FR3004605A1 - METHOD AND DEVICE FOR CONTROLLING POWER OR VOLTAGE CONTROL FOR THE POWER SUPPLY OF AN ELECTRICAL CONSUMER - Google Patents

Abstract

A method of controlling the power or supply voltage of an electrical consumer (10) using a power stage (12). The power or voltage control is done by pulse width modulation (PWM / PWM) with an adjustable duty cycle. In a measurement phase and under different operating conditions described by at least two operating parameters of the power stage (12), the actual voltage measured across the consumer is determined each time, and the duty cycle of the power supply is modified. pulse width modulation so that the measured effective voltage corresponds to the predefined effective target voltage. The cyclic ratio thus determined according to the operating parameters is stored in memory. In a phase of application of the operating conditions present, a corrected duty cycle is calculated from the cyclic ratios recorded in memory and to control the power or the voltage.

Description

Field of the Invention The present invention relates to a method of controlling the power or supply voltage of an electrical consumer using a power stage, the power or voltage control. pulse width modulation (PWM / PWM) with an adjustable duty cycle. The invention also relates to a power control device or voltage control device for supplying an electrical consumer with a power stage, the power control or the voltage control being effected by pulse width modulation ( PWM / MLI) with an adjustable duty cycle, and the power stage having a control unit. STATE OF THE ART In order to adjust the power, the effective voltage or the actual current, it is known to control an electrical consumer by pulse width modulation (PWM / PWM). For this, for example, a constant supply voltage of an electrical consumer is cut according to a duty cycle which ensures the breaking and feeding. The ratio of the connection time and the cut-off time makes it possible to regulate the electric power supplied to the user, the effective tension and the effective intensity. The switching operation is effected by a power stage which is appropriately controlled. The duty cycle is predefined in a controlled or set way.

In order to adjust the duty cycle, in the case of controlled systems, it is assumed that the electronic components used and therefore the curve of the voltage supplying the consumer as a function of time (chronogram) are ideal. The deviations from this ideal behavior, for example because of the limited slope of the signal flanks or of the delay, in particular of the power stage, have a direct effect on the power supplied to the consumer, that is to say the effective intensity and the effective tension. Deviations may arise from different responses of electronic components due to their tolerance. The slope of the sidewalls may furthermore be limited by requirements concerning electromagnetic compatibility (EMV compatibility). The deviations from this ideal behavior are particularly pronounced for the small cyclic ratios of the pulse width modulation. For example, the small duty cycle can result from the fact that the electrical consumers operate with different supply voltages. DE 10 2010 001004 A1 describes a method for controlling actuators powered by an electrical network with different operating voltages or variations in the network voltage as a function of time. Under these conditions it is envisaged to control the actuator (s) with control signals with different pulse width modulation by independently adjusting the pulse width and their period in the control signals by adapting them to the voltage functions. present provided by the on-board network. The exhaust gas sensors, for example the lambda sensors currently fitted to the heat engines for monitoring and regulating the composition of the exhaust gas, often have an electric heater for setting a predetermined operating temperature of the exhaust gas sensor. exhaust gas which is for example in a range of 800 ° C. The heating power is regulated by the pulse width modulation applied for example to a supply voltage of 12V. Applying the lambda probe in a system powered at 24V results in very small duty cycles. Deviations from the ideal behavior of pulse width modulation are compensated in controlled mode from a certain set point temperature by a temperature controller. In the controlled mode, for example, when a measured value of the exhaust gas sensor is not available for regulation, the deviations described with respect to the ideal behavior can lead to excessive temperature differences with high risk. of failure due to faulty operation.

