JP7779202B2 - 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.

If the calculation frequency of the current control is, for example, 4 kHz, which is within the human audible range (20 kHz or less), a 4 kHz sound is generated in synchronization with the output timing of the control voltage, which is the final output of the current controller. This sound can be unpleasant to some people.
If the calculation frequency could be increased to 20 kHz or higher, it would be outside the audible range and the problem would be alleviated, but with the calculation processing speed of current microcomputers, it is difficult to execute calculations for current control at 20 kHz or higher.

On the other hand, it is technically possible to change only the output timing of the control voltage, which is the final output of the current controller, to 20 kHz while keeping the calculation frequency for current control at 4 kHz (250 μs cycle). For example, by using DMA (direct memory access), a control voltage value calculated in advance can be set in memory and output at the desired time with almost no processing load.
For example, Patent Document 1 proposes a technology in which each motor electrical angle at each future point in time at intervals shorter than the calculation time interval is calculated by extrapolation from the current and past values of the motor electrical angle, and the duties of the d- and q-axes are converted to three-phase duties based on each motor electrical angle.

Special table 2019-083015 publication

However, the gain characteristics resulting from extrapolating the motor electrical angle have a high gain in the high frequency range, amplifying angle detection noise, which then gets mixed into the current control feedback loop, generating noise and vibration.
Therefore, an object of the present invention is to increase the frequency of the control voltage output while suppressing angle detection noise.

In order to solve the above-mentioned problems, one aspect of a motor control device according to the present invention includes a command value calculation unit that calculates voltage command values for each of two d and q axes; a conversion unit that converts the voltage command values for each of the two d and q axes into voltage command values for each phase of an n-phase motor for each calculation time interval; an lead-angle compensation unit that applies lead-angle compensation to the conversion unit and provides the conversion unit with a plurality of lead-angle amounts for each of a plurality of interpolation intervals into which the calculation time interval is divided, thereby causing the conversion unit to calculate the voltage command value for each phase of the n-phase motor for each of the plurality of interpolation intervals; and a storage unit that stores the voltage command value for each phase of the n-phase motor for each of the plurality of interpolation intervals for each calculation time interval, and outputs the voltage command value for each interpolation interval.
With such a motor control device, the amount of lead angle compensation is calculated for each of multiple interpolation intervals and provided to the conversion unit, so that gain increases are suppressed even in the high-frequency range, and the control voltage output is made higher frequency while angle detection noise is suppressed.

In the above motor control device, it is preferable that the advance angle compensation unit has a state estimation unit that estimates the rotational state of the n-phase motor, and performs the advance angle compensation based on the estimated rotational state. The state estimation unit can obtain a smooth state signal that indicates the rotational state of the n-phase motor, enabling smooth advance angle compensation based on the state signal.

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.
According to such an electric actuator, the control voltage output is increased in frequency to drive the motor, so that the drive noise can be shifted outside the audible range.

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, the driving noise can be shifted out of the audible range, so that abnormal noise during assist is suppressed.

This invention makes it possible to increase the frequency of control voltage output while suppressing angle detection noise.

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. 4 is a block diagram showing a functional configuration of a rotation speed estimation unit of the advance angle compensation unit. FIG. 2 is a block diagram showing a functional configuration of an advance angle compensation unit other than a rotation speed estimation unit. 10 is a graph showing the gain characteristics of a current control system. 10 is a graph showing the phase characteristics of a current control system.

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, an advance angle compensation unit 44, 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. Furthermore, the control unit 30 includes a memory 43 between the two-phase/three-phase conversion unit 46 and the PWM control unit 47. The motor 20 is, for example, a three-phase motor.

The functions of the current command value calculation unit 40, the advance angle compensation unit 44, 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, the advance angle compensation unit 44, 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 perform calculations at predetermined calculation time intervals.

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 voltage command value calculation unit 45 receives the current command values Iq0 and Id0 as input, as well as the fed-back actual current values id and iq. The voltage command value calculation unit 45 calculates the voltage command values Vrefq and Vrefd for the d and q axes, respectively, so that the difference between the current command values Iq0 and Id0 and the actual current values id and iq becomes zero. The voltage command value calculation unit 45 calculates the voltage command values Vrefq and Vrefd, for example, using PID (Proportional Integral Differential) control.

