JP2008278572A - Motor control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress noise generated by the drive of a motor, in a motor control device which controls the motor of an electric vehicle. <P>SOLUTION: At the start of the motor, a motor ECU 20 controls a PWM inverter 22 by using a relatively high carrier frequency until a condition that an inverter current is continued for a prescribe period of time or longer, and is included in a prescribed current value range, or a condition that the acceleration of the vehicle is smaller than a prescribed reference acceleration is satisfied. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a motor control device that controls a motor of an electric vehicle.

  Electric vehicles such as hybrid electric vehicles, electric vehicles, and fuel cell vehicles include a driving motor (electric motor) as a driving source. The driving motor is an AC motor that is driven by an AC current. When the AC motor is driven by a DC current, a power conversion device such as a PWM inverter is required. In the power conversion device such as a PWM inverter, the drive motor performs power conversion for high power by switching at a high frequency, so that the power transistor may be heated. Therefore, when controlling the drive motor, it is necessary to take measures to prevent heating of the power transistor.

  In Patent Document 1, when the inverter current is smaller than the predetermined lower limit current value, the carrier frequency of the PWM (pulse width modulation) signal, that is, the switching frequency of the power transistor is set high, and the inverter current is set to the predetermined upper limit current value. If it is larger, the carrier frequency is set low, and if the inverter current is in the middle between the lower limit current value and the upper limit current value, in order to avoid the occurrence of abnormal noise due to a sudden change in frequency, a predetermined frequency is set. A technique for performing control using a linear function is disclosed.

  Patent Document 2 discloses a technique for setting a low carrier frequency when the rotational speed of a motor is low and torque is high, and suppressing heat generation of a power transistor or a motor. Further, in Patent Document 2, when the rotation speed is high, the control is stabilized by setting the carrier frequency high. However, even when the rotation speed is not low, the carrier frequency is set low when the torque is high. A technique for suppressing heat generation is disclosed.

  Patent Document 3 discloses a technique in which an inverter is PWM-controlled at a low carrier frequency when the engine is started, and PWM-controlled at a high carrier frequency when a predetermined on-vehicle device such as a vehicle air conditioning compressor is driven.

JP-A-5-115106 JP 2002-10668 A JP 2002-153096 A

  As described above, when the rotational speed of the motor is low, the inverter is generally PWM-controlled at a low carrier frequency because the power transistor may be heated by the inverter current. Even at the time of starting the electric vehicle, the inverter is controlled at a low carrier frequency because the rotational speed of the motor is low immediately after the start.

  However, the time when the rotational speed is low at the start is very short, the rotational speed becomes high immediately after the start, the carrier frequency is switched to a high frequency immediately after the start, and the inverter is controlled. However, the motor may generate noise due to a ripple current generated when the inverter is driven at a low carrier frequency at the time of starting.

  An object of the present invention is to suppress noise generated by driving a motor in a motor control device that controls a motor of an electric vehicle.

  A motor control device according to the present invention includes a signal supply unit that supplies a pulse modulation signal having a predetermined carrier frequency to a PWM inverter that supplies electric power to a motor that is a driving source of an electric vehicle, and a rotational speed of the motor is predetermined. When the condition that the inverter current input to the PWM inverter is larger than a predetermined first reference current value is satisfied, the carrier frequency is made lower than when the condition is not satisfied. A carrier frequency setting unit that sets the first reference current value lower than the first reference current value when the inverter current is included in a predetermined current value range for a predetermined period or longer. And a reference current value changing unit for changing to the above.

  In one aspect of the motor control device according to the present invention, the reference current value changing unit is configured to perform the first reference current value regardless of the magnitude of the inverter current after a predetermined period has elapsed since the motor started. Is changed to the second reference current value.

  A motor control device according to the present invention includes a signal supply unit that supplies a pulse modulation signal having a predetermined carrier frequency to a PWM inverter that supplies electric power to a motor that is a driving source of an electric vehicle, and a rotational speed of the motor is predetermined. When the condition that the inverter current input to the PWM inverter is larger than a predetermined first reference current value is satisfied, the carrier frequency is made lower than when the condition is not satisfied. A carrier frequency setting unit that sets the first reference current value lower than the first reference current value when the inverter current is included in a predetermined current value range for a predetermined period or longer. And a reference current value changing unit for changing to the above.

  In the motor control device according to the present invention, the reference current value changing unit may change the first reference current value to the second value regardless of the magnitude of the vehicle acceleration after a lapse of a predetermined period from the start of the motor. The reference current value is changed.

