JP4536085B2 - Electric power steering control device - Google Patents

Description

  The present invention relates to an electric power steering control device that assists a driver driving a vehicle such as an automobile with a three-phase brushless motor.

  In an electric power steering device that assists a steering force of a vehicle such as an automobile with a motor, a driver's steering torque is detected by a torque sensor, and the motor current is feedback controlled to a target current set according to the steering torque. As a result, steering assist force is generated.

Hereinafter, the operation of the conventional apparatus using the three-phase brushless motor will be described with reference to the block diagram shown in FIG.
In the figure, an electric power steering apparatus 1 is attached to the torque sensor 2 for detecting the steering force of the driver of the automobile, the three-phase brushless motor 3 for assisting the steering force of the driver, and the three-phase brushless motor 3. It comprises a rotation sensor 4 for detecting an angle and a control device 5.

  The control device 5 includes an inverter circuit 51 that drives the three-phase brushless motor 3 and six field effect transistors (hereinafter referred to as FETs) 511 to 516 that constitute three arms composed of upper and lower pairs of the inverter circuit 51. The gate drive circuit 52 to be driven, the current detection resistors R1 to R3 inserted between the sources of the FETs 514 to 516 constituting the lower arm of the inverter circuit 51 and the ground G, and these current detection resistors R1 to R3 The current detection circuit 53 detects the current of each phase of the three-phase brushless motor 3 and the CPU 54 controls the energization current of the three-phase brushless motor 3.

  The CPU 54 reads the current of each phase of the three-phase brushless motor 3 detected by the current detection circuit 53 by the A / D converter B1, and rotates the rotation angle of the three-phase brushless motor 3 along with the three-phase brushless motor 3. The electrical angle is obtained in the electrical angle calculation block B2 by reading the detection result of the rotation sensor 4 that detects the above. Next, a q-axis current calculation block B3 calculates a q-axis current based on a predetermined arithmetic expression from the previously read three-phase current values and electrical angles. Here, the q-axis current is a current obtained by combining three-phase currents based on the electrical angle, and the output torque of the three-phase brushless motor 3 is directly proportional to the q-axis current.

  On the other hand, in the target current setting block B4, the q-axis target current is set according to the steering torque of the driver detected by the torque sensor 2. Next, in the current control block B5, a voltage command value for driving the three-phase brushless motor 3 is calculated so that the target current matches the q-axis current previously obtained in the q-axis current calculation block B3.

Next, in the three-phase voltage command calculation block B6, a three-phase voltage command value to be added to each phase of the three-phase brushless motor 3 is calculated from the voltage command value and the electrical angle. Next, the PWM pulse generation block B7 generates a PWM pulse to be applied to the three phases according to the three-phase voltage command value. The inverter circuit 51 is driven by the PWM pulse through the gate drive circuit 52 and energizes the three-phase brushless motor 3. As described above, the three-phase brushless motor 3 is energized with a current corresponding to the steering torque of the driver.

  Here, the electrical angle described above will be described. When the three-phase brushless motor 3 is, for example, a four-pole pair, that is, when there are four pairs of N poles and S poles of the magnets constituting the three-phase brushless motor 3, N The pole and south pole pair appears four times. That is, one-fourth rotation of the three-phase brushless motor 3 is one cycle of the pole pair. Since electrical control is performed on this pole pair, 360 degrees of one cycle of this pole pair is referred to as an electrical angle. That is, one-fourth rotation of the three-phase brushless motor 3 is 360 electrical degrees.

  In the three-phase brushless motor 3 described above, torque ripple, that is, fluctuation in motor output torque occurs for various reasons. This torque ripple appears as vibration and sound when steering the steering wheel in the electric power steering, and the steering feeling is remarkably deteriorated.

  As a device for suppressing the torque ripple of the motor, the torque ripple for one cycle of the electrical angle of the motor is measured in advance, and the motor current corresponding to the torque ripple is calculated and stored in the control device as a data table. There has been proposed an electric power steering device that adds a current in a phase opposite to that measured in advance and converted into a data table to a target current during operation of the device (see, for example, Patent Document 1).

JP 2003-137110 A

However, in the electric power steering device proposed in Patent Document 1, the torque ripple data for one cycle of the electrical angle is enormous, and further, the torque ripple of the three-phase brushless motor is related to the motor current and rotation. Since it differs depending on the speed, it is necessary to provide a large number of data tables corresponding to various currents and rotational speeds, and the apparatus is very expensive.

