Control device for regulating the RMS value of an electrical load current at a time-varying load, vehicle and process

Abstract

A control device (1) for controlling an RMS value of an electrical load current (5) at a time-varying load (2), characterized in that the control device (1) is configured to provide a voltage pulse train (4) having a predetermined duty cycle (10) at the time-varying load (2) and in at least one pulse phase (8) of the voltage pulse train (4): - to detect a respective sample value (16) of the electrical load current at the time-varying load (2), wherein the control device (1) is configured to detect the sample value (16) of the electrical load current in a last tenth of the pulse phase (8) and / or during a falling signal edge of a pulse of the voltage pulse train (4), - to determine an actual RMS value (11) of the electrical load current assigned for the sample value (16) of the electrical load current by means of a dependency (17) stored in the control device (1).- to determine a difference value (25) between the actual RMS value (11) of the electrical load current and a target RMS value (6) of the electrical load current, - to determine an adapted duty cycle (26) of the voltage pulse train from the difference value (25) of the electrical load current according to a predetermined procedure, and - to provide an adapted voltage pulse train (27), having the adapted duty cycle (26), to the time-varying load (2).

Description

The invention relates to a control device for regulating an RMS value of an electrical load current at a time-varying load, a vehicle with a control device and a method for operating the control device. Solenoid valves are used to control the hydraulic flow in a vehicle's power steering system. The position of the solenoid valve depends on the RMS value of the electrical load current flowing through it. This load current is generated by a voltage pulse train applied to the solenoid valve. Setting a specific target RMS value of the load current is achieved through pulse width modulation of the voltage pulse train. The RMS value of the electrical load current depends on the duty cycle of the voltage pulse train. To regulate the RMS value to a predetermined target RMS value of the load current, it is necessary to measure the actual RMS value of the load current and compare it to the target RMS value. When measuring the actual RMS value of the electrical load current, a problem arises because the solenoid valve represents an inductive and therefore time-varying load. This results in a complex load current waveform, specifically an exponential one with a time constant Tau (τ), which represents the time it takes for the load current to halve (half-life), double, decrease by a factor of 1 / e (e = Euler's constant), or increase by a factor of (1-1 / e). Therefore, it is necessary to determine the RMS value using measurement techniques. This can be achieved by summing the current waveforms and then averaging them using analog circuitry and an integrator. An alternative approach involves high-frequency sampling of the load current waveform.The summation and subsequent averaging are performed by a program in a control unit. The control unit requires sufficient processing power to evaluate the samples within the necessary time. In both cases, a measuring shunt is required to ensure a predetermined accuracy. One disadvantage of the described methods for determining the actual RMS value of the load current is that the control device for acquiring the actual RMS value of the load current has a large number of electronic components. This results in increased manufacturing effort and costs. Furthermore, a method for current control of an inductive load, in particular an electromagnetic pressure regulator in an automated motor vehicle transmission, is known from DE 10 2010 000 885 A1. In this method, a control equation is determined for an electrical reference variable of the inductive load, which is used to control the current output stage in order to precisely regulate the current flowing through the coil. The known method aims to improve the dynamics and accuracy of the control of electromagnetic actuators in automated transmissions. It is therefore an object of the invention to reduce the number of components required to determine an actual RMS value of an electrical load current at a time-varying load. The invention provides a control device for regulating the RMS value of an electrical load current at a time-varying load. The control device is configured to supply a voltage pulse train with a predetermined duty cycle to the time-varying load. The control device is configured to detect a sample value of the electrical load current at the time-varying load during at least one pulse phase of the voltage pulse train. Furthermore, the control device is configured to detect the sample value of the electrical load current in the last tenth of the pulse phase and / or during a falling edge of a pulse of the voltage pulse train.In other words, the controller is designed to capture a sampled value at a predetermined sampling time during at least one pulse phase of the voltage pulse train. This sampled value represents the current intensity of the electrical load current at that sampling time. The predetermined sampling time can depend on a phase angle of the voltage pulse train. The controller is configured to determine an actual RMS value of the electrical load current assigned to the sampled value by means of a dependency stored within the controller. In other words, the controller provides the dependency that allows the determination of the respective actual RMS value of the electrical load current for the captured sampled value.The