U.S. patent application number 17/260735 was filed with the patent office on 2021-08-12 for power supply current control device, electric actuator product, and electric power steering device.
This patent application is currently assigned to NSK LTD.. The applicant listed for this patent is NSK LTD.. Invention is credited to Yasutoshi MIKI.
Application Number | 20210245799 17/260735 |
Document ID | / |
Family ID | 1000005582700 |
Filed Date | 2021-08-12 |
United States Patent
Application |
20210245799 |
Kind Code |
A1 |
MIKI; Yasutoshi |
August 12, 2021 |
POWER SUPPLY CURRENT CONTROL DEVICE, ELECTRIC ACTUATOR PRODUCT, AND
ELECTRIC POWER STEERING DEVICE
Abstract
A power supply current control device including: a current limit
value calculation unit configured to calculate a current limit
value on a basis of a difference between a power supply voltage and
a predetermined set voltage, a power supply current, and a
resistance model representing a resistance component of the power
supply circuit; a power supply current limit unit configured to
limit a magnitude of the power supply current on a basis of the
current limit value; a change rate limit value calculation unit
configured to calculate a change rate limit value on a basis of the
difference and a change speed of the power supply voltage; and a
power supply current change rate limit unit configured to limit a
change rate of the power supply current on a basis of the change
rate limit value.
Inventors: |
MIKI; Yasutoshi;
(Maebashi-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NSK LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
NSK LTD.
Tokyo
JP
|
Family ID: |
1000005582700 |
Appl. No.: |
17/260735 |
Filed: |
February 7, 2020 |
PCT Filed: |
February 7, 2020 |
PCT NO: |
PCT/JP2020/004903 |
371 Date: |
January 15, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02M 1/0009 20210501;
B62D 5/0463 20130101; H02M 1/32 20130101; H02P 27/06 20130101; H02M
7/5387 20130101 |
International
Class: |
B62D 5/04 20060101
B62D005/04; H02M 1/00 20060101 H02M001/00; H02M 1/32 20060101
H02M001/32 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 13, 2019 |
JP |
2019-023750 |
Claims
1. A power supply current control device comprising: a voltage
detecting unit configured to detect a power supply voltage applied
from a power supply circuit; a current detecting unit configured to
detect a power supply current supplied from the power supply
circuit; a current limit value calculation unit configured to
calculate a current limit value on a basis of a difference between
the power supply voltage detected by the voltage detecting unit and
a predetermined set voltage, the power supply current detected by
the current detecting unit, and a resistance model representing a
resistance component of the power supply circuit; a power supply
current limit unit configured to limit a magnitude of the power
supply current on a basis of the current limit value; a change rate
limit value calculation unit configured to calculate a change rate
limit value on a basis of the difference and a change speed of the
power supply voltage; and a power supply current change rate limit
unit configured to limit a change rate of the power supply current
on a basis of the change rate limit value.
2. The power supply current control device according to claim 1,
wherein the change rate limit value calculation unit sets the
change rate limit value so that a change rate in an increasing
direction of the power supply current is more limited as a decrease
speed of the power supply voltage becomes larger.
3. The power supply current control device according to claim 1,
comprising a differentiator configured to calculate a differential
value of the power supply voltage detected by the voltage detecting
unit, wherein the change rate limit value calculation unit
calculates the change rate limit value on a basis of the difference
and the differential value.
4. The power supply current control device according to claim 3,
comprising a rate limiter configured to limit a change rate of the
differential value calculated by the differentiator or a rate
limiter configured to limit a change rate of a variable for
referring to the differential value used to calculate the change
rate limit value.
5. The power supply current control device according to claim 1,
comprising a resistance value estimation unit configured to
calculate an estimated value of the resistance component of the
power supply circuit, wherein the current limit value calculation
unit calculates the current limit value on a basis of the
difference, the power supply current detected by the current
detecting unit, and the estimated value.
6. The power supply current control device according to claim 1,
comprising a resistance value estimation unit configured to
calculate an estimated value of the resistance component of the
power supply circuit, wherein the change rate limit value
calculation unit calculates the change rate limit value on a basis
of the difference and a difference or a ratio between the estimated
value and a resistance value of the resistance model.
7. The power supply current control device according to claim 1,
comprising at least one of a filter configured to smooth a detected
value of the power supply voltage by the voltage detecting unit and
a filter configured to smooth a detected value of the power supply
current by the current detecting unit.
8. The power supply current control device according to claim 1,
comprising at least one of a rate limiter configured to limit a
change rate of the current limit value calculated by the current
limit value calculation unit and a rate limiter configured to limit
a change rate of the change rate limit value calculated by the
change rate limit value calculation unit.
9. An electric actuator product comprising: the power supply
current control device according to claim 1; and a motor configured
to be driven by the power supply current controlled by the power
supply current control device.
10. An electric power steering device configured to apply a
steering assistance force to a steering system of a vehicle by the
electric actuator product according to claim 9.
Description
TECHNICAL FIELD
[0001] The present invention relates to a power supply current
control device configured to limit a power supply current supplied
from a power supply circuit to a load, and an electric actuator
product and an electric power steering device using the same.
BACKGROUND ART
[0002] A technology has been proposed to limit a power supply
current so that a power supply voltage supplied to a load does not
drop below a predetermined lower limit value.
[0003] For example, when supplying power to a load such as an
electric power steering device, application of a steering
assistance force is stopped if the power supply voltage drops below
the lower limit value due to increased power consumption.
Therefore, when the power supply voltage drops, it is necessary to
suppress power consumption so as not to result in stop of the
steering assistance force even if the steering assistance force is
reduced.
[0004] Accordingly, an electric power steering device described in
PTL 1 below determines an upper limit current value of a power
supply current according to a proportional component and a
differential component of a deviation between a power supply
voltage and a set voltage, and performs feedback control so that
the power supply voltage becomes the set voltage.
CITATION LIST
Patent Literature
[0005] PTL 1: JP Pat. No. 4352268
SUMMARY OF INVENTION
Technical Problem
[0006] However, when the upper limit current value that limits the
power supply current is set solely on the basis of the power supply
voltage, the upper limit current value may be excessively small or
excessively large.
[0007] For example, when a maximum allowable current allowed by a
system is already flowing and therefore the power supply voltage is
approaching a lower limit value, there is little need to set the
upper limit current value lower than the maximum allowable current.
On the other hand, when the power supply voltage drops even though
not much power supply current is flowing, it is necessary to set a
lower upper limit current value to strongly limit the power supply
current.
[0008] In this case, if the upper limit current value is simply
lowered in response to the power supply voltage drop, the upper
limit current value may become excessively small or excessively
large.
[0009] The present invention has been made in view of the above
problem, and it is an object of the present invention to, when
limiting power supply current by an upper limit current value to
mitigate power supply voltage drop, suppress the upper limit
current value from being set excessively small or excessively
large.
Solution to Problem
[0010] To achieve the above object, a power supply current control
device according to one aspect of the present invention includes a
voltage detecting means configured to detect a power supply voltage
applied from a power supply circuit, a current detecting means
configured to detect a power supply current supplied from the power
supply circuit, a current limit value calculation unit configured
to calculate a current limit value on the basis of a difference
between the power supply voltage detected by the voltage detecting
means and a predetermined set voltage, the power supply current
detected by the current detecting means, and a resistance model
representing a resistance component of the power supply circuit,
and a power supply current limit unit configured to limit a
magnitude of the power supply current on the basis of the current
limit value.