The two-phase/three-phase conversion unit 46 converts the dq2-axis voltage command values Vrefq and Vrefd into three-phase voltage command values VrefA, VrefB, and VrefC. However, the two-phase/three-phase conversion unit 46 calculates multiple sets of three-phase voltage command values VrefA, VrefB, and VrefC for each calculation time interval based on the dq2-axis voltage command values Vrefq and Vrefd calculated for each calculation time interval. Each set of voltage command values VrefA, VrefB, and VrefC corresponds to one of multiple interpolation intervals obtained by dividing the calculation time interval. In other words, the two-phase/three-phase conversion unit 46 calculates three-phase voltage command values VrefnA, VrefnB, and VrefnC for each of the multiple interpolation intervals. Multiple sets of voltage command values VrefnA, VrefnB, and VrefnC are calculated for each calculation time interval and stored in memory 43.

The lead-angle compensation unit 44 applies lead-angle compensation to the two-phase/three-phase conversion unit 46 to compensate for the phase lag of the three-phase current. That is, the lead-angle value corresponding to the phase lag of the three-phase current relative to the phase of the three-phase voltage applied to the motor 20 is added to the electrical angle θE used when calculating the three-phase voltage command values VrefA, VrefB, and VrefC, thereby advancing the phase of the three-phase current. The lead-angle compensation unit 44 provides the two-phase/three-phase conversion unit 46 with a lead-angle value Δθn for each of the multiple interpolation intervals, causing it to calculate the voltage command values VrefnA, VrefnB, and VrefnC for each of the multiple interpolation intervals. The specific details of lead-angle compensation will be described in detail later.

The memory 43 outputs one set of voltage command values VrefnA, VrefnB, and VrefnC stored in the memory 43 to the PWM control unit 47 at each interpolation interval.
The PWM control unit 47 generates PWM-controlled gate signals based on the three-phase voltage command values VrefnA, VrefnB, and VrefnC. 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 VrefnA, VrefnB, and VrefnC 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 operations of the PWM control unit 47 and the inverter 48 are performed at each interpolation interval, and therefore have a high bandwidth relative to the operations at each calculation time interval. This allows the operating cycles of the PWM control unit 47 and the inverter 48 to be outside the human audible range, thereby suppressing abnormal noise.

The resolver 63 detects the angle (rotation angle) θ of the rotating shaft of the motor 20, and the detected angle θ of the rotating shaft is fed back to the current command value calculation unit 40 and used for vector control. In the following description, the detected angle of the rotating shaft is referred to as the "motor angle." A motor rotation angle sensor may be used instead of the resolver 63. Note that the rotational 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.

3 and 4 are functional block diagrams showing an example of the functional configuration of the lead angle compensator 44. As shown in FIG.
The lead angle compensation unit 44 has a rotation speed estimator 80 shown in Fig. 3, and Fig. 4 shows the functional configuration of the lead angle compensation unit 44 excluding the rotation speed estimator 80. The lead angle compensation unit 44 estimates the rotation speed of the motor 20 using the rotation speed estimator 80. The rotation speed estimator 80 is an example of a state estimator that estimates the rotation state of the motor 20, and in this embodiment, it estimates the rotation speed. Instead of the rotation speed estimator 80, the lead angle compensation unit 44 may be provided with a state estimator that estimates, for example, angular acceleration.

The functional blocks shown in FIG. 3 correspond to the following formulas (1) and (2).


however,
z: intermediate variable of the state estimator λ: characteristic root of the state estimator j [kgm ² ]: inertia of the motor in control d [Nm/(rad/s)]: viscosity of the motor in control k _T [Nm/A]: torque constant of the motor in control k: stiffness of the motor in control i: actual q-axis current value x ₁ : motor angle (= θ)
x ₂ (with ^): Estimated rotation speed (=ωest).

