Motor control device, electric actuator, and electric power steering device

Abstract

To suppress disturbance caused by counter electromotive voltage with a simple configuration having no appropriate element.SOLUTION: A motor control device comprises: a PID (Proportional Integral Differential) control unit that calculates a voltage command value by PID control based on a differential 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 performs positive feedback of the voltage command value between the PID control unit and the voltage output unit with delay without an external input, and thereby, suppresses disturbance by counter electromotive voltage.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a motor control device, an electric actuator, and an electric power steering device. [Background technology]

[0002] When a motor rotates, a back-EMF voltage is generated, which 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 the actual current to the motor according to the current command value, but the disturbance of the back-EMF voltage interferes with the PID controller's function, causing the current deviation (the difference between the current command value and the actual current) to increase. 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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-219870 [Patent Document 2] Patent Publication No. 2021-141691 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technology in 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. [Means for solving the problem]

[0005] 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.

[0006] Furthermore, it is preferable that the motor control device 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 providing a low-pass filter, sensitivity to current detection noise accompanying 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.

[0007] 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, s: Laplace operator ω c [rad / s]: Disturbance suppression band L[H]: Inductance of the motor R [Ω]: resistance of the motor The gain G is expressed as PID It is preferable to calculate the voltage command value by applying the gain G PIDHighly accurate disturbance suppression is realized by combining a simple PID control section that applies the above-mentioned difference value with the above-mentioned disturbance suppression section.

[0008] 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. [Effects of the Invention]

[0009] According to the present invention, disturbances caused by back electromotive force can be suppressed with a simple configuration without any adaptive elements. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a configuration diagram schematically illustrating an embodiment of an electric power steering device. [Figure 2] FIG. 2 is a functional block diagram illustrating an example of a functional configuration of a control unit. [Figure 3] FIG. 2 is a functional block diagram showing an example of a functional configuration of a voltage command value calculation unit. [Figure 4] 10 is a graph showing a frequency response of a q-axis actual current to an input of a current command value. [Figure 5] 10 is a graph of the rotation speed of a motor showing an example of a step response. [Figure 6] 10 is a graph of a q-axis current showing an example of a step response. [Figure 7] 10 is a graph of q-axis current showing an example of a lamp response. [Figure 8] 10 is a graph of d-axis current showing an example of a lamp response. [Figure 9] 10 is a graph showing an example of a response of a feedforward control during steering. [Figure 10] 6 is a graph showing an example of a response in the present embodiment during steering. [Figure 11] FIG. 10 is a functional block diagram showing another example of the functional configuration of the voltage command value calculation unit. [Figure 12] 12 is a graph showing a frequency response in the configuration example shown in FIG. 11. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described 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 description than necessary may be omitted. For example, detailed description of already well-known matters or redundant description of substantially identical configurations may be omitted. Furthermore, elements shown in earlier-described figures may be appropriately referenced in the description of later figures.

[0012] In this specification, an embodiment 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 having three-phase (A, B, and C) windings. However, the scope of the present disclosure also includes an electric actuator that supplies power from a power source to an n-phase motor having n-phase (n is an integer equal to or greater than 4) windings, such as four or five phases.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] The control unit 30 includes, for example, a processor and peripheral components such as a storage device. The computer may include a processor, such as a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). The storage device may include any of a semiconductor storage device, a magnetic storage device, and an optical storage device. The storage device may include a register, a cache memory, a memory such as a ROM (Read Only Memory) used as a main memory, and a RAM (Random Access Memory).

[0018] 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, such as a programmable logic device (PLD) such as a field-programmable gate array (FPGA).

[0019] 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.

[0020] 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 applied to the motor 20, respectively, based on the steering torque Th and the vehicle speed Vh. On the other hand, the currents i a, ib, ic flowing through each phase of the motor 20 are detected by current sensors 60, 61, 62 provided in each layer, and the detected currents i a, ib, ic are converted into actual current values ​​id, iq of the dq2 axes by the 3-phase / 2-phase conversion unit 49 and fed back.

[0021] The current command values ​​Iq0, Id0 and the fed back actual current values ​​id, iq are also input to a voltage command value calculation unit 45. 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 becomes 0. A two-phase / three-phase conversion unit 46 converts the voltage command values ​​vd, vq into three-phase voltage command values ​​va, vb, vc.

[0022] 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 the respective phases of the motor 20. As a result, the motor 20 is supplied with currents indicated by the current command values ​​Iq0 and Id0.

[0023] 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.

[0024] 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 to determine the electrical characteristics 21 and the torque constant K T , mechanical property 23, integral element 24, and EMF (back electromotive force) coefficient K E and

[0025] 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. Actual current and torque constant K T [Nm / A] acts to generate motor torque.

[0026] 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 the inertia J [kgm 2 ] and viscosity D [Nm / (rad / s)], which can be expressed as 1 / (Js+D). The angular velocity of the motor 20 passes through the integral element 24 to become the motor angle θ. The motor angle θ is detected by the resolver 63 (or the motor rotation angle sensor), and the detected value contains angle detection noise.

[0027] EMF coefficient K for angular velocity E The action of [V / (rad / s)] generates a back electromotive force, and the back electromotive force 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.

