) between the positive terminal of the DC power supply B and the power supply wiring 6 and between the negative terminal of the DC power supply B and the ground wiring 5 is turned on when the vehicle is driven and turned off when the vehicle is stopped. ) Is provided.

  Buck-boost converter 12 includes a reactor L1 and power semiconductor switching elements Q1, Q2. Reactor L 1 is connected between a connection node of switching elements Q 1 and Q 2 and power supply line 6. Further, the smoothing capacitor C 0 is connected between the DC power supply wiring 7 and the ground wiring 5.

  Power semiconductor switching elements Q 1 and Q 2 are connected in series between DC power supply wiring 7 and ground wiring 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 the embodiment of the present invention, an IGBT (Insulated Gate Bipolar Transistor), as a power semiconductor switching element (hereinafter simply referred to as “switching element”),
A power MOS (Metal Oxide Semiconductor) transistor, a power bipolar transistor, or the like can be used. Anti-parallel diodes D1, D2 are arranged for switching elements Q1, Q2. In the present embodiment, the arrangement of step-up / step-down converter 12 from DC voltage generator 10 # may be omitted, and the voltage from DC power supply B may be applied to inverters 20 and 30 and smoothing capacitor 30. Is possible.

  Inverter 20 includes a U-phase arm circuit 22, a V-phase arm circuit 24, and a W-phase arm circuit 26 provided in parallel between DC power supply wiring 7 and ground wiring 5. Each phase arm circuit is composed of switching elements connected in series between the DC power supply wiring 7 and the ground wiring 5. For example, U-phase arm circuit 22 includes switching elements Q11 and Q12, V-phase arm circuit 24 includes switching elements Q13 and Q14, and W-phase arm circuit 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.

  Motor generator 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. Motor generator MG1 is a permanent magnet motor in which a permanent magnet is attached to a rotor.

  Inverter 20 performs bidirectional power between DC voltage generation unit 10 # and motor generator MG1 by on / off control (switching control) of switching elements Q11-Q16 in response to switching control signals S11-S16 from control device 50. Perform the conversion.

  Smoothing capacitor C0 smoothes the DC voltage from step-up / down converter 12, and supplies the smoothed DC voltage to inverters 20 and 30. The voltage sensor 13 detects the voltage across the smoothing capacitor C 0, that is, the system voltage, and outputs the detected value VH to the control device 50. In the present embodiment, the smoothing capacitor C0 is taken up as a component that should be considered for ensuring the withstand voltage of the power conversion unit (PCU). Since the withstand voltage of the smoothing capacitor C0 has temperature dependence, the temperature sensor 14 may be arranged for the purpose of accurately grasping the temperature of the smoothing capacitor C0. The temperature detected by the temperature sensor 14 (capacitor temperature Tc) is output to the control device 50.

  Specifically, inverter 20 can convert a DC voltage received from DC power supply wiring 7 into a three-phase AC voltage according to switching control by control device 50, and output the converted three-phase AC voltage to motor generator MG1. it can. Thereby, motor generator MG1 is driven to generate a designated torque. Inverter 20 receives the output of engine 4 and converts the three-phase AC voltage generated by motor generator MG1 into a DC voltage according to switching control by control device 50, and outputs the converted DC voltage to DC power supply wiring 7. You can also.

  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.

Motor generator MG2 is configured similarly to motor generator 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). . As with motor generator MG1, one end of U-phase coil winding U2, V-phase coil winding V2, and W-phase coil winding W2 are connected to each other at neutral point N2, and the other end is a U-phase arm of inverter 30. 32, V-phase arm 34 and W-phase arm 36, respectively. Motor generator MG2 is also a permanent magnet motor having a permanent magnet attached to the rotor.

  Inverter 30 performs bidirectional power between DC voltage generation unit 10 # and motor generator MG2 by on / off control (switching control) of switching elements Q21-Q26 in response to switching control signals S21-S26 from control device 50. Perform the conversion.

  Specifically, inverter 30 converts the DC voltage received from DC power supply wiring 7 into a three-phase AC voltage according to switching control by control device 50, and outputs the converted three-phase AC voltage to motor generator MG2. it can. Thereby, motor generator MG2 is driven to generate a designated torque. Further, inverter 30 converts the three-phase AC voltage generated by motor generator MG2 by receiving the rotational force from wheel 65 during regenerative braking of the vehicle into a DC voltage according to switching control by control device 50, and the converted DC voltage Can be output to the DC power supply wiring 7.

  Note that regenerative braking here refers to braking that involves regenerative power generation when the driver operating the hybrid vehicle performs a footbrake operation, or regenerative braking by turning off the accelerator pedal while the vehicle is running, although the footbrake is not operated. This includes decelerating (or stopping acceleration) the vehicle while generating electricity.

