DE102007057502A1 - Control device and method for controlling a mean current through an inductive load - Google Patents

Abstract

The invention relates to a control device for regulating a mean current through an inductive load (L, R1), wherein the load by a switch (T1) with a voltage source (U) connectable and the average current through the duty cycle is adjustable, wherein the duty cycle for the control of the switch from the sum of a first value (pv) and a second Wet (pr) is formed, wherein the first value from a feedforward control (VS) can be determined and the second value of the difference (d) between the setpoint and Actual value of the average current by means of a control circuit (CIC) can be determined. Furthermore, the invention relates to a corresponding control method.

Description

The The invention relates to a control device for regulating a mean current through an inductive load. Manipulated variable is the supply voltage, which is pulsed by an actuator. Measured variable is the instantaneous current through the load at a defined time. Such control devices are used, for example, when the position of a solenoid valve is to be adjusted continuously between two extreme values.

Out the prior art is known, the average power of an electric Control consumer by changing the supply voltage to the consumer is pulsed. By adjusting the duty cycle between switch-on and turn off time can thus provide power consumption stepless between 0 and 100% can be set. A disadvantage of this type of control is that with an interference-prone System of actually flowing through the consumer Electricity is unknown. As a disturbance comes For example, a fluctuating supply voltage into consideration. You can continue the electrical parameters of the consumer in dependence from external influences, such as Temperature and age. this leads to that the absolute power consumed by the consumer is not is known.

outgoing From this prior art, the invention is based on the object to provide a control device and a control method in which the one flowing through the load Electricity independent of disturbances a setpoint can be controlled.

The The object is achieved by a control device for controlling a mean current through a Inductive load, in which the load through a switch with a Voltage source connectable and the average current through the duty cycle adjustable is, where the duty cycle for controlling the switch from the sum of a first value and a second value, wherein the first value consists of a Precontrol is determinable and the second value from the difference between desired and actual value of the average current by means of a Control circuit can be determined.

Farther is the solution the task in a method for controlling a mean current by a load in which the load is connected through a switch with a Voltage source is connectable and the average current through the Duty cycle set is, where the duty cycle for driving the switch from the sum of a first and a second value is formed, wherein the first value of a Precontrol is determined and the second value from the difference between desired and actual value of the average current by means of a Control circuit is determined.

According to the invention was realized that a fast and reliable control of a current through an electrical consumer can be realized if the duty cycle first by a pilot control for set a desired current setpoint value is and only remaining deviations of the actual value from the target value the current through a regulator, which a correction value of duty cycle provides, be corrected. In this way, disturbances, such as fluctuating supply voltages, changing temperatures and aging be balanced with the load. The control device according to the invention and the associated Methods are particularly suitable for inductive loads, in which Current and voltage do not run in phase in every operating state.

If the controlled system in the static case shows approximately proportional behavior, such as an inductive load, the pilot control can be designed in a particularly simple manner as a P-element. The proportionality factor k _{v of} the P element is the reciprocal of the static system gain: P v = k v × i Should

Provided the exact characteristic of the load is unknown or difficult to determine is, for example, because it depends on many parameters like Tension, temperature or aging, remains after adjustment of a duty cycle by the feedforward control a deviation between the measured actual value of the current and the desired reference value. According to the invention was recognized that to regulate these deviations a controller with sluggish dynamics is sufficient. Particularly preferred is a controller with integral Characteristic (I-controller) used.

The current-actual value can be measured in a manner known per se by the magnetic field of the supply line or a measuring resistor and a differential amplifier. Since the controller only the difference between the setpoint and actual value is to be supplied as a target variable, this difference is formed with an analog or digital subtractor. The controller itself can be realized either as analog or digital circuit. An analog circuit may for example comprise a plurality of operational amplifiers. A digital realization of the control circuit can be done by means of a microprocessor or a microcontroller, which performs the corresponding task in the form of software. The feedforward control can also be executed as analog or digital circuit. The first value of the manipulated variable can be calculated in the feedforward control or read from a table. This functionality can be realized, for example, with a numerical map matrix or a neural network.

to Avoiding overshoots with nominal value changes has the regulator according to the invention in a preferred embodiment a delay element on, which is before the formation of the difference between the setpoint and the actual value delays the target value. This avoids that when changing the setpoint value duty cycle and thus the load fed Power simultaneously from the pilot control and the control circuit is changed. Since the control circuit of the setpoint value only delayed this only controls the deviations that remain, after the feedforward has set the new target value for the duty cycle.