dependency can be, for example, a table of characteristic values ​​or a calculation rule (mathematical function), each of which can be stored in the controller. The controller is configured to determine a difference between the actual RMS value of the electrical load current and a predetermined setpoint RMS value of the electrical load current. In other words, the controller is configured to compare the determined actual RMS value of the electrical load current with the setpoint RMS value of the electrical load current to determine the difference. The controller is configured to determine an adapted duty cycle of the voltage pulse train from the difference value of the electrical load current according to a predetermined procedure (control procedure) and to provide a modified or adapted voltage pulse train, exhibiting the adapted duty cycle, to the time-varying load.In other words, the controller is configured to change the duty cycle of the voltage pulse train depending on the measured difference in the electrical load current, and to provide the adjusted voltage pulse train with the adjusted duty cycle to reduce the difference. Thus, while the voltage pulse train is being generated, its duty cycle can be changed in one or more pulse phases depending on the actual RMS value measured in each pulse phase. The duty cycle can therefore be a manipulated variable. This control method can be based, for example, on PID control (proportional, integral, differential) or PI control. The invention offers the advantage that the control device can determine the actual RMS value of the electrical load current from the sampled value. Furthermore, the invention eliminates the need for integration over the current waveform to determine the actual RMS value of the electrical load current. This makes it possible to determine the actual RMS value of the electrical load current without an integrator or control unit, thereby reducing the number of components required. A further development of the invention provides that the dependency includes a characteristic value table. In other words, the dependency comprises a table in which the respective actual RMS value of the load current is assigned to each discrete sampled value. This offers the advantage that no calculations are required by the controller to determine the actual RMS value. For example, the characteristic value table can be a conversion table from which the corresponding actual RMS value can be retrieved for each acquired sampled value. Such a conversion table is also referred to as a lookup table. A further development of the invention provides that the dependency includes a characterization function. In other words, the dependency has a mathematical function that makes it possible to calculate the respective actual RMS value of the electrical load current for each sampled value. This offers the advantage that the actual RMS value can be determined for a continuous range of samples. For example, the characterization function can be a model function that has been approximated to measurement points that describe a relationship between the respective sampled value and the respective actual RMS value of the electrical load current. A further development of the invention provides that the controller is configured to supply the voltage pulse train with a period of 1.5 ms to 3.5 ms. In other words, the controller is configured to generate the voltage pulse train with a period of 1.5 ms to 3.5 ms. This offers the advantage that the controller can provide the usual period. The period can, for example, be 2.5 ms. In principle, it is possible to control the duty cycle with any period, i.e., to adjust the duty cycle as described. The pulse duration of the voltage pulse train should preferably be shorter than 5 * Tau of the time-varying load (Tau = time constant of the time-varying load). A further development of the invention provides that the control device is configured to set a pulse duration of less than 5 * Tau of the time-varying load, where Tau is the aforementioned time constant of the time-varying load, and to determine the duty cycle in several or all pulse phases of the voltage pulse train as a function of a sample value determined in the respective pulse phase. In other words, the described steps for adjusting or changing the duty cycle can be carried out in some or all pulse phases of the voltage pulse train. This offers the advantage of being able to react to temporal changes. A further development of the invention provides that the control device is configured to supply the voltage pulse train as a square wave signal. In other words, the control device is configured to generate a square wave signal as a voltage pulse train, wherein a voltage within the voltage pulse train alternates between two voltage levels. These two voltage levels are an upper voltage level and a lower voltage level. A region exhibiting a high voltage value can represent a pulse within the voltage pulse train and have a pulse duration. This further development offers the advantage that the generation of the voltage pulse train is possible using simple switches. A further development of the invention provides that the control device is configured to acquire the sampled value of the electrical load current with a sensing period that is an integer multiple of the period of the voltage pulse train. In other words, the control device is configured to acquire the sampled value of the electrical load current at regular intervals, with the sensing period between acquisitions being an integer multiple of the period of the voltage pulse train. This offers the advantage that the sampled value is acquired at identical phases of the voltage pulse train. A further