JP7729263B2 - Motor control device, electric actuator, and electric power steering device - Google Patents

Description

The present invention relates to a motor control device, an electric actuator, and an electric power steering device.

When a motor rotates, a back-EMF voltage is generated, and this back-EMF voltage acts as a disturbance and enters the current control feedback loop. The PID (Proportional Integral Differential) controller in a motor control device has the role of passing an actual current to the motor according to a current command value, but the back-EMF voltage disturbance interferes with the PID controller's function, causing a large current deviation (the difference between the current command value and the actual current).
For this reason, for example, Patent Documents 1 and 2 propose motor control devices that have a function to suppress the influence of disturbances caused by back electromotive force.

JP 2013-219870 A Japanese Patent Application Laid-Open No. 2021-141691

However, the technology of Patent Document 1 uses an LR model that models the coil L and resistance R of the motor, so the values of the coil L and resistance R, which change due to variations during manufacturing and temperature changes during use, become adaptation factors, which are a factor in reducing the accuracy of disturbance suppression.
Furthermore, in the technology of Patent Document 2, since feedforward control is performed, there is an adaptive element, which causes a decrease in the accuracy of disturbance suppression.
Therefore, an object of the present invention is to suppress disturbances caused by back electromotive force using a simple configuration without adaptive elements.

In order to solve the above problem, one aspect of the motor control device according to the present invention includes a PID control unit that calculates a voltage command value by PID control based on a difference value between a current command value and an actual current value, a voltage output unit that outputs an output voltage value based on the voltage command value, and a disturbance suppression unit that suppresses disturbances caused by back electromotive force by positively feeding back the voltage command value with a delay between the PID control unit and the voltage output unit without an external input.
According to such a motor control device, disturbances caused by back electromotive force can be suppressed by a simple disturbance suppression unit that does not have any adaptive elements.

The motor control device preferably further includes a low-pass filter acting on the voltage command value between the PID control unit and the voltage output unit, and the disturbance suppression unit feeds back the voltage command value from the output side to the input side of the low-pass filter. By including a low-pass filter, sensitivity to current detection noise associated with detection of the actual current value is reduced. Furthermore, by positioning the low-pass filter between the PID control unit and the voltage output unit, sensitivity to voltage noise is approximately zero.

In the motor control device, the PID control unit calculates the difference value as follows:
G _PID = {ω _c L+(R/2)} [1+{ω _c /(2s)}+{s/(2ω _c )}]
however,
It is preferable to calculate the voltage command value by applying a gain G _PID represented by s: Laplace operator ω _c [rad/s], L [H]: inductance of the motor, R [Ω]: resistance of the motor. Highly accurate disturbance suppression is achieved by combining the disturbance suppression unit with a simple PID control unit that applies the gain G _PID to the difference value.

In order to solve the above problem, one aspect of the electric actuator according to the present invention includes any one of the motor control devices described above, and a motor to which a voltage controlled by the motor control device is applied.
With such an electric actuator, disturbances caused by back electromotive force are suppressed by the control of the motor control device, so that an actual current flows through the motor in accordance with the current command value, thereby obtaining a desired output.
In order to solve the above problem, one aspect of an electric power steering device according to the present invention includes any of the motor control devices described above, a motor to which a voltage controlled by the motor control device is applied, and a power steering mechanism driven by the motor.
According to such an electric power steering device, an actual current flows to the motor in accordance with the current command value, and a desired output is obtained, so that the steering assist accuracy is high.

This invention makes it possible to suppress disturbances caused by back electromotive force using a simple configuration without adaptive elements.