  According to the present invention, for example, at the time of starting the motor, comparison is made until the condition that the inverter current is continuously included in the predetermined current value range for a predetermined period or until the condition that the vehicle acceleration is smaller than the predetermined reference acceleration is satisfied. The PWM inverter is controlled by a higher carrier frequency. Therefore, it is possible to suppress noise generated by driving the motor, rather than controlling the PWM inverter with a relatively low carrier frequency.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment specifically showing the best mode for carrying out the invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing functional blocks of the electric vehicle according to the present embodiment. In FIG. 1, the electric vehicle includes a PWM inverter 22 that converts a discharge output of a DC power supply 40 into a three-phase AC, and a drive source motor 30 that is driven by the three-phase AC from the PWM inverter 22. The PWM inverter 22 has a power transistor 24, receives a switching signal (pulse width modulation signal) from the motor electronic control unit (motor ECU) 20, and sends a drive current to the motor 30.

  The motor ECU 20 includes a rotation speed sensor 32 that detects the rotation speed of the motor 30, a rotation speed of the motor 30, an inverter current I output from the PWM inverter 22 from the current sensor 26, and a torque value that is to be output from the motor 30. The command value is input from the hybrid electronic control unit (hybrid ECU) 10, the carrier frequency is calculated, and a switching signal is output to the PWM inverter 22.

  If the torque command value is large, the drive current sent to the motor 30 also becomes large. Here, the torque command value includes an accelerator signal indicating the amount of depression of the accelerator pedal by the driver, a brake signal indicating the amount of depression of the brake pedal by the driver, a shift position signal indicating the shift position input by the driver, and the like. Enter to calculate.

  Further, the calculation is performed so that the carrier frequency is low when the rotation speed of the motor 30 is low and the inverter current (that is, the torque of the motor 30) is large, and the carrier frequency is high when the rotation speed is high and the inverter current is small.

  Generally, when the condition that the rotational speed of the motor 30 is lower than a predetermined reference rotational speed and the inverter current is larger than a predetermined reference current value is satisfied, the amount of heat generated in the PWM inverter 22 is often large. It is set lower than the normal carrier frequency. The lower the motor speed, the more heat is generated because a current close to “direct current” flows through the power transistor 24 of the PWM inverter 22. Therefore, the reference current value of the inverter current (the torque threshold of the motor 30) must be lowered so that the lower the rotation speed, the lower the carrier frequency. Even when the electric vehicle is started, the above condition may be satisfied. However, the motor 30 does not satisfy the condition immediately after the start, and the carrier frequency set low before the PWM inverter 22 generates heat has a normal carrier frequency. Often switched to frequency. A region set to a low carrier frequency immediately after start-up is easy to use, and if a low carrier frequency is used, a ripple current is likely to be generated in the output current of the PWM inverter 22. That is, the waveform of the output current of the PWM inverter 22 is likely to be disturbed by a low carrier frequency. The generation of this ripple current may cause abnormal noise from the motor 30. On the other hand, even if the above condition is satisfied only for a short period when the motor 30 is started, the amount of heat generated in the PWM inverter 22 is not so large.

  Therefore, in the present embodiment, the noise generated by the motor 30 is suppressed by suppressing the fluctuation of the carrier frequency at the start-up while suppressing the amount of heat generated by the PWM inverter 22.

  When a relatively large amount of heat is not continuously generated in the PWM inverter 22 or the motor 30, the motor ECU 20 calculates a higher carrier frequency when starting the motor 30.

  More specifically, the motor ECU 20 holds two carrier frequency maps in the memory as shown in FIGS. 2A and 2B, and uses the carrier frequency map held in the memory with the rotation speed of the motor 30 and the inverter current as parameters. By referring to this, the carrier frequency is calculated as appropriate.

  2A and 2B, the vertical axis represents the inverter current I, and the horizontal axis represents the motor rotation speed N. The carrier frequency map is composed of two regions, and one carrier frequency is set for each region.

  In FIG. 2A, a region 100 is a region when the motor rotation speed N is lower than the reference rotation speed Nt and the condition (1) that the inverter current I is larger than the first reference current value It1 is satisfied. A first carrier frequency fc1 is assigned. On the other hand, the region 102 is a region when the condition (1) is not satisfied, and a second carrier frequency fc2 (fc1 <fc2) higher than the first carrier frequency is assigned as the carrier frequency.

  In FIG. 2B, a region 100 ′ is a region when the condition (2) that the motor rotational speed N is lower than the reference rotational speed Nt and the inverter current I is larger than the second reference current value It2 is satisfied. The first carrier frequency fc1 is assigned as the carrier frequency.