development of the invention provides that the dependency is specific to the respective time-varying load and the respective controller device. In other words, the respective controller device was calibrated for the respective time-varying load applied to it, so that the dependency describes the relationship between the sampled value and the actual RMS value for a specific combination of the respective controller device and the respective time-varying load. This offers the advantage that serial variations occurring in both the controller devices and the time-varying loads can be compensated for. For example, there may be serial variation in the acquisition of the sampled values ​​between individual controller devices.With time-varying loads, series fluctuations can occur, leading to differences in the respective time profiles of the load current between different solenoid valves. This can be due, for example, to variations in the inductances of the individual solenoid valves. By determining the relationship for each pair of controller device and load, these fluctuations are compensated for. A further development of the invention provides that the control device is configured to detect the sampled value of the electrical load current in the last tenth of the pulse phase. In other words, the sampling point is located in the last tenth of the respective pulse phase. This offers the advantage that the sampled value is detected at a time when the load current exhibits a smaller rise than at the beginning of the pulse phase. A further development of the invention provides that the control device is configured to detect the sampled value of the electrical load current during a falling signal edge of a pulse in the voltage pulse train. In other words, the sampling point is located during a fall-off phase in which the voltage value drops from the high voltage value to the low voltage value. This offers the advantage that the time of detection of the sampled value can be triggered by the signal edge. A further development of the invention provides that the control device includes a power MOSFET. In other words, the control device comprises a metal-oxide-semiconductor field-effect transistor configured for controlled conduction and blocking of electrical currents and voltages. This can be a so-called smart MOSFET, which includes a control unit and a pulse-width modulation (PWM) controller for regulating the RMS value of the load current via the duty cycle. The invention also includes a vehicle that has a control device for regulating the RMS value of an electrical load current at a time-varying load. The vehicle can, in particular, be a motor vehicle, such as a truck or passenger car. The control device can, for example, be configured to regulate the RMS value of an electrical load current in a magnetic valve as a time-varying load.The invention also includes a method for controlling the RMS value of an electrical load current at a time-varying load. In this method, a controller device sequentially provides several calibration voltage pulse sequences at a time-varying load, each calibration voltage pulse sequence having a different duty cycle. In other words, for a calibration, several calibration voltage pulse sequences are generated, each differing in its duty cycle. The controller device acquires a sample value of the electrical load current of the time-varying load in at least one pulse phase of each calibration voltage pulse sequence. In other words, the respective sample value is acquired for each of the calibration voltage pulse sequences.A sensor unit records the actual RMS value of the electrical load current at the time-varying load for at least one period of each calibration voltage pulse sequence. In other words, during calibration, the sensor unit records the actual RMS value of the electrical load current for each calibration voltage pulse sequence. The sensor unit can, for example, be configured to record and integrate the load current waveform and determine the actual RMS value from it. The sensor unit could be, for example, a multimeter, which can be connected to the time-varying load and the control device for calibration purposes. After calibration, the connection between the sensor unit and the control device and the time-varying load can be removed. The respective actual RMS value of the electrical load current is then determined for at least one period of each calibration voltage pulse sequence.The actual RMS value of the electrical load current, as measured by the sensor unit, is transmitted to the controller. The controller generates and stores a dependency in which the actual RMS value of the electrical load current is assigned to each sampled value of the electrical load current and each duty cycle of the calibration voltage pulse sequence. In other words, the controller generates the dependency in which the respective actual RMS value is stored for each sampled value and duty cycle. This can be done, for example, by a control unit of the controller. The dependency can be stored in the control unit. This enables the controller to determine the actual RMS value of the electrical load current using the dependency for each sampled value and duty cycle. In the next step, the controller applies a voltage pulse train to the time-varying load with a predetermined duty cycle. During at least one pulse phase of the voltage pulse train, the controller samples the electrical load current. Using the relationship stored within the controller, the controller determines the actual RMS value of the electrical load current, which is assigned to the sampled value and the duty cycle of the voltage pulse train. In other words, the controller uses this relationship to