According to another mode of operation, that is to say the protective heating mode, the lambda probe is set in heating phase at a low setpoint temperature, of the order of 100 ° C-200 ° C. The protective heater is used to evaporate the water from the lambda probe or the exhaust pipe, which minimizes the risk of rupture of the lambda probe sensor element ceramic due to high thermomechanical stress. during the subsequent heating phase with high voltage for efficient heating. To adjust the preset setpoint temperature with sufficient accuracy, the actual voltage applied to the heating device must be set. For this, the duty cycle of the voltage applied to the heating device is calculated from the value of the measured supply voltage and the desired effective voltage across the heating resistor in the event of a recurring voltage. ideal tangular, in the control unit. For the protective heating, this results in very small cyclic ratios of the order of 0.5-2 °) / 0. The deviations of the voltage curve from the ideal rectangular shape of the curve result in deviations between the setpoint value and the actual value of the actual voltage applied to the heater. For small, necessary duty cycles, this results in unacceptable level differences between the temperature of the lambda probe and the set temperature. Nevertheless, to allow reduced cyclical ratios in the controlled mode, fast, narrow tolerance (in the direction of high slope edges and small delay times) power stages for the control can be used. But this results in a significant EMV electromagnetic wave emission, unauthorized and a significant component cost. Another possibility is to use a DC / DC converter instead of pulse width modulation but resulting in high manufacturing costs. As another disadvantage, there is the large size of the converter (transformer) continuous / continuous and the high release of heat.

The measurement and adjustment of an appropriate average value of intensity or effective value require a large implementation in circuit and congestion and therefore a high cost. OBJECT OF THE INVENTION The object of the present invention is to provide a method for precise and economical control of the voltage or power of an electrical consumer by pulse width modulation even for small duty cycles. The invention also aims to develop a device implementing such a method. DESCRIPTION OF THE INVENTION AND ADVANTAGES OF THE INVENTION To this end, the object of the invention is a method for controlling the power or the supply voltage of an electrical consumer of the type defined above, characterized in that in a phase of under different operating conditions described by at least two operating parameters of the power stage, the actual voltage measured across the consumer is determined each time, the duty cycle of the pulse width modulation is modified. in order for the measured effective voltage to correspond to the predefined effective nominal voltage, the cyclic ratio thus determined according to the operating parameters is stored in memory, and in a phase of application of the operating conditions present, a cyclic ratio corrected to from the cyclic reports stored in memory and to control the power or voltage.

The actual voltage measured during the measurement phase is determined by appropriate resolution as a function of time to determine the voltage curve of the entire branch pulse and the resulting measured effective voltage across the consumer. For each power stage, the measurement can be done separately or advantageously for the predefined part of the power stage of the manufacturing load. During the application phase in regular mode, it is not necessary to measure the voltage across the consumer. Since the corrected duty cycle is calculated from the cyclic duty ratios in the memory, interpolation in a large data field is avoided so that the corrected duty cycle can be obtained quickly and with a reduced implementation of circuit means. The corrected duty cycle takes into account the deviations of the effective voltage curve from the ideal rectangular curve, taking into account the influence of the operating conditions present, which makes it possible to precisely adjust a predefined effective voltage even for small cyclical relationships. According to a particularly preferred development of the invention, in order to calculate the corrected duty cycle, the relation between the determined cyclic ratios dependent on the different operating parameters by adapted mathematical functions with appropriate coefficients is described at least by approximation. The corresponding functions and coefficients are stored in the memory and in the application phase, for the current operating parameters, the cyclic ratio corrected with the functions in memory and the coefficients in memory is defined. To calculate the corrected duty cycle, it suffices to memorize only the functions and the coefficients, which corresponds to a very small memory location. Calculation by mathematical functions makes it possible to very quickly determine the duty cycle according to the current operating conditions under which the power stage operates. The mathematical functions can be obtained from the determined relations between the duty cycle and the different operating conditions influencing the voltage curve, for example by corresponding adaptation functions or regression analyzes.