  In other words, the carrier frequency map shown in FIG. 2B has a higher carrier current I condition for the first carrier frequency fc1 than the carrier frequency map shown in FIG. 2A. Therefore, when the motor ECU 20 determines the carrier frequency using the inverter current I and the motor rotation speed N as parameters, it is more likely that the second carrier frequency fc2 is determined as the carrier frequency by referring to the carrier frequency map shown in FIG. 2B. high. Therefore, the motor ECU 20 can control the PWM inverter 22 with a relatively higher carrier frequency when referring to the carrier frequency map shown in FIG. 2B. Therefore, since the ripple current included in the inverter output current flowing to the motor 30 is reduced, the occurrence of abnormal noise can be suppressed. However, if the carrier frequency is set high, the amount of heat generated in the PWM inverter 22 increases depending on the number of rotations and torque of the motor 30. Therefore, depending on the number of rotations and torque (inverter current) of the motor 30 In some cases, it is better to set the carrier frequency lower.

  Therefore, in the present embodiment, the amount of heat generated in the PWM inverter 22 is taken into consideration, and the magnitude of the carrier frequency is changed even if the rotation speed of the motor 30 and the magnitude of the inverter current are the same. That is, the carrier frequency map referred to by the motor ECU 20 is changed.

  More specifically, it is from the start of the motor 30 until a predetermined period elapses, and the inverter current continues for a predetermined period and is not included in the predetermined current value range (that is, as shown in FIG. 3A). When the inverter current changes with a certain degree of fluctuation), the motor ECU 20 refers to the carrier frequency map shown in FIG. 2B because it is predicted that the amount of heat generated in the PWM inverter 22 is relatively small.

  On the other hand, even before the predetermined period elapses after the motor 30 is started, the inverter current continues for a predetermined period and is included in the predetermined current value range (that is, as shown in FIG. In the vicinity of the range 200), it is expected that a relatively large amount of heat is generated in the PWM inverter 22. Therefore, the motor ECU 20 refers to the first carrier frequency map shown in FIG. 2A instead of the second carrier frequency map.

  In addition, after a predetermined period has elapsed since the start of the motor 30, even if the inverter current continues for a predetermined period and is not included in the predetermined current value range, the heat generated in a short time is gradually accumulated. The amount of heat generated in the PWM inverter 22 is expected to increase as a result. Therefore, the motor ECU 20 refers to the first carrier frequency map shown in FIG. 2A regardless of the magnitude of the inverter current after a predetermined period has elapsed since the start of the motor 30.

  FIG. 4 is a flowchart illustrating a procedure for setting a carrier frequency map referred to by the motor ECU 20 when the motor 30 is started in the present embodiment.

  In FIG. 4, when the motor ECU 20 detects a motor start instruction from the hybrid ECU 10 (S100), the motor ECU 20 first reads the second carrier frequency map shown in FIG. 2B from the memory and sets it as a reference target map (S102). That is, the motor ECU 20 first refers to the second carrier frequency map and sequentially calculates the carrier frequency based on the inverter current I and the motor rotation speed N. Next, if the predetermined first period T1 has not elapsed after the motor start (the determination result of step S104 is negative “N”), the motor ECU 20 determines that the inverter current I is equal to the predetermined second period T2 (T2 <T T1) It is determined whether it is continuously included in the predetermined current range (S106). If it is not included as a result of the determination (the determination result of S106 is negative “N”), the process returns to step S104.

  On the other hand, after the predetermined first period T1 has elapsed (the determination result of step S104 is affirmative “Y”) or when the inverter current I is continuously included in the predetermined current range for the predetermined second period T2. (The determination result in step S106 is affirmative “Y”), the motor ECU 20 reads the first carrier frequency map as shown in FIG. 2A from the memory, and uses the first carrier frequency map instead of the second carrier frequency map as a reference target map. A frequency map is set (S108).

  As described above, in this embodiment, at the time of starting the motor, the inverter can be controlled with a relatively high carrier frequency until the condition that the inverter current is continuously included in the predetermined current value range for a predetermined period or longer is satisfied. It becomes possible. Therefore, since the generation of the ripple current is less than when the inverter is controlled with a relatively low carrier frequency, it is possible to suppress noise generated by driving the motor.

  Then, the modification of this embodiment is demonstrated. This modification differs from the above-described embodiment in that the reference carrier frequency map is changed depending on the magnitude of the acceleration of the electric vehicle immediately after the start of the motor 30, and the map is changed due to the fluctuation of the magnitude of the inverter current. . In addition, since the functional block of the electric vehicle in this modification may be the same as the functional block in embodiment, description is abbreviate | omitted. In this modification, the motor ECU 20 needs to acquire the acceleration of the vehicle. For example, the motor ECU 20 uses a known method based on the rotation speed of the motor 30 detected by the rotation speed sensor 32. What is necessary is just to calculate an acceleration.