determine the actual RMS value of the electrical load current. In a subsequent step, the controller calculates the difference between the actual RMS value of the electrical load current and a target RMS value of the electrical load current.From the difference value, a tailored duty cycle for the voltage pulse train is determined using a predetermined procedure (control procedure). The tailored duty cycle is then used to provide a tailored voltage pulse train in order to reduce the difference value of the electrical load current. The invention also includes further developments of the method according to the invention, which have features already described in connection with the further developments of the control device according to the invention. For this reason, the corresponding further developments of the method according to the invention are not described again here. An embodiment of the invention is described below. Figure 1 shows a control device 1; Figure 2 shows a curve of the load current I; Figure 3 shows a further curve of the load current I; Figure 4 shows current curves I as a function of the respective duty cycle X; Figure 5 shows a dependency 4; and Figure 6 shows a possible sequence of a method. The embodiment described below is a preferred embodiment of the invention. Furthermore, the described embodiment can also be supplemented by other features of the invention already described. In the figures, functionally identical elements are each provided with the same reference symbols. Fig. 1 shows a controller 1 electrically connected to a time-varying load 2. The controller 1 can, for example, include a smart FET. The time-varying load 2 can be a solenoid valve for controlling the hydraulic flow of a power steering system in a vehicle 3. The controller 1 can be configured to provide a voltage pulse train 4 to supply an electrical load current 5 with a predetermined setpoint RMS value 6 to the time-varying load 2. The voltage pulse train 4 can, for example, be a rectangular function with a period 7. The voltage pulse train 4 can include pulses 8 with a pulse duration 9. The ratio between the pulse duration 9 and the period 7 can be described by the duty cycle 10.The time-varying load 2 could, for example, be a solenoid valve, where the opening degree of the solenoid valve can depend on an actual RMS value 11 of the electrical load current flowing through the time-varying load 2. The time-varying load 2 can have inductances, which can cause the load current 5 to increase or decrease exponentially. By adjusting the duty cycle 10 using the controller 1, it may be possible to adjust the actual RMS value 11 of the electrical load current to the target RMS value of the electrical load current 5. The control device 1 can be used in a power steering system in the vehicle 3. The required motor power can depend on the degree of intervention of the power steering. The degree of intervention of the power steering can be adjusted via a solenoid valve. The solenoid valve can be a proportional valve, which is actuated and / or controlled by the control device 1. The solenoid valve can behave as follows: at a high electrical load current 5 through the valve, the valve can be closed. This minimizes the hydraulic flow in the power steering hydraulic circuit. The degree of power steering is at its minimum in this position. At a low electrical load current 5 through the solenoid valve, the solenoid valve can be open, and the hydraulic flow in the power steering hydraulic circuit is at its maximum.In this position, the level of steering assistance can reach its maximum. The position of the solenoid valve depends on the actual RMS value 11 of the electrical load current. The RMS value is the root mean square of the electrical load current 5. The ratio between the actual RMS value 11 of the electrical load current and the opening degree of the solenoid valve is inversely proportional. The solenoid valve is controlled by a pulse-width modulated voltage pulse train 4. This means that the actual RMS value 11 of the electrical load current is controlled via the pulse width of the voltage pulse train 4. During the calibration of the controller 1, a sensor unit 24 can be electrically connected to the controller 1 and the time-varying load 2 to determine the actual RMS value 11. After calibration, the sensor unit 24 can be removed. Fig. 2 shows a waveform of the load current 5. The voltage pulse sequence 4, which can be a rectangular function, can be applied to the time-varying load 2 by the controller device 1. The voltage pulse sequence 4 can have two voltage levels 12 and 13, with the voltage U being the upper voltage level 13 during a pulse 8 and the lower voltage level 12 outside of a pulse 8. The pulse 8 can have a pulse duration 9 and the voltage pulse sequence 4 a period 7. The pulse duration 9 can be limited by a rising edge 14 and a falling edge 15. From the rising edge 14 onwards, the load current 5 can increase. From the falling edge 15 onwards, the load current 5 flowing through the time-varying load 2 can decrease exponentially.By defining the duty cycle 10, and thus the ratio between the period 7 and the pulse duration 9, the actual RMS value 11 of the electrical load current flowing through the time-varying load 2 can be determined. According to the prior art, to determine the exact value of the actual RMS value 11 of the electrical load current, it is necessary to perform integration over the load current 5 using an analog circuit or software. Both methods have the disadvantage of being complex and requiring additional components. In the presented method, instead of integrating over the load current 5, a sample value 16 of the electrical load current can be