In order to take into account two operating parameters for the correction of the duty cycle, it is planned to calculate the corrected duty cycle by describing in at least approximate manner the relation of the determined cyclic ratios of a first operating parameter for different values of a second operating parameter using a first set comprising a first mathematical function and the corresponding first coefficients and describing in at least approximate manner the relation between first coefficients and second operating parameters, using a second set, comprising a second mathematical function and the corresponding second coefficients, storing the second coefficients and the mathematical functions, and in an application phase for the second current operating parameter, with the second memorized coefficients and the second mathematical function, we determine the first c coefficients corresponding to the second current operating parameter and in that with these first coefficients and the first mathematical function, the corrected duty cycle for the first current operating parameters is calculated. It is then sufficient to memorize the first and the second function as well as the second coefficients. The condition is that the dependence between the duty cycles determined as a function of the first operating parameter for different values of the second operating parameter is obtained by approximation by applying a common function with first respectively adapted coefficients. Correspondingly, a second mathematical function is sought with which, by adaptation of the second coefficients, the relationship between the first coefficients and the second operating parameter is described. The first set comprising the first mathematical function is thus of the first mathematical function and the first respectively adapted coefficients. The second set comprising the second mathematical function is the second mathematical function and the second respectively adapted coefficients. The cyclic ratio thus corrected takes into account the influence of the first and the second operating parameter on the resulting voltage curve.

It is possible to correct the influence of any number of operating parameters on the duty cycle in that for each other operating parameter, another set including another function and the other associated coefficients is defined. According to another characteristic, the relationship of the coefficients determined for an operating parameter taken into account previously of the different values of another operating parameter by another set comprising another mathematical function and the other coefficients is described at least by approximation. corresponding, we memorize the other coefficients and the other mathematical function and in a phase of application of the current value of the other operating parameter, we define the coefficients determined for the operating parameter previously taken into account. The actual voltage across the consumer is determined in a simple manner in that in the measuring phase the voltage curve across the consumer is recorded numerically and from the voltage curve the actual voltage measured at the terminals is determined. consumer terminals. The capture can be done using a fast analog / digital converter, to have the image of the curve of the sidewall that deviates from the rectangular shape. Since the voltage curve is determined only during the measuring phase, it is not necessary for the control device to have an analog / digital converter. The voltage curve can be determined at a measuring location suitably equipped for the respective power stages. The deviations from the ideal rectangular curve of the voltage produced by the limited slope of the flanks or because of the delay times have a significant effect on the effective voltage in the case of small duty cycles. For this reason, it is planned to make a correction of the duty cycle for a ratio of less than 5 ° / 0, in particular a duty ratio of less than 2 °) / 0. In the case of large cyclic ratios, no correction is made. Thus, functions and coefficients will only be determined for small cyclic ratios.

The parameters which dominate the switching behavior of the power stage such as, for example, the slope of the sidewalls or the delay times are generally strongly influenced by the supply voltage and the temperature of the power stage. In addition, the switching behavior can be influenced by the effects of aging. Therefore, it is intended to take into account as operating parameters at least the temperature of the power stage and / or the level of its supply voltage and / or the aging of the power stage. The dependence of the determined duty cycle or coefficients of the characteristic operating parameters, in particular the supply voltage and the temperature, follows the second degree polynomial plot. Therefore, second degree polynomials are used as functions to describe the relationship between the determined duty cycle and the operating parameters and / or to describe the dependence of the coefficients with respect to the operating parameters. The relationship between the determined duty cycle and the coefficients can depend on the predefined effective target voltage. If the user operates at different effective voltages, it is intended to determine coefficients and / or respective functions for the different effective voltages. The invention also relates to a device for controlling the power or the supply voltage of an electrical consumer using a power stage as described above, characterized in that the unit The controller has a memory for storing functions and corresponding coefficients for describing the relationship between the corrected duty cycle and the operating parameters of the power stage, and the control unit has at least one control program. execution to calculate the corrected duty cycle for the current values of the operating parameters using the coefficients and stored functions. The device according to the invention thus makes it possible to apply the method as described above. The method and apparatus preferably apply to power control or voltage control of an electric heater of an exhaust gas sensor installed in the exhaust gas channel. a heat engine. Drawings The present invention will be described in more detail below with the aid of examples of power control or supply voltage methods of an electrical consumer, shown in the accompanying drawings, in which: FIG. 1 shows an electrical diagram for the power control of an electrical consumer, FIG. 2 shows timing diagrams of a pulse width modulation for a short connection time, FIG. 3 shows first duty cycle curves. FIG. 4 shows first curves of the first coefficients as a function of the temperature, FIG. 5 shows second curves of the duty cycle, FIG. 6 shows third curves of the duty cycle, FIG. 7 shows the fourth curves of the duty cycle, Figure 8 shows second curves of suitable coefficients. DESCRIPTION OF EMBODIMENTS OF THE INVENTION FIG. 1 shows an electric power control circuit of an electrical consumer 10 according to the state of the art. In this embodiment, the electrical consumer 10 corresponds to an electric heating of a lambda probe installed in the exhaust duct of a heat engine. The supply voltage is supplied by a voltage source 14, one terminal of which is connected to ground 15. The electrical circuit comprises a control unit 11 to which is associated a power stage (power output stage) 12 and a means for determining the duty cycle TV, 13.

