JP4120403B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus that applies a steering assist force to a steering mechanism of a vehicle by driving an electric motor in accordance with an operation for steering the vehicle.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an electric power steering apparatus that applies a steering assist force to a steering mechanism by driving an electric motor in accordance with a steering torque applied to a steering wheel (steering wheel) by a driver has been used. In this electric power steering apparatus, current control (feedback control) is typically performed by a proportional-integral controller so that a current of a target value set based on the steering torque indicated by the torque detection signal from the torque sensor flows to the electric motor. Is done.
[0003]
The values of the proportional gain and integral gain (hereinafter referred to as “PI gain”) of the proportional-integral controller are desirably higher in order to increase the response of the entire system. However, since the electric power steering device includes a mechanical resonance system in which the torsion bar interposed in the steering shaft for detecting the steering torque is a spring element and the electric motor is an inertia element, If the value is too high, the system tends to become unstable (vibrating) in the vicinity of the resonance frequency of the resonance system, that is, in the vicinity of the mechanical vibration frequency of the electric power steering apparatus (specifically, in the vicinity of 10 to 25 Hz). Therefore, conventionally, a phase compensator is provided in order to stabilize the system without sacrificing the response of the entire system without setting the PI gain value too high, and to further improve the phase characteristics in the practical frequency band. Specifically, the torque detection signal from the torque sensor is given to the phase compensator, and the phase of the torque detection signal is advanced by the phase compensator, thereby improving the responsiveness of the entire system in the practical frequency band.
[0004]
However, the phase compensator is mainly aimed at improving the phase characteristics of the target control system, and for this frequency band where the gain characteristics become higher, a coping therapy design method such as adding a low-pass filter. Is often adopted. In this case, when the order of the phase compensator becomes high and the main part of the control device is realized by a microcomputer, there is a problem that the calculation load on the microcomputer becomes excessive.
[0005]
On the other hand, as a design guideline for phase compensation, there is also known a conventional technique that gives a transfer function and parameters of a phase compensator as follows.
(S²+ 2ζ₂ω₂s + ω₂ ²) / (S²+ 2ζ₁ω₁s + ω₁ ²(1)
0 <ζ₁<1 ... (2)
0 <ζ₂<1 (3)
Here, s is a Laplace operator (a Laplace transform variable corresponding to a differential operation), ζ₁Is the attenuation coefficient after compensation, ζ₂Is the attenuation coefficient of the compensated system, ω₁Is the natural angular frequency after compensation, ω₂Is the natural angular frequency of the compensated system.
[0006]
In addition, a stabilization compensator represented by the following transfer function is provided after the torque sensor to improve stability and responsiveness (for example, see Patent Document 1).
(S²+ 2a₁s + a₂) / (S²+ 2b₁s + b₂(4)
Where s is a Laplace operator and a₁, A₂, B₁And b₂Is a parameter determined according to the resonance frequency of a mechanical resonance system composed of an inertia element and a spring element.
[0007]
[Patent Document 1]
JP-A-8-290778
[0008]
[Problems to be solved by the invention]
However, in the conventional technology as described above, the degree of freedom of the parameter of the transfer function is large, and an optimum value is not specified. Therefore, the following problems occur depending on the parameter settings.
[0009]
ω₁> Ω₂Is set, the angular frequency ω of the natural vibration of the mechanical system in the electric power steering device_mIs the natural angular frequency ω after compensation₁Lower than (ω_m<Ω₁), The electric power steering device tends to be unstable (vibrating) as a whole system. Also, the compensated damping coefficient ζ₁0 <ζ₁<2^-1/2It is easy to become unstable even if set. Furthermore, the damping coefficient ζ of the compensated system₂2^-1/2<Ζ₂Even when <1 is set, it is likely to become unstable because sufficient phase compensation cannot be performed.
[0010]
The present invention has been made to solve the above-described problem, and provides an electric power steering device that improves the responsiveness while ensuring stability as a control system without increasing the order of the phase compensator. With the goal.