acquired during at least one pulse 8 of the voltage pulse train 4 to determine the actual RMS value 11 of the electrical load current.For example, the controller device 1 may be configured to acquire the sampled value 16 of the electrical load current in the last tenth of the phase of pulse 8. The controller device 1 can determine the actual RMS value 11 of the electrical load current by retrieving the actual RMS value 11 of the electrical load current stored for the respective sampled value 16 in a dependency 17. The dependency 17 may, for example, be a function or a table of characteristic values ​​stored in the controller device 1. A sampling point 18 of the sampled value 16 may be located in the last tenth of the phase of pulse 8. Fig. 3 shows another possible waveform of a load current 5. It depicts another voltage pulse sequence 4, where the lower voltage level 12 and the upper voltage level 13 can be identical to those in Fig. 2. The voltage pulse sequences 4 shown in Fig. 3 can have a lower duty cycle 10 than the voltage pulse sequence 4 in Fig. 2. The pulse duration 9 can, for example, be shorter, which means that the actual RMS value 11 of the electrical load current can be smaller than the actual RMS value 11 of the electrical load current in Fig. 2. The sampling time 18 of the sample value 16 can occur at the same phase angle as in Fig. 2. Due to the shorter pulse duration 9, the sample value 16 in Fig. 3 can be smaller than the sample value 16 in Fig. 2. Fig. 4 shows the waveforms of the electrical load current 5 as a function of the respective duty cycle 10. The depicted waveforms of the electrical load current 5 can be generated by respective calibration voltage pulse sequences 19, 20, 21, 22, 23, which can have identical lower voltage levels 12 and identical upper voltage levels 13 and can differ from one another in their respective duty cycle 10. The duty cycles 10 of the associated calibration voltage pulse sequences 19, 20, 21, 22, 23 can be, for example, 12%, 24%, 36%, 48%, and 60%. The respective sample value 16 of the respective waveform of the load current 5 is recorded in the last tenth of the pulse phase 8. It can be seen that, depending on the selected duty cycle 10, both the waveform of the load current 5 and the value of the sample value 16 of the electrical load current increase. Overall, this results in a relationship between the sampled value 16 and the actual RMS value 11 of the electrical load current.This relationship is used to generate the dependency 17 stored in the controller 1. To generate the dependency 17, the calibration voltage pulse sequences 19, 20, 21, 22, 23 can be successively applied to the time-varying load 2. For each of the calibration voltage pulse sequences 19, 20, 21, 22, 23, the controller 1 can acquire the respective sample value 16. A sensor unit 24 determines the actual RMS value 11 of the electrical load current. The respective actual RMS value 11 of the electrical load current can be transmitted by the sensor unit 24 to the controller 1 and assigned there to the respective acquired sample value 16 in the dependency 17.For example, the controller device 1 may create a characterization function as dependency 17, which makes it possible to calculate the corresponding actual RMS value 11 of the electrical load current for the detected sample value 16 of the electrical load current. Alternatively, dependency 17 may be a table of characteristic values ​​in which the respective actual RMS values ​​11 of the electrical load current and the corresponding sample values ​​16 are stored. Fig. 5 shows a dependency 17. The dependency 17 could, for example, be a table of characteristic values. An exemplary table of characteristic values ​​is shown, in which the respective actual RMS value 11 of the electrical load current is assigned to the respective sampled values ​​16. Fig. 6 shows a possible sequence of a method. The method can be carried out, for example, by a control device or regulator 1 to provide a target RMS value 6 of an electrical load current at a time-varying load 2. In a first step S1, the regulator 1 can provide a voltage pulse train 4 with a predetermined duty cycle 10, allowing an electrical load current to flow through the time-varying load 2 and the regulator 1. The regulator 1 can then acquire a sample value 16 of the load current at a predetermined sampling time 18. In step S2, the controller device 1 can determine the actual RMS value 11 of the electrical load current, for example, via a dependency 17 designed as a characterization function or characteristic value table. Here, the controller device 1 can calculate or read out the corresponding actual RMS value 11 of the electrical load current for the sampled value 16. In step S3, it may be provided that the controller device 1 compares the determined actual RMS value 11 of the electrical load current with the target RMS value 6 of the electrical load current to be achieved in order to determine a difference value 25 of the electrical load current. In step S4, it can be provided that, depending on the difference value 25 of the electrical load current, an adapted duty cycle 26 for the voltage pulse sequence 4 is calculated by the controller device 1. The controller device 1 can change the duty cycle 10 of the voltage pulse sequence 4, whereby the voltage pulse sequence 4 can be replaced by an adapted voltage pulse sequence 27 with the adapted duty cycle 26. The procedure can be carried out at least once. In a further step, it may be stipulated that the procedure be repeated from step S1 onwards. Overall, this example shows how the invention can enable a reduction in the number of components required to control the effective value of a load current.