In a further embodiment According to the invention, a device may be provided to the first Value from the feedforward to adjust if the second value from the Control circuit exceeds or falls below predefinable limit values. Thereby can be prevented that the control device according to the invention in undefined operating conditions device, if the control circuit correction values below 0% and above 100% for the duty cycle outputs. To best exploit the dynamics of the control circuit, can about that Be provided, which determined by the control circuit Correction values to smaller values than the theoretically possible Limit maximum values 0% and 100%. This ensures that big and longer term Deviations can be corrected by the pilot control and the control device only have to correct small deviations. The control circuit can then optimally matched to the intended control range in terms of dynamics become.

Around the values determined from the feedforward control as best as possible to the actual Adjust the characteristic of the load, the control device can continue have a device which from the difference of the desired value and by a delay element delayed Setpoint determines a further correction value for the duty cycle. exceeds this difference between the current and last target value is a predefinable Threshold, the input of the control circuit is a Gegensteueranteil switched. This measure reduces undershoots also in the areas of the characteristic curve, in which the second derivative of the characteristic is> 0. This will ensure that a desired target value of the stream in the shortest time potential Time is set.

following the invention is based on Ausführungsbespielen without limitation of General inventive concept will be explained in more detail. The embodiments are shown in the accompanying figures.

1 shows a block diagram of the control device according to the invention.

2 shows an adaptive controller with input delay to avoid overshoots in nominal value adjustments.

3 shows the controller after 2 , which has been supplemented by a counter-control to avoid overshoot or undershoot in desired value adjustments.

1 shows an inductive load L. A real inductive load always has an ohmic resistance, which in 1 symbolized by R1. An inductive load generates a voltage pulse of opposite polarity when interrupting the current flowing in the load. In order to avoid that further circuit parts and consumers in the electrical system are damaged by this voltage pulse, located near the inductive load, a quenching diode D1. This serves to short-circuit the voltage peak produced when the voltage at the inductive load L is switched off.

to Measurement of the inductance L flowing Stromes serves the measuring resistor R2. The voltage drop across R2 is after Ohm's Law directly proportional to the flowing stream. To measure the Voltage drop serves the differential amplifier DA. For stepless adjustment of the duty cycle and thus the average current at the load L is the transistor T1, which switches the supply voltage U on or off. By changing the duty cycle from 0% to 100%, the power converted in the load L can be steplessly adjusted between 0 and a maximum value.

The Switching the load with a single bipolar transistor T1 is in this case merely to be understood as a symbolic representation. The expert is self-evident familiar, that for switching other components such as thyristors or MOS-FET or a plurality of these components can be used.

The control device according to 1 is a setpoint I _set for the current. This setpoint is fed to a pilot control device VS. Based on the characteristic curve of the load L stored in the pilot control device VS, the pilot control device calculates a duty cycle with which the desired target current can probably be achieved. This duty cycle p _v is the switch T1 fed. In the simplest case, the precontrol VS proceeds from a linear characteristic with the proportionality factor k _v .

During operation of the load L with the clock ratio P _v , a mean current in the supply line of the load L sets, which can be measured by means of the measuring resistor R2 and the differential amplifier DA. This measured value I _ist is supplied to a subtractor, which forms the difference d between the nominal value and the actual value of the current. The deviation d is supplied to the control circuit CIC. The control circuit CIC calculates therefrom a correction value p _r for the duty cycle p _v . The correction value p _r is added to the originally specified value _v p, where p _{r is} the result of adding p can also be smaller than the initial value be _v with a negative correction value. This corrected value of the duty cycle is in turn supplied to the switch T1. As a result of continuous regulation, the desired setpoint I _{setpoint is applied} to the load L on average.