1 is a configuration diagram schematically illustrating an embodiment of an electric power steering device. FIG. 2 is a functional block diagram illustrating an example of a functional configuration of a control unit. FIG. 2 is a functional block diagram showing an example of a functional configuration of a voltage command value calculation unit. 10 is a graph showing a frequency response of a q-axis actual current to an input of a current command value. 10 is a graph of the rotation speed of a motor showing an example of a step response. 10 is a graph of a q-axis current showing an example of a step response. 10 is a graph of q-axis current showing an example of a lamp response. 10 is a graph of d-axis current showing an example of lamp response. 10 is a graph showing an example of a response of a feedforward control during steering. 6 is a graph showing an example of a response in the present embodiment during steering. FIG. 10 is a functional block diagram showing another example of the functional configuration of the voltage command value calculation unit. 12 is a graph showing a frequency response in the configuration example shown in FIG. 11 .

Embodiments of the present invention will be described below with reference to the drawings. However, to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art, more detailed descriptions than necessary may be omitted. For example, detailed descriptions of matters that are already well known or duplicate descriptions of substantially identical configurations may be omitted. Furthermore, elements shown in earlier-described figures may be referenced as appropriate in the descriptions of later figures.

In this specification, embodiments of the present disclosure will be described using as an example an electric actuator that supplies power from a power source to a three-phase motor with three-phase (A, B, and C) windings. However, the scope of the present disclosure also includes electric actuators that supply power from a power source to an n-phase motor with n-phase (n is an integer equal to or greater than 4) windings, such as four or five phases.

FIG. 1 is a schematic diagram showing the configuration of an embodiment of an electric power steering device.
The electric power steering device 100 of this embodiment is equipped with a steering mechanism having a steering wheel 1, a column shaft 2, a reduction gear 3, universal joints 4A and 4B, a pinion-rack mechanism 5, and a tie rod 6 for the steered wheels. The electric power steering device 100 also includes a torque sensor 10, a motor 20, a control unit 30, an ignition key 11, a vehicle speed sensor 12, and a battery 14. The combination of the motor 20 and the control unit 30 corresponds to one embodiment of the electric actuator of the present invention, and the control unit 30 corresponds to one embodiment of the motor control device of the present invention. The steering mechanism is driven by the motor 20.

A column shaft 2 of the steering wheel 1 is connected to a tie rod 6 of the steered wheels via a reduction gear 3, universal joints 4A and 4B, and a pinion rack mechanism 5. A torque sensor 10 that detects the steering torque of the steering wheel 1 is provided on the column shaft 2, and a motor 20 that assists the steering force of the steering wheel 1 is connected to the column shaft 2 via the reduction gear 3.
The torque sensor 10 detects the steering torque Th transmitted from the steering wheel 1 due to the driver's steering operation.

A control unit (ECU) 30 that controls the power steering device 100 is supplied with power from a battery 14, which is a power source, and also receives an ignition key signal from an ignition key 11. The control unit 30 calculates a steering assist torque using an assist map or the like based on the steering torque Th detected by the torque sensor 10 and the vehicle speed Vh detected by the vehicle speed sensor 12.
Then, the control unit 30 controls the current I supplied to the motor 20 so as to generate the calculated assist torque. A voltage controlled by the control unit 30 is applied to the motor 20, and the current I is controlled by the controlled voltage. The assist torque generated by driving the motor 20 is applied to the steering system as an assist force for the driver's steering operation (steering assist force), allowing the driver to operate the steering wheel with less force.

The quality of the steering feel is determined by the amount of assist torque generated from the steering torque Th output by steering and the vehicle speed Vh. Furthermore, the performance of the electric power steering device is greatly affected by the accuracy with which the current I required to generate the assist torque is passed to the motor 20.

The control unit 30 may be, for example, a computer including a processor and peripheral components such as a storage device. The processor may be, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit).
The storage device may include any of semiconductor storage devices, magnetic storage devices, and optical storage devices. The storage device may include memories such as registers, cache memories, and memory used as main storage devices, such as ROMs (Read Only Memory) and RAMs (Random Access Memory).