  Each of motor generators MG1, MG2 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 iu, iv, and iw is zero, the current sensor 27 detects the motor current for two phases (for example, the V-phase current iv and the W-phase current iw) as shown in FIG. It is enough to arrange it to do. Rotation angle sensor 28 detects a rotation angle θ of a rotor (not shown) of motor generators MG 1, MG 2 and sends the detected rotation angle θ to control device 50. Control device 50 can calculate the rotation speeds of motor generators MG1 and MG2 based on rotation angle θ.

  The motor current MCRT (1) and the rotor rotation angle θ (1) of the motor generator MG1 and the motor current MCRT (2) and the rotor rotation angle θ (2) of the motor generator MG2 detected by these sensors are the control device. 50. Further, control device 50 provides a motor command MG1 torque command value Tqcom (1) and a control signal RGE (1) indicating a regenerative operation, and a motor generator MG2 torque command value Tqcom (2) and a regenerative operation. The control signal RGE (2) indicating the operation is received.

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.
Switching control of the step-up / down converter 12 and the inverters 20 and 30 so that the motor generators MG1 and MG2 operate according to a motor command input from a host electronic control unit (ECU) according to a predetermined program process. Switching control signals S1 and S2 (step-up / down converter 12), S11 to S16 (inverter 20), and S21 to S26 (inverter 30) are generated.

Further, the control device 50 includes a charging rate (SOC: State of Charge) relating to the DC power source B.
) And input possible power amounts Win and Wout indicating charge / discharge restrictions are input. Thereby, control device 50 has a function of limiting power consumption and generated power (regenerative power) in motor generators MG1 and MG2 as necessary so that overcharge or overdischarge of DC power supply B does not occur.

  As is well known, acceleration and deceleration / stop commands for the hybrid vehicle 100 by the driver are input by operating the accelerator pedal 70 and the brake pedal 71. An operation (depression amount) of the accelerator pedal 70 and the brake pedal 71 by the driver is detected by an accelerator pedal depression amount sensor 73 and a brake pedal depression amount sensor 74. The accelerator pedal depression amount sensor 73 and the brake pedal depression amount sensor 74 output voltages corresponding to the depression amounts of the accelerator pedal 70 and the brake pedal 71 by the driver, respectively. Output signals ACC and BRK indicating the depression amounts of the accelerator pedal depression amount sensor 73 and the brake pedal depression amount sensor 74 are input to the control device 50.

  Next, operations of step-up / down converter 12 and inverters 20 and 30 in drive control of motor generators MG1 and MG2 will be described.

  During the step-up operation of buck-boost converter 12, control device 50 calculates a command value for DC voltage VH controlled by buck-boost converter 12 according to the operating state of motor generators MG1, MG2, and this command value and voltage sensor. Based on the detected value of the system voltage VH by 13, the switching control signals S1 and S2 are generated so that the output voltage VH becomes the voltage command value.

  In the step-up / down converter 12, during the step-up operation, the DC voltage VH obtained by boosting the DC voltage Vb supplied from the DC power supply B (this DC voltage corresponding to the input voltage to the inverters 20 and 30 is hereinafter referred to as “system voltage VH”) Is commonly supplied to the inverters 20 and 30. Further, during the step-down operation, the step-up / step-down converter 12 charges the DC power source B by stepping down the DC voltage (system voltage) supplied from the inverters 20 and 30 via the smoothing capacitor C0. More specifically, the duty ratio (ON period ratio) of the switching control signals S1 and / or S2 is controlled based on the command value and detection value of the system voltage VH.

Inverter 30 turns on / off switching elements Q21-Q26 in response to switching control signals S21-S26 from control device 50 when torque command value of corresponding motor generator MG2 is positive (Tqcom (2)> 0). (Switching operation) drives motor generator MG2 to convert the DC voltage supplied from smoothing capacitor C0 to an AC voltage and output a positive torque. Further, when the torque command value of motor generator MG2 is zero (Tqcom (2) = 0), inverter 30 converts a DC voltage into an AC voltage by a switching operation in response to switching control signals S21 to S26. Motor generator MG2 is driven so that the torque becomes zero. Thereby, motor generator MG2 is driven to generate zero or positive torque designated by torque command value Tqcom (2).

  Furthermore, during regenerative braking of the hybrid vehicle, the torque command value of motor generator MG2 is set to a negative value (Tqcom (2) <0). In this case, inverter 30 converts the AC voltage generated by motor generator MG2 into a DC voltage by a switching operation in response to switching control signals S21 to S26, and converts the converted DC voltage (system voltage) to smoothing capacitor C0. To the step-up / down converter 12.

  Thus, inverter 30 performs power conversion so that motor generator MG2 operates according to the command value by on / off control of switching elements Q21 to Q26 in accordance with switching control signals S21 to S26 from control device 50. Further, similarly to the operation of inverter 30 described above, inverter 20 causes motor generator MG1 to operate according to the command value by on / off control of switching elements Q11 to Q16 according to switching control signals S11 to S16 from control device 50. Power conversion.