The power stage 12 is an NMOS field effect transistor (FET) having a drain terminal 12.1, a source terminal 12.2 and a gate terminal 12.3. The source terminal 12.2 is connected to the ground terminal of the voltage source 14. The drain terminal 12.1 is connected to the consumer 10; the gate terminal 12.3 is connected to the means for determining the duty cycle TV 13. The voltage source 14 is connected by a terminal to the control unit 11 and to the consumer 10. In order to control the electrical power supplying the consumer 10, it is applies a pulse width modulation signal (PWM signal or PWM signal) to the terminal terminal 12.3. During the PWM signal connection time, the field effect transistor is on and a current flows from the voltage source 14 through the consumer 10 and the power stage 12 to return to ground 15. During the cut-off time, the current flow is cut off. The duty cycle TV of the PWM signal predefines the power used by the consumer 10. The duty cycle TW is set by the TV determining means 13 taking into account the available supply voltage. The gate terminal 12.3 is controlled by the TV determination means 13 to apply a predefined effective voltage to the consumer 10.

According to the presented structure of the electrical circuit, the power stage 12 of this example is grounded by a "low side" switch. FIG. 2 shows timing diagrams of the pulse width modulation for brief connection times as provided by the electrical circuit of FIG. 1 during the operation of an electric heating device of a lambda probe installed in the channel of FIG. exhaust gas from a heat engine. The control signal 22, the load current curve 23 and the drain-source voltage 24 are represented along the signal axis 20 (ordinate axis) and with respect to the time axis 21 (abscissa axis). ). According to FIG. 1, the control signal 22 is supplied by the TV means 13 to the gate terminal 12.3 of the power stage 12. The charging current curve 23 corresponds to the passage of the current in the consumer 10 while the drain-source voltage 24 represents the voltage curve applied to the field effect transistor of the power stage 12. The ideal control signal 22 is a rectangular signal. But because of the limited slope of the sidewall, or the delay of the power stage 12, the load current curve 23 and the drain-source voltage 24 differ from the ideal rectangular shape. In particular, for low cyclic ratios, this difference results in significant differences in the effective voltage applied to the consumer compared to the actual, predefined target voltage. The electrical power received by the consumer thus differs from the set value.