[0028] The control band setting unit 70 receives the current command value Iq0 and applies a gain G ref By applying the gain G ref teeth, G ref =ω ref / (s+ω ref ) however, s: Laplace operator ω ref [rad / s]: Current control bandwidth It is expressed as:

[0029] The PID control unit 71 receives the difference Eq between the current command value Iq0 and the q-axis actual current value iq, and calculates the voltage command value vq by PID control based on the difference Eq. PID teeth, 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 It is expressed as:

[0030] The first delay element 73 functions as an EMF suppressor 80 by means of delayed positive feedback to suppress EMF disturbances. In other words, the EMF suppressor 80 suppresses disturbances caused by the back electromotive force of the motor by providing delayed positive feedback of the voltage command value vq without external input. The gain G dly teeth, G dly =e -Tdly·s however, Tdly [μs]: Current control period It is expressed as:

[0031] 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 teeth, G DLY =e -TDLY·s however, TDLY [μs]: calculation time from current detection by the current sensors 60, 61, and 62 to duty reflection in the output of the inverter 48 It is expressed as:

[0032] The approximate expression of the transfer function in the functional block diagram shown in FIG. 3 is the following expression (1).

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[0033] 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 when there is no EMF suppression function, and the dotted line shows the frequency response when there is feedforward EMF compensation as disclosed in Patent Document 2. The thin dotted line shows the frequency response when there is an 11 Hz low-pass filter in the feedforward path, and the thick dotted line shows the frequency response when there is a 159 Hz low-pass filter in the feedforward path.

[0034] 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.

[0035] 5 and 6 are graphs showing examples of step responses. Figure 5 shows the time variation of the motor rotation speed, and Figure 6 shows the time variation of the q-axis current. The horizontal axes of both Figure 5 and Figure 6 indicate time, but the horizontal axis of Figure 6 is much larger than the horizontal axis of Figure 5.

[0036] 5 and 6, similar to Fig. 4, show an example of time variation for 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. Figures 5 and 6 show the step response when the target rotation speed is 3000 rpm. As shown in Figure 5, each graph shows a sharp rise from around 3 seconds.

[0037] In Fig. 6, step-type current command values ​​and the corresponding actual current values ​​are shown for each type of line on the graph. As shown in Fig. 6, in the 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 about 10 ms, and it was confirmed that the current deviation is small.

[0038] 7 and 8 are graphs showing examples of lamp responses. Figure 7 shows the time variation of the q-axis current, and Figure 8 shows the time variation of the d-axis current. The horizontal axis of Figures 7 and 8 represents time, and the vertical axis of Figures 7 and 8 represents the current value. 7(A) and 8(A) show example responses when a 159 Hz low-pass filter is included in the feedforward path. 7(B) and 8(B) show example responses when an 11 Hz low-pass filter is included in the feedforward path. FIG. 7(C) and FIG. 8(C) show examples of responses in this embodiment.

[0039] In Figure 7, the q-axis current command value is shown as a diagonal straight line graph, and in Figures 7(A) and 7(B), there is a deviation between the actual current value and the current command value. In contrast, in Figure 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 d-axis current command value is shown as a dotted line graph parallel to the horizontal axis, and in Fig. 8(A) and Fig. 8(B), there is a deviation between the actual current value and 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 FIGS. 5 to 8, in this embodiment, an actual current flows through the motor 20 in accordance with the current command value, and therefore, the electric actuator including the motor 20 and the control unit 30 can obtain a desired output.

[0040] 9 and 10 are graphs showing examples of responses during steering. The horizontal axis in Fig. 9 and Fig. 10 represents time, and the vertical axis in Fig. 9 and Fig. 10 represents current value. The upper parts of Fig. 9 and Fig. 10 show the time variation of the q-axis current, and the lower parts of Fig. 9 and Fig. 10 show the time variation of the d-axis current. In Fig. 9 and Fig. 10, the current command value is shown by a thin solid line, and the actual current value is shown by a thick solid line. Fig. 9 shows the response in feedforward control, and Fig. 10 shows the response in this embodiment.

[0041] As shown in Fig. 9, in the case of feedforward control, the graph of the actual current value is shifted from the graph of the current command value. In contrast, as shown in Fig. 10, in this embodiment, it has been confirmed that the responsiveness is so high that the graph of the actual current value overlaps the graph of the current command value, making it difficult to distinguish between them. Since the actual current that is in line with the current command value flows to the motor 20, the desired output can be obtained from the motor 20, and therefore the electric power steering device 100 shown in Fig. 1 has high steering assist accuracy.

[0042] 5 to 10, high responsiveness is confirmed in voltage command value calculation unit 45 shown in FIG. 3, but in the above formula (1), the sensitivity function to 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 has been implemented. 11, a low-pass filter 72 that acts on a voltage command value is included in the EMF disturbance suppression unit 80. 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.

[0043] 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 teeth, G LPF =ω LPF / (s+ω LPF ) however, s: Laplace operator ω LPF [rad / s]: cutoff frequency It is expressed as:

[0044] The approximate expression of the transfer function in the functional block diagram shown in FIG. 11 is the following expression (2).

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[0045] FIG. 12 is a graph showing the frequency response in the configuration example shown in FIG. Fig. 12 shows the frequency response of the q-axis actual current iq with respect to the input of the current command value Iq0, similar to Fig. 4. 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.

[0046] 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 effects of the current detection noise Δi.

[0047] Although 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, such as vehicle drive systems and robots, etc. In other words, the embodiments and scope of application of the present invention are not limited to power steering devices. [Explanation of symbols]

[0048] 100...electric power steering device, 1...steering wheel, 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...2-phase / 3-phase conversion unit, 47...PWM control unit, 48...inverter, 49...3-phase / 2-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

1. 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:

2. 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.

3. The PID control unit adjusts the difference value by: G ＰＩＤ ={ω ｃ L+(R / 2)}[1+{ω ｃ / (2s)}+{s / (2oh 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 gain G is expressed as ＰＩＤ 2. The motor control device according to claim 1, wherein the voltage command value is calculated by applying a voltage command value to the motor.

4. 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

5. 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

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