The control unit 30 may be configured with dedicated hardware, which will be described below, for executing each information processing.
For example, the control unit 30 may include a functional logic circuit configured in a general-purpose semiconductor integrated circuit, or may include a programmable logic device (PLD) such as a field-programmable gate array (FPGA).

FIG. 2 is a functional block diagram showing an example of the functional configuration of the control unit 30.
The control unit 30 includes a current command value calculation unit 40, a voltage command value calculation unit 45, a two-phase/three-phase conversion unit 46, a PWM (Pulse Width Modulation) control unit 47, an inverter 48, and a three-phase/two-phase conversion unit 49, and drives the motor 20 by vector control. The motor 20 is, for example, a three-phase motor.
The functions of the current command value calculation unit 40, the voltage command value calculation unit 45, the two-phase/three-phase conversion unit 46, the PWM control unit 47, and the three-phase/two-phase conversion unit 49 are realized, for example, by the processor of the control unit 30 executing a computer program stored in a storage device.

The current command value calculation unit 40 calculates current command values Iq0 and Id0 that indicate the currents of the d and q axes that should be passed to the motor 20 based on the steering torque Th and the vehicle speed Vh.
On the other hand, the currents ia, ib, ic flowing in each phase of the motor 20 are detected by current sensors 60, 61, 62 provided in each layer, and the detected currents ia, ib, ic are converted into actual current values id, iq of the dq2 axes by the three-phase/two-phase conversion unit 49 and fed back.

The current command values Iq0, Id0 are input to the voltage command value calculation unit 45, and the fed-back actual current values id, iq are also input. The voltage command value calculation unit 45 calculates voltage command values vq, vd such that the difference between the current command values Iq0, Id0 and the actual current values id, iq is zero. The two-phase/three-phase conversion unit 46 converts the voltage command values vd, vq into three-phase voltage command values va, vb, vc.

The PWM control unit 47 generates PWM-controlled gate signals based on the three-phase voltage command values va, vb, and vc. The inverter 48 is driven by the gate signals generated by the PWM control unit 47 and applies voltages indicated by the three-phase voltage command values va, vb, and vc to each phase of the motor 20. As a result, currents indicated by the current command values Iq0 and Id0 are supplied to the motor 20.

The resolver 63 detects the motor angle (rotation angle) θ of the motor 20, and the detected motor angle θ is fed back to the current command value calculation unit 40 and used for vector control. A motor rotation angle sensor may be used instead of the resolver 63. Note that the rotation angular velocity ω of the motor 20 calculated based on changes in the motor angle θ may be input to the current command value calculation unit 40 together with the motor angle θ or instead of the motor angle θ.

Fig. 3 is a functional block diagram showing an example of the functional configuration of the voltage command value calculation unit 45. Fig. 3 also shows a model of the motor 20. Fig. 3 shows the control functions for the d and q axes, but in the following explanation, the control of the q axis will be explained as a representative example. The d axis controller is designed in the same way as the q axis controller.
The function of the motor 20 is represented by a model having electrical characteristics 21, a torque constant _KT , mechanical characteristics 23, an integral element 24, and an EMF (back electromotive force) coefficient _KE .

An actual current is generated when a voltage is input to the electrical characteristic 21 of the motor 20. The voltage value input to the electrical characteristic 21 includes voltage noise. The gain of the electrical characteristic 21 is expressed as 1/(Ls+R) where L is an inductance [H] and R is a resistance [Ω]. The actual current is detected by current sensors 60, 61, and 62, and the detected value includes current detection noise.
A torque constant K _T [Nm/A] acts on the actual current to generate a motor torque.

The angular velocity of the motor 20 is generated by inputting the motor torque to the mechanical characteristic 23. The gain of the mechanical characteristic 23 is expressed as 1/(Js+D) where J is the inertia [kgm ² ] and D is the viscosity [Nm/(rad/s)].
The angular velocity of the motor 20 passes through an integral element 24 to become a motor angle θ. The motor angle θ is detected by a resolver 63 (or a motor rotation angle sensor), and the detected value contains angle detection noise.