[0011] As described above, calculating the current limit value on
the basis of not only the power supply voltage but also a detected
value of the power supply current and the resistance model of the
power supply circuit can suppress the current limit value from
being set excessively small or excessively large.
[0012] Note that when the current limit value is calculated on the
basis of the resistance model representing the resistance component
of the power supply circuit, the current limit value is affected by
an error between an actual resistance value of the power supply
circuit and the resistance model. Additionally, the actual
resistance value of the power supply circuit can easily
fluctuate.
[0013] For example, when a battery is used as a power supply, the
resistance value of the power supply circuit fluctuates due to
deterioration over time, connector contact resistance, harness
deterioration, temperature rise, or the like.
[0014] Additionally, for example, in the case of an electric power
steering device, if a battery terminal is dropped off and the
electric power steering device is directly connected to a
generator, power supply voltage easily drops due to increased power
supply current, so that an internal resistance of the power supply
circuit viewed from the electric power steering device appears to
have increased.
[0015] The error that occurs between the actual resistance value of
the power supply circuit and the resistance model used to calculate
the current limit value causes a state where the power supply
current is excessively limited by the current limit value, whereby
the power supply current and the power supply voltage may become
unstable.
[0016] Furthermore, in the case of an electric power steering
device, a sudden decrease in the steering assistance force due to a
sudden decrease in the power supply current reduces the feeling of
steering. Therefore, it is preferable to gently limit the power
supply current.
[0017] Thus, the power supply current control device according to
the one aspect of the present invention includes a change rate
limit value calculation unit configured to calculate a change rate
limit value on the basis of the difference between the power supply
voltage detected by the voltage detecting means and the
predetermined set voltage and a change speed of the power supply
voltage and a power supply current change rate limit unit
configured to limit a change rate of the power supply current on
the basis of the change rate limit value.
[0018] By limiting the change rate of the power supply current on
the basis of the change speed of the power supply voltage that
fluctuates depending on the actual resistance value of the power
supply circuit, it is possible to suppress the power supply current
and the power supply voltage from becoming unstable even when an
error occurs between the actual resistance value and the resistance
model.
[0019] Additionally, limiting the change rate of the power supply
current enables a gentle start of limitation on steering assistance
force in the case of an electric power steering device.
[0020] According to another aspect of the present invention, there
is provided an electric actuator product including the
above-described power supply current control device and a motor
driven by the power supply current controlled by the power supply
current control device.
[0021] According to still another aspect of the present invention,
there is provided an electric power steering device that applies a
steering assistance force to a steering system of a vehicle by the
above-described electric actuator product.
Advantageous Effects of Invention
[0022] According to the present invention, it is possible to, when
limiting power supply current by an upper limit current value to
mitigate power supply voltage drop, suppress the upper limit
current value from being set excessively small or excessively
large.
BRIEF DESCRIPTION OF DRAWINGS
[0023] FIG. 1 is a structural diagram illustrating an outline of an
example of an electric power steering device of an embodiment;
[0024] FIG. 2 is a block diagram illustrating an example of a
functional structure of a control unit of the embodiment;
[0025] FIG. 3 is a block diagram illustrating an example of a
functional structure of a current limit unit of a first
embodiment;
[0026] FIG. 4 is an illustrative diagram of an example of a
resistance model of a power supply circuit;
[0027] FIGS. 5A and 5B are time charts illustrating simulation
results of a power supply current and a power supply voltage when
current power supply is limited by a power supply current limit
unit;
[0028] FIG. 6 is an illustrative diagram of a first example of a
calculation map of a change rate limit value CrLim;
[0029] FIGS. 7A and 7B are time charts illustrating simulation
results of the power supply current and the power supply voltage
when the current power supply is limited by the power supply
current limit unit and change rate is limited by a power supply
current change rate limit unit;
[0030] FIG. 8A is an illustrative diagram of a second example of
the calculation map of the change rate limit value CrLim, and FIG.
8B is a first example of a gain calculation map;
[0031] FIG. 9A is an illustrative diagram of a third example of the
calculation map of the change rate limit value CrLim, and FIG. 9B
is a second example of the gain calculation map;
[0032] FIG. 10 is a flowchart of an example of a power supply
current control method of the embodiment;
[0033] FIG. 11 is a block diagram illustrating an example of a
functional structure of a current limit unit of a second
embodiment;
[0034] FIG. 12 is a block diagram illustrating an example of a
functional structure of a current limit unit of a third embodiment;
and
[0035] FIG. 13 is a block diagram illustrating an example of a
functional structure of a current limit unit of a fourth
embodiment.
DESCRIPTION OF EMBODIMENTS
[0036] Embodiments of the present invention will be described in
detail with reference to the drawings.
[0037] It should be noted that the embodiments given below are
those exemplifying devices and methods for embodying the
technological ideas of the present invention, and the technological
ideas of the present invention do not limit the structures,
arrangement, and the like of components to those described below.
The technological ideas of the present invention can be variously
modified within the technological scope defined by the claims
described in CLAIMS.
[0038] Hereinafter, there will be described an example in which a
power supply current control device of the present invention is
applied to an electric power steering device. However, the present
invention is not limited thereto, and is applicable to various
electric devices using a power supply. For example, the power
supply current control device of the present invention is applied
to an electric actuator product including a motor driven by power
supply current, and can be used to control the power supply current
that drives the motor.
First Embodiment
Structure
[0039] FIG. 1 illustrates a structural example of an electric power
steering device of an embodiment. A steering shaft (column shaft or
steering wheel shaft) 2 of a steering wheel 1 is connected to tie
rods 6 of steered wheels through a reduction gear 3, universal
joints 4A and 4B, and a pinion rack mechanism 5. The steering shaft
2 is provided with a torque sensor 10 that detects a steering
torque Th of the steering wheel 1, and a motor 20 that assists
steering force of the steering wheel 1 is connected to the steering
shaft 2 via the reduction gear 3.
[0040] Electric power from a battery 14 that is a power supply is
supplied to a control unit (ECU) 30 that controls the electric
power steering device, and also an ignition key signal is input to
the control unit 30 from an ignition key 11. The control unit 30
calculates a steering assistance command value of an assist command
using an assist map or the like on the basis of the steering torque
Th detected by the torque sensor 10 and a vehicle speed Vh detected
by a vehicle speed sensor 12, and controls a current I that is
supplied to the motor 20 on the basis of the calculated steering
assistance command value.
[0041] In the electric power steering device having such a
structure, the torque sensor 10 detects the steering torque Th by a
driver's steering wheel operation transmitted from the steering
wheel 1, and the motor 20 is driven and controlled by the steering
assistance command value calculated on the basis of the detected
steering torque Th and the vehicle speed Vh. The drive is applied
as an assistance force (steering assistance force) for the driver's
steering wheel operation to a steering system, so that the driver
can operate the steering wheel with light force. In other words,
the steering assistance command value is calculated by the steering
torque Th output by the steering wheel operation and the vehicle
speed Vh, and depending on how the motor 20 is controlled on the
basis of the steering assistance command value, it is determined
whether the steering wheel operation feels good or bad, and
performance of the electric power steering device is greatly
influenced.
[0042] The control unit 30 may include, for example, a computer
including a processor and peripheral components such as a storage
device. The processor may be, for example, a central processing
unit (CPU) or a micro-processing unit (MPU).
