JPH1173233A - Method and device for control over load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dynamically and speedily respond to variation in command by adapting the resistance value of the load. SOLUTION: A control circuit 160 determines a control signal U depending upon a desired current to be supplied to the load 100. With this control signal U, a switching means 120 is controlled. On the basis of the desired current and the resistance value of the load 100, a duty ratio setting circuit determines a main duty ratio. This duty ratio is applied to a switching means 120. The ohmic resistance of the load 100 depends upon temperature. The actual value of the current is compared with the command and on the basis of this value, a value representing the temperature dependency of the resistance of the load is determined to adapt the resistance value of the load so that the actual value reaches the command. Thus, the duty ratio is calculated by using the corrected resistance value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a load by controlling a clock at a predetermined duty ratio, the duty ratio being set depending on a resistance value of the load and a target current value.
The present invention relates to a method and a device for controlling a load.

[0002]

2. Description of the Related Art A method and a device for controlling a load are known from DE-OS 3529 742. This load is clocked and driven. This duty ratio is set depending on the resistance value of the load and the desired current target value. The current flowing through the load is measured and compared to a target value. Depending on the result of the comparison, the controller changes the duty ratio so that a desired current target value is obtained.

[0003] However, this approach causes problems when the demands on the system are inconsistent under clocked drives. The drive frequency needs to be as low as possible to avoid sticking friction conditions. At relatively low drive frequencies, the load maintains steady motion,
No adhesion friction occurs. However, a relatively low drive frequency also causes the current to fluctuate at a corresponding frequency. To prepare an appropriate actual value, this actual value is filtered by a low-pass filter. However, for relatively low clock frequencies, there is a large dead time due to this low-pass filter. This leads to the result that the actual value can only react very slowly to the changed target value. This inevitably results in a dynamically slow controller, which can only react to changes in the setpoint after a long delay.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and a device for controlling a driven load which is clocked at a relatively low clock frequency. To provide a quick controller.

[0005]

The above object is achieved according to the invention by adapting the resistance of the load.

According to the method of the present invention, the actual value can follow the change of the target value very quickly with respect to the current. This is possible even with a clocked drive at a small clock frequency.

[0007] The approach according to the invention provides a fast pilot control characteristic for a PI controller with fast pre-control. This is effective even with a small clock frequency and a relatively large dead time associated with the control section. Furthermore, with the method according to the invention, a uniform and periodic oscillation characteristic of the current control circuit occurs without depending on the current resistance of the load. Furthermore, there is no need for a compensation resistor for temperature compensation of the load. Thereby, additional output losses are also avoided.

[0008] Further advantageous embodiments and refinements of the invention are described in the dependent claims.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block circuit diagram of an apparatus according to the present invention. In this case, the load is connected on the one hand to the supply voltage source Ubat
, And on the other hand, to the ground via current measuring means 110 and switching means 120.

A differential amplifier 130 is connected to both terminals of the current measuring means 110, and an output signal thereof is sent to an AD converter 150 via a low-pass filter 141. This low pass filter is a resistor 14 in the illustrated embodiment.
0, and the resistor 140 is connected to the AD converter 150
And the output side of the differential amplifier 130. The resistor 140 is connected to the ground via the capacitor 145. The resistor 140 and the capacitor 145 form a low-pass filter.

The output signal of the AD converter 150 is supplied to a control circuit 160. The control circuit 160 applies a control signal U to the switching means 120.

The load 100 is, for example, a coil of a solenoid valve. In particular, in the case of a proportional operation type solenoid valve, the load 100
Is set to a predetermined value. The proportional operation type solenoid valve is set at a predetermined position depending on the current I flowing through the load 100.

Such a solenoid valve is used, for example, in an internal combustion engine. In this case, the solenoid valve is preferably used for pressure control. For example, in the case of a common rail system, the pressure in the accumulator is set to a predetermined value. For this, a proportional operating electromagnetic point is applied. Load 100
A predetermined flow rate of fuel flowing through the solenoid valve and a predetermined change in pressure are set depending on the current flowing through the solenoid valve.