  Thus, control device 50 controls driving of motor generators MG1 and MG2 in accordance with torque command values Tqcom (1) and (2), so that hybrid vehicle 100 generates vehicle driving force due to power consumption in motor generator MG2. Generation of charging power of DC power source B or power consumption of motor generator MG2 by power generation by motor generator MG1, and generation of charging power of DC power source B by regenerative braking operation (power generation) by motor generator MG2 It can be appropriately executed according to the state.

  The drive control of motor generators MG1 and MG2 by control device 50 is basically performed by motor current feedback control as described below.

  FIG. 2 is a control block diagram illustrating a motor control configuration in hybrid vehicle 100 shown in FIG.

  Referring to FIG. 2, current control block 200 includes a current command generation unit 210, coordinate conversion units 220 and 250, a PI calculation unit 240, and a PWM signal generation unit 260. The current control block 200 is a functional block of the control device 50 that is realized by executing a program stored in advance in the control device 50 at a predetermined cycle. Current control block 200 is provided corresponding to each motor generator MG1, MG2.

  Current command generation unit 210 generates current command values Idcom and Iqcom according to torque command values Tqcom (1) (Tqcom (2)) of motor generator MG1 (MG2) according to a table or the like created in advance.

  The coordinate conversion unit 220 is a current sensor that performs coordinate conversion (3 phase → 2 phase) using the rotation angle θ of the motor generator MG1 (MG2) detected by the rotation angle sensor 28 provided in the motor generator MG1 (MG2). The d-axis current id and the q-axis current iq are calculated based on the motor current MCRT (iv, iw, iu = − (iv + iw)) detected by the motor 27.

The PI calculation unit 240 includes a deviation ΔId (ΔId = Idcom− with respect to the command value of the d-axis current.
id) and a deviation ΔIq (ΔIq = Iqcom−iq) with respect to the command value of the q-axis current. PI calculating section 240 performs PI calculation with a predetermined gain for each of d-axis current deviation ΔId and q-axis current deviation ΔIq to obtain a control deviation, and d-axis voltage command value Vd # and q-axis corresponding to this control deviation Voltage command value Vq # is generated.

  Coordinate conversion unit 250 converts d-axis voltage command value Vd # and q-axis voltage command value Vq # to U-phase, V-axis by coordinate conversion using rotation angle θ of motor generator MG1 (MG2) (2 phase → 3 phase). It converts into phase voltage command value Vu, Vv, Vw of a phase and W phase. The DC voltage VH is also reflected in the conversion from the d-axis and q-axis voltage command values Vd # and Vq # to the phase voltage command values Vu, Vv and Vw.

  The PWM signal generation unit 260 is configured to switch the switching control signals S11 to S16 (S21 to S21) of the inverter 20 (30) shown in FIG. 1 based on the comparison between the voltage command values Vu, Vv, and Vw in each phase and a predetermined carrier wave. S26) is generated.

  The inverter 20 (30) is subjected to switching control in accordance with the switching control signals S11 to S16 (S21 to S26) generated by the current control block 200, whereby the torque command value Tqcom (1) for the motor generator MG1 (MG2). An AC voltage for outputting torque according to (Tqcom (2)) is applied.

  FIG. 3 is a waveform diagram for explaining the pulse width modulation (PWM) control in the PWM signal generation unit 260.

  The PWM control is a control method in which the average value of the output voltage for each period is changed by changing the pulse width of the square wave output voltage for every fixed period. In general, the above-described pulse width modulation control is performed by dividing a certain period into a plurality of switching periods corresponding to the period of the carrier wave and performing on / off control of the power semiconductor switching element for each switching period.

  Referring to FIG. 3, in PWM signal generation unit 260, signal wave 280 in accordance with each phase voltage command value Vu, Vv, Vw from coordinate conversion unit 250 is compared with carrier wave 270 having a predetermined frequency. And by switching on / off of the switching element in each phase arm of the inverter 20 (30) between the section where the carrier wave voltage is higher than the signal wave voltage and the section where the signal wave voltage is higher than the carrier wave voltage, As a phase inverter output voltage, an AC voltage as a set of square wave voltages can be supplied to motor generator MG1 (MG2). The fundamental wave component of the AC voltage is indicated by a dotted line in FIG. That is, the frequency of the carrier wave 270 (carrier frequency) corresponds to the switching frequency of each switching element constituting the inverter 20 (30).

  As shown in FIGS. 2 and 3, motor generators MG1 and MG2 are basically controlled by PWM control. However, in the application of the present invention, motor generators MG1 and MG2 do not always need to be controlled by pulse width modulation control, and PWM control and other controls such as rectangular wave voltage control depend on the motor state. May be selectively applied.