That is, the q-axis actual current value i and the motor angle _x1 are input to the rotation speed estimator 80, and the rotation speed estimator 80 outputs an estimated rotation speed value _x2 (added with ^). The first block 51, the second block 52, and the third block 53 of the rotation speed estimator 80 correspond to the first term, the second term, and the third term of equation (1), respectively. The fourth block 54 of the rotation speed estimator 80 corresponds to the second term of equation (2). The rotation speed estimated value _x2 (added with ^) is input to the first block 51, the motor angle _x1 is input to the second block 52 and the fourth block 54, and the q-axis actual current value i is input to the third block 53. The outputs of the first block 51, the second block 52, and the third block 53 are added together and input to the integral element 55. The outputs of the integral element 55 and the fourth block 54 are added together to obtain the estimated rotation speed value _x2 (added with ^).

The motor angle x ₁ (= θ) detected by the resolver 63 (or motor rotation angle sensor) is input to the rotation speed estimator 80. The motor angle x ₁ (= θ) is a signal containing angle detection noise, but the rotation speed estimator 80 shown in FIG. 3 can obtain the rotation speed estimate x ₂ (added ^) (= ωest) as a smooth signal. The rotation speed estimate x ₂ (added ^) (= ωest) obtained by the rotation speed estimator 80 is input to a second differentiator 83 shown in FIG. 4.

4, in the lead angle compensation unit 44, the motor angle θ is subjected to a first difference processing in a first differentiator 81 to calculate an angular velocity signal ω. A low-pass filter 82 acts on the angular velocity signal ω to suppress angle detection noise, thereby calculating a mechanical angular velocity signal _ωM .
Meanwhile, the rotation speed estimate ωest is subjected to a single difference process in the second differentiator 83 to calculate the angular acceleration signal dωest/dt. Because the rotation speed estimate ωest is obtained as a smooth signal, angle detection noise is suppressed in the angular acceleration signal dωest/dt after the single difference process, and vibrations in the current control system are also suppressed. Furthermore, because the rotation speed estimate ωest is obtained in the rotation speed estimator 80, the angular acceleration can be easily calculated by single difference process, reducing the computational load.

The angular acceleration signal dωest/dt is multiplied by a delay time _Δts in a multiplier 84 to calculate the angular velocity change Δωest after the delay time _Δts . The delay time _Δts is an adaptation element.
The mechanical angular velocity signal _ωM is added to the angular velocity change amount Δωest to calculate the mechanical angular velocity signal _ΔωM that takes into account the angular velocity change amount after the delay time _Δts . The mechanical angular velocity signal _ΔωM is multiplied by a gain (2πNp) to convert it from the mechanical angle dimension to the electrical angle dimension, and the electrical angular velocity signal _ΔωE is obtained, where Np is the number of pole pairs.

The electrical angular velocity signal Δω _E is multiplied by the sum Δt+Δtn of the calculation time interval Δt in current control and the interpolation interval Δtn (n=0, 1, 2, 3, 4) to calculate the lead angle Δθn (n=0, 1, 2, 3, 4) for each of the plurality of interpolation intervals. In this embodiment, as an example, the calculation time interval Δt is 250 μs, which corresponds to a frequency of 4 kHz, and the interpolation interval Δtn is 50 μs, which corresponds to a frequency of 20 kHz, obtained by dividing the calculation time interval Δt by 5, for example.
Each lead angle amount Δθn (n=0, 1, 2, 3, 4) is added to the motor electrical angle _θE obtained by multiplying the motor angle θ by the number of pole pairs Np, and the result is input as an input signal to a two-phase/three-phase converter 46. The two-phase/three-phase converter 46 also receives as input signals the voltage command values Vrefq and Vrefd for the dq two axes, and performs 2-3 coordinate transformation for each of the multiple interpolation intervals using the transformation matrix shown in FIG. 4. As a result, three-phase voltage command values VrefnA, VrefnB, and VrefnC that have been lead angle compensated are obtained.

