JP5403307B2 - Motor control device - Google Patents

Description

  The present invention relates to a motor control device that performs PWM (Pulse Width Modulation) control of a motor. Such a motor control device is used, for example, to control a motor as a drive source of the electric power steering device.

An electric power steering device is a device that assists steering by mechanically transmitting a driving force of a motor to a steering mechanism of a vehicle. The motor is controlled based on a target current value that is set according to the steering torque applied to the steering wheel, whereby a steering assist force according to the steering torque is applied to the steering mechanism.
In order to control the motor, a controller with a microcomputer is provided. The controller generates a PWM signal for PWM control of the motor. Further, in order to feedback control the motor, the current actually flowing through the motor is detected. The detected current is sampled by the controller at a predetermined sampling period and used for generating a PWM signal. That is, the PWM duty is set according to the deviation of the detected current value with respect to the target current value, and a PWM signal having this PWM duty is generated.

In order to generate the PWM signal, the controller generates a carrier wave having a predetermined carrier period. The sampling period of the motor current is set to be an integer multiple of the carrier wave period. Accordingly, it is intended that the motor current can be detected by eliminating the fluctuation of the motor current in the carrier wave period.
JP 2001-171536 A

However, it is not always easy to set the sampling period to an integer multiple accurately with respect to the carrier period, and a minute error may occur. Due to this error, the motor is driven periodically, which may cause low-frequency vibration (for example, vibration of several Hz) of the steering wheel.
This problem will be specifically described with reference to FIG.

  FIG. 4A shows the output signal of the current sensor for detecting the motor current. A signal when the motor current is zero is shown, and the output signal of the current sensor is a sine wave that oscillates at a carrier wave period (carrier wave frequency 20 kHz). The sampling period of the motor current is 200 μsec, which is four times the carrier wave period, and the sampling points SA are points where the motor current = 0.

  FIG. 4B shows a state in which the sampling period is shifted by a minute time to 199.995 μsec in the same situation as FIG. 4A. In this case, the current value at the sampling point SB does not become zero, and the current value after sampling varies at a low frequency (for example, 2 Hz) corresponding to the deviation of the sampling period from an integer multiple of the carrier wave period. FIG. 4C shows the sampling result of the current signal in the situation of FIG. 4B compressed in the time axis direction.

  As a result of the detection result of the motor current indicating such a low frequency fluctuation, the motor is driven at the same low frequency, which causes unpleasant vibration to the steering wheel and causes a feeling of steering discomfort. . Of course, the motor current varies with the carrier frequency, but the carrier frequency is sufficiently high so that it does not cause vibration of the steering wheel.

The above-described problem is common to not only a motor control apparatus applied to an electric power steering apparatus but also a motor control apparatus that performs PWM control of a motor.
SUMMARY OF THE INVENTION An object of the present invention is to provide a motor control device capable of suppressing or preventing undesired low-frequency driving of a motor.

The invention according to claim 1 for achieving the above object is a motor control device (10) for driving the motor (M) by PWM control, for the PWM control using a carrier wave of a predetermined carrier wave period. PWM signal generating means (23) for generating the PWM signal, motor current detecting means (25) for detecting the motor current at a predetermined sampling period, and based on the motor current detected by the motor current detecting means. The inter-cycle relationship detection means (26, 27) for detecting the inter-cycle relationship between the carrier cycle and the sampling cycle, and the carrier cycle or the sampling cycle is changed based on the deviation of the inter-cycle relationship with respect to a predetermined reference relationship. to and a period changing means (28), said circumferential period relationship detection unit, when the actual current is zero the motor, the sampling Period and includes a frequency analysis means (26) for determining the frequency of the sampling values of the motor current detecting means for oscillating at a lower frequency in response to the bias of an integral multiple of the carrier wave period, the period changing means, the frequency The motor control device is configured to change the carrier period or the sampling period based on the frequency of the sampling value obtained by the analysis unit so that the sampling period is an integral multiple of the carrier period. The alphanumeric characters in parentheses indicate corresponding components in the embodiments described later.