[0011]
[Means for Solving the Problems and Effects of the Invention]
  A first aspect of the invention includes a control device that controls driving of an electric motor in accordance with an operation for steering the vehicle, and steers the steering mechanism of the vehicle by driving the electric motor under the control of the control device. An electric power steering device for providing auxiliary power,
  The control device has a transfer function Gc (s) represented by the following equation:By series compensation methodPhase compensation means,
      Gc (s) = (s²+ 2ζ₂ω₂s + ω₂ ²) / (S²+ 2ζ₁ω₁s + ω₁ ²)
  Where ζ₁Is the attenuation coefficient after compensation, ζ₂Is the attenuation coefficient of the compensated system, ω₁Is the natural angular frequency after compensation, ω₂Is the natural angular frequency of the compensated system and is a parameter of the transfer function Gc (s),
  Of the phase compensation meansParameter ζ of transfer function Gc (s)₂And ω₂Is the torque open loop transfer function of the electric power steering deviceCancels the peak appearing in the gain characteristic of the transfer function of the second-order lag system approximatingIs set to a value likeAnd
  Transfer function G of the phase compensation means c ( s ) Parameter ζ ₁ And ζ ₂ Is set to satisfy the following formula:
      2 ^-1/2 ≦ ζ ₁ ≦ 1,
      0 <ζ ₂ ≦ 2 ^-1/2
  Transfer function G of the phase compensation means c ( s ) Parameter ω ₁ Is set to satisfy the following equation:
      ω ₁ <Ω _m
Where ω _m Is an angular frequency of the natural vibration of the mechanical system in the electric power steering apparatus.
[0012]
  According to such a first invention, the torque open loop transfer functionThe peak appearing in the gain characteristic of the transfer function of the second order lag system approximatingThus, it is possible to improve responsiveness while ensuring stability. In addition, in order to set the input / output steady gain of the phase compensation means to 1, ω as a gain correction coefficient in Gc (s) as in the following equation:₁ ²/ Ω₂ ²It can also take the form of multiplying.
  Gc (s) = ω₁ ²(s²+ 2ζ₂ω₂s + ω₂ ²) / {Ω₂ ²(s²+ 2ζ₁ω₁s + ω₁ ²)}
  Further, according to the first aspect of the invention, the parameter ζ to be the attenuation coefficient of the compensated system ₂ Is 0 <ζ ₂ ≦ 2 ^-1/2 Therefore, sufficient phase compensation can be performed, and the parameter ζ to be the attenuation coefficient after compensation is selected. ₁ 2 ^-1/2 ≦ ζ ₁ Since it is selected from the range of ≦ 1, responsiveness can be improved while ensuring stability by phase compensation.
  Furthermore, according to the first aspect of the invention, the parameter ω to be the natural angular frequency after compensation is set. ₁ Is the angular frequency ω of the mechanical vibration _m Therefore, it is possible to prevent instability of the control system due to the natural vibration of the mechanical system, and it is possible to improve the responsiveness while maintaining the stability more reliably.
[0015]
  SecondThe invention ofFirstIn the invention of
  Parameter ω of transfer function Gc (s) of the phase compensation means₁And ω₂Is characterized in that it satisfies the following formula and is set to a value in the vicinity of 2π × fp when the peak frequency in the gain characteristic of the torque open loop transfer function is fp.
      ω₁= Ω₂
[0016]
  like thisSecondAccording to the invention of ω₁= Ω₂This reduces the design parameter for phase compensation by one, and the parameter ω should be the natural angular frequency after compensation.₁Since the instability due to the natural vibration of the mechanical system is prevented by the value of 2π × fp, it is possible to further stabilize the control system and improve the responsiveness while simplifying the design of the phase compensation. it can.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
<0. Basic study>
First, basic studies made in the present invention will be described.
[0020]
The above-described conventional technology relating to phase compensation in the control design of an electric power steering apparatus has been proposed as a compensation for a mechanical system natural frequency peak (hereinafter referred to as “mechanical system peak”) that is a mechanical resonance frequency. However, this does not take into account the influence of the back electromotive force in the motor. That is, the peak in the gain characteristic of the electric power steering system, that is, the gain characteristic of the torque open loop transfer function (hereinafter referred to as “system peak”) is regarded as the mechanical system peak. However, as a result of the following simulation, the back electromotive force in the motor has a great influence on the system characteristics, and the mechanical system peak and the system peak (system peak) are different frequencies. There was found. This will be described with reference to FIG. The torque open-loop transfer function is a torque actually generated by the motor with the steering angle fixed (for example, the steering wheel at the neutral position) (hereinafter referred to as “motor torque”). ")" As an output. And since the target value of torque that should be generated by the motor corresponds to the current target value in the current control system, and the motor torque corresponds to the current that actually flows through the motor, the torque open loop transfer function is in a state where the steering angle is fixed. In the electric power steering apparatus, the current target value is input, and the current actually flows through the motor is output.
