DE112015005097B4 - Method for operating a device for supplying energy to an electrical consumer in an isolated operation and a corresponding device - Google Patents

Abstract

Method for operating a device for supplying energy to an electrical consumer (1) in an isolated operation; wherein the device comprises: an externally excited synchronous generator (2), which can be controlled via its excitation current (Ie); a drive (3) for the synchronous generator (2); a control device (11) for the drive (3) and one through the synchronous generator ( 2) rechargeable battery (13), which is connected to the electrical consumer (1) in such a way that the electrical consumer voltage (Uv) applied to the consumer (1) results from the internal battery resistance; the method comprising: the device is dependent on the Energy requirement of the consumer (1) is controlled; the speed (n) of the synchronous generator (2) is kept constant by regulating the excitation current (Ie); the drive (3) is operated in two power levels depending on the consumer voltage (Uv). ;whereby the drive (3) is switched on by means of the control device (11) at a lower limit voltage (Uin) and switched off at an upper limit voltage (Uoff), and whereby by means of the control device (11) when an upper threshold value (UL1) of the consumer voltage (Uv ) the power of the drive (11) is switched to the lower power level and when the consumer voltage (Uv) falls below a lower threshold value (UL2), the power of the drive (11) is switched to the higher power level.

Description

Technical area

The invention relates to a method for operating a device for supplying energy to an electrical consumer in an isolated operation with a synchronous generator that can be controlled via its excitation current and with a drive for the synchronous generator, the device being controlled depending on the energy requirements of the consumer, and to a device for supplying energy to an electrical consumer in an isolated operation.

State of the art

In order not to be dependent on the capacity of a battery in island operation, it is known to charge the battery depending on its state of charge via a generator, the drive of which is switched on when the state of charge falls below a predetermined threshold value, so that the operating time of the connected electrical extended accordingly. Because of their high efficiency, permanently excited synchronous generators are often used as generators, with the disadvantage that due to the linear dependence of the no-load voltage on the speed, control of the power to be delivered, which is essentially proportional to the generator current, is only possible in a simple manner via the speed, which results in poor efficiencies for the drive, which can hardly be operated in an optimal working range, especially when trained as an internal combustion engine. In addition, the drive's maximum power must be adapted to the maximum consumer power so that the consumer cannot brake the drive without limiting the consumer power.

Externally excited synchronous generators, such as those used as alternators in motor vehicles, are also known for charging batteries. In order to adapt the generator voltage to the battery voltage, the excitation current must be controlled accordingly, within a wide speed range of the synchronous generator, which in turn has a disadvantageous effect on the efficiency.

The functionality of a control unit for a generator is explained in US 2009/0234509 A1 described. The control unit includes a voltage regulator that is able to regulate the output voltage of the generator to a target voltage. If the speed of a drive machine driving the generator falls below a predetermined threshold value due to the load and there is therefore a risk of the drive machine designed as an internal combustion engine stalling, then the output power of the generator is reduced accordingly to relieve the load on the drive machine by reducing the target voltage. If the speed threshold is exceeded again due to this measure, the target voltage is reset to the initial value and the output power of the generator is thus increased.

Further revealed WO 2014/083487 A2 respectively US 2015/0315989 A1 a method of controlling a generator driven by an engine. A speed regulator is assigned to the motor and a voltage regulator is assigned to the generator. The voltage regulator gives the motor a speed setpoint depending on the torque and kinetic energy of the motor. Detecting a change in load due to monitoring the torque and the level of kinetic energy makes it possible to anticipate a drop in engine speed and take appropriate measures to limit such a drop.

A method for optimizing the operation of a combination of an internal combustion engine and a generator in a series hybrid drive is described DE 10 2008 049 225 A1 . According to a specified electrical target power of the generator, the torque and speed of the internal combustion engine are regulated along a characteristic curve specified by low-emission and low-consumption operating points. The internal combustion engine is controlled by adjusting torque and speed depending on the respective performance requirements.

Out of GB 2 417 378 A an intermittent battery charging device is known which comprises an internal combustion engine, a generator coupled to it and a control device. The control device generates a control signal that acts on the internal combustion engine in such a way that the generator delivers sequential charging current pulses to the battery.