[0043] 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 memories, such as register,
cache memory, and read only memory (ROM) and random access memory
(RAM) used as primary storage.
[0044] Note that the control unit 30 may be formed by dedicated
hardware for executing each information processing that will be
described below.
[0045] For example, the control unit 30 may include a functional
logic circuit set in a general-purpose semiconductor integrated
circuit. For example, the control unit 30 may include a
programmable logic device (PLD) such as a field-programmable gate
array (FPGA), or the like.
[0046] An example of a functional structure of the control unit 30
of the embodiment will be described with reference to FIG. 2. The
control unit 30 includes a basic current command value calculation
unit 31, a motor control unit 32, a current limit unit 33, and a
motor drive circuit 34.
[0047] Functions of the basic current command value calculation
unit 31, the motor control unit 32, and the current limit unit 33
are realized by, for example, causing the processor of the control
unit 30 to execute a computer program stored in the storage
device.
[0048] Additionally, the motor drive circuit 34 may be, for
example, an inverter having a bridge structure in which each of an
upper arm and a lower arm is formed by a switching element such as
a field effect transistor (FET).
[0049] The basic current command value calculation unit 31
calculates an assist current for energizing the motor 20 using the
assist map or the like on the basis of the steering torque Th
detected by the torque sensor 10 and the vehicle speed Vh detected
by the vehicle speed sensor 12, and calculates a current command
value that is a control target value of the assist current.
[0050] The motor control unit 32 generates a control signal of the
motor drive circuit 34 so as to cause the assist current calculated
by the basic current command value calculation unit 31 to flow to
the motor 20.
[0051] A power supply voltage VR is applied to the motor drive
circuit 34 by the battery 14, and a power supply current Ibat is
supplied thereto from the batter 14. A voltage sensor 35 serving as
a voltage detecting means detects an applied voltage applied to the
motor drive circuit 34 as the power supply voltage VR. A current
sensor 36 serving as a current detecting means detects the power
supply current Ibat flowing to the motor drive circuit 34. The
power supply current Ibat supplied to the motor drive circuit 34 is
on-off controlled by the control signal generated by the motor
control unit 32, and supplied to the motor 20 as the assist
current.
[0052] The current limit unit 33 controls the power supply current
supplied to the motor drive circuit 34 from the battery 14 on the
basis of the power supply voltage VR detected by the voltage sensor
35 and the power supply current Ibat detected by the current sensor
36. Hereinbelow, the power supply voltage VR detected by the
voltage sensor 35 may be referred to as "detected value of the
power supply voltage VR", and the power supply current Ibat
detected by the current sensor 36 may be referred to as "detected
value of the power supply current Ibat".
[0053] An example of a functional structure of the current limit
unit 33 of a first embodiment will be described with reference to
FIG. 3. The current limit unit 33 includes a subtractor 40, a
current limit value calculation unit 41, and a power supply current
limit unit 42.
[0054] The subtractor 40 calculates a difference (VR-VLo) obtained
by subtracting a predetermined lower limit voltage VLo from a
detected value of the power supply voltage VR. The lower limit
voltage VLo may be, for example, a voltage obtained by adding a
predetermined margin to a minimum value of a voltage applied to the
motor drive circuit 34 allowed by the electric power steering
device.
[0055] The lower limit voltage VLo is set by CAN transmission from
a vehicle-side control unit that performs power supply management
or set in the control unit 30.
[0056] The current limit value calculation unit 41 calculates a
current limit value IbatMAX that limits an upper limit of the power
supply current Ibat flowing through the motor drive circuit 34 on
the basis of the difference (VR-VLo), the detected value of the
power supply current Ibat, and a resistance model representing a
resistance component of a power supply circuit that supplies the
power supply voltage VR to the motor drive circuit 34.
[0057] An example of a method for calculating the current limit
value IbatMAX will be described below. Hereinbelow, the resistance
model representing the resistance component of the power supply
circuit that supplies the power supply voltage VR to the motor
drive circuit 34 is referred to simply as "resistance model".
[0058] FIG. 4 is an illustrative diagram of an example of the
resistance model. For example, the resistance model includes an
internal resistance Rb of the battery 14, contact resistances Rc1
and Rc2 of connectors connecting the battery 14 and a harness,
harness resistances Rh1 and Rh2, contact resistances Rc3 and Rc4
connecting the harness and the electric power steering device, and
a circuit resistance Rdc in the electric power steering device. A
voltage Vbat indicates a generated voltage of the battery 14 before
dropping due to the internal resistance Rb.
[0059] When a sum of resistance values of the above resistances Rb,
Rc1 to Rc4, Rh1, Rh2, and Rdc is represented by Rs, the following
equation (1) holds:
Vbat=VR+Rs.times.Ibat (1)
[0060] Here, the current limit value IbatMAX that is the upper
limit of the power supply current Ibat is set so as to be a power
supply current Ibat at which the power supply voltage VR reaches
the lower limit voltage VLo. In this case, the following equation
(2) holds:
Vbat=VLo+Rs.times.IbatMAX (2)
[0061] From equations (1) and (2) , equation (3) for calculating
the current limit value IbatMAX is obtained:
IbatMAX=(VR-VLo)/Rs+Ibat (3)
[0062] Here, the right first term ((VR-VLo)/Rs) represents an
amount of fluctuation in the power supply current Ibat when the
power supply voltage VR fluctuates from a current value detected by
the voltage sensor 35 to the lower limit voltage VLo by a
difference (VR-VLo).
[0063] In calculation equation (3), the sum of the amount of
fluctuation in the power supply current Ibat when the power supply
voltage VR fluctuates from the current value to the lower limit
voltage VLo and a current value of the power supply current Ibat
detected by the current sensor 36 is calculated as the current
limit value IbatMAX.
[0064] Accordingly, the current limit value IbatMAX is calculated
as the upper limit of the power supply current for setting the
power supply voltage VR to the lower limit voltage VLo.
[0065] Note that while calculation equation (3) has considered only
the resistance component, an impedance model of the power supply
circuit may be used in consideration of an inductance component and
a capacitance component in the power supply circuit to calculate
the current limit value IbatMAX.
[0066] In addition, while in the above description, the applied
voltage applied to the motor drive circuit 34 has been detected as
the power supply voltage VR, a power supply voltage detected at
various intermediate points between the battery 14 and the motor
drive circuit 34 can be used as the power supply voltage VR. For
example, when using a battery terminal voltage as the power supply
voltage VR, the sum Rs of the resistance values is a sum of the
internal resistance Rb of the battery 14 and the contact
resistances Rc1 and Rc2 of the connectors.
[0067] Reference will be made to FIG. 3. The current limit value
calculation unit 41 outputs the current limit value IbatMAX to the
power supply current limit unit 42. The power supply current limit
unit 42 limits the power supply current Ibat so that the upper
limit of the power supply current Ibat flowing to the motor drive
circuit 34 is the current limit value IbatMAX.
[0068] For example, the power supply current limit unit 42 may
limit the upper limit of the current command value calculated by
the basic current command value calculation unit 31 illustrated in
FIG. 2 to limit the power supply current Ibat.
[0069] FIGS. 5A and 5B illustrate simulation results of the power
supply current Ibat and the power supply voltage VR when the upper
limit of the power supply current Ibat is limited by the power
supply current limit unit 42. The simulation assumes a case where
the generated voltage Vbat of the battery 14 is 12 [V], the lower
limit voltage VLo is 9 [V], the sum Rs of the resistance values of
the power supply circuit is 0.05 [Q], and a current of 80 [A]
suddenly flows at a certain time (0.01 seconds).