According to this configuration, the relationship between the period of the carrier wave used for generating the PWM signal (carrier wave period) and the sampling period of the motor current is examined. When this inter-period relationship deviates from a predetermined reference relationship, the carrier wave period or the sampling period is corrected based on the deviation. Thereby, the carrier wave period or the sampling period can be corrected so as to reduce or eliminate the deviation. As a result, the inter-period relationship between the carrier wave period and the sampling period can be led to a desired relation, so that undesired low-frequency vibrations can be suppressed or prevented.
More specifically, when the actual current of the motor is zero, the frequency of the sampling value of the motor current detecting means that vibrates at a low frequency corresponding to the deviation between the sampling period and an integral multiple of the carrier period. The wave number is obtained by frequency analysis means. Based on that the obtained frequency, the sampling period is such that an integral multiple of the carrier wave period, the carrier wave cycle or sampling period is changed.
Invention according to claim 2, wherein the circumferential period relationship detection means, further, the sampling frequency of the sampling values obtained by the frequency analysis means is less than a predetermined frequency threshold value, and determined by the frequency analysis means Determination means (27) for determining whether the amplitude of the frequency component of the value exceeds a predetermined amplitude threshold, wherein the period changing means is the sampling value obtained by the frequency analysis means by the determination means. On the condition that the frequency of the sampling frequency is less than the predetermined frequency threshold and that the amplitude of the frequency component of the sampling value obtained by the frequency analysis means exceeds the predetermined amplitude threshold. The motor control device according to claim 1, wherein the cycle or the sampling cycle is changed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram showing an electrical configuration of an electric power steering apparatus according to an embodiment of the present invention. A steering torque applied to the steering wheel 1 as an operation means for steering the vehicle is mechanically transmitted to the steering mechanism 3 via the steering shaft 2. A steering assist force from the electric motor M is transmitted to the steering mechanism 3 via a speed reduction mechanism (not shown) or by a direct drive system.

  The steering shaft 2 is divided into an input shaft 2A coupled to the steering wheel 1 side and an output shaft 2B coupled to the steering mechanism 3 side. The input shaft 2A and the output shaft 2B are connected to the torsion bar 4. Are connected to each other. The torsion bar 4 is twisted according to the steering torque, and the direction and amount of the twist are detected by the torque sensor 5.

For example, the torque sensor 5 is configured by a magnetic sensor that detects a magnetic resistance that changes in accordance with a change in the positional relationship between the input shaft 2A and the output shaft 2B in the rotational direction. The output signal of the torque sensor 5 is input to a controller 10 (ECU: electronic control unit) as a motor control device.
In addition to the output signal of the torque sensor 5, a vehicle speed signal output from the vehicle speed sensor 6 is input to the controller 10. The controller 10 determines a motor current target value as a target drive value according to the steering torque detected by the torque sensor 5 and the vehicle speed detected by the vehicle speed sensor 6, and the steering assist force according to the steering torque and the vehicle speed is used for steering. The electric motor M is driven and controlled as given to the mechanism 3. The controller 10 controls driving of the electric motor M by supplying electric power from the in-vehicle battery 8 as a power source for supplying electric power to the electric components of the vehicle.

  The controller 10 includes a microcomputer 11, a motor drive circuit 13, and a motor current detection circuit 14 that detects a motor current flowing through the electric motor M. The motor drive circuit 13 receives supply of power from the in-vehicle battery 8. A current sensor 15 is provided in association with the motor drive circuit 13, and an output signal of the current sensor 15 is input to the motor current detection circuit 14.

The microcomputer 11 sets a motor current target value based on the steering torque detected by the torque sensor 5 and the vehicle speed detected by the vehicle speed sensor 6 and controls the motor drive circuit 13.
More specifically, the microcomputer 11 includes a CPU (central processing unit) and a memory (ROM, RAM, and nonvolatile memory), and functions as a plurality of function processing units by executing a predetermined program. . The plurality of function processing units include an assist characteristic storage unit 21, a motor current target value setting unit 22, a current PWM (Pulse Width Modulation) control unit 23 for driving the motor drive circuit 13, and a current deviation calculation unit 24. A sampling unit 25, a frequency analysis unit 26, a cycle determination unit 27, a cycle correction unit 28, a correction value storage unit 29, and a PWM carrier wave generation unit 30.