  The present invention eliminates such problems of the conventional apparatus, and does not require an enormous amount of data for correcting the torque ripple of the three-phase brushless motor. An object of the present invention is to provide an electric power steering control device capable of suppressing torque ripple.

The electric power steering control device according to the present invention adds a sinusoidal current having a frequency that is an integral multiple of the frequency of the electrical angle of the three-phase brushless motor or a frequency divided by an integer to the current corresponding to the steering force of the driver. The added current is used as the q-axis target current of the three-phase brushless motor, and the q-axis target current is feedback-controlled for the q-axis current of the three-phase brushless motor. In an electric power steering control device that includes a memory stored in advance and obtains the sine wave current by referring to the memory, the electrical angle of the three-phase brushless motor is represented by a binary digital value, and a predetermined bit of the digital value To obtain data of an integral multiple of the electrical angle or a frequency of a fraction of an integer, and respond to this data. It is intended to refer to the memory Te.

  According to the present invention, it is possible to provide an electric power steering control device capable of suppressing torque ripple with an inexpensive configuration without requiring an enormous amount of data for correcting torque ripple of a three-phase brushless motor. .

  Exemplary embodiments of an electric power steering control device according to the present invention will be described below with reference to the accompanying drawings.

Embodiment 1 FIG.
First, prior to the description of the first embodiment of the present invention, the cause of torque ripple in a three-phase brushless motor will be described.
FIG. 1 is a graph showing a specific example of torque ripple of a three-phase brushless motor, in which the horizontal axis represents two cycles of the electrical angle of the three-phase brushless motor, and the vertical axis represents the fluctuation of the output torque of the motor. Represents. As shown in the figure, the torque ripple appears periodically in synchronization with the electrical angle. FIG. 2 is a diagram showing the Fourier spectrum of the torque ripple shown in FIG. 1, in which the horizontal axis represents the frequency based on the electrical angle, and the vertical axis represents the ripple intensity. As shown in FIG. 2, the torque ripple shown in FIG. 1 is composed of frequency components of 0.5F, 1F, 2F, and 6F. Here, when the frequency of the ripple is 0.5 times the frequency of the electrical angle, it is called a 0.5F ripple. The same applies to the other 1F, 2F, and 6F. For example, when the frequency of the ripple is 6 times the frequency of the electrical angle, it is called 6F ripple.

  These torque ripples of each frequency component have their respective generation factors. When the rotation sensor that detects the rotation angle of the three-phase brushless motor includes a periodic error, for example, a torque ripple of 0.5 F is generated. Further, when a DC offset is included in the current detection circuit that detects the current of each phase of the three-phase brushless motor, a torque ripple of 1F is generated. Further, if there is a difference between the three phases in the wiring connecting the control device and the three-phase brushless motor, a torque ripple of 2F is generated. Further, a torque ripple of 6F occurs due to the dead time of the PMW pulse drive of the FET constituting the inverter circuit for driving the three-phase brushless motor. Here, the dead time is a method for driving a pair of upper and lower FETs that constitute the three arms of the inverter circuit, and the upper and lower FETs are turned on and off at the time of on / off switching transient so that the upper and lower FETs do not conduct at the same time. This is the time to drive both FETs off.

  As described above, the torque ripple of the three-phase brushless motor is a composite of a plurality of sine waves having an integral multiple of the frequency of the electrical angle of the three-phase brushless motor or a frequency that is a fraction of an integer. Yes. Therefore, by creating and synthesizing a plurality of sine waves having an integral multiple of the frequency of the electrical angle or a fraction of an integer in the control device, and applying a current in the opposite phase to the three-phase brushless motor Torque ripple of a three-phase brushless motor can be suppressed.

Next, an electric power steering control device according to Embodiment 1 of the present invention will be described. FIG. 3 is a block diagram showing the electric power steering control apparatus according to Embodiment 1 of the present invention. In this figure, the electric power steering control device 30 includes a group of blocks surrounded by a broken line of the CPU 300 that controls the energization current of the three-phase brushless motor 3, and an electrically erasable nonvolatile memory EEPROM 301. Except for the fact that it is equipped, it is the same as the conventional apparatus of FIG. As will be described later realizes a function of suppressing the occurrence of torque clip of the three-phase brushless motor 3 in surrounded blocks in the dashed line.