The EMF coefficient K _E [V/(rad/s)] acts on the angular velocity to generate a back electromotive force, which is reflected in the input of the electrical characteristic 21 .
The voltage command value calculation unit 45 includes a control band setting unit 70, a PID (Proportional Integral Differential) control unit 71, a low-pass filter 72, an EMF suppression unit 80 including a first delay element 73, and a second delay element 75.

The control band setting unit 70 receives the current command value Iq0 and applies a gain _Gref to the current command value, thereby setting a control band for current control of the motor 20 by the control unit 30. The gain _Gref of the control band setting unit 70 is expressed as follows:
G _ref =ω _ref /(s+ω _ref )
however,
s: Laplace operator ω _ref [rad/s]: current control band.

The PID control unit 71 receives a difference value Eq between the current command value Iq0 and the q-axis actual current value iq, and calculates a voltage command value vq by PID control based on the difference value Eq. The gain G _PID in the PID control unit 71 is expressed as follows:
G _PID = {ω _c L+(R/2)} [1+{ω _c /(2s)}+{s/(2ω _c )}]
however,
s: Laplace operator ω _c [rad/s]: disturbance suppression band L [H]: inductance of the motor R [Ω]: resistance of the motor.

The first delay element 73 functions as an EMF suppression unit 80 by positive feedback with a delay to suppress EMF disturbances. That is, the EMF suppression unit 80 suppresses disturbances due to the back electromotive force of the motor by positively feeding back the voltage command value vq with a delay without an external input. The gain G _dly in the first delay element 73 is expressed as follows:
G _dly = e ^-Tdly・s
however,
Tdly [μs]: Expressed as the current control period.

The second delay element 75 represents a delay in the feedback loop of the q-axis actual current value iq. The second delay element 75 outputs an output voltage value based on the voltage command value calculated by the PID control unit 71. The gain G _DLY in the second delay element 75 is expressed as follows:
G _DLY = e ^-TDLY・s
however,
TDLY [μs]: represents the calculation time from current detection by the current sensors 60, 61, 62 to reflection of the duty in the output of the inverter 48.

The approximate expression of the transfer function in the functional block diagram shown in FIG. 3 is the following expression (1).

however,
Iq0: current command value Δv: voltage noise Δi: current detection noise Δτ: torque disturbance Δθ: angle detection noise.
In equation (1), the matrix with the transpose symbol T is a sensitivity function, and the sensitivity function corresponding to the voltage noise Δv is approximately zero. In other words, equation (1) shows that the EMF suppression unit 80 with a simple configuration including the first delay element 73 can effectively suppress the voltage noise Δv.

FIG. 4 is a graph showing the frequency response of the q-axis actual current iq to the input of the current command value Iq0.
The horizontal axis in FIG. 4 is a logarithmic axis indicating frequency, and the vertical axis in FIG. 4 indicates amplitude in the upper part and phase in the lower part.
In Figure 4, the thin solid line shows the frequency response without EMF suppression function, and the dotted line shows the frequency response with feedforward EMF compensation as disclosed in the above-mentioned Patent Document 2. The thin dotted line shows the frequency response with an 11 Hz low-pass filter in the feedforward path, and the thick dotted line shows the frequency response with a 159 Hz low-pass filter in the feedforward path.

The frequency response in feedforward control shows that the responsiveness changes depending on the frequency band, and that the influence of EMF disturbances is significant.
In contrast, the frequency response of this embodiment, represented by the thick solid line, is flat over a wide frequency band. This shows that this embodiment suppresses EMF disturbances and achieves control with high response accuracy. Note that the response is reduced in the band above 400 Hz because the cutoff frequency of the control band setting is 400 Hz.
Next, a specific example of the response of the q-axis actual current iq to the input of various current command values Iq0 will be described.