[0021]
FIG. 1 shows a Bode diagram (a gain characteristic diagram and a phase characteristic diagram) of a torque open loop transfer function of an electric power steering apparatus using a brushless motor, obtained by simulation (numerical experiment). The Bode diagram about the case where non-interference is performed in the axis and q-axis current control system, and the case where non-interference is not performed is shown. By performing non-interference, it is possible to remove the influence of the back electromotive force and obtain mechanical characteristics. The conditions for this simulation are as follows.
Inertia on the motor output side: Im = 7.89 × 10^-Five[N ・ m ・ s²/ Rad],
Motor output side viscosity: Cm = 1.39 × 10^-3[N · m · s / rad],
Reduction gear reduction ratio: n = 9.7
Elasticity of torsion bar: K = 162.95 [N · m / rad],
Motor torque constant: K_T= 5.12 × 10^-2[N · m / A],
Motor inductance: L = 9.2 × 10^-Five[H],
Motor resistance: R = 6.1 × 10^-2[Ω],
Number of pole pairs of motor: P = 4,
Back electromotive force constant: φfp = 4.93 × 10^-2[V · s / rad],
Proportional gain of PI controller: Kp = L × (2π × 75),
Integration gain of PI controller: Ki = R × (2π × 75).
[0022]
Attention is paid to the diagram showing the gain characteristics of FIG. In FIG. 1, a curve a shows a gain characteristic when non-interference is not performed, and a peak frequency thereof, that is, a system peak frequency (hereinafter referred to as “system peak frequency” or simply “peak frequency”), and a symbol “fp”. ")" Is approximately 17 Hz. A curve b shows gain characteristics when non-interference is performed, and a peak frequency fp is about 22 Hz. Curve c shows the gain characteristic of only elasticity and inertia, that is, the gain characteristic of only mechanical elements, and the peak frequency is about 22 Hz. Therefore, the frequency of the mechanical system peak (hereinafter referred to as “mechanical system peak frequency” and represented by the symbol “fm”) is about 22 Hz, and it can be seen that the system peak is at a frequency different from the mechanical system peak.
[0023]
Next, attention is focused on FIG. 2 showing the gain characteristics of the torque open-loop transfer function when phase compensation is performed in the electric power steering apparatus. In FIG. 2, a curve d indicates a gain characteristic without phase compensation, which corresponds to the curve a in FIG. 1 (a curve indicating the gain characteristic without decoupling), and the gain indicated by the curve d. As described above, the peak P in the characteristics is a peak reflecting the influence of the counter electromotive force. The peak P is at a frequency lower than the mechanical system peak Pm (which corresponds to the peak of the curve b or the curve c in FIG. 1).
[0024]
In the above-described prior art, the influence of the counter electromotive force has not been taken into consideration, so that the peak P is regarded as the mechanical system peak Pm, and phase compensation is performed to cancel the peak P. For this reason, depending on the design of the phase compensator, the entire system may become unstable (become oscillating) due to the influence of the mechanical system peak Pm even after phase compensation. Therefore, in the electric power steering apparatus according to the present invention, the phase compensator is designed in consideration of the fact that the peak P of the gain characteristic of the entire system differs from the mechanical system peak Pm due to the influence of the back electromotive force. Hereinafter, such an embodiment of the present invention will be described with reference to the drawings.
