JPH08142884A - Control device for electric power steering device - Google Patents

Abstract

(57) [Abstract] [Purpose] In an electric power steering system controller, an H bridge capable of applying a maximum voltage corresponding to a duty ratio D corresponding to a current control value to a motor is used. A motor control circuit is provided. [Constitution] The converter 30 converts the current control value into a PWM signal and a current direction signal, and outputs drive signals for the FET1 to FET4 of the H bridge. For FET1 (FET2)
The PWM signal of the duty ratio D is fed to the FET3 (FET4) by the duty ratio (D-Δt) P obtained by subtracting the dead time Δt.
Output WM signal. At the rising edge of the PWM signal of the ratio D, the signal H is output to the FET1 and the PWM signal of the ratio (D-Δt) delayed by Δt is output to the FET3. Ratio (D-Δ
At the falling edge of the PWM signal of t), the signal H is output to the FET3, and at the falling edge of the PWM signal of the ratio D, the signal L is output to the FET1, and the voltage corresponding to the PWM signal not including the dead time is applied to the motor. .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an electric power steering device.

[0002]

2. Description of the Related Art An electric power steering apparatus for a vehicle detects a steering torque and a vehicle speed generated in a steering shaft by operating a steering wheel, and drives a motor based on the detection signal to drive the steering wheel. It assists the steering force of. In such an electric power steering device, in order to improve the steering performance, not only the steering torque and vehicle speed generated in the steering shaft but also the motor angular velocity, the motor angular acceleration, etc. are used to determine the steering assist force. Information is also used.

A conventional electric power steering device model
The drive control circuit of the motor controls the current command value, which is a control target value calculated based on the steering torque and the vehicle speed, and the actual motor.
The current control value corresponding to the difference from the current value is obtained, and the pulse width modulation signal of the pulse width corresponding to this current control value (hereinafter PW
The FET switching element is controlled by the M signal), and the sine / magnitude mode described below is used.
The motor control circuit is generally used, and the motor angular velocity,
The circuit is suitable for estimating the motor angular acceleration and the like.

A sine / magnitude type motor control circuit, as shown in FIG. 7, has two FET switching elements and a second arm in a first arm connected in an H-bridge type. 2 FET switching elements are placed in the
The first switching element of the arm is controlled based on the duty ratio of the PWM signal (time ratio for turning on / off the gate of the FET) to change the motor applied voltage. The second switching element of the second arm is controlled by the sign of the current control value to determine the direction of the motor current.

That is, the modes shown in (a) and (b) of FIG.
The control circuit uses FET1 and FE on the left arm of the H bridge.
T3 is arranged, FET2 and FET4 are arranged in the right arm, and the motor M is connected to the middle point of the left and right arms. now,
When the motor M is rotated in the forward direction, as shown in FIG. 7A, the FET2 is turned off according to the sign of the current control value,
When the FET4 is turned on and the FET1 is turned on for a predetermined time by the duty ratio of the PWM signal, the positive electrode of the battery B and the left terminal of the motor M in FIG. 7 (a) become conductive, and the current flows in the direction of arrow a. , The motor M rotates in the positive direction. When rotating the motor in the negative direction, as shown in FIG.
If the FET1 is turned off, the FET3 is turned on according to the sign of the current control value, and the FET2 is turned on for a predetermined time according to the duty ratio of the PWM signal, the positive terminal of the battery B and the right terminal in FIG. It conducts, current flows in the direction of arrow b, and the motor M rotates in the negative direction.

[0006]

However, in a motor control circuit using such an H bridge, the PWM
At the time when the signal is switched from H to L or from L to H based on the duty ratio of the signal, the two arms of the H bridge are simultaneously conducted, and as shown in FIG. As shown, the current in the direction of arrow a and the current in the direction of arrow bb due to the counter electromotive force generated in the motor simultaneously flow, which causes a short circuit. Therefore, it has been proposed to provide a dead time at the time of switching the PWM signal so as to prevent an arm short circuit.

That is, as shown in FIG. 7A, the motor M
In order to rotate the FET in the positive direction, when the ON / OFF of each FET is set, as shown in FIG. 8, the drive signal is delayed for FET1 by the dead time Δt with respect to the rising edge of the PWM signal. H is output, and the drive signal L is output at the falling edge of the PWM signal. Also, FE
With respect to T3, the drive signal L is output at the rising edge of the PWM signal, and the drive signal H is output at the time delayed by the dead time Δt with respect to the falling edge of the PWM signal.