Claims

A control device (1) for controlling an RMS value of an electrical load current (5) at a time-varying load (2), characterized in that the control device (1) is configured to provide a voltage pulse train (4) having a predetermined duty cycle (10) at the time-varying load (2) and in at least one pulse phase (8) of the voltage pulse train (4): - to detect a respective sample value (16) of the electrical load current at the time-varying load (2), wherein the control device (1) is configured to detect the sample value (16) of the electrical load current in a last tenth of the pulse phase (8) and / or during a falling signal edge of a pulse of the voltage pulse train (4), - to determine an actual RMS value (11) of the electrical load current assigned for the sample value (16) of the electrical load current by means of a dependency (17) stored in the control device (1).- to determine a difference value (25) between the actual RMS value (11) of the electrical load current and a target RMS value (6) of the electrical load current, - to determine an adapted duty cycle (26) of the voltage pulse train from the difference value (25) of the electrical load current according to a predetermined procedure, and - to provide an adapted voltage pulse train (27), having the adapted duty cycle (26), to the time-varying load (2). Control device (1) according to claim 1, characterized in that the dependency (17) is a characteristic value table. Control device (1) according to claim 1, characterized in that the dependency (17) is a characterization function. Control device (1) according to one of the preceding claims, characterized in that the control device (1) is configured to provide the respective voltage pulse sequence (4) with a period (7) of the voltage pulse sequence of 1.5 ms to 3.5 ms. Control device (1) according to one of the preceding claims, characterized in that the control device (1) is configured to set a pulse duration of less than 5*Tau of the time-varying load (2), where Tau is the time constant of the time-varying load (2), and to determine the duty cycle (26) in several or all pulse phases (8) of the voltage pulse sequence (4) as a function of a sample value (16) determined in the respective pulse phase (8). Control device (1) according to one of the preceding claims, characterized in that the control device (1) is configured to provide the voltage pulse sequence (4) as a square wave signal. Control device (1) according to one of the preceding claims, characterized in that the control device (1) is configured to detect the sample value (16) of the electrical load current with a detection period that is an integer multiple of the period (7) of the voltage pulse train. Control device (1) according to one of the preceding claims, characterized in that the dependency (17) is specific for the time-variant load (2). Control device (1) according to one of the preceding claims, characterized in that the control device (1) has a power MOSFET. Vehicle (3) with a regulator device (1) according to one of the preceding claims Method for controlling the RMS value of an electrical load current at a time-varying load (2), characterized in that: - several calibration voltage pulse sequences (19, 20, 21, 22, 23), each having a duty cycle (10), are successively provided at a time-varying load (2) by a controller device (1); - a respective sample value (16) of the electrical load current at the time-varying load (2) is detected by the controller device (1) in at least one pulse phase (8) of the respective calibration voltage pulse sequences (19, 20, 21, 22, 23); - a respective actual RMS value (11) of the electrical load current at the time-varying load (2) is detected by a sensor unit (24) for at least one period (7) of the respective calibration voltage pulse sequence; - the respective actual RMS value (11) of the electrical load current is transmitted from the sensor unit (24) to the controller device (1). is transferred- a dependency is generated and stored by the controller (1) in which the respective actual RMS value (11) of the electrical load current is assigned to the respective sampled values ​​(16) of the electrical load current and the respective duty cycle (10) of the calibration voltage pulse sequences (19, 20, 21, 22, 23), - a voltage pulse sequence having the duty cycle (10) is provided by the controller (1) at the time-varying load (2), - the sampled value (16) of the electrical load current at the time-varying load (2) is detected by the controller (1) in at least one pulse phase (8) of the voltage pulse sequence, - the actual RMS value (11) of the electrical load current assigned to the sampled value (16) of the electrical load current and the duty cycle (10) of the voltage pulse sequence (4) is determined by the controller (1) by means of the dependency (17) stored in the controller (1),- a difference value (25) between the actual RMS value (11) of the electrical load current and the set RMS value (6) of the electrical load current is determined by the control device (1), - an adapted duty cycle (26) of the voltage pulse train (4) is determined by the control device (1) from the difference value (25) of the electrical load current according to a predetermined procedure, and - an adapted voltage pulse train (27), having the adapted duty cycle (26), is provided by the control device (1) to the time-varying load (2).

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