5 and 6 are graphs showing examples of step responses.
Fig. 5 shows the time variation of the motor rotation speed, and Fig. 6 shows the time variation of the q-axis current. The horizontal axes of Fig. 5 and Fig. 6 both indicate time, but the horizontal axis of Fig. 6 is enlarged more than the horizontal axis of Fig. 5.

5 and 6, similar to FIG. 4, show an example of the time variation of this embodiment in the thick solid line, and the frequency response with feed-forward EMF compensation in the dotted line. The thin dotted line shows the case with an 11 Hz low-pass filter, and the thick dotted line shows the case with a 159 Hz low-pass filter.
5 and 6 show the step response when the rotation speed is set to 3000 rpm, and as shown in FIG. 5, each graph shows a sudden rise from around 3 seconds.

Figure 6 shows step-type current command values and the corresponding actual current values for each type of line on the graph. As shown in Figure 6, with feedforward control, indicated by the dotted line, it takes time to converge to the step-type command value, resulting in a large current deviation. In contrast, in this embodiment, the actual current value converges to the step-type command value in a short time of approximately 10 ms, confirming that the current deviation is small.

7 and 8 are graphs showing example lamp responses.
Fig. 7 shows the time variation of the q-axis current, and Fig. 8 shows the time variation of the d-axis current. The horizontal axis of Fig. 7 and Fig. 8 represents time, and the vertical axis of Fig. 7 and Fig. 8 represents current value.
7A and 8A show example responses with a 159 Hz low pass filter in the feedforward path.
7B and 8B show example responses with an 11 Hz low-pass filter in the feedforward path.
7(C) and 8(C) show examples of responses in this embodiment.

In Fig. 7, the q-axis current command value is shown as a diagonal straight line graph, and in Fig. 7(A) and Fig. 7(B), there is a deviation of the actual current value from the current command value. In contrast, in Fig. 7(C), the graph of the actual current value always overlaps with the graph of the current command value, confirming high responsiveness.
In Fig. 8, the current command value on the d-axis is shown by a dotted line graph parallel to the horizontal axis, and in Fig. 8(A) and Fig. 8(B), there is a deviation of the actual current value from the current command value. In contrast, in Fig. 8(C), the graph of the actual current value always overlaps with the graph of the current command value, confirming high responsiveness also for the d-axis.
As can be seen from Figures 5 to 8, in this embodiment, an actual current flows to the motor 20 in accordance with the current command value, and therefore, the electric actuator equipped with the motor 20 and the control unit 30 can obtain the desired output.

9 and 10 are graphs showing examples of responses during steering.
The horizontal axis in Figures 9 and 10 represents time, and the vertical axis in Figures 9 and 10 represents current value. The upper parts of Figures 9 and 10 show the time variation of the q-axis current, and the lower parts of Figures 9 and 10 show the time variation of the d-axis current. In Figures 9 and 10, the thin solid line shows the current command value, and the thick solid line shows the actual current value. Figure 9 shows the response in feedforward control, and Figure 10 shows the response in this embodiment.

As shown in Figure 9, in the case of feedforward control, the graph of the actual current value is offset from the graph of the current command value. In contrast, as shown in Figure 10, in this embodiment, the graph of the actual current value overlaps the graph of the current command value, and it has been confirmed that the responsiveness is so high that the two cannot be distinguished. Because the actual current that flows to the motor 20 is in line with the current command value, the motor 20 can obtain the desired output, and the electric power steering device 100 shown in Figure 1 provides high steering assist accuracy.

5 to 10, high responsiveness was confirmed in voltage command value calculation unit 45 shown in Fig. 3, but in the above formula (1), the sensitivity function for current detection noise Δi is 1. For this reason, it is desirable to have a measure against current detection noise Δi.
FIG. 11 is a functional block diagram showing an example of the functional configuration of the voltage command value calculation unit 45 in which a countermeasure against the current detection noise Δi is implemented.
11, the EMF disturbance suppression unit 80 includes a low-pass filter 72 that acts on the voltage command value. A first delay element 73 feeds back the voltage command value from the output side to the input side of the low-pass filter 72.