US 5,545,928 A discloses a method for controlling power generation in a hybrid vehicle. A target generator output is calculated based on a state of charge, a catalyst temperature, etc., and the target engine revolution number is calculated based on the target generator output. A field current is corrected in response to the comparison result between a control target range determined in response to the target number of motor revolutions and the detected number of motor revolutions, thereby achieving target control the number of engine revolutions is carried out. Then, a correction amount of a throttle angle is set in response to the comparison result between a control target range determined in response to the target generator output and the detected generator output, and the throttle angle is corrected, thereby performing target control of the generator output. Since target control of the speed is performed first and then target control of the generator power is performed, a control error due to high or low engine load can be prevented.

JP H06-121 406 A deals with the task of bringing the speed of an engine back into the range of an objective speed by adjusting the objective power of a generator so that the speed of the engine corresponds to the specified speed and correcting the amount of fuel. Injection occurs when the target power deviates from the specified range and the engine speed is outside the target speed range. For this purpose, a controller controls the power generated based on the output current of a generator and controls the target power based on the speed of a motor.

US 5,703,410 A describes a control system for an internal combustion engine, which is equipped with a motor generator, serves to suppress fluctuations and pulsations in the speed of a crankshaft in order to achieve optimal engine operation, improved fuel cost performance and improved exhaust gas purification.

DE 10 2012 201 270 A1 discloses a method for determining the operating point of a range extender of an electric vehicle comprising an electric machine and an internal combustion engine. Determining the operating point involves specifying the torque of the combustion engine and the speed of the electric machine. The target power of the range extender is determined. Depending on the target power of the range extender, a target speed level for operating the range extender is selected from a plurality of predetermined, discrete target speed stages of the electrical machine.

DE 10 2012 216 019 A1 describes a drive control device for serial hybrid vehicle.

AT 513 476 A1 discloses a method for operating a range extender for electric vehicles.

JP 2000-295 707 A discloses a power generation control device of a hybrid electric car capable of reducing noise more in the working mode. For this purpose, it is proposed that when a vehicle is in the driving state, power generation with a generator is started when the remaining capacity of a battery detected by a battery remaining capacity detector is less than 60%. When a power collection device that takes the driving power of an engine as work power is in the state in which work is possible, power generation with the generator is started when the remaining capacity of the battery is at most 35%. On the other hand, when the power extraction device is in the standby state, the generator is controlled to prevent power generation until the remaining capacity of the battery is 30% or less.

US 5,929,609 A describes a method that monitors battery status and engine conditions and controls a generator to selectively charge the battery depending on specific battery and engine conditions, thereby optimizing the health and operating characteristics of the battery and engine.

US 2014/0163801 A1 describes a vehicle, a method for controlling a vehicle and a control device of a vehicle, and in particular a technique for generating electrical energy by operating a motor and charging an energy storage device.

Sabine Piller, Marion Perrin, Andreas Jossen: “Methods for state-of-charge determination and their applications”, Journal of Power Sources, Volume 96, 2001, Issue 1, pages 113 to 120 , ISSN 0378-7753, deals with determining the state of charge (SOC) of batteries. Previous operating strategies used voltage limits only to protect the battery from deep discharge and overcharging. For improved battery control, the battery's SOC is a key factor. In recent years, a lot of research has been done to improve SOC determination. The operating conditions for batteries are different, for example in photovoltaic applications, hybrid electric vehicles or telecommunications. Therefore, a particular method of SOC calculation is more suitable for a particular application than another. The paper introduces common methods for SOC determination and establishes a relationship between the advantages of the different methods and the most common applications.

CN 1 03 359 115 A describes a method for controlling power generation for an electric vehicle with an extended range.

DE 10 2010 040 863 A1 describes a method and a device for operating a generator in a recuperation system of a motor vehicle.

DE 10 2009 044 942 A1 describes an electrical machine with a variable number of poles, in particular a generator or a starter generator for a motor vehicle.

Presentation of the invention

The invention is based on the object of creating a method for operating a device for supplying energy to an electrical consumer in an isolated operation and a corresponding device, which can be operated in such a way that a high level of efficiency is ensured, with a comparatively low control and Regulatory effort.

This object is achieved by a method according to claim 1 and a device according to claim 3. Preferred embodiments of the invention are the subject of claims 2 and 4.

The invention is based on the knowledge that the speed of the synchronous generator can be kept constant by controlling the excitation current and that the drive can be controlled depending on the electrical voltage applied to the consumer.

Due to these measures, the generator acts as a brake, with the braking torque being proportional to the generator current, which results depending on the generator's internal resistance due to the voltage difference between the generator idle voltage and the voltage applied to the consumer. An increase in the excitation current causes an increase in the generator idle voltage while the speed remains the same and thus an increase in the voltage difference relevant to the generator current, which, due to the larger generator current, leads to a higher braking torque, so that the speed can be regulated via appropriate control of the excitation current of the externally excited synchronous generator. With a power control of the drive depending on the consumer power, which can be detected via the consumer voltage, advantageous operating conditions can be ensured.