Now, as shown in FIG. 8, the PWM signals are L and F.
When the PWM signal becomes H while the drive signal of ET1 is L and the drive signal of FET3 is H, the drive signal of FET3 becomes L first due to the rising edge of the PWM signal, and the current in the direction of arrow bb stops flowing. After that, at the time point delayed by the dead time .DELTA.t, the drive signal H is output to the FET1 and the current in the direction of arrow a starts to flow.

Next, at the falling edge of the PWM signal,
The drive signal of the FET1 becomes L, and the current in the direction of the arrow a stops flowing. After that, the drive signal H is output to the FET3 at a time point delayed by the dead time Δt. As a result, the two arms of the H bridge are simultaneously conducted and the arrow a
It is possible to avoid the inconvenience that the current in the direction and the current in the direction of the arrow bb flow at the same time and a short circuit occurs.

When rotating the motor M in the negative direction, the FET1 is turned off, the FET3 is turned on, and the FET2 is turned on.
Although the FET4 and the FET4 are driven in the same manner as the FET1 and the FET3, the operation thereof is the same as that described above, and therefore the description thereof is omitted here.

As described above, by providing the dead time, the arm short circuit can be prevented. However, when dead time is set as described above, that much FE
The time width for driving T1 (FET2) decreases, and the voltage actually applied to the motor decreases.

When the duty ratio does not reach 100%, the influence of this decrease in voltage is corrected by the current feedback control. That is, the duty ratio is redefined by the current feedback controller so that the current command value and the current value actually flowing through the motor match. However, when the duty ratio reaches 100%, the duty ratio cannot be corrected any further, so the actual
The maximum value of the voltage applied to the controller decreases.

The maximum value Vmax of the voltage applied to the motor
Is represented by the following formula.

Vmax = (cycle of PWM signal−Δt) · V
_BAT / PWM signal cycle Here, Δt represents the dead time, and V _BAT represents the battery voltage.

That is, even if the PWM signal corresponding to the steering assist force is calculated based on the steering torque and the vehicle speed and the motor control circuit is driven based on the calculated PWM signal,
As a result, a voltage smaller than the voltage corresponding to the time defined by the PWM signal can be applied to the motor.

In order to compensate for the decrease in the maximum value of the voltage applied to the motor due to the dead time, the time width required for the rise and fall of the PWM signal is reduced, that is, the rising edge and the falling edge of the PWM signal are sharpened. It is possible. However, in this case, radio noise is generated and the noise is mixed in the car radio. In order to suppress the generation of radio noise, 1 / of the cycle of the PWM signal
It is necessary to set a dead time of about 10,
The decrease in the motor applied voltage cannot be sufficiently compensated.

In addition, in order to compensate for the decrease in the maximum value of the motor applied voltage due to the dead time, it can be considered to set the resistance R between the terminals of the motor to a small value. However,
Reducing the inter-terminal resistance R of the motor means enlarging the motor, resulting in an increase in the inertia of the motor, which is not preferable as an electric power steering device. The present invention aims to solve the above problems.

[0018]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems and is calculated from a current command value calculated based on at least a steering torque signal generated in a steering shaft and a detected motor current value. In a control device for an electric power steering device that controls the output of a motor that applies a steering assist force to a steering mechanism based on a current control value, first and second two connected to an H-bridge type.
A motor control circuit in which two switching elements, a first and a second switching element, are respectively arranged in one arm, and a first control circuit for controlling the current control value by a pulse width modulation method. The first switching element of the first arm is controlled to change the motor applied voltage, and the second switching of the second arm of the motor control circuit is controlled by the sign of the current control value. A control means for controlling the element to control the direction of the motor current is provided, and the control means is the first gate.
The first switching element of the drive system is driven by being matched with the pulse of the control signal, and the second switching element of the first drive system is driven by the pulse having a narrow pulse width which is delayed from the pulse of the control signal. It is characterized by doing.