The low-pass filter 72 cuts out the current detection noise Δi contained in the q-axis actual current value iq. The gain G _LPF of the low-pass filter 72 is expressed as follows:
G _LPF = ω _LPF / (s+ω _LPF )
however,
s: Laplace operator ω _LPF [rad/s]: Cutoff frequency.

The approximate expression of the transfer function in the functional block diagram shown in FIG. 11 is the following expression (2).

FIG. 12 is a graph showing the frequency response in the example configuration shown in FIG.
Similar to Fig. 4, Fig. 12 shows the frequency response of the q-axis actual current iq with respect to the input of the current command value Iq0. The thin solid line graph in Fig. 12 shows the frequency response in the configuration example of Fig. 3, and the thick solid line graph in Fig. 12 shows the frequency response in the configuration example of Fig. 11. In the example shown in Fig. 12, the cutoff frequency of the low-pass filter 72 of the EMF disturbance suppression unit 80 is 1 kHz.

Compared to the frequency response in the configuration example of Figure 3, the frequency response in the configuration example of Figure 11 has reduced responsiveness in the high frequency band, with a reduction of -3 dB or more at frequencies above 1 kHz. Because the current detection noise Δi is high-frequency noise, the reduced responsiveness in the high frequency band reduces the sensitivity of the actual current to the current detection noise Δi, thereby suppressing the influence of the current detection noise Δi.

Note that while the above description shows an example of application to a power steering device, the electric actuator and motor control device of the present invention can be applied to a wide range of fields, including vehicle drive systems and robots. In other words, the embodiments and scope of application of the present invention are not limited to power steering devices.

100... electric power steering device, 1... steering handle, 2... column shaft,
3...reduction gear, 4A, 4B...universal joint, 5...pinion rack mechanism,
6...steered wheel tie rod, 10...torque sensor, 11...ignition key,
12... vehicle speed sensor, 14... battery, 20... motor, 30... control unit,
40...current command value calculation unit, 45...voltage command value calculation unit, 46...two-phase/three-phase conversion unit,
47... PWM control unit, 48... inverter, 49... three-phase/two-phase conversion unit,
60, 61, 62...current sensors, 63...resolver, 70...control band setting unit,
71... PID control unit, 72... low-pass filter, 73... first delay element,
75... second delay element, 80... EMF disturbance suppression section

Claims (5)

a PID control unit that calculates a voltage command value by PID control based on a difference between a current command value and an actual current value;
a voltage output unit that outputs an output voltage value based on the voltage command value;
a disturbance suppression unit that suppresses disturbances caused by a back electromotive force of the motor by positively feeding back the voltage command value with a delay between the PID control unit and the voltage output unit without an external input;
A motor control device comprising: a low-pass filter acting on the voltage command value between the PID control unit and the voltage output unit;
The motor control device according to claim 1 , wherein the disturbance suppression unit feeds back the voltage command value from the output side to the input side of the low-pass filter. The PID control unit adjusts the difference value by:
G _PID = {ω _c L+(R/2)} [1+{ω _c /(2s)}+{s/(2ω _c )}]
however,
s: Laplace operator ω _c [rad/s]: disturbance suppression band L [H]: inductance of the motor R [Ω]: gain G represented by resistance of the motor The motor control device according to claim 1, wherein the voltage command value is calculated by applying _{a PID} . The motor control device according to any one of claims 1 to 3;
a motor to which a voltage controlled by the motor control device is applied;
An electric actuator equipped with The motor control device according to any one of claims 1 to 3;
a motor to which a voltage controlled by the motor control device is applied;
a power steering mechanism driven by the motor;
An electric power steering device equipped with