By regulating the speed of the synchronous generator to a constant value using the excitation current as a manipulated variable, simple conditions are created for operating the drive in an advantageous working range, which represents a significant contribution to improving efficiency, especially when using internal combustion engines. The excitation power, which is comparatively low, reduces the efficiency, but in the range of the nominal speed for which the device is designed, a significantly greater efficiency can be achieved over a wide torque and therefore power range, so that a correspondingly high overall efficiency can be ensured . The constant speed also brings advantages in terms of vibration control and noise behavior or noise perception, because noise changes are perceived more easily.

There are particularly simple control options for the drive, since according to the invention a battery is provided which is connected to the consumer and can be charged by the synchronous generator. In this way, the drive can only be switched on and off via its control device depending on the consumer voltage. A reduction in the consumer voltage below a predetermined lower limit causes the drive to be switched on and exceeding an upper limit causes the drive to be switched off, whereby the drive power can be controlled gradually between these limit values, since according to the invention the drive is operated in two power levels depending on the consumer voltage. By controlling the drive depending on the consumer voltage that can be tapped at the battery terminals, there is extensive independence from the type of battery used and its aging because, according to the invention, the internal battery resistance is automatically taken into account with this consumer voltage. In contrast to this, in the methods known from the prior art, the state of charge (SOC) of the batteries is determined and used for control.

In order to be able to operate a device for supplying energy to an electrical consumer in an island operation according to the method according to the invention, the excitation current is only determined via the control device for the synchronous generator connected to a speed sensor as a function of a target-actual value difference in the speed of the synchronous generator in the sense of regulating the target -Actual value difference to control, whereby the control device for the drive of the synchronous generator regulates the drive in terms of its power depending on the electrical voltage applied to the consumer. If the consumer is connected to a battery that can be charged by the synchronous generator, the drive for the synchronous generator can be switched on and off depending on the consumer voltage by the control device that can be supplied with the consumer voltage. Such a two-point control is achieved by further threshold values between The switch-on and switch-off limit values are supplemented in order to be able to operate the drive in different power levels but at a constant speed.

The drive for the synchronous generator can be designed as an internal combustion engine with a maximum power adapted to the maximum generator power. Different performance requirements for the energy source can therefore be met to the extent of the drive's performance, regardless of the consumer power, i.e. even in the event of overload.

Short description of the drawing

• 1 eine erfindungsgemäße Vorrichtung zur Energieversorgung eines elektrischen Verbrauchers in einem Inselbetrieb in einem schematischen Blockschaltbild;
• 2 eine der 1 entsprechende Darstellung einer Ausführungsvariante der erfindungsgemäßen Vorrichtung;
• 3 Kennlinien für die Leerlaufspannung des fremderregten Synchrongenerators in Abhängigkeit von der Drehzahl bei unterschiedlichen Erregerströmen;
• 4 den Generatorstrom über der Drehzahl für unterschiedliche Kennlinien der Leerlaufspannung des Synchrongenerators;
• 5 den zeitlichen Verlauf einer an den Batterieklemmen eines Fahrzeugs mit einem über eine Batterie gespeisten Elektromotor abgegriffenen Spannung für einen vorgegebenen Belastungsverlauf ohne und mit der erfindungsgemäßen Vorrichtung zur Energieversorgung;
• 6 einen zeitlichen Geschwindigkeitsverlauf eines Fahrzeugs mit einem von einer Batterie gespeisten Elektromotor und der erfindungsgemäßen Vorrichtung zur Energieversorgung;
• 7 den Leistungsbedarf des Elektromotors eines Fahrzeugs für den Geschwindigkeitsverlauf nach der 6 und die über den Synchrongenerator zur Verfügung gestellte Leistung;
• 8 den an den Batterieklemmen abgegriffenen zeitlichen Spannungsverlauf in Form der Spannungsdifferenz zwischen der Leerlaufspannung der Batterie und der Verbraucherspannung ohne und mit zugeschaltetem Synchrongenerator;
• 9 ein weiteres Beispiel eines Leistungsbedarfs eines Verbrauchers über der Zeitachse im Vergleich zum Leistungsangebot der erfindungsgemäßen Vorrichtung zur Energieversorgung ohne Batterieeinsatz;
• 10 den zeitlichen Verlauf der Verbraucherspannung in Form der Differenzspannung zu einer Sollspannung;
• 11 den zeitlichen Verlauf der Stellgröße für die Leistungsregelung der Verbrennungskraftmaschine zur Bereitstellung der benötigten Verbraucherleistung beispielsweise anhand einer Drosselklappenverstellung;
• 12 den Drehzahlverlauf bei der erfindungsgemäßen Drehzahlregelung des Synchrongenerators für einen Leistungsbedarf gemäß der 9 und
• 13 den zeitlichen Verlauf des Erregerstroms für eine Drehzahlregelung gemäß der 12.