However, the method according to the present invention is not limited to such an application example. The technique according to the invention is applicable to all loads of the type whose current is set to a predetermined value.

The switching means 120 is preferably embodied as a transistor, for example a field-effect transistor. The current measuring means 110 is advantageously configured as an ohmic resistor. The arrangement of the current measuring means 110 and the switching means 120 in FIG. 1 is selected as one example. The current measuring means 110 may be connected to ground or to a supply voltage source Ubat.

Next, the operation of this device will be described based on various signals shown in FIG. Depending on the desired current to flow through the load 100, the control circuit 160
Is determined. This control signal causes the switching means 12
0 is controlled. This signal is shown in FIG.
In this case, the frequency or period T is constant and is set depending on the operating parameters. The cycle period T is selected as follows. That is, the solenoid valve is selected so as not to cause the adhesion friction state. This state of sticking friction is avoided by constantly moving the valve needle. The frequency or period T is set accordingly.

Usually, this load is an inductive load. This means that when the current is turned on and the voltage U takes a high value, the current I
Means to rise. When switched off,
The current I drops again.

The current is set based on the inductive inductance of the load. This is shown in FIG. 2b. This signal is provided by the differential amplifier 130. However, this signal is not suitable for direct subsequent processing. Therefore, in the case of digital evaluation, an instantaneous value is usually sampled. This value changes very strongly depending on the sampling time. This signal is filtered using a low pass filter 141 to enable digital evaluation. From the output side of this low-pass filter, the signal IF
Is sent. This signal is shown in FIG. 2c.

Other suitable filters may be used in place of the illustrated RC filter. The problem here is that a long dead time occurs during the actual value detection based on the filtering. The change of the current value leads to the change of the signal IF only after a relatively long dead time.
However, this dead time is also desired on the one hand. This is because short-term current fluctuations as shown in FIG. 2b are compensated. However, this leads to a considerable dead time of the actual value detection when changing the target value.

The average current value IF substantially depends on the load resistance value R and the drive control duty ratio TV.
This duty ratio is determined by a ratio E / T between a period E during which the switching means flows a current and a period T.

The filtered current value IF is given by AD
It is supplied to the control circuit 160 via the converter. The control circuit 160 determines the control signal U based on the signal IF.

This 160 is shown in detail in FIG. In this case, the components already shown in FIG. 1 have the same reference numerals. Duty ratio setting circuit 300
Applies the control signal U to the switching means 120.

The duty ratio setting circuit 300 processes the output signal R at the node 310. This connection point 310
And the first input of the junction 320
An output signal of the O-setting circuit 330 is supplied. Junction 3
The second input of 10 is supplied with the output signal of node 320. An output signal K of the limiter 340 is supplied to a second input side of the connection point 320. This limiter 34
0 is supplied with a signal from the integrator 350. This integrator 3
50 processes the output signal of node 370. An output signal of the AD converter 150 is applied to a first input side of the connection point 370. The output signal ISF of the target value filter 380 is applied to a second input side of the connection point 370. A target value setting circuit 3 is provided on the input side of the target value filter 380.
60 output signals IS are provided. The target value setting circuit 360 also supplies the target value IS to the RO-setting circuit 330.

In the configuration of the present invention, the target value filter 380 can be omitted in some cases.

The control sections are separated by broken lines. Load 1
00 and the low pass filter 141 are shown as PT1 equipment.

This device operates as follows. The main duty ratio is determined by the duty ratio setting circuit 300 based on the desired current value IS and the resistance value R of the load 100. This duty ratio is applied to the switching means 120. Ohmic resistance R (T) of load 100
Depends on the temperature T. In this case, the relationship between the resistance R and the temperature T is expressed by the following equation.

R (T) = R (TO) * (1 + a * (TT)
O)) = RO * (1 + K) The value K is a value representing the temperature dependence of the resistance R of the load. The value RO is a resistance value of the load at a predetermined temperature TO. In this case, a normal value of about 20 ° generated during normal operation is used.

The duty ratio U is determined based on the resistance value RO and the coefficient K generated under the normal temperature TO. Under this normal temperature, the coefficient K assumes a value of zero. Under the corresponding control of the switching means 120, an average current IF results.