  FIG. 4 is a diagram showing the relationship between the carrier frequency and the inverter output current (motor current) in PWM control. 4 shows the U-phase output current of the inverter, the V-phase and W-phase output currents change similarly to the U-phase output current.

  Referring to FIG. 4, when the carrier frequency is low, the amplitude of the harmonic component (ripple current) included in the U-phase output current increases as shown by waveform WV1. On the other hand, when the frequency of the carrier wave 270 (FIG. 3) is increased without changing the period of the signal wave 280 (FIG. 3), the number of peaks of the carrier wave 270 included in one period of the signal wave 280 increases. . In this case, as indicated by the waveform WV2, the harmonic component becomes small, and the waveform of the output current approaches a sine wave. The waveforms WV1 and WV2 shown in FIG. 4 schematically show actual waveforms for explanation.

  When the output current of the inverter, that is, the motor generator MG (motor generator MG1, MG2 comprehensively described, the same applies hereinafter) waveform (motor current) is WV1, the waveform is WV2. Thus, the amount of heat generated by the motor generator MG, including the temperature of the permanent magnet (magnet temperature) attached to the rotor, can be relatively increased by increasing the eddy current in the stator due to the high-frequency current. Therefore, it is understood that the magnet temperature increase control for positively increasing the magnet temperature is possible by reducing the carrier frequency.

  Next, the temperature dependence of the motor induced voltage generated in the motor generator MG and the breakdown voltage of the power conversion unit will be described with reference to FIG. FIG. 5 shows the temperature dependence of the withstand voltage of the smoothing capacitor C0 as a representative example of the components of the power conversion unit. In addition, as an induced voltage (motor no-load induced voltage) 500 generated when motor generator MG is not loaded, a characteristic under a rated maximum rotation speed is shown.

  As shown in FIG. 5, both the motor no-load induced voltage 500 and the capacitor withstand voltage 510 are relatively high voltage at low temperatures, and have temperature dependency that becomes low voltage as the temperature rises. In particular, the temperature dependence of the motor no-load induced voltage 500 is caused by the demagnetization of the permanent magnet attached to the rotor of the motor generator MG due to the temperature rise, and the number of generated magnetic fluxes is reduced.

  Here, during the operation of the motor generator MG, if it is necessary to forcibly turn off each switching element due to an element failure of the inverters 20 and 30, the motor generator MG enters an uncontrolled state, and the rotational speed at that time According to the motor temperature (magnet temperature), a motor no-load induced voltage is generated according to the temperature dependency shown in FIG.

  For example, when the motor generator MG enters an uncontrolled state at the maximum rotation speed, if the motor temperature at that time is T1, an induced voltage Vb is generated. At this time, the voltage Vb is applied to the DC power supply wiring 7 of FIG. For this reason, if the capacitor temperature at this time is higher than the temperature T2 at which the withstand voltage becomes Vb, the smoothing capacitor C0 may be damaged by the application of an overvoltage.

  Conversely, if the current capacitor temperature is Ta, it is necessary from the point of equipment protection that the withstand voltage Va at that time is higher than the temperature Tb at which the motor no-load voltage is reached. It becomes. Although not shown, it is known that the withstand voltage of each switching element constituting the inverters 20 and 30 has the same temperature dependency as the capacitor withstand voltage (increased withstand voltage at low temperatures).

  Therefore, when the motor temperature (magnet temperature) is low, such as when the motor drive system is activated, it is necessary to quickly increase the motor temperature in relation to the temperature of the power conversion unit including the smoothing capacitor.

  FIG. 6 is a conceptual diagram showing an example of temperature rise characteristics of the motor temperature (magnet temperature) and the capacitor temperature. FIG. 6 shows a temperature rise characteristic with time in a state where a constant current is supplied to motor generator MG by inverters 20 and 30.

  Referring to FIG. 6, reference numerals 520 and 525 indicate rising characteristics of motor temperature (magnet temperature) Tm during a constant motor current supply operation. Thus, when driving with a constant current, the motor temperature Tm rises according to a constant slope. And in the high temperature area | region which is not shown in figure, the temperature rise is saturated.

Here, reference numeral 520 indicates a temperature rise characteristic when a motor current (that is, a current waveform of the waveform WV2 in FIG. 4) is supplied by pulse width modulation control at a normal switching frequency. On the other hand, reference numeral 525 represents a temperature rise characteristic at the time of supplying a motor current (that is, a current waveform of the waveform WV1 in FIG. 4) by pulse width modulation control at a switching frequency lower than normal. As can be understood from the comparison of the above, by setting a relatively low carrier frequency, the ripple current in the motor current is increased, thereby increasing the eddy current and promoting the increase in the motor temperature Tm. be able to.