[0025]
<1. First Embodiment>
<1.1 Overall configuration>
FIG. 3 is a schematic diagram showing the configuration of the electric power steering apparatus according to the first embodiment of the present invention, together with the vehicle configuration related thereto. This electric power steering apparatus includes a steering shaft 102 having one end fixed to a handle (steering wheel) 100 as an operation means for steering, a rack and pinion mechanism 104 connected to the other end of the steering shaft 102, a handle A torque sensor 3 for detecting a steering torque applied to the steering shaft 102 by an operation of 100, an electric motor 6 for generating a steering assist force for reducing a driver's load due to a steering operation (steering operation), and the motor 6 Is an electronic gear that controls the driving of the motor 6 based on sensor signals from the torque sensor 3 and the vehicle speed sensor 4 upon receiving power from the vehicle-mounted battery 8 and the reduction gear 7 that transmits the steering assist force generated by the vehicle to the steering shaft 102. And a control unit (ECU) 5. When the driver operates the steering wheel 100 in a vehicle equipped with such an electric power steering device, the steering torque by the operation is detected by the torque sensor 3, and the detected value of the steering torque Ts and the vehicle speed detected by the vehicle speed sensor are detected. Based on the detected value, the motor 6 is driven by the ECU 5. As a result, the motor 6 generates a steering assist force, and this steering assist force is applied to the steering shaft 102 via the reduction gear 7, thereby reducing the driver's load due to the steering operation. That is, the sum of the steering torque Ts applied by the steering wheel operation and the torque (hereinafter referred to as “steering assist torque”) Ta generated by the steering assist force generated by the motor 6 serves as a rack and pinion mechanism via the steering shaft 102 as the output torque Tb. 104. Thus, when the pinion shaft rotates, the rotation is converted into a reciprocating motion of the rack shaft by the rack and pinion mechanism 104. Both ends of the rack shaft are connected to a wheel 108 via a connecting member 106 composed of a tie rod and a knuckle arm, and the direction of the wheel 108 changes according to the reciprocating motion of the rack shaft.
[0026]
<1.2 Configuration of controller and related operations>
FIG. 4 is a block diagram showing a main configuration of the ECU 5 as a control device for the electric power steering apparatus according to the present invention. This electric power steering apparatus includes an ECU 5 for driving and controlling the electric motor 6 as described above. The ECU 5 is supplied with output signals from the torque sensor 3 for detecting the steering torque applied to the handle 100 and the vehicle speed sensor 4 for detecting the vehicle speed.
[0027]
The ECU 5 is configured to include a microcomputer, and substantially includes a plurality of function processing units when the microcomputer executes program processing. The plurality of function processing units perform a phase compensation by performing a filtering process on a torque signal that is an output signal of the torque sensor 3, and a torque signal and a vehicle speed after passing through the phase compensator 15. A target current value setting unit 16 that sets a target current value according to a vehicle speed signal output from the sensor 4 and a motor control that feedback-controls the electric motor 6 based on the target current value set by the target current value setting unit 16. Part 17.
[0028]
The torque sensor 3 detects a steering torque Ts given by operating the handle 100. That is, a torsion bar is interposed between a portion of the steering shaft 102 on the handle side and a portion to which the steering assist torque Ta is applied via the reduction gear 7, and the torque sensor 3 detects torsion of the torsion bar. Thus, the steering torque Ts is detected. The detected value of the steering torque Ts thus detected is output from the torque sensor 3 as a steering torque detection signal (hereinafter also referred to as “Ts”), and is output to the phase compensator 15 in the ECU 5. Entered.
[0029]
The phase compensator 15 performs a filtering process for phase compensation on the steering torque detection signal Ts, and outputs a signal after the process. On the other hand, the vehicle speed sensor 4 detects the vehicle speed of the vehicle on which the electric power steering device is mounted, and outputs a signal indicating the detected value as a vehicle speed signal. The target current value setting unit 16 calculates the target value of the current to be supplied to the motor 6 based on the signal after the filtering process for phase compensation and the vehicle speed signal, and outputs the target value as the target current value It. The motor control unit 17 receives the target current value It output from the target current value setting unit 16, and performs current control so that the current value Is that actually flows through the motor 6 matches the target current value It. As the current control, for example, proportional-integral control for calculating a command value of a voltage to be applied to the motor 6 is performed so that a deviation between the target current value It and the actual current value Is is canceled. The motor control unit 17 applies a voltage to the motor 6 according to the voltage command value.
[0030]
The motor 6 generates a torque Tm as a steering assist force corresponding to the current flowing by applying the voltage, and this torque Tm is transmitted to the steering shaft 102 as the steering assist torque Ta via the reduction gear 7.
[0031]
<1.3 Phase compensator>
It is known that the frequency characteristic of the torque open-loop transfer function indicating the characteristics of the electric power steering apparatus as a whole system can be approximated by a transfer function of a second-order lag system in a practical frequency band. FIG. 2 is a Bode diagram when the phase compensation is not performed and when the phase compensation according to the present invention is performed in the electric power steering apparatus according to the present embodiment. Also in FIG. 2, the characteristic of the transfer function of the second-order lag system appears.