[0070] FIGS. 5A and 5B illustrate a waveform (power supply current
before limitation) when there is no limitation by the power supply
current limit unit 42 and waveforms when there is limitation by the
power supply current limit unit 42.
[0071] Furthermore, as the waveforms when there is limitation by
the power supply current limit unit 42, there are illustrated a
waveform when there is no error between the resistance value Rs of
the resistance model and an actual resistance of the power supply
circuit and waveforms when the actual resistance value increases
with respect to the resistance value Rs of the resistance model and
there are error rates of 0.2, 0.4, 0.6, 0.8, and 1 (i.e., 20%, 40%,
60%, 80%, and 100%).
[0072] Hereinbelow, an error between the resistance value Rs of the
resistance model and the actual resistance value of the power
supply circuit is referred to as "model error". Additionally, the
model error is defined as a difference obtained by subtracting the
resistance value Rs of the resistance model from an actual
resistance value (the actual resistance value-the resistance value
Rs of the resistance model). In addition, a model error rate is
defined as a value obtained by dividing the difference obtained by
subtracting the resistance value Rs of the resistance model from
the actual resistance value by the resistance value Rs of the
resistance model {(the actual resistance value-the resistance value
Rs of the resistance model)/the resistance value Rs of the
resistance model}.
[0073] As illustrated in FIG. 5A, a current of 80 [A] flows when
there is no limitation by the power supply current limit unit 42,
whereas current is limited to less than 80 [A] when there is
limitation by the power supply current limit unit 42.
[0074] Additionally, when there is no model error, the limited
power supply current is immediately stabilized to the current limit
value IbatMAX ((12 [V]-9 [V])/0.05 [Q]=60 [A]), whereas when there
is a model error, the limitation becomes unstable, causing
oscillations of the power supply current Ibat and the power supply
voltage VR. Particularly, when the model error rate is 100%, the
oscillations do not converge. The reason that the oscillations
occur when there is a model error is because the following
situations (1) to (3) are repeated.
[0075] (1) When the power supply current Ibat is limited to 60 [A]
at a time of 0.01 seconds, an actual resistance is larger than the
resistance model, so that the power supply voltage VR excessively
drops and becomes lower than an ideal value.
[0076] (2) After that, the limitation on the power supply current
excessively works in response to the excessive voltage drop, thus
leading to a rapid recovery of the power supply voltage VR.
[0077] (3) In response to the rapid recovery of the power supply
voltage VR, the limitation on the power supply current is also
rapidly weakened, as a result of which the power supply current
rapidly increases, and the power supply voltage VR excessively
drops and becomes lower than the ideal value.
[0078] Reference will be made to FIG. 3. The current limit unit 33
includes a change rate limit value calculation unit 43 and a power
supply current change rate limit unit 44, and prevents a rapid
increase in the power supply current in the above situation (3) by
limiting a change rate in an increasing direction of the power
supply current.
[0079] The change rate limit value calculation unit 43 calculates a
change rate limit value CrLim responsive to the difference
(VR-VLo). The change rate limit value calculation unit 43 may use,
for example, a calculation map for the change rate limit value
CrLim having characteristics illustrated in FIG. 6 to calculate the
change rate limit value CrLim.
[0080] In the example of FIG. 6, when the difference (VR-VLo)
changes from 0 to a predetermined value V1, the change rate limit
value CrLim changes from 0 to a predetermined value CrLiml, and
when the difference (VR-VLo) is equal to or more than the
predetermined value V1, the change rate limit value CrLim is
maintained at the predetermined value CrLiml.
[0081] Reference will be made to FIG. 3. The power supply current
change rate limit unit 44 limits the change rate of the power
supply current Ibat on the basis of the change rate limit value
CrLim calculated by the change rate limit value calculation unit
43. For example, the power supply current change rate limit unit 44
limits the change rate of the power supply current Ibat so that a
change rate in the increasing direction of the power supply current
Ibat (i.e., a change rate in the increasing power supply current
Ibat) becomes equal to or less than the change rate limit value
CrLim.
[0082] For example, the power supply current change rate limit unit
44 may limit a change rate in the current command value calculated
by the basic current command value calculation unit 31 illustrated
in FIG. 2 to limit the change rate in the power supply current
Ibat.
[0083] FIGS. 7A and 7B illustrate simulation results of the power
supply current Ibat and the power supply voltage VR when the upper
limit of the current power supply Ibat is limited by the power
supply current limit unit 42 and the change rate is limited by the
power supply current change rate limit unit 44.
[0084] Simulation conditions and legend for each waveform are the
same as those of the FIGS. 5A and 5B.
[0085] It is shown that the change rate limitation by the power
supply current change rate limit unit 44 improves the unstable
limitation on the power supply current Ibat and the power supply
voltage VR due to the model error, and more stabilizes the power
supply current Ibat and the power supply voltage VR.
[0086] However, in the waveform of the power supply current Ibat
when there is no model error, the power supply current Ibat
increases gently compared with the waveform when there is no change
rate limitation (see FIG. 5A), which indicates that the limitation
is slightly excessive.
[0087] On the other hand, when the model error rate is 100%, it
takes time until the power supply current Ibat and the power supply
voltage VR are stabilized. Thus, it is desirable to strengthen the
change rate limitation to shorten the convergence time.
[0088] Accordingly, the present invention improves excessive or
insufficient limitation on the change rate by the power supply
current change rate limit unit 44 by changing a strength of the
change rate limitation by the power supply current change rate
limit unit 44 according to a magnitude of the model error (i.e.,
the amount of increase in an actual resistance value with respect
to the resistance value Rs of the resistance model).
[0089] For example, as the actual resistance value of the power
supply circuit increases and the model error becomes larger, the
change rate limitation by the power supply current change rate
limit unit 44 may be more strengthened. Conversely, as the model
error becomes smaller (the difference between the resistance value
Rs of the resistance model and an actual resistance value of the
power supply circuit (the actual resistance value of the power
supply circuit-the resistance value Rs of the resistance model)
becomes smaller), the change rate limitation by the power supply
current change rate limit unit 44 may be more weakened.
[0090] Here, there is used a property that when the actual
resistance value of the power supply circuit increases, the amount
of change in the power supply voltage VR (i.e., a change speed of
the power supply voltage VR) with respect to a change in the power
supply current Ibat equal in magnitude increases.
[0091] Therefore, the change rate limit value calculation unit 43
corrects the change rate limit value CrLim according to the change
speed of the power supply voltage VR.
[0092] In the first embodiment, the change rate limit value CrLim
is corrected according to a differential amount of the detected
value of the power supply voltage VR as the change speed of the
power supply voltage VR.
[0093] Reference will be made to FIG. 3. A differentiator 45
calculates a differential value .DELTA.VR of the detected value of
the power supply voltage VR. The change rate limit value
calculation unit 43 makes the change rate limit value CrLim smaller
as a differential amount (-.DELTA.VR) in a decreasing direction of
the detected value of the power supply voltage VR, that is, a
decrease rate of the detected value of the power supply voltage VR
(a magnitude of a negative differential value of the power supply
voltage VR) becomes larger, thereby more strengthening the change
rate limitation as the model error becomes larger.
[0094] As a result, the change rate limit value CrLim is set so
that the change rate in the increasing direction of the power
supply current Ibat is more limited as a decrease speed of the
detected value of the power supply voltage VR becomes larger.