The subject matter of the invention is shown, for example, in the drawing. Show it

• 1 a device according to the invention for supplying energy to an electrical consumer in an isolated operation in a schematic block diagram;
• 2 one of the 1 corresponding representation of an embodiment variant of the device according to the invention;
• 3 Characteristic curves for the no-load voltage of the externally excited synchronous generator depending on the speed at different excitation currents;
• 4 the generator current versus speed for different idle voltage characteristics of the synchronous generator;
• 5 the time profile of a voltage tapped at the battery terminals of a vehicle with an electric motor fed via a battery for a predetermined load profile without and with the energy supply device according to the invention;
• 6 a speed curve over time of a vehicle with an electric motor powered by a battery and the energy supply device according to the invention;
• 7 the power requirement of a vehicle's electric motor for the speed curve according to the 6 and the power provided via the synchronous generator;
• 8th the time curve of the voltage tapped at the battery terminals in the form of the voltage difference between the idle voltage of the battery and the consumer voltage without and with the synchronous generator switched on;
• 9 a further example of a consumer's power requirement over the time axis in comparison to the power offered by the device according to the invention for energy supply without the use of a battery;
• 10 the time course of the consumer voltage in the form of the difference voltage to a target voltage;
• 11 the time course of the manipulated variable for the power control of the internal combustion engine to provide the required consumer power, for example based on a throttle valve adjustment;
• 12 the speed curve in the speed control of the synchronous generator according to the invention for a power requirement according to 9 and
• 13 the time course of the excitation current for speed control according to 12 .

Way to carry out the invention

The device for supplying energy to an electrical consumer 1 in island operation has, according to the exemplary embodiment 1 a separately excited synchronous generator 2, which is driven by a drive 3, preferably an internal combustion engine, for example a two-stroke engine. To excite the synchronous generator 2, an auxiliary excitation machine 4 is provided, which feeds the excitation winding 5 via a rectifier 6. The excitation current is controlled via a control device 7, which includes a PID controller 8, which is subjected to a target-actual value difference in the speed. For this purpose, an actual value transmitter 9 and a setpoint value 10 are provided for the speed, which can thus be regulated to a constant value using the excitation current as a manipulated variable.

The power requirement of the consumer 1 must be covered by the power of the drive 3 operated at an advantageous design speed, which requires a corresponding power control of the drive 3 via a control device 11. This control device 11 controls an actuator 12, for example a throttle valve or an injection pump, for the internal combustion engine forming the drive 3. The respective consumer voltage to which the control device 11 is supplied can be used as a measure of the power consumption in order to be able to control the actuator 12 depending on the power requirement of the consumer 1. The advantages of a constant speed for efficiency, noise formation and perception as well as vibration behavior can therefore be used advantageously, under simple control conditions.

The exemplary embodiment according to the 2 differs from the one after the 1 essentially in that the consumer 1 is connected to a battery 13, which is operated by the syn chron generator 2 is charged when necessary. Accordingly, a rectifier 14 is provided between the battery 13 and the synchronous generator 2, via which the field winding 5 can also be fed. The excitation current controlled via the control device 7 depending on the target-actual value difference of the speed in turn serves as a manipulated variable for the speed control, so that with regard to the control of the synchronous generator 2 in comparison to the exemplary embodiment according to the 1 nothing changes. However, the drive 3 does not need to cover the full consumer power because of the battery 13, which enables much simpler control conditions for the drive 3 because, in the simplest case, the drive only operates at a given power level depending on whether the battery voltage falls below a lower limit and exceeds an upper limit - and needs to be switched off, so that the battery 13 is charged by the synchronous generator 2 depending on its state of charge.