[0032]
First, a case where phase compensation is not performed will be described. The curve d shows the gain characteristic when the phase compensation is not performed. From this curve d, the peak frequency fp of the gain characteristic of the torque open loop transfer function indicating the gain characteristic of the entire system is about 17 Hz, The gain at that time is about 9 dB, indicating that the stability is low. Further, it can be seen from the curve f indicating the phase characteristics when the phase compensation is not performed that the phase delay is large in the vicinity of 20 Hz to 30 Hz. A general expression of the transfer function G (s) of the second-order lag system is shown in the following expression.
G (s) = ω_n ²/ (S²+ 2ζ₂ω_ns + ω_n ²(5)
Where s is the Laplace operator and ζ₂Is the damping coefficient, ω_nIs the natural angular frequency.
[0033]
The transfer function Gc (s) of the phase compensator 15 is set so as to cancel the system peak P, which is a peak in the gain characteristic of the transfer function G (s) of the second-order lag system indicating the compensated system. In this embodiment, it is given by the following equation.
Gc (s) = (s²+ 2ζ₂ω₂s + ω₂ ²) / (S²+ 2ζ₁ω₁s + ω₁ ²) ... (6)
Where s is the Laplace operator and ζ₁Is the attenuation coefficient after compensation, ζ₂Is the attenuation coefficient of the compensated system, ω₁Is the natural angular frequency after compensation, ω₂Is the natural angular frequency of the compensated system. The present embodiment provides an electric power steering apparatus including a phase compensator in which parameters are set effectively in realizing a control system having desired frequency characteristics.
[0034]
Here, when there is a peak in the gain characteristic of the compensated system, the parameter ζ in the equation (5) representing the transfer function G (s)₂Is ζ₂<2^-1/2It is known that Therefore, the parameter ζ in equation (6) representing the transfer function of the phase compensator 15₂Is selected from the range represented by the following equation, sufficient phase compensation cannot be performed, and as a result, the electric power steering apparatus tends to become unstable (vibrating system) as a control system.
2^-1/2<Ζ₂<1 (7)
Therefore, the parameter ζ in the transfer function of the phase compensator 15₂Should be selected from a range other than the range represented by the above formula (7).
[0035]
Also, the attenuation coefficient ζ after compensation by the phase compensator 15₁Is selected within the range represented by the following equation, as described above, there is a peak in the compensated gain characteristic, and the compensated control system tends to become unstable.
0 <ζ₁<2^-1/2  (8)
Therefore, the parameter ζ in the transfer function of the phase compensator 15₁Should be selected from a range other than the range represented by the above formula (8).
[0036]
Therefore, in the present embodiment, the parameter ζ of the phase compensator 15 having the transfer function Gc (s) represented by Expression (6).₁And ζ₂Is set so that the following equation is satisfied.
2^-1/2≦ ζ₁≦ 1 (9)
0 <ζ₂≦ 2^-1/2  (10)
By setting in this way, responsiveness can be improved while ensuring stability.
[0037]
Further, as described above, the peak frequency fp of the entire system is different from the mechanical system peak frequency fm, and the mechanical system peak frequency fm is higher than the system peak frequency fp. Therefore ω₁In order not to become unstable (vibrating system) in the nearby frequency band, the angular frequency ω of the natural vibration of the mechanical system_mThe gain needs to be sufficiently reduced. ω_m<Ω₁Then ω_mGain does not drop sufficiently at ω₁It becomes a vibration system in a nearby frequency band. Therefore, the parameter ω of the phase compensator 15 is used to effectively compensate the mechanical system peak.₁Is preferably set so that the following equation is satisfied.
ω_m> Ω₁  ... (11)
[0038]
With the above settings (Equations (9) to (11)), gain characteristics as indicated by curve e and phase characteristics as indicated by curve g in FIG. 2 are obtained. From these, it can be seen that, according to the phase compensation by the above setting, the peak value of the gain is greatly reduced, and the phase delay near 20 Hz is improved.
[0039]
<1.4 Effects>
According to the present embodiment as described above, it is possible to obtain a torque open-loop transfer function having a desired frequency characteristic by ensuring the stability of the control system and improving the response while simplifying the phase compensation design. it can. Further, according to the present embodiment, the stability of the control system can be ensured without adding a low-pass filter or the like to the phase compensator in addition to the phase compensator of the transfer function Gc (s) of Expression (6). Both stability and responsiveness can be improved without increasing the order of the phase compensator.