[0019]

The first switching element of the first arm, which is controlled by the control signal in which the current control value is controlled by the pulse width modulation method, is driven in accordance with the pulse of the control signal, and the first switching element is driven.
The second switching element of the arm is driven by a pulse having a narrow pulse width with a time delay from the pulse of the control signal, so that the voltage corresponding to the current control value can be applied to the motor, and , And the two arms of the H-bridge do not simultaneously conduct and short-circuit.

[0020]

Embodiments of the present invention will be described below.
FIG. 1 is a view for explaining the outline of the configuration of an electric power steering apparatus suitable for carrying out the present invention, in which a shaft 2 of a steering handle 1 has a reduction gear 4, a universal joint 5a,
5b, through a pinion rack mechanism 7, it is connected to a steering wheel 8 of a steering wheel. The shaft 2 is provided with a torque sensor 3 for detecting the steering torque of the steering wheel 1, and a motor 10 for assisting the steering force is connected to the shaft 2 via a clutch 9 and a reduction gear 4. There is.

An electronic control circuit 13 for controlling the power steering device is provided from the battery 14 to the ignition key-1.
Power is supplied via 1. The electronic control circuit 13 calculates a current command based on the steering torque detected by the torque sensor 3 and the vehicle speed detected by the vehicle speed sensor 12, and supplies a current to the motor 10 based on the calculated current command value. To control.

The clutch 9 is controlled by the electronic control circuit 13. The clutch 9 is connected in a normal operation state, and is disconnected when the electronic control circuit 13 determines that the power steering device has a malfunction and when the power is off.

FIG. 2 is a block diagram of the electronic control circuit 13. In this embodiment, the electronic control circuit 13 is mainly a CP.
Although it is composed of U, the function executed by the program inside the CPU is shown here. For example, the phase compensator 21 does not represent the phase compensator 21 as an independent hardware, but the phase compensator function executed by the CPU. It goes without saying that the electronic control circuit 13 may not be configured by a CPU, but these functional elements may be configured by independent hardware (electronic circuit).

The function and operation of the electronic control circuit 13 will be described below. The steering torque signal input from the torque sensor 3 is phase-compensated by the phase compensator 21 to enhance the stability of the steering system, and is input to the current command calculator 22. The vehicle speed detected by the vehicle speed sensor 12 is also input to the current command calculator 22.

The current command calculator 22 is a motor 1 according to a predetermined calculation formula based on the input torque signal and vehicle speed signal.
The current command value I, which is the control target value of the current supplied to 0, is determined.

The circuit composed of the comparator 23, the differential compensator 24, the proportional calculator 25, the integral calculator 26 and the adder 27 ensures that the actual motor current value i matches the current command value I. This is a circuit for performing feedback control.

The proportional calculator 25 outputs a proportional value proportional to the difference between the current command value I and the actual motor current value i. Further, the output signal of the proportional calculator 25 is integrated by the integral calculator 26 to improve the characteristics of the feedback system, and the proportional value of the integrated value of the difference is output.

In the differential compensator 24, the current command calculator 22
In order to increase the response speed of the motor current value i actually flowing to the motor with respect to the current command value I calculated in step 1, the differential value of the current command value I is output.

The differential value of the current command value I output from the differential compensator 24, the proportional value proportional to the difference between the current command value output from the proportional calculator 25 and the actual motor current value i, and the integral calculation. The integrated value output from the device 26 is added and calculated in the adder 27, and the current control value E as the calculation result is output to the motor drive circuit 41 as a motor drive signal.

Next, the motor control circuit using the H bridge according to the present invention and the setting of the dead time will be described.

FIG. 3 shows a motor drive circuit 4 according to the present invention.
FIG. 4 is a timing chart for explaining the timing of the operation, showing the first embodiment of the constitution of FIG. FIG.
In 30, a conversion unit 30 converts the current control value E input from the adder 27 into a PWM signal and a current direction signal,
H is a circuit for outputting signals for driving left arm FET1 and FET3 and right arm FET2 and FET4 of the bridge, and FET1 (FET2) has a duty ratio D of P.
The WM signal and the duty ratio (D) obtained by subtracting the dead time Δt from the duty ratio D to the FET3 (FET4).
The PWM signal of −Δt) is output (see FIG. 4).

Reference numerals 33a, 34a, 33b and 34b are gate circuits for driving FET1, FET3, FET2 and FET4, respectively. Further, 31 and 32 are dead time circuits for delaying the rising edge of the PWM signal of the duty ratio (D-.DELTA.t) output from the conversion unit 30 by a predetermined dead time .DELTA.t.