The assist characteristic storage unit 21 stores a basic assist characteristic (assist map) in which a motor current target value corresponding to the steering torque and the vehicle speed is determined in advance.
The motor current target value setting unit 22 applies the steering torque detected by the torque sensor 5 and the vehicle speed detected by the vehicle speed sensor 6 to the basic assist characteristic stored in the assist characteristic storage unit 21, and the motor current target value Iobj. Ask for. The motor current target value setting unit 22 obtains a motor current target value Iobj by performing a known compensation control calculation such as so-called inertia compensation control or damping control on the motor current target value obtained from the basic assist characteristics. There may be.

  The motor current target value Iobj set by the motor current target value setting unit 22 is given to the current deviation calculation unit 24. On the other hand, the sampling unit 25 samples the output signal of the motor current detection circuit 14 every predetermined sampling period, and gives the motor current I to the current deviation calculation unit 24. The current deviation calculation unit 24 obtains a deviation (current deviation) of the motor current I with respect to the motor current target value Iobj, and gives this to the current PWM control unit 23. The sampling period in the sampling unit 25 can be changed.

  The current PWM control unit 23 determines the duty ratio by proportional / integral calculation so that the current deviation given from the current deviation calculation unit 24 becomes zero, that is, the motor current I becomes equal to the motor current target value Iobj. . The current PWM control unit 23 generates a current PWM signal having the duty ratio determined as described above and supplies the current PWM signal to the motor drive circuit 13. The current PWM signal is generated using a carrier wave generated by the PWM carrier wave generation unit 30.

  The PWM carrier wave generation unit 30 generates a carrier wave having a predetermined carrier wave period. The carrier cycle can be changed. For example, an initial value of a carrier wave period in the PWM carrier wave generation unit 30 is determined, and a correction value (correction value) for the initial value is given from the cycle correction unit 28 to the PWM carrier wave generation unit 30. As a result, the PWM carrier wave generation unit 30 generates a carrier wave having a carrier wave period obtained by correcting the initial value with the correction value, and supplies the carrier wave to the current PWM control unit 23. The correction value is stored in a correction value storage unit 29 composed of a nonvolatile memory. The period correction unit 28 reads the correction value from the correction value storage unit 29 and supplies the correction value to the PWM carrier wave generation unit 30.

The frequency analysis unit 26 performs frequency analysis of the motor current signal sampled by the sampling unit 25 by, for example, FFT (Fast Fourier Transform) frequency analysis. This analysis result represents the frequency of the motor current signal, which is given to the period determination unit 27.
The period determination unit 27 is based on the frequency of the motor current and the relationship between the carrier wave generated by the PWM carrier wave generation unit 30 (for example, one having an initial carrier wave period) and the sampling period of the sampling unit 25 is It is determined whether or not a predetermined reference relationship is established. More specifically, it is determined whether the sampling period is an integral multiple of the carrier period. Then, the cycle determination unit 27 obtains a deviation of the inter-cycle relationship with respect to the reference relationship, and gives this to the cycle correction unit 28.

The cycle correction unit 28 determines whether or not the correction value is stored in the correction value storage unit 29 when the vehicle start switch (ignition switch) is turned on, and if the correction value is not stored, Based on the deviation from the period determination unit 27, a correction value is calculated. The calculated correction value is written in the correction value storage unit 29.
The motor drive circuit 13 includes a switching element (power MOSFET) driven by a current PWM signal supplied from the current PWM control unit 23, and outputs the output voltage of the in-vehicle battery 8 to the electric motor M with the duty ratio of the current PWM signal. Apply.