Again 3 can be seen, in which the generator idle voltage U _g0 is plotted against the speed n of the synchronous generator 2, there is a linear relationship between the generator idle voltage U _g0 and the speed n, the slope of the characteristic curves depending on the size of the respective excitation current I _e . The characteristic curves 15 and 16 show the course of the generator idle voltage U _g0 for the lowest and the highest excitation current I _e , while the characteristic curve 17 corresponds to an average excitation current I _e . Depending on the selected characteristic curve 15, 16, 17 of the generator idle voltage U _g0 , the idle voltage U _b0 of the battery 13 is reached at different speeds n of the synchronous generator 2, which results in a generator current I _g when this idle voltage U _b0 is exceeded, as is the case Characteristic curves 18, 19 and 20 of the 4 show, which are derived from the characteristics 15, 16 and 17 for the generator idle voltage U _g0 . If you set the speed n, at which the generator idle voltage U _g0 corresponds to the idle voltage U _b0 of the battery 13 at the lower limit value for the excitation current I _e according to the characteristic curve 15, as the nominal speed n _n , then you can for different generator currents I _g and thus for different Load conditions, the nominal speed n _n can be set by a corresponding change in the excitation current I _e between the characteristic curves 18 and 19. This means that the speed n of the synchronous generator 2 can be regulated to a value n _n using the excitation current I _e as a manipulated variable. This of course also applies to synchronous generators 2, whose excitation current can only be partially changed because part of the excitation current is made available by permanent excitation.

In the 5 the voltage U _v that can be tapped at the battery 13 during a time power requirement of the consumer 1 is shown, which is used to control the drive 3. This drive 3 is switched on at a lower limit voltage U _on and switched off again at an upper limit voltage U _off . In addition, two power levels are provided for the drive 3, whereby when an upper threshold value U _L1 of the consumer voltage U _v is exceeded, the drive power is switched to the lower power level via the control device 11 and when the value falls below a lower threshold value U _L2, it is switched back to the higher power level. From characteristic curve 21 of 5 The result is that the battery 13 is discharged due to the power requirement of the consumer 1, which can be seen from the falling consumer voltage U _v . If there were no energy supply via the synchronous generator 2, the voltage curve shown in dashed lines would result. What is striking about this voltage curve is that there is an increase in voltage between times t ₁ and t ₂ , which suggests a short-term energy return from consumer 1 to battery 13, for example due to the recovery of braking energy.

However, since the consumer voltage U _v drops below the lower limit value U _a , the drive 3 is switched on via the control device 11, which in this exemplary embodiment leads to an increase in voltage and thus to charging of the battery 13. Since this voltage increase causes the upper threshold value U _L1 of the consumer voltage U _v to be exceeded, the drive 3 is operated in the lower power level, which is noticeable in a flatter increase in the voltage curve. Since the lower threshold value U _L2 is exceeded in the further course, the drive is activated again in the higher power level until the upper threshold value U _L1 is exceeded again, which results in a flatter increase in the voltage curve 21 before the drive 3 reaches the upper limit value U is switched _off . If the consumer 1 is switched off immediately after the drive 3 is switched on, a voltage curve results at the battery terminals corresponding to the characteristic curve 22 shown in dash-dotted lines, which causes the battery 13 to be charged.

The 6 until 8th illustrate the invention using a vehicle driven by a battery-fed electric motor with the energy supply device according to the invention. In the 6 a speed curve of the vehicle is shown, which is first accelerated to a speed V ₁ and then braked to a speed V ₂ before the vehicle is stopped. In the 7 is the quiet The power requirement P _v for this trip is shown in solid lines by the characteristic curve 23.

From the 8th , which shows the voltage curve at the battery terminals based on the consumer voltage U _v tapped at the battery terminals in comparison to the no-load voltage U _b0 of the battery 13, the voltage curve that can be tapped at the battery terminals without switching on the synchronous generator 2 results from the characteristic curve 24 shown in solid lines Braking energy recovered when the vehicle brakes at times t ₁ and t ₂ causes an increase in the consumer voltage U _v . From the in the 8th The drawn upper and lower limit values U _on and U _off as well as the threshold values U _L1 and U _L2 for the control of the drive 3 results in that when the lower limit value U on is undershot, the drive ₃ for the synchronous generator 2 is switched on and operated at the higher power level , like the characteristic curve 25 shown in dashed lines in the 7 can be recognized. The power P _g delivered by the synchronous generator 2 according to the characteristic curve 25 causes an increase in the consumer voltage U _v according to the dashed characteristic curve 26 of the 8th . With the braking energy recovered at time t ₁ , the consumer voltage U _v exceeds the threshold value U _L1 , with the result that the drive 3 is operated in the lower power level. The power P _g delivered by the synchronous generator 2 therefore decreases accordingly 7 on the characteristic curve 27, which causes a curve 28 of the consumer voltage U _v . However, after the vehicle has come to a standstill at time t ₂ , the drive 3 remains switched on until the voltage U _v reaches the upper limit value U _out .