  When the motor current increases, the slopes of reference numerals 520 and 525 become larger than in the case of FIG. 6, and when the motor current decreases, the slopes of reference numerals 520 and 525 become smaller than in the case of FIG. Therefore, the motor temperature Tm is estimated based on the motor current during actual operation of the motor drive system by previously obtaining the motor temperature rise characteristic (corresponding to the slope of the graph in FIG. 6) with respect to the magnitude of the motor current through experiments or the like. It becomes possible.

  Reference numerals 530 and 535 indicate rising characteristics of the temperature of the smoothing capacitor C0 (capacitor temperature Tc) during a constant current supply operation. Reference numeral 530 shows a temperature rise characteristic during pulse width modulation control at a normal switching frequency, as in reference numeral 520, and reference numeral 535 shows a relatively low frequency switching as in reference numeral 525. The temperature rise characteristic during the pulse width modulation control at the frequency is shown. That is, as for the capacitor temperature Tc, when the carrier frequency is low, the temperature rise is relatively large due to the increase in ripple current.

  The capacitor temperature Tc also rises as the constant motor current supply continues. As can be understood from the comparison of the reference numerals 520, 525 and 530, 535, the capacitor temperature Tc is different from the difference in heat generation characteristics and heat capacity. Tc tends to saturate in a lower temperature range as compared to the motor temperature Tm.

  Considering the temperature rise characteristics as described above, the motor no-load induced voltage equivalent to the withstand voltage corresponding to the saturation temperature Thc of the capacitor temperature Tc from the temperature dependency of the motor no-load induced voltage and the capacitor withstand voltage explained in FIG. It is understood that it is preferable to execute the motor temperature increase control so that the motor temperature (magnet temperature) Tm is rapidly increased to a temperature region higher than the temperature at which the maximum rotation speed is reached. Further, by lowering the carrier frequency (switching frequency) in the inverters 20 and 30 than in the normal state, motor temperature increase control can be realized without providing new components or the like.

  FIG. 7 is a functional block diagram illustrating motor temperature increase control in the motor control system according to the embodiment of the present invention. Here, the function of each block shown in FIG. 7 may be realized by software processing in the control device (ECU), or may be realized by producing a corresponding electronic circuit (hardware).

  Referring to FIG. 7, magnet temperature estimation unit 300 typically indicates the temperature of the permanent magnet based on the MG operation state value (typically the motor current value) indicating the operation state of motor generator MG. Motor temperature estimated value Tm # is calculated. For example, if the temperature rise characteristic of the motor temperature Tm shown in FIG. 6 is obtained experimentally in advance for each motor current value, the amount of increase in the motor temperature based on the motor current (MG operation state value) at that time. The estimated motor temperature Tm # can be calculated by integrating the estimated values.

  Since a temperature sensor (not shown) is generally arranged in the stator of motor generator MG, an initial value of estimated motor temperature Tm # is set based on the detected value of the temperature sensor. Can be.

  That is, magnet temperature estimating unit 300 can calculate motor temperature estimated value Tm # based on at least the MG operating state value or using the output of a temperature sensor provided in the stator.

  Capacitor temperature acquisition section 310 obtains capacitor temperature Tc, which is the temperature of smoothing capacitor C0, based on the INV operating state value indicating the operating state of inverters 20 and 30 and / or the output of temperature sensor 14 provided in smoothing capacitor C0. get. That is, even when the temperature sensor 14 for directly measuring the capacitor temperature Tc is not disposed, the INV operation state value (the supply current value from the power conversion unit, that is, the motor current value, or the cooling system of the power conversion unit (not shown)) The condenser temperature Tc can be acquired based on the estimation calculation based on the circulating cooling water temperature or the like.

  For example, if the temperature rise characteristic of the capacitor temperature Tc shown in FIG. 6 is experimentally obtained for each motor current value in advance, the rise in the capacitor temperature Tc is based on the motor current (INV operating state value) at that time. The amount can be estimated, and the capacitor temperature Tc can be estimated by integrating the estimated values.

  The reference temperature setting unit 320 sets the reference temperature Th according to the capacitor temperature Tc acquired by the capacitor temperature acquisition unit 310 and the characteristics of the capacitor breakdown voltage and the motor no-load induced voltage shown in FIG. If the motor temperature Tm is higher than the reference temperature Th, the reference temperature Th is such that the generated no-load induced voltage is lower than the capacitor withstand voltage even when the motor generator MG is in an uncontrolled state at the maximum rotation speed. It is necessary to set.

  For example, in FIG. 5, when the capacitor temperature Tc = Ta, the reference temperature Th = Tb or a predetermined margin is added, and Th> Tb is set.

  Alternatively, the reference temperature setting unit 320 may use, for example, the saturation temperature Thc shown in FIG. 6 with respect to the motor current at that time based on the motor current (INV operation state value) without using the capacitor temperature Tc at that time. Correspondingly, the reference temperature Th may be set. That is, the reference temperature setting unit 320 can be configured by creating a map for setting the reference temperature Th according to the motor current (INV operation state value) according to the experiment result of the temperature rise characteristic of the capacitor temperature Tc. It is.