[0040]
<2. Second Embodiment>
Next, a second embodiment of the present invention will be described. Since the present embodiment is the same as the first embodiment except for the configuration of the phase compensator, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will be omitted. The phase compensator 15 will be described. In this embodiment, the torque open-loop transfer function G (s) indicating the characteristics of the entire system of the electric power steering apparatus can be approximated by the equation (5), and the transfer function Gc ( s) is given by equation (6).
[0041]
<2.1 Phase compensator>
In order to realize a more preferable compensator design than the first embodiment, first, ω in the transfer function Gc (s) represented by the equation (6) is used.₁And ω₂To consider. ω₁Is the natural angular frequency after compensation, in other words, the target natural angular frequency. Where ω₁And ω₂Are different from each other, the natural angular frequency of the compensated system is not the target natural angular frequency. In the phase compensation in the control system of the electric power steering device, it is desirable that the natural angular frequency of the compensated system and the target natural angular frequency are the same.₁= Ω₂And Where ω_n= Ω₁= Ω₂Hereinafter, this is referred to as “compensator natural angular frequency”. The compensated natural angular frequency ω with respect to the peak frequency fp in the gain characteristic of the torque open loop transfer function indicating the gain characteristic of the entire system._nΩ_n= 2π · fp, the angular frequency ω corresponding to the mechanical peak Pm_mThe gain at is a sufficiently small value, and system instability (being vibrational) due to the influence of the mechanical system peak Pm is avoided. Further, as already described in the description of the first embodiment, ω is prevented so as not to become a vibration system due to the influence of the mechanical system peak Pm._m> Ω₁Is preferable.
[0042]
Therefore, in the present embodiment, the parameters of the transfer function of the phase compensator 15 are set so that the following expression is satisfied.
ω_m> Ω₁= Ω₂= Ω_n  (12)
ω_n= 2π · fp (13)
2^-1/2≦ ζ₁≦ 1 (14)
0 <ζ₂≦ 2^-1/2     ... (15)
[0043]
Ω like this₁And ω₂By setting to the same value, the design parameter is reduced by one, and the response and stability can be satisfied effectively and easily. The above equations (14) and (15) correspond to equations (9) and (10) for parameter setting in the phase compensator 15 in the first embodiment, respectively.
[0044]
Also, ω_n= 2π · fp (hereinafter referred to as the symbol “fn” to distinguish it from the system peak frequency fp, and referred to as “compensator natural frequency”), the peak is not the same as the peak frequency fp. A value in the vicinity of the frequency fp is sufficiently practical. Therefore, the compensator natural angular frequency ω_nMay be set as:
2π × (fp−α) ≦ ω_n≦ 2π × (fp + β) (16)
Here, α and β are parameters that vary depending on the value of fp. A method for setting the values of α and β will be described in the following modification. Note that the values of α and β are not limited to the following modifications, and may be values that can provide practically sufficient frequency characteristics.
[0045]
<2.2 Effects>
According to the present embodiment as described above, by designing the phase compensator as described above, it is possible to further simplify the phase compensation design without increasing the order of the phase compensator, and A torque open-loop transfer function having a desired frequency characteristic can be obtained while ensuring stability and improving responsiveness.
[0046]
<3. First Modification>
As described above, the compensator natural frequency fn is sufficiently practical (effective) as long as it is not the same value as the peak frequency fp but a value in the vicinity of the peak frequency fp. Therefore, a modified example will be described in which α and β, which are parameters of Expression (16) in the second embodiment, are calculated by multiplying by specific coefficients.
[0047]
α and β are calculated by multiplying fp by a specific coefficient. For example, α = fp × 0.1, β = fp × 0.2, and fp = 16 Hz. In this case, α = fp × 0.1 = 1.6 Hz, β = fp × 0.2 = 3.2 Hz, and the compensator natural angular frequency ω_n= 2π · fp is given by the following equation.
2π × (16-1.6) Hz ≦ ω_n≦ 2π × (16 + 3.2) Hz
Ie
2π × 14.4Hz ≦ ω_n≦ 2π × 19.2Hz
It is.