[0095] The change rate limit value calculation unit 43 may use a
plurality of calculation maps MAP-L and MAP-H illustrated in FIG.
8A to calculate the change rate limit value CrLim.
[0096] The plurality of calculation maps MAP-L and MAP-H are maps
that specify the change rate limit value CrLim for the difference
(VR-VLo) by using the difference (VR-VLo) as a parameter, and can
be used to calculate the change rate limit value CrLim responsive
to the difference (VR-VLo).
[0097] In the examples of the calculation maps MAP-L and MAP-H
illustrated in FIG. 8A, the change rate limit value CrLim increases
as the difference (VR-VLo) increases, and the change rate limit
value CrLim is constant in a range where the difference (VR-VLo) is
equal to or more than a threshold value.
[0098] The plurality of calculation maps MAP-L and MAP-H each
specify different change rate limit values CrLim for the same
difference (VR-VLo). Accordingly, the magnitude of a value of the
change rate limit value CrLim calculated by the calculation map
MAP-L is different from the magnitude of a value of the change rate
limit value CrLim calculated by the calculation map MAP-H.
[0099] Specifically, the value calculated by the calculation map
MAP-L for the difference (VR-VLo) equal in magnitude is smaller
than the value calculated by the calculation map MAP-H. Therefore,
the calculation map MAP-L is used to calculate the change rate
limit value CrLim relatively strong in limitation, and the
calculation map MAP-H is used to calculate the change rate limit
value CrLim relatively weak in limitation.
[0100] Additionally, the change rate limit value calculation unit
43 calculates a gain G1 using a gain calculation map illustrated in
FIG. 8B.
[0101] The gain G1 is responsive to the differential amount
(-.DELTA.VR) in the decreasing direction of the detected value of
the power supply voltage VR, that is, the decrease rate of the
detected value of the power supply voltage VR (the magnitude of the
negative differential value of the power supply voltage VR), and
gradually increases from the value "0" to the value "1" as the
differential amount (-.DELTA.VR) increases in a range where the
differential amount (-.DELTA.VR) is large to some extent.
[0102] The change rate limit value calculation unit 43 changes the
change rate limit value CrLim according to the differential amount
of the detected value of the power supply voltage VR by
synthesizing outputs of the calculation maps MAP-L and MAP-H
according to the gain G1 on the basis of the following equation
(4):
Change rate limit value CrLim=(MAP-H output).times.(1-G1)+(MAP-L
output).times.G1 (4)
[0103] Instead of the above, the change rate limit value
calculation unit 43 may use a single calculation map MAP
illustrated in FIG. 9A and a gain calculation map illustrated in
FIG. 9B to calculate the change rate limit value CrLim that changes
according to the differential amount of the detected value of the
power supply voltage VR.
[0104] The calculation map MAP is a map that specifies the change
rate limit value CrLim for the difference (VR-VLo) by using the
difference (VR-VLo) as a parameter, and can be used to calculate
the change rate limit value CrLim responsive to the difference
(VR-VLo).
[0105] In the example of the calculation maps MAP illustrated in
FIG. 9A, the change rate limit value CrLim increases as the
difference (VR-VLo) increases, and the change rate limit value
CrLim is constant in a range where the difference (VR-VLo) is equal
to or more than a threshold value.
[0106] The change rate limit value calculation unit 43 uses the
gain calculation map illustrated in FIG. 9B to calculate a gain G2
that is responsive to the differential amount (-.DELTA.VR) in the
decreasing direction of the detected value of the power supply
voltage VR and that gradually decreases from the value "1" as the
differential amount (-.DELTA.VR) increases in a range where the
differential amount (-.DELTA.VR) is large to some extent.
[0107] The change rate limit value calculation unit 43 multiplies
the change rate limit value calculated by the calculation map MAP
by the gain G2 to calculate the change rate limit value CrLim that
changes according to the differential amount of the detected value
of the power supply voltage VR.
[0108] Note that the above-described method for calculating the
change rate limit value CrLim is illustrative, and the present
invention is not limited thereto. The change rate limit value CrLim
may be calculated by various methods as long as the change rate
limitation by the power supply current change rate limit unit 44
can be more strengthened as the differential amount in the
decreasing direction of the detected value of the power supply
voltage VR becomes larger.
[0109] (Operation)
[0110] Next, an example of an actuator control method according to
the first embodiment will be described with reference to FIG.
10.
[0111] At step S1, the voltage sensor 35 detects the power supply
voltage VR.
[0112] At step S2, the current sensor 36 detects the power supply
current Ibat.
[0113] At step S3, the current limit value calculation unit 41
calculates the current limit value IbatMAX on the basis of the
difference (VR-VLo) obtained by subtracting the predetermined lower
limit voltage VLo from the detected value of the power supply
voltage VR, the detected value of the power supply current Ibat,
and the resistance model representing the resistance component of
the power supply circuit.
[0114] At step S4, the change rate limit value calculation unit 43
calculates the change rate limit value CrLim on the basis of the
difference (VR-VLo) and the change speed .DELTA.VR of the power
supply voltage.
[0115] At step S5, the power supply current limit unit 42 limits
the upper limit value of the power supply current Ibat on the basis
of the current limit value IbatMAX.
[0116] At step S6, the power supply current change rate limit unit
44 limits the change rate of the power supply current Ibat on the
basis of the change rate limit value CrLim.
[0117] After that, processing is ended.
Effects of First Embodiment
[0118] (1) The voltage sensor 35 detects the power supply voltage
VR applied from the power supply circuit including the battery 14.
The current sensor 36 detects the power supply current Ibat
supplied from the power supply circuit. The current limit value
calculation unit 41 calculates the current limit value IbatMAX on
the basis of the difference (VR-VLo) between the power supply
voltage VR detected by the voltage sensor 35 and the predetermined
set voltage VLo, the power supply current Ibat detected by the
current sensor 36, and the resistance model representing the
resistance component of the power supply circuit. The power supply
current limit unit 42 limits the magnitude of the power supply
current Ibat on the basis of the current limit value IbatMAX. The
change rate limit value calculation unit 43 calculates the change
rate limit value CrLim on the basis of the difference (VR-VLo) and
the change speed of the power supply voltage VR. The power supply
current change rate limit unit 44 limits the change rate of the
power supply current Ibat on the basis of the change rate limit
value CrLim.
[0119] In this way, calculating the current limit value IbatMAX on
the basis of not only the power supply voltage VR but also the
detected value of the power supply current Ibat and the resistance
model of the power supply circuit can suppress the current limit
value IbatMAX from being set excessively smaller or excessively
larger.
[0120] Limiting the change rate of the power supply current Ibat
can suppress the power supply current and the power supply voltage
from becoming unstable even when an error occurs between the
resistance model and the actual resistance value of the power
supply circuit.
[0121] Additionally, calculating the change rate limit value CrLim
according to the change speed of the power supply voltage VR can
improve excessive or insufficient limitation on the change rate of
the power supply current Ibat by the power supply current change
rate limit unit 44.
[0122] (2) The change rate limit value calculation unit 43 sets the
change rate limit value CrLim to more limit the change rate in the
increasing direction of the power supply current Ibat as the
decrease speed of the detected value of the power supply voltage VR
becomes larger. For example, the differentiator 45 may calculate
the differential value .DELTA.VR of the power supply voltage VR
detected by the voltage sensor 35, and the change rate limit value
calculation unit 43 may calculate the change rate limit value CrLim
on the basis of the difference (VR-VLo) and the differential value
.DELTA.VR. As a result, excessive or insufficient limitation on the
change rate of the power supply current Ibat by the power supply
current change rate limit unit 44 can be improved.