  Further, based on the assumed normal operation pattern of the motor generator MG, the saturation temperature Thc in the normal operation pattern is uniquely determined in advance, and the reference temperature setting unit 320 is made to correspond to the saturation temperature and the reference temperature Th. It is also possible to configure so that is set to a predetermined temperature.

  Carrier frequency setting unit 330 selects map 332 and map 334 based on a comparison between estimated motor temperature Tm # set by magnet temperature estimating unit 300 and reference temperature Th set in reference temperature setting unit 320. To determine the carrier frequency. The carrier frequency setting unit 330 outputs a signal Sfr indicating the carrier frequency determined by referring to the map 332 or 334 to the carrier wave generator 340.

  The carrier wave generator 340 generates a carrier wave (reference numeral 270 in FIG. 3) having a frequency set by the carrier frequency setting unit 330 according to the signal Sfr, and sends it to the PWM signal generation unit 260 shown in FIG.

FIGS. 8 and 9 show configuration examples of the maps 332 and 334, respectively.
Referring to FIG. 8, map 332 sets the switching frequency in accordance with the operating state of motor generator MG, typically torque and rotational speed. According to the example of FIG. 8, in the region of high rotational speed and high torque, the switching frequency is set to a relatively low frequency fb in order to suppress heat generation of the switching elements in the inverters 20 and 30 when a large current is supplied. Is done. On the other hand, in other regions, the switching frequency is set to the normal frequency fa (fa> fb).

  Note that the normal frequency fa is set to an appropriate predetermined value in consideration of power loss (increases as the frequency increases) and electromagnetic noise (generally decreases as the frequencies decrease) of the switching elements of the inverters 20 and 30. . The frequency fb is set lower than the normal frequency fa within a range that considers the influence on electromagnetic noise and the like so as to suppress heat generation in the switching element with respect to the normal frequency fa.

FIG. 9 shows a configuration example of a map 334 used at the time of magnet temperature rise control.
In the example of FIG. 9, the low frequency fb is set as the switching frequency and the frequency fb is set in FIG. 8 in the region where the normal frequency fa is used, corresponding to the motor operation region classification similar to FIG. In this area, the carrier frequency is set to a lower frequency fc (fb> fc).

  Thereby, when the map 334 is selected for the same motor operation state (rotation speed and torque), the switching frequency (carrier frequency) in the inverters 20 and 30 is relatively lower than when the map 332 is selected. Will be set to.

  Alternatively, as shown in FIG. 10, in the map 332, the switching frequency is uniformly set to fa at the normal time, whereas the switching frequency may be set to fc (or fb) at the time of motor temperature increase control. Note that the maps in FIGS. 8 to 10 are merely examples, and switching is performed at a lower frequency in the magnet temperature raising control (map 334) than in the normal time (map 332) for the same motor operation state. As long as the frequency (carrier frequency) is set, an arbitrary map configuration can be used.

  The magnet temperature raising control shown in FIG. 7 can also be executed by a program process by the control device (ECU) 50 shown in FIG. That is, the above-described magnet temperature rise control can also be realized by storing a predetermined program for executing a series of processes according to the flowchart shown in FIG. 11 in the ROM 52 and executing the program at a predetermined cycle.

  Referring to FIG. 11, in step S100, ECU 50 calculates motor temperature estimated value Tm # of motor generator MG based at least on the MG operation state value represented by the motor current. That is, the process of step S100 corresponds to the function of the magnet temperature estimation unit 300 in FIG.

  Further, the ECU 50 sets the reference temperature Th in step S110. That is, the process of step S110 corresponds to the function of the reference temperature setting unit 320 in FIG. As described above, the reference temperature Th may be variably set according to the capacitor temperature Tc or the motor current (INV operation state value), and is a predetermined value (fixed) according to the assumed normal operation pattern of the motor generator MG. Value).

  In step S120, ECU 50 compares estimated motor temperature Tm # calculated in step S100 with reference temperature Th set in step S110.

  When Tm # <Th (when YES is determined in S120), the process proceeds to step S130, and the carrier temperature corresponding to the current motor operating state is determined by referring to the magnet temperature increase control map 334. Set. On the other hand, when Tm # ≧ Th (when NO is determined in S120), ECU 50 proceeds to step S140 and refers to map 332 at the normal time to determine the carrier frequency corresponding to the current motor operating state. Set. Accordingly, as described with reference to FIGS. 8 to 10, for the same motor operation state, a carrier frequency that is relatively lower than the normal time (S140) is set during the magnet temperature increase control (S130). By setting, an increase in the ripple current in the motor current can promote an increase in the motor temperature.