Short connection times with working ratios of the order of 0.5% to 2% are for example provided for the operating mode "protective heating" according to which the lambda probe or probes and the water of the exhaust gas lines are evaporated at relatively low temperatures of the order of 100 ° C-200 ° C. There are very short cyclical reports, particularly in the field of heavy vehicles with a 24 V on-board grid voltage, higher than that of 12 V passenger vehicles. The protective heater avoids any breakage of the ceramic that could occur due to high thermomechanical stresses during the subsequent heating phase with an effective heating voltage, higher than the operating temperature of the sensor. lambda which is for example 800 ° C. So that during the protective heating (or precautionary heating) the lambda probe is neither too hot nor too cold, it is necessary to precisely respect the predefined effective voltage. Currently, for the heating of the lambda probe, the control unit 11 calculates the duty cycle from the measured supply voltage and the desired effective voltage across the heating resistor in the event of a rectangular tension, ideal. However, the deviation of the drain-source voltage curve 24 and the load current curve 23 from the ideal rectangular shape as shown in FIG. 2 gives, for the low cyclic ratios, large differences between the voltage desired effective voltage and actual applied voltage, which results in large temperature differences. According to the invention, the duty cycle is corrected, in particular for the small cyclic ratios, so that despite the difference between the voltage curve and the ideal rectangular shape, the voltage actually applied to the consumer corresponds to the voltage of the cone. - effective sign, predefined. For this, by measuring during a measurement phase, the necessary duty cycle for the power stage 12 used is determined, the ratio for which the measured effective voltage corresponds to the predefined effective target voltage. During the measurement, the voltage across the consumer is recorded according to an appropriate time resolution and from the measured values the actual voltage is calculated. A control loop adjusts the duty cycle until the desired actual desired voltage is obtained. The parameters which determine the switching behavior of the power stage 12 such as the large slope of the sidewalls and the time delay strongly depend on the operating conditions of the power stage. The main operating parameters are, for example, the supply voltage and the temperature of the power stage 12. This is why the measurement is repeated to obtain different values of the characteristic operating parameters such as at different levels. temperatures and different supply voltages, giving a multidimensional feature field from the corrected duty cycle. In the consecutive application phase in operation of the consumer 10 and the power stage 12, from the cyclic ratios determined and the measured operating parameters, by applying a calculation method, a corrected duty cycle is determined. Thus, during operation, it is no longer necessary to measure the voltage across the consumer 10. The number of measured values recorded depends on the required setting accuracy for the actual value as well as the individual switching behavior of the power stage 12. Figure 3 shows the first curves (timing diagram) of the cyclic ratios determined during a measurement phase.

Thus, a first curve TVkorr T1 32.1, a second curve TVkorr T2 32.2 and a third curve TVkorr T3 32.3 are shown along the axis TVkorr 30 and the axis Ubatt 31. FIG. 3 in combination with FIG. performing the correction of the duty ratio of the power stage 12 according to the two operating parameters, namely the temperature of the power stage 12 and the level of the supply voltage Ubatt. The first curve TVkorr T1 32.1 corresponds to the determined cyclical ratios that are obtained for different supply voltages Ubatt for a first temperature T1. The second curve TVkorr T2 32.2 and the third curve TVkorr T3 32.3 correspond to the cyclic ratios obtained for different supply voltages Ubatt for a second temperature T2 and a third temperature T3. In a first step of the method, for each of the temperatures T1, T2, T3, an approximation of the plot of the curve is made by an appropriate function according to the supply voltage Ubatt of the battery. The curves represented in this example are obtained by approximation, by polynomials of the second degree according to a first solution of a mathematical function: for Ti TVkorr (u) = aiu2 + b1U + ci for T2 TVkorr (u) = a2u2 + b2u + c2 for T3 TVkorr (U) = a3u3 + b3u + c3 In these formulas, for the first coefficients a, b and c, we have: ai = a (Ti); bi = b (Ti); ci = c (Ti). The supply voltage carries the reference u. Figure 4 shows the first curves of the first coefficients as a function of temperature. The coefficients adapted to (T) 42, b (T) 43, c (T) 44 were determined according to FIG. 3, as a function of the temperature; the curves are represented along the axis of the coefficients 40 and the temperature axis 41. In a second step of the method, an approximation of these curves of the first coefficient is made by a second solution of a second mathematical function. The curves represented in the exemplary embodiment are obtained by approximation with polynomials of the second degree: a (T) = s2T2 + if T + so b (T) = r2T2 + r1 T + ro c (T) = q2T2 + qi T + qo In these formulas, if, ri and qi represent the second coefficients. With the aid of the first function and the second function and the first and second coefficients, a corrected duty cycle is calculated for each permitted temperature and supply voltage. It suffices to record only the two functions and the second coefficients so, si, s2, ro, r1, r2, qo, q1, q2 in the control unit 11. These second coefficients and this second mathematical function make it possible to calculate, in the application phase, firstly the first coefficients as a function of the temperature of the power stage 12. With these first coefficients and the first function in mathematics, the corrected duty cycle for the supply voltage is then defined. existing. The functions with which the curves of FIGS. 3 and 4 are approximated are not limited to polynomials and especially polynomials of the second degree. It suffices to approximate the curves in the diagram by a similar function by adapting the respective coefficients. The method is not limited to the dependence of two operating parameters. Any number of parameters can be used as long as we obtain the functions allowing the approximation of the curves. FIGS. 5, 6, 7, 8 extend the method described with reference to FIGS. 3, 4 to another operating parameter, that of the aging of the power stage 12. FIG. - cliques obtained during a measurement phase; Figure 6 shows the third duty cycle curves obtained and Figure 7 shows the fourth duty cycle curves; in each case, the duty cycles are obtained as a function of the supply voltage and the temperature of the power stage 12 constituting the parameters. These representations correspond to those described with the help of FIG. 3. FIG. 5 shows the curves of the cyclic ratios for a first aging A1 of the power stage 12. A first curve TVkorr Ti Al 33.1, a second curve TVkorr T2 Al 33.2, a third curve TVkorr T3 Al 33.3 with respect to the axis TVkorr 30 and the axis Ubatt 31. FIG. 6 shows the curves of the duty cycle for a second aging A2 of the power stage 12 A first curve TVkorr Ti A2 34.1, a second curve TVkorr T2 A2 34.2, a third curve TVkorr T3 A2 34.3 with respect to the axis TVkorr 30 and the axis Ubatt 31 are thus represented.