Second Embodiment
[0123] Next, the current limit unit 33 of a second embodiment will
be described. Structures of the electric power steering device and
the control unit 30 are the same as those in the first embodiment
described above with reference to FIGS. 1 and 2.
[0124] If the detected value of the power supply voltage VR and the
detected value of the power supply current Ibat include a noise
component, noise is added to the current limit value IbatMAX
calculated by the current limit value calculation unit 41 and the
change rate limit value CrLim calculated by the change rate limit
value calculation unit 43, making inappropriate the limitations by
the power supply current limit unit 42 and the power supply current
change rate limit unit 44.
[0125] Therefore, the current limit unit 33 of the second
embodiment includes at least one of a filter configured to smooth
the detected value of the power supply voltage VR and a filter
configured to smooth the detected value of the power supply current
Ibat.
[0126] Reference will be made to FIG. 11. The current limit unit 33
of the second embodiment has the similar functional structure as
the first embodiment illustrated in FIG. 3, and the same reference
signs denote the similar components.
[0127] The current limit unit 33 of the second embodiment includes
a low pass filter (LPF) 60 configured to smooth the detected value
of the power supply current Ibat and a low pass filter 61
configured to smooth the detected value of the power supply voltage
VR.
[0128] The calculations of the current limit value IbatMAX and the
change rate limit value CrLim by the subtractor 40, the current
limit value calculation unit 41, the change rate limit value
calculation unit 43, and the differentiator 45 are the same as
those in the first embodiment except that the respective values
after smoothing are used instead of the detected value of the power
supply voltage VR as is and the detected value of the power supply
current Ibat as is.
[0129] Even third and fourth embodiments that will be described
below may include the low pass filter 60 configured to smooth a
detected value of the power supply current Ibat and the low pass
filter 61 configured to smooth a detected value of the power supply
voltage VR. Filters configured to smooth the detected values are
not limited to low pass filters, and an averaging method or other
methods can be used.
Effect of Second Embodiment
[0130] The current limit unit 33 includes at least one of the low
pass filter 60 configured to smooth the detected value of the power
supply current Ibat and the low pass filter 61 configured to smooth
the detected value of the power supply voltage VR. As a result, it
can be prevented that the limitations by the power supply current
limit unit 42 and the power supply current change rate limit unit
44 become inappropriate because noise is added to the current limit
value IbatMAX calculated by the current limit value calculation
unit 41 and the change rate limit value CrLim calculated by the
change rate limit value calculation unit 43 due to a noise
component included in the detected value of the power supply
voltage VR and the detected value of the power supply current
Ibat.
Third Embodiment
[0131] Next, the current limit unit 33 of the third embodiment will
be described. Structures of the electric power steering device and
the control unit 30 are the same as those in the first embodiment
described above with reference to FIGS. 1 and 2.
[0132] When the current limit value IbatMAX calculated by the
current limit value calculation unit 41 and the change rate limit
value CrLim calculated by the change rate limit value calculation
unit 43 oscillate, the limitations by the power supply current
limit unit 42 and the power supply current change rate limit unit
44 become unstable.
[0133] Therefore, the current limit unit 33 of the third embodiment
includes at least one of a rate limiter configured to limit a
change rate of the current limit value IbatMAX calculated by the
current limit value calculation unit 41 and a rate limiter
configured to limit a change rate of the change rate limit value
CrLim calculated by the change rate limit value calculation unit
43.
[0134] Additionally, the differential value .DELTA.VR of the
detected value of the power supply voltage VR tends to change
suddenly due to a noise component and an oscillation component
included in the power supply voltage VR. The same applies to the
above-described gains G1 and G2 calculated according to the
differential value .DELTA.VR.
[0135] Therefore, the current limit unit 33 of the third embodiment
includes a rate limiter configured to limit a change rate of the
differential value .DELTA.VR calculated by the differentiator
45.
[0136] Reference will be made to FIG. 12. The current limit unit 33
of the third embodiment has the similar functional structure as the
first embodiment illustrated in FIG. 3, and the same reference
signs denote the similar components.
[0137] The current limit unit 33 of the third embodiment includes a
rate limiter 62 configured to limit the change rate of the current
limit value IbatMAX calculated by the current limit value
calculation unit 41, a rate limiter 63 configured to limit the
change rate of the change rate limit value CrLim calculated by the
change rate limit value calculation unit 43, and a rate limiter 64
configured to limit the change rate of the differential value
.DELTA.VR calculated by the differentiator 45.
[0138] The calculation of the change rate limit value CrLim by the
change rate limit value calculation unit 43 is the same as that in
the first embodiment except for use of a value after change rate
limitation by the rate limiter 64 instead of the differential value
.DELTA.VR as is of the detected value of the power supply voltage
VR. The rate limiter 64 may be arranged so as to limit change rates
of the above-descried gains G1 and G2 calculated according to the
differential value .DELTA.VR instead of the change rate limitation
on the differential value .DELTA.VR of the detected value of the
power supply voltage VR.
[0139] In addition, the power supply current limit unit 42 limits
the upper limit value of the power supply current Ibat on the basis
of the current limit value IbatMAX after the change rate limitation
by the rate limiter 62. The power supply current change rate limit
unit 44 limits the change rate of the power supply current Ibat on
the basis of the change rate limit value CrLim after the change
rate limitation by the rate limiter 63.
[0140] An upper limit value of the change rate limited by the rate
limiter 62 may be different depending on whether the current limit
value IbatMAX increases or decreases. For example, the upper limit
of a change rate when the current limit value IbatMAX increases
(i.e., in a direction in which the limitation is relaxed) may be
set less than the upper limit of a change rate when the current
limit value IbatMAX decreases (i.e., in a direction in which the
limitation is strengthened).
[0141] Similarly, an upper limit value of the change rate limited
by the rate limiter 63 may also be different depending on whether
the change rate limit value CrLim increases or decreases. For
example, the upper limit of a change rate when the change rate
limit value CrLim increases may be set less than the upper limit of
a change rate when the change rate limit value CrLim decreases.
[0142] As a result, when relaxing the limitations by these limit
values IbatMAX and CrLim, rapid relaxation is prevented. On the
other hand, when it is necessary to immediately limit the power
supply current Ibat in response to a rapid decrease in the power
supply voltage VR, it is possible to make limitations less likely
to be applied on changes in the limit values IbatMAX and CrLim.
[0143] Furthermore, the rate limiter 62 may be configured so as not
to limit change in the current limit value IbatMAX when the current
limit value IbatMAX decreases. Similarly, the rate limiter 63 may
be configured so as not to limit change in the change rate limit
value CrLim when the change rate limit value CrLim decreases.
[0144] Similarly, an upper limit value of the change rate limited
by the rate limiter 64 may also be different depending on whether
the differential value .DELTA.VR increases or decreases. For
example, the upper limit of a change rate in the differential value
.DELTA.VR when the change rate limit value CrLim finally calculated
increases (i.e., in the direction in which the limitation is
relaxed) may be set less than the upper limit of a change rate in
the differential value .DELTA.VR when the change rate limit value
CrLim decreases (i.e., in the direction in which the limitation is
strengthened).