The frequency multiplication block B8 is a block that makes the electrical angle an integer multiple or a fraction of an integer, and the electrical angle is 0.5 times, 1 time, 2 times, 6 times corresponding to the numbers shown in FIG. To. Hereinafter, this electrical angle processing method will be described with reference to FIG. The electrical angle calculated by the electrical angle calculation block B2 described in FIG. 11 is stored as binary data in a predetermined register. FIG. 4 shows an example in which this register represents a total of 12 bits of data length from BIT0 to BIT11 and represents 720 degrees of two cycles of electrical angle. Since the electrical angle is composed of binary data, as shown in the figure, if the upper 10 bits are extracted, the frequency is 0.5 times the electrical angle, and if 10 bits of BIT1 to BIT10 are extracted, 1 of the electrical angle is obtained. If the 10 bits from BIT0 to BIT9 are taken out, the frequency becomes twice the electrical angle.

  Further, if the data having the double frequency is added three times to extract the upper 10-bit data, the frequency becomes six times the electrical angle. The operation of the angle data multiplied by 0.5 times, 1 time, 2 times and 6 times is shown in FIG. In FIG. 5, the horizontal axis represents the electrical angle, and the vertical axis represents the angle multiplied by 0.5 times, 1 time, 2 times, and 6 times, respectively.

Returning to FIG. 3, in the phase offset addition block B9 in the next stage, a predetermined offset angle is added to the angles multiplied by 0.5, 1, 2 and 6 as described above. In FIG. 3, the offset angles are described as θ1, θ2, θ3, and θ4, respectively. When the torque ripple shown in FIG. 1 is decomposed into sine waves of each frequency, the phase of each sine wave is shifted with respect to the electrical angle. The offset angles θ1, θ2, θ3, and θ4 to be added here are angles corresponding to the phase shift amount.

  Next, in the sine wave data table B10, the sine wave corresponding to the components of 0.5F, 1F, 2F, and 6F is referred with reference to the sine wave table in which the sine wave data is stored according to the angle data obtained by the above processing. Get wave data.

  Next, in the amplitude coefficient multiplication block B11, the sine wave data obtained by the above processing is multiplied by the amplitude coefficient. In FIG. 3, the amplitude coefficients are described as K1, K2, K3, and K4, respectively. This coefficient corresponds to the amplitude when the torque ripple shown in FIG. 1 is decomposed into sine waves of each frequency.

The sine waves of 0.5F, 1F, 2F, and 6F obtained by the above processing are shown in FIGS. 6, 7, 8, and 9. FIG. In these figures, the horizontal axis represents 720 degrees of two periods of electrical angles, and the vertical axis represents amplitude. Next, these sine wave data are added in the addition block B12. The result of addition is the same waveform as the torque ripple shown in FIG. Next, the added data is subtracted from the target current set in the target current setting block B4. That is, a current having a phase opposite to that corresponding to the torque ripple is added to the target current. As a result, a current that suppresses torque ripple is added to the current that flows through the three-phase brushless motor 3.

  By the way, since the phase and amplitude when the torque ripple shown in FIG. 1 is decomposed into sine waves of each frequency change depending on the rotation speed and current of the three-phase brushless motor 3, the offset angles θ1, θ2 are changed. , Θ3, θ4 and amplitude coefficients K1, K2, K3, K4 need to be set according to the rotation speed and current of the three-phase brushless motor 3.

  The correction data table B13 in FIG. 3 is a data table storing the offset angles θ1, θ2, θ3, θ4 and amplitude coefficients K1, K2, K3, K4, and data corresponding to each rotation speed and each current of the motor. Is stored. FIG. 10 shows the configuration of the correction data table B13. This correction data table B13 has a two-dimensional structure in which the rows correspond to the motor current, the columns correspond to the motor rotation speed, the rotation speed is mapped every 500 rpm, and the current is mapped every 20 A. Has been. The value between the mapped points is obtained by interpolation calculation.

  The rotation speed of the motor for referring to the correction data table B13 is calculated from the change speed of the electrical angle obtained in the electrical angle calculation block B2 in the rotation speed calculation block B14 shown in FIG. The q-axis current obtained in the q-axis current calculation block B3 is used as the motor current for referring to the correction data table B13.