FIG. 7 shows the curves of the duty cycle for a third aging A3 of the power stage 12. A first curve TVkorr T1 A3 35.1, a second curve TVkorr T2 A3 35.2, a third curve TVkorr T3 A3 35.3 by The curves shown in FIGS. 5, 6, 7 as a function of the supply voltage Ubatt can be represented by the approximation made with a polynomial of the second degree. by adapting the coefficients. The adaptation is made for each aging condition A1, A2, A3, each time for the first temperature T1, the second temperature T2 and the third temperature T3 of the power stage 12. The coefficients thus obtained can be plotted. as a function of the temperature of the power stage 12 and be described by an appropriate function with suitable coefficients.

Thus FIG. 8 shows second curves of appropriate coefficients as resulting from FIGS. 5, 6 and 7. The representation corresponds to the representation of FIG. 4 and is limited to the curve of coefficient a. This is represented as coefficient a A 1 (T) 45 for the first aging, as coefficient a A2 (T) 46 for the second aging and as coefficient a A3 (T) 47 for the third aging of the stage The curves of the coefficient (a) can be obtained by approximation with another suitable function, the coefficients of which will be adapted to the different states of aging of the power stage 12. According to the curves of the coefficient (a) represented In Figure 8, we can also approximate the coefficients (b) and (c) by functions whose coefficients will be adapted. On the basis of these functions and the coefficients as well as the functions obtained previously, it will be possible to determine, during the application phase, a corrected duty cycle taking into account the age (aging state) and the temperature of the the power stage as well as the level of the supply voltage.

In application of the method presented above, it will be possible to take into account any number of operating parameters. The process can be applied for each effective setpoint voltage which must be respected with great precision. The measurements made for the different actual setpoint voltages make it possible, by interpolation, to also obtain the cyclic ratios for the intermediate effective values. The heating of the lambda sensor requires only a measurement of the actual setpoint voltage required for the heating of the protec- tion. During another heating phase, cyclic ratios will be significantly larger so that the determination of the duty cycles provides sufficient accuracy assuming an ideal rectangular voltage.

The method allows a precise adjustment of the actual voltage across the consumer to compensate for the influences of the various operating parameters such as the supply voltage and the temperature of the power stage 12. No voltage measurement is necessary during operation. Depending on the manufacturing tolerances of the power stage 12 used, it is not necessary to separately measure each power stage 12; it suffices to measure a power stage 12 per manufacturing load. The method applies to any type of power stage 12 (whether these power stages are discrete, integrated, connected up or down side). The method applies both to the field of passenger vehicles and that of heavy vehicles. All you have to do is save a small number of parameters and functions in the control unit, which requires only a small amount of memory. The functions thus make it possible to quickly determine the correct duty cycle because there is no complex interpolation in an important data field.