The actual value II so determined for the current is compared at a junction 370 with a target value IS. The integrator 350 determines the value K based on this value.
This is performed, for example, as follows. If the actual value II is greater than the target value, the value K is increased by a predetermined value. This raising is performed until the actual value II becomes equal to the target value IS. If the actual value II is smaller than the target value, the value K is reduced by a predetermined value. This reduction is also performed until the actual value II becomes equal to the target value IS. The value zero is usually applied as the initial value for the integrator.

Subsequently, in the limiter 340, the value K is limited to a physically valid value. This value K is then multiplied by the value RO at the node 320. This result is then added to the value RO at node 310. These connection points 310 and 320 simulate the above equation.

The duty ratio is calculated using the value R thus corrected. The value K obtained as described above
Is always used for calculating the resistance R or calculating the control signal.

The current control consists of a pre-control of a load resistance value using a normal resistance value RO and a temperature-dependent correction coefficient K. When a change in the target value occurs, this change is directly linked to a change in the duty ratio based on the pre-control, and consequently to a change in the actual value II.

Changing the resistance of the load is usually very slow. This change is compensated for by adapting the coefficient K. The current magnitude of this coefficient K is the control deviation (II−
IS).

Regarding the integration time constant of the integrator 350, the adaptation speed can be set so as to be suitable for the time constant of the RC filter 141.

The calculation of the duty ratio is performed in a fixed time pattern. So this calculation is for example 10m
This is performed every s. A large time constant occupies the actual value detection.

The adjustment member, load 100, responds very quickly to the changed control signal. This means that the control section occupies only a very small time constant.

Due to the very small control frequency, which is preferably in the region of about 200 Hz, a large time constant results when filtering the actual values. This actual value is therefore obtained with a dead time.

The control of such a system with a dynamically good adjusting element for the detection of actual values, usually with a relatively long dead time, is very problematic. This means that the dead time of the filtering determines the control time of the entire control circuit.

The method according to the present invention has a given pre-control value for setting the duty ratio depending on the pre-control value RO and the desired current value for the resistor, and a special configuration of adapting the resistor using an integrator. Under the above condition, a very quick and accurate setting of the actual value current when the target current is changed can be achieved.
This quick response to the target value is ensured by the pre-control of the resistance value, and the control accuracy is ensured by the integrator 350. This integrator sets a correction factor K for the required value.

[Brief description of the drawings]

FIG. 1 is a schematic block circuit diagram of an apparatus according to the present invention.

FIGS. 2a, 2b and 2c are diagrams in which various signals are plotted over time.

FIG. 3 is a diagram showing the control of the load in detail.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 load 110 current measuring means 120 switching means 130 differential amplifier 140 resistor 141 low-pass filter 150 A / D converter 160 control circuit

Claims (8)

[Claims] 1. A method for controlling a load, wherein the load is controlled by a clock with a predetermined duty ratio, and the duty ratio is set depending on a resistance value of the load and a current target value. A method for controlling a load, characterized in that the resistance of the load is adapted. 2. The method for controlling a load according to claim 1, wherein the adaptation of the resistance of the load is based on a control deviation between a current actual value and a current target value. 3. The method for controlling a load according to claim 1, wherein the resistance value can be set based on a pre-control value and a correction coefficient. 4. The method for controlling a load according to claim 3, wherein said correction factor is configurable based on a comparison between an actual current value and a current target value. 5. The method for controlling a load according to claim 3, wherein the correction coefficient is settable by an integrator. 6. The method for controlling a load according to claim 3, wherein the calculation of the resistance value of the load is multiplied by a correction coefficient and a pre-control value, and the result is added to the pre-control value. . 7. The method for controlling a load according to claim 1, wherein the actual current value is filtered using a low-pass filter. 8. An apparatus for controlling a load, wherein a load is driven by being clock-controlled at a predetermined duty ratio and the duty ratio is set by control depending on a resistance value of the load and a current target value. Apparatus for controlling the load, characterized in that means are provided for adapting the resistance of the load.