  By the way, the torque ripple generated by the three-phase brushless motor 3 is different for each motor. An EEPROM 301 shown in FIG. 3 is an electrically erasable nonvolatile memory corresponding to this variation, and data to be described in the data table B13 is stored in advance corresponding to each motor. The control device 5 takes out data from the EEPROM 301 and transfers it to the correction data table B13 of the CPU 300 every time it is activated.

  As described above, in the electric power steering control apparatus according to the first embodiment, torque ripple generated by the three-phase brushless motor 3 by adding a plurality of sine waves having different frequencies to the target q-axis current. Is suppressed. That is, since the waveform of the torque ripple that appears to be complicated as shown in FIG. 1 is represented by only two data of the phase and amplitude of the four sine waves, the amount of data that the control device 5 should store is the torque ripple. Compared to the conventional apparatus that stores the waveform itself, the number is extremely small.

  As described above, according to the electric power steering control device according to the first embodiment, a sinusoidal current having an integral multiple of the frequency of the electrical angle of the three-phase brushless motor 3 that assists the steering force, or a frequency divided by an integer. The value is added to the current value set according to the steering force to obtain the q-axis target current, and the q-axis current of the three-phase brushless motor 3 is feedback controlled to this q-axis target current. Torque ripple can be suppressed with an inexpensive configuration without requiring an enormous amount of data.

  The electric power steering control device according to the present invention can be applied to an electric power steering device that assists the steering force of a driver who drives an automobile with a three-phase brushless motor.

It is the graph which showed the specific example of the torque ripple of a three-phase brushless motor. It is a figure showing the Fourier spectrum of the torque ripple shown in FIG. 1 is a block diagram showing an electric power steering control device according to Embodiment 1 of the present invention. FIG. It is a figure which shows the data structure of the electrical angle of a three-phase brushless motor. It is a figure for demonstrating the multiplication process of the electrical angle of a three-phase brushless motor. It is a figure corresponding to 0.5F component of torque ripple. It is a figure corresponding to 1F component of torque ripple. It is a figure corresponding to 2F component of torque ripple. It is a figure corresponding to 6F component of torque ripple. It is a figure which shows the structure of a correction data table. It is a block diagram which shows the electric power steering control apparatus using the conventional 3 phase brushless motor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,30 Electric power steering control apparatus 2 Torque sensor 3 Three-phase brushless motor 4 Rotation sensor 5 Control apparatus 51 Inverter circuit 52 Gate drive circuit 53 Current detection circuit 54,300 CPU
301 EEPROM
511 to 516 Field effect transistor B1 A / D converter B2 Electrical angle calculation block B3 q-axis current calculation block B4 Target current setting block B5 Current control block B6 Three-phase voltage command calculation block B7 PMW pulse generation block B8 Frequency multiplication block B9 Phase Offset addition block B10 Sine wave data table B11 Amplitude coefficient multiplication block B12 Addition block B13 Correction data table B14 Rotation speed calculation blocks R1 to R3 Current detection resistor G Ground

Claims (4)

A sine wave current having an integer multiple of the frequency of the electrical angle of the three-phase brushless motor or a frequency divided by an integer is added to the current according to the steering force of the driver, and the added current is added to the three-phase brushless motor. An electric power steering control device that feedback-controls the q-axis current of the three-phase brushless motor to the q-axis target current.
In an electric power steering control device comprising a memory pre-stored with sine wave data and obtaining the sine wave current with reference to this memory,
The electrical angle of the three-phase brushless motor is represented by a digital value in binary format, and data of an integer multiple of the electrical angle or a frequency of an integer is obtained by extracting a predetermined bit of the digital value. An electric power steering control device that refers to the memory according to The sinusoidal current in phase, the electric power steering control apparatus according to claim 1, characterized in that with respect to the electrical angle is obtained by setting a predetermined offset angle. After multiplying a predetermined amplitude coefficient sinusoidal current obtained by referring to the memory, an electric power steering control apparatus according to claim 1 or claim 2, characterized in that added to the target current value. The electric power steering apparatus according to claim 3, characterized in that the said amplitude coefficient and said offset angle is set according to the speed and current of the three-phase brushless motor.

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