The operation of this circuit will be described below with reference to the circuit diagram of FIG. 3 and the timing chart of FIG. here,
It is assumed that the motor M is rotated in the forward direction. The conversion unit 30 converts the input current control value E to obtain a PWM signal and a current direction signal. Then, the gate circuits 33b and 34b are driven based on the current direction signal to set the FET2 to OFF and the FET4 to ON.

As shown in the timing chart of FIG.
The gate circuit 33a is driven by the rising edge of the PWM signal of the duty ratio D to output the drive signal H to the FET1, and the rising edge of the PWM signal of the duty ratio (D-Δt) is set to the dead time circuit 31. The gate circuit 34a is driven by the delay time .DELTA.t, and the gate circuit 34a is driven to output the drive signal L to the FET3 at the time delayed by the dead time .DELTA.t from the rising edge of the signal.

Next, the PWM of the duty ratio (D-Δt)
The gate circuit 34a is driven by the trailing edge of the signal to output the driving signal H to the FET3 (the operation of the dead time circuit 31 is prohibited at the trailing edge of the PWM signal), and the PWM with the duty ratio D The gate circuit 33a is driven by the trailing edge of the signal to output the drive signal L to the FET1.

As a result, the FET1 is driven by the PWM signal having the duty ratio D, and the driving time is the dead time Δt.
Therefore, the maximum voltage corresponding to the duty ratio D defined by the PWM signal calculated based on the steering torque and the vehicle speed can be applied to the motor, and the motor applied voltage due to the dead time can be changed. There is no decrease.

The same applies when the motor M is rotated in the negative direction. In this case, FET1 is turned off and FET3 is turned on.
This is achieved by setting N and driving FET2 and FET4 like the above-mentioned FET1 and FET3, respectively.

FIG. 5 shows a motor drive circuit 4 according to the present invention.
The 2nd Example of the structure of 1 is shown. Reference numeral 30 denotes a conversion unit which converts the current control value E input from the adder 27 into a PWM signal and a current direction signal, and FET1 and F of the left arm of the H-bridge.
ET3, a circuit for outputting a signal for driving FET2, FET4 of the right arm, FET1, FET2, FET3, F
A PWM signal of a duty ratio (D-Δt) obtained by subtracting the dead time Δt from the duty ratio D is output to ET4.

Further, 35 and 37 are dead time circuits for delaying the falling edge of the PWM signal of the duty ratio (D-Δt) output from the converter 30 by a predetermined dead time Δt, and 36 and 38 are This is a dead time circuit for delaying the rising edge of the PWM signal of the duty ratio (D-Δt) output from the conversion unit 30 by a predetermined dead time Δt and outputting it.

The operation of this circuit will be described below with reference to the circuit diagram of FIG. 5 and the timing chart of FIG. here,
It is assumed that the motor M is rotated in the forward direction. The conversion unit 30 converts the input current control value E to obtain a PWM signal and a current direction signal. Then, the gate circuits 33b and 34b are driven based on the current direction signal to set the FET2 to OFF and the FET4 to ON.

As shown in the timing chart of FIG.
The gate circuit 33a is driven by the rising edge of the PWM signal having the duty ratio (D-Δt) to output the drive signal H to the FET1.
To the output of the PWM signal (the operation of the dead time circuit 35 is prohibited at the rising edge of the PWM signal).
The time when the rising edge of the PWM signal of the Tay ratio (D-.DELTA.t) is processed by the dead time circuit 36 and delayed by the dead time .DELTA.t to be output, and the gate circuit 34a is driven to delay the rising edge of the PWM signal by the dead time .DELTA.t. The drive signal L is output to FET3 with.

Next, the PWM of the duty ratio (D-Δt)
The gate circuit 34a is driven by the trailing edge of the signal to output the driving signal H to the FET3 (the operation of the dead time circuit 36 is prohibited at the trailing edge of the PWM signal), and the duty ratio (D- .DELTA.t) the falling edge of the PWM signal is processed by the dead time circuit 35 and delayed by the dead time .DELTA.t for output, and the gate circuit 33a is driven to drive the signal at the time delayed by the dead time .DELTA.t from the falling edge of the PWM signal. Output L to FET1.