Preferably, the control circuit CIC comprises an I-controller. Thus, the output value p _{r is determined} from a gain factor k _i and the integral of the difference between the set value and the actual value of the current: P r = k i ∫ (i Should - i is ) dt

Preferably, but not necessarily, the implementation of the control concept according to the invention takes place in a digital computer. This allows the implementation of the integration by means of a summer and a delay element. In this case, the correction value p _r in the (n + 1) -th step results from the correction value p _r and the deviation d of the n-th step from the formula p r (n + 1) = p r (n) + k i × d (n)

2 shows a block diagram of an alternative embodiment of the control device according to the invention. The inductive load L, R1 with erase diode D1 and the power supply U and the switch T1 are combined in one element, which in 2 The measuring device DA at the track is used to determine the actual value of the current I _ist 1 the difference d of the actual value and the desired value is determined. However, the setpoint value in the delay element DL is delayed. In the case of a digital realization of the controller concept, therefore, the difference d in the nth calculation step applies d (n) = I Should (n - 1) - I is (N)

The delay element DL causes that only target value deviations of the distance are always corrected by the control circuit CIC, which does not go back to a change in the setpoint itself. For this purpose, the desired value is passed without delay to the pilot control device VS, which calculates a desired value p _{v of} the duty cycle therefrom by means of the proportionality factor k _v . This target value p _v acts on the track without delay. Only when this has adjusted to the new target value, this new target value is compared with the measured actual value and remaining deviations are corrected. For this purpose, the clock frequency of a digital implementation of the circuit according to the invention is preferably smaller than the time constant of the path.

Furthermore, the I-controller of the control circuit CIC comprises a limiter LI. The limiter prevents the controller from reaching an undefined operating state when the maximum activation of 0% or 100% is reached. In addition, the limiter LI can be used to adjust the gain factor k _{v of} the pilot control device VS. For this predetermined thresholds are p _r ^min _and set p _r ^max within which the control circuit CIC is to determine a correction value p _r. The limit values p _r ^min _and p _r ^max can be adapted to the controller used and can also be larger or smaller than 0% and 100%. When the respective maximum or minimum value is reached, a change is made by adjusting the proportionality factor k _v Setpoint value p _{v provided} by the precontrol. This reduces the remaining deviations, which must be corrected by the control circuit CIC.

In order to avoid oscillation of the control device in the adaptation of the proportionality factor k _{v of} the pilot control device, the adaptation of the proportionality factor is preferably carried out stepwise. Furthermore, the adaptation can be suspended when the pilot control device VS has reached a ^maximum or minimum control value p _v ^max or p _v ^min . This correlates to an upper and a lower limit k _v ^max and k _v ^{min of} the amplification factor k _{v of} the pilot control device.

For stable operation of the controller, the free parameters k _i , k _v , p _r ^min and p _r ^{max must be} adapted to the behavior of the respective load L and the sampling time T _{A of} the digital controller. The sampling time T _A is for example about 1 ms to about 500 ms. In order to avoid oscillation of the control circuit CIC, k _i must be smaller than the reciprocal of the maximum gain k _v ^{max of} the pilot control device:

To allow more stable operation, the proportionality factor of the I-controller upstream reinforcing member are also selected to be smaller than this maximum value.

The parameters p _r ^min and p _r ^max are selected such that the following applies to each operating state with respect to the static characteristic curve: I = k v (p + Δp); Δp ε ⌊p min r , p Max r ⌋

The factor k _v depends on the operating state, but not on p. This means that each operating point can be approached on the characteristic curve of the pilot control VS in cooperation with the control device CIC.

An adaptation of the characteristic curve of the precontrol by adaptation of the gain k _v is ideally carried out whenever the characteristic curve of the route has changed due to environmental influences and / or due to aging. This is recognized by the fact that the limiting element LI of the control circuit limits the output value p _{r of} the control circuit. A particularly advantageous adaptation of the characteristic of the precontrol arises when this is carried out as slowly as possible in order to prevent a reaction on the control circuit CIC. For example, the adjustment may be about 0.1% to about 5% per adaptation step.