  As described above, according to the motor control system according to the embodiment of the present invention, the component (typical) of the power conversion unit PCU with respect to the no-load induced voltage when the motor generator MG enters the uncontrolled state. In a temperature region (Tm # <Th) where the withstand voltage of the smoothing capacitor may be secured, the magnet temperature rise control is set so that the carrier frequency of the inverter is set relatively low so that the temperature region is removed as soon as possible. Can be executed.

  As a result, the relationship between the motor temperature (magnet temperature) and the PCU temperature (capacitor temperature) is optimized in consideration of the temperature dependency of the no-load induced voltage of the motor generator MG and the component breakdown voltage of the power conversion unit (PCU). By doing so, the apparatus protection property of a power conversion unit can be improved efficiently. As a result, it is possible to achieve both an efficient design such as avoiding an increase in size for securing the breakdown voltage in the power conversion unit and an increase in the number of turns of the stator winding in the motor generator MG, and protection of the power conversion unit device. Cost reduction can be achieved.

  Note that the above-described motor temperature increase control based on the carrier frequency (switching frequency) may be performed independently for each of the motor generators MG1 and MG2, and in order to avoid different switching frequencies in the inverters 20 and 30, the motor You may perform in common with generator MG1, MG2. However, in the case of common control, magnet temperature estimation unit 300 preferably calculates estimated motor temperature value Tm # according to the minimum value of the estimated temperatures of motor generators MG1 and MG2. Furthermore, in this case, it is necessary to consider that demagnetization does not occur in the motor generator having the higher estimated temperature. In other words, when the estimated temperature of the motor generator on the high temperature side becomes higher than the predetermined temperature set corresponding to the occurrence of demagnetization, the decrease in the carrier frequency of the inverter may be stopped regardless of the estimated temperature of the motor generator on the low temperature side. preferable.

  In the above-described embodiment, the hybrid vehicle having the parallel hybrid configuration in which both the engine and the motor generator (MG2) can generate the wheel driving force is illustrated. However, the engine operates only as a power supply source to the motor and is directly connected. The present invention can be applied to equipment protection of a power conversion unit (inverter and smoothing capacitor) for motor control even in a hybrid vehicle having a series hybrid configuration in which wheel driving is performed by a motor.

  Similarly, in the above-described embodiment, the engine 4 and the motor generators MG1, MG2 are connected via the planetary gear mechanism, and the mechanical distribution type hybrid vehicle that performs energy distribution by the planetary gear mechanism is exemplified. The present invention can also be applied to an electric distribution type hybrid vehicle. In addition, the present invention can be applied to the protection of equipment in a power conversion unit for controlling an electric motor for all electric vehicles including a motor for generating wheel driving force, including an electric vehicle not equipped with an engine. Is described in a confirming manner.

  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 is a block diagram illustrating a configuration of a hybrid vehicle shown as an example of an electric vehicle mounted with a motor drive control system according to an embodiment of the present invention. FIG. 2 is a control block diagram illustrating a motor control configuration in the hybrid vehicle shown in FIG. 1. It is a wave form diagram explaining the pulse width modulation (PWM) control in the PWM signal generation part shown in FIG. It is a wave form diagram which shows the relationship between the carrier frequency and inverter output current (motor current) in PWM control. It is a conceptual diagram explaining the temperature dependence of the motor induced voltage which generate | occur | produces in a motor generator, and the proof pressure of a power conversion unit. It is a conceptual diagram which shows the temperature rising characteristic example of motor temperature (magnet temperature) and capacitor | condenser temperature. It is a functional block diagram explaining motor temperature rising control in the motor control system by an embodiment of the invention. It is a 1st figure which shows the structural example of the map (normal time) shown in FIG. FIG. 8 is a second diagram illustrating a configuration example of the map (at the time of motor temperature increase control) illustrated in FIG. 7. FIG. 8 is a third diagram illustrating a configuration example of the map illustrated in FIG. 7. It is a flowchart explaining the program structure for performing the motor temperature rising control in the motor control system by embodiment of this invention by software.