  FIG. 2 is a flowchart for explaining the operation of the microcomputer 11. When the ignition (IG) switch is turned on (step S1), the period correction unit 28 checks whether or not the correction value is stored in the correction value storage unit 29 (step S2). More specifically, the correction value storage unit 29 stores a correction calculation flag indicating whether or not a correction value has been stored. The period correction unit 28 refers to the correction calculation flag to determine whether the correction value has been calculated and the calculated correction value has been stored in the correction value storage unit 29.

  When the correction value has been calculated (step S3: NO), the period correction unit 28 reads the correction value from the correction value storage unit 29 (step S4), and provides this correction value to the PWM carrier wave generation unit 30. Thereby, the PWM carrier wave generation unit 30 generates a carrier wave with a carrier wave period obtained by correcting the initial value with the correction value. Thus, the correction value is reflected (step S5). Thereafter, processing of a main control routine for controlling the electric motor M based on the motor current target value Iobj is performed. In this case, the current PWM control unit 23 generates a PWM signal using the carrier wave generated by the PWM carrier wave generation unit 30.

  On the other hand, when the correction value is not stored in the correction value storage unit 29 (step S3: YES), the frequency analysis unit 26, the period determination unit 27, and the period correction unit 28 correct the carrier period. An operation for obtaining is performed. More specifically, the motor current is taken in every sampling period by the sampling unit 25 (step S6), and this is given to the frequency analysis unit 26 and subjected to FFT frequency analysis processing (step S7). At this point, the actual motor current is zero, but when the sampling period is deviated from an integral multiple of the carrier period, the value sampled by the sampling unit 25 is as shown in FIG. It fluctuates at a low frequency corresponding to the bias. The frequency and phase are obtained by the frequency analysis unit 26.

  The period determining unit 27 determines whether the frequency obtained by the frequency analyzing unit 26 is less than a predetermined threshold A (step S8). In this embodiment, the period determining unit 27 further determines whether or not the absolute value (amplitude) of the frequency component is larger than a predetermined threshold B (step S8). The threshold value A corresponds to the mechanical time constant of the electric power steering apparatus, and corresponds to a frequency corresponding to mechanical vibrations of the intermediate shaft (not shown), the torsion bar 4 and the like, for example. The threshold B corresponds to an amplitude that is generated as a steering torque vibration from the motor output (cogging torque or torque ripple) or the column reduction ratio. Therefore, if there is a frequency component whose frequency is less than the threshold A and whose amplitude exceeds B, it is determined that this frequency component is due to the sampling period being deviated from an integral multiple of the carrier wave period. The

If the determination in step S8 is negative (step S8: NO), the relationship between the sampling period and the carrier wave period (initial value) is appropriate, and there is no need to correct the carrier wave period. Therefore, the process of the main control routine is started without correcting the carrier wave period.
When the determination in step S8 is affirmed (step S8: YES), the period correction unit 28 obtains a correction value (step S9). That is, the period correction unit 28 obtains a correction value for correcting the carrier wave period based on the frequency of the frequency component whose amplitude exceeds the threshold B at a frequency less than the threshold A. More specifically, based on the frequency and phase, the initial carrier period is corrected to obtain a correction value for leading to a relationship in which the sampling period is an integral multiple of the carrier period.

The correction value in this case may be obtained in the form of a period, but the correction of the carrier wave period is synonymous with the correction of the carrier frequency, so the correction value may be obtained in the form of frequency. Of course, when correcting the initial carrier period, it is convenient to obtain the correction value in the form of a period, and when correcting the initial carrier frequency, it is convenient to obtain the correction value in the form of frequency.
The correction value thus obtained is stored in the correction value storage unit 29 (step S10). At this time, the cycle correction unit 28 rewrites the correction calculation flag with a value indicating that the correction value has been calculated and stores it in the correction value storage unit 29 (step S10).