3 shows the control device according to the invention according to 2 , wherein a further device GS is present, which supplies a counter control component to the I-controller. The device GS is the target value supplied without delay and after the delay by the delay element DL. The counter-control forms the difference. If the set value remains unchanged, the output value of the counter control is also 0.

If the difference i _{d of} the delayed and the instantaneous setpoint value is smaller than a predefinable threshold value, a stable change of the setpoint value is possible even without intervention of the device GS. This therefore does not output a correction value d _add .

If the difference i _{d of} the decelerated and the instantaneous setpoint value is greater than a predefinable limit, the counter-control GS generates a correction value d _add for the duty cycle, with which the controlled system is controlled. For the correction signal d _add generated in the counter-control GS, the following law applies in the case of a digital realization of the control device according to the invention: i d (n) = I Should (n - 1) - I Should (N) d add (n) = k add × (i d (n) - | i L |)

The free parameters of the device GS, k _add and i _L , are called loose parameters. The expert will adjust the size of these parameters individually to the characteristic curve of the load L to be controlled and the rate of change of the setpoint value ^I setpoint. For example:

The gain k _add is preferably smaller than the gain k _i of the gain element connected upstream of the I regulator. In particular, the expert will adjust the gain as a function of the characteristic of the load L to be controlled.

The device GS therefore checks whether the difference between the current and the last setpoint is above a predefinable threshold. In this case, a counter control component d _{add is} supplied to the input of the integrator of the I controller. As a result, the correction value p _r output from the control circuit CIC is reduced. The adaptation to the new target value takes place more slowly, but overshoots or undershoots are reduced or even completely avoided.

The skilled person is of course familiar that the in 3 illustrated realization of the device GS has only exemplary character. When adjusting the gain factor k _add the correction value d can be added before the _add also reinforcing member k _i to the difference signal d, when the gain factors of other circuit parts are adjusted accordingly.

Claims (10)

Regulating device for regulating a mean current through a load (L, R1), in which the load is connectable by a switch (T1) to a voltage source (U) and the average current through the duty cycle is adjustable, the duty cycle for driving the switch off the sum of a first value (p _v ) and a second value (p _r ) is formed, wherein the first value from a feedforward control (VS) can be determined and the second value from the difference (d) between the setpoint and actual value the average current by means of a control circuit (CIC) can be determined. Control device according to claim 1, characterized the control circuit (CIC) comprises an integrator. Control device according to one of Claims 1 or 2, characterized in that a device is provided for adapting the first value (p _v ) from the precontrol (VS) if the second value (p _r ) can be predetermined by the control circuit (CIC) Limit values (p _r ^min , p _r ^max ) are exceeded or fallen below. Control device according to one of claims 1 to 3, characterized in that a delay element is provided, before the formation of the difference (d) between the setpoint and the actual value to delay the target value. Control device according to claim 4, characterized in that a device is provided which determines from the difference (i _d ) of the desired value and the delayed desired value, a further correction value (d _add ) for the duty cycle. Method for regulating a mean current through a load (L, R1), in which the load is connectable to a voltage source (U) by a switch (T1) and the average current is set by the duty cycle, the duty cycle for driving the switch is formed from the sum of a first value (p _v ) and a second value (p _r ), wherein the first value (p _v ) is determined from a precontrol (VS) and the second value (p _r ) is determined from the difference (p d) between nominal and actual value of the average current is determined by means of a control circuit (CIC). A method according to claim 6, characterized in that the first value (p _v ) in the feedforward control (VS) is determined by a proportional element with the gain k _v . A method according to claim 7, characterized in that the second value (p _r ) in the control circuit (CIC) is determined by means of an I-controller and an upstream gain element, wherein for the gain factor k _{i of} the reinforcing member: k _i <1 / kg Method according to one of claims 6 to 8, characterized that before the formation of the difference (d) between the setpoint and the actual value the setpoint value is delayed becomes. A method according to claim 9, characterized in that from the difference (i _d ) of the setpoint value I _soll and the delayed setpoint value I _{soll, d,} a further correction value d _add for the duty cycle is determined.