Explanation of symbols

  4 Engine, 5 Ground wiring, 6 Power supply wiring, 7 DC power supply wiring, 10, 13 Voltage sensor, 10 # DC voltage generator, 12 Buck-boost converter, 14 Temperature sensor, 20, 30 Inverter, 27 Current sensor, 28 Rotation angle Sensor, 50 control unit (ECU), 60 drive shaft, 65 wheels (drive wheel), 70 accelerator pedal, 71 brake pedal, 73 accelerator pedal depression amount sensor, 74 brake pedal depression amount sensor, 100 hybrid vehicle, 200 current control block 210 current command generation unit, 220, 250 coordinate conversion unit, 240 PI calculation unit, 260 PWM signal generation unit, 270 carrier wave, 280 signal wave, 300 magnet temperature estimation unit, 310 capacitor temperature acquisition unit, 320 reference temperature setting unit, 330 Carrier frequency setting unit, 33 Map (during normal operation), 334 Map (during motor temperature rise control), 340 Carrier wave generator, 500 Motor no-load induced voltage, 510 Capacitor breakdown voltage, 520,525 Motor temperature rise characteristics, 530,535 Capacitor temperature rise characteristics, B DC power supply, C0, C1 smoothing capacitor, D1, D2, D11 to D16, D21 to D26 antiparallel diode, fa, fb, fc frequency, id d axis current, Idcom, Iqcom current command value, iq q axis current, iu, iv, iw Phase current (motor current), L1 reactor, MG1, MG2 motor generator, N1, N2 neutral point, PCU power conversion unit, Q1, Q2, Q11-Q16, Q21-Q26 Power semiconductor switching element, S1 , S2, S11 to S16, S21 to S26 Switching control Signal, Sfr signal (carrier frequency indication), Tc capacitor temperature, Th reference temperature, Thc saturation temperature (capacitor temperature), Tm motor temperature, Tm # motor temperature estimated value, Tqcom torque command value, U1, U2 U-phase coil winding , V1, V2 V-phase coil winding, Vb DC voltage, Vd d-axis voltage command value, VH DC voltage (system voltage), Vq q-axis voltage command value, Vu, Vv, Vw Each phase voltage command value, W1, W2 W phase coil winding, Win, Wout Inputtable electric energy, WV1 motor current waveform (at low carrier frequency), WV2 motor current waveform (at high carrier frequency), θ Rotor rotation angle.

Claims (8)

An AC motor having a rotor with a permanent magnet attached thereto;
A power conversion unit that controls power supply to the AC motor,
The power conversion unit is
An inverter configured to include a plurality of power semiconductor switching elements, and performing power conversion by on / off control of the plurality of power semiconductor switching elements according to pulse width modulation control;
A capacitor connected to the DC link side of the inverter,
Based on the operating state value of the AC motor, a magnet temperature estimation unit that calculates a temperature estimation value of the permanent magnet;
Based on a comparison between a reference temperature set in consideration of the temperature of the power conversion unit and a temperature estimated value by the magnet temperature estimating unit, in the first temperature region where the temperature estimated value is lower than the reference temperature, the temperature A motor drive system, further comprising: a carrier frequency setting unit that sets a frequency of a carrier used for the pulse width modulation control to be relatively low compared to a second temperature region having an estimated value higher than the reference temperature.   2. The reference temperature according to claim 1, wherein the reference temperature is a predetermined value set in advance to correspond to a temperature of the capacitor in a steady state according to a temperature rise characteristic of the power conversion unit during operation of the motor drive system. Motor drive system. A capacitor temperature acquisition unit that acquires the temperature of the capacitor based on at least one of an estimation calculation based on an operation state value of the inverter and a measurement value by a temperature sensor;
The motor drive system according to claim 1, further comprising a reference temperature setting unit that sets the reference temperature according to the capacitor temperature acquired by the capacitor temperature acquisition unit. A motor drive system according to any one of claims 1 to 3,
The AC motor is an electric vehicle configured to generate a vehicle driving force. A method for controlling a motor drive system, comprising:
The motor drive system includes:
An AC motor having a rotor with a permanent magnet attached thereto;
A power conversion unit that controls power supply to the AC motor,
The power conversion unit is
An inverter configured to include a plurality of power semiconductor switching elements, and performing power conversion by on / off control of the plurality of power semiconductor switching elements according to pulse width modulation control;
A capacitor connected to the DC link side of the inverter,
The control method is:
Calculating an estimated temperature value of the permanent magnet based on the operating state value of the AC motor;
Comparing a reference temperature set in consideration of the temperature of the power conversion unit and a temperature estimated value by the magnet temperature estimating unit;
Based on the comparison result in the comparing step, in the first temperature region where the estimated temperature value is lower than the reference temperature, the estimated temperature value is compared with a second temperature region where the estimated temperature value is higher than the reference temperature. A method for controlling a motor drive system, comprising: setting a frequency of a carrier wave used for pulse width modulation control to be relatively low.   6. The reference temperature according to claim 5, wherein the reference temperature is a predetermined value set in advance so as to correspond to the temperature of the capacitor in a steady state according to a temperature rise characteristic of the power conversion unit during operation of the motor drive system. Control method of motor drive system.   The method further comprises: acquiring the temperature of the capacitor based on at least one of an estimation calculation based on an operation state value of the inverter and a measured value by a temperature sensor, and setting the reference temperature according to the acquired capacitor temperature. 6. A method for controlling a motor drive system according to 5. The motor drive system is mounted on an electric vehicle,
The method for controlling a motor drive system according to any one of claims 5 to 7, wherein the AC motor is configured to generate a vehicle drive force of the electric vehicle.

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