Thereafter, the microcomputer 11 is once reset and restarted, and the processes after step S1 are resumed. At this time, since the correction value has already been stored in the correction value storage unit 29, the process branches from step S3 to step S4.
FIG. 3A and FIG. 3B are diagrams for explaining the effect of correcting the carrier wave period.
FIG. 3A shows a case where the sampling period is deviated from an integral multiple of the carrier period (carrier frequency = 20 kHz), and the sampled current varies at a low frequency (1.8 Hz in this example). In this case, as a result of driving the electric motor M in accordance with the sampled current change, a current is supplied to the electric motor M at a frequency of 1.8 Hz, and accordingly, the torque sensor 5 has a steering torque with a frequency of 1.8 Hz. Is detected. This causes unpleasant vibration of the steering wheel 1.

  On the other hand, FIG. 3B shows an example in which the carrier wave frequency is corrected and the carrier wave frequency is 20.1 kHz. As understood from the comparison with FIG. 3A, the low-frequency torque vibration disappears, and only the relatively high-frequency (119 Hz) torque vibration appears. Such high frequency vibrations are not perceived as unpleasant vibrations for the driver. Therefore, uncomfortable vibration is reduced and steering feeling is improved as compared with the situation of FIG. 3A.

  As mentioned above, although one Embodiment of this invention was described, this invention can also be implemented with another form. For example, in the above-described embodiment, the example in which the carrier wave period is corrected has been described. However, as indicated by a two-dot chain line in FIG. 1, instead of correcting the carrier wave period, the carrier wave period is corrected, and the sampling period is corrected. You may make it do. In this case, of course, the period correction unit 28 calculates a correction value for correcting the sampling period, and such a correction value is stored in the correction value storage unit 29.

In the above embodiment, the correction value is stored in the non-volatile memory. However, the corrected carrier wave period and / or sampling period is stored in the non-volatile memory, and this is used for the carrier wave. A period and / or a sampling period may be set.
Furthermore, in the above-described embodiment, the motor control device applied to the electric power steering device has been described. However, the motor control device of the present invention is for controlling an electric motor provided in a device other than the electric power steering device. May be applied.

  In addition, various design changes can be made within the scope of matters described in the claims.

1 is a block diagram showing an electrical configuration of an electric power steering apparatus according to an embodiment of the present invention. It is a flowchart for demonstrating the process which corrects a carrier wave period. It is a figure for demonstrating the effect by correction of a carrier wave period. It is a figure for demonstrating the problem which arises when the sampling period of an electric current has shifted | deviated from the integral multiple of the PWM carrier wave period.

Explanation of symbols

  11 ... Microcomputer, 15 ... Current sensor

Claims (2)

A motor control device for driving a motor by PWM control,
PWM signal generating means for generating a PWM signal for the PWM control using a carrier wave of a predetermined carrier wave period;
Motor current detecting means for detecting the current of the motor at a predetermined sampling period;
Based on the motor current detected by the motor current detecting means, the period relation detecting means for detecting the relation between the carrier period and the sampling period,
A period changing means for changing the carrier wave period or the sampling period based on a deviation of the inter-period relation with respect to a predetermined reference relation;
The circumferential period relationship detection unit, when the actual current is zero the motor, sampling values of the motor current detecting means for vibrating at correspondingly low frequency bias of an integral multiple of the carrier wave period and the sampling period It includes frequency analysis means for determining the frequency,
The period changing means changes the carrier period or the sampling period based on the frequency of the sampling value obtained by the frequency analyzing means so that the sampling period is an integral multiple of the carrier period. , Motor control device. The inter-period relationship detecting means further includes the frequency of the sampling value obtained by the frequency analyzing means being less than a predetermined frequency threshold, and the amplitude of the frequency component of the sampling value obtained by the frequency analyzing means is Determining means for determining whether or not a predetermined amplitude threshold is exceeded,
The period changing unit is configured such that the frequency of the sampling value obtained by the frequency analyzing unit is less than the predetermined frequency threshold by the determining unit and the frequency component of the sampling value obtained by the frequency analyzing unit is determined . The carrier wave period or the sampling period is changed on condition that the amplitude is determined to exceed the predetermined amplitude threshold value.
The motor control device according to claim 1.

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