In this embodiment, the control unit 30 calculates the voltage command values VrefnA, VrefnB, and VrefnC (n = 1, 2, 3, 4) for the future time in addition to the voltage command values VrefnA, VrefnB, and VrefnC (n = 0) at each calculation timing, in order to make the output timing of the voltage command values VrefnA, VrefnB, and VrefnC higher frequency than the calculation timing. Furthermore, when calculating the voltage command values VrefnA, VrefnB, and VrefnC (n = 1, 2, 3, 4) for the future time, the advance angle amount Δθn (n = 1, 2, 3, 4) for the future time is used. This suppresses gain increases in the high-frequency range and reduces angle detection noise. As a result, sound and vibration in the motor 20 are suppressed.

The following describes the results of a simulation that confirmed the characteristics of the current control system in a wide bandwidth output using the advance angle Δθn (n=1, 2, 3, 4) in the future time.
FIG. 5 is a graph showing the gain characteristics of the current control system.
In FIG. 5, the horizontal axis represents the frequency of the output signal, and the vertical axis represents the gain.
The gain of the current control system in this embodiment is maintained at 0 dB even when the output signal reaches 1000 Hz, confirming that angle detection noise is suppressed even in the high frequency range.

FIG. 6 is a graph showing the phase characteristics of the current control system.
The horizontal axis of Figure 6 represents the frequency of the output signal, and the vertical axis represents the phase. Figure 6 shows the phase characteristics for each of multiple interpolation intervals (n = 0, 1, 2, 3, 4) using different line styles. The phase characteristics at the calculation time (n = 0) indicate that the phase advances as the frequency of the output signal increases, confirming that appropriate lead-angle compensation is applied even in the high-frequency range. The phase characteristics at future times (n = 1, 2, 3, 4) also indicate that the phase advances as the frequency of the output signal increases. Furthermore, the phase characteristics at future times (n = 1, 2, 3, 4) indicate that the phase advances as time progresses further into the future, confirming that appropriate lead-angle compensation is applied even in the future.

In an electric actuator equipped with a motor 20 and a control unit 30, the control unit 30 outputs a control voltage at a higher frequency to drive the motor 20, making it possible to shift the drive noise outside the audible range. Furthermore, in the electric power steering device 100 shown in Figure 1, the drive noise can be shifted outside the audible range, suppressing abnormal noise during assist.

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.

1...Steering wheel, 2...Column shaft, 3...Reduction gear, 4A, 4B...Universal joint, 5...Pinion rack mechanism, 6...Tie rod of steered wheels, 10...Torque sensor
11... ignition key, 12... vehicle speed sensor, 14... battery, 20... motor,
30...control unit, 40...current command value calculation unit, 43...memory,
44... lead angle compensation 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, 80...rotation speed estimation unit,
100...electric power steering device

Claims (4)

a current command value calculation unit that calculates current command values indicating two-axis d and q currents to be applied to the n-phase motor;
a command value calculation unit that calculates voltage command values for the d and q two axes based on the current command values ;
a conversion unit that converts the voltage command values of the d and q two axes into voltage command values of each phase of the n-phase motor at each calculation time interval;
an advance angle compensation unit that provides the conversion unit with a plurality of advance angle amounts for each of a plurality of interpolation intervals obtained by dividing the calculation time interval, thereby causing the conversion unit to calculate the voltage command value for each phase of the n-phase motor for each of the plurality of interpolation intervals, for each calculation time interval;
a storage unit that stores the voltage command values of each phase of the n-phase motor at each of the plurality of interpolation intervals for each of the calculation time intervals, and outputs the voltage command values at each of the interpolation intervals;
A motor control device comprising:
the lead angle amount corresponds to an amount by which a phase of an n-phase current lags behind a phase of an n-phase voltage applied to the n-phase motor, and the conversion unit calculates the voltage command value for each phase of the n-phase motor using the lead angle amount . 2. The motor control device according to claim 1, wherein the advance angle compensation unit includes a state estimation unit that estimates a rotation state of the n-phase motor, and provides the advance angle amount to the conversion unit at each calculation time interval based on the estimated rotation state. The motor control device according to claim 1 or 2;
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 claim 1 or 2;
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