[0145] Even the fourth embodiment that will be described below may
include the rate limiter 62 configured to limit the change rate of
the current limit value IbatMAX calculated by the current limit
value calculation unit 41 and the rate limiter 63 configured to
limit the change rate of the change rate limit value CrLim
calculated by the change rate limit value calculation unit 43.
Effect of Third Embodiment
[0146] (1) The current limit unit 33 includes at least one of the
rate limiter 62 configured to limit the change rate of the current
limit value IbatMAX calculated by the current limit value
calculation unit 41 and the rate limiter 63 configured to limit the
change rate of the change rate limit value CrLim calculated by the
change rate limit value calculation unit 43.
[0147] This can suppress destabilization of the limitations by the
power supply current limit unit 42 and the power supply current
change rate limit unit 44 due to oscillations of the current limit
value IbatMAX and the change rate limit value CrLim.
[0148] (2) The current limit unit 33 includes the rate limiter 64
configured to limit the change rate of the differential value
.DELTA.VR calculated by the differentiator 45. This can suppress a
sudden change in the differential value .DELTA.VR due to a noise
component and an oscillation component included in the power supply
voltage VR and a sudden change in the above-described gains G1 and
G2 calculated according to the differential value .DELTA.VR.
Fourth Embodiment
[0149] Next, the current limit unit 33 of the fourth embodiment
will be described. Structures of the electric power steering device
and the control unit 30 are the same as those in the first
embodiment described above with reference to FIGS. 1 and 2.
[0150] As described above, the limitation on the power supply
current Ibat becomes unstable when there is a model error between
the resistance value Rs of the resistance model for use in the
calculation of the current limit value IbatMAX and the actual
resistance value of the power supply circuit.
[0151] Therefore, the current limit unit 33 of the fourth
embodiment calculates an estimated value Rse of the resistance
component of the power supply circuit, and calculates the current
limit value on the basis of the difference (VR-VLo) , the detected
value of the power supply current Ibat, and the estimated value
Rse.
[0152] Furthermore, the power supply current change rate limit unit
44 of the fourth embodiment calculates the gains G1 and G2 that
changes the change rate limit value CrLim on the basis of a
difference (Rse-Rs) or a ratio (Rse/Rs) between the estimated value
Rse and the resistance value Rs of the resistance model instead of
the differential value .DELTA.VR of the power supply voltage
VR.
[0153] As described above, the power supply current change rate
limit unit 44 intends to correct the change rate limit value CrLim
according to the magnitude of the model error (i.e., the amount of
increase in the actual resistance value with respect to the
resistance value Rs of the resistance model). Thus, calculating the
gains G1 and G2 on the basis of the difference (Rse-Rs) or the
ratio (Rse/Rs) between the estimated value Rse and the resistance
value Rs of the resistance model enables appropriate correction
according to an increase in the resistance of the power supply
circuit.
[0154] Reference will be made to FIG. 13. The current limit unit 33
of the fourth embodiment has the similar functional structure as
the first embodiment illustrated in FIG. 3, and the same reference
signs denote the similar components.
[0155] The current limit unit 33 of the fourth embodiment includes
a resistance value estimation unit 65 configured to calculate the
estimated value Rse of the resistance component of the power supply
circuit.
[0156] The resistance value estimation unit 65 calculates the
estimated value Rse of the resistance component of the power supply
circuit on the basis of detected values of the power supply voltage
VR and detected values of the power supply current Ibat at
different times.
[0157] When the power supply voltage, the power supply current, and
the generated voltage of the battery 14, respectively, at a certain
sampling time t1 are represented by VR1, Ibat1, and Vbat1, the
following equation (5) holds:
Vbat1=VR1+Rse.times.Ibat1 (5)
[0158] Additionally, when the power supply voltage, the power
supply current, and the generated voltage of the battery 14,
respectively, at a sampling time t2 different from the sampling
time t1 are represented by VR2, Ibat2, and Vbat2, the following
equation (6) holds:
Vbat2=VR2+Rse.times.Ibat2 (6)
[0159] When it is assumed that the generated voltage of the battery
14 does not much change and Vbat1.apprxeq.Vbat2, equation (7) for
calculating the estimated value Rse of the resistance component is
obtained from equations (5) and (6):
Rse=-(VR1-VR2)/(Ibat1-Ibat2) (7)
[0160] In other words, the resistance value estimation unit 65
calculates, as the estimated value Rse of the resistance component,
a ratio obtained by diving a difference (VR2-VR1) between the power
supply voltages VR1 and VR2 detected at the sampling times t1 and
t2 by a difference (Ibat1-Ibat2) between the power supply currents
Ibat1 and Ibat2 detected at the sampling times t1 and t2.
[0161] Note that, in order to maintain accuracy of the estimated
value Rse, the resistance value estimation unit 65 may adopt a
result of calculation of the estimated value Rse only when the
difference (VR2-VR1) between the power supply voltages VR1 and VR2
and the difference (Ibat1-Ibat2) between the power supply currents
Ibat1 and Ibat2 exceed a predetermined value. In addition, since
calculation equation (7) assumes that Vbat1 and Vbat2 are
substantially equal, it is preferable that the sampling times t1
and t2 are not too far apart in time.
[0162] The resistance value estimation unit 65 outputs the
calculated estimated value Rse to the current limit value
calculation unit 41 and the change rate limit value calculation
unit 43.
[0163] The current limit value calculation unit 41 calculates the
current limit value IbatMAX by replacing the Rs of the above
calculation equation (3) with the estimated value Rse.
[0164] The change rate limit value calculation unit 43 changes the
change rate limit value CrLim on the basis of the difference
(Rse-Rs) or the ratio (Rse/Rs) between the estimated value Rse and
the resistance value Rs of the resistance model instead of the
differential value .DELTA.VR of the power supply voltage VR.
[0165] In other words, the change rate limit value calculation unit
43 calculates the change rate limit value CrLim on the basis of the
difference (VR-VLo) and the difference (Rse-Rs) or the ratio
(Rse/Rs) between the resistance value Rs of the resistance model
and the estimated value Rse.
[0166] Here, when the resistance value of the power supply circuit
increases, the change speed of the power supply voltage VR with
respect to a current change equal in magnitude increases, and the
amount of the increase in the change speed of the power supply
voltage VR at this time is proportional to the amount of the
increase in the resistance value. Accordingly, calculating the
change rate limit value CrLim on the basis of the difference
(Rse-Rs) or the ratio (Rse/Rs) can be said to be equivalent to
calculating the change rate limit value CrLim on the basis of the
change speed of the power supply voltage VR.
[0167] The change rate limit value calculation unit 43 may change
the change rate limit value CrLim so that the change rate limit
value CrLim becomes smaller as the estimated value Rse becomes
larger than the resistance value Rs of the resistance model.
[0168] For example, the gain calculation maps of FIGS. 8B and 9B
may be changed to maps of the gains G1 and G2 responsive to the
difference (Rse-Rs) or the ratio (Rse/Rs) instead of the
differential amount (-.DELTA.VR) in the decreasing direction of the
detected value of the power supply voltage VR.
[0169] It should be noted that, in terms of correcting influence
due to an increase in the resistance value, it is more appropriate
to correct the change rate limit value CrLim on the basis of the
difference (Rse-Rs) or the ratio (Rse/Rs) between the estimated
value Rse and the resistance Rs of the resistance model than to
correct the change rate limit value CrLim according to the
differential amount (-.DELTA.VR) of the power supply voltage VR as
in the first embodiment.