Claims (2)

CLAIMS 1 °) A method of controlling the power or the supply voltage of an electrical consumer (10) using a power stage (12), the power or voltage control being done by modulation of pulse width (PWM / PWM) with an adjustable duty cycle, characterized in that in a measuring phase and under different operating conditions described by at least two operating parameters of the power stage (12) the effective voltage measured across the consumer is determined each time, the duty cycle of the pulse width modulation is modified so that the measured effective voltage corresponds to the predefined effective target voltage, the duty cycle is recorded in memory, and determined according to the operating parameters, and in a phase of application of the operating conditions present, a corrected duty cycle is calculated from the ratios cyclic stored in memory and to control the power or voltage. 2) Method according to claim 1, characterized in that for calculating a corrected duty cycle, the relationship between the determined duty cycle and the various operating parameters is approximated by at least approximation by appropriate mathematical functions with appropriate coefficients, stores the corresponding functions and coefficients in memory, and in the application phase, for the current operating parameters, the corrected duty cycle is determined by means of the stored functions and the memorized coefficients. Claim 1 or 2, characterized in that for calculating the corrected duty cycle the ratio of the defined duty cycles and a first operating parameter for different values of one second operating parameter by a first game comprising a first mathematical function and the first In the corresponding coefficients, the relation between the first coefficients and the second operating parameter is described by approximation by a second set comprising a second mathematical function and corresponding second coefficients. The second coefficients and the mathematical functions are recorded in memory. and in an application phase, for the second current operating parameter, with the second coefficients and the second mathematical function in memory, the first coefficients corresponding to the current second operating parameter are determined, and with these first coefficients and the first mathematical function, the corrected duty cycle for the first current operating parameter is calculated. 4) Method according to claim 1, characterized in that for each other operating parameter, is determined another set comprising another function and its other corresponding coefficients. Method according to Claim 1, characterized in that the relation is described at least by an approximation of the coefficients determined for an operating parameter previously taken into account for different values of another operating parameter by another. a game comprising another mathematical function and the other corresponding coefficients, the other coefficients and the other mathematical function are stored, and in one application phase, for the current value of the other operating parameter, the determined coefficients are determined. for the operating parameter previously taken into account. Process according to Claim 1, characterized in that in the measurement phase the voltage curve across the consumer (10) is measured numerically and the actual voltage is determined from the voltage curve. measured at the consumer terminals (10). 7 °) Method according to claim 1, characterized in that one makes a correction of the duty cycle for a duty cycle less than 5%, including a duty cycle less than 2 `) / 0. Process according to Claim 1, characterized in that at least the temperature of the power stage and / or the level of the supply voltage and / or the aging state is taken into account. of the power stage (12) as operating parameters. Method according to Claim 1, characterized in that a second degree polynomial is used as a function to describe the relation between the determined duty cycle and the operating parameters and / or to describe the relationship between the coefficients and the parameters. 3.3510 °) A method according to claim 1, characterized in that coefficients and / or respective functions are determined for the different effective setpoint voltages. 11 °) Power control or voltage control device for powering an electrical consumer (10) with a power stage (12), the power control or the voltage control being done by pulse width modulation (PWM) / MLI) with an adjustable duty cycle, and the power stage (12) having a control unit (11), characterized in that the control unit (11) has a memory for recording the functions and the corresponding coefficients for describing the relationship between the corrected duty cycle and the operating parameters of the power stage (12), and the control unit comprises at least one execution program for calculating the corrected duty cycle for the current values of the operating parameters using the coef- ficients and stored functions. 12 °) Application of the method and device according to any one of claims 1 to 11 for the power control or the voltage control of an electric heater (14) of an exhaust gas probe installed in the exhaust duct of an engine.