  FIG. 5 is a flowchart showing a procedure for setting a carrier frequency map referred to by the motor ECU 20 when the motor 30 is started in the present modification.

  5 is different from FIG. 4 in that step S106 is changed to step S107.

  In other words, in this modified example, if the motor ECU 20 has not passed the predetermined first period T1 after starting the motor (the determination result of step S104 is negative “N”), the motor ECU 20 has a predetermined vehicle acceleration. It is determined whether or not the acceleration is smaller than the reference acceleration (S107). If it is not included as a result of the determination (if the determination result in S107 is negative “N”), the process returns to step S104.

  On the other hand, after the predetermined first period T1 has elapsed (the determination result in step S104 is affirmative “Y”), or when the vehicle acceleration is equal to or greater than a predetermined reference acceleration (the determination result in step S107 is affirmative “Y”). The motor ECU 20 reads the first carrier frequency map as shown in FIG. 2A from the memory, and sets the first carrier frequency map instead of the second carrier frequency map as the reference target map (S108).

  As described above, in the present modification, when the vehicle acceleration at the time of starting the motor 30 is smaller than the reference acceleration, it is expected that a relatively large amount of heat is generated in the PWM inverter 22, and thus the motor ECU 20 uses the second carrier frequency map. Reference is made to the first carrier frequency map instead of.

  As described above, in this modified example, when the motor is started, the inverter can be controlled with a relatively high carrier frequency until the condition that the acceleration of the vehicle is smaller than the reference acceleration is satisfied. Therefore, since the generation of ripple current is less than when the inverter is controlled at a relatively low carrier frequency, it is possible to suppress abnormal noise generated by driving the motor.

It is a figure which shows the functional block of the electric vehicle in this embodiment and a modification. It is a figure which shows an example of the carrier frequency map referred when motor ECU calculates a carrier frequency based on motor rotation speed and an inverter electric current. It is a figure which shows an example of the carrier frequency map referred when motor ECU calculates a carrier frequency based on motor rotation speed and an inverter electric current. It is a figure for demonstrating the time change of the inverter electric current at the time of a motor start. It is a figure for demonstrating the time change of the inverter electric current at the time of a motor start. In this embodiment, it is a flowchart which shows the procedure at the time of setting the carrier frequency map which motor ECU refers at the time of the start of a motor. In this modification, it is a flowchart which shows the procedure at the time of setting the carrier frequency map which motor ECU refers at the time of the start of a motor.

Explanation of symbols

  10 Hybrid ECU, 20 Motor ECU, 22 Inverter, 24 Power transistor, 26 Current sensor, 30 Motor, 32 Revolution sensor, 40 Power supply.

Claims (4)

A signal supply unit that supplies a pulse modulation signal having a predetermined carrier frequency to a PWM inverter that supplies electric power to a motor serving as a drive source of the electric vehicle;
When the condition that the rotational speed of the motor is lower than a predetermined reference rotational speed and the inverter current input to the PWM inverter is larger than a predetermined first reference current value, the carrier frequency is satisfied with the condition. A carrier frequency setting unit that is set to be lower than when there is not,
A reference current value changing unit configured to change the first reference current value to a second reference current value lower than the first reference current value when the inverter current is continuously included in a predetermined current value range for a predetermined period or longer; ,
A motor control device comprising: The motor control device according to claim 1,
The reference current value changing unit changes the first reference current value to the second reference current value regardless of the magnitude of the inverter current after a predetermined period has elapsed since the start of the motor.
The motor control apparatus characterized by the above-mentioned. A signal supply unit that supplies a pulse modulation signal having a predetermined carrier frequency to a PWM inverter that supplies electric power to a motor serving as a drive source of the electric vehicle;
When the condition that the rotational speed of the motor is lower than a predetermined reference rotational speed and the inverter current input to the PWM inverter is larger than a predetermined first reference current value, the carrier frequency is satisfied with the condition. A carrier frequency setting unit that is set to be lower than when there is not,
A reference current value changing unit configured to change the first reference current value to a second reference current value lower than the first reference current value when the inverter current is continuously included in a predetermined current value range for a predetermined period or longer; ,
A motor control device comprising: The motor control device according to claim 3,
The reference current value changing unit changes the first reference current value to the second reference current value regardless of the magnitude of the vehicle acceleration after a predetermined period has elapsed since the start of the motor.
The motor control apparatus characterized by the above-mentioned.

Images