[0170] On the other hand, correction according to the differential
amount (-.DELTA.VR) of the power supply voltage VR can be
considered to have the following advantage.
[0171] Specifically, when responsiveness of the power supply
current limit unit 42 and the power supply current change rate
limit unit 44 is insufficient even if there is no model error, the
power supply current Ibat cannot be immediately limited according
to the current limit value IbatMAX and the change rate limit value
CrLim. Thus, by strengthening limitation on the change rate of the
power supply current Ibat according to the differential amount
(-.DELTA.VR) of the power supply voltage VR, it is possible to
preventively avoid delay of limitation on the power supply current
Ibat due to the insufficient responsiveness.
[0172] Accordingly, the change rate limit value calculation unit 43
may select a gain that lowers the change rate limit value CrLim
more from the gain G1 or G2 responsive to the differential amount
(-.DELTA.VR) of the power supply voltage VR and the gain G1 or G2
responsive to the difference (Rse-Rs) or the ratio (Rse/Rs), and
may use the selected gain. As a result, the change rate limit value
calculation unit 43 can achieve both a correction effect on the
increased resistance and an effect of preventing the insufficient
responsiveness to the limitation on the power supply current.
[0173] Note that in this way, when performing both the correction
of the change rate limit value CrLim by the differential amount
(-.DELTA.VR) of the power supply voltage VR and the correction of
the change rate limit value CrLim by the difference (Rse-Rs) or the
ratio (Rse/Rs), there may be included the rate limiter 64
configured to limit the change rate of the differential value
.DELTA.VR calculated by the differentiator 45.
Effects of Fourth Embodiment
[0174] (1) The resistance value estimation unit 65 calculates the
estimated value Rse of the resistance component of the power supply
circuit. The current limit value calculation unit 41 calculates the
current limit value IbatMAX on the basis of the difference
(VR-VLo), the detected value of the power supply current Ibat, and
the estimated value Rse.
[0175] This can suppress the limitation on the power supply current
Ibat from becoming unstable due to a model error.
[0176] (2) The change rate limit value calculation unit 43
calculates the change rate limit value CrLim on the basis of the
difference (VR-VLo) and the difference (Rse-Rs) or the ratio
(Rse/Rs) between the resistance value Rs of the resistance model
and the estimated value Rse. This enables the change rate limit
value CrLim to be more appropriately corrected according to an
increase in the resistance of the power supply circuit.
Modifications
[0177] (1) The current detecting means configured to detect the
power supply current Ibat is not limited to the current sensor 36.
The current detecting means may estimate the power supply current
Ibat, for example, on the basis of a value obtained by another
sensor.
[0178] For example, in the case of a motor drive circuit for use in
an electric power steering device or the like, energy balance is
represented by the following equation (8):
[Math 1]
[0179] VRI.sub.bat=K.sub.tIq.omega.+R 3/2(Id.sup.2+Iq.sup.2)+Ploss
(8)
[0180] In the above equation (8), VR represents a power supply
voltage that is an inverter applied voltage to be applied to the
inverter, Ibat represents a power supply current that is a battery
current flowing to the motor from the battery via the inverter, Kt
represents a torque constant of the motor, Iq represents a q-axis
current, Id represents a d-axis current, R represents a resistance
value per phase of the motor, and Ploss represents a power loss due
to iron loss, friction, or the like.
[0181] The right side of the above equation (8) corresponds to
consumed power, so that the power supply current Ibat can be
estimated by dividing the right side of the above equation (8) by
the power supply voltage VR.
[0182] (2) The voltage detecting means configured to detect the
power supply voltage VR is not limited to the voltage sensor 35.
The voltage detecting means may estimate the power supply voltage
VR, for example, on the basis of a value obtained by another
sensor.
[0183] Reference will be made to FIG. 4. Assume the case where the
power supply current Ibat is limited so that, as the power supply
voltage VR, for example, an input voltage Vi (i.e., an applied
voltage between a position of the contact resistance Rc3 and a
position of the contact resistance Rc4) to be input to an electric
power steering device is equal to or more than the lower limit
voltage VLo.
[0184] In this case, the sum Rs of the resistance values is defined
as a sum (Rb+Rc1+Rc2+Rh1+Rh2) of the internal resistance Rb of the
battery 14, the contact resistances Rc1 and Rc2 of the connectors
connecting the battery 14 and a harness, and harness resistances
Rh1 and Rh2.
[0185] The input voltage Vi can be estimated by the following
method, other than being directly detected by the sensor.
[0186] When an applied voltage (here referred to as "applied
voltage Va") of the motor drive circuit 34 is known, a sum Ro of
the resistances present between a position where the input voltage
Vi to be estimated as the power supply voltage VR is generated and
a position where the applied voltage Va is generated is a sum
(Ro=(Rc3+Rc4+Rdc)) of the contact resistances Rc3 and Rc4
connecting the harness and the electric power steering device and
circuit resistance Rdc in the electric power steering device.
[0187] Accordingly, detecting or estimating the power supply
current Ibat enables the input voltage Vi to be estimated by the
following equation (9):
Vin=Va+Ro.times.Ibat (9)
[0188] Conversely, when the input voltage Vi to be input to the
electric power steering device is known and the applied voltage Va
of the motor drive circuit 34 is estimated as the power supply
voltage VR, the applied voltage Va can be estimated by the
following equation (10):
Va=Vin-Ro.times.Ibat (10)
[0189] In this way, a voltage at any point in the power supply
circuit is estimated as the power supply voltage VR by the power
supply current Ibat and the resistance value present between the
position where voltage can be detected by the sensor or the like
and the position where the voltage to be estimated, whereby with
use of the estimated value thereof, the power supply current Ibat
can be limited so that the voltage at the any point becomes equal
to or more than the power supply voltage VLo.
[0190] All examples and conditional terms given herein are intended
for teaching purposes to help the readers understand the present
invention and the concepts provided by the inventor for the
advancement of technology. The present invention should be
interpreted without being limited to the examples and conditions
specifically described above and to the structures of such examples
in this specification, which are related to showing superiority and
inferiority of the present invention. While some embodiments of the
present invention have been described in detail, it should be
understood that various changes, substitutions, and modifications
can be made thereto without departing from the spirit and scope of
the present invention.
REFERENCE SIGNS LIST
[0191] 1: Steering wheel
[0192] 2: Steering shaft
[0193] 3: Reduction gear
[0194] 4A, 4B: Universal joint
[0195] 5: Pinion rack mechanism
[0196] 6: Tie rod
[0197] 10: Torque sensor
[0198] 11: Ignition key
[0199] 12: Vehicle speed sensor
[0200] 14: Battery
[0201] 20: Motor
[0202] 30: Control unit
[0203] 31: Basic current command value calculation unit
[0204] 32: Motor control unit
[0205] 33: Current limit unit
[0206] 34: Motor drive circuit
[0207] 35: Voltage sensor
[0208] 36: Current sensor
[0209] 40: Subtractor
[0210] 41: Current limit value calculation unit
[0211] 42: Power supply current limit unit
[0212] 43: Change rate limit value calculation unit
[0213] 44: Power supply current change rate limit unit
[0214] 45: Differentiator
[0215] 60, 61: Low pass filter
[0216] 62, 63, 64: Rate limiter
[0217] 65: Resistance value estimation unit
* * * * *