As a result, the FET1 is driven by the PWM signal having the duty ratio D, and the driving time is the dead time Δt.
Therefore, the maximum voltage corresponding to the duty ratio D defined by the PWM signal calculated based on the steering torque and the vehicle speed can be applied to the motor, and the motor applied voltage due to the dead time can be changed. There is no decrease.

The same applies when the motor M is rotated in the negative direction. In this case, FET1 is turned off and FET3 is turned on.
This is achieved by setting N and driving FET2 and FET4 like the above-mentioned FET1 and FET3, respectively.

If the dead time is set as described above when driving the FETs forming the H-bridge, the
In the region where the direction of the counter electromotive force generated in the capacitor and the direction of the current of the applied voltage are different, a non-continuous non-linear region of (0, -Δt / T) is generated at the maximum duty ratio as shown in FIG.
Here, T indicates the cycle of the PWM signal. If the steering wheel is returned to the neutral position by the self-aligning torque after turning the steering wheel, there is a possibility of passing through such a non-linear region, but Δt / T is sufficiently small, and There is no problem.

In the above embodiment, the PWM signal for driving the FET, the PWM signal with the duty ratio D, and
A PWM signal having a duty ratio (D-Δt) shorter than the duty ratio D by a dead time Δt is used. Such a pulse is given by the values of the duty ratio D and the dead time Δt. If possible, CPU that constitutes the control circuit
Can be freely formed.

[0047]

As described above, the control device for the electric power steering apparatus according to the present invention is controlled by the control signal obtained by modulating the current control value by the pulse width modulation method.
The first switching element of the arm is driven by the pulse of the control signal, and the second switching element of the first arm is driven by the pulse of the narrow pulse width which is delayed in time from the pulse of the control signal. Since it is driven, the maximum voltage corresponding to the duty ratio D of the pulse width modulation control signal corresponding to the current control value can be applied to the motor, and H
The two arms of the bridge do not conduct simultaneously and short circuit.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an outline of a configuration of an electric power steering device.

FIG. 2 is a block diagram of an electronic control circuit according to an embodiment of the present invention.

FIG. 3 is a circuit block diagram showing the configuration of the first embodiment of the motor drive circuit.

4 is a timing chart for explaining the drive timing of the switching element of the motor drive circuit shown in FIG.

FIG. 5 is a circuit block diagram showing the configuration of a second embodiment of the motor drive circuit.

6 is a timing chart for explaining the drive timing of the switching element of the motor drive circuit shown in FIG.

FIG. 7 is a circuit diagram illustrating the operation of a conventional motor drive circuit.

FIG. 8 is a timing chart for explaining the drive timing of the switching element of the conventional motor drive circuit.

FIG. 9 is a diagram illustrating a non-linear region in which the direction of the counter electromotive force generated by the motor and the direction of the current of the applied voltage are different.

[Explanation of symbols]

3 torque sensor 10 motor 11 ignition key 12 vehicle speed sensor 13 electronic control circuit 21 phase compensator 22 current command calculator 23 comparator 24 differential compensator 25 proportional calculator 26 integration calculator 27 adder 30 converter 33a, 33b , 34a, 34b Gate circuit 31, 32, 35, 36, 37, 38 Dead time circuit 41 Motor drive circuit 42 Motor current detection circuit

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hideaki Kawada 78 Toba-cho, Maebashi-shi, Gunma Nippon Seiko Co., Ltd.

Claims (1)

[Claims] 1. A steering assist force is applied to a steering mechanism based on at least a current command value calculated based on a steering torque signal generated in a steering shaft and a current control value calculated from a detected motor current value. In a control device for an electric power steering device that controls the output of a motor, two switching elements, a first and a second switching device, are connected to two first and second arms connected in an H-bridge type, respectively. The arranged motor control circuit and the first switching element of the first arm of the motor control circuit are controlled by a control signal in which the current control value is controlled by a pulse width modulation method. Control means for changing the applied voltage and controlling the second switching element of the second arm of the motor control circuit by the sign of the current control value to control the direction of the motor current. The control means drives the first switching element of the first arm so as to match the pulse of the control signal, and drives the second switching element of the first arm by the pulse of the control signal. A control device for an electric power steering apparatus, which is driven by a pulse having a narrow pulse width with more time delay.