[0048]
<4. Second Modification>
You may make it determine (alpha) and (beta) which are parameters of Formula (16) based on 2nd Embodiment based on the map produced previously. In this case, as α and β, corresponding values are obtained from the map according to the peak frequency fp.
[0049]
Here, for example, the map shown in FIG. 5 is created, and fp = 40 Hz. In this case, from FIG. 5, α corresponding to the peak frequency fp = 40 Hz is 2.0 Hz, and β is 4.0 Hz. Therefore, compensator natural angular frequency ω_nIs given by:
2π × (40−2.0) Hz ≦ ω_n≦ 2π × (40 + 4.0) Hz
Ie
2π × 38Hz ≦ ω_n≦ 2π × 44Hz
It is.
[0050]
<5. Other variations>
In each of the above embodiments, phase compensation is performed based on the steering torque detection signal Ts by performing predetermined filtering on the steering torque detection signal Ts from the torque sensor 3 (FIG. 4). The phase compensation may be performed based on the above.
[0051]
Although a motor with a brush is often used as a drive source in the electric power steering apparatus, the present invention is not limited to a motor with a brush, but an electric power steering using a brushless motor as a drive source. It is also applicable to the device.
[Brief description of the drawings]
FIG. 1 shows the characteristics of a torque open loop transfer function in an electric power steering apparatus by simulation, and is a Bode diagram for a case where non-interference is performed and a case where non-interference is not performed. .
FIG. 2 is a Bode diagram in the case where phase compensation is not performed in the electric power steering apparatus, and a Bode diagram in the case where phase compensation according to the present invention is performed.
FIG. 3 is a schematic view showing the configuration of the electric power steering apparatus according to the first embodiment of the present invention together with the vehicle configuration related thereto.
FIG. 4 is a block diagram showing a main configuration of the electric power steering apparatus according to the first embodiment of the present invention.
FIG. 5 is a diagram showing a map for setting parameters (compensator natural angular frequency) of a phase compensator in a modification of the second embodiment of the present invention.
[Explanation of symbols]
3 ... Torque sensor
4 ... Vehicle speed sensor
5 ... EUC (control device)
6 ... Electric motor
7 ... Reduction gear
8 ... Battery
15 ... Phase compensator
16 ... Target current value setting section
17 ... Motor controller
Ts: Steering torque (steering torque detection signal)
fp ... System peak frequency
fm ... mechanical system peak frequency
P: System peak
Pm ... Mechanical system peak

Claims (2)

An electric power that includes a control device that controls the driving of the electric motor in accordance with an operation for steering the vehicle, and that drives the electric motor under the control of the control device to give a steering assist force to the steering mechanism of the vehicle A steering device,
The control device includes phase compensation means using a series compensation method having a transfer function Gc (s) represented by the following equation:
Gc (s) = (s ² + 2ζ ₂ ω ₂ s + ω ₂ ² ) / (s ² + 2ζ ₁ ω ₁ s + ω ₁ ² )
Here, ζ ₁ is the attenuation coefficient after compensation, ζ ₂ is the attenuation coefficient of the compensated system, ω ₁ is the natural angular frequency after compensation, ω ₂ is the natural angular frequency of the compensated system, and the transfer function Gc (s ) Parameters,
The parameters ζ ₂ and ω ₂ of the transfer function Gc (s) of the phase compensation means cancel out the peak appearing in the gain characteristic of the transfer function of the second order lag system that approximates the torque open loop transfer function of the electric power steering device. It is set to a value,
The parameters ζ ₁ and ζ ₂ of the transfer function G c ( s ) of the phase compensation means are set so as to satisfy the following equation:
2 ^-1/2 ≦ ζ ₁ ≦ 1,
0 <ζ ₂ ≦ 2 ^-1/2
The electric power steering apparatus, wherein the parameter ω ₁ of the transfer function G c ( s ) of the phase compensation means is set to satisfy the following formula:
ω ₁ <ω _m
Here, ω _m is an angular frequency of mechanical natural vibration in the electric power steering apparatus. The parameters ω ₁ and ω ₂ of the transfer function Gc (s) of the phase compensation means satisfy the following formula, and both are 2π × fp when the peak frequency in the gain characteristic of the torque open loop transfer function is fp. The electric power steering apparatus according to claim 1 , wherein the electric power steering apparatus is set so as to have a value in the vicinity.
ω ₁ = ω ₂

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