In the 9 until 13 are the conditions of the energy supply of a consumer 1 according to the 1 illustrated without battery use. The power P _v required by the consumer 1 is shown by the dashed characteristic curve 29, while the power P _g delivered via the synchronous generator 2 is shown in a solid line 30. In order to be able to provide this power P _g , the drive 3, an internal combustion engine, must be controlled accordingly, which in the selected exemplary embodiment is done by adjusting the throttle valve via the actuator 12. In the 11 The respective throttle valve angle α can be seen from the characteristic curve 31. In the exemplary embodiment, the consumer load P _v exceeds the power P _g that can be delivered by the synchronous generator 2 from the time t ₁ . This means that in order to keep the speed n constant at the value n _n according to 12 , the excitation current I _e is reduced via the control device 7 compared to the change required to adapt the speed to the changed load, as is the case 13 can be seen. The overload therefore does not lead to a drop in speed n. Only the consumer voltage U _v is reduced 10 lowered.

As soon as the generator power P _g according to the 9 If the consumer power P _v exceeds again at time t ₂ , which is noticeable in an increase in speed, the excitation current I _e is correspondingly 13 raised to keep the speed n constant. At a constant speed n, only a voltage drop occurs in the event of an overload.

Claims (4)

Method for operating a device for supplying energy to an electrical consumer (1) in an isolated operation; wherein the device comprises: an externally excited synchronous generator (2), which can be controlled via its excitation current (I _e ); a drive (3) for the synchronous generator (2); a control device (11) for the drive (3) and a battery (13) which can be charged by the synchronous generator (2) and which is connected to the electrical consumer (1) in such a way that the electrical consumer voltage (U _v ) results from the internal battery resistance; wherein the method comprises: the device is controlled depending on the energy requirements of the consumer (1); wherein the speed (n) of the synchronous generator (2) is kept constant by regulating the excitation current (I _e ); wherein the drive (3) is operated in two power levels depending on the consumer voltage (U _v ); wherein by means of the control device (11) the drive (3) is switched on at a lower limit voltage (U _on ) and switched off at an upper limit voltage (U _off ) and by means of the control device (11) when an upper threshold value (U _L1 ) is exceeded Consumer voltage (U _v ), the power of the drive (11) is switched to the lower power level and when the consumer voltage (U _v ) falls below a lower threshold value (U _L2 ), the power of the drive (11) is switched to the higher power level. Procedure according to Claim 1 , characterized in that the synchronous generator (2) is driven by an internal combustion engine depending on the consumer voltage (U _v ). Device for carrying out the method according to Claim 1 or 2 , comprising: a separately excited synchronous generator (2); a drive (3) for the synchronous generator (2); a control device (7) for the synchronous generator (2), which comprises a PID controller (8); a control device (11) for the drive (3); a battery (13) which can be charged by the synchronous generator (2) and which is connected to the electrical consumer (1) in such a way that the electrical consumer voltage (U _v ) applied to the consumer (1) results from the internal battery resistance; wherein the control device (7) connected to a speed sensor (9) regulates the excitation current (I _e ) depending on a target-actual value difference in the speed (n) of the synchronous generator (2) and the control device (11) for the drive (3) of the Synchronous generator (2) controls the drive (3) depending on the consumer voltage (U _v ); wherein the device can be controlled depending on the energy requirement of the consumer (1) in such a way that the speed (n) of the synchronous generator (2) is kept constant by regulating the excitation current (I _e ); that the drive (3) is operated in two power levels depending on the consumer voltage (U _v ); that the drive (3) is switched on by means of the control device (11) at a lower limit voltage (U _on ) and switched off at an upper limit voltage (U _off ) and that by means of the control device (11) when an upper threshold value (U _L1 ) is exceeded Consumer voltage (U _v ), the power of the drive (11) is switched to the lower power level and when the consumer voltage (U _v ) falls below a lower threshold value (U _L2 ), the power of the drive (11) is switched to the higher power level. Device according to Claim 3 , characterized in that the drive (3) for the synchronous generator (2) is designed as an internal combustion engine with a maximum power adapted to the maximum generator power.

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